Additive and subtractive manufacturing method for sharp corner features

Abstract

The present application belongs to the technical field of 3D printing, and relates to a kind of additive and subtractive manufacturing methods for sharp corner features, comprising: 1) obtaining three-dimensional model slices, and dividing the slice profile of three-dimensional model slices into an outer contour and an inner hole;2) respectively in the outer contour and the inner hole obtained in step 1) sharp corner feature recognition is carried out;3) according to the identified sharp corner feature, a subtractive path for superfast laser subtractive operation is generated;4) combining the subtractive path obtained in step 3) and the additive path obtained from the slice profile for laser additive operation to obtain the printing path of the three-dimensional model slice;5) execute the printing path, complete the additive and subtractive manufacturing of the sharp corner feature containing. The present application provides an additive and subtractive manufacturing method for sharp corner features to ensure the geometric accuracy and forming quality of 3D printing.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of 3D printing, and relates to a subtractive and additive forming printing method, in particular to a subtractive and additive manufacturing method for sharp corner features. BACKGROUND

[0002] The selective laser melting additive manufacturing technology (SLM) is an advanced manufacturing technology that uses laser as a heat source, slices a three-dimensional model, and is driven by a filling path from bottom to top and layer by layer. A slice contour is obtained by slicing a three-dimensional model, and a large number of sharp corner features (defined as sharp corner features when the included angle of two adjacent line segments is less than 60 degrees) exist in the slice contour. Due to the inherent characteristics of laser forming, the sharp corners are often formed into fillets at the inflection points, and the smaller the included angle, the larger the corresponding arc at the inflection point, which affects the final forming quality.

[0003] At present, the forming error at the sharp corner is mainly eliminated through finishing after printing, but this method is low in efficiency, and additional labor cost and time cost are needed. For example, in the invention application with the application number 2021100033700.6, a laser additive and subtractive manufacturing method for large-size sandwich straight groove ring-shaped components is disclosed. A three-dimensional model suitable for laser melting deposition forming and laser cutting subtractive manufacturing of large-size sandwich straight groove ring-shaped components is established. Laser melting deposition forming process parameters and laser cutting subtractive manufacturing process parameters in the slice software platform are set. The growth direction is determined, and the three-dimensional model of the large-size sandwich straight groove ring-shaped component is placed and imported into the slice software platform which has been set to perform slice processing. The additive and subtractive manufacturing is performed under the protection of inert gas. After the forming is completed, the powder in the cabin is recovered, and the unseparated ring-shaped component and the substrate are annealed. The substrate and the ring-shaped part are separated by using wire cutting. The ring-shaped component is finally heat treated. The large-size sandwich straight groove ring-shaped component obtained by the application has high performance, low surface roughness and high forming precision, and provides a new method for the final manufacturing of large-size sandwich straight groove ring-shaped components. For another example, in the invention application with the application number 201910712621.5, a near-net forming method for fine workpieces based on laser additive and subtractive composite manufacturing is disclosed. The three-dimensional model is generated by software to generate the construction parameters of the slice layer, and laser additive processing is performed. In the laser additive processing process, ultrafast pulse laser subtractive processing is alternately performed to form a three-dimensional entity. The device includes a computer control device, a sealed forming chamber, an optical path selection system and an inert gas protection gas source. During additive processing, the computer control device controls the optical path selection system to select the laser of the additive laser emitter for laser additive processing. During subtractive processing, the optical path selection system controls the optical path selection system to select the ultrafast pulse laser of the subtractive laser emitter for ultrafast pulse laser subtractive processing.

[0004] However, ultrafast lasers have the characteristics of extremely short pulse width, extremely high peak power and extremely wide frequency range. They have many excellent properties in micromachining that traditional processes do not have. Using ultrafast lasers for fine processing of certain special structures in SLM technology will help to improve the overall forming accuracy of components. Summary of the Invention

[0005] In order to solve the above technical problems existing in the background technology, the present invention provides an additive and subtractive manufacturing method for sharp-angle features that ensures the geometric accuracy and molding quality of 3D printing.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A method for additive and subtractive manufacturing of sharp-angle features, characterized in that the method comprises the following steps:

[0008] 1) Obtaining a 3D model slice, and dividing the slice contour of the 3D model slice into an outer contour and an inner hole;

[0009] 2) identifying sharp corner features in the outer contour and inner hole obtained in step 1);

[0010] 3) generating a subtractive path for ultrafast laser subtractive operation based on the identified sharp corner features;

[0011] 4) combining the subtractive path obtained in step 3) and the additive path for laser additive operation obtained from the slice profile to obtain a printing path for the 3D model slice;

[0012] 5) Execute the printing path to complete the additive and subtractive manufacturing of sharp-angle features.

[0013] The above step 1) is specifically as follows: reading the binary STL model, performing equal thickness slicing operations, extracting the slice contours of each layer separately to obtain the slice contours of different layers, dividing the slice contours of each layer into multiple single-connected areas, and dividing the contour of each single-connected area into an outer contour and an inner hole.

[0014] The above step 2) is specifically as follows: in the outer contour and inner hole of each single-connected area obtained in step 1), traverse each point in the inner hole and the outer contour, calculate the angle between the vector formed by the current point and the previous reference point and the vector formed by the next reference point, and when the angle is less than or equal to the set value, treat the front and rear edges of the point as a sharp corner feature, and so on, to identify all sharp corner features in the inner hole and the outer contour.

[0015] The setting value in step 2) above is 60°.

[0016] In the step 2), when the current point is the first profile point, the last profile point of the inner hole or the outer profile is taken as the previous reference point; when the current point is the last profile point, the first profile point in the inner hole or the outer profile is taken as the next reference point.

[0017] The step 3) is specifically:

[0018] 3.1) respectively judge whether the previous and next two adjacent points of the current sharp corner feature point are sharp corner feature points, if the adjacent points are not sharp corner feature points, the extension length remains unchanged and is still the preset value; if the adjacent points are also sharp corner feature points, the extension length is corrected to 1 / 2 of the preset value;

[0019] 3.2) calculate the line segment length of the current point and the previous reference point to obtain the final subtractive path, when the line segment length is less than or equal to the extension length, judge whether the extension length exceeds half of the line segment length, if yes, take half of the line segment length as the subtractive path; when the line segment length is greater than the extension length, the subtractive path is a line segment with the extension length from the current point to the previous adjacent point.

[0020] The step 3.2) further includes:

[0021] 3.3) according to the ultrafast laser spot radius length, the subtractive path obtained in the step 3.2) is outwardly offset to be the final subtractive path.

[0022] In the step 4), the scanning direction of the subtractive path is opposite to the scanning direction of the additive path.

[0023] In the step 4), the scanning mode of the printing path is a raster scanning path, a reciprocating straight line path or a composite path.

[0024] The step 5) is specifically: the additive path is used to perform additive manufacturing by laser, after the additive manufacturing is completed, the subtractive path is used to perform subtractive manufacturing by ultrafast laser, and the additive and subtractive manufacturing containing the sharp corner feature is completed.

[0025] The advantages of the present application are:

[0026] In order to eliminate the influence of sharp corners on the forming quality, the application proposes a kind of additive and subtractive collaborative printing method for modifying special profile features by ultrafast laser, firstly, the sharp corner recognition method in the method can obtain all special structures of a slice profile, and after obtaining these special structures, the additive path can be modified as well as the subtractive path is generated; after obtaining the subtractive path by the method, after the additive process of the current layer is completed, the ultrafast laser is used for subtractive operation on these features, which can improve the forming precision and forming quality of the part at the sharp corner, and saves the production time and labor cost. The application can integrally complete the preparation of complex and fine structure parts with high precision, and overcome the technical difficulties of low forming precision, high roughness and inability to prepare fine and complex internal cavity of traditional laser additive manufacturing. DETAILED DESCRIPTION

[0027] The application mainly identifies the sharp corner features in the slice profile, and performs subtractive operation on the sharp corner feature area by ultrafast laser to achieve the expected geometric precision and forming quality. Firstly, the three-dimensional model equal-thickness layering algorithm is used to obtain the slice profile of each layer, the slice profile of each layer is divided into a plurality of single-connected regions, the profile of each single-connected region is divided into an outer contour and an inner hole, then the sharp corner feature recognition is performed on the outer contour and the inner hole, and the identified sharp corner features are saved in a specific data structure, the identified sharp corner features are converted into subtractive paths according to the counterclockwise scanning order of the outer contour path or the clockwise scanning order of the inner hole, then the additive path planning is performed on the slice profile, and the machining path for subtractive operation by ultrafast laser and the printing path required by laser additive are obtained. In the actual additive process, firstly, the laser is used for the additive process of the current layer, then the ultrafast laser is used for the subtractive process, and finally the post-processing is adopted to achieve the final forming quality.

[0028] The detailed implementation process of the method is as follows:

[0029] 1. Three-dimensional model slicing: firstly, read the binary STL model, perform equal-thickness slicing operation according to the interface input slice height, extract the slice profile of each layer for processing. Divide the slice profile of each layer into a plurality of single-connected regions, and divide the profile of each connected region into an outer contour and an inner hole to prepare data for the next sharp corner recognition process.

[0030] 2. Sharp corner recognition: sharp corner recognition is performed in the outer contour and inner hole of each single communication area, respectively. Each point in the inner hole and outer contour is traversed, and the included angle between the vector formed by the current point and the previous reference point and the vector formed by the next reference point is calculated. When the included angle is less than or equal to a set value (the set value is set according to experience, the accuracy requirement of the printed part, etc., and can be 60°, for example), the front and back edges of the point are taken as a sharp corner feature, and the same is done in turn to obtain all the sharp corner features in the inner and outer contours. Then subtractive path is generated from the sharp corner feature, and the detailed recognition process is as follows:

[0031] 2.1) Take each point in the contour to make the following judgment;

[0032] 2.2) Take the previous reference point and the next reference point of the current point to be judged to make the following judgment. If the current reference point is the first contour point, take the last point as the previous reference point. If the current point is the last contour point, take the first point in the contour as the next reference point.

[0033] 2.3) Calculate the included angle of the vectors formed by the current point and the two reference points. When the included angle is less than the set value, the next step of generating subtractive path is executed, otherwise the next contour point is judged until each point in the inner and outer contours is traversed.

[0034] 3. Generation method of subtractive path

[0035] 3.1) Judge whether the previous and next two adjacent points of the current sharp corner feature point are sharp corner feature points (take the previous adjacent point as an example, the latter is the same): if the previous adjacent point is not a sharp corner feature point, the extension length (the path extension length is the length of the subtractive path from the vertex to the front and back edges of the vertex) remains unchanged and is still the preset value; if the current adjacent point is also a sharp corner feature point, the extension length is corrected to 1 / 2 of the preset value; the preset value is the user input value.

[0036] 3.2) Calculate the length of the line segment of the current point and the previous point to obtain the final subtractive path: when the line segment length is less than or equal to the extension length, judge whether the extension length exceeds half of the line segment length. If it does, take half of the line segment length as the subtractive path; when the line segment length is greater than the extension length, the subtractive path is a line segment with the extension length from the current point to the previous adjacent point; the extension length refers to the length of the subtractive path from the vertex to the front and back edges of the vertex.

[0037] 3.3) Actual printing of subtractive path output, offset the subtractive path obtained in the previous step by a certain distance outward as the final subtractive path. Because the obtained forming track has a certain width in actual printing, the outward offset distance is taken as the length of the subtractive laser spot radius. This step can avoid the forming precision error caused by excessive subtractive material.

[0038] 4. Print path generation: Path planning is performed on the slice contour obtained by slicing. The path planning method mainly uses three ways of raster scan path, reciprocating straight line path and compound path. After identifying the sharp corners, they are converted into subtractive paths. The sharp corners on the outer contour are output in counterclockwise direction, and the sharp corner features on the inner contour are output in clockwise direction as subtractive paths.

[0039] 5. Additive and subtractive implementation sequence: After obtaining all the data, the additive process of the current layer is performed first, and then the subtractive process is performed according to the generated subtractive path for the identified sharp corner feature area.

Claims

1. A method for additive and subtractive manufacturing of sharp corner features, characterized by: The additive and subtractive manufacturing method for sharp corner features comprises the following steps: 1) Obtaining a 3D model slice, and dividing the slice contour of the 3D model slice into an outer contour and an inner hole; 2) identifying sharp corner features in the outer contour and inner hole obtained in step 1); 3) generating a subtractive path for ultrafast laser subtractive operation based on the identified sharp corner features; 4) combining the subtractive path obtained in step 3) and the additive path for laser additive operation obtained from the slice profile to obtain a printing path for the 3D model slice; 5) Execute the printing path to complete additive and subtractive manufacturing; The step 1) specifically comprises: reading a binary STL model, performing a slice operation of equal thickness, extracting the slice contours of each layer respectively to obtain the slice contours of different layers, dividing the slice contours of each layer into multiple single-connected areas, and dividing the contour of each single-connected area into an outer contour and an inner hole; Specifically, step 2) includes traversing each point in the inner hole and outer contour of each single-connected area obtained in step 1), calculating the angle between the vector formed by the current point and the previous reference point and the vector formed by the next reference point. When the angle is less than or equal to the set value, the front and rear edges of the point are regarded as a sharp corner feature, and so on, to identify all sharp corner features in the inner hole and outer contour.

2. The additive and subtractive manufacturing method for sharp corner features according to claim 1, characterized in that: The setting value of step 2) is 60°.

3. The additive and subtractive manufacturing method for sharp corner features according to claim 2, characterized in that: When traversing each point in the inner hole and the outer contour in step 2), when the current point is the first contour point, the last contour point of the inner hole or the outer contour is taken as the previous reference point; when the current point is the last contour point, the first contour point in the inner hole or the outer contour is taken as the next reference point.

4. The additive and subtractive manufacturing method for sharp corner features according to claim 3, characterized in that: The step 3) is specifically: 3.1) Determine whether the two adjacent points before and after the current sharp corner feature point are sharp corner feature points. If the adjacent points are not sharp corner feature points, the extension length remains unchanged at the preset value; if the adjacent points are also sharp corner feature points, the extension length is corrected to 1 / 2 of the preset value; 3.2) Calculate the length of the line segment between the current point and the previous reference point to obtain the final subtractive path. If the line segment length is less than or equal to the extended length, determine whether the extended length exceeds half the line segment length. If so, take half the line segment length as the subtractive path. If the line segment length is greater than the extended length, the subtractive path is the line segment from the current point to the previous adjacent point equal to the extended length.

5. The additive and subtractive manufacturing method for sharp corner features according to claim 4, characterized in that: The step 3.2) further includes: 3.3) The subtractive path obtained in step 3.2) is offset outward according to the length of the ultrafast laser spot radius to obtain the final subtractive path.

6. The additive and subtractive manufacturing method for sharp corner features according to any one of claims 1 to 5, characterized in that: In step 4), the scanning direction of the subtractive path is opposite to the scanning direction of the additive path.

7. The additive and subtractive manufacturing method for sharp corner features according to claim 6, characterized in that: The scanning mode of the printing path in step 4) is a raster scanning path, a reciprocating straight line path or a compound path.

8. The additive and subtractive manufacturing method for sharp corner features according to claim 7, characterized in that: The step 5) specifically includes: using a laser to execute an additive path to perform additive manufacturing, and after the additive manufacturing is completed, using an ultrafast laser to execute a subtractive path to perform subtractive manufacturing to complete the additive and subtractive manufacturing of the sharp-angle features.