19 November 2015

Consistent quality in series production of additively manufactured components

High-end additive manufacturing (AM) system provider, EOS, has established a holistic approach to quality assurance in series production. The process, which was mainly used for rapid prototyping in the early years, is increasingly making fully-fledged series production possible in many areas. Customers in a range of industries are constantly developing new applications, particularly in the medical and aerospace sectors.

Dr Tobias Abeln, Chief Technical Officer said, “Consistent and repeatable part quality is essential for series production applications. With its quality assurance concept, EOS has optimised the three technological elements of additive manufacturing that have a direct influence on the quality of an additively manufactured component, namely system, material and process.”

At the company’s headquarters in Krailling, there is an area of around 2,300 m² reserved for 70 additive manufacturing systems that are used for research and development into the manufacture of polymer and metal products, quality assurance, applications and training. At the EOS Oy plant in Finland, fifteen systems are being used for development, qualification and quality assurance of metal materials. An additional 20 systems are available at the international EOS technology centres in the US, Singapore and China.

Since 1998, EOS GmbH has been certified to ISO 9001:2008 for the development, manufacture, sales and service of systems and solutions for additive manufacturing using laser sintering technology. Numerous quality assurance measures are in place to guarantee the reliable observance of manufacturing standards during the production of metal parts.

They are tested and validated within the context of the EOS machine acceptance test, during which defined reference parts are manufactured and then examined for numerous decisive criteria such as mechanical properties, tensile strength, elongation at break, surface quality and component density. Current DIN and ISO standards are applied for these tests. A comprehensive check of all system components is carried out during the machine acceptance test.

Materials used also have a major influence on the quality of the manufactured component. With the aid of multi-dimensional quality management, EOS guarantees reliable consistent quality for every material batch. The EOS Oy branch in Turku, Finland has been certified to ISO 9001:2008 since 2013 and to the medical devices quality management system ISO 13485:2003 since 2012.

Various test methods are used for quality assurance of materials, starting with the delivery of the base powder. Every batch is examined for its correct chemical characteristics. With a view to additive manufacturing, consistent grain size distribution is also checked. A second quality evaluation takes place on the basis of a reference build job, where density cubes and tensile bars are manufactured according to fixed criteria under standardised conditions and then analysed. Further processing and packing only takes place once a batch has passed both test levels.

The corresponding mill test certificate is included with each delivery and details the test results. This provides customers with comprehensive documentation for their own internal quality management system.

The actual additive build process is the third pillar of the EOS concept in the sense of guaranteeing standard manufacturing quality. This is concerned with the quality assured development of parameter sets used in the AM build. At EOS, all the process parameters necessary for achieving certain component characteristics, such as laser power and layer thickness, are based on more than 20 years of experience and comprehensive testing. The required product characteristics can be achieved through the optimum combination of individual parameters. A corresponding material data sheet provides a detailed description of the material characteristics that can be achieved.

Image: The hall at the EOS headquarters in Krailling used for application and quality assurance of additive manufacturing systems.

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