Faculty: Engineering Mechanics and Engineering
Speciality: Metal-cutting machine tools and systems
PURPOSE AND OBJECTIVES MASTER’S WORK.Objective - enforcement of internal grinding wheels made of SHM, which provide the necessary quality of the surface layer of processed holes in work pieces of hard alloy tool and constructional steels.
Objectives:
1. Overview of problems that arise in solving the problem of quality of the surface layer of processed holes in the internal grinding of complex-instrumental and structural steel circles of SHM.
2. Review and analysis of solutions to the problem of quality of the surface layer of processed holes by internal grinding wheels made of steel billets SHM.
3. Definition of the surface layer of the work piece during its interaction with the grinding wheel in the process of internal grinding.
4. Develop recommendations on the mode of internal grinding wheels made of SHM, which provide the necessary quality of the surface layer of processed holes in work pieces of complex-tool and constructional steels.
URGENCY. Currently in grinding hard to get a surface without defects, so finding the optimal treatment conditions, which provide the required surface quality and relevance today.
SCIENTIFIC NOVELTY. In carrying out the work will be to obtain new relationships between the modes of processing and the quality of the surface layer of processed holes.
PRACTICAL RESULTS.Recommendations on choice of modes of internal grinding, depending on the desired quality of processed holes.
Grinding tool - cutting tool consisting of abrasive grains of the material, bound into one or another binder (binder) used for grinding materials.
Grinding tool is characterized by: a geometric shape and size, material, ligament, grain, hardness, structure and concentration of grain.
As the grinding materials used:
1. natural - natural diamond, corundum, flint, etc.;
2. synthetic - a synthetic diamond, cubic boron nitride, corundum, silicon carbide, boron carbide, and various compositions of them.
Abrasive materials must have chemical inertness to the material being treated at high temperatures developing in the zone of grinding. In some cases, this condition is not satisfied.
Figure 1.1. Scheme of the working layer of the grinding wheel.
The cutting of the grinding wheel is illustrated in Figure 1.1, is characterized by the following notions.
The outer surface of 1 - surface of a geometrically regular shape, drawn through the top of the outermost grains. The surface of the ligament 2 - surface of a geometrically regular shape, replacing the actual surface of the ligament in the intergranular space. Business layer - layer located between the outer surface of the disc and the surface of the ligament. Working surface - any surface in terms of geometrically regular shape, located at equal distances from its outer surface within the shell [1].
Reliability, durability and other performance properties of machine parts is largely dependent on the quality of machined surfaces. Under the surface quality implies the full range of parameters that determine the accuracy of processing, surface roughness and physical-mechanical properties derived from surface treatments using various technological means .
The impact parameters of the grinding process on surface roughness in a large number of studies, many parameters quantified with the precision index and roughness. Meeting the requirements of the roughness is provided by the choice of kinematics and modes of grinding, the selection of the characteristics of the circle, select the type and method of supplying COTS, suppression or the use of vibration [2].
Effect of grinding parameters on the physical and mechanical properties of the treated surface to a greater extent investigated qualitatively, and the extent to which different researchers characterize differently.
After reviewing the scientific literature on the effect of the parameters of the grinding process, the state of the surface layer of work pieces.
The main parameters of the process can be grouped into 4 groups:
- Indicators of the degree of deformation.
The grinding process is accompanied by plastic deformation of metals and release of a cutting zone of a large amount of heat. As a result of simultaneous action of-force and thermal factors of the final distribution of residual stresses in the depth of the surface layer becomes very complex. There are temporary thermo elastic and residual stresses. Temporary voltage as temperature equalization over the cross section the details disappear and the residual, which arose as a result of the presence of plastic deformations remain. The magnitude, sign, character and depth distribution of residual stresses depends on the mode of grinding, the material type and its initial state after heat treatment.
-The characteristics of the working surface of grinding wheel.
Circles of SHM in grinding are periodic and permanent power, thermal and physical-chemical actions, which resulted in their working surfaces are worn, blunt and salted.
Under wear understand the gradual separation of particles of the working layer of the grinding wheel, resulting in a decrease in its size and weight.
Wear of grinding wheels is mainly due to: mechanical abrasion of the vertices and edges of grains appear to have areas of wear, spalling (flaking) particulate grains under the action of power loads or cyclic alternation of rapid heating and cooling, creating a thermal shock; adhesive wear of grains associated with the periodic separation of adhering to their metal work piece with particles of abrasive grains and the formation of small craters; diffusion wear, which consists in the dissolution of grains in the material of the work piece or the formation of chemical compounds, oxidation of the grain atmospheric oxygen at high temperature, pulling out from the bunch of whole grains.
By clogging understand the process of transfer to the working surface grinding, the particles of sludge during processing. However, it should be borne in mind that the sludge particles can penetrate and hold in the space between the grains and in pores round, and stick to the grain material of work piece.
Blunting and clogging are the main cause of loss cutting power grinding wheels.
-Kinematic parameters of the grinding process.
To the kinematic parameters of the grinding process include: cross-sectional area of the layer of material sent off for one turn circle and slice thickness. These kinematic parameters depend on the length of the arc of contact, time and mode of grinding.
Length of arc of contact with the abrasive grain parts are given the equations of its path within the contact angle, from the moment of entry of grain in detail and the time of exit from the zone of treatment [3].
-Indicators of contacting surfaces in the cutting zone.
In the area of processing individual grains develop high contact temperature, often exceeding the melting point of steel, and the superficial layers of the workpiece, which absorb a large share of the resulting heat within thousandths of a second heated to 150-1250 C, and then just as quickly cooled to 20-350 C. The total amount of heat may be produced by grinding, far exceeds the heat buildup in the processing of cutting tools. This explains the need for a layer of lubricant between the grinding tool and the workpiece to reduce cutting forces and friction, reducing the heating, as well as its rapid removal [4].
Changing the values of these parameters from different groups leads to changes in quality parameters of surface treatment, but the strength of these effects can vary significantly.
List of main parameters that affect the state of the surface layer of the processed work pieces in grinding wheels made of SHM, and the results of their preliminary ranking of the degree of influence, are summarized in Table 1.
Table 1. Ranking of grinding parameters on the degree of influence on the state of the work piece.
Table 1 shows that the greatest impact on the state of the surface layer of processed holes exert power and thermal strain, as well as the arc length of contact and the blunting of the grains of the circle.
In the course of this work was carried out in the analysis of available scientific and technical literature data on the effect of the grinding process, the state of the surface layer of workpieces and their ranking on the degree of influence.
When writing this Autosummary master work was not yet gotova.Okonchatelnoe completion: December 2010 Full text of the work and materials on the topic can be obtained from the author or his manager after that date.