A method for machining a closed impeller on five axes

Abstract

This application relates to a five-axis machining method for closed impellers, belonging to the field of impeller automation machining technology. It includes drawing a blank graphic and reserving machining base allowances to adapt to process holes or dimensions; roughing the flow channels multiple times to initially connect the flow channels and remove most of the excess material; setting layered allowances for multi-segment milling of the flow channels; using a ball-end mill to perform layer-by-layer finishing milling of the flow channels, setting tool connection parameters at permissible locations for transition; and also includes face milling of the inclined leading edge allowance. This application achieves the technical effects of optimizing the five-axis machining process of closed impellers, facilitating chip removal, effectively removing excess material, rationally dividing the flow channel area, ensuring interconnected milling of the flow channels and avoiding interference, ensuring that the tool holder does not collide with the blank, and improving machining quality and efficiency.

Description

Technical Field

[0001] This application relates to the field of automated impeller machining technology, and in particular to a five-axis machining method for closed impellers. Background Technology

[0002] Turbine manufacturing technology plays a crucial role in cryogenic engineering and energy equipment. With the continuous development of related industries, the demand for closed impellers in turbine machinery is increasing daily. The integrated molding manufacturing technology of high-precision closed impellers directly affects the performance and efficiency of turbine machinery, thus playing a key role in the operation of the entire energy equipment system. Advances in precision machining technology for closed impellers can drive the development of cryogenic engineering and energy equipment towards higher precision and higher efficiency.

[0003] In the traditional machining of closed impellers for turbine expanders, several common methods are mainly used. One is split machining, where the impeller disk and blades are machined separately and then assembled together by welding or bolting. Another is casting, where the closed impeller is directly cast. Furthermore, when machining the transition zone at the blade root, a fixed cutter shaft direction is often used. These methods have provided feasible approaches to the manufacture of closed impellers for some time.

[0004] However, these existing machining methods have significant drawbacks. Split-type machining leads to accumulated assembly errors, and stress concentration easily occurs in the weld area, reducing the fatigue life of the impeller. Casting methods result in problems such as uneven and discontinuous physical properties of the casting material, as well as inconsistent geometric shapes between castings. Furthermore, when machining the transition zone at the blade root using a fixed cutter axis direction, it is easy for the tool to collide with adjacent blades, potentially resulting in the inability to machine to the designed dimensions, or even causing blade breakage and workpiece damage. Summary of the Invention

[0005] To address the problems of low machining efficiency and low machining accuracy in existing closed impeller machining technologies, this application provides a five-axis machining method for closed impellers.

[0006] The technical solution for a closed-loop impeller five-axis machining method provided in this application is as follows: A method for machining a closed impeller on five axes, comprising: S1. Draw the blank graphic and reserve the machining foundation amount, and match the process hole or process size according to the clamping fixture. S2. Through multiple roughening processes, the flow channel is initially opened and most of the excess material is removed. S3. Set layering allowance to perform multi-segment milling of flow channels; S4. Use a ball end mill to perform precision milling of the flow channel layer by layer using a spiral milling method, and set the tool connection parameters for transition at the allowable position of the flow channel.

[0007] Optionally, the steps also include: face milling the inclined leading edge allowance using a five-axis linkage, and milling along the inclined direction of the leading edge closed impeller by fixing the tool axis angle and following a helical toolpath.

[0008] Optionally, the face milling of the inclined leading edge allowance is performed using a five-axis linkage, with the milling occurring along the inclined direction of the closed impeller at a fixed tool axis angle. Specific steps include: For removing the leading edge allowance, face milling is used. A roughing method involving the X, Y, and Z axes and the A and C axes is employed. The A and C axes are fixed, and a tapered ball end mill is used with a helical feed. Starting from the small outer diameter of the workpiece's wheel cover, the milling proceeds along the inclined leading edge of the closed impeller, setting an inflection point at the lowest point of the leading edge. The milling continues on the extension surface of the flow channel until the tool retracts vertically from the small end face of the wheel and exits the workpiece surface. This process is repeated multiple times until the leading edge allowance meets the milling requirements of the flow channel. The depth of cut is 0.3–0.5 mm, the feed rate is 1000–2000 mm / min, the rotation speed is 6000–10000 rpm, and the machining allowance is 0.3–0.6 mm.

[0009] Optionally, the steps for initially opening the flow channel include: The roughing method employs the linkage of X, Y, and Z axes with A and C axes to restrict the toolpath from entering the area between the leading or trailing edges of the two blades. A flat-bottomed end mill with a large diameter that can pass through the flow channel is used. The machining depth and other parameters are controlled by adjusting the angle of the flow channel view (i.e., the direction parallel to the tool vector). Milling is performed from the leading and trailing edges to connect them. The flow channel is then connected by using two or three toolpaths with a large-diameter tool, which facilitates chip removal and guides the direction of subsequent roughing toolpaths. Several roughing paths are added from the leading and trailing edges to obtain a blank with a preliminary flow channel connection.

[0010] Optionally, the removal of most of the excess includes the following steps: First, use an extended flat end mill to remove most of the excess material at the flow channel connection. Then, use a small-diameter flat end mill to remove more excess material during the roughing process of the flow channel. Place the fixed axis angle from different directions at the leading edge and trailing edge, and roughen multiple times until the flow channel has a small amount of excess material remaining.

[0011] Optionally, the process involves first removing most of the excess material at the flow channel connection point using an extended flat end mill, and then removing even more excess material during the flow channel roughing process using a small-diameter flat end mill. Specific steps include: Select the largest cutting tool to meet the strength requirements, with a cutting depth of 0.3~0.5mm, a spindle speed of 2000~3000rpm, and a feed rate of 800~1500mm / min; subsequently, select a smaller diameter cutting tool with a cutting depth of 0.2~0.3mm, a spindle speed of 2000~3000rpm, and a feed rate of 300~500mm / min.

[0012] By adopting the above technical solution,

[0013] Optionally, the step of setting layered allowances for multi-segment milling of the flow channel includes: The flow channel is milled in at least three layers. In areas with a large allowance, the flow channel is offset, and the ball end mill is milled along the offset area. The milling area of ​​the ball end is observed. If it is greater than 0.25 times the diameter of the ball end, the offset flow channel is milled again until the milling area of ​​the ball end in a single operation is less than 0.25 times the diameter of the ball end, and then the offset is stopped.

[0014] By adopting the above technical solution,

[0015] Optionally, the step of using a ball end mill to finish mill the flow channel layer by layer through helical milling, and setting the tool connection parameters at the allowable position of the flow channel for transition, further includes: For cases of severe spatial distortion, the impeller flow channel is divided into at least three regions for progressive precision milling.

[0016] Optionally, dividing the impeller flow channel into at least three regions includes the following steps: The flow channel is divided into three regions: the leading edge, the trailing edge, and the middle section. Each region is machined using a tool path adjusted by the vector swing angle. The middle section is divided into a front section and a tail section. The two sections are connected by milling paths with opposite vector directions.

[0017] Optionally, the step of performing partitioned machining using the toolpath adjusted by the vector swing angle includes: Using a specially designed ball end mill, a larger tool vector swing angle is obtained, which allows for continuous milling of the flow channels without interfering with the flow channels and blades. During the finishing process, the tool vector direction and machining range are adjusted to ensure that the tool holder does not collide with the workpiece.

[0018] In summary, this application includes at least one of the following beneficial technical effects: 1. By performing phased composite shaft linkage machining, optimizing tool motion strategy and tool axis control, we can achieve efficient roughing and high surface integrity finishing of closed impellers, and ensure that the blade thickness tolerance is ≤ ±0.01mm and the surface roughness Ra is ≤ 0.4μm; 2. It avoids the cumulative assembly errors and weld stress concentration problems of split-type processing, as well as the defects in the physical properties and geometry of casting materials; 3. By adjusting the tool vector direction and performing zoned machining, collisions between the tool and adjacent blades are avoided, reducing the risk of workpiece damage. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the roughing of the flow channel in a closed impeller five-axis machining method according to an embodiment of this application.

[0020] Figure 2 This is a schematic diagram of layered milling machining of a closed impeller five-axis machining method according to an embodiment of this application.

[0021] Figure 3 This is a schematic diagram of the partitioned precision milling process of a five-axis machining method for a closed impeller according to an embodiment of this application.

[0022] Figure 4 This is a schematic diagram of the leading edge allowance milling process of a closed impeller five-axis machining method according to an embodiment of this application.

[0023] Explanation of reference numerals in the attached diagram: 1. Flat end mill; 2. Closed impeller; 3. Leading edge opening; 4. Trailing edge opening; 5. Ball end mill; 6. Middle section; 7. Layered zone; 8. Leading edge allowance. Detailed Implementation

[0024] The following specific embodiments illustrate the implementation of this application. Those skilled in the art can easily understand other advantages and effects of this application from the content disclosed in this specification.

[0025] Please see Figure 1-4 It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and to facilitate understanding. They are not intended to limit the scope of this application and therefore have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of this application, should still fall within the scope of the technical content disclosed in this application. Furthermore, the terms such as "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of this application. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of this application's implementation.

[0026] The following is in conjunction with the appendix Figure 1-4 This application will be described in further detail.

[0027] This embodiment discloses a five-axis machining method for closed impellers.

[0028] The five-axis machining method for closed impellers provided in this application includes steps such as drawing blank graphics, roughing multiple flow channels, setting layered allowances for multi-segment milling of flow channels, and finishing milling of flow channels using a ball end mill spiral milling machine. In this method, by performing staged compound axis linkage machining and optimizing the tool motion strategy and tool axis control, efficient roughing and high surface integrity finishing of closed impellers are achieved, ensuring that the blade thickness tolerance and surface roughness meet the requirements.

[0029] S1. Draw the blank graphic and reserve the machining foundation amount, and match the process hole or process size according to the clamping fixture. Specifically, in the process of drawing the blank graphic, sufficient production and machining allowance must be reserved, and corresponding process holes or dimensions must be made according to the actual suitable clamping fixture. In practice, machining the blank part on a conventional lathe or CNC lathe is a relatively fast and accurate method. The clamping fixture can be a chuck, a jig, etc., and different clamping fixtures have different requirements for process holes or dimensions. For example, when using a chuck for clamping, it may be necessary to machine process holes on the blank to facilitate chuck positioning; while when using a jig for clamping, specific process dimensions may be required to ensure the accurate installation of the blank in the jig.

[0030] S2. Through multiple roughening processes, the flow channel is initially opened and most of the excess material is removed. Reference Figure 1 To initially open the flow channel, a method of roughing using the X, Y, and Z axes in conjunction with the A and C axes is employed. This restricts the toolpath to only entering the area between the leading or trailing edges of the two blades. A flat-end mill with a larger diameter that can pass through the flow channel is used. The machining depth and other parameters are controlled by adjusting the angle of the flow channel view (i.e., the direction parallel to the tool vector). Milling is performed from the leading and trailing edges to connect the flow channel. Roughing with two or three toolpaths using a large-diameter tool further connects the flow channel. This facilitates chip removal and guides the direction of subsequent roughing toolpaths. Several roughing operations are added from the leading and trailing edges to obtain a blank with a preliminary flow channel. A large-diameter flat-end mill can quickly remove a large amount of material, improving roughing efficiency. In practical applications, other types of tools, such as ring mills, can also be considered, as they may have better chip removal performance and machining effects in certain situations. When removing most of the excess material, first use an extended flat-end mill to remove most of the excess material at the flow channel junction. Then, use a small-diameter flat-end mill to remove more excess material during roughing of the flow channel. Position the mill at a fixed axis angle from different directions at the leading and trailing edges, and roughing is repeated multiple times until only a small amount of material remains in the flow channel. Select the largest tool to meet strength requirements, with a depth of cut of 0.3-0.5 mm, a spindle speed of 2000-3000 rpm, and a feed rate of 800-1500 mm / min. Subsequently, use a small-diameter tool with a depth of cut of 0.2-0.3 mm, a spindle speed of 2000-3000 rpm, and a feed rate of 300-500 mm / min. The extended flat-end mill can reach deep into the flow channel for machining, while the small-diameter flat-end mill can perform fine machining on some narrow areas. In actual operation, the selection of tools also needs to consider the specific structure and material properties of the impeller.

[0031] S3. Set layering allowance to perform multi-segment milling of flow channels; When setting layered allowances for multi-segment milling of flow channels, the flow channel should be milled in at least three layers, referring to... Figure 2 In areas with ample allowance, the flow channel is offset, allowing the ball end mill to mill along this offset area. The milled area of ​​the ball end mill is observed; if it exceeds 0.25 times the diameter of the ball end mill, the offset flow channel is further milled until the area milled in a single pass is less than 0.25 times the diameter of the ball end mill. This layered milling method extends tool life and ensures milling quality. Ball end mills are advantageous for machining curved surfaces and irregular shapes. Selecting the appropriate ball end mill can improve machining quality; for example, ball end mills with different radii can be selected for processing flow channels with different curvatures.

[0032] S4. Use a ball end mill to finish mill the flow channel layer by layer using a spiral milling method, and set the tool connection parameters for transition at the allowable position of the flow channel. For cases with severe spatial distortion, the impeller flow channel should be divided into at least three regions for progressive precision milling, referring to... Figure 3 The flow channel is divided into three regions: the leading edge, the trailing edge, and the middle section. Each region is machined using a toolpath with adjusted vector wobble angles. The middle section is further divided into a front section and a tail section, with opposite vector directions used for milling paths to achieve tool connection. A specially designed ball end mill is used to achieve a larger tool vector wobble angle, ensuring continuous milling of the flow channel without interfering with the flow channel or blades. During finishing, the tool vector direction and machining range are adjusted to ensure the tool holder does not collide with the workpiece. The specially designed ball end mill can be designed according to the specific shape and spatial requirements of the flow channel to meet machining needs. In actual machining, advanced measurement technology can be combined to monitor the positional relationship between the tool and the workpiece in real time, further ensuring machining accuracy.

[0033] Furthermore, between steps S1 and S2, for the machining of the closed impeller with an inclined leading edge, the blank allowance of the inclined leading edge is not easily controlled by the lathe, resulting in the blank allowance not conforming to the dimensions of the process drawing before milling the blade shape. If the next programming step is carried out rashly, it may easily cause the adverse consequences of tool insertion. Therefore, before roughing the flow channel, face milling is required to mill the unfinished allowance of the impeller, referring to... Figure 4 When milling the inclined leading edge allowance, a roughing method using the X, Y, and Z axes in conjunction with the A and C axes is employed. The A and C axes are fixed, and a tapered ball end mill is used with a helical feed. The tool starts from the small outer diameter of the workpiece's wheel cover, following the inclined leading edge of the closed impeller, and sets an inflection point at the lowest point of the leading edge. Milling continues on the extension surface of the flow channel until the tool retracts vertically from the small end face of the wheel and exits the workpiece surface. This process is repeated multiple times until the leading edge allowance meets the milling requirements of the flow channel. The tapered ball end mill used here has good cutting performance and can adapt to the machining requirements of the inclined leading edge. In actual machining, similar tools can be selected according to specific circumstances, such as tapered ball end mills with special coatings to improve tool wear resistance and cutting efficiency. The depth of cut is 0.3–0.5 mm, the feed rate is 1000–2000 mm / min, the rotation speed is 6000–10000 rpm, and the machining allowance is 0.3–0.6 mm. These parameters are set to ensure processing efficiency and quality. Different impeller materials and processing requirements may require appropriate adjustments to these parameters.

[0034] The implementation principle of this embodiment is as follows: Through a phased compound shaft linkage machining method, and considering the different machining stages and characteristics of the closed impeller, the cutting tools and machining parameters are rationally selected, and the tool motion strategy and tool axis control are optimized. In the roughing stage, most of the excess material is removed through multiple roughing passes, improving machining efficiency. In the finishing stage, layered milling and partitioned machining are employed to ensure the milling connection of the flow channels and surface quality, avoiding interference between the cutting tool and the flow channels and blades. Ultimately, this achieves highly efficient roughing and high surface integrity finishing of the closed impeller. Compared with traditional machining methods, this reduces accumulated assembly errors and stress concentration problems, improves the impeller's fatigue life and machining quality, and promotes the advancement of closed impeller machining technology in turbine machinery.

[0035] The above embodiments are merely illustrative of the principles and effects of this application and are not intended to limit this application. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this application. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this application should still be covered within the protection scope of this application.

Claims

1. A closed impeller five-axis machining method, characterized by, include: S1. Draw the blank graphic and reserve the machining foundation amount, and match the process hole or process size according to the clamping fixture. S2. Through multiple roughing operations, the flow channel is initially opened. The roughing method of X, Y, Z axes and A, C axes is used to restrict the toolpath to enter from the area between the leading edge or trailing edge of the two blades. A flat-bottomed milling cutter with a large diameter that can pass through the flow channel is used. The machining parameters are controlled by placing the flow channel view angle, i.e., the direction parallel to the tool vector. Milling is performed from the leading edge and trailing edge to connect them. The flow channel is connected by using a large diameter tool with two or three toolpaths to roughing, which facilitates chip removal and guides the direction of subsequent roughing toolpaths. Several roughing operations are added from the leading edge and trailing edge to obtain a blank with a preliminary flow channel, and most of the excess material is removed. S3. Set layering allowance to perform multi-segment milling of flow channels; S4. Use a ball end mill to perform precision milling of the flow channel layer by layer using a spiral milling method, and set the tool connection parameters for transition at the allowable position of the flow channel.

2. A method of five-axis machining of a closed impeller according to claim 1, characterized in that, The steps also include: face milling the inclined leading edge allowance, using five-axis linkage, and milling along the inclined direction of the leading edge closed impeller by fixing the tool axis angle and following a helical toolpath.

3. The method of claim 2, wherein, The surface milling of the inclined leading edge allowance employs five-axis linkage, using a fixed tool axis angle to mill along the inclined direction of the closed impeller at the leading edge via a helical toolpath. Specific steps include: For removing the leading edge allowance, face milling is used. A roughing method involving the X, Y, and Z axes and the A and C axes is employed. The A and C axes are fixed, and a tapered ball end mill is used with a helical feed. Starting from the small outer diameter of the workpiece's wheel cover, the milling proceeds along the inclined leading edge of the closed impeller, setting an inflection point at the lowest point of the leading edge. The milling continues on the flow channel extension surface until the tool retracts vertically from the small end face of the wheel and exits the workpiece surface. This process is repeated multiple times until the leading edge allowance meets the milling requirements of the flow channel. The depth of cut is 0.3–0.5 mm, the feed rate is 1000–2000 mm / min, the rotation speed is 6000–10000 rpm, and the machining allowance is 0.3–0.6 mm.

4. The method of claim 1, wherein: The specific steps for removing most of the excess include: First, use an extended flat end mill to remove most of the excess material at the flow channel connection. Then, use a small-diameter flat end mill to remove more excess material during the roughing process of the flow channel. Place the fixed axis angle from different directions at the leading edge and trailing edge, and roughen multiple times until the flow channel has a small amount of excess material remaining.

5. A method of five-axis machining of a closed impeller according to claim 4, characterized in that: The process involves first removing most of the excess material at the flow channel connection point using an extended flat end mill, and then removing even more excess material during the roughing process using a small-diameter flat end mill. The specific steps include: Select the largest cutting tool to meet the strength requirements, with a cutting depth of 0.3~0.5mm, a spindle speed of 2000~3000rpm, and a feed rate of 800~1500mm / min; subsequently, select a smaller diameter cutting tool with a cutting depth of 0.2~0.3mm, a spindle speed of 2000~3000rpm, and a feed rate of 300~500mm / min.

6. The method for machining a closed impeller on five axes according to claim 1, characterized in that: The specific steps for setting layered allowances to perform multi-segment milling of flow channels include: The flow channel is milled in at least three layers. In areas with a large allowance, the flow channel is offset, and the ball end mill is milled along the offset area. The milling area of ​​the ball end is observed. If it is greater than 0.25 times the diameter of the ball end, the offset flow channel is milled again until the milling area of ​​the ball end in a single operation is less than 0.25 times the diameter of the ball end, and then the offset is stopped.

7. The method for machining a closed impeller on five axes according to claim 1, characterized in that: The step of using a ball end mill to finish mill the flow channel layer by layer through helical milling, and setting tool connection parameters at permissible locations in the flow channel for transition, further includes: For cases of severe spatial distortion, the impeller flow channel is divided into at least three regions for progressive precision milling.

8. The method for machining a closed impeller on five axes according to claim 7, characterized in that: The specific steps of dividing the impeller flow channel into at least three regions include: The flow channel is divided into three regions: the leading edge, the trailing edge, and the middle section. Each region is machined using a tool path adjusted by the vector swing angle. The middle section is divided into a front section and a tail section. The two sections are connected by milling paths with opposite vector directions.

9. A five-axis machining method for a closed impeller according to claim 8, characterized in that: The process of performing partitioned machining using a toolpath adjusted by vector swing angle includes the following steps: Using a specially designed ball end mill, a larger tool vector swing angle is obtained, which allows for continuous milling of the flow channels without interfering with the flow channels and blades. During the finishing process, the tool vector direction and machining range are adjusted to ensure that the tool holder does not collide with the workpiece.

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