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Gary Zunker recalls working with a company that moved a 30,000-pound die with a 25,000-pound-capacity forklift. Representatives from Toyota toured the facility, saw this, pointed out the safety hazard and left.
Soon after, the company had a 30K-cap die cart on the floor.
With the current state of the stamping industry, quick die change has transformed from a goal on the horizon to a necessity for a company's survival. Many contend that without some form of quick-die-change program, implementing lean can be a near impossibility. Small lot sizes and inventories require frequent, quick changeovers, and a press or a press line can no longer afford to shut down for hours for die changes.
"The goal should be to run as many dies on one press for as many hours as you can" while, in the spirit of lean, still maintaining low inventories and satisfying customer demand, says Zunker, president of Lightning Time Savers, a Nicholasville, Ky.-based consulting firm specializing in QDC.
According to Zunker, standardization often represents the first major hurdle to moving a QDC program forward. Why? "It costs money." That's a big hurdle, considering the industry's razor-thin margins and a hyper-competitive environment. Shops avoid spending money like the plague.
But not as much money is involved as many think, he says. Standardizing clamping, purchasing sub-plates and changing layouts to include organized pre-staging areas do require investment. But these are miniscule when compared with the massive automated die-changing systems found at many OEMs.
In short, QDC isn't really that complicated. A relatively small investment can transform a die change from hours to less than 30 minutes. "Quick die change is nothing more than being organized and studying the changeover times, then identifying the method and hardware improvement," Zunker explains. "And because it is so competitive, you need to do it with minimum cost."
PLANNING
Tooling differentiation can create major hindrances for QDC implementation, particularly since most involve some kind of retrofit. "You find everyone does things a little differently [on the press floor], even within the same organization," says Ron Demonet, vice president of system sales at Fenton, Mich.-based Atlas Technologies, "from different presses, different shut heights to different-sized bolsters, different heights of bolsters, to different ways to clamp the die; you name it, everything is different," he says. A typical stand-alone press might have 10 different dies, he adds, all with "different clamping locations and different heights, so it can be difficult to get a quick-die-change in there."
Working from this, the first step to QDC requires shops take stock of exactly what they have, as far as their press capability and shut heights, as well as a detailed catalog of all dies. This, Demonet adds, requires a cross-functional team involving everyone from operators and die setters to upper management.
"Often, we see companies install a die-change system, then run into either a new die coming in they didn't plan on, or one they didn't account for, and end up running that special die on a separate press," Demonet explains. "That really defeats the purpose of the system. Planning is a huge part of approaching QDC. Without it and you'll find you've wasted a lot of money."
Besides taking stock, the group must define the company's goals. In essence, how quick does quick-die change really need to be? The state-of-the-art systems at automotive OEMs have whittled down die change to two minutes or less, Demonet says. "They've implemented sophisticated systems that are totally programmable," he adds. "It's a major commitment. The higher the level of automation, the higher the price tag. For some, it has paid off."
But, Zunker adds, it has not paid off for all. "I believe in simplicity." Many plants have had a goal of eliminating labor out of the process. That, he says, has created an almost "tunnel vision" mentality with the goal of eliminating labor at all costs—a statement that defies logic. Sophisticated die storage and retrieval systems require immense capital expenditures, along with a budget for a maintenance staff if the systems should happen to go down. "For handling dies, automation is a great thing," Zunker says, "yet only if it can be economically justified."
TOOLING AND PRESS STANDARDIZATION
One simpler solution lies in integrating sub-plates, flat plates roughly the same size as the die bolster. Like a tool holder in a milling center, sub-plates on a stamping press ensure the press "sees" one standard size and replaces the array of various clamps different dies may have. This way, all dies can be put in and clamped down in all presses the same way every time. The sub-plate could slide in using side guides and locating pins or, if available on the press, with hydraulic clamping.
According to Demonet, attaching the dies to the sub-plate happens offline during production, "so it doesn't affect the die-change time at all," Demonet says.
If a die takes up every bit of a subplate, shops can modify the die shoe itself, performing cutouts on the die shoes, installing "ears" that fit standard clamping and adding V-notches for locating the die on the subplate.
To standardize shut heights, some use risers, either on the top or bottom, depending on where the material pass line needs to go. If their presses have the capability, others integrate motorized, programmable shut-height control, "so the press adjusts to the incoming die automatically," Demonet says, adding that the shut-height measurement is "a recipe that goes with the die, so to speak."
On the press itself, "the first thing you need to do is integrate T slots and get rid of the drilled and tapped holes" that traditionally hold the die, Zunker explains. "They're dinosaurs. It takes three times as long to clamp a die with drilled and tapped holes." Unused holes also require plugging during each change-out, to avoid getting dirt and scrap in them during operation. "That's another complete waste of time," he says.
Also note, says Zunker, that traditional clamping using drill-and-tap holes requires bolts to be lined up with a clamp or U piece on the die, "and then you have to thread it 15 or 25 turns to bolt or unbolt the dies." With a T slot, "you slide the die in, turn the clamps to a half quarter turn, and you're done," he says.
Standard die location is also a must. Among various methods, the most common involve using a combination of U or V grooves in the die shoe and two pins in the press bolster. "It's the most accurate and probably the best system out there," Zunker explains.
All aspects of die loading and unloading should be standard, "from how you grab the die and locate it in the press, to docking it at the press, to the press shut height, and docking it at the rack," Zunker says.
Also consider a press' utility connectors, says Demonet. Standardizing a press' utility connections—from those controlling die sensors, to pneumatics and hydraulics—speeds the setup process immensely. Once the die is changed, a setup person can, with the right equipment, engage all the utility connections at once. It's a relatively small time savings, but over many setups, that time savings adds up.
STANDARD LAYOUT AND STORAGE
Layout could be called the crux of a QDC system. Without a press layout that allows for die, coil and other material pre-staging, along with standardized scrap handling, investment in QDC doesn't make much sense. It boils down to fostering a cellular layout for presses.
"When I enter a facility, I can immediately tell whether they've implemented quick die change," Zunker says. "The first thing I look for are pre-staging areas. If they don't have them, they don't have quick die change."
Die-pre-staging generally takes one of two forms. The first involves one central area for dies, which are then transported to the pre-staging area. Once there, dies are quickly transported via die truck or other method to the press itself.
In another layout, all dies for a press cell sit in a pre-staging area near the press itself, with racks dedicated for die storage and changing. This fully adopts lean's cellular layout concept and, if done properly, can totally eliminate the need for a fork truck to transport the dies. Dies are transported by die truck or roller table between the pre-staging area and the press.
Myriad tools are available, from die tables to die pre-staging racks. And no matter how many tiers the pre-stage racks have or which die-storage strategy a shop chooses, "each die must have its own location," Zunker says. "Every die should have a label identifying the tooling and its location [in the rack]. These are simple things shops can do without spending money."
Of all tool standardization techniques, logical labeling becomes a no-brainer, Demonet adds. "Every plant has their own method, from numbering systems to color coding of die shoes for specific presses." In larger organizations, it makes sense to share labeling systems between plants as well.
All tools for that change-over, from wrenches to pry bars, "has to be in place before the press is shut down," adds Demonet.
Regardless of a plant's decision on layout, Zunker adds, don't base it on another plant's QDC system. "You have to develop a system for your tools, your presses, your layout and your product."
NO FORK TRUCKS REQUIRED
"One reason companies fail implementing QDC is that they do not make the layout fit the quick-die-change requirement, storage and scrap handling and retrieval," Zunker says, adding that companies "must move presses and equipment, if feasible, to provide pre-stage areas."
Regardless of layout, say sources, fork trucks shouldn't be used to transport dies, even though the practice remains largely the status quo for industry. "The first concern is the safety issue," Demonet says. Dies can be damaged, and part quality can suffer. Fork trucks are not safe, particularly on the oily floors in the stamping shop.
Alternatives include track-mounted and non-track-mounted die carts. "These have no quick starts and stops," he explains. "They are a lot safer, you have less damage to the die and less quality issues to the part."
"You dock right up to the press bolster, and you roll it on a plane straight across to the press," Zunker adds. "You're not slamming the die" onto the bolster. With a fork truck, "you have steel on steel, and the die can slide around"—not good for safety or die quality.
Besides, waiting for multi-purpose fork trucks to become available can take twice the amount of time as a complete quick-die-change, Zunker adds, something that, again, defies logic when implementing a QDC program.
Dedicated die-handling equipment allows companies to take on work that's become more common stateside—larger stampings requiring larger dies. "These heavier dies are pushing people toward dedicated die-handling equipment out of necessity," Demonet explains.
Sensors have also been a driver toward safer, more controllable die handling. Not only should the electrical connections to the sensors be standardized and easily accessible, but die damage through use of a fork truck or otherwise can ruin in-die sensors, sources say.
NO PRESS LEFT BEHIND
The stamping industry's downsizing does have a silver lining. The situation creates a large inventory of used presses on the market, says Zunker. If one press requires special tool sizes and doesn't fit with the QDC program, "there is a huge inventory of used presses out there today," he explains. "If you find a used press that's more inclined to fit your [standard] tools, that may be the way to go."
This implies what Zunker calls a steadfast rule for QDC: There's no going halfway. Some companies upgrade to QDC piecemeal, setting up pre-staging areas and cellular layouts one shop-floor section at a time, instigating change when the money becomes available. Exceptions always exist depending on the application, he says, but often this strategy can be like building a sports car with perfect fit and finish, but not getting any tires—the car goes nowhere.
Moreover, "finish [QDC for] one press, including all the tools that go on the press, before continuing on to the next press," Zunker says. "You must have a success story."
THE BIG PICTURE
QDC should be part of a broader strategic plan. "Companies should plan how the plant is going to look five or 10 years down the road," Zunker says. Questions to ask involve future product lines and future customers. What common attributes will those parts have? How will they be different, and how will this translate to part-flow requirements in the press room? This strategic plan—communicated from top management down—ideally should be in place before initiating QDC, Zunker says. It doesn't happen often, he adds, but it's an ideal worth striving for.
Herein lies one of the most challenging elements of QDC: the transition from an existing floor plan that evolved to meet current demand to one that predicts future customer demand. "So many small shops add equipment over time as projects come along," Demonet explains. "They stick a press here and stick a press there without considering what makes the most sense."
The cost of changing the layout depends on the press. A small floor-mounted press usually won't cause trouble, but a larger press with ancillary equipment like looping pits built into the building's foundation can become a major issue. "In these cases," Demonet says, "you have to weigh the options." What will be the cost versus the long-term benefit of transforming to a cellular layout?
He emphasizes that, if possible, do not leave the words "long-term benefits" out of the equation. Eventually, he says, more customers in more markets will expect stampers to have lean, flexible layouts. "It's not just automotive anymore."
Editor's Note: For more, visit: Atlas Technologies, www.atlastechnologies.com; and Lightning Time Savers, www.lightning timesavers.com.
author: By Tim Heston