Die casting

 

Pressure casting is abbreviated as die casting. It is a casting method that fills cavity of a steel mold with molten alloy liquid at high speed under high pressure, and solidifies alloy liquid under pressure to form a casting. Main characteristics of die casting that distinguish it from other casting methods are high pressure and high speed.
Die casting machine, die casting alloy and die casting mold are three major elements of die casting production, and none of them can be missing. So-called die casting process is to organically combine these three elements to enable stable, rhythmic and efficient production of castings with good appearance and internal quality and dimensions that meet requirements of drawings or agreements.
Advantages of die casting process
1). High dimensional accuracy and low surface roughness of die castings;
2). High strength and surface hardness of castings;
3). Wide application range, including lamp radiators, auto parts, furniture and bathroom hardware, electronic and electrical accessories, jewelry accessories, building materials, tableware, toys, sports equipment, gifts, mechanical hardware accessories, etc.
4). High productivity, automatic production can be realized;
5). High metal utilization.
Disadvantages of die casting process

1). During die casting, due to high speed of liquid metal filling cavity and unstable flow state, general die casting method is used. Casting is prone to pores and is not easy to heat treat.

2). Die casting is more difficult for castings with complex concave parts;
3). Life of die casting mold is relatively low. Mold life of aluminum alloy and magnesium alloy is about 80,000 molds, and melting point alloys such as copper and ferrous metals are even lower;
4). It is not suitable for small batch production. Main reason is that manufacturing cost of die casting mold is high, production efficiency of die casting machine is high, and small batch production is not economical;
5). Aluminum alloy die castings are not easy to achieve anodization, but some manufacturers have used special aluminum alloys to achieve anodization after die casting, but yield rate is still low;
Die casting machine

 

Classification of die casting machine
Hot chamber die casting machine: zinc alloy, magnesium alloy, etc.
Cold chamber die casting machine: zinc alloy, magnesium alloy, aluminum alloy, copper alloy, etc.
Vertical die casting machine: zinc, aluminum, copper, lead, tin
Difference between hot chamber and cold chamber is whether injection system of die casting machine is immersed in metal solution. Die casting machines can also be divided into horizontal and vertical types.
Die-casting metal materials
Main alloy materials for die-casting are tin, lead, zinc, aluminum, magnesium, copper, etc. Zinc and aluminum alloys are the most widely used, followed by magnesium and copper alloys. Currently, zinc, aluminum, and magnesium alloys are mainly used in electronics industry.
Die-cast zinc alloy
Molten state of zinc alloy has very good fluidity and a low melting point of only 365 degrees. Various post-processing treatments can be performed, such as electroplating. Therefore, it has a wide range of uses. It was also used a lot in mobile phone industry before, but it was gradually eliminated by aluminum alloys due to poor corrosion resistance. The most widely used industry is bathroom industry.
Commonly used alloys are 2, 3, 4, 5, and 7, and the most widely used is alloy 3.
Die-cast aluminum alloy
Aluminum alloy has low density but relatively high strength, close to or exceeding high-quality steel, good plasticity, can be processed into various profiles, has excellent electrical conductivity, thermal conductivity and corrosion resistance, and is widely used in industry, second only to steel in usage. Specific weight of aluminum alloy is only about 1/3 of that of iron, so it is very important in various industries at present, especially in lightweight process of aircraft, ships, automobiles, electronic instruments, etc.
Commonly used are AI-Si-Cu series, common ones are ADC12 (A383), ADC10 (A380), etc. There are also AI-S series, AI-Si-Mg series, AI-Mg series. What is currently called aluminum-titanium alloy is improved by adding titanium metal to above materials. Adding titanium metal can significantly improve mechanical properties of product.
Die-cast magnesium alloy
Magnesium alloy is an alloy composed of magnesium and other elements. Its characteristics are: low density, high specific strength, large specific elastic modulus, good heat dissipation, good shock absorption, greater impact load bearing capacity than aluminum alloy, good resistance to organic and alkali corrosion. Specific gravity of magnesium is about 2/3 of aluminum and 1/4 of iron. Therefore, it is widely used in mobile phones, communication equipment and other electronic equipment, auto parts, and medical equipment.
At present, the most widely used is magnesium-aluminum alloy, followed by magnesium-manganese alloy and magnesium-zinc-zirconium alloy. Common grades used are AZ91D, AM60B, AM50A, AS41B, etc.

Die casting process

 

Die-casting mold

Die-casting molds must be made of hot-working mold steel. Commonly used steels include: H13, 2344, 8407, 8418, SKD61, DAC, FDAC, etc.
Mold structure: (rear mold, front mold) mold frame, mold core, guide pin, guide sleeve ejector, sleeve, manifold, gate sleeve, slider, inclined guide pin, hydraulic core pulling.
Mold processing equipment: milling machine, CNC machining center, wire cutting (slow wire), (mirror) spark machine, grinder, lathe, welding equipment.

 

Die-casting peripheral equipment

Mold temperature controller - controls mold temperature, which is especially important for quality of thin-walled products such as mobile phones;
Automatic feeder - automatically adds baked metal ingots to furnace;
Melting furnace - melts metal ingots, magnesium alloy and zinc alloy will transfer soup to die-casting machine;
Automatic soup feeder - transfers molten aluminum soup to die-casting machine (exclusive to aluminum alloy die-casting machines);
Automatic sprayer - sprays release agent coating on mold;
Automatic pick-up machine - automatically clamps workpiece out after opening mold and places it on conveying equipment;
Conveying equipment - conveys product to trimming machine;
Inverter - energy-saving equipment;
Air compressor - provides compressed air;

Die casting machine and peripheral equipment layout

 

Post-processing technology and equipment

Punching and cutting nozzles
Die-cast products need to cut off head and nozzles, and remove most of excess material.
Equipment: hydraulic punch press, pneumatic punch press, etc.

 

Removing burrs
After cutting nozzle flow channel, there will be a lot of burrs left on product, which need to be removed manually or by machine.
Equipment tools: scraper, vibration grinder, magnetic grinder, grinder, etc.

 

Thread hole processing
Structural parts basically need thread hole processing. Different drill bits and taps are selected according to different specifications of thread holes.
Equipment: CNC drilling and tapping center, multi-axis drilling machine, multi-axis tapping machine.

 

Lathe processing
Lathe processing is mainly used for processing inner or outer circles.
Equipment: automatic lathe, CNC lathe.

 

CNC machining
Due to limitations of die-casting molds and process technology, some structures cannot be die-casted, so machining is required.
Equipment: CNC machining center.

 

Hot shaping
In various processes such as die casting, stamping, machining, surface treatment, etc., especially thin-walled parts, deformation will occur, so hot shaping is needed to correct it.
Equipment: Hot shaping machine.

 

Surface treatment process

Due to needs of surface decoration and corrosion protection, die castings generally need surface treatment. Following is a brief introduction to various processes:
Passivation (film) - a protective film is formed on metal surface, which is mainly used for internal components, especially magnesium alloy parts. Due to their active nature, film treatment must be done; aluminum alloys have good corrosion resistance and can be passivated, or only brightened;
Painting - spraying liquid paint can achieve a variety of colors and textures;
Powder spraying - spraying powder coating can achieve a variety of colors;
Electroplating - zinc alloy products can be electroplated in a variety of colors, application range on aluminum alloys and magnesium alloys is very narrow;
Anodizing - aluminum alloy die-casting products can achieve a variety of colors and metal texture will not be covered, but there are many restrictions on die-casting aluminum alloys at present;
Sandblasting - can better achieve a rough and textured surface.