Create a Die-Change Standard, and Never Stop Improving
That quote, from the book, Toyota Culture: The Heart and Soul of the Toyota Way, smartly implies that developing a process (the standard) is the key to attaining repeatable results. In a lean-manufacturing environment, a standardized process is critical to achieving continuous improvement. With a standard developed, a manufacturer can undertake incremental changes to further improve performance. The improvement process often used: plan, do, check and act (PDCA). We review the current standard, or a portion thereof, and envision an improvement (plan). We then implement the improvement (do), and then measure the results (check). If successful, we formalize and implement a new standard (act).
Die-Change Procedures Cry Out for a PDCA Cycle
Unfortunately, too many stampers still use poorly developed processes to perform die changes. They utilize fork lifts or other crude methods to exchange dies in their presses. Much skill is needed to insert a die, block it up to allow fork removal, tip the corner to pull out blocking, and then pull the forks out completely. This procedure drops the die on the bolster, and then the diesetter bumps and pries the die into final position.
At this point, a hodge-podge of clamps and tools are used to fasten the die into the correct location in the press. Setups for material feed, part handling and scrap removal follow a similarly crude process with a majority of the how-to knowledge in the head of the setup operator. Shops often fail to document much if any of this procedural information for future reference, eliminating any chance of repeatable results.
By contrast, TWB Co., Monroe, MI, provides a good example of a company with a well-developed standard procedure for changing dies. To develop an optimum die-change system for its application, Warren Kile, project manager for TWB, a manufacturer of tailor-welded blanks, worked with engineers at Green Valley Manufacturing, Inc., Mt. Zion, Inc. Together, Kile and Green Valley engineers used the PDCA cycle several times throughout the development process to address a unique application that required dies to be loaded via the press window. Also, very little floor space was available at TWB for staging of dies. And, improving die-change time was not TWB’s only goal. Other areas of focus included improving safety, consistency and reliability.
A solution came thanks to implementation of a customized single-station die-change table, after reviewing the following factors:
• Staging dies near the press. Specially designed die-staging racks are located near the die-change area so that the forklift operator can quickly and efficiently drop off and retrieve dies during a changeover. The racks were designed to place the die’s fork pockets in optimal view for the forklift operator during loading and unloading.
• Standardized common plates. Dies may vary in length and width but all dies must feature runners that align with die-change rollers on the table and in the press. The runners, mounted at a standard distance from the center of the die, allow the die to travel smoothly on the rollers.
• Die loading on the change table via forklift. Side guides flip up above the roller surface to help align and guide the die to the centered position on the table deck during forklift loading. Guides retract to allow powered transfer to and from the press.
• Die mobility to and from the press. Die-lift rollers in the press and rollers on the table provide minimal resistance to motion and avoid die and press damage.
• Die-transfer method. A powered rigid-chain push-pull system mounts to the opposite side of the press from the die table. The push-pull mechanism pushes the previously used die onto the die-change table. Then the mechanism attaches to the new die to pull it into the press.
• Push-pull attachment to die. A common grab hook mounts to each die used with the system.
• Die guiding. A central die feature mates with a channel on the table deck and bolster to keep the die centered as it travels in and out of the press.
• Die positioning in the press. Die position, front-to-back, is controlled by a guide-channel feature in the press. Removable hard stops, which move to a specific color-coded position depending on the die, locate the die left-to-right.
• Material feed and part handling. Material transfers through the press via six-axis robots.
• Scrap removal. A pneumatic shaker conveyor installed in each die minimizes setup time during changeover.
Reducing the Footprint
Another component of lean manufacturing and continuous improvement to consider is the environment. An innovative feature of the die-change table at TWB is the use of folding extensions at the rear of the die table. These extensions minimize the overall footprint of the structure while the table is not in use. When needed, the extensions lock into a die-change position, extended into an aisle. After die change, the extensions fold back against the table frame to free up valuable plant space.
At TWB, the standard for die changes is set. From now on, this standard will be periodically reviewed and improved.
Try applying the PDCA cycle throughout your lean-manufacturing journey to improve die-change performance. If you use forklifts and pry bars to changeout dies, establish that as the current standard and then begin to improve on that standard. Consider the following opportunities for improvement:
• Add die lifters for ease of transfer of dies to and from the press.
• Bolster extensions along with die lifters are a great way to keep the forks out of the press. Share a lift-off pair between several presses to minimize expense.
• Adding features to the die base to mimic a common plate offers an economical way around standard-sized common plates. For example, shops can install a pair of V-blocks to mate with press-mounted pins for accurate locating. Also, standard clamping lugs can be added to the dies to allow the use of uniform clamping systems.
• Acquire all of the required clamps, wrenches, etc., and identify storage locations for them to avoid wasting time looking for tools.
• Staging dies near the press with die-storage racks or staging tables minimizes wasted travel time during die exchange.
Little by little, review and improve the standard. Since perfection never quite comes, the continuous-improvement cycle never ends. MF
See also: Green Valley Manufacturing, Inc.
Related Enterprise Zones: Tool & Die
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