In this article, Olaf Diegel, Noah Mostow and Terry Wohlers discuss the complex, and often multi-faceted, obstacles that stand between AM and its wider adoption, and how those obstacles can be addressed and resolved in order to clear the path to achieving the technology’s potential.
Many companies approach metal AM as a direct replacement for conventional manufacturing, but in most cases, this is not an effective use of AM. It is vital that good approaches to design are applied when preparing to produce parts by metal AM. This not only improves build speed and cost, but it often improves the functionality and performance of a part by making it lighter and stronger, with features such as improved cooling.
The first step to adopting metal AM effectively is understanding its strengths, limitations, and when to use it. Due to the associated speed and cost, it is important to evaluate a part or assembly to determine whether it is a good candidate. If AM does not offer sufficient value to overcome the higher manufacturing costs, it is probably not a viable option.
Design for Additive Manufacturing (DfAM) can significantly impact this decision-making process and can make the difference in building a business case on whether to use AM. One of the primary goals of DfAM is to reduce the time-intensive melting of material. It is the inverse of designing for CNC machining, in which as little as possible is machined to minimise the required time. This results in parts with excessive amounts of material. With AM, more material means longer manufacturing times and higher cost per part. One way to reduce build time is to consolidate two or more parts into one, digitally, prior to manufacturing. This is one of the most important considerations of DfAM and a way to justify the use of AM.
Other ways to reduce material and scan time are topology optimisation and generative design. Both methods involve the use of mathematics to optimise the strength-to-weight ratio of a part, thus using the least amount of material required for the application. Another method of material reduction is to use lattice, mesh, or cellular structures inside the walls of a part. At its most basic, DfAM is about considering whether the material serves a useful engineering function. Post-processing is a major obstacle of metal AM, which requires sacrificial support material. These supports, also referred to as anchors, serve as a heatsink to the build plate. They are used to help secure the part and prevent it from distorting due to stress caused by heat while it is built. Downward facing surfaces will have a rougher surface finish than upwards facing or vertical faces. If not designed correctly, a part may require substantial post-processing to achieve the required engineering tolerances or cosmetic surface finish. An approach that works for some parts is to design a part so the support structures become permanent features, which reduces the time and expense of removing what would otherwise be support material. With experience, it is not difficult to achieve, although determining whether it is an option must be done on a case-by-case basis.
Over the past few years, DfAM has risen in importance, with hands-on courses on the subject being conducted around the world. These courses help to educate and train professionals on how to design for AM. As this field grows, it will become part of mainstream design and engineering education. We will continue to see a more skilled workforce emerge which, in turn, will help increase the acceptance of metal AM.
We have always done it this way Product design decisions, including the design of materials and features, are not always chosen because they are the best option. Many times, these decisions are based on what has been done in the past. Engineers and managers tend to be risk-averse: if something has worked well previously, they will continue using that process and material, even if the design and its performance can be improved with AM. Changes inherently cause hesitation. AM supports the notion of designing products in entirely new ways, such as features that reduce weight or improve the transfer of heat. If a part is designed for AM, it may use substantially less of a more specialised material, such as titanium, compared to a conventional design. This may improve the strength, reduce material and weight, and/or increase performance without increasing its cost.
Olaf Diegel, Noah Mostow and Terry Wohlers, Wohlers Associates Inc, Fort Collins, Colorado 80525 (USA) www.wohlersassociates.com