Application to crankshaft manufacturing methodology, results and analysis

The gain of productivity in machining is generally sought through tools and/or cutting conditions optimization however an increase in productivity is achievable too through the workmaterial optimization. The metallurgical structure as well as the chemical composition of steels widely influence their ability to be machined. Mittal Steel Europe R & D develops new steel grades such as the Super High Strength Steels whose tensile stresses may reach 1000 or 1200 MPa. A cooperative research program between Mittal Steel Europe R&D and ENSAM tends to propose a methodology able to sort the steel grades in terms of ability to be manufactured (in forging and machining). This study focuses on such an industrial application : the heavy vehicles crankshaft manufacturing. The operation investigated consists in deep hole drilling and is concerned with the lubrication holes. This paper proposes some relevant criteria to compare the different steel grades and/or structures. Some experimental results are proposed

Machinability in dry carbide drilling

Intensive weight savings and out-sizing programs are developed in automotive industry and lead to increase the mechanical properties of the material of the automotive parts. ArcelorMittal has developed specific steel grades known as Super High Strength Steels which are designed for both high ductility and toughness and fatigue resistance. This paper investigates machinability for a drilling operation using an experimental methodology. One of the materials is a new low bainitic steel grade. Experiments are performed with a coated carbide solid drill. Thrust force and torque measurements, chip morphology analysis, surface quality monitoring and tool wear tests are carried out. Experiments are performed with and without lubricant

Machinability testing for gear hobbing applications

ArcelorMittal focuses on both mechanical performances and machinability while designing new steel grades. ArcelorMittal has developed specific programs for machinability testing in turning, low and high speed drilling and gear machining. Machinability is evaluated through cutting forces, chip shape, surface quality and tool life. Gear machining is one of the main machining operations involved in powertrain manufacturing operations. The literature proposes many papers dealing with this process however there are too few studies interested in steel machinability evaluation while gear machining. This paper focuses on a particular gear manufacturing process, i.e. gear hobbing, and more precisely on steel machinability for gear hobbing applications. Tools as well as kinematics of gear hobbing are quite complex. This paper proposes a comprehensive experimental protocol for machinability testing. This protocol is based on a European standard. Tests are performed on a machine tool using a commercially available cutting tool. Tests provide the range of cutting conditions for five different steel grades. Both steels have a ferrite-pearlite structure with yield stress from 530 to 800 MPa and ultimate tensile stress from 680 to 900 MPa. Four grades are devoted to bar machining. The last one is devoted to forming and then machining operations. Many metallurgical solutions are investigated to enhance machinability such as lead addition or increase in sulfur content or calcium treatment. This paper analyses the influence of steel composition and structure on machinability. It shows the relevance of metallurgical solutions for machinability enhancement even for powertrain applications. Cutting conditions clearly depend on the metallurgical solution even if specific cutting force is finally close. The main difference is found on tool wear with tool life ratio from 1 to 1.5

Effects of three-body interactions on the structure and thermodynamics of liquid krypton

Large-scale molecular dynamics simulations are performed to predict the structural and thermodynamic properties of liquid krypton using a potential energy function based on the two-body potential of Aziz and Slaman plus the triple-dipole Axilrod-Teller (AT) potential. By varying the strength of the AT potential we study the influence of three-body contribution beyond the triple-dipole dispersion. It is seen that the AT potential gives an overall good description of liquid Kr, though other contributions such as higher order three-body dispersion and exchange terms cannot be ignored.Comment: 11 pages, 3 figures, LaTeX, to appear in J. Chem. Phy

Application to crankshaft manufacturing methodology, results and analysis

The gain of productivity in machining is generally sought through tools and/or cutting conditions optimization however an increase in productivity is achievable too through the workmaterial optimization. The metallurgical structure as well as the chemical composition of steels widely influence their ability to be machined. Mittal Steel Europe R & D develops new steel grades such as the Super High Strength Steels whose tensile stresses may reach 1000 or 1200 MPa. A cooperative research program between Mittal Steel Europe R&D and ENSAM tends to propose a methodology able to sort the steel grades in terms of ability to be manufactured (in forging and machining). This study focuses on such an industrial application : the heavy vehicles crankshaft manufacturing. The operation investigated consists in deep hole drilling and is concerned with the lubrication holes. This paper proposes some relevant criteria to compare the different steel grades and/or structures. Some experimental results are proposed

Coexistence of low and high overlap phases in a supercooled liquid: An integral equation investigation

The pair structure, free energy, and configurational overlap order parameter Q of an annealed system of two weakly coupled replicas of a supercooled \u201csoft sphere\u201d fluid are determined by solving the hypernetted-chain (HNC) and self-consistent Rogers-Young (RY) integral equations over a wide range of thermodynamic conditions \u3c1 (number-density), T (temperature), and inter-replicas couplings \u3b512. Analysis of the resulting effective (or Landau) potential W(\u3c1,T; Q) and of its derivative with respect to Q confirms the existence of a \u201cprecursor transition\u201d between weak and strong overlap phases below a critical temperature Tc well above the temperature To of the \u201cideal glass\u201d transition observed in the limit \u3b512\u21920. The precursor transition is signalled by a loss of convexity of the potential W(Q) and by a concomitant discontinuity of the order parameter Q just below Tc, which crosses over to a mean-field-like van der Waals loop at lower temperatures. The HNC and RY equations lead to the same phase transition scenario, with quantitative differences in the predicted temperatures Tc and To

Stress and heat flux distribution in rake face. Analytical and experimental approaches

International audienceMetallurgical solutions for an improvement in machinability currently use nonmetallic inclusions in order to create solid lubricants at the interfaces between tool and workmaterial. It is possible to identify and quantify these layers afterwards. However it is important to know the conditions for which these layers appear: tribological conditions, kinematical conditions (i.e. cutting speed, feed and depth of cut) and thermomechanical conditions (stress and temperature distribution in the interfaces). We focus on the tool / chip interface and more precisely on the thermomechanical conditions. This contribution is concerned with both the analytical modeling and measurement of the temperature distribution in the chip forming zone. We propose a correlation between theoretical and experimental values

Metallurgical Analysis of Chip Forming Process when Machining High Strength Bainitic Steels

In the following work, we propose a metallurgical approach to the chip formation process. We focus on a turning application of high strength steel in which chips are produced by adiabatic shear bands that generate cutting force signals with high frequency components. A spectral analysis of these signals is applied and highlights peaks above 4 kHz depending on the cutting conditions. A microscopic analysis on the chip sections provided data on chip breaking and serration mechanisms. Shear band spacing and excitation frequency of the whole cutting system were calculated and gave a good correlation with cutting forces spectra

Experimental study of Built-Up Layer formation during machining of High Strength free cutting steel

Machinability of high-strength steels can be improved without degrading the mechanical properties using metallurgical solutions to create or retain non-metallic inclusions. Such a metallurgical treatment usually leads, during machining, to the appearance of so-called Built-Up Layers (BULs) or transfer layers on the cutting tool. These BULs protect the tool against wear, and longer tool life or better productivity is achieved. Formation of such BULs on the cutting tool depends on many parameters i.e. tool geometry, tool material, cutting conditions. This paper proposes an experimental methodology to identify and describe BUL occurring on the tool rake face. Machining tests were carried out with a high strength free-cutting steel using an untested AlSiTiN coated carbide tool. BULs morphology and composition were determined for various cutting conditions. Temperature distributions at the tool-chip interface were measured during the cutting tests using an infrared camera. BUL appearance was then linked to the thermo-mechanical conditions at the tool-chip interface.Association Nationale de la Recherche et de la Technologi