Experimental study of the brittle–ductile transition in hot cutting of SG iron specimens

http://www.sciencedirect.com/science/article/pii/S0924013612002579The present paper investigates the brittle-ductile transition (BDT) of the primary shear zone during cutting of spheroidal graphite (SG) iron in the austenitization temperature range (around 1000 °C). The experimental tests were performed using a cutting test bench in the cutting speed range of 0.8 to 1.6m.s-1. The cut surfaces were studied using optical microscopy and Scanning Electron Microscope (SEM) analysis techniques. The obtained results revealed either consequent deep fractured regions governed by a brittle-cracking regime (BCR) or a crack-free cut surface governed by a ductile-shear regime (DSR) with large plastic deformations. When cutting data were discussed with respect to the influences of cutting parameters and obtained cut surface, the correlation is significantly rich. Both cut surface integrity, cutting force curves and metallographic results show a BDT indicating a change in the dominating hot cutting process mechanism. Such a transition is associated with the dynamic recrystallization promoting strain softening and hot cutting by ductile shearing

Performance impact of honing dynamics on surface finish of precoated cylinder bores

The surface modification of engine cylinder bores with improved sliding properties is often produced by the honing process. This multi-stage process is performed using abrasive stones loaded against the bore with simultaneous rotation and oscillation. To guarantee this process robustness with acceptable dimensional accuracy and surface quality, the stone dynamic effects in continuous balanced contact with the workpiece have to studied deeply. This paper highlights these effects on honed surface textures. The stone dynamic behavior was studied at conventional regime ranged from 0,5g to 1,5g as often used in mass production. In this range, the dimensional accuracy is ensured by opposition to the surface appearance. However, higher accelerations up to 2,5g improve simultaneously the form quality (especially straightness) and reduces the cycle time. This work shows, at least, that the bore surface finish can be dynamically controlled while honing. This technology is enabled by a micro scale regeneration mechanism of abrasive stones

Simulation of Roughness and Surface Texture Evolution at Macroscopic Scale During Cylinder Honing Process

The honing process produces surface liners with specific functional properties. Engine performances and life expectancy are directly impacted by the quality of honed surface. The form quality, the roughness and the surface appearance manufactured by honing determine the friction of the piston in the liner. The process is however mechanically complex and the selection of the process parameters is currently based on empirical methods. The aim of this paper is thus to develop a macroscopic simulation environment which will help end-users during this setting-up stage. The development of this virtual tool is based on a space-time discretization and a macroscopic cutting model taking into account local contacts between the workpiece and the abrasive stones. The space-time discretization allows representing the machine environment including the tool, the workpiece and the machine kinematics. The cutting model allows converting kinematics and abrasive contacts in dynamic data and material removal rate by calculation. The cutting model is initially adjusted based on simple experiments. The stock removal equation is then extrapolated to the whole range of stone cutting conditions. This approximation allows simulating the real process and a whole honing cycle. Results are validated by comparison with industrial context experiments. The simulation of the whole honing cycle allows predicting the form quality, one of the roughness criteria and the surface appearance. Moreover, simulation results are represented by means of maps that allow looking at quality criteria for each point of the surface

Macroscopic simulation of the liner honing process

The form quality, the roughness and the surface appearance produced by honing minimizes the friction of the piston in the liner. The process is however mechanically complex and the selection of the process parameters is currently based on empirical methods. The aim of this paper is thus to develop a macroscopic simulation environment of complete real honing cycles, which will help end-users during the setting-up. This virtual tool is based on a space-time discretization and a macroscopic cutting model taking into account local contacts between the workpiece and the abrasive tool. The space-time discretization allows representing the machine environment with the tool, the workpiece and the kinematics. Simulation results are finally validated by comparison with industrial experiments.Thèse CIFRe Renault SAS / MSMP PôleProcess ECO

Digital image correlation as a usefful tool of analysis of hot cutting process

This study deals with the use of Digital Image Correlation (DIC) to investigate the physical phenomena taking place during the orthogonal cutting of a SG iron specimen at high temperature (around 1,000 °C). After h aving recalled the scientific and industrial context, the experimental procedure developed to record the pictures of the tool covered with a speckle pattern at a frequency of 10,000 Hz (thanks to a high speed camera) is explained. The quantitative exploitation of these recordings is leading to a first set of results showing how the cutting speed and the rake angle of the tool have an influence on the physics of the cutting operation.Arts et Métiers ParisTech - DGAR

Running-in wear modeling of honed surface for combustion engine cylinder liners

The texture change during running-in alters the performance and efficiency of a tribo-mechanical system. During mass production of cylinder liners, a final finishing stage known as ‘‘plateau honing’’ is commonly added to reduce the running-in wear process of the liner surface. The majority of researchers think that this operation improves the engine efficiency and decreases oil consumption. It was believed that there are close links between the surface topography of honed cylinders change and their wear resistance during running-in. However, these interactions have not yet been established. Some running-in wear models were developed in the open literature to predict topographical surface changes without considering the running-in conditions. The present paper thus investigates the various aspects of the wear modeling that caused running- in problems in honed surfaces and its implications on ring-pack friction performance. To illustrate this, plateau honing experiments under different conditions were first carried out on an instrumented vertical honing machine. The plateau honing experiments characterize the surface modifications during running-in wear of cast-iron engine bores using advanced characterization method. Based on the experimental evidence, a running-in wear model was developed. Finally, a numerical extension of the developed model was applied to solve the Reynolds equation by taking into account the real surface topographies of the engine bore. This enables us to predict realistic friction performance within the cylinder ring-pack tribosystem

Mutual influence of cross hatch angle and superficial roughness of honed surfaces on friction in ring-pack tribo-system

The cylinder bore surface texture, widely produced by the honing technique, is an essential factor for a good engine performance (friction, oil consumption, running-in, wear etc.). This explains the improvement and development of various new honing techniques. These different honing processes generate surfaces with various texture features characteristics (roughness, valleys depth, cross hatch angle, etc.). This paper addresses a comparison of ring-pack friction for cylinder surfaces produced by plateau honing and helical slide honing. It takes in consideration the mutual effect of superficial plateau roughness amplitude and honing angle. A numerical model is developed to predict friction within the cylinder ring-pack system in mixed lubrication regime. The results show the effectiveness of helical slide honed surface texture in comparison to plateau honed bore surface

Numerical study on the chip removal and surface quality of CFRP/Ti6Al4V stacks

369-378Machining of multilayer stacks constituted by carbon fibre reinforced polymer (CFRP) composites and titanium (Ti) alloys has been a hot topic receiving extensive attention in both academia and industry due to their superior mechanical properties and widespread applications in the modern aircraft. Compared with the wide availability of experimental studies dealing with the cutting of CFRP/Ti6Al4V stacks, the present work aims to utilize a finite element (FE) method to address fundamentally the machining characteristics of this metallic-composite material. In this paper, a two-dimensional numerical model of orthogonal cutting configuration has been established to improve the mechanism investigations of the bi-material cutting process. The CFRP/Ti6Al4V model has been constructed by establishing three different physical constituents including the Ti phase, the interface and the CFRP phase. Disparate constitutive laws and damage criteria have been implemented to build the anisotropic machinability of the sandwich material. The key cutting phenomena including the chip removal process, machined surface quality and parametric effects on the stack cutting response have been addressed with a particular focus on the quantification of the machining-induced composite damage. The numerical analysis sheds light on several implicit mechanisms dominating the stack machining and offers a better CFRP/Ti6Al4V cutting understanding

A new insight on induced-tribological behaviour of hypereutectic Al-Si alloys manufactured by selective laser melting

In this work, the tribological behaviour of selective laser melting (SLM) processed hypereutectic Al-Si alloy is investigated by the ball on disc test with focus on the effect of silicon content (18 and 50 wt %). Different from the conventional casted sample, the SLM processed sample shows an ultra-fine microstructure with silicon size inferior to 5 μm. Indeed, the SLM processed hypereutectic Al-Si alloy illustrates a pseudo-eutectic microstructure consisted by supersaturated Al(Si) and primary silicon. Both the SLM processed Al-18Si and Al-50Si presents low wear rate about of 7.0 and 8.1◊10−4 mm3/(N◊m) respectively. Moreover, the wear mechanisms of conventional casted and SLM processed hypereutectic Al-Si alloys are compared and discussed

Flexible right sized honing technology for fast engine finishing

The paper discusses a flexible honing technology by describing the new prototype machine with its specificity. Three original methods produced by the flexible honing prototype have been studied. A path combines the two contemporary methods of industrial honing: the helical slide honing at 135 ° at the bottom of the cylinder and the conventional honing at 45 ° on the upper part. This method of honing shows the effectiveness of specific motion tracking to remove traces of inversions. Circular trajectories with large radii can be traveled quickly without consuming too much energy. The high cutting speed promotes the removal of material thus saving time. Finally, the multi-circle paths can get original textures thus proving the feasibility of all patterns