Eiichi Aoyama

Prevention of fatigue cracks in ultrahigh molecular weight polyethylene joint components by the addition of vitamin E.

Flaking-type wear, so-called delamination, is often observed in polyethylene joint components. This is thought to occur partly due to crack formation and propagation at grain boundaries. This study examined the effect of vitamin E on the crack formation and/or propagation in UHMWPE by using 2-dimensional sliding fatigue testing and micro indenter testing. An in vitro sliding fatigue test was performed under two simplified articulating movements, and the cracks produced were observed by scanning acoustic tomography (SAT). Gamma-irradiated ultrahigh molecular weight polyethylene (UHMWPE) specimens demonstrated a smaller area of accumulated cracks as compared to virgin specimens, when the loading movement was reciprocated on a single linear locus. However, four out of five gamma-irradiated UHMWPE specimens exhibited severe flaking-like destruction under the complicated sliding condition, suggesting that gamma irradiation accelerated crack propagation under multidirectional loading. All the gamma-irradiated vitamin-E-containing specimens demonstrated no subsurface crack formation and no flaking-like destruction. Results using micro indenter testing showed that the dynamic hardness at grain boundary was higher than that in grain, and was increased by gamma irradiation. This hardening at grain boundary was reduced by adding vitamin E. It is possible that the presence of vitamin E prevents crack propagation partly due to reduced hardness at grain boundaries. The gamma-irradiated vitamin-E-containing UHMWPE is a promising material to prevent flaking-like destruction of polyethylene joint components.

Investigation on cutting mechanism in small diameter drilling for GFRP (thrust force and surface roughness at drilled hole wall)

This study describes the relation between the cutting force and the surface roughness of a drilled hole wall in small-diameter drilling of GFRP for a printed wiring board. In order to investigate the characteristics of small diameter drilling for GFRP, the surface of the drilled hole wall is observed by SEM, and the surface roughness along the feed direction is measured at various edge position angles of the drilled hole. The cutting force during drilling is measured. Moreover, the thrust force is devided into two components (the static component and the dynamic component). It is shown that the dynamic components are related with the surface roughness of the drilled hole wall. In conclusion, it is found that the major cutting edge of the drill is more influential in the quality of the drilled hole wall than the chisel edge of the drill in small diameter drilling of PWB.

Influence of tool wear on internal damage in small diameter drilling in GFRP

Abstract In this study, drilled PWB is a type of glass/epoxy-resin GFRP, plain woven cloth, and thickness 1.6mm (8 plies). This workpiece is the copper clad laminate. In experiments, the drills are the diameters of 0.4–5.0 mm. The holes are drilled under drilling conditions of spindle speeds of 20000–80000 rpm and feed rates of 10–50 μm/rev. An amount of 30000 holes are drilled. The investigation is carried out from the view of the relationship between the internal damage around the drilled hole and the number of drilled holes. It is clear that drilling conditions are high feed rates to drill a great number of holes at a constant quality, and are low feed rates to drill a small number of holes at the high quality. Additionally, it is found that the ratio of the radius of the drill to the width of the yarn is one of the important factors in estimating the tool life of small diameter drills.

Drilled hole damage of small diameter drilling in printed wiring board

Abstract Of late, it has become necessary to improve the packaging density of printed wiring board (PWB), because the demand for size reduction of the electric devices is increasing. Therefore, the pitches between through holes in electric circuits have become fine for the high package density. On the other hand, various forms of damage occur around the holes after drilling. Much research has been done on internal damage in order to prevent the reduction of the insulation resistance between the holes after through hole plating, and the blow holes after soldering. This study is about the damage factors around the drilled hole wall in small diameter drilling of an PWB in order to prevent the ion migration between the holes. It is shown that there are two important factors of internal damage around the drilled hole: (1) the relative angles between cutting directions and fibre directions; (2) fibre bundle thickness of glass cloth at the drilled hole wall. In particular, it is demonstrated that the reduction of the fibre bundle thickness is effective to decrease the internal damage of drilled hole.

Study on small diameter drilling in GFRP

In small diameter drilling with the drilling machine, the drilled hole quality of the printed wiring board (PWB), made of GFRP, is evaluated by investigating the surface roughness and the internal damage to the hole. An investigation of the damage is conducted by changing the number of drilled holes. Additionally, in laser drilling using a CO2 source and a YAG source, the laser drilling process is clarified by observing the damage to the hole, and moreover the relation between the drilling conditions and the damage of the hole is obtained. In conclusion, it is shown that, in the case of the present drilling machine, the anisotropy of the hole surface roughness is able to be developed by the tool tip profile, and as the new process is of no contact drilling, the application of a laser beam machine using a CO2 laser source is effective in the smaller diameter drilling in PWBs.

Micro-Drilling of CFRP Plates Using a High-Speed Spindle

Fundamental characteristics in the micro drilling of carbon fiber reinforced plastic (CFRP) plates are investigated in the present paper. When micro drilling with a high-speed spindle, cutting forces during drilling, such as thrust force and torque, were measured by high resolution dynamometers and drill temperature was monitored by thermography. Comparing the experimental results of CFRP with that of drilling glass fiber-reinforced plastics (GFRP) revealed some unique tendencies. The cutting forces and drill temperature increased drastically. Moreover, drill wear rapidly accelerated. The tool life of CFRP plate drilling is much shorter than that of other plates.

Investigation of Eco-Friendly Fixed-Abrasive Polishing with Compact Robot

Rising demand for sustainable development motivated our eco-friendly polishing method. In this study, fixed-abrasive polishing using a compact robot was proposed based on a new approach that includes the idea of secondary tools. The effectiveness of using a compact robot was investigated by life cycle assessment for eco-friendly polishing processing. The actual polishing process was carried out with low pressure to determine the potential of the proposed polishing method. As a result, low-environmental-load processing was achieved by machine downsizing without affecting the processing results by designing an independent pressure mechanism along the equipment’s main axis. The nano-surface could also be obtained with this method for glass material.

CAM Systems Based on Traveling Salesman Problem From Time Perspective for High Density Through-Hole Drilling

This paper focuses on shortening drill-movement time in an X-Y plane. Traveling Salesman Problem (TSP) has been applied to determine a moving route of Printed Wiring Board (PWB) hole arrangements. Thus, some papers dealt with shortening the calculating time and increasing the accuracy of the TSP method to obtain the shortest route in geometrical problems. However, considering both the characteristics of PWB hole arrangements and the feed-control characteristics of machine tools, the shortest route for geometrical problems by TSP is not always in agreement with that of the moving time problem. Therefore, we propose a CAM system for PWB drilling considering the feed-control characteristics of machine tools using a new TSP method to obtain the shortest moving time.Copyright

Quality Estimating Model Based on Temperature of Hole Bottom in Laser Drilling of Blind Holes

The printed wiring board (PWB) has becomes relatively smaller due to the downsizing of electric devices. Higher densification has been advanced by the circuit formation of multi-layer PWBs in the current manufacturing of these boards. In current manufacturing of multi-layer printed wiring boards, a method frequently used is to laminate the core with insulating resin as build-up layers. Microvia drilling using laser technology has become the prevailing method of machining smaller blind via holes. Aramid fiber reinforced plastic (AFRP) is considered suitable material for the build-up layers, because it is efficient in laser drilling. However, heat damage in the hole has been a problem because the laser drilling cause a heat damage to the PWB materials. The poor hole quality, such as the carbonization of the resin and the peel around circuit copper foil/core material, causes decrease in the reliability of circuit connections. In the present report, first, we took multi layer PWB-reinforced by aramid unwoven cloth, and measured the temperature distribution of the circuit copper foil during laser drilling using a thermocouple. Second, we proposed a heat input prediction model using a finite element method (FEM), considering the change of laser absorption of the circuit copper foil surface. Finally, we carried out a thermal stress analysis based on the temperature distribution, and confirmed the efficiency of this analysis. As a result, the calculated temperatures by this model, considering the variation of the absorption of foil surface during laser drilling, are in good agreement with the experimental temperatures. It is confirmed that this model is effective in estimating the temperatures and thermal stresses in the bottom copper foil during laser drilling of the build-up layers.Copyright

Study on super-finishing by CBN stone (estimation of cutting performance using average crossing angle)

Abstract In super-finishing by cubic boron nitride (CBN) stones, it is considered that chips are formed by crossing of grain loci. Thus, crossing angles of grain loci are paid attention to as an important parameter. In this paper, the new method for prediction of cutting performance is proposed using average crossing angle of grain loci. On the other hand, chip formation process is classified into two types. Therefore, all crossing angles are calculated after considering these types of crossing of grain loci. Average crossing angle is defined as the mean value of those. Moreover, the relation between these average crossing angle and cutting performance is investigated by various calculations and experiments. As results, average crossing angle is one of the most important parameters to estimate the cutting performance on super-finishing using CBN stones.