Our Sites

Ask the Stamping Expert: What type of feed system is best for a transfer system?

Feed system

Tom Vacca discusses the characteristics, capabilities, advantages, and drawbacks of both destackers and coil feeders for feeding material through a transfer press line. Getty Images

Q: I work at a large Tier 1 company serving the automotive industry. Currently I’m researching which type of feed is best for our transfer press stamping operations. I’ve found that a destacker feed system eliminates the downtime that occurs with a coil change, so that increases uptime but also adds several processes and costs. Can you point me in the right direction?

A: There are two methods of feeding material through a transfer press line operation: coil feeding and blank feeding using a destacker. Without knowing the details of the operation, it is very difficult for me to give specific advice. But let’s take a closer look at some of the characteristics and capabilities of destackers and coil feeders:

  • Destackers generally add complications, equipment, maintenance, and longer changeover time as compared to coil feeds. This is not meant to be a negative statement; it’s just a fact.
  • For very short runs, destackers can be a good choice, because coil changes become irrelevant. In addition, coil feeders generally create more scrap than a destacker running custom blanks.
  • If your part is very thin with very short pitch, and you can get large coils that will run for days without a coil change, a destacker might not be the best choice.
  • For high-speed operations (400 strokes per minute or greater), a coil feeder will be more stable, more reliable, and less complex than a destacker.

Let’s assume you have a stamping that requires a flat piece of cold-rolled steel (CRS) stock that is 10 in. wide by 14 in. long by 0.050 in. thick. If you are simply trying to minimize downtime caused by coil changes, then you need to calculate the number of blanks you can get from the largest-diameter coils you can procure. For this example, let’s assume the annual volume is 100,000 pieces per year. In general, when calculating blank requirements versus coil stock, the rule of thumb is a ratio of about 10-to-1. That means for orders that require 50 coils, you would need 500 stacks of blanks of some quantity to make the same volume. The processing and handling of the stacks alone is a strong negative for using destackers. On the other hand, if the volume is 50 to 100 pieces, why handle large, heavy coils and deal with loading and unloading for changeovers? A few stacks of blanks are much easier to handle.

Cost also becomes a factor. Blanks generally cost about 10% more than coil because of the manufacturer having to cut, stack, and handle the blanks. For example, if annual volume of the 10-in.-wide CRS part described above is 250,000 pieces or more, using coiled raw material that costs $25/lb., you can save about $75,000 per year running coil stock versus blanks. This number adds up when running multiple lines. Some stampers offset this cost by setting up a line to cut the blanks off the coils in-house. However, this also adds the costs of new equipment, maintenance of that equipment, and overhead.

Feeding coil stock has many advantages. Coil stock uses about 30% less floor space than blanks. Coil feeding also involves fewer process steps, reduced cycle times, and a leaner manufacturing process. To run coil stock, you can incorporate the blank cutoff requirements in the first station of your tooling used in the manufacture of the final product. If you were to use a destacker, the blanks often must be handled twice—once when moved from the warehouse to the manufacturing line, and again when loaded into the destacker. In addition, the destacker requires more intervention in loading stacks to keep the press running than a single coil of stock. This results in lost productivity when waiting for stacks to be loaded.

Most destackers have continuous-run capabilities, but they still need to be properly loaded. Some lines have custom pallets for loading large batches of stacks at once, but this requires a substantial initial investment to facilitate. All the additional handling and equipment requirements for using stacks instead of coils do not make sense unless you are dealing with low volumes and you require changeovers to be done in minutes.

Also, consider material quality requirements. Blanks must be consistently flat and cut to the proper size. A specified blank flatness is required for most automated destacking machines to work efficiently. Not so with coil stock, and with the proper straightener and tooling, you can cut the blanks in-house as part of your stamping operation.

The traditional benefit of the destacker is that you can feed a variety of oddly shaped materials in the same machine. Square, triangle, rectangle, and custom-shaped blanks can be accommodated. One of the drawbacks of coil feeding is that additional tooling is required and valuable space under the press ram is used for cutoff to create the blanks.

Good luck, and happy stamping!

About the Author
Micro Co.

Thomas Vacca

Micro Co.

Has a shop floor stamping or tool and die question stumped you? If so, send your questions to kateb@thefabricator.com to be answered by Thomas Vacca, director of engineering at Micro Co.