Page 52 - MetalForming April 2017

Tooling by Design
By Peter Ulintz
Transfer Automation—Options Abound
When a metal- stamping process engineer looks at a part design, many ques- tions come to mind:
• What is the base-mate- rial type and thickness?
• What are the flat-blank dimensions?
• What are the daily, monthly or yearly volumes, and how long will the part be in production?
When quoting a new
part, the engineer may propose a process that fits existing equipment, rather than developing a more efficient process for the part at hand. One of the most important decisions the process engineer may make: Should the part be processed in a progressive or transfer die?
Transfer dies are basically line dies, with some minor but important differ- ences. Die stations are timed together and spaced evenly apart in a single press. Parts in a transfer die often are transported and positioned by rails and grippers, mounted either inside the die, on each side of the die or to a transfer system mounted to the outside of the press. During a press cycle, each rail
Peter Ulintz has worked in the metal stamping and tool and die industry since 1978. His back- ground includes tool and die making, tool engi- neering, process design, engineering manage- ment and advanced product development. As an educator and technical
presenter, Peter speaks at PMA national seminars, regional roundtables, international conferences, and college and university programs. He also pro- vides onsite training and consultations to the met- alforming industry.
Peter Ulintz
Technical Director, PMA pulintz@pma.org
travels inward, grips the parts with spe- cial fingers or grippers, and then trans- ports the parts to the next die station.
Common Transfer Processes
Transfer systems can perform numerous motions; the two basic types are two-axis (2D) and three-axis (3D or tri-axis). Two-axis systems work in a single plane—the x-y plane in a sta- tion-to-station transfer, or the x-z plane in crossbar applications.
Examples of two-axis systems include:
Shuttle transfer—These setups, while typically inexpensive, can present some die-design challenges, especially when they require part lifting. Here, die lifters must accurately position all parts to the exact same height; there are no position gauges to contain the part in the die-open position. The parts rest on flat pads or rails with nothing locating them in position before the transfer grippers engage.
Crossbar transfer—Here, suction cups or magnets mounted to the cross- bar system pick up the parts and move them between die stations. Crossbars typically find use in press-to-press transfer lines.
Progressive/walking-beam transfer
—This hybrid process offers stampers the flexibility to run a tool in a traditional
straightside press with- out having to deal with externally mounted transfer systems. Trans- fer components are designed and built as part of the die.
Three-Axis Transfers
...typically work in an x-y-z plane. They move inward to grip the parts, lift the parts
vertically, index them to the next sta- tion and then lower the parts onto the die. This three-axis movement allows parts to be lifted sufficiently high off of the die and placed within the perimeter gauge boundaries in the next station.
Examples of three-axis systems include:
Externally mounted tri-axis trans- fer—These systems may be plate- or press-mounted. Tooling components must be designed to allow sufficient clearance for the fingers’ return path to the original start position, to avoid interfering with lower tools, cams and die-guidance mechanisms. Designers also must account for upper die com- ponents, considering the timing of the tools relative to the incoming fingers.
In-die three-axis transfer—Some in-die transfer tools may run at a faster stroke rate than externally mounted transfer systems. In-die transfer systems present the same challenges as regular tri-axis transfers, along with having to deal with the added design complexity of in-die transfer components.
All transfer processes allow the tool to be designed at a pitch (the distance between die stations) to suit unique part requirements, without sacrificing mate- rial use, since transfer processes are not restricted by the part progression. The
50 MetalForming/April 2017
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