Successful injection moulding depends on the ability of the machine to operate under the correct conditions of pressure，temperature, and speed of operation for the component being moulded and the material being used. It also depends on the ability to control the conditions of operation within close limits for long periods and on the exact repetition of the cycle of operations many thousands， perhaps millions，of times.
These requirements can be considered first in terms of whether the machine is basically suited to the job, and then as to whether it can be controlled to the limits required.
Determination of whether the machine is capable of meeting the demands to be made upon it can be a matter of trial and error，but if some fairly straightforward calculations are made it is often possible to decide on the feasibility of a job without going any further.
Some assumptions need to be made and accepted because a full mathematical analysis of the injection moulding process is extremely complex and is not the kind of exercise which the average practical moulder would wish to undertake. If the assumptions are accepted, it becomes possible to arrive at simple mathematical approximations which will give results close enough for the purpose required. The type of information needed is:
- (a) What injection rate is required for satisfactory mould filling? In other words，how long is the injection time to be?
- (b) Assuming the injection rate in (a)，what will be the pressure requirements?
- (c) With the pressure requirements of (b) and the injection rate of (a)，what amount of hydraulic fluid will be required for actuating the machine， and how big a pump motor will be required to give the rate of flow at the pressure needed ?
Having decided on these matters，the question as to whether the machine can be controlled accurately over the required number of cycles and at the desired rate becomes a matter of machine mechanics.