CN110977348A - Method for improving machining precision of thin-wall part - Google Patents

Abstract

The invention discloses a method for improving the processing precision of a thin-wall part, which combines and controls the aspects of internal stress elimination, processing stress elimination, a clamping method, cutter angle selection, cutting heat control and the like of the thin-wall part respectively, thereby designing a processing method for effectively overcoming the deformation of the thin-wall part and ensuring the processing precision of the thin-wall part.

Description

Method for improving machining precision of thin-wall part

Technical Field

The invention belongs to the technical field of machining, and particularly relates to a method for improving the machining precision of thin-wall parts, such as cast or section machined disc parts and ring parts.

Background

As shown in fig. 1, one of the main factors affecting the machining accuracy of a thin-walled part is internal stress generated before and during machining, which is typical of the thin-walled part. Because of thin wall, poor rigidity and low strength, the thin-wall parts are influenced by factors such as clamping force, cutting heat and the like to generate large internal stress, and mainly include residual stress before working procedures, clamping stress in the working procedures, thermal stress generated by processing, extrusion stress generated by cutting of a cutter, internal stress of intergranular fracture generated by processing and the like. Under the influence of the stress, the workpiece is easy to generate clamping deformation, deformation caused by extrusion of a cutter, thermal deformation, vibration during processing and the like as shown in fig. 2 and 3, so that the dimensional precision, the form and position precision, the surface roughness and the like of the part are difficult to guarantee, and even the workpiece is scrapped. If the clamping force is too small, the part is easy to loosen under the action of cutting force in the cutting process, so that danger is generated. After processing, deformation after processing is caused by internal stress, thereby causing huge hidden quality troubles. Therefore, the processing of the thin-wall parts has more prominent difficulty, namely, the processing difficulty is high, the processing period is long, the processing cost is high, and the quality hidden danger is large.

Disclosure of Invention

The invention aims to provide a method for improving the machining precision of a thin-wall part, which comprehensively solves the problems existing in the machining of the thin-wall part in multiple directions, multiple angles and deep layers and mainly starts from the aspects of improving a clamping mode, optimizing machining process parameters, reducing cutting heat and the like, thereby improving the machining precision of a product, shortening the machining period, reducing the machining cost and eliminating accidents and quality hidden troubles.

In principle, firstly, the processing method of the invention adopts two internal stress relief processes, wherein the first process mainly relieves the casting internal stress, and the second process mainly relieves the processing stress, thereby relieving the stress deformation. And secondly, the invention adopts end face compression, thereby avoiding clamping deformation of the workpiece and vibration during processing. Thirdly, the invention selects reasonable cutting parameters and blade angles, reduces the generation of cutting heat and the vibration in the cutting process, thereby reducing thermal deformation, reducing the surface roughness of a workpiece, and improving the dimensional accuracy and the durability of the blade.

The invention is realized by the following technical scheme.

A method for improving the machining precision of thin-wall parts is used for casting or machining thin-wall disc parts and ring parts by profiles, and comprises the following steps:

firstly, eliminating internal stress of a thin-wall part before processing;

rough machining and semi-finish machining of the inner circle, the outer circle and the end face of the thin-walled part;

step three, eliminating the machining stress in the thin-wall part machining process;

step four, processing a standard;

and step five, finishing the thin-walled workpiece.

Further, in the step one and the step three, the method for eliminating the internal stress and the processing stress comprises natural aging and artificial aging.

Further, in the second step, the fourth step and the fifth step, the thin-wall part is clamped in an end face compression mode, the end face compression includes that a supporting force is applied to one end face of the thin-wall part in the thickness direction, a pressing force is applied to the other end face, and the pressing force corresponds to the position of the supporting force.

When the excircle and the groove of the thin-wall part are turned, the clamping mechanism comprises a disc, a fastening bolt and a top plate, the disc is fixed on a lathe disc by the bolt through the fastening bolt, the thin-wall part is pre-jacked on the disc through a tailstock and the top plate of the lathe, and after the workpiece is rounded, a tailstock handle is rotated to jack the thin-wall part tightly for turning;

when turning the inner hole and the groove, the clamping mechanism comprises a disc, a fastening bolt, a pressing plate and a screw, after the outer circle is machined, the pressing plate and the screw are used for pressing a workpiece from the outer circle, then the tailstock handle is rotated to loosen and take down the top plate, and finally the inner hole and the groove are turned.

Further, the processing modes in the second step, the fourth step and the fifth step comprise turning and grinding,

when turning is adopted, the control of cutting heat is realized by controlling the cutting depth, the feeding amount, the cutting speed and the cutter angle;

when grinding is used, control of the grinding heat is achieved by controlling the grinding depth, the speed of the grinding wheel, the speed of the workpiece and the feed rate.

Further, the tool angle comprises a tool main deflection angle, an auxiliary deflection angle, a negative chamfer, a blade inclination angle, a rake angle and a tool nose fillet radius.

Preferably, the tool angle is selected according to the following method:

when the inner circle and the outer circle are turned, the main deflection angle is 0 degree, and when the end face is turned, the main deflection angle is 90 degrees;

when the continuous surface is turned, the front angle gamma is 25-30 degrees;

the minor deflection angle is 6 degrees to 10 degrees, and the angle is 1 degree to 3 degrees when the groove is cut;

during rough machining, negative chamfering f is 0.5S, gamma f is-5 to-10 degrees, the front angle gamma is 10 to 15 degrees, during finish machining, negative chamfering is not required, and the front angle gamma is 5 to 10 degrees;

the inclination angle lambda of the rough-machined edge is 0-5 degrees, and the inclination angle lambda of the finish-machined edge is 0-5 degrees;

during rough machining, the radius R of the tool nose fillet is R1-R2, and during finish machining, the radius R of the tool nose fillet is R0.5-R1.

Preferably, the cutting and grinding parameters are according to the following method:

during fine grinding, the cutting depth is 0.1-0.4 mm, and during fine grinding, the grinding depth is 0.025-0.017 mm;

during fine grinding, the cutting speed is 90-114 m/min, during fine grinding, the workpiece speed is 12m/min, and the grinding wheel speed is 18-20 m/s;

when the precision grinding is carried out, the feeding amount is 0.07-0.11 mm/r; during fine grinding, the feeding amount is 10-20 mm/r or 10-20 mm/st.

Compared with the prior art, the method for improving the machining precision of the thin-wall part, provided by the invention, has the following advantages: the invention adopts a mode of eliminating stress twice, wherein the internal stress of casting is mainly eliminated for the first time, and the processing stress is mainly eliminated for the second time, thereby eliminating the stress deformation. The end face compression is adopted, so that clamping deformation of the workpiece and vibration during machining are avoided. According to the invention, by reasonably selecting factors such as cutting parameters, blade angle and the like, the generation of cutting heat and vibration in the cutting process are reduced, so that the thermal deformation is reduced, and the surface roughness and the dimensional accuracy of a workpiece and the durability of a blade are improved.

Drawings

FIG. 1 is a schematic view of a processing sample according to the present invention;

FIG. 2 is a schematic view of a clamping deformation of the annular part;

FIG. 3 is a schematic view of the deformation of a thin-wall long tubular part during clamping;

FIG. 4 is a schematic view of an added process pocket;

FIG. 5 is a schematic view of an additional process square hole

FIG. 6 is a graph showing the relationship between cutting amount and cutting temperature;

FIG. 7 is a schematic diagram of tool rake angle versus cutting temperature;

FIG. 8 is a schematic diagram of the relationship between the principal deflection angle and the cutting temperature;

FIG. 9 is a graphical illustration of the effect of clearance angle on tool durability;

FIG. 10 is a schematic view of a sample clamp of the present invention;

FIG. 11 is a schematic diagram of the geometric angles of the inner and outer turning tools of the machining sample piece according to the present invention;

fig. 12 is a schematic view of the geometry of the slot knife for processing a sample according to the present invention.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and specific embodiments, but it should not be understood that the scope of the subject matter of the present invention is limited to the following embodiments, and various modifications, substitutions and alterations made based on the common technical knowledge and conventional means in the art without departing from the technical idea of the present invention are included in the scope of the present invention.

In order to solve the problem of the contradiction between complicated complexity and mutual restriction in the high-precision machining of thin-wall parts, after a large number of tests, the embodiment provides a thought, namely a method for effectively overcoming part deformation is found from the aspects of optimizing the machining process, improving the clamping mode, reducing the cutting heat and the like, so that the machining precision of the parts is ensured and improved, and the method comprises the following contents:

1. changing a clamping mode:

the end face compression is used to reduce or even eliminate the radial clamping force, as shown in fig. 9 and 10.

The part is supported by the workbench or the supporting point in the thickness direction of the disc and is pressed at the supporting point, and the part cannot deform under the action of the pressing force, so that the pressing effect in the thickness direction of the disc is better. In order to compress the part in the thickness direction, a process pit or a square hole is cast for installing the pressure plate during casting, as shown in fig. 4 and 5. In a position with poor local rigidity, an auxiliary supporting device needs to be added. Some parts even need to change the design structure of the parts or increase a process boss so as to be suitable for the clamping mode of the parts.

As shown in fig. 9, when turning the outer circle and the groove, the clamping mechanism mainly comprises a disc, a fastening bolt, a top plate and the like. When the lathe is in operation, the disk is fixed on a lathe accessory, namely a faceplate, by bolts through fastening bolts, then a workpiece is pre-jacked on the disk through a tailstock and a top plate of the lathe, and after the workpiece is rounded, a tailstock handle is rotated to jack the workpiece tightly for turning.

As shown in fig. 10, when the inner hole and the groove are turned, the clamping mechanism mainly comprises a disc, a fastening bolt, a pressing plate, a screw and the like. After the outer circle is machined, the workpiece is pressed tightly from the outer circle by the pressing plate and the screw, the tailstock handle is rotated to loosen and take down the top plate, and finally, the inner hole and the groove are turned.

2. Optimizing the processing process:

1) before processing, a residual stress eliminating procedure is added, and the cutting processing performance is improved. Mainly eliminates the residual stress caused by casting, section molding, manufacturing and processing, and the like.

2) And an internal stress eliminating procedure is added before finish machining, so that the internal stress generated by semi-finish machining is eliminated.

3) And adding a semi-finishing process. And a little machining allowance is reserved for semi-finishing, so that clamping force and cutting force which are as small as possible are used for finishing, cutting heat and internal stress which are as small as possible are generated, and deformation generated during stress relief is taken into consideration, so that the finishing allowance is determined.

4) And a reference processing procedure or step before finish machining is added, and clamping stress, clamping deformation and the deformation degree after finish machining are effectively controlled.

During aging, the blank with a larger part structure adopts natural aging as much as possible; the middle and small workpieces of the cast or section bar and the workpieces in the processing process adopt artificial aging. During artificial aging of the casting, heating to 500-550 ℃ at a speed of 50-60 ℃/h, preserving heat for 3-5 h (according to the charging amount), cooling to about 200 ℃ at a speed of 30-50 ℃/h, discharging and air cooling. The furnace temperature is not higher than 150 ℃ and the heating speed is not higher than 60 ℃ during the internal stress relief annealing, otherwise the furnace is easy to warp and deform and even crack.

If the deformation amount is too large in the artificial aging before finish machining, the workpiece needs to be pressed from two end faces by using a tool shown in fig. 10 to eliminate stress. The rest is carried out according to the conventional heat treatment method. The optimized process method comprises the following steps:

for the casting:

1) heat treatment, annealing for eliminating internal stress;

2) roughly turning and semi-finely turning the inner circle, the outer circle and the end face;

3) heat treatment, stress relief annealing;

4) turning or grinding the datum;

5) finish turning, refining, or other finishing.

And (3) section bar aligning:

1) heat treatment, adjusting the cutting performance of the material;

2) roughly turning and semi-finely turning the inner circle, the outer circle and the end face;

3) heat treatment, stress relief annealing;

4) turning or grinding the datum;

5) finish turning, refining, or other finishing.

3. Control of cutting heat:

through a number of experiments, the effect of the cutting quantity on the cutting temperature is shown in fig. 6, and the effect of the cutter angle on the cutting temperature is shown in fig. 7. From the viewpoint of reducing the cutting temperature, cutting parameters slightly different from those of conventional machining are required in machining. As can be seen, the increase in rake angle from 10 ° to 18 ° is most pronounced with a 15% decrease in cutting temperature. At the same time, the friction between the chips and the rake face is also reduced, so that the cutting temperature is reduced, and the rake angle of the tool is generally selected to be 15-20 degrees. The effect of the tool relief angle on the cutting temperature is substantially the same as the tool rake angle.

Through tests, the cutter sharpening and cutting parameters are carried out according to the following requirements.

When the inner circle and the outer circle of the thin disc part are turned, a main deflection angle of 0 degree is selected, and the axial force is reduced. When the end face is turned, a main deflection angle of 90 degrees is selected, so that the axial force is reduced, and the vibration is avoided.

When the thin disc part is roughly machined, negative chamfer angles f are ground, f is 0.5S, gamma f is-5 degrees to-10 degrees, and a front angle gamma is 10 degrees to 15 degrees. During fine machining, negative chamfering is not required, and the front angle gamma is 5-10 degrees.

When the continuous surface is turned, the front angle gamma is 25-30 deg.

The size of the secondary deflection angle of the cutter is mainly determined by the height required by the surface roughness of the workpiece. The auxiliary deflection angle is 6-10 degrees. The cutting is performed at 1-3 deg.

When the requirement on the surface roughness of the processing surface is not high, the inclination angle lambda of the rough processing blade is 0-5 degrees; the angle of inclination lambda of the finished edge takes 0 DEG to-5 deg.

During rough machining, the radius R of the tool nose fillet is R1-R2. And R0.5-R1 is taken as the radius R of the corner round corner in the fine processing.

Cutting depth: when a casting with a hard skin on the surface layer is cut, the cutting depth is made to be larger than the thickness of the hard skin layer as much as possible so as to protect a tool tip. During finish machining, the cutting depth is 0.1-0.4 mm; and during fine grinding, the grinding depth is 0.025-0.017 mm.

Cutting speed: when the finish machining is carried out, the cutting speed is 90-114 m/min; and during fine grinding, the workpiece speed is 12m/min, and the grinding wheel speed is 18-20 m/s.

Feeding amount: when the precision grinding is carried out, the feeding amount is 0.07-0.11 mm/r; during fine grinding, the feeding amount is 10-20 mm/r (mm/st).

The material of the cutting tool, the grinding wheel, the cutting fluid and the like are selected according to a conventional method.

The method of the invention is described below with reference to the parts of figure 1:

the standard part shown in fig. 1 is a nodular cast iron thin plate part, the size precision is 7 grades, the form and position precision is 6 grades, the standard part is easy to deform after being processed, and the form and position tolerance is not easy to guarantee. The cutter sharpening is shown in figures 11 and 12, and the processing method comprises the following steps:

1) heat treatment, eliminating internal stress annealing, charging temperature not higher than 120 deg.c, heating to 560 deg.c in 60 deg.c/hr, maintaining for 4 hr, cooling to 200 deg.c in 50 deg.c/hr, and air cooling.

2) Rough turning, semi-finish turning the inner circle, the outer circle and the end face. And the allowance is 0.5-0.8 mm, and in order to reduce the workload of grinding the two end faces, the allowance is 0.4-0.5 mm on the two end faces.

3) Heat treatment, stress relief annealing, charging temperature not higher than 120 deg.C, heating to 520 deg.C at 55 deg.C/hr, holding for 4 hr (according to charging amount), cooling to about 200 deg.C at 50 deg.C/hr, and air cooling.

4) And grinding two end faces. The flatness of the other surface ground first is detected on a flat plate, and unevenness of the concave part is marked. And during grinding, the concave part is padded with paper, the thickness of the paper is uneven plus 0.03mm, and one surface is ground to obtain the paper. And turning over and grinding the other side, and then turning over and grinding.

Ensuring the parallelism and the thickness dimension. If the planeness of the turning is poor, the plane needs to be ground four times. During fine grinding, the grinding depth is 0.02mm, the feed rate is 12mm/r, the workpiece speed is 12m/min, and the grinding wheel speed is 120 m/min.

5) Finish turning: as shown in FIG. 9, the faceplate is assembled, and the faceplate is polished to one plane. And (5) installing a workpiece, calibrating the excircle, and enabling the runout to be not more than 0.1 mm. And (5) tightly pushing the workpiece by using a top plate, and turning the outer circle to the required position. As shown in fig. 10, the workpiece is pressed by the pressing plate without loosening the top plate, the top plate is loosened, and the inner hole is lathed to the required position. Cutting parameters: processing the inner circle and the outer circle, wherein the cutting depth is 0.3mm, the rotating speed is 80r/min, and the feeding amount is 0.08 mm/r. The inner and outer grooves are processed at the rotating speed of 50r/min and the feeding amount of 0.07 mm/r. The turning tool schematic diagrams are shown as 11 and 12.

Claims (8)

1. A method for improving the machining precision of thin-wall parts is used for casting or machining section bars and thin-wall disc parts and ring parts, and is characterized by comprising the following steps:

firstly, eliminating internal stress of a thin-wall part before processing;

rough machining and semi-finish machining of the inner circle, the outer circle and the end face of the thin-walled part;

step three, eliminating the machining stress in the thin-wall part machining process;

step four, processing a standard;

and step five, finishing the thin-walled workpiece.

2. The method for improving the machining precision of the thin-walled workpiece according to claim 1, wherein the method comprises the following steps: in the step one and the step three, the method for eliminating the internal stress and the processing stress comprises natural aging and artificial aging.

3. The method for improving the machining precision of the thin-walled workpiece according to claim 1, wherein the method comprises the following steps: in the second step, the fourth step and the fifth step, the thin-wall part is clamped in an end face compression mode, wherein the end face compression comprises the step of applying a supporting force on one end face of the thin-wall part in the thickness direction and applying a pressing force on the other end face, and the pressing force corresponds to the position of the supporting force.

4. A method of improving the machining accuracy of a thin-walled part according to claim 3, wherein:

when the excircle and the groove of the thin-wall part are turned, the clamping mechanism comprises a disc, a fastening bolt and a top plate, the disc is fixed on a lathe disc by the bolt through the fastening bolt, the thin-wall part is pre-jacked on the disc through a tailstock and the top plate of the lathe, and after the workpiece is rounded, a tailstock handle is rotated to jack the thin-wall part tightly for turning;

when turning the inner hole and the groove, the clamping mechanism comprises a disc, a fastening bolt, a pressing plate and a screw, after the outer circle is machined, the pressing plate and the screw are used for pressing a workpiece from the outer circle, then the tailstock handle is rotated to loosen and take down the top plate, and finally the inner hole and the groove are turned.

5. The method for improving the machining precision of the thin-walled workpiece according to claim 1, wherein the method comprises the following steps: the processing modes in the second step, the fourth step and the fifth step comprise turning and grinding,

when turning is adopted, the control of cutting heat is realized by controlling the cutting depth, the feeding amount, the cutting speed and the cutter angle;

when grinding is used, control of the grinding heat is achieved by controlling the grinding depth, the speed of the grinding wheel, the speed of the workpiece and the feed rate.

6. A method for improving the machining accuracy of a thin-walled part according to claim 5, wherein: the tool angle comprises a main deflection angle, an auxiliary deflection angle, a negative chamfer, a blade inclination angle, a front angle and a tool nose fillet radius.

7. The method for improving the machining precision of the thin-walled workpiece according to claim 6, wherein the method comprises the following steps:

when the inner circle and the outer circle are turned, the main deflection angle is 0 degree, and when the end face is turned, the main deflection angle is 90 degrees;

when the continuous surface is turned, the front angle gamma is 25-30 degrees;

the minor deflection angle is 6 degrees to 10 degrees, and the angle is 1 degree to 3 degrees when the groove is cut;

during rough machining, negative chamfering f is 0.5S, gamma f is-5 to-10 degrees, the front angle gamma is 10 to 15 degrees, during finish machining, negative chamfering is not required, and the front angle gamma is 5 to 10 degrees;

the inclination angle lambda of the rough-machined edge is 0-5 degrees, and the inclination angle lambda of the finish-machined edge is 0-5 degrees;

during rough machining, the radius R of the tool nose fillet is R1-R2, and during finish machining, the radius R of the tool nose fillet is R0.5-R1.

8. A method for improving the machining accuracy of a thin-walled part according to claim 5, wherein:

during fine grinding, the cutting depth is 0.1-0.4 mm, and during fine grinding, the grinding depth is 0.025-0.017 mm;

during fine grinding, the cutting speed is 90-114 m/min, during fine grinding, the workpiece speed is 12m/min, and the grinding wheel speed is 18-20 m/s;

when the precision grinding is carried out, the feeding amount is 0.07-0.11 mm/r; during fine grinding, the feeding amount is 10-20 mm/r or 10-20 mm/st.

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