Method for specifying stretch flange limit strain and method for determining feasibility of press forming

Patent metadata

Field	Value
Publication number	US-9953115-B2
Application number	US-201314436236-A
Country	US
Kind code	B2
Filing date	Oct 10, 2013
Priority date	Nov 19, 2012
Publication date	Apr 24, 2018
Grant date	Apr 24, 2018

Abstract

A method for manufacturing a press formed part, the method including specifying stretch flange limit strain in a metal sheet by using strain gradient in a radial direction and strain gradient in a sheet thickness direction. The strain gradient in the radial direction being directed from an end portion of the metal sheet at a time a press load is applied. The strain gradient in the sheet thickness direction being a direction of the metal sheet that intersects a loading direction. Additionally, the stretch flange limit strain satisfies the formula ϵ θlim =A[a·Δϵ θ /Δr+b·Δϵ θ /Δt]+c, where ϵ θlim represents the stretch flange limit strain in a tangential direction of the sheet edge, Δϵ θ /Δr represents the strain gradient in the radial direction, Δϵ θ /Δt represents the strain gradient in the sheet thickness direction, A, a, and b represent influence coefficients, and c represents the limit strain at a time the strain gradient is zero.

First claim

The invention claimed is:

1. A method for manufacturing a press formed part, the method comprising:
specifying stretch flange limit strain in a metal sheet so as to satisfy formula 1 by using: strain gradient in a radial direction directed from an end portion of the metal sheet at a time a press load is applied; and strain gradient in a sheet thickness direction of the metal sheet that intersects the loading direction; and
press forming the metal sheet to form the formed part,
wherein:
ϵ θlim =A[a·Δϵ θ /Δr+b·Δϵ θ /Δt]+c   formula 1

where ϵ θlim represents the stretch flange limit strain in a tangential direction of a sheet edge,
Δϵ θ /Δt represents the strain gradient in the radial direction,
Δϵ θ /Δt represents the strain gradient in the sheet thickness direction,
A, a, and b represent influence coefficients, and
c represents the limit strain at a time the strain gradient is zero.

2. A method for manufacturing a press formed part, the method comprising:
specifying stretch flange limit strain so as to satisfy formula 2 by using strain gradient in a sheet thickness direction of a metal sheet intersecting a loading direction at a time a press load is applied; and
press forming the metal sheet to form the formed part,
wherein:
ϵ θlim =A[b·Δϵ θ /Δt]+c   formula 2

where ϵ θlim represents the stretch flange limit strain in a tangential direction of a sheet edge,

Δϵ θ /Δt represents the strain gradient in the sheet thickness direction,
A and b represent influence coefficients, and
c represents the limit strain at a time the strain gradient is zero.

3. A method for manufacturing a press formed part, the method comprising:
acquiring stretch flange limit strain at a sheared edge of a metal sheet by executing a hole expansion test while changing a diameter of an initial hole and a shape of a hole expanding punch;
obtaining strain gradient in a radial direction of the initial hole near the sheared edge after the hole expansion test;
obtaining strain gradient in a sheet thickness direction near the sheared edge after the hole expansion test;
determining feasibility of press forming, which causes stretch flange strain, by using empirical formula 3; and
press forming the metal sheet to form the formed part,
wherein:
formula 3 represents a relation between stretch flange limit strain ϵ θlim and a value [a·Δϵ θ /Δr+b·Δϵ θ /Δt] obtained by adding the strain gradient in the radial direction with the strain gradient in the sheet thickness direction,
formula 3 is obtained by using: the stretch flange limit strain acquired in the step of acquiring the stretch flange limit strain; the strain gradient in the radial direction obtained in the step of obtaining the strain gradient in the radial direction; and the strain gradient in the sheet thickness direction obtained in the step of obtaining the strain gradient in the sheet thickness direction,
Δϵ θ /Δr represents the strain gradient in the radial direction,
Δϵ θ /Δt represents the strain gradient in the sheet thickness direction, and
a and b represent influence coefficients.

4. A method for manufacturing a press formed part, the method comprising:
acquiring stretch flange limit strain at a sheared edge of a metal sheet by executing a hole expansion test while changing a diameter of an initial hole and a shape of a hole expanding punch;
obtaining strain gradient in a sheet thickness direction near the sheared edge after the hole expansion test;
determining feasibility of press forming, which causes stretch flange strain, by using empirical formula 4; and
press forming the metal sheet to form the formed part,
wherein:
formula 4 represents a relation between stretch flange limit strain ϵ θlim and the strain gradient in the sheet thickness direction [b·Δϵ θ /Δt],
formula 4 is obtained by using: the stretch flange limit strain acquired in the step of acquiring the stretch flange limit strain; and the strain gradient in the sheet thickness direction obtained in the step of obtaining the strain gradient in the sheet thickness direction,
Δϵ θ /Δr represents the strain gradient in the radial direction, and
b represents an influence coefficient.

Assignees

• Jfe Steel Corp

Inventors

• Sonobe Osamu
• Ishiwatari Akinobu
• Urabe Masaki
• Kano Hirotaka
• Hiramoto Jiro

Classifications

• B21D19/00

  Flanging or other edge treatment, e.g. of tubes (connecting by making use of folds B21D39/00; flaring-out tube ends B21D41/02) · CPC title

• B21D53/88

  other parts for vehicles, e.g. cowlings, mudguards · CPC title

• G01N2203/0075

  Strain-stress relations or elastic constants · CPC title

• G01N2203/0254

  Biaxial, the forces being applied along two normal axes of the specimen · CPC title

• G01M99/007

  by applying a load, e.g. for resistance or wear testing (G01M99/001 takes precedence; testing the elasticity of structures G01M5/00) · CPC title