QMT Features: February 2013
Testing challenges
Responding to the global demands for  precise and reliable test results,  Zwick delivers innovation and automation. By Brendan Coyne, QMT.

The Zwick Roell Group is a world leader in the field of automated material and component testing.  Zwick began manufacturing testing machines in Ulm, Germany, back in 1938 and grew, in the ensuing decades, to become one of the world’s leading manufacturers of machines for materials testing. Its product range covers materials testing machines for compression, tensile and bending tests on material specimens, workpieces and components.

Some of the challenges facing the development of materials testing technology to meet the demands of researchers and industry are outlined by Dr. Jan Stefan Roell, chief executive officer of Zwick/Roell AG., “We see that customers in composite area  (aerospace and automotive sectors in particular) require more and more automated testing. This is a new field. and, for engineers,  very challenging because there are lots of different standards on how to test composites. So automation  is a challenge - which we gladly take on board. We have customers in Europe and North America  requesting this capability.

Another area that seems to be growing is high temperature testing (for metals.), where researchers are looking at constantly increasing environmental temperatures.  That’s also a challenge to build test systems and extensometers to test materials for temperatures beyond 1500 0C.
With non contact extensometers, we are faced with all kinds of materials that customers want to test without touching the specimen, while measuring the strain of the  specimen. We have to qualify the optics of the extensometer and that’s a challenge. Another challenge is also be able to qualify  coatings and surfaces of materials. This is a challenge for our newly acquired business in Dresden, ASMEC, which focuses on this technology”.

Recently, 1,200 users and experts gathered at Zwick/Roell headquarters in Ulm  to take part in a four-day informational exchange on materials testing. Visitors from countries including China, Russia, and the United States came to the 21st testXpo forum to learn more about the latest techniques and international standards for the characterisation of plastics, composites, automotive materials, metal alloys and biomaterials.
According to Dr. Jan Stefan , two major themes for this year’s event were innovation and automation. Each theme is a reflection of trends in the testing of materials and components. “As customers seek new ways to address the challenges within their respective markets, they look for solutions that optimise testing routines,”  he said. Following through on that theme,  Zwick then presented its new Allround-Line system for composites testing and the roboTest platform, which increases throughput via automation of test sequences,.

Materials testing requires the highest possible accuracy. The slightest deviation in the motion changes the material characteristics. For this reason, Zwick has been automating its materials testing machines with KUKA robots for over 10 years and now has over 300 robotic testing systems installed  around the globe.

The objective of the robotic testing system is to reduce deviations to a minimum. The main task of the KUKA robot is the exact loading and positioning of the material to be tested. It is only with a robotic system that materials testing really has a reproducible process without loss of value – the cycles are fixed.

Test  specimens can be anything from pieces or strips of metal to insulin pens or parts for medical components. Large steel bars are also tested, measuring up to 700 millimetres in length and weighing up to 15 kilograms. “A specimen is destroyed in 80 to 90 percent of the cases,” explains Robert Kaifler, automation product manager at Zwick. “The resulting control parameters are subsequently fed into the production system to optimize it. The principle is the same whether the system is a steel rolling mill, an injection molding machine or a machine for manufacturing insulin pens.”

Zwick customers mostly conduct standard tests. “The primary objective is, of course, cost reduction,” explains Robert Kaifler. 80 percent of applications for the KUKA robots with the Zwick testing systems involve destructive testing, while 20 percent are accounted for by non-destructive materials testing. The most commonly used robot types are the KR 6, KR 30 and KR 60.

Medical technology
For some years, Zwick has been actively involved in the field of medical technology. The reproducibility of the test results is critical when testing medical products. To meet this requirement, Zwick has developed a fully-automatic system for testing insulin pens, consisting of a Zwicki-Line materials testing machine with integrated torsion drive, combined with a KR 5 sixx robot from KUKA,

The testing machine measures the dosage setting and triggering force and calculates the administered dose in one continuous process. Test methods on the two test axes can be modified and combined as required. Automated specimen feed is carried out using the robotic handling system. Falsification of the test results caused by operator influence is eliminated.

The test process is made significantly more efficient by the increased specimen throughput, while testing can also be performed manually at any time if required.

In other examples relating to medical applications, automated Zwick testing systems can  be used to test the force required to unroll gauze bandages, the material properties of dental syringes or the child-proof caps of medicine containers. “A production process for medical products must be seamlessly documented in accordance with the FDA directive. Here, once again, automation with KUKA robots ensures precisely plannable and traceable sequences,” emphasizes Robert Kaifler.

Using KUKA’s open control concept, Zwick can adapt the testing systems to the specific requirements of the end customers. Furthermore, there is a wide range of expansion options available, making it easy to adapt the robot to changing requirements or new tasks. Robert Kaifler is convinced,
“Our success has proved us right. Opting for KUKA robots was the right decision.”

A good example of the sort of innovation Dr Roell is keen to highlight is the introduction of  short clamping-length grips. More and more tests require short specimens or short clamping lengths to be gripped and held securely in standard specimen grips. Innovative hydraulic grips developed by Zwick especially for these applications are increasingly being used for quality assurance testing in the automotive industry.

The ever-growing demands on active and passive vehicle safety have resulted in significant changes in safety design. Many different process stages (heat treatment, forming, welding, rivetting, bonding) are involved in the manufacture of structural components such as bumper assemblies or A and B pillars. In order to be able to check material properties accurately following each production step, specimens must be produced directly from the structural components. Due to the small surface areas involved these specimens are of necessity very small and could not be held securely and tested using existing specimen grips.

The new hydraulic grips close symmetrically. The patented precision mechanical guidance system fitted to the two hydraulic actuators actively counteracts the high tilting moments which arise on guides and actuators where short clamping lengths are involved. This provides parallel, uniform gripping of short specimen ends (= short clamping lengths) throughout the test. The guidance system also automatically ensures accurate alignment in the test and force axis. These new Zwick grips therefore guarantee reproducible testing of material properties directly after production stages.

Short specimens often rule out the use of conventional contact extensometers. An alternative solution for this application is offered by Zwick’s special optical extensometers (e.g. laserXtens Compact, videoXtens), which enable reproducible non-contact strain measurement on even the shortest or most inaccessible specimens. l
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