Page 21 - MetalForming-Dec-2018-issue

Here, a specimen is tested to help deter- mine sheetmetal drawability. The machine shown is employed for cupping and earing tests to examine sheetmetal ductility and investigate the influence of surface treatments, coatings and lubri- cants in typical forming applications.
solutions for tensile tests and, thus, require innovative methods.
For example, Donohue offers, ZwickRoell has patented hydraulic grips for short clamping lengths— needed to grip smaller specimens dur- ing testing. These grips enable testing of specimens with shoulder lengths as short as 6 mm as compared to lengths that typically measure at least 40 mm. Along with horizontal grip- ping force provided by two horizon- tally placed actuators, a third actuator provides vertical force for stabiliza- tion. Besides allowing for shorter grip- ping lengths and smaller specimens, the hydraulic grips present no visual or physical obstructions when employing optical or mechanical extensometers.
Drawability Determined
Our tour also included demonstra- tions of machines used for tests to examine sheetmetal ductility and investigate the influence of surface treatments, coatings and lubricants in typical forming applications. For its part, ZwickRoell provides its BUP series of machines for these purposes, avail- able in various force ranges. Typical test methods include Erichsen cupping tests, in which a hemispherical punch is pressed into a clamped test piece
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until a crack appears. The clamping ensures no inflow of material toward the stressed area of the test piece. The drawing formability of the sheetmetal is determined from the punch-pene- tration depth. With another test method, the earing test, circular blanks are punched, or inserted and drawn into cups. Here, material is allowed to inflow, and the deep-drawing charac- teristics of the sheetmetal are deter-
mined via an ear/height percentage ratio. Also employed via these machines: square-cup, hole-expansion, FLC and bulge tests.
Look for more coverage of testXpo, including an overview of sheetmetal- forming research by a ZwickRoell equipment user at Clemson Univer- sity, in a future issue of MetalForming, and online at www.metalforming- magazine.com. MF