The Six Typical Zinc Die Cast Processes
Nowadays there are mainly two different zinc die casting processes in die casting industry, they are hot chamber and cold chamber.
The hot chamber process requires to use alloys with low melting temperatures and a low attack rate on die casting mold tool steel. This process is the most common way of manufacturing zinc die casting products. In this process, the metal pump (gooseneck) is immersed in the molten zinc alloy, and the pumping metal directly ejected to the mold cavity from the furnace of casting machine quickly, then it solidified to become the desired casting product.. So the hot chamber die casting system would have shorter cycle times, smaller runner systems, and lower costs compared to cold chamber process.
The cold chamber process is very similar to the hot chamber process except that the molten metal is poured into a horizontal cylinder when cold chamber process. because the raw material of cold chamber process has higher melting point that should be pre-melt and poured into a die casting machine.
Whatever which type of die casting process is , both of them consist of six main stages, which can be described as below.
Step 1: Material and Mold Tool Preparation
Prior to casting process, we need to get right material to be melted with a certain temperature on the furnace of die casting machine. Meanwhile, our die casting mold tool should be correctly equipped on casting machine, and get the mold tools cleaned and tested if it can open and clamp smoothly.
Step 2: Clamping
After raw material and mold tool were properly located, it’s the time to clamp the mold tool tightly on the die casting machine as needed. Sufficient force must be applied to the mold tool and keep it securely closed while the molted material is injected.
Step 3: Injection
In this stage, the molten metal is injected into the mold to fill in the full cavity of mold tool by a high pressure, normally a heavy zinc die casting parts requires longer injection time. And the lighter parts need shorter injection time. A sufficient injection is very important as different part structure and thickness of wall. If shorter injection for a big parts, there will not be enough material to fill in. On opposite, a longer injection time would result in overflowing problem. The best way to balance it is to operate the injection trail by experienced technician.
Step 4: Cooling
The molten metal that is injected into the mold tool will begin to cool and solidify immediately after it stay in the mold cavity. Normally the cooling time is about 3~10 seconds. However this time might vary a little bit for different size, shape, and heavy of a casting product. For example, the thicker wall of part and big size part would require longer cooling time.
Step 5: Mold Open and Ejection
– After material solidification and cooling stage has completed sufficiently, the mold tool opened, and the ejection pin pushes the molded product out of the mold. A proper ejection pins with reasonable location and size would affect if the casting parts can be ejected smoothly. Normally a bigger casting parts requires bigger ejection pins, otherwise the pins might break or not enough to eject parts from mold tool.
Step 6: Trimming
When the casting part is ejected from a mold tool, it comes with injection gate and runner system. So we need to remove those extra material from our desired parts, which can be operated either by manual or automation.