A coordinate system alignment method and positioning clamp device for head processing of a shell part

Abstract

The present application relates to the technical field of numerical control milling processing, and provides a coordinate system alignment method and positioning fixture device for head processing of a shell part. The method positions pin holes H1 and H2 at the reverse end of the part in the processing technology, and uses H1 and H2 as the common angular reference for processing the front and back surfaces. During five-axis processing, the reference surface of the five-axis processing tooling and the positioning pin holes corresponding to H1 and H2 are used to establish the processing coordinate system, and the workpiece blank is fixed by the reverse pull of the process boss. During three-axis head processing, the cylindrical stepped positioning pin and the edge stepped positioning pin of the three-axis processing tooling are used to cooperate with the stepped surface large hole of the front end of the part to position, the reverse end surface of the part is measured to determine the zero point of the Zw axis, the H1 and H2 hole center coordinates are measured to calculate the processing origin and the included angle α, and the programming processing coordinate system is adjusted based on α. The scheme can realize the angular reference transmission and tool path connection for processing the front and back surfaces of the shell part.

Description

Technical Field

[0001] This invention relates to the field of CNC milling technology, specifically to a coordinate system alignment method and positioning fixture device for turning shell-type parts. Background Technology

[0002] In the aerospace field, some shell-type parts with complex features are widely used, such as the main shell of aerospace engines. These parts have a large number of complex features such as bosses, holes, stepped surfaces, recesses, and curved surfaces at both ends and sides. These parts are generally manufactured by CNC milling. Since some precision components are installed in these holes and bosses, their dimensional and geometric tolerances have high requirements.

[0003] For these complex shell-shaped parts, CNC milling typically involves heat treatment and fitting / repair processes, requiring multiple clamping operations. Furthermore, these parts require CNC milling at both ends separately; after the front end is machined on a five-axis machine, it must be turned around and machined on a three-axis machine for the reverse end. CNC milling of these parts presents several common challenges: the parts have various complex features on both ends and sides, necessitating the design of appropriate tooling fixtures for positioning without interfering with tool movement; and ensuring precise positioning and angular alignment during multi-process and turning operations to maintain consistency between the machining datum and coordinate system. Inaccurate angular positioning, especially during turning operations, can lead to disjointed toolpaths on the front and back sides, resulting in severe tool marks or even product scrap on the sides.

[0004] Therefore, there is an urgent need for a machining method and matching fixture that can ensure the machining datum and machining coordinate system remain consistent throughout multi-process machining, and that the parts are positioned accurately. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a coordinate system alignment method and positioning fixture device for the turning and machining of shell-type parts. The invention designs machining fixtures for both the front and back sides, and designs a pair of reference holes. It also formulates a machining coordinate system alignment technical solution, which solves the problem of accurate positioning and alignment of complex shell-type parts and effectively ensures the rapid conversion machining of parts on five-axis and three-axis machine tools.

[0006] To achieve the above objectives, the present invention employs the following technical solutions: A coordinate system alignment method for turning shell-type parts during machining, characterized by the following steps: S1, Blank preparation: Provide a blank for a shell-type part. The blank has a pre-set process boss for reverse tensioning and fixing. The process boss has a threaded hole. Process positioning pin hole H1 and process positioning pin hole H2 are machined at two finished hole positions on the reverse side of the part, respectively. H1 and H2 are used as a common angular reference for machining the front end and turning the reverse end. S2, Five-axis clamping and alignment: Install the five-axis machining fixture on the worktable of the five-axis CNC machine tool. The five-axis machining fixture has a reference surface for contacting the reverse end face of the part, and the five-axis machining fixture is provided with positioning pin holes H′1 and H′2 corresponding to the positions of H1 and H2 respectively. Measure the reference surface to determine the zero point of the machining coordinate system Zw axis, measure the center coordinates of H′1 and H′2, determine the line connecting the centers of H′1 and H′2 as the machining coordinate system Xw axis, and align the rotary worktable of the five-axis CNC machine tool so that the Xw axis is aligned with the direction of the five-axis machine tool coordinate system Xm axis. Determine the origin Ow of the machining coordinate system based on the center coordinates of H′1 and H′2, and determine the Yw axis perpendicular to the Xw axis. S3, Five-axis machining: Insert locating pins into H′1 and H′2, install the part blank, make H1 and H2 correspond to H′1 and H′2 respectively, and make the reverse end face of the part fit with the reference surface. Use screws to engage with the threaded holes on the process boss to pull and fix the part to the five-axis machining fixture, and complete the five-axis machining of the front end and side features of the part. S4, Reversing and Clamping, and Determining Zw: Install the three-axis machining fixture on the worktable of the three-axis CNC machine tool. The three-axis machining fixture has a stepped connecting surface and cylindrical stepped positioning pins and chamfered stepped positioning pins set on the stepped connecting surface. Insert the cylindrical stepped positioning pins and chamfered stepped positioning pins into the two large holes on the front end of the part formed by S3, so that the front end of the part is positioned with the three-axis machining fixture through the stepped hole positioning method, and the three-axis machining fixture and the part maintain a single contact surface. After clamping and fixing the part, measure the reverse end face of the part to determine the zero point of the machining coordinate system Zw axis. S5, Measurement, Calculation, and Adjustment of the Programming Machining Coordinate System: Measure the coordinates of the H1 and H2 hole centers located on the reverse side of the part. Calculate the origin Ow of the machining coordinate system based on the H1 and H2 hole center coordinates, and calculate the angle α between the line connecting the H1 and H2 hole centers and the Xm axis of the three-axis machine tool coordinate system. Adjust the programming machining coordinate system used for machining the reverse side based on the angle α, so that the reverse side machining coordinate system corresponds to the common angular reference determined by H1 and H2, thereby achieving angular connection between the reverse side machining toolpath and the front side machining toolpath.

[0007] Preferably, in step S2, the reference surface of the five-axis machining fixture is precision ground to ensure flatness.

[0008] Preferably, the coordinates X0 and Y0 of the machining coordinate system zero point Ow in the machine tool coordinate system OM are determined by centering the coordinates of the circle. The calculation formula is as follows: X0 = (X″1 + X″2) / 2 Y0 = Y″2 In the formula, X″1 is the X-axis coordinate of H′1 after alignment, X″2 is the X-axis coordinate of H′2 after alignment; Y″2 is the Y-axis coordinate of H′2 after alignment, and Y″2 after alignment is equal to the Y-axis coordinate Y″1 of H′1.

[0009] Preferably, in step S5, the coordinates of the center of holes H1 and H2 on the end face of the part are measured using the probe built into the three-axis machine tool. The coordinate values ​​X0 and Y0 of the origin Ow of the machining coordinate system in the machine tool coordinate system OM are calculated by centering out. The calculation formula is as follows: X0 = (X1 + X2) / 2 Y0 = (Y1 + Y2) / 2 In the formula, X1 is the coordinate value of H1 in the machine tool coordinate system OM, X2 is the coordinate value of H2 in the machine tool coordinate system OM; Y1 is the coordinate value of H1 in the machine tool coordinate system OM, and Y2 is the coordinate value of H2 in the machine tool coordinate system OM.

[0010] Preferably, in step S5, the angle α between the line connecting the hole centers and the Xm axis of the machine tool coordinate system is calculated using the hole center coordinates H1 and H2. The calculation formula is as follows: α = arctan( (Y2 - Y1) / (X2 - X1)); After calculating the included angle α, adjust the programming machining coordinate system in the CNC programming model so that the Xw axis of the machining coordinate system is aligned with the Xm axis of the machine tool coordinate system.

[0011] In addition, the present invention also provides a positioning fixture device for turning shell-type parts, characterized in that it includes a five-axis machining fixture and a three-axis machining fixture; The five-axis machining fixture is used to perform one-sided two-hole positioning and clamping on the reverse side of the part when machining the front side of the part. The five-axis machining fixture includes a first base, which has a fine grinding reference surface for fitting with the reverse side of the part. The fine grinding reference surface is provided with positioning pin holes H′1 and H′2 corresponding to the positions of process positioning pin holes H1 and H2 on the reverse side of the part, respectively. A cylindrical positioning pin is provided in H′1 and a chamfered positioning pin is provided in H′2. The first base is also provided with three pull screws, which are used to cooperate with the threaded holes on the process boss of the part to pull and fix the part to the fine grinding reference surface. The three-axis machining fixture is used to position and clamp the front end of the part with stepped holes when machining the reverse end of the part. The three-axis machining fixture includes a second base. The second base has a stepped connecting surface for fitting with a stepped surface of the front end of the part. The stepped connecting surface is provided with a cylindrical stepped positioning pin and a chamfered stepped positioning pin. The cylindrical stepped positioning pin and the chamfered stepped positioning pin are respectively used to insert into two large holes formed on the stepped surface of the front end of the part to limit the position and angular orientation of the part relative to the second base. The second base is also provided with three pressure plates for pressing the side windows and bosses of the part.

[0012] Preferably, both the positioning pin hole H′1 and the positioning pin hole H′2 are Φ20H7 pin holes, and both the cylindrical positioning pin and the chamfered positioning pin are Φ20h7 positioning pins.

[0013] Preferably, the cylindrical stepped positioning pin is a Φ38h7 stepped positioning pin and is used to insert into the Φ38H7 stepped hole on the front end of the part; the chamfered stepped positioning pin is a Φ30h7 stepped positioning pin and is used to insert into the Φ30H7 stepped hole on the front end of the part.

[0014] Preferably, the three-axis machining fixture and the part are kept in contact only through the stepped connection surface.

[0015] The present invention has the following advantages: This invention utilizes a pair of process pin holes H1 and H2 machined on the reverse side of the part as a reference for clamping and alignment on both sides, thus achieving a technical method for aligning the machining coordinate system and angular positioning. During the five-axis machining stage, physical alignment is achieved using the corresponding pin holes on the tooling, and a large stepped hole is machined on the front side as a position reference for transfer. During the three-axis machining stage, the position reference is retrieved using a stepped hole positioning fixture, and the actual coordinates of H1 and H2 are measured by the machine tool probe. The direction vector formed by H1 and H2 and its relationship to the machine tool coordinate system X are then calculated. M The included angle α between the axes, because a three-axis machine tool, unlike a five-axis machine tool, cannot swing its rotary axis, makes the line connecting H1 and H2 intersect with X. M Since the directions are consistent, the machining coordinate system in the programming model is adjusted during CNC programming to ensure that the X-axis is aligned. W With X M The directions are consistent, thus achieving the purpose of angular alignment during machining of both the front and back ends. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the reverse end structure of a shell-type part according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the front end structure of a shell-type part according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the blank structure according to an embodiment of the present invention; Figure 4 This is a schematic diagram of the five-axis machining tooling structure according to an embodiment of the present invention; Figure 5 This is a schematic diagram illustrating the principle of five-axis machining coordinate system alignment according to an embodiment of the present invention. Figure 6 This is a schematic diagram of the five-axis machining clamping state according to an embodiment of the present invention; Figure 7 This is a schematic diagram of the three-axis machining tooling structure according to an embodiment of the present invention; Figure 8 This is a schematic diagram of the three-axis machining clamping state according to an embodiment of the present invention; Figure 9 This is a schematic diagram illustrating the principle of coordinate system alignment for three-axis machining according to an embodiment of the present invention.

[0017] Among them, 1-finished workpiece, 2-Φ22.5H8 hole, 3-Φ22H8 hole, 4-Φ30H7 stepped hole, 5-Φ38H7 stepped hole, 6-incoming blank, 7-H1 process pin hole, 8-H2 process pin hole, 9-process boss, 10-edge-trimmed positioning pin, 11-positioning pin hole H′2, 12-cylindrical positioning pin, 13-positioning pin hole H′1, 14-reverse pull screw, 15-five-axis machining fixture, 16-pressure plate, 17-cylindrical stepped positioning pin, 18-edge-trimmed stepped positioning pin, 19-three-axis machining fixture. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings.

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0020] Example 1 This embodiment provides a positioning fixture device for turning shell-type parts, such as... Figure 4 and Figure 7As shown, the fixture device includes a five-axis machining fixture 15 and a three-axis machining fixture 19. The five-axis machining fixture 15 is used to position and clamp the reverse end of the part in a two-hole positioning manner when machining the front end of the part. It includes a first base with a finely ground reference surface on it. The reference surface is in contact with the reverse end face of the part. The reference surface has positioning pin holes H′1 13 and H′2 11. Both positioning pin holes H′1 13 and H′2 11 are Φ20H7 pin holes. A Φ20h7 cylindrical positioning pin 12 is inserted into the positioning pin hole H′1 13, and a Φ20h7 chamfered positioning pin 10 is inserted into the positioning pin hole H′2 11. The first base is also provided with three M10 pull screws 14. The pull screws 14 are used to thread into the threaded holes on the process boss of the part to pull the part back and fix it to the reference surface. The three-axis machining fixture 19 is used to position and clamp the front end of the part by means of stepped hole positioning when machining the reverse end of the part. It includes a second base with a stepped connecting surface. The stepped connecting surface is provided with a Φ38h7 cylindrical stepped positioning pin 17 and a Φ30h7 chamfered stepped positioning pin 18. The cylindrical stepped positioning pin 17 and the chamfered stepped positioning pin 18 are respectively inserted into the two stepped stepped surface large holes machined on the front end of the part. The second base is also provided with three pressure plates 16 for pressing the side window and boss of the part. Only one side of the stepped connecting surface is in contact with the part.

[0021] Example 2 Based on the clamping device provided in Embodiment 1, this embodiment provides a coordinate system alignment method for turning shell-type parts during machining.

[0022] like Figure 1 , Figure 2 As shown, the part is a shell type, containing various features such as large holes, deep holes, bosses, threaded holes, stepped surfaces, and curved walls. The front end is machined using a five-axis CNC machine tool, and the back end is machined using a three-axis machine tool. The front end requires rough and finish milling of various features on the end face and sides, necessitating a five-axis CNC machine tool. The back end mainly involves machining various holes on the end face, as well as shaping the outer contour of the end face; a three-axis machine tool can handle these features. To ensure cost-effectiveness, a three-axis CNC machine tool is used for machining the back end features. This embodiment uses a five-axis cradle-type double rotary table CNC milling machine, a three-axis CNC milling machine, and its built-in probe. The back end has holes 2—Φ22.5H8 and 3—Φ22H8, while the front end has stepped holes 4—Φ30H7 and 5—Φ38H7. In this embodiment, the back end of the part has a pair of process pin holes, denoted as H1 and H2.

[0023] S1 blank preparation like Figure 3As shown, on a three-axis CNC machine tool, the cylindrical bar is first machined into a blank 6. Its reverse end has already been machined on a three-axis CNC milling machine, with a pre-reserved process boss 9. To facilitate clamping and fixing, three process bosses 9 are evenly distributed around the circumference of the blank. Each process boss 9 has an M10 threaded hole machined on it for reverse tension fixing. Simultaneously, a process positioning pin hole 8—Φ20H7 is bored at hole 2 of product 1, and a process positioning pin hole 7—Φ20H7 is bored at hole 3 of product 1. That is, on the reverse end of the part, corresponding to the finished product Φ22.5H8 hole 2 and Φ22H8 hole 3, Φ20H7 process pin holes H2 and H1 process pin holes 7 are precision bored. These process pin holes serve as a unified angular reference throughout the entire turning process. S2 Five-Axis Clamping and Alignment Stage like Figure 5 , Figure 6 As shown, the five-axis machining fixture 15 is installed on the worktable of the five-axis CNC machine tool. The reference surface of the five-axis machining fixture 15 is in contact with the reverse end face of the part. The reference surface of the five-axis machining fixture 15 is precision ground to ensure flatness. The five-axis machining fixture 15 is provided with a locating pin hole H′1 13 corresponding to H1 and a locating pin hole H′2 11 corresponding to H2. The locating pin hole H′1 13 is equipped with a Φ20h7 cylindrical locating pin 12, and the locating pin hole H′2 11 is equipped with a Φ20h7 chamfered locating pin 10.

[0024] The H1 process pin hole 7 on the reverse side of the part corresponds to the cylindrical locating pin 12 on the five-axis machining fixture 15, and the H2 process pin hole 8 on the reverse side corresponds to the chamfered locating pin 10 on the fixture 15. During the alignment process, the machine tool's built-in probe is used to measure the coordinates H′2 (X′2, Y′2) and H′1 (X′1, Y′1) of the center of the locating pin hole H′2 11 and the locating pin hole H′1 13 in the machine tool coordinate system, respectively. Then, the machine tool automatically calculates the angle between the coordinate vectors of H′1 and H′2 and the Xm axis of the machine tool coordinate system, and swings the machine tool rotary table by the corresponding angle to make the machining coordinate system Xw axis determined by H′2H′1 consistent with the Xm axis of the machine tool coordinate system.

[0025] After recalibrating, use the machine tool probe to measure H′2 (X″2, Y″2) and H′1 (X″1, Y″1). At this point, Y″2 = Y″1. Then, center the coordinates based on the X coordinates of H′1 and H′2 to determine the origin Ow of the machining coordinate system. Based on the principle that the X and Y axes are horizontal and perpendicular, the Yw axis of the machining coordinate system can be established. Using the tool end face as the Z-zero point, determine the Zw axis of the machining coordinate system. By centering using the center coordinates, determine the coordinates X0 and Y0 of the zero point Ow of the machining coordinate system in the machine tool coordinate system OM. The calculation formula is: X0 = (X″1 + X″2) / 2 Y0 = Y″2 In the formula, X″1 is the X-axis coordinate value of H′1 after alignment, X″2 is the X-axis coordinate value of H′2 after alignment; Y″2 is the Y-axis coordinate of H′2 after alignment. Since the five-axis machine tool has aligned the worktable, the line connecting H′1 and H′2 is parallel to the X-axis of the machine tool. Therefore, after alignment, Y″2 is equal to the Y-axis coordinate Y″1 of H′1.

[0026] S3 5-axis machining Insert locating pins into the locating pin holes of the five-axis machining fixture 15. Install the Φ20h7 chamfered locating pin 10 at locating pin hole H′2 11, and install the Φ20h7 cylindrical locating pin 12 at locating pin hole H′1 13. Then, install the incoming blank 6, with the reverse end face of the part fitting against the end face of the fixture. Secure the part using three M10 pull screws 14 through the threaded holes on the process boss 9. Perform various feature machining operations on the front end face and side face on the five-axis machine tool, including rough milling and finish milling.

[0027] S4 turning and clamping, and Zw confirmation. like Figure 8 , Figure 9 As shown, the three-axis machining fixture 19 is installed on the worktable of the three-axis CNC machine tool. A cylindrical step locating pin 17 and a chamfered step locating pin 18 are inserted into the stepped joint surface of the three-axis machining fixture 19. The part is installed, with the front end of the part in contact with the stepped surface of the fixture. The Φ38h7 cylindrical step locating pin 17 of the fixture is inserted into the step hole 5 of the part, and the Φ30h7 chamfered step locating pin 18 of the fixture is inserted into the step hole 4 of the part. Only one side of the three-axis machining fixture 19 is in contact with the part. The end face of the part is measured with the probe of the three-axis machine tool to determine the zero point of the machining coordinate system Zw axis.

[0028] One of the large holes on the stepped surface of the front end of the part (such as Φ30H7 stepped hole 4) is equipped with a Φ30h7 chamfered stepped locating pin 18, and the other large hole on the stepped surface (such as Φ38H7 stepped hole 5) is equipped with a Φ38h7 cylindrical stepped locating pin 17. During fixing, three pressure plates 16 are used to press and clamp the part against the window and boss on the side, ensuring a stable clamping. Since only the series of holes on the end face and the side contour within 20mm of the end face are machined on the reverse side of the part, the pressure plates will not interfere with the tool movement.

[0029] S5 Measurement, Calculation, Adjustment, Programming, and Machining Coordinate System Using the probes built into the three-axis machine tool, measure the H1 process pin hole 7 and H2 process pin hole 8 on the reverse side of the part in the machine tool coordinate system O. M The coordinates of the hole center are denoted as H1(X1, Y1) and H2(X2, Y2). Based on the hole center coordinates of H1 and H2, calculate the coordinates X0 and Y0 of the machining coordinate system origin Ow in the machine tool coordinate system Om: X0 = (X1 + X2) / 2; Y0 = (Y1 + Y2) / 2.

[0030] Further, the angle α between the line connecting the center points of holes H1 and H2 and the Xm axis of the three-axis machine tool coordinate system is calculated. Unlike five-axis machine tools, three-axis CNC machine tools cannot align the line connecting the center points of holes H1 and H2 with the Xm axis by oscillating and rotating the worktable. Therefore, during CNC programming for the reverse side, the programming machining coordinate system is adjusted according to the angle α to ensure that the reverse side machining coordinate system in the programming model corresponds to the actual angular reference determined by H1 and H2, thereby guaranteeing correct angular connection between the reverse side machining toolpath and the front side machining toolpath.

[0031] First, the probe measures the H1 coordinates (X1, Y1) and H2 coordinates (X2, Y2) online. Then, using the probe built into the three-axis machine tool, the H1 and H2 hole center coordinates on the end face of the part are measured. The origin Ow of the machining coordinate system is then calculated in the machine tool coordinate system O using a centering method. M The coordinate values ​​X0 and Y0 in the figure are calculated using the following formula: X0 = (X1 + X2) / 2 Y0 = (Y1 + Y2) / 2 In the formula, X1 represents H1 in the machine tool coordinate system O. M The coordinates of H2 in the machine coordinate system O are X2 and X2 is the coordinate value of H2. M The coordinate values ​​below; Y1 is the coordinate value of H1 in the machine tool coordinate system O. M Y2 is the coordinate value of H2 in the machine tool coordinate system OM.

[0032] The angle α between the line connecting the hole centers and the Xm axis of the machine tool coordinate system is calculated using the hole center coordinates H1 and H2. The calculation formula is as follows: α = arctan( (Y2 - Y1) / (X2 - X1)); After calculating the included angle α, adjust the programming machining coordinate system in the CNC programming model so that the Xw axis of the machining coordinate system is aligned with the Xm axis of the machine tool coordinate system.

[0033] Unlike five-axis machine tools, three-axis machine tools cannot physically align the worktable. In the CNC system, the programming machining coordinate system is rotated by an angle α around the Z-axis so that the direction of the virtual machining coordinate system Xw axis is consistent with the direction of the H1-H2 line on the actual part. The programming machining coordinate system is then adjusted in the CNC programming model so that the direction of the machining coordinate system Xw axis is consistent with the direction of the machine tool coordinate system Xm axis, thus achieving correct toolpath angular connection between reverse and front machining.

[0034] Based on the machining characteristics of the part, this invention designs a set of tooling fixtures for machining both the front and back ends. The front and side features of the part are machined using a five-axis CNC milling machine. After the part is machined on the front end, it needs to be turned around for machining on the back end. According to the distribution of the large holes on the end face of the part, a pair of process pin holes are designed on the back end of the part. These process pin holes serve as the reference for clamping and aligning the front and back ends, realizing the alignment of the machining coordinate system and angular positioning.

[0035] This invention is not limited to the specific embodiments described above. The invention extends to any new feature or combination disclosed in this specification, as well as any new method or process step or combination disclosed herein.

Claims

1. A coordinate system alignment method for turning shell-type parts during machining, characterized in that, Includes the following steps: S1, Blank preparation: Provide a blank for a shell-type part. The blank has a pre-set process boss for reverse tensioning and fixing. The process boss has a threaded hole. Process positioning pin hole H1 and process positioning pin hole H2 are machined at two finished hole positions on the reverse side of the part, respectively. H1 and H2 are used as a common angular reference for machining the front end and turning the reverse end. S2, Five-axis clamping and alignment: Install the five-axis machining fixture on the worktable of the five-axis CNC machine tool. The five-axis machining fixture has a reference surface for contacting the reverse end face of the part, and the five-axis machining fixture is provided with positioning pin holes H′1 and H′2 corresponding to the positions of H1 and H2 respectively. Measure the reference surface to determine the zero point of the machining coordinate system Zw axis, measure the center coordinates of H′1 and H′2, determine the line connecting the centers of H′1 and H′2 as the machining coordinate system Xw axis, and align the rotary worktable of the five-axis CNC machine tool so that the Xw axis is aligned with the direction of the five-axis machine tool coordinate system Xm axis. Determine the origin Ow of the machining coordinate system based on the center coordinates of H′1 and H′2, and determine the Yw axis perpendicular to the Xw axis. S3, Five-axis machining: Insert locating pins into H′1 and H′2, install the part blank, make H1 and H2 correspond to H′1 and H′2 respectively, and make the reverse end face of the part fit with the reference surface. Use screws to engage with the threaded holes on the process boss to pull and fix the part to the five-axis machining fixture, and complete the five-axis machining of the front end and side features of the part. S4, Reversing and Clamping, and Determining Zw: Install the three-axis machining fixture on the worktable of the three-axis CNC machine tool. The three-axis machining fixture has a stepped connecting surface and cylindrical stepped positioning pins and chamfered stepped positioning pins set on the stepped connecting surface. Insert the cylindrical stepped positioning pins and chamfered stepped positioning pins into the two large holes on the front end of the part formed by S3, so that the front end of the part is positioned with the three-axis machining fixture through the stepped hole positioning method, and the three-axis machining fixture and the part maintain a single contact surface. After clamping and fixing the part, measure the reverse end face of the part to determine the zero point of the machining coordinate system Zw axis. S5, Measurement, Calculation, and Adjustment of the Programming Machining Coordinate System: Measure the coordinates of the H1 and H2 hole centers located on the reverse side of the part. Calculate the origin Ow of the machining coordinate system based on the H1 and H2 hole center coordinates, and calculate the angle α between the line connecting the H1 and H2 hole centers and the Xm axis of the three-axis machine tool coordinate system. Adjust the programming machining coordinate system used for machining the reverse side based on the angle α, so that the reverse side machining coordinate system corresponds to the common angular reference determined by H1 and H2, thereby achieving angular connection between the reverse side machining toolpath and the front side machining toolpath.

2. The coordinate system alignment method for turning and machining shell-type parts according to claim 1, characterized in that, In step S2, the reference surface of the five-axis machining fixture is precision ground to ensure flatness.

3. The coordinate system alignment method for turning and machining shell-type parts according to claim 1, characterized in that, In step S2, the zero point Ow of the machining coordinate system is determined in the machine tool coordinate system O by centering the coordinates of the circle. M The coordinate values ​​X0 and Y0 are calculated using the following formula: X0 = (X″1 + X″2) / 2 Y0 = Y″2 In the formula, X″1 is the X-axis coordinate of H′1 after alignment, X″2 is the X-axis coordinate of H′2 after alignment; Y″2 is the Y-axis coordinate of H′2 after alignment, and Y″2 after alignment is equal to the Y-axis coordinate Y″1 of H′1.

4. The coordinate system alignment method for turning shell-type parts during machining according to claim 1, characterized in that, In step S5, the probes built into the three-axis machine tool are used to measure the coordinates of the center of holes H1 and H2 on the end face of the part. The origin of the machining coordinate system Ow in the machine tool coordinate system O is calculated by centering. M The coordinate values ​​X0 and Y0 in the figure are calculated using the following formula: X0 = (X1 + X2) / 2 Y0 = (Y1 + Y2) / 2 In the formula, X1 represents H1 in the machine tool coordinate system O. M The coordinates of H2 in the machine coordinate system O are X2 and X2 is the coordinate value of H2. M The coordinate values ​​below; Y1 is the coordinate value of H1 in the machine tool coordinate system O. M The coordinates of H2 in the machine coordinate system O are Y2 and H2 is H2. M The coordinates below.

5. The coordinate system alignment method for turning and machining shell-type parts according to claim 1, characterized in that, In S5, the measurement of H1 in the machine tool coordinate system O M The coordinates of the hole center in the machine tool coordinate system Om are (X1, Y1), and the coordinates of the hole center in H2 are (X2, Y2). The angle α between the line connecting the hole centers and the Xm axis of the machine tool coordinate system is calculated using the coordinates of H1 and H2. The formula is: α = arctan( (Y2 - Y1) / (X2 - X1)); After calculating the included angle α, adjust the programming machining coordinate system in the CNC programming model so that the Xw axis of the machining coordinate system is aligned with the Xm axis of the machine tool coordinate system.

6. A positioning fixture device for turning shell-type parts during machining, characterized in that, Including five-axis machining fixtures and three-axis machining fixtures; The five-axis machining fixture is used to perform one-sided two-hole positioning and clamping on the reverse side of the part when machining the front side of the part. The five-axis machining fixture includes a first base, which has a fine grinding reference surface for fitting with the reverse side of the part. The fine grinding reference surface is provided with positioning pin holes H′1 and H′2 corresponding to the positions of the process positioning pin holes H1 and H2 on the reverse side of the part, respectively. A cylindrical positioning pin is provided in H′1 and a chamfered positioning pin is provided in H′2. The first base is also provided with three pull screws, which are used to cooperate with the threaded holes on the process boss of the part to pull and fix the part to the fine grinding reference surface. The three-axis machining fixture is used to position and clamp the front end of the part with stepped holes when machining the reverse end of the part. The three-axis machining fixture includes a second base. The second base has a stepped connecting surface for fitting with a stepped surface of the front end of the part. The stepped connecting surface is provided with a cylindrical stepped positioning pin and a chamfered stepped positioning pin. The cylindrical stepped positioning pin and the chamfered stepped positioning pin are respectively used to insert into two large holes formed on the stepped surface of the front end of the part to limit the position and angular orientation of the part relative to the second base. The second base is also provided with three pressure plates for pressing the side windows and bosses of the part.

7. The positioning fixture device for turning shell-type parts in machining according to claim 6, characterized in that, Both the positioning pin holes H′1 and H′2 are Φ20H7 pin holes, and both the cylindrical positioning pin and the chamfered positioning pin are Φ20h7 positioning pins.

8. The positioning fixture device for turning shell-type parts in machining according to claim 6, characterized in that, The cylindrical stepped positioning pin is a Φ38h7 stepped positioning pin, and is used to insert into the Φ38H7 stepped hole on the front end of the part; the chamfered stepped positioning pin is a Φ30h7 stepped positioning pin, and is used to insert into the Φ30H7 stepped hole on the front end of the part.

9. The positioning fixture device for turning shell-type parts in machining according to claim 6, characterized in that, The three-axis machining fixture and the part are kept in contact only through the stepped connection surface.

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