Chair of Product Development & Engineering Design, ETH Zurich
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Expectations are high for the future of 3D printing technology. Mechanical engineering firms are faced with the challenge of assessing this trend for the specific opportunities and risks it may offer their business and how to get on board with this technology.
In the media, there is talk of future scenarios that will revolutionise production as we know it. For businesses, however, additive manufacturing (AM) methods become a reality only with their first production component built using additive manufacturing. Companies that have already gone down this path have the ability to assess the technology and differentiate the hype from reality.
With little notice from the public, rapid-prototyping technologies have been making inroads into development and engineering departments since the 1990s. In most companies, they are now indispensable to making conceptual models, functional models and prototypes. The technologies have contributed significantly to shortening development and testing cycles in the industrial sector. Thanks to the advances made in the field, rapid-prototyping technologies these days offer a broad spectrum of methods and materials, and some of these materials have characteristics comparable to those used in conventional manufacturing methods. With low-cost 3D printers now widely available to consumers, a great deal of hype has been unleashed that is fuelling high expectations. Yet the single biggest change brought on by the technological advances in these methods is their availability. Rapid prototyping is now within everyone's reach – for end-customers as much as for industrial users. In industrial applications, it is the range of uses in particular that has expanded for these technologies. Initially used in working models and prototypes, the technologies are finding their way into production components in end-customer products.
Hype versus reality
Additive manufacturing (AM) is a catch-all term for several dozen distinct processes used in a vast range of applications. In many industries and applications, AM processes are creating entirely new markets (3D printers for home use); in others, their use is radically transforming an entire sector (dental technology). So what are the prospects of AM in mechanical engineering? A key feature defining the products of mechanical engineering firms is the value proposition they offer their customers, in terms of performance, reliability and life cycle. Most components are exposed to mechanical, thermal or chemical stress. A basic requirement is for them to work reliably over a long life cycle. This is why AM processing metallic materials is particularly attractive to mechanical engineering. Among metal-processing AM processes, selective laser melting (SLM) is the most important. In this process, a thin layer of metal powder is melted by a laser beam and, forming a hard metal layer as it goes solid, is covered with layer upon layer of powder, and then melted and solidified until a complete three-dimensional component is built up.
The dominant manufacturing processes in mechanical engineering are machining, casting and forming. This is not going to change. AM processes will not replace conventional mechanical engineering methods. Rather, they are a complementary manufacturing technology that offers a host of new opportunities and that are already firmly established among production methods. Even now, many innovations and competitive solutions with great differentiation potential would not exist if not for AM processes. These will not replace factories, as we know them today, on a massive scale. The potential of AM processes is in specific applications, and it is these applications that need to be identified and exploited.
Potential uses and their costs
Firms are facing the challenge of evaluating their own products in terms of their suitability for manufacturing using additive technology. The advantages, trends and future scenarios of AM technology are well known. However, it is still rare for AM components to be technologically and financially viable for mass production. The challenge comes down mainly to costs, precision in manufacturing, and component design. What does this mean in practice? How can the advantages ascribed to AM generally be applied to firms' own products to create high-value applications for customers and companies? There is no one right answer that applies to all additive processes. That said, it is helpful to look at one specific technology – selective laser melting – for illustration. SLM technology offers a high degree of freedom of design in engineering components. It has many advantages, but there is the important question of its limitations and constraints.
The costs of making SLM parts vary significantly. For reference, the unit costs1 for small volumes of less than 50 cm3 can cost as much as CHF 100/cm3; for large volumes, the marginal costs are currently around CHF 5/m3. Seventy-five per cent of these costs are equipment and material costs2. The reason the production costs for low volumes are exorbitant is that service providers allocate the fixed costs for setting up the equipment and changing powders to individual manufacturing orders. As a result, SLM provider prices may vary by as much as a factor of five in some cases. In the meantime, there are companies that specialise in creating transparency and enabling comparison shopping. The start-up Additively is one such company helping its customers compare offers from service providers.
For functional surfaces, ensuring their manufacturing accuracy and surface quality consistently requires post-machining. The accuracies achieved in manufacturing are within a tenth of a millimetre with a surface finish averaging Ra = 10 µm and a peak-to-valley height of Rz = 60 µm. In other words, surfaces need finishing using milling or abrading processes.
Although AM allows much freedom in designing parts, engineering AM parts requires consideration of a host of details. In particular, their design has a significant impact on costs, build quality and post-processing. However, this requires specific AM expertise that few engineers currently have.
Yet in terms of the importance of expertise, AM is no different from any other specialised manufacturing technology. A case in point is multi-component injection moulding. This established technology relies on a high level of engineering know-how found primarily among specialised manufacturing service providers and tool and dye-makers. The main role of in-house engineers is to evaluate when using a given production method makes sense and what designs are suitable. The detailed engineering work is then handled by specialised manufacturing service providers.
Precisely because of the high production costs involved, applications must be found that add significant value – the value added needs to justify the cost associated with the method. The leverage lies in making targeted use of structures and geometries that cannot be created by any other production method. This means that component structures need to be entirely reconceived in terms of their function in the system. Once developers begin to free themselves of the design constraints of conventional manufacturing methods, they can design components that truly exploit the many advantages of generative production methods. Invariably, the key question will be about the ideal geometry. At an abstract level, the potential benefits of AM can be clustered into four areas.
Functional integration: Design steps to integrate functions will significantly reduce the number of components per function group. Integration adds to component complexity but, having no impact on manufacturing costs, it will help bring total costs down. In addition to allowing multiple components to be collapsed into one, AM enables design engineers to add new functions, for example through integrated cooling channels. This again delivers cost savings by reducing the number of assembly and quality control steps required.
Lightweight designs: For lightweight designs, component structures are modified to perform optimally under the relevant stress scenarios yet weigh less. The great freedom of design afforded by AM permits directly producing the lightweight structures that were calculated using structural optimisation methods. This is where the production cost paradigm changes: most lightweight structures are associated with increasing geometric complexity of components. Whereas in conventional designs, production costs rise as components grow more complex, the opposite is true of AM components, whose main cost driver is their volume. The rule for AM components is: the more lightweight, the cheaper.
Customisation: The basic principle of multi-variant series production is to find a compromise between achieving high levels of productivity and adequately meeting individual customer needs. By eliminating the need for costly tooling, AM technology provides the flexibility necessary to tailor existing designs to individual customer requirements (by using different or additional components, for example), and to do so with efficiency and speed.
Improved performance: Performance gains can be achieved for flow-through components in particular, such as hydraulic manifolds. AM permits making even complex channels designed for optimal flow. By designing integrated cooling fins or cooling channels, dissipation of thermal energy can be improved, thereby boosting the performance of products such as extruder dyes.
AM creates new possibilities in that it permits structures that cannot be made by any other method. A case in point is the optics unit of a laser-cutter head.
Figure 1: Laser cutter head
Source: pdz ETH Zurich
On the inside, the component was designed and built for optimised flow conditions and structured for a discharge flow to prevent deposits of smoke gas particles. This geometry allowed significantly extending the laser cutter's service life between cleaning cycles. The ideal design of the flow geometry as calculated in the flow simulation was directly applied in the actual production unit, thus improving the unit's performance.
AM – an ongoing learning process for companies
Introducing AM to a company is a gradual process; it is not implemented overnight. This is demonstrated by leading AM users such as Airbus. In 2008, Airbus launched a first pilot study of an AM substitution component. In 2014, the company succeeded in having this component approved for in-flight testing. The component is the technology demonstrator that helps build the necessary expertise and confidence in the technology. Through such a pilot project, the technology can be established in the company. From project launch to completion, it is a one to two year process. By the end of such a pilot project, the first production AM component built should be available to the company as a technology demonstrator. The crucial point is that the pilot project should be a success. The best way to boost confidence in the technology is having a compelling in-house point of reference. The main initial hurdle in an AM pilot project is to identify the component or functional assembly suited to the technology. To be able to identify one unassisted, employees need to have formidable creative potential.
An interdepartmental, internal idea competition will be a good start, to raise awareness among employees and provide an efficient platform for them to generate initial ideas based on the company's own products. These ideas can then undergo systemic analysis and be evaluated for their technological feasibility, cost-benefit potential and cost to implement. The process allows giving each idea contributor specific feedback in AM terms. This approach to AM is a great tool for disseminating more detailed information on the technology and creating know-how within the company. Idea competitions of this kind tend to generate well over 40 different ideas. A short list of these can be narrowed down further to identify the most promising and viable two or three project ideas. They should be implemented in a project of six to twelve months' duration. The main point of such projects is to build AM experience based on actual in-house problems.
More opportunities than risks, and good timing
The technology is also prompting a host of concerns, especially in the context of product piracy and copying. This certainly is a risk to basic components without any special requirements regarding tolerances and strengths, but the same can be said of conventional parts. It is a fact, however, that AM components require a great deal of expertise in processing and post-processing. For example, producing a turbine blade such that it meets defined requirements takes immense engineering and processing skills, which in the longer term will be more of a strength than a weakness for companies that have mastered these technologies.
Now is the right time to embrace AM technology. In fact, the number of successful AM production parts is growing fast even as the associated costs remain high. The technical versatility and the efficiency of SLM processes are well known and proven. In other words, they will see continuous improvements in the years to come. At the same time, the costs of AM components are falling. There are more and more AM service providers, the systems technology is advancing and the range of materials available is growing. The two trends ensure that AM will become viable for a growing number of applications. Businesses now have a chance to experiment with the technology and develop solutions that will allow them to begin using AM when the time is right. The number of patents based on specific AM solutions is soaring and the greatest risk to late adopters of AM is that innovative solutions enabled by AM will be owned by the competition for the next 20 years.
The engineering and applications expertise will continue growing. The processes are becoming more stable, engineering standards are becoming more entrenched and support tools for computer aided design (CAD) and simulations are coming onto the market. We can look forward to exciting developments, and new AM-powered products and innovations are coming onto the market every day. Businesses that are first to successfully act on good ideas will be among the winners here.
1. Roland Berger Strategy Consultants: Additive Manufacturing. A game changer for the manufacturing industry? Munich, November 2013.
2. C. Lindemann et al: Analysing product lifecycle costs for a better understanding of cost drivers in additive manufacturing, in: proceedings of "International Solid Freeform Fabrication Symposium 2012", Austin Texas.
See also the event "Expert Forum on 3-D printing", which took place at the Centre for Global Dialogue in September 2015.
See also the summary of the event.
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