The difference between the blank of die casting and extrusion casting

In terms of shape, it is difficult to distinguish the blanks produced by these two processes. If you see a processed part, it is more difficult to distinguish. Therefore, we can only analyze and judge in reverse: The die casting is generally a “structural part”, while the die forging is a “functional part”. Frame, as opposed to feature. The latter generally refers to bearing impact, high temperature, pressure, strength (force), surface treatment (such as anodizing), heat treatment (solid fusion strengthening), etc. Typical products are engine block, hub, piston, connecting rod, brake shoe, pneumatic or hydraulic valve body (such as the common three position five-way valve), etc. The former includes door frame, instrument panel, engine cover, etc.Judging from material composition. Because die casting parts are generally cast alloy, for other grades of alloy, it is often produced by squeeze casting process.

Judging from the processing requirements of the blank to its outer surface. For example, for aluminum die casting, there are micro pores (commonly known as “water marks”) on the outer surface of the blank produced by the die casting process due to the silicon content, and there will be “black spots” on the surface of this material after anodizing treatment. Therefore, if anodizing is required, the blank will not be produced by ordinary die casting process.

Judging from metallographic structure. It’s easy to distinguish die casting from die forging in metallography. The former is dendrite like as cast structure, and the latter is homogeneous as forged structure with broken grains.

Eliminate some misconceptions

We can’t think that we can use the vacuum infiltration after die casting to solve the shrinkage and porosity defects of die casting parts, nor can we think that we can use the vacuum die casting process to produce the functional parts which can only be produced by continuous casting and continuous forging process. When the technology in the industry has made progress, we should have a scientific attitude of keeping pace with the times in terms of ideas and thoughts.

There are shrinkage cavity and porosity defects in vacuum die casting as in common die casting. Vacuum die casting is just a process which plays a little role in auxiliary exhaust compared with common die casting. There is no way to deal with shrinkage cavity and porosity caused by phase transformation shrinkage of liquid metal (its interior is vacuum and there is no gas).

The most common mistake that professionals make is that although they know that this blank can not be produced by ordinary die casting process, they choose a process called “reverse punch indirect and local extrusion”. They think that this process has the same effect as the liquid forging process, which is completely wrong. The essence of “reverse punch extrusion” process is still a die casting process! Only the type of “full projection area forging with positive punch” is the real liquid forging process.