Meat & Potatoes of Plastic Injection Moulding, Explanation & Guides Troubleshooting

Meat & Potatoes of Plastic Injection Moulding

Explanation & Guides Troubleshooting

Danny Kerridge

Copyright © 2015 Danny Kerridge

All rights reserved.

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Whenever we need the Instructions or 'How-To' on any subject, we get a step by step set of Instructions.

Now Here's the thing!

Do you ever wonder why a particular step is included? It may be a logical thing to do to complete an assembly or complete an assignment, but why do we need to take that step, and in that order?

Well...these series of books are aimed at the WHY we do things in the Plastic Injection Moulding arena, and I hope I have covered the information adequately.

If not, please drop me a line at www.injectionmouldingtips.com or even if you want to leave a comment on what you found in this or any other book published through Dankerr Enterprises

INTRODUCTION

This book is more than just a Troubleshooting Card, within the boundaries of the book lies insights into Troubleshooting, the causes, the whys, how material flows through a mould and what you can do to influence it.

This book also includes the Troubleshooters Ultimate guide to Troubleshooting faulty mouldings.

Although the book includes in-depth explanations on moulding faults and how to counteract them, it is not designed to explain a complete Die Trialling experience. This book is taking for granted that the moulding or process in question has been previously set up and run successfully. It WILL give a never before explained insight into what is happening within the process and what you can do to get back on track.

Now...This is a MUST to understand.

There are times at work when time constraints, pressure from above etc are going to take its toll on how you conduct yourself. It is Important to understand that when taking a shortcut to ease these burdens or pressures, take care NOT to keep repeating and continually taking these shortcuts because they WILL turn into habits and (in turn) reduce you to a fiddler, slap dash Die setter or troubleshooter.

Do not concern yourself about the speed of the troubleshooting. Like everything else, the more you 'format' your approach, the smoother (& thereby the speed) of the troubleshooting and getting to the root cause of the fault will become evident.

Frequently peruse these books to rekindle the correct way to conduct yourself thereby showing your boss what you are all about.

DO NOT JUST FIX THE FAULT, FIX THE ROOT CAUSE OF THE FAULT.

Table of Contents

Introduction

Brief Overview of A Moulding Fault

Causes of Moulding Faults

Process Change Considerations

Make up of Plastics (Polymers)

Troubleshooting Process

Part Quality

Understanding how Material Flows through the Mould

Quick Fixes

Fault Description

The Ultimate Secret to Troubleshooting

Points for Consideration

About the Author

BRIEF OVERVIEW OF A MOULDING FAULT

Before we get into the Nitty Gritty of Troubleshooting it is important to understand what we are trying to achieve, to that end please review the chapters from start to finish, only after this will you get a wholistic account of what Troubleshooting is all about, and from that point on, review relevant pages as required. Moulding faults are deemed faulty if they do not match the same quality as the master sample, which is laid down and accepted by the customer. Any faults can be found under the following situations PRE-MOULDING, MOULDING and POST-MOULDING.

PRE-MOULDING faults start with the material, is it pre-dried or is it contaminated, next we have the hopper, has it been cleaned properly prior to placing the next material in, the masterbatch feeder, has this been cleaned properly, next comes the barrel, was the previous material purged out and neutralised properly before elevating or dropping the temperatures to meet the new material. Noting that if the temperatures are elevated and the old material is still there, then the degradation and carbonising of this material is pending. All contamination comes from cutting corners, which is why procedures are laid down and insisted upon. For example: prior to starting a die change, the die setter must neutralise the barrel with a material such as polypropylene, change the nozzle or tip if necessary (to suit the next tool in) then drop or elevate the barrel temperatures to suit the next material. This procedure ensures that by the time the die change is complete, the barrel is ready for loading and running the next job.

MOULDING faults are generated through the moulding cycle, operator leaving the gate open, hot water unit cutting out unexpectedly, accumulator losing its charge, heater element burnt out etc, anything within the machine process operations.

POST-MOULDING faults are generated through part handling and finishing, such as placing the part in a jig incorrectly, screen printing errors, painting issues. If there are issues with warping etc after annealing a product, this is generally initiated in the Moulding cycle. With the Moulding faults, the best solution is to ensure that all quality monitoring pages on the machine are adjusted to suit the current moulding with the minimum tolerances set and adhered to. This ensures that the machine is going to pick up any deviations from the norm, before they become a nightmare in sorting good and bad parts.

CAUSES OF MOULDING FAULTS

Considering that the process has been setup correctly and that the job has been running successfully for a period of time, then the cause of the fault will typically not be that a machine variable needs adjusting, ie: injection speed, the fault will lie in the equilibrium of the mould, machine or polymer. For example, the material batch has changed and the MFI of the material is different. A hot water unit has cut out etc. Try looking at this type of focus before automatically grabbing for the controls and adjusting them.

FIX THE PROBLEM THAT CAUSED THE FAULT, DO NOT JUST CORRECT THE FAULT

For the analysis of moulding faults within the moulding cycle, consideration should be given to the following: Fill Time, Pack time, Cooling time, Ejection time and mould open time

Issues can occur in the following areas of operation, The injection Moulding Machine, the Mould and the Material. With