Manufacturing the metal frame that reinforces and supports the visible portion of an automobile's instrument panel is no small feat. Each substructure contains as many as 27 main components that have to be welded together under tight tolerances to meet stringent quality and design specifications. Space tolerances are minimal and are becoming even tighter as vehicles get smaller and lighter. In addition to the sheer volume of components, these panels are composed of very thin wall tubing and stampings that create additional welding and fixturing challenges.
For these reasons, Center Manufacturing in Byron Center, Michigan has turned to Lincoln Electric power sources with FANUC robots for its two main instrument dash panel lines. The company, which provides the panels to major automotive manufacturers, depends on robot welding for dependability, repeatability, accuracy and speed. Center Manufacturing estimates that it receives 60 to 70 percent higher productivity using robots than it would with manual welding methods. In fact, an entire instrument dashboard panel can be welded in approximately 1 ½ minutes (excluding the cooling time between welds) - an amazing accomplishment in relation to the difficulty of the job.
"I would say one of our primary challenges is to get all the components to come together in a dimensionally correct part," says Rodney Rockwell, Manufacturing Engineer at Center Manufacturing. "The designs are provided to us by customers and many have design gaps or other imperfections that cause welding problems on our end. Since we don't have control over the design, it is up to our engineering teams to use the robotic tooling, fixturing and programming capabilities to help us overcome these problems and still produce a quality part with the specifications set forth for us."
Center Manufacturing has a total of six plants that produce such items as automotive, ATV, motorcycle and consumer electronic parts. The company's three plants in the Western Michigan area employ nearly 425 people. They primarily account for the 40 percent of the business that is devoted to supplying the automotive industry. What makes Center Manufacturing unique is that the company, which has been in business since 1969, is run under an employee stock ownership program, meaning that 30 percent of the stock is held by the employees, giving them a stake and an active voice in their company's activities and performance.
At the Byron Center facility in particular, the company uses a total of 22 robotic welding cells, so the role they play in the overall manufacturing process is crucial.
Robotic Welding Lines
Many shops have robotic welding units that work independent of each other, but at Center Manufacturing there are three primary robotic welding work centers on each line that work in assembly line fashion. Each robot welds a portion of the panel and then transfer it down the line through a system of chutes and cooling racks until the welding is complete.
To understand how this works, we will examine in detail the complete manufacturing process at Center. First, coils of steel are brought to the company's stamping department where 24 different stampings are created. In addition to the raw steel, Center Manufacturing also purchases three different sizes of tubes that are cut to length, two of which go through CNC bending processes.
Before going to the robotic welding cells, some of the stampings and tubings are welded into subassemblies using a combination of six resistance welding cells and two robotic welding cells.
The assembly process for the instrument panel uses three primary welding centers, each containing cells that have dual FANUC R-J2 ARC Mate 100i robots. The first work center welds together two subassemblies with tubings and stampings. Since this cell has two robots in it, each robot welds one-half of the part (so that the left side is completed by one robot and the right by the other). The part is then sent via a system of chutes to the second work center where the robotic welding unit adds two more stampings and three additional subassemblies. The piece is now sent to the third and final work center where three more stampings are added and the welds on the bottom of the instrument panel are created.
After the robotic portion is complete, the part is sent to a visual inspection center where all the welds are examined to ensure that they meet the requirements. If there are any welds that the robot is unable to weld because of a design issue or minor repairs that need to be made, the panel is welded by hand with Lincoln CV-300 GMAW welding units. Also, it is at this stage where J-clips are added to the panel. Depending on the customer, the instrument dash panel may require from 8 to 14 clips.
At Center's Byron Center Plant there are two lines that run simultaneously completing dash panels in this assembly line fashion. The cycle time is a quick 14 to 16 seconds per robot.
Most robot cells at Center Manufacturing have Lincoln Electric's Power Wave® 450 ONE digitally controlled inverter power source. This unit features Lincoln's Waveform Control Technology™, which is capable of complex, high-speed waveform control. With this technology, the power source provides arc starting and waveform control capabilities, which results in reduced arc spatter, reduced fumes, and smooth arc welding performance. It can handle high output applications while still producing precise welds. The Power Wave is able to provide direct, seamless integration with the robotic controller and has the ability to select or have programmed in the optimum output waveform and then modify that waveform to adapt to weld puddle dynamics. All this is done within milli-seconds, making the robotic system capable of designing weld bead profiles, controlling heat input and maximizing travel speeds.
On average, each robot at Center Manufacturing puts down 10 welds, all of them being fillet welds. The welds are made on 1008 and 1010 metals that range in thickness from 0.8 mm to 1.5 mm. In addition to being placed on thin material, the welds are very short with the longest weld being 15 mm, but most averaging 5 to 10 mm. "In the automotive industry, a 10 mm long weld has to be 10 mm long or else it is not considered within specification," notes Rockwell. "Weld quality and dimensional quality are very important on this job."
"Overall we have had very good luck with the Lincoln power sources," explains Rockwell. We just program in the parameters we need to meet our cycle time targets and the robots do all the rest. The quality is very consistent - we have had absolutely no warpage or burn-through problems, even though the part is very thin. We don't have to mess with it - we just plug it in and it works." Center Manufacturing also uses Lincoln wire feeders that complement the system - Synergic 7 wire drives. The wire, which is Lincoln's .035" S-3 wire, is supplied in 500 to 900 lb. drums and uses a shielding gas mix of 90/10, Ar/CO2.
Center Manufacturing has also been very pleased with the operation of the FANUC robots. "I like the robots in terms of programming and support more so than other robots I've used," says Scot McLooth, Welding Engineer at Center Manufacturing. "They are fairly simple to learn to program and we've always received great support." And that is saying quite a bit considering the programming for this particular application is very intricate with many interference zones and difficult reaches.
Rockwell agrees. "I've worked with many competitive robotic products at other companies, and the results we are getting here are far better. We have had almost zero trouble with the robots, they are very durable and require a very small amount of maintenance." To that end, the company is very diligent about changing the batteries and greasing the machine as indicated by the manufacturer. Each year, Center also performs repeatability tests.
As far as robotic cell composition, each of the three main welding centers has horizontal ferris-wheel type fixtures so that the operator can be unloading and loading while the cell is welding. Fixturing for the cells is provided by a local integrator, BCM, Inc. Dual robots systems are used when necessary to be able to reach the welds and still maintain the desired cycle times.
Much of the day-to-day servicing issues are handled by Miller Welding Supply, a local distributor located in Grand Rapids, Michigan. "If we have a problem, we just call our distributor," states Rockwell. "They have been outstanding as far as direct support, any service work, consumables or replacement parts. They even keep spare parts on hand for us in case of emergencies. We usually receive same day or next day service."
Safety of the operators is another concern at Center. "Out of the various companies I've worked for, Center has great safety procedures," notes Rockwell. "All the cells are completely enclosed with fixed side walls and interlocking doors. Even the loading and unloading areas are protected by floor mats and safety curtains."
Training and Service
Although most of the day-to-day contact for welding supplies happens with the distributor, Center utilizes the resources of Lincoln Electric for training and updating them with the latest technologies. All of Center's maintenance personnel and welding engineers have attended Lincoln's robotic training at the world headquarters in Cleveland. "We have been pleased with the training provided, it has been very helpful, even to our more experienced people," says Rockwell.
In the realm of new technologies, Center Manufacturing is currently testing Lincoln's Surface Tension Transfer® (STT®) power source in a robotic application. "I'm very pleased with what Lincoln has come up with in the way of new technologies. They are constantly bringing us new things for demonstrations and trials since we are always looking for ways to improve processes and cut time or rework out of our product lines."
"I guess one of my complaints is the Lincoln/FANUC systems work too well," explains Rockwell. "I want to install some of the latest equipment, but what we have works fine and doesn't need to be replaced."
Center Manufacturing estimates that it will keep growing at a projected rate of 10 to 15 percent per year. To do this the company plans to open satellite facilities and continually use the skills it has developed. "On the welding side of the business, we plan to upgrade our equipment. We would love the opportunity to try out some of the latest power sources and robots," notes Rockwell.