Injection Molding Materials

Thermoplastics, and in practice nine families cover most production: ABS, PC, PVC, PP, PE, PA (nylon), POM, TPU and PEEK. Meco molds all nine plus blends such as PC-ABS and filled compounds, more than fifty grades in total. Commodity resins take the largest share by volume because they are cheap and mold fast, while engineering resins get specified when heat, wear or load rules them in.

Polypropylene, with polyethylene close behind. Both are low cost per kilogram, fill thin walls easily and cool quickly, which shortens cycle time and drops the cost per part again. ABS costs more per kilogram but often lands cheaper overall on a cosmetic part, because it needs no painting and scraps less. Pellet price is only one of four levers, alongside cycle time, cavity count and scrap rate.

It depends which kind of strength you mean. PEEK holds the highest strength at temperature and is the answer for continuous hot service. Glass filled nylon gives the best stiffness and load capacity for the money, which is why it dominates structural molded parts. Polycarbonate wins on impact, absorbing a drop that would shatter a stiffer resin. Specify the failure mode you are designing against and the answer narrows quickly.

Only within a narrow band. The cavity is machined oversize by that resin's shrinkage, so moving from ABS at 0.6 percent to POM at 2 percent puts every dimension out. Swapping between resins with similar shrinkage, such as ABS and PC-ABS, is usually workable with a process change. Anything wider needs steel adjustment or a new tool, which is why we lock the grade before cutting and leave critical dimensions steel safe when the choice is still open.

Most engineering resins do. Nylon, PC, PBT, POM, TPU and PEEK all pick up moisture from the air, and molding them wet causes splay marks, bubbles and a permanent drop in mechanical strength that no inspection of the surface will catch. Nylon needs to be below 0.2 percent moisture before it reaches the screw. Polypropylene, polyethylene and PVC do not absorb meaningful moisture and need no drying, which is one more reason they are cheap to run.

ABS for most cosmetic housings, PC when the part has to survive impact or transmit light. PC costs noticeably more per kilogram, molds hotter, and demands proper drying, so it carries a higher process cost as well as a higher material cost. PC-ABS is the middle option and is often the right one: it keeps most of the impact performance, molds in a wider window and prices between the two.

Yes, for parts where electrical insulation, chemical resistance and low material cost matter more than impact strength or heat resistance. Rigid PVC molds well but runs a narrower thermal window than ABS or PP: hold it too hot or too long in the barrel and it degrades and releases hydrochloric acid gas, so we run it on dedicated screws with tight purge procedures. It has weaker UV resistance and impact strength than most engineering resins, so parts stay indoors or get a protective finish where they are exposed outdoors.

Considerably. Amorphous resins such as ABS and PC shrink evenly and predictably, so they hold tighter tolerances more easily. Semi crystalline resins such as POM, nylon and PP shrink more and vary more with process conditions, which widens the achievable band. Our standard is 0.05 mm on molded features. The resin property table gives the achievable band per resin. Where one dimension has to hold tighter than the resin allows, we mold near net and machine that feature afterwards.

Yes. Resin certificates of analysis, REACH and RoHS declarations, conflict minerals reporting, PPAP packages, first article inspection and CMM results are all available on request, traceable to the resin lot and colour batch that produced your shipment. Where a grade carries food contact or medical documentation from the supplier, we pass that through with the parts.