Things to Know in Injection Moulding of Plastics
Pitfalls in Injection Moulding
Myth in Injection Moulding
A Guide to Injection Moulding of Plastics
Archives of Articles by Prabodh C. Bolur
Engineering Basics for Injection Moulding Machine
Millineum's MoldFlow User Meet
Answers to YOUR Questions
PITFALLS IN INJECTION MOULDING OF PLASTICS
During my tenor as Regional Manager of WINDSOR in Madras between 1978 ∓mp; 1990, I had come across numerous problems of machines, moulds, materials, processing, support equipment. Each of these affected my customers’ performance and also profitability. I took up their problems seriously and tried to apply my mind to understand the root causes of these problems. I used to discover and learn new things every time I tried to solve the problems. I used to document these learning and later on I tried to fit all jigsaw pieces to form a whole picture. The end result is this book " A Guide to Injection Moulding of Plastics". Truly I should be grateful to my customers who gave me this opportunity to understand the subject. Now I want to distribute this knowledge to all – particularly to the students’ community.
Steps in Injection Moulding
Injection Moulding of plastics involves quite a few steps before actual moulding operation. The first step has to be plastic part design. There after mould design, mould fabrication, selection of correct machine and process setting, post moulding operations, assembly etc.
Quality in Injection Moulding
The root causes of quality problem may or may not lie in the present step. The mistakes of the earlier steps may not be possible to correct at the later steps. Some time it may be possible to correct partly. Such corrections are expensive. The problems originating from the present step can only be solved in the present step.
In mechanical engineering Part design has to be manufacturable. Similarly plastic part has to be mouldable to high degree. If moldability is poor than, you have all types of quality and production problems. Therefore part design has to be modified to make it more than 90% mouldable. General assumption that any geometry of the part is mouldable perfectly is not correct. General understanding- that once the mould is filled with the melt every thing has to be perfect- is not correct.
APPLICATION of BASICS- Physics and Engineering
Similarly trainability of the people depend on their understanding of basics of school physics. Those who can recall meaning or definition of each technical terms -he uses every day- is trainable.
It is necessary to understand HEAT, TEMPERATURE. THERMAL CONDUCTIVITY and HEAT TRANSFER. In fact, with out understanding heat exchange that is taking place in the mould one can not understand the causes for inconsistent- shot to shot variation of - dimension, dimensional distortion or warping. Other important basic technical terms are Viscosity, Shear, Pressure/stress, Speed, Power, Energy. All these terms are learnt in secondary school. Therefore, knowledge of school physics is adequate to understand the processing of plastics.
Let us understand that the learning of any subject. The subject can be broken-down to number of elements / parts. These elements/parts can be grouped in to two groups. This grouping has to be based on the ease of grasping the each parts/elements.
THREE BALANCING TRICKS
I can summarize the successful moulding to three balancing tricks;
Any unbalancing on the above three balances will result in moulded-in stress. This is the biggest culprit for over 50% part failure
PITFALLS- not Obvious
My book " A Guide to Injection Moulding of Plastics" discusses the following not obvious topics;