Wednesday 7 July 2021

Rule of Thumb Polymer Processing: Effective Injection Moulding Troubleshooting using the 4M Approach

Hello and welcome to a new Rule of Thumb blog post. Today we discuss the 4M approach for effective troubleshooting in polymer injection moulding.

Background of the 4M approach

In general, troubleshooting in injection moulding means to solve problems which are related to the part, mould, machine, material, or process. The 4M approach was coined by Mr. Kerkstra and Mr. Brammer and is a systematic way to solve injection moulding issues. As a troubleshooter you can influence 4 main areas:

1. Moulding process

2. Mould

3. Machine

4. Material

4M approach for systematic troubleshooting in injection moulding

During troubleshooting, potential root causes can be hidden behind each of the 4M’s. Using the 4M approach allows you to systematically work through one category at the time and create a list of potential root causes.

Always ask: ''which of the 4M’s could be the reason for the defect and why?” Getting to the root cause is key. Also, avoid processing around issues when in reality a change in the tool is needed.

Another trap in troubleshooting is trying to solve the wrong problem. For example, one is reducing the injection speed to avoid burns, however the real reason for the burn are blocked vents in the mould. Therefore, one may always ask what has changed in the mould, material, moulding process or machine setting.

Additionally, working to solve a potential root cause at a time and to do so collecting data is key. One can change a thing and then observe the impact. Changing several processing settings at the same time will make it impossible to solve any problem. And if there is no impact when you have done the change, then switching back to the original documented setting is fine.

What are some additional troubleshooting techniques?

There are several additional troubleshooting techniques, such as

-5 Why

-Scrap recording sheets


-Fishbone diagram

-Is/Is Not analysis

-Design of experiments (DOE)

Main takeaways

Asking questions and exploring answers is a main task in troubleshooting. Also it is important to check if the moulding problem is a new one or is already longer there. In case it is a new problem, one needs to dig in and find out what may have changed. Only change one thing at the time. The moulding process takes time to stabilize and to see the effect. Another point to pay attention to is that the medicine should not make you sick, meaning that the problem solved should not create new problems.

Successful troubleshooting combines knowledge, a systematic approach and experience

Additionally, I made a short training video on injection moulding troubleshooting, which you can find here.

Thank you for reading and #findoutaboutplastics


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[1] Kerkstra / Brammer: Injection Molding Advanced Troubleshooting Guide, The 4M Approach

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