Die casting training materials to understand die casting

Time：2024-12-16 09:02:54 / Popularity： / Source：

1 Characteristics and process of aluminum die casting

1.1 Characteristics of aluminum die casting

1.1.1 Concept of aluminum die casting

Pressure casting is a special casting method with little or no cutting that has developed rapidly in modern metal processing technology. It is a process of pouring molten metal into a pressure chamber, filling mold cavity at high speed, then crystallizing and solidifying under high pressure to become a die casting. High pressure and high speed are main characteristics of pressure casting. General filling speed (gate speed) is 30m/s~80m/s, pressure (pressure that aluminum liquid bears when solidifying) is 40Mpa~120Mpa, and time for metal liquid to fill mold cavity is extremely short, which is 0.01s~0.16s.

1.1.2 Four major elements of aluminum die casting

1.1.3 Features of aluminum die-casting products

Advantages of aluminum die-casting products
1. Good product quality: high dimensional accuracy of die-casting parts; good surface finish; high strength and hardness; stable dimensions, good interchangeability; thin-walled and complex products can be directly formed.
2. High production efficiency: machine has high production efficiency, and horizontal cold chamber die-casting machine (2000ton) aluminum alloy automobile gearbox can produce 1580 pieces a day.
3. Good economic benefits: quite a few die-casting parts do not need to be cut and processed, are used directly, or processing volume is very small, which improves utilization rate of metal, reduces a lot of processing equipment and working hours.
4. Strong, high quality and light weight: With continuous optimization of aluminum alloy materials, strength of die-cast aluminum alloy products can also meet use requirements of many mechanical industries, especially automotive industry, but its quality is only 1/3 of cast iron (steel).
Disadvantages of aluminum die-casting products
1. It is easy to produce pores, internal pressure of pores is high, and heat treatment is generally not possible;
2. For products with "concave" structures with small mouths and large interiors, die-casting is more difficult;
3. It is not suitable for small batch production. Main reason is that cost of die-casting molds is high and production continuity requirements are strong.

1.1.4 Product characteristics of aluminum die casting blanks

1.1.5 Types of aluminum die-casting products

Aluminum alloy die-castings are widely used in automotive, aviation, electric (pneumatic) tools, lighting, decorations, furniture and other industries. Automotive industry is main one, and according to statistics, automotive industry accounts for 76% (by total weight)

1.2 Aluminum die casting process

1.2.1 Aluminum die casting process

1.2.2 Aluminum die casting process - injection process

Low speed
Press all aluminum liquid in melting cup to gate.
Low speed is generally 0.15m/s-0.25m/s. If speed is too slow, temperature of aluminum liquid will drop too much. If speed is too fast, aluminum liquid will splash when it moves forward and air in melting cup will be drawn into aluminum liquid.
High speed
Press aluminum liquid accumulated in melting cup to gate into mold cavity.
High speed (punch speed) is generally 2.5mis~4.5m/s. If speed is too slow, it is easy to produce cold shut, black product and other poor appearance. If speed is too fast, it is easy to draw air in mold cavity into product and aluminum liquid will seriously scour mold.
Supercharge
Solidify aluminum liquid under high pressure.
Boost pressure (pressure that aluminum liquid bears) is generally 40Mpa-120Mpa. If pressure is too high, impact on equipment and mold will be large. If pressure is too low, internal structure of product will not be dense.

Four major elements of die casting

2.1 Aluminum alloy

2.1.1 Characteristics of die-cast aluminum alloys

1. Low density and high specific strength.
2. Good mechanical properties at both high and room temperatures, especially good impact toughness.
3. Good electrical and thermal conductivity. Mechanical cutting performance is also very good.
4. There is a layer of aluminum oxide film with stable chemical composition and dense structure on the surface.
5. Good fluidity, small shrinkage, good surface roughness and small thermal cracking.

2.1.2 Commonly used die-cast aluminum alloys

Material brand	Cu	Si	Mg	Zn	Fe	Mn	Ni	Sn	Pb	Cr	Ti	Al
AISi9Cu3(Fe)	2.0-4. 0	8.0-11.0	0.05-0.55	1.2	1.3	0.55	0.55	0.25	0.35	0.15	0.25	margin
ADC12	1.5-3.5	9.6-12.0	0.3	1.0	1.3	0.5	0.5	0.2	0.2	-	0.3	margin
A380	3.0-4.0	7.5-9.5	0.1	3.0	1.3	0.5	0.5	0.35	-	-	-	margin

In addition to three aluminum alloys in table above, A360, AISi12 (Cu), ADC10, ZL102, ZL103, etc. are all commonly used die-cast aluminum alloys. The most commonly used aluminum alloys are "aluminum-silicon" aluminum alloys, because "aluminum-silicon" aluminum alloys allow 0.2%~0.5% impurities to exist, and old pots can be used for recycling to improve utilization rate of raw materials.

2.1.3 Key to quality of aluminum liquid

After aluminum liquid is melted, it undergoes several important process treatments such as refining, degassing, slag removal, and (tempering). These treatments are the key to ensuring quality of aluminum liquid.
① When aluminum liquid is at 660℃, solubility of H2 is 0.69cm3/100g, while solubility of H2 in solid aluminum at room temperature is only 0.001cm3/100g. Therefore, under natural conditions, 0.69cm3/100g of H2 will be precipitated during solidification of aluminum liquid and will be wrapped inside die casting. Degassing is to reduce hydrogen content in aluminum liquid.
② A1, Zn, Mg, etc. have good activity and are easily oxidized with oxygen, especially at high temperatures. Therefore, slag removal is to remove oxides and impurities in high-temperature aluminum liquid.
③ Tempering is mainly to refine grain and improve mechanical properties of aluminum die castings.

2.2 Die-casting machine

2.2.1 Basic structure - clamping mechanism

Mechanism name	Function
Fixed plate	Install fixed fixed mold
Moving plate	Install fixed moving mold
Tail plate	Support moving plate to move and lift elbow
Ejector mechanism	Eject product
Clamping cylinder	Drive moving plate to move
Gorilla column	Balance "three plates" of die-casting machine
Toggle	Lock mold by increasing clamping cylinder force
Motor	Drive hydraulic pump of the entire hydraulic system
Mold	Molding tool

2.2.2 Basic structure - injection mechanism

Mechanism name	Function
Energy accumulator	Store oil pressure energy to provide instantaneous energy for rapid injection and boosting
Boosting cylinder	Extrude hydraulic oil in injection cylinder to amplify its pressure
Injection cylinder	Push injection rod forward to perform injection
Injection rod	Connect injection cylinder and punch
Punch	Push aluminum liquid to fill mold cavity
Melting cup	Contain aluminum liquid

2.2.3 Schematic diagram of hydraulic system

2.3 Die-casting mold

2.3.1 Role of die-casting molds

Die-casting mold is an important tool in die-casting production process. It plays an extremely important role in production rhythm and quality of die-casting parts. It has a very close relationship with die-casting process and production operations, which are mutually influenced and restricted. There is a saying in die-casting industry that "mold accounts for 60%, process accounts for 30%, and manual operation accounts for 10%. From this, we can know that key to efficiency of die-casting lies in quality of mold.
Important role of mold is:
(1) Determines shape and dimensional tolerance grade of die-casting parts
(2) Pouring system determines filling state of aluminum liquid in mold
(3) Controls and adjusts thermal balance of die-casting process.
(4) Strength and technical parameters of mold limit maximum value of injection pressure
(5) Affects production efficiency of die-casting.

2.3.2 Structure of die-casting mold

◆ Molding system: core, cavity, etc. are made of high-quality hot-drying mold steel. (DAC55, 8407, DHA33-ES)
◆ Casting system: channel for introducing aluminum liquid into molding system.
◆ Mold frame system: functions of support, positioning and guidance. (cast steel)
◆ Core pulling system: holes and cavities of molded products perpendicular to direction of parting surface.
◆ Ejection system: facilitates product to be separated from mold.
◆ Cooling water system: balances mold temperature.

Gud Mould Industry Co., Ltd