Page 12 - MetalForming February 2022 Special Automotive Issue

Tooling by Design
By Peter Ulintz
Transfer-System Considerations
Consider transfer dies as basically line dies, with some minor but important differences. Die sta- tions are timed together and spaced evenly apart, usually in a single press (Fig. 1). Rails with fingers or grippers transport and position stampings. The rails can mount inside of the die, to the outside of the die or to the outside of the press. Transfer dies also can mount in individual presses. During a press cycle, each rail travels inward, picks up the stampings with special fingers or grippers, and transports them to the next die station or press.
Stampers can install transfer sys- tems in a variety of ways: mounted through the press window, mounted to the front and rear of the press, mounted to a transfer plate, or mount- ed externally between presses.
With a hybrid transfer, a coil-fed progressive die that performs some cutting, notching, forming or blank- ing operations combines with a trans- fer die that performs the remaining work. Here, a stamping separates from the progressive-die strip and the transfer unit transports it to the additional die station(s). If necessary, specialized transfer fingers can rotate or flip the workpiece over as it moves
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
Fig. 1—Transfer dies evenly spaced and mounted on a master die set.
through the transfer stations. In some cases, these systems use material inefficiently—depending on the blank shape—but they eliminate the need for offline blanking and a blank destacker.
A hybrid process also allows a pitch distance that suits the part require- ments without sacrificing material use, as the transfer portion is not restricted by the die progression. Increasing the pitch allows additional space in the die to accommodate side cams or to provide inserts in form stations to ease adjustability and maintenance. Reduc- ing the transfer pitch (after large draw reductions, for example) conserves space within the die, which can allow the designer to specify more working stations under the ram than with a constant-pitch progressive die.
Specialized systems integrated into the progressive die, hybrid systems usually are designed and produced by die shops rather than by transfer man- ufacturers (Fig. 2). One exception: the
hybrid Micro Transfer produced by Jacar Systems.
Transferring the Workpiece
The two basic types of transfer sys- tems, two-axis and three-axis (or tri- axis), can perform numerous motions. Two-axis systems, usually simpler and more economical than their three-axis counterparts, are limited in their appli- cation. Examples of two-axis systems:
• Shuttles, though typically inex- pensive, present some die-design chal- lenges, especially when part lifting is required. Here, die lifters must accu- rately position all parts to the exact same height. No position gauges exist to contain a part in the die-open posi- tion—the stampings rest on flat pads or rails with nothing locating them in position before the transfer tools engage the parts and move them to the next station.
• Crossbars use suction cups or magnets mounted to a tubular frame to lift stampings and move them
10 MetalForming/February 2022
www.metalformingmagazine.com