Samuel B. McSpadden

Fixed abrasive diamond wire machining—part I: process monitoring and wire tension force

The process monitoring and mechanics of fixed abrasive diamond wire saw machining are investigated in this study. New techniques to affix diamond particles to a steel wire core have advanced to make this process feasible for the machining of ceramics, wood, and foam materials. Developments in fixed abrasive diamond wire machining are first reviewed. Advantages of using fixed abrasive diamond wire machining are then introduced. The process monitoring and signal processing techniques for measuring the cutting forces, wire speed, down feed rate, and wire bow angle in diamond wire saw machining are developed. The application of a capacitance sensor to measure the wire bow and a procedure to convert the wire bow to vertical cutting force in a rocking motion wire saw machine are developed. The tension force of the wire during cutting is also derived and discussed.

Fixed abrasive diamond wire machining—part II: experiment design and results

Abstract Experimental results from fixed abrasive diamond wire machining of wood and foam ceramics are presented. Three types of wood—pine, oak, and fir, and three types of foam ceramic—silicon carbide, zirconia, and zirconia toughened alumina, are tested. The research investigates the life of diamond wire and effects of process parameters on the cutting forces, force ratio, and surface roughness. A scanning electron microscope is used to study the worn diamond wire, machined surfaces, and debris. The diamond wire saw is demonstrated to be very effective in machining foam ceramics. The wire life for cutting wood at slow feed rates is low. The short tool life for dry cutting of wood indicates that more research in new fixed abrasive diamond wire and wire saw machining technologies is necessary.

Wear mechanisms of diamond abrasives during transition and steady stages in creep-feed grinding of structural ceramics

Abstract A study was performed to quantify the wear mechanisms of diamond abrasives of a resin bonded diamond wheel (320 US mesh and 100 concentration) in creep-feed grinding of a silicon nitride material. This was achieved with a combined use of a lead-tape imprint technique and SEM. The wear mechanisms observed include attritious wear, fracture (or chipping), mixed mode of wear and fracture, and dislodgment (or pullout). The percentage of each wear mechanism was quantified for different points of the grinding process: five during the transition stage and six during the steady stage. The results indicate that: (1) the percentage of grits not involved in removing the first 10 cm 3 /cm volume of material per unit width was high (∼70%) and decreased as more material was removed (from −50% to 20% during the steady stage). (2) Attritious wear dominated the wear mechanism and the percentage increased as more material was removed (from ∼15% to 30% during the transition stage and from ∼50% to 75% during the steady stage). Correspondingly, the percentage of wear-flat area also increased. (3) The percentages of grit dislodgment and grit fracture were relatively higher during the transition stage than during the steady stage. (4) The number of active grits per unit area increased with cumulative volume of material removed. (5) Specific forces increase nonlinearly with wear-flat percentage and the percentage of worn grits.

HIGH SPEED AND HIGH MATERIAL REMOVAL RATE GRINDING OF CERAMICS USING THE VITREOUS BOND CBN WHEEL

Abstract High-speed (up to 127 m/s) and high material removal rate grinding experiments were conducted using a vitreous bond cubic boron nitride (CBN) wheel to investigate the effects of material removal rate, wheel speed, dwell time and truing speed ratio on cylindrical grinding of silicon nitride and zirconia. Experimental results show that operating the grinding wheel at a high surface speed can reduce grinding forces, enable high material removal rates, and achieve a higher grinding ratio (G-ratio). The material removal rate was increased to 9.6 and 7.6 mm3/s/mm for zirconia and silicon nitride, respectively, to explore the advantage of using high wheel speeds for cost-effective, high-material-removal-rate grinding of ceramics. Models for specific grinding force vs. the specific material removal rate and G-ratio vs. grinding wheel surface speed were developed based on the experimental results. Overall, this study showed that high grinding wheel surface speed is beneficial to the grinding of ceramics.

Wear of diamond wheels in creep-feed grinding of ceramic materials II. Effects on process responses and strength

Abstract Alumina specimens were ground with a resin bonded diamond wheel using three different work speeds in creep-feed up-cut mode. For each work speed, the wheel surfaces and the process responses were evaluated at five different wear states, which were generated by grinding 0, 29.6, 59.2, 88.8, and 118.4 cm3 volume of a selected silicon nitride material. The mechanisms of wheel wear have been studied and reported in Part I (Wear 211 (1997) 94–103). This paper investigates the effects of wheel wear on process responses and ground ceramic quality, particularly the flexural strength. Strong relationships between the wheel surface conditions and the process responses are found. During the initial stage of wheel wear (from the as-dressed state to the first 29.6 cm3 volume of material removal), the surface density of diamond grits, surface roughness and flexural strength decreased, and the specific normal force, specific tangenitial force, force ratio, and specific energy increased. The largest change in most of process responses, except the roughness, occurs at the lowest work speed. Right after grinding 29.6 cm3 volume of sillicon nitride material, process responses stayed approximately the same with some degree of expected fluctuation due to the competing influence of attritious wear and the wheels self-sharpening effect. The effect of wheel wear on the flexural strength of ground alumina specimens is found to be dominated by the effect of work speed.

Cost-Effective Grinding of Zirconia Using the Dense Vitreous Bond Silicon Carbide Wheel

Results of grinding zirconia using wheels with fine grain size SiC and dense vitreous bond are presented. Wheel wear results demonstrated that this type of SiC wheel could grind fully and partially stabilized zirconia (PSZ) very effectively. X-ray diffraction was used to analyze the percentage of monoclinic phase in the PSZ base material, ground surface, and debris. As expected, due to the stress- and temperature-induced phase transformation during grinding, the percentage of monoclinic phase on the ground surface was increased relative to the base material. However, X-ray diffraction showed no monoclinic phase in the PSZ debris. This suggests that, during grinding, the low thermal conductivity of zirconia and SiC, compared to that of diamond, facilitates heat retention in the chip and softens the work-material. This makes the efficient grinding of PSZ possible. Grinding temperature measurement results supported this hypothesis.@DOI: 10.1115/1.1559167#

Wear of diamond wheels in creep-feed grinding of ceramic materials I. Mechanisms

Abstract The main objective of this paper is to study and quantify the wheel wear mechanisms in creep-feed grinding of ceramic materials with diamond wheels. A resin-bonded diamond wheel was selected for this study. Nine different states of wheel working surface were generated by grinding specified volumes of a selected silicon nitride material. It is found that: (1) the roughness of wheel profile decreased quickly and stayed about the same after approximately 30 cm 3 volume of material removal; (2) diamond grits experienced attritious wear, grit fracture, and grit dislodgment; (3) the wheel wear mechanism was dominated by grit dislodgment in the first 2 cm 3 volume of material removal and by attritious wear thereafter; (4) grit density per unit area can be expressed as an exponential decay function of cumulative volume removal. The percentage of each wear mechanism was obtained by tracing grits in the same area after 2.1, 4.2, 7.4, and 10.6 cm 3 volume of material removal using the lead-tape imprint technique.