A method for leaving soft zone during induction quenching of ultra-long machine tool guide rails

Abstract

A method for induction quenching and leaving a soft zone for ultra-long machine tool guide rails is described. This method is suitable for machine tool guide rails that are prone to cracking at the initial end after quenching or require machining (such as milling or drilling). The method belongs to the field of heat treatment technology. The method includes the following steps: aging, machining, stress relief, medium-frequency induction quenching, and tempering the ultra-long guide rails. The medium-frequency induction quenching utilizes two inductors: one preheating inductor and one quenching inductor. The two inductors are spaced 15-20 mm apart, and the distance between the inductor surface and the quenching surface is 4-6 mm. Heating and quenching begin at a point more than 20 mm from the edge of the machine tool guide rail at the initial end of the quenching process. After this quenching process, the hardness of the quenched area of ​​the guide rail reaches 55-60 HRC, the layer depth reaches 5.0-7.6 mm, and the soft zone length is 20-25 mm. The soft zone still retains the original hardness of the cast iron.

Description

Technical Field

[0001] The invention belongs to the technical field of metal heat treatment, and relates to a method for leaving a soft zone by induction quenching of an ultra-long machine tool guide rail, which is suitable for medium-frequency induction quenching of large cast iron guide rails. Background Art

[0002] During the induction hardening process of guide rails, the initial quenching position of cast iron guide rails is often angular. Some integrated guide rails also have sidewall structures at their edges, directly connected to the guide rail. When induction hardening machine tool guide rails, angular edges are prone to the induction quenching sharp corner effect, causing the sharp corners to heat up rapidly, much higher than other parts. If the heating temperature is improperly controlled or the temperature rises rapidly and unevenly, it is very easy for the sharp corners to overheat and form quenching cracks, or for thermal stress concentration to cause end face cracking. For integrated machine tool guide rails, when the edges are formed by sidewall structures, the quenching induction coil has difficulty heating the edges due to limited space. In this case, improper heating positioning can also cause cracks in the guide rail. To prevent cracks from forming during induction hardening in areas with sharp corners and obstructive sidewall structures, some unhardened areas can be retained in these areas. In addition, when there is a need for processing after quenching the guide rail at the starting position, such as milling grooves and drilling, it is necessary to leave a certain distance of non-quenching area at this position to form a certain quenching transition zone at the starting position, and the hardness remains basically unchanged, which is called the quenching soft zone.

[0003] When quenching machine tool guide rails without leaving a soft zone, the quenching starts at the tip. When high-power, high-speed heating is used, the tip is heated by induction on both sides, causing the tip to heat up quickly. This can lead to overheating or burning at the edge of the guide rail, causing the sharp corners to melt or crack, and in severe cases, even fall off. For one-piece guide rails with sidewall machine tool structures at both ends, heating the edges is difficult when these edges hinder induction quenching. Quenching without proper heating can easily lead to cracks in the guide rail.

[0004] The purpose of this patent is to design reasonable induction quenching process parameters and set a reasonable soft belt distance to avoid problems such as melting, overburning and cracking caused by the increase in temperature at the quenching tip of the guide rail edge, and also to avoid problems such as cracks when quenching an integrated guide rail with a side wall structure. Summary of the Invention

[0005] Aiming at the phenomenon that ultra-long machine tool guide rails are prone to overheating, overburning, chipping and cracking at the initial position of the guide rail edge or the end of quenching after quenching, the present invention provides a method for induction quenching ultra-long machine tool guide rails to leave a soft zone.

[0006] Technical solution:

[0007] A method for induction quenching and leaving a soft zone for an ultra-long machine tool guide rail comprises the following steps:

[0008] Step 1: Perform stress relief and aging treatment on the extra-long machine tool guide rails;

[0009] Step 2: Machining the extra-long machine tool guide rail after aging treatment;

[0010] Step 3: Perform stress relief and aging treatment on the extra-long machine tool guide rail after machining;

[0011] Step 4: Perform medium frequency induction hardening on the extra-long machine tool guide rail after stress relief treatment, leaving a soft zone at the edge of the guide rail during quenching, with a width of 20~25mm;

[0012] Step 5: Temper the extra-long machine tool guide rail after quenching.

[0013] Furthermore, in step 1, an aging treatment is performed using a tempering device after casting and before rough machining. The aging treatment process is as follows: loading the furnace below 200°C, heating at a heating rate of 50-80°C / h to 320-380°C, holding at that temperature for 2-3 hours, heating at a heating rate of 40-60°C / h to 520-580°C, holding at that temperature for 6-8 hours, and cooling to below 250°C before being removed from the furnace.

[0014] Furthermore, in the step 2, after machining, the surface roughness Ra is less than 3.2, and the surface is visually free of defects.

[0015] Furthermore, in the step three, stress relief treatment is performed, the furnace is loaded below 200°C, the temperature is increased to 340-360°C at a heating rate of 50-80°C / h, and the temperature is kept for 1.5-2.5h, the temperature is increased to 530-550°C at a heating rate of 40-60°C / h, and the temperature is kept for 8-10h, and the furnace is cooled to below 200°C and taken out of the furnace.

[0016] Furthermore, in step four, the medium frequency induction quenching process parameters are as follows: the output power of the dual inductors is 40-70 kW, the frequency is 2-6 kHz, the transformer turns ratio is 9:2, the moving speed is 180-240 mm / min, the cooling medium is water or aqueous coolant, and a continuous spray cooling method is adopted to make the hardness reach 55-60 HRC and the layer depth reach 5.0-7.6 mm.

[0017] Furthermore, in step 4, medium-frequency induction hardening utilizes dual inductors for preheating and hardening. One inductor is a preheating inductor, without water spray, with a preheating temperature of 840-850°C; the other is a hardening inductor with built-in quenching water spray, with a quenching temperature of 880-930°C and auxiliary cooling. The inductors should be designed to conform to the cross-sectional shape of the light guide rail, either as a whole or in parts. The spacing between the two inductors is 15-20 mm. Heating and hardening should begin 20-25 mm above the starting end, leaving a soft zone to prevent surface overheating, overburning, and quenching cracks.

[0018] Furthermore, the distance between the sensor surface and the hardened surface of the light rail is 4 to 6 mm. The hardened surface sensor size should be 6 to 12 mm wider than the cross-section of the light rail. The water pressure is 2 to 3 MPa, and the water spray direction is opposite to the sensor's forward direction and at a 40 to 50-degree angle to the hardened surface of the rail. The air pressure of the blower is 6 to 8 MPa, and the wind direction is parallel to the rail surface to prevent water backflow.

[0019] Furthermore, in step 5, the tempering treatment should be completed within 12 hours after induction quenching, the tempering temperature is 180-260° C., and the tempering time is 6-8 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects.

[0021] A 20-25mm soft strip is left at the edge of the quenched rail, eliminating the need for induction hardening. This strip prevents overheating, burning, or chipping at the rail's tip. It also addresses issues like cracking during induction hardening of one-piece rails with sidewalls.

[0022] The size and dimensions of the soft band should be coordinated with the sensor type and dual sensor structure, and the application status of the machine tool guide rail and the impact of the soft band on the organization and stress should also be considered. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Crack image of guide rail edge of comparative example 1.

[0024] Figure 2 Characteristic diagram of crack along grain boundary of Comparative Example 1. DETAILED DESCRIPTION

[0025] The present invention is further described below.

[0026] A medium frequency induction quenching method for an extra-long bed cast iron guide rail, the specific implementation method is as follows:

[0027] Step 1: Aging the guide rails using tempering equipment. Aging treatment is performed after casting and before rough machining. The aging process is as follows: Load the furnace below 200°C, heat at a rate of 50-80°C / h to 320-380°C, hold at that temperature for 2-3 hours, then heat at a rate of 40-60°C / h to 520-580°C, hold at that temperature for 6-8 hours (the holding time depends on the furnace load and the wall thickness of the thickest part). Cool the furnace to below 250°C before removing from the furnace. After stress relief aging, residual stress in the casting is largely relieved, improving guide rail machining accuracy and reducing deformation caused by stress relief.

[0028] Step 2: Machining the guide rail after aging treatment to make the surface roughness Ra < 3.2 and visually free of defects.

[0029] Step 3: Stress relief treatment is performed on the machined guide rails. The guide rails are loaded into a furnace below 200°C and heated at a rate of 50-80°C / h to 340-360°C. The temperature is then held at this temperature for 1.5-2.5 hours. The temperature is then raised to 530-550°C at a rate of 40-60°C / h. The temperature is then held at this temperature for 8-10 hours. The guide rails are then cooled to below 200°C and removed from the furnace. Stress relief and aging treatment after machining can reduce machining stress, improve the dimensional stability of the guide rails, enhance subsequent machining accuracy, and reduce dimensional deformation caused by the release of machining stress.

[0030] Step 4: The stress-relieved guide rail undergoes medium-frequency induction hardening. The process parameters are as follows: dual inductor output power of 40-70 kW, frequency of 2-6 kHz, transformer turns ratio of 9:2, travel speed of 180-240 mm / min, water as the cooling medium, and continuous spray cooling to achieve a hardness of at least 55 HRC with a layer depth of at least 5 mm. Dual inductors are used for preheating and hardening: one inductor is a preheating inductor without water spray, with a preheating temperature of 840-850°C; the other is a quenching inductor with its own quenching water spray, with a quenching temperature of 880-930°C. Auxiliary cooling is also provided as needed. The inductor should be designed to conform to the cross-sectional shape of the guide rail, either as a whole or in a partially decomposed form. The distance between the inductor surface and the hardening surface is 4-6 mm. The size of the quenching surface sensor should be 6 to 12 mm wider than the guide rail cross-section. The water spray holes should be reasonably set according to the width of the sensor and evenly distributed. The water pressure should be 2 to 3 MPa. The water spray direction should be opposite to the forward direction of the sensor and 40 to 50 degrees to the quenching surface of the guide rail. The air pressure of the hair dryer should be 6 to 8 MPa, and the wind direction should be parallel to the guide rail surface to prevent water backflow. The distance between the two sensors is 15 to 20 mm. The quenching should start from a position 20 to 25 mm above the starting end. Using two sensors for quenching can make the depth of the hardened layer reach 5.0 to 7.6 mm. Reserving a certain soft quenching zone can help reduce overheating, overburning and chipping problems at the tip of the guide rail edge, and can reduce the formation of cracks on the guide rail edge.

[0031] Step 5: Temper the quenched guide rails. Tempering should be completed within 12 hours after induction quenching at a temperature of 180-260°C for 6-8 hours. Tempering within a short period of time helps reduce cracks caused by quenching stress release.

[0032] Example 1.

[0033] A medium frequency induction quenching method for an extra-long bed cast iron guide rail, the specific implementation steps are as follows:

[0034] Step 1: Use HT300 to age the guide rails. Use tempering equipment to age the guide rails. Perform an aging treatment after casting and before rough machining. The aging treatment process is as follows: load the furnace at 180°C, heat it up to 350°C at a heating rate of 60°C / h, hold it for 2 hours, heat it up to 550°C at a heating rate of 50°C / h, hold it for 6 hours, and cool it to 220°C before taking it out of the furnace.

[0035] Step 2: The guide rail after aging treatment is machined with HT300, with a surface roughness of Ra=2.8 and no defects.

[0036] Step 3: Use HT300 to stress relieve the machined guide rail, load it into the furnace at 180℃, heat it up to 350℃ at a heating rate of 50℃ / h, keep it warm for 2h, heat it up to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, and cool it to 180℃ before taking it out of the furnace.

[0037] Step 4: The stress-relieved guide rails are subjected to medium-frequency induction hardening using an HT300. The process parameters are as follows: preheating inductor output power of 50kW, frequency of 4kHz; quenching inductor output power of 60kW, frequency of 6kHz; transformer turns ratio of 9:2; traverse speed of 200mm / min; induction hardening temperature of 900°C; water as the cooling medium; and continuous spray cooling. Dual inductor hardening is employed: one preheating inductor without water spray, preheating temperature of 845°C; the other quenching inductor with its own quenching water spray, with auxiliary cooling added as needed. The inductor should be designed to conform to the cross-sectional shape of the guide rail, either as a whole or in a partially decomposed configuration. The distance between the inductor surface and the hardening surface is 5mm. The size of the quenching surface sensor should be 10mm wider than the guide rail section. The water spray holes should be reasonably set according to the width of the sensor and evenly distributed. The water pressure is 2MPa. The water spray direction is opposite to the forward direction of the sensor and is 45° to the quenching surface of the guide rail. The air pressure of the hair dryer is 6MPa, and the wind direction is parallel to the guide rail surface. The distance between the two sensors is 15mm, and heating and quenching starts from 25mm from the starting end.

[0038] Step 5: Temper the quenched guide rail with HT300. The tempering treatment should be carried out within 8 hours after induction quenching, the tempering temperature is 220℃, and the tempering time is 6 hours.

[0039] After the quenching process, the hardness of HT300 for guide rails reaches 55HRC, the layer depth is 5.0mm, and the soft zone length is 25mm.

[0040] Comparative Example 1.

[0041] A medium frequency induction quenching method for an extra-long bed cast iron guide rail, the specific implementation steps are as follows:

[0042] Step 1: Aging the guide rails with HT300 using tempering equipment. Aging is performed after casting and before rough machining. The aging process is as follows: Load the furnace at 180°C, heat at a rate of 60°C / h to 350°C, hold for 2 hours, then heat at a rate of 50°C / h to 550°C, hold for 6 hours, and cool to 220°C before removal from the furnace.

[0043] Step 2: The guide rail after aging treatment is machined with HT300, with a surface roughness of Ra=2.8 and no defects.

[0044] Step 3: Use HT300 to stress relieve the machined guide rail, load it into the furnace at 180℃, heat it up to 350℃ at a heating rate of 50℃ / h, keep it warm for 2h, heat it up to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, and cool it to 180℃ before taking it out of the furnace.

[0045] Step 4: The stress-relieved guide rails are subjected to medium-frequency induction hardening using an HT300. The process parameters are as follows: preheating inductor output power of 50kW, frequency of 4kHz; quenching inductor output power of 60kW, frequency of 6kHz; transformer turns ratio of 9:2; traverse speed of 200mm / min; induction hardening temperature of 900°C; water as the cooling medium; and continuous spray cooling. Dual inductor hardening is employed: one preheating inductor without water spray, preheating temperature of 845°C; the other quenching inductor with its own quenching water spray, with auxiliary cooling added as needed. The inductor should be designed to conform to the cross-sectional shape of the guide rail, either as a whole or in a partially decomposed configuration. The distance between the inductor surface and the hardening surface is 5mm. The size of the quenching surface sensor should be 10mm wider than the guide rail section. The water spray holes should be reasonably set according to the width of the sensor and evenly distributed. The water pressure is 2MPa. The water spray direction is opposite to the forward direction of the sensor and is 45° to the quenching surface of the guide rail. The air pressure of the hair dryer is 6MPa, and the wind direction is parallel to the guide rail surface. The distance between the two sensors is 15mm, and heating and quenching start from the starting end 0mm position.

[0046] Step 5: Temper the quenched guide rail with HT300. The tempering treatment is carried out 8 hours after induction quenching, the tempering temperature is 220℃, and the tempering time is 6 hours.

[0047] After the quenching process, the hardness of HT300 for the guide rail reaches 55HRC, the layer depth is 5.0mm, and there is no quenching soft zone. However, quenching cracks appeared at the edge of the guide rail during quenching. Figure 1 and Figure 2 shown.

[0048] Comparative Example 2.

[0049] A medium frequency induction quenching method for an extra-long bed cast iron guide rail, the specific implementation steps are as follows:

[0050] Step 1: Aging the guide rails with HT300 using tempering equipment. Aging is performed after casting and before rough machining. The aging process is as follows: Load the furnace at 180°C, heat at a rate of 60°C / h to 350°C, hold for 2 hours, then heat at a rate of 50°C / h to 550°C, hold for 6 hours, and cool to 220°C before removal from the furnace.

[0051] Step 2: The guide rail after aging treatment is machined with HT300, with a surface roughness of Ra=2.8 and no defects.

[0052] Step 3: Use HT300 to stress relieve the machined guide rail, load it into the furnace at 180℃, heat it up to 350℃ at a heating rate of 50℃ / h, keep it warm for 2h, heat it up to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, and cool it to 180℃ before taking it out of the furnace.

[0053] Step 4: The stress-relieved guide rails are subjected to medium-frequency induction hardening using an HT300. The process parameters are as follows: preheating inductor output power of 50kW, frequency of 4kHz; quenching inductor output power of 60kW, frequency of 6kHz; transformer turns ratio of 9:2; traverse speed of 200mm / min; induction hardening temperature of 900°C; water as the cooling medium; and continuous spray cooling. Dual inductor hardening is employed: one preheating inductor without water spray, preheating to 845°C; the other quenching inductor with its own quenching water spray, with auxiliary cooling added as needed. The inductor should be designed to conform to the guide rail cross-section, either as a whole or in a partially decomposed configuration. The distance between the inductor surface and the hardening surface is 5mm. The quenching surface sensor should be 10mm wider than the rail cross-section. The water holes should be reasonably positioned and evenly distributed according to the sensor width. The water pressure should be 2MPa, and the water spray direction should be opposite to the sensor's forward direction and at a 45-degree angle to the rail quenching surface. The air pressure of the blower should be 6MPa, with the wind direction parallel to the rail surface. The distance between the two sensors should be 15mm. Heating and quenching should be started 10mm from the starting point. To ensure that the starting position is heated to the quenching temperature, the heating period should be 5 seconds before starting the process.

[0054] Step 5: Temper the quenched guide rail with HT300. The tempering treatment is completed 8 hours after induction quenching, the tempering temperature is 220℃, and the tempering time is 6 hours.

[0055] After this quenching process, the hardness of the HT300 for the guide rail reaches 55HRC, the layer depth is 5.0mm, and the soft zone length is 10mm. There is a threaded hole with a hole depth of 15mm on the edge of the guide rail. Due to the high hardness of the guide rail surface, tapping operation cannot be performed.

[0056] Comparative Example 3.

[0057] A medium frequency induction quenching method for an extra-long bed cast iron guide rail, the specific implementation steps are as follows:

[0058] Step 1: Aging the guide rails with HT300 using tempering equipment. Aging is performed after casting and before rough machining. The aging process is as follows: Load the furnace at 180°C, heat at a rate of 60°C / h to 350°C, hold for 2 hours, then heat at a rate of 50°C / h to 550°C, hold for 6 hours, and cool to 220°C before removal from the furnace.

[0059] Step 2: The guide rail after aging treatment is machined with HT300, with a surface roughness of Ra=2.8 and no defects.

[0060] Step 3: Use HT300 to stress relieve the machined guide rail, load it into the furnace at 180℃, heat it up to 350℃ at a heating rate of 50℃ / h, keep it warm for 2h, heat it up to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, and cool it to 180℃ before taking it out of the furnace.

[0061] Step 4: The stress-relieved guide rails are subjected to medium-frequency induction hardening using an HT300. The process parameters are as follows: preheating inductor output power of 50kW, frequency of 4kHz; quenching inductor output power of 60kW, frequency of 6kHz; transformer turns ratio of 9:2; traverse speed of 200mm / min; induction hardening temperature of 900°C; water as the cooling medium; and continuous spray cooling. Dual inductor hardening is employed: one preheating inductor without water spray, preheating to 845°C; the other quenching inductor with its own quenching water spray, with auxiliary cooling added as needed. The inductor should be designed to conform to the guide rail cross-section, either as a whole or in a partially decomposed configuration. The distance between the inductor surface and the hardening surface is 5mm. The size of the quenching surface sensor should be 10mm wider than the guide rail section. The water spray holes should be reasonably set according to the width of the sensor and evenly distributed. The water pressure is 2MPa. The water spray direction is opposite to the forward direction of the sensor and is 45° to the quenching surface of the guide rail. The air pressure of the hair dryer is 6MPa, and the wind direction is parallel to the guide rail surface. The distance between the two sensors is 15mm, and heating and quenching starts from the starting end 50mm.

[0062] Step 5: Temper the quenched guide rail with HT300. The tempering treatment is carried out 8 hours after induction quenching, the tempering temperature is 220℃, and the tempering time is 6 hours.

[0063] After this quenching process, the hardness of the HT300 steel used in the guide rail reaches 55HRC, with a layer depth of 5.0mm and a soft zone length of 50mm. The induction hardening soft zone of a machine tool guide rail is 50mm. When the linear bearing on the guide rail runs into the unhardened area, the low hardness causes severe wear on the guide rail, seriously reducing the accuracy of the guide rail and the machine tool.

Claims

1. A method for induction quenching and leaving a soft zone for an ultra-long machine tool guide rail, characterized in that: The following steps are involved: Step 1: Perform stress relief and aging treatment on the extra-long machine tool guide rails; Step 2: Machining the super-long machine tool guide rail after aging treatment; after machining, the surface roughness Ra is less than 3.2, and the surface is visually free of defects; Step 3: Perform stress relief and aging treatment on the machined extra-long machine tool guide rails; for stress relief treatment, load the furnace below 200°C, heat it up to 340-360°C at a heating rate of 50-80°C / h, keep it warm for 1.5-2.5h, heat it up to 530-550°C at a heating rate of 40-60°C / h, keep it warm for 8-10h, and cool it down to below 200°C before taking it out of the furnace; Step 4: Perform medium-frequency induction quenching on the extra-long machine tool guide rails after stress relief treatment. During quenching, a soft zone with a width of 20-25mm is left at the edge of the guide rail. The medium-frequency induction quenching process parameters are as follows: the output power of the dual inductors is 40-70kW, the frequency is 2-6kHz, the transformer turns ratio is 9:2, the moving speed is 180-240mm / min, the cooling medium is water or aqueous coolant, and a continuous spray cooling method is adopted. Medium-frequency induction quenching uses dual inductors for preheating and quenching. One inductor is a preheating inductor without water spray, and the preheating temperature is 840-850℃; the other is a quenching inductor with its own quenching water spray, and the quenching temperature is 880-930℃, and it also has auxiliary cooling. The inductor should be designed for overall or partial decomposition profiling according to the cross-sectional shape of the guide rail. The spacing between the dual inductors is 15-20mm. Heating and quenching starts from 20-25mm above the starting end, and the soft zone is reserved. Step 5: Temper the quenched extra-long machine tool guide rail; The distance between the sensor surface and the quenching surface of the guide rail is 4 to 6 mm; the size of the quenching surface sensor should be 6 to 12 mm wider than the guide rail section; the water pressure is 2 to 3 MPa, the water spray direction is opposite to the forward direction of the sensor, and is 40 to 50 degrees to the quenching surface of the guide rail, the hair dryer pressure is 6 to 8 MPa, and the wind direction is parallel to the guide rail surface.

2. The method for induction quenching and leaving a soft zone for an ultra-long machine tool guide rail according to claim 1, characterized in that: In the step 1, aging treatment is performed using tempering equipment. After casting and before rough processing, aging treatment is performed once. The aging treatment process is as follows: charging the furnace below 200° C., heating to 320-380° C. at a heating rate of 50-80° C. / h, keeping the temperature for 2-3 hours, heating to 520-580° C. at a heating rate of 40-60° C. / h, keeping the temperature for 6-8 hours, cooling the furnace to below 250° C., and then removing from the furnace.

3. The method for induction quenching and leaving a soft zone for an ultra-long machine tool guide rail according to claim 1, characterized in that: In the step 5, the tempering treatment should be completed within 12 hours after induction quenching, the tempering temperature is 180-260° C., and the tempering time is 6-8 hours.

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