Mathew Kuttolamadom

Effect of Machining Feed on Surface Roughness in Cutting 6061 Aluminum

The general manufacturing objective during the fabrication of automotive components, particularly through machining, can be stated as the striving to achieve predefined product quality characteristics within equipment, cost and time constraints. The current state of the economy and the consequent market pressure has forced vehicle manufacturers to simultaneously reduce operating expenses along with further improving product quality. This paper examines the achievability of surface roughness specifications within efforts to reduce automotive component manufacture cycle time, particularly by changing cutting feeds. First, the background and attractiveness of aluminum as a lightweight automotive material is discussed. Following this, the methodologies employed for the prediction of surface roughness in machining are presented. The factors affecting surface roughness as well as practical techniques for its improvement through optimizing machining parameters are discussed next. Emphasis is placed on portraying the dominance of feed on surface quality over other controllable machining parameters, thus substantiating the motivation for this study. Controlled milling experiments show the relationship between feed and surface quality for 6061 aluminum, and the results are used to recommend machining practices for cycle time reduction while maintaining quality requirements.

Investigation of the Machining of Titanium Components for Lightweight Vehicles

Due to titanium’s excellent strength-to-weight ratio and high corrosion resistance, titanium and its alloys have great potential to reduce energy usage in vehicles through a reduction in vehicle mass. The mass of a road vehicle is directly related to its energy consumption through inertial requirements and tire rolling resistance losses. However, when considering the manufacture of titanium automotive components, the machinability is poor, thus increasing processing cost through a trade-off between extended cycle time (labor cost) or increased tool wear (tooling cost). This fact has classified titanium as a “difficult-to-machine” material and consequently, titanium has been traditionally used for application areas having a comparatively higher end product cost such as in aerospace applications, the automotive racing segment, etc., as opposed to the consumer automotive segment. Herein, the problems associated with machining titanium are discussed, and a review of cutting tool technologies is presented that contributes to improving the machinability of titanium alloys. Additionally, nonconventional machining techniques such as High Speed Machining and Ultrasonic Machining are also reviewed. Also discussed are additional factors that need to be considered especially pertaining to the machining of titanium alloys, a crucial one being the non-conformity with standard tool wear models. Subsequently, the results of a controlled milling experiment on Ti-6Al-4V is presented, to evaluate the relationship between certain tool preparation/process parameters and tool wear for a comparison with traditional wear models. INTRODUCTION Titanium is the seventh most abundant metal and the fourth most abundant structural metal in earth’s crust behind aluminum, iron and magnesium. Titanium and its alloys are considered as alternatives in many engineering applications due to their superior properties such as retained strength at elevated temperatures, high chemical inertness and resistance to oxidation. Titanium has traditionally been utilized as a lightweight, very strong and exceedingly corrosion resistant material in the aerospace industry, electric power plants, seawater desalination plants, and heat exchanges. Also, it has been used in industrial applications such as petroleum refining, nuclear waste storage, food processing, pulp and paper plants, and marine applications [1]. Nevertheless, when considering the use of titanium as an automotive component material, there are several conflicting aspects that must be addressed. First of all, the cost of titanium is relatively high in comparison to other common engineering materials such as aluminum, magnesium, and steel. For this reason, it specifically calls for implementation and use only when extreme conditions are to be met, such as in the aerospace industry. The main reason for the increased cost is due to the limited demand from other market segments, thus making the extraction of the titanium ore expensive. Also, the processing costs for converting the ore into commercially usable titanium and its alloys is extensive and requires special processing procedures and involves vast batch production and careful process control, making them difficult to automate. Second, the difficulty in efficiently manufacturing titanium components has a significant adverse effect on processing cost which is mainly due to its low modulus of elasticity and high yield stress. Another manufacturing concern that arises during the machining of titanium is its susceptibility to work hardening during the cutting process and its tendency to react with many cutting tool materials causing substantial tool wear. Additionally, titanium has poor thermal conductivity properties, making heat dissipation a problem, again contributing to higher tool wear. Of primary concern however is the lack of material grade development outside the aerospace industry in which most of the alloys are developed for extreme conditions. This severely limits the currently available grades suited for automotive applications. Thus, a suite of lower strength alloys with properties specially catered for commercial automotive use needs to be developed. This paper examines most of the issues traditionally associated with the machinability of titanium and titanium alloys. As mentioned before, some methodologies and techniques are recommended for mitigating the non-desirable effects during titanium processing and analyzed in more detail, is its unique tool wear characteristics especially in light of manufacturing automotive components. Thus, this study is expected to primarily assist in the reduction of the processing cost of titanium and its alloys for automotive component manufacture. This will help reduce the operating cost of a road vehicle in terms of better fuel economy due to the reduced mass, which in turn translates to better energy efficiency. TITANIUM IN THE AUTOMOTIVE

Correlation of the Volumetric Tool Wear Rate of Carbide Milling Inserts With the Material Removal Rate of Ti–6Al–4V

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti–6Al–4V. To capture the tool response, controlled milling experiments are conducted at suitable corner points of the recommended feed-speed design space, for constant stock material removal volumes. For each case, the tool material volume worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients, is quantified—these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW) which is a measure of the cutting tool efficiency, are related to the MRR—these provide a tool-life based optimal MRR for profitability. This work not only elevates tool wear from a 1D to 3D concept, but helps in assessing machining economics from a stock material-removal-efficiency perspective as well.

The Correlation of the Volumetric Wear Rate of Turning Tool Inserts With Carbide Grain Sizes

The objective of this paper is to analyze the effect of different carbide grain sizes on the tool material volume worn away from straight tungsten–carbide–cobalt (WC–Co) turning inserts. A previously developed metrology method for assessing the tool material volume worn away from milling inserts is adapted for quantifying the volumetric tool wear (VTW) of turning inserts. Controlled turning experiments are conducted at suitable points in the feed-speed design space for two sets of uncoated inserts having different carbide grain sizes. Three levels of Ti–6Al–4V stock removal volumes (10-cm3 each) are analyzed. For each insert, the tool material volume worn away (in mm3) as well as the three-dimensional (3D) wear profile evolution is quantified after each run. Further, the specific volumetric wear rate and the M-ratio (volume of stock removed to VTW) are related to the material removal rate (MRR). The effect of carbide grain size on VTW is examined using scanning electron microscopy and elemental analysis. Finally, the inverse dependence of the M-ratio on MRR enables the definition of actual usable tool life in terms of its efficiency in removing stock, rather than being based on a tool geometry related metric.

Machining Process Power Monitoring: Bayesian Update of Machining Power Model

Monitoring the CNC machine tool power provides valuable information that aids condition based maintenance, machine efficiency and machining process monitoring. Cutting force in machining process is an interesting variable to measure from monitoring and control point of view. Although the direct methods of measuring the cutting force exist, prohibitive costs do not allow deployment in industrial environment. In the indirect methods of measuring force, measuring the spindle motor current to estimate the cutting power and consequently the cutting force is popular.This work discusses the calibration of spindle current based torque sensor for the estimation of the cutting force in turning operation. The work undertakes handling uncertainty in measurement of the cutting torque measurement. Considering the steady state value, the cutting torque is represented as a polynomial function of the speed and measured power. Though the identification of the unknown coefficients can be done based on the offline tests, in current work, the Bayesian update of coefficients is proposed. This method allows online learning of these coefficients. The cutting torque value based on the model has some variability due to variation in the coefficients and unmodeled dynamics. The iterative learning happens in three stages, namely — Prior belief, likelihood function establishment and update in prior belief with observed data producing posterior belief. The establishment of the priors is done through some offline tests. The likelihood function accounts for noise in the measurement of torque. And finally, Markov Chain Monte Carlo (MCMC) simulations help sampling from unknown posterior distribution. This scheme has ability to sample from any distribution. A single update cycle shows high reduction in the variability of the torque. Experimental data is produced to verify the effectiveness of method; the Bayesian update scheme outperforms least-square polynomial fit method consistently for different cutting speeds and cutting load values.Copyright

Characterization of Forces in High-Speed Bone Cutting and Grinding for Haptics Rendering

This study characterizes the forces in high-speed bone cutting and grinding for the use of haptic devices in surgical simulations. Unrealistic force feedback due to the lack of vibrational features is one of the most common drawbacks. Generally, the force profile can be decomposed to a mean force and a vibrational force magnitude. These forces are experimentally measured under various motions, including feed rate and tool orientation, to mimic manual operations and to understand the effects of these parameters. Change in feed rate was found to be insignificant in the overall force feedback, while the change in tool orientation showed statistically significant effects. The grinding burr and cutting burr also exhibited different forces under an identical condition. The explanation for the behavior of the forces based on the cutting and grinding conditions is discussed along with the results.© 2016 ASME

The Correlation of Volumetric Tool Wear and Wear Rate of Machining Tools With the Material Removal Rate of Titanium Alloys

The objective of this paper is to assess the correlation of volumetric tool wear (VTW) and wear rate of carbide tools on the material removal rate (MRR) of titanium alloys. A previously developed methodology for assessing the worn tool material volume is utilized for quantifying the VTW of carbide tools when machining Ti-6Al-4V. To capture the tool substrate response, controlled milling experiments are conducted at suitable corner points of the feed-speed design space for constant stock material removal volumes. For each case, the tool material volumes worn away, as well as the corresponding volumetric wear profile evolution in terms of a set of geometric coefficients are quantified — these are then related to the MRR. Further, the volumetric wear rate and the M-ratio (volume of stock removed to VTW), which is a measure of the cutting tool efficiency, are related to the MRR — these provide a tool-centered optimal MRR in terms of profitability. This work not only elevates tool wear from a 1-D to 3-D concept, but helps in assessing machining economics from a stock material removal efficiency perspective as well.Copyright

On the Volumetric Assessment of Tool Wear in Machining Inserts With Complex Geometries: Need, Methodology and Validation

The objective of this paper is to qualitatively assess the inadequacies of the current manner of tool wear quantification and consequently to suggest/develop a more comprehensive approach to machining tool wear characterization. Traditional parameters used for tool wear representation such as flank and crater wear are no longer self-sufficient to satisfactorily represent the wear of the complex geometric profiles of more recent cutting tools. These complexities in tool geometries are all the more pronounced when catering to difficult-to-machine materials such as titanium and its alloys. Hence, alternatives to traditional tool wear assessment parameters are briefly explored and a suitable one is selected, that will help understand the very nature of the evolving wear profile itself from a three dimensional standpoint. The assessment methodology is further developed and standardized and suggestions for future use and development provided. The measurement system is evaluated using a gauge repeatability and reproducibility (R&R) study as well. The method is deployed for assessing tool wear during the machining of Ti-6Al-4V at selected process conditions for validation purposes. Further, concepts such as the M-ratio and its derivatives are developed to quantify the efficiency of the cutting tool during each pass as a function of time at a theoretically constant material removal rate (MRR).Copyright

A mechanistic force model for simulating haptics of hand-held bone burring operations

This paper presents a mechanistic model to predict the forces experienced during bone burring with application to haptic feedback for virtual reality surgical simulations. Bone burring is a hand-held operation where the force perceived by the surgeon depends on the cutting tool orientation and motion. The model of this study adapted the concept of specific cutting energy and material removal rate based on machining theory to calculate force distribution on the spherical tool surface in a three-dimensional setting. A design of experiments with three tool cutting angles and three feed motions was performed to calibrate and validate the model. Despite some variance in the results, model predictions showed similar trends to experimental force patterns. While the actual force profile also exhibits significant oscillation, the dominant frequencies of this oscillating force component were found to be independent of cutting and non-cutting instances, and hence could be imposed as a uniform background signal. Though the presented model is primarily applicable to abrasive burrs, it has far-reaching applications within other types of surgical simulations as well.