This paper gives a bibliographical review of the finite element methods applied to the analysis and simulation of welding processes The bibliography is an addendum to the finite element analysis and simulation of welding: a bibliography (1976–96) published in Modelling Simul Mater Sci Eng (1996) 4 501–33 The added bibliography at the end of this paper contains approximately 550 references to papers and conference proceedings on the subject that were published in 1996–2001 These are classified in the following categories: modelling of welding processes in general; modelling of specific welding processes; influence of geometrical parameters; heat transfer and fluid flow in welds; residual stresses and deformations in welds; fracture mechanics and welding; fatigue of welded structures; destructive and non-destructive evaluation of weldments and cracks; welded tubular joints, pipes and pressure vessels/components; welds in plates and other structures/components

Finite element analysis and simulation of machining: an addendum: A bibliography (1996–2002)

This study presents the investigation of the stiffness of the system formed by the machine-tool, shank and toolholder, collet and tool. Cutting forces induce the deflection of the system, and consequently an error appears on the machined surface. Comparing values obtained from cantilever beam models applied to the cutting tool, analytical or FEM, with those experimentally obtained, large differences have been observed, which in some cases are more than 50%. For this reason, we have proceeded to evaluate the stiffness of each of the existing elements between the machine bed and the tool tip. Thus, deflections of the machine-tool, toolholder and toolholder clamping in the spindle, tool clamping in the toolholder, and tool itself, were measured experimentally under the effects of known forces. The final application is the ball-end milling of complex surfaces, an operation commonly performed in the finishing of moulds or forging dies, where errors of more than 70 μm are not unusual. A great part of this error comes from the deflection of the machine-tool assembly, spindle, shank and tool, due to the high cutting forces of the high speed machining of tempered steels. Cutting forces can be estimated using a semi-empirical approach, and from here some values of probable errors may be taken into account to check if the CNC programs are sufficiently adapted. However, a previous study of the deflection chain in the cutting process is needed, as is presented in this work. Results show that stiffness of the slender and flexible tools is 15 times lower than that of the machine and toolholder system. But this correlation is only 5–7 times lower for shorter and thicker tools.

Evaluation of the stiffness chain on the deflection of end-mills under cutting forces

This paper introduces a novel approach for designing the stiffener layout inside large machine tools by applying the self-optimal growth principle of plant ramifications in nature. Firstly, numerical studies are carried out in order to confirm the potential of leaf venation as concept generators for creating the optimal load-bearing topology for stiffened machine tool structures. Then, a mathematical model explaining the optimality of plant morphogenesis is presented. Based on this, an evolutionary algorithm is developed, which uses three growth strategies to determine the candidate stiffeners to grow or atrophy with respect to the loads applied. The proposed growth-based method could generate a distinct stiffener layout, which is different to those produced by the conventional topology optimization methods, and thus offers unique possibilities of improving the design efficiency and commonality for machine tool development. The suggested approach is finally applied to the re-design of an actual grinding machine column, on which the numerical analyses and experimental tests conducted exemplify the performance enhancement, and therefore is a good choice for the stiffener layout design of machine tool structures.

Stiffness design of machine tool structures by a biologically inspired topology optimization method

Study on the stiffness of a 5-DOF hybrid machine tool with actuation redundancy

Modern industry requires high-precision machines and processes. This requirement implies the determination and reduction of all possible sources of error. For turning, a main error is related to machine–tool–workpiece deformation caused by cutting force. On the other hand, current turning centers are structurally more complicated than conventional lathes. However, stiffness values for this kind of machine are not described yet in literature. Thus, the aim of this work is to provide stiffness values for this type of machines clamping a common workpiece. To obtain this information an experimental methodology to measure static stiffness along kinematic chain of the turning center is proposed. The method may be useful for both users and machine manufacturers in order to consider this factor in the general error budget of the turning process. At the same time, stiffness values for lathes with a Y-axis incorporated in a three-axis turret and equipped with living tools are registered.

Analysis of the tool tip radial stiffness of turn-milling centers

In this paper, a single module method and a newly developed hybrid modeling method for analyzing the stiffness of machine tools are introduced in detail. Techniques include building suitable finite element models, determining equivalent loads, simulating the interface between two modules, considering boundary constraints, and interpreting results. By taking a detailed finite element mesh for one of the five modules (the headstock, the column, the table, the saddle and the bed), together with simplified meshes for the other four modules, a hybrid finite element model is assembled. The elastic modulli of the four simplified meshes are kept several orders higher than that of the detailed one. Therefore, the calculated stiffness of the hybrid model is essentially the stiffness of the softer module with the detailed mesh. The stiffness of the five modules can be obtained one after another in the same manner. By supporting the hybrid model only at the middle of the short edge on the bottom surface of the bed, the machine tool can be properly constrained, and its stiffness can be estimated correctly. The controversial issue as to how to simulate properly the boundary condition of the casters under the bed will not occur in this method. A cumbersome procedure to transform the external loads into the equivalent forces as required in SMM is also avoided. There is no local effect due to unevenly distributed nodal forces. It is shown that the hybrid modeling method is better than the single module method in accuracy and efficiency.

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David Te-Yen Huang

Papers

On obtaining machine tool stiffness by CAE techniques