Hydraulic Presses

Keeping a press ram parallel

By Russ Olexa

March 2010 - When a press squeezes anything, whether it’s steel or another material, between the die and punch, things can go wrong quickly.

One of the issues that can arise is off-center loading caused when the stamped material needs different pressures across the press bed for forming. This can twist the ram off parallel and damage the press and/or the tooling.

Beckwood Press Co., Fenton, Mo., has developed a new way of making sure its hydraulic press’ ram stays parallel. This is done through a new technology the company developed called active leveling control (ALC), which provides precise four-axis, self-leveling control over the ram’s parallelism and position.

Historically, keeping a stamping press’ ram properly aligned has been a problem for both hydraulic and mechanical presses, says Darrell Harrelson, lead applications sales engineer at Beckwood.

"Not every application can be perfectly center loaded beneath the ram," he says. "If you don’t have a center-loaded application, you want to rely on whatever mechanical method the press is using to maintain the ram’s parallelism to stop undue stress on the press’ components and tooling.

"For instance, let’s say you’re punching holes and using staggered punches to keep the overall tonnage down," he continues. "If all the tall punched holes are on the left side of the die and all the short ones on the right, the left side will make contact first and meet resistance while the right side hasn’t met any resistance yet. So the right side will have a tendency to travel down faster than the left side."

To overcome this improper bed loading, Beckwood worked with Delta Computer Systems Inc., Battle Ground, Wash., a company that makes hydraulic motion controllers.

"We worked with them on some single-cylinder applications for stamping to provide either force or positional control," says Harrelson. "Then we developed a system using a multi-axis controller and synchronized ram cylinders."

Each of the hydraulic cylinders is fitted with its own proportional, high-performance, directional-control valves and linear transducer controlled by a multi-axis hydraulic-synchronization control module.

The closed-loop controller can provide a desired ram position to within ±0.001 in. and parallelism control of ±0.002 in. corner to corner.

Information is sent to the motion controller that tells the proportional valves to open or close to maintain the ram’s parallel position, says Harrelson.

Using positioning devices, the software senses all four corners of the press, and if one begins to fall behind, its proportional valve will compensate to correct the ram’s parallelism.

"ALC can be used for any stamping application, such as progressive die applications, and where there’s off-center loading," says Michael Riehn, director of sales and marketing at Beckwood. "Companies are able to consolidate processes from multiple presses into one. Our ALC will monitor all four corners of the press to keep the ram parallel. Small dies can be safely run on a large-bed ALC press, even allowing for the smaller dies to be moved to the front of the press for better ergonomics. ALC eliminates ram cocking that could happen on these difficult applications, which can save the life of the press and die."

  Riehn also mentions that ALC can decrease press part breakthrough and reverse shock when stamping blanks. Additionally, a company can use the entire press bed for easier loading and unloading.

The largest machine Beckwood makes using this system is a 1,000-ton hydraulic stamping press, according to Harrelson.

"We can scale this system down to lower tonnages too," he says. "However, we use it on larger-bed systems such as ones that are 8 ft. or wider. Obviously, the bigger the bed, the more chance there is for off-center loading."

Another advantage with an ALC press is that a customer has the ability to produce a precision-dimensioned part, according to Harrelson.

This was needed by a Beckwood customer that makes deep-drawn gas tank parts for motorcycles.

The tanks are stamped in halves, and when they were done by another vendor, they had a lot of variation in them because they were stamped using a traditional hydraulic press.

Part repeatability was substandard, and each one was out of tolerance. Thus, the company was forced to match these gas tank parts together and manually rework them to get them to match up before welding them together.

With the Beckwood ALC press, the parts are all the same dimension, eliminating secondary rework.

It’s a closed case
Although another of Beckwood’s customers, Chicago-based Platt Luggage Inc., doesn’t use an ALC hydraulic press for traditional metalworking, the company needed a press that would keep the ram perfectly parallel for its unusual application: Platt purchased a Beckwood hydraulic press with ALC to cut foam inserts for its carrying cases. This was presenting challenges for the company when traditional metalworking presses were used.

"Platt Luggage focuses on cases for business and industry and moved away from leather luggage into plastic and aluminum cases," says Daniel Platt, owner and great-grandson of the company’s founder. "We make cases that are formed primarily out of thermoformed plastic using aluminum rims and hardware. We also produce tool, display, sample, medical, military and OEM cases.

"In the past, we would make the cases, and then if we needed foam for the inside of them, we would have a foam company make them," he continues. "Today, we get the large foam planks and buns and do all of our foam production in-house. We don’t make the foam itself--we purchase the raw, bulk foam and process it."

For high-volume jobs, the company uses hydraulic presses to cut custom pieces of foam. Primarily, Platt uses the stamping press to make pick-and-pluck foam.

This foam is diced into 0.5-in. or 1-in. squares, allowing end users to pull pieces out of the cases for equipment like a camera or meter. The foam helps prevent these products from being damaged.

Can’t cut it
To produce this foam, Platt uses steel-rule dies in various sizes and depths. The company has specific dies for each type of case, necessitating hundreds of them. Platt produces cases from 6 in. by 4 in. up to 33 in. by 23 in. Therefore, the company needs die-foam cutters for all of these sizes.

  "After scoring the foam, if we have one corner that didn’t quite get cut all the way through, we could have foam that can’t be pulled out by the customer," says Platt. "So the press has to give us even pressure in the stamping phase and cut all the way through the foam. If we send out a case and the foam is defective, it ruins its entire functionality."

But this was the problem. Platt says the company originally used traditional stamping presses to cut the foam, but it found that they didn’t do a good job. Platt needed a unique press to solve the problem. Platt purchased a Beckwood press for several reasons.

"One was the ALC the company offered because we need the press’ ram to be completely parallel and give the same level of pressure on all four corners," he says.

When the company began looking for a solution for this, Platt says, "We didn’t see too many other press companies that were specifically pushing this type of feature."

Getting squeezed
In Platt’s press, the steel-rule die is mounted on the bolster, and the foam is pushed into the die with the ram. Because foam doesn’t react like steel, a hydraulic press gives the company more control over the pressing sequence.

Once it’s compressed, the die has to stay down until the foam fully expands again from being squeezed during the press stroke.

Beckwood’s ALC hydraulic press lets the company handle its own foam production, which has many advantages, according to Platt.

"We haven’t had one complaint on the quality of the cut foam leaving the facility," he says. "We’ve been very happy with the press." FFJ

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