Mechanical presses adapt to meet current stamping challenges
June 27, 2002
This article outlines how mechanical presses are changing to meet a new marketplace. Stampers are adding extra stations to create a more complete part and stamping harder alloys. Servo-driven mechanical presses will make traditional flywheel presses obsolete because they use less energy and can be adjusted midstroke. Technological advances include real-time press monitoring, automatic die changes, and computerized troubleshooting.
Photos courtesy of Komatsu America Industries, Wood Dale, Illinois.
Described as a big hammer, a beast, and a cookie cutter, mechanical presses have been the underappreciated workhorses of stamping operations. While the physics of the presses haven't changed—they produce energy needed to force the tooling to stamp parts—stampers' attitudes toward them have.
Years ago stampers didn't have tight tolerances, and part accuracy was guaranteed with the tooling. Similar to forging, mechanical presses were used as big hammers to deliver energy. As tighter tolerances became the industry norm, press builders and stampers began looking at how the mechanical press interacts with the tooling.
The beast mentality is gone. Presses now are considered to be part of the tooling, said Jim Landowski, general manager of marketing at Komatsu America Industries, Wood Dale, Ill., a manufacturer of press systems for the automotive industry (www.komatsu.com).
"Because stampers are performing more sophisticated work, such as die tapping, tolerances are extremely tight, and the press has to be part of the tool," he said.
Because of the tight economy, increased foreign competition, and just-in-time manufacturing, stampers are forced to do more with less. Now a manufacturer may get a call on Monday from a supplier that needs a certain number of parts by Friday, Landowski said. This means it has to get the tool up and the parts out the door to stay competitive.
Stampers are squeezed to reduce costs, lower their price to their customers, and maintain zero defective parts. To improve profit margins and keep costs down, stampers are asked to provide subassemblies for stamped parts, said Dennis Cattell, regional sales manager for The Minster Machine Co., Minster, Ohio, a producer of mechanical power presses and related auxiliary equipment (www.minster.com). Instead of stamping a bracket or a flange and sending it to another supplier to drill a tap hole and insert a nut, stampers are pushing mechanical presses and progressive dies to create a more complete part.
Press manufacturers are responding with flexible mechanical press designs. Currently presses feature larger beds and bigger windows. "Because stampers are increasing progressive die operations, the press bed has to be longer to accommodate more stations," said Tony Mase, national sales director, The Heim Group, Chicago, a manufacturer of stamping presses (www.theheimgroup.com).
Many stampers need the flexibility to add a conveyor or transfer system to a second operation, which requires a press with a bigger window. To meet this requirement, presses are designed with windows large enough to make the entire bolster width usable.
"Stampers need the ability to pass parts or materials over the whole width of the bolster, unobstructed," Landowski said. Stamping Harder Materials
As devices become smaller and lighter, such as cellular phones and laptop computers, manufacturers are faced with the challenge of stamping titanium and titanium alloys with yield strengths of 130,000 to 140,000 pounds per square inch.
"These materials are hard and thin, require more tonnage from a press, and require tighter tolerances," Landowski said.
To keep up with higher tonnage needs and to maintain tighter tolerances and rigidity, press builders are evaluating how the press is made. For example, instead of using traditional gears and shafts that require a keyway—an interlocking groove or channel that supplies reinforcement to hold them together—manufacturers are adding spline connections for more efficient torque transfer and less maintenance. Spline connections have multiple points of contact, locking from one part to the next, as opposed to a keyway's two connections (see Figure 1).
"Over time, as operators blank harder materials, the keys start to roll, which makes a press sloppy," Landowski said. "Splines reduce press downtime because they are more stable and last longer."
Builders also are using design software to study dynamics, kinematics, and finite element analysis to optimize designs.
"We can design the press in the software and plug in operational parameters to simulate a shop's operating conditions and identify any problem areas up-front," said Chris Nantau, sales and marketing manager for Eagle Press & Equipment Co. Ltd., Oldcastle, Ont., a designer and manufacturer of metal, plastic, and composite forming presses and machines (www.eaglepresses.com).
As manufacturing technologies become intertwined with the Internet, mechanical presses soon will be wired. Electronics allow stampers to monitor press and tooling performance closely to ensure quality, spot trouble in advance, and reduce maintenance and repair costs.
Press controls, such as programmable logic controllers, and automation constantly are improving. Programmable logic controllers coordinate everything, including peripheral equipment attached to the press, into one system, explained Dennis Boerger, national sales manager for AIDA - Dayton Technologies Corp., Dayton, Ohio, a builder of metal forming and stamping presses (www.aida-america.com).
When a press system is integrated, programmable logic controllers can make die changes more efficient. For example, after a job is completed, the computer stores the die times and rotary cam settings. To make that part again, an operator simply punches in a job number and the die is set automatically to the correct parameters.
"As more work is done in the press, many dies are now more sophisticated and expensive," Landowski said. "Therefore, the need for real time die monitoring and overall system control has increased."
Spline connections have multiple points of contact, locking from one part to the next, as opposed to a keyway's two connections.
Because manufacturers are producing more complete stamped parts, a press line can be a block long when it includes a coil line and a straightener. To increase efficiency, everything has to be integrated and controlled from the operator position, Landowski said. If there is a buckle in the coil or loss of air pressure, the operator will know exactly where the problem started.
Instant and reliable troubleshooting via the Internet is another perk of computerized presses.
"Management will be able to see in real-time their total production environment anywhere in the world," Cattell said. "A reporting system allows engineers and operators to pick out and highlight all the reasons why a press is down. Through graphs, pie charts, and reports, management will be able to fine-tune the efficiency of its operations and immediately identify justifiable cost improvement areas."
A mechanical press with a flywheel soon will be as outdated as a typewriter. Manufacturers are gearing up to introduce servo-driven mechanical straight-side presses by mid-2002.
Capacities for these presses are more than 1,000 tons, with large bed areas and slide accuracy in the micron range. Stampers have been asking for presses with adjustable stroke, adjustable die height, adjustable tonnage, easy setup, and control with minimal maintenance. Servo presses offer them all, according to Landowski.
Traditional mechanical presses have a motor in the back with a belt that turns the flywheel, which stores the energy. When a press cycles, energy is taken from the flywheel and regenerated as it returns to the top of the stroke. With a servomotor, energy isn't stored, which is more cost-effective because the motor isn't running constantly.
When a flywheel mechanical press stamps high-tensile materials, breakthrough causes vibration and shock, called reverse load. Reverse loading prompted manufacturers to reinforce the frame and drive strength of mechanical presses.
For all presses, reverse load is directly proportional to the velocity of the slide. Servo presses can be adjusted in inches per minute, as opposed to strokes per minute; therefore, the slide velocity can be adjusted even at midstroke. Mechanical presses cannot be adjusted midstroke because the stroke is fixed.
"Servo presses minimize snap-through shock even beyond the thresholds of a link-motion drive, which not only enhances tool life but also simplifies the die design," Landowski said.
Besides reducing press downtime, reject parts, and scrap ratios, stampers also have to adapt to the new economy. This means the pressroom of the future will contain machines that run a variety of jobs—all day, every day.
"Shops running half of their mechanical presses will disappear," Boerger said. "You will see shops with five or 10 very productive machines."
Highly efficient pressrooms will become a reality through the use of mechanical presses capable of accurate, repeatable performance, stroke after stroke in conjunction with programs such as quick die change, robotics, die protection, tonnage monitoring, and improved material feeding equipment, according to David Stone, stamping consultant for Amada America, Buena Park, Calif. Amada manufactures precision sheet metal fabricating equipment, including stamping presses, CNC turret punch presses, lasers, press brakes, shears, flexible manufacturing systems, and software (www.amada.com).
"We will see more centralized monitoring of mechanical stamping presses, so users will know what their true performance is," Stone said. "Maintenance, downtime, die changes, setup, quality issues, tool monitoring, and other aspects will be measured and quantified to show what is working, what isn't working, and what needs improvement."
STAMPING Journal acknowledges the following sources used in preparing this article:
AIDA-Dayton Technologies Corp., 7660 Center Point 70 Blvd., Dayton, OH 45424, phone 937-237-2382, fax 937-237-1995, Web site www.aida-america.com.
Amada America Inc., 7025 Firestone Blvd., Buena Park, CA 90621, phone 800-626-6612, fax 714-739-9681, Web site www.amada.com.
Eagle Press & Equipment Co. Ltd., 5170 O'Neil Drive, Oldcastle, Ontario, Canada N0R 1L0, phone 519-737-1593, fax 519-737-1595, Web site www.eaglepresses.com.
The Heim Group, 6360 W. 73rd. St., Chicago, IL 60638, phone 708-496-7400, fax 708-496-7428, Web site www.theheimgroup.com.
Komatsu America Industries, 199 Thorndale Ave., Wood Dale, IL 60191, phone 630-860-3000, fax 630-860-5680, Web site www.komatsu.com.
The Minster Machine Co., 240 W. Fifth St., P.O. Box 120, Minster, OH 45865, phone 419-628-2331, fax 419-628-3517, Web site www.minster.com.
Schuler Inc., 7145 Commerce Blvd., Canton, MI 48120, phone 734-207-7235, fax 734-207-7222, Web site www.schuler-hydroforming.de.