Method of predicting damage of dies

a technology of die damage and method, applied in forging/pressing/hammering apparatus, forging/hammering/pressing machines, cutting tools, etc., can solve the problems of brittle fracture, death damage, and the methods of predicting die damage proposed so far are not effective for this kind of brittle fracture, and the formulae are not applicable to the brittle fractur

Inactive Publication Date: 2006-10-19
DAIDO STEEL CO LTD
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0006] The object of the present invention is to provide a method of predicting damage of dies enabling design of improved dies by predicting brittle fracture which give, among various factors causing damage to forging die, fatal influence to die lives.

Problems solved by technology

The brittle fracture is a sudden phenomenon occurring at an initial stage before substantial use of the die, and also called “initial crack”, which is a fatal damage.
However, methods of predicting damage of dies proposed so far are not effective for this kind of brittle fracture.
These formulae are, however, not applicable to the brittle fracture.

Method used

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  • Method of predicting damage of dies
  • Method of predicting damage of dies
  • Method of predicting damage of dies

Examples

Experimental program
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Effect test

example 1

[0029] SKD61, one of the steels for hot processing tools, was used as the die material and the hardness was adjusted to be HRC 46, 49 or 52. JIS No. 4 tensile test pieces were prepared and some of them were subjected to machining to provide surrounding V-shaped notches of depth 50%. The shapes and dimensions of the test pieces are shown in FIG. 1 (smooth surface), FIG. 2 (notch angle 30°), FIG. 3 (90°) and FIG. 4 (120°). Curvature of the bottom of the notches is 0.2 mm.

[0030] The test pieces were subjected to tensile tests to determine mean normal stress (σm) at which fracture occurs and at the same time whether the fracture is ductile fracture or brittle fracture was recorded. The equivalent stress (σeq) and the maximum principal stress (σ1max) were calculated. By plotting the mean normal stress (σm) in correspondence of the equivalent stress (σeq) there was obtained FIG. 5, by plotting the mean normal stress (σm) in correspondence of the maximum principal stress (σ1max), FIG. 6, ...

example 2

[0032] The prediction of die life according to the present invention was carried out in regard to a ring-die, a die for limiting the outer surface of the work forged by a punch and a counter punch from top and bottom used for hot forging a final gear, an automobile part, having the cross section shown in FIG. 8. A used die made of SKD61 steel was inspected and it was found that crack of the ring-die occurred from the outer surface.

[0033] The following three CG's were obtained by analyzing distribution of the critical fracture values Fc1 to Fc3 on the basis of the above database by computer simulation (FEM analysis).

FIG. 9 (former shape) Fc1=(σm / σeq)

FIG. 10 (former shape) Fc2=(σm / σ1 max)

FIG. 11 (former shape) Fc3=(σ1 max / σeq)

[0034] All the CG's showed that in some parts of outer surface of the ring-die Fc1 to Fc3 exceed the critical values. The fact agrees with the results of the above inspection.

[0035] Then, supposing the cases where the outer diameter of the ring-die is incre...

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Abstract

Disclosed is a method of predicting damage of dies for plastic processing of metallic materials, typically, forging dies, by predicting brittle fracture (“great crack” or “initial crack”) dominating die lives contribute to die design including choice of materials, hardness and configuration of the die. The method is characterized in that the die design is carried out by choosing the condition that none of the anticipated values of brittle fracture, Fc1 to Fc3, calculated by the formulae 1 to 3 below exceed the critical values depending on the material used. Fc1=(σm / σeq)  [formula 1]Fc2=(σm / σ1 max)  [formula 2]Fc3=(σ1max / σeq)  [formula 3]σm: mean normal stress loaded to the tensile side of the die σeq: Von Misese's equivalent stress σ1max: maximum principal stress

Description

BACKGROUND OF THE INVENTION [0001] 1. Technical Field [0002] The present invention concerns a method of predicting damages of dies. More specifically, the invention concerns predicting damages in dies for plastic processing of metals, typically, forging dies by predicting “great crack” damage caused by brittle fracture which dominates die lives, and utilizing the results for die design including choice of materials, hardness thereof and determining the die configuration so as to establish countermeasures for prolongation of die lives. [0003] 2. Prior Art [0004] At manufacturing and application of forging dies various methods of predicting damages in dies have been developed and utilized for enabling manufacture of dies of longer lives. As the method of prediction it is generally employed to calculate temperature and stress distribution in a die by finite element analysis and then substitute the calculated values for constitutive equations to predict low cycle fatigue lives and abras...

Claims

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Application Information

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IPC IPC(8): B21K5/20
CPCB21J13/02
InventorYOSHIDA, HIROAKIITOH, SHIGEKAZU
OwnerDAIDO STEEL CO LTD