This subject contains a significant amount of important information so it will be broken into two parts.
Part 1: Can Moldflow Validate the Quality of Your Part?
The short answer is YES. Validating your plastic injection molded part before it enters the field is the purpose for which the Moldflow software was created.
A well trained and seasoned user of the Moldflow software should be able to take a part through the entire injection molding optimization process and validate each of the factors that will ensure the part meets the design criteria. i.e. quality of the part.
For most parts, the criteria is very similar:
- The part must meet design tolerances and must have minimal deflection/warpage.
- Weld lines must form in acceptable places or perhaps weld lines are not allowed on specified surfaces.
- Air traps must be kept to a minimum and/or be vented properly.
- The process must have a large molding window so that any minor variations will not cause the part to fall out of specification.
- The design of the part must meet injection molding standards (correct draft, not have any regions that are die-locked, must have correct thickness ratios, etc.)
- The design of the mold must allow for adequate filling and cooling along with many other criteria such as proper ejection (that will not deform the part) and so-on.
What happens if you believe your part design and process is optimized properly only to find out that it fails in the field? This is a very common situation.
The purpose of the Moldflow software is to mitigate such a situation. I’ll explain.
In order to understand if a part is going to be molded correctly, the analyst must utilize the software to correctly optimize, at a minimum, each one of the following points.
1. Is the part filling at the right speed?
It is critical to fill the part with the proper flow front velocity (screw velocity profile). As the cavity is filling, the flow front of the polymer can cool off or heat up; both of which are critical with regards to how much stress is imparted in the polymer as it fills. Too much stress during the molding of the part can cause excessive post-molding stress relaxation and deflection.
2. Is the feed system designed correctly?
An improper feed system design can control cycle time or cause the pressure requirement to fill the cavity to become too high. Also, if the gate is not properly designed, it can freeze prematurely, not impart enough shear in the polymer to assist in the filling of the cavity or impart too much shear and damage the material or create cosmetic defects.
3. Is the cavity being packed effectively?
There are two primary factors when packing a part, pack pressure and pack time. The pack pressure controls the magnitude of shrinkage the part exhibits upon ejection and the pack time controls the variation of shrinkage in the part. Volumetric shrinkage is an important contributor to part deflection.
An over-packed part can cause flash in the tool and/or cause any action in the tool to stick. It can even cause the part to stick in the tool which can cause costly down-time and potential damage to the tool.
An under-packed part can cause excessive shrinkage, sink marks or even worse, voids.
If the 2nd stage packed is not optimized, it can create an excessive amount of stress in the part. This stress will reveal itself after the molding process (post-molding) as part warpage or even part failure in the field.
4. Is the part dimensionally stable?
A dimensionally stable part means the part will not deform during post-molding due to external stresses such as exposure to temperature cycling or a significant deformation during an assembly process. If the process has been optimized, the part will have minimal molded-in stress and be able to withstand a higher degree of post molding stress and not undergo a permanent deformation.
This brings us to the end of Part 1. In Part 2, we will continue discussing these critical points and also how to take the calculated stress data in Moldflow and export it so further post-molded tests can be conducted in FEA software.
Services
In addition to our Optimization service, we offer a live On Demand Mentoring Service that can coach your Team through all of these points so you have a thorough understanding of the usage of the Moldflow software. The details can be found at: https://bozillacorp.com/services/subscription-for-moldflow-support-services/
For more information, support with your Tool Design, assistance Troubleshooting any of your Plastics Injection Molded projects, or Autodesk Moldflow Training or Mentoring contact the Team at Bozilla Corporation.
Bozilla Corporation’s Plastics Injection Molding Team has over 20 years of experience analytically and on the floor. We specialize in optimization, consulting, engineering, troubleshooting and Autodesk Moldflow software training. Additionally, our plastics engineers have a full understanding of polymers and how they influence an injection molded part. Your success is our success. Our skilled Team is focused upon meeting the goals and timelines of our customers.
www.BozillaCorp.com, 800-942-0742, info@BozillaCorp.com
About Bozilla Corporation: https://youtu.be/HIUfzwf1x90
About the Author:
Chris Czeczuga is a Plastics Engineer, Injection molding expert, Military Veteran and the President of Bozilla Corporation. He has proven success with many Fortune 500 companies throughout the injection molding industry. A graduate from UMass Lowell, he is Expert Certified with Autodesk, has 20+ years of field experience, intimate knowledge of injection molding part, tool and feed system design. Bozilla Corporation’s success is built on providing the highest level of injection molding simulation and consulting advice to businesses who have short lead times, require an efficient, cost-effective molding process, and desire to produce a correct part the first time.