March/April 2020

| 26 | March/April 2020 www.smartmachinesandfactories.com | SOLUTIONS | the production stage due to the necessity for steel tooling, which is often intricate in nature. When looking at lower volume runs, traditionally manufactures have looked at CNC machining and/or vacuum casting. As a way of avoiding the need to produce costly and time-consuming tools for injection moulding, when the required run is low enough, these methods can offer an economical option but come with limitations of their own. Machining is a process that is restricted to relatively rigid materials; soft and flexible plastics do not machine well and produce inferior results. Vacuum casting works well with elastomer materials, however the process is not conducive to producing parts with complex geometries or with fine details. Because of these limitations, increasingly, manufacturers are assessing the use of SLS 3D printing for lower volume runs as an alternative to CNC machining and vacuum casting, and the reasons for this are based around the increasing sophistication of SLS 3D printing machines for industrial applications (greater accuracy and repeatability), the increasing palette of polymer materials that can be processed, and once again the ability to manufacture without the need for expensive mould tools. Benchmarking When assessing 3D printing, CNC machining, and vacuum castingas an alternative to injection moulding, generally speaking we are benchmarking processes where the look, feel, and functionality of the end- use parts are comparable on almost every level. Injection moulding, however, allows for the manufacture of intricate parts with tight tolerances, and it is economic to produce parts with ribs, metal inserts, and bosses etc… which would be totally impractical using machining / casting technologies and 3D printing. With injection moulding, the emphasis is on high volume and repeatability, as a well-made mould tool will last for a long time, and will be producing identical products again and again, extremely quickly and in a broad range of possible materials. The process also produces little in respect of waste, and even sprues and runners can be reprocessed and reused. The focus when benchmarking injection moulding against alternatives really only becomes relevant when the volume of the run is lower, and/or when there is a requirement for geometric complexity that it is impossible to achieve through injection into a mould tool. There will come a point when benchmarking alternative plastic manufacturing processes, that the volume required, will mean that the time and cost associated with tool fabrication is uneconomical. An expensive mould tool is cost-effective when it is producing millions of parts, but when runs are measured below around 10,000, the economies of scale change significantly. At this point machining, vacuum casting and SLS 3D printing demand attention. None of these processes require metal tooling, and they can produce plastic parts with shorter lead times while offering favourable economics. However, beyond the fact that machining can only be applied to rigid plastics, it is a subtractive process, N ow an established technology set, with a 30-year plus pedigree in industry, 3D printing is no longer just a solution for rapid prototyping applications. Today, many 3D printing processes, such as selective laser sintering (SLS), co-exist alongside traditional plastic manufacturing processes as a viable alternative, where it can rival them in terms of cost and lead times. For a growing number of applications, 3D printing for batch production offers clear economic and added-value advantages— acting as a spur to innovation and enabling the production of end-use products impossible or uneconomical to produce with the use of alternative methods. The Manufacturing Alternatives Broadly speaking, when manufacturers look to manufacturing in plastic, there are a range of alternatives to consider. Traditional routes to manufacture typically include injection moulding, CNC machining and/or vacuum casting. Manufacturers that do not bring the SLS3D printing process into the frame at this point are potentially doing themselves (and their bottom lines) a great disservice. From the get go, let’s be clear, if you are looking to mass manufacture plastic parts and components, then there really is only one viable option, and that is injection moulding. Injection moulding is precise and extremely repeatable and can process a huge range of plastics, as well as being fast at the actual production stage, and when the volumes are high enough, it is characterised by extremely low cost per part. Injection moulding’s Achilles Heel, however, is its high set up costs and the lengthy lead times to get to Additive manufacturing for production As additive manufacturing (AM) / 3D printing continues to evolve, many of the pre-conceptions concerning its usefulness as a production technology for plastic parts and components need to be revisited. Nick Allen, MD, 3DPRINT UK, reports.