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Bending automation: flexibility without tooling.

An automatic bending machine that uses one set of modular tooling to create an infinite number of panel shapes and sizes is truly a "universal" machine. Throw in automatic loading, easy programming, and one-minute automatic tooling changeovers, and you have quite a manufacturing asset.

Introduced in 1977 at EMO, the Salvagnini P4 was announced as the first programmable bending machine to create positive or negative 180-deg bends with varying radii using a single set of universal tooling. Operations that required several press-brake operations and multiple sets of dedicated tooling could be completed in one machine operation. The P4 was so fast, the best turret presses weren't fast enough to feed it, so two years later, Salvagnini developed the S4 punching and shearing machine to feed the P4. When the two were joined together, they formed the first fully integrated, flexible fabricating cell.

Today, the primary US users of the P4 or S4-P4 combination are in the metal-furniture, light-fixture, appliance, refrigeration-equipment, electrical-enclosure, or related contract-manufacturing industries. All use standard machines, despite a wide diversity of end products. Because of sales growth of 30% per year, the Italian company is implementing three satellite manufacturing organizations: here in Hamilton, OH, where the building is already in place, and two joint ventures just beginning in Russia and Japan. Meanwhile, its main facility in Sarego, Italy, continues to expand.

Why build here?

The key incentives for establishing a manufacturing presence in the US, says Tom Slager, vp and general manager, Salvagnini America, are to gain cost reductions from local sourcing, eliminate exchange-rate fluctuations, and reduce lead times from the present ten months to something closer to six months. The firm will assemble machines here by the end of this year, and plans to fully manufacture the S4 punching and shearing machine here in 1992. They have already recruited key manufacturing personnel who are being trained in Italy.

"Local sourcing will enable us to make our pricing more attractive," Slager adds. "Also, by enhancing our technical-support capability here, we will be better able to react to customer needs."

Slager is excited about the potential of building punching machines here and competing with turret-press builders. The new generation S4 will have features and cost advantages to penetrate the standalone punching-machine market. We hope to change people's thinking from using one or two standalone turret punches and a shear to using one standalone S4 machine. With the new design capabilities-larger shear blade, more tooling capacity, faster axis rates, and greater throughput-we have made replacement of standard turret-punch technology even more attractive."

The bending process

In the P4's bending process, the incoming blank is fed into the machine on a belt. To ensure part accuracy, the blank's corner notch is used as the NC reference location. The notch strikes a CNC-positioned locator, and two squaring guides fine-tune its position before being clamped at the blank center by the manipulator which holds it throughout the forming process.

After clamping, the CNC-controlled manipulator moves the part under the universal blank-holder, a compact arrangement of 1/2 die segments and incremental end blocks. The blank-holder rises to allow the manipulator to index the part to the programmed bend location. The blank-holder then lowers to hold the piece in position during the wiping/forming process. The C-shaped lower and upper wiping blades are CNC controlled to provide combinations of up and down bends, including the ability to incrementally bend and form radii.

After each bend, the blank-holder releases its grip to allow the manipulator to index the blank for each additional up or down bend. When all bending operations on a panel side are completed, the blankholder rises to clear the formed part, and the manipulator brings the part out of the forming area to rotate it for forming other sides of the panel or to send the finished part onto an exit conveyor.

All flange lengths are computed from the inside of the panel. Because bends are never gaged from the outside edges, any over or under, or out-of-square material condition appears in the finished panel's outermost flanges.

Machine limits

With everything CNC controlled, including tooling changeovers, the number of bends on a blank end are virtually unlimited. The only requirement is that the last be an up bend so the bottom of the part remains flat for transporting out of the machine (although side-ejection is an option). To clear the wipingblade throat, maximum bend height is limited to 8". For the popular P4 2420 machine, maximum blank length is 88.8" or a blank diagonal of 94.5". The larger P4 3020 handles material to 118" diagonal, 100" long. The largest material thickness that can be formed is 0.118"

One of the machine's key attributes is its precision: linear positioning accuracy of [plus or minus]0.004" (non-accumulative) and angular bend accuracy of 1 deg. Bend angles beyond 120 deg are achieved by a second bending operation, using the blank-holder. Typical cycle times range from 7 bends in 41 sec to 23 bends in 86 sec.

Springback effects may require some trial runs, but the material characteristics are usually predictable enough to hold the 1-deg bend tolerances. Materials can be steel, aluminum, stainless steel, galvanized, vinyl-clad, textured, or prepainted.

Setup automation

Because bending knowledge resides in software, not special die sets, part changeover is based on activating a new part program from computer memory, actuating the machine sequence to automatically group the proper array of die segments, and making any necessary changes in part handling to feed different sized blanks. Changeover times range from 30 to 90 sec.

Because some manufacturers don't need the full setup automation of the P4, a smaller and less-automated TB20 machine is available with tooling elements swung in and out manually. Manual changeovers take 5 min, but machine operation is essentially the same. Bending operations and cycle times on the TB20 are as fully automated as the P4.


All P4 programs are written in inch or metric dimensions, not code, and referenced from final box dimensions. The computer makes all the bend calculations, based on the material parameters. You simply identify desired bend angles, distance between bends, sequences, etc.

Unlike most metalcutting programming, there's no need to be concerned about any specific machine axes (values, positions, feedrates, etc). It's a relatively fast and simple process, geared to the typical operator's abilities. It is also easily transformed from one of several language options to another. On-line self-diagnostics provide continual production reports and ensure maximum up-time.


The P4 has several optional features. An auxiliary unit, actuated by a programmable command, moves special tools under the blankholder. A secondary bending blade creates special indents such as weld tabs. A lateral-discharge option can remove parts that have a final down bend. An NC rotary option manipulates parts to angles other than 90 deg to bend trapezoidal or octagonal shapes. A graphical-programming option displays final part shape based on the definition of the blank and its intended bends, much like a CAD system.

The latest refinements in the P4 include improvements in controls and cycle times and faster axis movements as this hardware has become available.

Cost justification

With the price for the P4 approximately $1 million and the price for the S4-P4 combination ranging from $2.2 to $2.5 million, cost justification can be a major hurdle.

To help people better define the costs and benefits of a jump to this technology, Salvagnini has prepared an evaluation guide. In addition to the general flexibility dividends (reduced inventory, WIP, floorspace, lead times, etc) the benefits from the machine's specific design and accuracy include: reduced scrap in both setup and part runs, increased material utilization, better part management, reduced inventory loss due to handling damage, no waste in separating multiple parts, fewer stock sizes, improved safety, and greatly reduced tooling costs.

The biggest savings are in direct and indirect labor, resulting from the elimination of multiple machines and secondary operations. In one case a single S4-P4 combination eliminated three turret presses, six press brakes, and 18 to 20 operators. Although some payback periods are as short as 8 months, others run to 24 months, and a lot depends on a company's justification math.

Recent applications

A lighting manufacturer knew that to stay in business, it had to be more flexible in creating market-entry products-difficult to do with hard tooling. The company purchased a S4-P4 flexible fabricating system, primarily for its ability to run 800 different parts. As the buyer's design group became more familiar with the system's potential, that number has grown to 1200, including upgrading previously hard-tooled parts to add new features based on the P4's capabilities. This new level of flexibility has enabled the firm to capture market share by being able to quickly develop new products.

A manufacturer of lighting panels was producing a total of 400 different parts and processing 7000 tons of sheet metal per year. They chose an array of four S4-P4 flexible centers and a shearing/blanking center. This system eliminated 43 standalone machine tools and 414 punching and forming tools; and it reduced scrap rate by 50%.

Salvagnini recently sold an S4-P4 machine combination to a company that intends to use it solely for product development. The buyer expects to gain important advantages in market entry-the ability to produce prototypes quickly and make a quick transition to final production.
COPYRIGHT 1991 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1991 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:Sprow, Eugene
Publication:Tooling & Production
Date:Sep 1, 1991
Previous Article:Composites impact on metalworking.
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