Selective laser melting (SLM)

Introduction to term - Selective laser melting (SLM)

Selective laser melting is a generative or additive, toolless manufacturing process for metallic materials. The SLM process is referred to in English as additive manufacturing (AM for short). The term 3D metal printing has become established as an overriding term.

Overview of the laser melting process

In selective laser melting, the metal to be processed is applied in powder form in a thin layer by a coater on a build plate. A high-energy fiber laser locally melts the fine metal in powder form. This then cools. The contour of the component is produced by redirecting the laser beam using a mirror deflecting unit (scanner). The component is built up layer by layer (layer thicknesses of 15 – 500 μm) by lowering the bottom of the build chamber, applying more powder and then melting again. This cycle is repeated until a 3D geometry is created. Reworking: The finished component is cleaned of any excess powder, the necessary support structures are removed and the component is reworked if necessary (surface finish, heat treatment etc.). It can be used immediately.


The materials used include:

  • Stainless steel
  • Tool steel
  • Aluminum alloys (Al)
  • Titanium and titanium alloys (Ti)
  • Cobalt-chromium alloys (CoCr)
  • Bronze alloys
  • Precious metal alloys
  • Nickel-base alloys

Assembly speeds and batch sizes:

The laser power factor (e.g. 1,000 W laser sources or multilaser technology) defines the assembly speed (cm3/h) of the 3D-printed components and therefore the economic efficiency of additive manufacturing. Selective laser melting (SLM) enables the highest variable fabrication of prototypes and unique products from a batch size of 1 through to industrial series production.

Exposure strategies:

A component can be divided up into various segments with different requirements. For example, the outer area of a 3D-printed component often requires higher strength and lower porosity than the inside of the component. In accordance with these requirements, the individual segments are processed using different exposure strategies. (Shell-core principle) Overhanging component surfaces, known as downsides, are regarded as a separate area. They need to be specially exposed due to their required support structure. The same thing applies to outer surfaces of components that face upward. The “upsides” can be provided with a dedicated exposure strategy in order to considerably minimize the roughness on the final component. A wide range of different factors such as density and surface quality can be configured in a targeted way with a stochastic exposure. This involves individual segments of each layer being successively processed by the laser. The patented process ensures a significant reduction in stresses within the component, which allows solid and large-volume components to be generated with low warping. It is often not possible to divide the component up into smaller segments in the case of thin-walled component structures. Continuous exposure is therefore suitable for this, with low jump times.

Component properties from selective laser melting (SLM):

Components which are produced by selective laser melting are noted for high component densities (> 99.5%). A 3D-printed component can also be fabricated specifically, in accordance with bionic principles, or with differently designed densities in order to ensure partial strength. In this process, certain areas of a component can be designed with low densities (e.g. honeycomb structures) in order to be more elastic or lighter. Other areas can be provided with high densities, for example in order to absorb lines of force in a targeted way. The risk of cavities no longer exists compared to a cast solution. 3D-printed components are generally noted for maximum precision, high density and good mechanical properties.

Topology optimization, bionics and lightweight construction – thanks to selective laser melting:

Topology optimization describes a computer-aided method for redesigning the component geometry. In the additive manufacturing process, this means that material is only applied at places at which forces act. The structuring of a component along its force lines generates a new lightweight design and thus saves resources. Topology-optimized components are therefore on average up to 20 – 30% lighter. The freedom of geometry that is provided in the additive manufacturing process enables bionic principles to be incorporated into the lightweight design. The basis is provided by solutions from nature which cannot be fabricated using conventional manufacturing methods due to their organic shapes. The mixed or hybrid design allows complex geometries to be manufactured additively and simple sections to be manufactured by means of machining.

Functional integration:

In order to boost performance, different functions such as kinematics, sensor technology or temperature control (e.g. cooling ribs or cooling channels) can be integrated in 3D-printed components.

General cost and time benefits from selective laser melting:

Compared to conventional processes (casting or milling technologies), selective laser melting (SLM) is noted for the fact that no tools or molds are used (mold-free manufacturing). This lowers the life cycle costs, development and product launch times (time to market) and improves the cost structure. Thanks to the one-shot option, it is even possible to manufacture flexible components directly from one piece, which considerably reduces the outlay on assembly. The outstanding benefits include parallel production of individual products in one build envelope and unmanned manufacturing (24/7). All of these effects combine to produce great flexibility, a lower production risk and high potential to add value in production.

Sustainability and green technology:

High energy efficiency, a digital process chain and preservation of resources are all vital contributions to helping to reduce CO₂ emissions and to sustainability. The material consumption results from the weight of the component and support structure. In addition to the general lightweight potential of a 3D structure, the material saving effects compared to a milled solution are extremely high (they range depending on the component from: 30 – 80%).

Applications and sectors

Selective laser melting can be used in different sectors:

  • Aerospace, with bionic, generative lightweight components being used instead of milled parts
  • Automotive engineering, from gearbox housings and car seats through to technical components in general
  • Dental technology for dental prostheses, implants, bridges and crowns in which dental laboratories act as service providers
  • Medical technology, i.e. medical devices, endoscopy, implants or orthopedics; examples include titanium plates used to treat injuries to the skull, hip or spinal implants
  • Mechanical engineering components and technical components
  • Turbine construction in power generation
  • Machine tool construction and mold making, e.g. inserts for conformal temperature control
  • Lifestyle products such as jewelry, fashion or watches
  • Prototyping and rapid prototyping.

Outlook: Paradigm shift and industrial series production by means of selective laser melting (SLM)

Selective laser melting opens up new product solutions and business models. 3D components can be more powerful, more quickly available, lighter and/or cheaper. In view of the assembly speeds and build envelope sizes that are already possible today, additive manufacturing has long since moved on from the prototyping phase. The megatrend of “Industry 4.0” or the 4th industrial revolution now awaits as a major challenge. In the aerospace sector, this paradigm shift has already become established in some places, which means that AM has become much more significant as a standard strategy. But to achieve this the previous machine solutions must on the one hand become even better, more efficient and more economical and on the other hand satisfy the basic concept of Industry 4.0. Digitization, automation and networking of the machines right through to the creation of a smart factory are regarded as the biggest challenges in this context.