Papers in JOURNAL OF THE JAPAN SOCIETY FOR TECHNOLOGY OF PLASTICITY
(Vol.39 No.455 December 1998)
Friction Coefficient Test for Thick Sheet Forming
Free from Stress Measurement
Kohzoh KATOH and Kazuyoshi KONDO
(Received on December 26, 1997)
In order to obtain the background information for a new friction test, we reviewed a series of friction tests which utilized a nomograph to evaluate the friction coefficient. The purpose of this study was to develop a new friction test in regard to stamping of thick sheets, in which the friction coefficient can be evaluated. In the test, the height of the deformed dome in the center of the disk was compared with a nomograph obtained from FEM analysis. The feasibility of the new test was first confirmed through a series of processes with 5 types of lubricants. The actual friction coefficients were obtained by comparison with a nomograph. In the next step improvement of the ring punch profile was studied by means of an analytical method using gthe slab method.h In this approach a modified model was adopted and the inflence of the friction condition on the neutral point in the compression region was evaluated instead of on the deformed dome height. From the results the superiority of the convex profile punch was confirmed.
Key words : friction test, tribology, slab method, rigid plastic FEM, lubricants, thick sheet, stamping,
neutral point
Analysis and Quantitative Consideration of Inlet Oil Film Thickness
in Cold Sheet Rolling with Oil in Water Emulsions
\\An Investigation of Friction and Lubrication in Cold Rolling VI\\
Akira AZUSHIMA and Kazuya NORO
(Received on October 22, 1997)
Analysis of inlet oil film thickness in rolling is performed in order to clarify the lubrication behavior in cold sheet rolling with oil in water emulsion. The oil film thickness in the inlet zone of the contact region is calculated based on the Reynolds equation considering the effect of temperature and pressure of viscosity of the lubricant by applying a starved model. The calculated inlet oil film thickness depends on parameters such as particle diameter in emulsion, emulsion concentration, and trapped ratio. For higher lubricant viscosity, the differences between inlet oil thickness for emulsion and neat oil become larger. In addition, the calculated values are compared with the inlet oil film thickness estimated by the surface grosses of sheets rolled with oil in water emulsions and with starved neat oils, and good agreements between them are obtained. Consequently, it is found that the inlet oil film thickness in cold sheet rolling with oil in water emulsion can be quantitatively calculated using the proposed starved model.
Key words : cold rolling, oil film thickness, emulsion, friction, lubrication
Performance of Solution-Type Lubricants in Rolling of Stainless Steel
\\Solution-Type Cold Rolling Lubricants T\\
Shigetoshi OGURA, Jun-ichi SHIBATA,
Takaki OHKUBO and Katsumi SEKI
(Received on November 10, 1997)
In order to develop a uniform rolling lubricant with fire resistance and high cooling efficiency, the performance of solution-type lubricants containing water-soluble polymers is evaluated and compared with those of neat-type and emulsion-type lubricants, in rolling of stainless steel. Solution-type lubricants exhibit superior lubricity, especially at high reduction, compared with the other types of lubricants. The strips rolled with solution-type lubricants show lower surface brightness than those rolled with neat-type lubricants at low reduction; however the opposite is true at high reduction. The performance of solution-type lubricants is attributed to the following: (1) the very low viscosity of water at high pressures is responsible for the very low shear stress of its liquid film within the contact arc compared with that of neat oil, (2) the liquid film becomes thick because of viscosity increase caused by heat separation of polymers around work rolls, resulting in reduced contact ratio, and (3) water prevents the formation of microscratches because it cools the heat spots generated between roll and strip surfaces.
Key words : cold rolling, stainless steel, lubricant, solution type, polymer, heat separation, surface brightness, atomic force microscope
Effects of Heat Separation of Water-Soluble Polymers
on the Performance of Solution-Type Rolling Lubricants
\\Solution-Type Cold Rolling Lubricants II\\
Shigetoshi OGURA, Jun-ichi SHIBATA,
Hideo YOKOTA and Katsumi SEKI
(Received on December 17, 1997)
In order to investigate the effects of the heat separation of water-soluble polyumers of the performance of solution-type lubricants in cold rolling of stainless steel, rolling tests were performed using lubricants containing several polymers and oiliness agents in water. It is suggested that a dissolved polymer, which is capable of heat separation, may be deposited on heated roll surfaces, enabling the resultant polymer-rich layer of higher viscosity to be dragged into the contact arc, leading to greater liquid film thickness and lower contact ratio between roll and strip surfaces. This mechanism is supported by the experimental results that (1) the surface temperature of the work roll is sufficiently high to cause heat separation of polymers from solution, (2) a solution containing a polymer of higher viscosity exhibits better lubricity when solutions of the same bulk viscosity are compared, and (3) in the case of different polymer content, solutions containing the same polymer show nearly the same lubricity unber the condition of high roll temperature, whereas these solutions provide different lubricity under the condition of low roll temperature. It is further found that an oiliness agent has distinct distribution characteristics in the polymer layer after heat separation.
Key words : cold rolling, stainless steel, lubricant, solution type, polymer, heat separation, surface brightness
Evaluation Method of Friction Characteristics in Combined
Forward Conical Can-Backward Straight Can Extrusion
Zhi-Liang ZHANG, Masaru ITOH and Tamotsu NAKAMURA
(Received on December 12, 1997)
Previously we developed a friction testing method based on combined forward conical can-backward straight can extrusion to evaluate friction characteristics at the punch in a can extrusion. However, the testing method could not necessarily estimate rational friction characteristic values at the punch in a can extrusion. In the present paper, the friction testing method was reconstructed by investigating some effects of material characteristics and friction boundary conditions between the die and the workpiece using FEM simulation. As a result, a new more convenient friction testing method based on combined forward conical can-backward straight can extrusion has been proposed. Some experimental friction tests have been performed using various aluminum alloys as the workpiece material and different kinds of lubricants.
Key words : forging, tribology, combined forward conical can-backward straight can extrusion, friction coefficient
Trial Evaluation of Die Damage
by a New Intermittent Sliding Friction Test for Forging
Masatoshi SAWAMURA, Yoshinari TSUCHIYA and Atsushi DANNO
(Received on January 7, 1998)
A new friction testing machine was developed to clarify the influence of various factors under frictional conditions in practical forging. In the testing machine, a rotating cylindrical punch is forced into a small columnar billet (¬18mm~9.5mm) at room and warm forging temperatures (`1200K) under the present load. The billet is replaced automatically during every test to simulate the practical frictional condition occurring in forging which is characterized by repeated intermittent sliding. The testing machine is also able to measure the coefficient of friction and to control independently sliding velocity, contact time, sliding length and testing (billet) temperature. Using this machine, the following tribological characteristics were clarified; 1) galling-prevention properties of lubricant oils for cold forging, 2) anti-galling properties of punch materials under warm forging conditions, and 3) softening behavior of a punch material resulting from different punch cooling conditions under warm forging conditions.
Key words : forging, tribology, friction test, lubrication, adhesion, galling
Evaluation of Galling Prevention Propety of Lubricants
for Cold Forging in Stainless Steel
Kazuhiko KITAMURA and Toshihide OHMORI
(Received on January 6, 1998)
Tapered plug penetration test carried out to evaluate the galling prevention property of
lubricants for cold forging in stainless steel. A bearing frustum cone was pushed into hollow workpieces of
17% Cr ferritic stainless steel. The galling prevention property of lubricants was evaluated from values of maxR
and deltaW. The parameter maxR indicates the largest reduction in the cross-sectional area without galling, and deltaW,
the increase inmass of tapered plugs by metal transfer from the workpiece. Commercial oils containing sulfide
and/or chloride type additives resulted in a 1 or 4% reduction. Some solid lubricants showed maxR values
greater 9%. Oils of high viscosity or high chemical reactivity showed superior performance. This test was
able to discriminate between the antigalling property of different oils better than the other severe tests
such as the backward extrusion test and the ball penetration test.
Key words : tribology, cold forging, stainless steel, lubricants, seizure, adhesion