RU2557042C2 - Multistage drawing of axially symmetric part from sheet blank at simple-action presses or multiposition automatic press - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to drawing of axially symmetric parts from sheet blanks. Semis are drawn at dies in job-by-job manner, first, at bottom mating that of axially symmetric part to extreme depth and with conical wall. Further jobs include configuring to the shape of axially symmetric part. At final job of drawing, semi-finished product results with wall, shape and sizes corresponding to those of box part with trimming allowances.

EFFECT: higher accuracy of sizes.

10 dwg

Description

The invention relates to sheet stamping and can be used for stamping axisymmetric parts of various configurations from sheet materials, metals and non-metals, mainly for stamping and drawing axisymmetric parts of cars, tractors, agricultural machines, household and other equipment on single-action presses or multi-position automatic presses.

The traditional method of multi-operation drawing of an axisymmetric part from a sheet stock is known, which consists in sequential operation drawing of cylindrical semi-finished products with decreasing diameter and increasing height from operation to operation, and which is described in the following information sources:

1. Romanovsky V.P. Handbook of cold stamping. - L .: Engineering, 1979, p. 121, fig. 103.

2. Forging and stamping: Handbook of 4 tons. T. 4 Sheet stamping. - M.: Mechanical Engineering, 1985-1987, p. 131, Fig. one).

3. Stamp Designer Handbook: Sheet Metal Stamping. Under the total. ed. L.I. Rudman. - M.: Mechanical Engineering, 1988, p. 244, fig. four.

4. Storozhev M.V., Popov E.A. Theory of metal forming. Textbook for high schools. Ed. 4th, rev. and add. M .: Engineering, 1977, p. 374, fig. 8.15.

5. Popov EA Fundamentals of the theory of sheet stamping. Textbook for universities. Ed. 2nd, rev. and add. M .: Engineering, 1977, p. 153, fig. 53.

Moreover, the first method is used as the closest analogue, namely: Romanovsky V.P. Handbook of cold stamping. - L .: Engineering, 1979, p. 121, fig. 103.

The disadvantage of this known traditional method of multioperational drawing of an axisymmetric part is that in the first and all subsequent drawing operations, except the last, the bottom part of the semi-finished products does not match in configuration, and is larger than the bottom part of the axisymmetric part, as a result of which on the wall of the axisymmetric part is elongated at the last operation of the hood, defects remain in the form of bumps and traces of radiusing at the bottom of the semi-finished products, stretched in all previous hoods, the surface quality of the axisymmetric part is deteriorated, and its accuracy is reduced. In production, this drawback with multi-operation drawing of an axisymmetric part leads to a large percentage of stamping defects, an unnecessary increase in the material consumption rate for one part and the cost of manufacturing an axisymmetric part. To eliminate defects, it is necessary to stop the automatic stamping line, refinement and debugging of a set of stamps for hoods and the entire stamping technology of this axisymmetric part, which leads to large production costs.

An object of the invention is to increase the dimensional accuracy of parts obtained by hood on single-acting presses or a multi-position automatic press by using the multi-operation method of extracting an axisymmetric part with a minimum number of drawing operations and saving sheet material from which the sheet stock is made.

The problem is solved due to the fact that in the method of multi-stage drawing of an axisymmetric part from a sheet blank on single-action presses or a multi-position automatic press machine, which includes sequential and step drawing in dies from a sheet of semi-finished products with a configuration from operation to operation approaching the configuration of an axisymmetric part characterized in that in the first operation, drawing in the initial stages form the bottom of the first semi-finished product, corresponding to the bottom of the axisymmetric part, in the subsequent steps, the first semi-finished product with a conical wall is pulled to the maximum depth, without destroying the workpiece, in subsequent drawing operations, the semi-finished products are drawn with the bottom part obtained in the first operation, with a consecutive and operational decrease in the taper angle of the wall of the first semi-finished product, the drawing depth is increased and the configuration semi-finished products from operation to operation are brought closer to the configuration of the axisymmetric part by pushing the conical wall of the semi-finished product into the head matrix MPa by the action of force on the die clamp from the press pad or die buffer, which presses the edge of the semi-finished product to facilitate the drawing process without destroying the semi-finished product, while for each drawing operation, the maximum depth and taper angle of the semi-finished wall are set so that at all stages of the drawing of the sheet blank the maximum increase tensile stress in a dangerous section of the wall of the extruded semi-finished product, and at the final stage - equal to the yield strength of the sheet stock, while on At the final stages of each drawing operation, simultaneously with the hood, the folds are allowed to be smoothed over the entire surface of the semi-finished product, admissible at the previous stages of the hood, and at the last hood operation, the shape and dimensions of the semi-finished product are performed according to the shape and dimensions of the axisymmetric part, taking into account the allowance for trimming the uneven edge of the semi-finished product.

The essence of the new drawing method is characterized by FIG. 1, 2, 3, 4, 5 and 6, in which the main front view shows a section along the axis of the stamp for implementing this method of drawing. In FIG. 1 shows the initial stage of drawing a sheet stock in the first operation: R is the radius of the outer contour of the sheet stock before drawing, r is the radius of the inner contour of the flange of the sheet, r _p is the radius of curvature of the edge of the punch, r _{m, 1} is the radius of curvature of the edge of the matrix, the values of r _p and r _{m, 1} set of reference books and specify when debugging die for drawing, γ ₁ - decreasing from one operation to another angle of taper of the working surface of the punch with respect to the vertical, d _p - internal diameter preset at a manufacturing drawing axially symmetric parts; in FIG. 2 - intermediate i-th stage of the first drawing of the sheet stock to a depth of h _i ; in FIG. 3 - the final stage of the first drawing of the sheet blank 9 into the first semi-finished product 10 with a conical wall and the maximum height, without destroying the blank, the bottom of the first semi-finished product immediately corresponding to the bottom of the axisymmetric part specified in the drawing, and this configuration of the bottom of the first semi-finished product do not change in subsequent operations hoods; in FIG. 4 is an intermediate step of drawing a first semi-finished product in a stamp for a second drawing operation; It is shown how, from a press cushion or a stamp buffer, on a stamp clamp pressing an edge of a semifinished product, a force is generated that pushes the conical wall of the semifinished product into the die matrix during the drawing process and facilitates the drawing process without destroying the semifinished product; in FIG. 5 - the final stage of drawing the second semi-finished product 11 from the first semi-finished product 10; in FIG. 6 - the final stage of the extraction of the third semi-finished product 12 from the second semi-finished product 11 in the stamp for the third drawing operation; in FIG. 7 - sheet blank 9 and semi-finished products 10, 11, 12 with a flange, respectively, after the first, second and third drawing operations; the last semi-finished product 12 after trimming the uneven edge becomes an axisymmetric part and is then used as intended; in FIG. 8 - sheet blank 9 and semi-finished products 10, 11 with a flange and the last semi-finished product 12 without a flange, respectively, after the first, second and third drawing operations; the last semi-finished product 12 after trimming the uneven edge becomes an axisymmetric part and is then used as intended.

The dies for the implementation of each operation of this method of drawing contain the following main working parts: punch 1, die 2 and clamp 3. Punch 1 is mounted on a fixed lower plate of die 4, and matrix 2 is mounted on a movable upper plate 5. Inside die 2 there is a pusher 6 stamped semi-finished product, acting from the pusher 7 using the device stamp or press (not shown). The clamp 3 through the pushers 8 rests on a press pad or a stamp buffer (not shown), which provides the necessary force to compress the flange of the sheet blank and push the conical wall of the previous semifinished product into the die matrix for drawing the subsequent semifinished product.

The method is as follows.

The diameter of the sheet stock is determined from the condition that the area of the middle surface of the axisymmetric part specified in the drawing and the sheet stock is equal, taking into account the allowance for trimming the uneven edge of the semi-finished product after the last drawing operation. Depending on the geometry and production conditions of the axisymmetric part, the blank contour can be simplified, for example, using a square sheet blank with cut or uncut corners.

The coefficient of extraction of the axisymmetric part K, equal to the ratio of the diameter of the workpiece D to the diameter of the median wall surface of the axisymmetric part, is calculated: K = D / (d-s), where d is the outer diameter of the wall of the axisymmetric part, s is the thickness of the axisymmetric part equal to the thickness of the workpiece.

If the coefficient of extraction of the axisymmetric part K is greater than the limiting coefficient of extraction, determined from the reference literature, then a multi-operation hood of the axisymmetric part is designed when the semi-finished product obtained in the previous operation of drawing is used as the initial billet for each subsequent operation of the drawing, and the configuration of the semi-finished products from operation to operation is all approach the configuration of the axisymmetric part. To reduce the number of drawing operations of an axisymmetric part and, thereby, reduce the cost of manufacturing an axisymmetric part, the plastic properties of the workpiece are used to the maximum at each operation, especially in the first drawing operation.

Knowing the shape and dimensions of the axisymmetric part and the sheet billet, in the first approximation, they design the calculation model of the first operation of drawing a semi-finished product with a clamp of a sheet billet, set the drawing depth, the taper angle of the wall of the first semi-finished product and other parameters of the stamp for drawing. The sheet blank 9 (Fig. 1 and 2) is deformed into the first semi-finished product 10 with a conical wall and the limit, without breaking the sheet blank, with a height of H ₁ , and from the sheet blank, the bottom of the first semi-finished product is formed, immediately corresponding to the bottom of the axisymmetric part specified in the drawing, to based on the following engineering analysis of the process of forming sheet blanks.

In the first operation of drawing with pressing the sheet blank, the deformation zone in the drawn semi-finished product is divided into four sections: 1) the first section of the deformation zone is a flange in the form of a circular ring, which is located between the pressing surfaces of the die 2 and the clamp 3 of the stamp and has an outer radius R = D / 2 and the inner radius r, 2) the second section of the deformation zone is the section of the sheet blank in contact with the edge of the matrix, 3) the third section of the deformation zone is the section of the sheet billet that is deformed without impact surface forces in the gap between the punch and the die, 4) the fourth section of the deformation zone is the portion of the sheet blank, the elements of which are curved along the edge of the punch and come into contact with this edge of the punch (Fig. 2). Of these four sections, the main section that has the greatest impact on the risk of destruction of the sheet stock during the drawing process is the first section of the deformation zone in the flange of the sheet stock.

When determining the maximum tensile stress σ _{ρ max} acting in a dangerous, from the point of view of destruction, section of the wall of the extruded semi-finished product, the stress fields in each of the four sections are successively determined, using the equality of the tensile stress at the boundary of adjacent sections as boundary conditions.

At each stage of the drawing, a dangerous section of the wall of the semi-finished product being drawn is at the intersection of this wall with a circular conical surface, at which the vertex lies on the axis of the stamp, and the generatrix passes through the vertex and the contact point of contact of the sheet blank with the edge of the punch perpendicular to the median line of the wall. In a dangerous section opposite this boundary point, the tensile stress from bending the sheet stock along the edge of the punch and the additional tensile stress from the first three sections of the deformation zone also act on the outer elementary layers of the sheet blank, therefore it is these external elementary layers of the sheet blank that first go into the plastic state and then, when the tensile stress reaches the ultimate strength, they will begin to collapse.

Since the drawing process is non-stationary, this process or the stroke of the stamp for drawing is divided into a large number of ix stages, i = 1, 2, 3, ..., N, where the number of stages N is selected depending on the drawing depth and other factors. To determine the stress-strain state (SSS) of each element of the first section of the deformation zone, namely, the flange of the sheet blank, at each stage of drawing, a calculation model of a plane axisymmetric stress state is adopted and a statically determined problem is solved in polar coordinates ρ, θ with a pole on the die axis from two equations with two unknowns σ _ρ and σ _θ, namely, jointly decide known from the theory of plasticity and metal working pressure equilibrium equation _{dσ ρ = - (σ ρ -σ} θ) dρ / ρ and equation plastichnos and σ _ρ -σ _θ = σ _s, where ρ - current radius of the middle surface of the flange element slab: r≤ρ≤R, σ _ρ - tensile stress acting in the element along the radius, σ _θ - compressive stress acting in the element in perpendicular to the tensile stress direction, σ _s is the yield stress increasing due to hardening of the sheet blank. If the die clamp is not flat, but conical, and when the stamp moves between the clamping surfaces of the matrix and the clamp, the conical flange of the workpiece is first formed and only then the central part of the workpiece is pulled by the punch into the die opening, then the curvilinear "x" coordinates are chosen in the calculations - the distance from the on the axis of the stamp the vertices of the middle surface of the conical flange to the workpiece element and θ is the longitude, after which instead of the x coordinate the coordinate ρ = xsinβ is used, where β is the angle between the stamp axis and the generatrix of the middle turn Nost conical flange. After substituting the plasticity equation into the equilibrium equation and integrating the resulting differential equation using the boundary condition that along the contour of the sheet stock with ρ = R, σ _ρ = 0, we obtain a formula for determining the tensile stress σ _ρ as a function of the radius ρ on the flange of the sheet stock: σ _ρ = σ _s ln (R / ρ). According to the last formula, the greatest tensile stress σ _{ρ is} calculated on the inner contour of the flange of the sheet stock of radius ρ = r at the first i-th stage of drawing for i = 1: σ _{ρ = r} = σ _s ln (R / r).

By setting the stroke of the stamp or the drawing depth h _{1, i} at subsequent ix stages of drawing, from the condition that the areas of the middle surfaces known from the geometric constructions of the semifinished product are equal to the initial sheet blank of radius R, the current i-th radius R _{i of the} sheet blank contour is calculated . According to the last formula, the greatest tensile stress σ _{ρ is} calculated on the inner contour of the flange of the sheet stock of radius ρ = r at each ith stretch step: σ _{ρ = r} = σ _s ln (R _i / r).

рассчитывают с учетом упрочнения заготовки по формуле Жаркова В.А.

,

(Жарков В.А. Методология компьютерного проектирования технологических процессов с учетом анизотропии штампуемого материала. - Кузнечно-штамповочное производство. Обработка материалов давлением, 2007, №1, с. 30-42), где предел текучести σ_Т, предел прочности σ_В и относительное равномерное удлинение δ_p определяют по ГОСТ 11701-84 "Металлы. Методы испытаний на растяжение тонких листов и лент". Интенсивность деформаций $$\overline{\epsilon }$$

находят из условия, что на i-м этапе вытяжки радиус R наружного контура листовой заготовки уменьшается до радиуса R_i, а радиус любого выделенного элемента фланца также уменьшается от исходного значения ρ₀ до текущего значения ρ. Из условия равенства площадей полученных двух элементарных круговых колец радиусов R, R_i и ρ₀, ρ сначала находят величину ρ₀, а затем величину

. При вытяжке по мере перемещения контура листовой заготовки ширина фланца, первоначально равная (R-r), постепенно уменьшается. На начальных этапах втягивания фланца листовой заготовки пуансоном в матрицу упрочнение листовой заготовки превалирует над уменьшением ширины фланца и растягивающее напряжение на внутреннем контуре фланца увеличивается. На заключительных этапах втягивания фланца листовой заготовки пуансоном в матрицу уменьшение ширины фланца превалирует над упрочнением листовой заготовки и растягивающее напряжение на внутреннем контуре фланца уменьшается. Значение интенсивности деформаций на внутреннем контуре фланца листовой заготовки радиуса r на i-м этапе вытяжки рассчитывают по последней формуле при ρ=r:

.Yield stress σ _s depending on strain rate $$\overline{\epsilon }$$

calculated taking into account the strengthening of the workpiece according to the formula V. Zharkov

,

(Zharkov V.A. Methodology of computer-aided design of technological processes taking into account the anisotropy of the stamped material. - Forging and stamping. Processing of materials by pressure, 2007, No. 1, pp. 30-42), where the yield strength σ _T , tensile strength σ _B and the relative uniform elongation δ _p is determined according to GOST 11701-84 "Metals. Tensile test methods for thin sheets and tapes." Strain rate $$\overline{\epsilon }$$

find from the condition that at the i-th stage of drawing, the radius R of the outer contour of the sheet blank is reduced to a radius R _i , and the radius of any highlighted flange element also decreases from the initial value ρ ₀ to the current value ρ. From the condition of equality of the areas of the obtained two elementary circular rings of radii R, R _i and ρ ₀ , ρ first find the value ρ ₀ , and then the value

. When drawing as the contour of the sheet blank moves, the width of the flange, initially equal to (Rr), gradually decreases. At the initial stages of retraction of the flange of the sheet blank by the punch into the matrix, the hardening of the sheet blank prevails over a decrease in the width of the flange and the tensile stress on the inner contour of the flange increases. At the final stages of retraction of the flange of the sheet blank by the punch into the matrix, a decrease in the width of the flange prevails over hardening of the sheet blank and the tensile stress on the inner contour of the flange decreases. The value of the strain intensity on the inner contour of the flange of a sheet stock of radius r at the i-th stage of drawing is calculated by the last formula at ρ = r:

.

In the process of drawing and moving the flange of the friction force 2µQ between two surfaces of a sheet blank of thickness s and the pressing surfaces of the matrix and the die clamp, which increase the tensile stress σ _{ρ = r} by the increment Δσ _{ρ, fr} , refer to the circular cross-sectional area on the inner contour of a flange of radius r : 2πrs and get Δσ _{ρ, fr} = µQ / (πrs). Finally, by setting the stamp stroke or the drawing depth h _i at the i-th drawing step and calculating the current i-th radius R _{i of the} sheet blank contour, tensile stress is found at the boundary of the first section of the deformation zone, namely, at the inner contour of the sheet blank flange, taking into account friction forces: σ _{ρ = r} = σ _s ln (R _i / r) + µQ / (πrs), where Q is the pressing force of the flange by pressing the die from the press pad or the buffer of the die, specified in the references and specified when debugging a die for drawing, µ - coefficient of friction, which is taken from the directories depending on t used in the extraction of lubricant, as well as depending on the materials of the sheet stock and the working parts of the stamp for drawing.

, иначе, exp(µα_i), где α_i - увеличивающийся от i-го этапа к (i+1)-му этапу вытяжки угол охвата листовой заготовкой кромок матрицы и пуансона. Влияние спрямления изогнутого элемента при сходе с кромки матрицы учитывают той же поправкой Δσ_ρ=σ_Ts/(4r_m,1+2s). Окончательно, задавая рабочий ход штампа или глубину вытяжки h_1,i на i-м этапе вытяжки и рассчитывая текущий i-й радиус R_i контура листовой заготовки, сначала из геометрических построений определяют угол α_i охвата листовой заготовкой кромок матрицы и пуансона и радиус r_b,1,i границы второго участка очага деформации в месте окончания контакта листовой заготовки с кромкой матрицы, а затем находят растягивающее напряжение, действующее на этой границе второго участка очага деформации:The sheet blank flange element moving to the center, initially adjacent to the inner contour of a flange of radius r, goes to the second section of the deformation zone, bends along the edge of the matrix and moves with friction to the edge of the matrix, and then straightens when it leaves the edge of the matrix and becomes part of the conical wall of the semi-finished product . The effect of the bending of the flange element on the tensile stress σ _{ρ is} evaluated by the bending correction Δσ _ρ = σ _T s / (4r _{m, 1} + 2s), by which σ _{ρ is} gradually increased in the bending zone. The effect of friction of the element during bending along the edge of the matrix is taken into account by the factor

otherwise, exp (µα _i ), where α _i is the angle of coverage of the edges of the matrix and punch by the sheet blank increasing from the i-th stage to the (i + 1) -th stage of drawing. The effect of straightening of a bent element when leaving the edge of the matrix is taken into account with the same correction Δσ _ρ = σ _T s / (4r _{m, 1} + 2s). Finally, by setting the stroke of the stamp or the drawing depth h _{1, i} at the i-th stage of drawing and calculating the current i-th radius R _{i of the} contour of the sheet stock, first, from geometric constructions, determine the angle α _{i of the} sheet edges of the matrix and punch and the radius r _{b, 1, i of the} boundary of the second section of the deformation zone at the end of contact of the sheet blank with the edge of the matrix, and then tensile stress acting on this boundary of the second section of the deformation zone is found:

.To determine the VAT of the third section of the deformation zone in the conical wall of the extruded semi-finished product, it is taken into account that this section is deformed without the influence of surface forces in the gap between the punch and the die, and therefore, as in the case of the flange, the calculated model of plane axisymmetric stressed condition. First, choose the curved coordinates: x is the distance from the top of the conical wall located on the axis of the stamp to the element of the workpiece; θ is the longitude, and then, instead of the x coordinate, the coordinate ρ = xcosα _{i is used} . Then they jointly solve the equilibrium equation dσ _ρ = - (σ _ρ -σ _θ ) dρ / ρ and the plasticity equation σ _ρ -σ _θ = σ _s , where σ _ρ is the stress acting along the conical wall, together with the theories of plasticity and metal forming. Since this third section during drawing is subjected to significantly less plastic deformations than the flange, it is assumed in the plasticity equation that the yield stress σ _s is equal to the yield stress σ _T according to GOST 11701-84. After integrating the obtained differential equation using the boundary condition that at the boundary of the second section of the deformation zone of radius ρ = r _{b, 1, i} , σ _ρ = σ ′ _ρ , a formula is derived for determining the tensile stress σ ″ _ρ as a function of radius ρ in the third section deformation zone:

.

In the fourth section of the deformation zone, the influence of the bending of the sheet blank element along the edge of the punch on the tensile stress is evaluated by the correction for bending Δσ _ρ = σ _T s / (4r _p + 2s), by which σ ″ _ρ is gradually increased in the bending zone.

As a result, the following formula of V. Zharkov is obtained. to determine the maximum tensile stress along the conical wall of the drawn axisymmetric semi-finished product in a dangerous section, which is located at the interface between the semi-finished product and the punch edge at ρ = r _{c, 1, i} (Fig. 2):

At certain stages of the drawing, some terms in the last formula need not be taken into account; for example, at all stages, after the contour of the sheet blank comes out from under the pressure of the stamp, the first and second sections of the deformation zone go into the wall of the drawn semi-finished product, and the corresponding terms need not be taken into account.

From the last formula it is established that the larger the radius r of the inner contour of the flange and, accordingly, the smaller the surface area of the first main portion of the deformation zone in the form of a flange of the sheet blank, the lower the stress σ _{ρ max} . Therefore, by increasing the radius of the aperture of the die matrix for the hood and, accordingly, the radius r of the inner contour of the flange of the sheet stock, instead of the previously unacceptable hood of the semi-finished product with a cylindrical wall, in the first operation, the hood of the semi-finished product with a conical wall that has become valid is carried out in a new way.

Since the VAT of the wall of the extruded semi-finished product in a dangerous section corresponds to the VAT of the sheet sample during tensile testing according to GOST 11701-84, the danger of destruction of the semi-finished product is evaluated by the criterion: the maximum tensile stress calculated in the above formula for the dangerous section of the wall of the extruded semi-finished product at all stages of the extraction should be less than or equal to the yield strength σ _T according to GOST 11701-84, namely:

σ _{ρ max} ≤σ _T.

During drawing, as the contour of the sheet stock moves, the width of the first main portion of the deformation zone, namely the flange, initially equal to (Rr), gradually decreases, while the surface area of the remaining three sections of the deformation zone increases. At the initial stages of retraction of the flange of the sheet blank by the punch into the matrix, the strengthening of the sheet blank prevails over a decrease in the width of the flange and the tensile stress in the dangerous section of the wall of the drawn semi-finished product increases. At the final stages of retracting the flange of the sheet blank with a punch into the matrix, a decrease in the width of the flange may or may not prevail over hardening of the sheet blank, and the tensile stress in the dangerous section of the wall of the drawn semi-finished product may both decrease or increase, depending on the parameters of the hood. Therefore, it is important at all stages of drawing the sheet stock to calculate the maximum tensile stress σ _{ρ max} in the dangerous section of the wall of the extruded semi-finished product using the above formula and compare it with the yield strength σ _T to assess the risk of destruction of the semi-finished product.

The formula for calculating σ _{ρ max is} valid for drawing any axisymmetric semi-finished product with both a cylindrical and a conical wall. In the first drawing operation, comparing the values of σ _{ρ max} in the dangerous section of the drawn semi-finished product with a conical wall, the minimum diameter of which is equal to the diameter of the axisymmetric part specified for manufacturing, according to this new method, and the semi-finished product with a cylindrical wall, the diameter of which is equal to the diameter of the same specified for manufacturing axisymmetric parts, according to the known method, with the same dimensions of the sheet stock and other other equal conditions, conclude that in the first case, according to the new method of drawing a semi-finished product with onicheskoy wall of the value of the maximum tensile σ voltage _{ρ max} is less than or equal to the limit σ _T fluidity and extractor semifinished product without destroying possible, and in the latter case by a known method hoods semi cylindrical wall value σ _{ρ max} greater σ _T, and in the drawing will lead bottom in a dangerous section of the cylindrical wall of the semi-finished product.

When the stress σ _{ρ max} reaches the yield stress σ _T during the drawing process according to the new method, the dangerous section of the semifinished product wall will begin to plastically deform and harden, however, the fracture of the semifinished product will not occur, since the stretching process is stopped. At the same time, such an extension of the semi-finished product, when at the last stage the stress σ _{ρ max} becomes equal to the yield strength σ _T , allows you to make the most of the plastic properties of the sheet stock in the first operation.

Knowing the tensile stress σ _ρ in each element of the deformation zone, the compressive stress σ _{θ is} found from the plasticity equation, which causes a loss of stability of the sections of the sheet blank with the formation of folds. The greatest danger of folding occurs in the first section of the deformation zone, namely on the flange of the sheet blank, therefore, to eliminate such a danger, a clamp is used in the stamp for drawing. The parameters of the hood are determined and refined when debugging a stamp for drawing in such a way that at the initial stages of drawing the folds on the drawn semi-finished product were of such minimum acceptable value that they could be smoothed out between the working surfaces of the die and the punch in the final stages of drawing.

The components of the deformed state of the elements of the deformation zone are calculated using the equations of the relationship between stress and strain known from the theories of plasticity and metal processing.

Thus, by setting, in the first and subsequent approximations, the drawing depth, the taper angle of the wall of the first semi-finished product and other parameters of the first drawing operation and calculating the value of σ _{ρ max} using the above formula, determine the rational parameters of the first operation and the stamp for drawing from the conditions so that the maximum tensile stress σ _{ρ max} in the dangerous section of the wall of the drawn semi-finished product at all stages of drawing the sheet stock gradually increased and at the last stage of drawing became equal to the yield stress σ _T , the drawing depth was extreme — without destroying the workpiece, the edge of the workpiece at the final moment of drawing did not slip out from under the die clamp, if possible — to exclude irreparable folding of the sheet blank, and so that at the final stages of drawing in the extreme lower position of the movable part of the stamp dressing (Fig. 3) of small folds acceptable at the previous stages of drawing along the entire surface of the semi-finished product.

In the second drawing operation, the second semi-finished product is drawn, the first semi-finished product is used after the first drawing operation, the shape and dimensions of the bottom of the first semi-finished product are left unchanged, corresponding to the bottom of the axisymmetric part, the first taper angle γ ₁ of the first semi-finished product wall is reduced to γ ₂ , the drawing depth is increased from the first limit value of H ₁ to the second limit, without destroying the semi-finished product, the values of H ₂ and the configuration of the semi-finished product in this second operation are brought closer to the axisymmetry configuration of the metric part, and from the press pad or the buffer of the stamp on the clamp of the stamp, pressing the edge of the semifinished product, create a force that pushes the conical wall of the semifinished product into the die matrix during the drawing process and facilitates the drawing process without destroying the semifinished product (Fig. 4), at the final stages of drawing simultaneously the hood performs the editing of the folds on the surface of the semi-finished product, the minimum allowable at the previous stages of this operation of the hood (Fig. 5).

The parameters of the second drawing operation are determined by the same methodology developed above for the first drawing operation, based on the following engineering analysis of drawing the first semi-finished product into the matrix in order to draw the second semi-finished product. The deformation zone in the extruded semi-finished product is divided into four sections: 1) a flange in the form of a circular ring that contacts the clamp 3 of the stamp (Fig. 4) and has an outer radius R ₂ and an inner radius r ₂ , where index 2 means operation number n = 2; 2) the section of the semi-finished product, which had a radius r _{m, 1 of the} matrix of the first die for drawing, and now on the second die for drawing, is straightened in the process of drawing to the wall of the semi-finished product increasing in length, and after straightening this second section of the deformation zone between the flange and the conical wall already form new elements of the flange of the sheet stock, bending along the radius r _{m, 2} matrices of this second stamp for drawing; 3) a section of the conical wall that deforms in the gap between the punch and the matrix; 4) a section of the semi-finished product, the elements of which during the drawing process are bent along the edge of the punch and come into contact with this edge of the punch.

When determining the maximum tensile stress σ _{ρ max} acting in a dangerous, from the point of view of destruction, section of the drawn semi-finished product, which is located at the interface between the drawn semi-finished product and the edge of the punch, the stress fields are successively determined in each of the four sections of the deformation zone, using boundary conditions equality of radial stresses at the boundary of adjacent sections.

, фиг. 5.Since the drawing process is non-stationary, this process or the stroke of the stamp for drawing is divided into a large number of ix stages, i = 1, 2, 3, ..., N, where the number of stages N is selected depending on the drawing depth and other factors. To determine the VAT of each element of the first section of the deformation zone, namely, the semifinished product flange, at each extraction stage, the same as above for the first extraction operation is adopted, the calculation model of the plane axisymmetric stress state and solve a statically determinable problem of two equations with two unknowns σ _ρ and σ _θ , in particular, jointly solve the equilibrium equation dσ _ρ = - (σ _ρ -σ _θ ) dρ / ρ and the plasticity equation σ _ρ -σ _θ = σ _s , where ρ is the current radius flange element semi-finished product, σ _s - yield stress. After integrating the obtained differential equation using the boundary condition that along the contour of the semi-finished product with ρ = R _{2, i} , σ _ρ = 0, we obtain the formula for determining the tensile stress σ _ρ as a function of the radius ρ on the semi-finished product flange: σ _ρ = σ _s ln ( R _{2, i} / ρ). According to the last formula, the greatest tensile stress σ _{ρ is} calculated on the inner contour of the semifinished product flange of radius r ₂ at the last drawing stage:

FIG. 5.

.By setting the stroke of the stamp or the drawing depth h _{2, i} at the next ix stages of drawing, from the condition that the areas of the middle surfaces known from the geometric constructions of the second semi-finished product are equal to the previous first semi-finished product, the current ith radius R _{2, i of the} contour decreases from stage to stage second semi-finished product. According to the last formula, the greatest tensile stress σ _{ρ is} calculated at the boundary of the first section of the deformation zone, namely, on the inner contour of the flange of the drawn second semi-finished product of radius r _{2, i} at each ith stretch stage:

.

.The yield stress σ _s , taking into account the strengthening of the semi-finished product during the drawing process, is determined by the above formula of VA Zharkov, in which the value of the strain intensity on the inner contour of the semi-finished product flange of radius r ₂ at the ith stage of the drawing is calculated at ρ = r ₂ :

.

In the second section of the deformation zone, which had a radius r _{m, 1 of the} matrix of the first die for drawing, and now on this second stamp for drawing, it is straightened into the conical wall of the semi-finished product increasing in length during drawing, and after straightening this second section of the deformation zone between the flange and the conical wall form already new elements of the flange of the sheet blank, bending along the radius r _{m, 2} matrices of this second stamp for drawing, the effect of the bending of the semi-finished elements on the tensile stress σ _{ρ is} evaluated the correction for bending Δσ _ρ = σ _T s / (4r _{m, 2} + 2s), by which stepwise increase σ _ρ at the boundary of this section of radius r _{b, 2, i} :

.

.

, выводят формулу для определения растягивающего напряжения σ″′_ρ в функции радиуса ρ на третьем участке очага деформации:To determine the VAT of the third section of the deformation zone in the conical wall of the extruded semi-finished product, it is taken into account that this section is deformed without the influence of surface forces in the gap between the punch and the die, and therefore, as in the case of the flange, the calculated model of plane axisymmetric stressed states and together solve the equilibrium equation dσ _ρ = - (σ _ρ -σ _θ ) dρ / ρ and the plasticity equation σ _ρ -σ _θ = σ _s known from theories of plasticity and metal forming. Since this third section of the deformation zone during drawing is subjected to significantly less plastic deformations than the flange, it is assumed in the plasticity equation that at all stages of drawing the yield stress σ _s is equal to the yield stress σ _T according to GOST 11701-84. After integrating the obtained differential equation using the boundary condition, that at the ith stage of drawing at the boundary of the second section of the deformation zone of radius ρ = r _{b, 2, i} ,

, derive a formula for determining the tensile stress σ ″ ′ _ρ as a function of radius ρ in the third section of the deformation zone:

.

.

In the fourth section of the deformation zone, the influence of the bending of the sheet blank element along the edge of the punch on the tensile stress is evaluated by the correction for bending Δσ _ρ = σ _T s / (4r _p + 2s), by which σ ″ ′ _ρ is gradually increased in the bending zone.

As a result, the following formula of V. Zharkov is obtained. to determine at the ith stage of the second drawing the maximum tensile stress along the conical wall of the drawn axisymmetric semi-finished product in a dangerous section that passes through the contact border of the semi-finished product with the punch edge at ρ = r _{c, 2, i} (Fig. 4):

.

.

At certain stages of the drawing, some terms in the last formula need not be taken into account; for example, in the last operation of drawing a cylindrical part with a vertical wall at all stages, after the formation of the vertical wall of the part, the bending of the semifinished product along the edge of the punch no longer occurs, and the last term does not need to be taken into account.

Since the VAT of the wall of the extruded second semi-finished product in a dangerous section corresponds to the VAT of the sheet sample during tensile testing according to GOST 11701-84, the danger of destruction of the semi-finished product is evaluated by the criterion: the maximum tensile stress calculated in the above formula in the dangerous section of the wall of the drawn semi-finished product at all stages of the drawing must be less than or equal to the yield strength σ _T according to GOST 11701-84, namely: σ _{ρ max} ≤σ _T. Knowing the tensile stress σ _ρ in each element of the deformation zone, the compressive stress σ _{θ is} found from the plasticity equation, which causes a loss of stability of the semi-finished product sections with the formation of folds. The parameters of the hood are determined and refined when debugging a stamp for drawing in such a way that at the initial stages of drawing the folds on the drawn semi-finished product were of such minimum acceptable value that they could be smoothed out between the working surfaces of the die and the punch in the final stages of drawing.

Thus, by setting, in the first and subsequent approximations, the drawing depth, the taper angle of the wall of the second semi-finished product and other parameters of the second drawing operation and calculating the value of σ _{ρ max} using the above formula, determine the rational parameters of the second operation and the stamp for drawing from the conditions so that the maximum tensile stress σ _{ρ max} in the dangerous section of the wall of the drawn semi-finished product at all stages of the drawing was less than or equal to the yield strength σ _T , the drawing depth was ultimate - without breaking the workpiece, not about an unrecoverable folding of the semi-finished product was created, and so that at the final stages of drawing in the lowermost position of the movable part of the stamp, dressing (Fig. 5) of small folds allowed at the previous stages of drawing was made over the entire surface of the semi-finished product.

Similarly, in all subsequent nth drawing operations, the taper angle γ _n of the prefabricated wall is successively and stepwise reduced in stamps, the drawing depth H _{n is} increased, the configuration of the semi-finished products is transferred from operation to operation to the configuration of an axisymmetric part, and the maximum tensile stress σ is calculated using the above formula _{ρ max} in the dangerous section wall drained semifinished all drawing stages and compared with the yield point σ _T slab to avoid destruction Semis that, and from the press pad or the buffer of the stamp on the clamp of the stamp pressing the edge of the semifinished product, create a force pushing the wall of the semifinished product into the die matrix during the drawing process and facilitating the drawing process without destroying the semifinished product, at the end stages of each drawing operation, wrinkles are also straightened out on the surface of the semi-finished product, minimally acceptable at the previous stages of this operation, hoods. If at the nth operation at the ith stage of drawing, the stress σ _{ρ max} in the dangerous section of the wall of the drawn semi-finished product is greater than the yield strength σ _T , then the drawing parameters are changed so that the stress σ _{ρ max} becomes equal to the yield stress σ _T.

In the last operation of drawing, the shape and dimensions of the semi-finished product are performed corresponding to the shape and dimensions of the axisymmetric part, taking into account the allowance for trimming the uneven edge of the semi-finished product, at the final stages of drawing, at the same time as the hood, they also make folds on the surface of the semi-finished product, which are minimally acceptable at the previous stages of drawing (Fig. 6) . As a result, the number of drawing operations specified for the manufacture of an axisymmetric part is determined.

Starting from the second drawing operation, in all drawing operations from the press cushion or the stamp buffer on the die clamp pressing the edge of the semifinished product, a force is created that forces the conical wall of the semifinished product to be pushed into the die matrix during the drawing process and facilitates the drawing process without destroying the semifinished product; this reduces the number of drawing operations and, accordingly, reduces the number of dies for drawing. By reducing the number of dies for drawing, the vacant positions on the same multi-position automatic press, on which the axisymmetric part is stamped using this new method, are used to stamp other parts, increasing labor productivity in production.

In FIG. 7 shows a sheet blank 9 and semi-finished products 10, 11 and 12 with a flange, respectively, after the first, second and third drawing operations; the last semi-finished product 12 after trimming the uneven edge either becomes a part with a flange, or after an additional operation of drawing only one flange, it becomes a part without a flange and then it is used as intended. With multi-operation extraction of an axisymmetric part on a multi-position automatic press, the semi-finished products at each position are not pulled to the end, but a small flange is left, as shown in FIG. 7, providing smooth transfer of the semi-finished product with a clamshell mechanism from position to position.

In FIG. 8, as a variant of this method, a sheet blank 9 and semi-finished products 10, 11 with a flange and the last semi-finished product 12 without a flange, respectively, are shown after the first, second and third drawing operations; the last semi-finished product 12 after trimming the uneven edge becomes a part and is then used as intended.

A new method of multioperational drawing is applicable for drawing axisymmetric parts of various configurations. In FIG. 9, as an option, an image of a multi-operation hood using this method of an axisymmetric part with a flange is shown, which, in the last n-th operation of the hood, is stamped with a conical wall, as shown in Fig. 10, so that after stamping, axisymmetric parts are inserted one into another for ease of transportation.

Due to the use of the multi-operation method of drawing high-axisymmetric parts from a sheet blank on single-action presses or a multi-position automatic press, the dimensional accuracy of the obtained axisymmetric parts with a smaller number of drawing operations is increased in comparison with the known method, and the surface quality is also improved, which affects to reduce the percentage of rejects in production and the consumption rate of sheet material, and in general the cost of manufacturing an axisymmetric part.

Claims (1)

A method of multi-stage drawing of an axisymmetric part from a sheet blank in a stamp on a single-action press or multi-position automatic press, comprising sequential and step-by-step drawing from a sheet of semi-finished products with a configuration from operation to operation approaching the configuration of an axisymmetric part, characterized in that in the first drawing operation in the initial stages, form the bottom of the first semi-finished product, corresponding to the bottom of the axisymmetric part, in the subsequent stages, the first semi-factory is pulled with a conical wall to the limit, without destroying the workpiece, the depth, in subsequent drawing operations, the semi-finished products are drawn with the bottom part obtained in the first operation, with a sequential and operational decrease in the taper angle of the wall of the first semi-finished product, the drawing depth is increased and the configuration of the semi-finished products is brought closer to the operation to the configuration of the axisymmetric part by pushing the conical wall of the semi-finished product into the die matrix by the action of force on the die clamp from the pillow essa or buffer stamp, pressing the edge of the semi-finished product to facilitate the drawing process without destroying the semi-finished product, while for each drawing operation, the maximum depth and the taper angle of the wall of the semi-finished product is specified from the condition that at all stages of the drawing of the sheet stock the gradual increase in the maximum tensile stress in the dangerous section of the wall of the drawn semi-finished product , and at the final stage - equality of the yield strength of the sheet stock, while at the final stages of each drawing operation simultaneously o with the hood, the folds allowed at the previous stages of the hood are carried out on the entire surface of the semi-finished product, and in the last operation of the hood, the shape and dimensions of the semi-finished product are performed in the corresponding shape and dimensions of the axisymmetric part, taking into account the allowance for cutting the uneven edge of the semi-finished product.

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