BreezeBlog

Well, it only seems a few days since the New Milton-based BEC Group started making the tool for our personal cooling product. And already they have moulded the "first offs". There’s lots more work to do, but here’s a summary of how we’ve got to where we are.

We started working with BEC some months ago to produce the final design of our product – we already had resin models and needed to transform these into the product that you’ll see.

The first step was to translate our resin concept model into a workable design which could be moulded from plastic. A lot of thinking has to go into this stage as the plastic housing will accommodate electronics components – which were being designed in parallel. So, there was a lot of to-ing and fro-ing between the plastics and electronics guys and gals.

The end result, after a lot of effort by all the team, was a set of CAD drawings. These not only show the external styling, but also a wealth of internal detailing.

As a consumer you may never take a look inside the products that you buy. Why would you? Well, if you did you’d see a tremendous amount of detail, each bit of which is there for a reason. Ribs to strengthen the product, pegs to locate electronics components, recesses for the control keypad…. All the details are there for a reason. Ours’ are.

Once the CAD is completed the process of cutting the metal tool starts. This is done, in 2 stages. First of all a part is milled to the right shape for the product. This is then used to “spark off” metal from a steel block which will become the final tool. This happens in a machine which places the template and the steel block in a water bath and pulses of current are passed between the two. Steel is “sparked off” little by little over a period of a few days. Thanks to Mike and Neil at BEC for talking me through this and, of course, for the stunning tool that will go to make up our product.

The end result is like a complex jelly mould which is then ready to use for making the first plastic components. These first impressions are quite rough compared to the finished product. Essentially they are used by our team to firm up the design prior to production runs. Last minute changes can be made and details added. Of course, the trick is to remember that with the tool you’re working with the opposite shape to the plastic component that pops out. So, if a plastic component needs to be thicker then the appropriate part of the tool is sparked thinner, enlarging the cavity. Mike and Neil obviously think “in reverse” and hang around while the rest of us catch up.

The catch is that you can’t go back! The trick is to work slowly towards the final version, little by little.

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.