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Technology for productivity - upgrading the press brake, part I.

Technology for productivity-- upgrading the press brake

For longer than many of us care to remember, a controversy has raged over the best way to power a press brake. A loyal, but aging, group of supporters still stands by the mechanical brake believing it offers the best combination of speed and accuracy. Today, a growing number of users are showing a preference for hydraulic brakes, citing exceptional control as their most outstanding virtue. A smaller, but equally devoted, group has clung to the hydramechanical design because it seems to promise the best of both worlds. And, you may even run into a pneumatically powered unit occasionally.

To determine state-of-the-art refinements in each of the three major types, and to learn how press brakes fit into the continuing move to automation and flexible manufacturing, we surveyed a long list of press-brake manufacturers and suppliers of control systems, gaging, and guarding devices. They provided insight along with advice to help you increase the productivity of your bending operations.

Hydraulic is hip

The most commonly mentioned advantages of hydraulic press brakes are constant tonnage through the entire stroke and ease in adjusting stroke depth. In addition, hydraulic brakes have a number of characteristics that make them popular:

Initial cost is normally lower. This is especially true for machines rated at 100 tons and above.

Reduced cost for repairs since hydraulic components are typically less expensive than mechanical ones.

They are normally more compact, requiring less floor space and head room.

The hydraulic bypass (relief valve) minimizes chances of machine damage caused by operator error.

Hydraulic brakes often result in faster production by using CNC to control depth settings for multi-bend parts.

Longer tool life results from ability to preset tonnage.

Greater operator safety stems from having more control over the machine cycle.

In general, there are more manufacturers, models, and types.

Four not three

One builder chided me for referring to three major types of press brakes in the survey questionaire. He commented, there are actually four different types of press brakes: mechanical, hydramechanical, hydraulic, and precision hydraulic. The main advantage a precision hydraulic has over the others is accuracy when air bending.

He estimates that air bending can improve productivity by 80 percent over bottom bending thanks to reduced setup time. Accuracies for each of the four types are listed in Table I.

Bottom bending is used in about 80 percent of US press-brake operations because most users have either mechanical, hydramechanical, or standard hydraulic machines. A precision hydraulic press brake used for air bending can also reduce capital investment for the following reasons:

Air bending requires less tonnage, so you can use a smaller machine.

It requires fewer machines--the part can be made in one handling on one machine instead of passing the part to several machines in a row.

Fewer machines add up to less tooling expense.

Fewer machines mean reduced overhead.

The consensus is that hydraulic press brakes are more versatile and safer to operate than mechanical units. With CNC, brakes can be programmed to produce any degree of bend. Parts often can be completed in one handling, making the CNC hydraulic brake more efficient.

One manufacturer summed it up: It is the ideal machine for companies processing a variety of materials and parts. As metalworkers continue their trend to smaller lot sizes, machine versatility will be the key to productivity.

Mechanical mainstays

Those who prefer hydraulic brakes cite many drawbacks with mechanical machines: too many points of wear creating inaccuracies in positioning; too time consuming to set up; no overload protection; requires skilled operator; not as safe to use; high maintenance; high cost; difficult to adapt CNC and presence sensing; single speed too fast for bending; cannot have bed-referenced stroke control. When not set properly, they can lock up and cause severe damage to the machine.

Others, however, hasten to point out benefits: simpler drive system, no oil filters, valves, etc; only need occasional clutch and brake lining replacements; allows sharper bends; accuracy is inherent; can be overloaded for coining.

Nevertheless, the biggest complaint is that they are difficult to control. But, now Triad Controls Inc, Clinton, PA, says it has developed a system for ram control on mechanical press brakes that enables the ram to be indexed to preset positions automatically. This can permit an operator to feed and remove work-pieces faster. Ram control also can be interfaced with the Triad Superlight V infrared light system to turn the brake into a fast, flexible production machine. Reportedly, this is done without modifying the clutch/brake assembly.

Suppliers of this type of machine seem to agree that mechanical brakes are extremely accurate, have good repeatability because of the mechanical linkage, and tend to be somewhat faster.

Hydramechanical half-breeds

Not everyone agrees on the advantages and disadvantages of hydramechanical press brakes. Among advantages mentioned are:

Lowest priced of all designs.

Fewer electrical components.

Less expensive hydraulic unit/components.

Reduced possibility of damage compared to a mechanical unit because of its hydraulic bypass.

Full tonnage throughout stroke and along the full length (this depends on the basic design, i.e., lever or eccentric).

Disadvantages most often cited include:

Difficult to set for multiple depth bends.

Less accuracy because of clearance in mechanical linkage that deteriorates from wear.

Increased floor space and weight requirements.

Shorter stroke than hydraulic.

More frequent repairs because of the combination of systems.

One manufacturer observes, "Not the best of both types, but a compromise.' Despite the controversy, some conservatives believe the hydramechanical designs provide a number of benefits over straight mechanical or hydraulic types.

Control data

The major accomplishments in machine control during the last two to three years have been in multiaxis CNC, servo valves, and graphics. CNC allows for rapid setup, part recall on reruns, and DNC where parts can be programmed offline and the program downloaded to the brake. A few companies are doing this now, but not many. The future is wide open and almost anything can be done and will be done with the new control systems.

In the years ahead, the most important advancements in brake control will be in three basic areas:

1. Modern press brakes will be able to use information now commonly maintained in the user's host computers. Even today, many control systems have manufacturing, tooling, and part data in memory. Some have DNC capabilities. Two way communication with a host computer makes the press brake a machine that fits comfortably in the factory with a future.

2. Expect adaptive controls on press brakes before too long. These machines will be able to sense material thickness, as well as material yield strength, and adjust ram bottom position to give accurate bends in materials that vary piece to piece, or lot to lot.

3. There will be a continuing trend toward user-friendly controls.

These advancements in control technology are essential to make metal forming on press brakes a realistic fabricating method for tomorrow's manufacturers.

Gaging devices

Today, brakes are available with five, six, or more axes of control. In many applications, being able to control the back gage fingers (or gage bar) left to right, up and down, back and forth, and taper, is an important step forward. In addition, many press brakes can be equipped with material support devices at both the front and back of the machine. These devices, combined with multiaxis gaging, make operating a brake for automatic forming of complex parts practical. The payoff for the user is more accurate gaging of complex parts and substantial material handling improvements.

Many industries are reducing their inventory and making production runs shorter. When production lots are small, setup time becomes the most critical factor in productivity. Manually setting gages for short runs will increase piece cost dramatically. CNC gaging systems decrease setup time to almost zero.

Moreover, because of new, more flexible electronic-hydraulic press brake designs, a wider range of jobs can be run. Additional control capability will ultimately allow complete automation of a brake.


Controls on new machines are being designed to interface with advanced guarding systems. Light curtains will be commonplace and eventually control automatic cycling of the brake. "Smarter' controls will make guarding easier to work with. CNC gaging systems themselves are a big safety feature because they eliminate manual adjustments, thereby keeping the operator away from the ram area.

Ultimately, the best guarding system is to design the worker out of the work by using robots and other material handling equipment.

Are robots really coming?

Some machine builders believe that robotics will play a part eventually; however, when this will occur is hard to predict and will be based on consumer demand and technology. Press brakes are a very difficult application for robots.

One manufacturer says that robotics will be introduced to the process in 1986 and will play a major role in press-brake operations. Robots and other material-handling devices will be used to increase productivity and help integrate a complete fabrication cell.

Then there are the disbelievers. Some say robotics will never play a major role because they are not as productive as an operator. The brake, they say, is best suited to short run jobs, where reprogramming a robot may not be practical.


Many industry observers see ground tooling as the proper type for highly accurate press work. One builder remarks, "American tooling is inferior in design and production--the ram pushes on the shoulder of the punch. European tooling (hardened and ground) is more accurate, stays accurate longer, and the ram pushes on the tang. Sectional tooling is tooling of the future.'

Another points out, "Using air bending with CNC gaging will eliminate the need for special tooling. Standardization is the trend.'

A third says, "Availability of precision (hardened and ground) tooling is lacking, which impacts setup speed (e.g., accuracy between the centerline of the die and the edge on the tongue so alignment can be maintained). Since the user has made do, most companies have not addressed this problem, but it will become more important to take advantage of the control available in the brake.'

Where is it all going?

Technical breakthroughs down the line for press-brake operations will be in adaptive forming, robotics, and tool changers. CAD/CAM with robotics will be available in 1986.

Tim Adams, VP at Pacific Press & Shear Corp, says, "We think press-brake operations are in the midst of a technical breakthrough today. One example is our Fabri-Former III Hammerle three-point bending machine. We feel a hydraulic brake, with ground segmented tooling, hydraulic clamping, sophisticated material handling and gaging, deflection compensation, and the three-point bending method can provide sheet-metal fabricators with paybacks on their investment in less than six months.

"This can be accomplished with accuracies measured in minutes rather than in degrees. Most fabricators are just now beginning to see the true payback they can obtain from modern press-brake technology. We see an exciting time ahead in the practical application of technology that was only a gleam in a designer's eyes three years ago.'


The movement to CAD/CAM and eventually computer integrated manufacturing (CIM) is not affecting application of brakes to any great extent. Some users want to download data from their main-frame or process-control computers, but this is not being done very often. Off-line programming on tape is sometimes used to avoid MDI at the machine.

Nevertheless, press brakes fit in nicely because they are versatile and can have sophisticated controls.

Sheet-metal fabrication will always play a major role in many manufacturing facilities. Press brakes will have a place in the factory with a future as part of flexible manufacturing cells, but not in the near term. Many problems will have to be overcome in the areas of material variations (thickness and tensile) and part shape (material handling).

Next month we will present specifications on a cross section of available press brakes, associated control systems, gaging devices, and guarding systems.

Table: 1

Photo: This LVD brake features CNC control and automatic material handling to boost accuracy and productivity.

Photo: CNC front and back gages can cut setup time to almost nothing compared to manual setting of stops for each bend.

Photo: Light curtains can be tied to the brake control system to provide safe, reliable operation.

Photo: CNC press-brake forming systems, such as this Wysong RT-4, feature up to 10-axis control and can reduce setup by as much as 80 percent.

Photo: Automatic front gages are useful when a workpiece has to be toleranced from an edge that cannot be referenced on a backgage because of part shape. This Automec unit is available with 12 and 24 travel and extension bars to handle larger workpieces.

Photo: These custom-designed, 100-ton mechanical press brakes were built by Heim Corp. They include a special shut height and an 8 stroke. They demonstrate the versatility with which press brakes can be adapted to special jobs.

Photo: Press brakes are often used for special operations. This Niagara Model 1B-90-8-10 unit is used to punch and notch steel strip prior to rollforming.

Photo: Light curtains offer a method of safeguarding the point of operation on press brakes. This Rockford system is for press brakes equipped with a mechanical friction clutch.
COPYRIGHT 1985 Nelson Publishing
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 1985 Gale, Cengage Learning. All rights reserved.

Article Details
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Author:Dobbins, Donald B.
Publication:Tooling & Production
Date:Jun 1, 1985
Previous Article:What's rough about surface finish?
Next Article:"Technology in focus" - a Vision '85 report.

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