INJECTION MOLDING GUIDE
Quick answer: Injection molding tolerances depend on resin shrinkage, part size, wall thickness, mold construction, cooling balance, and inspection requirements. In an RFQ, separate general dimensions from critical fit, sealing, movement, and assembly dimensions.
Why Injection Molding Tolerances Matter
A practical tolerance plan connects the drawing, material, mold design, process capability, and inspection method. Applying one tight tolerance to every feature can increase tooling cost without improving the part.
What Should Be Marked as Critical?
Fit and assembly interfaces
Identify holes, bosses, clips, connector interfaces, and dimensions that control assembly. Provide the mating component or assembly context when possible.
Sealing and functional surfaces
Gasket seats, sealing edges, fluid paths, and moving interfaces may require tighter control than cosmetic surfaces.
Datums and inspection references
Use a 2D drawing to show datums and how critical dimensions should be measured. A 3D model alone may not define the inspection method clearly enough.
What Affects Plastic Injection Molding Tolerance?
- Resin type, glass-fiber content, and expected shrinkage
- Part size, wall thickness, ribs, bosses, and warpage risk
- Cooling layout, cavity balance, gating, and ejection
- Mold steel, tool construction, and expected production volume
- Process control, sampling plan, and inspection equipment
What to Include in an Injection Molding RFQ
| RFQ item | Helpful detail |
|---|---|
| 3D CAD model | File type, units, revision, assembly context |
| 2D drawing | Datums, tolerance zones, threads, critical interfaces |
| Material target | Exact grade, filler, color, or performance target |
| Volume forecast | Prototype, annual volume, lifetime estimate |
Common Tolerance Mistakes
- Using tight tolerances for every dimension without a functional reason
- Sending a model without a material target
- Leaving cosmetic faces, sealing surfaces, or mating features unmarked
How Daremotion Reviews Tolerance Requirements
We review the CAD model, drawing, resin, quantity, surface requirements, and application before confirming tooling and inspection assumptions.
FAQ
Can every injection molded part hold very tight tolerances?
No. Achievable tolerance depends on geometry, material, tool design, process control, and measurement method.
Should I send a 2D drawing with my CAD model?
Yes, especially when the project has datums, critical dimensions, sealing requirements, threads, or inspection documentation.
Ready to Review Your Injection Molding RFQ?
Share your CAD files, drawings, material target, volume, and critical requirements through the Request a Manufacturing Quote page.