Assembly in Action: Automated System Welds Grills
June 23, 2008
Robert H. Peterson Co. (City of Industry, CA) produces gas grills for sale in North America and abroad. Founded in 1937, the company has revolutionized the way it manufactures its products through the use of automation. Every aspect of the production process takes place at the company’s 230,000-square-feet production facility, including sheet metal fabrication, laser cutting, robotic welding, die and press brake forming, grinding, polishing, assembly, testing and packaging.
Recently, the company hired systems integrator Countour-Arc Inc. (Laguna Hills, CA) to build a new CNC-controlled spot welding system to automate the welding of its stainless steel firebox assemblies. Central to the new system is a Sinumerik 802D controller from Siemens Energy & Automation (Elk Grove Village, IL) and an IS-120B inverter spot-welding power supply unit from Miyachi Unitek (Monrovia, CA).
The new welding system includes four separate welding fixtures mounted on a pair of rotary indexing tables. This configuration allows operators to safely load the fixtures on one side while the machine is performing spot welds on the other. In addition to controlling the system’s welding arm and tables, the Sinumerik 802D works with the IS-120B inverter to control and monitor the actual spot welding process.
To facilitate the welding process, the four part-holding fixtures had to be customized to accommodate the irregularly shaped parts that make up each firebox. They also had to be configured in such a way that part loading and unloading wouldn’t take longer than welding times. Because the shape of the assembly is such that mechanical clamps would get in the way of the welding head, the fixtures employ vacuum clamping to hold the requisite components in place.
“The advantage of the vacuum clamping system is that the operator can load and unload the fixtures in a matter of seconds, and nothing gets in the way of the machine’s welding head and electrode,” says Contour-Arc president Steven Pfahl. “This allows us to run the machine at its maximum speed. We also programmed the CNC to monitor a number of vacuum sensors placed in the fixtures, so if the vacuum level falls below the minimum set-point, machine motion will stop, and an alarm will display on the control panel.”
All the fixtures on the machine, including locating pins and quick disconnect electrical and vacuum fittings, can be changed out at the same time the robot is welding an assembly on the other side of the table, further reducing system idle time and maximizing the production on each shift.
“We spent a considerable amount of design time standardizing the part-holding fixtures, so that minimal or no changeover would be needed when going from one size to another,” says R. H. Peterson senior vice president Jon Bridgwater. “The fixtures have no moving parts or mechanical clamping devices that might interfere with the spot welding head. This system has allowed us complete flexibility in the models, sizes and quantities we can run at any time. This is the ultimate in lean manufacturing.”
Bridgwater adds that another advantage of the new system is ease of programming. A typical welding program can be written in less than one hour. Overall, the new system has cut welding time by 30 percent.
“On the floor at R.H. Peterson, we run eight different grill sizes of three different models,” Bridgwater says. “Once we set up the programs, no additional programming must be performed. After we program the CNC, it is a fully automated process. There is simply no comparison between the way we did things in the past and this new system.”
For more on systems controllers, visit www.siemenscnc.com or call 847-640-1595.
For more on welding and systems integration, call 949-837-5790 or visit www.contour-arc.com.