Thin-wall hole honing precision control method

Abstract

The invention discloses a thin-wall hole honing precision control method, and aims to solve the problems that a thin-wall hole structure is weak in rigidity, is easy to deform during honing and affects the honing precision by analyzing and testing the process of removing a force control feeding honing material. A prediction model of the aperture increment of the thin-wall hole under the action of single honing and a cutting depth formula of the oilstone under different feeding pressures are obtained, and a honing aperture prediction model is established according to the prediction model; carrying out deformation simulation research on the thin-wall hole in force control feeding honing, and correcting the prediction model; and finally, establishing a thin-wall hole honing precision control method in a force control feeding mode on the basis of the hole diameter prediction model, and verifying the thin-wall hole honing precision control method. According to the method, the deformation conditions of different sections of the thin-wall hole in the honing process can be predicted, compensation is conducted according to the deformation conditions, and the honing precision of the thin-wall hole is effectively improved.

Description

Technical Field

[0001] The present invention relates to a method for controlling the honing accuracy of thin-walled holes. By analyzing the process of honing material removal, conducting experimental research, and simulating the deformation behavior of thin-walled holes during force-controlled feed honing, a honing hole diameter is established. Based on the hole diameter prediction model, a honing accuracy control method is established, belonging to the field of high-efficiency precision honing processing technology. Background Art

[0002] The honing process is one of the key technologies in the field of hole finishing. Especially in industries with high-precision requirements such as aviation, automotive, and precision machinery, it is widely used and is an important means to ensure the accuracy and surface quality of hole parts. During the honing process, the feeding mechanism is responsible for expanding one or more oilstones configured on the honing head along the radial direction to ensure that they are in close and uniform contact with the inner wall of the hole. The honing tool rotates together with the machine tool spindle and is accompanied by a regular reciprocating motion to achieve efficient and uniform material removal. This process is particularly outstanding in terms of hole diameter, roundness, cylindricity, and surface roughness, and can achieve extremely fine tolerance control, ensuring high reliability during the machining process.

[0003] However, when machining thin-walled holes, due to the weak rigidity of the thin-walled hole structure, it is easily affected by the cutting force, resulting in regional springback deformation, that is, the "tool yielding" phenomenon. And due to the characteristics of the workpiece material distribution and the honing machining motion form, the deformation degree of the workpiece varies at different positions, which leads to changes in the cutting depth of the tool at different parts, causing inconsistent material removal and further affecting the machining accuracy.

[0004] Currently, for this problem, the mainstream solution is to customize special fixtures according to the parts. For example, clamping deformation is suppressed by multi-point pressure adjustment [Ogorodov V A. Hole shaping in the honing of thin-walled cylinders. 《Russ Engin Res》, 2017, 37(6): 549~553. Lin Jianxin. Design research on multi-point support fixtures for vibration suppression in thin-walled part machining. 《Today's Manufacturing & Upgrading》, 2024(10): 71~73]. However, such solutions have significant defects: such as poor economy, high cost for customizing special fixtures according to different workpiece geometric features; limited adaptability, only applicable to workpieces with specific shapes, and the fixture needs to be redesigned when the production line changes models; space limitation, complex fixtures occupy machining space, etc. These limitations severely restrict the popularization and application of this solution in small and medium batch, multi-variety production scenarios. Summary of the Invention

[0005] In order to overcome the deficiencies of the prior art, the present invention discloses a honing precision control method for thin-walled holes. Aiming at the characteristics of weak rigidity of the thin-walled hole structure, which is prone to deformation during honing processing and affects the honing processing accuracy, through the analysis and experimental research on the process of force-controlled feed honing material removal, a prediction model of the aperture increment of the hole under a single honing action and a cutting depth formula under different feed pressures of the oilstone are obtained, and a honing aperture prediction model is established based on this; a deformation simulation study of the thin-walled hole in force-controlled feed honing is carried out to correct the prediction model; finally, based on the aperture prediction model, a honing precision control method for thin-walled holes in the force-controlled feed mode is established and verified.

[0006] In order to achieve the above-mentioned invention purpose, the present invention adopts the following technical solutions:

[0007] A honing precision control method for thin-walled holes, the principle is as follows:

[0008] Step 1: Through the analysis and experimental research on the process of force-controlled feed honing material removal, a prediction model of the aperture increment of the hole under a single honing action and a cutting depth formula under different feed pressures of the oilstone are obtained, and a honing aperture prediction model is constructed.

[0009] Step 2: Conduct a simulation study on the deformation behavior of the thin-walled hole during honing, and correct the aperture prediction model according to the deformation simulation results of the thin-walled hole.

[0010] Step 3: Based on the aperture prediction model, a precision control method for controlling the reciprocating speed at different axial positions of the hole is proposed and verified.

[0011] In the above-mentioned Step 1, through the analysis and experimental research on the process of force-controlled feed honing material removal, a prediction model of the aperture increment of the workpiece under a single honing action and a cutting depth formula under different feed pressures of the oilstone are obtained, and a honing aperture prediction model is constructed. The specific process is as follows:

[0012] 1) Analysis of the process of force-controlled feed honing material removal

[0013] In the honing process using force-controlled feed, the key process parameters include feed pressure, spindle speed, and reciprocating speed. Among them, the feed pressure refers to the pressure applied by the machine tool spindle to the end face of the push cone, which determines the magnitude of the normal force between the oilstone and the workpiece, and further affects the cutting depth of the abrasive grains. The spindle speed and the reciprocating speed together determine the cutting path of the oilstone. For different combinations of spindle speed and reciprocating speed, the movement trajectory of the oilstone shows different degrees of density and different mesh angle sizes, and these trajectory characteristics further determine the number of times each area on the hole surface undergoes honing.

[0014] During the honing process, each time the honing stone passes over the hole surface, a certain hole diameter increment will be generated in this section. After multiple honing operations, the hole diameter continuously increases until the required size is finally reached. The number of turns of the honing stone at different cross-sections of the hole is defined as the number of honing passes experienced by this section.

[0015] In order to study the relationship between the hole diameter increment under a single honing pass and the process parameters, an orthogonal experiment with 3 factors and 4 levels was carried out. The experimental results show that the only significant factor affecting the hole diameter increment under a single honing pass is the feed pressure, while the honing speed and the combinations of different spindle speeds and reciprocating speeds have no significant effect on the hole diameter increment under a single honing pass. Therefore, the hole diameter increment under a single honing pass is mainly related to the feed pressure, and the number of honing passes on each cross-section of the hole is mainly affected by the spindle speed and the reciprocating speed.

[0016] 2) Prediction of the hole diameter increment under a single honing pass

[0017] The process of force-controlled feed honing material removal is mainly related to the feed pressure, spindle speed, and reciprocating speed. Among them, the feed pressure determines the normal force between the honing stone and the workpiece, and thus determines the cutting depth of the honing stone. The spindle speed and reciprocating speed determine the number of times each area on the workpiece surface is honed.

[0018] At the same time, due to the characteristics of the tool structure and feed method, the normal force between the honing stone and the workpiece is also related to other factors that affect the honing stone expansion distance (honing stone thickness and bottom hole diameter). In order to explore the specific relationship between the hole diameter increment under a single honing pass and the feed pressure, honing stone thickness, and bottom hole diameter, a single-factor experiment on honing feed pressure was carried out. Since it is necessary to obtain the hole diameter increment under different hole diameters and different honing stone thicknesses, multiple repeated experiments were carried out, and the number of reciprocations at each hole diameter measurement interval was controlled to ensure that the hole diameter increment under each hole diameter value and honing stone thickness could be collected.

[0019] The experimental data was analyzed by function fitting using the tool of artificial neural network, and a prediction model for the hole diameter increment under a single honing pass was established.

[0020] 3) Analysis of the contact state between the honing stone and the workpiece

[0021] On the basis of establishing the relationship between the honing hole diameter increment and the honing process parameters, in order to further study the mechanism of hole diameter evolution during the honing process, it is necessary to conduct an in-depth analysis of the contact state between the honing stone and the workpiece. During the honing process, the material removal of the workpiece is a complex and dynamic process. Due to the uneven bottom hole morphology on the contact surface of the honing stone, the parts with smaller hole diameters will come into direct contact with the honing stone and material removal will occur. For whether material removal will occur in the areas with larger hole diameters, it is necessary to further explore the specific contact state between the honing stone and the workpiece in this area.

[0022] The contact state between the oilstone and the workpiece is mainly determined by the normal force between the two and the aperture of the workpiece. When the oilstone presses on the inner wall of the workpiece hole, it initially contacts only the point with the minimum aperture. Under the action of the feed pressure at the end of the push cone, the oilstone will continue to expand radially before reaching force balance until the feed force exerted on the oilstone by the push cone is balanced with the force exerted on the oilstone by the workpiece. During this process, the depth of the oilstone cutting into the workpiece is the cutting depth at the current feed pressure.

[0023] To further study the relationship between the cutting depth of the oilstone and the feed pressure, the force condition during the oilstone honing process was analyzed, and a flat honing test was carried out. To obtain the relationship between the feed pressure and the axial force received by the push cone, a push cone axial force test was conducted. After obtaining the relationship between the axial force F P and the feed pressure P, the force on the oilstone under the feed pressure during honing can be simulated by monitoring the force on the dynamometer. Flat honing tests were carried out on the feed pressures from 4 bar to 9 bar respectively. After the test, the surface topography of the flat sample was collected by an S-Neox Sensofar 3D profilometer. The test data under each feed pressure were processed, and finally the cutting depth a of the oilstone was fitted p formula.

[0024] From this, the contact state between the oilstone and the workpiece under different feed pressures can be deduced. When the tool is under a certain feed pressure, the oilstone will expand outwards and first contact the point with the minimum aperture of the workpiece on the contact surface. As the oilstone continues to expand outwards, more positions on the workpiece surface will come into contact with the oilstone. When the force balance is reached between the oilstone and the workpiece, the oilstone will expand to the maximum position. At this time, the positions on the contact surface between the workpiece and the oilstone where the aperture difference from the minimum aperture is less than the cutting depth of the oilstone under this feed pressure will come into contact with the oilstone and remove materials during the honing process. For the positions on the contact surface where the aperture difference from the minimum aperture is greater than the cutting depth of the oilstone under this feed pressure, they will not come into contact with the oilstone and will not remove materials.

[0025] 4) Honing aperture prediction model

[0026] By analyzing the pore diameter evolution process during honing, a prediction model for the pore diameter evolution during honing can be established. At the beginning of honing, the oilstone expands and presses against the workpiece at the upper overtravel position. It will first contact point A with the smallest pore diameter on the contact surface. At this time, calculate the contact length between the oilstone and point A during the axial movement of the oilstone. Next, calculate whether the oilstone will contact a position with a pore diameter smaller than that at point A when it moves this length, and the difference in pore diameter between this position and that at point A is greater than the cutting depth under the current feed pressure. If so, record this pore diameter position as B. When the oilstone moves to position B, it will no longer contact point A, and recalculate the contact length between the oilstone and point A. If there is no point B, the contact length between the oilstone and point A remains unchanged. Next, according to the honing reciprocating speed and the contact length between the oilstone and point A, calculate the honing time experienced at point A, and then combine it with the spindle speed to calculate the honing times at point A. Next, load the neural network prediction model for the pore diameter increment per single honing. According to the pore diameter value, oilstone thickness, and feed pressure at point A, obtain the pore diameter increment under the action of single honing, and then get the new pore diameter value at point A after a time step with the honing times. Next, update all the pore diameter values on the oilstone contact surface. Those with pore diameters smaller than the new pore diameter value at point A are considered to be in direct contact with the oilstone during honing, resulting in material removal, and the pore diameter value is updated to the new pore diameter value at point A. For positions with pore diameters larger than the new pore diameter value at point A, they are not in direct contact with the oilstone, and the pore diameter value remains unchanged. Finally, the oilstone moves axially by a time step, and the above process is cycled.

[0027] In the second step, the deformation behavior of thin-walled holes during honing is studied by simulation, and the pore diameter prediction model is corrected according to the deformation simulation results of the thin-walled holes. The specific process is as follows:

[0028] 1) Deformation simulation of thin-walled holes during honing

[0029] In order to obtain the radial deformation of thin-walled holes at each axial position under the honing cutting force, a finite element simulation study on honing deformation was carried out. During the simulation, the feed pressure was applied to the end face of the push cone to make it move axially, and the radial feed of the oilstone was realized through the wedge surface fit. The simulation analysis steps were set to three steps. In the first step, the feed pressure was applied to the end face of the push cone. According to the common pressure, the feed pressures from 4 bar to 9 bar were set respectively. Under the action of the feed pressure, the oilstone would expand radially and gradually press against the hole wall until it reached a stable state. In the second step, the reciprocating motion during actual honing was simulated, and an axial displacement was applied to the tool rod to move from the upper overtravel position to the lower overtravel position. In the third step, it returned to the upper overtravel position again.

[0030] When analyzing the simulation results, take the cross-section at the center of the honing stone in the area where the honing stone contacts the workpiece, and analyze the radial deformation of the center point of the workpiece hole wall in the area where the honing stone contacts the workpiece. Combining with the actual method of measuring the aperture of the workpiece during honing, take the cross-section at the 23rd position of the workpiece for radial deformation analysis, with an interval of 2.5 mm between adjacent two analysis points. Obtain the radial deformation at different axial positions of the workpiece under various feed pressures.

[0031] 2) Correction and verification of the honing aperture prediction model

[0032] After obtaining the relationship between different feed pressures, different axial positions of the workpiece, and the radial deformation of the workpiece, compensate the difference in deformation at different axial positions of the workpiece into the prediction model of the single honing aperture increment. Obtain the new aperture prediction model after compensation.

[0033] To verify the effect of the new aperture prediction model after compensation, a honing test was carried out. The test results show that the prediction results of the prediction model are very close to the actual results. After compensating for the deformation of the workpiece, the prediction accuracy of the aperture prediction model has been greatly improved. After being verified by multiple groups of tests, the average error of the aperture prediction model is within 10%.

[0034] In the third step, based on the aperture prediction model, a precision control method for controlling the reciprocating speed at different axial positions of the workpiece was proposed and verified. The specific process is as follows:

[0035] 1) Honing precision control method

[0036] The process of honing aperture evolution is mainly determined by the single honing aperture increment and the honing times. The aperture increment under the action of single honing is mainly affected by the feed pressure, the bottom hole aperture, and the honing stone thickness. Among them, the bottom hole aperture and the honing stone thickness cannot be artificially controlled during the honing process. Although the feed pressure can be controlled artificially, it is necessary to purchase additional pressure control equipment for the machine tool, which is not only expensive, occupies space, but also requires a large amount of time cost to learn the pressure control software. The honing times can be directly controlled by the machine tool program to control the rotational speed and the reciprocating speed, which is much simpler than controlling the aperture increment under the action of single honing. Therefore, a precision control method for controlling the honing times to control the material removal accuracy at different axial positions is proposed.

[0037] The honing times at different axial positions of the workpiece are mainly related to the spindle speed, reciprocating speed, and effective honing distance at that position. Among them, the effective honing distance is jointly determined by the length of the oilstone, the overtravel amount, and the bottom hole condition near the axial position of the workpiece. Affected by the tool structure and stroke, the length of the oilstone and the overtravel amount are not suitable to be changed, and the bottom hole condition of the workpiece cannot be artificially changed; the reciprocating times affect the total aperture increment of the workpiece, but cannot affect its distribution law. Therefore, changing the reciprocating times cannot accurately remove the materials at different axial positions of the workpiece. Therefore, the key to changing the honing times at different axial positions of the workpiece lies in controlling the spindle speed n at different axial positions s and the reciprocating speed v a . Since the linear acceleration of the spindle of the machine tool is usually much greater than the angular acceleration, it is proposed to control the honing times by controlling the reciprocating speed at different axial positions of the workpiece, so as to control the consistency of the honed aperture and improve the honing accuracy of thin-walled holes

[0038] 2) Verification of the accuracy control method

[0039] Based on the aperture prediction model, the variable-speed honing accuracy control model is preliminarily verified, and the cylindricity is indirectly characterized by the predicted aperture difference

[0040] The results show that the shape of the hole after conventional honing is still similar to that before honing, and the ability to improve the shape error is limited. After variable-speed honing, the shape error of the hole is corrected. Compared with conventional honing, the variable reciprocating speed control strategy reduces the maximum aperture difference by about 55.79%, effectively improving the consistency of the aperture after honing

[0041] Beneficial effects

[0042] (1) A thin-walled hole honing accuracy control method provided by the present invention can predict the deformation conditions of different cross-sections of the hole during the honing process through simulation research on the deformation behavior of the thin-walled hole during the honing process, and compensate for the deformation conditions, effectively improving the honing accuracy of the thin-walled hole

[0043] (2) The accuracy control method controls the accuracy by optimizing the honing axial speed, without the need to customize special fixtures and purchase additional equipment, with high economy and high applicability Description of the drawings

[0044] Figure 1 Honing test workpiece and tool, where (a) honing test workpiece; (b) honing tool

[0045] Figure 2 Honing test and aperture measurement platform; (a) honing test platform; (b) in-situ aperture measurement; 1 - honing tool, 2 - cradle fixture, 3 - thin-walled sandwich, 4 - Fellows pneumatic gauge

[0046] Figure 3 Internal schematic diagram of honing tool; 5 - piston, 6 - push cone, 7 - oilstone, 8 - spring;

[0047] Figure 4 Schematic diagram of the oilstone feeding process;

[0048] Figure 5 Flat honing test platform; 9 - oilstone fixture, 10 - dynamometer, 11 - flat workpiece, 12 - flat fixture;

[0049] Figure 6 Force analysis diagram of the oilstone; (a) Force analysis in the x - z plane; (b) Force analysis in the x - y plane;

[0050] Figure 7 Schematic diagram of the axial force test of the push cone;

[0051] Figure 8 Relationship diagram between the feeding pressure and the axial force of the push cone;

[0052] Figure 9 Flow chart for predicting the honing hole diameter;

[0053] Figure 10 Force - controlled feeding honing simulation model;

[0054] Figure 11 Stroke of the simulation tool;

[0055] Figure 12 Schematic diagram of the workpiece deformation analysis under force - controlled feeding;

[0056] Figure 13 Deformation simulation result diagram of the force - controlled feeding honing;

[0057] Figure 14 Comparison of the hole diameter prediction results;

[0058] Figure 15 Flow chart for controlling the honing accuracy;

[0059] Figure 16 Schematic diagram of the variable - speed node;

[0060] Figure 17 Comparison of the hole diameter conditions between ordinary honing and variable - speed honing;

[0061] Figure 18 Comparison of the maximum hole diameter difference. Specific implementation manner

[0062] The technical solution of the present invention will be specifically described below in combination with specific embodiments:

[0063] Embodiment 1

[0064] A method for controlling the honing accuracy of thin - walled holes, the specific steps are as follows:

[0065] Step 1. Through the analysis and experimental research on the process of force-controlled feed honing material removal, a prediction model for the aperture increment of the workpiece under a single honing action and a cutting depth formula under different feed pressures of the oilstone are obtained, and a honing aperture prediction model is constructed. The specific process is as follows:

[0066] 1) Analysis of the force-controlled feed honing material removal process

[0067] In the honing process with force-controlled feed, the key process parameters include feed pressure, spindle speed, and reciprocating speed. Among them, the feed pressure refers to the pressure applied by the machine tool spindle to the end face of the push cone, which determines the magnitude of the normal force between the oilstone and the workpiece, and further affects the cutting depth of the abrasive grains. The spindle speed and reciprocating speed together determine the cutting path of the oilstone. For different combinations of spindle speed and reciprocating speed, the movement trajectory of the oilstone shows different degrees of density and different mesh angle sizes, and these trajectory characteristics further determine the number of times each area of the workpiece surface undergoes honing.

[0068] During the honing process, each time the oilstone honed across the workpiece surface, it would generate a certain aperture increment at this cross-section. After multiple honings, the aperture continuously increases until the required size is finally reached. Define the number of turns of the oilstone at different cross-sections of the workpiece as the number of honing times experienced by this cross-section.

[0069] In order to explore the relationship between the aperture increment under a single honing action and the process parameters, an orthogonal experiment with 3 factors and 4 levels was carried out. The orthogonal experiment table is shown in Table 1. Among them, the mesh angle θ represents different combinations of spindle speed and reciprocating speed.

[0070] Table 1 Experimental factors and level table

[0071]

[0072] The experiment was carried out on a DMG Ultrasonic 20Linear ultrasonic-assisted machining center, and the feed accuracy of the machine tool is 0.001 mm. The honing tool used is equipped with a multi-layer sintered oilstone with 230 meshes, as shown in Figure 1 (b). The test workpiece is a hole part made of AISI 9310 material with a diameter of 6.98 ± 0.01 mm, a hole height of 60 mm, and a wall thickness of 0.5 mm, as shown in Figure 1 (a), and the hardness after heat treatment is HRC33 - 42. The honing test device is shown in Figure 2 (a). The aperture measuring device is shown in Figure 2 (b). The Pfeifer pneumatic measuring instrument 4 is used, and a measuring head with a measuring range of 6.950 mm - 7.050 mm is selected, and the measuring accuracy is ±1 μm.

[0073] Due to the existence of overtravel in honing, the honing times at different axial positions of the workpiece are different. Therefore, for the convenience of calculation, only the 20-mm length in the middle of the workpiece is taken for the aperture calculation, and the aperture increment D of the workpiece under the action of a single honing n is calculated by the following formula:

[0074]

[0075] where D q is the total aperture increment after honing, and N l is the total honing times at this section and can be calculated by the following formula.

[0076]

[0077] where N is the reciprocating times, l s is the length of the oilstone, n s is the spindle speed, and v a is the reciprocating speed.

[0078] The variance analysis of the orthogonal test results of the aperture increment of the workpiece under the action of a single honing is shown in Table 2.

[0079] Table 2 Variance analysis table of the aperture increment under the action of a single honing

[0080]

[0081]

[0082] As can be seen from Table 2, the only significant factor for the aperture increment of the workpiece under the action of a single honing is the feed pressure, while the honing speed and the combinations of different spindle speeds and reciprocating speeds have no significant influence on the aperture increment under the action of a single honing. Therefore, the aperture increment under the action of a single honing is mainly related to the feed pressure, and the honing times at each section of the workpiece are mainly affected by the spindle speed and the reciprocating speed.

[0083] 2) Prediction of the aperture increment under the action of a single honing

[0084] The process of force-controlled feed honing material removal is mainly related to the feed pressure, the spindle speed, and the reciprocating speed. Among them, the feed pressure determines the normal force between the oilstone and the workpiece, and thus determines the cutting depth of the oilstone. The spindle speed and the reciprocating speed determine the honing times of each area on the workpiece surface.

[0085] At the same time, due to the characteristics of the tool structure and the feed method, the normal force between the oilstone and the workpiece is also related to other factors that affect the expansion distance of the oilstone. Figure 3It is a schematic diagram of the inside of a honing tool. While the push cone 6 moves axially under the action of the feed pressure, it will also be subjected to the reaction force brought about by the compression of the spring 8. Therefore, when the aperture of the workpiece is larger or the thickness of the oilstone becomes thinner due to wear, the oilstone needs a greater expansion distance to press against the hole wall. At this time, affected by the spring 8, the normal force between the oilstone 7 and the workpiece will decrease, and the aperture increment under a single honing action will also decrease accordingly.

[0086] Therefore, in order to explore the specific relationships among the aperture increment under a single honing action, the feed pressure, the oilstone thickness, and the bottom hole aperture, a single-factor experiment on honing feed pressure was carried out. The experimental factors and levels are shown in Table 3.

[0087] Table 3 Single-factor experimental design table for feed pressure

[0088]

[0089] Since it is necessary to obtain the aperture increment under different apertures and different oilstone thicknesses, multiple repeated experiments were carried out, and the number of reciprocations at each aperture measurement interval was controlled to ensure that the aperture increment under each aperture value and oilstone thickness could be collected.

[0090] In order to clarify the quantitative relationships among the aperture increment under a single honing action, the feed pressure, the oilstone thickness, and the bottom hole aperture, the experimental data were analyzed by function fitting using the method of artificial neural network.

[0091] The trained neural network prediction model was used to predict the aperture increment under a single honing action, and the results are shown in Table 4.

[0092] Table 4 Prediction results of the aperture increment under a single honing action of the neural network prediction model

[0093]

[0094] It can be seen from Table 4 that the mean square error between the measured value and the predicted value is very small, and at the same time, the mean value of the coefficient of determination is 0.9865, indicating that the prediction model has a high degree of fitting and prediction accuracy.

[0095] 3) Analysis of the contact state between the oilstone and the workpiece

[0096] On the basis of establishing the relationship between the honing aperture increment and the honing process parameters, in order to further study the mechanism of aperture evolution during the honing process, it is also necessary to deeply analyze the contact state between the oilstone and the workpiece.

[0097] During the honing process, the material removal of the workpiece is a complex and dynamic process. Due to the uneven bottom hole topography on the contact surface of the oilstone, the parts with smaller hole diameters will come into direct contact with the oilstone and material removal will occur. However, for whether material removal will occur in the areas with larger hole diameters, it is necessary to further explore the specific contact state between the oilstone and the workpiece in this area. Therefore, clarifying the characteristics of the contact state between the oilstone and the workpiece and its influence on material removal is the key to deeply understanding the evolution process of the honing hole diameter.

[0098] The contact state between the oilstone and the workpiece is mainly determined by the normal force between the two and the situation of the workpiece hole diameter. When the oilstone presses on the workpiece hole wall, it initially only contacts the smallest hole diameter. Under the action of the feed pressure at the end of the push cone, the oilstone will continue to radially expand before reaching force balance until the feed force acting on the oilstone by the push cone is balanced with the force exerted by the workpiece on the oilstone. During this process, the depth at which the oilstone cuts into the workpiece is the cutting depth under the current feed pressure. Figure 4 It is a schematic diagram of the oilstone feed process.

[0099] To further study the relationship between the oilstone cutting depth and the feed pressure, a flat honing test was carried out. The flat honing test platform is as Figure 5 shown. This test was carried out on a DMG Ultrasonic 20linear five-axis machining center. The used oilstone 7 is a 230-mesh CBN sintered oilstone, which is clamped on the oilstone fixture 9, and the oilstone fixture is installed on the machine tool spindle. In order to collect the normal force during the test, the flat workpiece 11 is clamped on the flat fixture 12 and connected to a Kistler 9129AA force gauge. During the test, the spindle feeds downward, pressing the oilstone 7 and the flat workpiece 11 tightly and applying a certain normal force. The magnitude of the normal force is monitored by the force gauge. When the normal force reaches the predetermined value, the machine tool spindle makes a horizontal movement, causing relative movement between the oilstone and the flat workpiece 11, thus completing the test.

[0100] When studying the relationship between different feed pressures and the normal force of the oilstone, it is necessary to conduct a separate force analysis on the oilstone. Taking the downstroke as an example, analyze the force situation of the oilstone. When calculating the upstroke, only the opposite of the reticulation angle needs to be taken for the force analysis of the oilstone.

[0101] During the honing process, since the material removal amount is usually at the micron level, the radial movement of the oilstone can be approximately regarded as stationary. At the same time, the oilstone makes a uniform rotational motion with the tool. If the centrifugal force of the oilstone is regarded as the actual acting force, it can be assumed that the oilstone is in a state of force balance at any time. Figure 6 It is the force analysis diagram of the oilstone in the x-z plane (a) and the x-y plane (b) during the honing process.

[0102] According to Figure 6 , the force balance equation of the oilstone in the x direction can be established:

[0103] F n +f bs,z +f bs,y =F cs,x +T s (1 - 3)

[0104] Among them, F n is the normal force of the oilstone feed; f bs,z and f bs,y are the component forces of the frictional force between the tool shank and the oilstone; F cs,x is the component force of the acting force between the push cone and the oilstone, and its calculation formula is shown in Equation (1 - 4); T s is the centrifugal force of the oilstone, and its calculation formula is shown in Equation (1 - 5).

[0105]

[0106] Among them, F P is the axial force that the push cone receives due to the feed pressure; is the angle of the mating wedge surface between the push cone and the oilstone.

[0107]

[0108] Among them, m s is the mass of the oilstone; ω is the angular velocity of the tool; r c is the distance from the center point of the contact surface between the push cone and the oilstone when the push cone is not expanded to the tool axis; d x is the radial feed distance of the oilstone.

[0109] The matrix material of the used oilstone is copper alloy, and the material of the tool shank is SKS3 die steel. The surface roughness of the contact surface between the two is relatively small, which is Ra0.4. In addition, during the processing, the friction state between the oilstone and the oilstone groove is lubricated friction, and the friction coefficient between the two is very small and can be ignored. Therefore, the simplified calculation formula for the normal force of the oilstone is:

[0110] F n =F cs,x +T s (1 - 6)

[0111] In order to obtain the relationship between the feed pressure and the axial force received by the push cone, a push cone axial force test was carried out. The machine tool and the force measuring instrument used in the test are the same as those used in surface honing. As Figure 7 shown, during the test, the honing tool was installed on the spindle of the machine tool, and the tool was adjusted directly above the force measuring instrument. The machine tool spindle applied a feed pressure to the push cone of the tool, and the push cone axially moved and pressed on the force measuring instrument under the action of the feed pressure, and the force measuring instrument recorded the axial force corresponding to different feed pressures. The test results are as Figure 8 shown.

[0112] From Figure 8 it can be seen that there is a linear relationship between the axial force F P and the feed pressure P. By performing a linear fit on the test results, the expression for F P is as follows:

[0113] F p = 6.691P - 24.736 (1 - 7)

[0114] After obtaining the relationship between the axial force F P and the feed pressure P, the force on the dynamometer can be monitored to simulate the force exerted by the feed pressure on the oilstone during honing. Before the test, in order to simulate the surface contact form between the oilstone and the workpiece in actual honing, the oilstone was dressed. The dressing process was carried out on the ultra-precision forming surface CNC grinding machine WAZA415X-NC. The grinding wheel used was a resin-based CBN grinding wheel with 1500 mesh. The dressing parameters were set as follows: the rotational speed was 3000 rpm, the forward and backward reciprocating speed was 100 mm / min, the left and right reciprocating speed was 15 m / min, and the downward feed speed was 0.2 μm / rev. The dressing of the test sample was also carried out on this machine tool. The flatness of the dressed sample surface could reach 2 μm, basically meeting the test requirements.

[0115] Flat honing tests were carried out on the feed pressure from 4 bar to 9 bar respectively. After the test, the surface topography of the flat sample was collected by the S-Neox Sensofar 3D profilometer. Since the exposed height of the abrasive grains on the oilstone surface is not consistent, the groove depths generated are also different. When performing statistical calculations, the average value of all groove depths is taken to characterize the oilstone cutting depth at this feed pressure. The test data at each feed pressure was processed, and finally the oilstone cutting depth a p The formula is as follows:

[0116] a p = -1.5F n -1 + 1.05 (1 - 8)

[0117] From this, the contact state between the oilstone and the workpiece under different feed pressures can be deduced. When the tool is under a certain feed pressure, the oilstone will expand outwards and first contact the minimum aperture value of the workpiece on the contact surface. As the oilstone continues to expand outwards, more positions on the workpiece surface will come into contact with the oilstone. When the force balance is reached between the oilstone and the workpiece, the oilstone will expand to the maximum position. At this time, the aperture difference between the position on the contact surface of the workpiece and the oilstone and the minimum aperture value, which is less than the oilstone cutting depth under this feed pressure, will come into contact with the oilstone and remove material during the honing process. For the position on the contact surface where the aperture difference from the minimum aperture value is greater than the oilstone cutting depth under this feed pressure, it will not come into contact with the oilstone and no material will be removed.

[0118] 4) Honing aperture prediction model

[0119] Through the analysis of the aperture evolution process during honing, a prediction model for the aperture evolution during honing can be established. At the beginning of honing, the oilstone expands and presses against the workpiece at the upper over-travel position, and will first contact point A with the minimum aperture on the contact surface. At this time, calculate the contact length between the oilstone and point A during the axial movement of the oilstone; next, calculate whether the distance the oilstone moves this length will contact a position with a smaller aperture value than that at point A, and the aperture difference between this position and that at point A is greater than the cutting depth under the current feed pressure. If so, record this aperture position as B. When the oilstone moves to position B, it will no longer contact point A, and recalculate the contact length between the oilstone and point A. If there is no point B, the contact length between the oilstone and point A remains unchanged; next, according to the honing reciprocating speed and the contact length between the oilstone and point A, calculate the honing time experienced by point A, and then combine with the spindle speed to calculate the honing times at point A; next, load the neural network prediction model for the single-pass honing aperture increment. According to the aperture value at point A, the oilstone thickness, and the feed pressure, obtain the aperture increment under the action of single-pass honing, and then obtain the new aperture value at point A after a time step with the honing times; next, update all the aperture values on the contact surface of the oilstone. Those with an aperture smaller than the new aperture value at point A are regarded as directly contacting the oilstone during the honing process and material removal occurs, and the aperture value is updated to the new aperture value at point A. For the positions with an aperture value greater than the new aperture value at point A, they do not directly contact the oilstone and the aperture value remains unchanged; finally, the oilstone moves axially by a time step and loop the above process. The flow chart is as Figure 9 shown.

[0120] Step 2: Conduct a simulation study on the deformation behavior of the thin-walled hole during honing, and modify the aperture prediction model according to the deformation simulation results of the thin-walled hole. The specific process is as follows:

[0121] 1) Deformation simulation of the thin-walled hole during honing

[0122] In order to obtain the radial deformation of the thin-walled hole at each axial position under honing cutting force, a finite element simulation study on honing deformation was carried out. When performing the finite element simulation, considering both simulation accuracy and efficiency, the workpiece mesh size was set to 0.2 mm and the number of meshes was 126,900. During the simulation, by applying a feed pressure to the end face of the push cone, its axial movement was realized, and through the cooperation of the wedge surface, the radial feed of the honing stone was achieved. The simulation loads are set as Figure 10 shown below.

[0123] The simulation analysis steps are set to three steps. In the first step, a feed pressure is applied to the end face of the push cone. According to the common pressure, the feed pressures from 4 bar to 9 bar are respectively set. Under the action of the feed pressure, the honing stone will radially expand and gradually press against the hole wall until it reaches a stable state. In the second step, the reciprocating motion during actual honing is simulated, and an axial displacement is applied to the tool rod, moving from the upper over-travel position to the lower over-travel position. In the third step, it returns to the upper over-travel position again. The simulation stroke is as Figure 11 shown below.

[0124] When analyzing the simulation results, take the cross-section at the center of the honing stone in the area in contact with the honing stone, and analyze the radial deformation of the center point of the workpiece hole wall in the area in contact with the honing stone. The positions selected for workpiece deformation analysis are as Figure 12 shown below.

[0125] Combined with the method for measuring the aperture of the workpiece during actual honing processing, take the cross-section at the 23rd position of the workpiece for radial deformation analysis, and the interval between adjacent two analysis points is 2.5 mm. The radial deformation of different axial positions of the workpiece under each feed pressure is as Figure 13 shown below.

[0126] 2) Correction and verification of the honing aperture prediction model

[0127] After obtaining the relationship between different feed pressures, different axial positions of the workpiece, and the radial deformation of the workpiece, the deformation difference of different axial positions of the workpiece is compensated into the prediction model of the single honing aperture increment. A new compensated aperture prediction model is obtained.

[0128] To verify the effect of the new compensated aperture prediction model, a honing test was carried out. The device used in the test is the same as that in the previous test, and the test parameters are as follows: feed pressure 5 bar, spindle speed 1135 rpm, reciprocating speed 3 m / min, and the number of reciprocations is 60 times. At the same time, the bottom hole and tool information are brought into the aperture evolution prediction model, and the aperture prediction results are obtained after 60 reciprocations with the same parameters. The comparison between the two is as Figure 14 shown below.

[0129] From Figure 14It can be seen that the prediction results of the prediction model are very close to the actual results. After the deformation compensation of the workpiece, the prediction accuracy of the aperture prediction model has been greatly improved. After multiple groups of experimental verifications, the average error of the aperture prediction model is about 9.48%.

[0130] Step 3: Based on the aperture prediction model, a precision control method for controlling the reciprocating speed of different axial positions of the workpiece is proposed and the precision control method is verified. The specific process is as follows:

[0131] 1) Honing precision control method

[0132] The process of honing aperture evolution is mainly determined by the aperture increment per single honing and the number of honing passes. The aperture increment under the action of a single honing is mainly affected by the feed pressure, the bottom hole aperture and the oilstone thickness. Among them, the bottom hole aperture and the oilstone thickness cannot be artificially controlled during the honing process. Although the feed pressure can be controlled manually, additional pressure control equipment needs to be purchased for the machine tool, which is not only expensive, occupies space, but also requires a large amount of time cost for learning the pressure control software. The number of honing passes can be directly controlled by controlling the rotational speed and the reciprocating speed of the machine tool program, which is much simpler than controlling the aperture increment under the action of a single honing. Therefore, a precision control method for controlling the number of honing passes to control the material removal accuracy of different axial positions is proposed.

[0133] The number of honing passes at different axial positions of the workpiece is mainly related to the spindle speed, the reciprocating speed and the effective honing distance at that position. Among them, the effective honing distance is jointly determined by the oilstone length, the overtravel and the bottom hole condition of the workpiece near that axial position. Affected by the tool structure and the stroke, the oilstone length and the overtravel are not suitable to be changed, and the bottom hole condition of the workpiece cannot be artificially changed; the number of reciprocations affects the total aperture increment of the workpiece, but cannot affect its distribution law. Therefore, changing the number of reciprocations cannot accurately remove the material at different axial positions of the workpiece. Therefore, the key to changing the number of honing passes at different axial positions of the workpiece lies in controlling the spindle speed n s and the reciprocating speed v a at different axial positions. Since the linear acceleration of the spindle of the machine tool is usually much greater than the angular acceleration, it is proposed to control the reciprocating speed of different axial positions of the workpiece to control the number of honing passes, thereby controlling the honing aperture consistency and improving the honing precision of thin-walled holes.

[0134] In order to be able to control the number of honing passes at different axial positions of the workpiece, it is necessary to clarify the reciprocating speed of each position. The flow chart of the precision control model is as Figure 15 shown.

[0135] The determination process of the reciprocating speed and the variable speed nodes of the precision control model is as follows:

[0136] (1) First, measure and read the bottom hole diameter. The interval between each measurement point is 2.5 mm to obtain the diameter value of the minimum hole diameter and the contact length with the oilstone within one stroke at this position.

[0137] (2) Load the single-pass honing hole diameter increment neural network, input the honing parameters and hole diameter information to obtain the single-pass honing hole diameter increment at the minimum hole diameter. At the same time, calculate the number of honing passes at this position for one reciprocation at the lowest reciprocating speed, and calculate the hole diameter after 60 reciprocations at this position. Let this hole diameter be the target hole diameter d. target 。

[0138] (3) Start the simulation of the honing process. The oilstone presses against the hole wall and contacts point A with the minimum hole diameter on the contact surface. At this time, calculate the contact length l that the oilstone will have with point A during axial movement. s,contact ,

[0139] (4) Next, calculate whether the distance that the oilstone moves this length will contact a position with a smaller hole diameter than that at point A, and the difference in hole diameter between this position and point A is greater than the cutting depth under the current feed pressure. If so, record this hole diameter position as B. When the oilstone moves to position B, it will no longer contact point A, and recalculate the contact length between the oilstone and point A. If there is no point B, the contact length between the oilstone and point A remains unchanged.

[0140] (5) Calculate the hole diameter increment value Δd required for the hole diameter at point A to reach the target hole diameter. need , as shown in formula (3-1). From the single-pass honing hole diameter increment neural network model loaded, obtain the single-pass honing hole diameter increment at point A according to the hole diameter value, oilstone thickness, and feed pressure at point A, and calculate the required number of honing passes N by combining the two. need The formula is as shown in (3-2), and calculate the number of honing passes N required within one stroke according to the number of reciprocations. once,need , and the calculation formula is as shown in (3-3).

[0141] Δd need =d target -d 0 (3-1)

[0142]

[0143] (6) Then, determine the honing time at point A from the spindle speed, and calculate the required reciprocating speed v at point A from the contact length with the oilstone. a,need , and the calculation formula is:

[0144]

[0145] (7) After determining the reciprocating speed, numerical simulation of honing material removal is started with the set time step as the unit. The oilstone moves axially by one time step. According to the single honing hole diameter increment and the honing times, the new hole diameter value at position A is obtained, and all the hole diameter values on the oilstone contact surface are updated. Those with a hole diameter smaller than the new hole diameter value at position A are considered to be in direct contact with the oilstone during the honing process, resulting in material removal, and the hole diameter value is updated to the new hole diameter value at position A. For positions with a hole diameter larger than the new hole diameter value at position A, they are not in direct contact with the oilstone, and the hole diameter value remains unchanged;

[0146] (8) Enter the next time step, and the oilstone continues to move axially, repeating the process in (7). Continuously detect the hole diameter situation during the process until the oilstone moves to the position of the new minimum hole diameter value. At this time, the reciprocating speed at this position needs to be recalculated. This position is the variable reciprocating speed node, as shown in Figure 16 shown. Return to step (3) and proceed downward.

[0147] 2) Verification of the accuracy control method

[0148] Based on the hole diameter prediction model, a preliminary verification of the variable-speed honing accuracy control model is carried out, and the cylindricity is indirectly characterized by the predicted hole diameter difference. The feed pressure used is 6 bar, the oilstone thickness is 2.7 mm, and the bottom hole diameter is measured according to the actual thin-walled hole. The final results of the predicted hole diameters of the two are as shown in Figure 17 shown. Different honing parameters are selected for multiple groups of predictions. The comparison of the maximum hole diameter differences between the bottom hole before honing and ordinary honing and variable-speed honing is as shown in Figure 18 shown.

[0149] From the results Figure 17 it can be seen that after conventional honing, the shape of the hole is still similar to that before honing, and the ability to improve the shape error is limited. After variable-speed honing, the shape error of the hole is corrected, but the overall hole shape slightly shows a trend of a drum-shaped hole, and the hole diameter values at the two cross-sections at the axial positions of 17.5 mm and 42.5 mm are larger than those in the middle section. This is due to the existence of the over-travel amount, resulting in a shorter contact length between the two ends of the workpiece and the oilstone than that in the middle end. In order to achieve the target hole diameter, the reciprocating speed of the oilstone at the two ends of the workpiece is slower, resulting in more material removal near the over-travel area of the workpiece.

[0150] From Figure 18 it can be seen that the maximum hole diameter difference of the bottom hole before honing is about 11.2 μm, which is reduced to about 5.61 μm after conventional honing, and further reduced to about 2.48 μm after variable reciprocating speed honing. Compared with conventional honing, the variable reciprocating speed control strategy reduces the maximum hole diameter difference by about 55.79%, effectively improving the consistency of the hole diameter after honing.

Claims

1. A method for controlling the honing precision of thin-walled holes, characterized in that: Here are the steps: Step 1: By analyzing and experimentally studying the material removal process of force-controlled feed honing, a prediction model for the aperture increment of thin-walled holes under a single honing operation and a cutting depth formula under different feed pressures of the oilstone are obtained, and a honing aperture prediction model is constructed; Step 2: Conduct simulation research on the deformation behavior of thin-walled holes during honing, and modify the aperture prediction model based on the deformation simulation results of the thin-walled holes; Step 3: Based on the aperture prediction model, a precision control method for controlling the reciprocating speed at different axial positions of the hole was proposed and verified.

2. The thin-wall hole honing precision control method according to claim 1, characterized in that: The specific process of step one is as follows: 1) Analysis of material removal process of force-controlled feed honing In the honing process with force-controlled feed, feed pressure, spindle speed and reciprocating speed are the process parameters to be investigated. The relationship between the hole diameter increment and the process parameters under a single honing is confirmed by orthogonal test. The test results show that the hole diameter increment under a single honing is mainly related to the feed pressure, and the number of honing times on each section of the hole is mainly affected by the spindle speed and reciprocating speed. 2) Prediction of hole diameter increment under single honing A single-factor test of honing feed pressure was conducted to explore the specific relationship between the aperture increment under a single honing operation and the feed pressure, oilstone thickness and bottom hole diameter. The test data were analyzed by function fitting using artificial neural network tools to establish a prediction model for the aperture increment under a single honing operation. 3) Analysis of contact status between oilstone and workpiece On the basis of establishing the relationship between the honing aperture increment and the honing process parameters, the contact state between the oilstone and the workpiece is deeply analyzed; the contact state between the oilstone and the workpiece is mainly determined by the normal force between the two and the aperture of the workpiece; when the tool is subjected to a certain feed pressure, the oilstone will expand outward and first contact the workpiece at the minimum aperture value on the contact surface; as the oilstone continues to expand outward, more positions on the workpiece surface will contact the oilstone; when the force balance is reached between the oilstone and the workpiece, the oilstone will expand to the maximum position; at this time, the position on the contact surface between the workpiece and the oilstone where the aperture difference with the minimum aperture value is less than the cutting depth of the oilstone under the feed pressure will come into contact with the oilstone and remove material during the honing process; while the position on the contact surface where the aperture difference with the minimum aperture value is greater than the cutting depth of the oilstone under the feed pressure will not come into contact with the oilstone and no material will be removed; 4) Honing aperture prediction model By analyzing the pore size evolution during the honing process, a prediction model for the pore size evolution during the honing process is established.

3. The thin-wall hole honing precision control method according to claim 1, characterized in that: The specific process of step 2 is as follows: 1) Deformation simulation of thin-walled holes during honing In order to obtain the radial deformation of thin-walled holes at various axial positions under honing cutting force, a finite element simulation study of honing deformation was carried out. During the simulation, feed pressure was applied to the end face of the push cone to make it move axially, and the radial feed of the oilstone was achieved through the wedge surface cooperation. 2) Modification and verification of honing aperture prediction model The deformation differences at different axial positions of the hole are compensated into the prediction model of the single honing aperture increment to obtain a new aperture prediction model after compensation; the experimental results show that the predicted results of the prediction model are very close to the actual results, and the average error of the aperture prediction model is within 10%.

4. The thin-wall hole honing precision control method according to claim 1, characterized in that: The specific process of step three is as follows: 1) Honing precision control method (1.1) Control the number of honing cycles to control the accuracy of material removal at different axial positions; (1.2) By controlling the reciprocating speed at different axial positions of the hole, the number of honing cycles can be controlled, thereby controlling the consistency of the honing hole diameter and improving the honing accuracy of thin-walled holes; 2) Verification of precision control methods The variable speed honing precision control model was preliminarily verified based on the aperture prediction model. The cylindricity was indirectly characterized by the predicted aperture difference. After variable speed honing, the shape error of the hole was corrected, which improved the consistency of the aperture after honing.

5. The thin-wall hole honing precision control method according to claim 2, characterized in that: 4) In the honing aperture prediction model, the prediction model for the aperture evolution during the honing process is: at the beginning of honing, the oilstone expands and presses against the workpiece at the upper overrun, and first contacts the minimum aperture point A on the contact surface. At this time, the contact length of the oilstone with point A during axial movement is calculated; the next step is to calculate whether the oilstone will contact a position with a smaller aperture value than point A after moving this length, and the difference between the aperture value at this position and point A is greater than the cutting depth under the feed pressure at this time. If so, the aperture position is recorded as B. When the oilstone moves to position B, it will no longer contact position A. The contact length between the oilstone and point A is recalculated. If point B does not exist, the contact length between the oilstone and point A remains unchanged. In the next step, the honing time at point A is calculated based on the honing reciprocating speed and the contact length between the oilstone and point A, and then the number of honing times at position A is calculated in combination with the spindle speed; in the next step, the single honing aperture increment neural network prediction model is loaded, and the aperture increment under single honing is obtained based on the aperture value at position A, the oilstone thickness, and the feed pressure, and then the new aperture value at position A after a time step is obtained by combining the number of honing times; in the next step, all aperture values ​​on the oilstone contact surface are updated, and those with apertures smaller than the new aperture value at position A are considered to be in direct contact with the oilstone during the honing process, resulting in material removal, and the aperture value is updated to the new aperture value at position A, and those with apertures larger than the new aperture value at position A are not in direct contact with the oilstone, and the aperture value remains unchanged; finally, the oilstone moves axially for one time step, and the above process is repeated.

6. The thin-wall hole honing precision control method according to claim 3, characterized in that: 1) In the deformation simulation of thin-walled holes during honing, the simulation analysis steps are set to three steps. The first step is to apply feed pressure to the end face of the push cone. Under the action of the feed pressure, the oilstone will expand radially and gradually press against the hole wall until it reaches a stable state; the second step simulates the reciprocating motion during actual honing, and applies axial displacement to the tool rod, moving from the upper overtravel to the lower overtravel; the third step returns to the upper overtravel.

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