Fundamental Research on Brazing Diamond Wire Saw by High-frequency Induction Heating
Author:Zhang Zi Zuo
Supervisor:zhu yong wei xiao bing
Diamond abrasive grains have some distinguished properties,such as extremely high hardness,superior thermal stability and excellent thermal conductivity,etc,Therefore diamond wire saws have been utilized and taken good effects in hard brittle non-metallic materials cutting off,such as silicon crystal and sapphire slice processing.However,engineering applications show that diamond abrasive grains easily losing or even coating peeling due to traditional diamond abrasive consolidation mode(such as resin bond or electroplated coating),the diamond fixed on the suface of resin or electroplated diamond wire saw mainly by mechanical mosaic effect with low abrasive holding strength,and the chip capacity space is narrow,so the resin binder or electroplated coating is easy to fall off,which restricted the diamond abrasive grinding performance into full play,also restricted the reliability of the machining efficiency during cutting processing.To sovle the problem,a new method which can realize the high strength joint between diamond grits and steel matrix based on active solder alloy,i.e.brazing diamond wire saw,is put forward in this paper.The main creative concepts are summarized as follows:(1)The brazing process of diamond wire saw is developed and the automatic production line is designed and built.The brazing diamond wire saw preparation technology is divided into three phases,the process parameters of each preparation section is determined.Raw materials were optimized through theoretical calculation and experiment analysis.The results show that Cu-Sn-Ti alloy as brazing filler metal,KSC82 carbon steel as matrix,17.44 mm/s for wire feed speed,3 kW for the output power of induction heating and 1.5s for soaking time would be reasonable.(2)High strength connection between diamond grits and steel matrix was obtained,and the source of the diamond grits holding force was revealed.The brazing morphology,microstructure and interface compounds of diamond grits were analyzed through scanning electron microscope,energy spectrometer and X-ray diffraction.The results show that compressive strength and impact strength of diamond grits have no obvious change before and after brazing.Better diamond brazing morphology can be obtained under the condition of3 kW heating power holding for 1.5 s and 15 l/min for argon flux.Ti elements accumulate aliquation in the diamond brazing interface,new phase TiC growing in the brazing interface of diamond provides a"bridge"for Cu-Sn-Ti alloy wetting diamond grits,TiC exists in the form of TiC_X(X=0.47-0.95)interstitial phase.(3)The chromogenic mechanism of Cu-Sn-Ti alloy was analyzed,the influence of atmosphere for diamond brazing was assessed.Cu-Sn-Ti alloy layer microstructure and elements distribution were analyzed through optical microscope and energy spectrometer under different argon flux.The results showed that the surface color of diamond wire saw depends on Ti oxidation degree of Cu-Sn-Ti alloy layer.Argon flux affects the oxygen partial pressure of brazing atmosphere,directly affects the thickness of Ti oxidation on the surface of Cu-Sn-Ti alloy layer,and determines the diamond wire saw surface color.Dimaond holding strength reduced greatly when the argon flux is less than 5 l/min.(4)Mechanical properties and brazing layer failure characteristics were analyzed through the tensile experiment,bending fatigue test and torsion test.The results showed that the comprehensive mechanics performance of the brazing diamond wire saw can satisfy the actual demand of granite slice processing.The micro-cracks occurred on the surface of diamond wire saw should beⅠ-type crack.Reducing the wire saw tension and fatigue bending curvature;improving the diamond grits distribution uniformity can effectively reduce the incidence of cracks occurrent.(5)Brazing diamond wire saw was made with the length of 500 mand 1.12 mm in diameter,then G663 granite slicing processing test was carried out by using this diamond wire saw.The results show that slice processing efficiency can be stable in 15 mm/min,granite removal stye is brittleness removal.Workpiece feed speed is one of the main factors influencing the machining surface quality.The wear modes of brazing diamond wire saw are abrasive grits abrasion wear including normal wear and tear,fracture and fall off,of which the falling off ratio is about 14.3%,cracks occurrence and extension in the brazing interface of diamond is the main reason for diamond falling off under bending fatigue stress and torsion fatigue stress.