Things to Know in Injection Moulding
Pitfalls in Injection Moulding
Mould Cooling Channels and
Cooling System in Factory
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
Q:Have you come across IDEAL moulding shop with IDEAL machine and and IDEAL mould?
Machine has to reproduce the set parameters non stop round the clock with out break-down. Parameters are set by the person in charge of the operations. The globally welknown makes are Battenfeld, Cincinnati, Engel, Husky, Krauss Mafei, Nisai, Sumitomo etc
Thereafter, it is the Mould which is truely responsible for quality and productivity. If you have best machine but poor mould you can not get quality and productivity.
Mould maker should first ensure, that part design has mouldability of high degree, say, greater than 90%. If ,say, mouldability of 50%, then it will require frequent -at regular interval- adjustment of pressure temperature etc. This is what is happening most of the moulding shop. It means that the process is not stabilised. Hence parameters required to produce aceptable quality fluctuate with time, eventhough the set parameter on the machine remains constant with in the limits of the machine.
Fluctuations are beceause, the process is unstable - varies with time. For example, no one measures mould temperature. If it remains with in two acceptable values, then it is ok. But if it keeps on increasing, then there is a problem. Other fluctuations can be viscosity of melt , which depends on melt temperature, polymer, screw design, and residence time. These parameters -including mould temperature -are not set directly on the machine they are not even measured. They are the net result of actual settings on the machine.
Melt in the plasticating unit is in the form of cylindrical shape before injection is actuated. When injected in to the clamped mould, it spreads inside the mould. The machine has no control on the movement of melt front in all direction from the sprue or gate. Ideally melt front should move uniformly towards all direction at uniform velocity. Melt front movement depends on part geometry. Melt splits in different directions depending on the resistance to flow in the mould and obstruction like hole or slot. Ideally resistance should be uniform. Resistance to flow is due to L/T ratio of the part in respective direction and mould surface temperature. Ideally, wall thickness should be uniform and ribs should be 60 to 70% that of wall thickness. Wall thickness over 3mm is not desired. Mould temperature should also be uniform all over the surface.
I have discovered that if part design is such that
(1) -resistance to flow is uniform in all direction, ( Flow balance- melt reaches boundary in all direction more or less at the same time- flow analysis through Moldflow analysis.Techinics are available to ensure flow balance)
(2)-mould temperature is uniform, ( Heat balance- heat in = heat out during cycle time, cooling channel design, placement, flow rate are crucial. It is better understood through Moldflow analysis)
(3)-melt freezes uniformly in all direction, (Uniform freezing - constant melt front velocity in all directions- It is better realised through Moldflow analysis)
then, most of the quality and productivity problems are sorted out.
When this fact (knowledge) is realised, one will be able to establish ideal moulding shop.
Study of Moldflow software will compel you to understand these facts.
What is the need of approved vendors from Europe to set up moulding shop in India for automobile sector.?
If you have poor part design and poor mould design, and you have used well known MICRON machines to fabricate the mould, even then, that mould is not likely give best reselt, even in HUSKY machine. That is why HUSKY offers to make mould for their customers.
In ideal situaltion, if the moulds are best, the machines do not break down, raw materials are produced with close tolerance, then, there is no role for technical shift supervisors. Shift in charge would be statician and not technical person. The company will need the over all chief, who is able understand and coordinate the activities of Mould (most technical person) chief, Production Chief (who understands indepth processing and all the qualty problems and the root causes) and Maintenance chief (who understands every engineering things in the machine).
Ideal situaltion may not exist in India today, that is the reason why we should try to know what is ideal in moulding shop. So that one day we can have ideal situation in our factories in India. Ideally, all Techinical persons should be able to visalise what is happening in side, plasticating unit, inside the mould, inside the melt, inside the machines etc.
I hope I have tried to explain IDEAL MOULDING SHOP. These are purly my own ideas based on my experience. You may not necessarily agree with my views.
I was involved in setting up of Moulding shop at AMARARAJA Batteries Ltd.in 1997-98.
Technical Papers by Prabodh C. BolurUnderstanding Energy Consumption in Injection Moulding Machine(1994)
Understanding Heat Exchange in Injection Moulds (1994)
Ideal Moulding Shop (2001)
Understanding Selection of Injection Moulding MachineThis paper was part of authors lectures at CIPET since 1980. It has been regularly updated.
Technological Solution to Injection Moulding of Plastics (1999)
Technological Tools for Part Design, Mould Design and Mould Fabrication (1999)
Extrusion of Thermoplastics(1998)
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