A sheet metal incremental forming method using a large angle rolling tool head

Abstract

The application relates to a sheet metal incremental forming machining method using a large-angle rolling tool head, which comprises the following steps: obtaining a closed curve track of each layer of machining tracks; obtaining a tangent vector of each track point according to the coordinates of each track point in a workpiece coordinate system; obtaining a normal direction vector of each track point according to the obtained tangent vector; determining the x direction of the track point coordinate system in the direction of the obtained normal direction vector, constructing the track point coordinate system by taking the direction perpendicular to the sheet metal in the workpiece coordinate system as the z direction of the track point coordinate system, and obtaining a rotation matrix of the track point coordinate system relative to the workpiece coordinate system; obtaining Euler angles of each track point coordinate system relative to the work coordinate system according to the rotation matrix; and controlling the movement of the large-angle rolling tool head according to the coordinate values of each track point in a tool coordinate system and the obtained Euler angles, and machining the sheet metal. The method has high applicability and low control difficulty.

Description

Technical Field

[0001] This invention relates to the field of plastic forming technology, and more specifically to a method for progressive forming of sheet metal using a large-angle rolling tool head. Background Technology

[0002] The statements herein provide only background information in relation to this invention and do not necessarily constitute prior art.

[0003] Incremental forming of sheet metal is a flexible processing method for forming three-dimensional curved surfaces of sheet metal. It features flexible forming methods, good forming performance, and high flexibility, making it particularly suitable for the production and processing of single-piece and small-batch sheet metal products, and enabling digital manufacturing. Incremental forming utilizes a three-dimensional digital model of the target component to directly manufacture prototypes, greatly reducing the cycle from design to production, and offering many advantages in manufacturing sheet metal parts.

[0004] Typically, the tool head used in incremental forming is a fixed, integral tool head with a spherical end. During forming, the tool head and the sheet metal are in a state of sliding friction, which easily leads to wear on the tool head surface, resulting in decreased forming accuracy, increased forming force, and scratches on the surface of the formed part. To address this, patent application CN101758135A proposes a rolling tool head for incremental forming, replacing sliding with rolling in the process, thus overcoming the aforementioned defects. However, during processing, the sidewalls of the ball bearing sleeve rub against the sheet metal. Patent application CN102581108A proposes a large-angle incremental forming rolling tool head and forming method, which solves this problem to some extent. However, the above processing methods rely on controlling the relationship between the spindle revolution speed and the tool holder rotation speed for trajectory planning, which is difficult to adapt to abrupt changes such as corners and edges, and increases the difficulty of spindle control. Summary of the Invention

[0005] In view of the shortcomings of the existing technology, the purpose of this invention is to provide a sheet metal progressive forming process using a large-angle rolling tool head, which overcomes the defects of the existing processing method that uses the spindle speed control method for path planning.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0007] Embodiments of the present invention provide a method for progressive forming of sheet metal using a large-angle rolling tool head, comprising the following steps:

[0008] Obtain the closed curve trajectory of each layer's processing path;

[0009] The tangent vector of each trajectory point is obtained based on the coordinates of each trajectory point in the workpiece coordinate system.

[0010] The normal direction vector of each trajectory point is obtained from the tangent vector.

[0011] The x-direction of the trajectory point coordinate system is determined by the direction of the normal direction vector. The z-direction of the workpiece coordinate system is used as the z-direction of the trajectory point coordinate system to construct the trajectory point coordinate system, and the rotation matrix of the trajectory point coordinate system relative to the workpiece coordinate system is obtained.

[0012] The Euler angles of each trajectory point relative to the working coordinate system are obtained from the rotation matrix;

[0013] The large-angle rolling tool head is controlled to process the sheet metal by using the coordinates of each trajectory point in the tool coordinate system and the obtained Euler angles.

[0014] Optionally, when processing sheet metal, the large-angle rolling tool head returns to the starting point of the closed curve trajectory and continues to move along the closed curve trajectory for a set distance.

[0015] Optionally, for each layer of the processing trajectory, a clustering algorithm is used to cluster the processing trajectory to obtain one or more closed curve trajectories.

[0016] Optionally, during processing, the large-angle rolling tool head moves in opposite directions along the closed curve trajectory of adjacent layers.

[0017] Optionally, for each closed curve trajectory, first obtain the centroid of the convex hull of the closed curve trajectory, then calculate the centroid vector of each trajectory point toward the centroid of the convex hull, and determine the x-direction orientation of the trajectory point coordinate system based on the orientation relationship between the centroid vector and the normal direction vector.

[0018] Optionally, if the length of the closed curve trajectory in the current layer is greater than the length of the closed curve trajectory in the next layer, then the centroid vector and the normal direction vector are in opposite directions, and the x-direction of the trajectory point coordinate system is in opposite directions to the normal direction vector; otherwise, they are the same.

[0019] Optionally, the tangent vector of the trajectory point can be cross-producted with the z-direction vector of the working coordinate system to obtain the normal direction vector of the trajectory point.

[0020] Optionally, the large-angle rolling tool head includes a tool holder, with a ball screw embedded at the bottom end of the tool holder at a set acute angle to the axis of the tool holder. A ball sleeve is threaded to the bottom end of the ball screw, and a shaped ball head is embedded at the bottom end of the ball sleeve. Multiple balls are provided between the shaped ball head and the spherical surface at the bottom end of the ball screw.

[0021] Optionally, the ball screw has a fixing part and a screw part. The fixing part is embedded in the mounting groove at the bottom of the tool holder, and the screw part is threadedly connected to the ball sleeve. The fixing part has a lubricating oil channel. One end of the lubricating oil channel extends to the end face of the fixing part, and the other end extends to the circumferential surface of the screw part. The tool holder has a lubricating oil filling hole that communicates with the lubricating oil channel.

[0022] Optionally, a set screw is threaded onto the tool holder, and the set screw contacts the fixing part, pressing the fixing part into the mounting groove.

[0023] The beneficial effects of this invention are as follows:

[0024] 1. The forming method of the present invention controls the movement of the large-angle rolling tool head according to the coordinate value of each trajectory point in the tool coordinate system and the obtained Euler angles to process the sheet metal. The Euler angles are used to plan the path, which meets the processing requirements of abrupt changes such as edges and corners, improves the universality of trajectory planning, reduces the control difficulty, and overcomes the defects of trajectory planning by controlling the spindle speed.

[0025] 2. In the processing method of the present invention, when processing sheet metal, the large-angle rolling tool head returns to the starting point of the closed curve trajectory and continues to move along the closed curve trajectory for a set distance, which avoids the defects of tool marks and non-closed trajectories of each layer, and ensures the processing quality. Attached Figure Description

[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0027] Figure 1 This is a flowchart of the processing method of Embodiment 1 of the present invention;

[0028] Figure 2 This is a schematic diagram of the tool machining trajectory in Embodiment 1 of the present invention;

[0029] Figure 3 This is a schematic diagram of the trajectory point coordinate system and the workpiece coordinate system in Embodiment 1 of the present invention;

[0030] Figure 4 This is a schematic diagram of the trajectory point coordinate system of Embodiment 1 of the present invention;

[0031] Figure 5 This is a schematic diagram of the large-angle rolling tool head of Embodiment 1 of the present invention;

[0032] Figure 6 This is a schematic diagram of the ball-core screw in Embodiment 1 of the present invention;

[0033] Among them, 1. tool holder, 2. set screw, 3. ball screw, 4. ball sleeve, 5. ball, 6. shaped ball head; 3-1. first channel section, 3-2. second channel section. Detailed Implementation

[0034] Example 1

[0035] This embodiment provides a method for machining sheet metal using a large-angle rolling tool head, such as... Figure 1 As shown, it includes the following steps:

[0036] Step 1: Obtain the closed curve trajectory of each layer's processing trajectory.

[0037] Specifically: The model of the target product is input into UG software, and the forward and reverse hybrid strategy in UG software is used to generate the tool path for each layer, that is, the tool head moves in opposite directions in the adjacent two layers of the machining path.

[0038] The method for generating the tool path can be achieved using existing technology, and will not be described in detail here.

[0039] like Figure 2 As shown, for the tool machining trajectory of each layer, the DBSCAN clustering algorithm is used to cluster the tool machining trajectory of each layer, so that the tool machining trajectory of each layer is one or more closed curve trajectories, which facilitates subsequent trajectory planning.

[0040] Step 2: For each layer of closed curve trajectory, first calculate the centroid of the convex hull of the closed curve trajectory, and then calculate the centroid vector m of each trajectory point on the closed curve trajectory toward the centroid of the convex hull. i The calculation methods for the convex hull centroid and centroid vector can be carried out using existing technologies, and will not be described in detail here.

[0041] Step 3: After determining the closed curve trajectory, the software can automatically obtain the coordinates (x, y, y) of multiple trajectory points on the closed curve trajectory relative to the workpiece coordinate system. i y i z i The tangent vector n for each trajectory point is obtained by using the coordinates of the trajectory points. i That is, among two adjacent trajectory points, trajectory point A i+1 Coordinates minus point A i The coordinates.

[0042] Step 4: Convert the tangent vector n of each trajectory point i The normal direction vector q of the trajectory point is calculated by cross product with the z-direction vector (0, 0, 1) of the workpiece coordinate system. i

[0043] Step 5: As Figures 3-4As shown, a coordinate system for the trajectory points is constructed, wherein the x-axis of the coordinate system is parallel to the normal direction vector of the trajectory points, and the orientation of the x-axis, i.e., the x-direction, is either opposite to or the same as the direction of the normal direction vector.

[0044] Specifically:

[0045] If the length of the closed curve trajectory in the current i-th layer is greater than the length of the closed curve trajectory in the next i+1-th layer, then the centroid vector and the normal direction vector are in opposite directions (i.e., the angle between the normal direction vector and the centroid vector is obtuse). In this case, the x-direction of the trajectory point coordinate system is opposite to the direction of the normal direction vector; otherwise, they are the same.

[0046] In the trajectory point coordinate system, the z-axis is parallel to the z-axis in the workpiece coordinate system, and the z-direction is the same as the z-direction in the workpiece coordinate system.

[0047] The y-axis of the trajectory point coordinate system is perpendicular to both the x-axis and z-axis. The y-direction vector of the trajectory point coordinate system is obtained by using the cross product of the x-axis direction vector and the z-axis direction vector.

[0048] Step 6: After obtaining the coordinate system of the trajectory points, calculate the rotation matrix R of the trajectory point coordinate system relative to the workpiece coordinate system. i .

[0049]

[0050] Where n x n y n z These are the cosine values ​​of the angles between the x-axis of the trajectory point coordinate system and the x, y, and z-axis of the working coordinate system, respectively. x o y o z Let a be the cosine of the angle between the y-axis of the trajectory point coordinate system and the x, y, and z-axis of the working coordinate system. x a y a z These are the cosine values ​​of the angles between the z-axis of the trajectory point coordinate system and the x, y, and z-axis of the working coordinate system, respectively.

[0051] The specific calculation method for the above rotation matrix can be achieved using existing technology, and will not be described in detail here.

[0052] Step 6: Calculate the Euler angles of each trajectory point relative to the working coordinate system.

[0053] Wherein, the Euler angle θ about the y-axis of the working coordinate system is -arcsin(n z )

[0054] Euler angle φ about the x-axis of the working coordinate system = arctan2(o z az )

[0055] Euler angles about the z-axis of the working coordinate system

[0056] If cos(θ) = 0;

[0057] Then φ = 0, or

[0058] The arctan2 function is an existing function and will not be described in detail here.

[0059] Step 7: Generate a G-code file from the calculated trajectory point data, which contains the coordinate values ​​of each trajectory point in the workpiece coordinate system and Euler angle information. During processing, the large-angle rolling tool head is controlled by the G-code file to move according to the set trajectory posture to process the sheet metal.

[0060] The above-mentioned technologies can be achieved using existing technologies, and will not be described in detail here.

[0061] like Figure 2 As shown, during sheet metal processing, defects such as non-closed trajectories at the cutting point may occur due to sheet metal springback and other factors. Therefore, for each closed curve trajectory, the large-angle rolling tool head returns to the starting point of the closed curve trajectory and continues to move along the closed curve trajectory a set distance to the ending point, forming an overlapping trajectory. This avoids cutting marks and defects such as non-closed trajectories at the cutting point, ensuring processing quality.

[0062] In this embodiment, as Figures 5-6 As shown, the large-angle rolling tool head includes a tool holder 1. The bottom of the tool holder 1 is provided with a mounting groove, in which a ball screw 3 is embedded. The axis of the ball screw 3 forms a set acute angle with the axis of the tool holder 1. In this embodiment, the ball screw 3 includes a fixing part and a screw part fixed to the bottom end of the fixing part. The fixing part is embedded in the mounting groove. The tool holder is threadedly connected with a set screw 2. The set screw 2 contacts the fixing part and presses the fixing part into the mounting groove. The outer circumference of the screw part is threadedly connected with a ball sleeve 4. The bottom end of the ball sleeve 4 is provided with a spherical groove. A shaped ball head 6 is embedded in the spherical groove. The shaped ball head 6 is slidably connected to the spherical groove so that the shaped ball head can roll freely. Multiple balls 5 are provided between the shaped ball head and the spherical surface at the bottom end of the ball screw 3. Rolling friction is used instead of sliding friction, which reduces the wear phenomenon on the surface of the shaped ball head 6 and ensures the machining accuracy.

[0063] The ball screw 3 is also provided with a lubricating oil channel, which includes a first channel section 3-1 and a second channel section 3-2 vertically disposed at the end of the first channel section 3-1. One end of the first channel section extends to the top surface of the fixing part, and the other end is vertically connected to one end of the second channel section. The other end of the second channel section extends to the circumferential surface of the screw part. Correspondingly, the tool holder is provided with a lubricating oil filling port that communicates with the first channel section.

[0064] In this embodiment, the forming ball head 6 and the ball are made of high-quality standard bearing balls, which are required to have high precision and high hardness. The ball sleeve 4 that holds the ball is required to have a hardness of 40HRC.

[0065] The tool holder 1 needs to be adjusted to a hardness of 28HRC, with a circular cross-section and a flat top that connects to the chuck on the progressive forming robot. The other end is used to fix the ball screw. The surface of this end is reinforced, resulting in high hardness and wear resistance.

[0066] Set screw 2 uses a standard screw, which is easy to purchase and has a low replacement cost.

[0067] Lubricating oil is injected from the lubricating oil filling port in the middle of the tool holder, flows out along the lubricating oil channel of the ball screw 3, and flows into the ball sleeve 5 along the thread of the lower half of the ball screw 3, achieving lubrication between the ball, the shaped ball head 6 and the spherical surface of the ball screw 3.

[0068] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for progressive forming of sheet metal using a large-angle rolling tool head, characterized in that, Includes the following steps: Obtain the closed curve trajectory of each layer's processing path; The tangent vector of each trajectory point is obtained based on the coordinates of each trajectory point in the workpiece coordinate system. The normal direction vector of each trajectory point is obtained from the tangent vector. The normal direction vector of the trajectory point is obtained by cross-product of the tangent vector of the trajectory point and the z-direction vector of the workpiece coordinate system. The x-direction of the trajectory point coordinate system is determined by the direction of the normal direction vector. For each closed curve trajectory, the centroid of the convex hull of the closed curve trajectory is first obtained, and then the centroid vector of each trajectory point toward the centroid of the convex hull is calculated. The orientation of the trajectory point coordinate system x-direction is determined according to the orientation relationship between the centroid vector and the normal direction vector. Construct the trajectory point coordinate system using the z-direction of the workpiece coordinate system as the z-direction of the trajectory point coordinate system; if the length of the current i-th layer closed curve trajectory is greater than the length of the next i+1 layer closed curve trajectory, then the centroid vector and the normal direction vector are opposite in direction, and the x-direction of the trajectory point coordinate system and the normal direction vector are opposite in direction, otherwise they are the same; And obtain the rotation matrix of the trajectory point coordinate system relative to the workpiece coordinate system; The Euler angles of each trajectory point relative to the workpiece coordinate system are obtained based on the rotation matrix; the large-angle rolling tool head movement is controlled based on the coordinate values ​​of each trajectory point in the tool coordinate system and the obtained Euler angles to process the sheet metal; When processing sheet metal, the large-angle rolling tool head returns to the starting point of the closed curve trajectory and continues to move along the closed curve trajectory for a set distance; during processing, the movement direction of the large-angle rolling tool head along the closed curve trajectory of adjacent layers is opposite; the large-angle rolling tool head includes a tool holder, and a ball screw with a set acute angle to the axis of the tool holder is embedded at the bottom end of the tool holder; The ball screw is also provided with a lubricating oil channel, which includes a first channel section and a second channel section vertically disposed at the end of the first channel section. The tool holder is provided with a lubricating oil filling port that communicates with the first channel section.

2. The sheet metal progressive forming method using a large-angle rolling tool head as described in claim 1, characterized in that, For each layer of the processing trajectory, a clustering algorithm is used to cluster the processing trajectory to obtain one or more closed curve trajectories.

3. The sheet metal progressive forming method using a large-angle rolling tool head as described in claim 1, characterized in that, The bottom end of the ball screw is threaded with a ball sleeve, and a shaped ball head is embedded in the bottom end of the ball sleeve. Multiple balls are provided between the shaped ball head and the spherical surface at the bottom end of the ball screw.

4. The sheet metal progressive forming method using a large-angle rolling tool head as described in claim 3, characterized in that, The ball screw has a fixing part and a screw part. The fixing part is embedded in the mounting groove at the bottom of the tool holder. The screw part is threadedly connected to the ball sleeve. The fixing part has a lubricating oil channel. One end of the lubricating oil channel extends to the end face of the fixing part and the other end extends to the circumferential surface of the screw part. The tool holder has a lubricating oil filling hole that communicates with the lubricating oil channel.

5. The sheet metal progressive forming method using a large-angle rolling tool head as described in claim 3, characterized in that, The tool holder is threaded with a set screw, which contacts the fixing part and presses the fixing part into the mounting groove.

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