Page 13 - MetalForming February 2022 Special Automotive Issue

Fig. 2—A custom-built servomechanical transfer system.
between die stations. Crossbars typically find use in press- to-press transfer lines.
• Walking-beam systems offer stampers the flexibility to run a transfer die in a press without the need for an exter- nally mounted transfer system. Designed and built as part of the die, transfer components lift parts and transfer them between stations.
Two-axis systems operate in a single plane—the X-Y plane in a station-to-station transfer, or the X-Z plane in crossbar and walking-beam applications.
Lifting and Transferring the Workpiece
Lifting the workpiece in a die requires motion in the X- Y-Z planes. This three-axis movement allows the lifting of stampings sufficiently high off of the die, and placed within the perimeter-gauge boundaries in the next station.
Three-axis systems are commonly plate- or press-mount- ed, with tooling components designed to allow sufficient clearance for the fingers’ return path to the original start position while avoiding interference with lower-die steels, cams and die-guiding components. Designers also must consider the timing of die closure relative to the incoming fingers.
Some die-mounted transfers run at a faster stroke rate than externally mounted transfer systems, due to shorter travel distances. In-die transfer systems present the same challenges as traditional three-axis systems, along with hav- ing to deal with the added design complexity of in-die transfer components.
Positioning the Workpiece
When the transfer fingers release the workpiece, orien-
tation must be maintained in all directions (including rotation).
A two-axis system uses spring pins to maintain workpiece positioning during finger retraction until the die closes. In a three-axis system, a combination of part geometry, nesting blocks and locator pins help to maintain location during finger retraction.
Pitch length also impacts part positioning. Due to the limited time in which a transfer system must com- plete all of its motions, a longer pitch will produce high accelerations, often resulting in unwanted vibra- tion and unstable movement of the stamping.
Less stiff than thicker materials, thin materials are particularly vulnerable to vibration. Meanwhile, larger, heavier workpieces require stronger transfer arms and fingers that gain their strength from increased mass. The increase in part weight, plus bar and finger mass, subjects the transfer system to
higher inertia loads, often requiring slower operating
speeds. In most cases, consider using transfer-motion simulation to determine a motion profile that produces acceptable levels of inertia, vibration and instability for optimized speed, accurate workpiece positioning and long
transfer-system life.
MF
Tooling by Design
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