Forming defects：Forming flaws, some arising from inadequate machine performance, poor mold design, or inherent material properties, with most issues resolvable through adjustments.
| Defect Name | Cause Description | Improvement Measures | |
| Shrinkage | Plastic begins to harden upon contact with the mold surface. As the molten plastic solidifies, density differences emerge, causing shrinkage—particularly noticeable in products with uneven thickness. The injection pressure applied to the thicker sections cannot compensate for shrinkage at the thinner edges, exacerbating the issue. | 1. Increase plastic metering, raise injection pressure, or extend holding pressure time. 2. Increase injection pressure and improve mold venting |
|
| Product Warping | Typically caused by demolding plastic parts while excessively hot or uneven wall thickness in the product. | Extend cooling time or ensure consistent wall thickness throughout the product. | |
| Uneven surface finish on finished product | 1. Insufficient injection pressure 2. Slow injection speed 3. Rough mold cavity surface |
1. Increase injection pressure 2. Repolish mold cavity inserts |
|
| Black streaks, yellow spots, black spots | Overheated material adheres to barrel walls | 1. Perform thorough dry shots 2. Lower material temperature and reduce heating time 3. Disassemble and clean the barrel |
|
| Air bubbles | 1. Caused by uneven wall thickness in the molded part 2. Volatilization of moisture in the plastic or thermal decomposition of additives |
1. Increase injection pressure 2. Increase holding pressure time 3. Thoroughly dry the plastic 4. Increase shot volume |
|
| Flash (Rough Edge) | 1. Overfilling 2. Improper mold design such as improper draft angles or undercuts |
1. Reduce injection pressure, time, speed, and dosage 2. Modify the mold |
|
| Cracking during mold opening or ejection | 1. Insufficient radius 2. Excessive proportion of recycled material |
1. Increase draft angle 2. Reduce reclaimed material ratio |
|
| Part sticking to mold | Excessive injection pressure and prolonged injection time cause over-injection of material | 1. Reduce injection time and injection pressure 2. Reduce shot weight 3. Decrease injection speed |
|
| Gate sticking to mold | 1. Improper gate location 2. Inadequate gate draft angle |
1. Modify mold 2. Increase gate draft angle 3. Polish gate insert | |
| Silver streaks, gas holes | 1. Plastic supercooled due to low mold temperature 2. Resulting in excessive nozzle temperature causing cold runner issues 3. Plastic contains moisture or volatile substances |
1. Improve effective flow rate to increase relaxation in the holding zone 2. Dry the plastic |
|
| Flow lines | 1. Plastic is supercooled 2. Mold temperature is too low 3. Inlet too small 4. Injection pressure and speed too low, causing wavy surface on molded part 5. Contaminated raw material |
1. Increase plastic and mold temperatures 2. Increase injection pressure and speed, enhance venting Inspect raw material |
|
| Weld lines | Formed when plastic flows through a hole, splits, then rejoins while obstructed by heated air | 1. Increase plastic temperature or accelerate plastic flow through the hole 2. Raise mold temperature or use material grades with better flowability 3. Increase injection speed and pressure |
|
| Incomplete Product Formation | 1. Injection pressure too low 2. Insufficient injection volume 3. Low barrel temperature 4. Mold temperature too low 5. Poor venting 6. Trapped air |
1. Increase pressure 2. Increase material feed rate 3. Extend injection cycle or gradually raise temperature 4. Reduce mold cooling water flow, increase mold temperature 5. Improve mold venting 6. Modify mold gate or add additional injection points |
|
| Screw Slip (Inability to Feed Material) |
1. Inlet section temperature of barrel is too low 2. Improper back pressure adjustment 3. Insufficient retraction stroke |
1. Increase barrel feed section temperature 2. Adjust to appropriate back pressure 3. Increase back-off stroke 4. Change nozzle size |
|
| Material leakage (dripping) |
1. Plastic is too hot 2. Nozzle is unsuitable 3. Nozzle center is misaligned 4. Re-align mold gate 5. Back pressure is too high 6. Reduce back pressure or back-off distance |
1. Lower material or nozzle temperature 2. Replace with suitable nozzle 3. Nozzle misalignment 4. Realign mold gate 5. Back pressure too high 6. Reduce back pressure or loosen/retract |