Yves Beauchamp

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.

Statistical investigation of modal parameters of cutting tools in dry turning

Abstract It is very important that optimized cutting parameters be selected in controlling the quality required for surface finishes. Unfortunately, surface roughness does not depend solely on the feed rate, the tool nose radius and cutting speed; the surface can also be deteriorated by excessive tool vibrations, the built-up edge, the friction of the cut surface against the tool point, and the embedding of the particles of the materials being machined. Hence, the forces, which can be considered as the sum of steady, harmonic and random forces, act on the cutting tool and contribute to the modification of the dynamic response of the tool, by affecting its stiffness and damping. These stiffness and damping variations are attributable to parameters that cannot be easily predicted in practice (regenerative process, penetration rate, friction, variation in rake angle, cutting speed, etc.). Furthermore, the effects of cutting parameters, which also contribute to the variation in the tool’s modal parameters, are more useful for controlling tool vibration. This study focuses on the collection and analysis of cutting-force, tool-vibration and tool-modal-parameter data generated by lathe dry turning of mild carbon steel samples at different speeds, feeds, depths of cut, tool nose radii, tool lengths and workpiece lengths. A full factorial experimental design (288 experiments) that takes into consideration the two-level interactions between the independent variables has been performed. This analysis investigated the effect of each cutting parameter on tool stiffness and damping, and yielded an empirical model for predicting the behavior of the tool stiffness variation.

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.

Comparison of a full factorial experiment to fractional and Taguchi designs in a lathe dry turning operation

Abstract This paper presents a comparison of three different experimental designs aimed at studying the effects of cutting parameters variations on surface finish. The results revealed that the effects obtained by analyzing both fractional and Taguchi designs (16 trials each) were comparable to the main effects and tow-level interactions obtained by the full factorial design (288 trials). Thus, we conclude that screening designs appear to be reliable and more economical since they permit to reduce by a factor 18 the amount of time and effort required to conduct the experimental design without losing valuable information.

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

Development of a new frequency weighting filter for the asessment of grinder exposure to wrist-transmitted vibration

The risk assessment of hand tool workers exposed to hand-arm vibrations is still problematic. It is based, accordingly to ISO 5349, on a frequency-weighted measurement recorded at the handle of the tool. Unfortunately, the frequency-weighted filter recommended by ISO 5349 does not take into account any amplification of the hand-arm system and underestimates the global rms acceleration transmitted to the hand. In this study, the vibration transmitted from the tool handle to the workers wrist is investigated in an industrial environment for seven commercial grinders, two subjects and three push forces. The results are compared with the ISO-5349 and ACGIH threshold limit values, and a new frequency weighting filter is proposed, by which the amplification close to the natural frequencies of the hand-arm system can be considered in the evaluation of the vibration transmitted to the wrist from vibration measurements at the tool handle in a grinding operation.

The effects of factors on human performance in the event of an unexpected robot motion

This study evaluates factors that could effect human performance in the event of an unexpected robot motion. The results of the study demonstrated many things. First, robot speed and task had an important impact on robot overrun distance. A longer overrun distance was observed with both increasing robot speed or task complexity. Second, illumination affected subjects performance; a longer overrun distance was observed with a low illumination level (10 Lux). Overrun distance, however, remained unaffected with increasing illumination level above 100 Lux. Furthermore, unexpected robot motions initiated in the peripheral field resulted in a longer overrun distance than motions initiated in the central field. The analysis of the robot speed by illumination interaction suggested that a low illumination level may further increase overrun distance with increasing robot speed. The analysis also suggested that when increasing robot motion speed, the overrun distance increases with low background-to-robot-arm luminance contrast ratios.

Application of visual analog scales (VAS) for the comparative evaluation of tool and equipment designs and work methods

For a few years now, researchers of the Equipe de recherche en securite du travail (EREST) at the Ecole de technologie superieure have been using psychophysical methods, VAS in particular, in their research work, in order to make precise assessments of tools, equipments and working methods. In all studies conducted, using VAS enabled the researchers to carry out precise evaluations and to recommend solutions for validating a choice, or to make the required modifications to tools, equipments or working methods. When physiological and/or physical measurements were also recorded at the same time as the psychophysical evaluations, results have consistently shown excellent correlation between these measurements. In this article, we present a summary of the main studies where the psychophysical technique of visual analog scales has been used successfully.

Determination of a safe slow robot motion speed based on the effect of environmental factors

The goal of this research was to determine a safe slow robot motion speed to be used for intervention tasks conducted in proximity to an industrial robot (e.g., programming and maintenance) when environmental factors were considered. The relevant factors associated with a robot station were dictated by previous research (Beauchamp and Stobbe, 1990). They were the illumination level, the luminance contrast between the robot and its background, the motion speed of the robot, and the field in which unexpected motions were initiated. The dependent variable measured was the distance the robot moved before the subject detected and responded to the unexpected robot motion. From the results, a multiple regression model was derived for predicting robot overrun distance. The model suggested that speeds in excess of 17 cm/s do not provide an adequate safety margin, and that 17 cm/s should be recommended as the maximum robot slow speed for work conducted in the vicinity of an industrial robot not equipped with dead-man switches.

Psychophysical measurements as an effective way of evaluating climbability of wood treated utility poles

Abstract The aim of this study is to evaluate linemens perception of hardness during the climbing of different wood species and treatment combinations in order to determine if psychophysical measurements could be used to evaluate “climbability” of wood treated utility poles. Twenty-four (24) linemen participated in the study. Twelve (12) wood poles, different species, preservative treatments and hardness, were erected inside a large tent. Each lineman was instructed to climb a pole and to record his perception of hardness on a visual analog scale (VAS). The results revealed that linemens perception of hardness, measured using the VAS, can discriminate a difference of 1 mm in Pilodyns penetration. The VAS is also found to be an effective tool to discriminate different species-treatment combinations. It is concluded that the use of a VAS to evaluate linemens perception of hardness could be an effective way to address “climbability” of wood treated poles.