Nobuhiro Koga

An experimental study on ejection forces of injection molding

In injection molding, the ejection forces decrease when the surface roughness of mold decreases. However, the ejection forces increase contrary in the area of surface roughness is less than 0.2 μmRa. Several kinds of PVD films are coated on the mold cores to prevent the increasing of ejection forces. Some of these PVD films showed effective prevention of increasing of ejection forces.

Deep-drawing of aluminum sheets without lubricant by use of diamond-like carbon coated dies

Abstract In this article we propose the use of a diamond-like carbon (DLC) film coated onto the die in order to deep-draw aluminum sheets without lubricant. The use of a DLC coating has, surprisingly, been found to eliminate the need for any lubricant to prevent adhesion of aluminum to the die material during up to about 6200 deep-drawing operations in which square cups, each with a size of 20 × 20 × 12 (depth) mm, were produced. The DLC was coated onto a WC-Co alloy drawing die by means of an ion plating apparatus in which a tri-electrode-type DC arc discharge ion source with a hot filament, an anode and a reflector were used with a precursor of benzene. The work material was 1 mm thick A5000 aluminum sheet. In contrast to the DLC-coated die, an uncoated WC-Co alloy deep-drawing die operated without any lubricant caused fracture of the aluminum sheet after only five repetitions of deep-drawing because of the strong adhesion of the material to the die. This demonstrates the dramatic effects of the DLC coating.

Tribological behavior of amorphous hard carbon films against zinc-plated steel sheets

Zinc-plated steel sheets extensively used in the automotive industry, particularly on body parts which are usually produced by stamping processes, such as deep drawing and blanking, are known to often cause flakes and powdering and consequent adhesion onto the tool when used without heavy lubricants. With heavy lubricants, strong degreasing agents must be used, which is detrimental to the environment. Accordingly, in an effort to achieve deep drawing of zinc-plated steel sheets either with a very light lubricant or, better yet, with no lubricant at all, various deep drawing dies, including those coated with amorphous hard carbon coatings such as DLC (diamond-like carbon) and WC/C (hard amorphous hydrogenated carbon), were subjected to a tribological test using a ball-on-disc tribometer, as well as to a field test. These amorphous hard carbon coatings showed excellent performance in terms of basic tribological properties. Furthermore, the results of the field test, in which the work material was deep drawn with no lubrication for 5000 operations using the WC/C coating, showed that even with no lubrication the coating can effectively reduce the chance of powdering that can cause surface damage or wrinkles over the cup product, thereby prolonging the die life.

Tribological behaviour of thin film coatings against high strength steels

The non-coated ball (SKD11; hardness 60 ± 2 HRC), balls coated with TiC-CVD, TiAlN-PVD, TiCN-CVD, TiCN-PVD and ball treated by VC-TD (thermal diffusion) have been evaluated in sliding contact against the disk which was made from automobile structural steel grade SAPH 440 and high strength steel grade SPFH 590. It was found that non-coated ball showed maximum specific wear rate and TiCN-CVD coated ball exhibited minimum specific wear rate. The effectiveness of hard thin film coated tool in metal stamping process is also investigated by performing U-bending experiment. In the case of non-coated tool, the result showed that adhesion of workpiece material on a die face was detected after 49 strokes for SPFH 590 steel. Whereas no adhesion was found on the tool coated with TiCN-CVD after 500 strokes. In order to understand the phenomenon, scratch tests were done on each type of coated tool to characterise the adhesion strength.

Forming Characteristics of cast magnesium alloy sheets manufactured by roll strip casting process

Plastic formability of cast magnesium alloy that were hot rolled after roll strip casting was investigated to ascertain the feasibility of semi-solid strip casting process of AZ31B magnesium alloy. Hot rolling and heat treatment conditions were changed to examine which conditions were appropriate for producing AZ31B wrought magnesium alloys after strip casting process. Microscopic observation of the crystals of the manufactured wrought magnesium alloys was performed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep drawing test of the cast magnesium alloy sheets after being hot rolled.

Production of a Precision Tube for Photosensitive Drum by DI Process

Abstract An improved drawing and ironing (DI) process has been employed to produce precision aluminum tubes for the photosensitive drum. The most serious technical barrier put in making the tubes only by DI process has been found to be the difficulty of obtaining the necessary accuracy in the roundness and cylindricality. This difficulty has been solved by providing a positive clearance between the punch and the ironed tube so as to eliminate possible distortion during stripping.

Development of a crack cutting method for glass plates used for flat panel displays

In this paper, a high precision breaking method for brittle materials by indentation using an inclined pyramid type indenter is proposed. It was reported that for an indentation angle of θ = 3°, a crack occurs straight in the inclination direction along the diagonal corners of the indent even for a single indent, and the probability of occurrence of the crack is rather high even for low loading. In this paper, the fracture coefficient distribution, the qualitative measurement of crack propagation and propagation position of the indentation are obtained from the FEM analysis. Intermittent indentation using an indenter with an indentation angle of θi = 3° at an interval of d = 30 mm along the ridge direction was performed. As a result, the connection between adjacent cracks along the diagonal could be achieved. On breaking the glass panel, a good surface could be obtained. Finally a prototype of the scribing machine based on the research esults was manufactured and was found to work satisfactorily.

Effects of Hot Rolling Conditions on Warm Formability of Cast Magnesium Alloy Sheets Manufactured by Continuous Strip Casting Process

This paper is concerned with the development of a continuous strip casting technology to facilitate the manufacture of magnesium sheet alloys economically whilst maintaining high quality. Established in the paper is warm formability of cast magnesium alloy sheets after being hot rolled by continuous casting process. Effects of manufacturing condition on possible forming were clarified in terms of casting temperatures and roll speeds. It has been found that magnesium sheet with 3.0 to 4.0 mm thickness could be produced at a speed of 25m/min. The temperatures of the molten magnesium, and the roll speeds were varied to find an appropriate manufacturing condition. Rolling and heat treatment conditions were also changed to examine which condition would be appropriate for producing wrought magnesium alloys with good formability. Microscopic observation of the crystals of the manufactured wrought magnesium alloys was performed. It has been found that a limiting drawing ratio of 2.7 was possible in a warm deep drawing test of the cast magnesium alloy sheets after being hot rolled.

Semi‐solid Twin‐roll Casting Process of Magnesium Alloy Sheets

An experimental approach has been performed to ascertain the effectiveness of semi‐solid strip casting using a horizontal twin roll caster. The demand for light‐weight products with high strength has grown recently due to the rapid development of automobile and aircraft technology. One key to such development has been utilization of magnesium alloys, which can potentially reduce the total product weight. However, the problems of utilizing magnesium alloys are still mainly related to high manufacturing cost. One of the solutions to this problem is to develop magnesium casting‐rolling technology in order to produce magnesium sheet products at competitive cost for commercial applications. In this experiment, magnesium alloy AZ31B was used to ascertain the effectiveness of semi‐solid roll strip casting for producing magnesium alloy sheets. The temperature of the molten magnesium, and the roll speeds of the upper and lower rolls, (which could be changed independently), were varied to find an appropriate manufa...

An Application of DLC Film to Knife for Cutting Piled Aluminum Thin Sheets

Abstract An experiment is described in which a knife for cutting a laminated pile of coated aluminum sheets and paper sheets used, e.g., for offset printing of newspapers, was coated with DLC film prepared by a plasma CVD type ion plating method using benzene as a precursor, and was subjected to a cutter life test using a 50mm-high pile of aluminum thin (0.24mm-thick) sheets with insertion of inexpensive (S) paper sheets for the prevention of aluminum adhesion to the knife surface. For comparison purposes, a cutter knife without any coating was also subjected to a test with insertion of much more expensive (R) paper sheets of the type currently used. The results show that a DLC-coated cutter with the less expensive S paper insertion has almost the same excellent cutter life as does the noncoated knife with the insertion of the best and expensive R paper.