Material Flow during Friction Stir Welding of Copper
2008 (English)In: 7th international Friction Stir Welding symposium: Awaji Island, Japan, 20-22 May 2008, 2008Conference paper (Refereed)
SKB (Swedish Nuclear Fuel and Waste Management Co) intends to use the FSW method to seal copper canisters for nuclear fuel waste. The understanding of the material flow in this process is essential in order to obtain good weld quality. Material and temperature flow in 50 mm thick friction stir welded (FSW) copper has been investigated in this study. The main experiments have been performed at SKB’s canister laboratory in Oskarshamn. By inserting dissimilar material into the weld zone before welding and then join the material, the flow can be analyzed. Ø4 mm brass rods were used. After welding, the weld line was sliced, etched and examined by optical microscope. A three-dimensional finite element model was used to describe mass and momentum transport as well as heat transfer. The shoulder moved the first brass to its new position after welding. Independent of where the rod was inserted, the brass was first observed in the area where the tool has passed at the advancing side close to the uppe rsurface. Most of the brass was seen in front of the position of the inserted rod, i.e. the brass had moved backwards. After the inserted rod, no brass was observed at the retreating side, but some was found at the advancing side. The pin moved the brass from the root of the weld upward towards the shoulder both on the advancing and retreating sides. The flow around the pin never appeared more than a few mm below the pin, or more than 6 and 8 mm outside the pin on the advancing and retreating sides, respectively. The model and the examined welds were compared showing a satisfactory agreement except for some of the vertical flow.
In the presence of brass, a distinct nugget, often with onion rings, could be observed. The material velocity was highest near the weld tool, but at the advancing side there was a clear drop in velocity a few mm from the pin. This drop could cause void formation if the welding parameters are not chosen properly. The retreating side has a higher temperature and lowerhardness compared to the advancing side in this weld. One of the reasons for the higher temperature is that the component width is less at the retreating side than at the advancing side. Consequently generated heat is concentrated to a smaller area at the retreating side.
Place, publisher, year, edition, pages
friction stir welding; material flow; viscosity; heat transfer; simulation, FEM
IdentifiersURN: urn:nbn:se:kth:diva-12013OAI: oai:DiVA.org:kth-12013DiVA: diva2:294148