Method for predicting thickness of burrs on top of machining area of complex thin-walled part

Abstract

The invention provides a method for predicting the thickness of burrs on the top of a machining area of a complex thin-walled part, and relates to the technical field of precision manufacturing of complex thin-walled parts for aerospace. (2) a milling area top burr thickness prediction model considering thin-wall part and tool deformation; the method is used for accurately predicting the thickness of the burrs at the top of the milling area of the complex thin-walled part, the prediction model only needs to use material characteristics, cutting parameters and tool geometric parameters, and experimental measurement of a shear angle and a friction angle is not needed; the problem that the prediction precision of the top burr thickness is low due to the fact that thin-walled parts and tool deformation in the milling machining process are ignored in an existing method is solved.

Description

Technical Field

[0001] The present invention relates to a method for predicting the burr thickness at the top of a complex thin-walled part processing area, and belongs to the technical field of precision manufacturing of complex thin-walled parts for aerospace use. The method is mainly used for accurately predicting the burr thickness at the top of a complex thin-walled part milling processing area taking into account the deformation of the thin-walled parts and the tool. Background Art

[0002] With the rapid development of aviation, aerospace, and weapons industries, thin-walled parts such as high-speed aircraft wings, aircraft fuselage skins, engine blades, and missile casings are widely used. Such complex thin-walled parts are mostly manufactured using milling technology. However, such parts are prone to deformation during processing, and a large number of fine or micro burrs are prone to be generated at the top, sides, inlet and outlet of the processing area, especially the top burr in the processing area. The thickness of the burr directly determines the dimensional accuracy, shape and position accuracy of the part, which ultimately affects the assembly accuracy of high-end equipment, the safety of aircraft control systems / weapon systems, etc., and reduces the performance and life of parts or complete machines. Therefore, in order to better ensure the processing quality of thin-walled parts, equipment accuracy, etc., accurately predicting the thickness of the top burr in the milling processing area of ​​thin-walled parts has important engineering application value.

[0003] Generally, there are two methods for predicting the thickness of the top burr in the milling area of ​​thin-walled parts. One is the finite element simulation method. The output result of the burr prediction model established by it is closely related to the input boundary conditions. However, the boundary conditions input in the simulation process are too ideal and simplified, which is significantly different from the actual processing conditions. Therefore, the prediction accuracy of this method is low. The other is the analytical modeling method. It reveals the burr formation mechanism of complex structures of thin-walled parts by studying the chip formation process and burr geometric characteristics, and performs analytical modeling on the top burr of the thin-walled parts processing area. This method is widely used. For details, see the literature [Pang Xueqi, Zhang Jiayang, Yin Xiaolong, Zhang Baoyu, Deng Wenjun. Analytical and experimental investigation of improved burr morphology prediction at the topedge in metal machining. The International Journal of Advanced Manufacturing Technology. 2020; 108: 1343–1355.] The method described uses mechanical and thermodynamic methods to study the formation mechanism of the top edge burr in the processing area of ​​the rigid part. It only models the burr morphology of the top edge of the processing area of ​​the rigid part, and does not consider the deformation of thin-walled parts and tools during milling. Summary of the invention

[0004] The present invention solves the problem of low prediction accuracy of top burr thickness caused by ignoring deformation of thin-walled parts and tools during milling in existing methods, and proposes a method for predicting top burr thickness in a processing area of ​​a complex thin-walled part.

[0005] In order to solve the above technical problems, the present invention adopts the following technical solution: a method for predicting the thickness of the top burr of the processing area of ​​a complex thin-walled part, comprising the following steps:

[0006] ① A method for characterizing the geometric parameters of the burr thickness on the top of thin-walled parts is proposed;

[0007] ② A prediction model for the top burr thickness in the milling processing area considering thin-walled parts and tool deformation.

[0008] The step flow chart of the present invention is as follows Figure 1 As shown,

[0009] Step ① The specific process is:

[0010] For the top burr of the slot milling reverse milling edge, the burr is generated when the milling tool moves from the material cutting end to the cutting end. This is mainly due to the existence of negative shear angle, such as Figure 2 As shown in the figure, during the milling process, the material is removed by the cutting tool. When the milling tool leaves the workpiece, a top burr is generated at the upper edge of the machining groove. The top burr shape is easy to measure, such as Figure 4 As shown in the figure; Considering the burr formation process, in order to more effectively predict the top burr thickness generated during the processing of geometric structures such as grooves according to the process, it is necessary to characterize the geometric parameters of the top burr thickness of thin-walled parts; due to the helix angle α of the milling tool, end milling is regarded as bevel cutting. By analyzing the motion trajectory of the milling tool when milling thin-walled parts, the cutting distance A1A2 of the milling tool along the feed direction within a certain instant dt is expressed as:

[0011] A1A2=Rdθ (1)

[0012] Where R represents the geometric radius of the tool, dθ represents the angle of rotation of the milling tool tip within the time dt; the relationship between the cutting distance of the milling tool along the axial feed direction and the cutting depth A1A3 of the cutting tool along the axial cutting direction is:

[0013]

[0014] Since both the tool and the thin-walled part will undergo slight deformation during the milling process of thin-walled parts, the distance A1A3 between the milling tool and the thin-walled part along the axial milling changes, and the changed distance A3A4 is expressed as:

[0015] A3A4=A1A3 cosΔα (3)

[0016] Where Δα is the deflection angle of the milling tool;

[0017] Combining equations (1), (2) and (3), we have:

[0018]

[0019] During the milling process, due to the helix angle α of the milling tool, the tool moves in opposite directions along the edges of the groove, and the negative shear angle β will cause the top burr to form. The relationship between the tool movement and the top burr formation during the milling of thin-walled parts is found as follows:

[0020]

[0021] Considering the actual processing conditions, dβ is very small, such as Figure 5 As shown, AA' is expressed as:

[0022] AA'=l'dβ (6)

[0023] The specific process of step ② is:

[0024] like Figure 5 As shown, in ΔA′BP and ΔABP, we have:

[0025] PB=l'sinβ=wtanβ0=B' t (7)

[0026] Where β0 is the initial shear angle, w is the distance between the tool and the part when a negative shear angle is generated, and B' t is the geometric thickness of the burr of thin-walled parts;

[0027] Combining equation (6) and equation (7), we have:

[0028]

[0029] In the formula, the maximum value of β may appear at π / 2; integrating formula (5) and formula (8) simultaneously, we have:

[0030]

[0031] Solving equation (9) yields:

[0032]

[0033] Combining equations (7) and (10), the geometric thickness value of the burr on the top of the thin-walled part is:

[0034]

[0035] Considering the geometric characteristics of thin-walled parts, the thin-walled parts are deformed during milling, resulting in measurement errors when measuring the original burr thickness due to the deformation of the thin-walled parts, such as Figure 6 As shown; therefore, the actual measured burr thickness It is expressed as:

[0036]

[0037] Where a, b are the influencing factors of the deformation state of thin-walled parts, a, b = [-1 1], is the angle between B'P' and BU in the yoz plane after the thin-walled part is deformed, γ is the angle between CP' and CU in the xoz plane after the thin-walled part is deformed;

[0038] Combining equations (11) and (12), the actual top burr thickness is measured for:

[0039]

[0040] In the actual milling of thin-walled parts, the actual angle θ of the machining process is difficult to measure accurately, so it is difficult to accurately predict it through equation (13); therefore, a micro-element cutting segment is taken from the cutting segment from chip formation to burr formation, and the work ΔW done by chip formation is c The work done by the burr formation ΔW b Equally, we have:

[0041] ΔW c =ΔW b (14)

[0042] The milling force during milling is:

[0043]

[0044] In the formula, F x 、F y 、F z is the milling force in the x, y, and z directions in the rectangular coordinate system; where F t 、F r 、F a They are tangential milling force, radial milling force and axial milling force respectively, φ is the immersion angle, and the top burr is formed by the negative shear angle β, which is mainly caused by the tangential milling force F t The component F ta Then, due to the existence of the tool helix angle α and the milling tool deflection angle Δα, the tangential milling force component F ta It is expressed as:

[0045] F ta =F t sinαcosΔα (16)

[0046] Chip formation work ΔW c It is expressed as:

[0047]

[0048] The work ΔW generated by the top burr b for:

[0049]

[0050] In the formula, σ e is the yield strength of the material, a p is the cutting depth;

[0051] Substituting equation (17) and equation (18) into equation (14), we get:

[0052]

[0053] Under various cutting conditions, the initial negative shear angle β0 of all materials is 20°, then the term with β0 in equation (19) is a constant, and equation (19) is rewritten as:

[0054]

[0055] In the formula,

[0056] Therefore, the top burr thickness is expressed as:

[0057]

[0058] Due to the deformation of the part, the original burr thickness will produce errors during measurement along with the deformation of the part boundary. By correcting formula (21), the actual burr thickness is It is expressed as:

[0059]

[0060] The present invention provides a method for predicting the thickness of burrs on the top of a complex thin-walled part processing area, which has the following beneficial effects:

[0061] (1) The proposed top burr thickness prediction model takes into account the deformation of thin-walled parts and tools. It does not need to measure the shear angle and friction angle in the meshing area between the tool and the workpiece during milling. It only needs to use material characteristic parameters, cutting process parameters and tool geometric parameters to calculate the top burr thickness in the machining area.

[0062] (2) The proposed top burr thickness prediction model has a prediction accuracy of 96.5%, which can easily and accurately predict the top burr thickness of the reverse milling edge during the slot milling process. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is a flow chart of the steps of the present invention;

[0064] Figure 2 This is a processing technology for milling grooves of thin-walled parts of the present invention;

[0065] Figure 3 It is a geometric analysis AA cross-sectional view of top burr formation in the milling of thin-walled parts of the present invention;

[0066] Figure 4 It is a BB cross-sectional view of the geometric analysis of the top burr formation in the milling of thin-walled parts of the present invention;

[0067] Figure 5 This is the process of forming top burrs when side milling thin-walled parts of the present invention;

[0068] Figure 6 is the top burr thickness of the thin-walled part of the present invention under deformation and non-deformation;

[0069] Figure 7 is the relationship between the burr thickness at the top of the processing area of ​​the thin-walled part and the spindle speed of the present invention;

[0070] Figure 8 is the relationship between the top burr thickness and the cutting depth under different feed rates per tooth of the present invention;

[0071] Fig. 9 It is the relationship between the burr thickness at the top of the processing area of ​​the thin-walled part and the feed amount per tooth of the present invention. DETAILED DESCRIPTION

[0072] The feasibility and effectiveness of the proposed method are illustrated by taking aluminum alloy slot milling and reverse milling as an example. Figure 1 As shown, a method for predicting the thickness of the top burr of a complex thin-walled part processing area of ​​the present invention includes the following steps:

[0073] ① A method for characterizing the geometric parameters of the burr thickness on the top of thin-walled parts is proposed

[0074] Since the milling tool has a helix angle α, end milling is considered as bevel cutting. By analyzing the motion trajectory of the milling tool when milling thin-walled parts, the cutting distance A1A2 of the milling tool along the feed direction within a certain instant dt is expressed as:

[0075] A1A2=Rdθ (1)

[0076] Where R represents the geometric radius of the tool, dθ represents the angle of rotation of the milling tool tip within the time dt; the relationship between the cutting distance of the milling tool along the axial feed direction and the cutting depth A1A3 of the cutting tool along the axial cutting direction is:

[0077]

[0078] Since both the tool and the thin-walled part will undergo slight deformation during the milling process of thin-walled parts, the distance A1A3 between the milling tool and the thin-walled part along the axial milling changes, and the changed distance A3A4 is expressed as:

[0079] A3A4=A1A3 cosΔα (3)

[0080] Where Δα is the deflection angle of the milling tool;

[0081] Combining equations (1), (2) and (3), we have:

[0082]

[0083] During the milling process, due to the helix angle α of the milling tool, the tool moves in opposite directions along the edges of the groove, and the negative shear angle β will cause the top burr to form. The relationship between the tool movement and the top burr formation during the milling of thin-walled parts is found as follows:

[0084]

[0085] Considering the actual processing conditions, dβ is very small, such as Figure 5 As shown, AA' is expressed as:

[0086] AA'=l'dβ (6)

[0087] ② Prediction model of top burr thickness in milling processing area considering thin-walled parts and tool deformation

[0088] like Figure 5 As shown, in ΔA′BP and ΔABP, we have:

[0089] PB=l'sinβ=wtanβ0=B' t (7)

[0090] Where β0 is the initial shear angle, w is the distance between the tool and the part when a negative shear angle is generated, and B' t is the geometric thickness of the burr of thin-walled parts;

[0091] Combining equation (6) and equation (7), we have:

[0092]

[0093] In the formula, the maximum value of β may appear at π / 2; integrating formula (5) and formula (8) simultaneously, we have:

[0094]

[0095] Solving equation (9) yields:

[0096]

[0097] Combining equations (7) and (10), the geometric thickness value of the burr on the top of the thin-walled part is:

[0098]

[0099] Considering the geometric characteristics of thin-walled parts, the thin-walled parts are deformed during milling, resulting in measurement errors when measuring the original burr thickness due to the deformation of the thin-walled parts, such as Figure 6 As shown; therefore, the actual measured burr thickness It is expressed as:

[0100]

[0101] Where a, b are the influencing factors of the deformation state of thin-walled parts, a, b = [-1 1], is the angle between B'P' and BU in the yoz plane after the thin-walled part is deformed, γ is the angle between CP' and CU in the xoz plane after the thin-walled part is deformed;

[0102] Combining equations (11) and (12), the actual top burr thickness is measured for:

[0103]

[0104] In the actual milling of thin-walled parts, the actual angle θ of the machining process is difficult to measure accurately, so it is difficult to accurately predict it through equation (13); therefore, a micro-element cutting segment is taken from the cutting segment from chip formation to burr formation, and the work ΔW done by chip formation is c The work done by the burr formation ΔW b Equally, we have:

[0105] ΔW c =ΔW b (14)

[0106] The milling force during milling is:

[0107]

[0108] In the formula, F x 、F y 、F z is the milling force in the x, y, and z directions in the rectangular coordinate system; where F t 、F r 、F aThey are tangential milling force, radial milling force and axial milling force respectively, φ is the immersion angle, and the top burr is formed by the negative shear angle β, which is mainly caused by the tangential milling force F t The component F ta Then, due to the existence of the tool helix angle α and the milling tool deflection angle Δα, the tangential milling force component F ta It is expressed as:

[0109] F ta =F t sinαcosΔα (16)

[0110] Chip formation work ΔW c It is expressed as:

[0111]

[0112] The work ΔW generated by the top burr b for:

[0113]

[0114] In the formula, σ e is the yield strength of the material, a p is the cutting depth;

[0115] Substituting equation (17) and equation (18) into equation (14), we get:

[0116]

[0117] Under various cutting conditions, the initial negative shear angle β0 of all materials is 20°, then the term with β0 in equation (19) is a constant, and equation (19) is rewritten as:

[0118]

[0119] In the formula,

[0120] Therefore, the top burr thickness is expressed as:

[0121]

[0122] Due to the deformation of the part, the original burr thickness will produce errors during measurement along with the deformation of the part boundary. By correcting formula (21), the actual burr thickness B is t m It is expressed as:

[0123]

[0124] Next, in order to calculate the theoretical result of the top burr thickness, the angular integration step and axial integration step of the milling tool are defined as:

[0125]

[0126] Where Δφ is the change in immersion angle; the angular integral cycle and axial integral cycle of the milling tool are:

[0127] i=1~K,j=1~L (24)

[0128] Then, the contact angle φ(i) at the bottom end point of the spiral groove of the milling tool is:

[0129] φ(i)=φ st +idφ (25)

[0130] The milling process uses a two-tooth milling cutter, and the contact angle φ(k) of the cutter tooth k is:

[0131] φ k =φ(i)+(k-1)θ p ,k=1,2 (26)

[0132] In the formula, θ P is the inter-tooth angle of the blade teeth,

[0133] The milling tool is in axial position a p (j) is:

[0134] a p (j) = jd(a p ) (27)

[0135] In addition, due to the existence of the tool helix angle α, the contact angle on the tool varies at different positions, as follows:

[0136]

[0137] During the milling process, only when the milling tool is in the cutting area (φ st ≤φ≤φ ex , for slot milling, φ st =0,φ ex =π) will produce cutting force, at cutting depth a p The instantaneous cutting thickness h on the milling tool tooth j is j (φ j (a p )) is expressed as:

[0138] h j (φ j (a p ))=f t ×sindφ j (a p ) (29)

[0139] In the formula, f t is the feed per tooth, in μm·z -1 ;

[0140] Therefore, the cutting forces in radial and tangential directions can be expressed as:

[0141]

[0142] In the formula, K tc is the tangential shear coefficient, K te is the tangential edge force coefficient, K rc is the radial shear coefficient, K te is the radial edge force coefficient;

[0143] According to formula (21), the top burr thickness of the micro-unit is expressed as:

[0144]

[0145] The tangential force is calculated by formula (30), and the top burr thickness changes with the contact angle as follows:

[0146]

[0147] Considering thin-walled parts and tool deformation, the top burr thickness in the micro-unit is:

[0148]

[0149] Then, according to formula (33), the entire top burr thickness of slot milling is calculated by integrating along the cutting depth direction, which is expressed as:

[0150]

[0151] In summary, the present invention is different from the existing analytical burr size prediction model. The proposed model fully considers the thin-walled parts and tool deformation to predict the top burr thickness. It only needs to use material properties, cutting parameters and tool geometric parameters to calculate the predicted burr thickness, without the need for experimental measurement of the shear angle and friction angle, and can accurately predict the top burr thickness in the processing area of ​​thin-walled parts.

[0152] The present invention uses an aluminum alloy thin-walled part to verify the feasibility and practicality of the present invention. The effect of the present invention is illustrated by a specific example below.

[0153] The experimental process parameters were selected as follows: reverse milling, the number of teeth N was 2, the tool radius R was 0.75 mm, the helix angle α was 45°, the part material used was Al 6061-T6, the spindle speed was 9000, 12000, 15000, 18000, 21000 rpm, the cutting depth was 0.2, 0.6, 1, 1.4, 1.8 mm, and the feed per tooth f t 1, 2, 3, 4, 5 μm·z -1 .

[0154] The above formula and data are used to calculate the top burr thickness of aluminum alloy reverse milling, and the top burr thickness under different process parameters is compared with the experimental results. Figure 7 , 8 , as shown in Figure 9.

[0155] This embodiment does not impose any formal limitation on the shape, material, structure, etc. of the present invention. Any simple modification, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention are within the protection scope of the technical solution of the present invention.

Claims

1. A method for predicting the thickness of burrs on the top of a complex thin-walled part processing area: comprising the following steps: ① A method for characterizing the geometric parameters of the burr thickness on the top of thin-walled parts is proposed; ② A prediction model for the top burr thickness in the milling processing area considering thin-walled parts and tool deformation.

2. According to the method for predicting the top burr thickness of a complex thin-walled part processing area according to claim 1, the geometric parameter characterization method of the top burr thickness of a thin-walled part is proposed, and the calculation formula is as follows: A1A2=Rdθ (1) Where R represents the geometric radius of the tool, dθ represents the angle of rotation of the milling tool tip within the time dt; the relationship between the cutting distance of the milling tool along the axial feed direction and the cutting depth A1A3 of the cutting tool along the axial cutting direction is: During the milling process of thin-walled parts, both the tool and the thin-walled parts will undergo slight deformation. Then the distance A1A3 between the milling tool and the thin-walled parts along the axial milling changes, and the distance A3A4 after the change is expressed as: A3A4=A1A3cosΔα (3) Where Δα is the deflection angle of the milling tool; Combining equations (1), (2) and (3), we have: During the milling process, due to the helix angle α of the milling tool, the tool moves in opposite directions along the edges of the groove, and the negative shear angle β will cause the top burr to form. The relationship between the tool movement and the top burr formation during the milling of thin-walled parts is found as follows: In actual processing, dβ is very small, and AA' is expressed as: AA'=l'dβ (6) This enables the characterization of the geometric parameters of the burr thickness on the top of thin-walled parts.

3. According to the method for predicting the top burr thickness of a complex thin-walled part processing area according to claim 1, the prediction model for the top burr thickness of a milling processing area taking into account the deformation of thin-walled parts and tools is calculated by the following formula: PB=l'sinβ=wtanβ0=B’ t (7) Where β0 is the initial shear angle, w is the distance between the tool and the part when a negative shear angle is generated, and B t ' is the geometric thickness of the burr of thin-walled parts; Combining equation (6) and equation (7), we have: In the formula, the maximum value of β appears at π / 2; integrating formula (5) and formula (8) simultaneously, we have: Solving equation (9) yields: Combining equations (7) and (10), the geometric thickness value of the burr on the top of the thin-walled part is: Actual measurement of the top burr thickness of thin-walled parts processing area for: Where a, b are the influencing factors of the deformation state of thin-walled parts, a, b = [-1 1], is the angle between B'P' and BU in the yoz plane after the thin-walled part is deformed, and γ is the angle between CP' and CU in the xoz plane after the thin-walled part is deformed. The measurement error caused by the deformation of the thin-walled part during the original burr thickness measurement is corrected by formula (12); Combining equations (11) and (12), the actual top burr thickness is measured for: Therefore, the top burr thickness of the milling area of ​​thin-walled parts can be obtained by formula (13):

4. The top burr thickness prediction model for milling processing area considering thin-walled parts and tool deformation according to claim 3 is characterized by: A top burr thickness prediction model considering thin-walled parts and tool deformation is established to solve the problem that the tool rotation angle θ in the milling process is difficult to accurately measure. The calculation formula is as follows: Take a micro-element cutting section from the cutting section from chip formation to burr formation in the milling process, then the work done by chip formation ΔW c The work done by the burr formation ΔW b Equally, we have: ΔW c =ΔW b (14) The milling force during milling is: In the formula, F x 、F y 、F z is the milling force in the x, y, and z directions in the rectangular coordinate system; where F t 、F r 、F a They are tangential milling force, radial milling force and axial milling force respectively, φ is the immersion angle, and the top burr is formed by the negative shear angle β, which is mainly caused by the tangential milling force F t The component F ta Then, due to the existence of the tool helix angle α and the milling tool deflection angle Δα, the tangential milling force component F ta It is expressed as: F ta =F t sinαcosΔα (16) Chip formation work ΔW c It is expressed as: The work ΔW generated by the top burr b for: In the formula, σ e is the yield strength of the material, a p is the cutting depth; Substituting equation (17) and equation (18) into equation (14), we get: Under various cutting conditions, the initial negative shear angle β0 of all materials is 20°, then the term with β0 in equation (19) is a constant, and equation (19) is rewritten as: In the formula, Therefore, the top burr thickness is expressed as: By correcting equation (21), the problem of the original burr thickness causing error during measurement due to the deformation of the part is solved. The actual burr thickness after correction is It is expressed as: Through the above calculation, the burr thickness at the top of the milling processing area considering the thin-walled parts and tool deformation is obtained.

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