Jacques Masounave

Effect of tool vibrations on surface roughness during lathe dry turning process

Abstract Choice of optimized cutting parameters is very important to control the required surface quality. In fact, the difference between the real and theoretical surface roughness can be attributed to the influence of physical and dynamic phenomena such as: built-up edge, friction of cut surface against tool point and vibrations. The focus of this study is the collection and analysis of surface roughness and tool vibration data generated by lathe dry turning of mild carbon steel samples at different levels of speed, feed, depth of cut, tool nose radius, tool length and work piece length. A full factorial experimental design (288 experiments ) that allows to consider the three-level interactions between the independant variables has been conducted. Vibration analysis has revealed that the dynamic force, related to the chip-thickness variation acting on the tool, is related to the amplitude of tool vibration at resonance and to the variation of the tools natural frequency while cutting. The analogy of the effect of cutting parameters between tool dynamic forces and surface roughness is also investigated. The results show that second order interactions between cutting speed and tool nose radius, along with third-order interaction between feed rate, cutting speed and depth of cut are the factors with the greatest influence on surface roughness and tool dynamic forces in this type of operation and parameter levels studied. The analysis of variance revealed that the best surface roughness condition is achieved at a low feed rate (less than 0.35 mnt/rev), a large tool nose radius (1.59 mm) and a high cutting speed (265 m/min and above). The results also show that the depth of cut has not a significant effect on surface roughness, except when operating within the built-up edge range. It is shown that a correlation between surface roughness and tool dynamic force exist only when operating in the built-up edge range. In these cases, built-uṕ edge formation deteriorates surface roughness and increases dynamic forces acting on the tool. The effect of built-up edge formation on surface roughness can be minimized by increasing depth of cut and increasing tool vibration. Key words:design of experiments, lathe dry turning operation, full factorial design, surface roughness, measurements, cutting parameters, tool vibrations.

An experimental design for surface roughness and built‐up edge formation in lathe dry turning

Investigates the effects of the most influential cutting parameters (cutting speed, feed rate, depth of cut, tool nose radius, tool length and work piece length) on surface roughness quality and on the formation of built‐up edge in a lathe dry turning process of mild carbon steel samples. A full factorial design (384 experiments), taking into account the three‐level interactions between the independent variables has been conducted. The results show that the following three‐level interactions: feed rate × cutting speed × depth of cut, feed rate × cutting speed × tool nose radius and tool nose radius × depth of cut × tool length have significant effects on surface roughness in this type of machining operation. Shows that the analysis of main effects alone and even two‐level interactions could lead to a false interpretation of the results. The analysis of variance revealed that the best surface roughness is achieved with a low feed rate, a large tool nose radius and a high cutting speed. The results also show that the depth of cut has no significant effect on surface roughness when operating at cutting speeds higher than 160m/min. Furthermore, it is shown that built‐up edge formation deteriorates surface roughness when machining mild carbon steel at specific feed rate, tool nose radius and cutting speed levels. Proposes a new model for evaluating the limiting cutting speed to avoid the built‐up edge formation. Finally, shows through experimentation that an increase in depth of cut would lead to improved surface roughness when tool vibration is increased.

Dynamic mechanical analysis of prestrained Al2O3/Al metal-matrix composite

The effect of prestraining on the elastic modulus,E, and damping capacity, tanφ, of 10 and 20 vol% Al2O3 particle-reinforced composites has been investigated as function of temperature using dynamic mechanical analysis. Both elastic modulus and damping capacity were found to increase with volume fraction. At 10 vol% the modulus and damping were relatively insensitive to prestrain. However, at 20 vol% it was observed that the modulus decreased with increasing prestrain while damping increased significantly. These results are discussed in terms of fraction of broken particles, particle size, and differential in thermal expansion between the matrix and Al2O3 particulate.

Effect of drill wear on cutting forces in the drilling of metal-matrix composites

Abstract Holes were drilled in 6061 T-6 aluminum alloy as well as in a particle reinforced metal matrix composite (MMCp) consisting of 20 vol.% SiC particles, 12 Am in diameter, in a 6061 aluminum matrix (6061/SiC/20p, or Duralcan« F3S.20S). HSS (high speed steel) drills of 10 mm diameter were used, and measurements were made of thrust (normal force), torque and flank wear for several feed rates and drill speeds. It was found that when drilling Duralcan« with unworn drills, both torque and thrust varied with feed rate raised to the power 0.81, as for classical materials. When flank wear Vb became significant, torque varied linearly with Vb and with f°.s but no empirical relation with physically meaningful parameters was found to fit the thrust data. Speed had no significant effect on wear or on drilling forces. Flank wear proceeded linearly with depth of material drilled, or with the total distance passed by the lip or cutting edge of the drill. A linear relation between both thrust and torque against flank wear was observed, so that either thrust or torque may be measured to give an indication of wear of the drill. The linear relation between torque and wear of the drill implies a linear variation of specific cutting energy with flank wear. Drilling forces are controlled by the matrix material and not by the particles.

Investigation of cutting parameter effects on surface roughness in lathe boring operation by use of a full factorial design

Abstract The main objective of this study is to investigate cutting parameter effects of surface roughness in a lathe dry boring operation. A full factorial design was used to evaluate the effect of six (6) independent variables (cutting speed, feed rate, depth of cut, tool nose radius, tool length and type of boring bar) and their corresponding two-level interactions. In this experiment, the dependant variable was the resulting fast cut surface roughness (R,). In order to perform all possible variable combinations, a total of 216 cuts were. The results revealed that using short tool length always provide good surface roughness and that only slight improvement on surface roughness can be achieved by properly controlling the cutting parameters and/or the type of boring bar used. The results also revealed that using a long tool length may results in vibration that could be efficiently controlled by the use of a damped boring bar. With such a long tool length, the cutting variables become important factors to control in order to significantly improve surface roughness results with both types of boring bars. A prediction model is proposed for each types of boring bar. Both models are highly significant, p

An Experimental Study of Dust Generation During Dry Drilling of Pre-Cooled and Pre-Heated Workpiece Materials

Abstract The generation of fine dust during dry machining is a serious problem both for the environment and for workers. During machining, the fine dust particles generated remain suspended in the air for long periods, during they can be inhaled by workers. The quantity of dust generated is influenced by factors such as material type and heat treatment condition, temperature, and the associated chip formation mode. The aim of this work is to discover how these parameters influence dust generation during dry machining, which could lead to the control of dust production in the future. The materials tested are the wrought 6061 and foundry A356 aluminum alloys and 70-30 brass. It is found that pre-cooling a workpiece material leads to changes in chip formation, in the reduction of cutting forces, and hence in a reduction in fine dust generation by at least 70%, depending on the materials and cutting conditions used. Also, pre-heating the workpiece increases chip ductility and dust production levels.

Wear in Zn-Al-Si alloys

Abstract The zinc-aluminum based casting alloy ZA-27 is useful in bearing applications. Its tribological properties may be improved by replacing its small copper content with silicon. These are further improved if the silicon particle size is controlled by suitable additions of strontium. This effect is related to the observation that wear properties of the alloy are governed by the development of a thin surface film of the Al-rich α phase. The integrity of this surface film during wear is controlled by the interplay between the lubricant film thickness and particle size. Wear performance is optimum when the silicon particles are larger in diameter than the lubricant film thickness, but small enough that they may embed in the bearing surface and be covered by the surface film. It is suspected that a similar conclusion may hold for particles such as grit from a dirty operating environment.

Prediction of tool life in turning aluminium matrix composites

Abstract The machining of aluminium matrix composites reinforced with particulates (MMCp) causes problems because of rapid tool wear due to the extremely high hardness of particles such as silicon carbide and aluminium oxide. Practical considerations for machining MMCp include selection of the cutting speeds and surface roughness. A rapid method for determination of the Taylor relation is presented.

Sliding Wear of Aluminum-Silicon Carbide Metal Matrix Composites

The sliding wear of an aluminum matrix composite, reinforced with different volume fraction of particles, against a stainless-steel slider has been studied. In dry conditions, i.e., unlubricated tests, the pairs (slider and specimen), wear. When rubbing against an aluminum alloy (unreinforced), the slider does not wear but the aluminum alloy wears quickly by adhesion. In dry conditions, both slider and composite wear, but there is a minimum wear rate for this pair at a critical volume fraction of reinforcing particles. Under lubricated conditions, the situation changes dramatically. The composite no longer wears, but the slider wears very quickly. Under water, results are a compromise between the two previous situations, dry and lubricated. These results are explained by a simple, descriptive mechanism, which takes in account both the effect of the shear rate, due to the sliding action in the composite, and the abrasive effect of the particles. A general relationship, which describes the effect of the applied pressure and volume fraction of particles in the composite, is proposed.

An experimental investigation of the dielectric properties of electrorheological fluids

A home-made electrorheological (ER) fluid, known as ETSERF, has been created with suspension-based powders dispersed in silicone oil. Because of the special structure of their particles, ETSERF suspensions present a complex behavior. In the absence of an electric field, the ETSERF fluid manifests a near-Newtonian behavior, but when an electric field is applied, it exhibits a pseudoplastic behavior with yield stress. The ER effect under DC electric fields has been experimentally investigated using both hydrous and anhydrous ER fluids. The ER properties are strongly dependent on the dielectric properties of ETSERF suspensions, and hydrous ER fluids have a high dielectric constant and a high relaxation frequency which show a strong electrorheological effect. The relationship between the electrorheological effect and the permittivity of ER fluids has also been extensively studied. Experimental results show that the interfacial polarization plays an important role in the electrorheological phenomenon. The ageing of ETSERF fluids was also studied and it was found that the dielectric properties (mainly the dielectric loss tangent) and ER properties are strongly related to the duration of ageing. A fresh ETSERF suspension exhibits high relaxation frequency and high dielectric constant. These results are mainly explained by the effect of interfacial polarizations.