Heisaburo Nakagawa

In-situ heat treatment system for die steels using YAG laser with a machining center

We propose a laser heat treatment system for die steels using a YAG laser on the machine tool table. Optical fiber is used to transmit the laser light from a source to the machine tool table in this system, which makes it possible to perform the cutting processes, the heat treatment and the grinding processes with a machining center. In the present report, the experiments of laser heat treatment were done in order to research suitable die steels for this system. Additionally, the temperatures based on a theoretical model were investigated during the laser irradiation. As a result, it is clear that the martensite start temperature (Ms point) of materials is an important factor to estimate the application of this heat treatment.

A Study on End Milling of Hardened Steel(2nd Report). Control for Constant Cutting Forces in Corner Profile End Milling Including Transitional Sections of Tool Paths.

In this paper, the proposed model for cutting forces during end milling of hardened steel is verified for its general usefulness by applying this model to the extended cutting conditions and other applications. The cutting conditions discussed here include concave contour cuttings with a small radius compared to that of the end mill. For this purpose, the operability region by two variables of the arc length of cutting engagement (L) and the maximum undeformed chip thickness(tm) is divided into a few regions of interest which correspond to the cutting conditions geometrically. The control of cutting forces in profile end milling using quadratic polynomials obtained in each region based on response surface methodology was fairly effective. Furthermore, this prediction model was applied for the case of transitional sections of tool paths where the cutting force changes rapidly with the change of feed rate and geometrical conditions, and it was found that the prediction and control of cutting forces was also possible for this problem.

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.

Effects of diamondcoated tools in micro-drilling of CFRP plates using a high-speed spindle

Abstract Superior performances of carbon fibre-reinforced plastics (CFRP) such as light and higher strength are attracted attention as an alternative material of metal. An application as a printed wiring boards (PWBs) material focuses on its higher thermal conductivity adding to the above properties. The PWBs need so many micro-drilled holes. However, CFRP is well known as one of the difficult-to-cut materials. In the present research, the fundamental micro-drilling phenomena of CFRP were revealed through an experimental approach. This study describes characteristics on micro-drilling, 1 mm or less in diameter, of a CFRP plate using a high-speed spindle. To investigate them, cutting forces such as a thrust force and torque were measured by high-resolution dynamometers and a drill temperature during drilling was monitored by a thermography. In particular, diamond-coated tools were prepared in order to improve tool life. As a result of comparison with conventional non-coated tools, some unique tendencies are revealed. Experimental result shows superior performance of diamond-coated tools for micro-drilling of CFRP.

Effects of laser heat treatment on mechanical properties of ceramic coated steelsPart 2 – Fracture strength of laser heat treated ceramic thin film

Abstract In our previous study, we proposed a new surface modification technique by combination of ceramic coating and laser heat treatment. By applying laser heat treatment after coating, it was possible to improve the adhesive strength and substrate hardness of ceramic coated steels without compromising the film hardness. However, the effects of laser heat treatment on the fracture strength of ceramic thin films were not investigated yet. In the present research, in order to demonstrate further development of this method, the fracture strength of laser irradiated ceramic thin films (CrAlN, TiAlN and CrN) was investigated by sphere indentation testing. To prevent heat induced changes in the substrate hardness, a cemented carbide WC–Co rather than steel was used as substrate material. While the fracture strength of each film decreased significantly through furnace heat treatment, it remained almost unchanged in case of the laser irradiated films. The application of laser heat treatment for the substrate quenching after coating process can effectively prevent the fracture strength loss of ceramic thin film.

A Proposal of Process Strategy for Micro-Cutting Edge Fabrication: Effects of Shape Formation after Laser Hardening

This paper proposes a novel process strategy for micro-cutting edge fabrication. Micro-cutting edges need a hardening process for the ridgeline parts that requires abrasive resistance, as well as edge sharpness and shape accuracy, based on their applications. Micro-cutting edge shapes also vary greatly in ridgeline profile and section. The proposed method is shape fabrication after laser hardening, which easily addresses these issues. In the present paper, effects of the proposed method are discussed and the results of a demonstration test are introduced.

An Experimental Study on Suppression of Chatter Vibration with Different Helix Angles End-Mill

In this study we attempted to suppress chatter vibration in end-milling of austenitic stainless steels with an end-mill having different helix angles. We showed there were two types of chatter vibration in end-milling with a conventional end-mill with regular helix angle. The two types of chatter vibration depend on the cutting speed. We detected these two types of chatter vibration by the developed monitoring method using laser Doppler vibrometers. We classified the two types of chatter vibration according to chatter generating tendency, frequency and vibration mode. We showed that chatter vibration generated at lower cutting speeds was regenerative chatter vibration. On the other hand, chatter vibration generated at higher cutting speeds was another type. We showed that a end-mill with different helix angles could prevent generative chatter vibration at lower cutting speeds and was also effective in suppressing chatter vibration at higher cutting speeds.

Circuit Connection Reliability Analysis of Laser-Drilled Blind Via Holes Using Data-Mining Method

The purpose of the present study is to analyze the circuit connection reliability of printed wiring boards (PWBs) with respect to thermal stresses on drilled hole walls. Micro-via drilling using laser technology has become the predominant method of machining smaller blind via holes. Moreover, a technique that uses copper foil in forming the circuit has been considered as a means of limiting the hole depth more accurately. After forming the blind via holes, copper plating must be used in order to maintain high reliability in circuit interconnectivity. In the present study, using the finite element method (FEM), we evaluated the effects of both the shape of the holes and the thickness of the copper plating on thermal stress occurring at the hole bottom. However, numerous factors are associated with the thermal stress, making the proper material composition and hole shape design difficult to determine. FEM must be applied to large amounts of data in order to identify quantitative tendencies. In addition, we applied a data-mining method to the thermal stress data, in an attempt to elucidate the factors that influence the reliability of blind via holes. The data-mining method revealed new factors that were hidden in the data; notably, the coefficient of thermal expansion in the thickness direction, despite the presence of other complex factors.Copyright

Laser irradiation method for high-efficiency pulsed laser milling integrated die/mold machining: effects of laser-tracking irradiation on laser milling accuracy

Abstract In small and precision die and mold making, small-diameter end mills are often used through rough to finish machining processes. However, higher-efficiency machining technology in die and mold manufacturing is needed because shorter delivery time has become essential in recent years. On the other hand, the demand for dies and molds made of difficult-to-cut materials such as cemented carbide and fine ceramics has increased. Therefore, the authors were motivated to apply a laser process because lasers can remove work independently of its mechanical properties. The authors proposed a novel process for high-efficiency die and mold machining. The process integrates laser milling for rough processing and cutting with micro-end-mill tools for finishing. In the present paper, some experiments were carried out to clarify the effects of a laser-tracking irradiation method for laser-milling quality in deep milling of a hardened die steel workpiece. As a result, it was found that the laser-tracking irradiation provided higher-accuracy laser milling while maintaining process efficiency.

Fabrication of Fine Mesh Filter Screen with Pulsed Laser

This paper proposes a novel manufacturing process of a fine mesh filter screen with a pulsed laser. The fine mesh filter screen, made of stainless steel, has many small diameter holes with high aspect ratio and fine pitch. In the conventional process, an electron beam drills in a vacuum. However, this is very costly because of the expensive equipment required and batch process. Therefore, a laser drilling process for small diameter hole drilling in air with higher flexibility was proposed. The post-processes after the laser drilling completed the fine mesh filter screen.