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Introduction Buying a plastic injection moulding machine (PIMM) 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 attributes of a PIMM is well worth the effort. A good PIMM produces consistent parts from shot to shot, and does so in re-runs of the same job. Choosing a PIMM simply on the basis of shot weight is too simplistic. Neither is clamping force alone sufficient. This article attempts to show the importance of other attributes to consider. The article 'How a plastic injection moulding machine works' is good pre-reading for the present one. The attributes are classified into quantifiable attributes, on-off attributes and non-quantifiable attributes. The first two types could be obtained from the specification and description of the machine, the last type could only be determined by user's measurement, usage or words of mouth.
2. The quantifiable attributes The quantifiable attributes are usually found in the specification of a PIMM. They should be considered together instead of individually in considering a selection. The significance of each is explained below. In short, this section steps the readers through how to read a PIMM's sspecification table. Most quantifiable attributes in a specification table are the maximum the machine is capable of. If so, a value at or below the maximum could be used. Table 1 lists the quantifiable attributes and whether they are specified as a maximum in a specification table. Quantifiable attribute | Maximum? | Comments | Shot weight | Yes | | Clamping force | Yes | | EUROMAP size rating | Inapplicable | | International size rating | Inapplicable | | Screw diameter | Inapplicable | Choice available | Screw L/D ratio | Inapplicable | Choice available | Injection pressure | Yes | | Injection stroke | Yes | | Injection volume | Yes | | Injection speed | Yes | | Injection rate | Yes | | Screw rotary speed | Yes | | Screw motor torque | Yes | | Plasticizing capacity | Yes | | Mould opening stroke | Yes | | Maximum mould height | Yes | | Minimum mould height | No, minimum | | Maximum daylight | Yes | | Space between tiebars | Yes | Mould length and width could be smaller | Platen size | Yes | Optional bigger platens available | Platen thickness | Inapplicable | | Tiebar diameter | Inapplicable | | Ejector stroke | Yes | | Ejector force | Yes | | Carriage stroke | Yes | | Carriage force | Yes | | Dry cycle time | No, minimum | | Electric motor rating | Nominal value | More power is used when overloaded | Electric heater power | Yes | Maximum used at power on | Total power | Nominal value | More power is used when motor is overloaded | Number of heating zones | Inapplicable | | Oil tank capacity | Yes | | Hopper capacity | Yes | | System pressure | Yes | | Machine dimension | Inapplicable | | Machine weight | Inapplicable | |
Table 1. Quantifiable attributes |
