Additive and subtractive composite manufacturing method and device based on powder extrusion printing

Abstract

This invention discloses a method and apparatus for additive and subtractive composite manufacturing based on powder extrusion printing, relating to the field of additive and subtractive manufacturing technology. The method includes the following steps: in response to a model import command, acquiring a three-dimensional model of the target part, and determining the powder extrusion additive forming area and subtractive finishing area of ​​the part based on the three-dimensional model; performing path fusion processing on the powder extrusion additive forming area and subtractive finishing area of ​​the part generated based on the same coordinate system, generating and outputting a processing command sequence; repeatedly executing the processing command sequence, extruding unsintered green blanks according to the powder extrusion path to form each layer, and performing dry subtractive processing on the unsintered green blanks according to the subtractive tool path, until the processing of the target part is completed. This invention solves the problems of limited printing materials and difficult processing in existing powder extrusion 3D printing technology.

Description

Technical Field

[0001] This invention relates to the field of additive and subtractive manufacturing technology, and in particular to a method and apparatus for manufacturing additive and subtractive composite materials based on powder extrusion printing. Background Technology

[0002] Currently, in the 3D printing manufacturing field, the mainstream additive and subtractive 3D printing technologies all use laser fused deposition modeling (LMD), wafer arc additive manufacturing (WAAM), and selective laser melting (SLM) as core additive methods, combined with conventional subtractive processing to form a composite process. The core logic of these additive and subtractive technologies is laser cladding additive forming and offline subtractive finishing, widely used in the forming and repair of metal parts. However, due to the technical characteristics of laser cladding, it can only be adapted to a few conventional metal materials, making it difficult to cover the processing needs of special metals. Furthermore, the high density and hardness of metal parts formed by laser cladding lead to severe tool wear and high cutting resistance when directly subjected to subtractive processing, resulting in high processing difficulty and extremely low processing efficiency. Summary of the Invention

[0003] The main objective of this invention is to propose a method and apparatus for additive and subtractive composite manufacturing based on powder extrusion printing, which solves the problems of limited printing materials and difficult processing in the prior art.

[0004] To achieve the above objectives, the present invention proposes an additive and subtractive composite manufacturing method based on powder extrusion printing, comprising the following steps: in response to a model import command, acquiring a three-dimensional model of the target part, and determining the powder extrusion additive forming area and subtractive finishing area of ​​the part based on the three-dimensional model of the target part; Based on the same coordinate system, the powder extrusion path and subtractive tool path generated in the powder extrusion additive forming area and subtractive finishing area of ​​the part are fused together to generate and output a machining instruction sequence. Based on the repeated execution of the processing instruction sequence, the unsintered green blank is extruded according to the powder extrusion path to form each layer, and the unsintered green blank is subjected to dry subtractive operation according to the subtractive tool path until the processing of the target part is completed.

[0005] In one implementation, determining the powder extrusion additive manufacturing zone and subtractive finishing zone of the part based on a three-dimensional model of the target part includes: Based on the characteristics of the part, the three-dimensional model of the target part is divided into a powder extrusion additive manufacturing area and a subtractive finishing area to be processed. The subtractive finishing area to be processed is thickened to obtain a subtractive finishing area with reserved milling allowance.

[0006] In one embodiment, performing the dry subtraction operation according to the subtraction toolpath includes: Based on the thickened contour, the subtractive tool path is made to correspond one-to-one with the powder extrusion layer. The tool moves along the thickened contour to remove the reserved allowance, and tool radius compensation and interference checks are automatically performed.

[0007] In one embodiment, the automatic tool radius compensation includes: The tool radius offset is automatically calculated based on the input tool diameter. The contour to be milled is offset inward or outward to generate the tool center trajectory; After compensation is completed, an interference check is automatically performed to confirm that there is no risk of collision between the tool and the printed preform.

[0008] In one implementation, generating and outputting the processing instruction sequence includes: For parts without enclosed internal cavities and where all machined surfaces can be directly machined from the outside, a cyclical pattern of N-layer additive manufacturing and one-time subtractive manufacturing is adopted for layer-by-layer printing, satisfying: 1≤N≤tool cutting edge length, where N is a positive integer; For parts with closed cavities, holes, undercuts, or complex curved surfaces, a layer-by-layer printing process is adopted, alternating between one layer of additive manufacturing and one layer of subtractive manufacturing.

[0009] In one embodiment, the powder extrusion uses a special powder extrusion feeder, and the extrusion temperature is 100°C to 200°C.

[0010] In one embodiment, the powder extrusion feed is formed by mixing and granulating powder material with an organic binder; the powder material is at least one of metal powder, ceramic powder, or plastic powder. Of which: the volume percentage of powder material is 45% to 85%; and the volume percentage of organic binder is 15% to 55%.

[0011] In one embodiment, the dry subtractive machining operation is synchronously linked to a negative pressure dust collection device, which has a dust collection box; when the dry subtractive machining operation is performed, the negative pressure dust collection device is turned on simultaneously, and the milling chips generated are sent into the dust collection box by negative pressure adsorption. After the dry subtractive processing stops, the negative pressure dust collection device shuts off after a delay of 1 to 2 seconds to remove residual chips.

[0012] In one embodiment, the thickness of a single layer of the extruded laminate is less than or equal to 0.8 times the nozzle outlet diameter.

[0013] This application also proposes an additive-subtractive composite manufacturing apparatus based on powder extrusion printing for performing the above-described method, characterized in that it includes: frame; The workbench is used to hold the printed parts; An additive manufacturing unit with an extruder for extruding printing material; The subtraction unit has a milling head for performing subtraction. A motion mechanism is provided, on which the additive manufacturing unit and the subtractive manufacturing unit are mounted, and the motion mechanism drives the additive manufacturing unit and the subtractive manufacturing unit to move relative to the worktable; Alternatively, the worktable is mounted on the motion mechanism, which drives the worktable to move relative to the additive and subtractive manufacturing units; A control system is used to automatically switch the operating states of the additive manufacturing unit and the subtractive manufacturing unit.

[0014] This application's additive-subtractive composite manufacturing method based on powder extrusion printing eliminates the need for laser melting, avoiding problems such as molten pool instability and interface cracking caused by the high melting point and low laser absorption rate of special metals like tungsten, molybdenum, and titanium alloys. Furthermore, by integrating the powder extrusion path and the subtractive tool path in the same coordinate system, additive and subtractive processes can be performed alternately at the same station and under the same reference, eliminating the need for offline transfer and secondary clamping, fundamentally eliminating positioning deviations and ensuring machining accuracy. Since dry subtractive processing is performed in the unsintered green state, the green hardness is low, making it easy to cut, resulting in less tool wear and lower cutting resistance. Compared to existing subtractive processing of high-hardness metal parts after laser cladding, this method effectively reduces machining difficulty and tool costs while improving subtractive efficiency. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of the printing method steps provided by the present invention; Figure 2 A schematic diagram of a complex material structure provided in one embodiment of the present invention; Figure 3 This is a schematic diagram of the printing device provided by the present invention.

[0017] Figure label: 100, frame; 200, additive manufacturing unit; 300, subtractive manufacturing unit.

[0018] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] It should be noted that if the embodiments of the present invention involve directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly.

[0021] Furthermore, if the embodiments of this invention involve descriptions such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the use of "and / or" or "and / or" throughout the text includes three parallel solutions. For example, "A and / or B" includes solution A, solution B, or a solution where both A and B are satisfied simultaneously. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0022] Please see Figure 1 In one embodiment of the present invention, an additive-subtractive composite manufacturing method based on powder extrusion printing is provided. The additive-subtractive composite manufacturing method based on powder extrusion printing includes the following steps: S100: In response to a model import command, a three-dimensional model of a target part is acquired, and the powder extrusion additive forming area and subtractive finishing area of ​​the part are determined based on the three-dimensional model of the target part; In this embodiment, the three-dimensional model can be a CAD model, an STL model, or other common three-dimensional data formats. Based on the three-dimensional model, according to the geometric structural features of the part such as its outer contour, inner cavity, hole, groove, and datum surface, the powder extrusion additive manufacturing area and the subtractive finishing area are automatically identified and divided in the slicing software or dedicated process planning software. The powder extrusion additive manufacturing area corresponds to complex irregular structures in the part that do not require high-precision machining or are difficult to perform subtractive machining in the future. The subtractive finishing area corresponds to the surface that requires high-precision machining.

[0023] It is understood that the complex irregular structure includes hollow parts, complex curved surfaces and other structures, and the high-precision machined surface includes mating surfaces, precision holes and grooves, reference surfaces and other surface structures.

[0024] S200: Based on the same coordinate system, the powder extrusion path and subtractive tool path generated in the powder extrusion additive forming area and subtractive finishing area of ​​the part are fused together to generate and output a sequence of machining instructions.

[0025] In this step, the powder extrusion path is generated by slicing layer by layer to control the movement trajectory of the extruder head; the subtractive cutting tool path is generated according to the contour to be milled in each layer to control the movement trajectory of the milling tool; then, the generated powder extrusion path and subtractive cutting tool path are placed in the same coordinate system for path fusion processing to generate a machining instruction sequence containing additive and subtractive instructions; in this machining instruction sequence, each instruction is arranged according to a preset machining order and includes parameters such as coordinate information, movement speed, extrusion amount, milling head and extruder head rotation speed; through path fusion, it is ensured that the additive and subtractive processes are based on the same machining datum, eliminating the need for secondary clamping.

[0026] It is worth noting that the process of merging the generated powder extrusion path and the subtractive cutting tool path in the same coordinate system includes: first generating the cutting path, then generating the printing path, and then merging them into a single G-code file. S300: Based on the repeated execution of the processing instruction sequence, the unsintered green blank is extruded according to the powder extrusion path to form each layer, and the unsintered green blank is subjected to dry subtractive operation according to the subtractive tool path until the processing of the target part is completed.

[0027] It should be noted that the unsintered green body mentioned in this embodiment refers to the intermediate green body that has not yet undergone degreasing and sintering processes after being formed by powder extrusion printing.

[0028] According to the processing instruction sequence generated by S200, the following operations are repeated: First, following the powder extrusion path, the extrusion head is controlled to extrude the powder into a special feedstock, which is heated and extruded layer by layer to form an unsintered green compact laminate. After each layer is extruded, the extrusion head is raised by one layer thickness and the next layer is extruded until the number of layers specified by the current processing instruction is reached. Then, after the current batch of additive operations is paused, the milling cutter is controlled to perform a dry subtractive operation on the formed unsintered green compact laminate according to the subtractive tool path. The dry subtractive operation is performed without cutting fluid. The above additive and subtractive operations are performed alternately until the processing of the entire laminate of the target part is completed.

[0029] During the alternation of additive and subtractive manufacturing, the extrusion head and milling cutter alternately enter the working position: when additive manufacturing is required, the extrusion head moves to the working position and the milling cutter returns to the waiting position; when subtractive manufacturing is required, the milling cutter moves to the working position and the extrusion head returns to the waiting position. The switching process does not require manual intervention.

[0030] After all the laminates are formed, the resulting green body is degreased and sintered to finally obtain dense metal, ceramic or plastic parts.

[0031] In the above method, steps S100 to S300 are executed sequentially and cyclically within the same printing device, on the same worktable, and in the same coordinate system until all processing of the target part is completed.

[0032] For example, taking a coaxial additive and subtractive manufacturing equipment integrating a powder extrusion printing unit and a CNC milling unit as an example, the specific operation process is as follows: The STL model of the target part is imported into the equipment control software. The software automatically identifies features such as internal cavities, external curved surfaces, and reference surfaces in the model, marks the areas where the internal cavities and external curved surfaces are located as subtractive finishing areas, and marks the solid filling areas as additive forming areas.

[0033] The software automatically generates powder extrusion paths and subtractive tool paths, and merges them in the same coordinate system to generate a complete machining G-code file.

[0034] The equipment executes G-code: First, the extruder prints layer by layer according to the path, pausing after every 3 layers; then, the milling head automatically switches to the working position, lightly mills the outer contour and inner cavity of the current green blank according to the corresponding tool path and vacuums the dust; after milling is completed, the milling head retracts, and the extruder continues to print the subsequent layers.

[0035] Repeat the above process until all parts are formed. Finally, remove the green blank from the workbench and place it in the sintering furnace to sinter, obtaining the final product.

[0036] This application's additive-subtractive composite manufacturing method based on powder extrusion printing eliminates the need for laser melting, avoiding problems such as molten pool instability and interface cracking caused by the high melting point and low laser absorption rate of special metals like tungsten, molybdenum, and titanium alloys. Furthermore, by integrating the powder extrusion path and the subtractive tool path in the same coordinate system, additive and subtractive processes can be performed alternately at the same station and under the same reference, eliminating the need for offline transfer and secondary clamping, fundamentally eliminating positioning deviations and ensuring machining accuracy. Since dry subtractive processing is performed in the unsintered green state, the green hardness is low, making it easy to cut, resulting in less tool wear and lower cutting resistance. Compared to existing subtractive processing of high-hardness metal parts after laser cladding, this method effectively reduces machining difficulty and tool costs while improving subtractive efficiency.

[0037] In one embodiment, step S100, determining the powder extrusion additive manufacturing area and the subtractive finishing area of ​​the target part based on the three-dimensional model of the target part, includes: dividing the powder extrusion additive manufacturing area and the subtractive finishing area to be processed in the three-dimensional model of the target part according to the characteristics of the part, and thickening the subtractive finishing area to be processed to obtain a subtractive finishing area with reserved milling allowance.

[0038] In this embodiment, the three-dimensional model of the target part is first imported into slicing software or process planning software in the field. The software automatically identifies the surface areas that need high-precision processing based on the geometric features of the part, marks these areas as subtractive finishing areas to be processed, and marks the remaining areas as powder extrusion additive manufacturing areas. Then, the marked subtractive finishing areas to be processed are thickened.

[0039] For example, the software adds a certain thickness outward along the normal direction of the surface to be machined based on the original model outline. This added thickness is the machining allowance reserved for subsequent milling. The size of the reserved allowance is determined according to the part material, dimensional accuracy requirements and tool type, and can be selected as 0.1mm to 0.5mm. Through the thickening process, a corrected three-dimensional model is obtained. In this model, the area that originally needed to be finished has more material layers that can be removed than the final product size.

[0040] In this embodiment, by thickening the subtractive finishing area to be processed, sufficient cutting material is provided for subsequent dry subtractive machining operations, avoiding the inability to achieve the desired surface finish due to insufficient allowance. Simultaneously, it is worth noting that by controlling the uniformity of the allowance, the fluctuation of cutting force during milling can be reduced, the impact on the green blank can be decreased, and deformation or chipping in thin-walled areas can be prevented. This is particularly suitable for areas with poor tool accessibility, such as internal cavities, deep holes, and corners, ensuring that these areas with poor accessibility achieve a smooth and precise surface after milling.

[0041] After the thickening process is completed, the software generates powder extrusion paths and subtractive cutting tool paths based on the thickened model, and then proceeds to the subsequent path fusion step.

[0042] In one embodiment, step S300, performing dry subtractive processing according to the subtractive tool path, includes: based on the thickened contour, making the subtractive tool path correspond one-to-one with the powder extrusion layer, moving the tool along the thickened contour to remove the reserved allowance, and automatically performing tool radius compensation and interference checks.

[0043] In this embodiment, the powder extrusion additive manufacturing process stacks green blanks layer by layer according to the set single-layer thickness. After each layer or several layers are printed, the system calls the subtractive tool path corresponding to that layer. The subtractive tool path is generated based on the model contour after the thickening process. That is, the tool path of each subtractive path is aligned with the geometric boundary of the powder extrusion layer of the same layer. By setting the corresponding layers, it is ensured that the allowance removed by the subtractive operation in each layer or each processing stage precisely matches the actual shape of the green blank in that layer, avoiding overcutting or undercutting caused by the cumulative error between layers.

[0044] During the dry subtractive machining process, the milling cutter moves along the contour line after the thickening treatment. The tool movement is mainly contour milling and internal cavity milling. That is, the tool mainly moves along the tangent direction of the surface to be machined, peeling off the pre-set allowance layer by layer. The cutting depth, feed rate and other process parameters of the tool are optimized according to the low hardness characteristics of the green blank. After the tool movement is completed, the excess material in the thickened area is completely removed, so that the area meets the dimensional requirements of the final product.

[0045] For example, the tool path adopts a light milling mode with small depth of cut and fast feed to reduce cutting force and prevent green blank deformation or edge chipping.

[0046] It is worth noting that since the subtractive toolpath is generated based on the model contour, and the tool has a certain radius during actual milling, if the tool center movement is directly controlled according to the contour line, it will lead to machining dimension deviation; therefore, in this embodiment, the system will automatically perform tool radius compensation.

[0047] For example, the software reads the milling cutter diameter input by the operator, automatically calculates the tool radius, and then offsets the original contour line inward or outward by a radius distance along the normal direction to generate the actual tool center movement trajectory; for the outer contour, the tool center trajectory is offset outward; for the inner cavity contour, the tool center trajectory is offset inward; through this compensation, it is ensured that the contact point between the tool cutting edge and the workpiece is exactly on the designed contour, thereby obtaining accurate machining dimensions.

[0048] In this embodiment, after the tool radius compensation is completed, the system automatically performs an interference check. It is understood that the interference check is used to confirm whether the tool holder, tool shank, and tool tip will collide with the printed green blank during the tool's movement along the compensated trajectory.

[0049] For example, interference checking includes: the software, based on the three-dimensional cumulative model of the printed blank, simulates the entire spatial area swept by the overall contour of the tool as it travels along the motion path, and uses a three-dimensional collision detection algorithm to determine whether there is a collision risk in the tool path segment by segment; if a potential collision is detected, the system will automatically adjust the tool path or prompt to replace it with a tool of a smaller diameter; if it cannot be avoided, the processing will be paused and an alarm will be triggered. By performing interference checking, the manufacturing method of this embodiment is particularly suitable for processing narrow internal cavities, effectively preventing tool chipping or blank breakage, and ensuring the reliability of the processing.

[0050] It is understood that the three-dimensional collision detection algorithm may be a detection method that discretizes space into a voxel mesh, or a detection method based on triangular mesh intersection.

[0051] It is understood that the automatic toolpath adjustment includes methods such as lifting the tool, detouring, or changing the cutting angle.

[0052] Through the synergistic effects of layered correspondence, thickened contour cutting, tool radius compensation, and interference checking, this embodiment can achieve high-precision and high-safety dry subtractive processing in the unsintered green state, providing dimensionally accurate and surface-smooth green parts for subsequent debinding and sintering.

[0053] It should be noted that operators only need to input the diameter parameters of the cutting tools used during equipment initialization. The remaining steps are automatically executed by the built-in algorithm of the specialized software used by those in the field, without the need for manual intervention. This effectively reduces the difficulty of operation and improves the efficiency and accuracy of process planning.

[0054] Furthermore, the automatic tool radius compensation includes: automatically calculating the tool radius offset based on the input tool diameter; shifting the contour to be milled inward or outward to generate the tool center trajectory; and automatically performing an interference check after compensation to confirm that there is no risk of collision between the tool and the printed blank.

[0055] In this further embodiment, when the equipment is initialized or the tool is replaced, the operator inputs the diameter parameter of the currently used milling tool through the user interface of the control system. After receiving the tool diameter, the control system automatically performs the following calculation: tool radius offset R = tool diameter / 2.

[0056] For example, when the diameter of the flat end mill is ø2mm, the system automatically calculates the tool radius as 1mm, and this radius value will be used as the basis parameter for subsequent contour offset.

[0057] It should be noted that this embodiment can also input the actual measured radius of the tool to calculate the tool radius offset; that is, for high-precision machining scenarios, the operator can measure the true radius of the tool through an external tool setter and input the value directly into the system to eliminate machining errors caused by tool manufacturing tolerances. The system performs subsequent offset calculations based on the input actual radius value, thereby further improving machining accuracy.

[0058] In this embodiment, considering factors such as the elastic recovery of the green material or subsequent sintering shrinkage, the operator can set an additional compensation coefficient α. At this time, the actual offset = tool radius + α. By introducing allowance compensation, an extremely thin thickening allowance layer can be reserved after one milling operation for subsequent finishing or sintering post-processing, further improving the dimensional accuracy and surface quality of the final part.

[0059] Based on the calculated offset of the tool radius ± compensation coefficient, the system performs offset processing on the original contour to be milled, generating the trajectory for the actual control of the tool center movement; the method for determining the offset direction is as follows: For the outer contour of the part: the tool needs to approach the workpiece from the outside and its cutting edge contacts the outer contour; therefore, the tool center trajectory is offset outward by a tool radius distance, that is, extended outward from the original contour by R; in this way, when the tool moves along the offset trajectory, the cutting edge just fits the original contour surface, achieving precise machining.

[0060] For the internal cavity contour of the part: the tool needs to enter the internal area to remove material, and its cutting edge contacts the inner wall; therefore, the tool center trajectory is offset inward by a tool radius distance, that is, it shrinks inward from the original contour by R; in this way, when the tool moves along the offset trajectory, the cutting edge cuts out the required internal cavity size.

[0061] The system automatically selects the offset direction based on the type of the identified outer contour or inner cavity contour, without the need for manual specification. During offsetting, the system uniformly samples point clouds on the surface of the 3D model and moves each sampled point along its normal direction by a tool radius distance. All the moved points are connected to generate the tool center trajectory. In this way, it can ensure that the offset trajectory and the original contour maintain a constant vertical distance at all points, thereby avoiding local overcutting or undercutting caused by uneven curvature of the surface.

[0062] After the tool radius compensation is completed and the tool center trajectory is generated, the system automatically triggers the interference check module. The execution flow of this module is as follows: the system obtains the three-dimensional cumulative model of the currently printed blank and obtains the compensated tool center trajectory and the three-dimensional geometric model of the tool. Then, it uses a collision detection algorithm based on voxel representation or triangular mesh intersection test to simulate the spatial envelope of the tool during its movement along the trajectory.

[0063] In this embodiment, a fully automatic and highly reliable tool radius compensation mechanism is achieved by using compensation calculations to ensure accurate machining dimensions and automatically selecting the offset direction of the appropriate contour type based on the calculation results for interference checks to ensure machining safety. This mechanism eliminates the need for manual intervention, reducing the difficulty of operation and dependence on operator experience, and effectively avoiding production accidents such as blank breakage, tool chipping, or equipment damage caused by tool collisions. It is especially suitable for high-precision dry subtractive machining of complex structural parts with narrow internal cavities, deep and long holes, and thin and fragile walls.

[0064] In one embodiment, step 200, generating and outputting the machining instruction sequence includes: for parts without closed internal cavities and all machining surfaces that can be directly machined from the outside, using an N-layer additive and one-time subtractive cyclic mode for layer-by-layer printing, satisfying: 1≤N≤tool cutting edge length, where N is a positive integer; for parts with closed internal cavities, holes, undercuts, or complex curved surfaces, using an alternating one-layer additive and one-time subtractive mode for layer-by-layer printing.

[0065] For simple parts, since there are no internal areas that the tool cannot reach from the outside, there is no need to frequently switch to subtractive operations during the machining process; therefore, an N-layer additive and one-time subtractive cycle mode is adopted, where N is a positive integer and its value range is determined by the cutting edge length of the tool.

[0066] It is worth noting that the cutting edge length of the tool refers to the axial length of the milling tool that actually participates in cutting. This value can be entered into the system by the operator according to the tool model used, or it can be automatically obtained from the tool database. In this embodiment, the value of N is: to print as many additive layers as possible within the height range that can be covered by a single subtractive operation, so as to improve the overall processing efficiency; satisfying: N × single layer thickness ≤ cutting edge length of the tool.

[0067] For example, if the cutting edge length of the tool is 3mm and the single layer thickness is 0.15mm, then N can be up to 20; at the same time, the lower limit of N is 1, that is, a one-layer additive and one-time subtractive mode is allowed.

[0068] For example, a cylindrical heat sink with a height of 10mm is printed. It has no internal cavity and the outer surface needs to be precision milled. The cutting edge length of the tool is 5mm and the single layer thickness is 0.2mm. The system calculates that the maximum number of layers that can be covered in a single subtraction is 5÷0.2=25 layers. The total height of the heat sink is 10mm, which corresponds to 50 layers. The system sets N=25, that is, after printing 25 layers, the subtraction is paused and the outer contour of the completed part is milled once. The entire processing can be completed by repeating this cycle twice.

[0069] For parts with closed cavities, deep holes, undercuts, or complex curved surfaces, since subsequent cutting tools cannot enter the cavity and deep hole areas for subtractive processing once the cavity and deep hole areas are closed, an alternating mode of one-layer additive and one-layer subtractive processing is adopted. That is, after each layer of powder extrusion printing is completed, dry subtractive finishing is immediately performed on the hard-to-reach areas such as the inner cavity wall, hole wall, and undercut lower surface of that layer.

[0070] In this embodiment, for complex parts, the subtraction operation of each layer is performed before the current layer is covered by the upper layer. The tool can freely enter the internal cavity and hole area, avoiding the problem of being unable to process due to the smaller opening or closure after multiple layers are stacked. At the same time, layer-by-layer milling can eliminate the cumulative error between layers to the greatest extent. Especially for mating surfaces with free curved surfaces or strict tolerance requirements, it can ensure the contour accuracy of each layer. For undercut structures, the lower surface of the undercut can be milled after one layer of additive material is added; otherwise, subsequent processing is not possible.

[0071] For example, see Figure 2 The system prints a cylinder with multiple external twisted stripes, each stripe only 3mm in diameter and 20mm deep. This would be difficult to achieve using multi-layer additive manufacturing followed by subtraction. Therefore, the system automatically identifies the part as a complex part and adopts a one-layer additive manufacturing and one-layer subtraction mode: after each layer is printed, the milling head immediately switches to the working position to perform precision milling on the outer wall of the part, removing the reserved allowance. This process is repeated until the top, ensuring that the flow channel is dimensionally accurate and has a smooth surface throughout.

[0072] Understandably, the switching between the two timing modes is automatically completed by specialized process planning software in this field, without the need for manual selection; the software determines whether there are closed areas that need to be processed from the inside by analyzing the spatial accessibility of the 3D model.

[0073] For example, in this embodiment, the timing mode switching step is as follows: Cavity detection: Detect all surfaces of the model and identify closed cavity regions.

[0074] Accessibility analysis: For each surface to be machined, the path of the tool approaching from the outside is simulated. If there is any direction in which the surface cannot be reached without passing through the solid material, it is determined that it needs to be machined layer by layer.

[0075] Hole feature recognition: Detect holes with a depth-to-diameter ratio greater than 3 and mark them as features that require layer-by-layer finishing.

[0076] For models marked as complex parts, the system forces the use of a one-layer additive and one-step subtractive manufacturing mode; for unmarked simple parts, the system automatically calculates the optimal N value and uses a loop mode.

[0077] It should be noted that the depth-to-diameter ratio refers to the ratio of the axial depth of a hole to its lateral feature dimension. Holes with a depth-to-diameter ratio greater than 3 are classified as deep holes, which have a large tool overhang during machining and are prone to vibration, tool deflection, or even interference and collision.

[0078] In one embodiment, in step S300, the powder extrusion uses a special feeder for powder extrusion, and the extrusion temperature is 100°C to 200°C.

[0079] During the printing process, the feed material is heated to a molten state through the heating chamber of the extruder head, and then extruded from the nozzle under the push of the screw or plunger, and stacked layer by layer to form the shape; in this embodiment, the extrusion temperature is set to 100°C to 200°C.

[0080] It is worth noting that when the temperature is below 100°C, the organic binder in the feed cannot be fully melted, resulting in poor feed fluidity and unstable extrusion, which can easily lead to defects such as broken wires, blocked heads, or uneven extrusion. At the same time, the interlayer bonding strength is insufficient, and the green body is prone to delamination and cracking.

[0081] Above 200℃: Organic binders undergo thermal decomposition, producing gases and low-molecular-weight products, causing the feed to become brittle, darken in color, and even produce irritating fumes; the decomposed binder loses its adhesive ability, the green body strength decreases significantly, and it cannot support subsequent dry subtractive processing; and high temperature will also accelerate the oxidation of powder particles, affecting the performance of the final sintered parts.

[0082] For example, the extrusion temperature can be: 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, 190℃, 195℃, 200℃, or any temperature value between any two of the above values.

[0083] Furthermore, the extrusion temperature is 140°C to 180°C. Powder extrusion printing can form unsintered green bodies under this temperature condition, which avoids the oxidative damage of the powder material caused by high temperature and prevents the decomposition and deterioration of the organic binder, thus ensuring the forming quality and processability of the green body. At the same time, this temperature range is compatible with the hot end design of conventional printing equipment, eliminating the need for a high-temperature industrial-grade heating system, thereby reducing equipment costs and energy consumption.

[0084] Furthermore, the powder extrusion feed is formed by mixing and granulating powder material with an organic binder; the powder material is at least one of metal powder, ceramic powder or plastic powder; wherein: the volume percentage of the powder material is 45% to 85%; and the volume percentage of the organic binder is 15% to 55%.

[0085] It should be noted that metal powder is suitable for manufacturing high-strength, high-temperature resistant metal parts, and can be titanium alloy, nickel-based high-temperature alloy, tungsten alloy, stainless steel, etc. The particle size of the metal powder is usually 5μm to 30μm, and it is spherical or nearly spherical to ensure the flowability and sintering activity of the feed.

[0086] Ceramic powder is suitable for manufacturing wear-resistant and corrosion-resistant ceramic parts. It can be made of alumina, zirconium oxide, silicon carbide, silicon nitride, etc. The particle size of ceramic powder is usually 0.5μm to 10μm. Its uniform distribution in the binder can be improved by adding dispersants.

[0087] Plastic powder is suitable for manufacturing lightweight, corrosion-resistant plastic parts, and can be made of polyetheretherketone, polyphenylene sulfide, nylon, polypropylene, etc.

[0088] In this embodiment, the organic binder system is typically composed of a variety of organic components, including polypropylene, polyethylene, ethylene-vinyl acetate copolymer, paraffin wax, microcrystalline wax, plasticizers, and surfactants, etc., which are used to provide fluidity in the low-temperature section so that the feed can be extruded smoothly and removed by thermal decomposition in the degreasing stage without leaving harmful residues.

[0089] In this embodiment, the volume percentage of the powder material is 45% to 85%; the volume percentage of the organic binder is 15% to 55%.

[0090] It should be noted that when the powder volume ratio is less than 45%, the powder particles in the feed are too sparse, the sintering shrinkage rate increases significantly, which can easily lead to out-of-tolerance dimensions, deformation or even cracking of parts; at the same time, due to the low powder content per unit volume, the degreasing time and sintering time are prolonged, resulting in a decrease in production efficiency.

[0091] When the powder volume ratio is higher than 85%, the melt flowability of the feed deteriorates sharply, making it difficult for the extruder to produce stable filaments, which can easily lead to filament breakage, clogging, or excessive extrusion pressure. In addition, the powder particles lack sufficient binder to coat them, resulting in insufficient green strength. In dry subtractive processing, interlayer peeling or edge chipping can easily occur.

[0092] In this embodiment, a powder volume ratio of 45% to 85% can achieve sufficiently high green density and strength while ensuring good extrusion flowability. The shrinkage after sintering is controllable, and the dimensional accuracy and mechanical properties can meet the requirements of engineering applications.

[0093] It is worth noting that fine-tuning can be made within this range for different powder materials: For spherical metal powders with good flowability, a powder volume ratio of 75% to 80% is preferred; For ceramic powders with irregular particle shapes, a powder volume ratio of 50% to 60% is preferred to reduce extrusion resistance. For stainless steel powder, the preferred powder volume percentage is 55% to 65%.

[0094] For example, the volume percentage of the powder material can be: 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, 60%, 61%, 62%, 63%, 64%, 65%, 66%, 67%, 68%, 69%, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, or any percentage between any two of the above values. Correspondingly, the volume percentage of the organic binder is 100% minus the volume percentage of the powder. For example, when the powder percentage is 75%, the binder percentage is 25%.

[0095] For example, the following table shows the volume ratio of a portion of the powder to the organic binder:

[0096] In one embodiment, in step S300, the dry subtractive machining operation is synchronously linked to a negative pressure dust collection device, which has a dust collection box. When the dry subtractive machining operation is performed, the negative pressure dust collection device is turned on synchronously to send the milling chips generated into the dust collection box through negative pressure adsorption. After the dry subtractive machining operation stops, the negative pressure dust collection device is turned off after a delay of 1 to 2 seconds to remove residual chips.

[0097] It is worth noting that the negative pressure dust collection device has a dust collection box, which is used to collect the sucked-in chips. The dust collection box can be equipped with a filter screen or cyclone separation structure to separate the chips from the airflow, but there is no need to install a high-precision filter, because the chips of the green blank are mostly dry particles in the millimeter to micron size, which are not likely to generate fine dust to pollute the environment.

[0098] When the control system issues a start command for the milling head, the negative pressure dust collection device is activated simultaneously. That is, as the milling head begins to rotate and cuts into the green blank for milling, a high-speed negative pressure airflow is immediately generated around the dust collection port, which instantly sucks the splashed or raised chips into the pipeline and sends them into the dust collection box. The simultaneous activation prevents the chips from being suspended and diffused in the air or from being compacted after falling on the surface of the green blank.

[0099] After the milling head stops rotating and performs the retraction action, the negative pressure dust extraction device does not shut off immediately, but continues to run for 1-2 seconds before automatically shutting off. This allows the dust extraction device to remove residual chips and fine particles adhering to the tool or workpiece surface during the brief interval between the milling head stopping and the tool not yet completely leaving the machining area. If shut off immediately, some chips may fall back onto the green surface due to the disappearance of airflow, or remain on the tool edge, affecting the next cut.

[0100] For example, the delay time can be 1 second, 1.2 seconds, 1.3 seconds, 1.5 seconds, 1.7 seconds, 1.8 seconds or 2 seconds, and the specific delay time can be determined by experiment based on the chip size, the distance of the suction port and the airflow speed.

[0101] In one embodiment, in step S300, the thickness of a single layer of the extruded laminate is less than or equal to 0.8 times the nozzle outlet diameter.

[0102] It should be noted that the nozzle diameter of powder extrusion printing determines the width of the extruded filament and the maximum allowable layer thickness. If the layer thickness is too large, the extruded filament is difficult to flatten into the desired layer shape, the bonding between adjacent layers is insufficient, and interlayer voids or peeling are easily generated. The surface roughness of the green body increases, and more allowance needs to be removed in subsequent subtractive processing, which increases tool wear and processing time. If the layer thickness is too small, although the surface quality is improved, the printing efficiency drops sharply.

[0103] It is worth noting that common nozzle diameters are 0.4mm, 0.6mm, 0.8mm, 1.0mm, and 1.2mm, etc.; the corresponding upper limits for single-layer thickness are: when the nozzle diameter is 0.4mm, the layer thickness is ≤0.32mm; when the nozzle diameter is 0.6mm, the layer thickness is ≤0.48mm; when the nozzle diameter is 0.8mm, the layer thickness is ≤0.64mm; when the nozzle diameter is 1.0mm, the layer thickness is ≤0.80mm; and when the nozzle diameter is 1.2mm, the layer thickness is ≤0.96mm.

[0104] In this embodiment, the layer thickness should not be less than the positioning accuracy of the equipment; when the layer thickness is lower than the positioning accuracy, the drive system cannot achieve precise layer height adjustment, resulting in uneven actual layer thickness.

[0105] For example, when using a 0.6mm nozzle, the single-layer thickness can be: 0.10mm, 0.15mm, 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, 0.48mm, or any other value not exceeding 0.48mm; when using a 0.8mm nozzle, the layer thickness can be: 0.15mm, 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.40mm, 0.45mm, 0.50mm, 0.55mm, 0.60mm, 0.64mm, or any other value not exceeding 0.64mm; when using a 1.0mm nozzle, the layer thickness can be: 0.20mm, 0.30mm, 0.40mm, 0.50mm, 0.60mm, 0.70mm, 0.80mm, or any other value not exceeding 0.80mm.

[0106] This embodiment limits the single-layer thickness to less than or equal to 0.8 times the nozzle diameter, allowing the extruded filament to be fully crushed and melted together. The green body has uniform mechanical properties in the thickness direction, making it less prone to interlayer cracking during subsequent dry subtractive processing. At the same time, it avoids the obvious step effect caused by excessive layer thickness, resulting in a relatively smooth green body surface and reducing the allowance and time for subtractive processing.

[0107] This application also proposes an additive-subtractive composite manufacturing apparatus based on powder extrusion printing, which is used to implement the composite manufacturing method described above. (See reference...) Figure 3 The additive-subtractive composite manufacturing apparatus includes a frame 100, a worktable, an additive manufacturing unit 200, a subtractive manufacturing unit 300, a motion mechanism, and a control system. The worktable is used to support the printed parts. The additive manufacturing unit 200 has an extrusion head for extruding printed material. The subtractive manufacturing unit 300 has a milling head for subtractive manufacturing. The additive manufacturing unit 200 and the subtractive manufacturing unit 300 are mounted on the motion mechanism, which drives the additive manufacturing unit 200 and the subtractive manufacturing unit 300 to move relative to the worktable. Alternatively, the worktable is mounted on the motion mechanism, which drives the worktable to move relative to the additive manufacturing unit 200 and the subtractive manufacturing unit 300. The control system is used to automatically switch the working states of the additive manufacturing unit 200 and the subtractive manufacturing unit 300.

[0108] Understandably, the frame 100, as the supporting skeleton of the entire device, is welded from high-strength steel and has sufficient rigidity and stability to withstand the dynamic loads during the additive and subtractive manufacturing processes. The frame 100 is equipped with transmission components such as guide rails and lead screws.

[0109] The worktable is used to hold the printed parts and is located in the working area of ​​the frame 100. The upper surface of the worktable is a flat structure. Optionally, it is equipped with a heating plate or vacuum suction holes to enhance the adhesion and flatness of the green part during the printing process.

[0110] The additive manufacturing unit 200 has an extrusion head for extruding printing material. The additive manufacturing unit 200 includes at least a feeding and conveying system, a heating chamber, a nozzle, and a temperature sensor. The feed particles enter the heating chamber through the conveying system, melt at 100℃ to 200℃, and are extruded from the nozzle, stacking layer by layer according to a preset powder extrusion path to form an unsintered green body.

[0111] The subtraction unit 300 has a milling head for performing subtraction; the subtraction unit 300 includes at least a milling spindle, a tool holder, a milling cutter, and a tool length measuring device; the milling cutter can be a small-diameter flat end mill or a ball end mill to adapt to the low hardness characteristics of the green blank and the machining requirements of complex internal cavities.

[0112] The motion mechanism is used to realize the relative movement between the additive manufacturing unit 200, the subtractive manufacturing unit 300, and the worktable. Optionally, the motion mechanism can be an XYZ three-axis linkage system. In one aspect of this embodiment, the additive manufacturing unit 200 and the subtractive manufacturing unit 300 are mounted on a motion mechanism, which drives them to move relative to a stationary worktable; this method has a smaller motion mass and is suitable for high-speed printing and milling.

[0113] In another aspect of this embodiment, the worktable is mounted on a motion mechanism, which drives the worktable to move relative to the stationary additive unit 200 and subtractive unit 300; this method has a compact structure and is suitable for machining heavier, larger parts.

[0114] Control System: This system automatically switches the operating states of the additive manufacturing unit 200 and the subtractive manufacturing unit 300. The control system includes at least an industrial computer, a motion control motherboard, I / O interfaces, a touchscreen, and dedicated process planning software. The control system reads the fused processing instruction sequence and issues instructions in chronological order: when additive manufacturing is required, it controls the extruder head to move to the working position while simultaneously controlling the milling head at a safe height; when subtractive manufacturing is required, it controls the milling head to move to the working position and the extruder head to return to the waiting position. The switching process is completed automatically according to preset timing logic without manual intervention. The switching time from the end of additive manufacturing to the start of subtractive manufacturing is preferably ≤5 seconds.

[0115] For example, when the motion mechanism is used as the motion head, and a one-layer additive and one-step subtractive printing method is adopted, the workflow of the device is as follows: Initial state: The extrusion head is located above the starting point of the worktable, and the milling head is in the waiting position; The control system reads an additive manufacturing instruction and sends a motion instruction to the motion mechanism: the extruder head moves along the preset path and extrudes and feeds material to print the first green body; After the first layer is printed, the control system issues a switching command: Z1 axis slide plate drives the extruder head to a safe height; The Z2 axis slide moves the milling head rapidly from the waiting position to the starting milling point of the first green blank; The control system issues a material reduction command: the axis where the milling head is located starts to the set speed, the negative pressure dust collection device is turned on simultaneously, and the milling head performs fine milling on the outer contour and inner cavity of the green blank along the tool path; the chips generated by milling are sucked in by the negative pressure dust collection device and fall into the dust collection box. After the material reduction is completed, the control system stops the rotation of the axis where the milling head is located, and shuts off the negative pressure dust collection device after a delay of 1 to 2 seconds; the milling head returns to the waiting position.

[0116] Repeat the printing steps, printing and milling layer by layer until the part is complete.

[0117] After all processing is completed, both the extrusion head and the milling head return to their original positions.

[0118] The above description is merely an exemplary embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention specification and drawings under the technical concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for manufacturing additive-subtractive composite materials based on powder extrusion printing, characterized in that, Includes the following steps: In response to the model import command, the three-dimensional model of the target part is obtained, and the powder extrusion additive manufacturing zone and subtractive finishing zone of the part are determined based on the three-dimensional model of the target part. Based on the same coordinate system, the powder extrusion path and subtractive tool path generated in the powder extrusion additive forming area and subtractive finishing area of ​​the part are fused together to generate and output a machining instruction sequence. Based on the repeated execution of the processing instruction sequence, the unsintered green blank is extruded according to the powder extrusion path to form each layer, and the unsintered green blank is subjected to dry subtractive operation according to the subtractive tool path until the processing of the target part is completed.

2. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 1, characterized in that, The determination of the powder extrusion additive manufacturing zone and subtractive finishing zone of the part based on the three-dimensional model of the target part includes: Based on the characteristics of the part, the three-dimensional model of the target part is divided into a powder extrusion additive manufacturing area and a subtractive finishing area to be processed. The subtractive finishing area to be processed is thickened to obtain a subtractive finishing area with reserved milling allowance.

3. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 2, characterized in that, The dry subtraction operation performed according to the subtraction tool path includes: Based on the thickened contour, the subtractive tool path is made to correspond one-to-one with the powder extrusion layer. The tool moves along the thickened contour to remove the reserved allowance, and tool radius compensation and interference checks are automatically performed.

4. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 3, characterized in that, The automatic tool radius compensation includes: The tool radius offset is automatically calculated based on the input tool diameter. The contour to be milled is offset inward or outward to generate the tool center trajectory; After compensation is completed, an interference check is automatically performed to confirm that there is no risk of collision between the tool and the printed preform.

5. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 1, characterized in that, The generated and output processing instruction sequence includes: For parts without enclosed internal cavities and where all machined surfaces can be directly machined from the outside, a cyclical pattern of N-layer additive manufacturing and one-time subtractive manufacturing is adopted for layer-by-layer printing, satisfying: 1≤N≤tool cutting edge length, where N is a positive integer; For parts with closed cavities, holes, undercuts, or complex curved surfaces, a layer-by-layer printing process is adopted, alternating between one layer of additive manufacturing and one layer of subtractive manufacturing.

6. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 1, characterized in that, The powder extrusion uses a special feeder for powder extrusion, and the extrusion temperature is 100℃ to 200℃.

7. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 6, characterized in that, The powder extrusion feed is made by mixing and granulating powder material with an organic binder; the powder material is at least one of metal powder, ceramic powder, or plastic powder. Wherein: the volume percentage of the powder material is 45% to 85%; the volume percentage of the organic binder is 15% to 55%.

8. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 1, characterized in that, The dry subtractive machining operation is synchronized with the negative pressure dust collection device, which has a dust collection box. When the dry subtractive machining operation is performed, the negative pressure dust collection device is turned on simultaneously, and the milling chips are drawn into the dust collection box by negative pressure adsorption. After the dry subtractive processing stops, the negative pressure dust collection device shuts off after a delay of 1 to 2 seconds to remove residual chips.

9. The additive-subtractive composite manufacturing method based on powder extrusion printing as described in claim 1, characterized in that, The thickness of a single layer of the extruded laminate is less than or equal to 0.8 times the nozzle outlet diameter.

10. An additive-subtractive composite manufacturing apparatus based on powder extrusion printing, for performing the method according to any one of claims 1 to 9, characterized in that, include: frame; The workbench is used to hold the printed parts; An additive manufacturing unit with an extruder for extruding printing material; The subtraction unit has a milling head for performing subtraction. A motion mechanism is provided, on which the additive manufacturing unit and the subtractive manufacturing unit are mounted, and the motion mechanism drives the additive manufacturing unit and the subtractive manufacturing unit to move relative to the worktable; Alternatively, the worktable is mounted on the motion mechanism, which drives the worktable to move relative to the additive and subtractive manufacturing units; A control system is used to automatically switch the operating states of the additive manufacturing unit and the subtractive manufacturing unit.

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