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Summary of the final work

Сontent

Introduction

Details of complex shape with shaped surfaces are widely used, therefore, the technological processes of their manufacture, which have some peculiarities, require close examination and improvement taking into account current trends. Existing traditional technological processes of processing shaped surfaces [1-6] are reduced to the use of one of two main methods: 1) a shaped cutting tool (cutter, broach, mill, countersink, grinding wheel), the shape of the cutting edge of which corresponds to the shape of the machined shaped surface and copies it; 2) a simple cutting tool (cutter, mill, grinding wheel), the cutting blade of which is in dotted or ruled contact with the shaped surface to be machined.

Obviously, the first method of processing is more productive, but less economical due to the need to develop and manufacture a special cutting tool. Depending on the size and shape of the treated surface. In the second case, the formation of the shaped surface is carried out in accordance with the machining process, which gives the tool corresponding to the curvilinear motion relative to the workpiece being machined, which provides copying systems or numerical control machines (CNC). The increase in the range of manufactured fittings, as well as the complexity of their geometric shapes, posed new shaping tasks, which led to the improvement of computer systems of CNC machines, providing wide possibilities for controlling the machining process [7, 8].

1. Theme urgency

Creating an effective model of a curved surface process is quite complex and proceeding in the treatment area. But despite such factors, the relevance of the topic has not changed its direction in the study of this issue.

Mechanical treatment of shaped surfaces is rather difficult and is provided by a complex kinematics of the movement of the cutting tool relative to the workpiece, and is also characterized by variable values ??of technological factors determining the processing conditions.

The master's work is devoted to an actual scientific task of increasing the efficiency of machining shaped surfaces with carbide cutting tools due to the choice of rational conditions of the cutting process. Thus, the establishment of relationships and mutual influence of all components of the process of machining the shaped surface should be carried out in a comprehensive manner, taking into account the changing parameters to control the cutting process and, as a result, – obtaining the specified quality parameters of the treated surface.

2. Goal and tasks of the research

The aim of the scientific work is to achieve an increase in the efficiency of processing of shaped surfaces with carbide-tipped cutters due to the choice of rational conditions of the cutting process.

The main objectives of the study :

  1. Analysis of the two main methods of machining shaped surfaces.
  2. Processing of complex shapes on CNC machines.
  3. Analysis of the accuracy of machining shaped surfaces, depending on the error settings tools for software operation.
  4. Search and identification of the characteristics of the physicomechanical properties of the surface layer (roughness, nature and magnitude of residual stresses, structural transformations).
  5. Management of cutting conditions in order to increase productivity and reduce processing costs.
  6. Increased periods of tool life, and as a result, reducing the number of their replacements and associated equipment downtime.
  7. Expanding the technical limitations of the machining process (for example, increasing the maximum cutting force).
  8. Ensuring the specified quality parameters of the treated surface.

Object of study: is the process of studying and detailing the processing features of shaped surfaces.

Subject of study: methodological, theoretical and practical aspects of the processing of shaped surfaces.

As part of the master's work, it is planned to receive topical scientific results in the following areas:

  1. Managing the process of machining the shaped surface of the part (by changing its geometric characteristics with the removal of the allowance).
  2. Comprehensive assessment of the possibilities of increasing the processing efficiency with regard to the variability of the conditions of the cutting process.
  3. Determining the dependence of deviations of the relative position of the surfaces on the accuracy of setting up a lathe for the operation of software processing.

For the experimental evaluation of the theoretical results obtained and the formation of the foundation for further research, as practical results planned development of the accuracy of the relative position of the mating surfaces with a radial generatrix, depending on the value of the error of the dimensional setting of the cutters of the CNC machine, left and right, for the operation of program processing:

  1. Dependence will allow for a given error of conjugation of surfaces with radius generators, to obtain the numerical values of the limits of the permissible error of the dimensional reference of tools.
  2. Selected two corner parameters – conjugation errors and numerical values will allow to calculate the dimensional reference error for the specific shaped surface and the clearance when checking for fit patterns.

3. Review of research and development

Since complex-shaped parts with shaped surfaces require close examination and improvement with current trends, consider a review of research and development. Modern computer systems of high-performance equipment exclude the possibility of automatic assignment of cutting conditions by the system itself. The system takes into account the current state of the workpiece, which allows you to create an optimization of the control program for processing modes in order to speed up the process, increase the efficiency of equipment use and improve the quality of processing. In this case, the tool path is divided into elementary areas with a given step.

By comparing the amount of material removed at each site, with the recommended given cutting conditions, the system assigns the optimum feed at each site. Although the system calculates optimal feed rates automatically, the initial parameters for certain machining conditions are determined by the technologist based on his own experience or on the cutting data tables provided by the tool supplier.[14-15-16-17]

However, these comparisons of the definition of optimal cutting conditions do not take into account the variability of processing parameters of shaped surfaces, which requires their further development.

Literature Review [7-9-10] showed that not all automatic control systems are built according to an optimization algorithm, and control program design systems for CNC machines are not able to design the optimal technology or take into account only the geometric conditions of forming the surface of the part. In addition, modern trends in the development of software products show that their improvement occurs in the direction of optimizing the cutting process and the entire technological processing system when designing control programs for CNC machines.

It is known that for any cutting process, the geometrical parameters of the allowance layer determine the process as a whole. These parameters depend on the shape of the workpiece, the actual shape of the tool surface and the actual trajectory of the forming movement, which determines the relative position of the tool and the workpiece during processing. As a result of the geometric interaction with the removal of the stock, the treated surface is formed, as well as its macro and microgeometry. The most complex processes occur during the formation of the physicomechanical properties of the surface layer (roughness, nature and magnitude of residual stresses, structural transformations). At the same time, the machining of the shaped surface is characterized by a constant change in the parameters of the cutting process, which necessitates a detailed study of their mutual influence, the establishment of links and regularities of their influence on the processes in the cutting zone. [2-11-20]

Comprehensive accounting and analytical determination of variable parameters underlying the study will most accurately simulate the processes in the cutting zone when machining a shaped surface (Fig. 1). Since the use of simplified analytical dependences in this case will lead to a decrease in the reliability of determining the existing constraints when calculating the optimal processing modes.

Modern research, reflected in the work of Professor Heifetz M.L. [21] showed that combined treatment methods are most effective. For one reason or another, the scope of use of many efficient processes is significantly limited, in such cases, combining them with another method can achieve a given state of the surface layer and expand technological capabilities.

Details of complex shape with shaped surfaces are widely used, therefore, the technological processes of their manufacture, which have some peculiarities, require close examination and improvement taking into account current trends. The existing traditional technological processes for processing shaped surfaces, considered in the works of Granovsky E.G, Dalsky A.M., Druzhinsky I.A., Firago V.P., Yazheritsyna P.I. [5-12] and others are reduced to using one of two main methods:

  1. Shaped cutting tool (cutter, broach, mill, countersink, grinding wheel), the shape of the cutting edge of which corresponds to the shape of the machined shaped surface and copies it;
  2. A simple cutting tool (cutter, mill, grinding wheel), the cutting blade of which is in dotted or ruled contact with the shaped surface to be machined.
Processing shaft with shaped surfaces

Figure 2 – Processing shaft with shaped surfaces
(animation: 16 frames, 4 cycles of repetition, 215 kb)

Obviously, the first method of processing is more productive, but less economical because of the need to design and manufacture a special cutting tool. In addition, the possibility of using shaped cutting tools directly depends on the size and shape of the treated surface. In the second case, the formation of the shaped surface is ensured by the kinematics of the machining process, which informs the tool the corresponding curvilinear motion relative to the workpiece being machined, which is ensured by the use of copying systems or numerical control machines (CNC), which have already been mentioned.

A large number of scientific works of scholars (among which worth mentioning are the works of Bazrov B.M., Bezhyazychny V.F., Bratan S.M., Butenko V.N., Vitrenko B.A., Gilmana A.M., Guseva V.V., Gordienko B.I., Dalsky A.M., Yermakova Y.M., Lukicheva A.V., Makarova A.D., Matalina A.A., Mikhailov A.N., Ryzhova E.V., Starkova V.K., Khandozhko A.V., etc.). The performed studies allowed to establish that at present there is practically no information on the justification of the choice of rational parameters of the cutting process, taking into account the features of machining of shaped surfaces.

Currently, methods of optimization of cutting processes according to the criteria of maximum productivity or minimum cost are well developed, however, these methods for determining optimal cutting conditions do not take into account the variability of processing parameters of shaped surfaces, which requires their further development.

Technological support of the operational properties of machine parts in the manufacturing process is the subject of a large number of studies by well-known scientists: Bazrova B.M., Bezyazychny V.F., Dyachenko P.E., Matalin A.A., Petreshina D.I., Ryzhova E.V., Suslova A.G., Schneider Y.G. The operational properties of parts and their joints (wear resistance, rigidity and strength, tightness of joints, strength of fit) determine the main indicator of the quality of machines – reliability.

In the Donetsk National Technical University (Department of Mechanical Engineering), methods for improving the efficiency of shaped surfaces, expanding the material base on this issue, as well as improving the performance of machine parts and cutting tools due to ion-plasma hardening of the surface layer, the development of deposition technology are widely developed. -oriented coatings, the development of progressive designs of gear couplings, increasing the efficiency of the rotor lines and goe else.

A review of literary sources has shown that, at present, the focus of the machining of shaped surfaces is on the management of the machining process in order to ensure accuracy.

Analysis of literary sources showed that the issues of ensuring high precision of machining of parts as a whole, and shaped parts (when quality indicators are variable along the profile) are well studied [12-17]. Ensuring accuracy in the considered works is achieved by managing the processes of designing and manufacturing the shaping tool, developing technological processes for machining parts, taking into account the phenomena of technological heredity and the mutual influence of surface quality indicators, using equipment with programmed control and stabilizing the kinematic parameters of the tool.

However, it should be noted that for solving the problem of ensuring the accuracy of processing, the authors performed studies for cylindrical surfaces and did not take into account the features of machining parts with a shaped profile. In the works devoted to the processing of shaped surfaces, the solution of this problem is determined by the assignment of variable regime processing conditions using techniques that take into account only one or several variable parameters. For effective management of the processing process in this case, it is advisable to perform on the basis of techniques that take into account the full range of process variables and their relationship.

The quality of products is understood as an aggregate of properties in the measure of the usefulness of products that satisfy certain social and personal needs in accordance with its purpose. Improving Quality – important condition for increasing production efficiency [18-20].

Information to substantiate the choice of optimal cutting conditions, taking into account the nature of processing shaped surfaces in the modern literature is quite limited. Constant machining conditions when turning a surface with a complex curvilinear generatrix cannot ensure high process efficiency for the following reasons: changing the kinematic geometric parameters of the tool; change cut parameters – width and thickness; change of tool path and continuously changing feed direction; variability of thermal processes in the treatment area.

Therefore, it is of interest to work on improving the efficiency of processing such surfaces directly with hard alloy blades, as well as with other tools in general.

4. Analysis of the selection of carbide cutter to improve efficiency

Over the past decades, the volume of various types of tool materials for blade tools consumed by metal processing industries of technologically developed countries has changed dramatically. Practically, carbon and alloy tool steels are not used for blade tools. Consumption of high-speed steels decreased significantly from 65…70% to 35%…40%, while the use of hard alloys increased from 30% to 55%, and cutting ceramics and superhard tool materials increased from 1% to 10%.

Of the hard alloys, the best indicators of both strength and wear resistance are materials made by powder metallurgy methods, which also allow you to form a billet that is as close as possible to the final shape of the cutting tool.

The share of using relatively inexpensive cermets (tungsten-free hard alloys), which in some cases are not inferior and sometimes superior in performance to traditional tungsten-containing hard alloys, is significantly increasing. In Japan, the use of cermets comes to 40% of the volume of carbide tools. Undoubtedly, one should expect a substantial increase in the use of cermets in the Russian industry.

A fundamentally new type of ultrafine-grained hard alloys with unique flexural strength, commensurate with the strength of high-speed steels, appeared. The production of billets of such solid alloys in the form of rods of different diameters leads to a tendency to manufacture the necessary end tools directly at the enterprises themselves using multi-axis CNC grinding machines.

Carbide inserts for turning tools are one of the most convenient types of cutting tools. The fact is that the cutters are available as with a one-piece construction, when the whole tool is solid and the cutting part is inseparably connected with everything else, and with removable parts, which is much more convenient during work, when you can remove and replace one plate with another. It is also convenient when replacing in case of breakage or wear. Plates for cutting cutters can be made of various materials and alloys, so that you can have several in the kit for one type of tool, which is useful for interacting with different types of blanks.

Buying replacement plates for turning tools comes out much cheaper than the tools themselves. The main advantage of these products is that they help to increase productivity, therefore, in production they will be indispensable. Given the growth of the product range in small-scale and medium-scale production, there is a need to automate many processes. Carbide plates have the following advantages:

  1. Low cost, in comparison with whole cutters;
  2. The ability to quickly change;
  3. Reliably manifest themselves even in intensive modes of operation;
  4. The possibility of readjustment plates;
  5. Management of cutting conditions to increase productivity and reduce the cost of processing;
  6. Greater unification of units and tools.

Carbide inserts for turning tools are classified according to the following parameters:

  1. Type, or for what tools they are used, as for cutting, grooving, cutting, shaped, boring and other varieties requires its own shape of the cutting profile, which is created according to the features that will have to meet in the work.
  2. The material from which the products are made may have a different composition. Despite the fact that they all belong to the carbide type, all the same, the ratio of tungsten, titanium and other metals may differ, depending on the required working conditions.
  3. Dimensions – Depending on the parts with which the work will go, the plates may have different sizes. When relatively small workpieces with small diameters are machined, a large cutter with a large plate may simply not get into it. For this purpose, identical in type and material, for different in size, products for turning cutters on metal are created.
  4. Back Angle – This parameter is indicated in the product brand. The roughness of the treated surface depends on it, the higher it is, the smoother the surface becomes. For soft metals, plates with a large back angle are used.
  5. Accuracy class – There are five accuracy classes for these products that provide varying degrees of stiffness in terms of dimensional tolerances.

Marking displays the composition that is included in the product. Replaceable carbide inserts for cutters are found with the marking T5K10 and T15K6. On the example of T15K6 it can be understood that they belong to the products of the titanium-tungsten group. The content of titanium carbide in it is 15%, cobalt – 6%.

For each type of these types of instruments, there is a GOST for which plates with certain parameters fall:

  1. GOST 19086-80 – This includes carbide materials for mechanical cutters of the cutting and support type, as well as chip breakers;
  2. GOST 19042-80 – refers to interchangeable multi-faceted products;
  3. GOST 25490-90 – carbide materials types 61, 62, 01, 02. These can be revolving tools, feedthrough and boring tools.
Carbide plates

Figure 3 – Carbide plates

Among the cutting ceramics, the most promising are ceramics hardened by filamentary crystals of silicon nitride and sialons.

From superhard materials, the appearance of a new type of polycrystalline diamond blade tools manufactured using chemical vapor deposition (CVD-diamond) technology should be noted. In the near future, we should expect the appearance on the market of a tool from monocrystalline diamond obtained by a similar technology, which will allow several times lower prices for single-crystal blade tools compared to a tool based on natural diamonds and diamonds produced by traditional synthesis technologies.

In this analysis, it is worth noting the promising application of wear-resistant coatings on the blade tool, which significantly increase tool durability or machining performance, however, the creation of new types of coatings and the expansion of their use is an unambiguous global trend to improve cutting efficiency, including for shaped surfaces.

Conclusio

The master's work is devoted to the actual scientific problem of creating an effective model for the processing of a curvilinear surface. In the framework of the research carried out:

  1. The analysis of the two main methods of processing of shaped surfaces.
  2. The analysis of the current state of issues of ensuring the accuracy and quality of machining parts with a shaped profile.
  3. The analysis of the influence of the variability of the machining of shaped surfaces on the provision of rational cutting conditions.
  4. The results of the well-known studies in the field of the effectiveness of the use of progressive cutting tools are presented.
  5. The technical limitation of the processing process has been extended.
  6. The task of quality parameters of the processed surface is provided.

Further research focused on the following aspects:

  1. Development of appropriate analytical techniques to determine the full range of features of the processing of the shaped surface by calculation without additional experimental studies.
  2. Managing the process of machining the shaped surface of the part (by changing its geometric characteristics with the removal of the allowance).
  3. Comprehensive assessment of the possibilities of increasing the processing efficiency with regard to the variability of the conditions of the cutting process.
  4. Development of solving problems of optimization of cutting processes of shaped surfaces.
  5. Ensuring an increase in the processing efficiency of shaped surfaces due to a reasonable combination of optimal processing conditions, cutting process control and the use of carbide tools under conditions of variability of cutting process parameters.

When writing this essay master's work is not yet completed. Final Completion: April 2019. Full text of the work and materials on the topic can be obtained from the author or his manager after the specified date.

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