Through the project, a new inspection tool based on digital radiography technology will be developed. With this technology, it will be possible to detect surface and sub-surface flaws. The whole system will be designed in such a way that it will be suitable for intensive industrial operation.
The objective of this project is to develop a Non-Destructive Testing (NDT) technique, which enables online quality assurance of ‘green parts’, by monitoring compacted material porosity, and identifying microscopic cracks. This innovative tool will use digital radiography to create a density map for each component, indicating the size and location of defects. As the system will be directly integrated into the production line, it will be possible to identify faulty parts in real-time.
Powder metallurgy is the major manufacturing route for a wide range of industrial parts such as transmission and gearbox steel parts for automotive, cemented carbides and high speed steels for metal, wood or stone-working, magnets and soft magnetic materials, fine ceramics, refractory metals, bearings, etc. All these parts are produced by cold pressing a powder in a die and sintering the sulting green body in a furnace. A tool set for die pressing costs between 1.000 and 100.000 €. The design of a tool set for a new product is made with a trial-and-error procedure that generates surplus costs (up to 50% of the initial tooling costs) and delays (several weeks or months). Furthermore, the optimization of the process is time consuming, due to the lack of fast and systematic systems instruments and procedures for the inspection of the material. In addition to the costs related to the development of the pressing tools, a major concern in powder metallurgy relies on the unpredictable formation of defects on the parts. While shrinking defects, and even surface cracks, are often detectable by inspection, internal defects are hard to detect. During the very early stage of compaction, the powder redistributes itself by flowing between sections of the die cavity. However, when the applied pressure is increased the powder movement gets restricted and shearing can occur unless the magnitude and the direction of the pressure are properly coordinated. Shearing can result in a density gradient within the parts.The density gradient is not always severe enough for an associated crack to form upon ejection. Unfortunately, nowadays there is no reliable method able to inspect parts and detect local defects in green state powder metallurgy parts. Test inspection systems, such as eddy current and magnetic bridge testing, magnetic particle inspection, X-ray radiography, gas permeability testing, and gamma ray density determination, have been demonstrated inaccurate, and often also too expensive for being introduced in the industry. The lack of an adequate inspection system has important implications from the point of view of production, since it increases the number of rejected parts after the sintering process. On the other hand, the widespread use of powder metallurgy parts instead of parts produced by other competing technologies (casting, mainly), is often hindered by the impossibility to ensure the absence of defects in powder metallurgy parts. The availability of a reliable inspection tool for detecting defects would result in substantial savings for the European industry through the reduction costs associated with the production and control of the parts. Besides, it would contribute to improve the reliability of powder metallurgy parts, thus increasing their competitiveness in front parts produced by alternative methods, and opening new markets demanding elements with accurate and well controlled mechanical properties. The aim of DIRAGREEN is to develop a new inspection tool for the improved assessment of green parts, which will prove affordable for SME’s. Such tool will reduce the production costs and will decrease the amount of powder used to generate the same number of parts, owing the fact that the powder of the rejected parts can be re-used. The main outcome of the project will be the realisation of a Non-Destructive Testing (NDT) technique, which enables online quality assurance of ‘green parts’, by monitoring compacted material porosity, and identifying microscopic cracks. This innovative tool will use digital radiography to create a density map for each component, indicating the size and location of defects. As the system will be directly integrated into the production line, it will be possible to identify faulty parts in real-time. Valuable data regarding part defects will be stored in a database, and used to improve mould/die design.