STRONG, CONSISTENT ROBOTIC WELDS STAND UP TO THE TEST.
The IRB-1400 robot welds clevis brackets onto the rod of the front axle for a power seat track.
Two 1/4-in., vertical down welds attach the washer, and three welds fasten the endcap to the outer rail.
A 1-in. circumferential weld around the 1/2 in. diameter axle rod firmly attaches a clevis bracket.
Automobile drivers and passengers may not know it, but a good weld could be what keeps them safe in their seats during an accident. This weld is on seat tracks, which hold them in place. A supplier to the automotive industry, Track Corp. of Grand Haven, Mich., pays close attention to the welds on these components. So, when the company opted to bring welding operations in-house, it hoped to reduce costs, but, more importantly, it wanted to gain a tighter control on quality. To accomplish both, it uses robotic welders.
Track is a leader in "All Belts To Seat" (ABTS) technology, a design that directly attaches all seat-belt connections to the seat and not the vehicle frame. Since the seat module takes so much stress during a crash, every part must be structurally sound. This includes an unseen and easily forgotten component of the seat, its track.
The company's power seat track incorporates four electric motors and has eight powered seat position adjustments, including recliner movements. Every week, Track conducts its own voluntary testing of the seat-adjustment track's structural integrity. With the track bolted to a fixture, hydraulic cylinders apply 3,000 lb of pressure to various points. This simulates a person belted into a vehicle during a crash (in accordance with Federal Motor Vehicle Safety Standards 207/210). Particularly important in ensuring the seat's safety are the parts of the seat and track in the "load path" — these parts must endure stress during a crash. Just one bad weld in a seat track component can contribute to a safety test failure.
Although it doesn't do all its welding in-house, Track wanted to internalize the work on two ABTS seat track components: a steel outer rail and a front axle. The track components were in the load path, so Track knew that weld quality and consistency were essential. But with a volume of 140,000 annually, the company needed to weld a lot of components in a short period of time. "Robotic welding gives consistent welds, and due to the volume of parts we produce, we knew it would be economical to automate," says Terry Plumert, senior process engineer for Track.
To get consistently good welds, Track worked with AccuBilt Inc. Automated Systems in Jackson, Mich. Because of Track's volume and high quality needs, AccuBilt recommended the IRB-1400 robot and IRBP 500C positioner from ABB Flexible Automation. The robotic welding system includes a robot, positioner, process equipment, and a variety of options and safety equipment.
"We demonstrated that the cycle times met Track's needs," says Troy Turk, sales engineer for AccuBilt. "For that kind of high volume welding, the system pays off."
In addition to cycle times, cost efficiency and turnaround time cinched Track's purchase of the ABB system.
"We received the robotic welding system in three weeks," Plumert says. "Other custom-made cells were quoted at 18 to 22 weeks for delivery. We had our off-the-shelf system up and welding in half the time it would have taken to have another system built for us."
The process and the equipment
The operator begins by loading the parts to either component onto the fixtures attached to the turntable — the front axle has seven parts and each outer rail has three parts. After stepping off the safety mat, the operator pushes a button to rotate the table, which stops in front of the robotic arm for welding. To prevent injury during high-speed rotation, the system stops immediately if the operator steps back onto the mat.
While the robot is welding, the operator unloads completed components and reloads parts to begin the process again. The rail is 3-mm-thick, 80-ksi steel, and all other parts are 3-mm-thick mild steel.
Welding takes place on one end of the outer rail. Two 1 /4-in., vertical down welds attach the washer to the rail. To attach the endcap, the process begins with a 3 /4-in. horizontal weld, continues around the corner of the endcap for a 1 /2-in. vertical down weld, and flows 1 /4-in. horizontal weld. The front axle is the more intricate component to weld. It involves four 1-in. circumferential welds around the 1 / 2-in.-diameter axle rod to attach six clevis brackets. Each process uses 0.035-in.-diameter S6 wire and 90% argon/10% CO2 shielding gas.
Track can weld two outer rails in a 32-sec cycle and one front axle in a 26-sec cycle. The system welds at 30 to 70 ipm. Fixture changeover from one component to the other takes about five to ten minutes and occurs twice a week.
Track's system incorporates an Auto Invision welding power source with pulsed-MIG capabilities from Miller Electric Mfg. Co., Appleton, Wis. Track chose the Auto Invision over a system without pulsing capabilities because pulsed MIG produces less spatter and allows for more welding options.
"Spatter doesn't contribute to the structure of a weld. It just gets all over the part and equipment. With pulsed MIG, we have less spatter and less cleanup," Plumert says. "Also, pulsed MIG gives us the ability to work with different metals, like aluminum. Some components of the seat track are made of aluminum, and we're considering bringing that welding in-house as well."
Because aluminum conducts and retains heat so readily, it is much more prone to warping and losing temper. The pulsed MIG process, which is a modified spray-transfer process, lessens this problem because it pulses the current between a peak and a background amperage level. The pulsed current has a lower average amperage than spray transfer, which constantly directs heat into the weldment. On aluminum parts like Track uses, pulsed MIG provides good penetration without overheating.
Another important feature of the ABB system is the Bulls-Eye tool-centerpoint system. The BullsEye system checks the tool centerpoint and automatically adjusts the robot. The system also adjusts for contact-tip wear and changes in wire, verifies that the robot arm is accurately calibrated, and automatically updates torch angle.
"The BullsEye is one of the great features of ABB robots," Turk says. "It's self-calibrating, so the operator doesn't have to make manual adjustments."
"It's a big time saver," Plumert adds. "If there is ever a quality problem with a weld, BullsEye checks the centerpoint and eliminates the problem for the next cycle. It has paid for itself over and over again."
Track chose the T-shaped IRBP-500C positioner over circular indexing tables because it has a good load rating per side and accommodates a variety of parts. The table's shape gives Track the ability to hang oddsized parts off the sides without disrupting rotation.
Track added automated features like a bin counter, smart fixtures, and torch cleaning to its system to reduce operator responsibilities and save on changeover time.
"Except for removing and adding parts, the machine mostly runs itself for sixteen hours a day," remarks Plumert. "We designed it to be as quick and easy as possible and to eliminate operator error."
The bin-counting feature tells the operator when a standard bin count has been reached by stopping the robot and displaying "bin is full" on the teach pendant. Track's smart fixture interface senses the fixture on the turntable to identify what part will be welded and runs the appropriate program. An integrated torch-cleaning system automatically cleans out spatter and buildup in the torch while lubricating the nozzle after every 20 welds.
Torch cleaning and other automated features are entered into the systems program. Offering technical support as an integrator, AccuBilt trained Plumert and co-worker Roger Hill in programming Track's robot. Although neither had previous experience in robotic welders, Plumert says that it was easy to learn. In addition, the ABB program, Easy Arc, gives Track the ability to add the features it needs.
Once Track's parts are complete, they mount onto a recliner assembly provided by Fischer Dynamics. This entire assembly is then supplied to Lear Corp., the world's largest supplier of automotive interiors. Lear adds cushions and leather to make a "seat complete" module, which is then supplied to the automotive companies. The entire seat is hooked onto the car frame, bolted in place, and electrical connectors attached. This method eases and speeds installation at the vehicle assembly plant.
All Belts To Seat design
One way automotive manufacturers are trying to reduce production cost while enhancing passenger comfort is a seat design called "All Belts To Seat" (ABTS), in which the seat belt, buckle, and all belt connections attach to the seat itself. This replaces a more rigid design that attaches the belts to the car's frame.
The ABTS design installs easily and quickly on the assembly line because it requires fewer connections. It is also a more comfortable design because, regardless of the seat's position, the seat belt is easy to access and consistently fits the passenger. This is particularly beneficial for shorter people who must adjust the seat in an extreme forward position.