Automation in the pressroom.

Today's pressworking is complex, requiring controls just as sophisticated as those used for metalcutting. Here's a look at aspects of automation for the press department.

More and more companies are turning toward automation in the pressroom. It is the solution to large inventory costs, long leadtimes, lack of production flexibility, and reduced production capacity. This according to Orchid Automation, Brentwood, TN. "There are many innovations in today's equipment that specifically handle these previously unavoidable limitations," says the firm's Melissa Washburn. "Automation is changing the way manufacturers everywhere do business."

There are many good applications to report. For example, a major manufacturer of electric motors needed the additional capacity to produce high volumes of several different parts. Enter Orchid to examine the application and supply a custom-designed rotary die-change system. It cuts changing time from 8 hours to 3 minutes, handling transfer dies measuring up to 144" x 48" and weighing 20,000 lb. It's done with minimal operator involvement, and a high degree of safety.

No, it's not total automation, but it achieves 90-percent efficiency and uptime for the press and its auxiliary equipment. A similar triple-station rotary die carrier serves another motor manufacturer, using two presses to simultaneously produce rotors and stators. Twelve die changes per day are provided, plus a method to store dies in minimum floor space. The JIT system also requires regular die maintenance.

How far should we go?

As reported, not all pressrooms benefit from total automation, but most benefit from some. Craig Schnelle of Minster Machine, Minster OH, says, "We consider the entire metalforming process, focusing on process changeover, versus just die changing."

According to Minster, there are eight areas in a press system where automation can be used. Parameters to set include press shut height, counterbalance pressure, die-cushion pressure, hydraulic overload, tonnage monitoring, signature analysis and die sensing. Limits for all these factors can be preset in the system or process control.

How much do we use? Mr Schnelle says, "We start with the basic components such as die changers and coil feeders, then make sure the operator has enough control to avoid delays in setup. A simple die cart or turnstile, for example, can be loaded before the time of a required die change. Then there's no delay when the cell operator decides to make that change.

"After we establish the basics, we start putting more extensive automated equipment into the system, using PLCs of our own design. In the ultimate system, the operator enters a six-digit tool number and the process automatically changes the parameters. It finds the coil and unloads it, sets the feed length, sets press shut height and counterbalance pressures, and finally threads up the material and gets the system going."

The knowledge and expertise of the stamper should also come into play. A stamper may say, "My metalforming process makes these parts well, but not those others. Can we change your part design or otherwise work together to improve the productivity of my press line? Let's look at both sides: the process and your part requirements."

For example, Mr Schnelle talks about a striking plate for an automobile door. It had been a stamped part requiring downstream welding of weld nuts, followed by plating. "Our customer worked with the auto builder and used his metalforming expertise to extrude bosses on the plate, then tap them," says Mr Schnelle. "This process eliminated the need for weld nuts, providing a one-piece assembly instead of four. The new design eliminated weld nuts, which caused assembly problems as well as corrosion in service. Now, the assembly is stronger, yet lighter."

Yes, in the real world, Minster has set up systems with full automation. The firm recently shipped metalforming systems to a furniture manufacturer and a producer of automotive parts. These employ automated process configuration based on operator input of a tool number. A programmable logic controller (PLC) recalls the data, so that servodrive mechanisms can set the process variables. The dies involved weigh close to 30,000 lb, working into a 120" wide press.

The die cart works between the press and die storage, traversing on rails. It picks the die off the storage area, loads it onto the cart, goes over to the press, then withdraws the used die from the press when the press stops. Next, it moves over to place the new die in the press, then goes back to place the used die back in the die-storage area for pickup by a lift truck or crane. The photos show temporary storage of three dies, but it's practical to place up to five or six storage tables along the rail.

In the next stage, the user might add an automatic die-storage and retrieval system for storing up to ten dies or more. Most users will send dies to the toolroom for maintenance, rather than leaving them in temporary storage by the press, however; and this could be part of an automatic route using AGVs.

The agile concept

Agile manufacturing, the emerging battle cry among automotive and other durable goods manufacturers, according to Atlas Technologies Inc, Fenton MI, involves many disciplines related to information utilization, intra-company interaction, and continuous customer satisfaction. But at the top of the list of concepts is response. The agile company must be able to produce-to-order, using highly flexible production equipment.

In decades past, automotive stampers pounded out a single body panel or structural fabrication for weeks at a time. Changeover leisurely consumed hours or even days.

No longer. In most stamping plants, response means meeting JIT demands, accommodating uprooted production schedules, and increasing die-maintenance checks to ensure quality--all without sacrificing aggressive production schedules. Beyond merely switching between hoods and roofs, for instance, press lines may be shared by several car lines or car companies. Lot sizes can be in the mere hundreds.

Atlas also reports that quick-die-change strategies, teams, and systems now help to achieve agile manufacturing in some plants. The firm reports hit-to-hit times of under three minutes, even on large body panel presses.

Many plants use a comprehensive system of equipment that includes flexible parts-handling automation (with automatic changeover of end effectors and tooling), plus die-handling automation that removes dies from the press as others are being put in, followed by fast and controlled transportation of the dies to and from storage-and-retrieval equipment.

Other new equipment includes automated die separator-turnovers that speed die washing, inspection, maintenance, and setup. The results include reduced inventory and work-in-process; shortened leadtimes; improved surface finishes; less scrap (because of enhanced die maintenance); and increased production capacity.

As an example of agility in action, Lennox Industries, Marshalltown, IA, installed an automatic system for producing standard and high-efficiency heat exchangers for its G23 and G26 furnaces.

Atlas Technologies designed and built the system for high-volume production. Changeover between the two models is as simple as engaging or disengaging punch tooling, which requires only a single control function. The blanks for all parts and models are the same size.

Stacks of sheet-metal blanks are automatically queued, destacked, formed into left-hand and right-hand clamshell panels on a transfer press, then mated, hemmed, crimped, and sized on a second transfer press. Finally, they are unloaded to a conveyor. No manual handling of the work-in-progress is required.

According to Glenn Harmelink, manufacturing engineering supervisor at Lennox, "We have typically used transfer presses for forming heat-exchanger clamshells, but this is the first time we've used a totally automated process to make both halves into a complete assembly. From an operational standpoint, we like the fact that the system provides us with easy access to presses, dies, and automation components for maintenance."

Besides designing and building the automation, Atlas integrated the total system, including specification of required presses and recommendations related to die design.

In operation, stacks of sheet-metal blanks are loaded onto a cranesaver conveyor that holds two stacks and keeps a continuous supply of blanks ready for destacking. The automatic destacker has vacuum cups that lower to the top of the stack and remove the top blank. The unit them raises the blank and releases it to an overhead magnetic roller conveyor, where it is checked by an electronic double-sheet detector to ensure that only one blank is present.

A conveyor then moves each blank through a roll-coater into a gage station, where it's positioned for pickup by the transfer-press automation.

Next, an Atlas Flex [R] 2000 transfer system moves the work through four dies in a 600-ton press to perform draw, form, trim, pierce, and flanging operations. The formed sheets are also separated into two parts: left-hand and right-hand.

The Flex 2000 is a servodriven, programmable system that allows transfer motions to occur independently of press actuation, providing efficient motion path and accel/decel profiles that have optimized the cycle times to 720/hr. The independent operation also makes die setup faster and provides better access inside the press for clearing scrap, inspecting dies, or performing maintenance.

After the Flex 2000 transfers parts out of the press, it turns the left-hand part 180 deg, and rotates it 90 deg on a windmill-style turnover unit. Then it lifts the right-hand and lowers it onto the left-hand part to mate the two halves of the clamshell.

Next, a second Flex 2000 transfer moves the parts through a 400-ton press to perform the hem, crimp, and sizing operations.

The transfer then unloads the completed heat-exchanger assembly onto a conveyor. Finally, operators manually unload the assemblies and place them on racks for transport to the furnace-assembly area.

Control survival

Most machine-tool builders design their own controls, even if they don't make them. Minster, for example uses Allen-Bradley and others, but has strong input into PLC design and, programming. Littell, Div Allied Products Corp, Chicago IL, noted for its press feeding systems, also provides.

Production Master electronic feed controls for its modular brushless AC servos to ensure precise closed-loop positioning of coil stock.

The feed control interconnects to adjoining equipment with minimum wiring. The press cam switch needs to provide only two isolated contacts to start the feed system: feed initiate and roll lift. The operator can adjust feed length and roll length, with an input keypad and LCD display. The control also provides diagnostics and status information, has micro feed-length adjustment in its automatic mode, and preprogramming of selected setup parameters for repeat jobs.

Deeco Systems, Hayward CA, offers Lucas computers and controllers, designed to survive rugged shop-floor conditions. With user-friendly programming, they employ SealTouch infrared touch systems to avoid problems with keyboards. They combine the speed of 486DX-2 CPUs at 66 MHz, or 486DX at 33 MHZ, providing high performance in spite of harsh manufacturing environments.

Automated guillotine 

It took several companies to provide fully automated production of heavy-capacity shelving, according to a report from the Heim Automation and System Integration Group, Chicago IL. The group spearheaded a new production system that starts with a 16"-wide steel coil on a double-arbor stock reel. The coil stock goes to a powered straightener, which, in turn, provides a continuous flow of material to a multistation rollformer. The material is 0.090"-thick mild steel, ultimately formed into a tube 5" x 2 1/2" with a 1" x 1 1/2" shoulder.

As the tubing exits the rollformer, an automated welding station finishes the forming process with a continuous weld. Finishing knives clean the weld for a smooth finished product. Because of the heat generated in the forming and welding processes, the tubing must be flooded with coolant, which is collected, filtered, and recirculated.

After the workpiece leaves the welding station, a servocontrol gathers line-speed data and matches that speed with a flying cut-off die to sever the tubing in lengths from 36" to 96". The length and required piece count are entered into the servocontrol as batch numbers. Various batches can be preprogrammed to follow one another without stopping the rollforming line. Thus the system boasts zero waste.

The flying cutoff mounts in a Heim 150-ton OBI press inclined 22 deg. The incline lets the shear blade penetrate the tubing at a corner, causing no deformation. The press, slaved to the servocontroller, runs in an automatic single-stroke mode. All press functions, plus the communication between the cutoff controller and the press, are controlled with a Heim press-mounted PLC. Press status is interfaced to the rollformer, so it will stop in the event of a system fault--with no wasted product.

The cut-to-length parts leave the press and go to an automated palletizer with magnetic pickup of the tubing for stacking in layers. After palletizing, the parts are delivered by conveyor to a final welding station, where they are automatically unstacked and where end brackets can be welded into place. From stock reel to final weld, this product never touches human hands.

One-button die changeover

Atlas Technologies recently supplied a totally automated die-changeover system for a major automotive stamping plant. Using die carts to handle dies weighing 50 and 60 tons, the system serves a tandem line of six presses with seven die carts that accomplish the entire changeover sequence with the push of a single button. The die carts bring prestaged dies to the presses and then exchange the dies (pull the old dies out of the presses as they accurately place the new dies into the presses). Automatic clamping is actuated, as well as electrical and pneumatic connections between the die set and the press; and the carts move the old dies away from the press line. All of this happens without die-cart operators.

The between-press robotic part handlers are indexed out of the way and repositioned as the carts clear the presses. Part grippers are also automatically changed. Hit-to-hit time is currently about 8 min.

The system allows four or more changeovers per day if needed to respond to changing production requirements cost effectively. Batch sizes and inventory-in-process are reduced, and accurate positioning of dies within the presses is held to [+ or -]0.010", a very good tolerance given the size and weight of the dies, and definitely desirable due to the robotic part loading.

Positioning of the dies is simplified by the use of Atlas standardized subplates, which act as a common toolholder for the different sizes of dies. This also eliminates the need for expensive die modifications. Once the die is attached to the common subplate, location of the die is maintained by the use of side guides on the cart and in the press. Locating shot pins in the floor ensures correct positioning of the cart at the press; specially designed locating pins in the press bolster achieve tight positioning.