A machining method of double tooth profile of DP steering rack

Abstract

The application discloses a machining method of a DP steering gear rack double-tooth profile, S1: milling a plane; the rack is placed into a rack clamp to mill the first plane, and then taken out and placed into the rack clamp again, clamped through a positioning assembly, and then the second plane is milled, and the machining allowance is completed at one time in the two times of milling; S2: gear grinding; the plurality of racks after burrs are removed are placed into the rack clamp to complete the precision machining of the tooth profile and the plane on the first plane; the racks are taken out and placed into the rack clamp again, clamped through the positioning assembly, and then the precision machining of the tooth profile and the plane on the second plane is completed; S3: heat treatment; the tooth profile on the first plane and the second plane is quenched and heated respectively, and then the whole rack is tempered and heated and cooled; and S4: straightening; the rack after the heat treatment is placed into a straightening machine to be straightened. While the tooth profile precision is guaranteed, the machining time can be effectively reduced, and the production efficiency is improved.

Description

Technical Field

[0001] This invention belongs to the field of automotive steering rack processing technology, specifically relating to a processing method for a double-tooth profile of a DP steering rack. Background Technology

[0002] like Figure 1 As shown, the DP steering rack has two tooth profiles, which are respectively located on a first plane and a second plane, with the first and second planes offset circumferentially from each other. The machining method for these two tooth profiles is as follows: the tooth profiles on the two planes are ground using rough milling and multiple grinding processes. Then, the tooth profiles on the first plane are heat-treated and straightened, followed by radial heat treatment and straightening of the tooth profiles on the second plane. While this machining method ensures accuracy, it is time-consuming and has low production efficiency. Summary of the Invention

[0003] This invention proposes a machining method for a double-tooth profile of a DP steering rack, which can effectively reduce machining time and improve production efficiency while ensuring tooth profile accuracy.

[0004] Therefore, the technical solution adopted by the present invention is: a method for machining a double-tooth profile of a DP steering rack, comprising the following steps:

[0005] S1: Milling the plane; multiple pre-processed racks are placed into the rack fixture, and then the milling machine is started to mill the first plane; after the multiple racks that have been milled on the first plane are taken out, they are placed into the rack fixture and positioned and clamped by the positioning component that positions the first plane, and then the milling machine is started to mill the second plane. In both milling operations, the machining allowance is completed in one operation.

[0006] S2: Gear grinding; First, deburr the multiple racks that have completed milling the plane in S1. Then, place the deburred racks into the rack fixture and start the grinding machine to complete the finishing of the tooth profile and plane on the first plane in one go. Then, take out the multiple racks that have completed grinding on the first plane and place them into the rack fixture. After positioning and clamping them by the positioning component that positions the first plane, start the grinding machine to complete the finishing of the tooth profile and plane on the second plane in one go.

[0007] S3: Heat treatment; First, the tooth profiles on the first plane and the second plane are quenched and heated respectively, and then the entire rack is tempered and heated and then cooled;

[0008] S4: Straightening; The heat-treated rack is placed into a straightening machine for straightening.

[0009] As a preferred option in the above scheme, the heat treatment equipment used in S3 is a scanning medium-frequency quenching machine, and a rack fixing device is provided in the scanning medium-frequency quenching machine for fixing the rack and preventing the rack from deforming; when heating the tooth shape on the first plane and the second plane, induction quenching is achieved by scanning quenching coil; spray cooling is used for cooling, and the rack is dried after cooling to room temperature.

[0010] Further preferably, the positioning component includes a mounting plate disposed on a milling fixture or a rack fixture, a support plate disposed on the mounting plate, and a rack hole disposed on the support plate for the corresponding rack to pass through. When the rack is placed on the corresponding fixture, the first plane of the rack is located at the rack hole. A wedge is disposed on either the left or right side of each rack hole to limit the position of the first plane, and the wedge is disposed in the rack hole in a way that allows it to slide up and down. A sliding cylinder is disposed at the lower end of the wedge to realize the up and down sliding of the wedge, and the sliding cylinder is disposed on the mounting plate.

[0011] Further preferably, the pretreatment includes semi-fine grinding and fine grinding of the outer circle of the rack in sequence, and after fine grinding, the surface roughness of the rack is guaranteed to be no higher than 0.4μm by roughness detection. During roughness detection, at least three tests need to be performed at at least three different locations and the average value is taken.

[0012] Further optimization involves correcting the tooth profile of the grinding wheel using grinding rollers after each processing step to ensure the accuracy and stability of the grinding wheel.

[0013] Further optimization involves first straightening in sections, then correcting the high points, then correcting the remaining points to bring them within the straightening tolerance, then performing sequential correction and fine correction to bring them within the acceptance tolerance range, and finally performing overall correction. The number of straightening operations in the entire straightening process should not exceed 25.

[0014] The beneficial effects of this invention are:

[0015] 1) Compared with the existing DP steering rack machining method, the machining allowance is completed in one step during milling, and the tooth profile and plane are finished in one step during grinding. The overall number of machining steps is less, and multiple racks can be machined at the same time, which can effectively reduce machining time and improve production efficiency.

[0016] 2) In this application, by adding a positioning component to the rack fixture, it is made suitable for clamping the DP steering rack. At the same time, the rack fixture is a milling machine fixture used for ordinary steering racks, so that the rack fixture can achieve universality between DP steering rack and ordinary steering rack fixtures, thereby effectively reducing costs.

[0017] 3) The combination of positioning components and rack fixtures can be used not only on milling machines but also on grinding machines, thus achieving universality between milling machine fixtures and grinding machine fixtures. This not only reduces the tedious work of fixture management but also avoids the problem of incorrect fixture use. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the DP steering gear rack.

[0019] Figure 2 This is a schematic diagram of the positioning component in this invention.

[0020] Figure 3 This is a perspective view of the positioning component in this invention.

[0021] Figure 4 This is a schematic diagram of the installation structure in this invention.

[0022] Figure 5 This is a schematic diagram of the positioning component installed on the rack and pinion clamp in this invention.

[0023] Figure 6 This is a schematic diagram of the scanning quenching coil equipped in the scanning medium-frequency quenching machine of the present invention.

[0024] Reference numerals: Mounting plate-16, Support plate-17, Rack hole-17a, Slide hole-17b, Wedge block-18, Sliding cylinder-19, Pad plate-20, Cylinder rod-21, Cylinder connector-22. Detailed Implementation

[0025] The present invention will be further described below with reference to the embodiments and accompanying drawings:

[0026] like Figure 2-6 As shown, a method for machining a double-tooth profile of a DP steering rack includes the following steps:

[0027] Step 1: Milling the plane. Milling the plane consists of two steps: milling the first plane and milling the second plane.

[0028] Milling the first plane: Multiple pre-processed racks are placed into a rack fixture, and the milling machine is started to mill the first plane. Milling the second plane: After milling the first plane, the racks are removed and placed into the rack fixture, and positioned and clamped by the positioning component that positions the first plane. The milling machine is then started to mill the second plane. In both milling operations, the machining allowance is completed in one pass. The rack fixture is the milling machine fixture disclosed in Chinese Patent CN117047425A.

[0029] When milling a plane, a CNC milling machine equipped with the rack and pinion fixture described in this application is used. The machine tool uses gear transmission and has a large cutting force, which can achieve a machining allowance of more than 5mm in one pass. Specifically, the rack and pinion fixture is equipped with 8 pads, meaning that 8 racks can be clamped at the same time. The machining allowance is 5mm, the depth of cut is 5mm, the machining cycle time is about 32.5s, the speed is 600-800r / min, and the feed rate is 400-500mm / min.

[0030] The pretreatment process includes semi-finish grinding and finish grinding of the outer diameter of the rack, with the surface roughness of the rack after finish grinding being tested to ensure it does not exceed 0.4 μm. During roughness testing, at least three measurements are taken at at least three different locations, and the average value is calculated. Both semi-finish grinding and finish grinding are performed using a CNC wide-wheel centerless grinder, with a wheel dressing interval of 180-220 times, each dressing increment being 0.1-0.3 mm, and the wheel linear speed between 30-35 m / s.

[0031] Step 2: Gear grinding. The multiple racks with milled surfaces in S1 are first deburred, and then the gears are moved to the grinding machine for grinding. Gear grinding is divided into two steps: machining the tooth profile on the first plane and machining the tooth profile on the second plane.

[0032] Machining of the tooth profile on the first plane: After deburring, multiple racks are placed into the rack fixture, and the grinding machine is started to complete the finishing of the tooth profile and plane on the first plane in one operation. Machining of the tooth profile on the second plane: After the multiple racks with the first plane gears are ground, they are placed into the rack fixture, and after being positioned and clamped by the positioning component that positions the first plane, the grinding machine is started to complete the finishing of the tooth profile and plane on the second plane in one operation.

[0033] After each grinding cycle, the tooth profile of the grinding wheel needs to be corrected using grinding rollers to ensure the accuracy and stability of the grinding wheel. After grinding, heat treatment is required to increase the hardness of the tooth profile, and then the rack is straightened using a straightening machine.

[0034] During gear grinding, a high-powered grinding machine manufactured by Hangzhou Machine Tool Co., Ltd. is used. This machine utilizes rollers to dress the grinding wheel teeth, and can grind more than 4mm of allowance in one pass, maintaining a tooth profile accuracy of grade 7 or higher. The rack fixture has six placement planes, allowing for the clamping of six racks at a time. The machining allowance is 4mm, the feed rate is 120-150mm / min, and the machining cycle is 34 seconds. The machined tooth profile accuracy is: span distance: ±0.015mm; tooth profile inclination angle: ±0.04°; tooth profile pressure angle: ±0.1°; surface roughness Ra0.8. After each grinding pass, the grinding wheel is dressed using rollers, with a dressing amount of 0.03-0.05mm.

[0035] The positioning components used above include a mounting plate 16 mounted on a rack fixture, a support plate 17 mounted on the mounting plate 16, and a rack hole 17a for the corresponding rack to pass through. When the rack is placed on the rack fixture, the first plane of the rack is exactly located at the rack hole 17a. A wedge 18 for limiting the position of the first plane is provided on either the left or right side of each rack hole 17a, and the wedge 18 is slidably disposed in the rack hole 17a. A sliding cylinder 19 for realizing the up-and-down sliding of the wedge 18 is provided at the lower end of the wedge 18, and the sliding cylinder 19 is mounted on the mounting plate 16, that is, a sliding groove 17b for the wedge to slide up and down is provided vertically through the support plate, and the sliding groove communicates with either the left or right side wall of the rack hole. The wedge height is adjusted by a sliding cylinder so that the wedge clamps the first plane after the previous machining into the rack hole, thus ensuring the phase angle of the first plane relative to the second plane during milling and gear grinding; during installation, the rack is simply passed through the rack hole, making installation convenient.

[0036] To facilitate the adjustment of the rack hole height and enable the machining of multiple racks of various specifications, a shim 20 is provided between the support plate and the mounting plate. A clearance groove is also provided on the shim and mounting plate corresponding to the slide groove to allow the output end of the sliding cylinder to pass through. To ensure the clamping effect of the rack, the end of the rack hole furthest from the slide groove is designed as a V-shaped structure with the opening facing the slide groove.

[0037] To allow for the mounting of more racks on the wedge, a convenient disassembly mounting structure is provided between the wedge and the output end of the sliding cylinder. The mounting structure includes a cylinder rod 21 located at the output end of the sliding cylinder, a cylinder connector 22 on the cylinder rod, and a T-slot (smaller at the top, larger at the bottom) at the upper end of the cylinder rod. Correspondingly, a T-block that can be inserted into the T-slot is provided at the lower end of the cylinder connector. An opening is provided on one side of the T-slot to facilitate the insertion of the T-block. The cylinder connector 22 is fixed to the wedge by threaded tightening, and a limiting nut is provided on the cylinder connector to restrict the tightening position of the wedge. When the wedge needs to be replaced, it can be done simultaneously with the replacement of the pad; that is, all wedges can be replaced by removing the support plate.

[0038] Step 3: Heat treatment. First, the tooth profiles on the first and second planes are quenched and heated separately. Then, the entire rack is tempered and heated before cooling. The equipment used is a scanning medium-frequency quenching machine. To prevent rack deformation during the heating process, a rack fixing device is provided. The rack fixing device used is the induction hardening device for automotive steering racks disclosed in Chinese Patent CN208748156U.

[0039] To further improve efficiency, the scanning medium-frequency quenching machine includes a quenching station and a return station, and both the quenching station and the return station are equipped with two independent scanning quenching coils (e.g., Figure 4 As shown, the rack can simultaneously perform heat treatment on two planes, namely quenching and tempering, with only one clamping operation. After tempering, it is cooled by spraying, and the rack is dried after cooling to room temperature. During quenching, it is necessary to ensure a layer depth symmetry of 0.2mm, metallographic grade 3-7, phase angle change ≤0.3°, span distance change ≤0.03mm, and runout ≤0.3mm at 50mm from both ends of the rack.

[0040] Step 4: Straightening. The heat-treated rack is placed into a straightening machine for straightening. During the straightening process, nine measuring points are set up: three measuring points at intervals for each tooth profile, and one measuring point at each end of each tooth profile. The straightening machine uses a self-learning straightening device, such as the DP steering rack straightening machine manufactured by Jilin Ruiming.

[0041] To ensure efficient and accurate straightening, the straightening machine employs the following strategy: first, segmental straightening; then, high-point correction; next, correction of the remaining points to within the straightening tolerance; then, sequential correction and fine correction to within the acceptance tolerance; and finally, overall straightening. The total number of straightening operations during the entire process does not exceed 25. During segmental straightening, the entire rack is divided into three segments: the left rack segment, the middle round bar segment, and the right rack segment, with each segment intersecting with the others. During the straightening of each segment, the measuring points on both sides of each segment are used as reference points. During overall straightening, the measuring points at both ends of the workpiece are used as reference points for straightening.

[0042] Overall straightening involves using the measuring points at both ends of the workpiece as a reference to measure and correct the middle measuring point until the correction reaches the set qualified value. If the straightening number exceeds 25 times and the set qualified value is still not reached, it is directly judged as a defective product. Usually, the straightness requirement of the DP steering gear rack is no more than 0.15mm.

Claims

1. A method for machining a double-tooth profile rack in a DP steering gear, characterized in that, Includes the following steps: S1: Milling the plane; multiple pre-processed racks are placed into the rack fixture, and then the milling machine is started to mill the first plane; after the multiple racks that have been milled on the first plane are taken out, they are placed into the rack fixture and positioned and clamped by the positioning component that positions the first plane, and then the milling machine is started to mill the second plane. In both milling operations, the machining allowance is completed in one operation. The positioning component includes a mounting plate (16) disposed on a rack fixture, a support plate (17) disposed on the mounting plate (16), and a rack hole (17a) disposed on the support plate (17) for the corresponding rack to pass through. When the rack is placed on the rack fixture, the first plane of the rack is located at the rack hole (17a). A wedge (18) for limiting the position of the first plane is disposed on either the left or right side of each rack hole (17a), and the wedge (18) is slidably disposed in the rack hole (17a). A sliding cylinder (19) for realizing the sliding of the wedge (18) is disposed at the lower end of the wedge (18), and the sliding cylinder (19) is disposed on the mounting plate (16). S2: Gear grinding; First, deburr the multiple racks that have completed milling the plane in S1. Then, place the deburred racks into the rack fixture and start the grinding machine to complete the finishing of the tooth profile and plane on the first plane in one go. Then, take out the multiple racks that have completed grinding on the first plane and place them into the rack fixture. After positioning and clamping them by the positioning component that positions the first plane, start the grinding machine to complete the finishing of the tooth profile and plane on the second plane in one go. S3: Heat treatment; First, quench and heat the tooth profiles on the first and second planes respectively, and then temper and cool the entire rack. S4: Straightening; The heat-treated rack is placed into a straightening machine for straightening.

2. The machining method for the double-tooth profile of the DP steering rack according to claim 1, characterized in that: In S3, the heat treatment equipment used is a scanning medium-frequency quenching machine, which is equipped with a rack fixing device to fix the rack and prevent it from deforming. When heating the tooth profile on the first and second planes, induction quenching is achieved by scanning quenching coils. Spray cooling is used for cooling, and the rack is dried after cooling to room temperature.

3. The machining method for the double-tooth profile of the DP steering rack according to claim 1, characterized in that: The pretreatment includes semi-fine grinding and fine grinding of the outer circle of the rack in sequence. After fine grinding, the surface roughness of the rack is guaranteed to be no higher than 0.4 μm by roughness detection. During roughness detection, at least three tests are required at at least three different locations and the average value is taken.

4. The machining method for the double-tooth profile of the DP steering rack according to claim 1, characterized in that: After each processing step, the tooth profile of the grinding wheel needs to be corrected using grinding rollers to ensure the accuracy and stability of the grinding wheel.

5. The machining method for the double-tooth profile of the DP steering rack according to claim 1, characterized in that: During the straightening process, first straighten in sections, then correct the high points, then correct the remaining points to bring them within the straightening tolerance, then perform sequential correction and fine correction to bring them within the acceptance tolerance range, and finally perform overall correction. The number of straightening operations in the entire straightening process should not exceed 25.

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