Plastic injection molding is a complicated and challenging process to undertake in the sense that it requires precision, experience, and detail. From material choice to tool design, all elements must be constituted in a way that helps them to be optimized to produce free-defect parts of the best quality.
Troubleshooting is quite important within this process to detect and solve the problems that could appear during the setup or processing of parts due to causes varying. It ensures the running and improvement in monetary concern with downtime and costs regarding production.
Common defects resulting from injection molding include warping, sink marks, and short shots. Learn more about troubleshooting these injection molding issues!
Injection Molding Defects (Image Source: Topworks)
Identifying Common Injection Molding Issues
Many potential problems may arise during the process of injection molding, which impacts the quality of your products. The common problems include:
- Short Shots
- Flash
- Warping
- Sink Marks
- Burn Marks
1. Short Shots
Short shots occur in cases where the material flow is inadequate or if the extent of injection pressure is low. The solution for this would be to increase the injection pressure and modify the mold design to ensure enough materials fill it entirely.
2. Flash
A flash occurs when excessive injection pressure or misaligned molds force the material to squirt out through the mold cavity. This condition can be avoided by keeping the injection pressure at the recommended level and properly aligning the molds to retain the shape and quality of the parts.
3. Warping
Warping is caused by uneven cooling or material shrinkage, distorting the parts. Improving the cooling systems and adequate material selection can reduce warping and maintain the shape and dimensions of the parts.
4. Sink Marks
These are depressions formed on the surface of parts due to inadequate cooling time or thick sections in the part design. Sink marks can, therefore, be eliminated to result in much smoother and more consistent parts by extending an appropriate cool time and redesigning the part to have a uniform thickness.
5. Burn Marks
These are the burn marks created when air is entrapped or injection speeds are too high. Reduce burning marks and provide improved venting. Lower the speed of injection to deliver parts with a clear, blemish-free surface.
Injection Mold Design Considerations
Mold design prevents many of the common issues associated with the manufacturing process. Key among these is the provision for uniform material flow through the mold cavity, achieved by proper attention to the position of gates, runner design, and overall geometry of the mold.
Properly designed gates and runners ensure that the molten material distribution is in equal quantity at the cavity and flow paths. This can help to reduce problems like flow marks, uneven shrinkage, and warpages. Cooling channel design is also critical to maintaining uniform mold temperatures.
Effective cooling enables faster cycle times while reducing defects such as sink marks and internal stress in parts involving final molding.
These designs, however, will incorporate strategically located cooling channels that facilitate uniform cooling across the mold surface and avoid hot spots, which may result in poor quality in parts. Proper injection mold design will not only provide quality and consistency in molded parts but will also bring increased efficiency and lower manufacturing costs.
Factors like material flow and cooling channel design, when taken into consideration, help reduce production complications and strive to improve overall performance in an injection molding process.
Troubleshooting Injection Molding Defects (Image Source: gmmoldtech)
Material Selection and Handling
The right material used in injection molding has to be compatible with specifications or requirements on mechanical properties, chemical resistance, thermal stability, and cost-effectiveness for various applications. As such, key considerations and practices related to the selection of materials and how to handle them include:
Material Selection Criteria
- Mechanical Properties: Strength, stiffness, impact resistance
- Chemical resistance: the capacity to endure exposure to chemicals or environmental conditions
- Thermal stability: heat resistance and dimensional stability at high temperatures.
- Cost: Material cost per unit and total processing cost.
- Appearance: The surface finish, color options, aesthetic requirements, etc.
Proper Drying and Handling of Materials
Many polymers absorb moisture and are, therefore, prone to creating defects, such as voids or splay marks, during the molding process. Pre-drying of polymers before processing aids in ensuring that the moisture level is within the acceptable limit. Of importance, too, is the storage of materials under dry conditions to prevent contamination and preserve their properties.
Material properties have a direct effect on the injection molding process. Of many, the viscosity of plastic would have a huge influence on how it flows into the mold cavity, probably the mold filling or even the quality of the part.
Having said that, different materials shrink differently as they cool. This would affect dimensional accuracy.
Warpage, which can be caused by uneven cooling or poor material flow, may severely affect the shape of the final part and hence its performance. Matching the coefficient of thermal expansion of the mold material is one of the ways to minimize stresses and deformation of molded parts.
Custom Injection Molding Solutions
Custom injection molding offers several benefits such as:
- Tailored Solutions: It allows manufacturers to design parts that precisely meet specific requirements, such as unique shapes, sizes, or functionalities.
- Cost Efficiency: Custom injection molding reduces costs by optimizing material usage and minimizing waste through precise molding techniques.
- Quality Control: Custom molds enable tighter control over part quality, ensuring consistency and meeting stringent standards.
- Flexibility: Manufacturers can quickly adjust production volumes and specifications based on demand fluctuations or design changes.
Case studies of successful Custom Injection Molding Projects
One of the main case studies for custom injection molding is Oraimo. Custom Molding has made Oraimo achieve highly accurate dimensional results and incorporate highly intricate features that standard molds could not include. This has helped them increase the performance and assurance levels of the product.
The same custom injection molding enabled the construction of parts that boasted specific mechanical properties in Honda’s automotive applications. This assured them of safety under strict performance requirements when the company required light but hard-wearing components.
Sink marks in Injection molded part (Image Source: SyBridge)
Conclusion
Injection molding typically requires a huge upfront investment in tooling. Accordingly, it will become important to design your mold right at the first instance, rather than finding serious defects after all the work is done. Those defects that are related to the molding process or material are relatively easy and inexpensive to solve. However, no matter what the cause may be, defects in molded products can hurt your bottom line tremendously thus you must curb them.
