Selective laser melting (SLM) is a powerful technology that shapes any desired metal part geometry by melting metal powder layer by layer. Using this digital approach, the optimum shape of complex parts can be produced in a single manufacturing step. Such a part not only delivers better performance, it is also more reliable than the complicated assembly it replaces. Furthermore, SLM technology is the right choice for small metal products, of which thousands can be produced simultaneously. In addition to countless industrial applications, the technology can be used for revolutionary orthopedic, maxillofacial and dental implants. The key concept is to produce high-grade parts in any preferred metal alloy using less material and no scrap, reducing unit weight by up to 80%.
Limitations of Metalworking Processes
Metal cutting, milling, EDM and other high-quality and efficient metalworking processes have a respectable track record on the production floor. Typical for these subtractive methods is that each, in their own way, is limited in removing part material despite many tools and accessories.
Design engineers know metalworking processes inside out and take into account their specific limitations up front. They design new parts knowing the limitations of the production method that will be applied. It would be better if they could concentrate on the functionality of the part to be produced. The geometric limitations of successive metalworking processes force designers to make choices that devaluate the functionality of the part or lead to a complicated assembly instead.
|Fig. 2. As design rules are packed in, selective laser melting (SLM) removes all obstacles in favor of extreme part optimization.|
Building Up Parts in Layers
“We reverse the entire process,” said Jonas Van Vaerenbergh, director of the industrial division of LayerWise, a Belgium-based technology firm. “Our core business is selective laser melting (SLM), a technology developed to build up material in layers instead of removing it in different steps. In the meantime, we have optimized the process for a variety of metals and alloys, such as rustproof steel, hardenable steel, titanium, aluminum and Inconel.”
In the machine, a high-precision laser is directed to metal-powder particles in order to selectively build up a 20- to 40-micron horizontal metal layer. The metal-powder particles pinpointed by the laser quickly and fully melt so that the new material properly attaches to the previous layer, without glue or binder liquid (Fig. 1).
The powerful fiber laser with high energy intensity operating in the inert area inside the machine guarantees that metal parts being built up exhibit a dense and homogenous material structure. CAD directly drives the machine without requiring any programming, clamping or tooling. The SLM approach is capable of simultaneously producing metal parts of different shapes in batches of up to 2,500 pieces, which results in favorable unit pricing and short delivery times.
Unlimited Freedom of Shape
In addition to producing small components efficiently and cost-effectively, SLM hardly imposes any limitations in terms of geometry. Van Vaerenbergh explains that the layered approach ensures that the laser gains systematic access to any location while building up parts. In this way, the most complex part shapes can be produced, including recess, ribs, cavities and internal features (Fig. 2).
“Usually, the products leaving our facility cannot be produced any other way, van Vaerenbergh said. “This is a different ball game for manufacturers because design rules are packed in, removing all obstacles in favor of extreme part optimization.”
A specific example is the burner component produced for Diametal. Similar to machine manufacturers for food and pharmaceutical companies, this company is regularly challenged with producing complex circulation pieces such as mixers, inlet and outlet components, dispensers, coupling parts and heat exchangers.
The Diametal burner component contains nine undercuttings and six internal cavities (Fig. 3). LayerWise applied SLM to manufacture this component as one unit in a single production step. This is called function integration, because this SLM-produced component replaces multiple parts manufactured using conventional metalworking processes. Assembling these parts takes time, particularly because they need to be connected hermetically, which reduces reliability.
SLM is a fit for resolving miniaturization, leakage and assembly issues. Shape complexity is not a problem because the production cost is dependent on the weight of the part (Fig. 4).
|Fig. 4. Usually, the products leaving the facility cannot be produced any other way. Shape complexity is not charged because the production cost is dependent on the weight of the part.|
Optimizing Circulation Channels
A perfect example of efficient and flexible design was the production of a component that connects cooling ducts. Firstly, the additive manufacturing process realized 75% weight reduction. Secondly, designers were able to drastically reduce flow resistance by defining channel geometry using free-form surfaces. The part was produced exactly according to the functional CAD design, resulting in an improvement of the circulation properties by 80% (Fig. 5).
According to Van Vaerenbergh, the manufacture of injection mold inserts also yields impressive results. “Thanks to SLM’s freedom of shape, the cooling channels can be positioned in conformity with the mold shape. This is a major improvement compared to conventionally drilled holes. Optimized channel geometry and location ensure a better-controlled cooling process that delivers higher-quality parts that do not warp and contain fewer hot spots. Imagine the economic advantage of reducing the serial production cycle time of molded plastic parts by 15%.”
|Fig. 5. Injection molding quality and speed can be increased by producing injection-mold inserts with optimal cooling channels.|
Production Machines Run Unattended
Production machinery consists of top-quality systems that run around the clock. Quickly producing prototypes is possible, but this activity is usually a leg up to serial production. As CAD files are directly converted into three-dimensional geometry, SLM is a cost-effective metalworking process that allows for unattended production.
After parts are taken out of the production machines, finishing actions start. If desired, conventional metalworking actions (such as drilling, cutting and EDM) can be applied. It is also possible to harden certain component surfaces. As a concluding step, customers can opt for a high-gloss polishing finish.
|Fig. 6. Through patented DentWise technology, geometry and surface-retention-related limitations set by traditionally molded or milled suprastructures no longer apply.|
Medical industries are a key user of SLM technology. Implant-supported suprastructures are one example. On the basis of patient-specific geometry data acquired through medical imaging or three-dimensional scanning, the personalized part structure is software-designed and then printed directly in titanium. As a concluding step, the dental technician finishes off the structure and completes the final prosthesis.
“Through digital SLM technology, geometry and surface-retention-related limitations set by traditionally molded or milled suprastructures no longer apply,” Peter Mercelis, director of the medical division, said. “In addition, the implant connections are completed with highest precision.”
DentWise suprastructures are manufactured using ultrastrong titanium alloy (Ti6Al4V, grade V), which outperforms the commonly used titanium grade II in terms of mechanical properties (Fig. 6).
|Fig. 8. An implant for a major maximillan reconstruction integrated a titanium layer structure that stimulates surface retention and strengthens the implant to withstand surgical manipulation.|
Orthopedic and Maxillofacial Implants
More medical applications exist for SLM technology. During a major maxillofacial reconstruction, sugeons inserted a zygoma manufactured by LayerWise. The complex shape of the implant was digitally derived through medical imaging and produced using SLM technology. This approach offers the ability to restore the facial symmetry of patients nearly perfectly (Fig. 8).
Concerning orthopedic implants, the process of building up metal in layers offers the possibility to design porous bone-replacing structures and integrate them into prosthesis. This allows for an excellent long-term fixation. In addition to personalized implants designed on the basis of medical imaging, the SLM technology is used for manufacturing medical instrumentation. A number of biocompatible metal alloys are offered for this purpose. IH
For more information: Contact Tom De Bruyne, account manager, LayerWise, Kapeldreef 60, 3001 Leuven, Belgium; tel: +32 (0)16 298 420; fax: +32 (0)16 298 319; e-mail: firstname.lastname@example.org; web: www.layerwise.com
|Fig. 7. Personalized orthopedic protheses are generally produced in titanium, equipped with a fine surface geometry that actively encourages surface retention. (courtesy of Mobelife)|
SIDEBAR: Focus on Technology Leadership
LayerWise is the first production center in Belgium that exclusively focuses on this additive production process for metal parts. The company was founded by Jonas Van Vaerenbergh and Peter Mercelis, both of whom were closely involved in the development of selective laser melting (SLM) at the Katholic University of Leuven. LayerWise intensively collaborates with the university and systematically invests 30% of its resources in research and development to push the boundaries of the technology.
“By bringing together technological expertise, production capacity and customer support, we occupy an unique position on a European level,” Van Vaerenbergh said. “Our engineers control SLM to such an extent that they are capable of perfecting the technology and realize the most challenging specifications. Today, we are able to produce with 15-micron geometric accuracy and build up walls as thin as 0.2 millimeters, something that is extremely difficult – if not impossible – using conventional technologies. Also, the implementation of process control tools in and around the melting zone is important to guarantee highest part quality.”
By acquiring full control over the production process, LayerWise achieves a homogeneous microstructure with a relative density of up to 99.98% for an increasing number of metals and alloys. Research shows that the mechanical properties are virtually the same as those of conventional metals. To prove this, LayerWise systematically carries out mechanical tests on the level of density, hardness, elongation and fatigue. The chemical composition of the bulk metal powders are examined in a chemical laboratory in advance.
Growing Along with the Technology
Two years after its inception, LayerWise has grown considerably. Recently, the company appointed a number of European distributors. This is part of the strategy to gradually operate on an international scale. “After propagating the SLM technology and its advantages to different industries, companies realize that they can truly benefit from the technology,” Van Vaerenbergh concluded. “Additive metalworking processes change design and production rules completely. By realizing projects together with customers, we offer companies plenty of opportunity to create more added value and produce more cost effectively.”