A combined clamping method for ceramic matrix composite segmented cylindrical structures

Abstract

The present application belongs to the field of aero-engine part clamping, and particularly relates to a combined clamping method for ceramic matrix composite segmented cylindrical structure. First, clamping of a workpiece is performed, and two sets of positioning pins are used to connect the workpiece lower rib plate and the fixture positioning reference surface; then, a bolt is used to clamp and fix the lower pressing plate, the workpiece lower rib plate and the fixture positioning reference surface, the pointers of two micrometers are placed on the inner wall surface of the workpiece between the upper rib plate and the lower rib plate, and the initial reading of the micrometer is zero; two sets of combined positioning pins are used to penetrate the pin hole I on the upper pressing plate and the workpiece upper rib plate and the upper support plate for clamping and fixing, in the process, the bolt connecting the support seat and the upper pressing plate is repeatedly adjusted to ensure that the micrometer reading does not change more than the limit value in the clamped state of the workpiece, indicating that the clamping of a workpiece is completed; the above steps are repeated to complete the clamping of the entire cylindrical structure; through the above method, the machining deformation of the cylindrical structure is effectively alleviated, and the machining precision is significantly improved.

Description

Technical Field

[0001] The invention belongs to the field of aerospace engine parts clamping, and in particular relates to a combined clamping method for a ceramic-based composite material segmented cylindrical structure. Background Art

[0002] As the temperature requirements of aircraft engines continue to increase, ceramic-based composite components are gradually being used in hot-end parts. The cylindrical structure of aircraft engines is common in casing parts. In order to increase their operating temperature, ceramic-based composite materials are used. Due to the hard, brittle, and heterogeneous characteristics of ceramic-based composite materials, large-scale molding is difficult, so they need to be molded and processed in sections. The use of a segmented processing method will result in height differences after the sections are spliced ​​together, which cannot meet the requirements of use. Segmented processing means that the parts are not combined and are processed individually; and the use of conventional combined processing methods is still difficult to achieve high-precision processing due to problems such as repeated clamping and workpiece deformation. Therefore, it is necessary to design a combined clamping method for ceramic-based composite segmented cylindrical structures to solve the processing problems of ceramic-based composite cylindrical structures. Summary of the Invention

[0003] In view of the deficiencies in the prior art, the present invention aims to provide a combined clamping method for a segmented cylindrical structure of a ceramic matrix composite material, so as to achieve high-precision machining of ceramic matrix composite parts.

[0004] A combined clamping method for a ceramic matrix composite segmented cylindrical structure comprises the following steps:

[0005] Step 1: First, clamp a workpiece. Set a lower pressure plate above the lower rib of the workpiece. Use the lower pressure plate to align the lower rib of the workpiece with the fixture positioning reference surface. Use two sets of positioning pins to connect the lower rib of the workpiece with the fixture positioning reference surface to limit the horizontal movement of the lower rib of the workpiece.

[0006] Step 2: Use bolts to clamp and fix the lower pressure plate, the lower rib of the workpiece, and the fixture positioning reference surface, so that the lower rib of the workpiece is in a clamped state and the vertical movement of the lower rib of the workpiece is restricted;

[0007] Step 3: Install two magnetic gauge stands inside the fixture. The pointer of the dial indicator on the magnetic gauge stand should be against the inner wall of the workpiece between the upper rib and the lower rib. The initial reading of the dial indicator should be zero.

[0008] Step 4: install the upper pressing plate on the upper part of the upper rib plate of the workpiece, and the lower part of the upper rib plate is provided with a support plate, and the upper pressing plate and the clamp are provided with a support seat, and the upper pressing plate and the support seat and the clamp and the support seat are fixed by bolts respectively; two sets of combined positioning pins are used to penetrate the pin hole I on the upper pressing plate and the upper rib plate of the workpiece and the upper support plate for clamping and fixing, and in this process, the bolts connecting the support seat and the upper pressing plate are repeatedly adjusted to ensure that the thousandth indication changes by no more than the limit value under the clamped state of the workpiece, indicating that the clamping of a workpiece is completed.

[0009] Step 5: repeat steps 1-4 to complete the clamping of other workpieces on the clamp, thereby completing the clamping of the entire cylindrical structure.

[0010] Step 6: carry out machining test using the clamping tool of the cylindrical structure completed in step 5.

[0011] In step 1, the flatness of the positioning reference surface of the clamp is not greater than 0.02mm.

[0012] In step 1, two sets of pin holes II are provided on the lower rib plate of the workpiece, and the positioning pins and the pin holes II are connected with the lower pressing plate and the lower rib plate of the workpiece in a clearance fit manner, and the position of the positioning pin is not greater than 0.02mm; the clearance between the positioning pin and the pin hole II is less than 0.05mm.

[0013] In step 2, the clamping torque acting on the bolt is not greater than 5MPa.

[0014] In step 4, the upper edge of the support seat is flush with the upper edge of the upper rib plate of the workpiece.

[0015] In step 4, the combined positioning pin is a combined structure of a top positioning pin and a bottom bolt, the top positioning pin connects the upper pressing plate and the upper rib plate of the workpiece, and the bottom bolt is tightened in the support plate, so that the upper rib plate of the workpiece and the upper pressing plate and the support plate can realize both horizontal limiting and vertical limiting; the top positioning pin and the pin hole I are also clearance fit, and the position of the top positioning pin is not greater than 0.02mm; the clearance between the positioning pin and the pin hole I is less than 0.05mm.

[0016] In step 4, the thousandth indication limit value is 0.005mm.

[0017] In step 6, the dimensional accuracy and runout of the machined workpiece is less than 0.04mm; the dimensional accuracy and runout change value of repeated clamping is less than 0.005mm.

[0018] In step 1, a copper foil with a thickness of not less than 0.5mm is arranged between the lower rib plate of the workpiece and the lower pressing plate.

[0019] The upper pressing plate, the support plate and the lower pressing plate are provided with chamfers on the side facing the workpiece.

[0020] The beneficial effects of the present invention are as follows:

[0021] By using the invented combined machining tooling for segmented cylindrical structures made of ceramic-based composite materials, deformation during machining of the cylindrical structure is effectively mitigated and machining accuracy is significantly improved. The runout error of the inner wall of the finished ceramic-based composite cylindrical structure is no more than 0.05 mm, meeting product requirements. This method avoids the need for grinding coatings on aircraft engines and significantly improves assembly efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Schematic diagram of a ceramic matrix composite material segmented cylindrical structure workpiece;

[0023] Figure 2 This is a top view of the combined processing tooling for ceramic matrix composite segmented cylindrical structures without the upper pressing plate installed;

[0024] Figure 3 Schematic diagram of the combined machining tooling and workpiece clamping for the segmented cylindrical structure of ceramic matrix composite materials;

[0025] Among them, 1. fixture; 2. workpiece; 3. support seat; 4. lower pressure plate; 5. positioning pin; 6. fixture positioning reference surface; 7. upper pressure plate; 8. support plate; 9. lower rib of workpiece; 10. upper rib of workpiece. DETAILED DESCRIPTION

[0026] The present invention will be described in detail below with reference to the accompanying drawings.

[0027] like Figures 1 to 3 As shown, a combined clamping method for a ceramic matrix composite segmented cylindrical structure includes the following steps:

[0028] Step 1: First, clamp a workpiece 2. Set a lower pressing plate 4 above the workpiece lower rib 9. A copper foil is placed between the workpiece lower rib 9 and the lower pressing plate 4. The thickness of the copper foil is not less than 0.5mm. Use the lower pressing plate 4 to fit the workpiece lower rib 9 to the fixture positioning reference surface 6. The positioning reference of the workpiece lower rib 9 is Correspondingly, a workpiece positioning reference is machined on the fixture 1. The matching fixture positioning reference surface 6 has high precision requirements. The overall plane processing of the fixture 1 is very likely to cause deformation of the workpiece. The fixture positioning reference surface 6 is a small boss surface processed on the fixture 1. The flatness of the fixture positioning reference surface 6 is not greater than 0.02 mm. In this embodiment, the flatness of the fixture positioning reference surface 6 is 0.01 mm. Two groups of pin holes II are provided on the lower rib plate 9 of the workpiece. Two groups of locating pins 5 are used to pass through the two groups of pin holes II on the lower rib plate 9 of the workpiece and connect with the fixture positioning reference surface 6 to limit the horizontal movement of the lower rib plate 9 of the workpiece. The locating pins 5 and the pin holes II adopt a clearance fit. The position of the locating pin 5 is not greater than 0.02 mm. The clearance between the locating pin 5 and the pin hole II is less than 0.05 mm.

[0029] Step 2: Use a torque wrench to clamp the lower pressure plate 4, the workpiece lower rib 9, and the fixture positioning reference surface 6 on the bolts, so that the workpiece lower rib 9 is in a clamped state and the vertical movement of the workpiece lower rib 9 is restricted; the clamping force torque acting on the bolts is not greater than 5 MPa, which is 5 MPa in this embodiment;

[0030] Step 3: Install two magnetic gauge bases inside the fixture 1. The pointer of the dial indicator on the magnetic gauge base is against the inner wall of the workpiece between the upper rib 10 and the lower rib 9. The initial reading of the dial indicator is zero.

[0031] Step 4: Install the upper pressing plate 7 on the upper part of the upper rib 10 of the workpiece, and provide a support plate 8 below the upper rib 10 of the workpiece. Provide a support seat 3 between the upper pressing plate 7 and the fixture 1. Fix the upper pressing plate 7 and the support seat 3, and the fixture 1 and the support seat 3 respectively by bolts; Use two sets of combined locating pins to penetrate the upper pressing plate 7, the pin holes 1 of the upper rib 10 of the workpiece and the upper support plate 8 for clamping and fixing. During this process, repeatedly adjust the bolts connecting the support seat 3 to the upper pressing plate 7 to ensure that when the workpiece 2 is clamped, the change in the thousandths display number does not exceed 0.005mm, indicating that one workpiece is clamped;

[0032] The combined locating pin is a combination structure of a top locating pin and a bottom bolt. The top locating pin connects the upper pressure plate 7 and the upper rib 10 of the workpiece, and the bottom bolt is tightened in the support plate 8, so that the upper rib 10 of the workpiece and the upper pressure plate 7 and the support plate 8 can achieve both horizontal and vertical limit. The top locating pin and the pin hole 1 also have a clearance fit, and the position accuracy of the top locating pin is not greater than 0.02mm; the clearance between the locating pin and the pin hole 1 is less than 0.05mm.

[0033] Step 5: Repeat steps 1 to 4 to complete the clamping of other workpieces on the fixture, thereby completing the clamping of the entire cylindrical structure;

[0034] Step 6: Use the clamping fixture of the cylindrical structure completed in step 5 to carry out processing tests. After processing, the dimensional accuracy and runout of the workpiece are less than 0.04mm; the processing accuracy meets the design requirements of the drawing, and the change in dimensional accuracy and runout after repeated clamping is less than 0.005mm.

[0035] In this embodiment, the upper pressing plate 7 , the supporting plate 8 , and the lower pressing plate 4 are chamfered toward the workpiece 2 .

[0036] The present invention adopts an over-positioning method to ensure effective positioning and clamping of the workpiece in the actual assembly state, thereby limiting the degree of freedom of the workpiece. During the clamping process, it is necessary to avoid over-positioning to prevent deformation of the workpiece and thus prevent the workpiece from exceeding the size tolerance. The upper rib 10 and the lower rib 9 of the workpiece adopt a one-side two-pin clamping method, and the bolts of the upper pressure plate, the fixture and the support seat are only involved in clamping.

[0037] According to the hard, brittle and heterogeneous characteristics of ceramic-based composite materials, the present invention connects the lower pressure plate 4 and the lower rib 9 of the workpiece through two groups of locating pins, and tightens them with bolts. The upper rib 10 of the workpiece is connected to the upper pressure plate 7 and the support plate 8 through a combination of locating pins. To prevent over-positioning, the present invention adjusts the tightening force of the bolts between the upper pressure plate 7 and the support seat 3, thereby facilitating the adjustment of the position and tightening force of the upper pressure plate 7 and the upper rib 10 of the workpiece, and uses a micrometer to assist, thereby preventing excessive clamping and causing deformation of the workpiece 2; at the same time, to prevent the lower pressure plate 4 from damaging the surface of the lower rib 9 of the workpiece and to ensure that the lower rib 9 of the workpiece is in good contact with the fixture positioning reference surface 6, copper foil is provided between the lower pressure plate 4 and the lower rib 9 of the workpiece.

Claims

1. A combined clamping method for a segmented cylindrical structure of a ceramic matrix composite material, characterized in that: The following steps are involved: Step 1: First, clamp a workpiece. Set a lower pressure plate above the lower rib of the workpiece. Use the lower pressure plate to align the lower rib of the workpiece with the fixture positioning reference surface. Use two sets of positioning pins to connect the lower rib of the workpiece with the fixture positioning reference surface to limit the horizontal movement of the lower rib of the workpiece. Step 2: Use bolts to clamp and fix the lower pressure plate, the lower rib of the workpiece, and the fixture positioning reference surface, so that the lower rib of the workpiece is in a clamped state and the vertical movement of the lower rib of the workpiece is restricted; Step 3: Install two magnetic gauge stands inside the fixture. The pointer of the dial indicator on the magnetic gauge stand should be against the inner wall of the workpiece between the upper rib and the lower rib. The initial reading of the dial indicator should be zero. Step 4: Install the upper pressing plate on the upper part of the upper rib of the workpiece. A support plate is provided below the upper rib of the workpiece. A support seat is provided between the upper pressing plate and the fixture. The upper pressing plate and the support seat, as well as the fixture and the support seat, are fixed by bolts respectively. Use two sets of combined locating pins to penetrate the upper pressing plate, the pin holes I on the upper rib of the workpiece and the upper support plate for clamping and fixing. During this process, repeatedly adjust the bolts connecting the support seat to the upper pressing plate to ensure that when the workpiece is clamped, the change in the thousandths display value does not exceed the limit, indicating that one workpiece is clamped. Step 5: Repeat steps 1 to 4 to complete the clamping of other workpieces on the fixture, thereby completing the clamping of the entire cylindrical structure; Step 6: Use the clamping fixture of the cylindrical structure completed in step 5 to carry out processing tests.

2. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 1, the flatness of the fixture positioning reference surface is not greater than 0.02 mm.

3. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 1, two groups of pin holes II are provided on the lower rib of the workpiece, and the locating pins and the pin holes II are connected to the lower pressure plate and the lower rib of the workpiece by a clearance fit method. The positioning accuracy of the locating pins is not greater than 0.02 mm; the clearance between the locating pins and the pin holes II is less than 0.05 mm.

4. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In the step 1, a copper foil is provided between the lower rib plate and the lower pressing plate of the workpiece, and the thickness of the copper foil is not less than 0.5 mm.

5. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 2, the clamping torque acting on the bolt is no more than 5 MPa.

6. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 4, the upper edge of the support seat is flush with the upper edge of the upper rib of the workpiece.

7. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 4, the combined locating pin is a combined structure of a top locating pin and a bottom bolt. The top locating pin connects the upper pressure plate and the upper rib of the workpiece, and the bottom bolt is tightened in the support plate, so that the upper rib of the workpiece and the upper pressure plate and the support plate can achieve both horizontal and vertical limiting. The top locating pin and the pin hole I are also clearance-fitted, and the position accuracy of the top locating pin is not greater than 0.02mm; the clearance between the locating pin and the pin hole I is less than 0.05mm.

8. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 4, the limit of the thousandth indication is 0.005 mm.

9. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: In step 6, the dimensional accuracy and runout of the workpiece after processing are less than 0.04 mm; and the change in dimensional accuracy and runout after repeated clamping is less than 0.005 mm.

10. The combined clamping method for a ceramic matrix composite segmented cylindrical structure according to claim 1, characterized in that: The upper pressing plate, the supporting plate and the lower pressing plate are provided with chamfers facing the workpiece side.

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