Design for manufacturing (DFM) in injection molding is about optimizing the design of a molded part so that it’s easy to make, cost-effective to produce, and meets your application requirements. DFM encompasses material selection, mold design, and process optimization but also accounts for quality, reliability, safety, time-to-market, compliance, and assembly.
Known also as design for manufacturability, DFM works best when part design informs mold design and vice versa. Part designers also need to understand the basics of the injection molding process, which begins when a polymer is heated and forced through a nozzle or sprue. Within the mold, this material passes through runners and gates. When the part is ready, the mold is opened and the part is extracted.
There are many DFM considerations, but several that are especially important for injection molding:
- material selection
- wall thickness
- undercuts
- draft angles
- gates
- vents
- structural reinforcements
- cycle times
The following sections explain.
Material Selection
Designers need to select materials that will meet requirements for performance, cost, availability, and approvals. Remember, too, that different materials have different flow rates. A polymer’s melt flow index (MFI) can affect DFM considerations ranging from wall thickness to gates and vents.
Wall Thickness
Walls that are too thin can weaken and result in part failure. Walls that are too thick can make the injection molded part too heavy, too expensive, or visually unappealing. Part wall thickness also affects corner radius, impact resistance, and thermal, electrical, and acoustic insulation.
Undercuts
Undercuts are indentations or protrusions that prevent the direct ejection of molded parts. They add costs to the mold and complexity to the manufacturing process. Some parts use undercuts for product assembly, but it’s usually better to avoid them by placing part features perpendicular to the draw line.
Draft Angles
Molded parts need a draft angle in the direction of the mold’s movement so that clearance is created as soon as the mold begins to open. Parts with deep, molded-in textures require more draft than parts with smooth surfaces. To avoid creating thick walls, design parallel drafts to keep the wall sections uniform.
Gates
Gates are transitional areas between the runner system and the molded part. They should be large enough to prevent unwanted interruptions of material flow, but small enough to easily separate the runner from the part. To minimize surface defects, locate the gates where the polymer impinges against the walls.
Vents
Mold cavities require venting to release the air that’s displaced during the in-flow of the molten material. Higher MFI materials need smaller vents, but these outlets can become clogged if they’re not large enough. Position your vents along the mold’s parting line, especially at the last-to-fill locations.
Structural Reinforcements
For parts that need added strength, some designs support the use of reinforcements instead of thicker walls. For example, ribs are raised structures that reduce stress and deflection. Bosses are projections that provide mounting points. They can be cored all the way to the bottom to accommodate a fastener.
Cycle Times
Faster cycle times enable part designers to get products to market more quickly. They also help to reduce manufacturing costs because there’s less production time required. Just as material selection affects melt temperature, cooling and other process variables are also a function of design.
Better Design for Manufacturing in Injection Molding
Part designers who want to improve design for manufacturability have plenty to consider. By choosing an experienced injection molder, however, you can leverage their expertise. It’s also best to engage an injection molder early in the design process. If you wait until a tight production deadline, you may not have enough time to optimize your design based on the recommendations that you receive.
Extreme Molding of Watervliet, New York (USA) is a leader in custom injection molding with silicones and plastics. We offer unmatched expertise in materials and mold complex part designs using highly precise and repeatable equipment. To learn more about how we can help you with DFM for injection molding, contact us.
