For this series, please refer to Die Casting Design Specifications—Basic Introduction, Introduction to commonly used materials, Introduction to die-casting mold technology, design (Part 1), design (Part 2), structural design self-inspection, treatment of defects in die-casting parts, 
This series mainly introduces specifications related to die-casting design, including an introduction to basic knowledge, material selection, structural design specifications, introduction to die-casting molds and materials, and how to self-check during structural design. Next, we will introduce them to you one by one. This article mainly introduces basic knowledge of die castings. Details are as follows;

Die casting, that is, pressure casting, is a method in which liquid metal or semi-liquid metal is filled into cavity of a die-casting mold at a high speed under high pressure and solidified quickly under pressure to obtain a casting.
Salient features of die-casting process are high pressure, high speed and high temperature. Its commonly used injection pressure is tens to hundreds of MPa, filling speed is about 10~50m/s, sometimes even up to more than 100m/s, and filling time is very short, usually 0.01~0.2s.
Temperature of molten metal in die casting is very high. Melt temperature during die casting is generally 610-670C for aluminum alloys and 400-450C for zinc alloys. Mold temperature is generally one-third of alloy temperature.

Advantages of die casting
1) Production efficiency is high, production process is easy to mechanize and automate.
2) Die castings have high dimensional accuracy and high surface quality. General tolerance level of die castings is IT13~IT15 in GB/T1800-2009. Higher precision can reach IT10IT11. Surface roughness Ra=3.2~1.6um, and some parts can reach 0.8um. Avoiding mechanical processing or using less mechanical processing improves utilization rate of alloy and saves a lot of mechanical processing costs.
3) Mechanical properties of die castings are relatively high. Metal melt cools quickly in die-casting mold and crystallizes under pressure. Therefore, layer near surface of die-casting has finer grains, denser structure, higher strength and hardness.
4) Complex thin-walled parts can be die-casted. Die castings can have complex part shapes, and wall thickness of parts can be smaller. Minimum wall thickness of aluminum alloy die castings is 0.5mm, minimum wall thickness of zinc alloy die castings can reach 0.3mm, and minimum casting hole diameter is 0.7mm; Minimum pitch is 0.75mm.
5) Parts of other materials can be embedded in die castings. This saves valuable materials and processing costs, enables parts with complex shapes and improved part performance to reduce assembly work.
Die casting disadvantages
1) Porosity is easy to occur in die castings. Since metal melt fills mold cavity at a very high speed during die casting, and mold material has no air permeability, die castings produced by general die casting methods are prone to pores. Due to existence of pores, strength of die castings cannot be improved by heat treatment and used at high temperatures; at the same time, machining allowance of parts cannot be too large, otherwise hardened layer on the surface of die casting will be removed, causing pores near surface to be exposed on the surface of die casting.
2) Not suitable for small batch production. Die-casting molds are complex and costly, so they are generally only suitable for larger batch production.
3) Mold life is low when die-casting high melting point alloys. Some metals (such as copper alloys) have high melting points, which require high thermal deformation resistance and thermal fatigue strength of die-casting materials, and life of mold is relatively low. At present, materials for die castings are mainly aluminum alloys, zinc alloys, magnesium alloys, etc. Ferrous metals are rarely processed by die casting.
Unique advantages of die casting
1) Compared with plastic parts: high strength, electrical conductivity, thermal conductivity and resistance to electric radiation.
2) Compared with gold: shape of parts is more complex, wall thickness can be changed, and one die-casting part can replace several gold parts, simplifying product structure.
3) Compared with machined parts: Die-casting parts are light in weight and have low processing costs.
4) Compared with other casting methods: product has high dimensional accuracy, good surface quality and high production efficiency.

Die-casting machines are divided into two categories: hot-pressure chamber die-casting machines and cold-pressure chamber die-casting machines.
Mold clamping mechanism of hot pressure chamber die casting machine and cold pressure chamber die casting machine are same, but difference lies in injection and pouring mechanisms. Pressure chamber and furnace of hot-pressure chamber die-casting machine are closely connected as a whole, while pressure chamber and furnace of cold-pressure chamber die-casting machine are separated.

 

Cold pressure chamber die casting machine

 

Hot pressure chamber die casting machine

 

 

Die casting process
For further article, please refer to Die-casting design specifications - introduction to commonly used materials.