Tetsuo Matsuo

Effect of Grain Shape on Cutting Force in Superabrasive Single-Grit Tests

Abstract Single grit microcutting and scratching tests were performed on steels and alumina with the use of CBN and diamond grains (#14-20). Both the tests were carried out using a reciprocating surface grinder. Thus, the cutting and grinding forces, as well as pile-up, were measured under different test conditions. In special, the effect of grain shape on the forces and pile-up was investigated. Microcutting speed ranged from 14 to 30m/min, and the maximum depth of cut was 25μm. Grinding speed was 12.7 and 30m/s, and the maximum depth of cut being 100μm. Normal cutting and grinding forces seem to be largely dependent upon grain shape. Also, it is evident that how the CBN grain differs in forces and pile-up from diamond grain.

Investigation on the Optimum Carbide Content and Machining Condition for Wire EDM of Zirconia Ceramics

Abstract Wire EDM has been performed on Conductive zirconias containing 23 to 45 vol% NbC or Tic, and thus, the optimum carbide content was clarified. The machining rate and surface roughness for various pulse duration and duty factors were evaluated, and consequently, the optimum machining conditions for the wire EDM were discussed. It is obvious that the maximum machining rate can be obtained with about 28-30 vol% Nbc or TIC content, and that there exists the optimum duty factor from a standpoint of machining rate. Also, the effect of second cut on the machining rate and surface roughness was investigated.

Force and Chip Formation in Single-Grit Orthogonal Cutting with Shaped CBN and Diamond Grains

Abstract Single-grit orthogonal cutting tests have been performed on a carbon steel with shaped CEN and diamond single grains (#20/24). The cutting tests were carried out by means of a reciprocating surface grinder. The cutting and thrust forces were measured under different cutting conditions. Chip formation mechanism was also studied. Thus, the effects of cutting speed and take angle on the forces on chip formation became clear for the two aprasive types. The CBN grain was much lower in cutting forces than the diamond grain, and the forces increased largely by changing a rake angle from −45° to −75°.

Removal Rate and Surface Roughness in High-Precision Lapping of Mn-Zn Ferrite

Abstract This paper describes the effect of the motion of diamond grains on material removal rate as well as surface roughness during lapping of Mn- Zn polycrystalline ferrite using a Sn lapping plate and 0.5 – 2.0 μ diamond abrasives. The diamond grains during lapping can be classified into fixed and loose grains, where the grains fixed on the lapping plate (fixed grains) can be observed by SEM. It is evident that among a large number of experimental parameters, the pitch size of the grooves on the lapping plate generated by facing operation has a significant effect on the removal rate. This effect can be accounted for by the number of loose grains calculated under various pitch sizes. The average removal rate with fixed and loose grains is about 2.7 times higher than that with only fixed grains, and from this result it is known that during lapping, the work material can be removed mainly by loose grains. It is also evident from AFM images that the lapped surface characteristic by only fixed grains differs very much from that by fixed and loose grains.

An Analysis of Saw-Toothed Chip Formation

Summary There are some researches on the saw-toothed chip formation, but there are many points which are uncertain. An important subject in this research is to elucidate the fracture mechanism of work material near the shear plane during cutting. In the present study, some examples of saw-toothed chip formation were pursued experimentally and analytically. In special, a dynamic torsion test has been applied to make clear the fracture mechanism of work material under compressive stress at different temperatures and strain rates. The test temperature was ranged from room temperature to 600°C, and the maximum shear strain rate was about 100 1/s. From this study, the following two fracture mechanisms were found. The first one is “ductile fracture mechanism” caused by overstrain under compressive stress, and the other is “high speed ductile fracture mechanism”, which is caused by strain concentration due to the local weakening by heat generation. It is evident that when the stainless steel or the maraging steel is cut the saw-toothed chip is formed by latter mechanism, while the former mechanism is applicable to the cutting of a low carbon steel.

Chipping in High-Precision Slot Grinding of Mn-Zn Ferrite

High-precision slot grinding was carried out on Mn-Zn ferrites to investigate the chipping mechanism and optimum slotting condition by measuring the chipping size at the slotted edges. The slot grinding was performed using a high-precision slicing machine with an air spindle and different type of 2mm wide diamond wheels. The size (width, length) of all chippings was measured by a specially designed form tracer with a knife edge pickup. Grinding forces were also measured. It is evident that chipping size depends on removal per grain and some ductile fracture modes are observed at lower removal rate ranges. Therefore, chipping size can be reduced largely by decreasing removal per grain.

Curvature in Surface Grinding of Thin Workpieces with Superabrasive Wheels

Abstract The warp of steel and brittle material thin workpieces in one-pass surface grinding has been studied, using WA, CBN, and diamond wheels. The grinding experiments were conducted on annealed and hardened steels, sintered alumina, cemented carbide and silicon, whose size was 1.5mm thickness and 100mm length, at depths of cut to 30μm. Grinding force, as well as residual stress, was measured to interpret the results of curvature. A SEM micrographic study of grinding affected zone was performed. Thus, the difference in curvature for the WA, CBN, and diamond wheels was evident. The superabrasive wheels, especially diamond wheel, tend to cause a convex curvature, and a major reason for the inclination to convex curvature is considered a plastically deformed layer.

An Investigation of some Shear Angle Theories

Summary In most shear angle theories in metal cutting, the relation between shear angle and other parameters, such as the mean angle of friction on tool face and the contact length between chip and tool, has been usually pursued on a steady state deformation process. But, it is difficult to make clear the reason why the steady state deformation of chip can be derived from each set of cutting conditions. In this study, an orthogonal dry cutting test was carried out using a carbide tool (P20) and diamond tool with the purpose of studying the compatibility of a machining equation. Intermittent cutting tests were also performed to study a transient chip formation. From an experimental result obtained in the cutting with a diamond tool, it was clear that the equation including the relation between shear angle and two machining parameters (rake angle and the product of cutting speed and depth of cut) is most adaptive as a machining equation. The reason why the shear angle depends on the product of cutting speed and depth of cut is as follows; the cutting temperature affects largely the chip material seizure on the tool face, and also, the thickness of secondary deformation zone. The chip material seizure and the thickness of secondary deformation zone are thought to be main causes of the variation in shear angle. As a result, it is concluded that, as temperature is approximately proportional to the product of cutting speed and depth of cut, the shear angle depends on the product of cutting speed and depth of cut.

High-Precision Surface Grinding of Ceramics with Superfine Grain Diamond Cup Wheels

Abstract High-precision surface grinding has been performed on the Si 3 N 4 and AI 2 O 3 -TiC ceramics and Mn-Zn Ferrite using an ultra-precision surface grinder and very fine grain diamond cup wheels, where the maximum depth of cut was 2 μm and the maximum through feed rate being 100 mm/min. The surface roughness and percent brittle mode area were measured using an atomic force microscopy (AFM). These characteristics were discussed by a parameter “ S max ” defined as S max = μa v f / v s (μ: successive cutting edge spacing, a: depth of cut, v f : through feed rate, v s : wheel speed). With decreasing grain size from #1200 to #16000, the surface roughness Rmax decreases to 20 to 30 nm. Similarly, a remarkable reduction in percent brittle mode area is seen by changing grain size. The effect of dressing stone on the ground surface was also investigated using 3D wheel surface topography.

The Rating of Wheels in Laboratory Snag Grinding

Summary Although it is often required in snag grinding factories to know which type of wheel is most suitable, correct selection of wheel types for given steel grades is hampered by the lack of exact information on snag grinding. In this study, a laboratory snag grinding test under constant load was made on S55C. SUS304 and SUJ2 steels to compare the grinding performance of different resinoid wheel types. Here, the metal removal rate, the wheel wear rate and the surface roughness were measured. Wheel wear mechanism was also studied with particular attention to grain feature at wheels working surface. It is apparent that there is little difference in metal removal rates between wheel types whereas the wheel wear rate is largely dependent on wheel type.