Method of determining friction coefficient between tool and blank

FIELD: plastic metal working.

SUBSTANCE: method comprises calculating the stress-strain condition of the tool and blank with regard for their materials and geometry, plotting a diagram "deformation force - friction coefficient" of the process of plastic deformation, determining experimentally the deformation force, which corresponds to the actual condition of the surfaces of tool, blank, and lubricant, and determining friction coefficient from the diagram.

EFFECT: enhanced accuracy and reduced labor consumption for determining.

3 dwg

 

The invention relates to the processing of metals by pressure and determining the coefficient of friction during plastic deformation of metals and can be used to determine the coefficient of contact friction at the various types of plastic deformation: wire drawing, rolling, forging, etc. and to assess the effectiveness of lubricants in the above-mentioned types of strain.

There is a method of determining the coefficient of friction, namely, that the sample in the form of a ring with applied surface coating is heated and stepped deform the free draught between parallel plates, measure the inner diameter of the ring, after each step new deform the coated sample and build a dependency graph of the diameter of the degree of deformation, and the value of the coefficient of friction is determined by the nomogram [USSR Author's certificate No. 1174835, CL G 01 N 19/02, 1985].

The disadvantage of this method is the complexity of implementation, the need to use to evaluate one material of a large number of the billets, and that sediment rings cannot adequately simulate real processes of metal forming, which significantly reduces the accuracy of determination of coefficient of friction.

There is a method of determining the coefficient of friction materiality loads, exceeding the yield strength by pulling the sample material between two rollers with simultaneous measurement required for this force, which is judged on the coefficient of friction [USSR Author's certificate No. 274449, CL G 01 N 3/56, 1978].

However, the measured force is the sum of the forces required to overcome friction forces and energy required for plastic deformation of the actual workpiece material, which does not allow high precision in the estimate of the coefficient of friction. In addition, this method may not adequately simulate real processes of metal forming.

There is a method of determining the coefficient of friction [USSR Author's certificate No. 783659, CL G 01 N 19/02, 1980], which consists in the fact that the sample applied load, set it's rotation around the axis relative to the fixed contrapasso to measure the friction force and determine the coefficient of friction. To determine the coefficient of friction during plastic deformation using the sample with the working cone angle selected from the conditions obtaining plastic deformation of contrapasso, is applied to the sample an additional burden, allowing it to move along a helical line along the axis of contrapasso, determine the angle of inclination of the helical line, and the coefficient of friction is determined by the formula:

g is e β angle equal to half the operating angle of the cone;

P - force loading;

α - the angle of the helix to the plane perpendicular to the axis of rotation;

F - rotational force.

The disadvantage of this method is the complexity of its execution, the need for accurate measurement of angles after the test, resulting a significant increase in time for its implementation. This method also does not allow to fully simulate the processing of metals by pressure.

The closest in technical essence and the achieved effect of the invention is a method of determining the coefficient of friction during plastic deformation [Friction and lubrication in metal forming. Aphrodi, Uwilling, Vttilq. Ref. Ed. - M.: metallurgy, 1982, s.312, pages 90-91]. The method consists in the fact that in the process of pressing measure acting on the punch force R. figure 1 shows the change of the pressing force during extrusion billet original length l0. To determine the coefficient of friction between the metal and the wall of the container at the steady state extrusion fix two force values P1and R2corresponding to the length of the billet in the container l1and l2.

The coefficient of friction calculated by the formula:

where D is the diameter of the PU is Nana;

σm- longitudinal stress near matrices;

- the average yield strength of the metal;

k - coefficient taking into account the uneven distribution of deformation in the volume of the workpiece, k=D/21+0,1;

p1and R2- pressure on the contact surface of the punch when the length of the billet in the container, respectively, l1and l2.

If the deformation zone covers less than the entire length of the billet (ingot), you should use the formula:

f=(p1-p2)D/[4(p2l1k1-p1l2k2)].

However, this known technical solution has the disadvantage of a rather laborious and lengthy process of determining the coefficient of friction, and is accurate enough, since it is not taken into account the process parameters, such as velocity and strain hardening of the material, heating of the workpiece material and tool in the deformation process. In addition, the coefficient of friction in this method is defined only in the container.

The objective of the invention is to improve the accuracy and reduce the complexity of determining the coefficient of friction during plastic deformation of metals.

The problem is solved in that in the method of determining the coefficient of friction between the tool and the workpiece when the plastic deformirovny the AI metals, namely, in the experimental determination of the force of deformation, unlike the prototype, pre-calculate the stress-strain state of the workpiece and tool with regard to their material and geometric dimensions, calculated data to build the chart “the strength of the deformation coefficient of friction” of the technological process of plastic deformation, then the same process experimentally determine the strength of the deformation corresponding to the actual condition of surfaces of the workpiece and tool and used lubricant, after which obtained earlier chart, the strength of the deformation coefficient of friction, determine the coefficient of friction corresponding to the experimentally obtained value of the force of deformation.

The claimed accuracy of the method depends on the accuracy of the estimated build the chart, the more process factors taken into account when modeling the deformation process, the higher will be the accuracy of determination of coefficient of friction. It is therefore proposed to build the chart according to the calculations made with the help of soft computing systems (STC), such as ANSYS, LS-DYNA, Q-Form and other. Modern software and computer complexes allow to take into account the real dimensions of the workpiece and is the instrument, physico-mechanical properties of a deformable material, strain rate, velocity and strain hardening of the material, heating the blank and tool in the process of plastic deformation, it allows to determine the values of the parameters of the deformation process at any time and in any point of the workpiece during its deformation. All this ensures high accuracy and reliability of the constructed diagrams, “the strength of the deformation coefficient of friction” and the definition of the coefficient of friction.

Figure 1 shows the curve of the change of the pressing force during extrusion billet.

Figure 2 shows a schematic diagram of a device for carrying out the process of drawing.

Figure 3 shows the calculated chart “power lug - coefficient of friction”.

A specific example of implementation of the method

The method is as follows. Originally calculate the stress-deformation state of the workpiece and tool.

For calculation of stress-strain state of the tool (elastic) and blanks (elastoplastic) use a software package ANSYS 5.7 with the following initial data:

- procurement: rod ⊘ 13 mm of steel GR;

- tool: portage of steel R6M5 - elastic body, providing 20%of the fact deformation is s rod when volochine.

From reference [Resistance to plastic deformation of metals and alloys. 2nd ed., Rev. and additional Reference. Polukhin P.I., Gong GY, Galkin A. M., M.: metallurgy, 1983, s.] choose from the following data:

- yield strength steel GR (annealed condition) σof 0.2=245 MPa;

- tensile strength for steel GR σin=540 MPa;

module hardening for steel GEy=50 MPa.

the young's moduli E1=250000 MPa (steel R6M5), and E2=230000 MPa (steel GR);

- Poisson's ratio for both steels adopted the same ν=0,3;

Then selected from the reference data based on the geometry of the tool and the workpiece is processed on the computer using software ANSYS 5.7. Further build on the obtained data chart, “the strength of the deformation coefficient of friction”. Power is drawn in the diagram is a special case of the forces of deformation.

Figure 3 shows the calculated chart “the force of deformation of the friction coefficient”, which includes the following notation: P1- the power drawn using blasting surface preparation of the sample and lubrication “ROSOL-101M”; R2- the power of drawing to use as a lubricant phosphate coating and emiliania; f1f2the coefficients of friction in the case of grobest Inoi preparation of the sample surface and lubrication “ROSOL-101M”, and phosphate coating emiliania respectively.

Using tool, the concept of which is shown in figure 2, containing 1 - fixed capture; 2 - a device for drawing; 3 - sample, 4 - fibrous; 5 - movable grip, carry out the drawing of a sample coated with a lubricating material. Simultaneously record the power lug, marked in figure 2 as R. For different lubricants power drawn under other equal conditions will be different.

Comparing the experimentally obtained values of the strength of drawing and design in a graph of the force of deformation, depending on the coefficient of friction (figure 3), determine the coefficients of friction for various lubricants and the actual condition of surfaces of the workpiece and the tool.

In the diagram (figure 3) shows an example of determining the coefficient of friction when drawing the sample coated with a lubricant. In the case of blasting surface preparation of the sample and lubrication “ROSOL-101M” coefficient of friction equal 0,052, and in the case of use as a lubricant phosphate coating emiliania - 0,069.

Thus, the claimed invention allows to improve the accuracy and reduce the complexity of determining the coefficient of friction during plastic deformation of metals.

The method of determining the ratios are the NTA friction between the tool and the workpiece during plastic deformation of metals, namely, in the experimental determination of the force of deformation, wherein the pre-calculated stress-strain state of the tool and the workpiece based on their material and geometric dimensions, calculated data to build the chart “the strength of the deformation coefficient of friction” of the technological process of plastic deformation, then the same process experimentally determine the strength of the deformation corresponding to the actual condition of surfaces of the workpiece and tool and used lubricant, after which obtained earlier chart, the strength of the deformation coefficient of friction, determine the coefficient of friction corresponding to the experimentally obtained value of the force of deformation.



 

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