BreezeBlog

Continuing the plastic tooling theme from my earlier post many of you may be unfamiliar with how a mould tool is used to make a consumer product.

Essentially the large steel tool is mounted on the end of an injection moulding machine. The machine consists of a heated screw which is located inside a pipe. Plastic material is introduced into the machine via a hopper. The screw heats the plastic polymer to a molten state. As the screw turns the molten material is injected into the tool, filling the cavities. Once the cavities are filled and the plastic cools, the tool is moved back and the finished plastic component is ejected. The process is then repeated until you have the desired number of components.

The link below leads to an animation of this process.

http://www.bpf.co.uk/downloads/files/InjectionMoulding.swf

The "First Offs" mentioned in my previous post are very rough initial test products from the tool. These show us where to remove more material from the cavities to strengthen the final product.

The "First Offs" also show where the cooling process inside the tool has lead to shrinkage of the resulting plastic product. This can happen where the material has been deliberately thickened to add strength.

One of our focus group members asked us to reinforce some fixing points on one component... "Imagine a soldier putting his Size 11 boot on it, or a pile of our kit being thrown from the back of an aircraft." he said. So, we thickened these places on the product and got some shrinkage in a couple of places. These marks can be avoided by adding a a powder or fibre stiffener to the plastic mix.

Of course, the tool can have a number of processes added to it which change the appearance of the finished product. Parts of it can be polished, leaving a shiny finish on the product.

We can also include other additives to the plastic mix, for example to prevent microbial growth or to prevent colour fading. We'll talk about these another time.