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Tool Design, The Key to Press Brake Automation

There’s more to effective press brake automation than robots and programs. You have to start with a tool concept that doesn’t require a human to adjust and compensate for the limitations of a mindless machine.

Most of the press brake builders who offer tool loading/unloading automation have adopted a tool design that was pioneered by Wila in the early ‘90s, either by using actual Wila tools or by adapting some ideas from their design. The key Wila patent has recently expired, so there are some competitors who have picked up on some parts of it.

The basic design wasn’t developed just for automation. Called “New Standard,” it was intended to improve features of both the American and European press brake tool designs. It provided consistently accurate tool location and clamping, boosting productivity by reliably setting tools without the need for adjustments. It lines tools up accurately, simplifying the loading of tools in segments, which requires great consistency in vertical and horizontal alignment of adjacent tools. An additional bonus for automation, it allows for vertical loading, with a “safety button” on tools that weigh up to 28 lbs., allowing robots or inline loaders to load tools in any sequence. In the years since the early ‘90s, they’ve added features that further improve automation efficiency.

“Looking at it now, taking a step back 20 years when we first came out with the New Standard tooling system, I think the company did a pretty good job of thinking ahead and developing a tool system that would lend itself to automation down the road,” said Gunter Glocker, Pres. of Wila USA. Wila’s home base is in the Netherlands. “Europe has been the forerunner in applying automation, because of their labor costs and expenses.”

The system got a boost in the late ‘90s and especially in the early 2000s, says Glocker, because the speed of lasers put increasing pressure on the forming end of fabricating. Press brakes, which are extremely versatile but not inherently fast, were struggling to keep up with the pace. This gave a big boost to automation, both on the tool-handling side and the work-handling side.

Basic design elements

To get it off to a good start, Wila began with very high machining accuracy on the punches, dies and the tool slots in the upper and lower clamping systems (manual, hydraulic, or pneumatic). The tool holders also have adjustments in the X and Y directions, which allow for perfect alignment of the bending line to the backgauge (X), and for parallelism between the punch and die (Y). They’re finished with creep-feed grinding to an accuracy of 0.0004 in. The accuracy speeds up manual tool alignment; with automation, it’s the basis for repeatable alignment with robots and other loaders that work, essentially, blind. Highly precise finishing has become a feature of competing tool systems, as well, since the advantages sparked customer demand.

The design of the tool tang is the most visible difference. The tall, wide tang is more stable than earlier designs, especially under heavy loads. The difference is most apparent when bending thick stock. Today’s high-strength steels also impose a higher load on bending.

Amada, among others, uses a full-fledged, multi-axis robot both to load tools and to manipulate workpieces. Handling the tools is easier, as with this hole-gripper.

Anyone familiar with the principles of precision locating will recognize how the New Standard tools have applied a key principle: locate against the absolute minimum number of surfaces. In other words, when you want to locate a tool as accurately as you can, resisting movement up-and-down and front-to-back, use only two surfaces if possible. This is carried to extremes in tools like master gages, where, for example, diamond-shaped dowels locate within a round hole. The dowels only touch the inside of the hole along two lines, which can be made more accurately than the clearance for a round dowel in a round hole. Pairs of holes and dowels locate in two directions – typically, in two perpendicular axes. The downside is that those lines of contact can’t absorb any significant load, and they are vulnerable to wear.

The New Standard tools get around that by locating on two large, flat surfaces – the inside top of the tool clamp and, typically, a flat front inside face of the clamp. The two surfaces are at 90 deg. to each other. To make the whole connection between tool tang and holder firm and stable, force is applied at an angle, pressing the tool tang against both locating surfaces at once. The force is applied by cone-ended pins that are driven against cone-shaped sockets in the tool tangs. The pins don’t bottom in the holes, so the locating principle is maintained. Avoiding additional clamping points avoids the inherent inaccuracy of locating multiple surfaces or clamps. The idea is easier to see than to describe; it’s shown in the drawing on page 28. Note that the tapered sockets are on both sides of the tool, allowing it to be reversed when using goose-neck tools, for example, facing either way.

When you have to locate tools accurately while dealing with a lot of force, two surfaces are the next best thing to two lines, and that’s exactly how the New Standard tools are built. But force, particularly the pounding that press brake tools take in service, presents another repeatability challenge: If you pound steel, even good tool steel, it’s going to get peened. When you slide tools along the clamping system day after day, you’re going to get wear. You may not be able to see it, but we’re talking about accuracies measured in tenths, and it’s going to catch up with you. The same peening and wear problem applies to the tool slots in the clamping system.

Heat-treating is in order.But if you through-harden a punch, it will be brittle and it is likely to break if it isn’t treated exactly right. If you apply a thin surface treatment, it may not hold up.

LVD Strippit’s straight-line tool loader is a departure from the usual multi-axis robot, but straight-line loaders are simpler and, often, faster.

Wila went through several development stages to get it right:

“When we first came out with the New Standard system back in the 1990’s, we through-hardened the tools, which made them very hard, but also made them very brittle. They were around 56 to 60 Rc all the way through. We quickly realized this isn’t good, because if a customer over-tonnages it or over-strokes it, it could explode,” said Glocker.

“We stopped that after a few months. In the early days, we flame-hardened the tools. Then we went to a laser hardening process, which at the time was very good and the best that was out there. But with laser hardening, we could only go to a depth of about a millimeter or so, about 0.040 in. That wasn’t enough for some of the high-tensile workpiece materials and abrasive materials, or cut edges after laser-cutting a sheet.

“So we came up with this flash induction hardening in a CNC control process, called CNC-Deephardening. We worked on it for about two to three years to figure out the right temperatures and speeds for all the different tool styles. We worked on getting consistent hardness and the depth of hardness that we needed without distorting the tool. Having gotten this worked out, we used the same approach to harden the tool slots of our clamping and crowning systems, to allow you to slide tools back and forth all day without wearing out the slot.” The hardness depth with this process runs around 4mm (0.157 in.). It establishes the right combination of wear life and toughness, says Wila.

The New Standard tool, showing the clamping features, the tang design, and the TIPS ID tag and communications board. A TIPS tag is built into each tool segment and the New Standard Premium Clamping Systems can be equipped with TIPS electronic communication boards. TIPS identifies the correct tool and all critical tool information, and monitors the exact position of the tools in the clamping system or storage rack.

A platform for automation

So that’s the foundation for effective, long-lived press brake automation. As we said earlier, these concepts have been adopted and modified by other tool makers, and by the machine tool builders who either use Wila tools or who incorporate some of the ideas into their own. And the variety of automation schemes they’ve built upon this beginning is broad. Fab Shop elaborates on the various systems from time to time, but for now, here is the gamut, and some of the further refinements Wila has added to enable various schemes for automation.

Trumpf, for example, adopted the New Standard system soon after it came out. “We had a joint R&D effort with them on automation,” said Glocker. “They wanted to have some additional capabilities, introducing intelligence into the clamping and the tooling to use with their bending cell. So we started a co-engineering project with them, giving them a three year head start as our launching customer. This resulted in TIPS, which stands for ‘Tool Identification and Positioning System.’”

Close spacing of clamping pins in the V-Lock groove automatically clamp, seat, and align tool segments, and prevent tool segments from being pulled out of the tool holder or knocked out of position by the sheet part.

TIPS consists of a passive electronic chip on the tool and electronics in the clamping system that identifies the tool location in the machine (see drawing on page 28). It has an interface to the press brake controller, which allows the system to identify tools for loading onto the machine, noting their location, and otherwise keeping track of tools in the automated process. There is more to it — it can perform several logic-and-mechanical functions in automating tool handling.

Trumpf uses the Wila system’s hydraulic clamping, except on their small electric brakes, which use a pneumatic system with a self-locking safety feature, co-developed with Wila. In general, most automated systems are using hydraulic clamping, but the pneumatic system is “lightning fast,” says Glocker, and he suggests that we will see more of it from other builders.

The pneumatic system was tricky to develop, because it normally involves high pressure and, potentially, a lot of sealing surfaces. Wila’s clamping system, however, is designed in such a way that it uses low workshop pressure and smart mechanical levers to connect cylinder piston and clamping pins. These clamping pins are spaced very close to each other — within 10mm (0.40 in.) of each other, to allow the use of small tools segments and to get uniform, reliable pressure clamping on the tools. It can use 15mm (0.59 in.)-wide tool segments and the pins will put individual pressure on each segment, locking it into position.

Trumpf’s robot on the TrueBend cell takes advantage of a robot’s versatility to load tools from a simple storage rack.

Loading tools, at this time, is handled mostly by multi-axis robots. LVD Strippit uses an inline system rather than a robot, conceptually similar to gantry loaders on lathes and mills, but actuated by the back gauge. Tool storage on these machines is behind the working area of the brake, providing a lot of storage space for tools. Salvagnini’s current system uses conventional punches but avoids changing dies by using a variable-opening, full-length die. Punches on their system are slid along the upper clamp, avoiding the need for frequent tool changes.

The issue of robots versus straight-line loaders has some interesting parallels with chip-making machine tools. A robot is a complex machine for simple loading and unloading, but on press brakes, unlike, say, CNC lathes, it can do double-duty and take full advantage of all the robot axes at the same time. This is where the legacy of press brakes’ manual origins leads to a difference from chip-making machines: All of the manipulation required to load, bend, and reposition a workpiece has not, so far, succumbed to simple, straight-line loading. It needs a stand-in for a human: a full-blown robot. But the efficiency of the whole system can be better with an automated press brake, because the robot can do double-duty, loading tools as well as manipulating work. Amada, among others, has some revealing demonstrations they display at trade shows, in which the robot practically does flips manipulating even large workpieces; changes its gripper; and then performs the straight-line task of loading and unloading tools.

This video shows Wila’s tool automation features, including this simple tool gripper that ‘spears’ tools through a drilled hole.

Wila has been involved in many of these projects, including the development of simple grippers for picking up and handling tools. The basic system is based on a hole drilled through the tool, which the robot gripper “spears” to pick the tool up from a rack or a carousel. It’s simple and effective.

The state of the art includes tool identification (like the TIPS system) to allow random-location storage of tools and avoids the need to re-teach tool positions after a distortion or loss of information; a robot or other loader/unloader; a tool and clamping system that allows consistent loading without shims; and some kind of coordination with a crowning system, also to avoid shimming the tools. It goes without mentioning that consistent tool length is also important, although, conceptually, it would be possible to gage and compensate for that with the automation – at additional cost.

Glocker knows about some new developments, from several builders, that he just can’t tell us about yet. We’re looking forward to seeing them. It sounds like there will be much more to it than just standing a robot in front of a press brake.

Wila USA