The key to producing precision parts in large volumes is a well-designed mold. Building a mold requires time and accuracy and can represent a significant investment in the manufacturing process. Therefore, getting it right is crucial to the success of a project. Here are some tips to ensure that your plastic injection molding process produces high-quality parts.
- Understand Your Plastic
The type of plastic being used will determine the design of the tool and the molding process. Different plastics have varying degrees of free-flowing properties and shrinkage rates. For example, crystalline or semi-crystalline plastics are more free-flowing and tend to shrink more than amorphous plastics. Engineering resins are often preferred for their better melt and less shrinkage properties.
- Add Draft Angles
Draft angles, or the angle at which a part's face is tapered, help ease its release from the injection mold. Precise calculation is required to ensure that the draft angle does not cause any design issues, such as interfering with mating parts. A minimum angle of 1° is recommended for untextured molds and 3° for textured ones.
- Ensure Resin Flows from Thick to Thin Sections
Thicker sections of a part must be positioned near the gate to allow for efficient resin flow. Plastics tooling often requires a combination of wall thicknesses to create the desired structure and increase strength. Resin flowing from thinner to thicker walls can have problems filling completely, so the gate must be positioned closest to the thickest sections.
- Reduce Sizes of Strengthening Ribs
Ribs are added to parts to make them stronger and stiffer, but they must be properly formed to avoid sink and other defects. A properly formed rib must balance three basic design features, including a base thickness that is no greater than 60% of the wall thickness, a rib height that is less than three times the part thickness, and an overall rib thickness that is less than the base thickness.
- Be Attentive to Resin Shrinkage
Resin shrinkage can impact the design and machining of the tool cavities. The cavities must accommodate the amount of shrinkage that can occur, which is based on the specific properties of the resin. This shrinkage can result in warpage or molded-in stress.
- Design a Strong Mold
A strong mold design is essential for a high-volume quality injection molding process. Gates must be correctly placed to allow for proper melt flow and pressure. Vents must also be placed in the right position and size to allow for the air displaced by the melted resin to escape the tool.
- Ensure Proper Cooling
A well-designed cooling system is crucial to maintaining a consistent temperature and minimizing cycle times to maximize production output.
- Size and Place Ejector Pins
The size and position of ejector pins must be determined based on the shape, size, and wall thickness of the part to avoid any defects.
- Utilize Samples Prior to Full Run
Testing the mold with a sample run can help identify any necessary adjustments to the mold, the resin selection, or molding parameters.
- Be Mindful of Cost
Plastic tooling cost can be influenced by several factors, such as the number of cavities, the mold base, part complexity, and the core metal. Working with an experienced plastic injection molding manufacturer can help optimize parts for performance and cost.
By following these tips, you can ensure that your plastic injection molding process produces high-quality precision parts in large volumes.