44 common defects and countermeasures of die castings

1 External defects

Defect 1----Cold shut

Other name: Cold connection (butt connection)
Defect phenomenon: Gap caused by low-temperature metal flows butt-jointing each other but not melting is irregularly linear, with two types of penetration and non-penetration, and has a tendency to develop under action of external force.

Causes

Analysis, judgment and solution

1. Low pouring temperature of molten metal or low mold temperature;
2. Alloy composition does not meet standard and has poor fluidity;
3. Molten metal is filled in strands and fusion is poor;
4. Gate is unreasonable and process is too long;
5. Filling speed is low or exhaust is poor;
6. Injection pressure ratio is low.

1. Product is black with flow marks. Appropriately increase pouring temperature and mold temperature;
2. Change alloy composition to improve fluidity
3. Look at flow direction of aluminum liquid when hot mold is hot. Cold shut caused by collision of metal liquid is generally vortex-shaped and accompanied by flow marks. Improve pouring system and improve filling direction of inner gate. In addition, a slag bag can be opened on the edge of casting to improve filling conditions:
4. Accompanied by far end pressure is not solid. Change gate position and cross-sectional area, improve overflow conditions, and increase overflow volume:
5. Product is dark, often accompanied by surface bubbles. Increase injection speed,
6. Casting is not compacted as a whole. Increase specific pressure (try not to use it).

Defect 2----Abrasion

Other names: Scratches, pull marks, mold sticking marks
Defect phenomenon: Along demolding direction, due to metal adhesion, mold manufacturing slope is too small, resulting in scratches on casting surface. In severe cases, it becomes a scratched surface or even cracks.

Causes

Analysis, judgment and solutions

1. Casting slope of core and mold wall is too small or there is a reverse slope:
2. There are indentations on core and mold wall;
3. Alloy adheres to mold;
4. Casting is tilted when ejected, or axis of core is tilted;
5. Surface of mold wall is rough;
6. Paint is often not sprayed;
7. Iron content in aluminum alloy is less than 0.6%;
8. Alloy pouring temperature is high or mold temperature is too high;
9. Pouring system is incorrect, directly impacting mold wall or core;
10. Filling speed is too high:
11. Surface of cavity is not nitrided.

1. Product generally pulls out bright marks and does not fuzz. Correct mold to ensure manufacturing slope;
2. Pulling or even cracking occurs. Polish indentation, replace core or weld mold wall;
3. Pulling and fuzzing. Polish mold;
4. Large-area pull on one side, abnormal sound during ejection, correct mold structure:
5. Pull is in the form of thin strips, multiple strips. Polishing surface:
6. Mold surface is overheated and aluminum is evenly adhered. Amount of paint should be thin and even, and paint should not be sprayed out;
7. Aluminum alloy is adhered to surface of cavity. Appropriately increase iron content to 0.6~0.8%:
8. Aluminum alloy is adhered to surface of cavity, especially near inner gate. Reduce pouring temperature and control mold temperature within process requirements;
9. Mold wall or core is seriously adhered to aluminum. Adjust position and filling direction of inner gate:
10. Mold cavity inner gate is severely scoured, accompanied by adhesion of aluminum alloy. Appropriately reduce speed;
11. Aluminum alloy is often adhered to surface of cavity. Surface nitriding treatment must be performed;

Defect 3 - Undercasting

Other names: insufficient pouring, unclear outline, incomplete corners
Defect phenomenon: Molten metal does not fill cavity, and incomplete filling appears on casting. It often appears at the end of casting or in a narrow deep cavity.

Causes

Analysis, judgment and solution

1. Poor alloy flow:
(1) High gas content in molten metal, severe oxidation, resulting in decreased fluidity.
(2) Alloy pouring temperature and mold temperature are too low.
(3) Gate speed is too low.
(4) Insufficient nitrogen pressure in accumulator.
(5) Low filling degree of pressure chamber and low specific pressure.
(6) Improper design such as too thin casting wall or large thickness difference.
2. Poor pouring system:
(1) Improper selection of gate position, flow diversion method, and number of gate strands
(2) Cross-sectional area of gate is too large
3. Poor exhaust conditions:
(1) Poor exhaust.
(2) Too much paint, not dried and burned out.
(3) Mold temperature is too high, gas pressure in cavity is high, and it is not easy to discharge.

1. Improve fluidity of alloy:
(1) Internal quality of product is poor, and there are many bubbles on the surface. Refine alloy liquid, remove gas and non-metallic inclusions as much as possible;
(2) Accompanied by cold shut and flow marks. Appropriately increase alloy pouring temperature and mold temperature;
(3) Small pits appear on the surface of product, and there is a cold shut around undercast. Appropriately increase injection speed;
(4) Pressure gauge has a buffering phenomenon and displayed value does not meet process requirements, and casting is accompanied by phenomenon of underpressure. Supplement nitrogen to increase effective pressure:
(5) There are traces of cold metal on the surface of casting, and there is also a phenomenon of underpressure. Adjust pressure chamber diameter, increase injection pressure ratio, and use quantitative pouring.
(6) There is an obvious cold shut or underpressure around undercast in thin wall. Improve casting structure, adjust wall thickness appropriately, and open an auxiliary gate;
2. Improve pouring system:
(1) Front end of undercast is accompanied by a cold shut and incomplete fusion. Select gate position, diversion method and number of gate strands according to filling simulation or actual hot mold;
(2) It is often accompanied by phenomenon of sticky gate. Increase cross-sectional area of gate or increase injection speed;
3. Improve exhaust conditions:
(1) Color around undercast is black, accompanied by impurity accumulation and bubbles. Add overflow grooves and exhaust channels. Deep concave cavities can be vented by ejector gaps or core gaps:
(2) Surface color is not bright and flow marks are serious. Use paint thinly and evenly, blow dry and burn out before closing mold;
(3) It is often accompanied by a lot of mold sticking, severe scratches, and surface bubbles. Reduce mold temperature to specified range of process.

Defect 4----Bubbles

Other name: Bubbling
Defect phenomenon: Bubbles formed by the expansion of accumulated gas under surface of casting sometimes burst, and there are two types: penetrating and non-penetrating.

Causes

Analysis, judgment and solutions

1. Mold temperature is too high and mold is opened too early.
2. Filling speed is too high, and metal flow is involved in too much gas.
3. Paint has a large amount of gas, too much is used, and it is not completely burned before pouring, so that volatile gas is wrapped in the surface of casting. In addition, paint contains a large amount of water.
4. Gas in cavity is not discharged, and exhaust is not smooth.
5. Alloy melting temperature is too high.
6. Aluminum alloy liquid is not completely degassed, and a lot of gas is absorbed. When casting solidifies, it precipitates and remains in casting.
7. Turbulence occurs during filling.

1. Temperature gun tests mold surface temperature, and displayed value exceeds specified range of process. Reduce mold surface temperature and increase holding time;
2. Metal flow pressed into gate on the surface of casting is obviously much brighter than other parts. Reason for high filling speed is that injection speed of equipment itself is high, and on the other hand, it may be caused by gate being too thin. Reduce injection speed and appropriately increase thickness of inner gate; Methods for judging thin inner gate: whether gate is easy to stick, reduce second fast speed to see if there is a serious failure to press at far end, do not press parts, and see if there are multiple streams of aluminum liquid:
3. Check whether color of mist is white during spraying, and check whether there is gas residue in cavity before closing mold. Replace paint or increase ratio of paint to water;
4. During hot mold stage, there are obvious vortices and paint accumulation on the surface of casting.
Judgment and solution: adjust opening gear, artificially produce mold expansion, if it is solved, it is necessary to open exhaust duct;
5. Metal flow pressed into inner gate on the surface of casting is particularly bright and accompanied by adhesion.
Appropriately reduce pouring temperature;
6. Take sample block to measure density to see if it meets requirements. Re-degassing treatment or re-refining in insulation furnace;
7. During hot mold stage, there are obvious traces of various flows not being melted together on the surface of casting accompanied by paint accumulation. Judgment and solution: Apply black oil to production, check whether there is accumulation of traces, analyze accumulation location, and solution is,
a, open or increase slag collection bag at corresponding location, b, adjust flow direction, position or filling direction of gate.

Defect 5--Flow marks

Other names: stripes, patterns
Defect phenomenon: After molten metal that first enters cavity forms an extremely thin and incomplete metal layer, it is filled by subsequent molten metal and leaves traces. Surface of casting is consistent with flow direction of molten metal, and local depression can be felt by hand. This defect has no development direction and can be removed by polishing.

Causes

Analysis, judgment and solution

1. Cross-sectional area of inner gate is too small and position is improper, causing metal flow to fill cavity asynchronously or splash and leave traces.
2. Mold temperature is low, such as zinc alloy mold temperature below 150℃ and aluminum alloy mold temperature below 180℃, which are prone to such defects.
3. Filling speed is too high.
4. Amount of paint is too much.
5. Pressure acting on molten metal is insufficient

1. Apply black oil to hot mold to see flow direction and filling order of metal flow. Adjust cross-sectional area, position or filling direction of inner gate to achieve purpose of synchronous filling:
2. Measure mold temperature with a mold temperature gun. Adjust mold temperature to within process requirements;
3. On the surface of product, metal flow at gate will appear particularly bright. Appropriately adjust filling speed to change flow state of metal liquid filling cavity;
4. Surface of product is black, and paint accumulation will occur locally. Adjust paint concentration, and use paint thinly and evenly;
5. Opposite side of gate on casting surface is prone to failure to be pressed, accompanied by darkening of surface. Appropriately adjust injection pressure.

Defect 6---Depression

Other names: shrinkage, shrinkage, air holding, edge collapse
Defect phenomenon: Concave part on smooth surface of casting is in a naturally cooled state.

Causes

Analysis, judgment and solution

1. Structural design of casting is unreasonable, wall thickness difference is too large, there are local thick parts, and hot nodes are generated.
2. Alloy shrinkage rate is large.
3. Cross-sectional area of inner gate is too small and position is improper.
4. Injection ratio is low.
5. Local temperature of mold is too high.
6. Caused by damage and cracking of die casting mold
7. Caused by air holding, when metal liquid is filled, local gas is not discharged and is compressed between cavity surface and metal liquid surface.

1. Check corresponding parts of product or feel it by hand to see if there is a large wall thickness difference and thick wall. Communicate with customer's designers to improve structure of casting without affecting use function, so that wall thickness tends to be uniform. Joints with large thickness differences should gradually ease transition and eliminate heat nodes;
2. Take out sample block and test it with a density tester, and observe degree of depression when sample block solidifies. Select alloys with small shrinkage and refine alloy liquid;
3. Small cross-section of inner gate makes far end of casting not compacted or metal flow docking occurs. Check whether position of inner gate is conducive to shrinkage compensation and filling wall thickness. Correctly set alloy pouring position and appropriately increase cross-sectional area of inner gate:
4. Far end of casting has an overall phenomenon of not being compacted. Increase injection force;
5. Use a mold temperature gun to measure temperature of corresponding part of mold where defect occurs. Appropriately adjust mold thermal balance conditions, use temperature control devices and point cooling, etc., spray area for a longer time, and force cooling:
6. Check whether corresponding part of mold is damaged, bulged, and cracked, and repair mold;
7. Concave surface is smooth, outline is generally regular and circular, which is clearly distinguished from other surface colors. Improve exhaust conditions, move second-stage injection position later, reduce first-stage injection speed appropriately, and reduce second-stage injection speed appropriately;

Defect 7----Cracks

Defect phenomenon: Alloy matrix on casting is destroyed or broken to form filamentary cracks, which are of two types: penetrating and non-penetrating, and have a tendency to develop. Cracks can be divided into cold cracks and hot cracks. Main difference between them is that metal at crack of cold crack castings is not oxidized, while metal at crack of hot crack castings is oxidized.

Causes

Analysis, judgment and solution

1. Casting structure is unreasonable, shrinkage is hindered, and casting radius is too small.
2. Core pulling and ejection devices are deflected during operation, and force is uneven.
3. Temperature of mold, especially core, is low.
4. Mold opening and core pulling time are too late.
5. Improper alloy selection or excessive harmful impurities reduce plasticity of alloy. Zinc alloy: lead, tin, cadmium, and iron are too high, aluminum alloy: zinc, copper, and iron are too high, copper alloy: zinc and silicon are too high, magnesium alloy: aluminum, silicon, and iron are too high,
6. There are particularly thick and large hot junctions in casting structure.
7. Alloy liquid pouring temperature is too high.
8. Mold core is bent or mold surface is damaged or there is a reverse slope.
9. Cracks when punching edge to remove casting system

1. Check casting structure, three-coordinate detection size, and confirm whether shrinkage ratio is appropriate. Modify mold and select a suitable shrinkage ratio. Negotiate with customers to improve structure of castings, reduce wall thickness difference, and increase casting radius;
2. There will be scratches on core or surface in a certain direction. Correct mold structure to ensure smooth ejection and demolding;
3. There is a cold shut in core hole. Increase working temperature of mold;
4. There may be scratches on core hole or side. Shorten mold opening and core pulling time;
5. Check chemical composition of alloy through spectral analysis to confirm whether it meets technical requirements. Strictly control harmful impurities, adjust alloy composition, comply with alloy smelting specifications or reselect alloy grade;
6. Concavities or cracks will appear on the surface of thick and large hot junctions. Negotiate with customers to change structure without affecting function;
7. There are particularly bright areas or mold sticking scratches on the surface of casting, and depressions appear at wall thickness. Control pouring temperature to within process requirements;
8. There are serious scratches and fuzzing on the side of hole or damaged surface. Replace core or repair mold;
9. Main cracks are near gate. Repair punching die and clean cutting edge.

Defect 8--imprint

Other names: push rod imprint, insert or movable block splicing imprint
Defect phenomenon: Surface of casting is left with convex and concave marks due to collision of mold cavity, splicing of push rod, insert, movable block and other parts.

Cause

Analysis, judgment and solution

1. Push rod is not adjusted properly or end is worn.
2. Mold cavity, slider splicing part and its movable part are not well matched, such as uneven convexity and large gap.
3. Push rod area is too small.
4. Side wall surface of casting is formed by inserts that intersect movable and fixed molds.
5. Caused by mold damage, such as scratches and bumps on cavity surface
6. Movable or sliding part of mold is loose or worn

1. Check state and size of push rod. Adjust push rod to correct position or repair and replace push rod;
2. Check state of mold splicing part. Tighten insert or other movable parts to eliminate undesirable concave and convex parts;
3. Push rod mark on casting often becomes deeper or corresponding part is fixed. Appropriately increase push rod area or increase number;
4. Improve casting structure, eliminate interlaced inlay form of die-casting mold, and improve die-casting mold structure;
5. Repair mold surface:
6. Depth of impression on casting surface is inconsistent. Repair mold.

Defect 9---Network burrs

Other names: network marks, network patterns, cracked burrs
Defect phenomenon: Network raised marks and metal burrs on casting surface formed due to thermal fatigue on mold cavity surface.

Causes

Analysis, judgment and solutions

1. Traces caused by cracks on the surface of mold cavity. Heat conduction near gate area is the most concentrated, friction resistance is the largest, erosion of molten metal is the strongest, cold and hot alternation is the most severe, stress concentration is most likely to occur, resulting in thermal cracking and cracking.
2. Improper mold material or incorrect heat treatment process.
3. Large temperature difference between hot and cold molds
4. Alloy liquid pouring temperature is too high, and mold is not preheated enough.
5. Surface roughness Ra of mold cavity is too large.
6. Metal flow rate is too high and positive wall is eroded.
7. Die-casting mold wall is thin or has sharp corners
8. Surface of mold cavity has been partially welded, and welding stress has not been eliminated in time.

1. Check records of mold production and stress relief treatment. Use mold according to mold use and maintenance regulations, perform stress relief treatment in time. Add point cooling or use insert structure in parts prone to fatigue cracking. Pay attention to spraying of this part during production process and strengthen forced cooling;
2. Check composition and mechanical properties of mold material. Correctly select mold materials and reasonable heat treatment process;
3. Find out temperature imbalance of cavity through simulated temperature field analysis. Set point cooling or point heating structure to ensure temperature balance of cavity. Temperature balance also needs to be achieved by spraying paint during production process;
4. Judge by alloy liquid temperature gun and mold surface temperature gun. Reduce alloy pouring temperature as much as possible. Mold must be preheated to working temperature range before die casting:
5. Use a roughness detector to detect surface roughness of cavity. Polish mold cavity surface to required range, and Ra value does not exceed 0.2:
6. Mold surface in high-speed area is prone to dent damage. Under good molding conditions, reasonably reduce metal liquid filling speed. Change its filling direction;
7. Surface of casting is obviously shiny at thin wall. Trim mold structure:
8. Check mold production times, and cracks should occur at weld repair site very early. Mold should be welded according to correct mold welding process.

Defect 10---Colored spots

Other names: oil spots, black spots
Defect phenomenon: Spots on the surface of casting that are different from base metal are generally formed by coating carbides or punch oil.

Causes

Analysis, judgment and solution

1. Impure coating or excessive use
2. Excessive graphite in coating.
3. After mold is opened, parts are taken out during spraying process or after spraying, causing coating to splash onto surface of casting during spraying.
4. Position and time of punch oil spray are incorrect.
5. During transfer process between processes, water or oil is splashed on casting

1. Color of spots is lighter. Coating should be used thinly and evenly, without accumulation, compressed air should be used to blow it away and blow it evenly;
2. Color of spots is black. Reduce graphite content in coating or use graphite-free ink-based coating;
3. Color of spots is lighter. After mold is opened, casting must be taken out before next cycle of spraying can be carried out;
4. Color of spots is generally dark red. Punch oil can only be sprayed after mold is opened and casting is taken out. It is not allowed to brush punch oil directly on the front section before punch returns. It is not allowed to spray punch oil directly into pouring port;
5. Color of spots is not fixed. Color is lighter when splashed with water, and dark red when splashed with oil. Protection must be taken during transportation between processes.

Defect 11-Pockmarked Surface

Defect phenomenon: During filling process, due to low mold temperature or alloy liquid temperature, a fine pockmarked distribution area is formed on the surface of casting under conditions close to underpressure.

Cause

Analysis, judgment and solution

1. During filling, metal is dispersed into dense droplets and hits mold wall at high speed.
2. Thickness of inner gate is too small.
3. Inner gate speed is too fast.
4. Mold temperature is low.

1. When mold is first hot, it will be found that metal liquid flow is dispersed. Correctly design pouring system to avoid splashing of metal liquid, improve exhaust conditions, and avoid too much gas from being involved in liquid flow;
2. When mold is first hot, it will be found that metal liquid flow is in a jet shape. Appropriately adjust inner gate thickness:
3. When mold is first hot, it will be found that metal liquid flow is in a jet shape. Appropriately reduce inner gate speed:
4. Surface of casting is dark and accompanied by cold shut. Increase mold temperature to range of process requirements. Method is to connect mold heater or spray less and hot more molds.

Defect 12---Flash

Other names: burrs, flying wings
Defect phenomenon: metal flakes appearing on the edge of casting or at joint of cavity.

Cause

Analysis, judgment and solution

1. Clamping force of machine is not adjusted properly before injection.
2. Mold and slider are damaged, and locking element fails.
3. Mold insert and slider are worn.
4. The overall strength of mold, especially mold base, is not enough to produce elastic deformation.
5. Debris on parting surface is not cleaned up
6. Projection area is not calculated correctly, exceeding clamping force.
7. Injection speed is too high, resulting in a high pressure shock peak.

1. Check clamping force or boosting situation, adjust injection boosting mechanism, and reduce injection boosting peak:
2. Check degree of damage to mold slider and repair it by coloring mold to ensure that locking element works;
3. Check wear and repair or replace insert:
4. Correctly calculate mold strength. Solution is to add support columns as much as possible on the back of moving mold base;
5. Straightening state of crank arm during mold closing can be used to judge, debris on parting surface can be removed and polished appropriately before continuing production;
6. Determine whether clamping force of equipment is sufficient through calculation. If internal quality requirements are not strict, low-pressure and high-speed process parameters can be used to solve problem. If internal quality requirements are strict and pressure testing is required, a larger tonnage die-casting machine must be replaced for production;
7. Check process parameter settings: whether they exceed process requirements by a lot. Appropriately reduce injection speed.

Defect 13-Lamination

Other names: skin separation, skin insertion, peeling
Defect phenomenon: There are obvious metal layers on local casting

Causes

Analysis, judgment and solutions

1. Mold rigidity is poor, and mold plate shakes during metal liquid filling process.
2. Punch of pressure chamber does not cooperate well with pressure chamber, and forward speed is not stable during injection.
3. Gating system is improperly designed, and filling sequence of each flow is inconsistent, causing metal filled later to be superimposed on metal flow filled earlier.
4. Clearance between sliding parts and splicing parts of mold cavity becomes larger, and aluminum skin is sandwiched, which penetrates into casting during die casting.
5. Local temperature of mold cavity plane is too high, causing alloy to adhere to mold and peeling on casting surface.
6. Chemical composition of alloy liquid changes, resulting in increased affinity with mold cavity surface, resulting in local sticking to mold, peeling or skin insertion on casting surface.
7. Mold has serious aluminum leakage during die-casting production process, and it is not cleaned in time. Aluminum skin is attached to parting surface, which penetrates into casting surface when next casting is die-cast, forming a skin insertion.

1. Check the overall size of mold and confirm strength. Strengthen mold rigidity and tighten mold parts:
2. Measure punch diameter and inner diameter of pressure chamber, check wear status of punch and pressure chamber hole. Adjust or replace injection punch and pressure chamber to ensure good fit.
3. Filling order of metal flow can be observed through black oil traces during hot stamping. Reasonably design position, cross-sectional area of gate and runner to ensure simultaneous and uniform filling and sequential solidification as much as possible:
4. Check gap between sliding and splicing parts in cavity. Repair or replace sliding and splicing parts to ensure that matching gap does not exceed 0.1mm;
5. Find local high temperature area of cavity through temperature field simulation analysis or on-site mold temperature measurement and actual temperature measurement. Treat by increasing point cooling or increasing local spraying time to force cooling;
6. Check chemical composition of alloy liquid through spectral analysis. Adjust corresponding metal content to process requirements;
7. Check whether flash at parting surface is thick. Repair mold or check and adjust equipment clamping mechanism.

Defect 14 - Deformation

Other names: twisting, warping
Defect phenomenon: Overall or local deformation of casting where geometry does not meet design requirements.

Causes

Analysis, judgment and solutions

1. Poor structural design of castings causes uneven shrinkage.
2. Mold opening too early, insufficient rigidity of castings
3. Casting slope is too small, and mold force is large.
4. Improper operation of removing castings.
5. Improper arrangement of push rod position, ejection deviation.
6. Unreasonable stacking of produced castings.
7. Unreasonable gate removal method, especially gate layout is a curved structure.
8. Local damage to mold cavity, severe strain causes local deformation.
9. Poor demoulding of paint, deformation caused by mold sticking.
10. Uneven spraying of paint causes inconsistent demoulding and deformation.
11. Large temperature difference between different parts of cavity, causing inconsistent demoulding or local mold sticking.
12. Caused by subsequent treatment such as shot peening.
13. Unreasonable transportation and packaging methods.

1. Deformation can be clearly found in castings after they are placed out of mold for a period of time. Improve structure of casting to make wall thickness uniform.
2. There is concavity in thick and large parts of casting, and material cake may be piled up. Appropriately increase holding time to strengthen rigidity of casting;
3. Surface with too small casting slope has traces of pulling and scratching. Increase casting slope if possible;
4. There are traces of bumps on the surface. Be careful when taking and placing casting, and do not hook casting body when taking casting out of cavity;
5. Manually eject after opening mold to check whether one end of casting is ejected first. Increase or reduce local ejector accordingly to ensure balanced ejection;
6. Special workstation equipment should be used for stacking castings, they should be separated and protected with cardboard;
7. For easily deformed castings, pouring gate method should be used, and direction must be paid attention to. The best method is to use a punching die;
8. Mold surface is damaged, corresponding parts of casting are scratched and fluffed. Repair mold;
9. Corners of casting or core are seriously sticky with aluminum. Replace paint;
10. Sticking to mold, there is an abnormal sound when ejecting and demolding. Uniform spraying:
11. If casting is partially stuck to mold, use a mold temperature gun to check mold cavity temperature. Add local point cooling or increase spraying amount locally for forced cooling to ensure that the overall temperature of mold cavity tends to be balanced;
12. Judge by measuring dimensions before and after shot peening. Use a reasonable shot peening process, such as speed, time, etc. Use a stable hanging method and use a special fixture when necessary;
13. Product is squeezed. Use high-strength outer packaging to separate and protect parts. Use box trucks as much as possible for transportation.

Defect 15----Misalignment

Other names: wrong thread, wrong seam
Defect phenomenon: one part of casting is offset from other part on parting surface, and relative displacement occurs (called wrong thread for thread)

Cause

Analysis, judgment and solution

1. Displacement of mold insert.
2. Wear of mold guide (closing guide pin).
3. Manufacturing error of cavity inserts of two half molds.
4. Assembly gap between mold cavity insert and mold base is too large, resulting in inconsistent assembly status multiple times.
5. Severe mold expansion during mold production causes side draw position offset.
6. Wear or failure of side draw slider lock.

1. Check insert position without pressing parts. Adjust or replace insert and tighten it:
2. Check wear of guide and measure its size. Replace guide pin and guide sleeve:
3. Check and measure relative assembly position size of mold insert. Perform trimming to eliminate errors;
4. Check assembly gap between cavity insert and mold base. Adjust and repair mold;
5. Dimension detection must be performed when mold expansion occurs during production process. Repair mold or adjust equipment clamping mechanism to ensure that mold does not expand;
6. Check state of slider locking and check it through matching method. Repair or replace locking device.

Defect 16--Bump

Defect phenomenon: scars on casting surface caused by impact.

Causes

Analysis, judgment and solutions

1. Castings are piled up in each operation process when opening mold or punching edges.
2. Castings are piled up in each operation process.
3. Improper operation by operators in each operation process, such as throwing parts.
4. Transfer between processes, such as no separation protection, collapse, etc.
5. Bumps of operating tools in each operation process, such as die-casting pick-up hooks, pick-up pliers, etc., files and punches in cleaning process, etc.

1. Be careful when picking up parts, and bumps are not allowed.
2. According to operating instructions, stacking is not allowed, and each piece must be neatly placed in workstation equipment;
3. Throwing is not allowed, and it must be handled with care. For example, castings in die-casting process must slide down workbench slowly and are not allowed to collide with each other;
4. Castings in workstation equipment must be protected and separated, and transfer must be slow to prevent collapse or falling castings;
5. Use operating tools correctly to prevent collisions. It is not allowed to hook or clamp casting body when taking out die-casting. Cleaning files and punches must be accurately operated on parts that need to be cleaned.

Defect 17--Cold beans

Defect phenomenon: Surface of die casting is embedded with cold beans and metal particles that are not completely fused with casting. (Usually in undercasting area)

Causes

Analysis, judgment and solution

1. Molten metal enters the cavity too early:
1) Direction of gate is on lower side of material cup
2) Fast injection position is improper and too late
2. Cavity is partially stuck to mold and not cleaned in time.
3. Filling speed is too fast, and jetting causes cold metal particles to form at the front end.
4. Position of gate is unreasonable, molten metal stream cannot be well fused or directly hit core and wall.
5. Position of overflow slag bag is unreasonable, and cold metal cannot be discharged.
6. Mold temperature is low.
7. Casting temperature is low.
8. Product structure is unreasonable, and there is a particularly deep cavity, that is, a dead zone.
9. Insoluble, unknown metal or non-metal particles are mixed in molten metal.

1. Defect position is not fixed.
1) Adjust position of inner gate, especially for mold structure with multiple cavities in one mold, it must be ensured that molten metal cannot flow back at the beginning of fast injection;
2) Adjust starting position of fast injection to avoid molten metal entering cavity during slow injection;
2. Check thin wall or narrow deep cavity of casting or mold cavity, and clean mold in time;
3. There may be multiple defects. Appropriately reduce filling speed;
4. There is a cold shut at position where defect exists. Adjust position of inner gate to ensure stability of metal flow filling as much as possible;
5. Most defects are located at entrance of non-slag collection bag. Change position of slag collection bag or add a slag collection bag aisle:
6. Surface of the overall casting is dark, and there are multiple cold shuts. Increase mold temperature;
7. Surface of casting far from inner gate is dark, and there are multiple cold shuts. Appropriately increase alloy casting temperature;
8. In many cases, defects appear at the bottom of deep cavity, accompanied by cold shuts. Appropriately increase casting temperature or increase boost pressure. If possible, open a branch runner for auxiliary filling. The best way is to negotiate with customer to change structure:
9. Shape and position of defect are not fixed. Aluminum liquid must be thoroughly refined to ensure purity. When taking material from ladle or spoon, take it below liquid surface as much as possible.

Defect 18----Erosion

Defect phenomenon: There are pits or convex patterns on the surface of die casting. It can be polished flat, but sometimes there will be pits in corresponding position, which mostly occur in the area near gate.

Cause

Analysis, judgment and solution

1. Gate position is unreasonable and directly impacts mold wall.
2. Filling direction of gate is incorrect, such as directly flushing corresponding part of cavity.
3. Gate is too thin, filling speed is too fast, and gate area is flushed.
4. Cooling conditions are not good, especially overheated parts.
5. There is a problem with mold cavity material and resistance to thermal fatigue is poor.
6. There is a problem with heat treatment of mold cavity, and surface is not nitrogen-desalinated or oxidized.
7. Alloy casting temperature is too high.

1. There are long protrusions and tortoise cracks at gate of casting. Adjust gate to avoid direct impact on mold wall;
2. There are long protrusions near gate, and there are regional fatigue tortoise cracks at protrusions away from gate. Adjust position and filling direction of gate;
3. In this case, cracking and erosion occur fastest at gate. Appropriately increase thickness of gate;
4. During production process, use mold temperature measurement to find high temperature area. Add cooling points in high temperature area. Spraying in high temperature area takes longer and forced cooling:
5. Take a sample of mold cavity material to test its composition; replace mold cavity material;
6. Check surface hardness of mold cavity. If defect is minor, perform surface nitriding or oxidation treatment after polishing. If defect is serious, it is necessary to perform surface reduction treatment before surface nitriding or oxidation treatment. Remake mold cavity;
7. Use an aluminum liquid temperature measuring gun to check aluminum liquid temperature. Appropriately reduce pouring temperature of alloy.

Defect 19---Friction ablation

Defect phenomenon: Rough surface is generated at certain positions on the surface of die casting. Position and time of defect are not fixed. It is uneven.

Cause

Analysis, judgment and solution

Caused by the die casting mold itself:
1) Local surface roughness of cavity is poor during manufacturing.
2) Repair during use.
2. Improper position, direction and shape of gate, unreasonable design scheme, causing vortex in metal flow.
3. Alloy liquid filling speed is too fast, causing local cavitation.
4. Local temperature of mold cavity is too high.
5. It is difficult to demold local mold cavity.
6. Aluminum is stuck on the surface of mold cavity.

1. Shape, area and position of defect are completely consistent. Polish and repair mold cavity;
2. Defect position is roughly same, but area size is inconsistent. Adjust position, filling direction and shape of gate to ensure sequential filling as much as possible;
3. Defect position is roughly same, but area size is inconsistent. Appropriately reduce filling speed;
4. During production process, use mold temperature measurement to find out high temperature area. Add cooling points in high temperature areas. Spraying in high temperature areas takes longer and forced cooling is required:
5. There are phenomena of pulling up and sticking to mold; increase spraying amount for defective parts;
6. Check corresponding parts of mold. Polish and repair corresponding surface of mold.

Defect 20--Traces of adhesion

Defect phenomenon: Metal or non-metal residues different from alloy material are attached to surface of die casting

Cause

Analysis, judgment and solution

1. There are metal and non-metal residues on the surface of die casting model cavity.
2. Impurities in material cup are brought into cavity and attached to cavity surface.
3. Pouring tool---ladle or pouring spoon is not clean before use, impurities are brought into cavity and attached to cavity surface.
4. Surface of aluminum liquid in insulation furnace has impurities, which are brought into cavity during pouring and attached to cavity surface.

1. Check surface of mold cavity. Blow it clean with a spray gun. If necessary, find a mold repair person to clean surface of mold cavity:
2. Check inner cavity of material cup. Clean inner cavity of material cup to ensure cleanliness;
3. Check pouring tool. Ladle or pouring spoon must be evenly coated with paint to ensure cleanliness;
4. Check whether alloy liquid surface of insulation furnace is clean, and clean slag or other floating objects on alloy liquid surface of insulation furnace in time before pouring production;

Defect 21----Meaty

Defect phenomenon: Surface of die casting has raised and redundant nodules due to mold damage. If it is on non-working surface or surface to be processed, it can be cleaned with a file or grinding wheel.

Cause

Analysis, judgment and solution

1. Due to manufacturing of die-casting mold, heat treatment effect is not good, resulting in mold cavity falling off.
2. Mold has exceeded its service life, resulting in severe cracking and falling off.
3. Mechanical damage to surface of mold cavity, such as bumps, extrusion, etc., resulting in depressions.
4. Joint between side-drawing slider and liner is not cleaned cleanly, and it is crushed when mold is closed.
5. Improper use and maintenance of mold, especially untimely stress relief and tempering treatment, causes cavity to crack and fall off prematurely.

1. Short-term solution is to weld and repair mold falling off part, and long-term solution is to re-manufacture mold cavity;
2. Re-manufacture replica mold;
3. Weld and repair damaged part of mold:
4. Check side-drawing state in time, and use a spray gun to blow away residual aluminum or other debris on joint surface. Repair matching and splicing parts of mold side slider;
5. According to mold use maintenance and management regulations, timely stress relief and tempering treatment should be carried out to ensure that mold does not crack or crack prematurely.

Defect 22----- Lack

Defect phenomenon: Surface of die casting is concave due to mold damage, bumps, etc. Irregular shape, unfixed position. Non-working surface can be remedied by welding

Causes

Analysis, judgment and solution

1. Due to mold manufacturing reasons, cavity is partially meaty or individual dimensions are wrong.
2. Mold has exceeded its service life, cracked heavy cavity local protrusion.
3. Mechanical damage to surface of mold cavity, such as bumps, extrusion, etc., causing local protrusions.
4. Side pull slider and liner are worn at junction, causing slider to move forward.
5. It is caused when removing pouring system, such as incorrect direction or method of throwing gate. Inner gate is too thick.
6. During process transfer, slag, falling, bumping or throwing, etc., cause casting to lack meat at corners, edges or planes.
7. There are adhesives in cavity.
8. Edge of processing surface collapses and processing surface is indented during processing.

1. Size detection judgment. Repair mold cavity;
2. Surface quality inspection can be found. Repair mold or re-manufacture replica mold;
3. Surface quality inspection can be found. Repair mold cavity surface;
4. Dimension detection and judgment. Repair mold side slider matching and splicing parts;
5. Reasonably design thickness of inner gate and remove pouring system. It is best to use punching mold;
6. Strictly implement product handling operation instructions and operation instructions of each sequence. Pay attention to protection between castings;
7. Check and clean mold in time;
8. Select correct parameters during processing, such as speed, feed rate, etc. In addition, direction of tool should also be reasonably selected. Clamping process should be careful and serious.

Defect 23--Bulging

Defect phenomenon: Surface of die casting is partially convex, and in severe cases, convexity will produce cracks.

Cause

Analysis, judgment and solution

1. Local subcutaneous bubbles are generated, gas expands and bulges after mold is removed, and even bursts
2. Diameter of ejector pin is selected to be small, and ejection force area is small.
3. Holding time is short, mold is opened and ejected before it is completely solidified.
4. Local surface of mold is damaged and concave.
5. Slow injection speed is fast, and alloy liquid rolls air when it is pushed into material cup.
6. Fast injection comes early and fast injection speed is too fast, and gas in cavity cannot be discharged in time.
7. Position and structure of exhaust groove are not good,

1. Bulge is not concave or even bulges at the same time. After knocking it open, bulge is a cavity. Adjust process or improve exhaust system of mold to discharge the gas:
2. Ejector pin mark at bulge is obviously concave. Replace ejector pin with a larger diameter or increase number of ejector pins;
3. Ejector pin mark at bulge is obviously concave. Strictly implement holding time specified in process;
4. Tap bulge to find that it is a solid mold rather than a cavity. Repair mold;
5. Reduce full pressure injection speed;
6. Reasonably adjust starting position and speed of fast pressure injection:
Improve position and structure of exhaust groove;

Defect 24---Surface peeling after shot blasting

Other names:
Defect phenomenon: After shot blasting, a thin layer of skin on the surface of casting rises or even falls off, which can be easily removed by hand, size, area and position are not fixed.

Causes

Analysis and solutions

1. Casting is not compacted, there are casting defects such as cold shut, stratification, bubbles and poor alloy flow fusion on surface.
2. Steel shot ejection speed is too high.
3. Shot blasting time is too long.
4. Hanging method is unreasonable, unstable, and knocks against each other.
5. Shape and quality of steel shot are poor and not smooth.
6. Steel shot contains sharp impurities.

1. Surface of casting is dark. Notify die-casting process or chief engineer to adjust die-casting process parameters or equipment parameters;
2. Appropriately reduce ejection speed of shot peening machine:
3. Appropriately reduce shot peening time;
4. Use reasonable hangers to ensure that casting is fixed during shot peening process. If necessary, special clamps can be used;
5. Purchase steel shots with regular shapes;
6. Screen or replace steel shots.

Defect 25---Black marks on the surface after shot blasting

Defect phenomenon: After shot blasting, casting has a black overall surface or obvious black marks and spots on some parts. Some can be thrown away, while others have been immersed in casting matrix. Area and position are not fixed.

Cause

Analysis, judgment and solution

1. Defects that existed before shot blasting brought from die casting process:
(1) Excessive use of black oil in die casting;
(2) Punch oil splashes when opening mold;
(3) Paint splashes during die casting;
2. Product has been placed for a long time or temperature is humid, and surface is corroded, moldy or dusty.
3. Dust removal device of shot blasting machine fails, and there is a lot of dust in steel shot.
4. Operator did not wear gloves as required and directly touched surface of casting after shot blasting with his hands, resulting in fingerprints.
5. After shot blasting, casting has been placed for a long time, dust has fallen on the surface or water and oil have been splashed on it, environment is humid and oxidized.

1. Defect is not all over casting surface. Strengthen control and management of die casting process.
(1) It is black oil, black in color;
(2) It is punch oil, dark red in color;
(3) It is paint, different in color from light color of casting surface:
2. After shot peening, surface marks are shallow and cannot be removed because they have been immersed in casting matrix. Strengthen management of product placement and do not place them for too long. If they need to be placed for a long time, they must be covered and protected, placed in a suitable environment;
3. The entire casting surface is black and dark. Resume dust removal or replace new steel shots;
4. Operators must be required to operate according to operating instructions. Gloves must be worn.
Shot peening should be inspected, packed and stored as soon as possible. If they need to be stored for a period of time, strict protection must be carried out.

Defect 26---Black marks on the surface after finishing

Defect phenomenon: After finishing, casting is blackened as a whole or has obvious black marks and spots locally. Some can be thrown away, while others have been immersed in casting matrix. Area and position are not fixed.

Causes

Analysis, judgment and solutions

1. Defects that existed before finishing brought over by die-casting process:
(1) Too much black oil is used in die-casting;
(2) Punch oil splashes when opening mold;
(3) Paint splashes during die-casting;
2. Product is placed for a long time or temperature is humid, and surface is corroded, moldy or dusty.
3. Water flow of finishing machine is too small or there is no water flow to remove sediment.
4. Operator did not wear gloves as required and directly touched surface of casting after shot peening with his hands, resulting in fingerprints.
5. Surface is not cleaned for a long time after finishing, and there are oxidation or water stains on surface.

1. Defects are not all over casting surface. Strengthen control and management of die-casting process.
(1) It is black oil, black in color:
(2) It is punch oil, dark red in color;
(3) It is paint, color is different from light color of casting surface
2. After finishing, surface marks are shallow and cannot be removed because they have been immersed in casting matrix. Strengthen management of product placement, and it should not be too long. If it needs to be placed for a long time, it must be covered and protected, placed in a suitable environment;
3. Appropriate water flow must be added as required to clean powder and other deposits in abrasive:
4. Operator must be required to operate according to operating instructions. Gloves must be worn;
After finishing, it must be cleaned and packed in a box for protection. If it needs to be stored for a period of time, it must be strictly covered and protected

2. Internal defects

Defect 27----Porosity

Other names: air hole, air eye
Defect phenomenon: Gas in pressure chamber, runner and cavity is drawn into interior of die casting to form a hole with a relatively regular shape and a relatively smooth surface.

Causes

Analysis, judgment and solution

Mainly caused by entrained gas
1. Improper selection of gate position and diversion angle, resulting in frontal collision and vortex of molten metal entering cavity.
3. Poor runner shape design.
4. Insufficient filling of pressure chamber.
4. Too high gate speed, resulting in turbulence.
5. Poor exhaust.
6. Pyrolysis, i.e. dead zone, exists deep in cavity. Along metal flow filling direction: there is a sudden thickening part in mold cavity.
7. Too much paint, not burned out before filling.
8. Alloy liquid contains excess gas and poor refining.
9. Too much machining allowance.
10. Unreasonable die casting process, such as low specific pressure.
11. There is a thick part at the end of filling (far from gate), i.e. hot knot,
12. Slow shot speed is fast, fast shot is early, pressurization is late or pressurization is not established, accumulator lacks nitrogen, etc.

Under conditions, vacuum die casting is the best.
1. Parts prone to pores and hot junctions may have traces of metal flow docking or depressions on the surface, which can be detected and judged by X-ray flaw detection. Select gate position and diversion angle that are conducive to removal of gas in cavity to avoid metal liquid closing overflow system on parting surface first;
2. Nozzle cross-sectional area of sprue should be as large as possible than cross-sectional area of inner gate:
3. There may be traces of metal lamination on the surface of casting, and there will be air vortexes. Improve filling degree of pressure chamber, choose a smaller pressure chamber as much as possible and use quantitative pouring;
4. Metal flow at inner gate of casting is obviously brighter than other parts, welding between different metal flows is not good. Under condition of good molding, increase thickness of inner gate to reduce filling speed:
5. Far end of casting is not bright, there are air vortices and paint accumulation, especially when using black oil hot molds. It is easier to find. Open an overflow groove at last filling part of cavity, avoid overflow groove and exhaust channel being closed by metal liquid.
6. There are depressions on the surface of pyrolysis part, which can be judged by X-ray flaw detection. In deep cavity pyrolysis area, gap between inlays is used to increase exhaust. If die-casting equipment has function of secondary extrusion, it can also be effectively solved;
7. There are obvious traces of paint accumulation at the end of filling or deep cavity. Amount of paint is thin and uniform, and paint with low gas emission is used after burning out;
8. Density test can be determined by sampling. Degassing and refining of alloy liquid must be thorough, and smelting process must be strictly followed;
9. Found after trial processing. Select a smaller processing allowance when processing is satisfied;
10. Surface of casting may have unsolid pressure, weld marks, and excessive brightness in special areas. Both fast injection speed and slow injection speed should not be too high. Secondary injection position should be as late as possible, pouring temperature should be reduced, and specific pressure should be increased.
11. There are cold shuts, paint accumulation, and unsolid pressure on the end surface. Increase specific pressure and filling speed, increase overflow trough and exhaust area at this place, the most effective way is to open a sub-runner and fill hot junction directly.
12. X-ray flaw detection castings have obvious pores inside, and castings are obviously unsolid. Reasonably set process parameters. During equipment inspection, boost pressure was in a normal state.

Defect 28-shrinkage

Other names: shrinkage eye, shrinkage cavity
Defect phenomenon: Irregular shape and rough surface holes caused by insufficient internal compensation during condensation process of die castings

Causes

Analysis, judgment and solution

1. Alloy pouring temperature is too high.
2. Wall thickness of casting structure is uneven, resulting in heat nodes and a large number of thickened parts.
3.Specific pressure is too low.
4. Overflow tank capacity is insufficient and overflow is too thin.
5. Filling degree of pressure chamber is too small, residual material (cake) is too thin, and final shrinkage compensation does not work.
6. Internal gate is small.
7. Local temperature of mold is high.

1. Local surface of casting is particularly bright. Comply with alloy smelting specifications, alloy liquid should not be overheated for too long, and pouring temperature should be reduced;
2. Concavities are prone to occur in wall thickness, accompanied by cold shut and failure to press. Consult with customer's technical engineer to improve casting structure, eliminate metal accumulation areas, and make wall thickness uniform and transition slowly without affecting use function. If equipment conditions allow, secondary extrusion is an effective method:
3. There is a phenomenon of uncompacted casting surface. Appropriately increase specific pressure;
4. There are traces of paint and cold metal accumulation on casting surface near overflow tank. Increase overflow tank capacity, thicken overflow port, and reasonably select overflow port position;
5. There is a lamination phenomenon on local surface of casting, cross-section of inner gate is uncompacted and loose. Increase filling degree of pressure chamber, use quantitative pouring, and control thickness of material cake:
6. Surface of casting is black, uncompacted, and there is a cold shut. Appropriately improve pouring system and increase cross-sectional area of inner gate to facilitate good pressure transmission;
7. Use a mold temperature gun to check local area of mold. Control local temperature of mold to achieve temperature balance, and add point cooling if necessary. Spray local high temperature area for a longer time to achieve a cooling effect.

Defect 29----Hard spots

Other names: Oxidation inclusions
Defect phenomenon: There are tiny particles or lumps in casting matrix that are harder than metal matrix, making processing difficult and causing severe tool wear. After processing, casting often shows hard spots of different brightness.

Causes

Analysis and solution

Metal or non-metal substances harder than base metal are mixed or precipitated into alloy, such as AL203 and free silicon.
1. Alumina (AL203)
(1) Aluminum alloy is not well refined
(2) Oxide is mixed in during pouring.
2. A complex compound composed of aluminum, iron, manganese and silicon, mainly formed by MnAL3 in colder part of molten pool, then Fe is precipitated with MnAL3 as core, silicon and other substances participate in reaction to form a compound.
3. Free silicon mixed in.
(1) Aluminum silicon alloy has a high silicon content.
(2) Aluminum silicon alloy is poured in a semi-liquid state, and free silicon exists.
4. Product of reaction between alloy liquid and refractory bricks and coatings.
5. Metal material is impure and contains other foreign matter. Alloy material is adhered to oil and tools are not clean.
6. Metal hard spots.
(1) Undissolved silicon element raw materials are mixed in.
(2) Raw materials that promote growth of primary silicon crystals are mixed in.
(3) Mixed with substances that generate intermetallic compound crystals.
7. Segregation hard spots. Due to densification of quenched structure, components that are easy to segregate are separated and become hard spots.
8. The alloy liquid is placed in the insulation furnace for too long.
9. Alloy liquid at the bottom of insulation furnace has not been removed for a long time, resulting in deposition.

Analysis and judgment: Since this defect is inside casting, it cannot be observed with naked eye. In addition, X-ray flaw detection cannot be identified, and only through processing can nature of hard spots be identified.
1. Reduce unnecessary stirring and overheating during smelting to keep alloy liquid pure. When aluminum alloy liquid is kept warm in furnace for a long time, it should be refined and degassed periodically. Do not scoop oxide on the surface of alloy liquid into spoon during casting. Oxide on melting tool must be removed, and coating on melting tool cannot react with aluminum;
2. When aluminum alloy contains titanium, manganese, iron and other components, it should not be segregated and kept clean. It should be refined with a dry refining agent, but when aluminum alloy contains magnesium, it should be compensated;
3. When aluminum alloy contains a lot of copper and iron, silicon content should be reduced to less than 10.5%, and pouring temperature should be appropriately increased to avoid silicon precipitation;
4. Use refractory bricks and coatings that do not react with aluminum, and replace furnace lining regularly;
5. Strictly manage furnace charge, and do not allow foreign matter or foreign materials to be mixed. Return charge is not allowed to be contaminated with oil, sand and dust. Rust and oxide on tool should be removed in time;
6. To adjust alloy composition, silicon elements cannot be added directly, and intermediate alloys should be used. Melting temperature should be high and time should be long to fully dissolve silicon. When adding materials, prevent alloy ingot from solidifying molten alloy. Reduce components that promote growth of primary silicon as much as possible. Reduce temperature fluctuation range, and do not make alloy temperature too high or too low. Control content of materials that produce metal compounds, and melt them at high temperatures if necessary. Control temperature fluctuation range to keep alloy in a molten state;
7. After alloy is poured into pressure chamber, it should be immediately injected and filled. Alloy components that are prone to rapid cooling, such as Ca, Mg, and Na, should not be contained as much as possible, and Ca should be controlled below 0.05%;
8. Alloy liquid that has been placed in insulation furnace for a long time must be taken out and re-melted, and materials should be mixed as soon as possible;
9. Alloy liquid at the bottom of insulation furnace should be taken out in time according to process regulations, and structure should be set to re-add new alloy liquid.

Defect 30-Brittleness

Defect phenomenon: Basic metal grains of casting are too coarse or fine, making casting easy to break or smash.

Cause

Analysis, judgment and solution

1. Alloy liquid is overheated or insulation time is too long.
2. Intense overcooling and too fine crystallization.
3. Content of impurities such as zinc and iron in aluminum alloy is too much.
4. Copper content in aluminum alloy exceeds specified range.
5. Coating layer of melting tool falls off.

1. Monitoring of temperature control system of melting furnace and temperature control furnace. Alloy should not be overheated to avoid long-term insulation;
2. According to simulation analysis of temperature field of mold cavity, find out area with large temperature changes, add point cooling or point heating, increase mold temperature, and reduce pouring temperature;
3. Check chemical composition of alloy through spectral analysis, strictly control content of zinc and iron in alloy;
4. Check chemical composition of alloy through spectral analysis, and strictly control content of copper in alloy;
5. Keep coating layer of melting tool intact and good;

Defect 31----Leakage

Defect phenomenon: Die casting leaks water, air or water after testing. Red light of dry pressure tester is on.

Causes

Analysis, judgment and solution

1. Insufficient boost pressure.
2. Poor design of pouring system.
(1) Far from leakage area, poor internal quality:
(2) Poor fusion of metal flow, resulting in cold shut;
(3) Small cross-sectional area of inner gate, inadequate boost transmission, formation of pores or shrinkage at far end;
3. Improper alloy selection, poor fluidity, unsuitable for die casting production.
4. Poor exhaust, local defects such as pores, shrinkage and cold shut.
5. Unreasonable casting design, uneven or too thick wall thickness, heat knot, pores, shrinkage and cracking, etc. that seriously affect air tightness.
6. Large processing volume, damage to surface oxidation dense layer or thinning of wall thickness, especially double-sided processing parts.
7. Alloy melting temperature is too high, insulation time is long, shrinkage and cracking are easy to occur at thick wall during die casting.
8. Coating gas emission is large, which is easy to produce pores.
9. Failure of pressure test equipment.
10. Sealing surface is damaged or does not meet roughness requirements. For example, there are scratches and indentations on machined surface. Roughness of non-machined sealing groove is poor due to cracking.
11. Deformation of casting causes sealing surface to warp.

1. Far end or wall thickness of part is not pressed firmly. Increase specific pressure:
2. It can be analyzed and judged based on simulated filling or actual sample debugging. Reasonably improve pouring system;
3. Select good alloys.
4. Analyze whether there is air entrainment and poor alloy flow fusion in local part of casting during hot mold stage. Reasonably add slag collection bags and exhaust ducts
5. Use X-ray flaw detection to find hot knot. If hot knot is indeed a leakage point, you can negotiate with customer engineer to change structure there and reduce wall thickness. In addition, secondary extrusion process can be used to solve leakage at pyrolysis point:
6. Try to avoid processing or use the smallest possible processing allowance:
7. X-ray flaw detection to check internal quality of casting. Appropriately reduce melting temperature;
8. X-ray flaw detection to check internal quality of casting. Use paint with low gas emission; impregnate castings;
9. Use qualified castings to identify pressure test equipment. Repair and inspect equipment;
10. It can be found through pressure test. Strengthen process protection and repair molds in time;
11. It can be found through flatness inspection. Control the production process, and pressure holding time must be sufficient. Prevent squeezing, pressing, and falling during process operation.

Defect 32---Pinhole

Defect phenomenon: There are tiny holes inside die casting, which appear in pieces in many cases. It is not easy to be found by X-ray flaw detection and can only be seen on processed surface.

Causes

Analysis and solution

1. Charge is not clean and contains impurities containing gas, especially use of return material.
2. Melting temperature is too high, causing alloy liquid to absorb air.
3. Alloy liquid after refining and degassing is kept for too long.
4. Gas products of air or lubricant enter metal during bulk filling.
5. Gas precipitation during metal melting
6. Exhaust effect of mold cavity is poor.
7. Mold temperature is too high, and condensation speed of alloy liquid is slow after filling.
8. State of alloy flow filling is unreasonable, forming turbulence, causing gas to enter alloy

1. Use clean charge. For returned materials and scrap parts, they must be used in a graded manner, and unqualified materials must be processed before they can be used;
2. Check temperature control display of melting furnace; melting temperature must be controlled within process requirements;
3. Treated alloy liquid should be used as soon as possible, and it cannot be placed in melting furnace or holding furnace for too long. Alloy liquid stored for a long time must be reprocessed before it can be used:
4. Try to increase metal flow speed during bulk filling. Reduce pressure chamber diameter, reduce cross-sectional area of inner gate or increase injection speed.
5. Analyze gas content in metal liquid through density detector. Reasonably refine in melting furnace and thoroughly degas after leaving furnace;
6. Increase cross-sectional area of exhaust groove and reasonably set overflow groove around casting:
7. Reasonably design mold cooling system to increase solidification speed of alloy liquid through cooling of the entire mold;
8. Reasonably design position, direction and cross-sectional area of inner gate to ensure continuous filling of metal flow and achieve sequential solidification.

Defect 33---Slag inclusion

Other name: Slag hole
Defect phenomenon: Metal and non-metal particles different from material of die casting exist inside die casting, which are not fixed in position and are not easy to be found during X-ray flaw detection. They can only be seen on processed surface.

Cause

Analysis, judgment and solution

1. Mixed slag:
1) Lining of melting furnace, transfer bag and holding furnace falls off.
2) Slag is not removed thoroughly before leaving furnace after refining in melting furnace.
3) Surface slag is not removed after degassing in transfer bag.
4) When alloy liquid is poured into holding furnace, guide groove is not clean and not filtered.
5) During pouring, slag on the surface of holding furnace is not removed and enters pressure chamber with pouring spoon.
2. Graphite inclusions:
1) Edge of graphite crucible has fallen off and entered alloy
2) There is too much graphite in coating

1. Use following means to prevent slag from entering cavity as much as possible:
1) Repair furnace or replace furnace lining in time;
2) Remove slag in melting furnace in time according to process requirements until it is thorough and clean:
3) After transfer bag is degassed, scum on the surface must be removed:
4) Ensure that guide trough is dry and a filtering device must be installed at the front end:
5) Scum on the surface of insulation furnace is cleaned. When scooping alloy liquid with a pouring spoon, scoop it from below liquid surface as much as possible:
2,
1) Add a protective cover to the edge of graphite crucible;
2) Use coating evenly and in an appropriate amount. Use a coating with less graphite content;

Defect 34-Looseness

Defect phenomenon: Surface of casting shows a loose macrostructure. There are areas of loose material inside, accompanied by shrinkage holes. It can be found during X-ray flaw detection but it is a bit vague.

Cause

Analysis, judgment and solution

1. Alloy shrinks greatly, mostly in thick and large parts, that is, alloy volume shrinks too much.
2. There is a drastic transition on casting, such as directly transitioning from a thin wall to a thick and deep cavity, and transition radius is small.
3. Boost pressure is not enough.
4. Die-casting machine boost is established late, pressure holding time is short or it cannot hold pressure.
5. Mold cavity temperature is too high
6. Alloy liquid is poured in small quantities, that is, material thickness is too thin and boost cannot be conducted.
7. Too much paint spraying
8. Alloy pouring temperature is low.

1. Change alloy grade if possible. Reduce thickness of casting as much as possible;
2. Adjust structure of casting, and drastic changes must be smooth transition:
3. Phenomenon of non-pressurization can be found on the surface of casting. Increase boost pressure:
4. Repair die-casting machine to ensure boost pressure;
5. Use a temperature gun to detect temperature of each part of mold cavity. The overall mold balance sets point cooling and line cooling. Spray more in local high-temperature area for forced cooling;
6. Use quantitative pouring. Thickness must be controlled within specified range of process;
7. Coating is sprayed evenly and thinly;
8. Appropriately increase alloy pouring temperature.

3. Other defects

Defect 35---Chemical composition does not meet requirements

Defect phenomenon: After photoelectric spectroscopy and metallographic microscope analysis, alloy elements of casting do not meet requirements or there are too many impurities.

Causes

Analysis, judgment and solution

1. Alloy ingots or raw materials have unqualified or inaccurate components when entering factory.
2. Alloy ingots or raw materials have many impurities in metallographic analysis.
3. Recycled materials are not processed, analyzed and put into use immediately, proportion added is too much.
4. Extraction or treatment method of sample is incorrect.
5. Improper smelting process, such as excessive temperature and severe burnout, causes changes in content of certain alloy elements.
6. Alloy insulation time is too long or alloy liquid in lower half of insulation furnace is not cleared as required, resulting in deposition and inclusions in casting. In addition, it may also cause changes in content of certain alloy components.
7. Smelting tools are not painted or paint is peeling off.

1. Spectral inspection of alloy ingots and raw materials before entering factory. Return to supplier:
2. Metallographic inspection of alloy ingots and raw materials before entering factory. Return to supplier:
3. X-ray flaw detection or fracture analysis. Strictly abide by use and management regulations of returned materials;
4. Strictly implement sample selection operation method and correctly polish surface to be inspected. If necessary, re-sample for re-inspection. In production, castings should be regularly tested for processability:
5. Timely conduct photoelectric spectrum analysis and metallographic inspection. Strictly control alloy melting temperature and pouring temperature, and try to eliminate various factors that form oxides in alloy;
6. Timely remove and clean furnace according to process requirements:
7. Strictly implement operation procedures for use of melting tools.

Defect 36---Mechanical properties do not meet requirements

Other names:
Defect phenomenon: Strength, hardness, elongation, etc. of casting alloy do not meet standards. Mainly reflected in processing and assembly use.

Cause

Analysis, judgment and solution

Chemical composition of alloy does not meet the standards:

1) Low hardness: low content of Si, Cu, Ni and Zn
2) Low strength: low content of Si, Ni, Mn and Cr
3) Poor toughness: high content of Si, Mg, Zn, etc.
4) Poor cutting performance: low content of Si, Cu, Ca
2. There are casting defects such as pores, shrinkage holes, slag inclusions and looseness inside casting.
3. Sample treatment method is not equal.
4. Unreasonable structure of casting limits casting from reaching standard.
5. Improper smelting process produces oxides and other compounds.

1. Chemical composition of ingredients should be strictly controlled during melting to keep it within standard requirements, preferably close to median;
2. Strictly abide by smelting and die-casting process to avoid and reduce internal defects.
3. Make samples as required and conduct process tests on castings regularly during production.
4. Improve structure of castings to avoid internal stress concentration as much as possible and ensure smooth transition:
5. Strictly control alloy melting temperature and pouring temperature to eliminate various factors that cause alloy oxides to form.

Defect 37----Mold expansion

Other names: aluminum leakage, splashing
Defect phenomenon: When mold is opened after injection process is completed, a certain thickness of flash is generated on parting surface (non-cavity part), which directly affects size of casting. Sometimes flash is in liquid state and splashes directly from parting surface or sliding joint during injection process.

Causes

Analysis, judgment and solution

1. Before mold closing, mold parting surface is not clean, and there is residual aluminum or other adhesives.

2. Moving and fixed molds are not tight when adjusting mold closing, and gap is large.
3. Die-casting machine has insufficient clamping force.
4. Moving and fixed mold surfaces of die-casting mold are not parallel.
5. Stress of four clamping bars of die-casting machine is uneven.
6. Injection pressure is very large, which seriously exceeds process requirements.
7. Gap between sliding splicing inserts becomes larger.
8. Side-drawing slider lock fails, causing slider to retreat.
9. Die-casting machine installs mold plate is not parallel, which may be a problem with plate itself, or gap between bar and guide sleeve is too large.
10. Injection pressure becomes larger, and material cup with a smaller diameter may be replaced or injection pressure may suddenly increase.

1. Check mold parting surface, and mold expansion state is not in four directions. Remove any adhesion on parting surface to ensure that parting surface is clean before closing mold;
2. Check state of bend during closing mold. Mold expansion state is relatively uniform in four directions. When parting surface is clean, adjust mold forward;
3. Through theoretical calculation and adding a certain insurance coefficient, it can be found whether clamping force of die-casting equipment is appropriate. Mold expansion state is basically uniform in all directions. Replace die-casting equipment with large tonnage. Under premise of ensuring product quality, reduce area of pouring system;
4. Under condition of ensuring that mold parting surface is clean, color and grind mold (on die-casting machine). Usually, part of parting surface is not colored or coloring is light. Remove mold, use platform and height gauge to check parallelism of moving and fixed mold surfaces. If parallelism is unqualified, repair mold;
5. In the case of inspection work in Article 4, if mold inspection parallelism is qualified, consider adjusting stress of die-casting machine bar;
6. Check equipment injection pressure gauge. Mold expansion state is basically uniform in all directions. Reduce injection pressure.
7. When sliding joint is cleaned, check gap with a feeler gauge. Replace or repair insert.
8. When side pull joint is cleaned, color and grind. Repair or replace locking fastener;
9. First, confirm that moving and fixed mold planes of mold are parallel, then confirm that stress of four large bars is even. During die casting, aluminum may run from one side or one corner, resulting in mold expansion. Repair equipment;
10. State of mold expansion is that large flash appears evenly on all sides. Replace raw material cup and use a large-tonnage die-casting machine. Keep injection pressure stable.

Defect 38---Dimensional deviation

Defect phenomenon: Dimensions of die casting do not conform to drawings, dimensional tolerances and form and position tolerances.

Causes

Analysis, judgment and solution

1. Dimensions of casting do not meet requirements:
1) Design errors, the shrinkage of casting and thermal expansion of mold material are not calculated.
2) Guide device of mating surface or movable part is not processed accurately.
3) Holding time is too long or too short, shrinkage is inconsistent, and size is deviated.
2. Dimensions of vertical parting surface are incorrect:
1) Mold expands during die casting process
2) Mold has poor rigidity and elastic deformation occurs at the moment of injection.
3) Fixed and sliding inserts perpendicular to parting surface are loose.
3. Dimensions of side draw are incorrect:
1) Slider has poor rigidity and impact deformation,
2) Position accuracy of slider slide is poor.
3) Locking block is not strong enough and fails
4. Dimensions formed by live block are incorrect:
1) There are burrs or damage on fixed part of live block, which causes live block to shift, dislocate and tilt, resulting in uneven wall thickness of casting.
2) Live block is not preheated and placed incorrectly
5. Inconsistency in sizes of different half molds:
1) Two half mold cavities are misaligned during manufacturing
2) Two half molds are worn.
6. Incorrect hole size of casting:
1) Core is wrong, bent, or damaged.
2) Reduction ratio is wrong or manufacturing is wrong, resulting in incorrect core hole position.

1. Judge by size detection or inspection of inspection tool.
1) After die-casting process is constant, modify mold cavity size according to actual shrinkage value obtained after casting is measured;
2) Modify mold until size is qualified;
3) Check holding time display table. Set holding time according to process requirements;
2. Judge by size detection or inspection of inspection tool.
1) Choose a large-tonnage die-casting machine. Repair mold and equipment clamping mechanism to ensure that there is no mold expansion:
2) Add as many support columns as possible on the back side of movable mold base to enhance rigidity. Replace material of corresponding part of mold:
3) Repair or replace insert;
3. Judge by dimensional inspection.
1) Replace slider material or increase its rigidity:
2) Repair mold slider guide mechanism;
3) Replace or repair side-drawn slider locking block:
4. Check wall thickness and corresponding dimensions with a wall thickness gauge,
1) Repair mold cavity movable block fixing part:
2) Follow operating instructions. Must be preheated for use;
5. Visual observation or dimensional inspection.
1) Re-repair mold or obtain allowed offset part;
2) Replace mold guide column and guide sleeve:
6. Judge by three-coordinate detection.
1) Replace core:
2) Select appropriate shrinkage ratio according to actual casting inspection data and correct core hole position.

Defect 39--Poor corrosion resistance

Defect phenomenon: Surface of die casting is oxidized or corroded by moisture prematurely during assembly and use.

Cause

Analysis, judgment and solution

1. Deviation of content of various elements in alloy:
1) Content of Cu is too high
2) Content of Mg is too low;
3) Content of Ni is too high;
2. Casting has not been treated with surface protection.
3. Damage to surface protective layer, such as peeling of processing surface and coating

1. Photoelectric spectrum analysis. Chemical composition of ingredients must be strictly controlled during melting to keep it within standard requirements, preferably close to median;
2. If working environment is not extremely harsh, shot peening or finishing can be performed. If working environment is harsh, surface needs to be chrome-plated or nickel-plated;
3. Processing surface is best used as assembly surface. Strictly control quality of coating, and no peeling, flaking or missing plating defects are allowed;

Defect 40--Poor surface coating quality

Defect phenomenon: Die casting has non-standard defects during surface coating, such as peeling, patterns and non-coating.

Cause

Analysis, judgment and solution

1. Peeling during chrome plating, nickel plating and surface passivation. Main reasons:
1) There are defects in the surface quality of die casting. Such as cold shut, uncompacted pressing and surface bubbles.
2) Poor surface treatment before coating, such as long water sandblasting time and fast speed.
2. Inconsistent surface coating color. Main reasons:
1) There are defects such as flow marks, patterns and paint accumulation on casting surface.
2) Unqualified surface treatment before coating, such as uneven polishing.
3. Surface is not coated or coating peels off
1) There is a problem with die casting coating
2) Coating process is unreasonable. Such as coating time, temperature, etc.

1.
1) Adjust die casting process so that there are no or as few casting defects as possible on casting surface;
2) Control quality of various pre-treatments before coating
2.
1) Working environment is not extremely harsh, and shot peening or finishing can be performed. Working environment is harsh, and surface needs to be chrome-plated or nickel-plated:
2) Polishing and other treatments before coating must be strictly controlled:
3.
1) Replace or adjust die-casting coating;
2) Adjust coating process.

Defect 41-sticking mold

Defect phenomenon: During die casting process, alloy adheres to core, cavity partially or even the whole cavity.

Cause

Analysis, judgment and solution

1. Mold manufacturing problem, core and local deep cavity have small die draft.
2. Mold or core heat treatment problem, no nitriding or oxidation treatment.
3. Poor release agent effect.
4. Less and uneven spraying of release agent.
5. Wrong ratio of release agent, too much water.
6. Design problem or structural problem of casting itself, fixed mold has a greater mold force than moving mold, so that casting sticks to fixed mold as a whole.
7. Diameter of ejector pin is selected to be thinner, which penetrates casting and makes it stick to moving mold as a whole.
8. Side-drawn core is returned to matching hole, and release agent cannot be sprayed.

1. Local surface or hole of casting is scratched. Modify die draft to ensure that it is above 1.5°;
2. Local aluminum adhesion of cavity is serious. Cavity is nitrided or oxidized on the surface. Core must be nitrided;
3. Replace mold release agent with good quality;
4. Spray mold release agent evenly and sufficiently, especially spray more in overheating area.
5. Prepare according to mold release agent preparation requirements;
6. Roughen mold wall or directly add grooves in parts that do not affect product function to increase mold holding force of movable mold:
7. Replace ejector with a larger diameter or increase number of ejectors;
8. Adjust core pulling program of equipment, keep core in inserted state during spraying, and ensure spraying of mold release agent.

Defect 42-hole deviation

Defect phenomenon: Due to wrong position or bending of core, black skin is exposed when processing light hole or threaded hole. Interference may also occur during assembly.

Causes

Analysis, judgment and solution

1. Hole position is wrong during design and manufacturing.
2. Wrong selection of reduction ratio.
3. Deviation of processing positioning benchmark, such as casting deformation, positioning surface damage, etc.
4. Core bending.
5. Processing process program error.

1. Dimension detection. Adjust hole position;
2. After process is stable, measure casting, determine shrinkage ratio, and adjust hole position:
3. Strictly control production process, strengthen inspection of blank casting, and eliminate deformation. Repair positioning surface damage in time:
4. Strain appears on the side of hole. Strengthen process inspection and operator self-recommendation. Replace core in time;
5. Dimension inspection. Adjust processing procedure;

Defect 43-Broken Core

Defect phenomenon: Core or molded part that forms round hole or special-shaped hole is broken.

Cause

Analysis and solution

1. Core is seriously sticky to aluminum and is pulled off;
2. Core manufacturing quality is poor, strength is insufficient, and surface is not nitrided.
3. Position of gate is unreasonable, directly impacting core.
4. Casting is deflected when ejected, and core is broken.
5. The whole or part of casting is sticky to mold, and core is broken when baking or picking residual parts.
6. Side of core is damaged or bent, resulting in increased mold force.

1. Increase amount of spraying, check aluminum sticking of core in time, and polish it in time;
2. Strengthen inspection of core entering factory and re-manufacture core;
3. Adjust position of gate or change gate structure, so that alloy flow bypasses core to avoid direct impact on core;
4. Use reset pull rods of same length as much as possible to avoid direct use of ejector rods:
5. Control die-casting operation process to avoid sticking to mold as much as possible. When taking out remaining parts after sticking mold, refer to actual casting and pay attention to core part;
6. Replace core;

Defect 44---Black skin on processed surface

Defect phenomenon: After processing, processing part of casting has a phenomenon of not being processed locally, exposing cast surface.

Causes

Analysis, judgment and solutions

1. Core is bent, resulting in black skin on one side after hole processing.
2. When manufacturing mold, size of processing part is small, resulting in small processing allowance.
3. Surface to be processed is uneven, that is, processing allowance is uneven, resulting in black skin on local processing.
4. Casting is deformed, positioning reference changes, and position of processing part changes.
5. Processing part of cavity is damaged or adheres to debris, causing processing surface of casting to be concave and processing volume is insufficient.
6. Processing part corners are damaged by collision, resulting in concave.
7. Positioning changes during processing or casting is incorrectly clamped.

1. Check and replace core in time;
2. Repair mold and increase processing allowance;
3. Repair mold and make up processing allowance;
4. Increase holding time to ensure that casting is not deformed or deformation is small. Subsequent correction and solution;
5. Check cavity in time, repair and polish mold;
6. During process transfer and delivery, castings must be protected to prevent knocks, collisions, falls, and squeezing;
7. Strictly implement processing technology and strengthen self-inspection.