Air Bubbles and Slits in the Plastic Molding Part2016-06-07

In precision plastics CNC parts machining process, we use plastic rods with precise external diameter for efficiency CNC fabrication.




How to obtain plastic rods?


First, we will inject and press the melted raw plastics into metal mold to form plastic rods with high pressure, and then harden the rods by forced air cooling. These plastic rods can be used for CNC precision manufacturing.




What cause an extrusion plastic rod to develop a crack?


Regarding the cracks in plastic workpieces, four conditions have to be carefully considered during the extruding process: heat, pressure, flow, cooling, and the quality of the material. Recently, we received a batch of PPS plus 40%GF plastic raw material rods from an Australia customer. Unfortunately, we observed lots of internal cracks in the rods when pre-cutting the material into billet before the CNC precision manufacturing process. See below cut parts photos.




This type of cracking caused by internal stress mainly results from cavity working pressure and also forced-air cooling. Also, material quality is another possible factor. Plastics with poor quality is likely to have inner cracks. Sometimes, these cracks can damage the cutting tool when we manufacture plastic machined precision parts. Besides, gas or liquid leakage might happen to the plastic components with cracks inside.