Aim and objectives of research
A brief review of existing research
When using plates from carbide and mineralokeramiki main obstacle is the high hardness and brittleness.Despite the application at the finish machining of a large number of high — precision processing methods such as ultrasonic, laser, etc., the most widely used and productive at the present time is the diamond grinding.Processes occurring during the destruction of an allowance for diamond grinding in the future affect the operational characteristics of the plates.
Development of the modern world engineering is associated with the expansion of the scope and range of hard materials (very hard alloy, heat-resistant steels, cast iron and other alloys), when cutting in which the contact zone with the tool having a high temperature (above 800 C). This led to an increase of total world consumption of cutting ceramics from 2% in the 70-ies 1 to 5% for the 90 th year (with an estimated trend growth of the amoount of CC in industrialized countries, up to 12% in 2000) 2 of the total scope of instrumental materials.Accrdiny to theestablished tendensy nowdays world consumption of CC is in the range 7 — 8%, while in industrialized countries is reaches 10 — 12%.
Significant superiority of hard alloys (their cutting properties) over the other tool materials led to the emergence and wides development of high — speed cutting of metals, as well as the possibility of machining
Goal of work — Modernization of the surface grinding machine for processing plisti low carbide and mineraloceramiks.
The main objectives the work of are:
—designing, and modernization of the construction the surface grinding; machines, at the expense of new design features;
—ensuring the universality of devices and the greatest productivity;
—calculating and studying of the aids for the processing of ceramics;
—work up the technological process machining of hard alloy and mineraloceramics;
—Ensure minimum defects of hard alloy and mineraloceramics;
In the process (Fig. 1) of grinding as a cutting tool we usie abrasive wheels. Grinding wheel consists of a large number of sharp and hard abrasive grains, connected with a special weight — band. Grinding wheel can be considered as a mill with a large number of small teeth. Indeed, in the process of grinding each grain at the periphery of the circle works as a cutter tooth, removing the chips of variable section.Figure 3. represented by a diamond abrasive grinding wheel. Specide features of the wheel compared with other cutting tools are, on the one hand, very high hardness of the teeth (grains), on the other hand, the ability of communities to self — sharpening, which is due to the fact that the blunt grains on the surface range chip, and works the new sharp grain. Due to the high hardness of the abrasive grains grinding can be processed by metals of any hardness, including hard alloys and nonmetallic materials such as glass, marble and stone).Figure 2 shows the grit grinding wheel.
Hard alloys are the primary tool materials, providing highly-efficient processing of materials by cutting.Now the total amount of carbide tools used in machining industry, is up to 30%, while the tool is removes up to 65% of the chips as the cutting speed, used in the processing of this tool is 2 — 5 times higher than that of high — speed tools.
Recommended for finishing alloys are with lower cobalt content and a high content of carbides. Roughing - on the contrary.Figure 4 shows the effect of cobalt on the properties of hard alloy group (VC)
The main feature of the cutting of ceramics is the lack of binding phase, which significantly reduces the degree of softening when heated in the process of deterioration, increases the plastic strength, which determines the possibility of using high cutting speeds, far exceeding the speed of cutting tool carbide.If the ultimate level of cutting speeds for carbide tools in turning of steels with thin slices and small criteria bluntness is 500 — 600 m / min, tool, equipped with cutting ceramics, the rate increases to 900 — 1000 m / min. In Fig.5 is presented zavisimostisostavlyayuschey cutting force Pz by wear hz tool.
Shape of the plates shown in Fig. 6
Theoretical analysis. Analyzing the options presented above we can draw conclusions that it would be better to use diamond abrasive grinding.
Ways to enhance the efficiency of processing:
—choice of the optimum thickness of slice
—Selection of optimum cutting conditions such as cutting speed, feed, machine power
—best choice of the grinding wheel, namely, grain, hardness, and a bunch of circle
—Optimal choice of the dimensions of the grinding wheel
Mechanical treatment must not result in exceeding the size and density of defects above a certain allowable value based on their distribution and orientation in the surface layer. Intensification of the regime grinding, primarily due to increase in supply causes an increasing in cutting forces, leads to defecting in the surface layer of products and, consequently, reducing of their strength. Changing the mode settings we can controlled defect of the machined surface of plates of hard alloys and mineraloceramics, providing a given strength of products. Deficiency that occurs during processing, must not exceed the level of structural defects. In this case the strength of plates made of hard alloys and mineraloceramics is not reduced.
The use of carbide tips and mineraloceramics provides:
— increasing of resistance by 20-25%;
— raising of the possibility of cutting conditions due to ease of restoring the cutting properties of the plates by means of their rotation;
— reducing of abrasive consumption;