Aim: To prove a disruptive compliant inspection tech strategy that allows the “in process” controlled layer by layer non-destructive testing (NDT) of parts during the powder bed fusion by laser.
Challenges: Process monitoring systems of laser-based powder Additive Manufacturing (L-PBF) utilising multi-laser systems in the same part are not being certified by all the unknown effects which are extremely difficult to control and demonstrate (even with two lasers). Not easy to know are: the real relative position of the lasers in real time, the effect of laser superposition under different geometrical and thermal conditions, the interaction of multiple lasers with the gas flow and spatter. Existing on-axisprocess monitoring systems can partly solve these issues by providing information about the stability of the process using the measurement of various properties of the melt pool. However, they suffer two major issues: First, there is no compliant framework by means of which these data can be used to certify the part. Second, on-axis monitoring technologies have to be installed on each optical path, which will be hard to implement in the next generation machines with multiple lasers working in parallel. The new control system aims at substituting a more costly process currently implemented after AM process by the end-user, at providing compliant certificates about the manufactured part right after the fabrication, and at being compatible with future multilaser machines.
Benefits: This system allows the “in process” controlled layer by layer non-destructive testing (NDT) of molten metal during the L-PBF. The system consists of miniaturized electromagnetic sensors with a custom-built hardware tuned to the process characteristics. This way, the system is able to map each new layer to a subsurface depth (adjustable in the range 0-1mm). The system is very simple and based on standardized electromagnetic sensing technology for surface breaking and near-surface NDT of metallic materials. The system produces a layer-based map of signatures showing information about the defects and their size according to the recent ASTM E3166-20 standard. The system has also the possibility to make metrology measurements of dimensions of the manufactured part for each layer; and additionally can be used to measure the real density and characteristics of the deposited powder, thus producing a map of powder density which can be used in any powder deposition processes. This system will enable to measure the real impact of all the parameters set on the part itself and the variability of this quality in time. The system is easy to be scaled as each sensor is independent and there are no cross effects among them. This way, any machine can be equipped with an array of sensors covering the whole build plate width, independently of the added complexity of the laser machines. Furthermore, largely regulated sectors like aeronautics will benefit from a quality, in-process NDT system.
Activities & Present achievements: The objective of the experiment is to apply the already existing prototype developed by AMiquam, in a commercial machine by a L-PBF user who has experience in the usage of the L-PBF technology and demonstrate its potential in different areas such as, material related process parameter optimisation, geometry based parameter tuning, part quality measurement in process, machine related maintenance, avoidance of in-process wiper collisions.
Current Status: Both deliverables for the development phase of the project were completed on time and passed the acceptance. The initial software was based on robust communication, the parsing has been modified and is now able to deal with these interruptions. The project will take advantage of these improvements. We plan to have our first data taken in the Renishaw machine in May, i.e. during the second month of Phase 2 as planned in the project.
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