Mandy Gebhardt, team leader for marketing/PR, and Maximilian Genz, sales and product manager for DMP systems, 3D-Micromac
Laser sintering—also known as selective laser sintering (SLS) and selective laser melting (SLM)—is an additive manufacturing (AM), or 3D printing, technology. Laser microsintering (LMS) combines the advantages of AM and micromachining. It is an industrial technology, used to produce metal microparts for several industries, including aerospace, medical device, semiconductor, jewellery and watchmaking.
LMS allows for the realisation of complex metal microparts that exhibit exceptional accuracy, detail resolution and surface finish. These advantages mean that moveable parts and assemblies can be manufactured in a single step. Furthermore, LMS offers high flexibility in the manufacturing process, low operating costs and user-friendliness.
3D Microprint and its founders, EOS and 3D-Micromac, have developed a LMS technology and continually look to its improvement.
Functional principle of laser microsintering
A 3D CAD model of the target geometry contains all details of the final laser microsintered part. This model is split into several cross-sections that, together, are made up of hundreds or thousands of layers. At the start of the LMS process, a thin layer of metal powder is deposited directly on a metal build platform. A laser beam then selectively fuses this layer according to the geometry of the cross-section. Next, the build platform is lowered so that a second layer of powder can be deposited on top of the first layer, this second layer is fused, the build platform is lowered again and so on. This layer-by-layer process is repeated until the micropart is complete.
The combination of a very small laser spot size and a metal LMS powder affording a particle size of ≤5 μm allows for the realisation of microparts that have super-thin layers and high densities. For non-industrial LMS, the master oscillator power amplifier (MOPA) fibre laser affording an average power of 70 W is used. However, for industrial LMS, the infrared (IR) fibre laser holds the clear advantage in terms of acquisition, maintenance costs and lifetime. The high-precision IR laser beam position is achieved by way of a high-speed galvo scanner. According to the used beam shaping, a laser spot diameter below 30 µm in standard resolution mode or below 20 µm in high resolution mode can be achieved.
LMS is able to process non-reactive and reactive materials such as stainless steel alloys or titanium alloys. Furthermore, specific customer materials can be processed and optimised for LMS.
The functional principle of LMS from CAD.
Laser microsintering for complex microparts possessing finer details
Conventional technologies such as micromilling, microturning and microcasting have their limits, at least in terms of achieving complex shapes, cavities and inner structures. AM technologies such as LMS can offer unique possibilities to create innovative products.
A comparison of conventional and AM technologies often proves a function-driven redesign of products to be advantageous. In particular, LMS ensures higher levels of accuracy, detail resolution and surface finish. Furthermore, it allows for the integration of more functionalities into one micropart and thus enables the manufacture of a complete assembly in one step. This eliminates the need to assemble multiple tiny parts by hand, a delicate task that can only be performed by highly skilled people. It can therefore be said that increased micropart complexity can shorten time to market and reduce manufacturing costs significantly.
Flow probe case study
Accuracy is mandatory in fluid dynamic measurement technology. Flow probes help to ensure that fluid flows simply and accurately. In order to increase the efficiency of flowed-on products such as aircraft engines and compressors, and road vehicles, flow probes are used to measure fluid flow parameters, for example, speed, pressure and angle of attack. Following evaluation of the measurement data, geometries can be optimised or controlled in operation.
The conventional manufacture of flow probes is carried out using various technologies, but these are generally lacking in user-friendliness and geometric flexibility, leading to insufficient robustness, stability and therefore service life. Furthermore, the smaller the dimensions of a flow probe, the more complicated its assembly.
LMS was used to manufacture a complex flow probe that required significantly higher detail resolution on filigree structures and significantly lower roughness than are achievable using conventional and other AM technologies. The design of the flow probe was first of all evaluated to ensure LMS producibility. A great deal of emphasis was placed on the channel geometries inside the flow probe, the probe neck and the support structure. As a result of several iterations of design optimisation, LMS and testing, the removal of powder from the channels and the structural safety of the filigree internal structures were significantly improved.
The laser microsintered probe was separated from the construction platform by wire-cut electrical discharge machining (EDM). Its surfaces were then optimised via post-processing steps to minimise roughness-induced flow changes. The resulting optimised flow properties and functional integration of the probe made it suitable for applications in all fields of microfluidics. Furthermore, as it was manufactured as one solid part, no assembly was necessary and durability and robustness were increased.
Gripper case study
Grippers are used in numerous industries from aerospace to medical technology. If conventionally manufactured, grippers comprise at least four parts, namely the two parts of the forceps, a rotary axis and a securing element.
LMS was used to manufacture a gripper as a single yet movable complex part. The absence of joints between the individual parts increased the robustness and quality of handling of the grippers. The swivel joint was structurally adjusted as required in the LMS process, thus allowing for the manufacture of functional modules and mechanisms made of metal. This functionality was created directly during the building process. No assembly was necessary and the gripper could be used immediately.
Industrial laser microsintering machines
3D-Micromac and 3D Microprint have collaborated closely on the development of a range of industrial LMS machines for the manufacture of complex metal microparts and named it DMP 7x.
DMP 7x machines are designed for flexible series production. They deliver exceptional results in terms of micropart accuracy, detail resolution and surface finish. A very small laser spot size and a metal LMS powder affording a particle size of ≤5 μm allows for the generation of microparts that have super-thin layers of ≤5 μm and high densities of >99 percent.
The machines’ software offers high flexibility and stability for both industry and research users. Automated programs and single parameters can be set for individual microparts.
A recoater system for the powder handling and a purifying inert gas system together ensure an extremely low concentration of water vapour and oxygen, with values below 1 ppm.
A rapid transfer port (RTP) ensures both powder and operator are protected. The RTP is for powder, micropart and filter handling under argon (Ar) atmosphere at all times. Operators do not necessarily need to wear any personal protective equipment (PPE), and filter exchange of high reactive materials such as titanium alloys is becoming safe.
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A laser microsintered surgical gripper with integrated pivot joint.
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A closeup of the pivot joint, which has a clearance of 25 µm.
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The DMP 74 industrial LMS system for additive micromanufacturing of metal microparts.
Conclusion
LMS is a powder-based AM process for microparts possessing microcharacteristics. Using digital CAD data, a DMP 7x machine builds a micropart layer by layer, using a fibre laser to selectively fuse a metal micropowder. Product designers benefit from increased design freedom. Furthermore, the ability to integrate more functionalities into one micropart and thus manufacture a complete assembly in one step allows for sustainable production.
Advantages of LMS over conventional manufacturing technologies include: no tool costs; no material waste; no minimum order volumes; geometries that can be modified at any time during the development and manufacturing phases; and no additional assembly steps. LMS is not restricted to certain industries or applications, rather it is a potential manufacturing process for wherever complex high-quality metal microparts are required.
3D-Micromac