Fineblanking: Beyond Flat
There is something about the Swiss and precision and craftsmanship. Whether it is a watch or a chocolate bar, the people there seem to have a real edge.
Fineblanking—a pressworking operation for precision parts production-has its roots in Switzerland. Feintool, a company whose founder helped develop fineblanking in the 1950s, is, not surprisingly, based in Switzerland. Feintool U.S. operations are located in Cincinnati. Here in the U.S. the firm provides presses and tooling; it also operates a parts-making operation.
As there is greater interest in producing better parts, parts with superior geometric and surface quality characteristics, there is increased use of fineblanking among North American automakers and their suppliers, says Karl Summers, Feintool VP of Sales & Marketing. "Five years ago," he points out as an example, "flat clutch brakes were stamped. Now they are being fineblanked." Brake backing plates, transmission components, and a variety of other parts are fineblanked, too. Typically, there has been a transition from conventional methods to fine blanking.
"But not all brake backing plates are fineblanked," Summers points out. "Perhaps the existing ones work fine in the application or they have not been redesigned to take advantage of the characteristics of fineblanking."
The general rule of thumb is that if flatness, precision tolerances and cleanly sheared edges are required, then fineblanking may be the way to go.
Briefly, unlike conventional stamping operations, fineblanking is essentially a cold extrusion operation. The material—which has to be malleable so that it will slide (Summers notes that if material is good for machining in that it produces nice chips, it probably isn't good for fineblanking: the easier it is to machine, the harder it will be to fineblank)—is held in compression. The dies—which are typically produced with wire EDM (another area where the Swiss have made their mark)-have tight clearances, as in 1% or less, between the punch and die, unlike the 5 to 10% clearance characteristic of conventional dies. Since the material is held in compression, and since the fineblanking presses and tooling are designed to maintain the relationship between the punch and die during the operation with no lateral moves (e.g., there is a bottom-up counterforce to the top-down ram force; a V-ring piece of tooling can keep the material from moving out of place), the parts coming out of the press are flat and have clean edges. (Typical material thickness processed with fineblanking: 0.020 to 0.500 in.)
In conventional stamping, the material is initially in compression (for about the first third of its thickness), but then it goes into tension and the material is ripped and oil cans downward. Nitrogen cylinders and springs are often used to counteract these effects, but Summers notes that neither provides the kind of tonnage that fineblanking machines do.
One of the trends occurring today in fineblanking is the implementation of progressive dies. This means, of course, that multiple operations are performed on a given part. One of the consequences of the progressive die approach is the production of parts that aren't simply 2-D, or flat. A third dimension, within some limits, can be generated. Consequently, parts that may have been cast and then machined or stamped and then welded can be made with fineblanking in a single press setup. Summers points out that the tools can be devised so that in some areas the material is worked with the fineblanking process but in other areas, where the tolerances aren't as tight, the tooling is more conventional.
Although the fineblanking press is more expensive than a comparable stamping press of the same size, Summers notes that the fineblanking press has more features, such as the additional hydraulics to provide the counterforce and built-in, in-and-out feed units. And while it may seem that a part that has been fineblanked may be more expensive than one that has been conventionally stamped, there is also the consideration that the stamped piece may require some additional operations-double-disc grinding to attain flatness; heat treating (tool-induced work hardening can be tailored to part requirements in some fineblanking tooling)-that aren't necessary for fineblanked parts.
"If an engineering group takes a fresh look at their designs and redesigns components to take advantage of fineblanking, they can achieve improved performance or cost savings," says Summers, who adds, "Fineblanking isn't for all parts. In some cases, conventional stamped parts or powdered metal will do the trick."
How good can fineblanked parts be?
- Dimensional accuracy to within 0.002 in.
- Edges perpendicular to top and bottom faces to within <0.000.5 in.
- Holes spaced closer than material thickness from each other or from an edge What kind of materials are fineblanked?
- 90%: mild or alloyed steels
- 8%: aluminum or aluminum alloys
- 2%: copper, copper alloys, other.
Improved Stamping at Dana Parish
One of the jobs at the Dana Corp.'s Parish Div. facility is the manufacture of components for a Ford light-truck frame program. The components are made with 1010 steel; material thick-ness ranges from 0.080 to 0.250 in.
Initially, engineers at the plant set as a goal the elimination of spray lubricant on the presses. Prelubricated stock was determined to be the answer. Early on in production a waxy lubricant was used along with prelubricated stock, but its use caused productivity problems. For one thing, lubricant had to be removed after forming but prior to component welding. Also, excess lubricant on tooling resulted in increases in die changeover time because it was necessary to clean off the lube from the tooling and press area before installing new dies.
And even with the lubricant, there were galling and metal pick up problems with the tooling, which meant that there was significant die maintenance-usually once per shift-and higher than desired scrap rates.
The solution to this problem was the elimination of the spray lubricant and the use of a die coating on critical forming tools.
According to Bernard J. Janoss, program manager at Multi-Arc, Inc. (Rockaway, NJ), which is the source of the physical vapor deposition (PVD) coating selected for the tools, there was a step-by-step methodology developed with team members from both Dana and Multi-Arc.
First up, the tool material was selected. They picked D-2 steel because of its wear resistance, hardenability and toughness. (M-2 and M-4 are also considered possibilities for future requirements.)
PVD coatings don't level inconsistencies in a surface. They follow contours. So the surface condition prior to coating is important. Weld porosity, nicks, scratches, and heat checks are not acceptable. What's more, die forming surfaces that come in direct contact with the part blank need to be diamond polished to a mirror finish. Multi-Arc conducted training for all three shifts of Dana Parish die maintenance personnel on surface requirements.
Also important are heat treatment parameters. It is important that the heat treating be performed so that it is compatible with the coating. All of the dies used in the program are heat treated to have a core hardness of 58-60 Rc.
Finally, the coating is applied. This application uses Multi-Arc Ion Bond 7-24. It is a chromium nitride coating. The coating is said to combine hardness, toughness, low coefficient of friction, and corrosion resistance. The material is applied in a thickness range of from 0.0004 to 0.0005 in. It is deposited with a cathodic arc process.
Briefly, the arc evaporation process involves striking an electric arc under high vacuum. Plasma sources surround the workpiece. A stream of metal ions, electrons, and neutrons is charged from the evaporators; a reactive gas (e.g., nitrogen or a hydrocarbon) is introduced, forming a plasma. The metal and gas ions then deposit on the surface of the workpiece, forming the coating. In this case, the coating is deposited at temperatures between 400 and 450oF. Because of the high energies involved, there is said to be good adhesion and structure of the coating layer.
As a result of using the coating, the sprayed lubricant has been eliminated. Because the chromium nitride eliminates metal pick-up and galling, die polishing has been essentially eliminated: some dies have produced more than 250,000 parts without the need for polishing.
Listen to a couple of people from the plant:
"The performance of the coating has been spectacular," said Charlie Fair, Tooling manager at Dana Parish. Jim Zimmerman, Tool and Die Maintenance, remarked, "In the 17 years I've been here, this coating is the best I have seen."
Helping Build the Beetle
One of the biggest buzzes today in the auto world relates to Volkswagen's new Beetle. This vehicle is being produced in Volkswagen de Mexico's plant in Puebla, Mexico, along with the Golf and Jetta.
Because the automaker need to increase its production from the plant, it contracted with a German company, Umformtechnik Erfurt, a press manufacturer. (Erfurt, Inc., Rolling Meadows, IL, is a subsidiary). The objective was to improve the press room. This included the modernization/refurbishment of five press lines, which consist, in total, of 29 presses, not only Erfurt presses, but also equipment from Clearing, Danly, Schuler, and Weingarten.
The program included the integration of new programmable controllers from Allen-Bradley, retrofitting of feeder systems from ISI, and the integration of quick-die-change systems from Orchid International. One of the goals was to achieve at least a 15-minute die change time and the ability to have changeover from part-to-part occurring in from 15 to 20 minutes. These presses, which are rated at from 825 to 1,323 tons, utilize dies that weigh between 33 and 55 tons.
It's worth noting that some of these presses are vintage. For example, Weingarten presses were built between 1953 and 1957, and a Clearing DF4-1300-156 press was built in 1958. The Weingarten presses will get new major components and be upgraded with hydraulically actuated clutch/brake combinations and Erfurt drawing cushions. The Clearing press will get new majors for its main drive system, gear link unit and link drive mechanism.
As mentioned, Erfurt is a press builder. But it has also established the means to modernize, upgrade, refurbish, recondition, and retrofit presses—its own builds and those of other companies, thereby providing automakers with the means by which they can substantially improve their pressworking operations without necessarily having to buy new equipment. In addition to the job in Mexico, it also recently completed a modernization of a Thyssen/Budd stamping plant in Ludwigsfelde, Germany.
Safer Is Better
When it comes to safety (or any other types of industrial equipment, for that matter), safety is paramount. According to Mouhammad A. Naboulsi, application engineer at Pilz Industrial Electronics (Farmington Hills, MI), the Pilz PSS 3000 programmable safety controller is "the only device of its kind."
The system, which is based on a programmable controller (PLC) platform, utilizes three central processing units. This means triple redundancy in running machine diagnostics and fast cycle times. Microprocessor sources include Motorola, Intel, and Siemens.
Naboulsi explains that safety relays were once the means by which safety for presses was assured. Then people started using PLCs. Typically, he says, companies use 2 PLCs. This redundancy setup is such that one checks the other. But Naboulsi points out that this might not work as well as expected: "If one PLC has a problem, then the other is likely to, too. Both will agree on the same mistake." This is why they use more than one brand of microprocessor in each of the PSS 3000 systems.
During operation of the PSS 3000, input from the press goes into the safety controller through an optocou-pling device. The signals are examined by each of the three processors. If they all agree, then things proceed. If there is a disagreement, then the control initiates a stop loop so that a safe state is assured.
In the event of the problem, the PSS 3000 provides diagnostic information, all the way to indicating where there might be a problem with a wire. This can help get maintenance personnel and minimize equipment downtime.
From an investment standpoint, Naboulsi says that the PSS 3000 is less expensive than a two-PLC setup. Whereas the PSS 3000 would cost on the order of $7,500 for an eccentric or hydraulic press (the price goes down for subsequent safety controllers because the price of the first one includes programming software that can be used by the follow-on units), two PLCs and the attendant hardware and software comes in at around $15,000.
Down in Mexico
To increase its pressworking capabilities at its assembly plant in Silao, Mexico, General Motors decided to take six Danly presses that had been built in the early 1970s, bring them back up to snuff (as in electricals, controls, hydraulics, and pneumatics; and new loaders, unloaders, transfer units, destackers, load tables, and racking), and install them at the Silao site.
It selected the Aftermarket Div. of CNB International Inc. to handle the job. (The Aftermarket Div. is based in Hastings, MI; CNB is headquartered in Buffalo, NY. It may be more familiar to people as the company that produces Clearing Niagara and Bliss presses.)
The CNB Aftermarket personnel served as both the rebuilder and general contractor for the project. The presses-3,800-ton double action tandem; four 500-ton single-action tandem, and one 500-ton single action die tryout units—were disassembled in the U.S., then shipped to a facility in Mexico where the work was done.
There were some fairly significant changes made to the press. For example, CNB engineering developed new moving bolsters for the line presses (two for each press). The bolster on the die tryout press had moved from front to back; it had to be modified to move right to left in order to match the other presses in the line.
Better Progressive Ops
Progressive die operations can be a challenge given the various motions involved in processing a strip into parts. However, a press series (ranging in tonnage from 220 to 1,100) from AIDA-Dayton Technologies Corp. (Dayton, OH) is said to overcome typical problems through improved engineering.
Speaking of the PMX line, Doug Plank, the product market manager, observed, "Production rates can be increased compared to conventional crank and eccentric shaft motions." The PMX employs a link motion design. Plank continued, "When slide velocity for optimum metal forming is reached, the slide returns at a much faster rate. Stampers can expect improved part accuracy and reduced die cost. This is due to the fact that the PMX slide motion minimizes heat and vibration found in dies that are run in conventional crank or eccentric shaft presses."
Historically, stamping operations have been deafening. Fortunately for people who work in them, there are now regulations and requirements—both company- and OSHA-based—that are designed to keep the decibel levels down. On a recent job for Ford Motor, noise minimization on five Clearing-Niagara presses was achieved by the implementation of sound-deadening doors. Specifically, the doors, which are 7-ft, 2-in. high and 17-ft, 7-in. wide were specifically developed by Industrial Acoustics (IAC; Bronx, NY). They are called "Noise-Lock" vertical lift doors and are built right into the frames of the presses. The doors are fitted with display windows. Two of the five feature doors that allow entry into the bolster area by personnel.