While it is now regarded as a fairly cost-effective process, injection moulding is fundamentally a higher cost manufacturing route. However, the advantages that it offers in terms of precision, stability, fast throughput and repeatability make it desirable. If you are considering using it as a production method, but think that it doesn’t quite fit your manufacturing model, perhaps you should look at how it can be modified to reduce costs without skimping on all of the really desirable attributes.
The injection moulding process is actually a lot more flexible than you may think, and there are many elements of it which can be tweaked to reduce both the costs of the moulds and the products that they are used to make. With a little thought and some collaboration with your mould designer and manufacturer, you could soon see injection moulding as a viable process for even fairly low-number runs.
General Issues:
Optimise mould design. The key here is to collaborate with your manufacturer. Create a project plan and include regular reviews with the manufacturer not just on the form of the mould but on any cost-saving elements too. If there are savings to be made, your machinist will know about them. Collaboration ensures that you not only make the best use of your sub-contractors but also reduces the possibility of mistakes being incorporated into the final design.
Embrace CAD/CAM. The data from the CAD file – usually in the universally accepted IGIS form – can be used by your manufacturer to program their CNC machinery. Make sure that they are happy to work like this to help reduce costs and make the design flexible as it can be updated almost in real time, so if you do find cost savings, adding them to the product and updating the model is simple. CAD/CAM is hugely powerful and can help you get your moulding right the first time, but also lets you hone the process and update existing processes, once a fully detailed model is available.
Moulding temperatures. The injection moulding process has to be carried out with the feedstock in a semi-molten state so that it can flow into all the required areas. If you have a simpler design, you could look at reducing the feed temperature, which lowers heating costs and also helps reduce cycle time. This can also apply to the moulding pressures used as a less complex design might require a lower pressure to force the material in, reducing stress and wear on the internal components, and maximising its usable life.
Component-Specific Issues.
Look at component materials. The list of polymeric materials that can be used for injection moulding feedstock is constantly growing, and what you have in mind might not be the most cost-effective. Research materials and see if there is something that is just as effective but cheaper.
Use Fillers. The expensive feedstock can be extended by using all manner of filler materials to take up some of the space in the final product while not adversely affecting the overall physical properties of the final product. Fillers such as glass fibres and talk are frequently added to the feedstock to bulk up the material and reduce the need for so much virgin material. But fillers can have other advantageous uses too; lubricants and mould-release agents can reduce cycle time, plasticisers can increase flow, and specialist additives can make the final product flame retardant or protect against UV radiation.
Examine component design. Most components have added features that increase the aesthetics but also boost the costs too. Examine your component for the most obvious redundant features, such as overly large draft angles, curves and radii where they are not really needed and other aesthetics. Remove these and reduce costs.
Reduce exotic surface finishes. Your components might have areas with different surface textures; those will add cost without necessarily adding functionality, so remove them unless they are really necessary. If you have an area where grip is required, change the design to include a graspable shape – such as flat sides – rather than costly textured surfaces, which have to be formed on the inside of the mould.
Mold-in parts. Usually termed ‘over moulding’, if you have extra components that are going to be fitted post moulding, you could determine whether they could be actually constructed during the moulding process, saving time and money on post-processing. This principle can be applied to either pre-completed polymer parts or metal components, allowing other, possibly more complex parts to be incorporated into your design.
Mould-Specific Issues.
Mould materials. While normally made from high tensile steel, a mould used for lower product runs can be made from lower-grade steels or even selected aluminium alloys. The actual moulding area needs to be able to retain high dimensional stability throughout the moulding operation and needs to be of an appropriately strong material, but the rest of the mould can be less substantial material. Discuss the most appropriate material with your mould manufacturer.
Use inserts. If you are uncomfortable with making the whole mould from lower grade materials, you could inquire about using high-grade steel inserts in a lower-grade body. By having high tolerance mould inserts set in less stringent bodies, the time spent manufacturing them is significantly reduced, which will impact the overall cost. This will also make your mould more flexible as you will be able to fit different inserts in for different component production runs.
