First of all, we should know what a cushion in injection molding is? Just like a cushion protects and gives rest to our head. Similarly, a cushion in the injection molding machine gives protection to the screw. It depends upon the size of the product that how much the material is to be set. For example, if we require a product of 60 grams, we need to set 100 mm of the material. By doing this, this much material will be injected into the mold at the time of injection. During injection, a condition called switch over position or transfer position is set. After the injection, the phase is called the holding situation. During this phase, some of the material is transferred after being held for some time. Switch on position means we are getting switched from the injection phase to the holding phase. For example, we have kept 10mm of material for switching over the position. So, 5 mm is used for holding position out of it. The rest of the 95 percent of the material is used for holding position. The remaining 5 percent or 5mm of the material is called a cushion.
In injection molding, generally, we use a cushion ranging between 3 mm to 6 mm. The advantage of the cushion is that since it accumulates between the tip of the nozzle and the tip of the barrel, it prevents the nozzle tip from coinciding with the barrel tip.
If the cushion is kept low, holding time is less, and holding material also lessens, thus there are chances of getting the damage in the screw. Even if the cushion is kept very high, like 10 mm or 15 mm, there are damage chances like a black spot or burn mark. The excess material accumulated between the nozzle tip and barrel tip can cause the cushion material degradation, allowing the black spot and burn effect can be seen on the product.>
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