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Moving towards zero defect additive manufacturing and welding of INVAR

General

Check out the collaboration between several INTEGRADDE partners to monitor, and to evaluate the monitored data of the WAAM process in their trials to create a zero-defect weld of additive manufactured feature



In Integradde University West is working with WAAM, Wire Arc Additive Manufacturing. This WAAM equipment is built with standard equipment as industrial robot, MAG welding machine and standard welding torches. To monitor, and to evaluate the monitored data of the process, University West is working together with INTEGRADDE partners like New Infrared Technologies (NIT), that have developed a camera that suits this technique very well, and Brunel University London that works with analyzing all data recorded during the trials. See hereunder and experimental set-up for single bead on plate welding trials.


In the trials to reach zero defects, we setup a four variable test matrix, 16 trials plus one center point.

The parameters varied in this test matrix are:

  • Welding speed

  • Wire Speed 

  • Stickout, CTWD

  • Dyn Corr (current adjustment)

Off course there is no such thing as zero defects so in this case zero defects are defined as defects less than 0.1 mm is neglectable. 

The Evaluation is done according to table below:


Tests

Some of evaluated parameters are, more or less, subjective observations like fluidity, other parameters are correlated to the wanted geometry to be produced like bead surface.
The most important evaluation is about material integrity. In this case pores and Lack of Fusion, LOF, are considered as the most critical defects. Those are detected by doing a shaving test. Shaving test is a destructive penetrant test that is done by successively removing a small amount of material and after each machining step, perform a penetrant test. A defect seen in several layers is defined as a LOF and if it could be seen in just one or two layers it is defined as a pore, cracks could be detected in several layers or just a single layer according the propagation of the crack. In this test no cracks were detected.


The size of defects detected by this method is less than 0.1 mm and that match the definition of zero defects well. As seen in the picture above a certain pattern is detected in some of the samples. Those defects are typically lack of fusion in the weld toe of the bead. Other more randomly placed defects are defined as pores.

Analyze (Evaluation)

Next step in this evaluation of the test matrix is to correlate measurement of current and voltage to those defects i.e. trying to detect the signal from the process that indicates that there could be a pore formation or crack.


If it is possible to detect weld imperfections by analyzing the signals from the process, then it could be possible to actually point out where these imperfection exists and in the progress of this development, be able to take action before the actual imperfection happens. Reaching that point will enable us to actually create a zero-defect weld of additive manufactured feature.

Linked files