Bells and whistles won't make good parts
January 14, 2010
Expensive options on a press brake won't guarantee knowledge transfer from a veteran press brake operator to a shop floor rookie. For knowledge transfer to occur, a shop needs experienced workers that can communicate and a younger work force eager to learn because they see a future in metal fabricating.
That controller is no guarantee that press brake operators know the reason a certain tool is required for a bending job. That comes only with successful knowledge transfer from experienced and well-trained operators. Photo courtesy of Cassandra Birocco, CB Group/ Seconn Fabrication, Waterford, Conn.
Quite a bit can be said for state-of-the-art press brakes; a lot can be said for the tried-and-true too.
Getting the most from your press brake, however, is not about the type of machine, method of forming, or tooling—it's about having a common understanding of the press brake throughout your organization and using that information properly. It's having a common language, one that is unique and trade-specific, to establish communication among all levels of your operation.
This type of communication allows for the free flow of information among customers, engineering, the shop floor, and back again, bringing understanding to everyone.
In the past when new employees joined a shop, the first course of business was to get them trained. Training was, in most cases, from the ground up, allowing the new employees to become skilled and productive craftspeople over time.
However, when it came to the training on the press brakes, the process seemed to hit a wall. Press brakes seemed to be run not with skill or knowledge, but black magic—or at least some other form of secret knowledge known only to a select few and never to be shared with the masses.
Consider the following interaction between a seasoned veteran and the new kid on the block:
"Which tools should I use to bend this part?"
"The 1/2 inch V-die and that 1/16 radius gooseneck punch."
"Why those tools?"
"Because they work."
"Yeah, but why?"
"Because they work. Now get the tools and make some parts!"
The reluctance of old-timers to share this "sacred knowledge" has always been considered their way of protecting their jobs and positions from the younger bucks. In reality, though, most of the old-timers are more than happy to share their knowledge with the less experienced. So why did that sharing stop at "use this or that tool"?
It's not because they didn't want to share the knowledge; it's that they really had no idea why it worked or how to explain it. And they didn't know how it worked because they learned it the same way—with no explanation or through trial and error.
Today that problem seems to have gotten worse. Regardless of the press brake's vintage, fewer and fewer people are staying in the trade long enough to learn the machine, and those with experience are leaving in droves, with no one left to replace them.
How many of your employees remember what it was like to work in a precision sheet metal shop 25 or 30 years ago? Could they lay out a complex part without CAD/ CAM?
Where did that knowledge go? Things as simple as using a radius gauge or reading a vernier scale are uncommon now. How are we going to get the most out of our equipment when the old knowledge is disappearing?
The functions on a new state-of-the-art controller are meaningless if only a few people understand how the function is to be applied (see Figure 1). A good example of that is dwell. On a press brake, it means pausing at the bottom of the stroke, allowing enough time for the machine to come to full pressure while allowing the plastic or permanent deformation to set in the material. Most operators don't know when it makes sense to apply dwell and why dwell needs to be applied at all.
"Now just wait a minute," you're thinking. "How can that be? Even if I don't have a newer press brake with CAD/CAM or precision-ground tools, it's not rocket science ... it's metal boxes. Do we really still need all that expensive skilled help at every level of the operation? The equipment salesperson convinced me I wouldn't really need them anymore."
"Our engineers have taken a six-month course in CAD/CAM at the community college and they're working out OK. And the operators just need to call up the right programs and run parts, right?"
In some ways, those statements are correct, but what if your operators understood what those controller functions really meant? What if your engineers truly understood the different processes involved in forming?
This lack of understanding at all levels in the sheet metalworking trade and the inability of almost everyone to communicate trade-specific information effectively are limiting our bottom lines.
So, where does that leave us? Right back where we started: "It just works, that's why. Now download the program and run the parts."
Twenty or 30 years ago, no one made their way into an engineering position without first having served many years on the shop floor. The general knowledge required just to work in the trade was greater then, and it didn't include management skills.
Time was that the production of a sheet metal part would require the sheet metal mechanic or his apprentice (we didn't have "operators" then) to do everything, including laying out the part, designing complicated corner notches, punching and notching one hole or corner at a time, and forming.
These seasoned mechanics may not have been able to communicate why something was formed or notched a certain way, but they knew with certainty what would happen and could use that information to benefit the manufacturing process from layout to completion. That certainty is uncommon today.
Of course in those days, sheet metal projects were somewhat less complicated than today, mostly because everything was coined or bottom-bent, stamping the inside radius. Today we air form, and as we all know, if the radius isn't stamped, the inside radius is no longer predictable or assured. Or is it? (See sidebar "Bottoming, Air Forming, and the Inside Radius.")
So you have a situation where seasoned mechanics that knew what was happening during the metal bending process are retiring at an incredible rate and where new methods of bending in the hands of new operators are not as repeatable as yesterday's metal bending efforts. This only underscores the need for across-the-board communication, and to accomplish this a common language in the shop is needed.
Can your people determine what's going on? Can they communicate that knowledge effectively? Is your design consistent with method?
It's communication that bridges the gap between old and new, and a common language is the starting point. Get your employees some professional training. Sit your engineers, design staff, upper managers, middle managers, and your best lead operators down at a table where they can learn to communicate in a common language.
What does it mean to communicate in a common language? It means everyone understands what's being done in the shop, how to perform those tasks, and what resources are available. You might begin with:
While upper managers don't need to be an expert in every aspect of the business to succeed, they, too, must understand the common language and have a good grasp of how each piece of equipment works.
In general, one skilled operator can do the same volume of work as five "warm-body" operators. So for the same amount of product, you could have:
It's knowledge that makes skilled operators so efficient, and their ability to apply that knowledge and produce correctly designed and engineered parts makes them worth the money.
With only a few seasoned veterans left to pass on the knowledge, and even fewer apprentices to pass it on to, who will use our equipment efficiently now and in the future?
To bridge the gap between old and new, we need on one side of the river a solid bank of knowledge and the ability to communicate it; on the other side we need the solid footing of people who can see a future in that precision sheet metal industry and are willing to learn because of it.
Old equipment or new, latest tooling or not, making sure your equipment is used efficiently requires leadership from you. Contact your local trade organization and get your people some professional training. Buy them the reference materials, books, and software they need. Include management in that training. Make sure they all meet and learn to communicate in a common language.
When all levels receive training and speak the common language of the trade, they will understand how the processes work, and the "black magic" aspect of press brake operation will disappear.
How is air forming different from bottoming or coining? It is different in one big way—the way in which the bend radius is achieved.
Every time the die opening changes, so does the inside bend radius of the part being bent. Use the wrong radius, and the bend deductions won't work; the part will be either too big or too small.
Depending on the tensile strength of a particular material, you can find a consistent inside radius quickly for use in flat-part development equations. This phenomenon is referred to as the 20 percent rule because in 304 stainless steel, the resulting air-formed inside bend radii will equal 20 percent of the tool opening.
Some common percentages are:
304 stainless = 20-22 percent
Mild cold-rolled steel = 15-17 percent
H32 series aluminum = 14-16 percent
Hot-rolled pickled and oiled (HRPO) = 12-14 percent
To determine an accurate percentage for most material types, reference your material specifications book or the Internet and compare the tensile and yield to a baseline of 60,000 tensile mild cold-rolled steel. For example, if the new value is 60,000, the percentage will be 15 to 17 percent, and if the tensile is 120,000, the percentage will be 30. These percentages are only estimations, but they can help you understand how to arrive at the appropriate bend radii.
Whether you're using bottoming or air forming, and regardless of whether your press brake is old or new, your engineers need to know which method and tools are to be employed. And unless you have special tools, any bends other than 90 degrees are, by default, air-formed. Therefore, it's conceivable that some parts will have a combination of bends that are air-formed and bottom-bent with the same tool set. Depending on the operator, all the bends may be air-formed.
By the same token, an operator on the floor needs to know how to match radii and tool sets with the desired results.