1 Introduction
With the progress of science and technology and the development of modern industry, hard and brittle materials ( such as laser and infrared optical crystal, ceramic, quartz glass, silicon crystal and stone ) is widely used. Because of hard and brittle materials with high hardness, brittleness, its physical and mechanical properties especially the toughness and strength compared with metallic materials have very big difference, therefore these materials are difficult or even impossible to be the ordinary processing method for processing. Diamond is known to nature the highest hardness material, its outstanding performance in the field of machining hard and brittle materials have broad prospects. At present, the diamond tools for cutting and grinding of hard and brittle materials is still an effective processing method, such as the use of diamond cutting tools cutting stone, diamond wheel grinding ceramics.
Machining of hard and brittle materials diamond tools are mainly all kinds of diamond saw and diamond grinding wheel, although various tools application scope and the processing characteristics of different, but their wear mechanisms are roughly the same. Because the diamond tool wear on the processing quality of the workpiece and the processing effect is very big, the tool wear performance is a reflection of tool performance, process parameters is reasonable or not is an important indicator, so the diamond tool wear mechanism of diamond tools to guide reasonable manufacturing and rational selection of technological parameters have important significance. For a long time, many scholars at home and abroad dedicated to the study of wear mechanism of diamond tools, and has made gratifying achievements.
Study on wear mechanism of diamond tools 2
Diamond tools for machining hard and brittle materials, because of the intense friction, temperature effect, tool inevitably produces wear, and the wear is a very complex process.
( 1) the three stage wear
Diamond tool wear consists of three stages: the initial rapid wear stage ( also known as phase transition ), wear rate is approximately constant stable wear stage and subsequently accelerated wear stage. Accelerated wear stage show tools cannot continue to work, need to trim.
( 2) abrasive wear form
Abrasive wear forms can be divided into: abrasive, abrasive, macro micro crusher crushing abrasive, abrasive and abrasive wear off. The wear form proportion is decided by different wear stage, the instruments used and processed materials. T W Liao quantitative studies of micro feed grinding structure ceramic diamond grinding wheel wear and pointed out: at the transition stage and stable stage of wear, the wear of grinding wheel is different. Phase transition of wear is not only decided by the grinding wheel specifications, material properties and machining conditions, more important decisions in the grinding wheel preparation method. During the transition phase, because the wheel just trimmed, abrasive reached maximum, a plurality of abrasive particles do not participate in cutting, so the whole grains proportion than in stable stage high; at the same time, dressing made many abrasive out too large, control force is not enough, abrasive loss ratio than the stable phase at high; in addition, dressing will weaken some abrasive, abrasive of broken ratio than the stable phase at high. Stable phase of the abrasive wear is the main wear, low micro broken abrasive ratio and relatively high friction and wear ratio of grinding wheel 's self sharp phenomenon, this is adverse to processing. Hit enemies army through the diamond wheel for grinding of alumina ceramics, points out that the wear of grinding wheel are mainly abrasive wear and abrasive loss. S Y LUO on diamond saw blade for cutting granite are studied, that saw the failure is mainly due to abrasive macroscopic breakage and ( or ) abrasive grain shedding, when breaking and shedding of grains over 1 / 3, tool failure. Huaqiao University, Yu Yiqing and so on through to cut stone, concrete and other materials in the process of diamond tools diamond and binder surface state a large number of observations and SEM analysis showed that: abrasive stay longer, easier processing, tool wear is also higher; macroscopic fracture state will lead to the diamond protrusion height decreased significantly, and even lost cutting tools cutting ability; for quite a long time, abrasive nature blunt edge, highly reduced, along with abrasive grains bonded to wear around, holding to the diamond to diamond weakened, falling. Xu Xipeng study of sawing granite, diamond segment wear of diamond, that actual wear process through different paths: from complete crystal form, experience and the macro micro crusher broken, finally fall off; can also began to fall off. Depending on the quality of diamond, the load and the bonding agent and other factors. And for the retention of the metal bond of diamond carrier wear process has a more complex tribological properties. Granite cutting and diamond chip in cutting fluid drive erosion binder surface, formed in its surface erosion traces, binders in similar fluid grinding conditions by erosion. The front end of the crater pits diamond displayed in sawing process fluid caused by formation of cavitation erosion. In addition, binder also by granite on the hard spots in scraping and plough, its shape is similar to the metal grinding processing of texture.
( 3) diamond tool wear mechanism
The wear mechanism of diamond cutting tools has the following kinds roughly: friction and wear, abrasive, abrasive wear broken broken, binder, surface fatigue and impact, friction and wear to abrasive blunt and grinding, the abrasive grains bonded broken off, wear and tear due to weakening the bond strength and promote grain shedding. Different machining process and its wear mechanism are different, such as: diamond wheel for micro feed grinding structure ceramics, diamond grinding wheel wear mainly has three kinds of forms: friction and wear, wear particle fragmentation and bond breaking; besides, another kind is bonded abrasive wear. Yiyang Zhou ceramic bonded grinding wheel grinding sapphire, ceramic bonded grinding wheel wear is the main binder brittle fracture, and the metal and resin bonded grinding wheel wear and abrasion wear. Literature [ 5 ] the author by diamond saw blade for cutting granite, pointed out: the tool wear mechanism has four main: friction and wear, abrasive wear, surface fatigue and impact. Xu Xipeng study of sawing granite, diamond segment wear of diamond, think to granite with direct friction and wear at the same time, also by granite cutting debris impact and corrosion, the wear types can be summed up as: abrasive wear, abrasion and erosion caused by solid particles in fluid. X P XU quantitative analysis of the effect on the abrasive on the load and the cutting zone temperature, think abrasive is broken by impact force caused by temperature change, but also is very important, because it will cause thermal fatigue damage and thermal stress.
Effects of 3 factors of wear of diamond cutting tools
( 1) tool
Diamond grade, content, particle size, bond and Diamond Match and tool shape and the tool itself related factors are important factors affecting tool wear.
Often diamond content is low, power consumption is low; but the diamond content is too low, the macroscopic broken will increase, thereby causing the protrusion height is insufficient, so that the power consumption increases; diamond content is high, then the power consumption increase, which led to the diamond tool wear resistance drops off. If the diamond grade higher in lower case, content, its complete crystal rate is still high, block high wear resistance, low power consumption, but the diamond grade and binder selection matching. Wu Jian analysis of the diamond quality dispersion on the sawing process, it is pointed out that the high quality diamond abrasion resistance, must request the binder is also very good wear resistance, only in this way can we give full play to the role of high quality diamond. The low quality of diamond, because of its compression and impact resistance capacity of poor, even cutting the easier mineral composition may also occur when the more obvious wear and breakage, in particularly difficult cutting part, generally occur macroscopically broken and lost cutting ability, this time on bond wear resistance requirements should be relatively low, in order to ensure adequate protrusion height of diamond. Literature [ 10 ] points out at the same time, we should try to reduce the diamond quality dispersion. Literature [ 8 ] through analysis of vitrified bond diamond grinding wheel manufacturing sapphire process ( spindle deformation deformation said grinding required for normal load variations), found that the changing form of periodic change, illustrate the wheel with self sharpness, reason is ceramic bonded grinding wheel wear is bonded material brittle fracture, which will quickly appear new particle. While the metal and resin bond grinding wheel wear for friction and wear and abrasion. Y C Fu gives a grinding optimization model, with the help of this model, according to processing requirements and grinding parameters to optimize the grinding wheel ( including grain size, concentration, stretch rate and effective abrasive particle space ), can also be based on the grinding wheel and grinding parameters optimization of processing requirements ( including grinding depth, speed of the grinding wheel and workpiece feed speed ). In addition there are many scholars have carried out studies in this area.
( 2) the processing conditions
Because the diamond tool wear and load state are closely related, so the processing conditions on the wear produced marked effects. Dai Xiangguo analysis of the diamond grinding wheel cutting engineering ceramics process parameters on grinding wheel life, think that when other parameters are constant, each one corresponding to the cutting depth has an optimum wheel speed; when the cutting depth and wheel speed is given, there exists an optimal feed rate; the process parameters on the radial wear of grinding wheel influence orders for: wheel speed, cutting depth and feed rate. Literature [ 17 ] points out, tool wear and machining process parameters and process parameters have great relations coordination, it is necessary to optimize the process parameters. Z J Pei analysis of grinding silicon wafer on the circumstances, draw the following conclusions: when the rotating speed of the grinding wheel chuck speed for 4350rpm, 590rpm, grinding force increases gradually, when reaching a certain peak, back to lower values, and continue to press the cycle, that gradually become blunt when grinding wheel, grinding force reaches a certain value when the abrasive broken; when the rotating speed of the grinding wheel chuck speed for 2175rpm, 40rpm, grinding wheel in grinding force is small broken. Therefore, the grinding force is substantially constant and high wear rate.
( 3) the material to be processed
Different workpiece materials, fracture toughness, hardness, differ bigger, so the nature of the material also has the effect of diamond tool wear. Literature [ 19 ] was studied using diamond circular saw cutting of stone tool wear and pointed out: when cutting hard granite, diamond saw blade wear is the main wear particle macroscopic breakage and shedding, reason is the control force is not enough, the cutting condition is abominable; when cutting softer granite, complete crystal shape and grains micro breaks accounted for a large proportion, and grinding grain shedding the proportion is still high, the wear the saw blade cutting to maintain ability. Xu Xipeng thinks: Granite in different mineral property and deformation mechanism is to determine the key failure mode of diamond. Quartz content higher, more intense diamond wear; orthoclase content if obviously high, then the sawing process is relatively difficult; in the same cutting condition, coarse grained granite than fine-grained granite more difficult to cleavage fracture.
Key words: diamond, material
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