Method for reducing residual stress of ultra-long cast iron integrated guide rail and lathe bed

Abstract

The invention belongs to the technical field of heat treatment, and relates to a method for reducing residual stress of an ultra-long cast iron integrated guide rail and a lathe bed. After the ultra-long cast iron integrated guide rail and the lathe bed are subjected to medium-frequency induction quenching and tempering treatment on the surface of the guide rail, on one hand, a workpiece is only subjected to phase change on the surface of the guide rail, and the structure of the lathe bed is not changed; the residual stress in the ultra-long cast iron integrated guide rail, the lathe bed and the induction quenching surface layer is obviously reduced; and on the other hand, the problem that the overall quenching and tempering heat treatment of the ultra-long cast iron integrated guide rail and the lathe bed is difficult is solved by adopting the process parameters of medium-frequency induction quenching.

Description

Technical Field

[0001] The invention belongs to the technical field of heat treatment and relates to a method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed. Background Art

[0002] As a key basic structural component of a machine tool, the machine tool bed directly affects the dimensional accuracy of the machine tool itself during operation and the service life of the machine tool. In the machine tool manufacturing industry, the output of large machine tools accounts for an increasingly large proportion; extra-long cast iron guide rails generally refer to cast iron guide rails with a length of more than 10m. The existing extra-long cast iron integrated guide rails and bed bodies often have large residual stress problems during the preparation process, resulting in serious deformation of the extra-long cast iron integrated guide rails and bed bodies, and even causing the guide rails to crack.

[0003] Therefore, a process method is now needed to reduce the residual stress of the extra-long cast iron integrated guide rails and bed, thereby improving the dimensional stability of the cast iron during processing and assembly, and laying the foundation for high-end CNC machine tools to achieve higher precision retention during service. Summary of the invention

[0004] In view of the above technical problems, the present invention proposes a method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed, which solves the problem of irregular changes in guide rail dimensions and even guide rail cracking caused by excessive residual stress during the processing and assembly of the extra-long cast iron integrated guide rail and the bed.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions.

[0006] A method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed, comprising the following steps: Step 1: Performing the first artificial aging treatment on the super-long cast iron integrated guide rail and bed after casting to reduce the casting stress; Step 2, rough machining the super-long cast iron integrated guide rail and bed after aging treatment in step 1, so that the surface roughness of the guide rail Ra is less than 3.2, and each machined surface has no defects; Step 3, performing a second artificial aging treatment on the extra-long cast iron integrated guide rail and bed after rough machining in step 2; Step 4, pre-deform the guide rail subjected to the second artificial aging treatment in step 3, wherein the pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the super-long cast iron integrated guide rail and bed after the pre-deformation processing are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface; Step 5, rough grinding the guide rail of step 4, the surface roughness Ra <3.2, stress relief treatment is performed on the rough-ground extra-long cast iron one-piece guide rail and bed, so as to obtain an extra-long cast iron one-piece guide rail and bed with reduced residual stress.

[0007] Furthermore, in step 1, the specific process of the first artificial aging treatment is: charging the furnace below 200°C, heating to 340°C-360°C at a heating rate of 50-80°C / h and keeping warm for 2-3h, heating to 550°C-580°C at a heating rate of 40-60°C / h and keeping warm for 8-10h, and cooling to below 250°C before taking out of the furnace.

[0008] Furthermore, in step 3, the specific process of the second artificial aging treatment is: charging the furnace below 200°C, heating to 340°C-360°C at a heating rate of 50-80°C / h and keeping warm for 1.5-2.5h, heating to 530°C-550°C at a heating rate of 40-60°C / h and keeping warm for 8-10h, and cooling to below 200°C before taking out of the furnace.

[0009] Furthermore, in step 4, the process parameters of medium frequency induction quenching are as follows: output power 40-70kW, frequency 2-6kHz, transformer turns ratio 9:2, moving speed 180-240mm / min, induction heating temperature 880-930℃, cooling medium is water, and continuous spray cooling is adopted.

[0010] Furthermore, in step 4, the tempering temperature is 180-260°C, the insulation time is 6-8h, and after the insulation is completed, the steel is cooled to below 100°C and taken out of the furnace.

[0011] Furthermore, in step 5, the specific process of stress relief treatment is: charging the furnace at room temperature, heating the temperature to 160°C-220°C at a heating rate of 30-50°C / h and keeping the temperature for 8-10 hours, and cooling the furnace to below 80°C after the insulation is completed.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows.

[0013] 1. After the medium-frequency induction quenching and tempering treatment of the surface of the extra-long cast iron integrated guide rail and bed, on the one hand, the workpiece only undergoes phase change on the surface of the guide rail, and the structure of the bed does not change. After stress relief and tempering treatment, the residual stress in the extra-long cast iron integrated guide rail and bed and the induction quenching surface layer is significantly reduced; on the other hand, the process parameters of medium-frequency induction quenching are adopted to overcome the problem of difficult overall quenching and tempering heat treatment of domestic extra-long cast iron integrated guide rails and bed.

[0014] 2. During the stress relief annealing process, the residual austenite in the guide rail structure decomposes, and a large amount of carbides precipitate, which further reduces the residual stress generated during quenching and machining. DETAILED DESCRIPTION

[0015] In order to make those skilled in the art better understand the technical solution of the present invention, the present invention is further described below in conjunction with specific embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. These embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents recorded in the present invention, all other embodiments obtained after various changes or modifications made to the present invention based on the technical solution and embodiments of the present invention also fall within the scope of protection of the claims of the present invention.

[0016] A method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed, which is specifically implemented as follows: Step 1: Use tempering equipment to perform the first artificial aging treatment on the super-long cast iron integrated guide rail and bed after casting; the aging treatment process is as follows: load the furnace below 200℃, heat up to 340-360℃ at a heating rate of 50-80℃ / h, keep warm for 2-3h, heat up to 550-580℃ at a heating rate of 40-60℃ / h, keep warm for 8-10h (the holding time depends on the load and the wall thickness of the thickest part), cool down to below 250℃ and take out of the furnace; Step 2: Rough machining is performed on the extra-long cast iron integrated guide rail and bed after artificial aging treatment, so that the surface roughness of the guide rail Ra is less than 3.2, and each machined surface has no defects; Step 3: Perform a second artificial aging treatment on the super-long cast iron integrated guide rail and bed after rough machining in step 2, load the furnace below 200°C, heat it to 340-360°C at a heating rate of 50-80°C / h, keep it warm for 1.5-2.5h, heat it to 530-550°C at a heating rate of 40-60°C / h, keep it warm for 8-10h, and cool it to below 200°C with the furnace and take it out of the furnace; Step 4: Pre-deform the guide rails treated by the second artificial aging in step 3. The pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the ultra-long cast iron integrated guide rails and bed after pre-deformation are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface. The medium-frequency induction quenching process parameters are as follows: output power 40-70kW, frequency 2-6kHz, transformer turns ratio 9:2, moving speed 180-240mm / min, induction heating temperature 880-930℃, cooling medium is water, continuous spray cooling is adopted, tempering temperature is 180-260℃, insulation time is 6-8h, and after the insulation is completed, it is cooled to below 100℃ with the furnace and taken out of the furnace; Step 5: Roughly grind the guide rail of step 4 to a surface roughness of Ra < 3.2, and perform stress relief treatment on the rough-ground extra-long cast iron integrated guide rail and bed. Load the guide rail and bed at room temperature, and heat the temperature to 160°C ~ 220°C at a heating rate of 30 ~ 50°C / h and keep it warm for 8 ~ 10 hours. The holding time depends on the amount of furnace loaded and the wall thickness of the thickest part. After the holding is completed, cool the furnace to below 80°C and take it out of the furnace to obtain an extra-long cast iron integrated guide rail and bed with reduced residual stress.

[0017] Example 1.

[0018] The method to reduce the residual stress of the extra-long cast iron integrated guide rail and bed is as follows: Step 1: Use tempering equipment to perform the first artificial aging treatment on the super-long cast iron bed casting after casting; the aging treatment process is as follows: load the furnace at 180℃, heat up to 360℃ at a heating rate of 70℃ / h, keep warm for 3h, heat up to 570℃ at a heating rate of 50℃ / h, keep warm for 8h, cool to 200℃ with the furnace and take out of the furnace; Step 2: Rough machining of the extra-long cast iron integrated guide rail and bed after the first artificial aging treatment, with a surface roughness Ra < 3.2 and no defects on the machined surfaces; Step 3: Perform a second artificial aging treatment on the rough-machined super-long cast iron integrated guide rail and bed, load the furnace at 140℃, heat it to 360℃ at a heating rate of 50℃ / h, keep it warm for 2.5h, heat it to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, cool it to 150℃ with the furnace and take it out of the furnace; Step 4: Pre-deform the guide rail treated by the second artificial aging in step 3. The pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the ultra-long cast iron integrated guide rail and bed after pre-deformation are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface. The medium-frequency induction quenching process parameters are as follows: output power 60kW, frequency 3kHz, transformer turns ratio 9:2, moving speed 200mm / min, induction heating temperature 920℃, cooling medium water, and continuous spray cooling; tempering temperature is 220℃, tempering time 8h, and after the insulation is completed, it is cooled to 80℃ with the furnace and taken out of the furnace; Step 5: Roughly grind the guide rail of step 4 to a surface roughness of Ra < 3.2, and perform stress relief treatment on the rough-ground extra-long cast iron one-piece guide rail and bed. Load the guide rail and bed into the furnace at room temperature, heat the temperature to 200°C at a heating rate of 30°C / h and keep it warm for 10 hours. After the insulation, cool the furnace to 60°C and take it out of the furnace to obtain an extra-long cast iron one-piece guide rail and bed with reduced residual stress.

[0019] Example 2.

[0020] The method to reduce the residual stress of the extra-long cast iron integrated guide rail and bed is as follows: Step 1: Use tempering equipment to perform the first artificial aging treatment on the super-long cast iron bed casting after casting; the aging treatment process is as follows: load the furnace at 180℃, heat up to 360℃ at a heating rate of 60℃ / h, keep warm for 3h, heat up to 580℃ at a heating rate of 40℃ / h, keep warm for 10h, cool to 200℃ with the furnace and take out of the furnace; Step 2: Rough machining of the extra-long cast iron integrated guide rail and bed after the first artificial aging treatment, with a surface roughness Ra < 3.2 and no defects on the machined surfaces; Step 3: Perform a second artificial aging treatment on the rough-machined super-long cast iron integrated guide rail and bed, load the furnace at 140°C, heat it to 360°C at a heating rate of 60°C / h, keep it warm for 2.5h, heat it to 550°C at a heating rate of 60°C / h, keep it warm for 8h, cool it to 150°C with the furnace, and take it out of the furnace; Step 4: Pre-deform the guide rails that have been artificially aged for the second time in step 3. The pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the ultra-long cast iron integrated guide rails and bed after pre-deformation are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface. The medium-frequency induction quenching process parameters are as follows: output power 70kW, frequency 5kHz, transformer turns ratio 9:2, moving speed 200mm / min, induction heating temperature 930℃, cooling medium water, and continuous spray cooling; tempering temperature is 240℃, tempering time is 8h, and after the insulation is completed, it is cooled to below 100℃ and taken out of the furnace; Step 5: Roughly grind the guide rail of step 4 to a surface roughness of Ra < 3.2, and perform stress relief treatment on the rough-ground extra-long cast iron one-piece guide rail and bed. Load the guide rail and bed into the furnace at room temperature, heat the temperature to 200°C at a heating rate of 30°C / h and keep it warm for 10 hours. After the insulation, cool the furnace to 60°C and take it out of the furnace to obtain an extra-long cast iron one-piece guide rail and bed with reduced residual stress.

[0021] Example 3.

[0022] The method to reduce the residual stress of the extra-long cast iron integrated guide rail and bed is as follows: Step 1: Use tempering equipment to perform the first artificial aging treatment on the super-long cast iron bed casting after casting; the aging treatment process is as follows: load the furnace at 180℃, heat up to 340℃ at a heating rate of 80℃ / h, keep warm for 2.5h, heat up to 580℃ at a heating rate of 60℃ / h, keep warm for 8h, cool to 200℃ with the furnace and take out of the furnace; Step 2: Rough machining of the extra-long cast iron integrated guide rail and bed after the first artificial aging treatment, with a surface roughness Ra < 3.2 and no defects on the machined surfaces; Step 3: Perform a second artificial aging treatment on the rough-machined super-long cast iron integrated guide rail and bed, load the furnace at 140°C, heat it to 360°C at a heating rate of 80°C / h, keep it warm for 2h, heat it to 550°C at a heating rate of 60°C / h, keep it warm for 8h, cool it to 150°C with the furnace, and take it out of the furnace; Step 4: Pre-deform the guide rail treated by the second artificial aging in step 3. The pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the ultra-long cast iron integrated guide rail and bed after pre-deformation are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface. The medium-frequency induction quenching process parameters are as follows: output power 50kW, frequency 3kHz, transformer turns ratio 9:2, moving speed 220mm / min, induction heating temperature 900℃, cooling medium water, and continuous spray cooling; tempering temperature is 240℃, tempering time is 6h, and after the insulation is completed, it is cooled to 80℃ with the furnace and taken out of the furnace; Step 5: Roughly grind the guide rail of step 4 to a surface roughness of Ra < 3.2, and perform stress relief treatment on the rough-ground extra-long cast iron one-piece guide rail and bed. Load the guide rail into the furnace at room temperature, heat it to 220°C at a heating rate of 50°C / h and keep it warm for 8 hours. After the insulation, cool it to 60°C and take it out of the furnace to obtain an extra-long cast iron one-piece guide rail and bed with reduced residual stress.

[0023] Comparative example 1.

[0024] The method to reduce the residual stress of the extra-long cast iron integrated guide rail and bed is as follows: Step 1: Use tempering equipment to perform the first artificial aging treatment on the super-long cast iron bed casting after casting; the aging treatment process is as follows: load the furnace at 180℃, heat up to 360℃ at a heating rate of 70℃ / h, keep warm for 3h, heat up to 570℃ at a heating rate of 50℃ / h, keep warm for 8h, cool to 200℃ with the furnace and take out of the furnace; Step 2: Rough machining of the extra-long cast iron integrated guide rail and bed after the first artificial aging treatment, with a surface roughness Ra < 3.2 and no defects on the machined surfaces; Step 3: Perform a second artificial aging treatment on the rough-machined super-long cast iron integrated guide rail and bed, load the furnace at 140℃, heat it to 360℃ at a heating rate of 50℃ / h, keep it warm for 2.5h, heat it to 550℃ at a heating rate of 40℃ / h, keep it warm for 8h, cool it to 150℃ with the furnace and take it out of the furnace; Step 4: Pre-deform the guide rail treated by the second artificial aging in step 3. The pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the ultra-long cast iron integrated guide rail and bed after pre-deformation are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface. The medium-frequency induction quenching process parameters are as follows: output power 60kW, frequency 3kHz, transformer turns ratio 9:2, moving speed 200mm / min, induction heating temperature 920℃, cooling medium water, and continuous spray cooling; tempering temperature is 220℃, tempering time 8h, and after the insulation is completed, it is cooled to 80℃ and taken out of the furnace to obtain an ultra-long cast iron integrated guide rail and bed.

[0025] The residual stress of the extra-long cast iron bed obtained by X-ray detection in Example 1 is 68 MPa, the residual stress of the extra-long cast iron bed obtained in Example 2 is 84 MPa, the residual stress of the extra-long cast iron bed obtained in Example 3 is 92 MPa, and the residual stress of the extra-long cast iron bed obtained in Comparative Example 1 is 172 MPa. By comparing Example 1, Example 2, Example 3 and Comparative Example 1, it can be found that the present invention can significantly reduce the residual stress of the extra-long cast iron bed.

Claims

1. A method for reducing residual stress in an extra-long cast iron integrated guide rail and a bed, characterized in that: The following steps are involved: Step 1: Performing the first artificial aging treatment on the super-long cast iron integrated guide rail and bed after casting to reduce casting stress; Step 2, rough machining the super-long cast iron integrated guide rail and bed after aging treatment in step 1, so that the surface roughness of the guide rail Ra is less than 3.2, and each machined surface has no defects; Step 3, performing a second artificial aging treatment on the extra-long cast iron integrated guide rail and bed after rough machining in step 2; Step 4, pre-deform the guide rail subjected to the second artificial aging treatment in step 3, wherein the pre-deformation processing parameter requirements are that the alignment along the length direction does not exceed 0.05mm, and the alignment along the side height direction does not exceed 0.02mm; and the super-long cast iron integrated guide rail and bed after the pre-deformation processing are subjected to medium-frequency induction quenching and tempering treatment on the guide rail surface; Step 5, rough grinding the guide rail of step 4, the surface roughness Ra <3.2, stress relief treatment is performed on the rough-ground extra-long cast iron one-piece guide rail and bed, so as to obtain an extra-long cast iron one-piece guide rail and bed with reduced residual stress.

2. The method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed according to claim 1, characterized in that: In the step 1, the specific process of the first artificial aging treatment is: charging the furnace below 200°C, heating to 340°C-360°C at a heating rate of 50-80°C / h and keeping it warm for 2-3h, heating to 550°C-580°C at a heating rate of 40-60°C / h and keeping it warm for 8-10h, cooling to below 250°C and taking out of the furnace.

3. The method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed according to claim 1, characterized in that: In step 3, the specific process of the second artificial aging treatment is: charging the furnace below 200°C, heating to 340°C-360°C at a heating rate of 50-80°C / h and keeping warm for 1.5-2.5h, heating to 530°C-550°C at a heating rate of 40-60°C / h and keeping warm for 8-10h, and cooling to below 200°C before taking out of the furnace.

4. The method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed according to claim 1, characterized in that: In step 4, the process parameters of medium frequency induction quenching are as follows: output power 40-70kW, frequency 2-6kHz, transformer turns ratio 9:2, moving speed 180-240mm / min, induction heating temperature 880-930°C, cooling medium is water, and continuous spray cooling is adopted.

5. The method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed according to claim 1, characterized in that: In the step 4, the tempering temperature is 180-260° C., the holding time is 6-8 hours, and after the holding is completed, the furnace is cooled to below 100° C. and then taken out of the furnace.

6. The method for reducing residual stress of an extra-long cast iron integrated guide rail and a bed according to claim 1, characterized in that: In step 5, the specific process of stress relief treatment is: charging the furnace at room temperature, heating the temperature to 160°C-220°C at a heating rate of 30-50°C / h and keeping the temperature for 8-10 hours, and cooling the furnace to below 80°C after the insulation is completed.