Aims and objectives of research
Scientific novelty of the results
The practical significance of the results
Investigation of methods for processing of flat surfaces
Operational properties of machine parts and state of the surface layer
Heat cutting at high speed milling of hard materials
Review of results. Conclusions
It is generally accepted that the primary means of intensification of production is a scientific and technical progress, which must be provided accelerated development of mechanical engineering, has radically improved the quality of produced machines. Improving the quality of machines — the most important task of scientists and machinists. Of course, the quality of the machine lays the designer in the design of rational choice of schemes and progressive work processes, using modern advances in methods of calculating the dynamics and strength machines, which are essential to avoid investing in the construction of redundant material, choice of materials with a mandatory orientation to the future technology of production, using standardized units , parts, appliances, already proven in operation, and many other factors. Rightly argue that the quality of the machine built into the surface layer of detail. Methods of casting, forging, stamping, rolling, welding, heat treatment, mechanical machining, including grinding and polishing — the main technological methods of production engineering to create machines that, when the rational design forms and the correct choice of materials can be light, tough and durable. However, the durability of the machine will depend on how quickly or slowly will wear a variety of friction surfaces, how quickly or slowly will arise and develop cracks, especially under alternating loads, ie longevity will depend on the quality of the surface layer of detail. The object of this study are the housing parts, in particular, will consider the item "punch" to the surface where high demands. In addition, work will be considered treatment of milling and grinding. The essence of the work is an integrated approach to scientific investigation and technological support milling and surface plastic deformation of the system parameters of the surface layer in the light of operational properties, as well as to develop practical recommendations for their implementation in a production environment. It is through this approach can solve the problem of improving the quality of machine parts. Development of recommendations for selecting modes of processing, software creation methodology for calculating the parameters of optimal processing conditions using nonlinear programming needed to address the most important tasks to ensure quality processing of body parts and determine the relevance of master's work.
The purpose of the work — to improve productivity and processing quality of machine parts due to the choice of rational conditions for the use of modern tools of materials.
Research Objectives:
1. Linking performance properties of body parts with the parameters of their state of the surface layer.
2. A theoretical study of the regularities of formation of the state parameters of the surface layer in the processing of milling and grinding.
- study the roughness of the surface layer;
- study the degree of hardening of the surface layer;
- study of residual stresses in the surface layer;
- study of the state parameters of the surface layer, taking into account operating properties;
3. Theoretical investigation of thermal phenomena in detail and instrument for milling and grinding.
4. Development of mathematical models of optimization of cutting conditions in rough and finish milling applications by non-linear programming, one that permitted the simultaneous optimization of cutting speed and feed on the criterion of maximum performance with regard to the existing limitations in machining.
5. Justification of power and temperature limits for roughing and high-speed machining
6. Software Development of theoretical calculations of the optimum cutting and rational parameters of the surface layer
7. Development of recommendations for selecting processing modes, ensuring the most cost-effective to obtain the required parameters of the state of the surface layer of body parts.
8. Technological and engineering software processing details "stamped".
9. Substantiation requirements for parameters of the surface details of a "stamp" in the light of operational properties;
10. Study the parameters of cutting process parameters and surface roughness of the surface layer in the processing of flat surfaces to verify the developed models in a production environment
11. The economic rationale for the use of high-speed milling
Scientific novelty of the results is:
- to develop a model for determining the temperature of the cutting thin turning parts according to cutting conditions;
- to develop a mathematical model for determining the roughness of the surface layer, depending on cutting conditions.
- determination of optimal cutting conditions on the criterion of minimum cost according to the method nelenyynogo programming
On the basis of the research productivity increased by 30 — 40% by optimizing the cutting conditions. The recommendations on the choice of the optimal design of the cutting
Processing of flat surfaces can be produced by different methods on different machines — planing, slotting, milling, broaching, turning, boring, multipurpose, shabrovochnyh (blade tool), grinding, polishing, finishing (abrasive tool) [8,9].
1. Obrabotka flat surfaces of the blade tool.
Planing finds great use in small batch and unit production due to the fact that work on the planer does not require sophisticated tools and instruments. This treatment method is very flexible in switching to other operating conditions. However, he maloproizvoditelen: processing is edged tools (planer cutters) at moderate cutting conditions, and the presence of auxiliary turns increases the processing time. In addition, to work on these machines require highly skilled workers. Planing is made on cross-planing (surface treatment of small size) and planing-milling machine (for handling planes of relatively large size). Milling is currently the most common method of handling planes. In mass production milling superseded used earlier planing. Milling is carried out on milling machines, which are divided into horizontal milling, vertical milling machines, universal milling machines, Planing, milling drum, rotary milling, multi-purpose. Are more productive machines. The following types of milling: a cylindrical, face, bilateral and trilateral. Widespread use now finds milling face mills, and for sufficiently large diameter cutters (90 mm) — milling head (face cutters with inserted knives). This is explained by the following advantages of these milling cutters in front of the cylindrical milling cutters:
- The use of cutters of large diameter, which increases processing performance;
- Simultaneous participation in handling a large number of teeth, providing a more productive and smooth operation;
- Lack of long bars, which gives greater rigidity retention tool and, therefore, able to work with high feed (depth of cut);
- Simultaneous machining on different sides.
One of the most productive ways of milling is the machining of planes on the Roundabout-milling drums, milling machines, which is possible on a continuous loop. As a way of reducing the main time use speed and power milling. High-speed milling is characterized by increasing cutting speed the processing of steel up to 350 m / min, cast iron — up to 450 m / min, non-ferrous metals — up to 2000 m / min at low feed per tooth cutters: 0,05 — 0,12 mm / tooth — with Steels and 0,3 — 0,8 mm / tooth — with cast iron and nonferrous alloys. Power milling is characterized by high feed per tooth cutter. How fast and forceful milling is performed cutters equipped with hard metal and ceramic plates. Thin milling is characterized by small depth of cut (t = 0.1 mm), low feed rates (Sz = 0.05 ... 0.10 mm) and high-velocity cutting. Broaching. For external broaching used primarily vertically and horizontally broaching machines. Broaching outer planes due to its high performance and low cost is increasingly used in large scale and mass production. This method of treatment cost effective, despite the high cost of equipment and tools. Currently, milling is often replaced by an external pulling. In mass production for outdoor use high-performance multi-position pull-broaching machines and tools of continuous operation. Scraping performed by the cutting tool — scraper — manually or mechanically. Scraping by hand — the process inefficient, time consuming and highly skilled workers, but also ensures high accuracy. Mechanical method operates on a special machine on which doctor performs a reciprocating motion. Accuracy scraping determine the number of spots in the area of 25x25 mm (when checking the control plate). The more sunspots, the more precise handling. The essence of the scraping is scraping scraper metal layers (thickness of about 0,005 mm) to obtain a flat surface after finishing pretreatment. Scraping is called thin if the number of sunspots over 22 and Ra 0,08 m, and finishing when the number of spots 6-10, as Ra 1.25 microns.
2.Obrabotka flat surfaces of an abrasive tool.
Grinding flat surfaces carried on the plane grinding machines Phillips or a round table as a normal execution, and CNC. Surface grinding is one of the main methods of processing planes of machine parts to achieve the desired quality. In some cases, surface grinding can replace milling. Along with providing the required high level of roughness, this method has serious drawbacks. Firstly, due to high cutting temperature, the surface layer having adverse residual stresses, may cause burns of the surface. Secondly, as a result of allocating a large number of abrasive dust, it is environmentally unsafe. It should be noted that the grinding of metals are prone to phase transformations, increasing the heating sanding product may lead to structural changes due to the emergence of residual stresses of different signs and in most cases, reduce operational properties of the metal surface layer. Grinding flat surfaces can be accomplished in two ways: the periphery and the end of the circle. Periphery of the grinding disk can be done in three ways: multiple working strokes, set the size of the circle, stepped around. In the first method the cross-feed traffic circle is made after each of the longitudinal course of the table, and vertical — after a stroke over the entire surface length of the parts. In the second method abrasive range is set at a depth of removal, and at a low velocity of the workpiece table for the entire length. After each working stroke of the grinding wheel is moved in the transverse direction of the height range of 0,7 — 0,8. To finish the stroke leave allowance 0,01 — 0,02 mm and shoot it the first way. This method is used in processing on the powerful grinding machines. When sanding third way round profiles stairs. Allowance, distributed between the individual steps, it is removed in one stroke. Grinding is usually done with GM. Polished surfaces — a method of finishing treatment. As the abrasive tools used elastic grinding wheels, sandpaper. Lapping planes carried out on ploskodovodochnyh machines. Fine tuning of planar surfaces produce lapping at a pressure of 20 — 150 kPa, with less pressure, the higher the quality of the machined surface. Velocity for fine tuning of small (2 — 10 m / min). With increasing pressure and speed of productivity increases.
The main indicator of quality machines — the reliability is determined by the performance characteristics of parts and their joints: friction and wear resistance, hardness and strength, tightness of joints, strength landings [11,12,14]. Abrasion resistance measures the ability of the surface layers of parts to resist fracture in friction-slipping, sliding, rolling, and when micromovings due to vibration. Wear resistance in many cases can be improved by simply changing the type of treatment or even cutting conditions or the geometry of the cutting tool. Improve the property of machine promotes hardening of the metal prior povehnostnogo layer, which reduces the crushing and abrasion of the surfaces in the presence of their direct contact, and mutual implementation of the surface layers, which arises when the mechanical and molecular interaction [6,7,14]. Fatigue strength — the ability to machine parts to resist fracture during a certain period of time under the action of alternating loads. This property is strongly dependent on surface roughness of machine parts. The presence of surface detail, working in a cyclic and alternating loads, individual defects and irregularities promotes stress concentrations that may exceed the tensile strength of the metal. In this case, the surface defects and obrabotochnye risks play a role of submicroscopic foci of discontinuities of the metal surface layer and the loosening of which are the primary cause of fatigue cracks. This property is very much dependent on the size, character and depth distribution of residual stresses of the surface layer. Numerous studies have established that the presence of the surface layer of residual compressive stresses the endurance limit of parts increases, and in the presence of residual tensile stresses — is reduced. For steels with high hardness increase fatigue limit due to the action of compressive stresses up to 50%, and decrease it under the action of tensile — 30% [6,7,8]. Increased wear resistance is an important reserve for improving the reliability of products in use, because it is the achievement of maximum allowable wear the most critical parts is the main cause of failure of most machines. Wear resistance of machine parts is largely dependent on the state of their surface layer formed during machining. In connection with this very urgent task is to investigate the technological capabilities of machining methods to improve the wear resistance of machine parts. According to modern concepts, the performance characteristics of parts, including wear resistance, linked with a whole set of state parameters of the surface layer. However, currently in the appointment process procedures of machining is usually taken into account only one indicator of the roughness — the arithmetic mean deviation of profile Ra. The purpose of this study is to compare the different methods of processing of flat surfaces on the criterion of the relative change in wear resistance, taking into account the full range of parameters of the surface layer and the conditions of machining. Known equation for calculating the wear rate during the normal wear and tear under constant conditions of work and physical and mechanical properties of the material depending on the parameters of the surface layer can be represented by:
where l — coefficient taking into account the change of the number of cycles in connection with the surface residual stress; tm — relative to the reference profile length at the midline; H — Surface Microhardness; Ra - arithmetic mean deviation of profile; Sm — average spacing irregularities; Wz — option waviness; Hmax — maximum makrootklonenie. K — a constant factor depending on the material in detail and the conditions of its loading. To assess the durability of it is expedient to introduce a relative measure of change in the wear rate obtained on the basis of well-known equation of the wear rate [7] and is determined depending on the relative performance parameters of the surface layer with different methods of mechanical treatment in comparison with the method adopted for the base:
Table. 1. are relative parameters of the state of the surface layer with different methods of processing of flat surfaces. Information about the parameters of the surface layer to that achieved in the processing of flat surfaces of the methods of milling and surface plastic deformation is taken according to the reference and normative literature. In calculations of relative parameters of the basis for comparison adopted parameters of the surface layer during milling.
Pict. 1 shows the plots of the relative performance of the wear rate of the main Io relative performance of state parameters of the surface layer — the arithmetic mean deviation of profile Roa and medium pitch irregularities Som with different methods of processing of flat surfaces.
The results indicate significant improvement in wear rate, ie the reduction of wear resistance when used as a final polishing treatment method of flat surfaces in comparison with Mill finished. Using the same methods of finishing and strengthening treatment of surface plastic deformation — rolling can improve the wear resistance of flat surfaces in comparison with the finishing edge cutting processing of 2-5. The proposed method allows to quantify the change in the rate of wear of machine parts, depending on the complex parameters of the surface layer for edge cutting, diamond grinding and finishing, hardening process flat surfaces. At its basis, quantitative methods justified the choice of finishing-hardening treatment by surface plastic deformation, which provides a guaranteed increase of wear resistance of machine parts. Thus, the proposed technique allows to quantify the change in the rate of wear of machine parts, depending on the complex parameters of the surface layer with different methods of edge cutting, diamond grinding and finishing-hardening treatments are cylindrical and flat surfaces. At its basis, quantitative methods justified the choice of finishing-hardening treatment by surface plastic deformation, which provides a guaranteed increase of wear resistance of machine parts.
When machining is allocated each time the mass of heat. When selecting the optimum cutting conditions can provide such treatment conditions under which the surface temperature of the cutting corresponds to the initial temperature. That's why turning to high-speed machining. An important advantage of this treatment is that most of the heat given to the cutting of wood shavings. Based on the study of processing of materials with high strength and toughness equations are obtained by means of which it is possible to calculate the surface temperature of the cutting parts, depending on cutting conditions. On the structure and properties of the cut surface during processing greatly affects the heat cutting. To get the exact details of a given shape in the final finishing cutting conditions must be chosen so as to ensure the lowest possible heat transfer is cut in the workpiece. Studies have shown that in this case, the surface temperature of the cutting parts can even match the initial temperature. The temperature of the cut surface also determines the magnitude and direction of residual stresses in the surface layer after processing. Since the high thermal loads are responsible for the appearance of tensile stresses in the machined surface, which in turn can lead to hair cracks in the surface details. What are the cutting conditions are responsible for cutting the minimum heat: In general, it is known that during high-speed machining reduces the heat entering the workpiece, because most of the heat of cutting chip removal. There is no doubt that increasing the cutting speed increases and the total amount of heat cutting. So far, no exact data on what proportion of the total heat cutting actually goes into the workpiece in the processing of high-speed cutting. Such information may be obtained on the basis of experimental high-speed milling of tool steels with high strength and hardness. Such experiments allow the identification of the influence of cutting speed and feed on the surface temperature of the cutting directly in the process of milling. It is also possible to determine the optimum cutting conditions corresponding to the minimum heat transfer of cutting in the workpiece. For practical use of the identified interdependencies are represented in the form of the equations. The temperature of the cut surface of workpiece can be expressed as a function of total heat cutting. The real justification for such a mathematical expression is that the temperature of the cut surface depends on the part of the overall heat cut, which goes into the workpiece. In turn, the total cutting heat is the product of cutting speed vc and the cutting force Fc. Cutting force was measured during experiments at the same time the surface temperature of the cutting. The work of cutting and heat cutting: Technical value of the "mechanical work", which corresponds to one second of processing (cutting) is approximately equivalent to the total amount of heat released during the same time. Empirical equation for determining the mechanical work of A, which occurs within one second of processing, is as follows: A [J / s] = Fc [N] xv [m / s]. Mechanical work, corresponding to the total processing time taken for the work of cutting. Mechanical work allows to estimate the cutting process from the energy point of view and determine the required drive power machine tools. Energy costs of milling increased in proportion to the filing. Milling with the filing fz, equal to 0.05 mm / tooth, is the least energy-consuming. Cutting power (mechanical work per unit time) increases with increasing cutting speed. Most of the mechanical work in cutting is converted into heat. The question is whether, as part of the total cutting heat entering the workpiece, varies depending on cutting speed and feed. Amount of heat entering the workpiece is unknown. However, between the temperature of the cut surface and the amount of heat entering the workpiece, there is a direct proportional relationship. When milling with feed 0.05 mm / tooth ratio of these parameters increases with increasing cutting speed. When milling with feed 0.125 mm / tooth ratio of these parameters increases even more pronounced with increasing cutting speed, ie part of the heat cutting entering the workpiece is also reduced, while the linear increase in the productivity of machining. Relative change operation and temperature in cutting: To identify the relative change in the work of cutting and the surface temperature of the cutting workpiece temperature of the surface, measured at the minimum cutting speed 300 m / min (vc, min), taken as 100%. In a similar way to have dealt with the work of cutting . The work of cutting increases almost linearly with increasing cutting speed, although the cutting force Fc decreases with increasing cutting speed. With increasing cutting speed by 228% cutting force is reduced "only" 40%. This suggests that the decrease in cutting force has only a minor effect. You can draw the following conclusions: the work of cutting increases with increasing cutting speed on the meaning of the corresponding cutting speed 300 m / min (vc, min); when cutting speed 1150 m / min (vc) job of cutting the 227% higher, regardless of the selected feed; increase the surface temperature of cutting the workpiece reaches a minimum value at the maximum supply; part of the heat cutting, moving into the work piece, obviously depends on the flow, with increased flow, this heat is reduced; discrepancy between the curves of the relative temperature and relative work cut evidence of a change of the cutting heat entering the workpiece; at cutting speeds from 500 to 1000 m / min decreases the heat cutting, moving into the workpiece, with cutting speeds of more than 1000 m / min, this part of the cutting heat increases.
Conclusions: The experimental steels with high strength and hardness showed that even in the processing of such materials is a shift in the range of high-speed processing. When the cutting speed from 500 to 1000 m / min decreases the heat cutting, flowing into the workpiece. Feed has a more intense impact on this part of the heat cutting than cutting speed. For a large supply of heat cutting, moving into the workpiece is reduced in proportion to excess, and the surface temperature of the cutting workpiece is reduced (although the total amount of heat cutting increases). Hence it is concluded that treatment with high feed (treatment with high material removal details) surface-treated parts exposed to lower thermal loads. It was found that the surface temperature of cutting increases with cutting speed, despite the reduction of cutting heat entering the workpiece. Consequently, the total amount of cutting heat is constantly increasing with increasing cutting speed.
The experimental steels with high strength and hardness showed that even in the processing of such materials is a shift in the range of high-speed processing. When the cutting speed from 500 to 1000 m / min decreases the heat cutting, flowing into the workpiece. Feed has a more intense impact on this part of the heat cutting than cutting speed. For a large supply of heat cutting, moving into the workpiece is reduced in proportion to excess, and the surface temperature of the cutting workpiece is reduced (although the total amount of heat cutting increases). Hence it is concluded that treatment with high feed (treatment with high material removal details) surface-treated parts exposed to lower thermal loads. It was found that the surface temperature of cutting increases with cutting speed, despite the reduction of cutting heat entering the workpiece. Consequently, the total amount of cutting heat is constantly increasing with increasing cutting speed. Thus, produced a review of existing research and development, the results of some theoretical studies on the quality assurance process flat surfaces, examined ways to improve the quality of the surface layer. Investigated operational properties of machine parts, such as wear resistance, fatigue strength, integrity. Studied the technological capabilities of various processing methods to increase wear poverhnosti.Priveden analysis of heat cutting at high speed milling. Considered in this paper, the theme is quite extensive and provides ample opportunity for the researcher. Improvement of modern technology and the intensification of work processes in engineering leads to complication of the working conditions of machines. Due to the increasing performance requirements has proven components are constantly increasing their quality requirements. All these factors determine the prospects for further research quality and find new ways to improve it, both at the design stage and manufacturing.
During the writing of this abstract master's degree work is not yet complete. Final completion: December of 2011. Complete text of work and materials on the topic can be got for an author or his leader after the named date.