May 4, 2004
Quick die change is not just a way of setting up dies; it's a mindset for the elimination of waste.
Material waste, of course, is readily identified and quantified. Waste caused by lost time, however, is more subjective, and quantification often becomes a matter of opinion, which makes it more difficult.
In the current business climate, cost reduction and waste elimination are the watchwords of the day. Therefore, it is imperative for today's metal stamping businesses to take a renewed hard look at the adoption of quick die change procedures.
What can the implementation of quick die change processes do for stamping efficiency? One stamping facility, after carefully researching the possibilities, embarked on a program of changing its conventionally equipped shop into a fully equipped quick die change stamping shop.
The goal was to bring cost-effective run sizes down to 50 parts or fewer when necessary, reduce stamping floor space, reduce part storage space, reduce raw material inventory requirements, and perform just-in-time (JIT) stamping. Stamped parts would be moved directly to the assembly line to be installed in units within eight hours.
The company replaced existing presses with new ones specifically designed for quick die change with T-slotted rams and bolsters. The presses were rearranged to accommodate die staging on tables equipped with ball rollers, as well as for raw material staging. All dies underwent minor clamping and shut height modifications to create a common clamping height. Shut height variations between the dies also had to be reduced, which required adding plates or parallels.
In the end, 13 punch presses designed for quick die change replaced 36 standard punch presses. Meanwhile production was maintained at similar or higher volumes. As a result of JIT manufacturing, the company realized a significant reduction in time to market for new products.
Obviously, a complete stamping facility changeover like this is not feasible, or even desirable, for all stamping shops. However, stamping shop managers should explore what quick die change is and what it can do for their companies.
The amount of time saved by adopting quick die change procedures varies from shop to shop and job to job. Also, the degree to which a shop has converted to quick die change in terms of equipment plays a major role. Therefore, this comparison will examine a conventional manual bolt-and-clamp setup shop and a shop with standard, off-the-shelf quick die change equipment.
A typical conventional setup involves:
This sequence of activities usually takes 30 to 90 minutes, depending on circumstances. Adding automatic press feed setup adds 15 to 30 minutes to the setup time. A well-equipped quick die change shop with trained people can achieve this sequence of activities in three to five minutes, or 20 minutes with an automatic feed.
With this significant setup time reduction, the time available for production increases. By comparing two average production runs of 1,000 parts per run, which can be run at 350 parts per hour, hand-loaded, stampers can see the time savings:
|Conventional||Quick Die Change|
|Setup||1 hour||5 minutes|
|Completion time||7.72 hours||5.89 hours|
If two shops, each with five comparable presses performing the same operations but using these different approaches, try to compete against each other, one will be at a distinct disadvantage. The conventional-setup shop requires 38.6 hours, compared to 29.45 hours for the quick die change-equipped shop. In other words, the quick die change-equipped shop can produce the same work with one less machine.
The results are even more dramatic when considering the same scenario using progressive dies. Assuming the same respective die setups and adding 20 minutes for setup of the automatic feed, a press speed of 60 strokes per minute would yield these results:
|Conventional||Quick Die Change|
|Setup||1.33 hours||0.42 hour|
|Total time per run||1.61 hours||0.70 hour|
The lack of available cash is the most frequently cited barrier to implementing quick die change. Of course, a company preparing for quick die change will need punch presses with programmable CNC, which changes the machine setup parameters (speed, shut height, feed length part, and slug removal) when a new part number is entered.
However, a company can begin reaping some of the benefits of quick die change without large expenditures. Many elements necessary in preparation for quick die change have relatively low costs and can be achieved by most shops in-house: common clamping height and common die shut height, achieved through minor die modification; common clamps; and T bolts and slots.
When a company has achieved that much, the benefits of quick die change begin to be realized. The other elements—hydraulic clamping systems and hydraulic lift rollers for the press bolsters, die staging tables, and raw material staging equipment—can be added over time as cash is available or as customer requirements dictate.
While the cost of quick die change can be daunting, before shops finally determine feasibility, they must consider the cost benefits of improved efficiency:
Quick die change actually creates a savings chain reaction. Shorter setup times save setup labor-dollars and make more productive labor-hours available. This, in turn, results in reduced equipment needs and consequently frees up floor space.
Because shorter production runs are possible, less in-process storage is required, and product can be shipped to the customer or sent to assembly as needed, which also reduces the finished-goods storage requirement. This also results in the ability to purchase smaller quantities of raw material. The reduction in the storage of in-process and finished-goods inventory, in addition to the space freed up by reduced raw material requirements, makes more manufacturing floor space available.
Of course, cost justification isn't the only concern in implementing quick die change. It requires a company's commitment to continuous improvement, as well as some out-of-the-box thinking and spreading out of costs, if necessary. Above all, a company trying to achieve quick die change must keep at it. The benefits are real and limited only by the extent of the company's creativity.
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