Design & 
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Injection Moulding

CNC milling machines provide an excellent way of manufacturing precise moulds for use in injection moulding. This project uses the equipment provided in the TEP injection moulding kit to inject plastic from a glue gun into a mould made on a CNC machine.

The mould is made from a plastic material called Tufset. This plastic machines well and can withstand the temperatures involved in the process. The billet (uncut material we start with) is 100mm wide, 50mm high and 10mm deep. It has 6mm diameter mounting holes along the centreline 82mm apart to allow it to be quickly mounted on the cnc machine and also to mate up with the TEP injection moulding equipment.

Glue enters the mould as shown in the diagram below, and air escapes through a breather hole. The design must allow glue to flow easily to all areas and allow hot air to escape through the breather. The design should not go too close to the mounting holes, as the cutting tool might foul on the bolts which are holding the workpiece to the milling machine. There should be no narrow passages which would constrict the flow of the glue.

In practice, the width of passage which can be cut is limited by the smallest tool available on the CNC machine, in this case 2mm diameter. You should be aware that the CNC machine cannot cut sharp internal corners - the diameter of the radius in the corner again matches that of the smallest tool. Sharp external corners, however, are possible.

The template file is a DrawFile which can be downloaded by clicking here and then saving the file to disc. Load the file into a drawing program and then add your design, making sure that you keep within the dashed box, and that your design covers both the inlet sprue position and the breather hole.

Copyright D&T Online 1997