Zhrgang Wang

A Consideration of Optimum Conditions for Surface Smoothing Based on Lubricating Mechanisms in Ironing Process

The purpose of this paper is to clarify the mechanism of a smooth surface generation in the ironing process under contact states with a largely relative slide. In this case, the outflow behavior of lubricant trapped in the oil pits is the most important point in the surface smoothing process. It was deduced from ironing experiments that lubricant flows out from oil pits as a result of plastic deformation of the metal surface layer, mainly in the friction direction. A model has been proposed to estimate variations in the friction stress during ironing. This model can explain experimental results that the metal surface is best smoothed under the condition in which the minimum friction stress appears.

FEM simulation of surface smoothing in the ironing process

Abstract The purpose of this paper is to simulate surface smoothing in the ironing process by elasto-plastic FEM. The simulated results show that surface smoothing is largely developed during a very short contact length from the entrance of the contact zone where the material is in the elastic state and can be remarkably promoted by the plastic deformation in the surface layer. With increase in the reduction in thickness, in the die angle and in the friction coefficient on the punch side, the surface smoothing of the workpiece can be accompanied at the shorter contact position from the entrance of the contact zone. The simulated results are in good agreement with experimental results.

Effects of Average Lubricant Velocity and Sliding Velocity on Friction Behavior in Mild Steel Sheet Forming

A series of experiments was carried out using a rolling-type tribometer to investigate the frictional dependence on the average velocity of the lubricant V at the contact zone inlet and the relative sliding velocity ΔV between the roll and workpiece during deformation. Experiments using mild steel strips with a dull surface of 0.63 μm Ra showed that the friction coefficient decreases with increasing forming velocity, especially at high forming velocity. This variation in the friction coefficient may be due to the increase in ΔV derived from the increase of the forming velocity, because the friction coefficient decreases with increasing ΔV but varies little with increasing V. It was also confirmed that an increase of ΔV or a decrease in V promotes flattening of the workpiece asperities.

Investigation Into Relationship Between Friction Behavior and Plastic Deformation Using a Newly Devised Rolling-Type Tribometer

A new rolling-type tribometer has been devised to investigate the effects on friction behavior of the average velocity of the lubricant at the inlet to the contact zone and the relative sliding velocity during deformation independently. This paper shows the principle of operation of the tribometer and deformation mode of the workpiece, especially considering the relationship between friction and bulk deformation. Experiments using mild steel strips with a dull surface showed that the friction stress on the friction roll, which has a smaller velocity than that of the traction roll, is mainly controlled by lubricating conditions on the friction roll side. The contact pressure is mainly decided by the friction conditions on the traction roll side. It was also revealed that, with an increase of the reduction in the workpiece thickness, the friction stress on the friction roll side remains constant when the friction roll is rotated. The friction stress increases when the friction roll is stopped after a certain reduction in the workpiece thickness.

Surface Smoothing Mechanism by Replication in Ironing Process

The purpose of this paper is to clarify the surface smoothing process under contact states with a small relative slide between the tool and workpiece. An internal ironing apparatus was developed to observe the surface during the processing. Observation revealed that the surface smoothing process is largely developed during a very short contact length from the entrance of the contact zone where the bulk material is in the elastic state and can be markedly promoted by the plastic deformation in the surface layer. It was also confirmed that the ironed surface roughness decreases by increasing the ironing reduction in thickness and reaches the surface roughness of container R a =0.01 μm under dry condition and 30 percent in the reduction when initial surface roughness R a is about 0.07 μm. The surface smoothing process could be understood by the slip-line field theory

Research into mirror surface finishing by the ironing process

Abstract The object of this paper is to clarify the mechanism of mirror surface finishing by the ironing process. The mirror surface is in demand for electro-optical parts such as optical drums and magnetic discs, which hitherto have been finished by diamond bite cutting, lapping, etc. In the ironing process, the metal surface on the die side becomes a rubbed surface ( Ra = 0.05 μ m for high-viscosity oil) which is markedly inferior to the die surface ( Ra = 0.006−0.011 μ m ); when oils of lower viscosity are used galling often occurs. The metal surface on the punch side becomes a near replica of the punch surface, the degree of replication increasing with larger reductions and lower viscosity oils or when the ironing is carried out dry. In these experiments, the metal surface was finished to Ra = 0.004 μ m under the following conditions: dry on the punch side; high-viscosity oil on the die side; and 50% reduction.

FEM analysis of contact mechanism in press-forming of lubricant pre-coated steel sheet

Abstract This paper describes the contact situation between the die and the lubricant pre-coated steel sheet in the press-forming by using FEM simulation. The FEM simulation is carried out by supposing that the lubricant pre-coated steel sheet consists of the lubrication layer and thick galvanized layer. Both the lubrication layer and galvanized layer are assumed as rigid–plastic material. The variations in the contact situation between the die and the lubricant pre-coated steel sheet are investigated by changing the friction coefficient between the die and lubrication layer, the thickness and hardness of lubrication layer, the velocity ratio of the relative sliding velocity to pressing velocity, etc. The simulated results show that the contact area ratio is influenced largely by the average contact pressure, the velocity ratio, the thickness of lubrication layer, and friction coefficient.

Lubricity of volatile lubricants in sheet metal rolling

Abstract A series of experiments is carried out by using a rolling type tribometer to investigate the lubricity of the volatile lubricants at high speed forming. The roll material is the die steel alloy SKD11, and the workpiece material is the mild steel SPCE with a rough surface and the aluminum alloy A3004 with a smooth surface. Experimental results show that the friction coefficient decreases with increasing working velocity for both SPCE and A3004, in any lubricant. With an increase of reduction in thickness, the friction coefficient decreases for SPCE, but increases for A3004. Some volatile lubricants have the same lubricity as the generally used mineral oil with low-viscosity by judging from the value of friction coefficient, the surface appearance of rolled workpiece and the roll surface damage.

Improvement on Magnesium Alloy Sheet Forming at Warm Temperatures by Computer Simulation and Experiment

A proper forming temperature range was determined, and the effects of blank holding forces on the workpiece quality were analyzed by warm deep drawing of cups in magnesium alloy sheets. The conditions of process defects as flange wrinkling and ruptures were analyzed by computer simulation with explicit finite element method to optimize the process parameters. Therefore, appropriate process parameters were selected to avoid forming defects effectively. In the paper, a rigid blank holder was used to adjust blank holding forces. A special liquid lubricant PTFE was used on the tool surfaces. Efforts were made to optimize process parameters by analyzing the causes of defects in order to improve the Limit Drawing Ratio of magnesium alloy workpieces. It is found that rolled magnesium alloy sheets are of good deep drawing formability at a forming temperature range of 105–170°C with the higher Limit Drawing Ratio up to 2.44. It is also necessary to control the time of heating blanks. The formability will be reduce...