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Shelkynova Dasha

Faculty of engineering mechanics and mechanical engineering

Speciality: Technology of mechanical engineering

Scientific adviser: Ivchenko Tatiana

Theme of master's work:

Technological support of operational properties of machine parts using the methods of surface deformation

Summary on the topic of graduation

The Actuality of the Work

One of the most promising methods of improving the quality of the machined surface of machine parts during machining is a finishing and hardening processing of surface-plastic deformation (SPD). In this regard, researches of diamond burnishing are rather relevant.

From a perspective of operational properties, this method of processing provides a favorable combination of roughness parameters, of a microrelief of the surface layer, micro hardness, sizes and nature of the distribution of processing residual pressure during manufacturing of a wide range of important parts such as rods, pipes, shafts, axles and some other ones made, as a rule, of highly strong kids of steel which work in conditions of high speeds, increased wear and alternating cyclic loads.

The aims of the work

The aim of this work is to increase the productivity of machining and the quality of a surface layer of machine parts based on the use of one of progressive methods of SPD – a diamond burnishing.

To achieve the aim, the following tasks have been put:

1. To justify the use of diamond burnishing as a final method of machining during processing of groups of parts of bodies of rotation.

2. To explore the thermal state of details during diamond burnishing.

3. To explore the regularities of formation of the state parameters of a surface layer (roughness, degree of hardening, residual stresses) during diamond burnishing.

4. To explore an influence of state parameters of a surface layer on the operational properties of machine parts (wear resistance, strength, tightness).

5. To develop a technological process of machinig of a"pipe" with the use of diamond burnishing.

6. To develop some recommendations for the choice of treatment parameters for diamond burnishing.

Scientific novelty

1. Determination of the temperature in a surface layer of parts during diamond burnishing.

2. Разработка методики расчета параметров эксплуатационных свойств: износостойкости, прочности и герметичности при алмазном выглаживании.

3. Development of methodology for calculating the parameters of operational properties: durability, strength and tightness during diamond burnishing.

Review of existing researches

Analyzing the works on the subject, we can say that many scientists were engaged in issues of surface plastic deformation. For example, Odintsov L.G. in his book "Hardening and finishing of parts by a method of surface plastic deformation" gives basic information about some methods of SPD, tools and equipment used ,about operating properties of parts treated with SPD.

Papshev D.D., Smelyansky V.M., Reznikov A.N. , also studied the diamond burnishing . In their books they considered basic regularities of processes occurring at this physical phenomena. The basic data on various types of abrasive and diamond tool, its design and features of exploitation, as well as various methods of abrasive and diamond processing.

The basic part

The essence of diamond burnishing consists in plastic deformation of workpiece with a sliding instrument –a smoother. The tool pushes apart the metal , forming a groove on its surface. (Figure 1).

Fig. 1 Diagram of diamond burnishing

(Animation: the number of frames - 10, the number of cycles - 10, size - KB 137)

In the formation of the surface layer of parts, thermal effects in the processing zone of SPD play a very important role, as the process of plastic deformation is accompanied by intense heat apportionment and by a rise of temperature of contact tool’s surfaces and the part.

During a diamond burnishing much attention must be paid to studying of the thermal state of the part ,as it is the quality of its surface layer, depending on the temperature,which must be ensured at the final processing operations of SPD.

The aim of this work is the analysis of regularities of formation and ways of managing heat flows and temperature in the processing zone during a diamond burnishing.

The main source of heat released during diamond burnishing, is the work of forces of elastoplastic deformation of the work piece material.

Fig. 1 Schematization of diamond burnishing

During the process of diamond burnishing of the parts of radius R, rotating at a speed V (Fig. 1.)a diamond indenter having the shape of a sphere with radius r, plastically deforms the material to a depth h. The quantity Δ represents the elastic recovery of the part material after passage of the tool. The total length of the contact between the tool and the part ABC is divided into two sections, called (by analogy with the cutting tool) the front surface AB (defined by the angles φ, γ and ε1) and the rear surface (defined by the angles α and ε2).

The projection of the contact area between the spherical working part of the tool and the cylindrical surface of the part has a shape of an ellipse during a static indentation. Due to the movement of the indenter and the deformation of the material of the part , the surface shape is different from an ellipse, but with a sufficient precision the contact surface can be replaced by a rectangle of width b (in the direction of the movement of feeding of the indenter S) and length l = (l₁ + l₂), where l₁ -a contact length on the front surface (arc AB), l₂ – on the rear one (arc AC).

The forces acting on the contact areas bxl₁ and bxl₂ on the front and rear surfaces of the indenter are defined in such a way:

where Р_Т - is a tangential force acting in the direction of the velocity of the main movement and determined depending on the radial force of burnishing R.

During the schematization of the components of the studied system, a part is considered as a halfspace, a tool - as half-closed rod having a configuration of the contact zone of the tool and the part.

In the processing zone, there are two main sources of heat: q_1Т –in a zone of plastic deformation on the front surface AB and q_2Т – in a zone of elastic renewal on the back surface BC (the maximum intensities of the sources q₀₁ and q₀₂). It is assumed that the laws of the intensity distribution of the sources are dissymmetrical normals:

The densities of the heat flows uniformly distributed on the areas bxl₁ and bxl₂ on the front q₁ and rear q₂ surfaces of the indenter are determined from the system of equations [2]:

where λ_д, λ_и, ω_д, ω_и are the coefficients of thermal conductivity and thermal diffusivity of materials of the part and the tool respectively; M₁, M₂, N₁, N₂ are dimensionless functions that determine the heating of areas on the front and rear surfaces of the tool; К_о is a coefficient taking into account the limited source of width b , К_о = 0,87; К_с - a coefficient of shape for two-dimensional fast moving source with a dissymmetric normal distribution, taking into account the difference from a source with a uniform distribution, К_с = 0.55; coefficient β = l₂/ l₁; coefficients χ₁ = 0,6, χ₂ = 0,75 [2].

As a result of a solving of the system (4) we determine the densities of heat flows (runoff) moving from the part to the instrument on the front q₁ and rear q₂ surfaces of the indenter :

The appropriatenesses of changings of heat flows on the front q₁ and rear q₂ surfaces of the indenter depending on the burnishing process parameters - the radius r of the indenter and the efforts of burnishing P are shown in Fig. 2.

Fig. 2. Diadrams of changes in the density of heat flows on the front q₁ and rear q₂ surfaces of the indenter depending on the radius of the indenter r-a) and the efforts of burnishing P-b)

The calculations were performed for the following conditions: the material processed – steel 45 (σ_в = 750 MPa), the diameter of the part d = 200mm; velocity V = 3m / s.

Based on these analytical expressions (6) and (7) can be calculated heat flow at the front of q₁ and q₂ rear surfaces of the indenter for any conditions diamond burnishing.

While analysing temperatures in the processing zone during the operations of diamond burnishing a part should be considered.

The total distribution of temperatures in the part during burnishing is determined by all the sources operating in the processing zone :

where Θ₁(x,y) is a distribution of temperatures that occurs under the influence of heat source q₀₁ in a zone of plastic deformation on the front surface of the indenter; Θ₂(x,y) - under the influence of heat source q₀₂ in zone of elastic renewal on the back surface of the indenter; Θ₃(x,y) - under the influence of heat flow from the part to the tool on the front surface of the indenter q₁; Θ₄(x,y)-under the influence of heat flow from the part to the tool on the back surface of the indenter q₂.

When describing the temperature field inside of the part according the method of sources they use a well- known analytical expression for the band* fast moving source:

where ψ = x/l₁, ψ_u= x_u /l₁, ν = y/l₁, - dimensionless coordinates; n_i = q_i /q₀₁- dimensionless quantities, taking into account the difference of heat flows: : n₁ = 1, n₂ = q₀₂/q₀₁, n₃ = q₁/q₀₁, n₄ = q₂/q₀₁; ∆ - the upper limit of the integral: ∆ = ψ when 0 ≤ ψ ≤ 1 и ∆ = 1 при ψ > 1; f(ψ_и)- the distribution of the density of heat flow; P = K_оl₁q₁/2λ_д(πР_е)⁰⁵- dimensional factor ;P_e= Vl₁/ω-Peclet number.

Regularities of formation a temperature on the surface of a part (y = 0) during burnishing that occur under the influence of different heat flows are shown in Fig.3

Fig. 3. Diagrams of the temperature distribution on the surface of a part during burnishing

These presented dependences allow to determine the coordinates of the points on the surface of parts with the maximum temperature.

Fig. 4 shows the diagrams of dependence of the maximum temperature of the part Θ_Σmax the radius of the indenter at different values of the efforts of burnishing: P = 100N (curve 1), P = 150N (curve 2) and F = 200N (curve 3).

Fig.4. Diagrams of the maximum temperature of the surface of the part with the radius of the indenter Θ_Σmax r

As one can see from the graphs, for small radii of the indenter and the significant efforts of burnishing, the maximum temperature on the surface of the part is very high and can reach 1000°С. With increasing the radius of the indenter and a reduction of burnishing efforts,the maximum temperature quickly falls, due to improved conditions for heat taking into the indenter and reducing the total quantity of heat.

So the methodology of calculation of heat flows and of temperatures in the processing zone for diamond burnishing has been developed. The effect on heat flows and the temperature parameters of the burnishing - the radius of the indenter and the efforts of burnishing has been analysed, and this allows to manage the thermal condition of the part and to reduce its temperature.

The developed technique can be widely used for other types of finishing and hardening processing of SPD.

Expected practical results

1. Increasing of operational properties by 20-30% when using diamond burnishing.

2. Development of recommendations for the choice of processing parameters during diamond burnishing taking into account the operational properties.

When writing this autosummary master's work was not completed. Completion - December 2009 Full text of the work and materials on the topic can be obtained from the author or his manager after that date.

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