5 Mold Design Tips for High Volume, Tight Tolerance Injection Molding

When it comes to molding a quality part, it starts with the mold, and when you’re producing high volume tight tolerance components you want to run as fast as possible, and the tool needs to last.  Building molds for this type of product puts a lot of emphasis in design and below are 5 tips to help you avoid common pitfalls in the tool and production development process.

  1. Cut Critical Dimensions Steel Safe: When working with tight tolerances such as 0.05mm (0.002”) total on a dimension you shouldn’t rely on material shrink rates when cutting steel.  A thorough review of blueprint tolerances, and critical dimensions are important to plan the tool build so you can tune in those dimensions specifically to the process you are running.  When you need a tool to run millions of cycles you want to make sure you are using virgin steel and not welding to get a dimension to print.
  2. Maximize Ejector Pin Size: In injection molding time is money, and it couldn’t be truer for high volume injection molding.  The goal when developing the process is to run as fast as possible and that means ejecting parts as fast as possible as part of cycle optimization.  The issue many molders run into is pin push, where the part is still hot enough that the ejector pins make a depression into the part.  By designing the tool to maximize not only the number of ejector pins but the surface area of those pins, you can eject the parts sooner, decreasing overall cycle time.
  3. Use Parting Line Locks: When building tools to hold tight tolerances matching mold halves together adds another layer of tolerance stack-ups to account for.  To ensure the mold halves line up as closely as possible so you don’t have “mismatch” add parting line locks to the mold, so you don’t rely on leader pins and bushings alone.  Don’t forget to add replacing parting line locks to your predictive maintenance routine.
  4. Build Spare Inserts: Build spare inserts for important part forming details, or fragile mold components to avoid unnecessary downtime.  In High volume injection molding, where tools run every week to keep up with demand, there usually isn’t enough time to replace broken or fatigued inserts.  Building spares will help you avoid making risky quality decisions like blocking a cavity off to try and build a bank of parts to get tool work done.
  5. Double Coat Finished Steel: For Molds that are running abrasive resins, coat the tool steel to help it last longer.  With two coatings of different color (black and gold for example), you can identify wear before it gets to virgin steel, helping the tool last longer and avoid tool related quality issues.

When designing injection molds to run high volume and maintain high quality you need to think of the long term.  By Cutting dimensions steel safe, maximizing ejector pin surface area, utilizing parting line locks, building spare inserts and coating the tool steel, you can run your mold faster and longer than the competition.

Author:  Adam Smith, President of Millennium Plastics.

Millennium Plastics is a high-volume injection molding company that specializes in tight tolerance molding.  Utilizing the latest technologies and engineering expertise, Millennium Plastics provides best-in-class quality.

To learn more about how Millennium Plastics utilizes expert experience in tool design to guarantee product quality for high volume, tight tolerance injection molding visit www.millennium-plastics.com

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