Challenges in Sheet Metal Testing
Determining the most vital material properties of sheet metal can be completed during a uniaxial tensile test. Results, such as Ultimate Tensile Strength, Yield Strength and Elongation, are typically reported. More challenging requirements is the determination of r and n values. These properties are of great importance for applications of sheet metal as they determine the desirable behaviors that make metals suitable for processes including deep drawing and stretch forming.
The three largest markets for sheet metal are:
- Automotive (largest growth is seen here)
- Consumer Products
The automotive industry, which is the largest consumer of sheet metal products, is causing the biggest change for different types of sheet metal producers. The driving force for change is the need to lower the overall un-sprung weight of vehicles, helping to reduce emissions output to meet stricter legislation and improve their customer’s satisfaction by meeting their efficiency expectations.
Due to their high-strength properties, composite materials are being more actively considered by automotive producers as they can offer significant weight reductions. Cost of manufacture is still high for these materials, and sheet metals formability properties are incredibly advantageous for high-volume production. What's the solution? Higher strength sheet metals.
Sheet metal producers are working closely with the automotive industry to develop specific products that are stronger, so that a smaller cross section can be used, thus reducing overall weight. Steels are now being produced much stronger to achieve automobiles weight goals. However, aluminum production has also increased as its strength is now comparable with steel, making it more viable for new applications.
What are the implications of the market trends for your testing regime?
- Increased Load Capacity of Testing Equipment
- Gripping Issues
- Violent Specimen Failures
- Reduced Formability
- More Testing Required
Metallic materials require massive amounts of mechanical testing in all phases of use and application – from development, to qualification, to production, and to quality control. The various combinations of testing, along with the sheer number of tests required to make statistically meaningful conclusions, points to the need for some sort of automation, particularly in Quality Control.
Over the course of multiple interviews and working with key metals producers, we have found that the dominant issues in Quality Control labs are:
- Variability: it is inevitable that the introduction of human input into a process will introduce some element of variability. Robotization can eliminate most or all of this by doing things exactly the same way, every time.
- Throughput: Globally, labs are seeking ways to do more with less. Whereas a robotic system may not always be able to outperform a human in terms of (testing) speed, they are able to work at odd hours and without supervision – thereby increasing the number of tests per unit of labor time.
- Repetitive Tasks: QC testing can involve a lot of repetitive motion and tasks, which may not necessarily be the best use of skilled labor – which it typically required to meet the challenging needs of precision mechanical testing. An automated testing process can allow skilled technicians to do more value-added tasks around the lab.
- Safety & Ergonomics: mechanical testing requires frequent placement of operator hands/fingers in the test area, mainly to insert/remove specimens, attach/remove extensometers, and the like. Every such instance has a potential safety concern and should be treated as such. Automation/robotization of these activities/tasks not only increases the overall safety of the lab but also addresses the ergonomic issues resulting from the continuous repetition of these motions by the operator.
Based on these insights, it is increasingly common for lab managers to find ways that best remove the operator from the test cycle without compromising accuracy and repeatability, but yet produce the kinds of results necessary to support production or R&D.
When exploring the various levels of automation in your lab, the key areas to focus on are a combination of process and product:
- Specimen identification and data entry (bar-coding)
- Specimen measurement (digital measurement devices with direct input to the computer)
- Gripping (automatic pneumatic and hydraulic powered grips)
- Extensometry (automatic hands-free strain measurement devices, contacting, and non-contacting)
- Specimen Handling Systems (Cartesian, robotic)
Combining process and product into an automated solution contributes toward minimizing variability of results, making better use of skilled labor in the lab, increasing safety, and increasing laboratory throughput.
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Global growth within the construction industry is anticipated over the next decade — bridges, roadways, hotels, stadiums — all requiring reinforcement bar (rebar). Rebar manufacturers and suppliers are facing challenges due to increased production volumes, the need for higher strength and larger diameter rebar, an increased requirement for stainless and coated grades, and more construction applications that require mechanical couplers.
Thomas Wodcke, Product Engineer and Applications Specialist for Instron's Industrial Products Group, talked with AZoM.com about these industry demands.Read the full interview
Presentations & White Papers
- Sheet Metal Testing Challenges
- Metallic Materials for Tensile Testing: ISO 6892-1:2009
- System Compliance and ISO 6892-1:2009 Method A
- Rebar Tensile Testing Guide
About Strain Measurement
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