The injection moulding process is a staple of the manufacturing industry. With its ability to create highly detailed, dimensionally accurate and stable components from a variety of materials, it is fast, efficient and flexible. For many, that is enough and they never look beyond the process that they might be running, but there are many different ways in which the process can be improved, and the whole manufacturing process more streamlined.
Design Considerations. Making your process easier usually means making the part easier to mould and extract, and there are a number of ways that you can help your process. When you are designing your part, you have a certain function in mind and it is easy to simply become blinkered to how the part will work rather than pay consideration to how the part is manufactured, but this is where you have many opportunities. Design for manufacture (DFM) is an increasingly important part of the design process and one that can not only save you time in the long run but also money while making a more considered component. DFM is the process of proactively designing products to;
- optimise all the manufacturing functions including fabrication, assembly, test, procurement, shipping, delivery, service to achieve the best from the part or assembly.
- assure the best cost, quality, reliability, regulatory compliance, safety, time-to-market, and customer satisfaction through design.
DFM is a process that encompasses all relevant areas of the business to ensure that the part isn’t simply the work of the designer, but takes on all the attributes that other departments would like to see, too. In this way, the manufacturing and even service teams get to discuss what they want from the design, giving everyone ownership.
Through DFM, areas such as draught angles, radii, and gating positions can be reviewed alongside major areas such as the actual form of the component, ensuring that everything is optimised.
Use CAD Simulations. Many injection moulded parts are sensitive to many of the functions of the process, and this can be exacerbated by the design of the part itself, particularly with regard to ingates and cooling areas. If a moulded component has markedly different sectional sizes, cooling can be a major issue, especially if it is subject to a fast cycle time and may be ejected from the mould while still at an elevated temperature. To prevent this becoming a problem, CAD simulations can be used to identify thermal gradients and simulate the flow characteristics of the hot material, highlighting any problems that may occur before they do and allowing time to modify the mould as necessary.
CAD can also be used to analyse the forces that will act on the part in service and create a full and detailed stress analysis report that perfectly emulates the part and identified potential problems. There are many CAD packages that will carry out this kind of analysis, and it would be foolish not to use one.
Materials Considerations. There are now many thousands of materials that can be used for the injection moulding process, including many common thermoplastics and thermosets, and that means there might always be credible alternatives to a material that you initially have in mind. Depending upon the final application, there could be a range of acceptable substitutes that are lower in cost or have better properties that decrease the cycle time, which is also a cost-saving practice.
But in addition to the raw materials, there are many different additives that can either augment the moulding process or help shorten the cycle time, both of which are advantageous. These can be as simple as pigments to alter the final colour of the part, or something a little more useful to production such as plasticizers – which increase the fluidity of the stock material and allow it to enter even the smallest sections of the mould with ease – and mould release agents that assist with easing the component from the mould, further cutting down on cycle time.
Look at the whole system. While much of the work surrounding the injection moulding process examines the mould itself, there is much that can be done with the feed system too. This can include the periodic cleaning of the system – including system purges with appropriate materials – and not just when you change feedstock material or commence a new production run. Periodic cleaning and maintenance of the feeder system prevent the build-up of material on the surfaces and ensures smooth delivery of the material throughout your production run.
Ideally, you should strip down your whole system following completion of a run and inspect every area for wear and damage. While all the internal components are likely to be manufactured from a suitable steel, they will still be subject to wear over time and will require replacement.
If you treat your moulding system right, you should be able to get years of continuous use out of it and manufacture components that are of a standard expected by your clients. Fail to do these things and it could all go wrong, and quickly too.