Injection molding design for manufacturability (DFM) processes are necessary to guide product design, mold design, and tooling creation with ease of manufacturing in mind. Properly done, this can enhance the efficiency of production and quality of end-products while also lowering costs. At D&M Plastics, our engineering team has years of experience optimizing part designs for plastic injection molding. Our DFM review process enables us to evaluate part designs and make the necessary adjustments to ensure high-quality, efficient, and cost-effective manufacturing.
Understanding Injection Molding
Plastic injection molding is a type of manufacturing process that involves injecting molten plastic materials at high speeds and pressures into a mold. There, the plastic cools and solidifies to form the part. Once cooled, the part is ejected from the mold and the process repeats itself. Because this process is so repeatable, it is commonly used for high production runs that range from hundreds to millions of parts.
Common plastic resins used in the injection molding process include:
- Acrylonitrile butadiene styrene (ABS)
- Acrylic (PMMA)
- Copolymer polypropylene
- Glass-filled nylon
- Liquid-crystal polymer (LCP)
- Polypropylene copolymer acrylonitrile butadiene styrene (PC ABS)
- Polyethylene (PE)
- Polystyrene (PS)
Injection Mold Design
When designing the mold for plastic injection molding, it’s important to consider the type of injection molding process that will be used. In addition to standard injection molding, other common types include:
- Insert molding and overmolding in a vertical press. Using a vertical press for insert molding or overmolding offers quicker yields, increased flexibility for mold design, and the ability to hold the workpiece without having to fight gravity.
- Stack molding. Stack molding involves “stacking” a series of molding faces together to create several levels or faces for molding. Each face serves as a parting line and is used to produce a molded product. The primary benefit of stack molding is its ability to increase the output of molding operations.
- High cavitation molding. Cavitation refers to the number of components a mold can make per cycle. Although high cavitation molding comes with higher tooling costs, it reduces the price per part and enhances machine efficiency.
The design and construction of an injection mold are very complex and can require a considerable amount of time and money. Optimizing the mold design based on a project’s particular requirements will not only reduce costs but will also ensure efficient manufacturing.
In addition to the type of injection molding, you also need to consider the complexity, application, production volume, and lifetime requirements of the tool. For example, if a mold will be used in high-volume production, it will be most beneficial to invest in more expensive tooling that will last for the long term. For low-volume production, it may be better to use a less costly prototype tool until production increases. Other factors to consider during DFM for injection molds include:
- Part design
- Mold material
- Cores and cavities
- Cooling system
- Venting system
- Ejection system
Factors to Consider When Choosing Mold/Tooling Options
When choosing mold and tooling options for a plastic injection molding project, it’s important to keep in mind the following:
- Production Quantity. High production volumes may require a high tooling cost, but the cost is offset by a lower cost per part.
- Tolerance, Size, and Complexity. The complexity, size, and geometry of the part will affect the influence the mold and tooling design options. Some parts may require undercut sidepart actions or complex cavity and core configurations.
- Material Properties. The plastic materials selected for injection molding can also affect the tooling process, as each one has different flexibility levels, heat resistance, and other characteristics.
At D&M Plastics, we perform injection molding services using a hot runner system. Compared to cold runner systems that require the time-consuming removal of runners from each part, hot runners offer faster cycle times, reduced material waste, and improved part quality.
Tips for Designing for Manufacturability With Injection Molding
Before tooling is created, it’s important to incorporate the following key elements into your DFM practices:
- Uniform Wall Thickness. Uniform wall thickness is critical in preventing thick sections in the finished part. If the part requires different thicknesses, make the transition as smooth as possible to ensure the material flows evenly throughout the mold cavity. This ensures the mold will be completely filled, decreasing the risk of defects. Selecting the right wall thickness plays a key role in production costs and manufacturing speed.
- Proper Draft Angles. When designing your injection molded part, make sure you incorporate the proper draft angles. By adding a few degrees of taper, the part can be removed from the mold much more smoothly, with minimal scraping and friction. By preventing damage to the part’s surface, the process can move much more efficiently.
- Avoidance of Sink Marks. Sink marks can occur if part walls are too thick. Sinking can be prevented by using ribs or by carefully controlling the cooling process.
- Proper Placement of Gates. Gate placement is crucial in injection molding design. The gate is the location in the mold and on the part where the material will be injected into. The gate is typically placed at a thicker, intersectional area of the part where it can be removed without sacrificing the structural integrity of the part.
- Prioritize Early Collaboration Between Designers and Manufacturers. Early collaboration is key to avoiding costly changes later. By working closely together, designers and manufacturers can optimize part designs and tooling to ensure quality and efficient production.
High-Quality DFM Services From D&M Plastics
At D&M Plastics, our experts can work with customers to enhance part designs and create the most effective tooling for their project. Our team can help optimize production for low- and high-volume production runs for injection-molded parts of various complexities. By following DFM best practices and using the right tools and processes, we can achieve high-quality finished products at an affordable price. Contact us today to learn more about our capabilities or request a quote to get started.