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forming & fabricating


The fi ve steps of the SpotMeld process.


In addition to its ability to join dissimilar and lightweight materials, benefi ts include high-quality joints with a small heat affected zone, consistency in weld duplication, as well as being environmentally cleaner and safer with no fi ller ma- terial, spatter, smoke, radiation or shield gasses. Compared to laser welding and other aluminum-joining techniques, SpotMeld is an easier process to fi xture and it’s more tolerant of imperfections. It also is designed to have the same basic footprint and work envelope as a resistance spot-weld robot, putting it in a familiar context for OEMs. Additionally, the electricity cost is much lower than that of resistance welding since there is no need for the huge cur- rent. The only utility cables are the servo lines that connect to the servomotor and some water cooling for the tools.


Coldwater’s RFSSW process consists of fi ve phases: t Weld head closing t Friction Phase—Both the pin and sleeve are placed


on the surface of upper sheet and rotate to generate suffi cient frictional heat for plunging.


t Advance Phase—Sleeve advances into materials and pin retracts, pulling softened material from the metal sheets into the tool.


t Retract Phase—Sleeve retracts and pin advances fl ush with sleeve, pushing displaced material back into the hole and forging the finished weld.


t Weld is complete—weld head opens. A major advantage of this approach is that the tool


doesn’t fully penetrate through the bottom sheet, leaving a smooth surface with potential for use on exterior body panels. Alternative friction spot welding techniques typically use a solid pin that does not retract, so the pin advances


partially into the sheet, a little more than halfway through the joint, leaving a surface that has some material offset on it. Additionally, this creates a 3–4 mm hole on the center in the center of the weld. Currently, Coldwater can join a stack-up of materials from 0.8 to 8 mm, weld dissimilar aluminums in one stack and join multiple sheets across the edge of a panel.


Example of Material Stack-up Three sheets of 3.0-mm material 6000 series + one sheet


of 1.5 mm 5000 series t Friction Phase: 1800 rpm, 0.4 seconds; t Advance Phase: 1800 rpm, 3.0 seconds advance, 7.7-mm depth


t Retract Phase: 1800 rpm, 2.5 seconds. t 5PUBM 8FME 5JNF = 5.9 seconds


On The Horizon


The foray by manufacturers into new lightweight materials is certainly not going to subside. Coldwater is staying ahead of the curve by focusing on the development of solid-state joining technologies for high-production environments, especially in the areas of refi ll friction stir spot welding. This year, its devel- opment partner will have a system installed at a low-volume exotic vehicle manufacturer in addition to two other RFSSW systems ordered for a helicopter manufacturer, all in Europe. To date, the repeatability and viability of joining alumi- num to aluminum and aluminum to magnesium has been well documented. Next on the agenda is investigating the feasibility of joining aluminum to carbon-fi ber materials and aluminum to steel.


66 — Motorized Vehicle Manufacturing 2016


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