Production process of hub bearing

Abstract

The invention relates to the field of hub bearing machining, and discloses a hub bearing production process which comprises three stages: hot forging forming, residual temperature control cooling and structure stabilization stage, hot forging forming comprises upsetting, pre-forging, finish forging and rapid cooling, finish forging adopts a finish forging die for machining, an infrared thermometer is mounted on the finish forging die for monitoring, and the infrared thermometer is mounted on the finish forging die for cooling. During finish forging, the temperature fluctuation of the forge piece is controlled to be smaller than or equal to + / -15 DEG C, and the finish forging temperature is controlled to be 950-1050 DEG C; and the time interval from finish forging to rapid cooling starting should be smaller than or equal to 30 s. An infrared thermometer is adopted for monitoring the finish forging temperature, the fluctuation is controlled to be smaller than or equal to + / -15 DEG C, the temperature is maintained to be 950-1050 DEG C, it is ensured that the forge piece is located in an ideal thermal deformation interval, overheating or overburning or insufficient mold filling is avoided, and fine and uniform austenite grains are obtained; and the starting interval from finish forging to rapid cooling is smaller than or equal to 30 s, temperature drop fluctuation is reduced, cooling continuity is guaranteed, and structure coarsening is prevented.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of hub bearing processing, in particular to a production process of a hub bearing. BACKGROUND

[0002] In the field of hub bearing processing, the flange parts of passenger car hub bearings are often formed by hot die forging with medium carbon steel, and the blanks are made by normalizing treatment, and then the finished products are made by cutting processing, local induction quenching and grinding processing. For products with high load and high reliability requirement, the blank after forging must be treated by quenching and tempering (quenching and high temperature tempering) process instead of ordinary normalizing. In order to save energy and improve production efficiency, the blank after forging is generally treated by normalizing process, but the traditional normalizing process can improve the hardness and strength of the material to a certain extent, but it cannot reach the quenching and tempering level.

[0003] In the prior art, the segmented normalizing method and device for medium carbon steel automobile hub forgings disclosed in the patent application with publication number CN118360471A adopts a segmented normalizing method after forging, controls the organization transformation form, and uses a specific cooling aid with specific cooling characteristics for auxiliary cooling in the second stage of normalizing at residual temperature, so that the mechanical properties of the forgings are improved by more than 30% compared with ordinary normalizing, and by 15% compared with continuous normalizing at residual temperature, which can reach the quenching and tempering process level. However, the existing technology still has room for improvement in the control of the final forging temperature in the hot forging forming stage and the time interval from the final forging to the start of rapid cooling.

[0004] The present technical solution aims to improve the production quality and efficiency of hub bearings by more precise control of the final forging temperature and the time interval from the final forging to the start of rapid cooling in the hot forging forming stage, and by introducing an infrared temperature measuring instrument to monitor the final forging temperature. SUMMARY

[0005] The present application provides a production process of a hub bearing to solve the above technical problems.

[0006] To solve the above technical problems, the present application solves the problems by the following technical solutions:

[0007] A production process of a hub bearing, including three stages: hot forging forming, residual temperature control cooling and organization stabilization stage, the hot forging forming includes upsetting, pre-forging, final forging and rapid cooling, wherein:

[0008] The final forging is processed by a final forging die, and an infrared temperature measuring instrument is installed on the final forging die for monitoring. The temperature fluctuation of the forgings during final forging is controlled to be ≤±15℃, and the temperature of the final forging is controlled to be 950℃-1050℃;

[0009] The time interval from the final forging to the start of rapid cooling should be ≤30s, and according to the cooling rate formula of forced air cooling stage:

[0010]

[0011] wherein:

[0012] dT / dt: rate of change of temperature;

[0013] h: convective heat transfer coefficient (W / (m 2 ·K));

[0014] A: surface area of the forging (m 2 );

[0015] Tforge: temperature of the forging after final forging;

[0016] Tambient: temperature of the workshop in which the forging is located;

[0017] p: density of the material (kg / m 3 );

[0018] V: volume of the forging (m 3 );

[0019] Cp: specific heat capacity (J / (kg·K)

[0020] As a preference, Tambient is between 20°C and 30°C, with a humidity of < 60%.

[0021] As a preference, during the residual temperature control cooling process, a thermocouple and an infrared thermal imager are installed, combined with a PLC system to achieve closed-loop control of the cooling rate, ensuring that the austenite decomposition path in the forging meets the requirements of the TTT curve, and the TTT curve fitting formula is as follows:

[0022] T p = A·exp(Q / (R·T))

[0023] wherein:

[0024] A: material constant;

[0025] Q: activation energy (J / mol);

[0026] R: gas constant (8.314 J / (mol·K));

[0027] T: absolute temperature (K).

[0028] As a preference, during the microstructure stabilization stage, sampling detection of the metallographic and mechanical properties is carried out, and the grain size of the forging is quantitatively evaluated according to the grain size calculation formula, which is as follows:

[0029] G = (log N / log 2) - 3

[0030] G: grain size

[0031] N: the number of crystal grains in a unit area

[0032] As preferred, the final forging die comprises an upper die and a lower die, the end face of the upper die is attached to the end face of the lower die, the upper die extends into the lower die and forms a die cavity, the upper die comprises an upper die ejector rod, an upper die core and an upper die sleeve, the upper die core is interference-fitted with the upper die sleeve, the upper die ejector rod extends into the upper die core and is interference-fitted therewith; the lower die comprises a lower die ejector rod, a lower die core and a lower die sleeve, the lower die core is interference-fitted with the lower die sleeve, the lower die ejector rod extends into the lower die core and is interference-fitted therewith.

[0033] As preferred, the lower end face of the upper die sleeve is provided with a protruding part at the inner end, the die cavity side wall of the lower die sleeve is provided with a notch, and when the lower end face of the upper die sleeve is attached to the upper end face of the lower die sleeve, the protruding part is clamped into the notch.

[0034] As preferred, the tip of the upper die ejector rod is interference-fitted with the upper die core, and the upper die gap is provided between the upper die ejector rod and the upper die core; the tip of the lower die ejector rod is interference-fitted with the lower die core, and the lower die gap is provided between the lower die ejector rod and the lower die core.

[0035] As preferred, the lower end face of the upper die ejector rod is flush with the lower end face of the upper die core, and the lower end face of the upper die core is a plane; the upper end face of the lower die ejector rod is flush with the upper end face of the lower die core, and the upper end face of the lower die core is a plane.

[0036] The present application has the following technical effects due to the above technical solutions:

[0037] The infrared temperature measuring instrument is used to monitor the final forging temperature, and the fluctuation is controlled to be ≤±15℃, and the temperature is maintained at 950℃-1050℃, so that the forging is ensured to be in the ideal hot deformation interval, overheating, overburning or insufficient filling are avoided, fine and uniform austenite grains are obtained; the interval between the final forging and the start of rapid cooling is ≤30s, the temperature drop fluctuation is reduced, the cooling continuity is ensured, and the organization is prevented from being coarsened; the parameters are quantitatively analyzed based on the cooling rate formula, the cooling rate is accurately controlled, the forging organization transformation is more uniform and controllable, the mechanical properties such as the hardness and strength of the forging are finally improved, the production efficiency is optimized, and the energy consumption is reduced. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 is a structure diagram of the final forging die of the present application.

[0039] The part names referred to by the numbers in the above drawings are as follows:

[0040] 10-die cavity, 11-upper die ejector rod, 12-upper die core, 13-upper die sleeve, 14-lower die ejector rod, 15-lower die core, 16-lower die sleeve, 17-upper die gap, 18-lower die gap, 131-protruding part, 161-notch. DETAILED DESCRIPTION

[0041] The following will be described in combination with the drawingsFigure 1 The application will be further described in detail with examples.

[0042] Example 1

[0043] A production process of a hub bearing includes three stages: hot forging forming, residual temperature controlled cooling and microstructure stabilization stage, the hot forging forming includes upsetting, pre-forging, finish forging and rapid cooling, wherein:

[0044] The finish forging is processed by using a finish forging die, the forging piece is made of medium carbon steel, an infrared temperature detector is installed on the finish forging die for monitoring, the temperature fluctuation of the forging piece during finish forging is controlled to be ≤±15℃, the temperature of finish forging is controlled to be 950℃-1050℃, and the temperature higher than 1100℃ is easy to cause grain coarsening (grain size ≤3 levels), and the temperature lower than 900℃ increases the deformation resistance and induces micro cracks;

[0045] The time interval from the finish forging to the start of the rapid cooling should be ≤30s, and according to the cooling rate formula of forced air cooling stage:

[0046]

[0047] Wherein:

[0048] dT / dt: the change rate of temperature;

[0049] h: the convective heat transfer coefficient (W / (m 2 ·K)), which is related to the wind speed and the surface roughness of the forging piece (when forced air cooling);

[0050] A: the surface area of the forging piece (m 2 );

[0051] Tforging: the temperature of the forging piece after finish forging;

[0052] Tambient: the temperature of the workshop where the forging piece is located;

[0053] ρ: the material density (kg / m 3 , the medium carbon steel takes 7850kg / m 3 );

[0054] V: the volume of the forging piece (m 3 );

[0055] Cp: the specific heat capacity (J / (kg·K), the carbon steel takes 460J / (kg·K))

[0056] The forging piece is rapidly cooled from the finish forging temperature (950℃-1050℃) to the critical temperature of austenite decomposition at a fixed cooling rate (usually 0.8℃ / s-1.4℃ / s) to make the microstructure transform. After cooling to room temperature, the forging piece is naturally stacked or low-temperature tempered to eliminate residual stress, and finally the stabilized microstructure is obtained.

[0057] Forced air cooling stage needs to ensure uniform air speed distribution (recommended convective heat transfer coefficient > 0.8) to avoid local cooling rate deviation caused by airflow dead angle exceeding ±0.3℃ / s. For asymmetric forgings (such as gear blanks), multi-nozzle array or adaptive flow guide device can be used to make the core surface temperature difference ≤20℃.

[0058] Fast cooling uses air cooling, and the air cooling pipeline is cleaned every month to prevent dust accumulation (pressure drop should be <5% of the rated value), and the cooling agent filter core is replaced every quarter (filtering precision ≤10μm) to prevent nozzle blockage causing uneven cooling.

[0059] T environment is 20-30℃ and humidity ≤60% to avoid cooling medium condensation caused by moisture absorption, affecting heat exchange efficiency.

[0060] Residual temperature control installs thermocouples and infrared thermometers during the cooling process, combined with PLC system to realize closed-loop control of cooling rate, to ensure that the austenite decomposition path in the forging meets the requirements of TTT curve, and the TTT curve fitting formula is as follows:

[0061] T p =A·exp(Q / (R·T))

[0062] Where:

[0063] A: material constant (1.2×10-8s for medium carbon steel);

[0064] Q: activation energy (J / mol, 1.8×105J / mol for pearlite transformation);

[0065] R: gas constant (8.314 J / (mol·K));

[0066] T: absolute temperature (K).

[0067] Microstructure stabilization stage carries out sampling detection of metallography and mechanical properties, and quantitatively evaluates the grain size of forgings according to the grain size calculation formula, which is as follows:

[0068] G=(logN / log2)-3

[0069] G: grain size

[0070] N: number of grains per unit area

[0071] For example: G=3.5 level indicates that the grain size is about 50μm.

[0072] 3-5 pieces of each batch are randomly selected for metallographic analysis (grain size, pearlite interlamellar spacing) and hardness testing (HV fluctuation ≤20). If mixed grains (grain size difference ≥2 levels) or abnormal structure are found, the cooling parameters need to be traced back and the thermodynamic model needs to be recalibrated.

[0073] Hot forging also includes blanking and heating, using medium carbon steel round steel (such as φ40mm-φ90mm) as raw material, heating to 1150℃-1250℃ after blanking to ensure full austenitization. Then perform upsetting, pre-forging, final forging and rapid cooling, followed by trimming and shaping to remove flash.

[0074] The residual temperature normalizing saves the energy consumption of secondary heating in the traditional quenching and tempering process by directly utilizing the forging residual heat. According to research, about 400kW·h of electricity can be saved per ton of steel, and the comprehensive energy consumption is reduced by 30%-40%26. In addition, the process cycle is shortened by 25%-30% compared with quenching and tempering, improving the production efficiency.

[0075] Grain refinement: By controlling the cooling rate to inhibit grain coarsening, the residual temperature normalizing process can make the grain size reach 3-4 levels, the surface decarburization layer depth ≤0.3mm, and form a uniform mixture of pearlite and ferrite structure.

[0076] Mechanical property improvement: Compared with traditional annealing, the tensile strength is increased by 15%-20% (typical value reaches 600-650MPa), and the hardness range is stable at HB160-190, meeting the cutting processing needs of medium carbon steel parts.

[0077] It is suitable for simple shape and uniform wall thickness forgings (such as shafts, flange parts), especially for low carbon steel and medium carbon steel. For example, the creep limit and endurance strength of 12CrMoV boiler pipe after residual heat normalizing after rolling can be comparable to the conventional normalizing process.

[0078] No need for complex cooling devices or high-precision temperature control systems, mainly relying on forced air cooling or natural cooling, with lower equipment investment and maintenance cost, suitable for small and medium-sized production line applications.

[0079] Example 2

[0080] Example 2 has basically the same characteristics as Example 1, except that the final forging die includes an upper die and a lower die, the end face of the upper die is in contact with the end face of the lower die, the upper die extends into the lower die and forms a die cavity 10, the upper die includes an upper die ejector pin 11, an upper die core 12 and an upper die sleeve 13, the upper die core 12 is in interference fit with the upper die sleeve 13, the upper die ejector pin 11 extends into the upper die core 12 and is in interference fit with it; the lower die includes a lower die ejector pin 14, a lower die core 15 and a lower die sleeve 16, the lower die core 15 is in interference fit with the lower die sleeve 16, the lower die ejector pin 14 extends into the lower die core 15 and is in interference fit with it.

[0081] The upper die sleeve 13 is provided with a protruding part 131 at the inner end of the lower end surface, the protruding part 131 is an annular protruding part, and the lower die sleeve 16 is provided with a notch 161 on the side wall of the die cavity 10. When the lower end surface of the upper die sleeve 13 is attached to the upper end surface of the lower die sleeve 16, the protruding part 131 is clamped into the notch 161.

[0082] The end of the upper die ejector pin 11 is in interference fit with the upper die core 12, and the upper die gap 17 is arranged between the upper die ejector pin 11 and the upper die core 12; the top end of the lower die ejector pin 14 is in interference fit with the lower die core 15, and the lower die gap 18 is arranged between the upper die ejector pin 11 and the upper die core 12.

[0083] The lower end surface of the upper die ejector pin 11 is flush with the lower end surface of the upper die core 12, and the lower end surface of the upper die core 12 is a plane; the upper end surface of the lower die ejector pin 14 is flush with the upper end surface of the lower die core 15, and the upper end surface of the lower die core is a plane.

[0084] The worker first places the bearing forging raw material in the forging lower die, and then performs stamping treatment on the bearing forging raw material through external hydraulic equipment. After stamping, the forging is removed from the inside of the forging lower die by moving the lower die ejector pin 14.

[0085] Because the upper die has a protruding structure corresponding to the lower die, the die cavity 10 will close early to prevent the forging material from overflowing. After the upper die and the lower die are completely closed, the final forging is obtained. The forged workpiece will be closely attached to the mold. At this time, the lower die ejector pin 14 can be used to eject the forging, which improves the forging efficiency of the bearing.

Claims

1. A production process for a wheel hub bearing, characterized in that The three stages include hot forging forming, temperature control cooling and microstructure stabilization stage, the hot forging forming includes upsetting, pre-forging, finish forging and rapid cooling, wherein: The finish forging is processed by using the finish forging die, the infrared temperature detector is installed on the finish forging die for monitoring, the temperature fluctuation of the forged piece during the finish forging is controlled to be less than or equal to ±15℃, and the temperature of the finish forging is controlled to be 950℃-1050℃; The time interval from the finish forging to the start of the rapid cooling should be less than or equal to 30s, and according to the cooling rate formula of the forced air cooling stage: Wherein: dT / dt: the change rate of the temperature; h: convective heat transfer coefficient (W / (m 2 • K)); A: forged piece surface area (m 2 ); Tforged piece: the temperature of the forged piece after the finish forging; Tenvironment: the temperature of the workshop where the forged piece is located; ρ: Material density (kg / m³) 3 ); V: volume of the forging (m3) 3 ); Cp: the specific heat capacity (J / (kg·K).

2. A process for producing a hub bearing according to claim 1, characterized in that: The Tenvironment is 20℃-30℃, and the humidity is less than or equal to 60%.

3. The production process of a hub bearing according to claim 1, characterized in that: The thermocouple and the infrared thermal imager are installed during the temperature control cooling process, the closed loop control of the cooling rate is realized by combining the PLC system, the austenite decomposition path in the forged piece is ensured to meet the requirements of the TTT curve, and the fitting formula of the TTT curve is as follows: T p = A - exp(Q / (R - T)) Wherein: A: the material constant; Q: the activation energy (J / mol); R: the gas constant (8.314 J / (mol·K)); T: the absolute temperature (K).

4. The production process of a hub bearing according to claim 1, characterized in that: The sampling detection of the metallographic and mechanical properties is carried out in the microstructure stabilization stage, the grain size of the forged piece is quantitatively evaluated according to the grain size calculation formula, and the formula is as follows: G=(logN / log2)-3 G: the grain size N: the number of grains per unit area.

5. The production process of a hub bearing according to claim 1, characterized in that: The finish forging die includes an upper die and a lower die, the end face of the upper die is attached to the end face of the lower die, the upper die extends into the lower die and forms a die cavity (10), the upper die includes an upper die ejector rod (11), an upper die core (12) and an upper die sleeve (13), the upper die core (12) is in interference fit with the upper die sleeve (13), and the upper die ejector rod (11) extends into the upper die core (12) and is in interference fit with the upper die core (12); the lower die includes a lower die ejector rod (14), a lower die core (15) and a lower die sleeve (16), the lower die core (15) is in interference fit with the lower die sleeve (16), and the lower die ejector rod (14) extends into the lower die core (15) and is in interference fit with the lower die core (15).

6. A production process of a hub bearing according to claim 5, characterized in that: A protruding part (131) is arranged at the inner end of the lower end face of the upper die sleeve (13), a notch (161) is arranged on the side wall of the die cavity (10) of the lower die sleeve (16), and when the lower end face of the upper die sleeve (13) is attached to the upper end face of the lower die sleeve (16), the protruding part (131) is clamped into the notch (161).

7. A process for producing a hub bearing according to claim 5, characterized in that: The end of the upper die ejector rod (11) is in interference fit with the upper die core (12), and the upper die gap (17) is arranged between the upper die ejector rod (11) and the upper die core (12); the top end of the lower die ejector rod (14) is in interference fit with the lower die core (15), and the lower die gap (18) is arranged between the upper die ejector rod (11) and the upper die core (12).

8. The production process of a hub bearing according to claim 5, characterized in that: The lower end face of the upper die ejector rod (11) is flush with the lower end face of the upper die core (12), and the lower end face of the upper die core (12) is a plane; the upper end face of the lower die ejector rod (14) is flush with the upper end face of the lower die core (15), and the upper end face of the lower die core is a plane.

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