A novel tool monitoring approach for diamond wire sawing

Mobile diamond wire sawing is a highly flexible, productive and, versatile cutting process. Accordingly, it is used in many areas, such as the dismantling of nuclear power plants or wind turbines. Despite the widespread use of the process, the cutting process requires continuous manual monitoring by the machine operator. This is due to the continuously changing cutting conditions. A common process error is tool breakage. It is often caused by the displacement of the grinding segments (cutting beads). Due to the cutting speed (up to 30 m/s), these failures cannot be detected and prevented by the machine operator. However, a measuring system or process monitoring does not exist yet. Accordingly, a damaged diamond wire can become hooked, which often results in wire breaks. As a result, grinding segments break away from the wire, which can lead to deadly accidents. Therefore, a new approach for monitoring the tool for diamond wire grinding will be investigated. The paper is divided into five sections. First, the requirements for the sensor system are derived. After the selection of a measuring principle and the functional verification in the grinding process, the monitoring approach is presented and features for monitoring the tool with regard to the displacement of grinding segments are described. It was shown that the developed approach is suitable for monitoring the diamond wire tool during the sawing process. The investigation on a prepared diamond wire tool also demonstrated that the feature allows the detection of displacing grinding segments already from 2 mm.

Research on suppressing brittle fracture and implementing ductile mode cutting for improving surface quality at silicon wafers manufacturing

Single crystal silicon is an important basic material used to manufacture electronic and photovoltaic devices. Ductile mode of diamond wire sawing is a promising method for silicon wafering in order to produce wafers with minimal surface damage. To achieve ductile mode, the correct applying of cutting parameters and careful wire design is necessary. This study investigates the scratching of monocrystalline silicon by the abrasive particles of different geometry, which simulates the material removal process in diamond wire sawing. Diamonds, crushed and spherical tungsten carbide (WC) particles served as abrasives. Experiments show that spherical abrasives enhance ductile mode cutting significantly decreasing brittle damage when compared to irregular shape particles. Spherical WC particles permit to increase the critical load and critical cut depth of ductile-to-brittle transition from 5 to 10 times. The depth of the damaged subsurface layer decreased from 5 µm to 0.2 µm due to the absence of brittle cracks. A uniform regular distribution and appropriate suitable density of abrasive particles is obligatory for cracking reduction. For that, the method of diamond particles uniform deposition with the controlled density by a polymer binder combining high modulus and adhesive capacity with good flexibility was elaborated. The method includes preliminary diamond particles fixation on a thin resin layer providing high uniformity and subsequent strong fixation by a thicker resin layer. The research on ovalization of diamond particles was performed for smoothening cutting edges. The method is based on the activation of the graphitization process at sharp edges of particles under the action of metal salts at increased temperatures.