Assembly in Action: Robotic Welding Cell Keeps Shop on Top
"We’ve always considered ourselves a value-added supplier," says Royal Clippert, tooling manager. "We provide quality, processes and services outside the boundaries of the typical stamping supplier classification. Early on, we began offering assembly processes for many of the components we stamped. And today, in addition to production stampings and assemblies, the Schaller Group has been formed and has become a source for a broad range of stamping services, including development of prototype parts, and tool and die building."
This value-added aspect also extends to the company’s ongoing goal to continuously improve. One example of process improvement is the acquisition and installation of two robotic welding cells at the company. The cells were engineered and built by Custom Machines Inc. (CMI, Adrian, MI), specialists in the manufacture and integration of custom assembly machines and complete turnkey systems. The new cells have replaced older systems that were a combination of automation and manual operations. These systems were made virtually obsolete by part changes for the 2002 vehicle model year.
The new CMI cells provide a high level of flexibility, allowing for potential engineering and future design changes. They also have reduced manpower requirements. "The new assemblies required a quantum jump in the process," Clippert notes, "with the part size and number of components doubling, and the addition of a secondary forming operation. The robotic welding cells have been the bridge we needed to achieve the quality, throughput and machine reliability required."
The parts and assemblies being formed and assembled by the cells are referred to as left and right side cab hold-down brackets. Each consists of a rail, a subassembly and three tap plates, which are welded together to form a single unit. The assembled, U-shaped brackets are used to build pickup trucks. After attachment to the cab floor plan, these brackets function as the mounting surface between the cab and the vehicle’s frame. They also provide a secure means for attaching the seating mechanisms via the tap plates. The brackets weigh approximately 10 pounds, measure 3 feet long and are 8 inches wide.
Prior to the installation of the two new systems, the dedicated units consisted of a four-station rotary table with eight welding guns, in addition to a material handling person. Also, the previous assembly configuration consisted of only three components.
There is a cell for the left side and one for the right side bracket. These cells include the secondary forming press, an intracell material handling robot, two seven-axis servo robots equipped with resistance welding guns, a six-station 89.2-inch-diameter indexing table, a fourth robot that unloads and packs the assemblies into their dedicated shipping containers, and a feed and positioning mechanism for the tap plates.
The first robot picks up the rail from the stamping press and loads it at the first position of the indexing table. It then picks up the subassembly from its load conveyor and places it in position on the rail. The table rotates to the first welding station, where the robot welds the three tap plates in place and places two welds on the subassembly. The table rotates again to the second station, where the second welding robot completes eight additional welds on the subassembly.
A total of 16 welds are performed on each bracket. Incorporated into the cell are sensors that ensure tap plate pickup and placement, plus rail and subassembly presence. There is also a station for checking threads on the subassembly. The cycle time to complete one hold-down bracket is 23.5 seconds, resulting in approximately 153 pieces per hour.
The final rotation moves the assemblies into position for the fourth robot to unload the assemblies, placing them in the shipping containers that hold 102 units. A single cell attendant delivers parts to the cell and removes shipping containers when full.
To develop the system, Schaller first defined and created an overview of the process. This plan was presented to CMI engineers, and working together, the two teamed up to refine and formalize the system’s design. From there, CMI completed the engineering work and building process, including software generations and control integration between the various units.
A critical factor in the success of the cells, according to Clippert, has been the synchronization of the assembly and welding operations with the cycle time and performance of the press. "The man-machine interface is one of the system’s most impressive features," he notes. "The overall control is eloquent in its performance, a powerful voice that speaks to all the other elements and makes them function as one."
For more information on welding cells, call Custom Machines Inc. at 517-265-5759, visit www.custommachinesinc.com or Reply 1.