Adoption of additive manufacturing (AM) as a viable means of production continues to increase, offering substantial advantages for the manufacture of low volume, high mix parts and complex geometries prohibitive under conventional techniques. As the scope of applications increases, demand for quality evaluations of key processes such as powder metallurgy also increases.
Physical testing enables quantitative analysis of supplier quality, adherence to procedures, and process performance. Maintaining quality in powder metal fabrication begins with the testing of the powders themselves. Metal powders are tested for correct chemistry, particle size distribution, and mechanical properties. Components manufactured by powder metal processes are typically tested for hardness, impact resistance, tensile strength, and density. AM part suppliers that develop the procedures to assess end-to-end quality position themselves effectively for growth. Consistency, reliability, and proof of performance represent integral elements for industry sectors with a low tolerance for risk, such as aerospace and medical device.
Perfecting powder practices
Powder metallurgy is the foundation upon which AM parts are built. Assessing the integrity of raw material improves yield and directly impacts performance. Increasingly, AM part producers are performing their own particle characterisation tests, comparing the results with those specified on vendor certification documents. Testing of this type is typically undertaken as part of the inbound goods acceptance process. Shipments that pass inspection move into inventory with any lots that fail initiating follow up communications with vendors.
“We are seeing growth in applications for additive manufacturing in the aerospace industry on both the production and maintenance sides of the sector. With the industry’s focus on material validation, it is essential that suppliers evaluate all aspects of quality, from the purity of raw materials to the mechanical performance of parts,” explains Boris Plach, product manager for testing machines at Zwick Roell.
Delivering consistently reliable 3D metal printers
AM processes such as selective-laser-melting (SLM) offer outstanding creative freedom in design and thus, provide tremendous potential for lightweighting initiatives. A great deal of the foundational work with SLM technologies centres on lightweight parts for aerospace applications, where traditional manufacturing constraints, such as tooling and physical access to surfaces for machining, restrict the design of components.
In SLM, a 3D metal printer uses laser technology to fuse powdered metals into functional prototypes and end-use parts. The process involves deposition of each layer of material by melting sections of a bed of powder using a high-power density laser. After each layer, the powder is spread uniformly by a wiper and the process repeats, the melted particles fusing and solidifying to form a component, layer by layer.
SLM accurately forms complex geometries not possible with other metal manufacturing methods and enables builds to near-net or net shape, delivering cost-effective production of parts at relatively low volumes.
SLM Solutions Group AG, headquartered in Lübeck, Germany is a global supplier of 3D metal printers that use the SLM manufacturing method. As with conventionally manufactured metallic components, parts produced via 3D metal printers must also be tested for their strength values. For this purpose, SLM Solutions uses a Zwick ProLine 100 kN testing system.
“Delivering 3D metal printers that function with the highest levels of precision and repeatability is of the utmost importance to our customers at SLM Solutions Group. Characterising the material properties of parts produced with each system allows them to ensure proper functionality. Materials testing plays a vital role in determining quality and functional integrity,” adds Plach.
Part production through AM with a 3D metal printer from SLM Solutions Group may involve powder aluminium, tool steel, stainless steel, nickel-base alloys, cobalt-chrome or titanium. For each of these materials, process parameters must be separately identified and qualified. These parameters include, for example, laser power, scanning speed and coating thickness. To complete a parameter qualification, a tensile test is performed to check whether the new parameters reach or exceed the required mechanical characteristic values.
The Zwick testing system offers the capabilities SLM Solutions Group requires to maintain high levels of quality.
"The robustness, high quality and ease of operation have won us over," states Daniel Brück, research and development engineer at SLM Solutions Group.
Ensuring performance in aerospace applications
Conventional aerospace requirements involve strict validation of materials with qualification processes that can span 12 to 18 months or longer. Applications for space flight often have even more stringent requirements due to the extreme service conditions parts must endure.
Fuel tanks bearing liquid hydrogen deliver the propulsion needed for launch vehicles. Metal alloys used in such applications must be able to maintain mechanical performance under high loads and at temperatures in the -250 to -280°C range.
Based in Garching, Germany north of Munich, KRP Mechatec specialises in the development and analysis of materials and structures for the aerospace industry. KRP has established a test program to explore the potential of AM for the lightweight construction of parts for launch vehicles. For this purpose, material samples are produced from the aluminium and titanium alloy-based parts produced via AM. The company uses a Zwick 250kN testing machine to conduct a variety of tests on the samples under non-ambient testing conditions.
KRP’s testing requirements resulted in the development of a special device that allows various tests ranging from tensile and compression to shear and hole expansion tests in a cryostat. In the cryostat, material samples are cooled to -196°C using liquid nitrogen or to -269°C using liquid helium and are then tested below this temperature.
"Zwick Roell provides us with the support we need to carry out our special test tasks. The testing machine and the software enable flexible use in the research and development environment, "explains Dr.-Ing. Christoph Zauner, technical manager at KRP Mechatec.
“Flexibility and ease of use represent areas of importance for customers engaged in development work. Our testXpert III testing software incorporates features that go beyond modern convenience to enhance accuracy in measurement and help ensure reliable test results,” states Plach.
Intelligent user management in Zwick’s testXpert III testing software reduces the number of required operator inputs, revealing only the options and information important to each user. Administrators retain full access privileges and the opportunity to control access levels based on roles and training levels. The software also logs all test- and system-relevant actions and settings, preserving a record for management review. This ensures traceable results that cannot be manipulated.
As AM continues to find applications across multiple industry sectors, one thing remains a constant – the need to validate performance of produced parts and components. Testing plays an essential role in AM, enabling quality management of raw materials through completed products.