How Custom Injection Molding Works: From Design to Final Product

1. Product Design & Feasibility Analysis

Before manufacturing begins, engineers and designers must ensure the part is optimized for injection molding.

Key Steps:

✔ Define Requirements – Function, material, tolerances, and industry standards (e.g., FDA for medical parts).
✔ 3D Modeling (CAD) – Software like SolidWorks or Autodesk Fusion 360 is used to design the part.
✔ Design for Manufacturability (DFM) Review – Check for:

• Wall thickness uniformity (to avoid sinks & warpage)

• Draft angles (for easy ejection)

• Undercuts & side actions (may require sliders or lifters)
  ✔ Material Selection – ABS, PP, PC, or engineering plastics like PEEK.

2. Mold Design & Fabrication

Once the part design is finalized, the custom mold (tooling) is engineered and machined.

Key Steps:

✔ Mold Base Selection – Standard (faster, cheaper) vs. custom (complex geometries).
✔ Core & Cavity Machining – CNC milling, EDM (electrical discharge machining), or 3D printing for prototypes.
✔ Cooling System Design – Proper cooling channels reduce cycle time.
✔ Ejection & Gating System – Pin ejection, valve gates, or hot runner systems for efficiency.

 Common Mold Types:

• Single-cavity mold (low volume)

• Multi-cavity mold (high volume)

• Family mold (multiple parts in one tool)

3. Prototyping & Test Runs (T0 & T1 Samples)

Before full production, test shots are done to verify mold performance.

Key Steps:

✔ Trial Injection (T0) – Initial test to check filling, cooling, and ejection.
✔ Adjustments – Modify temperature, pressure, or gate size to fix defects (sink marks, flash, etc.).
✔ T1 Sample Approval – Customer evaluates dimensions, surface finish, and function.

 Common Defects & Fixes:

• Short shots → Increase injection pressure or melt temp.

• Warping → Optimize cooling channels.

• Sink marks → Adjust wall thickness or packing pressure.

4. Mass Production & Quality Control

Once the mold is approved, full-scale production begins.

Key Steps:

✔ Cycle Time Optimization – Faster cycles = lower costs (e.g., robotic part removal).
✔ Process Monitoring – Sensors track pressure, temperature, and defects in real time.
✔ Quality Checks – CMM (coordinate measuring machine), visual inspection, or CT scanning.

 Industry Standards:

• ISO 9001 (Quality Management)

• IATF 16949 (Automotive)

• ISO 13485 (Medical Devices)

5. Post-Processing & Finishing

Depending on the application, additional steps may be required:
✔ Deburring – Remove sharp edges.
✔ Painting/Coating – UV protection or aesthetic finishes.
✔ Assembly – Ultrasonic welding or adhesive bonding.

6. Common Challenges & How to Avoid Them

❌ High Tooling Costs → Use modular molds or simplify geometry.
❌ Long Lead Times → Partner with experienced mold makers.
❌ Material Waste → Optimize runner systems (cold vs. hot runners).

Conclusion

Custom injection molding is a collaborative process involving design, engineering, and precision manufacturing. By following these steps—from DFM analysis to final QC—you can ensure high-quality, cost-effective production.