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Solving Common Defects of Sheet Metal Stamping



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Services & Tech >> Solving Common Defects of Sheet Metal Stamping
How To Solving Common Defects of Sheet Metal Stamping
Sheet Metal fabrication is fairly predictable, as many fab shops use measurement tools, automation, and other tools to assure quality.
Below are solutions for the most common defects of sheet metal fabrication, including unexpected sizing, deformation, and more: 
According to Stamping Simulation, Wrinkles occur when the...stamping process produces compressive strains that 'push' material together, causing the material to overlap each other in the worst case.
Because "a thicker material resists the compressive forces more than a thinner. A thin material will wrinkle more easily."
To solve this common issue, stretch or draw the material instead of forming or "crushing" without pads or binders restraining the flat sheet. For complex 3D shapes, pads, binders, and draw beads are necessary for maximum stretch and wrinkle prevention.
Stamping Simulation defines splitting as "when strains cause the material to thin beyond the material’s safe limits."
Certain metals innately have work-strengthening characteristics that increase formability as strains increase, but a finite limit and the direction of strains determines if or when a piece will split.
It begins as a localized yield (called necking) before a full split occurs due to yielding and passing its tensile strength threshold. Tensile strength is the resistance of a material to breaking under tension.
To solve this common issue, use a forming limit diagram prior to design. If a split occurs, carefully consideration material type, material thickness, minimum form radius, form depth, number of forming stages, and blank shape/size.
Stamping simulation software is often needed to cost effectively analyze and solve a splitting problem [in order] to avoid cost prohibitive trial and error on the shop floor.
According to Stamping Simulation, "A springback defect [occurs] when an unexpected shape change takes place after forming or stamping is completed. The final part dimensional shape does not match the desired nominal shape and falls outside of required tolerances."
Springbacks are caused by the elastic region of the stress-strain curve on a piece of metal. The piece is strained and then relaxed according to its innate characteristics.
High-strength materials have severe springback problems that are caused by a small difference between yield strength and tensile strength. Yield strength is the stress at which a specific amount of deformation is produced.
To solve this common issue, "overbend" or "compensate"the forming tool shape. If this doesn’t work on its own, induce "positive stretching to increase part strength such that the product becomes stiffer and stronger than the original material."
Like splits, an advanced simulation software is needed to cost effectively solve a springback defect.
Creating a bend means stretching the metal over the outer radius and compressing it on the inner. How the metal handles this stretching and compression determines the extent of deformation.
To solve this common sheet metal issue, fabricators must pay detailed attention to the following five factors:
1. Grain direction. Bend across the grain instead of along it to reduce the risk of cracking.
2. Work hardening. Bend faster to reduce work hardening, which reducing the bending force necessary.
3. Hardness and thickness variation. Specifications for sheet metal allow for a range of hardness and thickness.
4. Hole positions. Any hole should be at least three times the material thickness away from the start of the bend.
5. Sheet size. The force necessary for a bend into a sheet metal piece is proportional to the length of the bend.
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