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CLIMATIC & STRESS TESTING: MEASUREMENT  Traditional mechanical test equipment is


being used for haptic feedback testing of switches, below; while automotive composite coil springs are a complex testing challenge


which display the switch condition cycle and any deterioration in displacement or pressure values required to change the condition over time. Each cycle creates a plot and subsequent


cycles should overlay the original loop. Any shift in the pattern demonstrates mechanical wear in the switchmechanism.


COMPOSITE SPRING TESTING Coil springs are a challenge for compression testing – they’re difficult to hold, the relationship between force and displacement isn’t linear and to get a true representation of the spring characteristics, it is important to avoid plastic deformation. According to Zwick Roell Applications


Newtricks pass the test


Jonathan Newell visits Zwick Roell to find out how traditionalmaterials testing equipment is finding new uses in the automotive industry


W


ith its roots planted in 19th century Germany, Zwick Roell has a long history of producingmaterials testing equipment that has been


squeezing, stretching and bending products to breaking point formore than 100 years. This is still the core of its business which


manufacturesmechanical testing equipment at its Ulmfacility in southern Germany, which I visited to see the latest ways in which such flexiblemachinery can be deployed. With a strong automotive industry in


Germany, Zwick Roell naturally responds to its demands for innovative approaches to testing increasingly complex products and two areas have emerged where mechanical testing equipment is being used in challenging,modern applications.


36 /// Environmental Engineering /// December 2016


HAPTIC TESTING With no standards existing to specify the way an indicator, high beamor wiper control should click fromone state to another, the way the final product works comes down to a recognised perception of quality. The aggravation of a high beam that switches on too easily or the lack of a satisfying click achieved with just the right amount of pressure is enough to damage the reputation of the brand, something which localmanufacturers are very keen to avoid. Testing this haptic feedback fromswitch


controls is a new application for traditional compression test equipment fromZwick Roell, which is attached to computers


Engineer, Stephanie Roesner, a number of factors need to be considered, such as subtractingmachine deformation fromthe results and the way the spring ismounted for testing. “Fixturing is part of Zwick Roell’s know-how and we provide customers with support on all their fixturing requirements as well as supplying the test equipment,” she says. The fixturing is extremely important in


reproducing real-world conditions on the testmachine.When a coil spring is compressed, there’s a torsional component to the load that tends to try and rotate the spring. If the end is restrained, the spring stiffens and the force vectormigrates.


AUTOMOTIVE SPRINGS With traditional suspension geometry where the damper is in line with the spring, the force vector is less important but it becomes a crucial element in complex suspension constructions, such as those used inmotorsport andmore expensivemodern cars. Knowing this force vector for the spring configuration is essential for optimising the handling characteristics of the car. For this reason, suspension suppliers use


the Zwick spring tester to provide the car manufacturer with the full spring characteristics and the OEMs use themfor design, development and conformance testing. In such circumstances, the attachment of


the spring to the testingmachine can either be free formfor development work or it can replicate the vehiclemounting structure for production testing. Tomeasure the spring forces, six load


cells are attached so that all the complex force components throughout the coil are fed into the computer for analysis. Using such equipment has led to the successful development of extremely light composite springs being used to reduce unsprung weight and improve handling. EE


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