Heat Sensors Case Study
Carrs have been working for the aerospace industry for over 6 years now. We have been awarded the AS9100 quality standard for 4 years running, proving Carrs’ consistency and standard of work.
Previous work on the Airbus A380 as well as with companies including BAE Systems and Esterline shows that Carrs are reliable and have been trusted by major companies for our laser welding services.
In the aerospace industry, sensors hold a very important role as it is crucial for the safety of all staff/customers to assess the thermal state of an engine during testing and flight conditions. For this reason, Carrs Welding Technologies Ltd. were approached to weld a heat sensor consisting of several tube arrays into a housing on a GE engine.
The Context and Challenge
Project background and description
As mentioned, the project consisted in the welding of several arrays of 2mm diameter tubes into a housing on a GE engine. The chosen material was the Nimonic alloy C263 due to its combination of good aged strength and excellent fabrication characteristics.
The shape and tight spacing between arrays of tubes meant that the application was unable to be rotated. At the same time, the small tube diameter and thin wall thickness meant that the volume of material available to disperse the heat from the welding operation was severely reduced. This posed two problems:
- The first issue was the fact that a 6 Axis Robot arrangement was not precise enough to follow a circle with such small diameter accurately due to evident process intolerances, i.e. the robot trying to create a circular shape with linear paths.
- The second issue was directly linked to the customer’s request to weld the outside diameter without melting the internal diameter whilst achieving a full weld depth to the base plate which meant two things, the need for a fast weld (as not to overheat the material) and the tight weld depth/width tolerance (i.e. usually the weld depth varies during the welding operation due to a temperature build-up on the base metal as the weld progresses).
Project goals and objectives
The project goal was to weld arrays of tubes all around without melting the internal diameter whilst achieving a full weld depth onto the base plate.
The process and insight
Continuous wave laser welding was chosen for this application due to several key aspects; the ability to perform faster welds (when compared to Pulsed Laser Welding) allowing for the decrease of the heat input; and the ability to enter the keyhole mode which would allow for weld profiles with lower weld width to weld depth ratios, i.e. deeper welds without melting the walls of the tubes.
The solution to the tight spacing between tubes and inability to be rotated was the design of an offset cam arrangement to manipulate the tubes and achieve the continuous weld under a stationary laser head. The next step was to find the right weld profile, by adjusting the laser interaction time and laser power.
The actual parts could not be shown, but the test piece on figure 1 shows the spacing between the arrays. The disk laser welded each tube with a 0.2mm spot to maintain the heat source as concentrated in one small area as possible without damaging the opposite tubes and by elevating the weld speed Carr’s was able to control the heat input and weld all-round the outside diameter without melting the inside diameter.
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