Top 10 Injection Molding Machine Problems and How to Solve Them

Injection molding machines are the workhorses of plastic manufacturing. When they run smoothly, production flows like a well-tuned orchestra. When problems appear, scrap rates rise, delivery schedules slip, and costs quietly multiply. Understanding the most common injection molding machine problems and knowing how to fix them quickly is essential for stable, high-quality production.

Below are the top 10 injection molding machine problems and practical solutions used by experienced technicians worldwide.

1. Short Shot (Incomplete Filling)

Problem: The plastic part is not fully filled, leaving missing sections or thin edges.

Common Causes:

• Insufficient injection pressure or speed
• Low melt temperature
• Blocked nozzle or runner
• Poor venting in the mold

Solutions:

• Increase injection pressure and speed
• Raise barrel and mold temperature gradually
• Clean nozzle, runners, and gates
• Improve mold venting

2. Flash (Excess Plastic on Parting Line)

Problem: Unwanted thin plastic forms around the part edges.

Common Causes:

• Low clamping force
• Worn mold parting surfaces
• Excessive injection pressure

Solutions:

• Increase clamping force appropriately
• Reduce injection pressure
• Inspect and repair worn mold surfaces

3. Burn Marks

Problem: Black or brown marks appear on the molded parts, usually at the end of flow.

Common Causes:

• Trapped air compressed and overheated
• Excessive injection speed

Solutions:

• Improve mold venting
• Reduce injection speed
• Lower melt temperature slightly

4. Sink Marks

Problem: Small depressions appear on the surface of thick sections.

Common Causes:

• Insufficient holding pressure or time
• Uneven wall thickness
• Poor cooling

Solutions:

• Increase holding pressure and holding time
• Optimize part design for uniform thickness
• Improve cooling efficiency

5. Warping deformation (Deformation)

Problem: The molded part bends, twists, or distorts after ejection.

Common Causes:

• Uneven cooling
• Internal stress from fast cooling
• Poor mold design

Solutions:

• Balance mold cooling channels
• Adjust cooling time and temperature
• Reduce internal stress through optimized processing parameters

6. Silver Streaks (Splay Marks)

Problem: Silvery lines appear on the surface of the part.

Common Causes:

• Moisture in raw material
• Trapped gas in melt

Solutions:

• Dry raw materials thoroughly before processing
• Reduce injection speed
• Improve venting

7. Flow Lines

Problem: Visible wavy lines or patterns on the part surface.

Common Causes:

• Inconsistent melt flow
• Low injection speed
• Low mold temperature

Solutions:

• Increase injection speed
• Raise mold temperature
• Optimize gate location and size

8. Machine Cannot Reach Set Pressure

Problem: Injection pressure fails to reach the programmed value.

Common Causes:

• Hydraulic system leakage
• Worn screw or barrel
• Malfunctioning pressure sensor

Solutions:

• Check hydraulic oil system and seals
• Inspect screw and barrel wear
• Calibrate or replace sensors

9. Unstable Cycle Time

Problem: Production cycle time fluctuates, affecting consistency.

Common Causes:

• Temperature control instability
• Inconsistent material feeding
• Servo or hydraulic system issues

Solutions:

• Stabilize barrel and mold temperature control
• Ensure consistent material supply
• Inspect servo motor or hydraulic components

10. High Scrap Rate and Low Repeatability

Problem: Parts vary from shot to shot, causing quality issues.

Common Causes:

• Poor machine repeatability
• Inconsistent process parameters
• Lack of machine maintenance

Solutions:

• Use high-precision injection molding machines
• Standardize process settings
• Implement regular preventive maintenance

Conclusion

Most injection molding problems are not caused by a single factor but by the interaction between machine performance, mold design, material quality, and process settings. By identifying issues early and applying the correct solutions, manufacturers can significantly reduce downtime, scrap rates, and production costs.

A stable, reliable injection molding machine is not just equipment, it is the foundation of consistent quality and long-term profitability.

If you are interested in the machine, please contact us for a quote. Service hotline: +868618958305290