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Study on Failure Modes of Vacuum Brazed Diamond Wire Saw

1.Vacuum brazed diamond wire saw

Diamond wire saw slicing technology is one of the main slicing technologies for monocrystalline silicon materials. This technology has the advantages of high cutting processing efficiency and good cutting quality of workpieces. Diamond wire saws mainly include resin bonded diamond wire saws and electroplated diamond wire saws. In recent years, in order to overcome the phenomenon of abrasive particle shedding during the cutting process of resin bonded diamond wire saw and electroplated diamond wire saw, many scholars have carried out research on the preparation process and used relatively mature vacuum brazing diamond wire saw technology. Vacuum brazed diamond-bonded abrasive wire saw is used to improve the working life of the wire saw and the cutting quality of the workpiece.

The working principle and working method of vacuum brazed diamond wire saw and electroplated diamond wire saw are basically the same. At the same time, the wire saw abrasive grains and solder layer will also be subject to friction and impact from the workpiece material, under the combined action of force, friction and impact. Wire saws are subject to wear and failure. In the research work on the wear of traditional brazed diamond tools, the wear of diamond abrasive grains is the main research object, and the loss of cutting ability of a single layer of diamond abrasive grains is the criterion for the failure of brazed diamond tools.

2.Failure mode of vacuum brazed diamond wire saw

2.1 Failure Mode Analysis

The failure of vacuum brazed diamond wire saw can be divided into two types, one is normal failure and the other is abnormal failure. The main form of normal failure is: the brittle fracture that occurs when the wire saw works under alternating stress for a long time. The main forms of abnormal failure are: the improper selection of cutting parameters leads to excessive normal force F, and the wire saw fails due to accidental fracture; the solder layer falls off unexpectedly, causing the wire saw to lose its cutting ability and fail.

2.2 Normal failure modes

The normal failure mode of the wire saw refers to the brittle fracture of the wire saw under the action of alternating stress for a long time. Take the workpiece feed speed V.=0.6 mm/min, wire saw wire speed V=1.73m/s, at this time the measured F is 1.17, the force curve is relatively stable, the force curve is relatively stable, continuous cutting single crystal The silicon material fractured at 2 hours. As shown in the fracture morphology, the wire saw fracture is relatively flat, there is no “necking” phenomenon in the tensile test, and the fracture presents obvious rough areas and smooth areas, indicating that the wire saw was used for a long time. Brittle fracture occurs under alternating stress.

2.3 Abnormal failure modes

The abnormal failure modes of vacuum brazed diamond wire saw mainly include the breaking of the wire saw and the shedding of the solder layer. The accidental breakage of the wire saw usually occurs when the cutting parameters are not selected properly, which is easy to damage the workpiece and cause processing accidents. At this time, the normal force on the wire saw often exceeds its allowable maximum value. When the feed speed of the workpiece is V=2.4mm/min and the wire saw wire speed V=1.73m/s, the wire saw will break within 10 seconds of cutting, and the instantaneous value of the normal force F of the wire saw measured before the breakage is 2.60N .Exceeds its allowable maximum value of 2.37. From the fracture morphology of the wire saw, it can be clearly seen that the wire saw fracture presents the “necking” phenomenon of its tensile test. The reason is that the setting of the cutting parameters is unreasonable, resulting in excessive feed pressure during the cutting process, so that the stress value on the wire saw exceeds the tensile strength of the wire saw, and the wire saw is directly broken.

The bonding strength between the solder layer and the substrate was tested by the bending method, which is the cross-sectional appearance of the wire saw after repeated bending, from which it can be seen that there is a gap between the solder layer and the substrate, and there are parts that fall off from the substrate. possible. For typical brazed single-layer diamond tools, such as brazed diamond grinding wheels, the bonding strength between the brazing filler metal layer and the substrate is rarely discussed for two reasons. One is to prepare a vacuum brazed diamond grinding wheel, the vacuum brazing time is longer, the infiltration and diffusion between the solder and the substrate are sufficient, and the interface bonding strength is higher; the other is the load on the substrate during the processing of the vacuum brazed diamond grinding wheel Relatively single, even if the infiltration between the solder layer and the substrate is not sufficient, the phenomenon of solder layer shedding rarely occurs. Considering the thermal damage of the small-diameter wire saw substrate and micropowder diamond abrasive grains, the brazing heating time of vacuum brazed diamond wire saw is generally short. From the morphology of the interface between the wire saw substrate and the solder layer, it can be seen that the interface between the two is relatively clear, and the permeation layer is not obvious: the working conditions of the vacuum brazed diamond wire saw and the vacuum brazed single-layer diamond grinding wheel are greatly different. The difference is that during the cutting process, the wire saw produces tensile, torsion and bending movements. Under long-term alternating stress, if the bonding strength between the solder layer and the substrate is low, the solder layer may fall off. Therefore, in order to prevent the copper-based alloy powder solder layer from falling off the substrate, relevant technological measures should be taken during the preparation process to improve the bonding strength between the solder layer and the substrate, such as degreasing the wire substrate before solder coating Decontamination treatment, roughening of wire matrix surface and weak acid etching treatment, etc.

3.Research conclusion on failure mode of vacuum brazed diamond wire saw

In this paper, the prepared vacuum brazed diamond wire saw was used to cut single crystal silicon materials under different parameters, and the failure mode and mechanism of vacuum brazed diamond wire saw in the process of cutting single crystal silicon materials were studied. The conclusions are as follows:

(1) The failure mode of vacuum brazed diamond wire saw is divided into normal failure mode and abnormal failure mode. The normal failure mode is mainly the brittle fracture caused by the crack expansion on the surface of the wire saw, and the extraordinary failure mode is mainly the accidental breakage of the wire saw. and the peeling off of the solder layer;

(2) In order to avoid abnormal failure modes and premature normal failure modes of vacuum brazed diamond wire saws, in addition to selecting appropriate cutting parameters, efforts should also be made to optimize the vacuum brazing process of the wire saw to reduce the heat loss of the wire matrix. The purpose of improving the bonding strength between the solder layer and the wire matrix, reducing the thermal stress of the wire saw and reducing the surface cracks of the wire saw.