In the automotive industry, on your typical parts, you have a lot of short welds,” says Craig Jennings, president of Motoman Inc. (www.motoman.com; West Carrolton, OH). He then ticks off examples of arc-welded part: seat frames, mufflers, suspension components. So, the engineers at Motoman (and at Yaskawa Electric Corp., in Japan, the parent company of Motoman; http://www.yaskawa.co.jp/en/products/robot.htm) set about to develop a faster way to weld. Speaking of the result of that work, Jennings observes, “The actual welding time doesn’t change.” Which might lead one to move on to something of more interest. But weld process time—as in the amount of time the torch is putting down wire between points A and B, then B and C, and C and . . .—is only part of the issue. Jennings points out that the amount of time that there is no welding going on during a “welding operation,” especially in the case of multiple short welds, can range from 25 to 50% of the total cycle. “We didn’t change the welding technology. So if you welded at 60 ipm, you’re still welding at 60 ipm. The weld time is the weld time. But getting from the end of one weld to the start of the next weld, that’s where we’ve made the dramatic improvement,” Jennings says, speaking of the new SSA2000 six-axis vertically articulated robot. Based on the company’s already fast EA series, the “dramatic” increase that he’s talking about is a 40% improvement in axis speed, which directly results in a minimization of air cut time (i.e., moving in space with no torch on). In one example, a seat frame requiring 8 welds and a weld time of 50 cm/min, the results are as follows:
|SSA2000||9.4 s||22.2 s||31.6 s|
|EA1400N||12.7 s||23.1 s||35.8 s|
In addition to the reduction in the air cut time, you’ll notice that there is a slight difference in the time of welding. The high acceleration/deceleration rates achieved by the SSA2000 are based on having a heavier-duty gear reducer in the S-axis than is used for the EA1400N. That addresses the air cut. As for the weld cycle improvement, that’s based on high-speed contactors used for motion control. That is, during the process a robot sends a signal to the power source for arc on-off. So what Motoman has done is to reduce the amount of time delay between this such that there is a savings of 0.1 seconds per weld. While that is short period in isolation, when having a part with multiple welds, it all adds up. According to Jennings, on average, “The net effect is that you’re gaining 15% on the total cycle time.”
What is the most dramatic aspect of all of this is that even with this 15% improvement, Motoman is not increasing the price of the robot. The EA1400 has a list price of $48,000. The SSA2000 has a list price of $48,000. (Jennings notes, of course, that there are typical price adjustments based on volume purchases.) “That’s a 15% improvement in total productivity with no price increase,” he says, describing this as “an instant formula to drive down costs.” He suggests that those suppliers that are looking for a means to reduce production costs or to take on more business without making additional capital investments, the SSA2000 is a way to do it.
One aspect of the SSA2000 (and the EA1400 before it) that facilitates welding speed is that there is no external weld package. Rather, there is a patented internal cabling design, so it is not a case where the cabling is being swung through space external to the arm. This also has the benefit of widening the area where welding can be performed. Jennings points out another advantage: Because the torch cable for the SSA2000 doesn’t bend, there is less deflection of the wire that’s being fed than is the case when there is an external torch cable. “Even though you’re feeding the wire through an orifice, the weld wire will come out with a cast,” he says of situations when the torch cable is bended during operation. He then explains that this means that the wire is not being fed straight into the weld joint, and when you’re welding with, say, a 0.035-in. diameter wire, there can be quality issues.