Die casting is a process of metal smelting and processing. It is a casting method that fills cavity of a steel mold with molten alloy liquid at high speed under action of high pressure, and solidifies alloy liquid under pressure to form a casting. It is somewhat similar to " Plastic Injection Molding". Main features that distinguish die casting from other casting methods are high pressure and high speed.

 

1) Aluminum alloys can be divided into anti-rust aluminum (LF), duralumin (LY), super duralumin (LC) and wrought aluminum (LD).
2) Cast aluminum alloys are divided into four types according to main alloying elements added: aluminum-silicon (AL-Si), aluminum-copper (Al-Cu), aluminum-magnesium (Al-Mg) and aluminum-zinc (Al-Zn). Commonly used grades are ADC12 (A383), ADC10 (A380).
3) Advantages of aluminum alloy die casting
Good product quality: castings have high dimensional accuracy, good surface finish, high strength and hardness, and strength is generally 25-30% higher than sand casting, but elongation is reduced by about 70%, with stable dimensions and good interchangeability. It can die-cast aluminum thin-wall complex castings, for example: current minimum wall thickness of zinc alloy die-casting can reach 0.3mm, and aluminum alloy die-casting can reach 0.5mm. High production efficiency: Machine has high productivity. For example, domestic JⅢ3 horizontal cold air die-casting aluminum machine can die-cast aluminum 600-700 times in eight hours on average, and small hot-chamber aluminum die-casting machine can die-cast aluminum 3000-7000 times in eight hours on average. Excellent economic effect: Due to precise size of die-casting aluminum parts, surface is smooth and clean. Generally, it is used directly without mechanical processing, or processing amount is very small, so it not only improves metal utilization rate, but also reduces a lot of processing equipment and man-hours. Casting is cheap, can be combined with die-casting aluminum and other metal or non-metal materials, which not only saves assembly man-hours but also saves metal.
4) Disadvantages of aluminum alloy die casting
Due to high speed of filling cavity with liquid metal and unstable flow state during die casting, general die casting aluminum method is used, castings are prone to pores and cannot be heat treated. Die casting is more difficult for complex concave castings. Aluminum alloy die-casting mold has a relatively low service life, and service life is about 80,000 times. It is not suitable for small batch production, main reason is that manufacturing cost of die-casting aluminum mold is high, and small batch production is uneconomical. Aluminum alloy die-casting is not easy to achieve anodic oxidation, because many air bubbles or sand holes are easy to be left after die-casting, resulting in the appearance that cannot be well repaired, resulting in appearance problem that cannot be covered after oxidation.
Note: Here we focus on die-casting times and life of aluminum die-casting, grade of die-casting aluminum and reasons why appearance of oxidation cannot be done.

Following is flow chart of die casting

 

Die-casting molds must use heat to make mold steel. Commonly used steels are: H13, 8407, 2344, 8418, SKD61, DAC, FDAC, etc.
Following is a diagram of die-casting process

 

 

 

 

 

 

Following is a picture of die-casting finished product

 

After product is formed, subsequent nozzle punching, deburring, tapping, thermal shaping, etc. are required to obtain initial product that meets design requirements.
Following is working drawing of punch to remove nozzle

 

Note: Here we focus on learning how aluminum die-casting is performed, what steel material is used for aluminum mold, what product looks like when it comes out, and what to do next.

1) Phosphating of aluminum; 2) Physical polishing of aluminum surface; 3) Alkaline electrolytic polishing of aluminum (this is very commonly used); 4) Environmentally friendly chemical polishing of aluminum and aluminum alloys; 5) Electrochemical surface strengthening of aluminum and its alloys; 6) Electroplating treatment after aluminum alloy polishing.
Note: In order to simplify process, no detailed explanation is given. In fact, for our structure, as long as effect of desired product is proposed, manufacturer can choose polishing method according to effect, and there is no need to know number in detail. In order to reduce costs, physical polishing is basically used. If you want to know more, you can search online by yourself.

Anodizing: Extruded aluminum alloy profiles have poor surface corrosion resistance, so surface treatment must be performed by anodizing to increase corrosion resistance, wear resistance and appearance of aluminum profile.
Electrophoretic painting: Surface of electrophoretic painted profiles has a soft luster, can resist erosion of cement and mortar acid rain.
Powder electrostatic spraying: Powder electrostatic spraying profiles are characterized by excellent corrosion resistance, acid, alkali and salt spray resistance are much better than oxidation colored profiles.
Titanium plating and titanium plating process: aluminum profile titanium plating process belongs to coating technology, It adds pre-plating and electroplating process steps on the basis of conventional titanium plating process. Pre-plating process is to place activated plated parts in an aqueous solution of salt and hydrochloric acid for chemical treatment, so as to produce colorful effects.
Wood grain transfer printing: Vacuum wood grain coating technology is to transfer wood grain to surface of workpiece by thermal transfer after electrostatic spraying of metal product is completed. It is not easy to fade, and wood grain is realistic, which improves quality of product.
Note: Since all aluminum is electrolytic aluminum, surface treatment method is basically same as previous two articles, with similarities and minor differences. However, it should be noted that molding methods of these three processes lead to different surface effects of primary products obtained, and selected surface treatment effects are also different.
Then the most suitable surface treatment for aluminum alloy die-casting is electrophoretic painting and powder painting or spraying (we often say baking paint), surface defect rate will be greatly reduced.

1) Space rockets, space shuttles, artificial satellites, aircraft, automobiles, trains, ships, and other internal components; 2) Communication electronics, home appliances and other industrial appearance parts or internal components
Epilogue
1) In structural design of aluminum alloy die castings, try to design as little as possible structure of lifter, so that it is very difficult to prevent subsequent deburring.
2) When designing structure of aluminum alloy die-casting parts, attention should also be paid to average thickness of glue and smooth flow of the glue, which can reduce many problems such as poor appearance caused by molding and increase subsequent polishing review.
3) If you choose a relatively soft grade, you still need to consider structural strength when designing load-bearing structure, otherwise it will be easy to break.