How to Tell if a Product is Made by Injection Molding

1. Visual Clues

① Parting Line (Mold Seam)

• A faint line running along the edge of the product where two halves of the mold meet.

• Often smoothed in high-quality parts but still detectable under close inspection.

② Ejector Pin Marks

• Small circular or rectangular indentations on non-visible surfaces (where pins pushed the part out of the mold).

③ Gate Mark (Injection Point)

• A tiny bump or depression where molten plastic entered the mold (common types: edge gate, submarine gate, or pinpoint gate).

2. Design Features

④ Uniform Wall Thickness

• Most injection-molded parts have consistent thickness (typically 1–4mm) to prevent warping or sink marks.

⑤ Ribs & Reinforcements

• Thin supporting structures (ribs) are often added to strengthen parts without adding excess material.

⑥ Draft Angles (Tapered Sides)

• Slight angles on vertical walls to help eject the part smoothly (textured surfaces may hide this).

3. Material & Surface Finish

⑦ Plastic Material

• Common thermoplastics like ABS, PP, PC, PS, or nylon suggest injection molding.

• Silicone or metal parts usually require different processes (but LSR silicone can be injection-molded).

⑧ Smooth/Textured Surfaces

• High-gloss finishes (from polished molds) or textured patterns (via mold etching) are typical.

4. Production & Quality Signs

⑨ High Consistency

• Identical parts with minimal variation (unlike 3D-printed items, which may show layer lines).

⑩ No Machining Marks

• Unlike CNC-machined parts, injection-molded products lack tooling marks unless post-processed.

5. Limitations of Injection Molding

⑪ No Fully Enclosed Hollows

• Internal voids usually require slides, lifters, or assembly (unless using advanced techniques like gas-assisted molding).

⑫ Size Constraints

• Small to medium parts are common (large items like car bumpers need specialized machines).

6. Comparing with Other Processes

7. Advanced Verification Methods

• Microscope Inspection – Check for gate vestiges or flow lines.

• CT Scanning – Detect internal mold flow patterns.

• Material Testing – Confirm thermoplastic properties.

Common Injection-Molded Products:

✅ Consumer Goods – Toothbrush handles, LEGO bricks.
✅ Electronics – Phone cases, remote buttons.
✅ Medical Devices – Syringe barrels, IV connectors.

If a plastic product has parting lines, ejector marks, uniform walls, and draft angles, it’s likely injection-molded. For complex cases, consult a manufacturing expert!