Z.R. Wang

Finite element simulation of a new deformation type occurring in changing-channel extrusion

Abstract There has been a number of investigations in recent years reporting the results obtained on the structure and properties of metals deformed to large strain. Being deformed to large strain, ultra-fine grains (UFG) are usually formed, and materials with UFG structure display many abnormal characteristics, which have attracted a growing research interest. The method often used to obtain large strain is equal-cross-section lateral extrusion (ECSLE) or equal channel angular pressing (ECAP). However, according to the simulation results, there is large tensile stress in the workpiece during deformation, which may lead to cracking. In this paper, a new method, changing channel extrusion (CCE), is presented, which could decrease the tensile stress and increase the hydrostatic pressure in the workpiece, which is good for the plastic deformation of low ductility materials.

Defects caused in forming process of rotary forged parts and their preventive methods

Abstract In this paper, the characteristics of rotary forging deformation and their mechanic analysis are briefly described; meanwhile the four kinds of defects caused generally in the deformation are introduced: chevron crack in the thin workpiece, peripheral crack in the flange with a rod, instability and overlapping, and not thoroughly forging. Then, it is pointed out that the defects such as crazing and pressed-subsidence are frequently caused in the centre of an upper die, because of the particularities of the rotary forging technology: there is a small contact area throughout between the upper die and the workpiece and the pressure is high, and the upper die suffers from the effect of thermal fatigue during hot rotary forging. Finally, the measures to prevent the defects and the methods for improving the service life of the die are proposed. For thick workpieces and flanges with a rod, the feed per rotation should be properly controlled; for thin workpieces, the feed per rotation should be increased. In cold rotary forging of flanges with a rod, the surface quality of blanks should be considered and the die-workpiece clearance should be controlled so that the defects of cracking, instability, overlapping and so on can be decreased.

CNC incremental sheet forming of an axially symmetric specimen and the locus of optimization

Abstract CNC incremental sheet forming is a new flexible sheet forming process. It does not need a dedicated die and can form sheet parts with a higher forming limit and of complicated shape by use of a CNC device. This process is suited to the forming of sheet parts of small volume, diversification and complicated shape in space-flight, automobile and civil production. Taking the arc locus as an example in this paper, axially symmetrical forming is analyzed and the method that controls the flow of metal to obtain more even deformation is discussed. The analysis provides the theoretical foundation for the selection of the forming locus in CNC incremental forming.

Research on rotary forging and its distribution of deformation

Abstract This paper introduces the working principle of the rotary machine and its application.v Then it concentrates on the discussion on the mesh method and the photoplastic method used to test the non-uniform distribution of plastic deformation on the upper end, the lower end, and the meridional plane of workpieces of different shapes. Finally it sums up the regularity of stress and strain distribution in workpieces. The experimental results obtained are valuable for realizing the regularity of metal flow in rotary forging and for reference in designing dies correctly.

Numerical and experimental research of the cold upsetting–extruding of tube flanges

Abstract In this paper, the cold upsetting–extruding process of a tube flange is discussed in detail. Finite element method (FEM) simulation, using the program DEFORM2D, was carried out to analyze the influence of the tube dimensions and interface friction on the material flow and the cause of forming defects. Based on the FEM simulation results, the relational curves between the flange width and the extreme friction factors were established. The concept of a forming limit diagram for cold upsetting–extruding of a tube flange is presented. The results from the process simulation were then used in tube blank and die plan and lubricant selection. The subsequent experimental results showed reasonable agreement with the numerical simulation results.

The integrally hydro-forming process of pipe elbows

In this paper, a hydro-bulging technology for manufacturing pipe elbows is proposed to overcome difficulties in manufacturing large diameter elbows using traditional technology. The section profile variation of the toroidal shell during the forming process is discussed. It is demonstrated experimentally that manufacture of a pipe elbow using integrally hydro-bulging technology is feasible.

Study on isothermal precision forging technology for a cylindrical aluminium-alloy housing

High-precision forging is becoming increasingly popular in modern plastic working. The effects of forging force, die chilling, residual stress and lubricant are significant in a hot precision forge. Producing aluminium-alloy precision forgings of reasonable complexity is a difficult operation. Temperature control within narrow ranges, high-accuracy dies and suitable forming methods are necessary in order to develop desirable microstructures, properties and the near-net shape of forgings. Therefore, isothermal forging is a prime method from the precision forming viewpoint. This paper presents details of isothermal precision forging technology for a cylindrical aluminium-alloy housing.

Stamping and stamping simulation with a blankholder gap

Abstract Applying a blankholder gap is the main method of control of the blankholder in stamping or its simulation. In this paper, the nature of stamping with a blankholder gap is provided as well as two advantages of stamping simulation with a blankholder gap. Finally, a reasonable blankholder gap for cup deep drawing and the reverse drawing process is proposed.

A consistent relationship between the stress- and strain-components and its application for analyzing the plane-stress forming process

Abstract An important problem in metal forming is the final variation of the shape and the size of blank/billet after deformation. However, it is very difficult to make a quantitative calculation of the total deformation by the Levy—Mises equation expressed with the components of deviator and strain increments. The author has modified the calculation into a form of qualitative description called the consistent relationship between the stress- and strain-components, on the basis of the Levy—Mises equation for the condition of non-proportional loading. As the examples of its application, the tendency of the size-variation of the workpiece plane-stress forming processes is given also.

Numerical simulations for extrusion and ironing and die-angle optimization

Abstract In this paper, the rigid-plastic Finite-Element Method (FEM) is adopted to analyze the steady-deformation stage of extrusion and ironing, and to optimize the semi-cone angle of the extrusion die, according to the principle of minimal deformation force, the optimization results being found to agree very well with the results of experiment. Further, this paper provides a new way to optimize the working curve of the die.