Injection molding is an excellent resource for producing parts as it works quickly with various types of plastics. The process is reliable as it delivers durable final products with meticulous detail. The proper design allows your mold to cycle rapidly, elevate productivity, and retain strength through the years, ultimately improving your bottom line. However, plastic injection molding is a complex process and you may encounter challenges. Flaws in the mold can result in decelerated productivity and other failures. Awareness of potential design issues increases the likelihood of production success.
One of the best ways to minimize the risk of problems with injection molding is to discuss the design with experts. The design professionals at Advantage Engineering are dedicated to helping customers through the pre-production phase with low-volume plastic injection molding. We give customers the advantage by rapidly producing custom molds for the complex geometries they need. Here, we offer a list of possible challenges you may experience with your designs and how to fix them.
Dealing with Molding Defects
Numerous flaws can occur with plastic molding, including specific defects and consequences from choosing a low-quality mold. Preemptively consider the following possible design issues and how to remedy them.
- Burn Marks
High injection speeds or excessive heating can cause rusty discolorations, called burn marks, on part surfaces. Burn marks may also arise due to trapped air overheating and forming etches on surfaces.
Lowering injection speeds, decreasing the mold and melt temperatures, and enhancing the degassing quality may prevent these discolorations. - Flash
Flash happens when portions of the molten plastic escape the mold cavity via ejector pins, parting lines, and other similar pieces. Inaccurately cut or inadequately built molds, loose clamps, and high injection pressures cause this issue. Expired molds may also cause this flaw.
Increasing the clamp pressure and confirming your mold doesn't require maintenance can resolve this issue. You should also check the injection pressure, speed, and mold temperature to ensure they do not cause this defect. - Flow Lines
Flow lines are off-tone lines, patterns, or streaks that emerge on parts due to different flow rates of the molten plastic or changes in the thickness of the mold’s walls. Low injection speeds or improper gate mold venting may also cause this issue.
To mend flow lines, boost injection pressure and speed to evenly fill the cavities. You can also increase the temperature in the mold or the molten plastic to keep the plastic from rapidly cooling. If the problem is the mold’s walls, round areas of varied thickness to create a uniform flow path for the plastic. - Jetting
If molten plastic does not adhere to the mold’s surface, wavy folds, or jetting, appear on the part’s surface. This defect is due to a combination of low melt temperature, incorrect injection speed, and high viscosity of the molten plastic.
Elevating mold and melt temperatures and increasing the gate size will slow the injection speed, preventing jetting. Confirming appropriate contact between the mold and molten plastic also helps avoid this defect. - Sink Marks
If the finished prototype begins shrinking, small depressions called sink marks appear in thicker areas of the injection molding. These marks arise if there are issues with the cooling time, cavity pressure, or heat at the gate.
Minimizing the mold temperature and increasing the holding time and pressure can solve for the effects of sink marks. Providing more time for the plastic to cool and cure inside the mold may also remedy this defect. - Warping
Uneven cooling inside the plastic molding may cause warping in the finished part.
Slower cooling rates will inevitably prevent warping, but maintaining a regular wall thickness can also inhibit the defect as it encourages molten plastics to flow in one direction. Bear in mind certain plastics are more likely to warp, like semi-crystalline varieties, so take time to consider what materials you're using. - Weld Lines
Improper bondage between multiple flow fonts results in seams where two areas of molten plastics meet.
These seams, called weld lines, can be eliminated by lifting the temperature of the mold or molten plastic. Changing the flow pattern to a single-source flow, elevating the injection speed, and switching to less viscous plastic may also correct the issue. - General Contamination
With time, all injection molds become exposed to carbon, grease, oil, rust, and material gassing. Without proper maintenance, they can decline in use and potentially go to waste.
This reality makes cleaning molds crucial to their longevity. Consistent upkeep also helps lower production costs in the long run and ensures the molder can handle repairs and design changes.
- Burn Marks
Reduce Design Challenges with Professional Assistance
Design defects with plastic injection molding can occur in any situation, but the risks minimize when you partner with an organization that offers design for manufacturing (DFM) as a service. These partnerships encourage frequent communication between the customer, toolmaker, and molder to ensure consistent outcomes and mitigate possible information loss. That’s why Advantage Engineering offers a DFM support team of product designers that ensure you get the parts you expect on time. A one-stop shop for injection molding, we provide in-house assembly, post-processing, logistics, and sequencing to best serve our clients' needs.
Give Your Product Designs the Advantage
For over 25 years, Advantage Engineering has helped countless partners launch new products by providing rapid prototyping, bridge tooling, and low-volume production. We recognize how hard it is to bring innovative products to life, so we simplify the process with intelligent and fast-moving production solutions. For more information on plastic injection molding and other services we offer, request a quote through our online portal or contact us today.
