Injection molding is one of the fastest and most reliable ways to mass-produce plastic parts. If you’re sourcing parts for automotive, appliances, industrial components, or consumer products, understanding the basics can save you time, money, and a lot of rework.

Below is a clear, practical guide to how injection molding works, what affects cost and lead time, and how to avoid common issues.

1) What is injection molding?

Injection molding is a manufacturing process where plastic pellets are melted and injected into a mold cavity under pressure. After cooling, the part is ejected and the cycle repeats—often in seconds.

It is ideal for:

• Medium to high-volume production
• Tight repeatability (same part, same quality)
• Complex geometries (ribs, snaps, bosses, textures)

2) The injection molding process (step-by-step)

Step 1 — Material drying (if needed)
Some resins (e.g., PA/Nylon, PC, PET) absorb moisture. If not dried properly, you may see splay marks, bubbles, or weak parts.

Step 2 — Plasticizing (melting)
Pellets enter the barrel and are heated and mixed by the screw until fully molten.

Step 3 — Injection & packing
Melt is injected into the mold cavity. Then packing pressure compensates for shrinkage while the gate freezes.

Step 4 — Cooling
Cooling usually takes the most time. Mold cooling design strongly affects cycle time and warpage.

Step 5 — Ejection & inspection
The part is ejected. For production, parts are checked for key dimensions, appearance, and function.

3) What determines part cost?

The main cost drivers are:

• Mold cost: steel type, cavities, complexity, slides/lifters, texture
• Cycle time: cooling time, part thickness, material
• Material: resin grade (virgin vs recycled), additives, color
• Volume: unit price decreases as volume increases
• Secondary processes: printing, plating, assembly, ultrasonic welding

Quick rule: If you reduce cycle time and improve yield (less scrap), your part cost drops quickly.

4) Typical lead time

• Prototype tooling: ~7–20 days (depends on complexity)
• Production tooling: ~20–45 days (common range)
• First sampling (T0/T1): after mold completion
• Mass production: after sample approval

Lead time can be shortened when DFM (Design for Manufacturing) is done early.

5) Common defects and how to prevent them

• Warping: uneven cooling, too thick walls, poor gate location
• Sink marks: thick sections, insufficient packing
• Short shot: low injection speed/pressure, thin walls, venting issues
• Flash: parting line mismatch, worn mold, too high pressure
• Weld lines: multiple flow fronts, low melt temperature

Best prevention steps:

• Keep wall thickness uniform
• Add proper draft angle
• Use ribs instead of thick walls
• Confirm gate type/location with your supplier

6) What info should you send for a fast quotation?

To get an accurate quote quickly, prepare:

• 3D file (STEP/IGES preferred)
• Material requirement (or application & environment)
• Color and surface finish
• Annual volume / target order quantity
• Any critical dimensions & tolerance requirements
• Assembly method (screws, snaps, inserts, welding)

Need help selecting the best process?

If you share your 3D file and application, we can suggest the right resin, mold structure, and cost-saving DFM improvements.
Contact us for a quick technical review and quotation.