Hydraulic Press with Special Die Produces Family of Large Parts

Mayflower Vehicle Systems, Shadyside, OH, is producing three super-sized stampings using one set of adjustable tooling and a versatile, triple-action hydraulic press.

By Donald B. Dobbins, Editor

The parts in question are used on a CAT excavator. One stamping is used on each excavator. The size of the stamping depends on the size of the machine. Located at the lower rear of the cab, it functions as a counterweight to prevent the excavator from tipping over when the bucket is handling a heavy load. As stamped, the parts weigh about 300 lbs, 280 lbs. and 260 lbs., respectively.

At Mayflower Vehicle Systems, Shadyside, OH, Dick Robbins, assistant manufacturing facilitator (left) and Marion Estes, plant manager, look over a 300-lb. stamping destined to become a counterweight assembly for a CAT Excavator. The 1800-ton, triple-action hydraulic press and the adjustable die that produces three different part sizes is visible in the background.

In addition to observing the press, the tooling and one of the first parts produced during tryout, I had the opportunity to learn more about the project by talking to Bruce Whiston, director of Whiston Industries LTD, West Midlands, England, who was intimately involved in the design, construction and tryout of the die, and Marion Estes, project manager at Mayflower's Shadyside facility. (Estes has recently been named plant manager.)

Three Production Sites
Whiston explained that, altogether, three sets of tools have been built to form this part. One set is in Belgium, one set is in Japan, and one set is being used in the United States at Mayflower Vehicle Systems plant in Shadyside, OH. The one built for Mayflower Shadyside is the most complex of the three tooling sets. It is adjustable such that one set of tooling can make three different sized parts. This is accomplished by using inserts in the center of the die. Japan built three sets of dies-- a large one, a medium one and a small one. Belgium made only a large one. They are cutting the parts in two, removing a section and welding them back together to make the different sizes.

According to Estes, officials in Belgium and Japan both said the U.S. stamping operation would not be able to construct one set of tooling that would make all three parts. But, he emphasized, that is because they do not have the right kind of production press capable of doing it.

The presses in Japan tend to be single action whereas the Shadyside press is a triple-action, 1800-ton hydraulic, (see feature "New Hydraulic Press Improves Large Panel Capability," MetalForming, April 1995, pages 49-56). It's the press capability that makes this job possible. To form the part they use what they call equalizers, which are conical-shaped devices that do two jobs. They hold the die together during the stamping operation and they help to equalize pressure to all sections of the stamping.

One of the things that Caterpillar designers in the United States did-- that was not done in Japan or Belgium-- was to modify the engineering design of the stamping to make it more compatible with the drawing process. That was the first step in the project, redesign the stamping. The second step was to produce computer models of the new design. "It is important to note that the three different sized parts produced in Japan, Belgium and the United States are all identical with respect to size," Estes points out. "The only difference is in the production method."

"The next consideration was in design of the tool," Whiston explains. Obviously, it is exposed to very high bursting loads, so material strength is a major specification. There also are vertical walls on the draw so there has to be a design consideration to produce the stamping with a sectionalized die.

"The next consideration is what I call the production marriage," Whiston continues, "which is combining the technology of the tool with the technology of the press-- bringing both technologies together to produce the final result. That's what makes this project special."

Serving the Customer
"The idea to go to one die originated at Caterpillar," Estes explains. "They thought it might be feasible but they had to find a supplier who was capable of producing it. Of course, a single set of tooling was considerably less expensive than three sets of tooling. So, I guess you could say the major consideration on the part of the customer was reduced tooling cost."

How Parts Are Used
Each supplier makes parts for production facilities in its region; i.e., Japan stampings are used by production facilities in Japan, European stampings are used to construct excavators in Europe. Shadyside stampings are used by Caterpillar at production sites in the United States. Stampings produced at the Mayflower Vehicle Systems plant in Shadyside, OH, are shipped to Wisconsin where they are laser trimmed. After that, plates are welded onto the inside of the drawn stamping along with baffles. Cement and scrap steel are used to fill the hollow volume of the counterweight. Finally the completed assembly is painted and installed on the excavator. The weight of the final assembly corresponds to the bucket load of the machine when it is in operation. While the stamping itself weighs slightly more than 300 lb., the final weight of the installed part is much higher.

Production capacity of all three sizes produced at Shadyside add up to a total volume of approximately 2800 parts per year. The stamped part replaces a totally fabricated version that required extensive welding and lengthy production finishing operations. All three sizes are formed using 0.118 in. steel sheet. The stamped part shown in Fig. 1 is the largest of the three parts produced. The largest stamping is 3 m x 1 m. The smaller parts are almost as large and weigh nearly as much in the as-stamped condition.

About the Die
"The actual tonnage involved in forming the part is quite high," Whiston points out. "In addition there are vertical walls on the draw -- because they're required in the finished component. Therefore, the bursting pressure on the sectionalized die had to be considered very seriously. The design that we came up with balances out this pressure by using a cone system (Fig. 2). The cone system resists the forces and ties the tool together. We also use other devices to tie the die sections together, so the cones are not the only method, but we think they are an interesting concept."

This 35-ton die is used to produce three different sized parts from 0.118 in. steel sheet. The insert die shown at the right is positioned and held in place by locator cones. Five-axis machining was needed to produce this tool at Whiston Industries LTD, England.

Whiston reports the manufacture of the tool also proved interesting. Because of the depth of the draw, which is approximately 420 mm, it required five-axis machining capability. And, since tool weight is 35 tons, it required specialized equipment. Tooling production was done at the Whiston Industries facility in England.

The entire design work for the tooling was accomplished using a CAD system. Because of the size of the stamping and the material gage being used, Whiston and Mayflower Vehicle Systems initially produced a reduced-size scale model. While the performance of the scale model die was not an exact reproduction of the full-size part, (they were not able to get the full-size draw beads in the same location as the finished die), it was representative of metal flow and proved useful in finalizing the design of the part as well as the tooling. It also was useful in predicting the final blank size required to form the part.

Marriage to the Press
One of the greatest advantages Mayflower Vehicle Systems has at its Shadyside, OH, plant is the triple- action programmable hydraulic press. "If you tried to use a conventional, single-action machine," Whiston points out, "with the depth of draw on this part and the initial contact tonnage that would be required, there is no mechanical press being built anywhere in the United States or even the world that would produce this draw. So, it's the recent developments in the field of hydraulic presses that allows this part to be produced as a stamping.

"The part has an eight-meter profile, which requires about 500-550 tons of blank-holding pressure. When you look at starting the draw 420 mm up on the stroke, it becomes evident that single-action mechanical presses do not have the necessary energy to make this part. The LVD-manufactured press at Shadyside has more than 700 tons of blank-holding pressure available, which is more than enough to form this part."

Production quantities on these parts are expected to be about 2800 units per year, including all three sizes. This would amount to approximately 700 units produced on a quarterly production schedule. However, at the time of my visit to Mayflower Shadyside, the exact quantities and shipment schedules were yet to be worked out with the customer.

Size changes are done off the press rather than on the press. This maximizes press uptime and also gives die maintenance a better chance to examine the die for dull or worn components. Die maintenance is an extremely important element in the production of this stamped part because, as Estes points out, it does require a class one surface and it is expected to be equal to that you would find on an exterior door panel of an automobile. MF

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