Additive manufacturing at HERMLE

HERMLE is known primarily for developing systems designed to remove material. Whether milling or cutting, less is more: shaping, contouring, profiling. When a workpiece passes through one of HERMLE's machining centres, it always comes out lighter – not to mention machined to the utmost precision. That's because material is removed where it's not needed. So what, you might ask, has HERMLE got to do with additive manufacturing? The answer? A lot, as it happens – and for longer than you might think. That's because with its unique MPA technology, HERMLE has developed an additive manufacturing process that not only lives up to but also builds on the company's mission and promise: milling at its best. But let's start at the beginning.

What is additive manufacturing?

If you search for additive manufacturing on the internet, you'll likely encounter all manner of terms. Indeed, there are seven types of additive manufacturing: binder jetting, material jetting, material extrusion, sheet lamination, vat polymerisation, powder bed fusion and directed energy deposition. However, these all simply describe different methods of creating three-dimensional objects not by sculpting a solid block to the desired shape through a process of material removal but instead by adding layer upon layer on the basis of a CAD representation. You've probably heard the term '3D printing', and that's essentially what additive manufacturing is. Both terms reflect that the technologies share the theme of material addition or joining within a 3D work envelope under automated control, without the need for expensive tooling and increasingly with the support of artificial intelligence. Additive manufacturing can also be combined with techniques such as topology optimization and is subject to ISO/TC 261, which aims to standardise the processes involved. Though it comes with its own challenges (e.g. management of residual stress, measurement of melt pool temperature), additive manufacturing – also known as generative manufacturing – is considered to be highly innovative, while methods involving the removal of material – subtractive manufacturing – are regarded as traditional. HERMLE is both: innovative by tradition. After all, even our CNC machining centres are innovative in quite extraordinary ways. For this reason alone, additive manufacturing is merely a logical continuation of our future-oriented corporate strategy. So if you ever wonder what additive manufacturing is, our answer is clear: 'MPA' – or 'metal powder application'.

3D printing and its advantages  

What are some of the advantages of additive manufacturing? Let's deal with the basic principle first:

• Layer-by-layer addition: Material is added layer by layer using a CAD representation. The material in question is usually plastic but might also be a resin. At HERMLE, we use a metal powder consisting of materials such as hot-working steel, cold-working steel, stainless steel, invar, pure iron, copper, bronze and more. To find out which ones exactly, go here.
• 3D printing: Here, too, the range of solutions is as extensive as the number of 3D-printing-capable materials – FDM, SLA, SLS, LMF and so on. FDM stands for 'fused deposition modelling' – which, incidentally, is the most widely used 3D printing technique – while SLA stands for 'stereolithography'. A number of techniques also involve the use of lasers – SLS ('selective laser sintering'), LFM ('laser metal fusion') and laser fusion. And then there's MPA. With HERMLE's MPA technology, metallic powder particles are deposited through a nozzle layer by layer at supersonic speed onto the substrate and then compacted to build a solid form.
• Design freedom: This technology allows engineers, designers and manufacturers across a wide range of industries to let their imaginations run wild because the object to be created can simply be programmed into the machine. For HERMLE, this offers opportunities for components manufactured using hybrid methods and exhibiting impressive properties such as masses of several hundred kilograms and diameters of more than 500 mm. This opens up a tremendous degree of design freedom, resulting in even more benefits and capabilities such as those outlined below:
• Individualisation: If something can be programmed on a computer equipped with the right software, then there's nothing stopping you from designing it in line with your customer's standards and exact requirements. Incidentally, this is one of the reasons why HERMLE's MPA technology is offered not in the form of a separate machining centre but instead as a service. And it is a service that more and more customers are taking advantage of. Read on to find out why:
• Prototype manufacture: Given all the advantages outlined above, the following reason should come as no surprise: it's now possible to test innovative ideas more quickly than ever before. And what better way to illustrate this than with our sailing boat project, in which a blank with integrated pure copper for the deck and roof surfaces was created in an additive manufacturing process by means of MPA, after which the copper surfaces were then exposed by means of milling. One reason for this – and, more generally, another argument in favour of additive manufacturing:
• Resource efficiency: This is yet another clear benefit because additive manufacturing uses pretty much only the material that is actually required, while subtractive processes generate significant amounts of waste because they involve removing material. Customers reap the benefits of resource efficiency with MPA technology too, although there's one important factor that should be clarified here – and this is where HERMLE once again plays a key role with its very own, long-standing core area of expertise: 'milling at its best'.

Given all the benefits of 3D printing, let's not forget that additive manufacturing alone will never be capable of creating a fully finished product. Some degree of post-processing will always be necessary. Post-processing can involve any number of tasks such as removing support structures, finishing and painting parts and smoothing – or 'milling' – the surfaces. This is done not only because cut edges have to be chamfered and deburred, but also because any excess material applied needs to be removed again. You might wonder why this is necessary at all given that everything is carefully programmed, so it's worth taking a closer look at the manufacturing process itself.

How the process works

The following description of the MPA layering technique might seem a little dramatic, but then that's the only way to do justice to what is in reality a dramatic process. Imagine a nozzle blasting out powder consisting of equiaxed particles at pressures of 10 GPa onto the substrate. The metal powder hits the substrate at supersonic speed and, like a comet, the powder particles embed themselves in the substrate. Instead of leaving a crater, however, it fills the – plastically deformed – impact pit. The equiaxed particles undergo significant deformation at the interfacial areas, while those deposited on the upper curve of the resulting layer undergo less deformation. The temperature generated at the interfaces can be as high as 1,000°C, which fuses the substrate and powder particles. This is known as 'isothermal heating', and the process is repeated with every new layer. The successive deformation of the particles means that the elongated grains distribute themselves around the interfacial areas, which ultimately results in a rough layer that will later need to be smoothed and milled.   

As you can see, the whole process is essentially a combination of additive manufacturing and milling – and not in a single, one-time pass but in multiple, alternating cycles. This can be demonstrated particularly vividly using the example of a marble run with an embedded copper insert. The process involves five separate steps:

1. A channel is milled into the prepared blank.
2. The channel is filled with a water-soluble filling material.
3. A layer comprising hot-working steel is applied and the contours of the copper insert undergo milling.
4. A layer of copper is applied in a generative process onto the pre-milled contour and the copper insert is milled to the right shape.
5. Another layer, this time made of steel, is created in a generative process. Finally, the openings for the copper insert are milled and the remaining filling material is dissolved.

Additive manufacturing applications

So where can additive manufacturing actually be used? The simple answer is: everywhere! Basically, wherever customised prototypes are required and users want the ability to conserve resources. But, of course, we can go into some more detail here.

An overview of applications:

Architecture and construction: 3D printing is already employed here to create models and even entire building elements. The technology is ideal for developing prototypes quickly or planning complex architectural geometries.

Automotive industry: Here, too, additive manufacturing is increasingly being employed in the development of prototypes, although it is already widespread in the production of replacement parts and lightweight components. In both cases, additive manufacturing boosts efficiency and reduces material consumption.

Education and learning: Additive manufacturing was developed in universities and research centres and is now used in educational institutions as well as for teaching purposes in many degree and apprenticeship programmes. School pupils use 3D printing to better understand technological and design concepts in a variety of sectors of science and industry. And, of course, HERMLE too is engaged in strong partnerships with local universities.

Electronics: 3D printing is used in the electronics production industry to manufacture enclosures and special structures for electronic components. This is an especially fertile field for 3D printing (see our marble run demonstration above) – and indeed for HERMLE's MPA technology.

Art and design: Designers have been leading the way for some time, but now artists too are increasingly exploring the possibilities of 3D printing and additive manufacturing to create their artistic works (e.g. sculptures). HERMLE's sailing boat project represents the midway point between design – it was, after all, primarily a prototyping project – and art, with many considering it truly artistic in execution. 

Food industry: Even here, specialists are experimenting with the 3D printing of food to generate mouth-watering shapes and textures. This is happening in both the catering trade and food production industry. Of course, we're mentioning this only for its curiosity value and not because HERMLE sees any opportunities here in the foreseeable future – even if we do have form here with our Swabian dumplings in aluminium (milled only).

Aviation and aerospace: Like in the automotive industry, additive manufacturing is used to develop prototypes, lightweight components and complex structures. The technology helps to not only speed up the development process but also, at the production stage, reduce the weight of aircraft components, which, in turn, can help to cut CO₂ emissions.

Medicine and healthcare: This is an especially exciting field of application because additive manufacturing enables the development and production of customised implants and prosthetic devices. It is also ideal for creating anatomical models and medical machines and equipment. All these tailor-made solutions ultimately help to enhance patient care.

Jewellery making: This represents a whole new area of interest for designers and the jewellery trade. 3D printing can be used to fashion highly intricate, custom jewellery. And who knows? Like in the field of art and design, and given all the reference products that HERMLE has fabricated – from the Eiffel Tower to a rhinoceros – to demonstrate the myriad applications of milling technology, maybe we too might soon be unveiling 3D-printed models that are akin to jewellery.

Defence and arms industries: Yet another field of application for additive manufacturing.

Dental medicine: The potential of additive manufacturing in medicine and healthcare applies every bit as much to the field of dental medicine, where it is increasingly being employed in the production of dentures. The use of additive manufacturing in combination with the tried-and-tested mechanical, bio-compatibility and aesthetic properties of ceramics offers considerable potential in this field.

Of course, this list is far from exhaustive – how could it be? While additive manufacturing is subject to certain dimensional limits, many things that were unthinkable even just a few years ago are now suddenly within the realms of possibility. And R&D work in this field is progressing all the time. We can say this with certainty because we have achieved tremendous advances in the more than ten years since we started experimenting with MPA technology – and we continue to make great strides to this day. So as you can see, the potential applications of additive manufacturing are increasing all the time. This technology is now an unstoppable force because it is capable of manufacturing ever more products and processing ever more materials. Whether metals and alloys, plastics and polymers – the list is (almost) endless. The methods and technologies involved in generative manufacturing are opening up more and more possibilities and opportunities in product development. Current examples of additive manufacturing at HERMLE include near-surface cooling for injection moulds, semi-finished products, integrated copper cores for heat conduction and integrated heating elements.

Additive manufacturing and 'milling at its best' – a perfect partnership

We at HERMLE offer our impressive MPA technology as a service at our Ottobrunn site, focusing exclusively on projects that complement our core area of expertise: milling. These methods, deployed in combination, result in solutions that save resources, reduce weight and simplify planning processes – not to mention open up whole new opportunities and potential. Do you need a metal part or section featuring complex geometries and the desired surface finish that is manufactured with flawless quality? We offer the tools, software and systems needed to make this possible, so that what we programme on the computer in the planning phase is exactly what is created by means of additive manufacturing technology and then undergoes milling in post-processing – and that ultimately meets our customers' expectations. Sounds exciting, doesn't it? Sounds like the future too. Maybe something for you? Then let's talk – and even better, allow us to demonstrate the power of MPA technology. Ideally, on our premises. Make an appointment. Come visit us. We can't wait to see you.