Testing Technology Quality Assurance of AM components
A great advantage of 3D printing is that the materials often have a higher homogeneity. However, the more important it is to ensure the quality of the manufactured parts through appropriate material testing.
Additive manufacturing is becoming increasingly important in the metal sector. This production method can be used cost-efficiently, especially for small quantities, since, unlike castings, for example, no tooling costs are incurred. Complex work steps such as grinding or milling are completely eliminated. This is of great interest, for example, when building prototypes, also known as "rapid prototyping". The creation of a prototype often takes only a few hours. This can be a decisive competitive advantage when project lead times are becoming ever tighter. Another advantage of 3D printing is that the materials often have a higher homogeneity. This makes it all the more important, however, to ensure the quality of the manufactured parts through appropriate material testing.
Micro Laser Sintering - Special Form of Additive Manufacturing
The company 3D Micro Print GmbH manufactures small metal components and carries out tests to examine the mechanical parameters such as tensile strength, mating limit and elongation at break. 3D Micro Print GmbH has specialized in the production of micro components and uses the process of so-called Micro Laser Sintering. In principle, this manufacturing process is interesting for all industries, but especially for medical technology, aerospace, the semiconductor industry, sensor technology, filtration and flow technology. In contrast to traditional casting, for example, this is a relatively new production technology that has been used in the industrial environment for 10 years. The aim is to establish this technology alongside existing casting technologies in the series and mass market.
The model, designed in 3D on the computer, is produced using the powder bed method. In this process, the powder material of a workpiece is applied and consolidated layer by layer. In micro laser sintering, the material is melted in a structured manner by laser and thus bonded together layer by layer. This procedure requires no additional tools and is carried out by means of digital data exchange.
The main feature of micro laser sintering is to create wall thicknesses of less than 100 µm with a material density of more than 99% while maintaining dimensional accuracy and full material properties. These market requirements can be met and in some cases even surpassed by an in-house powder specification and the corresponding Micro Laser Sinter technology. Due to these high resolutions of the component geometries and -properties, the same or in some cases higher quality standards can be achieved compared to the Metal Injection Moulding process.
Particularly with regard to surface roughness, Rz values of less than 10-25 µm are achieved with simultaneously high densities of over 99.5%. Component quantities of several thousand pieces are thus available in a few days or weeks, while at the same time offering full flexibility in component design.
In order to ensure these properties for industrial sectors such as medical technology, customer requirements for in-house certification according to ISO 9001:2015 are examined on the one hand, and these are already being processed and documented according to the requirements of ISO 13489 (safety-specific standard).
For the tensile test on metallic materials in accordance with DIN EN ISO 6892, the specimen forms in accordance with DIN 50125 prove to be a good basis, but require detailed investigation. Especially the radii and transitions between the specimen head and the specimen waist often cannot be used in the usual way. Although it can be produced without any problems, short and sharp transitions, such as in thread or shoulder specimens, lead to local stress increases and corresponding failure at these points - the tensile tests with this fracture position would all be invalid. Depending on the manufacturing process, the surface must be reworked and cannot be tested "as-built". Further limitations in the choice of a sample shape occur especially in high-precision and expensive manufacturing processes, as the samples should be as short as possible. Classical specimen grips, such as wedge grips or screw grips, can only be reduced with great effort. Much simpler then are form-fit holders, but without thread. Flat or round tensile specimens with a shoulder as counter bearing can be easily produced and tested.
Due to these high requirements, the quality assurance department of 3D Micro Print GmbH has been working together with Hegewald & Peschke Meß- und Prüftechnik GmbH for some time. The company is a specialist in the field of testing technology for additive manufacturing processes and has long experience in testing and measurement technology.