Appearance inspection: There are stripes on the surface of casting that are consistent with flow direction of molten metal, there are obviously non-directional lines that are different in color from metal matrix, and there is no development trend.

 

1. Causes of flow marks are as follows:
1) Mold temperature is too low
2) Poor runner design and poor location of inner gate
3) Material temperature is too low
4) Low filling speed and short filling time
5) Pouring system is unreasonable
6) Poor exhaust
7) Spray is unreasonable
2. Cause of patterns is excessive paint spraying in mold cavity or poor paint quality. Solutions and prevention methods are as follows:
1) Adjust cross-sectional area or position of gate
2) Increase mold temperature
3) Adjust gate speed and pressure
4) Properly select paint and adjust dosage

Appearance inspection: There are traces of protrusions or depressions like hairlines on the surface of die-casting parts, which continue to expand and extend as number of die-casting times increases.

 

Reasons are as follows:
1) There are cracks on the surface of die-casting mold cavity
2) Uneven preheating of die-casting mold
Solutions and prevention methods are:
1) Die-casting mold should be annealed regularly or after a certain number of die-casting times to eliminate stress in cavity.
2) If cracks have appeared on the surface of cavity, molding surface should be polished to remove crack layer.
3) Mold must be preheated evenly

Appearance inspection: Surface of die-casting parts has obvious, irregular, sunken linear lines (both penetrating and non-penetrating), which are small and long in shape. Sometimes edges are smooth, and there is a possibility of disconnection under action of external force.

 

Reasons are as follows:
1) The two metal streams are connected to each other, but they are not completely fused and there is no inclusion between them, and bonding force between two metal streams is very weak.
2) Pouring temperature or die-casting mold temperature is too low
3) Sprue position is wrong or flow path is too long
4) Low filling speed
Solutions and prevention methods are:
1) Properly increase pouring temperature
2) Increase injection ratio, shorten filling time, and increase injection speed.
3) Improve exhaust and filling conditions

Visual inspection: There are smooth indentations (like a dish) on the surface of thickest part of die casting.

 

Reasons are as follows:
1) Caused by contraction
Improper design of die castings and too large wall thickness difference
Improper sprue position
Low injection pressure and short holding time
Local temperature of die-casting mold is too high
2) Cooling system design is unreasonable
3) Open mold too early
4) Pouring temperature is too high
Solutions and prevention methods are:
1) Wall thickness should be uniform
2) Transition between thickness and thickness should be gentle.
3) Correctly select introduction position of alloy liquid and increase cross-sectional area of inner runner
4) Increase injection pressure and extend pressure holding time
5) Appropriately reduce pouring temperature and die-casting mold temperature
6) Local cooling is required for local high temperatures
7) Improve overflow conditions

Appearance inspection: Traces left by contact between surface of casting and surface of die-casting mold cavity or step marks on the surface of casting.

 

Reasons are as follows:
1. Caused by ejection components
1) End face of ejector pin is worn
2) Adjustment length of ejector rod is inconsistent
3) Splicing part of die-casting mold cavity does not match well with other parts.
2. Caused by splicing or moving parts
1) Inlaid part is loose
2) Moving parts are loose or worn
3) Side wall surface of casting is formed by inserts inserted into movable and fixed molds.
Solutions and prevention methods are:
1) Length of ejector rod should be adjusted to appropriate position
2) Fasten inserts or other movable parts
3) Eliminate sharp corners during design and adjust clearance accordingly
4) Improve casting structure so that die-casting mold eliminates interspersed inlay form and improves die-casting mold structure

Appearance inspection: Small flakes and base parts of metal or non-metal and metal are partially welded, and small flakes peel off under action of external force. Some of surfaces of peeled castings are shiny and some are dark gray.

 

Reasons are as follows:
1) There are metal or non-metallic residues on the surface of die-casting model cavity
2) During pouring, impurities are first brought in and attached to surface of cavity
Solutions and prevention methods are:
1) Before die casting, clean cavity pressure chamber and pouring system to remove metal or non-metallic adherents
2) Poured alloy must also be cleaned
3) Choose appropriate coating and coating should be uniform

Appearance inspection or damage inspection: There are obvious layers of metal in parts of casting.

 

Reasons are as follows:
1) Mold is not rigid enough. During filling process of molten metal, mold plate will vibrate.
2) Punch crawls during injection process
3) Improper design of sprue system
Solutions and prevention methods are:
1) Strengthen rigidity of mold and tighten mold parts to make them stable
2) Adjust cooperation between injection punch and pressure chamber to eliminate crawling phenomenon
3) Reasonable design of sprue

Appearance inspection: Surface of die-casting part produces rough surfaces in some locations.

 

Reasons are as follows:
1) Improper position, direction and shape of gate caused by die-casting mold (mold)
2) Insufficient cooling of parts where molten metal is eroded violently in inner runner caused by casting conditions.
Solutions and prevention methods are:
1) Improve position and direction of pouring channel and poor pouring performance
2) Improve cooling conditions, especially areas where molten metal is eroded violently
3) Add paint to ablated part
4) Adjust flow rate of alloy liquid so that it does not produce air pockets
5) Eliminate alloy adhesion on mold (mold)

Appearance inspection: There are pits or ridges in local parts of die-casting parts.

 

Reasons are as follows:
1) Improper setting of gate sprue position
2) Poor cooling conditions
Solutions and prevention methods are:
1) Thickness of gate must be appropriate
2) Modify location, direction and setting method of ingate
3) Strengthen cooling of eroded parts.

Appearance inspection: Place casting in an alkaline solution and cracks will appear dark gray. Damage and cracking of metal matrix are linear or wavy, with narrow and long lines, and tend to develop under action of external forces.

 

Reasons for cracks in aluminum alloy castings:
1) Iron content in alloy is too high or the silicon content is too low; content of harmful impurities in the alloy is too high, which reduces plasticity of alloy; aluminum-silicon alloys and aluminum-silicon-copper alloys contain too much zinc or copper; aluminum-magnesium alloys contain too much magnesium
2) Mold retention time is too short and pressure holding time is short; wall thickness of casting changes drastically.
3) Local tightening force is too large and force is uneven during ejection.
Solutions and prevention methods:
1) Correctly control alloy composition. In some cases: pure aluminum ingots can be added to alloy to reduce magnesium content in alloy; or aluminum-silicon master alloy can be added to alloy to increase silicon content.
2) Increase temperature of mold (mold); change casting structure, adjust core pulling mechanism or make push rod evenly stressed
3) Increase draft angle and use strong release agent locally
4) Increase mold retention time and pressure holding time