Truckin' along through a stamping plant
Redesigned truck cab leads to new plant, processes
International Truck and Engine Corporation's Springfield, Ohio, plant recently undertook the challenge of building a high-performance truck with the dimensional tolerances that meet today's quality standards within a cost structure that would allow it to remain competitive. This new product launch was the first of its kind for the company in more than 20 years.
The earlier cab models were built in a facility that was converted in 1921 to produce the model S truck line, a truck with a 1.5-ton load capacity and a top speed of 30 MPH. The company determined that it could not competitively launch a new line of vehicles without building a new facility, retraining its staff, redesigning its processes, and purchasing new equipment.
The old body plant had a mixture of mechanical presses, the newest being four Danly presses purchased in 1974 and the oldest purchased in the early 1900s. The processes at this plant were labor-intensive, and the equipment and facility required constant maintenance and repair. The average die change time was 55 to 60 minutes.
After designing the new cab and determining the size and tonnage requirements, the company set out to benchmark the best stampers in the country by visiting many facilities. The decision was made to go with Schuler Inc. hydraulic presses. According to the company, although hydraulic presses have a slight speed disadvantage compared to mechanical presses, they offer many advantages from a control standpoint and are easier to maintain.
The new plant's 315,000-square-foot Cab Assembly and Stamping (CAS) facility is home to a Schuler Inc. hydraulic press tandem line integrated by FANUC Robotics. Here major body panels are stamped and delivered to an Intelligent Body Assembly System (IBAS) that robotically assembles and resistance-welds them into cabs. The cabs travel automatically from there to an adjoining paint facility and then on to the assembly plant where they become finished trucks.
The cab-in-white production system starts with a blank-receiving area that is designed to stage about two shifts' worth of production material. The material is blanked to shape by a local supplier, which delivers the finished blanks on pin pallets.
Pin Pallets, Pallet Carts
The pallets are delivered to one of two rolling pallet carts at the front of the press line. While one cart is in position, the other is being loaded with blanks, allowing uninterrupted production. Once the empty pallet cart is loaded, it automatically advances into location, where four fanner magnets move into position and separate the blanks to allow the first robot to pick up the material.
During the production run, sensors on the robot end-of-arm tooling identify when the blanks have been depleted, causing the fanner magnets to retract and the pallet cart to move the empty pin pallet to the unload position. The robot moves to the full pallet while the empty pallet is returned to the blank-receiving area.
Blank Washing, Lubrication
The first robot in the process picks up a blank and deposits it onto a conveyor that delivers it to a blank washer and lubricator. A sensor on the feed conveyor sends a signal to advance the blank through the washer.
The washer is designed with two sets of rolls. The first set of rolls is flooded with a cleaning compound, which removes oil and normal dirt. The second set of rolls squeegee the blank dry. Then a water-based lubricant is applied by spray nozzles, which control application ranging from a fine spray to a flood.
The blank, now lubricated top and bottom, moves to an exit conveyor, where it is centered and prepared for loading in the first press in the tandem line. A double-blank detector on the first robot and in the centering station prevents the robots from picking up two blanks at a time, eliminating the possibility of a die crash or damage to the washer.
The Stamping Process
Once the blank is centered and verified, it is robotically picked up and placed into the lead press in the line, a 1,650-ton hydraulic press with a bed size of 108 by 144 inches.
The panel is drawn and transferred to the second of three remaining 825-ton hydraulic presses with the same bed size as the lead-off press. The panel is trimmed, pierced, and reshaped in the remaining operations. At the end of the line, the last of six FANUC robots loads the finished panel onto an exit conveyor, where it is visually inspected by an operator for surface defects and manually placed in custom racks.
Tool and die technicians who determine dimensional compliance check the first and last panels on individual inspection fixtures. Statistical process control data also is collected and delivered to the quality department, where it is analyzed to verify that processes maintain a capability of 2.0 CP.
All the scrap from the stamping operations falls off the dies and through the bolsters, where it is collected on an underground conveyor. The offal is conveyed to one of two collection trailers outside the facility and is evenly distributed until one trailer is full. At that point the scrap dealer is automatically notified via modem to dispatch another empty trailer.
Single-point Change of Dies, Robots
At the end of each production run, the operator initiates a die change from the master control panel. Here the operator selects the next job to be run from a menu of part numbers. At the click of a mouse, the four presses and six robots simultaneously begin to change to the next scheduled job. The robots deposit the last job's end-of-arm tooling into the outbound tooling nest and pick up the next job's end-of-arm tooling from the inbound nest.
Training and development are integral parts
of the company's business plan.
During the robot tooling exchange, the slide is lowered, and the hydraulic die clamps on the upper half of the die are unclamped and retracted. The slide is raised and locked in place. The safety gates raise, and the rolling bolster moves the next die set into place. The slide is unlocked and lowered onto the die.
The programmable hydraulic die clamps advance and actuate to the clamped position. With the upper half of the die clamped in place, the slide is raised to the programmed top dead center, and the press is ready to cycle. After the robot tooling and die exchange are completed, the operator sends the start-up command from the master control panel, and the press line is back in operation. This entire process is completed in less than four minutes.
All 19 die sets were designed and built by Fuji Technica. The dies have a lean construction. One of the major differences in construction from traditional-style dies is that all die sections are a cast tool steel and flame-hardened on-site. This eliminates the need to send steels out of the plant for time-consuming annealing or heat treating.
When a die section needs repair, a diemaker welds the section with the proper welding rod, grinds it back to its original specification, and then it is ready for production. This is a must in a lean manufacturing facility, where production requirements prevent long turnaround times for repairs.
All the dies were built with about the same shut height to aid in the quick die change. They all have two part-presence sensors to ensure proper placement of parts, eliminating die crashes from improper loading or loading of two parts in the die.
Upon completion of the production prove-out process, the draw dies were sent to Teikuro Corporation in Springfield for a chrome surface treatment, which protects the draw die surface and corrects defects such as cracks, pits, and porosity. In addition, chrome die surfaces have a reduced tendency to strain or split. Routine maintenance (such as polishing) decreases, and product integrity is protected.
Hydraulic Production Presses
Stroke times of less than four seconds are common. Operators can control the speed and pressure at any point during the press stroke.
A panel view at each press allows the operator to store critical information such as top dead center, bottom dead center, working stroke, cylinder control, and automated die functions, eliminating variations from setup to setup. The result is that the first part off a new production run has the same dimensional quality as the last part off the last run. This is a critical component in quick die change times as the industry measures changeover times from last good piece to first good piece.
Keeping the dies and presses operating properly is a top priority. Input from the tool and die technicians and machine repairmen helped the company develop and maintain a comprehensive preventive maintenance program.
The company purchased a hydraulic spotting and die-splitting press designed by the PH Group, Columbus, Ohio. Once the operator has opened the die, he rolls out the lower bolster while the top bolster automatically flips the upper die 180 degrees. The operator has the option to move the die to his workstation or send it via an automated conveyor to a programmable die washer, which washes the die and applies a rust inhibitor. The dies are cleaned and stored in a staging area midway between the die spotting station and the press line.
Training and development are integral parts of the company's business plan. For example, eight of its tool and die technicians traveled to Japan for special training in lean die techniques. Each employee spent 12 weeks studying Fuji die drawings, pattern construction techniques, CNC machining, finishing, polishing, welding, and flame hardening. They also participated in the die buy-off process.
Over a period of four weeks, two trainers from the Schuler Customer Information Center trained operators in the basics of hydraulic press technology. The operators learned the functions of the mechanical, hydraulic, and electrical components in the presses, as well as the responsible operation of the manufacturing system.
Since the training, the company's average die change time on its large tandem presses has been eight minutes hit to hit, throughput is 300 hits per hour, and acceptable first-time quality parts average 99 percent.
The company says it believes it has opportunities to automate the unload process, improve throughput to 325 hits per hour, and lower die change times to seven minutes. It is working toward ISO 9000: 2000 certification and expects to be compliant by June 2003.
The company also has made preparations to install a second press line, which will probably comprise the same type of equipment.
STAMPING Journal is the only industrial publication dedicated solely to serving the needs of the metal stamping market. In 1987 the American Metal Stamping Association broadened its horizons and renamed itself and its publication, known then as Metal Stamping.