Gud Mould Industry Co., Ltd. is a professional manufacturer of plastic injection mold and die casting mould.
In manufacturing industry, injection molds and die-casting molds are two key tools that play a vital role in production of plastic and metal parts. Although the two molds may look similar in appearance, they have significant differences in structure, working principles, operating conditions and materials, application fields, advantages and disadvantages.

 

▲ Schematic diagram of injection mold guide system
Injection mold is composed of two parts, namely movable mold and fixed mold. However, there are still seven major systems in injection mold, which are mainly composed of gating system, molding system, lateral core pulling system, ejection system, temperature control system, exhaust system, guide and positioning system.
Die-casting mold is mainly composed of two parts: fixed mold and movable mold. In order to ensure movement of mold and smooth exit of workpiece, there is a complex system and structure. Common structures include: molding cavity, gating system, overflow exhaust system, guide parts, push-out mechanism, heating and cooling system, support and fixing parts, lateral core-pulling mechanism.
In design of mold, die-casting molds rarely have three-plate molds, while plastic molds have three-plate molds more commonly. When designing exhaust system for die-casting molds, it cannot be exhausted by ejector pins like plastic molds, so parting surface is generally made into a slag exhaust package.

 

▲Structure diagram of die casting machine
When injection mold is working, injection molding machine first provides power to push movable mold plate to fixed mold plate for mold closing. Molten plastic is pressurized by nozzle and injected into mold. After passing through main channel and runner, it enters cavity. After plastic fills the entire cavity, it begins to cool down and solidify after maintaining pressure. After solidification is completed, injection molding machine separates movable mold and fixed mold. At this time, product still stays on fixed mold plate. Ejection mechanism such as ejector pin and ejector plate on the inside of fixed mold plate pushes product out and separates it from mold. After product is taken out, injection molding machine starts next mold closing for next production. Cycle from the first mold closing to next mold closing is called injection molding cycle. Length of injection molding cycle directly determines production efficiency of plastic products.
Working principle of die-casting molds is similar to that of injection molds, but slightly different. Die-casting machine also pushes away movable mold plate of die-casting mold, then spraying equipment sprays release agent on cavity parts of movable mold plate and fixed mold plate. Then movable and fixed molds are closed, and liquid metal is extruded by injection punch in cold chamber or hot chamber. Liquid metal enters mold cavity through runner under high pressure, and forms a product after cooling under pressure. Then mold is opened, and product is taken out by a robot or manually to produce next die-cast product. Similarly, die-casting cycle has become an important parameter to measure production efficiency of die-casting products.

 

▲Challenges that die casting brings to molds
Operating environment temperature of injection mold is generally around 80-160℃, and injection pressure is generally 50-90MPa. This mainly depends on type of plastic being injected, components such as front and rear mold cores and ejector inserts on both sides of cavity mainly bear high temperature and pressure of plastic. Therefore, in processing design of injection molding molds, cold work mold steels such as SKD11 and DC11 are commonly used for mold cores because they have good hardenability, high toughness, high wear resistance, good anti-tempering stability, small heat treatment deformation, and relatively low material cost.
Working conditions of die-casting molds are worse than those of injection molds. Operating temperature is generally 230-280℃, and pressure in mold cavity is 70-100MPa. Taking aluminum alloy as an example, temperature at which aluminum alloy is poured into cavity is generally around 670-710℃, so mold core needs to withstand a higher temperature. Due to high temperature and high pressure environment, die casting molds generally use hot work mold steels such as H13 and H11. When Cr element content in alloy is high, thermal expansion coefficient is small. At high temperatures, Cr element can produce a stable oxide layer to prevent continued oxidation. Cr Elements can also improve wear resistance of steel and improve hardenability of steel.

 

▲ Schematic diagram of 3D printed conformal waterway
Injection molds are widely used in production of plastic products. They can produce different plastic products such as PP, PE, PVC, etc., and are widely used in home appliances, automobiles, electronics, toys and other industries. And injection molds have advantages of high production efficiency, low cost, and high product precision, so they occupy an important position in production of plastic products.
Die-casting molds are mainly used to produce metal parts, especially parts requiring higher strength and complex shapes. Since die-casting equipment and die-casting molds are relatively expensive, die-casting molds are suitable for producing large quantities of high-precision metal parts, such as automobile engine blocks, cylinder heads, crankcases, etc. In addition, die-casting molds can also be used to produce high-precision, high-complexity metal products such as artworks and decorations.

Injection molds and die-casting molds have their own advantages and disadvantages due to their respective use scenarios and processing characteristics. Precision of injection molds is relatively high: dimensional accuracy of injection molds is generally required to be within ±0.01mm. Position accuracy is generally required to be within ±0.02mm. Normally, accuracy requirements for die-casting molds in terms of dimensional accuracy are ±0.02mm, and accuracy requirements for positional accuracy are ±0.05mm. Under normal circumstances, injection molds have lower costs due to use of steel, the overall processing and manufacturing costs are also low. However, die-casting molds use hot-worked mold steel and have relatively harsh working conditions, which have higher requirements on performance of mold steel and cost. Naturally, a rising tide lifts all boats, and mold production cycle will be longer.

Generally speaking, injection molding and die-casting are both powerful means of industrial mass production. They are used in different scenarios and in production of different industrial products. There are significant differences between injection molds and die-casting molds in terms of structure, working principle, and application fields. Understanding these differences helps us better choose appropriate mold type to meet production needs of different products. At the same time, with advancement of science and technology, development of manufacturing industry, these two molds still have a lot of room for development and improvement potential in the future.