Papers by Keyword: Truing

Abstract: Grinding is a widely used process in many industries due to the precise geometric tolerances and excellent surface finishes it can offer, which makes it very useful when high quality parts have to be manufactured. Due to the wear that the grinding wheel suffers, a process known as dressing is periodically carried out to recover the cutting ability of the wheel. Dressing is an extremely important part of the grinding process, as it can alter and improve the cutting conditions of the wheel.During the dressing of vitrified bonded CBN wheels, the real dressing depth of cut is significantly lower than the theoretical depth of cut, leading to dimensional errors in the dressed grinding wheel, which consequently translate into the ground part. However, while deformations during grinding have been widely studied, this phenomenon has not been yet analyzed during dressing. Therefore, the main objective of this work is to determine the influence of the dressing parameters on the real depth of cut. Also, the effect of dresser wear and the deformations has been determined separately.To this end, a new methodology has been developed to measure the real depth of cut using a laser displacement sensor. Moreover, experimental tests have been carried out to characterize the influence that the dressing speed ratio (q_d) and set depth of cut (a_{d_set}) have on the actual depth of cut (a_{d_real}). It has been seen that the use of negative q_d results in a more accurate real depth of cut, and therefore a more efficient dressing process. While the error using negative q_d is about 10 %, using positive q_d is about 25 %.

Abstract: Metal bond grinding wheels can retain their shape and size under extreme grinding conditions. On the other hand, it is difficult to true them accurately and efficiently due to the severe wear of truing tools. To solve the problem, this paper proposes a new truing device based on electro-contact discharge machining. The device is designed so that the position of the electrode working face remains unchanged even if the electrode is worn. Some truing experiments were carried out using a prototype truing device for a metal bond diamond wheel of grain size #1000 under dry conditions. As a result, relatively high truing accuracy has been achieved in combination with an additional truing by a GC stone.

Abstract: Needs of precision optical mirrors are increasing in the astronomical space telescope. In the space having extremely large temperature differences, the aspheric optical mirror made of low thermal expansion ceramic is very effective in reducing the focus errors due to the thermal expansion. In order to develop the mirror made of a new low thermal expansion ceramic, parabolic mirror of the ceramic is ground and polished to test. By the grinding and polishing test, changes of form deviation profiles and surface roughness profiles are evaluated and machinability of the proposed ceramic is studied.

Abstract: An electroformed diamond tool with a tool tip radius of 0.2 mm was developed to achieve a surface roughness of less than 10 nm Rz on a mould made of cemented carbide. A polycrystalline diamond disc with a primary grain size of 0.5 µm and a diameter of 15 mm was used as a truer. A concentric guide groove with a reverse profile relative to the hemispherical tool and a surface roughness of 0.5 µm Rz was preformed on the truer by laser machining and wet lapping. It was verified through a truing test that 93 % of the diamond grains on the tool working surface could be flattened when the tool was placed in elastic contact with a guide groove with a depth of 50 µm. A grinding test revealed that the tool had the potential to efficiently fabricate a ground surface with a roughness of less than 10 nm Rz on cemented carbide with a hardness of 2600 Hv.

Abstract: Grinding process using superabrasive metal-bonded wheels is unavoidably linked to long and inefficient truing and dressing processes. This document presents the application of electro-discharge dressing process as an alternative to form wheels. The accuracy of the process and its efficiency has been analyzed on wheels of different grit size. To do so, complex geometry has been completely profiled to a 1A1 type wheels. Results show that the process can provide the desired geometry at the cost of a high processing time. The comparison between fine and large grit size grinding wheels shows that there is apparently no geometric limitation imposed by the grit size apart from that associated to grit diameter in corners and inner radii.

Abstract: The results of truing and dressing depend on: sharpness of the dresser, speed of dressing, depth of cut and vibration phenomena. Prediction of the optimum wheel surface for grinding which produces an accurate profile and cuts most efficiently can minimize the time and cost and optimize performance of the operation before it is performed in the shop. It has especially significant meaning in truing and dressing of hard CBN wheels. The research described in this paper shows computer simulated and visualized wheel surface before and after the wheel dressing process. This paper provides additional results to those was reported in [8] taking into account the influence of vibrations. It is a companion paper to [8].

Abstract: Truing and dressing are time-consuming processes in precise finishing with super-abrasive wheels because of the hard super-abrasive grains which cause extensive wear of truer. In this paper, laser-assisted truing method for super-abrasive wheels is introduced. Feasibility of the proposed method is confirmed by fundamental experiments conducted with metal-bonded diamond wheel and pulsed Nd:YAG laser. On the surface of wheel irradiated with laser beam, it is found that the abrasive grains are degraded and the machinability of surface layer is remarkably improved.

Abstract: A truing technique that can be used to shape the tip of an electroformed diamond tool into a hemisphere and flatten diamond grains on the tool working surface at the same level as the bond face was developed. A polycrystalline diamond disk whose top surface roughened by electrical discharge machining was partially flattened by grinding was used as a truer. Diamond grains on the tool working surface were successfully flattened along the hemispherical tool profile when the grains mesh size of #1000 was employed. In addition, a grinding test using glasslike carbon as a work material revealed that a surface roughness of less than 50 nm Rz could be obtained in both cases when moving the tool on contour and scanning paths.

Abstract: In recent years, there has been a great demand for large-diameter wafers with high flatness of hard and brittle materials that are used as optical and sensor elements. To meet these demands, we have developed an ultra-precision plane honing method as a highly efficient surface finishing technique using a fixed abrasive. This technique offers good finish surface roughness, shallow subsurface damage and high machining efficiency. However, there is a need to improve the surface flatness, which is dependent on the grinding wheel surface flatness and the tilt of the spindles. In this paper, the relationship between grinding wheel surface flatness and the shape of a truer is investigated by calculating the contact length of a point on the grinding wheel with the truer. It was found that there is an optimum shape of the truer to make the grinding wheel surface flat, and the machined 3-inch glass wafer is controlled to a flatness of less than 1µm by using the optimum truer.

Abstract: In V-groove ELID grinding process, to achieve optimal grinding performance and satisfactory surface quality and profile accuracy, metal bonded diamond grinding wheels need to be carefully sharpened. In this paper, we applied the proposed new micro-truing method consisting of electro-discharge truing and electrolysis-assisted mechanical truing to sharpen the edge of large grinding wheels. The minimum wheel tip radiuses of 6.3 and 8.5µm were achieved for the #4000 and #20000 grinding wheels. The truing mechanisms and sharpening performance are also discussed.