Force required For Coining/ Impressing Design

[david mabe]

Please help me figure this out.
Looking for a formula to estimate required tonnage to impress or coin an impression .045 inches deep into 1018 steel bar stock. I make leather stamping tools and have a 75Ton Ferracute Coing/Impression Press. If yield strength is 32kpsi the design is .45 inches (area) and I want to impress a flower design .045 deep the basic calculation says I need 14,400 psi. Doesn't work though because I know that 50 tons on a hydraulic press didnt cause the metal to flow. I have been impressing the tools under a 180lb drop hammer with steel heated to approximately 1800 degrees.
Point is I saw a formula that took into account the yield strength of the material, material thickness and desired depth of impression. Cant find it now.
Thank you.

 

[Rickyb]

Please help me figure this out.
Looking for a formula to estimate required tonnage to impress or coin an impression .045 inches deep into 1018 steel bar stock. I make leather stamping tools and have a 75Ton Ferracute Coing/Impression Press. If yield strength is 32kpsi the design is .45 inches (area) and I want to impress a flower design .045 deep the basic calculation says I need 14,400 psi. Doesn't work though because I know that 50 tons on a hydraulic press didnt cause the metal to flow. I have been impressing the tools under a 180lb drop hammer with steel heated to approximately 1800 degrees.
Point is I saw a formula that took into account the yield strength of the material, material thickness and desired depth of impression. Cant find it now.
Thank you.

You are on the right track just using the wrong reference value. You did say what you needed without knowing it. You need to find the “flow” stress for 1018 which is well above yield and closer to uts. Flow stress is dependent on the temperature you will coin at. Same calculation as for your hammer forging just a flow stress adjusted for temp.
formula is just the 0.45”sq projected area x flow stress. No need to consider the impression features.

 

[michiganbuck]

I should know this from coining seat belt parts ..but darn..I forget.

 

[john.k]

Soft iron might be more suitable.