Viswanathan Madhavan

Machining as a Wedge Indentation

A case is made for the consideration of single-point machining of ductile metals as a special type of wedge indentation process. A general-purpose finite element analysis of machining using iterative rezoning is developed based on this analogy. The accuracy of this analysis, which does not incorporate any separation criterion, is limited only by our knowledge of the material properties and the friction conditions at the tool-chip interface. Strain hardening, strain rate effects, and the temperature dependence of the properties of the work material can be taken into consideration. While Coulomb friction is assumed at the chip-tool interface in the present model, it can easily be reformulated to include more complicated frictional interactions such as adhesion. An analysis of the cutting/ indentation of an isotropic work-hardening material at slow speeds under two different friction conditions is presented. It is shown that many of the important features of machining processes are consistently reproduced by the analysis.

Direct Observations of the Chip-Tool Interface in the Low Speed Cutting of Pure Metals

An experimental study of the chip-tool interface and its evolution in the low speed cutting of metals has been carried out. Specially prepared transparent glass and sapphire tools have been used to cut commercially pure metals such as lead, aluminum and copper. The chip-tool interface has been observed in situ using optical microscopy and recorded on film and video tape. By observing the motion of inhomogeneities in the chip, and profilometry of the chip and tool surfaces, it has been established that there is intimate sliding contact between the chip and the tool at and near the cutting edge. Farther away from the cutting edge and close to the end of the chip-tool contact, metal transfer and sticking are observed between the chip and tool surfaces. It has been shown that metal deposition on the rake face initially occurs near the point at which the chip curls out of contact with the tool and progressively extends outward and away from the cutting edge in conjunction with an increase in the length of contact as cutting progresses. The sticking and sliding zones are unchanged when these pure metals are machined with tungsten carbide tools. @DOI: 10.1115/1.1398546#

A novel ultra-high speed camera for digital image processing applications

Multi-channel gated-intensified cameras are commonly used for capturing images at ultra-high frame rates. The use of image intensifiers reduces the image resolution and increases the error in applications requiring high-quality images, such as digital image correlation. We report the development of a new type of non-intensified multi-channel camera system that permits recording of image sequences at ultra-high frame rates at the native resolution afforded by the imaging optics and the cameras used. This camera system is based upon the concept of using a sequence of short-duration light pulses of different wavelengths for illumination and using wavelength selective elements in the imaging system to route each particular wavelength of light to a particular camera. As such, the duration of the light pulses controls the exposure time and the timing of the light pulses controls the interframe time. A prototype camera system built according to this concept comprises four dual-frame cameras synchronized with four dual-cavity pulsed lasers producing 5 ns pulses in four different wavelengths. The prototype is capable of recording four-frame full-resolution image sequences at frame rates up to 200 MHz and eight-frame image sequences at frame rates up to 8 MHz. This system is built around a stereo microscope to capture stereoscopic image sequences usable for 3D digital image correlation. The camera system is used for imaging the chip‐workpiece interface area during high speed machining, and the images are used to map the strain rate in the primary shear zone.

Uncertainty of temperature measurements by infrared thermography for metal cutting applications

This paper presents a comprehensive analysis of the uncertainty in the measurement of the peak temperature on the side face of a cutting tool, during the metal cutting process, by infrared thermography. The analysis considers the use of a commercial off-the-shelf camera and optics, typical of what is used in metal cutting research. A physics-based temperature measurement equation is considered and an analytical method is used to propagate the uncertainties associated with measurement variables to determine the overall temperature measurement uncertainty. A Monte Carlo simulation is used to expand on the analytical method by incorporating additional sources of uncertainty such as a point spread function (PSF) of the optics, difference in emissivity of the chip and tool, and motion blur. Further discussion is provided regarding the effect of sub-scenel averaging and magnification on the measured temperature values. It is shown that a typical maximum cutting tool temperature measurement results in an expanded uncertainty of U = 50.1 °C (k = 2). The most significant contributors to this uncertainty are found to be uncertainties in cutting tool emissivity and PSF of the imaging system.

A calibrated dual-wavelength infrared thermometry approach with non-greybody compensation for machining temperature measurements

We report the development of a new approach for determining temperatures using the dual-wavelength infrared thermometry technique, which does not presume greybody behaviour and compensates for the spectral dependence of emissivity. This approach is based on Plancks radiation equation and explicitly accounts for the wavelength-dependent response of the IR detector and the losses occurring due to each of the elements of the IR imaging system that affect the total radiant energy sensed in different spectral bands. A thorough calibration procedure is utilized to determine a compensation factor for the spectral dependence of emissivity, which is referred to as the non-greybody compensation factor (NGCF). Calibration and validation experiments are carried out on Aluminum 6061-T6 targets with two different surface roughnesses. Results show that this alloy does not exhibit greybody behaviour, even though the two spectral bands used were relatively close to each other, and that the spectral dependence of emissivity is influenced by the surface finish. It is found that non-greybody behaviour of low emissivity surfaces can lead to significant systematic error in dual-wavelength IR thermometry. The inclusion of the NGCF eliminates the systematic error caused by the invalidity of greybody assumption and thus improves the accuracy of the measurements. Non-greybody-compensated dual-wavelength thermography is used to measure the chip temperature along the tool–chip interface during orthogonal cutting of Al 6061-T6 and sample results at three different cutting speeds are presented.

Exploration of contact conditions in machining

Abstract The contact conditions along the tool-chip and tool-work interfaces in the machining of metals are analysed and discussed. The principal experimental techniques used are direct optical measurements of the interfaces at visible and infrared wavelengths using transparent tools, measurements of the variation of forces with flank wear and microstructural changes produced in steel surfaces during machining and perturbation of the tool-chip interface using low-frequency modulation. The application of these techniques has provided new insights into the motion of the chip relative to the tool along the rake face, enabled measurement of the full-field temperature along the rake face and suggested avenues for modifying friction conditions along the tool rake and flank faces. It is shown that important differences as well as similarities exist between the rake face and flank face boundary conditions. The implications of these results for the theoretical analysis of machining are discussed.

Full-field IR measurement of subsurface grinding temperatures

A multiple-element, forward looking IR system is used to measure the subsurface temperature field produced by dry grinding of steel with both aluminum oxide and cubic boron nitride (CBN) grinding wheels. The technique is base don imaging the IR radiation obtained from the side of the specimen. A recent theoretical analysis of heat partition and surface temperatures in grinding is reviewed. The analysis partitions heat on the two length scales pertinent to grinding between the workpiece, wheel, coolant and chips. Spectral analysis is combined with FFT techniques to calculate subsurface temperature contours from the predicted heat partition. The numerical predictions of the model are shown to agree wit the experimental results taken for a range of grinding conditions. It is found that heat partition varies over a wide range depending on grinding conditions. Also, heat partition is a strong function of position inside the grinding zone. The presence of the fluid inside the grinding zone can reduce the heat flux into the workpiece and the workpiece temperature significantly. For typical grinding of steel with CBN, or creep feed grinding of steel with aluminum oxide or CBN, it is possible to keep the fluid active and therefore to reduce thermal damage. However, the analysis suggests that the fluid may not be effective inside the grinding zone, in the conventional grinding of steel with aluminum oxide, due to boiling. It is also found that a moderate ratio of the workpiece velocity to wheel velocity gives high temperatures and therefore should be avoided.

The Flow Stress of AM IN 625 under Conditions of High Strain and Strain Rate

Additively manufactured (AM) nickel superalloy (In 625) with known processing history and quasi-static properties has been investigated under extreme strains up to about 100% and strain rate up to about 104/s by machining. A model for the calculation of the component of force that is due to indentation by the tool cutting edge was utilized to correct the measured shear force and material flow stress. The results are compared to flow stress measurements produced by Kolsky compression testing under strains of about 25% and strain rate of about 103/s. The highly instrumented setups utilized for the machining testing made possible an accurate description of the strain and strain rate at the primary shear zone (PSZ), and the temperature at the tool rake face that prevailed throughout the machining. The strain and strain rate were determined by digital image correlation. The temperature was determined by through-the-tool thermography. Differences observable during the cutting and dynamic compression of additive and wrought In 625 are outlined.

Realistic immersion of a user into humanoids of different sizes and proportions in lmmersive virtual reality

In immersive virtual reality simulations in which users are immersed into full body humanoids, it is typically the case that the humanoid size and proportions have to match those of the immersed user for the immersion to be realistic. However, a key aim of these simulations may be to study how users of different body sizes and proportions interact with the environment. We have developed a real time motion retargeting method by which users can be immersed into different humanoids and other kinematically similar avatars, and still experience a realistic feeling of immersion. A set of experiments aimed at studying the realism of the immersion indicate that users indeed experience a realistic sense of immersion into different humanoids.