Method for eliminating interlayer longitudinal gap of friction stir additive manufacturing component

Abstract

The invention belongs to the technical field of friction stir additive manufacturing, and particularly relates to a method for eliminating a longitudinal gap between layers of a friction stir additive manufacturing component, which comprises the following steps of: assembling a stirring head on a main shaft of a friction stir additive machine, and starting a main machine, a wire feeder, a constant-pressure control system and a constant-temperature water cooling system of the friction stir additive machine; the stirring head is moved to the material adding starting point of the base plate, multi-pass deposition is conducted in sequence according to a set path, and a first layer of added materials is formed; the stirring head is lifted and moved to the material adding starting point of the second layer, material adding of the n layers is completed according to the set path, the deposition pass center line of the n layer deviates by a set distance relative to the deposition pass center line of the (n-1) layer, and a stirring needle of the stirring head can be inserted into the material of the (n-1) layer; by the adoption of the method, interlayer longitudinal gaps of the multi-channel and multi-layer additive component can be thoroughly eliminated, the Z-direction mechanical property is improved, a weak connection interface is avoided, the compactness of the component is improved, the production cost is low, and the efficiency is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of friction stir additive manufacturing, and particularly relates to a method for eliminating longitudinal gaps between layers of a friction stir additive manufacturing component. BACKGROUND

[0002] Friction stir additive manufacturing technology is a new solid-phase additive manufacturing method derived from the principle of friction stir welding. The method is based on friction stir welding, and through friction heat generation and plastic deformation work of a stirring head, additive metal is first connected with a base plate to form a deposited layer, and then the plasticized material is stacked layer by layer along a set additive path to finally form a three-dimensional component.

[0003] Current friction stir additive manufacturing mainly focuses on single-channel multi-layer components, and it is difficult to realize multi-channel multi-layer additive manufacturing of large-size components. The root problem lies in the inherent defects of layer-by-layer discrete manufacturing: after completing the deposition of a layer of material, the stirring head needs to be lifted, returned and pressed again to deposit the next layer. This process causes the top of the deposited material in the lower layer to be exposed to cooling and the temperature to decrease significantly. When the stirring head starts to deposit the next layer, the two layers of material are difficult to fully heat and plastic flow and metallurgical combination, resulting in the formation of "longitudinal gaps" such as micro-unfused, holes or weakly combined interfaces between layers; and there may also be defects such as holes, weak connections or poor metallurgical combination between passes (as shown in the accompanying drawings). Not only does it seriously weaken the mechanical properties and density of the component (especially in the Z direction), but also the process parameters (such as rotation speed and pressure) need to be frequently adjusted during the additive process to compensate for heat loss, increasing the process complexity, tool wear and energy consumption. Figure 1

[0004] In the prior art, an external heat source (induction preheating / laser assistance) is used to locally preheat (200-500 DEG C) the surface of the cooled lower layer of material before stirring deposition, so as to compensate for the temperature difference between layers and improve the plastic flow of the material. The essence is to compensate for the heat input afterwards, and the heat source and stirring action are time-separated (preheating first and then stirring), which cannot form a continuous heat-force coupling, and the heat interruption between layers is still not solved. Moreover, preheating only increases the temperature and does not enhance the Z-direction material extrusion force, so the micro-gap is still difficult to eliminate, and the lack of temperature control precision also easily leads to local overheating (grain coarsening / oxidation). This scheme passively alleviates the discontinuity of heat input, and does not solve the dual contradictions of "heat management time sequence" and "insufficient Z-direction mechanical action" simultaneously, so the interlayer bonding strength is still limited. Therefore, it is an urgent need to develop a method that can actively maintain an ideal heat state between layers, strongly promote the combination of Z-direction materials, and eliminate longitudinal gaps between layers, to improve the quality of FSAM components. SUMMARY

[0005] The purpose of the present application is to provide a method for eliminating longitudinal gaps between layers of a friction stir additive manufacturing component, at least to solve the problems in the background art. ​

[0006] In the present application, the interlayer longitudinal gap refers to the gap between adjacent passes in the same height region, for example, in the first layer material region of the additive, the gap between the adjacent parts of the first pass additive region and the second pass additive region.

[0007] The present application provides the following technical solutions: A method for eliminating the interlayer longitudinal gap of a friction stir additive manufacturing component, comprising the following steps: Step 1, assemble the stirring head on the spindle of the friction stir additive machine, turn on the main machine of the friction stir additive machine, and set the process parameters; Step 2, start the wire feeder, constant pressure control system and constant temperature water cooling system, the wire feeder is used to continuously feed the wire to the stirring head, the constant pressure control system is used to control the working pressure of the stirring head, and the temperature control system is used to control the working temperature of the stirring head; Step 3, move the stirring head to the starting point of the additive on the substrate, and sequentially deposit multiple passes according to the set path to form the first layer additive; Step 4, lift the stirring head and move to the starting point of the second layer additive, and sequentially complete the second, third,..., n layer additive until the additive is completed, during the process of depositing the n layer additive (n≥2), the center line of the deposition pass of the n layer is offset from the center line of the deposition pass of the n-1 layer by a set distance, and at least one stirring pin of the stirring head can be inserted into the interior of the n-1 layer material.

[0008] Further, the stirring head comprises a connecting rod for connecting with the spindle of the friction stir additive machine, the lower end of the connecting rod is provided with a coaxial threaded rod, the lower end of the threaded rod is formed with a shoulder, the lower end surface of the shoulder is provided with a long stirring pin and at least two short stirring pins, the long stirring pin is arranged at the center of the lower end surface of the shoulder, the short stirring pins are uniformly distributed on the lower end surface of the shoulder, the length of the long stirring pin is H, the length of the short stirring pin is h, and H>h; during the process of depositing the n layer additive, the lower segment of the long stirring pin stirs at the interlayer connection part of the n-1 layer.

[0009] To further enhance the flowability of the material between the passes and the layers, generate more intense friction heat and extensive plastic material flow at the interface between the passes and the layers, forcibly realize sufficient mechanical mixing and metallurgical bonding of the material between the passes and the layers, eliminate defects such as weak connection, unmelted and longitudinal gap at the interface, and improve the Z-direction mechanical properties and overall density of the component, the length H of the long stirring pin of the stirring head satisfies: H=2h.

[0010] To further reduce the gap between the passes of the same layer additive and avoid the weak connection defect at the interface between the passes, in steps 3 and 4, the center line distance x1 between the adjacent two deposition passes of the same layer additive satisfies: x1≤D, wherein D is the single pass deposition width.

[0011] To further optimize the Z-direction mechanical properties and overall density of the component, in step 4, the center line of the n-th layer deposition pass is offset by x2 relative to the center line of the n-1-th layer deposition pass, ; the long stirring needle is inserted into the non-fused area between the n-1-th layer passes, and the insertion depth δ2 of the long stirring needle satisfies: δ2≥h.

[0012] To further eliminate the longitudinal gap between the layers of the component, in steps 3 and 4, when the first layer or the n-th layer is added, the depth δ of the short stirring needle inserted into the substrate or the n-1-th layer added satisfies: δ=0.05~0.1h.

[0013] To further improve the additive density of the component, the long stirring needle and the short stirring needle are both conical structures, and the tip radius R of the long stirring needle and the short stirring needle is greater than or equal to 0.3mm.

[0014] To further improve the density and mechanical properties of the component, in step 3, the rotation speed of the stirring head is 1500~1800rpm, and the travel speed is 120-150mm / min; in step 4, the rotation speed of the stirring head is 1200~1400rpm, and the travel speed is 180~220mm / min.

[0015] To prevent substrate penetration failure and maintain the rigidity of the substrate, the thickness T of the substrate satisfies: T≥1.5H, and H is the length of the long stirring needle.

[0016] Compared with the prior art, the present application has the following technical effects: The present application adopts the synergistic effect of the long stirring needle and the short stirring needle, the long stirring needle directly penetrates the current layer and strongly intervenes in the non-fused area of the lower layer during the additive, enhances the flow of materials between the layers, generates intense friction heat at the interlayer interface through the long stirring needle and the plastic material flow, forcibly realizes the full mechanical mixing and metallurgical bonding of the materials between the layers, completely eliminates the longitudinal gap, and makes the additive sample achieve nearly isotropic mechanical properties; through the short stirring needle, (x1≤single pass width D) path design, it is ensured that the long stirring needle can accurately insert into the non-fused area between the lower layer passes to eliminate the weak connection defects between the passes; Compared with the conventional friction stir additive manufacturing technology of the same specification, under the synergistic effect of the constant pressure control system and the constant temperature water cooling system, the present application can effectively maintain the ideal heat state between the layers, avoid local overheating or heat interruption, improve the Z-direction mechanical properties (such as tensile strength and shear strength) of the component by 30%~50%, the density is more than 99.8%, the porosity between the passes is reduced to <0.5% (the traditional FSAM is 3-5%), the weak connection interface disappears completely, and the overall density of the component is improved to more than 99.8%; The application innovatively combines the "additive-welding" synergistic mechanism in the process, and the long stirring needle synchronously completes deposition and interlayer defect repair, cancels the traditional interlayer preheating, lifting and returning processes, and can reduce about 40% of the non-production time; through the constant pressure control system and the constant temperature water cooling system, the influence of pressure change and heat accumulation on the forming effect of the component during the additive process can be effectively reduced, and the forming quality and forming efficiency of the component are improved; at the same time, the process parameters of high rotating speed and low travel speed of the first layer of the stirring head and the subsequent dynamic adjustment further simplify the operation, and reduce the tool wear and energy consumption; the application discards the external heat source (such as laser / induction preheating), which can reduce the complexity of the equipment, reduce the energy consumption by about 20-30%, reduce the tool wear rate by about 40%, and has significant comprehensive cost advantage; the conical frustum-shaped stirring needle takes into account efficiency and durability, and is suitable for multiple material systems such as aluminum alloy, titanium alloy and steel, and provides an effective solution for high-performance and large-size FSAM component manufacturing. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 is a working schematic diagram of the traditional friction stir additive manufacturing; Figure 2 is a structural schematic diagram of the stirring head of the embodiment of the application; Figure 3 is a working schematic diagram of the stirring head of the embodiment of the application; Figure 4 is a working schematic diagram of the stirring head of the application; Figure 5 is a schematic diagram of a large component formed by the embodiment of the application.

[0018] In the figure: traditional stirring head 1 ’ , stirring needle 11 ’ , first deposited layer 2 ’ , current layer 3 ’ , un-melted area 4 ’ (area / position where the longitudinal gap appears between layers); stirring head 1, connecting rod 11, threaded rod 12, long stirring needle 13, short stirring needle 14, first deposited layer 2, current layer 3, un-melted area 4 (before the action of the long stirring needle 13). DETAILED DESCRIPTION

[0019] The following will be further described in detail through specific embodiments: Embodiment 1

[0020] First, the stirring head 1 of the embodiment will be described, as Figure 2As shown, the stirring head 1 includes a connecting rod 11 for connecting to the main shaft of the stir friction additive machine, and the lower end of the connecting rod 11 is coaxially fixed with a threaded rod 12, and the lower end of the threaded rod 12 is formed with a shoulder; a long stirring needle 13 and two short stirring needles 14 are fixed on the lower end surface of the shoulder, the long stirring needle 13 is arranged at the center of the lower end surface of the shoulder, and the two short stirring needles 14 are circumferentially distributed on the lower end surface of the shoulder; the length of the long stirring needle 13 is H, and the length of the short stirring needle 14 is h, H=2h; the long stirring needle 13 and the short stirring needle 14 are both truncated cone structures, and the tip radius R of the long stirring needle 13 and the short stirring needle 14 is ≥0.3mm.

[0021] A method for eliminating longitudinal gaps between layers of a friction stir additively manufactured component comprises the following steps: Step 1: assemble the stirring head 1 on the main shaft of the friction stir additive machine, turn on the main machine of the friction stir additive machine, and set the process parameters; Step 2: Start the wire feeder, constant pressure control system, and constant temperature water cooling system. The wire feeder is used to continuously feed the wire to the stirring head 1. The constant pressure control system is used to control the working pressure of the stirring head 1. The temperature control system is used to control the working temperature of the stirring head 1. Step 3: Move the stirring head 1 to the starting point of the substrate, and perform multiple depositions in sequence at a rotation speed of 1700 rpm, a travel speed of 130 mm / min, and a set path to form the first layer of additives; Figures 3-5 As shown, the thickness T of the substrate satisfies: T≥1.5H, the depth δ of the short stirring needle 14 inserted into the substrate satisfies: δ=0.1h, and the center line spacing x1 of two adjacent deposition passes satisfies: x1≤D, where D is the single-pass deposition width; Step 4: lift the stirring head 1 and move it to the starting point of the second layer of material addition. The stirring head 1 completes the second, third, ..., nth layer of material addition in sequence at a speed of 1300 rpm, a travel speed of 190 mm / min, and a set path until the material addition is completed; wherein, if Figures 3-5 As shown, the centerline spacing x1 of two adjacent deposition passes of the same additive layer also satisfies: x1≤D; and, during the n-th additive process (n≥2), the centerline of the deposition pass of the n-th layer is offset by x2 relative to the centerline of the deposition pass of the n-1th layer. The lower end of the long stirring needle 13 stirs at the interlayer connection position of the n-1 layer, and the depth δ of the short stirring needle 14 inserted into the n-1 layer of additive also satisfies: δ=0.1h.

[0022] Comparative Example: Using Figure 1 The conventional mixing head 1 shown ’ Multiple passes of additive manufacturing were performed, and the process parameters during the additive manufacturing process were the same as those in Example 1.

[0023] In one of the test schemes, taking the aluminum alloy additive as an example, the first layer additive has a total of 201 deposition passes, corresponding to 200 interlayer connection parts, and the second layer additive has a total of 200 deposition passes, corresponding to 109 interlayer connection parts. After two layers of additive are implemented in the schemes in Example 1 and Comparative Example, defect detection (RT) is performed on the first layer additive area. The results show that: in Example 1, there is only one hole in the first layer additive area of the corresponding sample, and there is no lack of fusion defect, indicating that the longitudinal gap between the layers of the friction additive manufacturing component is effectively eliminated; in Example 2, there are about 21 holes in the first layer additive area of the corresponding sample, and there are 148 lack of fusion defects.

[0024] One of the core technical points / technical ingenious points of the present application: the use of the aforementioned specific structure of the stirring head 1 in cooperation with a specific working path to smoothly eliminate the interlayer longitudinal gap in the additive area during the additive process.

[0025] The method of the present application, through the synergistic effect of long / short stirring needles, combined with precise filling of the lower layer of unfused area by additive pass offset, forcibly realizes deep mechanical mixing and metallurgical combination between layers / passes, completely eliminates the longitudinal gap, greatly improves the forming quality of the component, the hole rate of the obtained component is ≤0.5%, the Z-direction tensile strength reaches more than 95% of the base material, the elongation is increased by 50%, and the compactness is ≥99.8%; and the equipment is simple, the process is less, the operation is simple, the production efficiency is high, the production cost is low, and it can be widely applied to the manufacturing of large-size, high-performance FSAM components in the fields of aerospace, etc.

Claims

1. A method for eliminating longitudinal gaps between layers of a friction stir additively manufactured component, comprising the following steps: Step 1, assembling the stirring head (1) on the main shaft of the friction stir additive machine, turning on the main machine of the friction stir additive machine, and setting the process parameters; Step 2, starting a wire feeder, a constant pressure control system and a constant temperature water cooling system, wherein the wire feeder is used to continuously feed wire to the stirring head (1), the constant pressure control system is used to control the working pressure of the stirring head (1), and the temperature control system is used to control the working temperature of the stirring head (1); Step 3, moving the stirring head (1) to the additive starting point of the substrate, and performing multiple depositions in sequence according to the set path to form the first additive layer; Step 4, lift the stirring head (1) and move it to the starting point of the second layer of additive manufacturing, and complete the second, third, ..., nth layer of additive manufacturing in sequence according to the set path until the additive manufacturing is completed. During the nth layer of additive manufacturing, n ≥ 2, the center line of the deposition pass of the nth layer is offset by a set distance relative to the center line of the deposition pass of the n-1th layer, and at least one stirring needle of the stirring head (1) can be inserted into the interior of the n-1th layer of material.

2. The method for eliminating longitudinal gaps between component layers according to claim 1, characterized in that: The stirring head (1) includes a connecting rod (11) for connecting to the main shaft of the stir friction additive machine, the lower end of the connecting rod (11) is provided with a coaxial threaded rod (12), the lower end of the threaded rod (12) is formed with a shaft shoulder, and a long stirring needle (13) and at least two short stirring needles (14) are provided on the lower end surface of the shaft shoulder, the long stirring needle (13) is arranged at the center of the lower end surface of the shaft shoulder, and the short stirring needles (14) are evenly distributed on the lower end surface of the shaft shoulder, the length of the long stirring needle (13) is H, and the length of the short stirring needle (14) is h, H>h; during the process of adding the nth layer, the lower section of the long stirring needle (13) stirs at the interlayer connection position of the n-1th layer.

3. The method for eliminating longitudinal gaps between component layers according to claim 2, characterized in that: The length H of the long stirring needle (13) of the stirring head (1) satisfies H=2h.

4. The method for eliminating longitudinal gaps between component layers according to any one of claims 1 to 3, characterized in that: In steps 3 and 4, the centerline spacing x1 of two adjacent deposition passes of the same layer of additive material satisfies: x1≤D, where D is the single-pass deposition width.

5. The method for eliminating longitudinal gaps between component layers according to claim 4, characterized in that: In step 4, the center line of the nth layer deposition pass is offset by x2 relative to the center line of the n-1th layer deposition pass. .

6. The method for eliminating longitudinal gaps between component layers according to claim 5, characterized in that: In step 3 and step 4, when performing the first or nth layer of additive manufacturing, the depth δ of the short stirring needle (14) inserted into the substrate or the n-1th layer of additive manufacturing satisfies: δ=0.05~0.1h.

7. The method for eliminating longitudinal gaps between component layers according to claim 3, characterized in that: The tip radius R of the long stirring needle (13) and the short stirring needle (14) is ≥0.3 mm.

8. The method for eliminating longitudinal gaps between component layers according to claim 6, characterized in that: In step 3, the rotation speed of the stirring head (1) is 1500-1800 rpm, and the travel speed is 120-150 mm / min; in step 4, the rotation speed of the stirring head (1) is 1200-1400 rpm, and the travel speed is 180-220 mm / min.

9. The method for eliminating longitudinal gaps between component layers according to claim 6, characterized in that: The thickness T of the substrate satisfies: T≥1.5H, where H is the length of the long stirring needle (13).

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