Key Engineering Materials Vols. 656-657

Abstract: Currently, geometric deviations of machined parts can be measured following the recommendations outlined in ISO standards such as ISO-12780, ISO-12781, ISO-12180 and ISO-12181. Coordinate measuring machines have now become widely used for inspection hence the tracing and probing strategies recommended in these standards have become much more important. Unfortunately, only minimum number of sections and points are mentioned. Generally, in each section, only a single point will be sampled for the inspection processes. However, the interval between each pair of sampling points has to be smaller than half of the wavelength of the machined surface. Hence, in this research, a method for determining a suitable number of sampling sections and points for geometrical deviation assessment of machined parts made from CNC machining centers is introduced. In this method, the wavelength of a machined surface is predicted from the results of tests used to assess machine performance. Using Finished Test Pieces in ISO 10791-7-A160 as a case study, experimental results indicated that the number of assessed sections and points, calculated according to the introduced method, can be used for accurate measurements of the geometrical deviations of machined parts.

Abstract: In this paper, a new truing method is proposed instead of the conventional mechanical truing that has low truing rate for metal bonded diamond grinding wheels. In the proposed method, the metal-bond diamond grinding wheel is rubbed by a steel truer rotating at high speed. Generated frictional heat increases the oxidization and the diffusion of carbon into the steel truer, then diamond grains are thermally attrited on the wheel surface, so that the machinability of wheel is improved. Subsequently, high truing rate is achieved by mechanical truing with abrasive stones. These experiments are conducted using bronze bonded diamond abrasive stones and stainless steel truers, and the relation between truing resistance, truing temperature, and truing rate are investigated. The truing temperature is measured using the thermo couple embedded in the truer. The thermo couple consists of the steel wire embedded and the bronze which is the bonding material of the abrasive stone. The surface profiles of abrasive stones are measured by scanning stylus before and after truing, then the removal volume of abrasive stones is derived from these profiles. Truing rate is also obtained from the removal volume and the truing time. Experimental results for diamond abrasive stones are as follows: The waviness of bronze bond is decreased by proposed truing method. Truing rate is increased as truing resistance and truing temperature increase.

Abstract: This paper presents experimental examples of machining damages resulting from a piercing process in CFRP laminates. A circular perforation was formed in CFRP cross-ply specimen with a punch jig using different blade angles and two distinct dimensional conditions. Surface, cross-sectional, and internal changes to the CFRP specimens after the hole-punching were observed using optical microscopy and X-ray analysis to quantitatively evaluate damage, including delamination, around the perforation area. Results indicate that the optimum piercing is achieved when the blades are parallel to fiber direction at an elevated temperature with blade angles essentially irrelevant.

Abstract: Ni-based superalloys are typically difficult-to-cut materials. During machining, the cutting forces and temperatures of these superalloys are generally higher than those of other materials. Therefore, the tool life of the coated carbide cutting tools used for superalloy machining is shortened. This study evaluates the damage of the coated end mills during interrupted cutting of alloy 718 and finds the coating properties necessary for improved cutting of Ni-based superalloys. Damage of the PVD-TiN-coated cutting tools was observed by scanning electron microscopy and transmission electron microscopy of the surfaces and cross sections. In addition, friction forces were measured during turning for some coatings, and hardness of the coatings was measured after annealing. Plastic deformation of the coating and crack formation was shown to occur at the coating cross section. In addition, we determined that the major factor for the damage was high friction force between the coating surface and work material at high temperatures. In summary, coatings with stability at high temperatures and low friction forces during machining can reduce the damage of coated cutting tools, thus increasing the tool life.

Abstract: This paper presents a novel concept for extending the life of the tools that are used in the milling process of carbon-fiber-reinforced plastic (CFRP) composites. Three types of tools were compared in milling tests; tool I: an uncoated tungsten carbide (WC-Co) tool, tool II: a polycrystalline diamond (PCD) tool, and tool III: a combination tool comprising a PCD layer surface with a thickness of 100 μm and a WC-Co substrate flank surface. The measurement of changes in cutting forces over cutting distance revealed that tool III had a better (tool) life performance than the other tools. Additionally, observation of changes in the edge profiles of the tools revealed that the effective edge sharpness of tool III remains constant during the milling tests. The difference between the wear rates of the PCD rake and WC-Co flank surfaces in tool III maintained a constant effective sharpness during the milling process, and it extended the tool life. Based on our findings, we concluded that using the difference between the wear rates of rake and flank surfaces is an effective technique for tool life extension in the milling process of CFRP laminates.

Abstract: We have developed a novel polishing technique by scanning a small magnetic tool in hydrogen peroxide solution for smoothing a 2-inch SiC wafer. Obtained results show that the surface roughness in almost areas on the 2-inch SiC wafer is improved markedly. Our proposed method effects a dramatic improvement in a surface microroughness from 0.699 nm Rms to 0.079 nm Rms.

Abstract: In this paper, driven rotary cutting of maraging steel was carried out and the influence on tool wear of difference cutting conditions was investigated. As cutting conditions, different coolant conditions, cutting speeds, circumferential velocity ratios, tool inclination angles, tool rotation directions and normal rake angles were tested. We found that as the coolant quantity decreased and cutting speed increased, the width of flank wear increased. It was also found that the circumferential velocity ratio, tool inclination angle, tool rotation direction and normal rake angle have optimal conditions that decrease wear. Optimal conditions were chosen, and a tool life test was carried out. As a result, driven rotary cutting was achieved with 11 or more times the tool life of conventional turning.

Abstract: We examined the relation between the cutting force and the cutting characteristics of CFRP in diamond saw cutting. When a larger cutting force was applied, the cutting had been propagated with a mixed mechanism of the cutting by cutting edges and the cleaving of carbon fiber by shear force. While a good cutting surface was formed in the case of cutting with less than 23 N of cutting force. In this condition, the cutting had been propagated only by the cutting with cutting edges.

Abstract: In dry grinding of hard carbon parts, the grinding performance of wheel is remarkably lost by carbon chips loading on wheel surface. The deterioration in grinding performance of wheel affects the grinding accuracy and efficiency. Generally, the grinding performance of loading wheel recovers by dressing. However, the dressing is not suitable from a viewpoint of the wheel life and the production cost because many abrasive grains having sharp edges under loading carbon chips on wheel surfaces are lost by dressing. In this study, we propose the application of dry ice blasting as a removal method of loading carbon chips. The dry ice is little influence on the working environment because of the quick sublimation of dry ice particles to carbon dioxide. In addition, the dry ice blasting might be suitable for the chip removal method because the dry ice doesn’t remain on wheel surfaces after blasting without the damage of wheel surfaces. The dry ice blasting tests of resinoid bond diamond wheel surface with no grinding performance by loading carbon chips are carried out, and the effects of dry ice blasting on removal of loading carbon chips are investigated, analyzing the protrusion height of abrasive grains, the impact pressure in the dry ice blasting and so on.

Abstract: The high-pressure coolant supply cutting has attracted attention from a viewpoint of chip evacuation and tool life. In this study, the influence of high-pressure coolant supply on chip shape, cutting force and tool wear were investigated. The tests were carried out during external turning of stainless steel with cemented carbide cutting inserts. The results suggest that the length and radius of the chips got shorter with high-pressure coolant supply, especially supply pressure more than 5MPa. The cutting force was increase slightly with high-pressure coolant supply. However the thrust force was decrease. The uniform flank wear and crater wear were reduced and tool life was improved by high-pressure coolant supply.