Buying a plastic injection moulding machine is not a small investment.
Too much machine for the job at hand is wasteful; too little machine does not get the job done.
Careful matching of the job's needs and the factor of a plastic injection moulding machine is well worth the effort.A good plastic injection moulding machine produces consistent parts from shot to shot, and does so in reruns of the same job.
Choosing a plastic injection moulding machine simply on the basis of shot weight is too simplistic.
The following is the three main factor to choose plastic injection moulding machine.
1. Shot weight:
Shot weight is an important factor of the injection unit of a plastic injection moulding machine.
Expressed in ounces or grams, this is by far the most commonly used single factor to choose a plastic injection moulding machine.
Once the plastic material is selected, it has a weight. A plastic injection moulding machine with sufficient shot weight is then chosed.
Some manufacturers prefer to use injection volume as the starting point to state the shot weight of their machines, instead of using measured shot weight.
2. Choosing a machine which is not too big:
A plastic injection moulding machine of a specified shot weight can be used to mould article including the runners weighing from 35% to 85% of the shot weight.
If a big machine is used to mould small articles, the melt in the barrel could degrade due to unduly long residence time.
Moulding small parts with a big machine is inefficient in energy usage per kg of material processed, also known as specific power consumption.
Having multicavities per mould to increase the articles' weight and to increase the mould size are solutions to using bigger machines.
Alternatively, lowering the barrel temperature would help avoid degradation due to long residence time.
3. Clamping force:
Clamping force is an important factor of the clamping unit of a plastic injection moulding machine.
It is the maximum force the machine is capable of to keep the mould closed against the cavity pressure during injection.
Insufficient clamping force gives rise to flash at the mould joint. Most plastic injection moulding machines today use their clamping force (in tonnes) in their model name,
It is advisable to use a sufficient clamping force below the maximum. The sufficient clamping force is proportional to the projected area of the cavity.
Projected cavity area is the cavity area projected onto the plane at the mould parting surface.

Posted by Nancy

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