Key Engineering Materials Vol. 625

Abstract: This paper describes the applicability of air jet assisted (AJA) machining to stainless steel and titanium alloy at high cutting speeds in terms of tool wear and tool life. A specially designed tool holder with an air nozzle very close to the tool tip was prepared for turning stainless steel. From the experimental results, it was found that the application of flood coolant from the side of the end flank face leads to better result in tool life in AJA machining of stainless steel than that from the side of the side flank face. The assistance of air jet can improve the tool life of the M35 CVD coated insert in machining of the stainless steel by 36 to 100% under the optimal conditions in comparison with wet machining. It was also found that the air jet assistance extended the tool life of the S10 PVD coated insert by 48% in turning titanium alloy. The tool life extension of the coated insert in AJA machining titanium alloy is much longer than that of an uncoated carbide insert.

Abstract: A coordinate measuring machine (CMM) is a measuring system with the means to move probing system and capability to determine spatial coordinates on working surface. CMM is used in many industry fields from few micrometers of work pieces to a 5-meter truck. The verification method of CMM is done following international standard. The artifacts for calibrated reference length are the end standards, such as gauge block and step gauge, or laser interferometer for large size CMM. The current laser interferometer is operated by continuous laser and interference fringe counting. One constraint of continuous laser is an incremental measurement. The measurement path cannot be interrupted during the measurement period. We developed a new absolute interferometer system from a short-pulse mode-locked fiber laser. A Fabry–Pérot etalon (FPE) is used to select high-frequency parts of repetition-frequency modes of the mode-locked comb laser at the wavelength of 1.55 μm. The 5-GHz repetition-modified laser beam, which is realized by a new fiber-type FPE, is transmitted to a fiber-type Michelson interferometer. The interference fringes exhibit a temporal coherence interference and can be used for measuring spatial positioning. The temporal coherence between different pairs of modified pulse trains is referred to as absolute length standards. The performance of CMM was determined directly from different positions of two interference fringe patterns.

Abstract: An atomic force microscope (AFM) was used to image the ultra-precision machined surfaces of K9 glasses, potassium dihydrogen phosphate (KDP) crystals, and silicon wafers. Each surface was generated by two machining techniques: (1) coarse-grain-sized diamond wheel grinding and regular polishing were used on K9 glasses; (2) single-point diamond turning and deliquescent polishing were performed on KDP crystals; (3) standard chemical mechanical polishing and atmospheric pressure low temperature plasma polishing were employed on silicon wafers. One-dimensional and two-dimensional power spectral densities (PSDs) of each sample surface were calculated from the measurement data. The influence of each machining process on the sample surface texture was analyzed based on the PSDs. The experiment results indicate that the power spectral density is a great guidance for the selection and improvement of ultra-precision machining techniques.

Abstract: An apparatus capable of comparing displacements with picometer accuracy is currently being designed at NIST. In principle, we wish to compare one displacement in vacuum to a second, equal displacement in gas, in order to determine gas refractive index. If the gas is helium, the refractive index is expected to be amenable to high-accuracy ab initio calculations relating refractive index to gas density or to the ratio of pressure and temperature (P/T); the measured refractive index can then be used to infer (P/T) with an accuracy goal of about 1×10^-6 (relative standard uncertainty). If either the pressure or temperature is known, the refractive index measurement will allow us to determine the second quantity. Our goal is to achieve an uncertainty limited primarily by the uncertainty of the Boltzmann constant (before redefinition of SI units, which will give the Boltzmann constant a defined value). The technique is an optical analog of dielectric constant gas thermometry and can be used in a similar manner. The dimensional metrology is uniquely challenging, requiring picometer-level uncertainty in the comparison of the displacements.

Abstract: Large-scale comparators of over 30m range are traceable devices of dimensional measurement in advance large-scale manufacture domain. High precision large-scale laser comparator is an open air laser interferometric measurement device, mainly made up of length measurement system, guiding rail system and control system. The length measurement system use laser interference system to get displacements, the main source of the measurement uncertainty of displacements comes from the air temperature measurement uncertainty. This paper put forward a novel air temperature compensation method by weighting-section compensation in the large-scale laser comparator optical path. The method can improve the length measurement uncertainty of large-scale laser comparator to 2×10^-8 level with changing the hardware of air temperature measurement system.

Abstract: Step gauge is the most typical multiple target standard of plane distance with a wide range of applications. The calibration of step gauge is, however, difficult because of its unique structure. In this paper, a new method for measuring plane distance is presented. The principle of light-section microscope is used in accurate positioning of the planes being measured. Then the optical interferometry techniques are used to realize continuous dynamic measurement of the plane distance. Based on this method, a novel optical probe is built and installed on a laser interferometer for length measurements. A series of experiments were carried out for determining the accuracy of positioning the optical probe and repeatability of the measuring system. Experimental results show that measurement repeatability is better than 16 nm, and measurement uncertainty (k=2) is less than 0.03 μm + 1.0×10^-6L, for a total length of L being measured in micrometers.

Abstract: Fast/slow tool servo (FTS/STS) technology plays an important role in machining freeform surfaces for the modern optics industry. The accuracies of these surfaces not only depend on the performance of the FTS/STS but also on the methods of tool path generation (TPG). Current methods of pre-compensating tool nose radius and control dynamics still do not address the inherent profile errors arise from the methods of TPG. Furthermore, it is also not efficient to characterize a freeform surface in the post-machining stage, giving a high risk of failing to meet the accuracy requirements. In this paper, a profile error analysis (PEA) is introduced into the pre-machining stage to address this inherent profile error. PEA is carried out to compare two methods of TPG, namely the constant angle and constant arc methods and optimizes the number of cutting points in the TPG. Thus, the profile accuracy can be pre-determined to meet accuracy requirements by determining the appropriate TPG method with a least number of the cutting points. In the experiments, sinusoidal wave grid and micro-lens array surfaces are fabricated and their profiles successfully achieve the accuracy tolerance of 1 μm. These further credit the capability of PEA as an effective and accurate tool in improving profile accuracies and meeting accuracy requirements.

Abstract: This paper proposes a new lubricant environment when MWCNTs was used in MQL for AISI 304L in the turning machine. The effects of dry cutting, MQL cutting, and MWCNTs/MQL were compared to the surface roughness of work pieces, cutting temperature and the tool wear. In the past, the studies have shown that the MQL process can prolong tool life and improve surface accuracy in machining. The purpose of using MWCNTs suspensions is to increase the thermal conductivity of cutting fluid and to reduce the temperature during the cutting and decrease the thermal wear of tool simultaneously. The present study investigated the characterization of the MWCNTs was applied into MQL during the turning process of AISI 304L experimentally. The results showed that the MWCNTs will be a very good additive to MQL, not only with the benefits of improving surface roughness but also with ability of prolonging life of tool by reducing the cutting temperature in turning AISI 304L.

Abstract: The main purpose of this paper is to study the carbide tip's surface temperature and the cutting forces of milling stainless steel with nose radius worn tools. A new cutting temperatures model incorporating tool worn factor and using the variations of shear and friction plane areas occurring in tool worn situations are presented in this paper. The frictional forces and heat generation on elementary cutting tools are calculated by using the measured cutting forces and the oblique cutting analysis. The tool tip and cutting edges are treated as a series of elementary cutting tips. The carbide tip’s temperature distribution is solved by finite element analysis (FEM) method. Keywords: Milling, stainless steel, cutting temperatures, nose radius tools, FEM

Abstract: We propose a supervisory technique to monitor the material removal state and tool wear condition as well as the estimation method for overall power consumed in the machining from the effective spindle power change. The effective power (VAcosφ) was the optimal motor related parameter to represent the motor load. The cutting condition can be related with the effective power change by using the averaged effective power for 0.2 seconds. The mean effective power is in proportion to the material removal rate. In addition, the averaged effective power can monitor continuously the tool wear condition and tool breakage. There was a series of cutting conditions where the specific effective power becomes minimum in the grooving operation. Under the cutting conditions with the minimum specific effective power, the cutting would have been conducting at the least cutting resistance and less overall power consumed. These facts indicates that we can determine the cutting conditions, where the cutting resistance and overall power consumed are getting minimum at the same time, by measuring the effective spindle power change during the operation.