Page 26 - MetalForming July/August 2009

Transfer Job
online design-review tools allows these meetings to occur cost effectively and successfully. This is particularly true for programs where dies are being built offshore.
First-Hand Experience
Says Murray Brooks, president of tooling supplier J.P. Bowman Tool & Die Ltd., in Brantford, Ontario: “Our experience allows us to candidly tell the customer (stamper) that we would like the option of quoting tooling to run in a transfer system. It opens the door to many more opportunities to produce complex stampings compared to run- ning them in progressive dies. We look for opportunities to implement nesting of blanks to optimize material usage; part rotation within the process to allow parts to be contacted in the ram direc- tion, if required, to minimize costly cam requirements; and increase pitch between parts to allow the use of cams for dimensional control. All of these contribute toward reducing piece-part costs with improved quality and repeatability, opportunities that would not otherwise be possible in a progres- sive-die process.
“Prior to designing and engineer- ing a production transfer-stamping die,” Brooks continues, “the primary require- ment is for our customer to provide accurate and current CAD information for the transfer system and the stamp- ing press—press stroke, ram speed and specifications related to the integration of the transfer system to the press. In some cases, with a short press stroke there is insufficient daylight between the upper and lower die assemblies to transfer the part at a desired production rate. This may mean that in order to run a particularly deep part at an acceptable production rate, a press with a longer stroke might be preferred. This allows the equipment to engage the transfer of the part from station to station on the up stroke and drop it off on the down stroke, optimizing the strokes per minute and resulting in a smooth trans- fer motion.
“All of these parameters,” Brooks surmises, “allow an experienced tooling
source to develop a stamping process that will not only produce the stamped part with optimum quality, but also to successfully transfer the part in the cus- tomer’s production equipment with a maximum run rate.”
The Key to Speed
Optimizing transfer-press produc- tivity requires specification of the right transfer-system parameters, ensuring that the system has the optimum horse- power in its actuators to run the heav- iest parts with the largest motion pro- files. The stamper must consider not only its current programs but also any future parts that the press might be required to produce, including potential takeover work.
Drive-train selection software— developed over many years using data from previously developed actuators— is a valuable tool used during this process. Due to the specific nature of transfers, customized application soft- ware often is used for specifying drive- train parameters. The stamper must provide the transfer source with accu- rate information regarding payload weights, which must include any other equipment—receivers, accumulators and other ancillary equipment that will add substantial weight to the transfer bars. The transfer source uses this infor- mation, combined with the maximum part weights, to size and select the prop- er motors, gear heads, pulleys, belts and other components that will comprise the drive train.
Proprietary transfer-system design software allows a vendor to address key issues such as transfer-bar deflection and motion profiles, based on the use of link-motion presses or eccentric. For example, if most of the stamped parts have a very aggressive grip stroke, the stamper can achieve higher run rates with a different bar profile.
Do not underestimate the expected run rates by basing specifications on previous experiences running similar parts on older mechanical transfers. Today’s servo transfers have much smoother motion and minimal bar deflection, and can therefore achieve
very high run rates not considered pos- sible in the past. Any speed concerns should only center on the capabilities of the press or the die.
Let Your Fingers Do the Walking, But Don’t Lose Those Parts
When it comes to designing and developing end-of-arm finger tooling, failure to appreciate the importance of this task and the attention to detail required can cause a stamper to pay the price in run rate, equipment down- time and startup time. Some stamp- ings can easily be transferred at high rates using simple and inexpensive shovel-style tooling. Other parts require the use of pneumatic grippers or mag- nets to stabilize the part when transfer- ring at high rates. Automation such as servo rotation, part ejection, lateral rotation and linear motion can be added to the transfer rails to manipulate the part, which helps the die designer sim- plify die design and achieve higher run rates. Tooling with quick-release mech- anisms will expedite die changes.
Common methods for mounting end-of-arm tooling:
• Fixed tooling—the bars and fingers are changed out and stored on a rack near the press or with the die.
• Receivers placed in incremental locations on the bars where the end effectors are inserted. This setup is most common on large transfer presses with rolling bolsters and two sets of bars, and offers advantages when running a large number of parts and where min- imum die-change times are required.
• A common plate located on the bars that includes several fixed finger stations. These plates typically store on racks located near the press.
Each of these mounting setups has advantages and disadvantages related to cost, flexibility, die-change simplici- ty and efficiency. Factors that affect the selection include the number of parts being run; bolster size—on some small presses, the bars and fingers can be eas- ily handled manually; part complexity; the footprint of the press cell; storage capacity; and any jobs that might come down the pike in the future. MF
24 METALFORMING / JULY/AUGUST 2009
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