What is die-casting:
Pressure casting, also known as die casting in the industry, is a precision casting process that rapidly injects molten alloy liquid into a carefully designed steel mold cavity under extremely high pressure, and solidifies the alloy liquid under continuous pressure to accurately form castings. The key to the uniqueness of die-casting technology lies in its significant high-pressure and high-speed characteristics.
The successful implementation of die-casting production strictly relies on three core elements: high-performance die-casting machines, adaptable die-casting alloys, and precision manufactured die-casting molds, which complement each other and are indispensable. Die casting technology cleverly integrates these three aspects, ensuring stable and orderly production process with efficient rhythm through precise control, thus producing high-quality castings with exquisite appearance, excellent internal quality, and precise dimensions that meet the requirements of design drawings or contract specifications in bulk.
Advantages of Die Casting Process:
During the die-casting process, the liquid metal fills the mold cavity at high speed, resulting in an unstable flow state. If conventional die-casting methods are used, the castings are prone to porosity and subsequent heat treatment is difficult.
For castings with complex concave structures, it is difficult to implement the die-casting process.
3. The lifespan of die-casting molds is relatively short, especially for molds used for aluminum alloy and magnesium alloy die-casting, with a lifespan of about 80000 molds. For high melting point alloys such as copper and black metals, the lifespan of molds is even shorter.
4. Die casting technology is not suitable for small batch production because the manufacturing cost of die casting molds is high, and the production efficiency of die casting machines is extremely high. Small batch production is not cost-effective economically.
5. There are challenges in achieving anodizing of aluminum alloy die castings. Although some manufacturers have attempted to use special aluminum alloys for anodizing treatment after die casting, the yield rate is still low.
Disadvantages of Die Casting Process:
In the die-casting process, the high-speed filling of the mold cavity with liquid metal leads to unstable flow state. Conventional die-casting methods are prone to producing porosity in castings and are difficult to perform heat treatment.
Castings with complex concave structures face significant challenges during the die-casting process.
The lifespan of die-casting molds is limited, and aluminum alloy and magnesium alloy molds need to be replaced after about 80000 cycles. High melting point alloys such as copper and black metal molds have a shorter lifespan.
The manufacturing cost of die-casting molds is high, and coupled with the efficient production of die-casting machines, small-scale production appears uneconomical.
The anodizing of aluminum alloy die-casting parts is difficult, and although there are special aluminum alloys that can be achieved, the yield rate is relatively low.
Classification of die-casting machines:
Hot chamber die casting machine is suitable for zinc alloys, magnesium alloys, etc;
Cold chamber die casting machines are suitable for various materials such as zinc alloys, magnesium alloys, aluminum alloys, and copper alloys;
The vertical die-casting machine can process various metals such as zinc, aluminum, copper, lead, tin, etc.
The difference between a hot chamber and a cold chamber lies in whether the injection system of the die-casting machine is immersed in a metal solution. Die casting machines can also be divided into horizontal and vertical types.
Process flow of die-casting products:
Die casting molds:
Die casting molds need to be made of hot work mold steel, and commonly used materials include H13, 2344, 8407, 8418, SKD61, DAC, and FDAC.
The mold structure includes the rear and front mold frames, mold cores, guide columns and sleeves, ejector pins and runners, splitter cones, sprue sleeves, sliders, inclined guide columns, and hydraulic core pulling components.
The equipment required for mold processing includes milling machines, CNC machining centers, wire cutting machines (slow wire), mirror spark machines, grinders, lathes, and welding repair devices.
Die casting peripheral equipment:
Mold temperature control machine - controlling mold temperature is crucial, especially for the quality of thin-walled products such as mobile phones;
Automatic feeder - automatically adding dried metal ingots into the furnace;
Melting furnace - melting metal ingots, magnesium alloy, zinc alloy will transfer the soup to the die-casting machine;
Automatic soup feeding machine - transfers melted aluminum soup to the die-casting machine (exclusive to aluminum alloy die-casting machines);
Automatic spray machine - spray release agent coating onto the mold;
Automatic picking machine - after mold opening, the workpiece is automatically clamped out and placed on the conveyor equipment;
Conveyor equipment - transport products to the edge cutting machine;
Variable frequency drive - energy-saving equipment;
Air compressor - provides compressed air;
Post die casting processing technology and equipment:
-Punching water outlet
Die cast products need to remove material heads and nozzles to reduce excess materials. Common equipment includes hydraulic presses and pneumatic presses.
-Remove burrs and edges
After cutting off the water outlet channel, there are often residual burrs on the surface of the product, which need to be removed manually or using equipment such as scrapers, vibration grinders, magnetic grinders, and grinders.
-Thread processing
Most structural components require tooth hole machining, and suitable drill bits and taps should be selected according to the tooth hole specifications. The required equipment includes CNC drilling and tapping centers, multi axis drilling machines, and multi axis tapping machines.
-Lathe machining
Lathe machining is mainly used for precision machining of inner or outer circles, and the required equipment includes automatic lathes and CNC lathes.
-CNC machining
Due to limitations in die-casting molds and processes, some structures cannot be die cast and rely on CNC machining centers for machining.
-Hot forming processing
Thin walled parts are prone to deformation in processes such as die-casting, stamping, machining, and surface treatment, and require the use of specialized thermoforming machines for calibration.
-Surface treatment process
Die cast parts often require surface treatment to meet decoration and anti-corrosion requirements. The various processes are briefly described as follows:
Passivation (film) is used to construct a protective film on the surface of metals. Magnesium alloys require a film due to their active nature, while aluminum alloys have good corrosion resistance and can be treated with passivation or only bright treatment;
Spray painting achieves a colorful texture through liquid paint;
Powder coating is used for powder coating to achieve multiple color effects;
Electroplating is suitable for multi-color treatment of zinc alloys, while the application of aluminum alloys and magnesium alloys is limited;
Anodizing allows aluminum alloy die-casting products to exhibit multiple colors and maintain a metallic texture, but its application is limited;
Sandblasting can create a rough textured surface.
Basic requirements for materials in die-casting production:
Metal die-casting production mainly uses alloy materials such as aluminum, zinc, magnesium, copper, lead, tin, etc. Among them, aluminum alloy and zinc alloy are the most widely used, followed by magnesium alloy and copper alloy. These alloys have good flowability when moderately overheated and are easy to fill complex cavities, ensuring the surface quality of die-casting parts. They have a low tendency for thermal cracking, a narrow range of crystallization temperatures, low shrinkage rates, and high strength at room temperature, making them suitable for the production of large thin-walled complex parts. At the same time, they have weak physical and chemical interactions with metal cavities, reducing the risk of mucous membranes and alloying, possessing good processing performance and corrosion resistance, and a low melting point.
