Injection Molding


Injection molding is a manufacturing process for producing plastic parts from both thermoplastic and thermosetting plastic materials. Material is fed into a heated barrel, then mixed and forced into a mold cavity by a reciprocating screw or a ram injector, where it cools and hardens to the configuration of the mold cavity. After a part is designed, usually by an industrial designer or an engineer, molds are then manufactured by an injection mold company, where it is assigned to a mold maker or toolmaker. The mold is usually constructed using either steel or aluminum and precision-machined to form the features of the desired part. Injection molding is widely used for manufacturing a variety of parts, from the smallest component to entire body panels of cars. 

Plastic injection molding is the preferred process for manufacturing plastic parts. Injection molding is used to create many things such as electronic housings, containers, bottle caps, automotive interiors, pocket combs, and most other plastic products available today. It is ideal for producing high volumes of plastic parts, due to the ability of making multi-cavity injection molds, where multiple parts are made with one cycle. 

Some disadvantages of this process are expensive tooling investment, the need to prototype (some custom complex parts may encounter problems during the injection molding process, such as warp) and surface defects. 


  • High tolerances 
  • Repeatability 
  • Wide range of material selection 
  • Low labor cost 
  • Minimal scrap losses 
  • Little need to finish parts after molding 


Molding tolerance is a specified allowance on the deviation in parameters such as dimensions, weights, shapes, or angles, etc. To maximize control in setting tolerances there is usually a minimum and maximum limit on thickness, based on the process used. Injection molding typically is capable of tolerances equivalent to an IT Grade of about 9–14. The possible tolerance of a thermoplastic or a thermoset is ±0.008 to ±0.002 inches. In specialized applications tolerances as low as ±5 micrometres on both diameters and linear features are achieved in mass production. Surface finishes of two to four microinches or better can be obtained. Rough or pebbled surfaces are also possible.


Glossy Surface, Diamond Buff Polish 

  • SPI Finish A-1 — Grade #3, 6000 Grit Diamond Buff 
  • SPI Finish A-2 — Grade #6, 3000 Grit Diamond Buff 
  • SPI Finish A-3 — Grade #15, 1200 Grit Diamond Buff 

Non-Glossy Surface, Paper Polish 

  • SPI Finish B-1 — 600 Grit Paper 
  • SPI Finish B-2 — 400 Grit Paper 
  • SPI Finish B-3 — 320 Grit Paper 

Rough Surface, Stone Polish 

  • SPI Finish C-1 — 600 Grit Stone 
  • SPI Finish C-2 — 400 Grit Stone 
  • SPI Finish C-3 — 320 Grit Stone 

Very Rough Surface, Dry Blash Polish 

  • SPI Finish D-1 — 600 Stone Prior to Dry Blast Glass Bead #11 
  • SPI Finish D-2 — 400 Stone Prior to Dry Blast #240 Oxide 
  • SPI Finish D-3 — 320 Stone Prior to Dry Blast #24 Oxide 


  • Molded-in Inserts 
  • Overmolding 
  • Custom Colors 
  • FDA / Medical Grade Resins 
  • Unlimited Undercuts 
  • Internal / External Threads 
  • Multi Component Assemblies 
  • Tight Tolerances

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