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How to Reduce Costs in Short-Run Injection Molding Projects?
Created on Today
In situations where businesses are designing their new hardware equipment, producing their medical equipment, or making their industrial parts, mass production is generally not where the process begins. Businesses opt for short-runinjection molding. The process entails the production of small batches of plastic items, which generally range anywhere from 100 to 10,000 items, using specially made molds. Short-run injection molding is the process thatlinks prototyping to actual mass production.
However, low-volume manufacturing introduces a distinct financial hurdle: amortization. When you produce 1 million parts, a $50,000 mold adds only $0.05 to the cost of each part. If you only produce 1,000 parts, that same mold adds $50.00 to every single unit. Balancing these upfront tooling investments with ongoing production expenses is the primary challenge of low-volume projects.
Fortunately, you can significantly lower these expenses. By optimizing part designs, selecting appropriate tooling materials, and streamlining factory operations, you can minimize financial waste while maintaining excellent part quality.
Optimize Part Design for Lower Costs
One surefire method for reducing production costs is optimizing your part design at the beginning stages, while it's still virtual. As much as 80% of the cost of making a product is based on its design geometry. A simple alteration in your computer will save you thousands in future tooling costs.
1. Prioritize Design for Manufacturability (DFM)
Before having tools fabricated, work with your manufacturing partner to have an official Design for Manufacturing (DFM) review done on your part. A DFM review is an engineering consultation that allows your manufacturer to look at your digital part file for any possible production mistakes, mold issues, or cost considerations.
2. Maintain Uniform Wall Thickness
Parts made from plastics cool down starting from the exterior. If you have sections that are alternately thick and thin, the thick sections will take more time to cool down, resulting in internal voids or weak spots, as well as surface irregularities, which are called “sink marks.”
To avoid such problems and reduce material waste, try to keep the same wall thickness throughout your design. If any portion needs reinforcement, avoid increasing wall thickness—stick to the same baseline throughout your part.
3. Minimize Undercuts and Add Proper Taper
An undercut is any design feature, such as a side hole, internal thread, or latch, that prevents a molded part from ejecting straight out of the mold cavity.Resolving undercutsrequires the mold tool to use side-action slides or hand-loaded inserts. These mechanical additions significantly increase mold complexity and fabrication costs. Eliminate undercuts wherever possible by shifting holes to the parting line or altering latch orientations.
Moreover, you should ensure that there is a draft included in the design. The draft is a very small slope, normally one to two degrees, applied on the sides of the part that are vertical.
Importance of Drafts: In the absence of any slope, the shrinking plastic holds onto the core of the mold very tightly. As the ejection pins push the part out, friction can cause scratches, stress, or distortion.
4. Utilize Ribs and Gussets for Structural Integrity
In case the wall of your component requires increased stiffness or must handle large structural loads, avoid increasing the overall wall thickness. Large plastic walls lead to higher expenses for raw materials and longer cooling times, resulting in higher costs of manufacturing.
The right strategy here is to include ribs and gussets that are much thinner. By general recommendation, the thickness of ribs that will serve as additional support should make up 40 to 60 percent of the main wall’s thickness.
5. Consolidate Multiple Components
Look at assemblies that consist of several plastic parts and determine if they could be combined into one piece. Though a unified solution may increase the complexity of the mold, it will eliminate the costs related to the hardware used to assemble the components, as well as ultrasonic and solvent welding methods. It will simplify your logistics and reduce the costs incurred.
Choose Affordable Tooling and Materials
High-volume manufacturing requires the use of hardened steel molds that last for decades with millions of cycles. However, it is not necessary to invest in hardened steel for short-run workpieces. By using economical tooling and resins for the project at hand, you can save money right away.
1. Choose Aluminum Tooling Over Steel
In terms of manufacturing batches of 100-10,000 parts, aluminum tooling tends to offer better economy in comparison. Aircraft-grade aluminum like QC-10 is softer than tool steel; hence, it is machinable at a rate of 40% faster by using the CNC machining process.
Furthermore, aluminum transfers heat significantly faster than steel. This high thermal conductivity allows the injection mold to cool down rapidly after each shot of molten plastic, shortening the manufacturing cycle time and reducing per-part processing costs.
2. Utilize 3D Printed Molds for Small Batches
Should your desired volume be very low – under 100 pieces – and should your resin be one that requires low temperatures, ask your manufacturing partner whether it's possible to use 3D printed molds. High-temperature resins used in industrial processes such as stereolithography are strong enough to withstand the heat and pressure of molding, thus eliminating the need for expensive metal machining.
The benefit of opting for this type of molding is that you will receive production-quality parts at a significantly lower price than metal molding would entail.
3. Select Standard, Cost-Effective Resins
Avoid asking for high-performance engineering plastics when your application does not require their usage. Resins such as PEEK, Ultem, or custom fluoropolymers are expensive and require high temperatures during injection molding.
Instead, consider designing your product using common plastic resins that do not necessitate special properties. For instance, Polypropylene (PP), Polyethylene (PE), Polystyrene (PS), and Acrylonitrile Butadiene Styrene (ABS) are easily available and predictably processed.
4. Partner with Dedicated Short-Run Suppliers
High-volume production companies have optimized their manufacturing plants for million-unit production processes, and hence, a high premium is charged for any short run, as changing molds will interrupt their automated system.
In order to control your manufacturing costs, it is advisable to collaborate with molding specialists who have optimized their plants specifically for short-run moldings. Such experts can help you with advice on structural shortcuts, local material sourcing options, and design simplification ideas.
Improve Production Efficiency
Once your part design is locked and your tooling material is chosen, optimizing production efficiency helps control final assembly and operational costs.
1. Reduce Cycle Times Through Optimized Design
In injection molding facilities, machine time is billed by the second. The total time required to complete one full molding cycle—clamping the mold, injecting plastic, cooling the part, and ejecting it—is known as the cycle time.
Cycle Stage | Primary Drivers | Cost-Reduction Action |
Injection & Clamping | Machine size, injection pressure | Minimize part volume, use standard resins |
Cooling Phase | Wall thickness, material type | Maintain thin, uniform walls; use aluminum molds |
Ejection & Reset | Draft angles, part geometry | Ensure 1-2° draft angles; eliminate undercuts |
Because the cooling phase accounts for over 60% of the entire cycle, using uniform walls and aluminum tooling directly lowers production costs by keeping machines running efficiently.
2. Optimize Your Order Sizes
Work with your manufacturer to determine the optimal batch size for production runs. While ordering 200 parts every month might seem safer for cash flow than ordering 1,200 parts once a year, every independent setup requires machine calibration, material purging, and initial testing scrap. Combining separate requests into a single, optimized production run spreads setup fees across a larger volume, lowering your average cost per part.
3. Minimize Post-Molding Secondary Operations
Secondary operations—such as manual flash trimming, gate removal, custom color painting, pad printing, and component assembly—require manual labor that increases unit costs.
Minimize these expenses by designing your part to be functional straight out of the mold:
- Utilize standard mold textures (such as SPI or VDI standards) to hide minor surface blemishes, eliminating the need for post-mold painting.
- Incorporate snap-fit joints or living hinges directly into the plastic geometry to remove the need for manual mechanical fastening during assembly.
4. Maintain Clear, Documented Communication
Miscommunications regarding quality tolerances, surface finishes, or packaging requirements can lead to production delays, expensive component re-runs, and unexpected air-freight fees.
Provide your manufacturing partner with clean, finalized 3D CAD files alongside explicit 2D engineering drawings. Ensure your documentation clearly marks critical dimensions, acceptable tolerance fields, and specific resin grades. Resolving ambiguities before production prevents unexpected administrative fees and ensures your project finishes on budget.
Conclusion
Reducing expenses in a short-run injection molding project requires balancing product design with production reality. By focusing on design for manufacturability, utilizing uniform walls, and incorporating proper draft angles, you minimize factory defects and raw material waste. Selecting aluminum tooling and standard commodity resins lowers upfront capital requirements, while streamlining cycles and avoiding secondary manual labor controls your ongoing operational expenses.
Every successful low-volume production run begins with early engineering alignment. Contact an experienced manufacturing partner today to request a comprehensive DFM review and obtain a detailed project quote for your upcoming project.
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