A method of segmented additive and subtractive manufacturing

Abstract

The present application relates to a kind of sectional additive and subtractive machining methods, belong to machining and 3D printing additive technology field, solve the poor reachability of existing technology deep cavity machining tool, complex deep cavity processing efficiency low or poor adaptability one of problems.The sectional additive and subtractive machining method of the present application, including step 1: cylinder is divided into section along axial direction;Step 2: according to section number, determine the number of additive and subtractive alternation;Step 3: select additive substrate;Step 4: blank model design and electric arc additive path planning;Step 5: according to the structure characteristics of different section inner cavity of cylinder, select inner cavity numerical control subtractive scheme and positioning fixture;Step 6: carry out inner cavity feature processing, complete cylinder additive and subtractive machining.The present application realizes sectional additive and subtractive machining, processing efficiency is high and the adaptability of fixture is good.

Description

Technical Field

[0001] This invention relates to the fields of machining and manufacturing and 3D printing additive manufacturing technology, and in particular to a segmented additive and subtractive manufacturing method. Background Technology

[0002] Large, complex, deep-cavity, thin-walled cylinders are core components in aerospace, high-end equipment manufacturing, and other fields. Their structures are characterized by large external dimensions, deep internal cavities, complex cavity structures, thin and uneven wall thickness, high precision requirements, and strict weight control, placing extremely high demands on manufacturing technology. Currently, the manufacturing of these cylinders mainly relies on traditional casting / forging + machining methods and conventional additive / subtractive processing methods. Both methods have numerous technical bottlenecks and are insufficient to meet the performance and precision requirements of high-end equipment for these components.

[0003] In traditional machining methods, a special mold must first be designed and manufactured according to the cylinder structure. The mold preparation cycle is long and the cost is high. Moreover, due to the limitations of the mold structure, it is impossible to efficiently form complex internal ribs, irregular deep cavities, closed partitions and other delicate structures. After forming, the blank has a large allowance, which needs to be removed by a lot of machining. This not only has a long processing cycle and serious material waste, but also easily causes deformation of thin-walled cylinders due to uneven machining allowance and excessive cutting force, affecting the machining accuracy. At the same time, for deep cavity areas, especially narrow deep cavities and the root of partitions, the tool accessibility is poor, which easily leads to defects such as machining interference and undercutting, making it difficult to guarantee the machining quality of deep cavity features.

[0004] In conventional additive and subtractive manufacturing processes, the "integral additive forming followed by concentrated subtraction" method is often adopted. Although it eliminates the need for complex molds, it still has significant shortcomings: First, after integral additive forming, the internal stress of the workpiece accumulates severely, easily leading to large deformations. Subsequent concentrated subtraction is difficult to completely correct, resulting in insufficient machining accuracy. Second, the tool accessibility problem in deep cavity areas is not fundamentally solved, and the machining efficiency and quality of complex deep cavity features remain limited. Third, additive substrates are mostly made in specialized fixtures and need to be removed later, increasing machining steps and material waste. Furthermore, multiple clamping and datum conversion processes are prone to datum transfer errors, resulting in insufficient connection accuracy between sections. Fourth, unreasonable additive path design and unoptimized blank allowance distribution not only result in low additive efficiency but also further increase the workload and material loss in subsequent subtraction.

[0005] In addition, existing processing technologies suffer from problems such as long development cycles, high manufacturing costs, and poor adaptability, making it difficult to adapt to the rapid iteration of products and the processing needs of cylinders of different specifications, and failing to meet the increasingly stringent performance, precision, and cost requirements of the high-end equipment field. Summary of the Invention

[0006] Based on the above analysis, the present invention aims to provide a segmented additive and subtractive machining method to solve one of the problems of poor accessibility of existing deep cavity machining tools, low efficiency or poor adaptability of complex deep cavity machining.

[0007] The objective of this invention is mainly achieved through the following technical solutions: A method for manufacturing by adding or subtracting materials in sections includes the following steps: Divide the cylinder into sections along the axial direction; The number of times materials need to be added or removed is determined based on the number of sections; Select additive substrate; Raw material model design and arc additive manufacturing path planning; Select the internal cavity material reduction scheme and cylinder positioning fixture according to the internal cavity structural characteristics of different sections of the cylinder; Perform internal cavity feature machining to complete the addition and subtraction of materials in the inner cavity of the cylinder.

[0008] Furthermore, the number of additive manufacturing steps corresponds to the number of structural sections in the cylindrical body.

[0009] Furthermore, a substrate material with properties consistent with the cylinder material is selected; Determine the thickness of the partition and allow for rough machining allowance; A standardized process reference system, including reference surfaces, reference holes, and locating pin holes, is processed on the substrate for positioning and reference transfer in all subsequent processing sections. During the overall machining stage of the cylinder, the substrate is machined into an integrated process reference boss by utilizing the machining allowance reserved on the substrate.

[0010] Furthermore, for narrow and deep cavity areas, a horizontal machining center is selected in conjunction with a high-rigidity extended rod tool for machining, and material reduction is carried out by using segmented cylinder positioning fixtures and integral workpiece cylinder positioning fixtures respectively.

[0011] Furthermore, the planned arc additive manufacturing path adopts a composite motion mode that combines circular motion with reciprocating short linear motion.

[0012] Furthermore, based on the location of the ribs in the inner cavity of the cylinder and the location of the end sealing partitions, and combined with the limit depth of the inner cavity that the equipment can process, the cylinder is divided into several independent structural process sections along the axial direction.

[0013] Furthermore, after each material addition or subtraction processing step is completed, process benchmark testing and correction are performed.

[0014] Furthermore, after completing the alternating processing of added and subtracted materials, the process also includes precision machining of the cylinder's shape.

[0015] Furthermore, clamping bosses are symmetrically added to the front and rear ends of the cylinder. The clamping bosses are used for positioning and machining of the front and rear end face features of the cylinder.

[0016] Furthermore, during the internal cavity material reduction process, a cylinder positioning fixture is used for clamping.

[0017] Furthermore, the cylinder positioning fixture includes a first end, a positioning rod, a second end, and a clamping part. The two ends of the positioning rod are respectively connected to the first end and the second end, and multiple sets of the clamping parts are arranged at intervals along the length direction of the positioning rod. The clamping part includes a fixing part, a support frame, and a conforming mechanism. The fixing part is locked and fixed to the outside of the positioning rod. The support frame is fixedly installed on the outside of the fixing part. The conforming mechanism is disposed on the support frame and is used to fit against the outer wall of the cylinder.

[0018] Furthermore, the conformal mechanism includes a conformal fixing part, a movable part, a spring, and a conformal plate. One end of the conformal fixing part is mounted on the support frame, and the other end of the conformal fixing part is connected to the movable part. The movable part can slide along the axial direction of the conformal fixing part. The spring is sleeved on the outside of the rod of the conformal fixing part, and both ends of the spring abut against the movable part and the support frame, respectively. The conformal plate is disposed at the end of the movable part and fits against the outer wall of the cylinder.

[0019] Furthermore, the support frame includes a first support plate and a second support plate. The first support plate has an arc-shaped plate structure and the arc radius matches the arc radius of the outer wall of the cylinder. The second support plate is arranged along the circumference of the first support plate. The conformal fixing part is arranged on the inner side of the first support plate, and the conformal mechanism is arranged along the length direction of the second support plate.

[0020] Furthermore, both the first end and the second end are provided with mounting holes for installing the positioning rod. The mounting holes are elongated structures, and the positioning rod can be adjusted in assembly position along the length of the elongated adjustment hole to adapt to cylinders of different diameters.

[0021] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. To address the issues of poor tool accessibility and machining interference in the machining of large, complex, deep-cavity, thin-walled cylinders in existing technologies, this invention employs a segmented, alternating additive and subtractive machining mode. The large, deep-cavity, thin-walled cylinder is divided axially into several structural process sections with adaptable machining depths to different equipment, achieving "divide and conquer" machining of large, deep cavities. After additive machining is completed in each section, targeted subtraction is immediately performed, resolving the problems of poor tool accessibility and machining interference in existing deep-cavity machining technologies. This method is particularly suitable for machining cylinders with large external dimensions, complex internal structures, and thin walls.

[0022] 2. To address the problems of difficult reference transfer and poor connection accuracy between sections due to error accumulation during segmented machining in existing technologies, this invention adopts an integrated design of the base plate and the inner cavity partition plate of the cylinder. The base plate directly serves as the machining blank for the partition plate, eliminating the need for subsequent removal and becoming an integral part of the workpiece body. This reduces machining steps and material waste, resulting in high efficiency in machining complex deep cavities. Simultaneously, a standardized process reference system is designed on the base plate. Through a reference-based, fully reusable transfer mode, combined with reference detection and correction after each material addition or subtraction, the problems of difficult reference transfer and error accumulation in segmented machining are solved. This ensures that the connection accuracy of each section and the overall machining accuracy, as well as key indicators such as cylinder contour and position accuracy, meet design requirements.

[0023] 3. To address the problem of poor clamping effect of conventional fixtures in the prior art, which easily leads to cylinder deformation or poor adaptability, the cylinder positioning fixture in the internal cavity sublimation process of the present invention adopts multiple sets of conformal support structures. Multiple sets of clamping parts are arranged along the length direction of the positioning rod to meet various clamping requirements of the cylinder. At the same time, the conformal plate can move synchronously with the moving part to extend and retract with the moving part, adaptively conforming to the irregular curved surface of the cylinder cavity, with uniform conformation and force distribution, reducing the deformation of thin-walled workpieces during processing.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the specification or be learned by practicing the invention. The objectives and other advantages of this invention can be realized and obtained from the content specifically pointed out in the text and accompanying drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 This is a schematic diagram of the thin-walled cylindrical structure of Example 1; Figure 2 This is a schematic diagram of the substrate structure in Example 1; Figure 3 This is a schematic diagram of the first section of the workpiece blank structure in Example 1; Figure 4 This is a schematic diagram of the first section of the workpiece structure in Example 1; Figure 5 This is a schematic diagram of the second section of the workpiece blank structure in Example 1; Figure 6 This is a schematic diagram of the overall workpiece blank structure in Example 1; Figure 7This is a schematic diagram (a) of the second section workpiece cylinder positioning fixture in Embodiment 1; Figure 8 This is a schematic diagram (II) of the integral workpiece cylinder positioning fixture in Example 1; Figure 9 This is a schematic diagram of the workpiece cylinder positioning fixture in Example 2; Figure 10 This is a schematic diagram of the clamping part structure in Embodiment 2; Figure 11 This is a schematic diagram of the conformal component structure in Embodiment 2.

[0027] Figure label: 1-Cylinder body; 11-First section workpiece; 12-First section workpiece blank; 13-Second section workpiece blank; 14-Integral workpiece blank; 2-Substrate; 3-Separator; 4-Positioning clamp; 41-First end; 42-Positioning rod; 43-Clamping part; 431-Following mechanism; 4311-Following fixing part; 4312-Spring; 4313-Moving part; 4314-Following plate; 432-Support frame; 4321-First support plate; 4322-Second support plate; 433-Fixing part; 44-Second end. Detailed Implementation

[0028] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0029] This invention provides a method for manufacturing by adding or subtracting materials in sections, comprising the following steps: Step 1: Divide the cylinder into sections along the axial direction.

[0030] Based on the structural characteristics of the thin-walled cylinder, the equipment processing capabilities, and the blank allowance, the cylinder is designed to be divided into several sections along the axial direction. The structure of the thin-walled cylinder is as follows: Figure 1 As shown, specifically, the structural boundaries are determined by the location of the inner cavity ribs and the location of the end sealing partitions, and the process constraints are combined with the maximum depth of the inner cavity that the equipment can process. The cylinder is divided into several independent structural process sections along the axial direction for the segmented processing of large deep cavity structures.

[0031] Step 2: Determine the number of alternations between adding and subtracting materials based on the number of sections.

[0032] Based on the number of cylindrical structure segments defined in step 1, a matching scheme is designed for the number of arc addition operations and CNC subtraction operations, where the number of arc addition operations corresponds to the number of cylindrical structure segments. It is worth noting that the number of CNC subtraction operations can be flexibly adjusted according to the machining accuracy level, the required removal of blank allowance, and the complexity of the segment structure. For segments with complex structures and concentrated allowances, 1-2 intermediate subtraction operations can be added to reduce subsequent machining interference and control workpiece deformation.

[0033] Step 3: Select the additive substrate.

[0034] To address the core issues of difficulty in datum transfer and error accumulation in segmented additive and subtractive material processing, and considering the structural characteristics of the inner cavity partition plate of the cylinder and the datum transfer requirements after flipping processing, an integrated design scheme of base plate and inner cavity partition plate is adopted. The base plate directly serves as the processing blank for the partition plate, eliminating the need for subsequent removal, and is directly integrated into the core component of the workpiece body. The specific steps include: Step 31: Selection of substrate material and size.

[0035] Select a substrate material with the same chemical composition, mechanical properties, and coefficient of thermal expansion as the cylinder material to ensure the connection strength, molding consistency, and heat treatment compatibility between the substrate and the cylinder body. Simultaneously, when designing the substrate's external dimensions, it is necessary to ensure it is 200mm-300mm larger than the maximum outer contour dimension of the cylinder, reserving sufficient clamping and positioning space and subsequent machining allowance to reduce clamping interference.

[0036] Step 32: Determine the partition thickness and rough machining allowance.

[0037] Based on the design drawings of the inner cavity partition of the cylinder, the theoretical design thickness of the partition is determined, and a rough machining allowance of 3mm-5mm is reserved according to the additive deformation law to provide sufficient space for subsequent precision machining and ensure that the final dimensional accuracy, flatness and perpendicularity of the partition meet the design standards.

[0038] Step 33: Processing technology benchmark.

[0039] A standardized process reference system is designed on the substrate, including reference surfaces, reference holes, and locating pin holes, for positioning and reference transfer in all subsequent machining sections. During the first CNC subtractive machining, the substrate is first finely leveled around its perimeter. Using the design reference center of the first section as a reference, high-precision reference holes are machined on the substrate with a tolerance of ±0.01mm. Repetitive positioning is achieved in subsequent machining sections through locating pins, thus establishing a reference transfer system that can be reused throughout the entire process.

[0040] Step 34: Machining the reference boss.

[0041] During the overall machining stage of the cylinder, the machining allowance reserved on the substrate is used to process the substrate into an integrated process reference boss. This boss also serves as the core positioning reference for the machining of the shape and the hole, thereby improving the consistency of the overall machining reference.

[0042] Step 4: Blank model design and arc additive manufacturing path planning.

[0043] Based on the structural characteristics and allowance distribution of different sections of the cylinder, professional metal additive manufacturing deformation simulation software is used to predict and compensate for deformation trends by inputting material thermophysical parameters and additive manufacturing process parameters, thereby optimizing the design of the blank model and allowance distribution scheme. Simultaneously, an efficient electric arc additive manufacturing path is planned, employing a composite motion mode combining circular motion and reciprocating short linear motion. Specifically, the electric arc additive spindle head performs high-frequency short linear reciprocating motion, while the rotary table synchronously performs uniform circular motion. The fitting of these two motions forms the shortest forming path for electric arc additive manufacturing.

[0044] Considering the overall characteristics of thin-walled cylindrical additive forming, the allowance distribution is optimized through deformation simulation. The design specifies an inner cavity allowance of 4mm and an outer shape allowance of 5mm, ensuring that the workpiece still has sufficient material reduction allowance after deformation.

[0045] Step 5: Select the internal cavity material reduction scheme and positioning fixture according to the internal cavity structural characteristics of different sections of the cylinder.

[0046] Based on the depth and structural complexity of the cylinder's internal cavity, appropriate machining equipment is selected. For narrow, deep cavity areas, a horizontal machining center is used with a high-rigidity extended-rod tool. The tool rigidity must meet the requirement that the vibration amplitude during deep cavity machining is ≤0.02mm. A cylinder positioning fixture is used to clamp and coaxially position the workpiece. The fixture's positioning surface mates with the base plate's process datum boss, ensuring a clamping repeatability accuracy of ≤±0.02mm.

[0047] Step 6: Perform internal cavity feature machining to complete the addition and subtraction of materials in the cylinder.

[0048] Following the designed arc additive manufacturing path and CNC subtractive manufacturing path, multiple alternating additive and subtractive machining processes are used to complete the blank forming and internal cavity feature machining of the complex thin-walled cylinder. Specifically, the blank is formed by arc additive manufacturing using the shortest path, and the end face and root area of ​​the closed partition are machined using a horizontal machining center with a 45° milling head, while the inner cavity sidewalls are machined using a right-angle milling head. After each additive and subtractive machining process, the process datum is checked and corrected. The datum accuracy is checked using a dial indicator and a coordinate measuring machine. If deviations occur, compensation is made by fine-tuning the datum boss or datum hole to reduce error accumulation.

[0049] To further improve the machining accuracy and forming quality of the cylinder's external features, and to ensure that the external dimensions, contours, and positional accuracy meet design standards, a finishing process for the external features is added after the alternating addition and subtraction machining is completed in step 6 above. The specific steps are as follows: Using CNC machining equipment, the selected machining scheme and the overall workpiece shape reduction fixture follow the phased machining principle of "rough machining - semi-finishing - finishing" to gradually remove the shape allowance and complete the finishing of the overall shape features of the complex thin-walled cylinder, so that the machining accuracy meets the design requirements.

[0050] It should be noted that the selected overall workpiece shape subtractive jig must provide sufficient rotational accuracy to reduce jig rotational deviations that may cause defects such as out-of-tolerance contours and unqualified surface roughness in the shape machining, thereby further improving the stability of the cylinder shape machining quality.

[0051] Compared with existing technologies, this invention provides a segmented additive and subtractive manufacturing method. This invention employs an alternating segmented additive and subtractive processing mode, dividing a large, deep-cavity, thin-walled cylinder axially into several structural process segments with adaptable equipment processing depths, achieving "divide and conquer" processing of large, deep cavities. After additive processing is completed in each segment, targeted subtraction is immediately performed. This not only solves the problems of poor tool accessibility and processing interference in deep-cavity machining in existing technologies, but also timely releases internal stress generated during additive processing, reducing overall workpiece deformation and improving machining accuracy. It is particularly suitable for machining cylinders with large external dimensions, complex internal cavity structures, and thin walls. The invention adopts an integrated design of the base plate and the internal cavity partition plate of the cylinder. The base plate directly serves as the machining blank for the partition plate, eliminating the need for additional special fixtures or subsequent removal, and is directly integrated into the workpiece body, reducing processing steps and material waste. Meanwhile, a standardized process reference system is designed on the substrate. Through a transfer mode of one reference and full reuse, combined with reference detection and correction after each addition or subtraction of materials, the problems of difficulty in reference transfer and error accumulation in segmented processing are solved, so that the connection accuracy of each segment and the overall processing accuracy, as well as key indicators such as cylinder contour and position accuracy, meet the design requirements.

[0052] Example 1 This embodiment focuses on the segmented addition and subtraction machining of a large, complex, deep-cavity, thin-walled cylinder made of ER4220 aluminum alloy. The cylinder is an irregularly shaped, thin-walled, ribbed structure with an envelope diameter of 630mm, a length of 1200mm, and a wall thickness of 3.5mm at its thinnest point. After addition and subtraction machining, the finished wall thickness reaches the design standard of 4mm. Features such as stops and mounting holes are distributed at the front and rear ends. The weight control requirement is that the overweight should not exceed 1% of the theoretical weight, and the overall contour accuracy requirement is ±0.3mm.

[0053] The manufacturing steps of the cylinder 1 in this embodiment are as follows: Step 1: Divide the cylinder into sections along the axial direction.

[0054] Based on the distribution of the internal ribs of the cylinder 1, the position of the end sealing baffles, and the depth of the processing equipment, the cylinder 1 is divided axially into three independent process sections: the first section 11, the second section, and the third section. Figure 3 and Figure 4 As shown, the substrate 2 serves as part of the partition 3 within the inner cavity of the cylinder 1, enabling the processing of large deep cavities by breaking them down into smaller parts, thus solving the problem of poor tool accessibility in deep cavity processing.

[0055] Step 2: Determine the number of alternations between adding and subtracting materials based on the number of sections.

[0056] Based on the division into three sections, an alternating processing logic of three arc additive manufacturing steps and five subtractive manufacturing steps is designed. The specific processing flow is as follows: First reduction of material, such as Figure 2 As shown, the processing and reference correction of substrate 2 are completed so that the reference accuracy of the substrate meets the requirements of subsequent processing. The first arc additive manufacturing process completes the forming of the first section of workpiece blank 12 according to the preset path. The second subtractive machining process completes the machining of the inner cavity and process reference of the first section, providing a positioning reference for the additive machining of the next section. Secondary arc additive manufacturing, such as Figure 5 As shown, the second section workpiece blank 13 is formed. The third subtraction process completes the machining of the inner cavity sidewalls and the bottom surface of the substrate in the second section, and the process benchmarks are reviewed and corrected. The third type of arc additive manufacturing, such as Figure 6 As shown, the third section of the blank is formed, and the overall workpiece blank 14 is printed. The fourth material reduction process completes the machining of the entire inner cavity, removing all excess material from the inner cavity; The fifth material reduction process completes the roughing and semi-finishing of the overall shape of the cylinder, laying the foundation for subsequent finishing.

[0057] All of these processes require coordination and precision testing of the process reference using a coordinate measuring machine. The testing error must be controlled within ±0.01mm. The testing data will be used as the positioning reference for the next section of arc additive manufacturing to reduce error accumulation.

[0058] Step 3: Select the additive substrate.

[0059] Based on the structural features of the partition 3 inside the cylinder 1 and the reference transfer requirements after the flipping process, the design and processing of the substrate 2 are completed according to the following detailed steps. The substrate 2 ultimately becomes the partition 3 inside the cylinder. The specific steps are as follows: Step 31: Select a substrate material and appropriate size that matches the material of cylinder 1. Select ER4220 aluminum alloy, which is the same as the workpiece material, as the substrate material. The substrate design size is 500mm×700mm, with a thickness of 30mm and a 10mm machining allowance in the thickness direction, so that the substrate size is larger than the maximum outer contour size of the cylinder (405mm×620mm), leaving sufficient clamping space and machining allowance.

[0060] Step 32: Determine the thickness of partition 3 and the rough machining allowance. Based on the structural requirements of the partition in the inner cavity of the cylinder, the theoretical thickness of partition 3 is determined to be 22mm, while a rough machining allowance of 4mm is reserved to ensure that the subsequent finishing process can meet the design accuracy requirements.

[0061] Step 33: Design process references on the substrate for positioning and reference transfer in subsequent processing. Machine six slots on substrate 2 for fixing substrate 2 to the processing table; during the first subtractive processing, readjust the dimensions around the substrate and, referring to the reference center of the first section, machine four φ16H7 reference holes on substrate 2 to provide positioning references for subsequent processing of each section, achieving one reference and full reuse.

[0062] Step 34: During the overall shape finishing stage of the cylinder 1, the machining allowance reserved on both sides of the base plate 2 is used to process an integrated process reference boss with a height of 5mm and a width of 20mm, providing a reliable reference for shape machining and hole machining.

[0063] Step 4: Blank model design and arc additive manufacturing path planning.

[0064] By using professional simulation software, combined with the material properties of ER4220 aluminum alloy and the parameters of electric arc additive manufacturing process, the deformation trend of the overall shrinkage of the cylinder forming is analyzed and the blank model and allowance distribution are optimized.

[0065] The specific parameters for arc additive manufacturing are as follows: welding current controlled at 180-220A, welding voltage at 22-26V, wire feed speed at 8-12m / min, arc length at 3-5mm, additive layer thickness at 2-3mm, scanning speed at 300-500mm / min, and shielding gas using 99.99% pure argon with a flow rate of 18-22L / min. The specific parameter setting process is a conventional method in this field and will not be elaborated here. It is worth noting that, due to the overall inward shrinkage trend during the forming of the thin-walled cylinder, an inner cavity allowance of 4mm and an outer diameter allowance of 5mm were determined to ensure sufficient material reduction machining allowance after deformation. The arc additive manufacturing path adopts a combination of circular motion and reciprocating short linear motion. Preferably, the arc additive manufacturing spindle head performs a high-frequency short linear reciprocating motion with a stroke of 5mm, while the rotary table simultaneously performs a uniform circular motion at a speed of 5r / min. The fitting of these two motions forms the shortest forming path, which improves additive manufacturing efficiency while ensuring the density and surface flatness of the additive blank.

[0066] Step 5: Select the CNC material reduction scheme and positioning fixture for the inner cavity based on the structural characteristics of the inner cavity in different sections of the cylinder.

[0067] Based on the internal cavity depth and structural characteristics of the three sections, differentiated material reduction schemes were formulated, and dedicated positioning fixtures were designed: The first section has a smaller depth (≤200mm) and more features on the end faces of the partition plates, so it is machined using a vertical machining center with a roughing allowance of 2.5mm; the second section has an internal cavity depth of approximately 540mm, and the overall workpiece blank 14 has an internal cavity depth of approximately 1050mm, with an overall inverted conical shape, so it is machined using a horizontal machining center with a 45° extended milling head (550mm long) and a 90° extended milling head (600mm long). During machining, the workpiece rotates 360° along the A-axis of the lathe, and is positioned using the front and rear end stops. The positioning fixture for the second section workpiece cylinder is as follows: Figure 7 As shown, this is a traditional subtractive fixture consisting of a blocking disc and a tie rod. When subtracting material from a single workpiece, the second section workpiece cylinder positioning fixture is removed, and a single-piece workpiece cylinder positioning fixture is used for clamping. The structure of the single-piece workpiece cylinder positioning fixture is as follows: Figure 8 As shown, both are traditional clamps in the form of a stopper disc and a lever.

[0068] Step 6: Perform internal cavity feature machining to complete the addition and subtraction of materials in the cylinder.

[0069] The process involves alternating between three electric arc additive manufacturing processes and five multi-stage controlled subtractive manufacturing processes to complete the forming of the cylindrical blank and the machining of the deep cavity features.

[0070] Furthermore, during the additive manufacturing process of the blank, two process clamping bosses are reserved at the rear end of the cylinder and two process clamping bosses are reserved at the front end when removing the substrate allowance. The front and rear four process clamping bosses are used for positioning to complete the processing of the front and rear features of the cylinder. After the bosses are processed, they can be flexibly retained or removed according to the product design requirements.

[0071] Furthermore, since the main body of the cylinder has a wall thickness of only 3.5mm (reaching the design requirement of 4mm after machining) and a length of approximately 1200mm, it belongs to a thin-walled long cylinder structure. Therefore, a fixture for integral workpiece shape reduction is designed. Preferably, the integral workpiece shape reduction fixture is a rotary positioning fixture in the form of a blocking disc and a pull rod. The structure and assembly of the integral workpiece shape reduction fixture are conventional techniques in this field and will not be elaborated here. Machining the outer surface requires three stages: roughing, semi-finishing, and finishing. Small-diameter round nose end mills with a diameter of φ10 or less are preferred to reduce cutting forces during machining and control workpiece deformation. The wall thickness is measured in real time during machining to ensure it is not less than 4mm. Areas with a cumulative wall thickness not exceeding 100cm² are allowed to have a thickness less than 4mm but not less than 3.5mm. The overall shape contour is controlled to meet the design requirement of ±0.3mm.

[0072] Example 2 A specific embodiment of the present invention provides a positioning fixture 4 for internal cavity subtraction, such as... Figure 9 As shown, the method for adding or subtracting material in the cylindrical body segment processing provided in Embodiment 1 aims to solve the problem of deformation of the irregular outer wall surface of the cylindrical body and the rigid clamping during the alternating subtraction processing of the cylindrical body segments, where the existing conventional subtraction fixtures are mostly single-segment fixed structures.

[0073] Specifically, the positioning fixture 4 includes a first end 41, a positioning rod 42, a clamping part 43, and a second end 44. The positioning rod 42 is the core support and positioning base of the positioning fixture. The two ends of the positioning rod 42 are connected to the first end 41 and the second end 44 respectively. Preferably, the connection is detachable with bolts, which facilitates the overall disassembly and maintenance of the fixture and the replacement of components. The clamping part 43 is set on the positioning rod 42 and is used for fitting, clamping, and supporting the internal part of the cylinder to be processed. Multiple sets of clamping parts 43 are provided, and the multiple sets of clamping parts 43 are arranged along the length direction of the positioning rod 42. The arrangement spacing matches the spacing of the axial processing sections of the cylinder, which can simultaneously support and position multiple processing areas of the cylinder.

[0074] Furthermore, to adapt to the irregular curved surface of the thin-walled cylinder and reduce rigid clamping deformation, each assembly clamp 43 is equipped with an adaptive support structure, such as... Figure 10 As shown, it specifically includes a conforming mechanism 431, a support frame 432, and a fixing part 433. The fixing part 433 serves as the positioning base of the clamping part 43 and is locked and fixed to the outside of the positioning rod 42 to achieve overall positioning. The support frame 432 is fixedly installed on the outside of the fixing part 433 to provide a stable installation carrier and support foundation for the conforming mechanism 431. The conforming mechanism 431 is an adaptive fitting component that can adaptively adjust the support fitting state according to the curvature and wall thickness of the outer wall of the cylinder to achieve clamping and positioning.

[0075] Specifically, such as Figure 11 As shown, the conformal mechanism 431 includes a conformal fixing part 4311, a spring 4312, a movable part 4313, and a conformal plate 4314. The conformal fixing part 4311 is a columnar fixed base, with one end of the conformal fixing part 4311 fixedly mounted on the support frame 432. The movable part 4313 is slidably sleeved on the other end of the conformal fixing part 4311, and the movable part 4313 can be extended and slidably adjusted along the axial direction of the conformal fixing part 4311. The spring 4312 is sleeved on the outside of the rod of the conformal fixing part 4311, with both ends of the spring 4312 elastically abutting against the end face of the movable part 4313 and the end face of the support frame 432, respectively, providing an outward elastic pressing force to the movable part 4313, forming a buffer structure. The conformal plate 4314 is fixedly assembled on the outer end of the movable part 4313, directly contacting the outer wall of the cylinder, and moves synchronously with the movable part 4313 to achieve conformal adaptation.

[0076] The support frame 432 includes a first support plate 4321 and a second support plate 4322. The first support plate 4321 is an arc-shaped plate structure, and the arc curvature matches the standard arc curvature of the outer wall of the cylinder to be processed, so that it can fit against the outer wall of the cylinder to achieve support and positioning. The second support plate 4322 is a flat support seat structure, which is evenly arranged and fixed along the circumference of the first support plate 4321. The conformal fixing part 4311 is evenly arranged on the inner side of the arc-shaped plate surface of the first support plate 4321, and the conformal mechanism 431 is arranged in an array along the length direction of the second support plate 4322, so that the support force is even and the deformation during the cylinder processing is reduced.

[0077] Furthermore, to address the issue of poor adaptability of existing fixtures, the positioning rod 42 is a threaded telescopic structure, enabling axial length adjustment. This allows for dynamic adaptation of the rod's total length based on the machining depth of different machining sections of the cylinder and the real-time machining height of the workpiece. The first end 41 and the second end 44 are integrally formed hollow annular plate structures, with the central hollow area directly facing the machining area within the cylinder's inner cavity. This eliminates physical obstructions, freeing up space for material reduction machining within the inner cavity and reducing tool interference. The inner sides of the first end 41 and the second end 44 feature integrally formed annular grooves with outer diameters matching the outer edge dimensions of the cylinder's ends. During machining, the edges of both ends of the cylinder abut against the grooves on either side, achieving axial positioning and preliminary radial limiting of the cylinder.

[0078] Furthermore, mounting holes for mounting positioning rods 42 are provided on the edges of both the first end 41 and the second end 44. Preferably, the mounting holes are elongated adjustment holes. The positioning rods 42 can slide laterally along the elongated adjustment holes to adjust the assembly spacing. After adjustment, they are fixed by end locking bolts. This allows for fine-tuning of the overall assembly span and support position of the fixture according to the diameter, wall thickness, and outer wall assembly dimensions of the cylinder to be processed. This enables the fixture to flexibly adapt to the clamping and positioning requirements of cylinders of different specifications, improving the structural adaptability and versatility of the fixture.

[0079] It is worth noting that when performing material reduction in the inner cavity of the cylinder, this fixture is equipped with two differentiated support modes to specifically reduce clamping deformation defects: For cylinders with a wall thickness ≥3mm, the elastic clamping action of the conforming mechanism 431 is used to make the conforming plate 4314 fit against the outer wall of the cylinder to achieve clamping and fixation, reducing cutting vibration and thermal stress deformation during the material addition and subtraction process; For cylinders with a wall thickness <3mm, the conforming mechanism 431 is contracted, the elastic clamping force is eliminated, and the support is only achieved by the arc-shaped outer tangent of the first support plate 4321 fitting against the outer wall of the cylinder (the positioning rod 42 and the clamping part 43 are both located outside the cylinder and do not interfere with the inner cavity material reduction), replacing point clamping with surface support, reducing clamping stress, reducing cylinder pressure indentation, outer wall deformation, and dimensional deviation problems, adapting to various positioning requirements, and improving the versatility of the device.

[0080] Before actual processing, the length of the positioning rod 42 is first adjusted according to the total length of the processing section. Then, the corresponding number of clamping parts 43 are matched, and the multiple clamping parts 43 are locked and fixed in the corresponding positions of the positioning rod 42 in sequence, so that each clamping part 43 corresponds to a different axial processing section of the cylinder. After the overall assembly of the fixture is completed, the fixture is used to clamp / support the outer wall of the cylinder. The first end 41 and the second end 44 are used to limit and fix the fixture to the processing equipment and the end of the cylinder. During the processing, the elastic extension and contraction characteristics of the spring 4312 drive the movable part 4313 and the conformal plate 4314 to fit the irregular curved surface of the outer wall of the cylinder, compensating for the forming deviation of the cylinder, without the need for repeated manual fine-tuning of the centering.

[0081] Compared with existing technologies, the positioning fixture adopts a multi-component, three-dimensional conformal support structure, which can be adapted to the continuous machining of multi-segment cylindrical bodies with added or subtracted materials. It eliminates the need for frequent disassembly and replacement of fixtures throughout the process, simplifies the clamping process, and improves the overall machining efficiency of large, deep-cavity, thin-walled cylindrical bodies. It adopts a spring-flexible conformal adaptive structure, which can adapt to the irregular curved surface errors of the outer wall of the cylindrical body, ensuring uniform fit and distributed force, and reducing the deformation of thin-walled workpieces during machining. At the same time, it differentiates the support modes based on wall thickness, taking into account both the stability of conventional cylindrical body clamping and the protection of thinner cylindrical body machining, thus improving adaptability and versatility.

[0082] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing by adding or subtracting materials in sections, characterized in that, Includes the following steps: Step 1: Divide the cylinder into sections along the axial direction; Step 2: Determine the number of times materials need to be added or removed based on the number of sections; Step 3: Select the additive manufacturing substrate; Step 4: Blank model design and arc additive manufacturing path planning; Step 5: Select the internal cavity material reduction scheme and cylinder positioning fixture according to the internal cavity structural characteristics of different sections of the cylinder; Step 6: Perform internal cavity feature machining to complete the machining of the cylinder's internal cavity for adding or subtracting materials.

2. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 2, the number of additive manufacturing steps corresponds to the number of cylindrical structural sections.

3. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, Step 3 includes: Step 31: Select a substrate material with properties consistent with the cylinder material; Step 32: Determine the thickness of the partition and allow for rough machining allowance; Step 33: Process a standardized process reference system on the substrate, including reference surfaces, reference holes and locating pin holes, for positioning and reference transfer in all subsequent segment processing; Step 34: In the overall shape finishing stage of the cylinder, the substrate is processed into an integrated process reference boss by utilizing the machining allowance reserved on the substrate.

4. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 5, for narrow and deep cavity areas, a horizontal machining center is selected in conjunction with a high-rigidity extended rod tool for machining, and material reduction is carried out by using segmented cylinder positioning fixtures and integral workpiece cylinder positioning fixtures respectively.

5. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 4, the planned arc additive manufacturing path adopts a composite motion mode that combines circular motion with reciprocating short linear motion.

6. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 1, the structural boundary is based on the position of the inner cavity ribs and the position of the end sealing partition, and the limit depth of the inner cavity that the equipment can process is used as the process constraint. The cylinder is divided into several independent structural process sections along the axial direction.

7. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 6, after each material addition or subtraction process is completed, process benchmark testing and correction are performed.

8. The segmented additive and subtractive material processing and manufacturing method according to claim 1, characterized in that, In step 6, after completing the alternating addition and subtraction of materials for forming, the outer shape of the cylinder is also finished.

9. The segmented additive and subtractive material processing method according to claim 8, characterized in that, symmetrical clamping bosses are added to the front and rear ends of the cylinder. The clamping bosses are used for positioning and machining of the front and rear end face features of the cylinder.

10. The segmented additive and subtractive material processing manufacturing method according to claim 1, characterized in that, During the internal cavity material reduction process, a cylinder positioning fixture is used for clamping.

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