On the temperature distribution in orthogonal machining

The measurement and calculation of tool temperature distributions in orthogonal machining is reviewed. An investigation is described in which the trial traversing thermocouple probe method previously reported by Balint and Brown [1] was further developed to obtain three-dimensional tool temperature distributions on end-, clearance- and rake-faces and, using a split-chip technique, within the chip-tool interface. Analytical temperature distributions are obtained, using a conformal transformation method and are compared with results from the above technique and those by other workers.     

Empirical model of effects of pressure and temperature on electrical contact resistance of metals

Abstract

An important input property in the development of process models for resistance spot welding is electrical contact resistance. A model for the pressure and temperature dependence of electrical contact resistance was developed from established concepts of contact resistance. The key to developing the desired relationship is determining surface roughness characteristics, which is experimentally problematic. To overcome this difficulty the electrical resistance of contacting interfaces was measured as a function of the pressure applied across the interfaces. Using known information about the temperature dependence of bulk resistivity and mechanical properties, a curve fitting procedure was used to establish the desired relationship of contact resistance to pressure and temperature. This empirical model agrees well with experimental measurements in the regime of low applied pressure. At high pressures, predictions underestimate contact resistance, and this was attributed to strain hardening of asperities at the contacting interface. The model also predicts that the competing effects of bulk resistance and contact resistance will produce a peak in the variation of contact resistance with temperature. The model provides a suitable means for incorporating the pressure and temperature dependence of contact resistance into process models of the resistance spot welding process.     

The effects of cryogenic cooling on surface integrity in hard machining: A comparison with dry machining

This paper presents results of an experimental study of cryogenic machining of hardened AISI 52100 steel, focusing on surface integrity. Experiments were performed under dry and cryogenic cooling conditions using CBN tools varying cutting speeds, workpiece hardness and tool geometry. Surface integrity parameters (surface roughness, white layer thickness, residual stresses, metallurgical conditions including grain size, phase transformation, etc.) were investigated to establish the effects of cryogenic cooling on the surface integrity of the machined component, and results were compared with those from dry hard machining. Overall, cryogenic cooling provides improved surface integrity leading to extended product life and performance.     

Evaluation of shaping accuracy upon electrochemical machining of metals

This work investigates the influence of the pulse repetition frequency on the profile generated within pulse electrochemical dimensional machining of nickel foil using a cylindrical electrode tool. Geometrical criteria for the shaping accuracy characteristics are introduced. It has been demonstrated that, irrespectively of the criterion calculation method, the significant influence of the pulse repetition frequency on the shaping is observed. Herewith, the frequency variation makes it possible to determine the extreme criterion point corresponding to the best replication of the electrode tool. It is established that the variation of the pulse repetition frequency influences first of all the region of generation of the outer corner of the formed profile.     

Theoretical investigation of temperature in hot machining

To predict temperature for the case of orthogonal hot machining using resistance heating, analysis of electrical resistance from chip-tool interface to shear plane is made. Total electrical resistance is assumed to be the sum of (i) contact resistance at chip-tool interface, (ii) chip material resistance, and (iii) spreading resistance at shear plane. To get total heat input, electrical energy dissipated at various zones is found out and is coupled with mechanical energy absorbed due to deformation at shear plane and friction at tool face. Analysis of cutting tool temperature proposed by Lowen and Shaw [1] is then applied to predict temperature at chip-tool interface for the case of hot machining. Orthogonal cutting tests are carried out with En-24 steel at a heating current of 200 A. The temperature of the tool is measured by tool-work-thermocouple method. A good agreement between theoretical and experimental results is observed.     

The doping effects on the critical temperature of high-temperature superconductors

X-ray diffraction, dc magnetization, and electrical resistance have been measured for several high-temperature superconductors at temperatures between 18 and 295K. The dc magnetization and electrical resistance measurements showed almost the same trends for basic YBCO and Dy-doped YBCO superconducting materials. T_c was about 92K for both the samples. These results indicates that the electronic structures are different at temperatures above and below T_c and the electron density is higher in superconducting state than in normal state. The PBCO compound was an insulator with little defects structure. The hole filling or hole localization mechanism was proposed for the decrease in T_c with an increase in Pr content.     

Platinum-catalyzed high temperature oxidation of metals

Samples of Al, Cr, Ni, and Zr were sputter-coated with porous Pt-films with a particle size of 20-30 nm. Thermal oxidation of these samples was studied by gas phase analysis (GPA) and secondary ion mass spectrometry (SIMS). SIMS analysis on partly Pt-coated samples of Al, Cr, Ni, and Zr at different oxide depths in areas with Pt and in areas away from Pt indicates an enhanced inward oxide growth in the Pt area and mm-ranged distance from Pt-area. Weight gain measurements on Pt-coated Ni samples show a reduced or increased oxidation rate depending on the amount of porous Pt-coating. Pt has two effects on the thermal oxidation of metals and the overall effect of Pt on the oxidation of metals depends on the mechanism of oxide growth in the absence of Pt.     

Modeling of 3D temperature fields for oblique machining

Fast and accurate temperature prediction for oblique cutting processes is still one of the most complex problems and challenges in the machining research community. For the first time in this article, a novel 3D temperature prediction model based on the finite difference approach for oblique cutting processes is presented. An elliptic structural grid generation method is implemented. Representing different oblique cutting geometries is straightforward now. Moreover, since the resulting equation system is algebraic, the model allows much faster calculations compared to available finite element method based machining temperature models. 3D oblique simulation results verify that temperatures are in good agreement with experimental results.     

Centreless burnishing and influence of its parameters on machining effects

The article presents the results of examining the centreless roller burnishing technology worked out by the authors. The structure and the construction details of a prototype device for the centreless burnishing of shafts were presented. The experiments were carried on using 41Cr4 steel workpieces. The effects of the workpiece hardness, the surface roughness before burnishing, the deformation multiplicity and the tool interference on the roughness and the geometric structure after burnishing were investigated. The significant influence of the above parameters was confirmed and described as a mathematical power model. It also showed a beneficial effect of centreless burnishing parameters on roughness and geometric structure of the surface.     

Thin Film oxidation of metals at the Curie temperature

Anomalies in the Arrhenius plot of the thin film (10²–10⁵ Å) oxidation of nickel and iron at the Curie temperature are discussed. Amongst the various theories, a mechanism which takes into account the importance of both the surface-state charge at the metal/oxide interface and the space charge int he oxide during the logarithmic oxidation of metals, is considered suitable to explain such anomalies.     

The Corrosion of metals in an oxidizing-chloridizing environment at high temperature

An investigation has been undertaken into the behaviour of metals which form the basis of high-temperature alloys in an argon ?5.5% oxygen ?0.96% hydrogen chloride ?0.86% sulphur dioxide gas mixture at 900°C. The intention has been to ascertain the reaction products, with particular emphasis on the formation of volatile species which can cause considerable degradation of commercial alloys in this environment. From consideration of the thermodynamics of the gas system, the potentials of the reactive species can be determined and correlated with the possible reaction products. In this gas mixture, the oxides of nickel, iron, cobalt, chromium, molybdenum and tungsten are the stable phases with respect to the corresponding metals. Indeed, on exposure of the metals to the environment, the appropriate oxide scales are developed. However, the reactions are complicated by formation of volatile corrosion products, particularly for nickel, cobalt and molybdenum. Although a Cr₂O₃ scale is established on chromium, there is evidence for penetration of chlorine-containing species to the scale/alloy interface. The oxide scale on tungsten is not very protective and thickens rapidly while that on molybdenum is volatile, resulting in rapid consumption of the specimen.     

Modelling of temperature and forces when orthogonally machining hardened steel

This paper initially considers heat generation in single-point metal cutting and the direct/indirect techniques employed to measure cutting temperatures. The development of analytical models of the cutting process is briefly reviewed, including more recent work involving finite element (FE) methods. Details are given of the different FE packages and formulation methods used by different researchers. Following on from this, an FE model is presented using FORGE 2® to simulate cutting forces and temperature distributions when orthogonal turning a hardened hot work die steel, AISI H13 (52HRC), with polycrystalline cubic boron nitride (PCBN) tooling. Experimental data from infrared chip surface temperature measurements and cutting force output are used to validate the model. Good correlation was obtained between experimental and modelled results for temperature; however, the FE analysis underestimated feed force results due to a lack of adequate workpiece property data and simplistic tool/chip friction assumptions.     

On the measurement and prediction of temperature fields In machining AISI 1045 steel

Infrared microscopic measurements of the temperature fields at the tool-chip interface in steady-state, orthogonal, machining of AISI 1045 steel are presented for a range of chip thicknesses The measurements are verified using an energy balance method and simple finite difference calculations (see [14]) These results are compared to the predictions of a finite element calculation using a commercial package for three different material models obtained from the literature Results are highly dependent on the material model and friction behavior, indicating that caution be used when finite element analysis is to predict rather than interpret machining temperatures.     

花岗石异型面高效加工磨削温度场实验研究

石材加工中温度对异型面形成机理和成形刀具的磨破损规律有重要的意义,而理论分析过程比较复杂,准确率还有待修正提高。为有效指导实际生产,掌握金刚石刀具磨削石材的规律,摸索适于高效花岗石磨削的加工工艺,以降低温度对生产的不良影响,提出了基于红外成像的测量和分析方法。实验中,分析了两种石材异型面干切削加工中热量的产生及切削温度的变化,发现花岗石异型面磨削弧区的表面最高温度随主轴转速及刀具切削深度的提高而上升;单独提高刀具的进给速度会使磨削区温度先升后降。     

The application of an inclined end mill machining strategy on 3-axis machining centres

An inclined end mill machining strategy offers an effective machining method for manufacturing low curvature free-form surfaces. The machined surface profile is a close match to the required surface geometry, and standard end mills are available at competitive prices. The amount of surface finishing work is therefore reduced, and the inclined cutting action prolongs the tool life. Although this machining strategy has these advantages, it is not commonly used in manufacturing industry, because it needs the facilities of costly 5-axis machining centres and appropriate post processors are required to generate the NC codes for these advanced machine tools. This paper proposes a simple method which extends the machining capability of the conventional 3-axis machining centre to give the same specifications as a 5-axis machine, and therefore allow the inclined end mill machining strategy to be used on 3-axis machines. The method involves tilting the workpiece instead of tilting the end mill during the machining process. The tool paths are determined by the workpiece rotation and cutter contact point offset equations. The amount of excess material on the machined surface is minimized by choosing optimum pitching and rolling angles at the work set-up stage. The experimental results indicate that the quality of the machined surfaces is improved in comparison with the surfaces machined by ball-nosed cutters, e.g. the resulting cusp volume is reduced by 64%. The research suggests that the need for advanced and expensive 5-axis machining could be satisfied in a more economical machining environment. As a result, the machining cost of the products may be significantly reduced.     

Thermoelectric signal characteristics and average interfacial temperatures in the machining of metals under geometrically defined conditions

The Herbert/Gottwein dynamic thermocouple method of temperature measurement was applied in order to experimentally evaluate the average interfacial temperatures arising in the external cylindrical turning of aluminium, brass, mild steel and stainless steel using high speed steel cutting tools. A detailed investigation of the EMF signal generated was undertaken for purposes of explanation of the DC and AC components which arise and of the influence of the cutting tool condition on the EMF signal generated. The thermoelectric characteristics of each material in conjunction with HSS were determined by means of the furnace method of calibration. A critical appraisal of each phase associated with the dynamic thermocouple method of cutting temperature measurement is undertaken in this paper and interfacial temperatures under a wide range of machine setting parameters for each workpiece material are presented and discussed.     

Free machining steels and the effects of sulfide and siliceous nonmetallics

A discussion of sulfide and siliceous nonmetallics—including their physical characteristics, size, shape, and distribution—and their effects upon the free machining qualities of steels.     

Three-dimensional temperature predictions in machining processes using finite difference method

The purpose of this study is to determine the three-dimensional temperature fields on the chip, tool and workpiece during machining, which is one of the most important characteristic of machining processes; since the fields can affect other properties such as residual stresses and tool wear, and thus tool life and fatigue life of finished parts. The finite difference method (FDM)-based model proposed in this paper offers very rapid and reasonably accurate solutions. Finite difference-based simulation results are validated with infrared thermal measurements which are determined from the machining of AISI 1050 and AISI H13 materials under various cutting conditions.