Cutting component costs with Multi-shot Moulding
Andrew Kownacki, Technical Director of Ceetak, takes a look at the latest moulding techniques.
Traditionally, high volume metal and plastic or rubber component assemblies used in products such as pneumatic valves and cylinder, pumps and motors, have been constructed from a combination of materials that are bonded, welded or riveted together.
Although in many applications these construction techniques are effective, they can add considerably to component to component cost and weight. Perhaps as importantly, the process of, for example, bonding plastic or rubber to metal can create a number of problems, both during assembly with the need to purge all air pockets from the adhesives used, and in use where sudden changes in operating temperatures or pressures can result in differential expansion of the various materials.
Now, however, new developments in multi-shot plastic moulding techniques are enabling manufacturers to overcome these technical issues, while improving component performance and quality and reducing both unit price and, in many applications, delivery times.
Multi shot injection moulding techniques optimize the co-polymerisation characteristics of hard and soft plastics, with two or more thermoplastic and TPE (thermoplastic elastomer) rubber compounds being molecularly bonded using conventional injection moulding machines.
Now, through close collaboration between material suppliers such as Ceetak, injection moulding machine supplier and mould tool designers it has been possible to make significant improvements in both mould tolerances and the level of control over process conditions.
As a result it is now possible to produce components by injecting hard plastic material, then rotating the mould tool or using multiple tools or mould cavities to make further or simultaneous injections of elastomeric TPE’S to create single, integrated piece parts. These parts can be made in large volumes, to consistent quality standards and to the exceptionally tight tolerances required in many high value industrial and consumer products.
Perhaps as importantly, components manufactured using the multi-shot moulding process offer levels of mechanical performance and aesthetics that are difficult to achieve using traditional material combinations. Forr example, complex shapes can be easily created without the need for secondary machining operations and multiple colours can be incorporated, while problems such as metal corrosion or fatigue can be eliminated.
Ultimately, it is likely to be the ability to reduce component costs that will prove most attractive to manufacturers. Although it is difficult to generalize, as each application will have a unique specification, a typical example is replacement parts for pneumatic valves, which are often produced from brass and rubber: by re-engineering the part using thermoplastic and TPE rubber compounds it is possible to cut costs by as much as 50%-80% while maintaining identical standards of quality and producing better mechanical properties.