J.C. Outeiro

Residual stress analysis in orthogonal machining of standard and resulfurized AISI 316L steels

Abstract Residual stresses induced by orthogonal cutting in AISI 316L standard and resulfurized steels have been investigated, with attention given to the role played by the cutting parameters, such as cutting speed, feed rate, tool geometry and tool coating. Depth profiles of residual stress have been determined using the X-ray diffraction technique. The effect of cutting conditions and tool nature on residual stresses are analyzed in association with thermal and mechanical events, recorded during the cutting tests. The tool temperature distribution has been determined by a specific CCD infrared camera technique and the cutting forces by a Kistler table set up on the lathe.

MACHINING RESIDUAL STRESSES IN AISI 316L STEEL AND THEIR CORRELATION WITH THE CUTTING PARAMETERS

It is well known that machining results in residual stresses in the workpiece. These stresses correlate very closely with the cutting tool geometrical parameters as well as with the machining regime. This paper studies the residual stress induced in turning of AISI 316L steel. Particular attention is paid to the influence of the cutting parameters, such as the cutting speed, feed and depth of cut. In the experiments, the residual stresses have been measured using the X-ray diffraction technique (at the surface of the workpiece and in depth). The effects of cutting conditions on residual stresses are analyzed in association with the experimentally determined cutting forces. The orthogonal components of the cutting force were measured using a piezoelectric dynamometer.

Experimental Assessment of Temperature Distribution in Three-Dimensional Cutting Process

Abstract In metal cutting a large amount of the external energy supplied to the cutting system is converted into heat. Therefore, the study of the thermal phenomenon developed in the metal cutting process is of prime concern. This phenomenon has a great influence on many metal cutting variables as tool wear, residual stress, and part distortion. This article presents the experimental analysis of the temperature distribution in the three-dimensional cutting process. Specially designed thermal imaging equipment, included both hardware and software, was developed in order to determine the temperature distribution in the deformation zone. A detailed description of this equipment, its calibration procedure and a full analysis of the emissivity of the cutting system components (chip, tool, and workpiece) are discussed. The designed thermal imaging equipment was proven to be very powerful to analyze the influence of the cutting parameters (cutting speed, cutting feed, depth of cut, work material, tool geometry, and tool material) on this temperature distribution. This equipment can also be useful for the construction and validation of numerical and analytical models of the three-dimensional cutting process.

Metal Cutting Mechanics, Finite Element Modelling

This chapter presents a short analysis of the basics of traditional metal cutting mechanics, outlining its components and the basics of finite element modelling (FEM) of the metal cutting process. Based on a previously proposed definition of metal cutting, advanced metal cutting mechanics considers the power spent in metal cutting as the summation of four components: the power spent on the plastic deformation of the layer being removed, the power spent on the tool–chip interface, the power spent on the tool–workpiece interface, and the power spent in the formation of new surfaces (cohesive energy). Energy partition in the cutting system and the relative impact of the parameters of the machining regime are discussed. Analyzing the basics of FEM and presenting examples, this chapter considers the errors in such modelling and their major sources. It points out the importance of the selection, verification and validation of the physically justifiable model.

Experimental and FEM Analysis of Cutting Sequence on Residual Stresses in Machined Layers of AISI 316L Steel

The reliability of a mechanical component depends to a large extent on the physical state of its surface layers. This state includes the distribution of residual stresses induced by machining. Residual stresses in the machined surface and subsurface are affected by the cutting tool, work material, contact conditions on the interfaces, cutting regime parameters (cutting speed, feed and depth of cut), but also depends on the cutting procedure. In this paper, the effects of cutting sequence on the residual stress distribution in the machined surface of AISI 316L steel are experimentally and numerically investigated. In the former case, the X-ray diffraction technique is applied, while in the latter an elastic-viscoplastic FEM formulation is implemented. The results show that sequential cut tends to increase superficial residual stresses. A greater variation in residual stresses is observed between the first and the second cut. Moreover, an increase in the thickness of the tensile layer is also observed with the number of cuts, this difference also being greater between the first and the second cut. Based on these results, the residual stress distribution on the affected machined layers can be controlled by optimizing the cutting sequence.

MODELING OF THE CONTACT STRESS DISTRIBUTION AT THE TOOL-CHIP INTERFACE

ABSTRACT This paper deals with the modeling of the contact stress distribution at the tool-chip interface. It includes a comprehensive critical review of the various attempts that have been made to determine the stress distribution over this interface. It reveals that more than ten different types of contact stress distribution have been reported in literature. According to the latest reported results, the uniform distribution of normal and shear stresses is the case in metal cutting. To understand the real contact stress distribution, the tool-chip interface was modeled as a contact problem of indentation of the deformable work material by a rigid punch. The analytical and FEM results are obtained, discussed, and compared with those obtained experimentally. It is proven conclusively that the distribution of normal and shear stresses is not uniform. The real stress distribution is discussed on the basis of the obtained results.

Surface Integrity of H13 ESR Mould Steel Milled by Carbide and CBN Tools

The quality of a mechanical component such as its geometrical accuracy stability and fatigue life are significantly affected by the surface integrity generated by machining process. Residual stresses are a major part of the mechanical state of a machined layer and they can be beneficial or detrimental depending of their nature and magnitude. This study concerns phase analysis and residual stress profile characterization by X-ray diffraction (XRD) technique and microhardness profile of AISI H13 ESR mould steel, milled using carbide and CBN tools. Analysis of the cross-section of the AISI H13 ESR samples, milled using both tools, reveal a martensitic microstructure, with a very thin layer heavily deformed due to the machining process. However, no phase transformation was detected by XRD. Concerning the residual stresses, the results show that they are predominantly compressive at the samples surface. However, depending of the cutting tools, the in-depth residual stresses profiles present different evolutions. This difference in the in-depth residual stresses profiles between the two kind of cutting tools is attributed to the different cutting tool parameters, including the tool geometry.

Modelling of Tool Wear and Residual Stress during Machining of AISI H13 Tool Steel

Residual stresses can enhance or impair the ability of a component to withstand loading conditions in service (fatigue, creep, stress corrosion cracking, etc.), depending on their nature: compressive or tensile, respectively. This poses enormous problems in structural assembly as this affects the structural integrity of the whole part. In addition, tool wear issues are of critical importance in manufacturing since these affect component quality, tool life and machining cost. Therefore, prediction and control of both tool wear and the residual stresses in machining are absolutely necessary. In this work, a two‐dimensional Finite Element model using an implicit Lagrangian formulation with an automatic remeshing was applied to simulate the orthogonal cutting process of AISI H13 tool steel. To validate such model the predicted and experimentally measured chip geometry, cutting forces, temperatures, tool wear and residual stresses on the machined affected layers were compared. The proposed FE model allowed us ...

Minimized Wear and Debris Generation Through Optimized Machining of Co-Cr-Mo Alloys for Use in Metal-on-Metal Hip Implants

More than 380,000 hips are replaced with total joint prostheses each year in the U.S. Wear debris generated by metal-on-metal implant designs is of concern due to potential adverse biological effects arising from chronic exposure of human tissue to the wear debris. This paper presents a new methodology for optimizing the wear performance of prosthesis made of Co-Cr-Mo alloys by varying tool edge geometry and machining conditions to alter the wear behavior of this alloy, while also controlling the residual stresses induced during the machining process. The machining process causes inhomogeneous inelastic deformations near the surface layer of machined parts which create residual stresses in the surface of machined components. Residual stresses in the machined surface and the subsurface are affected by cutting tool material, tool geometry, workpiece, tool-work interface conditions, and the cutting parameters such as feed rate, depth of cut and cutting speed. In the current work, residual stresses were measured using X-ray diffraction technique (XRD). The surface residual stresses in two directions (radial and hoop) were measured on the machined pins after machining with different machining conditions, but prior to the wear test. Wear behavior of Co-Cr-Mo alloy pin specimens, produced from machining with varying tool edge geometry and machining conditions, was studied using a custom-made biaxial motion pin-on-disc tribological testing system in which the pin specimen is immersed in a simulated bio-fluid environment. Wear-induced weight loss (± 10 μg) and changes in surface roughness (± 0.001 μm) were obtained at 100,000 cycle intervals upto 500,000 cycles. Metallographic analysis was performed on the machined pin specimens to analyze the microstructure and microhardness before and after testing. The rate of wear for the specimens was lowest for those pins where the change of the subsurface microhardness was small due to prevention of additional steady state wear after the initial run-in wear in the wear tester. A combination or response surface methodology and genetic algorithm (GA) was used in to optimize the various machining parameters for minimized wear generation. The optimal combination of the four machining parameters (feed 0.18mm/rev, nose radius 0.6 mm, cutting speed 27.6 m/min and depth of cut 0.38) produced the largest compressive residual stresses on the surface and subsurface of the implants thereby reducing the wear/debris generation by about fifty percent.Copyright

On Designing for Enhanced Product Sustainability by Considering the Induced Residual Stresses in Machining Operations

For improving product sustainability, a number of measures can be adopted during the product design stage for manufacturing. The modeling and control of the residual stresses and surface roughness generated by machining are among the major measures which have been shown to demonstrate the strongest influence on the machined component’s performance during its service life. The proper control of the residual stresses would provide increased product lifetime, reduced part distortion, reduced weight and reduced and less frequent maintenance and inspection of the product while maintaining the same safety level, or perhaps even improving it. This paper presents an analysis of the influence of machining parameters on the residual stresses generated in machining operations. This analysis was performed on several work materials, including carbon steels, stainless steels, Inconel alloys and tool steels. This allows developing a number of feasible means to control the residual stresses during manufacturing.Copyright