Several critical elements must be considered while manufacturing a high-quality molded part, including part design, fabrication, material selection, and production. Designing elements based on practical requirements is vital while preserving the design objective or end-use.
Before all of the components get finally documented and sent to a molder for production, the injection-molded product design goes through multiple stages of development. It is the most crucial step in the development process since design modifications can no more be done sans considerably increasing project costs or delays.
Hence your focus must be on adopting product design best practices and the below discussed influential design parameters that affect an injection molded part.
Top 7 Crucial Things to Keep in Mind While Designing High-Quality Molded Parts
1. Material consideration
Manufacturers frequently use a recognized polymer grade from a similar application or rely on vendor suggestions. Material selection is a challenging feat that necessitates several variables, including-
- Temperature- Thermal stress can develop under standard and high operating conditions and during assembling, processing, and shipment.
- Chemical resistance- Refers to the effects that emerge when a solid, liquid, or gas interacts with a part.
- Assembly- The material’s interaction in all assembly phases, such as binding, mechanical fasteners, and welding.
- Finish- The material’s capacity to provide the required finish as it emerges from the mold, such as glossy, smooth, and other aesthetic attributes.
- Costing- Resin pricing and cost analysis for manufacture, maintenance, assembly, and teardown to save money on the workforce, machining, finishing, and other expenses.
- Availability- The resin’s supply in terms of the quantity required for manufacturing.
2. Tolerance parameters
One of the most complicated issues confronted while designing a part through injection molding is allowing enough tolerance variability in the design. Numerous factors affect tolerance variation, including materials, process management, and tool design. Tolerance limits in a design vary substantially from one molder to another.
Designers must negotiate feasible critical tolerance parameters with molders and examine possibilities for future mold changes. It may necessitate purposely designing some features with additional clearance, which will subsequently get tightened by removing steel from the mold. Molders could advise various approaches for sustaining tight tolerance control, such as post-machining, gate locations, and fixturing.
3. Gate location
A manufacturer should preferably specify the location of the gate. The type of gate and its placement significantly impact the overall quality and viability of the part. To mention a few, it influences the aesthetics, tolerances, warpage, surface finish, molded-in stresses, wall thickness, and physical attributes.
Gates are essential for maintaining appropriate resin flow into the mold. They are responsible for regulating the resin flow from the runners and distributing it throughout the part.
4. Mold shrinkage
The shrinkage that happens during the molding of parts can be as high as twenty percent by volume. Thermal shrinkage is more common in crystalline and semi-crystalline materials. Amorphous materials shrink less than solid solids. Here are a few simple strategies to prevent molding shrinkage-
- Alter the formulation.
- Alter the mold design to achieve the desired dimension based on the expected shrinkage.
- Process parameters including melt temperature, molding temperature, injection speed, pressure, duration, and cooling time should get optimized.
5. Orientation of draft angle
Draft angles should be included on all surfaces in line with the draw when you commence developing a design and translating it into a functional injection molded part. Most of the time, the draft orientation is evident. However, the draft might be oriented toward the core or cavity in some cases. These selections impact tool design, component fit, parting lines, and cost.
There are situations where the parting line placement could unduly complicate the mold and raise tooling expenses. Addressing these aspects during the development phase ensures that the product is optimized for low cost and maximum performance when it is passed to the molder for manufacturing.
6. Steel safe areas
Design features and elements that cannot be recreated reliably by a molder are designed to be “steel safe” frequently. Steel safe indicates that the design feature is specified with adequate clearance for a toolmaker to entirely machine off steel in the mold after initial test shots get molded to tighten up the clearances. Most molders prefer to take these precautions to prevent welding material further into the mold, which will then be machined.
7. Wall thickness
Developing your molded parts with constant wall thickness will help you avoid various design flaws that can emerge during the production process. When the material melts, it migrates to places of low resistance. If your part has varying thicknesses throughout, the melt may at first stream into the thick sections depending on gate locations.
When this happens, the thin portions may not fill adequately. Furthermore, thicker regions cool more gradually and are prone to voids or sinking flaws. Creating your part with rounded edges will also help with proper part filling during the molding process.
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Working with a competent injection molder and design team is essential for preventing various challenges during the design and development phase. If you consider the above-discussed critical factors during the design phase and work with experts, you can produce and deliver your products and parts on time and under budget.
About the Author:
Peter Jacobs is the Senior Director of Marketing at CNC Masters. He is actively involved in manufacturing processes and regularly contributes his insights to various blogs on CNC machining, 3D printing, rapid tooling, injection molding, metal casting, and manufacturing in general.