Injection moulding is an example of a mature industry where 3D printing with metals offers a great deal of potential to improve production.
Thermo-plastic injection moulding is used for large-scale mass production of a wide range of mass-produced items, from plastic car parts, homewares and furniture, medical parts, electrical tool cases, toothbrushes, toys, caps, pipes and grommets – to name just a few. The processes used for injection moulding have a direct bearing on productivity and the quality of the end product.
Challenges faced by moulders and mould-makers include guarding against warping, the appearance of flow lines, sink marks, the occurrence of vacuum voids, burn marks, jetting and flash and where uneven cooling occurs, thermal stresses in particular sections can reduce tool life. Any of these issues can result in losses through rejects, part-failure and recalls. However, 3D printing with metals could have a revolutionary impact on the industry, through the design and production of conformal cooling inserts.
Why is conformal cooling considered such a game changer? Put simply, conformal cooling makes use of cooling lines that follow the geometry of the part including curves allowing for uniform cooling providing better product outcomes while reducing cooling times.
Attaining uniform cooling rates in all sections of the mould is not always achievable in the current form of mould production. The traditional method of securing cooling channels in close proximity to the mould cavity in injection moulds is through drilling in secondary machining operations. But drilling is linear in nature, and straight lines can present challenges with cooling efficiencies particularly when complex moulds are required.
Toolmakers can build inserts in channels with baffles to create more cooling and in some instances the mould is split into segments, milled and soldered together again. Unfortunately soldering can deteriorate over time shortening the mould life. 3D metal printing offers solutions through specifically designed mould inserts of completely redesigned core moulds. Mould inserts are less costly but a highly effective process.
Conformal cooling is a proven technology, following a study undertaken at RMIT’s Advanced Manufacturing Precinct in Melbourne. After experimentation to identify the optimal material suitable for 3D building, a conformal mould insert was generated using the selective laser melting (SLM) process in the Precinct’s SLM 250HL machine. Later machined to get the desired finish, the insert was tested under research conditions with cooling temperatures recorded throughout the process. The outcome indicated a decrease of 10 degrees Celsius recorded from the baffle-cooled insert, demonstrating cooling advantages.
Recently the VTT Technical Research Centre of Finland ran tests in conjunction with SLM Solutions for ABB Oy Drives and Controls, a company that produces cabling grommets from thermoplastic elastomer (TPE). Using an SLM280 laser system, six different tooling inserts were first designed and optimised in CAD, then 3D-printed. The channel profiles optimised at the design phase, were to take account of factors such as the angles of surfaces facing down – reducing the need for supports, to achieve a minimum wall thickness between channels and to effectively enhance the dimensions and shapes of the channels. The tooling inserts were built in the SLM280 build chamber using metal-powdered steel 1.2709, then heat-treated for the desired hardness of 54HRC, after which the outer shape was conventionally machined.
The six profiles were each tested for cooling effectiveness to determine the ‘best’ design and then placed in the injection mould tool. The results were significant, with reductions in cooling times from 60 seconds to less than 15 seconds. On implementing the ‘best’ design ABB Oy calculated they would achieve an overall reduced cooling time of the (plastic) TPE of some 80%, reducing production time and cost. Additionally the company identified less defective products due to a more equal cooling surface. These advantages amounted to significant benefits to ABB Oy, who produce millions of cabling grommets annually for world-wide distribution.
Cost-saving technology is welcome in any manufacturing capacity, and the use of 3D-printed injection mould inserts is a way of improving an already well developed process. Recognised as a potential industry growth opportunity by the European Union Final Report (2016) on current and future applications of additive manufacturing in Europe, a number of case studies have since been identified in Europe and the USA where successful applications of 3D-printed inserts are reducing costs and production times, and encouraging injection moulders to take on more complex tasks, never before possible. This opportunity is available to Australian injection moulders too.