Additive Manufacturing & Injection Molding for Prototyping and Production
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Additive manufacturing and injection molding — a new vision for production lifecycles

There’s currently a great deal of interest in hybrid processes amongst manufacturers: the practice of combining multiple manufacturing techniques to achieve results that would be difficult (or even impossible) otherwise. This is a key part of additive manufacturing’s move from being purely a prototyping tool to a viable production technique. While much has been written on how AM will eventually replace traditional, subtractive methods in production workflows, the current evidence does not support this vision. Recent AM innovations and success stories indicate that it is in fact the development of effective hybrid processes — and robust systems to make use of them — that will establish AM as standard part of production lifecycles.

Consider projects where injection molding is typically utilised (car parts, for example). For years, best practice has been to utilise additive manufacturing techniques during the prototyping stage, then use injection molding for the final production parts. This is a logical system — AM means one-off prototypes can be delivered quickly, and with minimal cost, while injection molding delivers consistency, quality and cost-effectiveness when large-scale production begins. However, this approach is not without its disadvantages.

Metal molds are expensive and time-consuming to produce, with production typically taking around six weeks and tooling costs often becoming a major ongoing expense. This has previously made them impractical for use in the prototyping stage, where parts will often go through a number of iterations, each of which will require its own mold. To counteract this limitation, the use of 3D-printed injection molds for production parts is slowly rising in popularity. This way, molds can be produced in a quick and cost-effective way whenever they are needed, delivering prototypes with the same material qualities as the planned production parts.

The key challenge here is in selecting printable materials that will deliver the mechanical qualities required for injection moulding. Plastic molds react very differently to heat, for example, so it’s important to take this into account during the planning stages of a project in order to avoid warping. Furthermore, plastic tools need to be cooled for longer after use (ideally using air), which must be factored into the overall project timelines. They will also typically produce less parts than a tooled steel mold would, delivering around 50 parts before they become unusable.

Metal molds are therefore the most practical option once large-scale production begins, although AM offers opportunities for new process enhancements and cost-savings here as well. The rise of 3D metal printing techniques (such as DMLS) means that metal molds can be printed as well, to the same exacting standards as tooled versions, without the usual waiting times — an attractive option for low production runs, one-off parts, or projects where it is necessary to test a mold before its is produced in large numbers.

It’s therefore not simply a question of plugging a 3D printer into an established prototyping/production cycle — a whole new workflow will need to be established to achieve optimal results. However, the potential rewards are great, allowing manufacturers to take a faster, more agile approach to both prototyping and production. Prototypes can be produced using the exact same materials that will be used for the production versions, allowing errors to be identified and fine-tuning to take place at a much faster rate. This will rapidly decrease the time needed to move from prototype to production. Once production begins, new molds can be produced on an as-needed basis, helping to reduce storage costs and drive operational efficiency.

The use of 3D printed molds is already being explored across a range of sectors, including medical (for the creation of surgical parts, which are subject to very strict regulations) and automotive (for the creation of tyres and other car parts), although any sector where flexibility in part creation is needed could easily benefit from the approach.

This is just one example of how additive manufacturing can be used to complement traditional methods rather than replace them. When they are brought together as part of a well-managed workflow, their respective disadvantages are mitigated, and their strengths enhanced.