Introduction
Plastic injection moulding is one of the most widely used manufacturing processes for producing high-precision plastic components in sectors such as automotive, medical devices, electrical equipment, agriculture, and industrial machinery.
Despite its advantages in scalability and design flexibility, the process can encounter a range of defects that affect part quality, performance, and production efficiency. Understanding common injection moulding defects, their root causes, and how to prevent them is critical for manufacturers aiming for consistent quality and reduced rejection rates.
Common Injection Moulding Defects: Causes and Solutions
1. Short Shots
What it is: A short shot happens when molten plastic does not fully fill the mould cavity, resulting in incomplete or non-functional parts.
Causes:
- Insufficient injection pressure
- Inadequate venting
- Premature cooling of the melt
- Improper material flow or high viscosity
Solutions:
- Increase injection pressure and hold time
- Improve venting with air traps or vacuum assist
- Use polymers with better flow characteristics
- Optimize gate and runner design to ensure uniform fill
2. Warpage and Distortion
What it is: Warpage occurs when parts cool unevenly, causing bending or deformation from the intended shape.
Causes:
- Uneven cooling
- Asymmetrical part design
- Fiber orientation in reinforced plastics
- Inconsistent packing pressure
Solutions:
- Design conformal cooling channels
- Use mould flow simulation
- Optimize packing and holding conditions
- Balance part geometry and wall thickness
3. Sink Marks and Voids
What it is: Sink marks are depressions on the surface; voids are internal gaps.
Causes:
- Shrinkage during cooling
- Inadequate packing pressure
- Thick wall sections
- Trapped gases
Solutions:
- Maintain consistent pressure during solidification
- Design for uniform wall thickness
- Use microcellular foaming or counter-pressure
- Improve mould venting
4. Flash Formation
What it is: Flash is excess plastic that escapes along the mould’s parting lines.
Causes:
- Excessive injection pressure
- Poor mould alignment
- Gaps in the parting line
- Insufficient clamping force
Solutions:
- Adjust injection pressure and clamping force
- Maintain mould components
- Use precision-machined moulds
- Reinforce high-wear areas
5. Weld Lines
What it is: Visible lines where two molten fronts meet and fail to bond fully.
Causes:
- Low melt temperature
- Poor flow control
- Contaminated resin
- Inadequate pressure during fusion
Solutions:
- Increase melt and mould temperature
- Optimize gate location
- Use clean, high-quality resin
- Improve mould venting
6. Jetting
What it is: Wavy or worm-like surface pattern due to high-speed polymer flow.
Causes:
- High injection velocity
- Poor gate design
- Low viscosity material
- Lack of proper flow control
Solutions:
- Reduce initial injection velocity
- Modify gate location or size
- Use flow-stabilizing additives
- Implement sequential or valve gating
Final Thoughts: Ensuring Defect-Free Plastic Injection Moulding
Defects can lead to increased costs, delays, and performance issues. Proactive strategies such as optimized process control, advanced mould design, material selection, and simulation tools help reduce these problems. Regular quality control and predictive maintenance also ensure reliable production.
About Malhar Auto Industries
Malhar Auto Industries is a trusted name in plastic injection moulding with over three decades of experience across the automotive, agriculture, and electrical sectors.
- Established in 1988 with ISO 9001:2008 certification
- Expertise in labour-based and full-cycle moulding services
- Mould development from 2D/3D drawings or physical samples
- Capability to scale from concept to mass production
- Commitment to zero-defect manufacturing
Whether you need automotive plastic parts, PVC extrusion profiles, or precision moulded components, Malhar Auto Industries ensures reliable, cost-effective, and scalable solutions tailored to your needs.
🔗 Visit our website
📧 Email: info@malharind.com
📱 WhatsApp: +91-8380081730
📍 Based in India | Serving global customers