Page 43 - MetalForming-January-2019-issue

Fig. 2
N-value relates to the slope of the stress-strain curve before uniform elongation and ultimate tensile strength are reached. Basically, a higher-sloped curve indicates a greater increase in strength for each additional amount of defor- mation (Fig. 2).
The curve from yield strength to tensile strength does not form a straight line. The slope of the stress-strain curve levels off as force is applied, eventually approaching zero at the ultimate tensile strength.
This tells us that if we are going to report the slope of
this curve—the n-value—then we also must report the range of data used to determine the slope. When you receive a metal cert, the range over which n-value is calculated must be included in order for it to comply with ASTM standards. Many end-users also require range reporting.
An interesting behavioral difference between some steel and aluminum alloys: The more formable grades of each have uniform-elongation values of around 25 percent. Most of these steel alloys exhibit increased duc- tility after necking but prior to fracture, resulting in a total elongation approaching 50 percent.
In contrast, post-uniform ductility in aluminum alloys only increases a few percentage points, leading to total- elongation values of around 30 percent. That’s why you may have noticed little wiggle room between when an
aluminum stamping starts to neck and when the part cracks. When it comes to sheetmetal stampings, fracture comes after failure. A stamped part fails when a neck first forms. Uniform elongation and n-value can be used to determine how the sheetmetal contributes to that failure. MF Learn about evaluating your organization and developing best practices when Bill Frahm from 4M speaks at PMA’s Metal Stamping and Tool & Die Conference in Nashville on January 29-30. Visit www.pma.org/mstd-conference for details
and registration.
The Science of Forming
Typical Stress-strain Curve
Tensile strength
F
AB CD
Uniform Elongation— deformation from beginning of forming through necking
FFF
ABABAB
Fracture
Total Enlongation— deformation from beginning of forming through splitting
Necking begins
CD
C D
C D
F FFF
Engineering Strain (%)
Premier Conference for Metal Stamping and Tool &DietobeHeldin January
Presented by PMA, in association with MetalForming magazine, the 2019 Metal Stamping and Tool & Die Conference will take place January 29-30 in Nashville, TN. Participants will learn from industry-leading professionals in the metal-stamping and tool-and-die communities, and have the opportunity to network with industry peers.
Topics include:
• Avoiding Legal Risks in Labor and
Employment Relationships
• Navigating the Steel Market
• Best Contracting Practices for Manu-
facturing and Minefields to Avoid
• Latest Innovations in High-Speed
Stamping
• Cutting and Punching High-Strength
Steels and Aluminum.
Visit www.pma.org/mstd-conference for
complete details and registration.
New Online Training Resource for the Metalforming Industry
Increase productivity and improve employees’ skills in 2019 with METALFORM EDU, PMA’s new flexible, convenient, low- cost online training resource designed specifically for the metalforming industry.
For more, visit www.pma.org/metal- formedu or contact Erin Riffle at 216/901- 8800 or eriffle@pma.org with questions.
Upcoming Calendar of Events
January 28, Tool & Die Division Meet- ing, Nashville, TN
January 29-30, Metal Stamping and Tool & Die Conference, Nashville, TN February 12-13, Lubrication Technolo- gy for Metalformers, Chicago, IL February 19-20, Die Maintenance and Troubleshooting Seminar, Greenville, SC
Spotlight on PMA
February 20-22, Metal Spinning Divi- sion Meeting, New Orleans, LA
Visit www.pma.org or contact PMA at 216/901-8800 or info@pma.org for details about these upcoming events.
PMA Welcomes Its
Newest Members
• Cozzi Recycling, LLC, Bellwood, IL
• Crum Manufacturing, Waterville, OH • High Value Manufacturing Consulting,
Brentwood, TN
• Jireh Metal Products, Inc., Grandville, MI • Komatsu America Industries,
Hermitage, TN
• Lapham-Hickey Steel, Fort Wayne, IN • Pennant Moldings, Inc. Tennessee,
Lebanon, TN
• Reynolds Services Inc., Auburn, IN Join PMA and experience the power
of membership! Contact Diana Novak at 216/901-8800 or dnovak@pma.org with questions.
www.metalformingmagazine.com
MetalForming/January 2019 41
Engineering Stress (ksi or MPa)