Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.38 No.433 February 1997)
Simulation of Shearing
Kazutake KOMORI
(Received on January 16, 1996)
The objective of the present work is to clarify ductile fracture phenomena in bulk metal forming by FE
analyses and experiments. We have developed a computer program based on a conventional computer program
of FEM by which behavior of crack propagation after ductile fracture can be analyzed. The phenomenon that
a material is divided into two by shearing has been simulated by the program, and the following results are
obtained. First, in order to perform simulation precisely, we have developed a method of representing the
sharp change in direction of material flow at tool corners, a method of controlling tool displacements so that
an element is fractured in each step and a method of separating nodes at fracture. Second, analytical results
of shape of sheared surface, length of sheared surface and fractured surface, and maximum punch load are
found to agree with experimental ones. Hence, we have shown the validity of the methods.
Key words : shearing, numerical analysis, rigid plastic FEM, ductile fracture
Effect of Heat Treatment for Galling behavior of Tool steels
|Role of Carbide in Suppression of Galling I|
Yoshinari TSUCHIYA, Tohru ARAI and Susumu SHIMA
(Received on January 29, 1996)
Tribological properties of carbon tool steels and high speed tool steels with various arbide contents prepared by various heat treatments are examined, focusing on their galling behavior when used as metal forming dies. For carbon tool steels, the surface damage during a drawing type friction test is classified into five stages from little damage to severe damage. The anti-galling ability of carbon tool steels is suppressed at a certain tempering temperature for each carbon content; in this case hardness is about 50HRC independent of carbon content. In the case of high speed tool steels, the anti-galling ability depends on carbide content and not on the hardness.
Key words : friction test,galling behavior,metal forming die, tool teel,adhesion, carbide, heat treatment.
Galling Behavior of Role of Carbide Tool Partially Coated with VC
|Role of Carbide in Suppression of Galling ‡U|
Hiroyuki KAWAURA, Tohru ARAI and Susumu SHIMA
(Received on January 29, 1996)
The effect of carbide on suppression of initiation and growth of galling is examined; steel dies partially coated with VC in a stripe pattern made by photoetching technique are used in a drawing type friction test. Galling which appears at a steel stripe tends to extend to the next one according to increase in drawing length. In somecases galling grows severely after coalescence of galling over the VC stripes. When a steel stripe is narrow, however, growth of galling is limited within the steel stripes because of the effect of the VC stripes.
VC suppresses the growth of galling not only parallel but perpendicular to the die surface, hence preventing severe growth of galling.
Key words : friction test, tribology, metal forming die, adhesion, galling, photoetching, VC coatings, stripe pattern coating
Analysis of the Residual Stress Induced by Bar and Wire Drawing
Norihito KUNTANl and Motoh ASAKAWA
(Received on February 28, 1996)
The residual stresses after cold drawing were analyzed experimentally during field operation and theoretically using the elastoplastic finite element method (FEM). It was clarified that the residual stress was a maximum for conventional die angles and drawing reduction. The straightness of shafts after processing was improved by appropriate selection of drawing conditions.
Key words : drawing, residual stress, straightening, elastoplastic FEM, experimental analysis
Fractal Analysis of Adhesion Particles on Tool Surface in Compression of Aluminum Strips
Yasushi KUROSAKI, Masahito MATSUI, Yasuhiro ASANO and Kenichi MURAI
(Received on March 18, 1996)
Fractal geometry is applied to the analysis of particles adhered to the tool surface in simple compression of aluminum strips. The shape of particles is found to be self-similar, and their estimated fractal dimension depends on the surface topology of specimens, irrespective of the compression strain, tool surface finishing techniques and lubrication. The ratio of the total adhesion area to the apparent contact area increases with an increase in the fraclal dimension of the tool surface. The cumulative frequency of each particle size (area) and the behavior of particle growth are also examined. A method for computer simulation of the adhesion feature is presented, and satisfactory images are constructed.
Key words : material testing, compression test, aluminum sheet, tribology, adhesion, measurement, tool surface, adhesion particles, fractal, self-similar.
Influence of Microstructure on Formability of Ultrahigh-Strength Steel Sheet
|Formability of Ultrahigh-Strength Steel Sheet ll|
Kazumasa YAMAZAKI, Yaichirou MIZUYAMA and Yoshikuni OKUNAGA
(Received on April 26, 1996)
The influence of microstructure on the formability of ultrahigh-strength cold rolled steel sheets used for automotive structural parts is investigated. Deep drawability is affected by the shoulder radius of the forming tools, and steel that has inhomogeneous microstructure, which is the cause of poor local ductility, shows poor deep drawability. Shrink flanging fracture is affected by the volume of retained austenite; steel that has a large amount of retained austenite has a tendency to undergo shrink flanging fracture easily. For biaxial stretch deformation, steel that has good total elongation shows good biaxial stretch formability when it is formed with tools with a large shoulder radius. Steel that has good local elongation shows good biaxcial stretch formability when it is formed with tools with a small shoulder radius. With respect to stretch flangeability, steel that has homogeneous microstructure shows good stretch flangeability. Cold work embrittlement is affected by the
volume of retained austenite; steel that contains a small amount of retained ausutenite shows good resistance against cold work embrittlement.
Key words : formability test, deep drawing, stretch flanging, shrink flanging, burring, material property,ferrous metal
Hot Strip Crown Control Hereditary Method that Distribution in makes Lateral Use of Crown-Ratio Hereditary Distribution in LateralDirection
Yuichi HONGO, Tosio YANAI and Hiromu TUNEDA
(Received on May 14, 1996)
A three-dimensional rigid plastic finite element method is applied to control the profile of a hot strip.Lateral metal flow takes place in a rolled material within an area of some distance from the edge of material,which means that the crown-ratio hereditary coefficients in the lateral direction are not uniform but is distributed in the hill form. These physical properties are tested on a working hot strip mill at Nippon Steel Oita Works. Center crown control applied to former finishing stands can change the central area of the strip
crown, while edge crown control applied to latter finishing stands can change the edge area of the strip crown,by the use of these physical properties.
Key words : rolling mill, strip rolling, profile, hot strip mill, crown-ratio heredity
Some Contrivances On the Pipe Bending Method Using Floating Expanding Plug
Kiyotaka HAYASHI, Masao NAKAMURA, Seijiro MAKI and Yasunori HARADA
(Received on June 13, 1996)
In order to obtain a bent pipe with an improved shape and a smaller bending radius by the pipe bending method using a floating expanding plug, first an r-plug expected to remove redundant shear deformation at the entry was used, and then an oval plug expected to reduce cross-sectional flattening was used, and the diameter of the pipe was further pre-reducted. ( I ) Use of the r-plug decreases the bending radius limit, the wall thickness difference
difference and the roughness of the inner and outer bent surfaces. (2) Use of the oval plug can reduce cross-sectional flattening for small bending radiuses. (3) Use of the pre-reduced pipe enables the realization of a bent pipe with its original diameter and wall thickness, along with a smaller bending radius limit and wall thickness difference.
Key words : tube forming, bending, expanding, new forming process, forming
property
Development and Characterization of Planetary Roller Reducer
Manabu KIUCHI and Ken SHlNTANI
(Received on June 17, 1996)
A new type of pipe reducer called a planetary roller reducer (PRR) was proposed. PRR has six or eight small work rolls which are installed around a pipe's periphery and driven to rotate along its surface. Each work roll, with appropriate elevation angle and offset angle, compresses the pipe surface along a spiral orbit.Thus the diameter of the pipe is reduced. A prototype PRR machine was built and a series of reduction tests were carried out for steel, stainless steel and aluminum pipes. The limit of reduction, roundness and wall thickness distribution of reduced pipes, real feeding velocity and surface smoothness were investigated.The usefulness of PRR has been clarified.
Key words : pipe reducer, planetary roller reducer, elevation angle, offset angle, straight pipe, taper pipe, limit of reduction, spiral orbit.
Roundness of Improvement and Tubes Using PRR Straightening Machine
Manabu KlUCHI and Ken SHlNTANI
(Received on June 27, 1996)
A prototype planetary roller reducer (PRR) machine was built and used for improvement of cross-sectional roundness and straightness of aluminum, steel and stainless steel pipes. In the test, pipes with oval cross sections and longitudinal curvature were treated using the PRR test machine.The irregularity of pipe cross section is effectively corrected by the proposed planetary roller reduction process, and a high level of cross-sectional roundness can be obtained easily using this process with appropriate OD reduction. When the effect of welded beads is negligible, the PRR machine can be used to obtain good straightening of aluminum and stainless steel pipes. However, when the mechanical properties of welded beads are very different from those of other portions, the PRR machine cannot perform satisfactory straightening operation of welded steel pipes.
Key words : reducing, planetary roller reducer, irregular pipe, cross-sectional roundness, straightness.