When designing an injection molded part or prototype, it’s important to consider various design aspects. Everything from the manufacturer’s capabilities and equipment to the part’s angles and edges can influence the quality and cost efficiency of the end product. The key method for minimizing potential problems is simple – communication with your preferred plastic molder.

Each molder has his or her own tooling preferences and techniques for molding parts, which can have a significant effect on your part design. We recommend forming a close partnership with your molder as early in the design process as possible.

Design related parameters that affect your injection molded part(s) include:

  • Material Options
  • Critical Tolerances
  • Sink Marks
  • Steel Safe Areas
  • Gate Location
  • Shut Off Angles

Material Options
Materials are often specified early in the design process and should be mutually agreed upon by both parties. A resin may be chosen for specific physical or chemical-resistance properties but may be difficult to mold or maintain specified tolerances. It’s important to speak to your molder about material options and overall part requirements. You can learn more about common plastic molding resins in this article.

Critical Tolerances
Providing enough clearance in a design for tolerance variation can be one of the greatest challenges a designer faces. Tolerance variation depends upon several variables, including materials, process control and tool design. It’s important to discuss reasonable critical tolerance specifications with your molder and consider options for possible mold revisions if required. Your molding partner may offer a number of suggestions for maintaining tight tolerance control, including post machining, fixturing and gate locations.

Sink Marks
Avoiding sink marks in injection molded parts can be challenging. Most molders recommend a maximum wall thickness at the base of a rib or boss of less than 60% of the perpendicular face wall. Close collaboration with your molding partner could lead to simple solutions like minimizing draft or rib heights.

Steel Safe Areas
Details that cannot be confidently reproduced by a molder, such as snap fits or interlocking parts, are often designed ‘steel safe.’ Steel safe means that the design feature is detailed with enough clearance to allow a tool maker to easily machine away steel in the mold to tighten up the clearances after initial test shots are molded. Close communication with your molder early in design process will help minimize design revisions.

Gate Location
The gate location is critical to virtually every attribute of an injection molded part. It affects appearance, warpage, tolerances, surface finish, wall thickness, molded in stresses and physical properties to name a few. Gate location should be specified by a designer, molder and tool maker.

Shutoff Angles
Shutoff angle and bypass refer to the minimum angel between the core and cavity. Molders typically want as much angel between the core and cavity as possible, opposed to designers who want minimal angles. The compromise usually lies within a minimum of 3° to 5°. Be sure to speak with your molder about their minimum angle requirements.

Following the above guidelines when designing injection molded parts and prototypes will ensure the final product is cost-efficient and high quality. At Bangor Plastics, we have the necessary capabilities and equipment to produce your molds and execute mass production. If you’re interested in working with Bangor Plastics, contact us today. You can also request a quote here.