Standard Injection Molding

Standard injection molding produces repeatable plastic parts by injecting molten polymer into a hardened mold, ideal for moderate-to-high volumes and consistent geometries.

Overview

Standard injection molding forms plastic parts by injecting molten polymer into a machined steel or aluminum mold, then cooling and ejecting the solidified part. It supports complex 3D geometries, detailed features, living hinges, and molded-in text or logos, with cycle times from seconds to under a minute depending on part size.

This process shines at medium to very high production volumes, where tooling cost is amortized across many parts. It delivers consistent dimensions, good surface finish, and a wide material selection including rigid, tough, or chemically resistant plastics. Limitations include high upfront mold cost, sensitivity to wall thickness variation, and constraints from draft, gate, and parting line requirements. Very thick sections, extremely sharp corners, and uncontrolled shrink expectations drive problems and cost. For most plastic housings, brackets, covers, clips, and functional components, standard injection molding is the default choice when you expect thousands of parts or more.

Common Materials

  • ABS
  • Polycarbonate (PC)
  • Nylon 6/6
  • Polypropylene (PP)
  • Acetal (POM)
  • PC-ABS

Tolerances

±0.002" to ±0.005" on critical features; looser on overall dimensions

Applications

  • Electronics housings and covers
  • Automotive interior and under-hood components
  • Consumer product enclosures and handles
  • Connectors, clips, and fasteners
  • Small gears and motion components
  • Medical device housings and disposable components

When to Choose Standard Injection Molding

Choose standard injection molding when you need thousands to millions of identical plastic parts with consistent quality and predictable dimensions. It suits parts with moderate wall thickness, clear draft, and materials available as standard thermoplastic pellets. This is usually the go-to for production plastic components once the design is stable and volume justifies tooling.

vs Overmolding

Choose standard injection molding when your part is a single-material component without the need for soft grips, seals, or bonding multiple materials in one shot. It is simpler to tool, lower risk, and usually cheaper per mold cavity than overmolding for the same geometry and volume.

vs Insert Molding

Choose standard injection molding when your part does not require embedded metal inserts, threaded bosses with metal strength, or integrated contacts. You avoid insert sourcing, loading fixtures, and handling costs, and you gain faster cycle times and simpler automation.

vs Thin Wall Molding

Choose standard injection molding when your wall thicknesses are moderate and do not require extreme flow lengths or very high injection speeds and pressures. Standard molding uses more forgiving design rules, more common materials, and less demanding tooling, which reduces tooling cost and risk compared to thin-wall-optimized parts.

vs Compression Molding

Choose standard injection molding when you are using thermoplastics, need faster cycle times, and want better automation for higher volumes. It is the better fit for detailed features, complex 3D geometries, and integrated snaps or living hinges, where compression molding struggles or becomes uneconomical.

vs Rotational Molding

Choose standard injection molding for smaller to medium-sized parts that need tighter tolerances, finer detail, and higher production volumes. It provides better surface finish, more consistent wall thickness at smaller scales, and much shorter cycle times than rotational molding for most engineered plastic components.

Design Considerations

  • Aim for uniform wall thickness and transition gradually between sections to control shrink and avoid sink marks
  • Add draft (typically 1–2° or more) on all faces perpendicular to the mold opening direction to ensure reliable ejection
  • Limit rib thickness to about 40–60% of the adjacent wall to reduce sink and warpage while still providing stiffness
  • Use generous internal radii and avoid sharp corners to improve flow, reduce stress concentration, and simplify tool manufacturing
  • Place parting lines and gates in non-cosmetic or less critical areas and call out acceptable locations on the drawing or model
  • Specify realistic tolerances based on process capability and part size, tightening only truly critical features to keep tooling and part costs under control