A method for optimizing a chip rest angle of a dry cutting hobbing machine tool

Abstract

The application discloses a kind of dry cutting hobbing machine tool chip rest angle optimization design methods, first, according to the geometric structure and space layout features of dry cutting hobbing machine tool, the mathematical representation model of chip rest angle is established;Second, the feature parameter of rest angle model is determined in combination with the workbench structural features of dry cutting hobbing machine tool and the flow rule of chip;Then, with the minimum heat accumulation of workbench as control target, with the top adjusting distance and bottom adjusting distance of workbench as regulation and control variable, with the gap between workbench and its cover and the distance between workbench cover and machine tool inner baffle as constraint condition, the chip rest angle optimization model of dry cutting hobbing machine tool is established;Finally, by using genetic algorithm, the chip rest angle optimization model is solved in the value range of regulation and control variable, and the optimal chip rest angle is obtained.The application can effectively reduce the accumulation and residence time of high-temperature chip on the workbench, thereby reducing the thermal deformation of the workbench, and finally improving the gear machining precision.

Description

Technical Field

[0001] This invention relates to the field of metal cutting machine tool technology, and in particular to a method for optimizing the chip repose angle of a dry gear hobbing machine. Background Technology

[0002] Dry hobbing machines are a type of green and advanced gear processing machine tool, boasting advantages such as high production efficiency, low unit cost, and minimal environmental pollution. However, during operation, the high-speed hobbing motion of the cutter and workpiece, coupled with the lack of cutting oil for cooling and lubrication, causes the temperatures of the cutter, workpiece, and chips to rise rapidly. In dry hobbing, chips are the primary heat transfer medium, carrying away over 80% of the cutting heat. Therefore, quickly removing chips from the machine tool is a crucial measure to reduce thermal deformation of dry hobbing machines.

[0003] During chip removal, the chips first detach from the cutting contact area, then fall onto the outer cover of the worktable under the influence of gravity and friction, finally sliding on the cover and entering the chip conveyor. If the chip repose angle (the angle between the inclined surface of the worktable cover and the horizontal plane of the worktable) is inappropriate, it will hinder rapid chip removal and easily lead to chip accumulation on the worktable. The continuously accumulating high-temperature chips continuously transfer heat to the worktable, and excessive heat accumulation will inevitably cause thermal deformation of the worktable, ultimately affecting the gear machining accuracy.

[0004] However, the chip repose angle of existing dry gear hobbing machines is usually designed based on subjective experience, lacking a systematic quantitative design method, especially an optimization design method that considers minimizing heat accumulation on the worktable. Therefore, how to reduce the accumulation and residence time of high-temperature chips on the worktable through optimized chip repose angle design, thereby reducing thermal deformation of the worktable, is a problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the purpose of this invention is to provide a chip repose angle optimization design method for dry gear hobbing machines. By optimizing the chip repose angle, the accumulation and residence time of high-temperature chips on the worktable are reduced, thereby reducing the problem of thermal deformation of the worktable.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] A method for optimizing the chip repose angle of a dry gear hobbing machine includes:

[0008] S1. Establish a mathematical model for the chip repose angle. Specifically, based on the geometric structure and spatial layout characteristics of the dry hobbing machine, establish a mathematical representation model for the chip repose angle.

[0009] S2. Determine the characteristic parameters of the angle of repose model, specifically combining the table structure characteristics of the dry hobbing machine and the flow law of the chips, to determine the chip fall time, chip residence time, and contact area between the chips and the table.

[0010] S3. Establish an optimization model for the chip repose angle. Specifically, the goal is to minimize the heat accumulation of the worktable. The adjustment distances at the top and bottom of the worktable are used as control variables. The clearance between the worktable and its outer cover, as well as the distance between the worktable outer cover and the inner baffle of the machine tool, are used as constraints.

[0011] S4. Determine the optimal chip repose angle. Specifically, use an intelligent algorithm to solve the chip repose angle optimization model within the range of values ​​of the control variables to obtain the optimal chip repose angle.

[0012] Furthermore, the mathematical model for the chip repose angle α established in step S1 is as follows:

[0013]

[0014] In the formula, x t Top adjustment distance: the horizontal movement distance of the upper end of the worktable cover from its original position; x b The bottom adjustment distance is: the horizontal movement distance of the lower end of the worktable cover from its original position; h2 is the height of the lower section of the worktable; R t R b These are the distances from the upper and lower ends of the workbench cover to the central axis of the workbench, respectively.

[0015] Preferably, in step S2, the chip falling time t f The time taken for the chip to detach from the workpiece and just before contacting the outer cover of the worktable is expressed as follows:

[0016]

[0017] In the formula, h is the total tooth height of the workpiece, and d a V is the outer diameter of the workpiece. 0x V 0z V represents the components of the initial chip velocity in the horizontal and vertical directions, respectively. 0x =V0cosγ,V 0z =V0sinγ; V0 is the initial velocity of the falling chip, V0 = πn h r h / 30; g is the acceleration due to gravity; μ is the surface friction coefficient of the worktable cover; h1 is the height of the upper part of the worktable; n h r is the hob rotation speed. h γ is the hob radius; γ is the chip flow angle.

[0018] Furthermore, in step S2, the residence time t of the chip... r The time it takes for the chips to roll off the surface of the worktable after contacting it is expressed as follows:

[0019]

[0020] In the formula, V is the magnitude of the velocity of the chip along the inclined plane at the instant it contacts the outer cover of the worktable, V = V 0x cosα+(V 0z +gt f sinα;

[0021] In step S2, the contact area between the chip and the worktable is defined by the contact length l between the hob and the workpiece. w And the length l of the chips rolling off the worktable cover r It was jointly determined that:

[0022]

[0023]

[0024] Furthermore, step S3 includes:

[0025] S31, Establish the objective function for the chip repose angle optimization design, namely:

[0026]

[0027] In the formula, n is the number of chips generated during machining a single gear; k is the number of gears machined by the machine tool in one machining period; ε is the thermal conductivity of the worktable cover; w is the contact width between the chip and the worktable cover; T c T represents the chip temperature. s δ represents the temperature of the workbench cover; δ represents the thickness of the workbench cover.

[0028] S32, Determine the constraints. Specifically, considering that the heat transfer properties of metallic materials are generally stronger than those of air, the outer cover of the workbench should not be in direct contact with the workbench to minimize heat accumulation on the workbench. Therefore, a certain distance l1 should be maintained between the outer cover of the workbench and its internal structure, i.e.:

[0029] h3x t +(h2-h3)x b ≥(R b -R t )h3+(R2+l1-R b h2

[0030] In the formula, R2 represents the structural parameters of the worktable of the dry gear hobbing machine.

[0031] To ensure that the outer cover of the dry hobbing machine's worktable can guide the chip flow and allow the chips to be quickly discharged from inside the machine, the variable x is adjusted. t The range of values ​​for is as follows:

[0032] R1-R t ≤x t ≤l t +R1-R t

[0033] In the formula, R1 represents the structural parameters of the dry gear hobbing machine table;

[0034] To ensure that chips do not impact the machine tool's inner baffle, which primarily prevents cutting heat from being transferred to other machine tool components, the distance between the outer cover and the inner baffle should be greater than zero, thereby controlling the variable x. b The range of values ​​for is as follows:

[0035]

[0036] In the formula, h3 represents the structural parameters of the worktable of the dry gear hobbing machine.

[0037] S33, Establish an optimization model for the chip repose angle, namely:

[0038] F(x t ,x b )=inQ total

[0039]

[0040] Furthermore, step S4 includes:

[0041] S41, Determine the range of values ​​for the control variable, specifically based on the structural parameters of the dry gear hobbing machine's worktable;

[0042] S42, to find the optimal control parameters, specifically by using a genetic algorithm to solve for the optimal control parameters that satisfy the optimization objective function;

[0043] S43, determine the optimal chip rest angle by substituting the optimal control variable into the mathematical representation model of the chip rest angle to obtain the optimal chip rest angle.

[0044] Compared with the prior art, the present invention has the following beneficial effects:

[0045] 1. This invention establishes an optimization model for the chip repose angle of a dry gear hobbing machine, providing a quantitative basis for the design of the chip repose angle, which helps to avoid the problem of poor chip removal effect caused by empirical design.

[0046] 2. The present invention takes minimizing heat accumulation on the worktable as the optimization control objective. While ensuring efficient chip removal from the dry hobbing machine, it can effectively reduce the residence time and quantity of high-temperature chips on the worktable, which is conducive to reducing thermal deformation of the worktable and thus improving gear machining accuracy.

[0047] 3. By optimizing the chip repose angle, this invention can also reduce the spindle skewness of the worktable, which is beneficial to improving the machining accuracy of dry hobbing machines and thus improving the machining quality of gears. Attached Figure Description

[0048] Figure 1 This is a flowchart illustrating a specific implementation of the present invention;

[0049] Figure 2 Diagram of the chip repose angle model;

[0050] Figure 3 This is a schematic diagram of the chip flow angle;

[0051] Figure 4 The heat-affected zone of the workbench cover under high-temperature cutting action;

[0052] Figure 5 The adjustment range for the chip repose angle of the worktable;

[0053] Figure 6 This is a diagram illustrating the implementation effect of the present invention. Detailed Implementation

[0054] To make the purpose, technical solution, and advantages of the invention clearer, the invention will now be described in further detail with reference to the accompanying drawings.

[0055] See Figure 1 The present invention provides a method for optimizing the chip repose angle of a dry gear hobbing machine, comprising the following steps:

[0056] S1. Establish a mathematical model for the chip repose angle. Specifically, based on the geometric structure and spatial layout characteristics of the dry hobbing machine, establish a mathematical representation model for the chip repose angle.

[0057] S2. Determine the characteristic parameters of the angle of repose model, specifically combining the table structure characteristics of the dry hobbing machine and the flow law of the chips, to determine the chip fall time, chip residence time, and contact area between the chips and the table.

[0058] S3. Establish an optimization model for the chip repose angle. Specifically, the goal is to minimize the heat accumulation of the worktable. The adjustment distances at the top and bottom of the worktable are used as control variables. The clearance between the worktable and its outer cover, as well as the distance between the worktable outer cover and the inner baffle of the machine tool, are used as constraints.

[0059] S4. Determine the optimal chip repose angle. Specifically, use an intelligent algorithm to solve the chip repose angle optimization model within the range of values ​​of the control variables to obtain the optimal chip repose angle.

[0060] Compared with existing technologies, this invention establishes an optimized chip repose angle model for dry hobbing machines based on the flow characteristics of chips during dry hobbing, thereby achieving quantitative analysis of the chip repose angle. Simultaneously, the chip repose angle determined by the model reduces heat accumulation on the dry hobbing machine's worktable, optimizing the temperature distribution of the worktable and reducing the thermal deformation of the worktable spindle.

[0061] For a better explanation of the embodiments of the present invention, please refer to Figure 2 , Figure 2 The chip repose angle model diagram is based on the above embodiment:

[0062] The mathematical model for the chip repose angle α established in S1 provided by this invention is as follows:

[0063]

[0064] In the formula, x t The top adjustment distance (i.e., the horizontal movement distance of the upper end of the worktable cover from its original position) is in mm; x b h1 is the bottom adjustment distance (i.e., the horizontal movement distance of the lower end of the worktable cover from its original position), mm; h2 is the height of the lower section of the worktable, mm; R t R b These are the distances from the upper and lower ends of the worktable cover to the central axis of the worktable, respectively, in mm;

[0065] In the formula, x t x represents the horizontal distance the upper end of the workbench cover moves from its original position, in mm; b h1 represents the horizontal movement distance of the lower end of the workbench cover from its original position, in mm; h2 represents the height of the lower section of the workbench, in mm; R t R b These are the distances, in mm, from the upper and lower ends of the worktable cover to the center axis of the worktable.

[0066] For a better explanation of the embodiments of the present invention, please refer to Figure 3 , Figure 4 , Figure 3 This is a schematic diagram of the chip flow angle. Figure 4 The heat-affected zone of the workbench cover under high-temperature cutting action is based on the above embodiments:

[0067] In S2 provided by the present invention, the chip falling time t f(The time it takes for the chip to detach from the workpiece and just before contacting the outer cover of the worktable) can be expressed as follows:

[0068]

[0069] In the formula, h is the total tooth height of the workpiece, in mm, and d... a V represents the outer diameter of the workpiece, in mm. 0x V 0z Let V be the components of the initial chip velocity in the horizontal and vertical directions, respectively, in m / s and V. 0x =V0cosγ,V 0z =V0sinγ; V0 is the initial velocity of the falling chip, m / s, V0 = πn h r h / 30; g is the acceleration due to gravity, 10 m / s². 2 μ is the surface friction coefficient of the worktable cover; h1 is the height of the upper part of the worktable, mm; n h R is the hob rotation speed, in r / min; h γ is the hob radius, in mm; γ is the chip flow angle.

[0070] In S2, the residence time t of the chip r (i.e., the time it takes for the chips to roll off the surface of the worktable after contacting it) can be expressed as follows:

[0071]

[0072] In the formula, V is the magnitude of the velocity of the chip along the inclined plane at the instant it contacts the outer cover of the worktable, V = V 0x cosα+(V 0z +gt f sinα, m / s;

[0073] In step S2, the contact area between the chip and the worktable is defined by the contact length l between the hob and the workpiece. w And the length l of the chips rolling off the worktable cover r It was jointly determined that:

[0074]

[0075]

[0076] For a better explanation of the embodiments of the present invention, please refer to Figure 5 , Figure 5 The adjustment range for the chip repose angle of the worktable is based on the above embodiments:

[0077] S3 provided by the present invention includes:

[0078] S31, Establish the objective function for the chip repose angle optimization design, namely:

[0079]

[0080] In the formula, n is the number of chips generated during machining a single gear; k is the number of gears machined by the machine tool in one machining period; ε is the thermal conductivity of the worktable cover, W / (m·℃); w is the contact width between the chip and the worktable cover, mm; T c T represents the chip temperature, in °C. s δ represents the temperature of the workbench cover, in °C; δ represents the thickness of the workbench cover, in mm.

[0081] S32, Determine the constraints, the control constraints include the gap between the worktable and its outer cover, and the distance between the worktable outer cover and the machine tool inner baffle, etc.

[0082] Considering that the heat transfer properties of metals are generally stronger than those of air, the outer cover of the workbench should not be in direct contact with the workbench to minimize heat accumulation on the workbench. Therefore, a certain distance l1 should be maintained between the outer cover of the workbench and its internal structure, i.e.:

[0083] h3x t +(h2-h3)x b ≥(R b -R t )h3+(R2+l1-R b h2

[0084] In the formula, R2 is the structural parameter of the dry gear hobbing machine table, in mm.

[0085] To ensure that the outer cover of the dry hobbing machine's worktable can guide the chip flow and facilitate rapid chip removal from the machine's interior, the following should be ensured: t >0, meaning there is a gap between points A1 and A2. The control variable x t The length of the control interval l t It can be obtained through the following formula, and x can be obtained. t The range of values ​​for;

[0086]

[0087] R1-R t ≤x t ≤l t +R1-R t

[0088] In the formula, R1 is the structural parameter of the dry gear hobbing machine table, in mm.

[0089] To ensure that chips do not impact the machine tool's inner baffle (which is mainly used to prevent cutting heat from being transferred to other parts of the machine tool), the distance l2 between the outer cover and the inner baffle should be greater than zero. Simultaneously, x is determined based on points A2 and P2. b The right boundary of the control range, point Q;

[0090] Regulation variable x b The length of the control interval l b The following formula can be used to calculate x, and x can be obtained. b The range of values ​​for;

[0091]

[0092]

[0093] In the formula, h3 is the structural parameter of the worktable of the dry gear hobbing machine, mm, and l3 is the initial distance between the outer cover of the worktable and the inner baffle, mm;

[0094] S33, Establish an optimization model for the chip repose angle, namely:

[0095] F(x t ,x b )=inQ total

[0096]

[0097] After establishing the above model, the optimal x is solved using a genetic algorithm. t and x b The value of x, then t and x b Substituting the optimal solution into the mathematical representation model of the chip repose angle α, the optimal chip repose angle can be obtained.

[0098] As a preferred embodiment, S4 provided by the present invention includes:

[0099] S41, Determine the range of values ​​for the control variable, specifically based on the structural parameters of the dry gear hobbing machine's worktable;

[0100] S42, to find the optimal control parameters, specifically by using a genetic algorithm to solve for the optimal control parameters that satisfy the optimization objective function;

[0101] S43, determine the optimal chip rest angle by substituting the optimal control variable into the mathematical representation model of the chip rest angle to obtain the optimal chip rest angle.

[0102] To verify the effectiveness of this invention, the method disclosed herein was applied to the machining of a reverse gear in an automobile on a dry hobbing machine, and a simulation experiment was conducted. The structural parameters of the worktable were obtained by consulting the machine tool design manual. The spindle speed of the dry hobbing cutter was 670 r / min, the axial feed rate was 1.6 mm / r; the hob diameter was 80 mm, the number of hob heads was 2; the workpiece module was 2 mm, and the number of teeth was 36. The machining time for one gear was 63 s (hobbing time was 48 s, auxiliary time was 15 s). The ambient temperature in the workshop was 22℃, which is also the initial temperature T of the worktable cover. s The temperature is 22℃. The value of n is determined by the ratio of the change in mass of a single gear before and after machining to the average mass of a single chip. The value of w is determined by combining the contact characteristics between the chip and the worktable cover. The chip temperature T is... c It is the average value obtained by taking multiple photos using an infrared thermal imager.

[0103] Based on this, the objective function and constraints of the above-mentioned angle of repose optimization model were written into an optimization calculation program based on a genetic algorithm. Finally, x was obtained. t x b The optimal values ​​are -10.0 mm and 5.7 mm, respectively. Substituting these values ​​into the mathematical model for the chip repose angle α, we obtain the optimized chip repose angle α. opt It is 55.31°.

[0104] Furthermore, a dry gear hobbing simulation experiment was conducted using finite element analysis software. Through geometric modeling of the worktable, mesh generation, process parameter settings, and post-processing, temperature change contour maps and thermal deformation contour maps of the worktable were obtained. By comparing the temperature field and thermal deformation before optimization, it was found that the maximum temperature and maximum thermal deformation of the worktable both decreased. (See [link to relevant documentation]). Figure 6 As shown, the optimized design of the chip repose angle of the worktable, taking into account the heat transfer effect of high-temperature chips on the worktable, reduces the maximum temperature and maximum thermal deformation of the worktable, which is beneficial to improving the machining accuracy of gears.

[0105] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described with reference to preferred embodiments, those skilled in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A method for optimizing the chip repose angle of a dry gear hobbing machine, characterized in that, include: S1. Establish a mathematical model for the chip repose angle. Specifically, based on the geometric structure and spatial layout characteristics of the dry hobbing machine, establish a mathematical representation model for the chip repose angle. S2. Determine the characteristic parameters of the angle of repose model, specifically combining the table structure characteristics of the dry hobbing machine and the flow law of the chips, to determine the chip fall time, chip residence time, and contact area between the chips and the table. S3. Establish an optimization model for the chip repose angle. Specifically, the goal is to minimize the heat accumulation of the worktable. The adjustment distances at the top and bottom of the worktable are used as control variables. The gap l1 between the worktable and its outer cover and the distance l2 between the worktable outer cover and the inner baffle of the machine tool are used as constraints. S4. Determine the optimal chip repose angle. Specifically, use an intelligent algorithm to solve the chip repose angle optimization model within the range of values ​​of the control variables to obtain the optimal chip repose angle. The mathematical model for the chip repose angle α established in step S1 is as follows: ； In the formula, x t Top adjustment distance: the horizontal movement distance of the upper end of the worktable cover from its original position; x b The bottom adjustment distance is: the horizontal movement distance of the lower end of the worktable cover from its original position; h2 is the height of the lower section of the worktable; R t R b These are the distances from the upper and lower ends of the workbench cover to the central axis of the workbench, respectively. In step S2, the chip falling time t f The time taken for the chip to detach from the workpiece and just before contacting the outer cover of the worktable is expressed as follows: ； In the formula, h is the total tooth height of the workpiece, and d a V is the outer diameter of the workpiece. 0x V 0z V represents the components of the initial chip velocity in the horizontal and vertical directions, respectively. 0x =V0cosγ,V 0z =V0sinγ; V0 is the initial velocity of the falling chip. g is the acceleration due to gravity; h1 is the height of the upper part of the worktable; n h r is the hob rotation speed. h γ is the hob radius; γ is the chip flow angle. In step S2, the residence time t of the chip r The time it takes for the chips to roll off the surface of the worktable after contacting it is expressed as follows: ； In the formula, V is the magnitude of the velocity of the chip along the inclined plane at the instant it contacts the outer cover of the worktable. μ is the surface friction coefficient of the worktable cover; In step S2, the contact area between the chip and the worktable is defined by the contact length l between the hob and the workpiece. w And the length l of the chips rolling off the worktable cover r It was jointly determined that: ； 。 2. The chip repose angle optimization design method for dry gear hobbing machine tools as described in claim 1, characterized in that, Step S3 includes: S31, Establish the objective function for the chip repose angle optimization design, namely: Optimmize Q total = ; In the formula, Q total ε is the heat accumulation on the dry gear hobbing machine table; n is the number of chips generated during machining a single gear; k is the number of gears machined by the machine in one machining cycle; ε is the thermal conductivity of the table cover; w is the contact width between the chip and the table cover; T c T represents the chip temperature. s δ represents the temperature of the workbench cover; δ represents the thickness of the workbench cover. S32, Determine the constraints. Specifically, considering that the heat transfer properties of metallic materials are generally stronger than those of air, the outer cover of the workbench should not be in direct contact with the workbench to minimize heat accumulation on the workbench. Therefore, a certain distance l1 should be maintained between the outer cover of the workbench and its internal structure, i.e.: ； In the formula, R2 is the bottom radius of the worktable of the dry gear hobbing machine; To ensure that the outer cover of the dry hobbing machine's worktable can guide the chip flow and allow the chips to be quickly discharged from inside the machine, the variable x is adjusted. t The range of values ​​for is as follows: ； In the formula, R1 is the radius of the center of the worktable of the dry gear hobbing machine; To ensure that chips do not impact the machine tool's inner baffle, which primarily prevents cutting heat from being transferred to other machine tool components, the distance between the outer cover and the inner baffle should be greater than zero, thereby controlling the variable x. b The range of values ​​for is as follows: ； In the formula, h3 is the bottom height of the worktable of the dry gear hobbing machine; S33, Establish an optimization model for the chip repose angle, namely: 。 3. The chip repose angle optimization design method for dry gear hobbing machine tools as described in claim 1, characterized in that, Step S4 includes: S41, Determine the range of values ​​for the control variable, specifically based on the structural parameters of the dry gear hobbing machine's worktable; S42, find the optimal control variable, specifically using a genetic algorithm to solve for the optimal control variable that satisfies the optimization objective function; S43, determine the optimal chip rest angle by substituting the optimal control variable into the mathematical representation model of the chip rest angle to obtain the optimal chip rest angle.

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