The journey from a brilliant concept to a tangible, market-ready product is paved with countless design decisions. While initial sketches and prototypes focus on form and function, a pivotal transition occurs when the design must be prepared for mass production. This is where the principles of Design for Injection Molding (DfIM) and DFM for Medical Devices come into play, offering a systematic approach to creating parts that are not only effective but also efficient to produce. For plastic injection molding, DFM is a foundational practice that directly impacts cost, quality, and production speed, with one of its most potent strategies being the simplification of part geometry.
Simplifying a part's geometry is not about dumbing down the design or compromising its purpose. Instead, it is a sophisticated process of refining features to align with the capabilities and constraints of the injection molding process. By thoughtfully reducing complexity, designers and engineers can eliminate potential manufacturing defects, shorten cycle times, and lower tooling costs, all while preserving the part's essential function and structural integrity. This strategic refinement is what separates a merely functional design from one that is truly optimized for production through plastic part design optimization.
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One of the most fundamental principles in DFM for injection molding is maintaining a uniform wall thickness throughout the part. When molten plastic is injected into a mold cavity, it flows and cools to form the final shape. If a part has sections with varying thicknesses, the plastic will cool at different rates. Thicker sections will cool and shrink more slowly than thinner sections, creating internal stresses that can lead to a host of problems, including warping, sink marks (small depressions on the surface), and voids.
To avoid these issues, the goal is to design a part with walls that are as uniform in thickness as possible. When a design requires added strength or rigidity, the instinct may be to simply make the walls thicker in that area. However, a much better approach is to incorporate ribs or gussets. These features add mechanical support without creating thick masses of plastic. By coring out thick sections and replacing them with a network of well-designed ribs, a part can often be made stronger and lighter, while also being significantly easier to mould consistently. This approach not only improves the part's quality but also reduces material consumption and shortens the cooling time required for each cycle.
Another powerful method for simplifying a product's overall design is part consolidation. This strategy involves redesigning what might have initially been multiple separate components so they can be produced as a single, more complex injection-moulded part. While this may seem counterintuitive to the idea of "simplifying geometry," it simplifies the product at a higher level by eliminating the need for assembly and secondary manufacturing processes.
Consider a device that requires a housing, a mounting bracket, and a battery cover. Traditionally, these might be three separate parts that need to be manufactured and then assembled, often with screws or clips. Through clever design, these three functions could potentially be integrated into a single moulded component. This consolidation eliminates the costs associated with producing multiple tools, managing the inventory for several parts, and the labour required for assembly. Furthermore, it removes the potential for failure at the joints or connection points between the original parts, leading to a more robust final product. The key is to analyse the function of each component in an assembly and identify opportunities where features can be combined without making the mould itself unmanufacturable.
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Even in a simplified design, certain geometric features are necessary for the injection molding process to work effectively. Two of the most important are draft angles and radii. At the same time, certain complex features, known as undercuts, should be avoided whenever possible, as they dramatically increase the complexity and cost of the tooling.
Draft refers to a small angle incorporated into the vertical walls of a part, allowing it to be easily ejected from the mold without being damaged. Without a draft, the friction between the part's surface and the steel mold can create drag marks or even prevent the part from releasing at all. Similarly, adding a radius or fillet to the sharp corners of a part is a simple change that yields significant benefits. Sharp internal corners create stress concentrations in the finished part, making it weaker. They also make it more difficult for the molten plastic to flow smoothly into every part of the mold. By rounding these corners, material flow is improved, stress is distributed more evenly, and the tool itself is stronger and less prone to wear.
Undercuts are features like snaps, clips, or side holes that prevent the part from being pulled directly out of the mold's core half. To produce a part with an undercut, the mold must include a complex mechanism, such as a side-action or lifter, that moves into place to form the feature and then retracts before the part is ejected. These mechanisms add substantial cost and complexity to the mold's construction and maintenance. A primary goal of design for manufacturing solutions is to eliminate undercuts if the function can be achieved in another way. This may involve redesigning a snap-fit to be a "pass-through" feature or creating an opening in the part that allows a tool to form the feature without creating a trapping condition. This type of geometric simplification has one of the largest impacts on reducing injection molding tooling costs and lead times.
At Aprios, our engineering team excels at applying DFM services and injection molding services to help optimize your part designs for injection molding. We work collaboratively with our clients to simplify geometry, consolidate parts, and refine features to reduce production costs while upholding the highest standards of quality and functionality. If you are ready to streamline your design for efficient and reliable manufacturing, contact Aprios today to learn how we can support your project from the initial concept to full-scale production.