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Sheet Metal Testing Challenges


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With a wide range of applications varying from white goods, automotive, and aerospace applications, sheet metals are often high in strength relative to their cross section area. It’s important to note that formability and ductility is also crucial, for which the common testing requirements are similar across applications. Explore the challenges in sheet metal testing.

Published in: Engineering

Sheet Metal Testing Challenges

  1. 1. Sheet Metal Testing Challenges
  2. 2. 2 Table of Contents • Sheet Metal Key Industries • Challenges of Testing Stronger Material • Challenges Determining Formability Properties • Extensometer Selection • Effect of Efficiency
  3. 3. 3 Sheet Metal Industries The top three industries that sheet metal is sold to: 1. Automotive (Largest growth) 2. Consumer products 3. Aerospace
  4. 4. 4 Automotive Sheet Metal Industry Summary • Reduce Emissions • The metals industry is producing stronger material than ever before! • Competition from Composite Material to Replace Metal • Formability is a key differentiator for metals • Increasing strength attempts to minimize composite material benefits • Aluminum ‘Taking’ Traditional Steel Market Share • Increased testing scrutiny from Automotive OEMs • GROWTH! • Growth = More metal needed = More testing required E F USA Changing Regulatory Requirements U.S. CAFE standards in 2016 Average fuel consumption needs to increase to 34.1MPG E F USA Changing Regulatory Requirements U.S. CAFE standards in 2016 Average fuel consumption needs to increase to 34.1MPG
  5. 5. 5 Stronger Material: Challenges • Increased Load Requirement • Is your current machine capable? • Higher wear on your system • Do you need higher testing machine capacity? • Gripping Issues • Are you having to increase clamping pressure? • Sign of worn jaw faces leading to specimen slippage • Violent Specimen Failures • Have you seen damage to your extensometer? • Increased wear on knife edges • Extensometer slippage  false readings • Reduced Formability • Measure r- and n-values accurately and repeatedly
  6. 6. 6 Formability: Challenges Metals Formability = Unique Selling Point (USP) vs. Composite Materials • Are the Formability Properties Important to You? • Calculating r- and n-values can be much simpler • Do You know the Yielding Behavior of Each Material? • Switching testing machine control modes is vital depending on the yielding type • Are You Testing More and More Specimens? • Learn how to increase your efficiency on your testing system
  7. 7. 7 Formability: r-value • The plastic strain ratio (r) of sheet metal is its ability to resist thinning or thickening when subjected to a tensile or compressive force • Difficult to measure thickness change; preferable to measure the length and width changes • Requires axial and transverse strains to be measured
  8. 8. 8 Formability: n-value • Sheet metal material’s, response to cold working is given by the strain-hardening exponent, n • It is a measure of the increase in strength due to plastic deformation Sheet metal with a high n-value exhibits a high increase in strength with minimal movement σ-Stress ε - Strain High n-value Low n-value
  9. 9. 9 Extensometers for r- & n-values
  10. 10. 10 Efficiency: Extensometer Comparison Specimen Measurement Minutes 1 2 3 AutoXBiax Clip-On > 30% FASTER! Specimen Insertion Extensometer Setup Test Time with Extensometer Removal Specimen Removal Total Cycle Time: 172 Seconds AVE 2 Total Cycle Time: 121 Seconds Total Cycle Time: 115 Seconds
  11. 11. 11 Tests Per Day Clip-On AutoXBiax Time Savings *Total per year 50 143 min 96 min 48 min 200 hours 100 287 min 192 min 95 min 401 hours 200 573 min 383 min 190 min 801 hours 300 860 min 575 min 285 min 1202 hours Effect on Throughput *Presuming 253 working days in a year In 1 year, that’s 401 hours of time saved
  12. 12. 12 Influencing Factors Specimen Measurement Specimen Insertion Extensometer Setup Test Time with Extensometer Removal Specimen Removal Automatically Calculated & Entered Vs Manually Entered Hydraulic Grips Vs Manual Grips Specimen Stops Vs Manual Alignment Automatic Contacting Vs Advanced Video Non Contacting Vs Clip-On Axial Vs Axial & Transverse Strain Rate Control Vs ‘Stress’ Rate Control Vs Crosshead Rate Control Hydraulic Grips Vs Manual Grips = Most Efficient Total Cycle Time Automatic Removal Vs Manual Removal
  13. 13. 13 The Differences • 6 measurements/specimen • ~42 keystrokes/specimen 10 TESTS = 420 KEY STROKES • Time spent aligning by eye • Grip closing time is longer • Time spent aligning by eye • Time to pause test to remove • Repeatable alignment • Automatically removes without pausing Specimen Measurement Specimen Insertion & Removal Extensometer Attachment & Removal Control Type • Automatic Gain Adjustment • Optimized test times INCREASED USER INTERACTION MINIMIZED USER INTERACTION • Specimen inserted quickly and easily with alignment devices • Grips close quickly • 6 measurements/specimen • ~7 keystrokes/specimen 10 TESTS = 70 KEY STROKES • Time spent tuning tests with specimens • Longer test times
  14. 14. 14 Potential Time Savings
  15. 15. 15 Software Efficiency Modifications Multiple Users Multiple Materials Multiple Inputs CAN COST $£ Some changes can be made quickly and easily to existing Bluehill® test methods to: • Decrease individual test time • Minimize downtime between tests • Allow for extra time spent on more value-added tasks +
  16. 16. 16 Software Efficiency Modifications: Prompted Methods • Optimal for a multiple-operator environment • Consistent entries • Consistent test flow from operator to operator • Customizable for different tests • Prompt before sample, before specimen, after specimen, after sample, etc.
  17. 17. 17 Software Efficiency Modifications: Yield Types Do you know the material’s yielding behavior? • Different methods needed for different material • False YPE will be calculated if the method is not setup for discontinuous material • If setup in strain control the machine could go out of control as yielding occurs outside the G.L. Instron® Bluehill® TestProfiler provides: • Automatic switch over for compliant method • Automatic end of YPE conditions dictate changeover • Machine control remains stable YPE/Ae = Yield Point Elongation
  18. 18. 18 Get your lab prepared today. Contact your local Instron® Sales Representative Visit for more information