A method for high-precision boring of bracket-type holes

Abstract

This invention belongs to the field of machining technology, specifically relating to a high-precision boring method for bracket-type parts, comprising the following steps: Step 1: Rough machining of each hole in the bracket-type part; Step 2: Flat grinding of the bottom surface of the flat plate and the outer surfaces of the two vertical plates of the bracket-type part; Step 3: Fixing an L-shaped backing fixture to the machining equipment, fixing the bracket-type part on the L-shaped backing fixture with surface D facing upward; setting a reference block under surface A, leveling the flatness of surface D, and then precision machining two holes a, and precision machining three holes b using holes a as a reference; Step 4: Disassembling the bracket-type part and checking that the dimensions and geometric tolerances of the two holes a and three holes b are qualified before proceeding to the next step; Step 5: Fixing and aligning the support assembly on the machining equipment; Step 6: Fixing the bracket-type part on the support assembly; aligning the machine tool using a dial indicator; Step 7: Precision machining of the four holes c, and disassembling the bracket-type part after finishing.

Description

Technical Field

[0001] This invention belongs to the field of machining technology, specifically relating to a method for high-precision boring of bracket-type holes. Background Technology

[0002] A type of mounting bracket part is made of ultra-high strength steel 35Cr2Ni4MoA, a Class II forging. The part has high hardness and tensile strength σb≥1230MPa. The part has a U-shaped structure, complex shape, poor rigidity, and nine through holes of different diameters distributed on three mutually perpendicular planes. The dimensional and positional accuracy requirements of each hole are high, between IT5 and IT7. The coaxiality of the two Ф26H7 (+0.021 0) through holes on the two parallel planes of the U-shaped opening of the part is Ф0.012, and the perpendicularity to end face A is Ф0.02. The positional tolerance of the three Ф12H7 (+0.015 0) through holes is Ф0.03, and the positional tolerance to each reference plane is Ф0.05. The bottom surface of the U-shaped structure of the part has four Ф15H7 (+0.018 0) through holes, with a positional tolerance of Ф0.03, and a symmetry of 0.035 with the Ф26H7 (+0.021 0) through holes and with the U-shaped opening. Currently, this part is in small-batch production, with an annual output of approximately 150 pieces.

[0003] The machining of this part must not only ensure the dimensional accuracy of each hole, but also meet the positional requirements between the holes and with respect to each reference surface. See Figure 1 Typically, machining bracket-type parts with complex spatial shapes and high precision requirements for the positioning of multiple holes requires the use of a high-precision five-axis machining center. The part is clamped in one setup, and the machining of the precision holes on each surface is completed sequentially by changing the direction of the machine spindle. Alternatively, a high-precision four-axis machining center can be used, where the part is fixed on the fourth axis, and the precision holes on each surface are machined sequentially by rotating the fourth axis. Currently, the electromechanical equipment manufacturer responsible for machining this bracket does not possess high-precision five-axis or four-axis machining centers and is unable to successfully complete the machining of the bracket parts. Summary of the Invention

[0004] Purpose of the invention: To utilize several high-precision CNC three-axis machining centers or digital display coordinate boring machines existing in the electromechanical equipment manufacturing plant, along with simple tooling fixtures, to complete the machining of bracket-type parts with complex spatial shapes and high requirements for the positional accuracy of multiple holes, so as to meet the dimensional and geometric tolerance requirements of the design drawings. This solves the problem that when precision boring high-precision holes in bracket-type parts, it is impossible to clamp and align all holes at once, resulting in deformation of the machined parts, out-of-tolerance hole dimensions, and difficulty in meeting various geometric tolerances.

[0005] Technical solution: A method for high-precision boring of bracket-type parts, wherein the bracket-type part to be processed includes a horizontal plate, the bottom surface of which is denoted as H surface, two vertical plates are arranged parallel above the horizontal plate, each of the two vertical plates has a coaxial hole a, one of the vertical plates has three holes b on its edge, the outer surface of this vertical plate is denoted as D surface, and the outer surface of the other vertical plate is denoted as A surface; a hole c is opened at each of the four corners of the horizontal plate; The processing method includes the following steps: Step 1: Roughly machine each hole of the bracket-type parts, leaving a finishing allowance for each hole; Step 2: Grind the bottom surface of the flat plate and the outer surfaces of the two vertical plates of the support-type part. Step 3: Fix the L-shaped backing fixture to the processing equipment, fix the bracket-type parts on the L-shaped backing fixture with the D side facing up; set a reference pad under the A side, level the flatness of the D side, and then finish machine the two holes a, and finish machine the three holes b with the holes a as the reference. Step 4: Disassemble the bracket-type parts and check the dimensions and geometric tolerances of the two holes (a) and three holes (b). If they are within acceptable limits, proceed to the next step. Step 5: Fix the support assembly to the processing equipment and align it; Step Six: Fix the bracket-type parts to the support assembly; align the machine tool using a dial indicator; Step 7: Perform precision machining on the four C-holes. After precision machining, disassemble the bracket-type parts. Step 8: Check whether each hole meets the requirements.

[0006] Furthermore, in step one, a finishing allowance of 1mm to 2mm is left for each hole.

[0007] Furthermore, in step two, the parallelism between the ground surface D and surface A is no greater than 0.02 mm, and the perpendicularity between the ground surface D and surface A and surface H is no greater than 0.02 mm.

[0008] Furthermore, in step three, the flatness of the leveled surface D is within 0.02mm, and the coaxiality of the two finished holes a is no greater than 0.012mm and the perpendicularity to the reference surface A is no greater than 0.02mm. The positional tolerance of the three finished b holes shall not exceed 0.03 mm, and the positional tolerance of the three b holes relative to surface D, surface B, and line E shall not exceed 0.05 mm. Surface B is the inner surface of hole a, and line E is perpendicular to surface H and intersects the axis of hole a.

[0009] Furthermore, in step five, the support assembly includes: a convex plate, a support mandrel, and two bolts; The vertical plate of the convex plate has a central hole, and a support mandrel is installed in the central hole through a bushing; a threaded hole is provided at each of the two ends of the top of the vertical plate, and a bolt is screwed into each threaded hole; Ensure the parallelism between the axis of the support mandrel and the horizontal plane is no greater than 0.015mm; then remove the mandrel for later use.

[0010] Furthermore, in step six, the support mandrel passes through the central hole and two holes a of the support-type part to fix the support-type part to the support assembly, and at the same time, the parallelism of the H surface of the support-type part is adjusted by adjusting the two bolts. For aligning bracket-type parts, the runout within a 130mm × 80mm area on the H-side should be within 0.02mm; The overlap error of the left and right ends of the support mandrel should not exceed 0.015mm; The center error between the machine tool spindle and the A and D planes should not exceed 0.015mm.

[0011] Furthermore, in step six and step seven, when finishing the four C-holes, the cutting is performed in multiple passes, with each pass removing 0.3mm to 0.5mm of excess material.

[0012] Furthermore, in step eight, the detection standard is as follows: Use a dial indicator to check whether the diameters of holes a, b, and c meet the seventh-grade tolerance requirements; Use a coordinate measuring machine to measure whether the coaxiality of the two holes a is no greater than 0.012mm, and whether the perpendicularity of the two holes a to surface A is no greater than 0.02mm; Check whether the positional accuracy of the three b holes is no greater than 0.03 mm, and whether the positional accuracy of the three b holes relative to surface D, surface B, and line E is no greater than 0.05 mm; Check whether the symmetry of the four holes c with the axis of hole a is not greater than 0.035mm, and whether the symmetry with the center of symmetry of surfaces A and D is not greater than 0.035mm.

[0013] Furthermore, in steps three and five, the processing equipment is a three-axis machining center or a digital display coordinate boring machine with a displacement accuracy of no more than 0.015 mm.

[0014] Beneficial effects The method of this invention for machining high-precision holes in the mounting bracket ensures the required diameter and geometric tolerances of the holes on all surfaces of the space. This method utilizes a conventional three-axis machining center or a digital display coordinate boring machine, combined with simple tooling supports, pressure plates, and L-shaped fixtures, enabling convenient part installation, reliable positioning, and rapid alignment. The method is easy to operate, requires minimal operator skill, guarantees quality, and achieves a high part qualification rate, thus improving production efficiency and saving production costs. Attached Figure Description

[0015] Figure 1 This is a simplified diagram of the mounting bracket structure; Figure 2 These are schematic diagrams of the mounting bracket's various planes and vertical surfaces; Figure 3 This is a schematic diagram of the clamping process on the mounting bracket, which has two Ф26H7 through holes and three Ф12H7 through positions. Figure 4 This is a schematic diagram of the four Ф15H7 through-holes on the bottom surface of the mounting bracket for machining and installation; 1. Support assembly, 2. Support spindle, 3. M10 bolt, 4. Mounting bracket. Detailed Implementation

[0016] A method for high-precision boring of bracket-type holes includes: a mounting bracket part to be machined, a support assembly for installation and fixation, a Ф26 support mandrel with a clearance of no more than 0.015mm between it and two Ф26H7 holes on the mounting bracket, two M10 bolts with a length of 15mm, and an L-shaped backing clamp.

[0017] Mounting brackets are complex-shaped, high-precision parts, making them difficult to clamp and align during machining, and the dimensional and positional accuracy of each hole is hard to control. This method avoids using high-precision five-axis or four-axis machining centers, utilizing existing machine tools and simple tooling fixtures to complete the boring of high-precision holes on three mutually perpendicular surfaces of the mounting bracket in steps. This method involves first rough machining each through hole and then finish machining each reference plane. The part is then fixed to an L-shaped support, and two Ф26H7 holes and three Ф12H7 through holes are completed sequentially. Next, the part is mounted on a support assembly fixed to the machine tool and pre-adjusted for relative positioning. Each time the part is installed, the Ф26 support mandrel is inserted into the hole that mates with the support assembly, and the two ends of the mandrel are leveled. By adjusting two M10 bolts, the bottom surface of the part is made horizontal and fixed. Through symmetrical clamping and support using this fixture, the part experiences uniform force and is less prone to deformation during machining. Finally, the machine tool is aligned with the outer diameter of the Ф26 mandrel and the two U-shaped sides of the part (dimension 800.05) to achieve symmetry. The four Ф15H7 (+0.018 0) through holes on the bottom surface of the mounting bracket are then bored in two to three passes to achieve high dimensional and positional accuracy. This method utilizes existing machine tools and simple tooling fixtures to install parts, enabling rapid installation, alignment, clamping, and machining of mounting bracket parts. It meets the dimensional and geometric tolerance requirements of various precision holes in the parts, allowing ordinary operators to complete high-precision hole machining of mounting bracket parts.

[0018] The steps for precision boring of high-precision holes in this type of bracket are as follows: (1) First, rough machine the two Ф26H7, three Ф12H7 and four Ф15H7 through holes on the mounting bracket, leaving a 1-2mm finishing allowance for each hole; (2) Grind the vertical and parallel surfaces of the U-shaped structure of the mounting bracket to ensure that the parallelism and perpendicularity of each reference plane are no greater than 0.02mm. The positions of each surface are shown in the figure. Figure 2 Schematic diagram; (3) See Figure 3 First, fix the L-shaped support on a three-axis machining center or digital display coordinate boring machine with a displacement accuracy of no more than 0.015mm. Then, clamp the mounting bracket parts onto the L-shaped support, with surface D facing upwards. Use a reference shim to level surface A, ensuring the flatness of surface D is within 0.02mm. Boring two Ф26H7 through holes in three passes: the first pass uses a cutting depth of 0.5mm, a cutting speed of 1000m / min, and a feed rate of 600 mm / min for rough boring; the second pass uses a cutting depth of 0.30mm, a cutting speed of 1200 m / min, and a feed rate of 800 mm / min for finish boring. After checking the dimensions with a dial indicator, the third pass uses a cutting depth of 0.1mm-0.2mm and a cutting speed of 1200 m / min. The holes are precision bored to the final size at a feed rate of 1200 mm / min, while simultaneously meeting the requirements of coaxiality of the two holes at Ф0.012 mm and perpendicularity to the A-plane reference plane at 0.02 mm. Then, using the two machined Ф26H7 holes as references, each hole is bored twice. The first cut has a depth of cut of 0.6-0.7 mm, a cutting speed of 800 m / min, and a feed rate of 600 mm / min. The second cut has a depth of cut of 0.2-0.4 mm, a cutting speed of 1000 m / min, and a feed rate of 800 mm / min. Three Ф12H7 through holes are bored in sequence, meeting the requirements of hole diameter Ф12+0.018 0, positional tolerance Ф0.03, and positional tolerance Ф0.05 ​​mm relative to each reference plane D, B, and E. (4) Disassemble the mounting bracket parts and inspect each hole on the parts on the coordinate measuring machine. After each hole meets the size and form and position tolerance requirements, proceed to the next process for further processing. In particular, the size of the two Ф26H7 through holes, Ф26+0.021 0 and the coaxiality Ф0.012mm, affect the installation, fixing and processing of the next process. (5) See Figure 4 Place the support assembly 2 on a three-axis machining center or digital display coordinate boring machine with a displacement accuracy of no more than 0.015mm; screw two M10 bolts 3 into the threaded holes on the upper surface of the support assembly 1; insert the Ф26 support mandrel 2 into the inner hole of the Ф26 (+0.025 +0.015) bushing that matches the support assembly 1, straighten and align the mandrel in the X direction by no more than 0.015mm, then press the support assembly 1 with a pressure plate, and remove the Ф26 support mandrel 2 for later use; (6) As shown in Figure 5, insert the mounting bracket 4 upside down into the boss of the support assembly 1, and insert the Ф26 support spindle 2 into the Ф26 (+0.025 +0.015) hole of the mounting bracket 4 and the support assembly 1; adjust the two M10 bolts 3 and tighten the parts, level the H surface of the mounting bracket 4 within the range of 130mm 80mm with the runout within 0.02mm, and fix it with a pressure plate.

[0019] (7) Use a dial indicator on the machine tool to align the center lines of the outer circles at both ends of the Ф26 support spindle 2, ensuring that the coaxiality error is no greater than 0.015mm; use a dial indicator to align the symmetrical center planes of surfaces A and D of the mounting bracket 4, ensuring that the symmetry error is no greater than 0.015mm. Prepare a boring tool and bore the first Ф15H7 hole in three passes. The parameters for the first pass are: depth of cut 0.5-0.7mm, cutting speed 800m / min, feed rate 600 mm / min; the parameters for the second pass are: depth of cut 0.3-0.4mm, cutting speed 1000m / min, feed rate 800 mm / min; and the parameters for the third pass are: depth of cut 0.1-0.2mm, cutting speed 1200m / min, feed rate 800 mm / min. After the first hole is machined to a satisfactory condition, move the machine tool coordinates and complete the machining of the second Ф15H7 hole in three feeds. Then continue machining the third and fourth Ф15H7 holes. After machining is completed, reset the machine tool, loosen the two M10 bolts 3, remove the Ф26 support mandrel 2, and the part can be disassembled.

[0020] Hole Diameter Inspection: The diameters of the through holes at two locations (Ф26H7 +0.021 0), three locations (Ф12H7 +0.015 0), and four locations (Ф15H7 +0.018 0) on mounting bracket 4 are measured using a dial indicator. Then, a coordinate measuring machine is used for initial positioning to check the coaxiality (Ф0.012mm) of the two Ф26H7 holes and their perpendicularity to datum A (0.02mm); the positional accuracy (Ф0.03mm) of the three Ф12H7 holes and their positional accuracy (Ф0.05mm) to datums D, B, and E; and the symmetry (Ф0.035mm) of the four Ф15H7 holes relative to the datum hole (Ф26H7) and their symmetry (Ф0.035mm) to datums A and D.

Claims

1. A method for precision boring of high-precision holes in bracket-type structures, characterized in that: The support-type parts to be processed include a horizontal plate, the bottom surface of which is denoted as surface H. Two vertical plates are arranged parallel to each other above the horizontal plate. Each of the two vertical plates has a coaxial hole a. One of the vertical plates has three holes b on its edge. The outer surface of this vertical plate is denoted as surface D. The outer surface of the other vertical plate is denoted as surface A. A hole c is opened at each of the four corners of the horizontal plate. The processing method includes the following steps: Step 1: Roughly machine each hole of the bracket-type parts, leaving a finishing allowance for each hole; Step 2: Grind the bottom surface of the flat plate and the outer surfaces of the two vertical plates of the support-type part. Step 3: Fix the L-shaped backing fixture to the processing equipment, and fix the bracket-type parts on the L-shaped backing fixture with surface D facing upwards; set a reference block under surface A, level the flatness of surface D to within 0.02mm, finish machine the coaxiality of the two holes a to no more than 0.012mm and the perpendicularity to the reference surface A to no more than 0.02mm, and finish machine the three holes b with the holes a as the reference, the positional tolerance of the three holes b to no more than 0.03mm, and the positional tolerance of the three holes b to the surface D, surface B and line E to no more than 0.05mm; surface B is the inner surface of hole a, and line E is perpendicular to surface H and intersects the axis of hole a; Step 4: Disassemble the bracket-type parts and check the dimensions and geometric tolerances of the two holes (a) and three holes (b). If they are within acceptable limits, proceed to the next step. Step 5: Fix the support assembly onto the processing equipment and align it; the support assembly includes: a convex plate, a support mandrel, and two bolts; the vertical plate of the convex plate has a central hole, and the support mandrel is installed in the central hole through a bushing; there is a threaded hole at each end of the top of the vertical plate, and a bolt is screwed into each threaded hole; align the parallelism between the axis of the support mandrel and the horizontal plane to no more than 0.015mm; then remove the mandrel for later use; Step Six: Fix the bracket-type parts to the support assembly; align the machine tool using a dial indicator; fix the bracket-type parts to the support assembly by passing the support mandrel through the center hole and the two holes a on the bracket-type parts, while adjusting the parallelism of the H-face of the bracket-type parts by adjusting the two bolts; align the H-face of the bracket-type parts by 130mm. The runout within 80mm is within 0.02mm; the overlap error of the left and right ends of the support spindle is not greater than 0.015mm; the center error of the machine tool spindle and the A and D planes is not greater than 0.015mm. Step 7: Perform precision machining on the four C-holes. After precision machining, disassemble the bracket-type parts. Step 8: Check whether each hole meets the requirements.

2. The method according to claim 1, characterized in that: In step one, each hole is left with a finishing allowance of 1mm to 2mm.

3. The method according to claim 2, characterized in that: In step two, the parallelism between the ground surface D and surface A is no greater than 0.02 mm, and the perpendicularity between the ground surface D and surface A and surface H is no greater than 0.02 mm.

4. The method according to claim 3, characterized in that: In step six and step seven, when finishing the four C-holes, the cutting is performed in multiple passes, with each pass removing 0.3mm to 0.5mm of excess material.

5. The method according to claim 4, characterized in that: In step eight, the detection standard is: Use a dial indicator to check whether the diameters of holes a, b, and c meet the seventh-grade tolerance requirements; Use a coordinate measuring machine to measure whether the coaxiality of the two holes a is no greater than 0.012mm, and whether the perpendicularity of the two holes a to surface A is no greater than 0.02mm; Check whether the positional accuracy of the three b holes is no greater than 0.03 mm, and whether the positional accuracy of the three b holes relative to surface D, surface B, and line E is no greater than 0.05 mm; Check whether the symmetry of the four holes c with the axis of hole a is not greater than 0.035mm, and whether the symmetry with the center of symmetry of surfaces A and D is not greater than 0.035mm.

6. The method according to claim 5, characterized in that: In steps three and five, the processing equipment is a three-axis machining center or a digital display coordinate boring machine with a displacement accuracy of no more than 0.015 mm.

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