Advanced Analysis of Nontraditional Machining

Laser machining has a wide range of industrial applications. However, laser energy can cause thermal damage to composite materials during the shaping operation following curing. Such damage leads to poor assembly tolerances and reduces long-term performance. In this study, we investigated the laser machining-induced formation of anisotropic heat-affected zones (HAZs) in fiber-reinforced plastics (FRP). The degree of HAZ is estimated by the isotherm of the matrix char temperature. Analysis revealed that both the laser energy per unit length and the fiber orientation-dependent thermal conductivity are key factors in determining the extent of HAZ. An experimental measurement of anisotropic thermal conductivity for composite materials is developed. Heat conduction is greater along fibers than it is across a fiber section, thus laser scanning direction relative to fiber orientation affects the HAZ geometry. The study also investigated the principal-axis and nonprincipal-axis grooving of unidirectional (UD), [0/90], Mat, and MatUD laminates. An analytical model based on a moving point heat source using the Mirror Image Method and immersed heat source to model principal-axis grooving is adopted to correlate HAZ anisotropy with various process parameters. Finite difference method (FDM) with an isotherm conductivity model and eigenvalue method is applied to simulate the HAZ resulting from nonprincipal-axis grooving.

Electrical discharge machining (EDM) is considered suitable for machining materials that are extremely hard or strong, and are wear or temperature resistant. In Chap. 2, we outline EDM characteristics of carbon fiber-reinforced carbon composites and AISI D2 tool steel. This article is organized as follows: first, the effects of EDM processing variables on delamination, the recast layer, surface roughness, and material removal rate (MRR) of carbon fiber-reinforced carbon composites are presented. Rotation of the workpiece allows fresh dielectric material to enter for effective spark discharge, and to provide better machining performance. Therefore, the second section of this chapter is devoted to a study of the effects of rotary EDM parameters on MRR and surface roughness of AISI D2 tool steel. The EDM process produces a damaged layer with different mechanical behaviors from those of the base metal. An understanding of the strength of an EDM sample is required. The third section describes an investigation of EDM AISI D2 tool steel surface characteristics and machining damage. EDM damage was studied using a new damage variable. An understanding of the surface texture of EDM specimens on the nanoscale is required. In the fourth section, surface morphology, surface roughness, and micro-cracks of AISI D2 tool steel machined by the EDM process were analyzed by atomic force microscopy (AFM). Experimental results show that the thickness of the recast layer, micro-crack depth, surface roughness, and residual tensile stress increase with the increase in power input. The EDM process effectively produces excellent surface characteristics in specimens, under low discharge energy conditions.

Electrochemical machining has attracted increasing attention for micro-machining applications. The first section discusses a process to erode a hole of hundreds of microns diameter in a metal surface using a moving electrode. The discussion provides a method to predict the enlargement of the produced hole and to taper under the applied machining conditions. A computational model illustrates how the machined profile develops over time and as the electrode gap changes. The analysis is based on Faraday’s laws of electrolysis and the mathematical integral describing a tool. The effectiveness of the model is tested by experiments that apply several electrode movement schemes.

This chapter discusses the surface roughness of several common die materials produced by traditional machining, whereby the internal and external cylindrical surface are electropolished by different electrode designs. Electropolishing efficiency of die materials and parts should be high to improve surface roughness in the shortest amount of time possible, thereby reducing surface residual stresses. The study aims to identify an optimal electrode design, which will help broaden electromachining applications in the future. For electropolishing of internal holes, completely inserted feeding electrodes are supplied with both continuous and pulsed direct current. In the external electropolishing studies, we consider the design of the turning tool electrode, arrowhead electrode, ring-form electrode, and disc-form electrode. For internal electropolishing, an electrode featuring a helix discharge flute performs better than that without a flute or with a straight flute. The borer type electrode performs better an electrode with a lip on the leading edge. Pulsed direct current can improve the polishing, but the machining time and costs are increased. In the case of external electropolishing, a smaller nose radius or end radius produces greater current density and provides a faster feed rate and better polishing. Ultrasonic-aided electropolishing improves the polishing effect with no increase in machining time, thus improving efficiency and reducing costs.

Chemical mechanical planarization (CMP) has emerged as an indispensable processing technique for planarization in submicron multilevel VLSI. An analytic model of the material removal rate is proposed for CMP. The effects of applied pressure and polishing velocity are derived by considering the chemical reaction as well as the mechanical bear-and-shear processes. The material removal rate is less linearly correlated to the pressure and relative velocity than that predicted by the frequently cited empirical Preston equation [1]. The effects of CMP kinematic variables on wafer nonuniformity are also investigated. The significance of velocity uniformity is demonstrated by both analysis and experiment. For the endpoint detection, an accurate in situ monitoring method can significantly improve both yield and throughput. A model for CMP polishing pad temperature that is capable of predicting the CMP endpoint in situ is established, based on the total consumed kinematic energy. The process endpoint is detectable by application of the proposed regression method to the measured temperature rise. In addition, the chapter develops an endpoint monitoring method that uses acoustic emissions that occur during CMP. The method considers differences in friction characteristics between the polishing pad and the copper metal overlay. For the flow of slurry between wafer and pad, this study provides a visualized characterization of the amount and distribution of the fluid film between wafer and pad. Digital photographs taken through the transparent carrier and dyed fluid are used to analyze the fluid film.

Ultrasonic machining (USM), using shaped tools, high-frequency mechanical motion, and abrasive slurry is effective for materials of extreme hardness or brittleness. Unlike other nonconventional machining methods such as laser beam and electrical discharge machining, USM does not thermally damage the workpiece. This is important for the longevity of materials in service. However, the tool experiences wear, which causes a reduction machining efficiency. Composite materials offer advantages in structural applications because of their high specific strength and directional properties. In many applications, composites are cured in their final shape; however, machining is necessary at both the prepreg and product stages. In traditional drilling, delamination and splintering at the edges of holes often occur due to anisotropy and the lamination of composite materials. USM is suitable for such materials for its mode of material removal, which utilizes small individual abrasives. In this chapter, we discuss on-line tool-wear monitoring during USM, the effect of abrasive and drilling parameters on material removal rate, hole clearance, edge quality, tool wear, and surface roughness of composites for application in the manufacturing industry. This chapter shows that USM can provide greater profits than other nonconventional machining processes offer.

Water jet drilling, in spite of its advantages of no tool wear and thermal damage, often creates delamination in composite laminate at bottom. An analytical approach to study the delamination during drilling by water jet piercing is presented. This model predicts an optimal water jet pressure for no delamination as a function of hole depth and material parameters.

Moreover, the kerf formation of a ceramic plate cut by an abrasive waterjet is discussed. The mechanism and the effectiveness of material removal are studied. The kerf is slightly tapered with wider entry due to decreased cutting energy with kerf depth. A high-power input per unit length produces a small taper but a wide slot.

Abrasive waterjet is adequate for machining of composite materials thanks to minimum thermal or mechanical stresses induced. The feasibility of milling of composite materials by abrasive waterjet is discussed. The basic mechanisms of chip formation, single-pass milling, double-pass milling followed by the repeatable surface generation by multiple-pass milling are studied. High volume removal rates as well as a neat surface are desired. Based on the results of single-pass milling tests, this chapter discusses the double-pass milling considering the effect of lateral feed increments. The study then extends to six-pass milling. The obtained surface roughness from the six-pass milling is expressed as a function of the width-to-depth ratio and the lateral increment. With the knowledge of the volume removal rate and the surface roughness as well as the effects of the major process parameters, one can proceed to design a milling operation by abrasive waterjet.

We analyze a laser dragging process capable of ablating a groove pattern, and producing sophisticated 3D features, on a polycarbonate (PC) sheet through a shaped mask opening. To predict the machined profile during the dragging process, we developed a mathematical model that describes the relationship between laser machining parameters and the produced profile. In addition, we manufacture a miniature lamp lens by varying the mask shape, and dimensions based on the proposed model. The effects of the micro-size lamp lens on light efficiency are investigated. On the other hand, this chapter also introduces a study of sub-micron-structure machining on silicon substrates by a direct writing system using a femtosecond laser with the central wavelength of 800nm, pulse duration of 120fs and repetition rate of 1kHz. Three types of experiment are studied: (1) The effect of photoresist on silicon, (2) The machinability of different orientations of silicon: spike morphologies were observed on all three orientations of silicon substrates without obvious directional difference of these spikes on the different silicon substrates, (3) Micro-structure size and cross-section shape: a numerical model of the machining parameters has been proposed to simulate the cross-section of the micro-structure resulting from a given ablation energy. The predicted shape, determined by simulation, fitted the profile of the cross-section shape well.

Beams of electrons and ions of energies ranging from a few keV to over 100keV and diameters in the single nanometers have become standard nanofabrication tools. Electron beams are routinely used to expose resist down to dimensions of 10nm. In principle, ion beams can be and have been used similarly to expose resist. However, what motivates this chapter is that both ion beams and electron beams can be used to directly produce structures without the usual multistep lithography process. Ion beams can simply locally sputter a surface, i.e., carve predesigned structures. In addition both electron beams and ion beams can be used to deposit material if a suitable precursor gas is adsorbed on the surface. The beam causes the adsorbed molecules to dissociate leaving some constituent behind. Similarly, if the adsorbate is a reactive gas, such as Cl₂ or XeF₂, a chemical reaction is induced where the beam is incident, and the material is locally etched. These material shaping techniques have found many applications and there are many types of structures have been built. However, the beam solid-interaction is complicated and factors other than the diameter of the beam limit the size of the structure that can be fabricated. In addition, these point-by-point fabrication techniques are slow. Typically to add or remove 1cm³ may require several tens of seconds. The finer the resolution needed the longer the fabrication time. Nevertheless these electron and ion nanobeam tools are widely used in research and in industry.

Ultrasonic machining (USM), using shaped tools, high-frequency mechanical motion, and abrasive slurry is effective for materials of extreme hardness or brittleness. Unlike other nonconventional machining methods such as laser beam and electrical discharge machining, USM does not thermally damage the workpiece. This is important for the longevity of materials in service. However, the tool experiences wear, which causes a reduction machining efficiency. Composite materials offer advantages in structural applications because of their high specific strength and directional properties. In many applications, composites are cured in their final shape; however, machining is necessary at both the prepreg and product stages. In traditional drilling, delamination and splintering at the edges of holes often occur due to anisotropy and the lamination of composite materials. USM is suitable for such materials for its mode of material removal, which utilizes small individual abrasives. In this chapter, we discuss on-line tool-wear monitoring during USM, the effect of abrasive and drilling parameters on material removal rate, hole clearance, edge quality, tool wear, and surface roughness of composites for application in the manufacturing industry. This chapter shows that USM can provide greater profits than other nonconventional machining processes offer.