In the rapidly evolving field of plastic manufacturing, companies constantly seek ways to streamline processes and reduce costs while maintaining high quality in their products.  A well-designed part does not need mold complexity to fix poor design choices. In this blog let’s explore the principles of minimizing plastic part mold complexity, a critical factor in achieving efficient and cost-effective production.
The Principle of Simplicity in Mold Design
Taking steps to simplify part design at the conceptual stage can significantly reduce tooling lead times and lower tooling costs.  A streamlined design minimizes moving inserts, such as side pulls and lifters, within the mold. This speeds up the manufacturing process and reduces the potential for errors, maintenance headaches such as wear and flash, and mechanical failures.
Avoiding Undercuts and Side Pulls
Undercuts, although sometimes necessary for complex shapes, can add significant costs and complications to mold design. Â They require either clever design solutions or specialized mechanisms like side pulls and lifters, the latter not only increase the tool cost but can also impact the reliability and maintenance cost of the tooling.Â
Tolerances and Detail Limitations
Specifying liberal tolerances and limiting details to functional necessities can greatly influence the ease of manufacturing and the lifecycle of the mold.  Over-specifying tolerances or unnecessary details can lead to increased costs and extend the tooling lead times due to the finer precision required in tool making. Time equals cost!
Collaborative Design Process
Engaging in a dialogue with both the molder and toolmaker during the design phase is crucial to enabling success. Discussing aspects such as the gate type, quantity and location, the parting line locations, ejector pin quantity and locations, wall thickness, ribbing, coring and tolerances can lead to a design that is more conducive to ease of manufacturability. Part design will dictate the parting line. Steps in the parting line will increase the machining required. While a more planar parting is desirable, it may not be possible. Mold Flow Analysis is always recommended. Remember that uniform wall thickness, gentle transitions, no sharp corners and avoiding concentrated mass are essential to a good part, and therefore an efficient tool design. Ribbing is important. Not only do ribs add stiffness to the part, but they can also aid flow and damp vibration. But be cautious about sink marks due to concentrated mass, obey the guidelines. This cooperation ensures that all parties understand the requirements and constraints of the project, leading to better outcomes and fewer revisions.
Standardization and Tool Material Choices
Using standardized mold frames and components whenever possible can lead to significant reductions in both cost and time. Â Additionally, selecting mold materials that are aligned with the projected production volumes can optimize tool life, cost and performance. Â Ordering tool steel early in the process, based on a stable part design (i.e. size and shape), can decrease overall lead time as tool steel lead times can be significant.
Post-Tooling Considerations
For covers and appearance parts, an important tip is to avoid texturing the mold until all tool corrections have been completed. Textured walls require extra draft, at least 5o, to effectively eject parts without causing damage to the texture or the part itself. It’s essential to ensure that the base mold is correct and all tooling reworks are completed before adding such final touches.
By adhering to these principles, manufacturers can significantly simplify the injection molding process. This not only reduces costs but also enhances the reliability and efficiency of production. In an industry where every second and penny counts, optimizing mold design and manufacturing processes can provide a substantial competitive edge. The examples below demonstrate some of the design choices that can reduce complexity in mold design, ultimately leading to a more streamlined, cost-effective and successful manufacturing operation.
AUTHOR
Henry T. Bober
Subject Matter Expert, Srushty Global Solutions
Henry is a seasoned Mechanical Design Engineer with 40 years at Xerox Corporation, specializing in Product Development, Cost-Effective Design, and Technology Development. He holds degrees from West Virginia University and the University of Rochester and has 35 patents to his name. After retiring, he founded Fast Forward Engineering, consulting for clients like Xerox, Diebold, NCR, and Siemens Medical Products. Now a Subject Matter Expert at Srushty Global Solutions, Henry lives in Fairport, NY, with his wife Leslie and their pets. He enjoys Western-style horse riding, Japanese garden landscaping, woodworking, naval warfare history, and animal welfare advocacy.