Over-positioning grinding method for hard and brittle pipe fitting with large length-diameter ratio

Abstract

The invention discloses an over-positioning grinding method for a hard and brittle pipe fitting with a large length-diameter ratio, and belongs to the technical field of grinding. Although an existing grinding machining method can improve the grinding precision of the outer circle of the hard and brittle pipe fitting, the coaxiality of the outer circle and the inner circle of the ground hard and brittle pipe fitting cannot be guaranteed at the same time, and therefore the wall thicknesses of the ground hard and brittle pipe fitting are inconsistent. The rigid mandrel, the supporting plate and the guide wheel are used for carrying out over-positioning supporting on the hard and brittle pipe fitting in the machining process, the guide wheel is driven to rotate forwards, the hard and brittle pipe fitting with the large length-diameter ratio is fed into a grinding area, the guide wheel makes contact with the hard and brittle pipe fitting and drives the hard and brittle pipe fitting to move forwards and meanwhile rotates reversely, and the grinding wheel rotates reversely and feeds towards the side of the hard and brittle pipe fitting; along with grinding and feeding of the grinding wheel, the guide wheel and the supporting plate are fed towards the hard and brittle pipe fitting side so that over-positioning supporting of the guide wheel, the supporting plate and the rigid mandrel on the hard and brittle pipe fitting can be kept all the time, and grinding machining of the hard and brittle pipe fitting with the large length-diameter ratio can be achieved along with moving of the hard and brittle pipe fitting. The method is used for grinding the hard and brittle pipe fittings.

Description

Technical Field

[0001] The invention belongs to the field of grinding technology, relates to the field of cylindrical grinding of hard and brittle materials, and in particular to an over-positioning grinding method for hard and brittle pipe fittings with a large aspect ratio. Background Art

[0002] At present, hard and brittle pipe fittings with a large length-to-diameter ratio are widely used in semiconductor, nuclear energy, chemical and other fields. Hard and brittle pipe fittings with a large length-to-diameter ratio used under special working conditions need to have higher size and shape accuracy. Due to the preparation process, the rough tubes of hard and brittle pipe fittings with a large length-to-diameter ratio have large size and shape accuracy errors and cannot directly meet the use requirements. This means that it is necessary to perform certain processing on the hard and brittle pipe fittings to ensure their accuracy. However, due to the structural characteristics of the large length-to-diameter ratio and the high hardness and high brittleness material properties of hard and brittle pipe fittings with a large length-to-diameter ratio, it is difficult to perform high-precision and high-efficiency precision molding of such parts, which greatly limits the application of such parts in various industries.

[0003] The existing outer circle processing of hard and brittle pipe fittings generally adopts external cylindrical grinding, but the current processing method cannot improve the grinding accuracy of the outer circle of the hard and brittle pipe fittings, and also ensure the coaxiality of the outer circle and the inner circle of the hard and brittle pipe fittings after grinding, which will lead to inconsistent wall thickness of the hard and brittle pipe fittings after grinding. Summary of the invention

[0004] In view of this, the present invention provides a method for over-positioning grinding of hard and brittle pipe fittings with a large aspect ratio, which can provide over-positioning support for the hard and brittle pipe fittings during the processing to improve the grinding accuracy of the outer circle of the hard and brittle pipe fittings, while ensuring that the outer circle and inner circle of the hard and brittle pipe fittings after grinding are coaxial, thereby achieving high-precision processing of hard and brittle pipe fittings with a large aspect ratio.

[0005] The technical solution adopted by the present invention to solve the above technical problems is:

[0006] A method for over-positioning grinding of hard and brittle pipe fittings with a large aspect ratio. The specific grinding process is as follows:

[0007] S1, assembly and positioning of hard and brittle pipe fittings: the rigid mandrel passes through the inner hole of the hard and brittle pipe fittings with a large aspect ratio and is clearance-matched with the hard and brittle pipe fittings, the rigid mandrel is tensioned and the hard and brittle pipe fittings are kept level, and the two ends of the rigid mandrel and the positions close to the hard and brittle pipe fittings are each supported by a vibration reduction device to reduce the vibration amplitude and frequency of the rigid mandrel during the processing of the hard and brittle pipe fittings; the support plate contacts the outer pipe surface of the hard and brittle pipe fittings and supports the hard and brittle pipe fittings;

[0008] S2, determine the grinding area: arrange the grinding wheel and the guide wheel on both sides of the hard and brittle pipe respectively, and keep the axes of the grinding wheel and the guide wheel at the same height, adjust the height of the two so that there is a height difference between the axes of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe, and the grinding surface of the grinding wheel is positively opposite to the guide support surface of the guide wheel. The grinding wheel, the guide wheel and the support plate enclose the grinding area of ​​the hard and brittle pipe, and the rigid mandrel is used to position and support the hard and brittle pipe;

[0009] S3, guide wheel positioning: the hard and brittle pipe is moved to the grinding area, and the guide wheel is moved toward the side of the hard and brittle pipe until the guide bearing surface of the guide wheel contacts and squeezes the outer surface of the hard and brittle pipe, so that there is a pre-pressure between the guide wheel and the hard and brittle pipe, and the hard and brittle pipe is moved out of the grinding area, and the guide wheel is kept in place;

[0010] S4, tool setting: drive the guide wheel to rotate forward, and send the hard and brittle pipe with a large aspect ratio into the grinding area. The guide wheel contacts and drives the hard and brittle pipe forward while rotating in the opposite direction. The grinding wheel rotates in the opposite direction and feeds a small amount to the side of the hard and brittle pipe to achieve tool setting operation.

[0011] S5, grinding of hard and brittle pipe fittings: set the rotation speed and feed speed of the guide wheel and the rotation speed and feed speed of the grinding wheel, and set the grinding amount of hard and brittle pipe fittings; drive the guide wheel to rotate forward to feed the hard and brittle pipe fittings with a large aspect ratio into the grinding area. The guide wheel contacts and drives the hard and brittle pipe fittings forward while rotating in the opposite direction. The grinding wheel rotates in the opposite direction and feeds toward the side of the hard and brittle pipe fittings. As the grinding wheel grinds and feeds, the guide wheel and the support plate feed toward the side of the hard and brittle pipe fittings to always maintain the over-positioning support of the guide wheel, the support plate and the rigid mandrel on the hard and brittle pipe fittings. As the hard and brittle pipe fittings move, the grinding of the hard and brittle pipe fittings with a large aspect ratio is achieved.

[0012] Furthermore, in the above-mentioned S5, the linear speed of the grinding wheel is 30 m / s.

[0013] Furthermore, in the above-mentioned S5, when the outer diameter of the grinding wheel is 400 mm, the rotation speed of the grinding wheel is 1400 rpm / min to 1500 rpm / min.

[0014] Furthermore, in the above-mentioned S5, the operating speed of the guide wheel is 15 rpm / min to 20 rpm / min.

[0015] Furthermore, the matching clearance between the rigid mandrel and the hard and brittle pipe fitting ranges from 0.2 to 0.5 mm.

[0016] Furthermore, the support plate is arranged close to the grinding wheel side and obliquely supports the hard and brittle pipe fittings. The supporting surface of the support plate is an inclined surface, and the inclination angle of the supporting surface is 30°.

[0017] Furthermore, the grinding wheel is a parallel grinding wheel.

[0018] Furthermore, the grinding wheel is a cup-shaped grinding wheel, and there is an offset angle θ between the axis of the cup-shaped grinding wheel and the axis of the hard and brittle pipe, θ>0.

[0019] Furthermore, in S2, the height difference between the axis of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe is obtained by the following method:

[0020] Assume that the outer radius of the hard and brittle pipe with a large aspect ratio is R w , the radius of the guide wheel is R c , the radius of the grinding wheel is R g , let the height difference between the axis of the hard and brittle pipe fitting and the axis of the grinding wheel be h; when the grinding wheel contacts the hard and brittle pipe fitting, let the initial contact point between the grinding wheel and the hard and brittle pipe fitting be A, and the tangent at point A be l; when the guide wheel contacts the hard and brittle pipe fitting, let the initial contact point between the guide wheel and the hard and brittle pipe fitting be B; when the support plate contacts the hard and brittle pipe fitting, let the initial contact point between the support plate and the hard and brittle pipe fitting be C;

[0021] Assume the axis of the hard and brittle pipe is O and the center of the guide wheel is O c , the grinding wheel center is O g , ∠AOC=α, ∠BOC=φ, ∠AO g O c =β g , ∠O g O c B=β c , β is the grinding angle of the grinding wheel, δ is the angle between OA and the horizontal line, the inclination angle of the supporting surface of the support plate is γ, and O g Establish a rectangular coordinate system for the center of the circle, and the tangent point A is in the coordinate system xO g The coordinates in y are (x, y); when there is an offset angle θ between the axis of the grinding wheel and the axis of the hard and brittle pipe, the grinding wheel grinds at the offset angle θ, and the contour projection of the grinding wheel in the cross section perpendicular to the feed speed direction is at xO g The elliptic curve equation in y can be expressed as:

[0022]

[0023] Where y is the height difference between the tangent point A and the axis of the grinding wheel, and x is the horizontal distance from the tangent point A to the vertical axis y;

[0024] The following relationship is obtained from formula (1):

[0025] x=R g sinθcosβ g (2)

[0026] y=R g sinβ g(3)

[0027] The slope of the tangent line l passing through the tangent point A on the elliptic curve can be expressed as:

[0028]

[0029] Since the tangent value of the slope of the tangent line l is the angle between the tangent line l and the x-axis, the angle δ between the tangent line l and the x-axis is obtained from formula (4):

[0030]

[0031] According to the geometric relationship, the following formula is obtained:

[0032] β c ≈h / (R w +R c )(6)

[0033] h=y+R w sinδ (7)

[0034] β=β c +δ=π-φ-α (8)

[0035] δ, y, β c Substituting into equations (7) and (8), we obtain:

[0036]

[0037] In trigonometry, when the angles are small, the following simplifications occur:

[0038]

[0039] cot(β g )≈1 / β g (12)

[0040] Therefore, substituting formula (11) and formula (12) into formula (9) and (10) can be transformed into:

[0041]

[0042] h=R g β g +R w β g sinθ (14)

[0043] Combining formulas (13) and (14) we get:

[0044]

[0045] Furthermore, the process of obtaining the grinding angle β is as follows:

[0046] According to the geometric relationship, the following formula is obtained:

[0047]

[0048] Stability growth factor A i The expression is:

[0049]

[0050] Combining formulas (4)-(17), formula (18) can be converted into variables with only angles β and γ, and formula (18) becomes:

[0051]

[0052] Based on open source software python and stability growth coefficient A i Get the stability diagram, when A i When >0, it is a stable region, and the range value of β is selected in the stable region according to the inclination angle γ of the supporting surface of the support plate.

[0053] Compared with the prior art, the present invention has the following beneficial effects:

[0054] 1. The support plate obliquely supports the surface of the hard and brittle pipe fittings. The guide wheel and the grinding wheel also support and position the hard and brittle pipe fittings. The support plate, guide wheel and grinding wheel all support the hard and brittle pipe fittings upward and form a grinding area. The rigid mandrel and the hard and brittle pipe fittings are clearance-matched, which not only ensures the rotation and advancement of the hard and brittle pipe fittings, but also keeps the hard and brittle pipe fittings horizontal when the rigid mandrel is tensioned, that is, the hard and brittle pipe fittings are pressed in the grinding area and supported and positioned at multiple points during the processing, which not only realizes the stable support of the over-positioning of the hard and brittle pipe fittings, but also provides a positioning reference for the processing of the outer circle of the workpiece. Under this over-positioning support, the hard and brittle pipe fittings can improve the grinding accuracy of the outer circle of the hard and brittle pipe fittings, and can also ensure that the outer circle and the inner circle of the hard and brittle pipe fittings after grinding are coaxial, so as to realize high-precision processing of hard and brittle pipe fittings with a large aspect ratio.

[0055] 2. The guide wheel adopts a single-leaf hyperboloid structure, which can not only drive the workpiece to rotate stably and realize uniform processing of the outer cylindrical surface of the workpiece, but also drive the workpiece to move forward at a uniform speed and realize uniform processing of the workpiece in the length direction.

[0056] 3. The grinding wheel can be a parallel grinding wheel or a cup-shaped grinding wheel. When the grinding wheel is a cup-shaped grinding wheel, the rotation axis of the cup-shaped grinding wheel is perpendicular to the direction of the speed, so that the grinding in the feed direction becomes the outer cylindrical surface grinding, rather than the plane grinding, which can reduce the grinding force. The outer cylindrical surface of the grinding wheel removes material and has a smaller contact area, so the workpiece can be more finely controlled for cutting, which is especially suitable for high-precision outer cylindrical grinding and can achieve higher surface quality and dimensional accuracy. At the same time, the cutting area of ​​the cup-shaped grinding wheel is concentrated, and the force during grinding is small, which reduces the influence of the cutting force. The movement trajectory of the abrasive grains on the end face of the grinding wheel is parallel to the material forming surface, which can not only achieve large cutting depth grinding, but also reduce the grinding force of the grinding wheel on the workpiece, avoid damage to the workpiece with hard and brittle characteristics, and obtain a workpiece surface with less sub-surface damage. Properly adjusting the angle or trimming the cup-shaped grinding wheel can extend its service life and reduce the frequency of abrasive tool replacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The accompanying drawings are incorporated as part of this application and are used to provide a further understanding of the present invention.

[0058] Figure 1 It is a schematic diagram of the overall structure of the hard and brittle pipe fittings and the over-positioning grinding device.

[0059] Figure 2 This is a schematic diagram of the contact between the grinding wheel shape and the hard and brittle pipe fittings during processing of hard and brittle pipe fittings.

[0060] Figure 3 This is a schematic diagram of the positioning cooperation among the grinding wheel, rigid mandrel, support plate and guide wheel when machining hard and brittle pipe fittings.

[0061] Figure 4 Schematic diagram of the working principle of the positioning geometry layout during grinding of hard and brittle pipe fittings.

[0062] Figure 5 To determine the grinding angle based on the stability diagram.

[0063] Figure 6 This is a physical picture of the hard and brittle pipe fittings after positioning grinding. A one-meter silicon carbide pipe was ground and samples were taken to observe the measurement of its wall thickness.

[0064] Figure 7 This is the roundness error of the hard and brittle pipe after processing. The actual object in the picture is the result after measurement of a 100mm long silicon carbide pipe.

[0065] Explanation of the reference numerals: 1-rigid mandrel; 2-hard and brittle pipe; 3-supporting plate; 4-guide wheel; 5-grinding wheel; 6-vibration reduction device. DETAILED DESCRIPTION

[0066] The present invention is described in detail below in conjunction with specific embodiments.

[0067] See also Figure 1 and Figure 2 In this embodiment, a method for over-positioning grinding of a hard and brittle pipe with a large aspect ratio is implemented by using an over-positioning grinding device, such as Figure 1 The figure shows the overall structure diagram of the assembly of the hard and brittle pipe fitting and the over-positioning grinding device. The over-positioning grinding device includes a rigid mandrel 1, a vibration reduction device 6, a support plate 3, a grinding wheel 5 and a guide wheel 4. The rigid mandrel 1 is horizontally arranged and used to support the hard and brittle pipe fitting 2 with a large length-to-diameter ratio. Since the hard and brittle pipe fitting 2 is a pipe fitting with a large length-to-diameter ratio, and the rigid mandrel 1 passes through the inner hole of the rigid mandrel 1 and is used to support the hard and brittle pipe fitting 2, the rigid mandrel 1 is also a support member with a large length-to-diameter ratio. The rigid mandrel 1 is easy to bend downward, so when the rigid mandrel 1 supports the hard and brittle pipe fitting 2, the two ends of the rigid mandrel 1 are tensioned by a tensioning device to keep the rigid mandrel 1 and the hard and brittle pipe fitting 2 always horizontal. The support plate 3 is arranged below the rigid mandrel 1 and is also used to support the hard and brittle pipe fitting 2 with a large length-to-diameter ratio. The support of the hard and brittle pipe fitting 2 by the rigid mandrel 1 and the support plate 3 keeps the hard and brittle pipe fitting 2 in a horizontal state during the processing. There are two vibration damping devices 6, which are respectively arranged at both ends of the rigid mandrel 1 and used to support the rigid mandrel 1. Since the hard and brittle pipe 2 will vibrate during the processing, the rigid mandrel 1 will also vibrate under the action of inertia. The vibration damping device 6 can reduce the vibration amplitude and frequency of the rigid mandrel 1, thereby reducing the vibration frequency and amplitude of the hard and brittle pipe 2 and improving the processing accuracy of the hard and brittle pipe 2. The guide wheel 4 is installed on one side of the rigid mandrel 1, and is used to rotate the workpiece and push the workpiece forward to ensure the smooth processing of the workpiece. The grinding wheel 5 is installed on the other side of the rigid mandrel 1, and is used to grind the outer circle of the hard and brittle pipe 2.

[0068] The over-positioning grinding process of hard and brittle pipe fitting 2 is as follows:

[0069] S1, Assembly and positioning of hard and brittle pipe fittings: Figure 1 As shown, the rigid mandrel 1 passes through the inner hole of the hard and brittle pipe fitting 2 with a large aspect ratio and is clearance-matched with the hard and brittle pipe fitting 2. The value range of the clearance between the rigid mandrel 1 and the hard and brittle pipe fitting 2 is 0.2-0.5 mm, which ensures that the hard and brittle pipe fitting 2 can move along the length direction of the rigid mandrel 1, and can also realize the positioning support of the hard and brittle pipe fitting 2, tighten the rigid mandrel 1 and keep the hard and brittle pipe fitting 2 horizontal; the two ends of the rigid mandrel 1 and the position close to the hard and brittle pipe fitting 2 are each supported by a vibration reduction device 6 to reduce the vibration amplitude and frequency of the rigid mandrel 1 during the processing of the hard and brittle pipe fitting 2, thereby reducing the vibration frequency and amplitude of the hard and brittle pipe fitting 2 and improving the processing accuracy of the workpiece; the support plate 3 slightly contacts the outer tube surface of the hard and brittle pipe fitting 2 and obliquely supports the hard and brittle pipe fitting 2, the support plate 3 is arranged close to the grinding wheel 5, and the supporting surface of the support plate 3 is a 30° inclined surface;

[0070] S2, determine the grinding area: arrange the grinding wheel 5 and the guide wheel 4 on both sides of the hard and brittle pipe 2 respectively, and keep the axes of the grinding wheel 5 and the guide wheel 4 at the same height, adjust the heights of the two so that the axes of the guide wheel 4 and the grinding wheel 5 are lower than the axis of the hard and brittle pipe 2, the grinding surface of the grinding wheel 5 is positively opposite to the guide bearing surface of the guide wheel 4, and the rigid mandrel 1, the grinding wheel 5, the guide wheel 4 and the support plate 3 enclose the grinding area of ​​the hard and brittle pipe 2 with positioning support;

[0071] S3, guide wheel positioning: the hard and brittle pipe 2 is moved to the grinding area, and the guide wheel 4 is moved toward the side of the hard and brittle pipe 2 until the guide bearing surface of the guide wheel 4 contacts and squeezes the outer pipe surface of the hard and brittle pipe 2, so that there is a pre-pressure between the guide wheel 4 and the hard and brittle pipe 2, and the hard and brittle pipe 2 is moved out of the grinding area, and the guide wheel 4 is kept in place;

[0072] S4, tool setting: drive the guide wheel 4 to rotate forward, and send the hard and brittle pipe 2 with a large aspect ratio into the grinding area. The guide wheel 4 contacts and drives the hard and brittle pipe 2 forward while rotating in the reverse direction. The grinding wheel 5 rotates in the reverse direction and feeds a small amount to the side of the hard and brittle pipe 2 to achieve the tool setting operation;

[0073] S5, grinding of hard and brittle pipe fittings: set the speed and feed speed of the guide wheel 4 and the speed and feed speed of the grinding wheel 5, and set the grinding amount of the hard and brittle pipe fittings 2; drive the guide wheel 4 to rotate forward, and the working speed of the guide wheel 4 is 15rpm / min

[0074] ~20rpm / min, the hard and brittle pipe 2 with a large aspect ratio is fed into the grinding area, the guide wheel 4 contacts and drives the hard and brittle pipe 2 to move forward while rotating in the opposite direction, the grinding wheel 5 rotates in the opposite direction and feeds to the side of the hard and brittle pipe 2, the linear speed of the grinding wheel 5 is 30m / s, when the outer diameter of the grinding wheel 5 is 400mm, the rotation speed of the grinding wheel 5 is 1400rpm / min~1500rpm / min; with the grinding and feeding of the grinding wheel 5, the surface of the hard and brittle pipe 2 is gradually As the pre-tightening force of the guide wheel 4 and the support plate 3 on the hard and brittle pipe fittings 2 is gradually removed, it will gradually decrease, which will affect the processing accuracy of the hard and brittle pipe fittings 2. Therefore, as the hard and brittle pipe fittings 2 are processed, in addition to the gradual feeding of the grinding wheel 5, the guide wheel 4 and the support plate 3 are also gradually fed to ensure that the pre-tightening force on the hard and brittle pipe fittings 2 is relatively constant. At the same time, the guide wheel 4, the support plate 3 and the rigid core shaft 1 always maintain the over-positioning support for the hard and brittle pipe fittings 2. As the hard and brittle pipe fittings 2 move, the grinding processing of the hard and brittle pipe fittings 2 with a large aspect ratio is realized.

[0075] like Figure 3 and Figure 4As shown, since the support plate 3 is arranged on the side close to the grinding wheel 5 and obliquely supports the surface of the hard and brittle pipe 2, the contact points of the guide wheel 4 and the grinding wheel 5 with the hard and brittle pipe 2 are both lower than the axis of the hard and brittle pipe 2. Therefore, when the hard and brittle pipe 2 is ground, the guide wheel 4 and the grinding wheel 5 also play a supporting and positioning role for the hard and brittle pipe 2. However, the support plate 3, the guide wheel 4 and the grinding wheel 5 all support the hard and brittle pipe 2 upward and form a grinding area. The rigid mandrel 1 and the hard and brittle pipe 2 are clearance-matched, which can not only ensure the rotation and advancement of the hard and brittle pipe 2, but also keep the hard and brittle pipe 2 horizontal when the rigid mandrel 1 is tensioned, that is, the hard and brittle pipe 2 is pressed tightly in the grinding area and supported and positioned at multiple points during the processing, which not only realizes the stable support of the over-positioning of the hard and brittle pipe 2, but also provides a positioning reference for the processing of the outer circle of the workpiece. Under the positioning support, the hard and brittle pipe fittings 2 can improve the grinding accuracy of the outer circle of the hard and brittle pipe fittings 2, and can also ensure that the outer circle and the inner circle of the hard and brittle pipe fittings 2 after grinding are coaxial, so as to achieve high-precision processing of hard and brittle pipe fittings 2 with a large aspect ratio, such as Figure 3 In the figure, the dotted circular contour line is the contour line of the hard and brittle pipe 2 at the initial position, and the solid circular contour line is the contour line of the hard and brittle pipe 2 after grinding. Figure 3 It can be seen that the two contour lines before and after grinding are coaxial and coaxial with the inner circle, so the coaxiality of the inner circle and the outer circle of the workpiece after grinding is guaranteed.

[0076] The guide wheel 4 in this embodiment adopts a single-blade hyperboloid structure, which can not only drive the workpiece to rotate stably and realize uniform processing of the outer cylindrical surface of the workpiece, but also drive the workpiece to move forward at a uniform speed to realize uniform processing of the workpiece in the length direction. The grinding wheel 5 can be a parallel grinding wheel or a cup-shaped grinding wheel; when the grinding wheel 5 is a cup-shaped grinding wheel, the rotation axis of the cup-shaped grinding wheel is perpendicular to the direction of the speed, so that the grinding in the feed direction becomes outer cylindrical surface grinding instead of plane grinding, which can reduce the grinding force, remove material from the outer cylindrical surface of the grinding wheel, and have a smaller contact area, so that the workpiece can be cut more finely, which is especially suitable for high-precision outer cylindrical grinding and can achieve higher surface quality and dimensional accuracy. At the same time, the cutting area of ​​the cup-shaped grinding wheel is concentrated, and the force during grinding is small, which reduces the influence of the cutting force. The abrasive movement trajectory of the end face of the grinding wheel is parallel to the material forming surface, which can not only achieve large cutting depth grinding, but also reduce the grinding force of the grinding wheel on the workpiece, avoid damage to the workpiece with hard and brittle characteristics, and obtain a workpiece surface with less sub-surface damage. The cup-shaped grinding wheel is properly adjusted or trimmed to extend its service life and reduce the frequency of replacement of the grinding tool. Since the cup-shaped grinding wheel uses the annular grinding surface at the cup mouth to achieve material removal, if the axial direction of the cup-shaped grinding wheel is perpendicular to the axial direction of the workpiece, it will cause the cup-shaped grinding wheel and the workpiece surface to have two grinding contact surfaces, resulting in repeated grinding of the workpiece, affecting the processing quality of the workpiece. Therefore, there is an angle between the grinding surface of the cup-shaped grinding wheel and the workpiece surface, and the angle θ>0, so that the cup-shaped grinding wheel and the workpiece surface are point contact grinding with a smaller area to avoid low damage to the workpiece. The parallel grinding wheel has only one grinding end face, so when using the parallel grinding wheel for processing, the parallel grinding wheel can be parallel to the hard and brittle pipe 2.

[0077] When the workpiece enters the grinding area for grinding, the supporting surface of the support plate 3 slightly contacts the workpiece surface to achieve the supporting purpose. It should be noted that before the guide wheel 4 contacts the workpiece surface, there is only slight contact between the support plate 3 and the workpiece surface. When the guide wheel 4 contacts and drives the workpiece to rotate and advance, the workpiece and the supporting surface of the support plate 3 change from slight contact to contact, and the contact surface between the two becomes larger. The guide wheel 4, the rigid mandrel 1 and the support plate 3 produce a suitable preload force on the workpiece to ensure the machining accuracy of the workpiece surface; if before the guide wheel 4 contacts the workpiece surface, there is a large area of ​​contact support between the support plate 3 and the workpiece surface. When the guide wheel 4 contacts and drives the workpiece to rotate and advance, the supporting force between the support plate 3 and the workpiece becomes larger, which easily leads to a deterioration in the machining accuracy of the workpiece. In addition, the inclination angle of the supporting surface of the support plate 3 is preferably about 30°. The stability range within the angle range of the support plate is the largest, and the rounding effect is the best.

[0078] In the actual processing process, it is necessary to first determine the grinding angle of the grinding wheel for grinding. However, when adjusting the position of the guide wheel, the grinding wheel and the hard and brittle pipe, it is difficult to measure the grinding angle, which increases the difficulty of adjusting the position of the guide wheel, the grinding wheel and the hard and brittle pipe. Therefore, this embodiment determines the height difference h between the axis of the hard and brittle pipe and the axis of the grinding wheel based on the grinding angle β, which makes it easier to adjust the position of the grinding wheel and the guide wheel.

[0079] like Figure 4 The figure shows the working principle of the positioning geometry layout when grinding hard and brittle pipes. The height difference h between the axis of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe is obtained by the following method:

[0080] Assume that the outer radius of the hard and brittle pipe with a large aspect ratio is R w , the radius of the guide wheel is R c , the radius of the grinding wheel is R g , let the height difference between the axis of the hard and brittle pipe fitting and the axis of the grinding wheel be h; when the grinding wheel contacts the hard and brittle pipe fitting, let the initial contact point between the grinding wheel and the hard and brittle pipe fitting be A, and the tangent at point A be l; when the guide wheel contacts the hard and brittle pipe fitting, let the initial contact point between the guide wheel and the hard and brittle pipe fitting be B; when the support plate contacts the hard and brittle pipe fitting, let the initial contact point between the support plate and the hard and brittle pipe fitting be C;

[0081] Assume the axis of the hard and brittle pipe is O and the center of the guide wheel is O c , the grinding wheel center is O g , ∠AOC=α, ∠BOC=φ, ∠AO g O c =β g , ∠O g O c B=β c , β is the grinding angle of the grinding wheel, δ is the angle between OA and the horizontal line, the inclination angle of the supporting surface of the support plate is γ, and O g Establish a rectangular coordinate system for the center of the circle, and the tangent point A is in the coordinate system xO g The coordinates in y are (x, y); when there is an offset angle θ between the axis of the grinding wheel and the axis of the hard and brittle pipe, the grinding wheel grinds at the offset angle θ, and the contour projection of the grinding wheel in the cross section perpendicular to the feed speed direction is at xO g The elliptic curve equation in y can be expressed as:

[0082]

[0083] Where y is the height difference between the tangent point A and the axis of the grinding wheel, and x is the horizontal distance from the tangent point A to the vertical axis y;

[0084] The following relationship is obtained from formula (1):

[0085] x=R g sinθcosβ g (2)

[0086] y=R g sinβ g (3)

[0087] The slope of the tangent line l passing through the tangent point A on the elliptic curve can be expressed as:

[0088]

[0089] Since the tangent value of the slope of the tangent line l is the angle between the tangent line l and the x-axis, the angle δ between the tangent line l and the x-axis is obtained from formula (4):

[0090]

[0091] According to the geometric relationship, the following formula is obtained:

[0092] β c ≈h / (R w +R c )(6)

[0093] h=y+R w sinδ (7)

[0094] β=β c +δ=π-φ-α (8)

[0095] δ, y, β c Substituting into equations (7) and (8), we obtain:

[0096]

[0097] In trigonometry, when the angles are small, the following simplifications occur:

[0098]

[0099] cot(β g )≈1 / β g (12)

[0100] Therefore, substituting formula (11) and formula (12) into formula (9) and (10) can be transformed into:

[0101]

[0102] h=R g β g +R w β g sinθ (14)

[0103] Combining formulas (13) and (14) we get:

[0104]

[0105] The process of obtaining the grinding angle β in this embodiment is as follows:

[0106] According to the geometric relationship, the following formula is obtained:

[0107]

[0108] Stability growth factor A i The expression is:

[0109]

[0110] Combining formulas (4)-(17), formula (18) can be converted into variables with only angles β and γ, and formula (18) becomes:

[0111]

[0112] Based on open source software python and stability growth coefficient A i The stability diagram is obtained as Figure 5 As shown, when A i When >0, it is a stable region, and the range value of β is selected in the stable region according to the inclination angle γ of the supporting surface of the support plate.

[0113] This embodiment determines the height difference h between the axis of the grinding wheel (the axis of the guide wheel) and the axis of the hard and brittle pipe based on the grinding angle β of the grinding wheel. After the position of the hard and brittle pipe is determined, the height of the grinding wheel and the guide wheel can be determined based on the height difference h, thereby reducing the difficulty of installing the grinding wheel and the guide wheel.

[0114] In addition, the height difference h determined based on the grinding angle β of the grinding wheel can ensure the grinding accuracy of the outer circle of the hard and brittle pipe fittings, and avoid the height difference h being too high, which makes the guide wheel unable to stably drive the workpiece to rotate, causing the workpiece to jump. If the height difference h is too low, roundness will be produced on the surface of the hard and brittle pipe fittings. The height difference h determined based on the grinding angle β can effectively ensure the stable rounding of the outer diameter of the hard and brittle pipe with a large aspect ratio.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention, rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A method for over-positioning grinding of hard and brittle pipe fittings with a large aspect ratio, characterized in that: The specific grinding process is as follows: S1, assembly and positioning of hard and brittle pipe fittings: the rigid mandrel passes through the inner hole of the hard and brittle pipe fittings with a large aspect ratio and is clearance-matched with the hard and brittle pipe fittings, the rigid mandrel is tensioned and the hard and brittle pipe fittings are kept level, and the two ends of the rigid mandrel and the positions close to the hard and brittle pipe fittings are each supported by a vibration reduction device to reduce the vibration amplitude and frequency of the rigid mandrel during the processing of the hard and brittle pipe fittings; the support plate contacts the outer pipe surface of the hard and brittle pipe fittings and supports the hard and brittle pipe fittings; S2, determine the grinding area: arrange the grinding wheel and the guide wheel on both sides of the hard and brittle pipe respectively, and keep the axes of the grinding wheel and the guide wheel at the same height, adjust the height of the two so that there is a height difference between the axes of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe, and the grinding surface of the grinding wheel is positively opposite to the guide support surface of the guide wheel. The grinding wheel, the guide wheel and the support plate enclose the grinding area of ​​the hard and brittle pipe, and the rigid mandrel is used to position and support the hard and brittle pipe; S3, guide wheel positioning: the hard and brittle pipe is moved to the grinding area, and the guide wheel is moved toward the side of the hard and brittle pipe until the guide bearing surface of the guide wheel contacts and squeezes the outer surface of the hard and brittle pipe, so that there is a pre-pressure between the guide wheel and the hard and brittle pipe, and the hard and brittle pipe is moved out of the grinding area, and the guide wheel is kept in place; S4, tool setting: drive the guide wheel to rotate forward, and send the hard and brittle pipe with a large aspect ratio into the grinding area. The guide wheel contacts and drives the hard and brittle pipe forward while rotating in the opposite direction. The grinding wheel rotates in the opposite direction and feeds a small amount to the side of the hard and brittle pipe to achieve tool setting operation. S5, grinding of hard and brittle pipe fittings: set the rotation speed and feed speed of the guide wheel and the rotation speed and feed speed of the grinding wheel, and set the grinding amount of hard and brittle pipe fittings; drive the guide wheel to rotate forward to feed the hard and brittle pipe fittings with a large aspect ratio into the grinding area. The guide wheel contacts and drives the hard and brittle pipe fittings forward while rotating in the opposite direction. The grinding wheel rotates in the opposite direction and feeds toward the side of the hard and brittle pipe fittings. As the grinding wheel grinds and feeds, the guide wheel and the support plate feed toward the side of the hard and brittle pipe fittings to always maintain the over-positioning support of the guide wheel, the support plate and the rigid mandrel on the hard and brittle pipe fittings. As the hard and brittle pipe fittings move, the grinding of the hard and brittle pipe fittings with a large aspect ratio is achieved.

2. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: In the above-mentioned S5, the linear speed of the grinding wheel is 30 m / s.

3. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: In the above-mentioned S5, when the outer diameter of the grinding wheel is 400 mm, the rotation speed of the grinding wheel is 1400 rpm / min to 1500 rpm / min.

4. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: In the above-mentioned S5, the operating speed of the guide wheel is 15 rpm / min to 20 rpm / min.

5. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: The fitting clearance between the rigid mandrel and the hard and brittle pipe fittings ranges from 0.2 to 0.5 mm.

6. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: The support plate is arranged close to the grinding wheel side and obliquely supports the hard and brittle pipe fittings. The supporting surface of the support plate is an inclined surface, and the inclination angle of the supporting surface is 30 degrees.

7. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: The grinding wheel is a parallel grinding wheel.

8. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 1 is characterized in that: The grinding wheel is a cup-shaped grinding wheel, and there is an offset angle θ between the axis of the cup-shaped grinding wheel and the axis of the hard and brittle pipe, θ>0.

9. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 8, characterized in that: In the above S2, the height difference between the axis of the guide wheel and the grinding wheel and the axis of the hard and brittle pipe is obtained by: Assume that the outer radius of the hard and brittle pipe with a large aspect ratio is R w , the radius of the guide wheel is R c , the radius of the grinding wheel is R g , let the height difference between the axis of the hard and brittle pipe fitting and the axis of the grinding wheel be h; when the grinding wheel contacts the hard and brittle pipe fitting, let the initial contact point between the grinding wheel and the hard and brittle pipe fitting be A, and the tangent at point A be l; when the guide wheel contacts the hard and brittle pipe fitting, let the initial contact point between the guide wheel and the hard and brittle pipe fitting be B; when the support plate contacts the hard and brittle pipe fitting, let the initial contact point between the support plate and the hard and brittle pipe fitting be C; Assume the axis of the hard and brittle pipe is O and the center of the guide wheel is O c , the grinding wheel center is O g , ∠AOC=α, ∠BOC=φ, ∠AO g O c =β g , ∠O g O c B=β c , β is the grinding angle of the grinding wheel, δ is the angle between OA and the horizontal line, the inclination angle of the supporting surface of the support plate is γ, and O g Establish a rectangular coordinate system for the center of the circle, and the tangent point A is in the coordinate system xO g The coordinates in y are (x, y); when there is an offset angle θ between the axis of the grinding wheel and the axis of the hard and brittle pipe, the grinding wheel grinds at the offset angle θ, and the contour projection of the grinding wheel in the cross section perpendicular to the feed speed direction is at xO g The elliptic curve equation in y can be expressed as: Where y is the height difference between the tangent point A and the axis of the grinding wheel, and x is the horizontal distance from the tangent point A to the vertical axis y; The following relationship is obtained from formula (1): x=R g sinθcosβ g (2) y=R g sinβ g (3) The slope of the tangent line l passing through the tangent point A on the elliptic curve can be expressed as: Since the tangent value of the slope of the tangent line l is the angle between the tangent line l and the x-axis, the angle δ between the tangent line l and the x-axis is obtained from formula (4): According to the geometric relationship, the following formula is obtained: b c ≈h / (R w +R c )(6) h=y+R w sinδ (7) β=β c +δ=π-φ-α (8) δ, y, β c Substituting into equations (7) and (8), we obtain: In trigonometry, when the angles are small, the following simplifications occur: cot(b g )≈1 / β g (12) Therefore, substituting formula (11) and formula (12) into formula (9) and (10) can be transformed into: h=R g b g +R w b g sinth (14) Combining formulas (13) and (14) we get:

10. The over-positioning grinding method for hard and brittle pipes with a large aspect ratio according to claim 9, characterized in that: The process of obtaining the grinding angle β is as follows: According to the geometric relationship, the following formula is obtained: Stability growth factor A i The expression is: Combining formulas (4)-(17), formula (18) can be converted into variables with only angles β and γ, and formula (18) becomes: Based on open source software python and stability growth coefficient A i Get the stability diagram, when A i When >0, it is a stable region, and the range value of β is selected in the stable region according to the inclination angle γ of the supporting surface of the support plate.

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