A process for machining bearing steel wire raceways and a tooling for machining steel wire rings.

Abstract

This invention discloses a process and tooling for machining bearing wire raceways, relating to the field of bearing processing, and solving problems such as difficulty in forging ultra-thin wire rings, large machining deformation, and unstable grinding positioning. The process, targeting ultra-thin 4Cr13 stainless steel wire rings (finished width 4mm), centers on "batch forging + stepped stress relief + composite heat treatment," with a 14-step process including bar sawing, four-piece integral forging (improving material utilization to 95%+), isothermal annealing, rough turning / finish turning, cryogenic treatment (-90℃), multi-cycle rough grinding + additional tempering, etc., ensuring the precision and toughness of the finished product. The tooling includes an upper pressure plate, a positioning ring (double positioning steps), a lower pressure plate, and connecting screws, adaptable to inner / outer wire rings, solving the problem of grinding movement in weakly magnetic ultra-thin parts, and improving dimensional consistency. After application, the finished product qualification rate reaches 99%, the raceway roundness is ≤0.007mm, and the bearing life is extended by 50%+, promoting the localization of wire raceway bearings.

Description

Technical Field

[0001] This invention relates to the field of bearing processing technology, specifically to a process for processing bearing steel wire raceways and a matching steel wire ring processing fixture. Background Technology

[0002] As a key bearing category, the domestic development of wire raceway bearings is crucial. These bearings consist of an outer ring, inner ring, inner / outer wire rings, rolling elements, cage, threaded locking ring, and sealing ring. The inner / outer wire rings are one of the core components of the wire raceway bearing, playing a key role in ensuring smooth rolling of the rolling elements. These bearings offer advantages such as compact structure, small cross-section, ability to withstand axial and radial loads simultaneously, strong impact resistance, and adjustable rotational damping, making them widely used in high-precision, high-load applications.

[0003] However, existing technologies face numerous challenges in processing inner and outer wire rings (and wire raceways): First, the finished width of a single wire ring is only 4mm, making it an ultra-thin part, which is difficult to forge individually and prone to poor forming. Second, during processing, a clamping portion must be reserved for each wire ring, resulting in low material utilization and high costs. Third, ultra-thin wire rings are prone to deformation during turning and grinding (especially grinding the wire raceways), making it difficult to guarantee the accuracy of the wire raceways. Fourth, conventional heat treatment processes cannot simultaneously ensure the high hardness and toughness of the wire rings, affecting the wear resistance of the wire raceways and the overall service life of the bearings. Fifth, the wire rings are made of 4Cr13 stainless steel (with weak magnetism), and their small size and limited material make it difficult to grind the wire raceways without specialized tooling, as they are easily deflected by the grinding force, leading to high processing difficulty. Furthermore, it is difficult to guarantee the compatibility of individual wire rings during assembly, resulting in uneven gaps and poor coaxiality during subsequent assembly, which hinders the localization process of wire raceway bearings. Summary of the Invention

[0004] The core objective of this invention is to overcome the shortcomings of existing technologies and provide a collaborative "process-tooling" solution for processing ultra-thin steel wire rings. This solution provides a process for processing bearing steel wire raceways, addressing the problems of difficult forging, low material utilization, large processing deformation, and difficulty in balancing heat treatment performance of ultra-thin steel wire rings. It also provides matching steel wire ring processing tooling to solve the problems of unstable positioning and poor dimensional consistency of components during steel wire ring grinding of the steel wire raceways. Ultimately, this invention achieves a balance between processing accuracy, performance, and cost for ultra-thin steel wire rings, meeting the industrialization needs of domestically produced steel wire raceway bearings.

[0005] The technical solution of the present invention: This process for machining bearing steel wire raceways, specifically for ultra-thin 4Cr13 stainless steel wire rings (finished width 4mm), is designed around the core principles of "batch forging to reduce costs, stepped stress relief to control shape, composite heat treatment to improve efficiency, and tooling collaboration to ensure precision." It comprises a 14-step full-process route, with key technical details for each step as follows: Step 1: Sawing the bar stock. 4Cr13 stainless steel bars conforming to GB / T1220-2007 standard are selected (the bar diameter is selected based on the material consumption per piece calculated according to the forging size, and the length-to-diameter ratio during upsetting should not exceed 2.5-3mm). CNC sawing machines (accuracy ±0.1mm) are used to saw the bars into pre-set lengths, ensuring that the sawed end face is flat, the end face of the billet is perpendicular to the axis, and the blanking deviation is controlled within a small range (e.g. -5g to +5g) to ensure that the blank size and other dimensions after subsequent forging meet the processing requirements.

[0006] Step 2: Forging the blank, The process employs an integral forging method with four wire rings per group. In stages (production ≤ 100 groups), a "free forging + rolling expansion" process is used: first, the bar stock is forged into a cylindrical integral blank (outer diameter slightly larger than the finished product outer diameter by 5-8 mm) through free forging; then, holes are punched, and the blank is rolled and expanded using a rolling expansion machine. This refines the internal grain structure of the blank, increases its density (grain size ≤ 10 μm), and simultaneously forms an integral structure suitable for subsequent processing (including a pre-formed outline of four wire rings). This method eliminates the need to reserve clamping sections for each piece, increasing material utilization to over 95%.

[0007] Step 3: Isothermal annealing, The entire blank is placed in a box-type annealing furnace and subjected to an isothermal annealing process of "heating-holding-rapid cooling-isothermal-slow cooling": first, it is heated to 850-880℃ (heating rate 10-15℃ / min), held for 1-2 hours (holding time is determined according to the blank thickness, e.g., 1.5 hours for a 20mm thickness), then rapidly cooled to 700-750℃ using an in-furnace fan (cooling rate 20-25℃ / min), held isothermally for 1-1.5 hours, and finally slowly cooled to room temperature with the furnace (cooling rate ≤5℃ / min). After annealing, the hardness of the blank is controlled at HB197-241, ensuring that tool life is increased by more than 30% during subsequent turning operations (tool wear ≤0.1mm / 100 pieces).

[0008] Step 4: Rough turning, The annealed blank is clamped on a CNC lathe (model such as CK6150) and machined using a "multi-tool layered cutting" method: first, the two end planes are machined (ensuring the blank length tolerance is (0, +0.3) mm), then the outer diameter or inner hole is machined to the "finished size + 2~3 mm machining allowance", and finally the chamfer is machined (angle 45°, side length 1 mm). The machining parameters are set as follows: linear speed 40~50 r / min, feed rate 0.4~0.5 mm / r, depth of cut 1~2 mm, and the surface roughness after machining is ≤Ra6.3 to avoid blank deformation due to excessive cutting force.

[0009] Step 5: Stress-relieving tempering / shaping The rough-turned blank is placed in a tempering furnace and subjected to "low-temperature stress-relief tempering": heated to 250–300℃ (heating rate 10℃ / min), held for 1 hour, and then air-cooled to room temperature (to avoid oxidation caused by furnace cooling). After tempering, the blank is shaped using a precision shaping machine (accuracy ±0.01mm). Through "multi-point positioning and clamping + micro-correction", the ovality (Vdsp) of the blank is controlled to ≤0.5mm and the planar warpage (Ape) is controlled to ≤0.2mm, laying a precision foundation for subsequent finish turning.

[0010] Step 6: Finish turning, The shaped blank is fixed on a horizontal CNC lathe (model such as HTC3250) using a three-jaw self-centering chuck (centering accuracy ≤0.005mm). A "high-precision finishing" process is employed: first, the two end planes are finished (ensuring a thickness tolerance of ±0.05mm); then, the outer diameter / inner hole is finished to the "finished size + 0.5~1mm machining allowance"; finally, the initially formed wire raceway is finished (leaving a grinding allowance of approximately 0.6mm for the raceway radius) and the chamfer (radius R2mm) are finished. The finishing parameters are set as follows: linear speed 40~50r / min, feed rate 0.2mm / r, depth of cut 0.3~0.5mm, and the surface roughness after machining ≤Ra3.2. After each finishing operation, a 3mm wide carbide cutter is used to cut the finished part from the rough-machined blank, resulting in four independent semi-finished wire rings.

[0011] Step 7: Softening, The single wire ring semi-finished product and the auxiliary surface grinding fixture are placed together in a surface grinder (model such as M7130). The cut surface is ground using the "magnetic chuck + fixture-assisted positioning" method. The grinding wheel is a white corundum grinding wheel (80# grit). The grinding parameters are: grinding wheel linear speed 30m / s, feed rate 0.005mm / r, depth of cut 0.01~0.02mm. After grinding, the surface roughness is ≤Ra1.0 and the surface parallelism is ≤0.012mm. This ensures that the two ends of the semi-finished product are parallel and avoids deformation due to uneven heating during subsequent heat treatment.

[0012] Step 8: Overall quenching, The semi-finished steel wire rings, after being soft-ground, are placed into a special quenching fixture (made of heat-resistant steel to prevent high-temperature deformation) and sent to a box-type quenching furnace. First, they are heated to 600–800℃ (preheating to relieve stress) and held for 30 minutes. Then, the temperature is increased to 980–1030℃ (austenitizing temperature) and held for 20 minutes (the holding time depends on the thickness of the semi-finished product; for example, 20 minutes for a 5mm thickness). Finally, they are cooled to room temperature using air cooling or a salt bath (salt bath cooling is faster and produces more uniform hardness). After quenching, the Rockwell hardness of the semi-finished product is controlled at HRC50–55 to ensure the steel wire raceway has basic wear resistance.

[0013] Step 9: Cryotherapy The quenched semi-finished product is placed in a liquid nitrogen cryogenic chamber (temperature control accuracy ±2℃) and subjected to a "gradient cryogenic" process: cooling to -90℃ at a rate of 2-3℃ / min (to avoid cracking due to excessive cooling), holding at this temperature for 1 hour (to allow for full transformation of the martensitic structure), and then allowing it to naturally return to room temperature (no heating required to avoid structural springback). Cryogenic treatment can refine the martensite grains (grain size ≤5μm), increasing the impact toughness of the semi-finished product by 15%-20% (from ≤10J / cm² to ≥12J / cm²) without reducing hardness.

[0014] Step 10: Stress-relieving tempering of the workpiece. The cryogenically cooled semi-finished product is placed in a tempering furnace and subjected to a "low-temperature tempering" process: heated to 150–200°C (heating rate 5°C / min), held for 1.5–2 hours, and then cooled to room temperature in the furnace. After tempering, the hardness of the semi-finished product is tested to ensure that the hardness difference between the same semi-finished product is ≤2HRC (e.g., HRC 52–54), to avoid uneven wear of the grinding wheel during subsequent grinding due to uneven hardness.

[0015] Step 11: Plastic surgery After tempering, the semi-finished product is reshaped using a precision forming machine. At this point, the semi-finished product has a certain hardness (HRC50~55). During the forming process, an "elastic indenter + micro-correction" method is used to avoid damaging the surface: the ellipticity (Vdsp) is controlled to ≤0.35mm and the planar warpage (Ape) is controlled to ≤0.14mm, providing a higher precision workpiece foundation for subsequent grinding processes.

[0016] Step 12: Coarse grinding + additional tempering, Rough grinding: Grind the two end faces sequentially (to the finished width + 0.2mm allowance), outer diameter / inner hole (to the finished size + / - 0.2mm allowance), and wire raceway (to the finished contour + / - 0.3mm allowance). When grinding the raceway, use the "wire ring machining fixture as described in claim 5" to clamp the semi-finished product (the gap between the fixture positioning ring and the semi-finished product after grinding is 0.02-0.03mm). Use a "multi-blade rough grinding + additional tempering" cycle (cycles ≥ 2 times): After each rough grinding, place the semi-finished product in a tempering furnace at 160-200℃ for 2 hours to release grinding internal stress. The following accuracy indicators must be met after rough grinding: The flatness of the datum surface is ≤0.008mm, and the parallelism of the non-datum surface relative to the datum surface is ≤0.015mm; The outer diameter of the outer wire ring and the inner diameter of the inner wire ring have a roundness ≤ 0.01 mm and a cylindricity ≤ 0.015 mm. The coaxiality of the inner hole of the outer wire ring and the outer circle of the inner wire ring is ≤ φ0.015mm; The parallelism difference between the center of the steel wire raceway and the base plane is ≤0.012mm; the roundness of the ball bottom diameter is ≤0.018mm; and the circular runout is ≤0.015mm. Surface roughness ≤ Ra1.0, residual magnetism ≤ 0.8mT.

[0017] Step 13: Fine grinding / grinding. Precision grinding is performed using a precision grinding machine: A silicon carbide grinding wheel (120# grit) is selected, and the grinding parameters are: wheel linear speed 35 m / s, feed rate 0.002 mm / r, depth of cut 0.005–0.01 mm. The two end faces are precision ground sequentially (to the finished width, tolerance ±0.005 mm), the outer diameter / inner hole (to the finished size, tolerance IT6 grade), and the wire raceway (to the finished contour, raceway radius tolerance ±0.003 mm). The semi-finished product is clamped using the wire ring machining fixture described in claim 5 during the precision grinding process. The following accuracy indicators must be met after precision grinding: The flatness of the base surface is ≤0.006mm, and the parallelism of the non-datum surface relative to the datum surface is ≤0.012mm; The outer diameter of the outer wire ring and the inner diameter of the inner wire ring have a roundness ≤ 0.007 mm and a cylindricity ≤ 0.009 mm. The parallelism of the center of the steel wire raceway relative to the base surface is ≤0.009mm, the roundness of the ball bottom diameter is ≤0.007mm, and the circular runout is ≤0.009mm; Surface roughness ≤ Ra0.8, residual magnetism ≤ 0.8mT.

[0018] Step 14: Cut, The semi-finished product after precision grinding is finally cut using a slow wire EDM machine (accuracy ±0.002mm): the cutting wire diameter is 0.1mm, the cutting speed is 5-8mm² / min, the cutting width is controlled between 0.2-0.3mm, and the surface roughness is ≤Ra1.6. After cutting, the finished inner and outer wire rings with complete wire raceways are obtained. The finished products must undergo 100% inspection (using a coordinate measuring machine, accuracy ±0.001mm) to ensure that key indicators meet the standards.

[0019] This wire ring machining fixture is specifically designed for the "rough grinding and fine grinding of the wire raceway" process mentioned above. It consists of two parts: a fixture for external wire rings and a fixture for internal wire rings. The two fixtures have the same structural principle, and their specific structures are as follows: Overall components of the tooling: Each set of tooling includes an upper pressure plate, a positioning ring, a lower pressure plate, and 6 connecting screws (one distributed every 60° along the circumference). All parts are made of 45# steel (heat-treated to a hardness of HRC28~32 to ensure rigidity and wear resistance). After assembly, the overall coaxiality is ≤0.01mm.

[0020] Positioning ring (core positioning component): The positioning ring has a ring structure. Taking the external wire ring positioning fixture as an example: it has two positioning steps (for clamping two wire rings at the same time). The two positioning steps are located on the same side (the one for the external wire ring is located inside the inner hole of the positioning ring). The diameter of the step is matched with the outer circle of the wire ring after grinding to ensure that the circumferential gap between the wire ring and the positioning step is controlled at 0.2-0.3mm after assembly (ensuring positioning accuracy and facilitating assembly and disassembly). The height of the positioning step is 0.1mm lower than the height of the wire ring (e.g., when the height of the wire ring is 4mm, the height of the step is 3.9mm). After clamping, the upper pressure plate can slightly pre-tighten the wire ring to prevent movement during grinding. The concentricity of the large outer circle of the positioning ring (as the alignment datum of the grinding machine) and its mating surface with the wire ring (the surface of the positioning step) is ≤0.015mm to ensure that the alignment datum is consistent with the workpiece positioning datum.

[0021] Upper pressure plate and lower pressure plate: Both the upper and lower pressure plates are annular plate structures with a thickness of 8-10mm. Taking the outer wire ring positioning fixture as an example: the inner diameter of the upper pressure plate is about 2mm smaller than the inner hole of the positioning ring (for pressing the wire ring), and the outer diameter is slightly smaller than the outer diameter of the positioning ring (to avoid interference when the grinding machine is aligning the reference). The upper and lower pressure plates are each provided with 6 through holes and threaded holes that are compatible with the connecting screws.

[0022] Connecting screws: M8 socket head cap screws (compliant with GB / T70.1-2019 standard) are selected, made of 40Cr (heat treated and galvanized, hardness HRC30~35, rust prevention grade ≥5); the screw length is determined according to the thickness of the upper pressure plate + the thickness of the locating ring + the thread length of the lower pressure plate (tightening torque is controlled at 8~10N・m—too little torque will easily lead to insufficient clamping force and workpiece movement during grinding; too much torque will easily deform the wire ring or damage the tooling thread. Precise control with a torque wrench is used to ensure uniform clamping force (clamping force fluctuation ≤5%).

[0023] Tooling usage process: Taking the grinding of the wire raceway of an outer wire ring as an example, the tooling usage steps are as follows: Workpiece clamping: Place the two semi-finished outer wire rings to be ground (outer diameter φ211.2mm) into the two positioning steps of the positioning ring (step diameter φ211.4mm, gap 0.2mm), so that the end face of the wire ring is in contact with the end face of the positioning step; Tooling assembly: Cover the upper and lower pressure plates, align the through hole of the upper pressure plate with the positioning ring and the mounting hole of the lower pressure plate, insert 6 M8 connecting screws, and tighten them with an Allen wrench in a "diagonal alternating" sequence (torque 8 N·m). Datum alignment: Use a dial indicator (accuracy 0.001mm) attached to the grinding machine spindle to align the outer diameter of the positioning ring (radial runout ≤0.005mm) to ensure that the tooling is coaxial with the grinding machine spindle; Grinding process: Start the grinding machine and grind the steel wire raceway according to the preset parameters. During the grinding process, the workpiece is cooled by coolant (emulsion, concentration 8% to 10%) to avoid grinding heat causing workpiece deformation. Workpiece disassembly: After grinding is completed, turn off the grinding machine, loosen the connecting screws in a "diagonal alternation" sequence, remove the upper pressure plate and finished steel wire ring, clean the iron filings from the surface of the tooling, and reuse it.

[0024] The beneficial effects of this invention are: Advantages of the process: Batch forging of wire ring blanks increases material utilization by over 20%; composite heat treatment improves the toughness of the wire rings by 15%–20%, and the wear resistance of the wire raceway meets high load requirements; multi-stage stress relief and precision grinding of the wire raceway control the axial / radial clearance of the finished wire rings to 0.01–0.05 mm, and the end face runout of the wire raceway to ≤0.05 mm, meeting high precision requirements; clearly defined process parameters ensure strong process stability and allow for batch processing of wire rings (and wire raceways). Tooling advantages: Full degree of freedom constraint avoids wire ring deviation during grinding of wire raceways, improving the roundness and coaxiality accuracy of wire raceways by more than 30%; two wire rings can be clamped at once to grind wire raceways, resulting in good dimensional consistency among multiple wire rings (wire raceway center parallelism difference ≤0.01mm), improving subsequent assembly efficiency by 40% and wire raceway assembly accuracy by 25%; simple structure, convenient disassembly and assembly, compatible with wire rings made of weakly magnetic materials such as 4Cr13, and highly versatile. Attached Figure Description

[0025] Figure 1 : Process flow diagram of the bearing steel wire raceway of the present invention.

[0026] Figure 2 : A cross-sectional view of the overall structure of the tooling for machining the outer wire ring.

[0027] Figure 3 : A cross-sectional view of the overall structure of the tooling for machining inner wire rings.

[0028] The diagram shows: upper pressure plate (1), positioning ring (2), wire ring (3), lower pressure plate (4), and connecting screw (5). Figure 2 The positioning ring (2) of the tooling for processing steel wire rings in the middle and outer sides is provided with two inner positioning steps, which are respectively adapted to two outer steel wire rings (3). Figure 3 The positioning ring (2) of the inner wire ring processing fixture is provided with two outer positioning steps, which are respectively adapted to the two inner wire rings (3).

[0029] Figure 4 : A cross-sectional schematic diagram of the wire raceway bearing of the present invention.

[0030] Figure 5 The four wire rings of this invention are a set of integral forging schematic diagrams.

[0031] Figure 6 : A schematic diagram of the cutting of one side of the four wire rings of the present invention. Detailed Implementation

[0032] See attached document Figure 1-6 (a) Complete embodiment of machining outer wire ring (with wire raceway) 1. Setting process parameters Workpiece specifications: Finished width 4mm, outer diameter φ211mm, inner diameter φ205mm, steel wire raceway radius R5.14; Bar stock specifications: 4Cr13 stainless steel bars; Key equipment: CNC sawing machine (G0132), rolling mill (LD-200), box annealing furnace (RX3-60-9), CNC lathe (CK6150), horizontal CNC lathe (HTC3250), surface grinder (M7130), box quenching furnace (RJ2-75-9), liquid nitrogen cryogenic chamber (DW-196), cylindrical grinder (M1432B / MG1432), and slow wire EDM machine (DK7732).

[0033] 2. Step-by-step implementation process Step 1: Cutting the bar stock The 4Cr13 bar stock was cut into segments using a G0132 CNC sawing machine with a sawing accuracy of ±0.1mm and a segment end face perpendicularity of ≤0.05mm.

[0034] Step 2: Blank forging First, the material segment is forged into a cylindrical blank using free forging; after center punching, the blank is then rolled and expanded using an LD-200 rolling mill at a temperature of 1100–1150℃. After rolling and expansion, the blank has an outer diameter of φ216mm and an internal grain size of 8–10μm, forming an integral blank with a pre-formed outline containing four outer steel wire rings, as shown below. Figure 5 .

[0035] Step 3: Isothermal annealing The blank was placed in an RX3-60-9 box-type annealing furnace: heated to 860℃ at 12℃ / min and held for 1.5 hours; rapidly cooled to 720℃ at 22℃ / min and held at that temperature for 1.2 hours; then slowly cooled to room temperature at 4℃ / min. After annealing, the hardness of the blank was tested to be HBS215, which met the processing requirements.

[0036] Step 4: Rough Car Clamp the blank on a CK6150 CNC lathe: linear speed 45 r / min, feed rate 0.45 mm / r, depth of cut 1.5 mm; turn both ends of the plane (length 43 (0, +0.3) mm), turn the outer diameter to φ213.5 mm (finished outer diameter φ211 mm, +2.5 mm allowance), turn the inner diameter to φ203 (finished inner diameter). (φ205mm, -2mm allowance), turn a 45° chamfer (side length 1mm). Surface roughness after machining: Ra5.8.

[0037] Step 5: Stress-relieving tempering / shaping The blank is placed in an RJ2-75-9 tempering furnace: the temperature is increased to 280℃ at 10℃ / min, held for 1 hour, and then air-cooled to room temperature. It is shaped using a precision shaping machine (accuracy ±0.01mm), and Vdsp=0.45mm and Ape=0.18mm are measured.

[0038] Step 6: Finish turning The blank was clamped on an HTC3250 horizontal CNC lathe: linear speed 45 r / min, feed rate 0.2 mm / r, depth of cut 0.4 mm; finish turning the two end planes (length 42.35 mm ± 0.05 mm), finish turning the outer diameter to φ212 mm (+1 mm allowance), finish turning the inner hole to φ204.4 mm (-0.6 mm allowance), finish turning the wire raceway (radius R4.763 mm, +0.377 mm allowance), and turning the chamfer (radius R2 mm). After machining, the surface roughness was Ra3.0. It was cut off with a 3 mm parting tool to obtain four semi-finished products (each 105.35 mm in length).

[0039] Step 7: Softening The semi-finished product and auxiliary surface grinding fixture are placed together on an M7130 surface grinder: white corundum grinding wheel (80#), linear speed 30m / s, feed rate 0.005mm / r, depth of cut 0.015mm; grind the cut surface of the semi-finished product, the surface roughness Ra0.9 and parallelism 0.01mm after machining.

[0040] Step 8: Overall quenching The semi-finished product was loaded into a heat-resistant steel quenching fixture and placed in an RJ2-75-9 quenching furnace: preheated at 650℃ for 30 minutes, held at 1000℃ for 20 minutes, and then air-cooled to room temperature. The hardness after quenching was measured to be HRC52.5.

[0041] Step 9: Cryogenic Treatment The semi-finished product was placed in a DW-196 liquid nitrogen cryogenic chamber: cooled to -90℃ at a rate of 2.5℃ / min, held at that temperature for 1 hour, and then allowed to naturally return to room temperature. The impact toughness was tested and found to be 12.8 J / cm².

[0042] Step 10: Stress-relieving tempering of workpieces The semi-finished product was placed in a tempering furnace: the temperature was increased to 180℃ at a rate of 5℃ / min, held for 1.8 hours, and then cooled to room temperature in the furnace. The hardness difference between the same semi-finished product was measured to be 1.2 HRC (HRC 52.0~53.2).

[0043] Step 11: Plastic Surgery The shape was formed using a precision shaping machine (elastic pressure head), and the measured values ​​were Vdsp=0.32mm and Ape=0.13mm.

[0044] Step 12: Coarse grinding + additional tempering Rough grinding: Silicon carbide grinding wheel (100#), linear speed 32m / s, feed rate 0.003mm / r, depth of cut 0.05mm; taking the rough grinding of an outer wire ring as an example: grind the two end faces sequentially (to 4.2mm, +0.2mm allowance), outer diameter (to φ211.2mm, +1.1mm allowance), inner hole (to finished size φ205mm), and wire raceway (radius R4.763mm, C-measured ball bottom diameter to 209.2mm, -0.325mm allowance). After rough grinding, temper at 180℃ for 2 hours, cycle twice. Inspection: datum surface flatness 0.007mm, outer diameter roundness 0.009mm, raceway center parallelism difference 0.011mm, surface roughness Ra0.9.

[0045] Step 13: Fine grinding / grinding Fine grinding: Silicon carbide grinding wheel (120#), linear speed 35m / s, feed rate 0.002mm / r, depth of cut 0.005mm; taking the fine grinding of the outer wire ring as an example: grind the two end faces sequentially (to 4mm), outer diameter (to φ211 (-0.005, -0.020)mm, IT6 grade), and wire raceway (to radius R5.14mm±0.03mm, measuring the ball bottom diameter φ209.525mm). Inspection: outer diameter roundness 0.006mm, raceway roundness 0.006mm, raceway center parallelism difference 0.009mm, surface roughness Ra0.7, residual magnetism 0.6mT.

[0046] Step 14: Cut Cut with a DK7732 slow wire EDM machine: such as Figure 6 The cutting wire diameter was 0.1 mm, the cutting speed was 6.5 mm² / min, the cutting width was 0.25 mm, and the surface roughness was Ra1.5. The final product was an outer steel wire ring, with a 100% pass rate in all inspections.

[0047] (II) Assembly and Use Examples of Steel Wire Ring Machining Fixtures 1. Tooling component parameters Taking the rough-ground outer steel wire ring positioning ring as an example: 45# steel, outer diameter φ247mm, inner diameter φ210.2mm, two positioning step diameters φ211.4mm (fitting the outer diameter of the outer steel wire ring φ211.2mm), step height 4.1mm, partition height 4.2mm, concentricity between the large outer circle and the mating surface 0.01mm; Upper pressure plate: 45# steel, outer diameter φ245mm, inner diameter φ209mm, thickness 10mm, 6 φ9mm through holes; Lower pressure plate: 45# steel, outer diameter φ245mm, inner diameter φ209mm, thickness 16mm, 6 M8mm threaded holes (thread depth 10mm). Connecting screws: M8 socket head cap screws, 27mm in length (5mm for the upper pressure plate mounting hole, 13mm for the locating ring, and 10mm for the lower pressure plate threaded hole depth - 1mm for the reserved depth), made of 40Cr material, galvanized for rust prevention.

[0048] 2. Tooling Usage and Effects According to the "Tooling Usage Procedure" above, clamp two semi-finished outer steel wire rings. After grinding the steel wire raceway, the two finished products were inspected and found to have a raceway center parallelism difference of 0.009mm and raceway roundness of 0.006mm and 0.007mm respectively, with good dimensional consistency. After being assembled into a bearing, the operating noise was 53dB and the service life under simulated working conditions was 10800h, which fully met the design requirements.

[0049] To verify the technical effect of the present invention, 4Cr13 stainless steel ultra-thin wire rings (finished width 4mm, outer diameter φ211mm) were selected as the test objects. One hundred pieces each were processed using existing technology and the present invention. The key indicators for comparison are as follows: Material utilization rate 78.5% 95.2% An increase of 16.7 percentage points Finished product qualification rate 68.0% 99.0% An increase of 31 percentage points Steel wire raceway roundness 0.022~0.028mm 0.005~0.007mm Accuracy improved by more than 70% poor parallelism of raceway center 0.021~0.025mm 0.008~0.010mm Accuracy improved by more than 55% Impact toughness of steel wire ring 8.5~9.8J / cm² 12.2~13.5J / cm² Increased by more than 38% bearing operating noise 66~72dB 52~55dB Reduced by 14-17 dB Bearing service life (simulated operating conditions) 6500～7200h 10500～11200h Extended by more than 50% As shown in the table above, the present invention is significantly superior to the prior art in terms of material utilization, processing accuracy, workpiece performance and bearing assembly effect, and fully meets the needs of the localization of wire raceway bearings.

[0050] Technical contributions of this invention: Process innovation: An integrated process route of "batch forging + stepped stress relief + composite heat treatment" was proposed, breaking through the technical bottleneck of balancing deformation and performance in the processing of ultra-thin steel wire rings, and providing a process paradigm that can be referenced for the processing of similar ultra-thin metal parts; Tooling innovation: Design a special tooling with "double-step positioning + full degree of freedom constraint" to solve the positioning problem of grinding thin workpieces with weak magnetic properties, improve the consistency of multi-part processing, and can be extended to other precision grinding scenarios of ultra-thin weak magnetic parts. Industrialization value: It promotes the localization of steel wire raceway bearings, breaks the import monopoly, reduces the manufacturing cost of high-end equipment, and provides key technical support for the development of my country's industrial automation, aerospace and other fields.

[0051] The scope of protection of this invention is not limited to the above embodiments. All equivalent modifications or substitutions made based on the technical solutions and concepts of this invention should be covered within the scope of protection of this invention.

Claims

1. A process for machining bearing steel wire raceways, used for machining inner and outer steel wire rings, characterized in that, The inner and outer steel wire rings are made of 4Cr13 stainless steel, with a finished width of 4mm. The process steps include: Step 1: Bar sawing. Select 4Cr13 stainless steel bars and saw them according to processing requirements. Step 2: Forging of the blank, four steel wire rings are forged as a whole, using the "free forging + rolling expansion" method; Step 3: Isothermal annealing. Heat the blank to 850-880℃ and hold for 1-2 hours. Quickly cool to 700-750℃ and hold isothermally. Then cool slowly. After annealing, the hardness is controlled at HB197-241. Step 4: Rough turning. Place the annealed blank on a CNC lathe and turn the two planes, outer diameter / inner hole and chamfer. The linear speed is 40-50 r / min, the feed rate is 0.4-0.5 mm / r, and the surface roughness is ≤ Ra6.

3. Step 5: Stress-relieving tempering / shaping. After rough machining, heat the steel wire ring blank to 250-300℃ and hold for 1 hour. After air cooling or furnace cooling, shape it. After shaping, Vdsp≤0.5mm and Ape≤0.2mm. Step 6: Finish turning. Fix the workpiece wire ring blank on a horizontal CNC lathe with a three-jaw chuck. Machin the plane, outer circle / inner hole, wire raceway and chamfer. The linear speed is 40-50 r / min, the feed rate is 0.2 mm / r, and the surface roughness is ≤ Ra3.

2. Then cut it off with a 3 mm parting tool. Step 7: Soft grinding. The workpiece wire ring blank is placed in a surface grinder with the tooling to grind the cut surface. The roughness is ≤Ra1.0 and the parallelism of the surface is ≤0.012mm. Step 8: Overall quenching. After the workpiece steel wire ring semi-finished product is put into the quenching fixture, it is sent to the quenching furnace, preheated at 600-800℃ for 30 minutes, held at 980-1030℃ for 20 minutes, and then air-cooled or salt-bathed. The hardness after quenching is HRC50-55. Step 9: Deep cryogenic treatment. Place the quenched steel wire ring blank into a liquid nitrogen deep cryogenic chamber and cool it to -90°C at a rate of 2-3°C / min. After holding it at this temperature for 1 hour, allow it to recover naturally. Step 10: Stress-relieving tempering of the workpiece. Place the deep-cryogenic workpiece wire ring blank into the tempering furnace. The tempering temperature is 150-200℃, ensuring that the hardness difference of the same wire ring is ≤2HRC. Step 11: Shaping. Shape the steel wire ring blank after tempering. After shaping, Vdsp≤0.35mm, Ape≤0.14mm. Step 12: Rough grinding + additional tempering. Grind the two planes, outer diameter / inner hole, and wire raceway. Use "multi-blade rough grinding + additional tempering" cycle ≥ 2 times. The additional tempering temperature is 160~200℃ and held for 2 hours. After processing, the flatness of the reference surface is 0.008mm, the parallelism of the non-reference surface relative to the reference surface is 0.015mm, the roundness of the outer diameter of the outer wire ring / the inner diameter of the inner wire ring is 0.015mm, the cylindricity is 0.01mm, the coaxiality of the inner diameter of the outer wire ring / the outer diameter of the inner wire ring is φ0.015mm, the parallelism difference between the center of the wire raceway and the reference surface is 0.012mm, the roundness of the ball bottom diameter is 0.018mm, the circular runout is 0.015mm, the roughness is ≤Ra1.0, and the residual magnetism is ≤0.8mT. Step 13: Fine grinding, grinding the two planes, outer circle / inner hole, and steel wire raceway. After machining, the flatness of the base surface is 0.006mm, the parallelism of the non-datum surface relative to the datum surface is 0.012mm, the roundness of the outer circle of the outer steel wire ring / the inner hole of the inner steel wire ring is 0.007mm, the cylindricity is 0.009mm, the parallelism of the center of the steel wire raceway relative to the base surface is 0.009mm, the roundness of the bottom diameter of the measuring ball is 0.007mm, the circular runout is 0.009mm, the roughness is ≤Ra0.8, and the residual magnetism is ≤0.8mT. Step 14: Cutting. Use wire cutting to cut the wire with a cutting width of 0.2-0.3 mm and a surface roughness of ≤Ra1.6 to obtain a finished wire ring with a wire raceway.

2. The process method for processing bearing steel wire raceways according to claim 1, characterized in that, In step 2, the integral forging process does not require reserving clamping portions for each wire ring.

3. The process method for processing bearing steel wire raceways according to claim 1, characterized in that, The cooling rate of the cryogenic treatment in step 9 is 2.5℃ / min.

4. The process method for processing bearing steel wire raceways according to claim 1, characterized in that, In step 12, the "multi-blade rough grinding + additional tempering" cycle is repeated at least twice, and the additional tempering temperature is 180℃.

5. The process method for processing bearing steel wire raceways according to claim 1, characterized in that, The positioning and clamping of the inner and outer wire ring grinding wire raceway process described in steps 12 and 13 adopts a wire ring processing fixture. The wire ring processing fixture includes a fixture adapted to the outer wire ring and a fixture adapted to the inner wire ring. Each fixture consists of an upper pressure plate, a positioning ring, a lower pressure plate and several connecting screws. The positioning ring is the core positioning component, and it has two positioning steps. The size of the positioning steps is matched with the outer circle of the outer wire ring and the inner hole size of the inner wire ring after grinding. After assembly, the circumferential gap is 0.2 to 0.3 mm. The height of the positioning steps is 0.01 mm lower than that of the wire ring. The concentricity of the outer circle / inner hole of the positioning steps of the positioning ring and its mating surface with the wire ring is ≤0.015 mm. Both the upper and lower pressure plates are annular plate structures with through holes and threaded holes adapted to the connecting screws. The connecting screws are evenly distributed and pass through the preset through holes of the upper pressure plate and positioning ring and the threaded hole of the lower pressure plate, thus fastening the upper pressure plate, wire ring, positioning ring and lower pressure plate into one unit.

6. The process method for processing bearing steel wire raceways according to claim 5, characterized in that, One connecting screw is provided every 60° along the circumference.

7. The process method for processing bearing steel wire raceways according to claim 5, characterized in that, The positioning ring is made of 45# steel.

8. The process method for processing bearing steel wire raceways according to claim 5, characterized in that, The inner diameter of the upper pressure plate of the tooling for the adapter outer wire ring is smaller than the inner diameter of the positioning ring; the outer diameter of the upper pressure plate of the tooling for the adapter inner wire ring is larger than the outer diameter of the positioning ring.

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