Efficient machining method for large-diameter fine hole of aircraft structural part

Abstract

The invention discloses an efficient machining method for a large-diameter fine hole of an aircraft structural part, and belongs to the technical field of machining and manufacturing. The method comprises the steps that firstly, large-diameter fine hole machining equipment is selected, the specification of a large-diameter fine hole machining tool is determined, and parameters of the large-diameter fine hole machining tool are determined; secondly, a path support cone model is established, a spiral angle is calculated, a bidirectional spiral progressive hole milling cutter path is established, semi-finishing of a large-diameter fine hole is carried out, and the hole diameter size and the surface quality are evaluated; thirdly, a radius compensation value N is set according to a semi-finish machining measurement result, and finish machining of the large-diameter finish hole is carried out; and finally, measuring and inspecting the precise hole by using a three-coordinate measuring machine, and verifying whether the size, the shape precision and the surface roughness of the precise hole meet the design requirements or not. The machining efficiency of the large-diameter fine hole of the aircraft structural part can be improved; operation is easy, and potential quality hazards and risks are low; the processing cost is low, and the economy is good; large-diameter fine holes are good in up-and-down consistency, and the machining quality is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of machining manufacturing, relates to numerical control machining manufacturing technology, and specifically is an efficient numerical control machining method for large-diameter precision holes of aircraft structural parts. Background Technique

[0002] In aircraft structural parts, there are often some precision hole structures for assembly. The precision levels of these holes are generally H7 - H9, which are mainly used to install aviation standard parts such as bearings and bushings to achieve the connection between various parts of the aircraft and the pose change of the functional structure. In machining, the machining of these assembly precision holes is an important and challenging task. The parts are usually machined for all processes such as numerical control milling, fitter work, surface treatment, and heat treatment, and finally the finishing machining of the assembly holes is carried out. Once there is a problem with the precision level, the manufacturing of the parts will be in vain. Therefore, the operator is extremely cautious when machining the assembly precision holes. Since the aperture of the large-diameter precision holes of the aircraft is relatively large, it is impossible to use the methods of numerical control drilling, reaming, and boring for machining. At the same time, the precision levels of these assembly precision holes are mostly H7 - H9, and the tolerance band of this precision level is relatively small. Generally, it is impossible to achieve the machining of this precision level through numerical control milling. The most common machining method at present is: drilling (rough milling of the hole) - semi-precision milling of the hole - precision boring of the hole. The main problems in the traditional numerical control machining of large-diameter precision holes of aircraft structural parts are as follows:

[0003] 1) The overall machining efficiency of large-diameter precision holes is low;

[0004] In the traditional numerical control machining process of large-diameter precision holes of aircraft structural parts, the drilling tool is a general drill bit, the rough milling tool for the hole is a milling cutter, and the boring tool for the hole is a special boring tool. This process requires frequent tool change and calibration, resulting in an increase in the machining cycle and a decrease in machining efficiency. At the same time, the boring machining has high requirements for both the machine tool and the operator. Sometimes, it is necessary to switch to a special boring machine for machining, resulting in secondary positioning and clamping, which greatly increases the machining and manufacturing cycle of the parts. Or it is necessary to wait for an operator with rich boring experience to come to the machining machine for boring machining, resulting in the shutdown of another machine tool and a decrease in the overall production efficiency. During the boring machining process, the boring blade changes the tool diameter by the method of manual adjustment using a special wrench. This process of shutdown - opening the door - measuring - adjusting - resuming machining also increases the machining cycle.

[0005] 2) The operation difficulty is high, the requirements for the operator are high, and there are quality hazards and risks;

[0006] When performing boring machining, the operator needs to manually adjust the scale of the boring tool after calculation, often through manual programming. During machining, an internal diameter micrometer is used for measurement while machining, and an internal hexagonal wrench is used to adjust the position of the boring blade according to the measurement results. This places relatively high requirements on the operator and there is a certain threshold. Especially, there are many specifications of boring tools and the adjustment methods vary to some extent. Most CNC milling operators have limited practical operation experience in boring, resulting in unskilled operators being prone to quality problems during final boring and having a high risk of exceeding tolerances and scrapping.

[0007] 3) High tool cost, poor adaptability, and poor overall economy;

[0008] The adjustment range of the boring blade for parts is limited, usually 2 mm. Since aircraft structural parts contain many precision hole structures with different size distributions, in order to meet the full-size coverage of precision holes for multi-aircraft assembly, a large number of boring tools with different specifications need to be purchased. Its boring machining tool system includes multiple components such as a clamping boring tool shank, a clamping boring head, a cemented carbide boring tool rod, a clamping boring tool necking rod, a wrench for clamping tools, and a boring blade. Among them, according to different materials to be machined, different varieties of boring blades such as boring blades for machining aluminum alloy, boring blades for machining titanium alloy, boring blades for machining hardened steel, and boring blades for machining superalloy also need to be purchased. At the same time, due to different interfaces of different machine tools, including BT50, HSK63, HSK100, etc., multiple sets of boring machining tool systems for full-size coverage of all aircraft models need to be purchased according to different machine tool interfaces. The boring tool that meets all the above conditions often has a machining range that can only cover 2 - 10 mm, resulting in a large number of boring tools, complex varieties, difficult storage and management, low usage frequency, high procurement cost, and poor overall economy.

[0009] 4) The precision holes machined by CNC milling are prone to being machined into tapered holes, and tool marks are likely to occur in the depth direction;

[0010] CNC milling holes are mainly used for semi-finishing before boring. When machining precision holes by CNC milling without axial layer-by-layer machining, due to the inconsistent stiffness of the tool in the depth direction of cutting, the tool deflection at the bottom is more obvious, resulting in a larger size at the hole opening and a smaller size at the hole bottom, and the situation of machining into a tapered hole occurs. If layer-by-layer machining is carried out, tool marks are likely to occur between different layers when the cutting edge is short; when the cutting edge is long, more machining times are carried out for the first layer compared to the last layer, and the situation of inconsistent upper and lower dimensions in the hole depth direction will also occur.

[0011] Therefore, aiming at the CNC machining problems of large-diameter precision holes in aircraft structural parts, it is urgent to develop a more efficient, safe, economic, and low-degree-of-artificial-intervention machining method to solve the problems of low overall machining efficiency, high operation difficulty, high requirements for operators, high quality risk, high tool cost and poor adaptability, and easy machining into tapered holes during the process of CNC precision holes machining for the above-mentioned structural parts. Summary of the Invention

[0012] To solve the above technical problems, the present invention provides an efficient numerical control machining method for large-diameter precision holes of aircraft structural parts, and its main process flow is as Figure 1 shown.

[0013] The technical solution of the present invention is as follows:

[0014] An efficient numerical control machining method for large-diameter precision holes of aircraft structural parts, comprising the following steps:

[0015] The first step: Select large-diameter precision hole machining equipment.

[0016] According to information such as the diameter size, axis direction, hole type (stepped hole, through hole, blind hole, etc.), hole position, hole accuracy, surface roughness requirements, etc. of the precision hole, select finishing tools and machine tools. First, select the part finishing machine tool according to the axis direction of the precision hole to ensure that the degrees of freedom of the machine tool can cover the hole axis, so that the part can be machined for the precision hole at the same station of the same machine tool after finishing. Since the machine tool with a C swing angle can cover a wide angle range, generally a machine tool with a C swing angle is selected for the finishing of this type of part and the machining of the precision hole.

[0017] The second step: Determine the specifications of the large-diameter precision hole machining tool.

[0018] The large-diameter precision hole machining tool selects a solid carbide milling cutter, the tool diameter is d, the cutting edge length is l, and the depth of cut is t. The pre-machined precision hole diameter is D, the hole depth is H, and the allowance in the radial direction after semi-finishing is P. Then D - 4P - 10 ≥ d ≥ H / 2. Select the machining tool diameter downward within this range, which can ensure the tool stiffness, reduce the radial runout at the tool tip position, and reduce the cutting force, thereby reducing the machining deviation caused by part springback. If H / 2 ≥ D - 4P - 10, the hole is too deep and this method is not applicable for machining. When using this method, the cutting edge length l of the tool should completely cover the hole depth H, but should not be too large to cause a reduction in tool rigidity. The cutting edge length selection formula is l = H + (5 - 10). The depth of cut t should be as small as possible without causing collision to reduce the radial circular runout of the tool tip. Generally, t = l + (10 - 20). The helix angle of the tool can be selected according to the material to be machined, generally about 30°, which can achieve a better balance in cutting force, chip removal, and cutting stability. Thus, the specifications of the diameter precision hole machining tool are determined. In this step, the dimension unit is mm.

[0019] The third step: Determine the machining tool parameters of the large-diameter precision hole.

[0020] Determine the milling speed Vc of the two-way spiral progressive milling hole program according to the material to be machined, which should be consistent with the cutting speeds of the roughing and finishing tools of the part body. Set the feed per tooth fz of the tool between (0.025 - 0.5) mm / z, and apply the formula

[0021] F = f z × Z × N

[0022] V c = π × D × N / 1000

[0023] The tool rotation speed N and feed rate F in the two-way spiral progressive hole milling program can be calculated accordingly.

[0024] Step 4: Establish a path support cone model and calculate the helix angle of the two-way spiral progressive hole milling tool path.

[0025] The diameter of the pre-machined precision hole is D, the diameter of the machining tool is d, and the allowance in the radial direction during hole finishing is P, generally P = 0.5 mm. The diameter of the small end of the path support cone is D1, and the diameter of the large end is D2. Set D1 at the orifice position of the precision hole to be machined, and set D2 at the bottom position of the precision hole to be machined, where D1 = D - 2P - d, D2 = D - d. Using 3D modeling software, create a path support cone model on the digital model of the precision hole to be machined with a small end diameter of D1, a large end diameter of D2, and a height of H. The outer surface of this cone model is the tool path support surface for subsequent precision hole milling.

[0026] During the CNC milling of large-diameter precision holes, the machining form is spiral progressive in both the depth direction and the diameter direction. The helix angle of this two-way spiral progression is A, and the Rockwell hardness of the part to be machined is X. The calculation formula for A is as follows:

[0027]

[0028] Step 5: Establish the two-way spiral progressive hole milling tool path, generate the two-way spiral progressive hole milling program and conduct simulation analysis.

[0029] The two-way spiral progressive hole milling tool path includes circular arc progressive feed - two-way spiral progressive hole milling from the orifice to the bottom - circular contour milling at the bottom of the hole - circular arc progressive retraction. Among them, the feed is in the form of a circular arc at the orifice of the small end of the path support cone, and the retraction is in the form of a circular arc at the orifice of the large end. The radius of the circular arc is generally R5 - R10 mm. For the two-way spiral progressive hole milling tool path from the orifice to the bottom, use the outer surface of the path support cone in Step 3 as the tool machining path support surface, and the helix angle A in Step 4 as the helix angle of the tool machining path to generate the tool machining path along the outer surface of the path support cone from the orifice to the bottom direction. The circular contour milling path at the bottom of the hole follows the two-way spiral progressive hole milling path. With the diameter of the pre-machined precision hole being D, generate 2 - 3 circumferential contour milling hole paths at the hole depth H, that is, at the bottom of the hole. Then, in the programming software, compile the two-way spiral progressive hole milling program based on the two-way spiral progressive hole milling tool path, output the two-way spiral progressive hole milling postprocessor program in the form of I and J values and conduct simulation analysis to check the overcut and allowance status of the precision hole after finishing. Thus, the two-way spiral progressive hole milling is completed.

[0030] Step 6: Perform semi-finishing of large-diameter precision holes and evaluate the hole diameter size and surface quality.

[0031] Locate the part on the selected machine tool and perform rough and finish machining of the part to the state of a 2P radius allowance for the large-diameter precision hole. Call the large-diameter precision hole machining tool selected in Step 2 and call the two-way spiral progressive finish milling hole program prepared in Step 5. Set the tool radius compensation value N to -P and perform semi-finishing of the large-diameter precision hole, machining the hole to the state of a P radius allowance. According to the capabilities and accessories of the machine tool used, use a machine tool probe or an internal diameter micrometer to measure and evaluate multiple different depth positions from the hole mouth to the hole bottom in the depth H direction after semi-finishing the large-diameter precision hole and record the actual measured values of the hole diameter size. Check whether the actual measured values are all within the semi-finishing tolerance band and whether the surface roughness meets the design requirements.

[0032] Step 7: Set the radius compensation value N according to the semi-finishing measurement results and perform finish machining of the large-diameter precision hole.

[0033] The maximum hole diameter measured along the hole depth direction after semi-finishing the large-diameter precision hole is Da, the minimum hole diameter is Di, the diameter of the large-diameter precision hole is D, the lower deviation is 0, the upper deviation is M, the tolerance band is M, and the radius allowance of the large-diameter precision hole after semi-finishing is P.

[0034] First, check the uniformity of the hole diameter size along the depth direction. If Da - Di < 0.8M, subsequent processing can be carried out; if Da - Di ≥ 0.8M, the finish machining of the large-diameter precision hole should be stopped, and check whether the tool radius compensation value is correct, whether the tool is worn, the tool runout situation, the machine tool positioning accuracy, the repeat positioning accuracy, etc.

[0035] On the premise that the hole diameter uniformity meets the finish machining conditions, set the finish machining radius compensation value N.

[0036] If D - 2P + M > Da > Di > D - 2P, set the finish machining radius compensation value N to N = -0.1M and then perform finish machining of the large-diameter precision hole. After finish machining, perform radius compensation in increments of 0.1M based on the measurement results until the hole diameter size of the large-diameter precision hole meets the accuracy level required by the design.

[0037] If D - 2P > Da or Da > D - 2P > Di, set the finish machining radius compensation value N to N = 0 and perform finish machining of the large-diameter precision hole. And based on the multiple hole diameter measurement results in the hole depth direction after finish machining, perform radius compensation in increments of 0.1M until the hole diameter size of the large-diameter precision hole meets the accuracy level required by the design.

[0038] If Da > D - 2P + M > Di, set the finish machining radius compensation value N as N = D - Da - 2P, then perform the finish machining of the large-diameter finish hole, and based on the measurement results of multiple hole diameters in the hole depth direction after finish machining, perform radius compensation with an increment of 0.1M as a unit until the hole diameter size of the large-diameter finish hole meets the accuracy level required by the design.

[0039] If Di > D - 2P + M, the machining should be stopped, and check whether the tool radius compensation value is correct, whether the tool is worn, the tool runout situation, the machine tool positioning accuracy, the repeat positioning accuracy, etc.

[0040] Step 8: Use a coordinate measuring machine to measure and inspect the finish hole, verify whether the size, shape accuracy, and surface roughness of the finish hole meet the design requirements, and the high-efficiency NC machining of the large-diameter finish hole of the aircraft structural part is completed.

[0041] The beneficial effects of the present invention:

[0042] (1) Improve the machining efficiency of the large-diameter finish hole of the aircraft structural part;

[0043] Compared with the original machining method, the high-efficiency NC machining method of the large-diameter finish hole of the aircraft structural part proposed by the present invention reduces the process of frequently replacing, calibrating, and adjusting the tool. At the same time, there is no need to use a special boring machine. It eliminates the increase in the cycle of secondary positioning and clamping and adjustment caused by switching to a special boring machine for machining. NC milling hole realizes the co-location and co-tool machining of finish hole machining and part structure machining, without the need to replace and adjust the boring tool multiple times, shortens the machining cycle of the large-diameter finish hole of the aircraft structural part, and improves the production efficiency.

[0044] (2) Simple operation, low quality hidden dangers and risks;

[0045] The high-efficiency NC machining method of the large-diameter finish hole of the aircraft structural part proposed by the present invention does not require the operator to manually adjust the scale of the boring tool after calculating the hole diameter. Even if the hole diameter size of the large-diameter finish hole is out of the tolerance range after finish machining, compensation machining can be directly performed through the tool radius compensation and length compensation functions of the machine tool. It eliminates the error hidden dangers during manual calculation and adjustment of the boring tool scale, reduces the quality risk of finish hole machining out-of-tolerance, and the overall operation difficulty is low.

[0046] (3) Low machining cost and good economy;

[0047] Since the two-way spiral progressive milling hole can machine machining holes of multiple diameters without replacing the tool, no longer uses a boring tool for finish hole machining, and there is no need to purchase a large number of boring inserts, boring tool holders, indexable boring heads, boring tool bars, etc. according to different workpieces and different machine tool interfaces, which greatly saves the tool purchase cost and saves the tool storage space.

[0048] (4) The upper and lower consistency of the large-diameter precision hole is good, and the machining quality is high;

[0049] In the high-efficiency numerical control machining method for large-diameter precision holes of aircraft structural parts proposed by the present invention, the method of bidirectional spiral progressive milling is applied. The machining tool makes a feed movement along the spiral trajectory, with both axial feed movement and circumferential feed movement. Its end edge and circumferential edge participate in cutting at the same time, realizing uniform cutting in both axial directions of the precision hole diameter, greatly reducing the axial force, solving the problems of inconsistent hole diameters in the hole depth direction and obvious tool mark connection in layer machining, which are common in numerical control milling of holes, and the machining quality of the hole wall is high. Brief Description of the Drawings

[0050] Figure 1 Process flow chart of the high-efficiency numerical control machining method for large-diameter precision holes of aircraft structural parts;

[0051] Figure 2 Schematic diagram of a large-diameter precision hole of a typical aircraft structural part;

[0052] Figure 3 Schematic diagram of the cross-section of a large-diameter precision hole;

[0053] Figure 4 Schematic diagram of the path support cone model;

[0054] Figure 5 Schematic diagram of the bidirectional spiral progressive milling hole tool path;

[0055] In the figure: 1 is a typical aircraft structural part; 2 is a large-diameter precision hole; 3 is the positioning web surface; 4 is the machining tool; 5 is the path support cone model; 6 is the outer surface of the path support cone; 7 is the bidirectional spiral progressive milling hole tool path; 8 is the feed path; 9 is the retraction path. Detailed Description of the Invention

[0056] The following further illustrates the present invention in combination with specific implementation cases.

[0057] In the attached drawing embodiment, it is a typical aircraft structural part 1, the part material is TA15M titanium alloy, and there is a precision hole structure - a large-diameter precision hole 2 on the typical structural part 1, and its hole diameter is The hole depth is 50 mm, the surface roughness Ra is 1.6, and the specific structural form is as Figure 1 shown. The specific implementation process of the high-efficiency numerical control machining method for large-diameter precision holes of this aircraft structural part is as follows:

[0058] The first step is to select the machining equipment for the large-diameter precision hole 2.

[0059] The dimensional and precision requirements for the large-diameter precision hole 2 are as follows: hole diameter D = 120 mm, hole depth H = 50 mm, surface roughness not lower than Ra1.6, tolerance grade H7, tolerance band M = 0.035 mm, perpendicularity of the hole axis to the end face 0.05 mm. The rough and finish machining of the typical aircraft structural part 1 is based on the ventral plate surface 3 as the positioning plane, that is, the XY plane of the machining coordinate system. At this time, the angle between the large-diameter precision hole 2 and the positioning ventral plate surface 3 is 24.5°. The typical aircraft structural part 1 has a stepped hole structure, and only the large-diameter precision hole 2 has assembly precision requirements. As the stepped depth increases, the hole diameter gradually decreases, and the remaining stepped holes are all non-assembly precision holes. In order to ensure that the finish machining of the large-diameter precision hole 2 can be carried out at the same station of the same machine tool after the finish machining of the typical aircraft structural part 1, it is necessary to ensure that the degrees of freedom of the machine tool can cover the axis of the large-diameter precision hole 2, that is, the machine tool spindle can be swung to the coaxial position with the axis of the large-diameter precision hole 2. Therefore, the selected machining machine tool is a five-axis gantry machining center, and this equipment has BC swing angles. The swing angle range is C360° and B±110°, which can meet the requirements of in-position machining.

[0060] In the second step, determine the specifications of the cutting tool 4 for machining the large-diameter precision hole 2.

[0061] The allowance in the radial direction after semi-finish machining of the large-diameter precision hole 2 is P = 0.5 mm. The cutting tool 4 selected for its machining is a solid carbide milling cutter with a diameter of d, a cutting edge length of l, and a plunge depth of t. Then 120 - 2 - 10 ≥ d ≥ 50 / 2. Select the cutting tool diameter d downward within the range of (25 - 108) mm. While ensuring the tool stiffness and reducing the radial runout at the tool tip position, reduce the cutting force and further reduce the machining deviation caused by part springback. According to the formula, the cutting edge length of the cutting tool 4 is selected in l = 50 + (5 - 10), and the plunge depth is selected in t = l + (10 - 20). Therefore, the specifications of the cutting tool 4 for machining the large-diameter precision hole 2 are determined as a solid carbide milling cutter with a diameter d = 30 mm, a cutting edge length l = 55 mm, a plunge depth t = 70 mm, a helix angle of 30°, and 4 teeth for machining TA15 titanium alloy.

[0062] In the third step, determine the machining parameters of the cutting tool 4 for machining the large-diameter precision hole 2.

[0063] Based on the cutting tool machining parameters for the NC finish machining of TA15 M titanium alloy parts, the milling speed during the machining of the large-diameter precision hole 2 is selected as Vc = 50 m / min. The feed per tooth fz during machining is selected as 0.02 mm / z. Then the rotational speed N during the milling of the large-diameter precision hole 2 is N = 1000×50 / π / 30 = 530 rpm, and the feed speed F of the tool milling is F = 0.02×4×530 = 48 mm / min.

[0064] In the fourth step, establish the path support cone model 5 and calculate the helix angle A of the two-way spiral progressive milling hole tool path.

[0065] The finishing allowance P in the radial direction of the large-diameter precision hole 2 is 0.5 mm. The diameter of the small end of the path support cone is D1 = 120 - 2×0.5 - 30 = 89 mm, and the diameter of the large end is D2 = 120 - 30 = 90 mm. Using 3D modeling software, a path support cone model 5 with a small end diameter of 89 mm, a large end diameter of 90 mm, and a height of 50 mm is created on the 3D model of the large-diameter precision hole 2 to be machined. At the same time, the outer surface 6 of the path support cone is obtained, and the outer surface 6 of the path support cone is the tool path support surface for the subsequent precision hole milling. When numerically controlling the milling of the large-diameter precision hole 2, the helix angle of the bidirectional spiral progressive tool path is A. If the Rockwell hardness of the part to be machined, TA15M titanium alloy, is X = 35 HRC, then the helix angle is A = 82.8 + 35 / 6 - 35 2 / 1050 = 87.473°.

[0066] Step 5: Determine the bidirectional spiral progressive hole milling tool path 7, generate the bidirectional spiral progressive hole milling program and conduct simulation analysis.

[0067] The bidirectional spiral progressive hole milling tool path 7 consists of an arc progressive feed path - a bidirectional spiral progressive milling path from the hole entrance to the hole bottom - a circumferential contour milling path at the hole bottom - an arc progressive retraction path. Among them, the tool feeds in the form of an arc at the small end hole entrance of the path support cone model 5 and retracts in the form of an arc at the large end hole entrance of the path support cone model 5. The feed and retraction tool paths are set as 90° arcs with a radius of R5 mm. Taking the outer surface 6 of the path support cone as the tool machining path support surface and the helix angle of 87.473° as the helix angle of the tool machining path, a bidirectional spiral progressive milling path is generated along the outer surface 6 of the path support cone from the hole entrance to the hole bottom direction. Finally, a circumferential contour milling path with a diameter of Φ120 mm is generated for 3 revolutions at the 50 mm depth position of the large-diameter precision hole 2. Thus, the bidirectional spiral progressive hole milling tool path 7 is generated. Generate the bidirectional spiral progressive hole milling postprocessor program in the form of I and J values and conduct simulation analysis to check the overcut and allowance status of the precision hole after finishing.

[0068] Step 6: Conduct semi-finishing of the large-diameter precision hole 2 and evaluate the hole diameter size and surface quality.

[0069] Locate the part 1 to be machined on a five-axis gantry machining center, and perform rough and finish machining on the part until the radius allowance of the large-diameter precision hole 2 is 1 mm. Call the machining tool 4 for the large-diameter precision hole 2 selected in the second step, call the two-way spiral progressive milling hole program compiled in the fifth step, set the tool radius compensation value to -0.5 mm, and start the semi-finish machining of the large-diameter precision hole, machining the hole to a state with a radius allowance of 0.5 mm. Use an internal micrometer to measure and record the actual measured values of the hole diameters at three depth positions of 15 mm, 30 mm, and 45 mm from the hole mouth to the hole bottom along the depth direction of the large-diameter precision hole 2. The maximum is Φ119.037 mm, and the minimum is Φ119.013 mm. Check the surface roughness of the hole after radius machining. If the precision inspection meets the Ra1.6 requirement, finish machining can be carried out.

[0070] In the seventh step, based on the semi-finish machining measurement results, set the finish machining radius compensation value N and perform the finish machining of the large-diameter precision hole.

[0071] After the semi-finish machining of the large-diameter precision hole 2, the maximum hole diameter measured along the 50-mm hole depth direction is Da = 119.041 mm, the minimum hole diameter is Di = 119.008 mm. The diameter of the large-diameter precision hole is 120 mm, the lower deviation is 0, and the upper deviation is 0.035 mm. After the semi-finish machining, the radius allowance of the large-diameter precision hole is 0.5 mm.

[0072] First, check the uniformity of the hole diameter size along the depth direction. (119.037 - 119.013) = 0.024 < 0.028 = (0.8 × 0.035), so subsequent machining can be carried out. Then, set the finish machining radius compensation value N.

[0073] After determination, Da = 119.041 > 119.035 > Di = 119.008. Calculate the finish machining radius compensation value N for the large-diameter precision hole 2. N = D - Da - 2P = 120 - 119.041 - 2 × 0.5 = -0.041 mm. Call the two-way spiral progressive milling hole program edited in the fifth step, set the program tool radius compensation value to -0.041 mm, and perform machining. After machining, use an internal micrometer to measure and record the actual measured values of the hole diameters at three depth positions of 15 mm, 30 mm, and 45 mm from the hole mouth to the hole bottom along the depth direction of the large-diameter precision hole 2. The maximum is Φ120.010 mm, and the minimum is Φ119.988 mm. It does not all fall within the range of (120 - 120.035) mm. Therefore, with an increment of 0.0035 mm as a unit for radius compensation, call the two-way spiral progressive milling hole program edited in the fifth step, set the finish machining radius compensation value N to -0.041 + 0.0035 = -0.006 mm, and perform hole machining until the hole diameter size of the large-diameter precision hole 2 meets the tolerance requirements.

[0074] In the eighth step, a coordinate measuring machine is used to measure and inspect the precision holes to verify whether the dimensions, shape accuracy, and surface roughness of the precision holes meet the design requirements, and the NC machining of the large-diameter precision hole 2 of the aircraft structural part is completed.

[0075] The above-described embodiments only represent the implementation modes of the present invention, but should not be construed as limiting the scope of the patent of the present invention. It should be noted that for those skilled in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. An efficient machining method for large-diameter precision holes of aircraft structural parts, characterized in that, It includes the following steps: The first step: Select large-diameter precision hole machining equipment; The second step: Determine the specifications of large-diameter precision hole machining tools; The third step: Determine the machining tool parameters of large-diameter precision holes; The fourth step: Establish a path support cone model and calculate the helix angle of the two-way spiral progressive milling hole tool path; The fifth step: Establish a two-way spiral progressive milling hole tool path, generate a two-way spiral progressive milling hole program and conduct simulation analysis; The sixth step: Conduct semi-finishing machining of large-diameter precision holes and evaluate the hole diameter size and surface quality; The seventh step: According to the semi-finishing machining measurement results, set the radius compensation value N and conduct finish machining of large-diameter precision holes; The eighth step: Use a coordinate measuring machine to measure and inspect the precision holes, verify whether the dimensional, shape accuracy and surface roughness of the precision holes meet the design requirements, and the high-efficiency NC machining of large-diameter precision holes in aircraft structural parts is completed.

2. The high-efficiency machining method for large-diameter precision holes of an aircraft structural part according to claim 1, wherein, The specific content of the first step is as follows: According to the information such as the diameter size, axis direction, hole type, hole position, hole accuracy and surface roughness requirements of the precision hole, select the finishing tool and machine tool; first select the part finishing machine tool according to the axis direction of the precision hole to ensure that the degrees of freedom of the machine tool can cover the hole axis, so that the part can be machined for the precision hole at the same station of the same machine tool after finishing.

3. The high-efficiency machining method for large-diameter precision holes of an aircraft structural member according to claim 1, characterized in that, In the first step, a machine tool with a C swing angle is selected for the finishing and precision hole machining of this type of part.

4. The high-efficiency machining method for large-diameter precision holes of an aircraft structural part according to claim 2, characterized in that, The specific content of the second step is as follows: For large-diameter precision hole machining tools, a solid carbide milling cutter is selected. The tool diameter is d, the cutting edge length is l, and the depth of cut is t; the diameter of the pre-machined precision hole is D, the hole depth is H, and the allowance in the radial direction after semi-finishing is P; then D - 4P - 10 ≥ d ≥ H / 2; if H / 2 ≥ D - 4P - 10, the hole is too deep and this method is not applicable for machining; the cutting edge length l of the tool should completely cover the hole depth H, and the formula for selecting the cutting edge length of the tool is l = H + (5 - 10); the depth of cut t is t = l + (10 - 20), and the helix angle of the tool is selected according to the work material; thus, the specifications of the large-diameter precision hole machining tool are determined; in this step, the dimension unit is mm.

5. The high-efficiency machining method for large-diameter precision holes of an aircraft structural part according to claim 4, characterized in that, The specific content of the third step is as follows: Determine the milling speed Vc of the two-way spiral progressive milling hole program according to the work material, which is the same as the cutting speed of the rough and finish machining tools of the part body; set the feed per tooth fz of the tool between (0.025 - 0.5) mm / z, and apply the formula: F = f z × Z × N V c = π × D × N / 1000 Then the tool speed N and feed rate F in the two-way spiral progressive milling hole program can be calculated.

6. The high-efficiency machining method for large-diameter precision holes of an aircraft structural member according to claim 5, characterized in that The specific content of the fourth step is as follows: The diameter of the pre-machined precision hole is D, the diameter of the machining tool is d, the allowance in the radial direction during hole finish machining is P, the small end diameter of the path support cone is D1, and the large end diameter is D2; set D1 at the hole entrance position of the to-be-machined precision hole, and set D2 at the hole bottom position of the to-be-machined precision hole, where D1 = D - 2P - d, D2 = D - d. Using 3D modeling software, create a path support cone model on the digital model of the to-be-machined precision hole with a small end diameter of D1, a large end diameter of D2, and a height of H. The outer surface of this cone model is the tool path support surface for subsequent precision hole milling; When performing CNC milling machining on large-diameter precision holes, the machining form is spiral progressive in both the depth direction and the diameter direction. The spiral angle of this two-way spiral progression is A, and the Rockwell hardness of the part to be machined is X. Then the calculation formula of A is as follows:

7. The high-efficiency machining method for large-diameter precision holes of an aircraft structural member according to claim 6, characterized in that, The allowance P = 0.5 mm.

8. The high-efficiency machining method for large-diameter precision holes of an aircraft structural member according to claim 6, characterized in that, The fifth step mentioned above, the specific two-way spiral progressive milling hole tool path is as follows: The tool feeds in the form of an arc at the small end orifice of the path support cone and retracts in the form of an arc at the large end orifice. The arc radius is R5 - R10 mm; for the two-way spiral progressive milling hole tool path from the orifice to the bottom of the hole, the outer surface of the path support cone in the third step is used as the tool machining path support surface, and the spiral angle A in the fourth step is used as the spiral angle of the tool machining path. The tool machining path is generated along the outer surface of the path support cone from the orifice to the bottom of the hole; the circumferential contour milling path at the bottom of the hole is after the two-way spiral progressive milling hole path. With the diameter of the pre-machined precision hole being D, 2 - 3 circumferential contour milling hole paths are generated at the bottom of the hole at the hole depth H; then in the programming software, a two-way spiral progressive milling hole program is compiled with the two-way spiral progressive milling hole tool path, and the two-way spiral progressive milling hole postprocessor is output in the form of I and J values and subjected to simulation analysis to check the overcut and allowance status of the precision hole after finishing; thus, the two-way spiral progressive milling hole is completed.

9. The high-efficiency machining method for large-diameter precision holes of an aircraft structural member according to claim 8, characterized in that, The sixth step mentioned above is specifically as follows: Locate the part on the selected machine tool, and perform rough and finish machining of the part to the state of the radius allowance 2P of the large-diameter precision hole; call the large-diameter precision hole machining tool selected in the second step, call the two-way spiral progressive precision in the fifth step, set the tool radius compensation value N to -P, perform semi-finishing machining of the large-diameter precision hole, and machine the hole to the state of the radius allowance P; according to the capabilities and accessories of the used machine tool, use the machine tool probe or internal micrometer to measure and evaluate multiple different depth positions from the orifice to the bottom of the hole in the depth H direction after semi-finishing machining of the large-diameter precision hole and record the measured values of the hole diameter size, and check whether the measured values are all within the semi-finishing machining tolerance band and whether the surface roughness meets the design requirements.

10. The high-efficiency machining method for large-diameter precision holes of an aircraft structural part according to claim 9, characterized in that The seventh step mentioned above is specifically as follows: After semi-finishing machining of the large-diameter precision hole, the maximum hole diameter measured along the hole depth direction is Da, the minimum hole diameter is Di, the diameter of the large-diameter precision hole is D, the lower deviation is 0, the upper deviation is M, the tolerance band is M, and the radius allowance of the large-diameter precision hole after semi-finishing machining is P; First, check the uniformity of the hole diameter size along the depth direction. If Da - Di < 0.8M, subsequent machining can be carried out; if Da - Di ≥ 0.8M, the finish machining of the large-diameter precision hole should be stopped, and check whether the tool radius compensation value is correct, whether the tool is worn, the runout of the tool, the machine tool positioning accuracy, and the repeat positioning accuracy; On the premise that the hole diameter uniformity meets the finish machining conditions, set the finish machining radius compensation value N: If D - 2P + M > Da > Di > D - 2P, set the finish machining radius compensation value N to N = -0.1M and then perform the finish machining of the large-diameter precision hole. After finish machining, perform radius compensation with an increment of 0.1M based on the measurement results until the hole diameter size of the large-diameter precision hole meets the accuracy level required by the design; If D - 2P > Da or Da > D - 2P > Di, set the finishing radius compensation value N to N = 0 and then perform the finishing of the large-diameter precision hole. Based on the measurement results of multiple hole diameters in the hole depth direction after finishing, perform radius compensation with an increment of 0.1M as a unit until the aperture size of the large-diameter precision hole meets the accuracy level required by the design; If Da > D - 2P + M > Di, set the finishing radius compensation value N to N = D - Da - 2P and then perform the finishing of the large-diameter precision hole. Based on the measurement results of multiple hole diameters in the hole depth direction after finishing, perform radius compensation with an increment of 0.1M as a unit until the aperture size of the large-diameter precision hole meets the accuracy level required by the design; If Di > D - 2P + M, the machining should be stopped to check whether the tool radius compensation value is correct, whether the tool is worn, the tool runout condition, the machine tool positioning accuracy, and the repeat positioning accuracy.

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