Yi Qing Yu

Improvement of the Performance of Diamond Segments for Rock Sawing, Part 1: Effects of Segment Components

An investigation is reported on how to improve the performance of diamond-impregnated segments for the circular sawing of natural rock materials. T hese serial papers consist of three parts. Part 1 is concerned with the service performance of diamond segments fabricated at a wide range of conditions. The service performance of the segments was evaluated in terms of t he characteristics of segment wear and the consumed power. The worn surfaces of the seg m nts were monitored in an effort to relate the working surface state of the segments w ith their service performance. The percentage of diamond working conditions on the worn segment surfaces w s found to be closely related to the wear performance of the segments and the consume d pow r. The diamond working conditions and hence the segment performance are attributed to t he combined effects of such parameters as grain size, concentration and quality of diamonds, proper ties of bond matrix and granite. Introduction It is estimated that one of the biggest consumptions of synthetic di amond abrasive lies in the processing of rock materials, in which case sawing is perhaps the most important with regard to the production cost and efficiency. The tools most widely used for primary s wing are circular saw blades with diamond impregnated segments. With the increasing use of natural rock materials as decorative materials around the world, there is a great demand on opt imizing the wear behavior of diamond sawblades so as to reduce the overall production cost. Diamond impregnated segments consist of randomly dispersed diamond cr ystals embedded in a metal matrix. As sawing proceeds the segments wear down and new iamonds emerge from the matrix and cut the workpiece. During the sawing process, the main role of the metal bond matrix is to ensure maximum cutting productivity of the diamond by holding it fir mly until it is worn out. Generally speaking, the matrix and the diamond wear rates should be appropriately matched in order to facilitate constant efficient cutting as well as mi ni ze the wear of the diamond segments. Unfortunately, diamond segments that are popularly used in the practica l fields of producing granite products are frequently worn in unexpected modes, in which case diamond gr its prematurely fail either through pop-out or by fracture and the bond matrix wears much slowe r or faster than diamond grits. A fundamental understanding of what mainly affects the wear of diamond segments is required in order to provide a technological basis for optimizing the design of diamond segments and consequently improving their performance. These serial papers consist of three parts. Part 1 is mainly de vote to elucidate the influences of segment components including the compositions of bond matrix, diamond grit s ize, and the concentration and quality of diamond grits, on the performance of diamond se gments fabricated and used under different conditions. Coupled with the findings of this first part, Part 2 will focus on studying the mechanisms for the retention of coated diamond grits, whereas an attempt is to be made in Part 3 to improve the performance of bond matrix through an addi tion of rare earth elements. It is hoped that the findings of these serial papers ca n provide more technical supports for the selection of diamond grits and optimal design of the compositions of bond matrix in order to improve the performance of diamond segments for the sawing of natural rock materia ls. Key Engineering Materials Online: 2003-09-15 ISSN: 1662-9795, Vol. 250, pp 46-53 doi:10.4028/www.scie tific.net/KEM.250.46

A Comparative Study on the Dressing of Metal-Bonded Diamond Saws

An investigation is reported of the dressing of metal-bonded diamond saw blades with four different dressing methods – stirring the blade segments in rock slurries, surface grinding the blade segments with Al2O3 wheels, dressing the blade segments with SiC wheels, and dressing the blades through sawing of refractory materials. The surfaces of dressed blade segments were examined by a scanning electron microscope. The protrusion of the diamond grits on the dressed segments was quantitatively assessed using a digital optical microscope. The vertical and horizontal force components and the spindle power were measured in the refractory sawing. The grit protrusion generated by the stirring method was found to be the highest and most diamond grits remained their original crystal shapes. But it took a quite long period to let the diamond grits protrude from the bond matrix. The protrusion produced by the surface grinding ranked the lowest among the four methods. The height of grit protrusion for either SiC dressing or refractory sawing was found to be about 20% of the diamond average size, which might be an optimal point with respect to the segment sawing performance. Force analysis indicated that the force per diamond grit in refractory sawing was much lower than the diamond compressive strength. The changes of spindle power in the sawing of refractory materials can be used to in-process monitor the dressing process. Introduction Circular sawing with diamond impregnated segments mounted on a circular steel core is the most extensively used process for natural stone materials. In newly fabricated segments, diamond grits are usually embedded and covered by the metal bond matrix. Although new diamonds can emerge from the matrix while the segments wear down and cut the stone workpiece as sawing proceeds, they need to be dressed before sawing to achieve an efficient cutting in most cases. Since the dressing of metal-bonded diamond wheels is regarded as the key technology in high-performance, high-speed and high-precision grinding processes, tremendous studies have been conducted on the dressing of diamond wheels for grinding ceramics and steels [1-2]. In the field of rock sawing, however, much fewer studies covered this topic in the past few decades. In an early study on the dressing of diamond saw blades [3], Wright and Ford investigated the selection of dressing wheels and the effects of grit sizes. They developed a special-purpose dressing rig, which consisted of a grinding wheel mounted on a spindle and driven through an electric motor. Unlike previous studies, this present investigation focuses on the comparison of four different methods for dressing diamond a kind of saw blade segment. It is hoped this work will be of benefit to the choice and improvement of dressing methods for metal-bonded diamond tools widely used in the processing of stone materials. Experimental Fabrication of Metal-bonded Diamond Saws. Iron, copper, tin, cobalt and nickel were used as the constituent metal powders for the manufacturing of diamond segments, in which case iron was about 50% wt. The diamond segments were fabricated on an automatic hot pressing machine installed with an infrared device for monitoring sintering temperature. Diamond of 40/45 (355-425μm) US mesh Key Engineering Materials Online: 2006-02-15 ISSN: 1662-9795, Vols. 304-305, pp 19-23 doi:10.4028/www.scientific.net/KEM.304-305.19

Sawing of Granite with Side-Slotted Diamond Segments

The present study was undertaken to examine the feasibility of circular sawing of granite with a newly shaped diamond saw blade. Three slots were formed on each side of each segment of the saw blade. Side-slotted segments and traditional segments were compared under same operating parameters. Measurements were made of the horizontal and vertical force components and the consumed power in order to obtain the tangential and normal force components. The surfaces of worn blade segments were examined by a scanning electron microscope. The consumed powers, normal and tangential force components for the side-slotted segments were found to be lower than those of the traditional segments. The position of resultant forces for the side-slotted segments is a little further away from the bottom of the cutting zone than the traditional segments. SEM observations indicated that the wear of the side-slotted segments was similar to sawing with traditional segments.

Mechanical Behaviors of Metal-Bonded Diamond Abrasive Tools with Different Grit Sizes

The present study was undertaken to compare the hardness and transverse rupture strength (TRS) of metal-based tooling composites containing diamonds of different grit sizes. Two kinds of bond matrix, copper-based and iron-based, were applied in the fabrication of the composites. In the copper-based matrix, rare earth was used as an additive. Diamonds of three different grit sizes were incorporated into two bond matrix, thereby forming six kinds of diamond composites. SEM and EDS were used to analyze the fractured surfaces of the composites. It was found that the diamonds of medium grit size in the copper-based bond matrix led to the highest hardness and TRS. For the iron-based bond matrix, however, the hardness and TRS of the composites containing the coarsest diamonds were found to be the highest. In same bond matrix, a close relationship between TRS and hardness was established.

The Effects of Rare Earth on the Hot Pressing of Cu-Sn-TiH2 Bonded Diamond Composites

The present study was undertaken to examine the effects of rare earth (RE) in hot pressing of Cu-Sn-TiH2-bonded diamond composites. Two kinds of composite specimens – with RE and without RE – were fabricated. As an additive to the Cu-Sn-TiH2 bond matrix, the RE was used in the form of misch-metal. The hardness and transverse rupture strength (TRS) of the specimens were measured. SEM and EDS were used to analyze the fracture surfaces of the specimens. Both hardness and TRS of the specimens with RE were found to be higher than the specimens without RE. SEM observations indicated that the pop-outs of diamonds on the fracture surface of the segments without RE are more than the specimens with RE. But more diamonds were fractured on the fracture surface of the segments with RE.

Material Removal Mechanisms in Grinding Aeronautical Alloys, Part 2: Analysis and Discussion

This is the second in a series of two papers concerned with the material removal mechanisms in grinding two kinds of aeronautical alloys. In Part 1, temperatures reached in the grinding zone were in-process detected and the morphological features of workpiece surfaces under different grinding temperatures were observed. This second part is devoted to the analysis of material removal mechanisms and wheel-workpiece interfacial reactions. Prevailing mechanisms in the grinding of the two alloys were found to be mainly governed by the adhesion between the abrasives and workpiece at elevated grinding temperatures. Introduction Grinding with abrasive wheels is one of the most important methods for cost-effectively machining aeronautical materials, in which case nickel-based and titanium alloys best satisfy the requirements when compared to steel [1]. As already indicated in the first part of these serial papers, high temperatures are easily generated in the grinding zone due to the unique properties of the aeronautical alloys. Plastically deformed coatings and smeared materials were found on the ground surfaces of the Ni-alloy and Ti-alloy at elevated grinding temperatures. Despite of the numerous papers published on the machining of aeronautical alloys, the majority of them focus mainly on the thermal damage to workpiece other than the interfacial interactions between abrasives and workpiece [2-5]. The material removal mechanisms in the grinding of aeronautical alloys have not yet been understood thoroughly and quantified. Based on the results in Part 1, this second part focuses mainly on the analysis of the material removal mechanisms through following the morphological features of abrasive wheels at different grinding temperatures. Experimental Details of grinding tests were already presented in the first part of these serial papers. Abrasive wheel surfaces were observed and analyzed after grinding using scanning electron microscopes (SEM) and an SQ Energy Dispersive Spectrometer (EDS). For these observations, the wheel surfaces were coated with a carbon or gold film. Particles Adhering to Worn Abrasive Grits Fig.1 shows the micro observations made on the worn surfaces of Al2O3 wheel after grinding the Ni-alloy with high grinding temperatures. Adhering materials can be found on Al2O3 grits when the temperature is up to 1000 o C (see Fig.1a). EDS analysis of the adhering materials shows that there is no difference in compositions between the adhering layers and workpiece (see Fig.1b). In addition to directly adhering to the leading edges of abrasive grits, adhering materials can also be seen in chip storage space as shown in Fig.1c. In some cases, a grit failure similar to adhesive wear can be observed on Al2O3 grits as indicated in Fig.1d. Similar phenomena were also observed on SiC wheel in the grinding of Ti-alloy. The presence of materials adhering to the abrasive grits indicates the Key Engineering Materials Online: 2004-03-15 ISSN: 1662-9795, Vols. 259-260, pp 324-328 doi:10.4028/www.scientific.net/KEM.259-260.324

Analysis of Temperatures in Sawing of Granite Based on Parabolic Heat Distribution

A temperature model was advanced based on a parabolic heat flux distribution in sawing contact zone in the present paper. It is found that the maximum temperature for parabolic distribution is more higher than that for triangular distribution in the sawing contact zone, and the location point of the maximum temperature for parabolic distribution in the sawing contact zone is much nearer the entrance than that for triangular distribution.

Mechanisms for Sawing of Refractory Bricks with Diamond Blades

Experimental studies were undertaken to investigate the mechanisms for circular sawing of refractory bricks with diamond segmented saw blades. Three kinds of diamond segments of different hardness were fabricated for the saw blades. The vertical and horizontal force components and the spindle power were measured in sawing. Based on the measurements of force and power, the specific energy and the normal force per diamond grit were obtained. The normal force per grit in the sawing of refractory bricks was found to be only 5% of the static compressive strength of diamonds used in the present study, but fractures of diamonds were still popular on the segment working surfaces after sawing. The power, horizontal force, and the specific energy were found to increase with segment hardness. The specific energy obtained from the measured power was basically comparable to the values obtained from a theoretical equation to calculate the specific energy associated with slurry erosion to the bond matrix of segments.

Specific Energies in Sawing with Diamond Segments and Grinding of a Diamond Segment

An experimental study was undertaken to compare the mechanisms of two different processes to dress metal-bonded diamond segments. In one case, a piece of vitrified SiC wheel was used as workpiece and sawn by diamond segments attached to a sawblade. In another process, a diamond segment was used as workpiece and ground by an Al2O3 wheel. Spindle power was measured in sawing and horizontal force was monitored in grinding, in which case the latter was then used to get the consumed power in grinding. Specific energies were then calculated from the measured or converted power. For sawing of SiC wheel with the diamond sawblade, the maximum specific energy was found to be only 0.5 J/mm3, whereas the specific energy was up to 25 J/mm3 in the grinding of the diamond segment.

The Effects of Coatings at Diamonds on the Mechanical Behavior of Metal-Diamond Composites

The present study was undertaken to examine the effects of metal coatings at the surfaces of diamonds impregnated in metal bond matrices. Diamonds with or without coatings were incorporated into same bond matrix to form two metal-diamond composites in order to reveal the effects of coatings. Diamonds with same coatings were applied to three bond matrices to check the influences of matrix properties on the effects of coatings. The transverse rupture strength (TRS) of the composites was measured to ssess their mechanical behavior. Circular sawing was also conducted to reveal the contribution of coatings to diamond retention. SEM was used to analyze the fractured surfaces of the composites. For same bond matrix, the coatings at diamonds were found to increase the TRS of the composites. However, it is difficult to compare the effects of coatings in different bond systems.