FOCUS ON WELDING
Pressure testing at Linde Engineering . notes on material certificates and operator qualifications .
“ In addition to welding guidelines , material certificates and operator qualifications are what ensures a consistent standard of product quality for additively manufactured components ,” explained Manfred Schörghuber of Fronius R & D .
The individual test pieces were subjected to non-destructive and destructive testing as per the requirements of prEN 13445-14 . Visual and dimensional tests ( VT ), volume tests ( RT-D ) and surface tests ( PT ) were used as non-destructive testing processes to provide evidence that the pieces were free from faults , both externally and internally .
“ We demonstrated that the mechanical and technological requirements for the additively manufactured material and the hybrid connection were met by checking the chemical composition , and by conducting tensile and bending tests perpendicular to the direction of the deposition layer . We then performed metallographic analyses at the start and end points , and at the hybrid connection ,” explained Martin Boche from TÜV SÜD .
Planning and simulating the robot path
Dye penetration testing at TÜV SÜD .
process ) are outlined below for the model qualification of the pressure vessel :
■ The highest possible deposition rate .
■ A reduced-heat process to avoid or minimise the cooling requirement and distortion .
■ No lack of fusion in the connection to the base material .
■ Insensitive to changes in the distance between welding torch and component .
■ Absolute reproducibility of the high material quality required within the qualified limitations of the deposition process .
■ Suitability for large components .
Based on the requirements , the MIG-based CMT process was chosen for the additive build-up of the weld layers .
Specifically , this involved CMT mix for the first layers and CMT Additive Pro for the subsequent wall build-up , where the use of power correction significantly influenced the heat input .
Qualifying the process
Due to the different wall thicknesses of the transition from the base pipe to the branch , the scope of application of prEN 13445-14 required three separate process qualifications ( DPQR ).
The resulting deposition procedure specifications ( DPS ) are binding for the additive welding process .
The final “ recipe ” for metal 3D printing , the so-called additive manufacturing procedure specification ( AMPS ), therefore comprises three deposition procedure specifications , instructions for the welding sequence and
The path for the robotic welding task was planned using a three-dimensionally modelled pipe branch in the CAM software ( computeraided manufacturing software ) developed at Fronius .
“ We calculated the proposed additive buildup — the actual welding program — by entering the layer height , position , speed and build-up strategy . The welding path was visualised in a robotic welding cell that we modelled in our software ,” added Leonhard Reiter of Fronius R & D .
The component was scanned using Fronius WireSense so that it could be correctly positioned and corrective action taken on the manufacturing tolerances . This sensor technology uses the wire electrode as a tactile sensor and scans the welding contour pointby-point .
If the electrode extension touches the surface , a short circuit occurs which triggers a distance signal and transfers it to the welding robot .
The system ’ s software compares the target value programmed offline with the actual value of the WireSense travel and corrects the welding path for additive manufacturing as necessary . The wire then immediately moves backward and — while the robot continues moving the welding torch — forward again to the next point , where a further short circuit is triggered , a distance signal is generated and the welding path is modified again , if necessary . This minimises geometric deviations .
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