Innovative Robotic Laser Cutting And Heavy-Part Material Handling Helps A Leading Automotive Supplier Reduce Operating Costs And Increase Production Flexibility
by Ian Orr
FANUC America Corporation Posted 06/04/2004
UPF, Inc. is a leading supplier of truck and bus frames to the automotive industry. Based in Flint, Mich., UPF supplies thousands of truck and bus frames to its automotive customers each year. A key to UPF's success is its ability to deliver small, medium and large batch runs of many different frame configurations. Though a competitive advantage, the complicated production process prompted UPF to design a state-of-the-art facility that incorporated a wide range of automation solutions to solve the following challenges:
- Customers provided as little as eight hours notice of a batch-run order for frame rails.
- Frame and stiffener rails have cutouts (round, square or rectangular holes) located in one, two or all three sides. The cutouts are used either to attach other assemblies, including cross-frames, or to route utilities for the vehicle, such as fuel hoses, electrical cables, hydraulic lines, etc.
- Truck and bus frame and stiffener rails vary in length from eight to over 40 feet, and weigh 200 to 900 pounds each. A successful automation solution is critical to handle this extreme range, especially with little or no time allowed for changeover.
UPF, along with two of its integrators, Citation Tool and Custom Machines, designed and built a robotic automation system that incorporated two state-of-the-art robotic laser-cutting cells and two heavy-payload material handling articulated gantries. The laser-cutting robots use a patented, shape generation software package. The articulated gantries use a patent-pending approach where a single robot controller drives two independent robot arms to function as a giant re-configurable gripper.
The automation system consists of two parallel lines, which converge into a single manual frame assembly line. The parallel automation lines provide UPF with the flexibility to manufacture completely different frame rails on each line, or to increase throughput with the same type of rail on both lines.
Both automation lines begin with large CNC punch presses fed by servo-driven pullers. The punch-press indexing slide punch and button holders are pre-loaded with the multiple hole sizes to be punched in the frame rail. A blank frame rail or stiffener rail is attached to the servo-puller, which positions the rail lengthways within the press.
After leaving the press, the servo-puller delivers the rail to a FANUC ARC Mate 120iB laser-cutting robot. FANUC Robotics’ ShapeGen software is used to program the ARC Mate 120iB to cut pre-determined holes or shapes through the vertical sides of the rail using a CO2 laser. The servo-puller accurately positions the rail in the X axis in the laser cell, and the robot positions the laser head in the Z and Y axes for hole location accuracy.
The rail is then conveyed into an automated material handling area where one of three things may happen:
- The rail may pass through to the frame assembly area. This occurs if no further processing is required, and/or there are no rails currently downstream.
- The rail may be buffered (stored temporarily) on a storage rack. When a partially assembled frame rail is still present in the downstream frame assembly area, there is no room to receive rails from the laser-cutting cell. If the rail were to remain on the conveyor, it would act as a roadblock to all upstream laser cutting, and eventually to the punch press. To prevent this roadblock, a FANUC dual-arm Toploader (articulated gantry) robot, consisting of two R-2000iA/200T robot arms mounted to the same overhead linear track, will remove the rail from the conveyor and automatically place it onto a storage rack. This buffering process allows the laser and punch-press operations to continue without interruption. Then, when the frame assembly area can accept a new rail, the dual-arm Toploader takes a rail from the storage rack, using FIFO (first-in, first-out) logic, and places it onto a conveyor to assembly.
- The frame rail may be combined with a stiffener rail. Many of the assembled truck and bus frames require a stiffener rail be added to the main frame rail. These stiffener rails are matched to a particular frame rail (they receive the same punch-press and laser-cutting process). An additional complication is that the frame and stiffener rails come in left- and right-handed variations (an assembled truck or bus frame has one left-hand and one right-hand frame rail connected by smaller cross-frames). To ensure they are combined with the correct frame rail, the stiffener rails are manufactured just after the matching frame rails – the Toploader robot must then match the appropriate rails to one another. When the frame and stiffener rails arrive in the material-handling area, the FANUC Toploader robots match and combine the left- and right-hand rails and stiffeners. Simultaneously, the robots align the various holes and shapes in the frame rail with the matching holes and shapes in the stiffener rail.
How the System Works
To reduce expensive work in process (WIP), UPF only stocks blank frame and stiffener rails. After receipt of an order, the appropriate frame rail is manually loaded onto a conveyor in front of one of the two punch presses, and connected to a linear servo-puller. The C-shaped frame rails are positioned on the conveyor so that the horizontal ‘‘back’‘ of the C is flat against the conveyor, and the L-shaped stiffener rails are positioned as needed. Through-hole shapes are then stamped in the rails by the CNC punch press. The linear servo-puller positions the rail lengthways under the punch press -- positioning of the rail and the action of the press are coordinated by a PLC to guarantee accurate and repeatable hole locations.
The servo-puller removes the rail from the punch press and moves it down to the CO2 laser-cutting cell. At this cell, various shapes are cut through the vertical ‘‘sides’‘ of the frame and stiffener rails. Under control of a PLC, the servo-puller positions the rail within the work envelope of the FANUC ARC Mate 120iB laser-cutting robot, and the PLC sends a signal to the robot controller to begin the cutting process. The robot controller, running FANUC Robotics’ patented ShapeGen software, makes a two-step laser cut on the rail. The first cut uses a low-power laser setting to remove the paint along the path of the desired cut. Removing the paint ensures a clean, efficient final cut. For the second cut, the laser power is increased to ensure the desired shape is cut completely through the rail. The ShapeGen software gives the robot programmer a choice of pre-determined shapes (circle, hexagon, rectangle, slot, keyhole, or pommel), or they can easily configure a custom shape. The ShapeGen software also supports setting a kerf (cutting angle) to optimize the cut. As the rail is removed from the laser-cutting cell, it is pulled through a brush to remove any small metal particles created by the cutting process. Once the laser cutting is complete, the servo-puller releases the rail onto a conveyor for delivery to the Toploader robots.
If the rail does not require any additional processing and the downstream frame assembly area is clear, the rail is conveyed straight through to the assembly area. If the frame rail has to be buffered to one of the eight adjacent storage areas or combined with a stiffener, then a FANUC Robotics R-2000iA/200T dual-arm Toploader robot is pressed into action. FANUC Robotics introduced the innovative Toploader robots in 1997. By attaching a conventional five-axis articulated robot to a one-axis overhead rail, FANUC was able to combine the benefits of a standard articulated robot (including dexterity, high reliability and a spherical work envelope) with those of an overhead linear or area gantry (extended linear reach and overhead mounting). To handle UPF frame rails with lengths ranging from eight to 40 feet and weights from 200 to 900 pounds, FANUC Robotics provided a dual-arm R-2000iA/200T Toploader robot, powered by a single robot controller. Each robot is capable of a payload of up to 440 pounds and is equipped with electromagnetic grippers, providing up to 16,000 pounds of lifting force in a simple, lightweight package. Short rails (less than 15 feet long) are light enough to be lifted from the conveyor by a single robot. However, long rails (in excess of 15 feet long) are too heavy and cause excessive wrist loading to be handled by a single robot.
The UPF solution uses FANUC Robotics’ patent-pending approach, where a single controller precisely coordinates the motion of both robots, in essence turning them into one 12-axis servo-gripper. When a long rail enters the work envelope of the dual-arm R-2000iA/200T, one or both robots change position along the linear rail to ensure each robot arm shares the load equally. The position of a robot arm, relative to the second robot arm, and also to the rail to be picked, varies considerably with each unique rail length – this ‘‘on-the-fly’‘ adjustment is servo-controlled, meaning future rails of unknown lengths can be added at any time.
Once the two robot arms are positioned correctly along the rail, they move down and pick the rail up using the electromagnetic grippers. When the electromagnets are turned on and grip the rail, both robot arms are mechanically ‘‘coupled’‘, in that they must move together to lift, move and place the rail. The motion of both arms is perfectly synchronized by the single robot controller, whether the robots are moving under program (automatic) control or under jog (manual operation) control. The rail is then either moved to the buffer location (one of eight rack storage areas) or, in a series of pick-place motions, it is combined with a stiffener rail. A rail stored in the buffer location will be removed by the dual-arm Toploader and placed on the outbound conveyor when the downstream frame assembly area becomes clear.
Benefits/advantages of the system
UPF has realized many short and long-term benefits and advantages in applying the automated robotic laser cutting and heavy-part material handling system including:
- Ability to produce and ship complete frame rails with minimal advance notice.
- Eliminates storage of expensive, partially processed rails.
- Flexibility to handle a large number of frame and stiffener rails with little or no changeover.
- Provides opportunity to process new rail designs through simple re-programming of multiple servo-controlled devices including; CNC punch press, servo-puller and FANUC ARC Mate 120iB and dual-arm R-2000iA/200T Toploader robots.
‘‘The laser cells gave us the flexibility to run multiple numbers of programs, and also made us process capable in terms of quality standards,’‘ said Steve Williams, senior director, BBK, Ltd. ‘‘Previously, we combined plasma cutting and manual drilling for this operation. Since we implemented the new FANUC robotic laser cutting system, we’ve been able to increase throughput, eliminate overtime, and improve the safety conditions of that work cell.’‘
‘‘In addition, the overhead robots provided a safer work environment, higher throughput and reduced work in process,’‘ added Williams.
When production at a major automotive company was threatened by the failure of one of its Tier One suppliers, the company assigned BBK, Ltd. (Southfield, MI) to move in and take over the troubled supplier's operations top to bottom. BBK has an extensive history of helping the automotive sector in process capability by enhancing or redesigning production lines and stabilizing quality in ways that not only have preserved and enhanced the profitability of the individual business, but have also protected the ongoing relationships of the OEMs, the Tier Ones and their sub-suppliers.