Method for producing blank, method for producing press-formed part, method for judging shape, program for judging shape, apparatus for producing blank, and blank

A method for producing a blank by using a punching and shearing device having a punch having an upper blade and a die having a lower blade,

• the upper blade comprising a first inclined part, second inclined part, and third inclined part provided in that order in a cutting line direction of the metal sheet,
• an angle θ1 of the first inclined part with respect to the metal sheet in the cutting line direction, an angle θ2 of the second inclined part with respect to the metal sheet in the cutting line direction, and an angle θ3 of the third inclined part with respect to the metal sheet in the cutting line direction satisfying
• θ2≤θ1/2 and
• θ2≤θ3/2, and
• at the time of the punching, the first inclined part and the third inclined part contacting the metal sheet, then the second inclined part contacting the metal sheet,
• wherein,
• in a point cloud (xn, yn) of the shape of the upper blade comprising sets of cutting line direction positions (xn) and displacements (yn) of the upper blade along the direction of movement of the punch corresponding to the xn in a direction away from the metal sheet,
• a second order difference quotient J2n=(yn+1−2yn+yn−1)/(Δx)2, a maximum value J2max of the second order difference quotient, and J3n=J2n/|J2max| are defined, a first point where an absolute value of a type judgement value J3n becomes a predetermined threshold value δ2 or more is a boundary position of the first inclined part and the second inclined part, and a last point is a boundary position of the second inclined part and the third inclined part, and
• wherein the predetermined threshold value δ2 is 0 or more and not more than 1, and θ1, θ2, and θ3 mean respectively the average values of the maximum values and minimum values of the angles formed with the metal sheet by tangents at any points of the first inclined part, the second inclined part, and the third inclined part,
• the method comprising:
• producing the blank, using the punching and shearing device having the punch having the upper blade and the die having the lower blade, by punching the metal sheet placed between the punch and the die.