January 9, 2007
Many stampers rely on the machines and equipment you already have for moving and changing stamping dies. Using dedicated items such as die carts and shuttle tables can make die change more efficient.
In efforts to cut waste from stamping operations, many stampers focus quite a bit of attention on reducing die handling time. Additionally, many companies try to reduce or eliminate fork truck traffic in stamping areas as a safety measure. When looking at efficiency and safety, stampers must be aware of the many factors that dictate which improvements are justifiable and, more important, advisable. It is not uncommon for a stamping team to embark on an improvement project by starting off in one direction and later, after considering all of the factors, changing direction.
A good starting point is to keep two guidelines in mind: (1) Have a place for everything and keep everything in its place, and (2) use the right tool for the job. Incorporating these two guidelines into your improvement plans can help to create a safer and more efficient environment.
It can be difficult to acquire the correct tool for the job. Many times the project leader is not aware of all of the equipment and options available. Another challenge is a lack of knowledge on how to calculate and show a financial justification for a particular piece of equipment.
Buying dedicated die handling equipment can help you meet both of the previously mentioned guidelines. Using dedicated equipment standardizes the die handling process and ensures that the equipment is available when needed, whereas relying on fork trucks and cranes usually means having to wait until the equipment is free. Furthermore, special-use equipment can be designed for a particular application.
Perhaps more than any other factor, floor area organization determines your shop's level of die handling efficiency. In unorganized shops, it never fails that when a crew needs a die, they first must find it, then clear a path to get to it. Having a place for every die and keeping each die in its assigned location go a long way in efficient die retrieval. Dedicated die storage shelves or racks can optimize valuable floor space (see Figure 1). Multiple-level racks provide high-volume storage in a relatively small footprint. Additionally, well-organized die storage cuts time retrieving and storing dies for service.
Delivering dies throughout a plant can cost your company time and money if you use an inefficient transporting method. A forklift usually carries a die oriented so that the die's length straddles the forks, which requires wide aisle spacing. This can present problems in congested facilities. An alternative is a dedicated die transporter (see Figure 2). A transporter can be designed so that the die is oriented the other way, allowing passage through narrow aisles. A transporter has a small footprint because it supports the load over its rolling structure rather than counterbalancing it as a forklift does.
Using a transporter eliminates the time wasted in waiting on fork trucks or cranes that are busy performing tasks in other areas of the facility. Specialty units can allow bay-to-bay transfers in facilities that use overhead cranes and have expanded beyond a single-crane bay area.
When it comes to actually changing the dies at the presses, the existing processes and facility layout can point to a solution that might not seem obvious.
For example, one stamping company solicited bids for a die cart to improve its die changing operations. After further reviewing the current processes, the stamper changed the project focus significantly. The press was set up for side loading with die lifters in the press and bolster extensions on both the front and the back of the press. The crew used an overhead crane to take the new die to the press and set it on the bolster extensions. A fork truck pushed it into the press while simultaneously pushing the existing die out of the press onto the opposite bolster extension pair. The company sought a way to improve this die transfer method.
The plant layout and the desire to deliver dies to and from the press with the crane caused the focus to change from a die cart to a much simpler and economical die transfer table. The table shown in Figure 3accepts subplate-mounted dies from the crane and performs the side transfer into the press while pushing the old die out to the remaining bolster extensions on the back of the press. Choosing the die transfer table over the die cart saved the company money and resulted in a simple, easy-to-use piece of dedicated equipment.
If you have several presses and all are accessible by a mobile vehicle, you might consider investing in a cart that can be shared among all the presses. By factoring in the press bed height, the die shut height, and the weight of the dies, it is possible to use an over/under-style die cart for die changeovers (see Figure 4). This type of cart allows you to stage the incoming die on one station; dock to the press; remove the outgoing die and put it onto the empty cart station; change the deck elevation to align the incoming die with the press; and insert the incoming die.
A mobile die changer should include a docking feature to align the unit precisely with the press and also secure the cart to the press during die transfers. A mobile die change cart has the benefit of serving several presses and die storage racks, but it also has some of the drawbacks of transporting dies with a fork truck and requires continuous, level floors at each press.
For simplicity and speed during changeovers, it doesn't get any better than a two-station die shuttle (see Figure 5). The incoming die is prestaged by either a die transporter, fork truck, or overhead crane. When a production run is complete, the crew removes the outgoing die, indexes the shuttle deck one pitch, and inserts the incoming die into the press. This process can be accomplished in less than five minutes with dies weighing more than 50,000 pounds.
One time-consuming operation involved in die maintenance is the splitting and reassembly of dies. Many stamping shops rely on forklifts or cranes for these processes. Obviously, these are imprecise methods. The operator must align, level, and guide the mating components manually, which can result in die damage, wasted time, and unsafe situations. Choosing a die splitter designed specifically for the tools to be serviced not only addresses these concerns, but likely will enable more frequent die servicing because the process will be substantially easier and less time-consuming (see Figure 6).
Understanding what options are available and how they can be used can help you choose the right tool for the job and improve both throughput, which shows up on the production floor, and profitability, which shows up in the financial statements.
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