Page 43 - MetalForming Magazine May 2023

Normal Material-Property Variation (such as yield strength shown here)
Normal variation in material properties requires a robust stamping process capable of accommodating the full range of potential properties.
itly calls out those parameters. In addi- tion, the surface profile of the sheet contributes to how the lubricant and the surfaces of the tool and sheet metal interact, and, therefore, influences material flow during stamping.
For those shops that rely on expe- rience, with little to no simulation, many of the same recommendations apply. Tryout during soft- and hard- tool development may involve the same batch of sheet metal and create one data point of success. The full vari- ability of a grade may not come for months or even years.
Regardless of the scenario, ensure that production personnel know what’s normal when it comes to sheet metal properties, and what’s unlikely but allowed in the specification to which you ordered the material. Making tool- ing changes to accommodate rare properties might upset an otherwise stable process. MF
Metal Matters
0.60
0.50
0.40 Relative Frequency 0.30
0.20
0.10
0.00
160 180
-3σ = 170 MPa
95%of all coils are within ± 2σ of the average
200 220 240
Strength (MPa)
99.7 percent of all coils are within ± 3σ of the average
260 280
+3σ = 270 MPa
Average
-1σ= 203 MPa
+1σ= 237 MPa
68%of all coils are within ±1 σ of the average
-2σ= 187 MPa
+2σ= 253 MPa
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