Papers by Keyword: Wire Sawing

Abstract: The wear behavior of monolayer brazed diamond beads was investigated during wire sawing of granite. Diamonds were bounded onto the beads by brazing in vacuum. Brazed beads were abrasive sawed on a wire sawing machine and the wear of the brazed diamond beads were traced and observed by using a digital microscope. The results reveal that the wear of root fractured, characterized by breaking off grit at its bonding level, was the fatal failure of the cutting ability of grit as well as the main wear behavior of brazed grits on brazed bead.

Abstract: Wire sawing with diamond tools is a highly flexible cut-off grinding process with regard to machinable component structure and composition. Nowadays, it is deployed in many fields of application e.g. the dismantling of nuclear or industrial plants. Here, steel has to be cut which results in lower productivity and tool life compared to the conventional processing of natural stone. To ensure a properly designed process the mechanical and thermal tool loads have to be known in advance. This paper presents an analytical model that predicts the mechanical load as a function of the process parameters.

Abstract: Mechanical preparation of mono-and multicrystalline silicon wafers by sawing, lapping, or grinding damages the surface. Depending on the mechanical impact of the treatment different degrees of damage structures occur. It is necessary for further processing of wafers to have damage free and contactless methods to characterize structures such as changes of the lattice structure by phase transformations or plastic deformations, and microcracks below the surface. In this paper we present results of investigations on the sub-surface damage by two contactless optical methods: Scanning infrared reflection polarimetry with SIREX and Raman spectroscopy. The investigations were carried out on silicon wafers sawn with the multi-wire technique using diamond coated wires. The sub-surface damage mainly consists of microcracks of different length, which penetrate several micrometers into the bulk. The results were compared with confocal microscopy and scanning electron microscopy analyses of the same damage structures.

Abstract: Diamond wires are widely used in cutting hard and brittle materials such as silicon, sapphire, etc. However, present low production efficiency of diamond wires causes their high cost. To solve the problem, a drum-type manufacturing method for electroplated diamond wire tools was developed. Multi diamond wire tools could be manufactured simultaneously at high speed with a single machine. Electroplating characteristics of developed method were evaluated. Additionally, composite electroplating experiments were carried out to find optimal conditions for manufacturing diamond wire tools.

Abstract: Wire cutting, originally developed for the processing of natural stone, is increasingly used for the machining of reinforced concrete and metallic structures. In this field of application the diamond wire sawing tools are subjected to a higher-than-average wear. Furthermore the metallic bonding of the cutting beads is not suitable for machining metallic structures, because of a missing self-sharpening effect. Within this paper, conventional wire sawing tools are investigated in pure steel structures. These tools are supposed to be suitable for the cutting process in accordance to their tool concept. The manufacturing process and the grain sizes have an influence to the tool performance. From these investigations requirements for a new tool concept will be derived.

Abstract: Fixed-abrasive wire saw, with its ability to cut hard brittle material, such as silicon ingots, crystals and quartz, has emerged as a leading technology for production in semiconductor and photovoltaic industry. There are some defects in conventional fixed-abrasive wire saw such as significant low holding abrasive ability, low machining efficiency, high running costs, etc. A new fixed-abrasive wire, namely brazed diamond wires have been developed to overcome these problems. In this paper, brazed diamond wire were carried out to braze two different size diamond grits onto two different thin steel wires by using a nickel-based powder as brazing alloy. The mechanical properties of brazed diamond wire were evaluated by tensile and breaking twist experiment. The experimental results showed that the heating in the brazing process has litter influence on the wire mechanical properties. The addition of brazed alloy and diamond grits sharply decreased the wire mechanical properties significantly, both in the tensile strength and breaking twist angle. Bigger diamond grit would make the accumulation of brazed alloy which leaded to the deterioration of diameter consistency of wires.

Abstract: The wire sawing process is a highly flexible cut-off grinding process. Nowadays it is not only used in its traditional field of application (processing of natural stone) but also in the civil construction industry and for the destruction of metallic structures. In order to extend the knowledge about the process it is one goal of the Institute of Production Engineering and Machine Tools (IFW) of the Leibniz Universität Hannover, Germany, to investigate the cutting mechanisms. These are supposed to be the basis for a tool design taking into account the specific field of application. The results presented within this paper describe an approach to explain the interdependencies of the system and manipulable variables for the wire sawing process. From these interrelationships the cutting mechanisms will be derived.

Abstract: Multi-wire sawing process has been widely used for wafer slicing of silicon substrates for solar cells. Usually there are two different kinds of wire saw in multi-wire sawing process including free abrasive wire sawing with SiC grits and fixed abrasive wire sawing with diamond wire. For free abrasive wire sawing process, the material removal mechanism can be considered as lapping and the fixed abrasive wire sawing can be considered as grinding. This paper is to investigate the characteristics of the surface texture of silicon substrate fabricated by these two wire sawing process. Experimental results have been observed by white light interferometry and SEM. Some different properties of both processes have compared been with variant characteristics including 2-D and 3-D surface roughness parameters. Results of this paper can be further used to evaluate the feasibility of wire sawing process of silicon substrates for solar cells.

Abstract: Multi-wire sawing process with slurry has been popularly adopted for wafer slicing of silicon substrates for solar cells. This paper is to investigate the chip size estimation for effective blending ratio of mixing slurry of wire sawing. Different combination of slurry has been studied with microscopic pictures of abrasive grits by SEM and distribution of particle size of slurry. The chip size can be estimated by the developed method and then the TTV of sliced substrates is used to evaluate the blending ratio of slurry for cost efficiency of wire sawing. Experimental results indicate that the slurry with certain ratio of reborn grits increases the TTV value of sliced substrates. As the weight percentage of silicon chips is above 6 % for the blending ratio of 50% reborn abrasive grits after sawing run 2, the slurry is suggested to be changed to new slurry for wire sawing. Under this developed rule, the average TTV can be maintained under 0.016 mm for nominal thickness of 200 m silicon substrates. Results of this paper can be used to estimate the feasible blending ratio for maintaining the TTV under the desired specifications of silicon substrates for cost efficiency.

Abstract: An investigation was undertaken to elucidate the mechanisms for the fracture failure of brazed diamonds in wire sawing. Diamonds were brazed by high-frequency induction in vacuum. The changes of compressive strength and the appearances of the diamonds at different brazing temperatures were obtained. The morphologies of the diamonds after sawing were also observed. Together with the stress analysis of a brazed grit, it is found that the fracture failure of brazed grit is the result of the brittle fracture happening on the root section of the grit, the interface between the grit and the brazing alloy. The degradation of mechanical properties of grits in brazing is a key factor to the reduction of their resistance to fracture. Lower machining forces as well as grit exposure are in favor of preventing grits from fracture.