Device and method for milling of complex grid-type ribbed member by precise machining allowance

Abstract

The method uses a device that includes a frame structure with a base plate 1, a positioning plate 6, circumferential positioning adjustment mechanisms 4, and an axial positioning adjustment mechanism

Description

DEVICE AND METHOD FORMILLING OFCOMPLEX GRID-TYPE RIBBED MEMBER BY PRECISE MACHINING ALLOWANCE Field of Invention The present disclosure relates to the technical field of machining of ribbed metal members, and in particular to a device and a method for milling of a complex grid-type ribbed member by precise machining allowance. Background Aluminum alloy grid-type ribbed members, due to their advantages such as strong load capacity and high overall stiffness, are widely used in high-end aerospace equipment such as panels of tanks of launch vehicles and wings of aircrafts. The precision of final dimensions of such aluminum alloy grid-type ribbed members is of critical significance to the safety and reliability of the aerospace equipment. In the formation of such a metal member, a machining allowance is usually left for the purpose of clamping, positioning, etc., and then after the formation, the machining allowance is removed. In the case of an ordinary member, after the formation, the machining allowance can be manually removed using a wire saw, an electric saw, etc.; however, in the case of a large-scale and complex ribbed member, especially grid-type high ribs, the machining allowance cannot be removed manually as above, or such manual removal can lead to low precision, making it impossible to fit the member. For this reason, the present disclosure proposes a method and a device for cutting a machining allowance from a grid-type high-rib panel to achieve precise cutting of machining allowances from large-scale grid-type high-rib panels so as to improve the safety and reliability of equipment. Summary of Invention An objective of the present disclosure is to provide a device for milling of a complex grid-type ribbed member by precise machining allowance to achieve precise cutting of machining allowances from large-scale grid-type high-rib panels so as to improve the safety and reliability of equipment. To achieve the above objective, the present disclosure provides a device for milling of a complex grid-type ribbed member by precise machining allowance. The device includes: a frame structure, a positioning structure, a support structure, and a clamping structure. The frame structure includes a base plate provided thereon with a plurality of transverse plates and a plurality of longitudinal plates that are arranged parallel to one another in a transverse direction and a longitudinal direction, respectively, and the frame structure has a top surface that is a cambered support surface matching a cambered surface of a complex grid-type ribbed member to be machined. The positioning structure includes circumferential positioning adjustment mechanisms located on two sides of the frame structure in the transverse direction, an axial positioning adjustment mechanism located on one of ends of the frame structure in the longitudinal direction, and a positioning plate located on the other one of the ends of the frame structure in the longitudinal direction. The support structure includes support plates provided around a top of the frame structure and a downwardly recessed interference avoidance platform provided at a central position of the cambered support surface, two support plates located on respective ones of the two sides of the frame structure in the transverse direction being each provided with a plurality of adjustable bolts. The clamping structure includes a plurality of clamping assemblies provided on the two sides of the frame structure in the transverse direction, the plurality of clamping assemblies and the plurality of adjustable bolts being arranged in a staggered manner. Further, the base plate, the transverse plates, and the longitudinal plates are each provided with a plurality of lightening holes, the holes on the base plate being arranged avoiding the transverse plates and the longitudinal plates. Further, the frame structure is provided, on respective ones of the two ends in the longitudinal direction, with first support plates, a second support plate parallel to and spaced apart from the first support plate is provided on an near side of the first support plate close to the end on which the axial positioning adjustment mechanisms is located, and two second support plates are connected between the second support plate and the first support plate that is close to the end on which the positioning plate is located. The first support plates, the second support plate, and tops of respective ones of the transverse plates are each provided on both ends thereof with undercuts, all the undercuts being located on a far side of the two third support plates. Further, each of the third support plates is provided with 4 to 6 adjustable bolts that are spaced apart from one another, and the support plates each have a width of 70 to 100 mm. Further, the interference avoidance platform is a platform formed by cutting downward for a depth of 10 to 20 mm from a center point of the cambered support surface. The present disclosure also provides a method for milling of a complex grid-type ribbed member by precise machining allowance. The method is performed by the above described device to cut off a machining allowance from a grid-type ribbed member. The method includes the following steps. S1-Positioning of the member: A complex grid-type ribbed member to be machined is lifted onto the milling device. An end of the member in a length direction is enabled to closely press against the positioning plate using the axial adjustment mechanism. The member is then enabled to be centrosymmetric using the circumferential adjustment mechanisms on the two sides of the device in the transverse direction. S2-Fixing of the member: Metal blocks are placed between the third support plates and an inner molded surface of the member, or the adjustable bolts in the third support plates are adjusted so that the bolts support the inner molded surface of the member. The member is then fixed using the clamping assemblies on the two sides of the device in the transverse direction. After completion of the fixing, a Z coordinate of a top of a central rib and Z coordinates of tops of two side ribs on the member that are arranged symmetrically in the transverse direction are measured using a machine tool. If a difference value between the Z coordinates of the tops of the two side ribs arranged symmetrically in the transverse direction is within 0.5 mm, it indicates that the member is in good position after being clamped and fixed. The positioning plate is removed, and initial flatness of the sides of the member is measured using the machine tool. S3-Rough cutting of the member: A final cutting line is drawn on the member using the machine tool to avoid over-cutting. The member is then roughly cut. Chord length machining allowances of 5 to 10 mm are left on respective ones of two sides during the rough cutting to avoid severe deformation of the member caused by release of residual stress, and meanwhile a plurality of processing structures is left on the two sides of the member in the transverse direction to ensure that the member still has sufficient stiffness during the cutting. After completion of the rough cutting, the clamping assemblies are removed first; then chord lengths of two ends of the member in the length direction are measured using the machine tool; the member is lifted up so that the member is in an upright and free state; and chord lengths of an upper part and a lower part of the member are measured and compared with the chord lengths of the two ends measured on the machine tool. S4-Precise cutting of the member: The member having undergone the rough cutting in S3 is repositioned and re-fixed by repeating steps S1 and S2. The member is precisely cut multiple times by an average chord length method to gradually reduce the machining allowances on the two sides of the member in the transverse direction until the machining allowances on respective sides become 0.2 to 0.5 mm. Finally, light cutting is performed to reduce surface roughness of the member. S5-Flat milling of the lower part: After the precise cutting of the two sides of the member, an end face of the lower part is milled flat. S6-Precision measurement: The processing structures remaining on the two sides of the member in the transverse direction are manually removed. A thickness of the end face of the lower part of the member is measured using an ultrasonic thickness gauge. The member is lifted upright so that the inner molded surface is scanned for precision measurement. Further, in step S1, after completion of the positioning, coordinates of a central rib of the member are measured in an axial direction using the machine tool to check if the central rib is on a straight line. If not, the member is slightly adjusted using the circumferential adjustment mechanisms until a requirement is satisfied. Further, in step S2, clamping is performed simultaneously at symmetrical positions on the two sides of the member in the transverse direction in order to prevent the member from tilting to one side when being clamped and fixed, and a dial indicator is placed at each clamping position when the clamping and fixing is performed, a deformation indicated on the dial indicator being controlled to be within 0.5 mm. Further, in step S4, during first precise cutting, a machining allowance of 0.8 to 1.5 mm is left on each of the two sides of the member in the transverse direction; and after the cutting, the chord lengths of the upper and lower parts of the member are measured on the machine tool; then each time a machining allowance of 0.6 to 1 mm is precisely cut off from each of the two sides of the member in the transverse direction, until the machining allowance on each side becomes 0.2 to 0.5mm. Further, after each cutting, a difference value between the chord lengths of the upper and lower parts is d after each cutting; and after completion of the precise cutting, the chord length of the upper part of the member is a sum of a final target chord length plus half of the difference value d, and the chord length of the lower part of the member is a difference between the final target chord length and half of the difference value d. Compared with the existing technologies, the present disclosure brings the following beneficial effects. (1) The device for milling of a complex grid-type ribbed member by precise machining allowance according to the present disclosure includes three types of positioning structures, namely the positioning plates, the circumferential positioning adjustment mechanisms, and the axial positioning adjustment mechanisms, which, together with the coordinate measurement by the machine tool, realize precise positioning of the member. Further, a high-rib member, due to a large difference between its overall stiffness and local stiffness, is prone to slight over-bending or insufficient bending after being molded, and therefore in the present disclosure, tops of the transverse and longitudinal plates of the device are milled flat. In this way, when a middle portion of the member has large stiffness which leads to small deformation, the middle portion of the member does not interfere with the tops of the transverse and longitudinal plates. The device is provided, on the two sides thereof in the transverse direction, with the third support plates, the third support plates being each provided with bolt holes in each of which an adjustable bolt is provided. When a gap exists between the member and the third support plate, in order to prevent vibration during cutting, the bolts can be adjusted so that top portions of the bolts support the member, or a metal block can be placed between the third support plate and the member. During clamping, in order to prevent the member from deforming seriously or tilting to one of the sides due to clamping, the member is clamped at symmetrical positions simultaneously, and a degree of the deformation due to the clamping is controlled by using a dial gauge. To ensure sufficient stiffness of the member during the cutting, the machining allowance is not completely cut during the cutting, and the processing structures of a certain allowance are left for subsequent manual removal. To facilitate fitting together of the member and other parts, the member is cut by an average chord length method which adopts an average of the chord lengths of the upper and lower parts, so that errors are evenly distributed and do not concentrate at one position. Moreover, chord lengths at different positions of the member on the machine tool after cutting are compared with chord lengths at different positions of the member when the member is in an upright state, a good consistency is found between the two. With the above arrangements, the device of the present disclosure ensures that the chord lengths of the member measured on the machine tool after cutting are consistent with the chord lengths measured when the member is in a free state, and that deformation and swelling due to cutting are eliminated. This is beneficial to subsequent fitting. (2) The device for milling of a complex grid-type ribbed member by precise machining allowance according to the present disclosure is provided with undercuts, so that the cutter of the machine tool does not damage the device during cutting. In addition, the milling device of the present disclosure is provided with a structure compatible with members having different axial lengths, and is therefore suitable for cutting members of different lengths. In addition to the objectives, features, and advantages described above, the present disclosure has other objectives, features, and advantages. The present disclosure will be described in further detail below with reference to the accompanying drawings. Brief Description of Drawings The accompanying drawings are intended to provide a further understanding of the embodiments of the present disclosure and constitute a part of the description. They, together with the specific embodiments below, are intended to explain, rather than limiting the embodiments of the present disclosure. In the accompanying drawings: Fig. 1 is a schematic diagram showing an overall structure of a device for milling of a complex grid-type ribbed member by precise machining allowance in the present disclosure; Fig. 2 is a schematic diagram showing an overall structure of fitting together of a panel and the device in the present disclosure; Figs. 3 (a) and (b) are schematic structural diagrams showing fixing of the panel in the present disclosure, among which (a) is an enlarged structural schematic diagram of section M in Fig. 2, and (b) is a transverse cross-sectional structural schematic diagram of section M in Fig. 2; and Fig. 4 is a schematic diagram showing cutting on two sides of the panel in a transverse direction in the present disclosure (only part is shown). 1-base plate, 2-transverse plate, 3-longitudinal plate, 4-circumferential positioning adjustment mechanism, 5-axial positioning adjustment mechanism, 6-positioning plate, 7-support plate, 7.1first support plate, 7.2-second support plate, 7.3-third support plate, 7a-undercut, 8-interference avoidance platform, 9-adjustable bolt, 10-clamping assembly, 11-processing structure, A-complex grid-type ribbed member, A1l-central rib, A2-side rib. Detailed Description The embodiments of the present disclosure are described in detail below with reference to the accompanying drawings. The present disclosure, however, can be implemented in many different ways as defined and covered by the claims. Referring to Figs. 1 to 4, a device for milling of a complex grid-type ribbed member by precise machining allowance according to an embodiment of the present embodiment includes a frame structure, a positioning structure, a support structure, and a clamping structure. Specific structures are as follows. The frame structure includes a base plate 1, a plurality of transverse plates 2, and a plurality of longitudinal plates 3. The plurality of transverse plates 2 are arranged parallel to one other on the base plate 1 in a transverse direction and the plurality of longitudinal plates 3 are arranged parallel to one other on the base plate 1 in a longitudinal direction. The base plate 1, the transverse plate 2, and the longitudinal plate 3 are each a grid plate provided with a plurality of lightening holes. The holes on the base plate are arranged avoiding the transverse plates 2 and the longitudinal plates 3. The transverse plates and the longitudinal plates provided with the holes are connected by welding. The frame structure has a top surface that is a cambered support surface matching a cambered surface of a complex grid-type ribbed member A to be machined. The positioning structure includes a plurality of circumferential positioning adjustment mechanisms 4 located on two sides of the frame structure in the transverse direction, a plurality of axial positioning adjustment mechanisms 5 located on one of ends of the frame structure in the longitudinal direction, and a plurality of positioning plates 6 located on the other one of the ends of the frame structure in the longitudinal direction. Specifically, the frame structure is provided, on each of the two sides in the transverse direction, with two circumferential positioning adjustment mechanisms 4; and the frame structure is provided, on the one end in the longitudinal direction, with two axial positioning adjustment mechanisms 5, and is provided, on the other end in the longitudinal direction, with three positioning plates 6. The support structure includes support plates 7 provided around a top of the frame structure and a downwardly recessed interference avoidance platform 8 provided at a central position of the cambered support surface (a top of a symmetrical center of the device). Two support plates 7 located on respective ones of the two sides of the frame structure in the transverse direction are each provided with a plurality of adjustable bolts 9. The support plates 7 include first support plates 7.1, a second support plate 7.2, and third support plates 7.3. The frame structure is provided, on respective ones of the two ends in the longitudinal direction, with first support plates 7.1; a second support plate 7.2 parallel to and spaced apart from the first support plate 7.1 is provided on an near side of the first support plate 7.1 close to the end on which the axial positioning adjustment mechanisms 5 is located; and two third support plates 7.3 are connected in the longitudinal direction between the second support plate 7.2 and the first support plate 7.1 close to the end on which the positioning plates 6 are located. In order to avoid damage to the device by a cutter of a machine tool during cutting, the two first support plates 7.1 and the second support plate are each provided on both ends thereof with undercuts 7a, and each of the transverse plates is provided on both ends of a top thereof with undercuts 7a, all these undercuts being located on a far side of the two third support plates 7.3. The clamping structure includes a plurality of clamping assemblies 10 provided on the two sides of the frame structure in the transverse direction. The plurality of clamping assemblies 10 and the plurality of adjustable bolts 9 are arranged in a staggered manner. In a specific embodiment, each of the third support plates 7.3 is provided with 4 to 6 adjustable bolts 9 that are spaced apart from one another, and each of the support plates has a width of 70 to 100 mm. The frame structure is provided, on each of the two sides in the transverse direction, with 5 to 8 clamping assemblies 10, the clamping assemblies on the two sides being arranged symmetrically. The interference avoidance platform 8 is a platform formed by cutting downward for a depth of 10 to 20 mm from a center point of the cambered support surface on the top surface of the frame structure. A method for milling of a complex grid-type ribbed member by precise machining allowance according to an embodiment of the present disclosure uses the above described device to cut off a machining allowance from a grid-type ribbed member. In the present embodiment, the grid-type ribbed member A is specifically a panel. The method includes the following steps. S1-Positioning of the panel: First, the panel to be machined is lifted onto the milling device. An end of the panel in a length direction is adjusted to be closely pressed against the positioning plates 6 using the axial adjustment mechanisms 5. The panel is then adjusted to be centrosymmetric using the circumferential adjustment mechanisms 4 on the two sides in the transverse direction. After the positioning is completed, coordinates of a central rib of the panel are measured in an axial direction using the machine tool to check if the central rib is on a straight line. If not, the panel is slightly adjusted using the circumferential adjustment mechanisms 4 until a requirement is satisfied. This is as shown in Fig. 2. S2-Fixing of the panel: In practice, an inner molded surface on two sides of the molded panel does not contact surfaces of the transverse and longitudinal plates of the device. In order to avoid vibration of the panel during machining, metal blocks are first placed between the third support plates 7.3 and the inner molded surface of the panel, or the adjustable bolts 9 in the third support plates 7.3 are adjusted so that the bolts support the inner molded surface of the panel. The panel is then fixed using the clamping assemblies 10 on the two sides of the device in the transverse direction. In order to prevent the panel from tilting to one side during clamping and fixing, clamping is performed simultaneously at symmetrical positions on the two sides of the panel, and when the clamping and fixing is performed, a dial indicator is placed at the clamping positions so that a deformation indicated on the dial indicator is controlled to be within 0.5 mm. This can achieve tight pressing and can also avoid deformation of the panel due to too much pressing. After the fixing is completed, a Z coordinate of a top of the central rib Al and Z coordinates of tops of two side ribs A2 on the panel that are arranged symmetrically in the transverse direction are measured using the machine tool. If a difference value between the Z coordinates of the two side ribs A2 arranged symmetrically in the transverse direction is within 0.5 mm, it indicates that the panel is in good position after being clamped and fixed. The positioning plates 6 are then removed and initial flatness of the sides of the panel is measured using the machine tool. Specifically, any two side ribs symmetrically arranged on the two sides of the central rib may be selected, and positions on the two side ribs that are located on either side of a beam of the panel and are close to the beam are preferred. S3-Rough cutting of the panel: First, a final cutting line is drawn on the panel using the machine tool to avoid over-cutting. The panel is then roughly cut. Since cutting of the machining allowance on the panel may lead to release of residual stress which can cause severe deformation, a chord length machining allowance of 5 to 10 mm may be left on each side during the rough cutting. To ensure that the panel still has sufficient stiffness during the cutting, a plurality of processing structures 11 having a width of 20 to 50 mm and a thickness of 3 to 10 mm is left on the two sides of the panel, as shown in Figs. 2 and 4. An order of cutting the panel is to first cut the high ribs and then cut a skin. After the rough cutting is completed, the clamping assemblies 10 are first removed, and then chord lengths of the two ends of the panel in the length direction (namely the longitudinal direction of the device) are measured using the machine tool. The panel is then lifted up to be in an upright and free state, and chord lengths of an upper part and a lower part are measured manually using a tape measure. The chord lengths of the upper part and the lower part are compared with the chord lengths of the two ends measured using the machine tool. It is found that the chord lengths measured by the two methods are the same, which indicates that the chord lengths of the panel measured using the machine tool may be used to represent the chord lengths measured in the upright and free state. In this structural arrangement, an end of the panel close to the axial positioning adjustment mechanisms 5 is provided with a lifting lug, which can be used to easily lift the panel up. When the panel is lifted up, an upper end (the end provided with the lifting lug) is called the “upper part”, and a lower end (the end opposite to the lifting lug) is called the “lower part”. Meanwhile, for ease of later description, in steps S4 to S6, the end provided with the lifting lug will continue to be called the upper part, and the other end opposite to the upper part will be called the lower part. During the rough cutting, machining allowances on the two sides of the panel in the transverse direction are intermittently cut using a cutter, and an uncut portion between two adjacent cutting lines is called a “processing structure”. S4-Precise cutting of the panel: The panel having undergone the rough cutting is repositioned and re-fixed by repeating steps S1 and S2. Due to different stiffness in different areas of the complex grid-type ribbed member, after its formation there is a tiny difference value between the chord lengths of the upper and lower parts. In order to facilitate subsequent fitting, the panel is precisely cut multiple times by an average chord length method to gradually reduce the machining allowances on the two sides of the panel in the transverse direction until the machining allowances on respective sides become 0.2 to 0.5 mm. Finally, light cutting is performed to reduce surface roughness of the panel. Specifically, during first precise cutting, a machining allowance of 0.8 to 1.5 mm is left on each of the two sides of the panel in the transverse direction; and after the cutting, the chord lengths of the upper and lower parts of the panel are measured on the machine tool. Thereafter each time a machining allowance of 0.6 to 1 mm is precisely cut off from each of the two sides of the panel in the transverse direction, and chord lengths of the upper and upper parts of the panel are then measured, until the machining allowance on each side becomes 0.2 to 0.5 mm. The difference value between the chord lengths of the upper and lower parts is d after each cutting. After the precise cutting is completed, the chord length of the upper part of the member is a sum of a final target chord length plus half of the difference value d, and the chord length of the lower part of the member is a difference between the final target chord length and half of the difference value d. In a specific embodiment, the final target chord length of the member is 2500 mm. During rough cutting, a chord length allowance of 5 mm is left on each of the left and right sides, and the cutting is performed from the lower part to the upper part. After the rough cutting, the chord length of the lower part is 2510 mm, and the chord length of the upper part is 2513 mm. Precise cutting is then performed using the average chord length method. If, after the rough cutting, it is determined by measurement that the difference value d between the chord lengths of the upper and lower parts is 3 mm, then a final chord length of the lower part to be achieved is 2498.5 mm and a chord length of the upper part to be achieved is 2501.5 mm. During first precise cutting, a chord length allowance of 1 mm is left on each of the left and right sides, and the cutting is performed from the lower part (the 1 mm-allowance is defined here with respect to the 2498.5-mm chord length), in which case the chord lengths after the cutting are 2500.5 mm and 2503.5 mm, respectively, i.e., a target chord length during the first precise cutting is 2502 mm. During second precise cutting, a chord length allowance of 0.3 mm is left on each of the left and right sides, the cutting is performed from the lower part, in which case the chord lengths after the cutting are 2499.1 mm and 2502.1 mm, respectively, i.e., a target chord length during the second precise cutting is 2500.6 mm. Finally, the chord length allowance of 0.3 mm on each side is removed by quick light cutting so that surface roughness is improved and 2498.5 mm and 2501.5 mm are obtained, i.e., the target chord length for light cutting is 2500 mm. In the above precise cutting method, the difference value between the chord lengths of the upper and lower parts after each cutting remains basically the same, namely 3 mm. During the first precise cutting, a machining allowance of 1 mm is left on each of the two sides in the transverse direction; the machining allowances on the two sides of the panel are then gradually reduced by repeated cutting, until the machining allowance on each side becomes 0.3 mm. Before each precise cutting, the difference value between the chord lengths of the upper and lower parts of the panel is d. After each precise cutting, the chord length of the upper part of the panel is the sum of the final target chord length of the panel plus half of the difference value d, and the chord length of the lower part of the panel is the difference between the final target chord length of the panel and half of the difference value d. For example, if the difference value between the chord lengths of the upper and lower parts after rough cutting is 1 mm, then the chord length of the upper part after first cutting is the final target chord length of the panel plus 0.5 mm, and the chord length of the lower part is the final target chord length of the panel minus 0.5mm. S5-Flat milling of an end face of the lower part: After the precise cutting of the two sides of the panel, an end face of the lower part is milled flat. The end face of the lower part is roughly milled first, and then precisely milled with light cutting to ensure that the end face has a thickness that meets a target requirement. Finally, flatness of the end face of the lower part is measured using a dial indicator. S6-Precision measurement: The processing structures remaining on the two sides of the panel in the transverse direction are removed manually. The thickness of the end face of the lower part of the panel is measured using an ultrasonic thickness gauge. The panel is then lifted upright so that the inner molded surface thereof is scanned for precision measurement. The above described is merely preferred embodiments of the present disclosure and is not intended to limit the present disclosure. For a person skilled in the art, various modifications and changes may be made to the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

Claims 1. A device for milling of a complex grid-type ribbed member by precise machining allowance, comprising: a frame structure, a positioning structure, a support structure, and a clamping structure, wherein: the frame structure comprises a base plate (1) provided thereon with a plurality of transverse plates (2) and a plurality of longitudinal plates (3) that are arranged parallel to one another in a transverse direction and a longitudinal direction, respectively; the frame structure has a top surface that is a cambered support surface matching a cambered surface of a complex grid-type ribbed member to be machined; the positioning structure comprises circumferential positioning adjustment mechanisms (4) located on two sides of the frame structure in the transverse direction, an axial positioning adjustment mechanism (5) located on one of ends of the frame structure in the longitudinal direction, and a positioning plate (6) located on the other one of the ends of the frame structure in the longitudinal direction; the support structure comprises support plates (7) provided around a top of the frame structure and a downwardly recessed interference avoidance platform (8) provided at a central position of the cambered support surface, two support plates (7) located on respective ones of the two sides of the frame structure in the transverse direction being each provided with a plurality of adjustable bolts (9); and the clamping structure comprises a plurality of clamping assemblies (10) provided on the two sides of the frame structure in the transverse direction, the plurality of clamping assemblies (10) and the plurality of adjustable bolts (9) being arranged in a staggered manner.

2. The device according to claim 1, wherein the base plate (1), the transverse plates (2), and the longitudinal plates (3) are each provided with a plurality of lightening holes, the holes on the base plate being arranged avoiding the transverse plates (2) and the longitudinal plates (3).

3. The device according to claim 1, wherein: the frame structure is provided, on respective ones of the two ends in the longitudinal direction, with first support plates (7.1); a second support plate (7.2) parallel to and spaced apart from the first support plate (7.1) is provided on an near side of the first support plate (7.1) close to the end on which the axial positioning adjustment mechanisms (5) is located; , and two second support plates (7.3) are connected between the second support plate (7.2) and the first support plate (7.1) that is close to the end on which the positioning plate (6) is located, wherein the two first support plates, the second support plate, and tops of respective ones of the transverse plates are each provided on both ends thereof with undercuts (7a), all the undercuts being located on a far side of the two third support plates (7.3).

4. The device according to claim 3, wherein: each of the third support plates is provided with 4 to 6 adjustable bolts (9) that are spaced apart from one another; and the support plates each have a width of 70 to 100 mm.

5. The device according to claim 1, wherein the interference avoidance platform (8) is a platform formed by cutting downward for a depth of 10 to 20 mm from a center point of the cambered support surface.

6. A method for milling of a complex grid-type ribbed member by precise machining allowance, the method performed by the device according to any one of claims 1 to 5 to cut off a machining allowance from a grid-type ribbed member and comprising the following steps: S1-positioning of the member, which comprises: lifting a complex grid-type ribbed member to be machined onto the milling device; enabling an end of the member in a length direction to closely press against the positioning plate (6) using the axial adjustment mechanism (5); and enabling the member to be centrosymmetric using the circumferential adjustment mechanisms (4) on the two sides of the device in the transverse direction; S2-fixing of the member, which comprises: placing metal blocks between the third support plates (7.3) and an inner molded surface of the member, or adjusting the adjustable bolts (9) in the third support plates (7.3) so that the bolts support the inner molded surface of the member; fixing the member using the clamping assemblies (10) on the two sides of the device in the transverse direction; after completion of the fixing, measuring a Z coordinate of a top of a central rib (Al) and Z coordinates of tops of two side ribs (A2) on the member that are arranged symmetrically in the transverse direction using a machine tool, wherein a difference value between the Z coordinates of the tops of the two side ribs arranged symmetrically in the transverse direction being within 0.5 mm indicates that the member is in good position after being clamped and fixed; and removing the positioning plate (6), and measuring initial flatness of the sides of the member using the machine tool; S3-rough cutting of the member, which comprises: drawing a final cutting line on the member using the machine tool to avoid over-cutting; roughly cutting the member, wherein chord length machining allowances of 5 to 10 mm are left on respective ones of two sides during the rough cutting to avoid severe deformation of the member caused by release of residual stress, and a plurality of processing structures (11) is left on the two sides of the member in the transverse direction to ensure that the member still has sufficient stiffness during the cutting; after completion of the rough cutting, removing the clamping assemblies (10) first, then measuring chord lengths of two ends of the member in the length direction using the machine tool, lifting up the member so that the member is in an upright and free state, measuring chord lengths of an upper part and a lower part of the member, and comparing the chord lengths of the upper part and the lower part with the chord lengths of the two ends measured on the machine tool; S4-precise cutting of the member, which comprises: repositioning and re-fixing the member having undergone the rough cutting in S3 by repeating steps S1 and S2; precisely cutting the member multiple times by an average chord length method to gradually reduce the machining allowances on the two sides of the member in the transverse direction until the machining allowances on respective sides become 0.2 to 0.5 mm; and performing light cutting to reduce surface roughness of the member; SS5-flat milling of an end face of the lower part, which comprises: after the precise cutting of the two sides of the member, milling an end face of the lower part flat; and S6-precision measurement, which comprises: manually removing the processing structures remaining on the two sides of the member in the transverse direction; measuring a thickness of the end face of the lower part of the member using an ultrasonic thickness gauge; and lifting the member upright so that the inner molded surface is scanned for precision measurement.

7. The method according to claim 6, wherein in step S1, after completion of the positioning, coordinates of a central rib (Al) of the member are measured in an axial direction using the machine tool to check if the central rib (Al) is on a straight line, wherein if not, the member is slightly adjusted using the circumferential adjustment mechanisms (4) until a requirement is satisfied.

8. The method according to claim 6, wherein in step S2: clamping is performed simultaneously at symmetrical positions on the two sides of the member in the transverse direction in order to prevent the member from tilting to one side when being clamped and fixed; and a dial indicator is placed at each clamping position when the clamping and fixing is performed, a deformation indicated on the dial indicator being controlled to be within 0.5 mm.

9. The method according to claim 6, wherein in step S4: during first precise cutting, a machining allowance of 0.8 to 1.5 mm is left on each of the two sides of the member in the transverse direction; and after the cutting, the chord lengths of the upper and lower parts of the member are measured on the machine tool; and each time a machining allowance of 0.6 to 1 mm is precisely cut off from each of the two sides of the member in the transverse direction, until the machining allowance on each side becomes 02 to 05 mm.

10. The method according to claim 9, wherein: after each cutting, a difference value between the chord lengths of the upper and lower parts is d after each cutting; and after completion of the precise cutting, the chord length of the upper part of the member is a sum of a final target chord length plus half of the difference value d, and the chord length of the lower part of the member is a difference between the final target chord length and half of the difference value d. Amendments to the Claims have been filed as follows: Claims: I. A method for milling of a complex grid-type ribbed member by precise machining allowance, wherein: the method is performed by a device for milling of a complex grid-type ribbed member by precise machining allowance to cut off a machining allowance from a grid-type ribbed member, the device comprising: a frame structure, a positioning structure, a support structure, and a clamping structure, wherein: the frame structure comprises a base plate (1) provided thereon with a plurality of transverse plates (2) and a plurality of longitudinal plates (3) that are arranged parallel to one another in a transverse direction and a longitudinal direction, respectively; the frame structure has a top surface that is a cambered support surface matching a cambered surface of a complex grid-type ribbed member to be machined; the positioning structure comprises circumferential positioning adjustment mechanisms (4) located on two sides of the frame structure in the transverse direction, an axial positioning adjustment mechanism (5) located on one of ends of the frame structure in the longitudinal direction, and a positioning plate (6) located on the other one of the ends of the frame structure in the longitudinal direction; the support structure comprises support plates (7) provided around a top of the frame structure and a downwardly recessed interference avoidance platform (8) provided at a central position of the cambered support surface, two support plates (7) located on respective ones of the two sides of the frame structure in the transverse direction being each provided with a plurality of adjustable bolts (9); and the clamping structure comprises a plurality of clamping assemblies (10) provided on the two sides of the frame structure in the transverse direction, the plurality of clamping assemblies (10) and the plurality of adjustable bolts (9) being arranged in a staggered manner, wherein: the frame structure is provided, on respective ones of the two ends in the longitudinal direction, with first support plates (7.1); a second support plate (7.2) parallel to and spaced apart from the first support plate (7.1) is provided on a near side of the first support plate (7.1) close to the end on which the axial positioning adjustment mechanisms (5) is located; and two second support plates (7.3) are connected between the second support plate (7.2) and the first support plate (7.1) that is close to the end on which the positioning plate (6) is located, wherein the two first support plates, the second support plate, and tops of respective ones of the transverse plates are each provided on both ends thereof with undercuts (7a), all the undercuts being located on a far side of the two third support plates (7.3); and the method comprises the following steps: S1-positioning of the member, which comprises: lifting a complex grid-type ribbed member to be machined onto the milling device; enabling an end of the member in a length direction to closely press against the positioning plate (6) using the axial positioning adjustment mechanism (5); and enabling the member to be centrosymmetric using the circumferential positioning adjustment mechanisms (4) on the two sides of the device in the transverse direction; S2-fixing of the member, which comprises: placing metal blocks between the third support plates (7.3) and an inner molded surface of the member, or adjusting the adjustable bolts (9) in the third support plates (7.3) so that the bolts support the inner molded surface of the member; fixing the member using the clamping assemblies (10) on the two sides of the device in the transverse direction; after completion of the fixing, measuring a Z coordinate of a top of a central rib (Al) and Z coordinates of tops of two side ribs (A2) on the member that are arranged symmetrically in the transverse direction using a machine tool, wherein a difference value between the Z coordinates of the tops of the two side ribs arranged symmetrically in the transverse direction being within 0.5 mm indicates that the member is in good position after being clamped and fixed; and removing the positioning plate (6), and measuring initial flatness of the sides of the member using the machine tool; S3-rough cutting of the member, which comprises: drawing a final cutting line on the member using the machine tool to avoid over-cutting; roughly cutting the member, wherein chord length machining allowances of 5 to 10 mm are left on respective ones of two sides during the rough cutting to avoid severe deformation of the member caused by release of residual stress, and a plurality of processing structures (11) is left on the two sides of the member in the transverse direction to ensure that the member still has sufficient stiffness during the cutting; after completion of the rough cutting, removing the clamping assemblies (10) first, then measuring chord lengths of two ends of the member in the length direction using the machine tool, lifting up the member so that the member is in an upright and free state, measuring chord lengths of an upper part and a lower part of the member, and comparing the chord lengths of the upper part and the lower part with the chord lengths of the two ends measured on the machine tool; S4-precise cutting of the member, which comprises: repositioning and re-fixing the member having undergone the rough cutting in S3 by repeating steps S1 and S2; precisely cutting the member multiple times by an average chord length method to gradually reduce the machining allowances on the two sides of the member in the transverse direction until the machining allowances on respective sides become 0.2 to 0.5 mm; and performing light cutting to reduce surface roughness of the member; SS5-flat milling of an end face of the lower part, which comprises: after the precise cutting of the two sides of the member, milling an end face of the lower part flat; and S6-precision measurement, which comprises: manually removing the processing structures remaining on the two sides of the member in the transverse direction; measuring a thickness of the end face of the lower part of the member using an ultrasonic thickness gauge; and lifting the member upright so that the inner molded surface is scanned for precision measurement.

2. The method according to claim 1, wherein the base plate (1), the transverse plates (2), and the longitudinal plates (3) are each provided with a plurality of lightening holes, the holes on the base plate being arranged avoiding the transverse plates (2) and the longitudinal plates (3).

3. The method according to claim 1, wherein: each of the third support plates is provided with 4 to 6 adjustable bolts (9) that are spaced apart from one another; and the support plates each have a width of 70 to 100 mm.

4. The method according to claim 1, wherein the interference avoidance platform (8) is a platform formed by cutting downward for a depth of 10 to 20 mm from a center point of the cambered support surface.

5. The method according to claim 1, wherein in step S1, after completion of the positioning, coordinates of a central rib (Al) of the member are measured in an axial direction using the machine tool to check if the central rib (Al) is on a straight line, wherein if not, the member is slightly adjusted using the circumferential positioning adjustment mechanisms (4) until a requirement is satisfied.

6. The method according to claim 1, wherein in step S2: clamping is performed simultaneously at symmetrical positions on the two sides of the member in the transverse direction in order to prevent the member from tilting to one side when being clamped and fixed; and a dial indicator is placed at each clamping position when the clamping and fixing is performed, a deformation indicated on the dial indicator being controlled to be within 0.5 mm.

7. The method according to claim 1, wherein in step S4: during first precise cutting, a machining allowance of 0.8 to 1.5 mm is left on each of the two sides of the member in the transverse direction; and after the cutting, the chord lengths of the upper and lower parts of the member are measured on the machine tool; and each time a machining allowance of 0.6 to 1 mm is precisely cut off from each of the two sides of the member in the transverse direction, until the machining allowance on each side becomes 0.2 to 0.5 mm.

8. The method according to claim 7, wherein: after each cutting, a difference value between the chord lengths of the upper and lower parts is d after each cutting; and after completion of the precise cutting, the chord length of the upper part of the member is a sum of a final target chord length plus half of the difference value d, and the chord length of the lower part of the member is a difference between the final target chord length and half of the difference value d.

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