Friction stirring welding process and welding fixture for food-grade material trays

Abstract

This invention discloses a friction stir welding process and welding fixture for food-grade material trays, relating to the field of food processing equipment manufacturing technology. The process includes the following steps: Step S1, pre-welding preparation: Selecting food-grade austenitic stainless steel sheet as the base material, and completing the blanking and precision machining of the weld edges according to the material tray drawings; Step S2, clamping and positioning: Placing the pre-treated sheet material to be welded on a dedicated welding fixture; Step S3, friction stir welding: Setting the friction stir welding process parameters, starting the equipment to rotate the stirring head at a set speed and press it down to a preset depth; Step S4, post-weld treatment. This friction stir welding process and welding fixture for food-grade material trays solves the problems of porosity, insufficient weld strength, micro-cracks, and substandard food hygiene and safety in fusion welding processes, while also achieving precise control of welding deformation, improving production efficiency and product consistency.

Description

Technical Field

[0001] This invention relates to the field of food processing equipment manufacturing technology, and in particular to a stirring friction welding process and welding fixture for a food-grade material tray. Background Technology

[0002] Food-grade trays are widely used in food processing, cold chain storage, catering delivery, baking and other industries. They are core equipment in the food production and distribution process. They are mostly made of food-grade austenitic stainless steel (304 / 304L / 316 / 316L) and are formed by welding together sheet metal during the production process.

[0003] Friction stir welding (FSW) is a solid-state joining technology where the material does not melt during the welding process. Instead, the friction and stirring of the stirring head bring the material to a thermoplastic state, forming a dense, forged weld under pressure. This fundamentally avoids defects such as porosity and cracks inherent in fusion welding, offering advantages such as minimal weld deformation, high joint strength, and environmental friendliness. However, currently, there is no dedicated FSW process for food-grade food trays, and a lack of specialized welding fixtures adapted to their structures. This prevents the resolution of core issues such as deformation control in thin-plate welding, food-grade weld formation, and consistency in mass production, hindering the large-scale application of FSW technology in the food-grade food tray industry. Summary of the Invention

[0004] The purpose of this invention is to provide a friction stir welding process and welding fixture for food-grade material trays, which solves the problems of porosity, sand holes, insufficient welding strength, micro-cracks, and failure to meet food hygiene and safety standards in fusion welding processes. At the same time, it achieves precise control of welding deformation, thereby improving production efficiency and product consistency.

[0005] This invention provides a friction stir welding process for food-grade material trays, comprising the following steps: Step S1: Pre-welding preparation. Select food-grade austenitic stainless steel sheet as the base material. Complete the material cutting and precision machining of the welding edges according to the material tray drawing. Perform food-grade cleaning treatment on the welding area. Select a stirring head that matches the thickness of the base material and complete the installation, leveling, and functional debugging of the special welding fixture. Step S2, clamping and positioning: Place the pre-treated plate to be welded on a special welding fixture, complete the precise alignment of the seam through the positioning component, start the rigid clamping mechanism, clamp the plate to be welded evenly along the length of the weld, and at the same time ensure that the back of the weld is completely in contact with the back support bushing of the weld of the fixture. Step S3: Friction stir welding. Set the friction stir welding process parameters, start the equipment to make the stirring head rotate at the set speed and press down to the preset depth. After holding the pressure and preheating, move at a constant speed along the weld direction to complete solid phase welding. During the welding process, high-purity inert gas is used to protect the welding area from oxidation. When welding to the end of the weld, the welding key hole is led out to the outside of the base material through the arc-retracting plate to avoid welding defects in the base material area. Step S4: Post-weld treatment. After welding, keep the tooling clamped until the workpiece cools to room temperature. After unclamping, perform food-grade surface finishing on the weld. Then, perform a comprehensive cleaning and performance test on the finished product tray. After passing the test, the food-grade tray is obtained.

[0006] Preferably, in step S1, the base material is austenitic stainless steel.

[0007] Preferably, in step S1, the stirring head includes a shoulder and a stirring pin, and the stirring head is made of tungsten-rhenium alloy, nickel-based high-temperature alloy or cubic boron nitride.

[0008] Preferably, in step S2, the clamping force of the rigid clamping mechanism is set according to the thickness of the plate.

[0009] Preferably, in step S3, the welding process parameters are set according to the thickness of the plate.

[0010] Preferably, in step S4, the surface finishing process involves polishing both sides of the weld using a food-grade scouring pad or non-woven fabric.

[0011] A welding fixture for friction stir welding of a food-grade material tray includes a fixture base, a positioning component, a rigid clamping mechanism, a weld back support bushing, and an anti-deformation support component. The fixture base is a high-strength steel platform with an array of T-slots on its surface. The positioning component includes side positioning blocks and end positioning blocks. The rigid clamping mechanism includes several independent clamping units, which are evenly distributed at equal intervals along the weld length. The clamping ends of the clamping units are covered with a food-grade silicone layer. The weld back support bushing is positioned directly below the weld joint and is detachably connected to the fixture base. The top surface of the weld back support bushing is fully in contact with the back of the material to be welded. The top surface of the weld back support bushing has a zero-gap forming groove corresponding to the weld joint. The anti-deformation support component is positioned in the non-welding cavity area of ​​the material to be welded and is detachably connected to the fixture base.

[0012] Preferably, the back support bushing of the weld is made of H13 mold steel or tungsten steel.

[0013] Therefore, the present invention adopts the above-mentioned stirring friction welding process and welding tooling for a food-grade tray to solve the problems of porosity, sand holes, insufficient welding strength, micro-cracks and failure to meet food hygiene and safety standards in the fusion welding process, while achieving precise control of welding deformation and improving production efficiency and product consistency.

[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the stirring friction welding process for a food-grade material tray according to the present invention. Figure 2 This is a schematic diagram of the overall structure of the welding fixture for the friction stir welding process of a food-grade material tray according to the present invention. Figure 3 This is a schematic diagram of the stirring head of the welding fixture used in the friction stirring welding process of a food-grade material tray according to the present invention.

[0016] Figure Labels 1. Tooling base; 2. Positioning component; 3. Rigid clamping mechanism; 4. Weld back support bushing; 5. Anti-deformation support component; 6. Plate to be welded; 7. Stirring head; 71. Shoulder; 72. Stirring needle. Detailed Implementation

[0017] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0019] The terms "first," "second," and similar words used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed after the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0020] Example 1 like Figures 1-3 As shown, the present invention discloses a friction stir welding process for a food-grade material tray, comprising the following steps: Step S1: Pre-welding preparation. Select food-grade 304 austenitic stainless steel sheet as the base material, with a thickness of 1.5mm. Complete the blanking and precision machining of the welding edges according to the material tray drawing. Perform food-grade cleaning treatment on the welding area. Use a CNC milling machine to precision mill the welding edges of the two plates to be welded, ensuring that the flatness of the welding edges is ≤0.05mm / m and the perpendicularity is ≤0.03mm, and remove edge burrs. Use anhydrous ethanol to repeatedly wipe the front and back of the plates within a 20mm range on both sides of the welding edges to remove oxide film, oil stains and impurities. After wiping, dry with a dust-free non-woven cloth for later use. Select a stirring head 71 that is compatible with the thickness of the base material and complete the installation, leveling and functional debugging of the special welding fixture. The stirring head is made of tungsten-rhenium alloy, with a shoulder diameter D=6mm (4 times the plate thickness), and the shoulder end face is decorated with concentric vortex texture; the stirring pin has a tapered thread structure, with a length L=1.3mm, a root diameter d=3mm, a tip diameter of 1.2mm, and a thread helix angle of 4°. The special welding fixture is installed on the worktable of the gantry-type friction stir welding machine. The levelness of the fixture base is calibrated to ≤0.02mm / m, and the pneumatic clamping unit is tested for smooth operation and precise clamping force adjustment, thus completing the fixture debugging.

[0021] In step S1, the stirring head 7 includes a shoulder 71 and a stirring pin 72. The stirring head 7 is made of tungsten rhenium alloy, nickel-based high-temperature alloy or cubic boron nitride.

[0022] Step S2: Clamping and positioning. Place the pre-treated weldable plate 6 on a dedicated welding fixture. Use the positioning component 2 to precisely align the weld seams, ensuring the seam gap is ≤0.05mm and the plate misalignment is ≤0.03mm. Activate the rigid clamping mechanism 3 to evenly clamp the weldable plate 6 along the weld seam length, ensuring the back of the weld seam is fully fitted with the weld seam back support bushing 4 of the fixture. The fitting gap is ≤0.02mm. Simultaneously, install anti-deformation support blocks 5 in the material tray cavity area to ensure complete fit with the back of the plate.

[0023] Step S3: Friction stir welding. Set the friction stir welding process parameters, start the equipment to make the stirring head 7 rotate at the set speed and press down to the preset depth. After pressure holding and preheating, move at a constant speed along the weld direction to complete solid phase welding. During the welding process, high-purity inert gas is used to protect the welding area from oxidation. When welding to the end of the weld, the welding key hole is led out to the outside of the base material through the arc-retracting plate to avoid welding defects in the base material area.

[0024] In step S3, the welding process parameters are set according to the thickness of the plate material: spindle speed 1200 rpm, welding speed 150 mm / min, shoulder pressing amount 0.15 mm, welding tilt angle 2.5°, stirring head pressing speed 20 mm / min, and pressure holding and preheating time 3 s. High-purity argon gas (99.999% purity) is used to protect the welding area at a flow rate of 8 L / min. The equipment is started, the stirring head 7 rotates at the set speed, presses down to the preset depth, holds pressure and preheats for 3 s, and then moves at a uniform speed along the weld direction to complete the welding of the entire weld. Welding is completed at the arc-end plate area, and the keyhole is led out to the outside of the base material. The welding parameters are kept stable throughout the process.

[0025] Step S4: Post-weld treatment. After welding, keep the tooling clamped until the workpiece cools to room temperature. After unclamping, perform food-grade surface finishing on the weld. Then, perform a comprehensive cleaning and performance test on the finished product tray. After passing the test, the food-grade tray is obtained.

[0026] In step S4, the surface finishing process involves polishing both sides of the weld with a food-grade scouring pad or non-woven fabric. The weld surface roughness Ra is lightly polished with a food-grade scouring pad to ensure it is ≤0.8μm, consistent with the surface finish of the base material, and free of burrs and flash. The entire tray is then ultrasonically cleaned with a food-grade neutral detergent to remove residual impurities, rinsed with water, and dried. The finished tray undergoes performance testing: visual inspection reveals uniform weld formation, free of defects such as porosity, cracks, and incomplete penetration; a water pressure test at 0.3MPa for 30 minutes shows no leakage; a tensile test shows a weld tensile strength of 520MPa, reaching 98% of the base material standard value, with the fracture location within the base material region; and heavy metal migration is far below the limit requirements, thus passing the test and yielding the finished food-grade tray.

[0027] A welding fixture for friction stir welding of food-grade material trays includes a fixture base 1, a positioning component 2, a rigid clamping mechanism 3, a weld back support bushing 4, and an anti-deformation support component 5. The fixture base 1 is a high-strength steel platform that can be detachably fixed to the worktable of a friction stir welding machine. The surface of the fixture base 1 is provided with an array of T-slots for flexible installation and position adjustment of the other components. The positioning component 2 includes side positioning blocks and end positioning blocks, which can be detachably installed on the fixture base 1 to limit the sides and ends of the material to be welded 6, respectively, to ensure the accuracy of the joint alignment. The rigid clamping mechanism 3 includes several sets of independent clamping units, which are evenly distributed at equal intervals along the length of the weld. The clamping force of the clamping unit is independently adjustable. The clamping end of the clamping unit is covered with a food-grade silicone layer to prevent scratching the surface of the sheet material. The weld back support bushing 4 is positioned directly below the joint. The weld back support bushing 4 is detachably connected to the tooling base 1. The top surface of the weld back support bushing 4 is fully in contact with the back of the sheet material 6 to be welded. The top surface of the weld back support bushing 4 has a zero-gap forming groove corresponding to the joint to suppress weld collapse and back flash. The anti-deformation support component 5 is positioned in the non-welding cavity area of ​​the sheet material 6 to be welded. The anti-deformation support component 5 is detachably connected to the tooling base 1. The top surface of the support is fully in contact with the back of the sheet material 6 to be welded to suppress warping deformation of the sheet material 6 during welding. The weld back support bushing 4 is made of H13 mold steel or tungsten steel.

[0028] Example 2 like Figures 1-3 As shown, the present invention discloses a friction stir welding process for a food-grade material tray, comprising the following steps: Step S1: Pre-welding preparation. Select food-grade 316L austenitic stainless steel sheet as the base material, with a thickness of 4mm. Complete the blanking and precision machining of the welding edges according to the material tray drawing. Perform food-grade cleaning treatment on the welding area. Use a CNC milling machine to precision mill the welding edges of the two plates to be welded, ensuring that the flatness of the welding edges is ≤0.05mm / m and the perpendicularity is ≤0.03mm, and remove edge burrs. Use anhydrous ethanol to repeatedly wipe the front and back of the plates within a 20mm range on both sides of the welding edges to remove oxide film, oil stains and impurities. After wiping, dry with a dust-free non-woven cloth for later use. Select a stirring head 71 that is compatible with the thickness of the base material and complete the installation, leveling and functional debugging of the special welding fixture. The stirring head is made of tungsten-rhenium alloy, with a shoulder diameter D=16mm (4 times the plate thickness), and the shoulder end face is decorated with concentric vortex texture; the stirring pin has a tapered thread structure, with a length L=3.75mm, a root diameter d=8mm, a tip diameter of 3mm, and a thread helix angle of 4°. The special welding fixture is installed on the worktable of the gantry-type friction stir welding machine. The levelness of the fixture base is calibrated to ≤0.02mm / m, and the pneumatic clamping unit is tested for smooth operation and precise clamping force adjustment, thus completing the fixture debugging.

[0029] In step S1, the stirring head 7 includes a shoulder 71 and a stirring pin 72. The stirring head 7 is made of tungsten rhenium alloy, nickel-based high-temperature alloy or cubic boron nitride.

[0030] Step S2: Clamping and positioning. Place the pre-treated weldable plate 6 on a dedicated welding fixture. Use the positioning component 2 to precisely align the weld seams, ensuring the seam gap is ≤0.08mm and the plate misalignment is ≤0.05mm. Activate the rigid clamping mechanism 3 to evenly clamp the weldable plate 6 along the weld seam length, ensuring the back of the weld seam is fully fitted with the weld seam back support bushing 4 of the fixture. The fitting gap is ≤0.02mm. Simultaneously, install anti-deformation support blocks 5 in the material tray cavity area to ensure complete fit with the back of the plate.

[0031] Step S3: Friction stir welding. Set the friction stir welding process parameters, start the equipment to make the stirring head 7 rotate at the set speed and press down to the preset depth. After pressure holding and preheating, move at a constant speed along the weld direction to complete solid phase welding. During the welding process, high-purity inert gas is used to protect the welding area from oxidation. When welding to the end of the weld, the welding key hole is led out to the outside of the base material through the arc-retracting plate to avoid welding defects in the base material area.

[0032] In step S3, the welding process parameters are set according to the thickness of the plate material: spindle speed 2000 rpm, welding speed 60 mm / min, shoulder 71 pressure 0.25 mm, welding angle 3.5°, stirring head 7 pressure speed 15 mm / min, and pressure holding and preheating time 5 s. High-purity argon gas (99.999% purity) is used to protect the welding area at a flow rate of 10 L / min. The equipment is started, stirring head 7 rotates at the set speed, pressure is applied to the preset depth, and pressure holding and preheating is performed for 3 s. Then, it moves at a uniform speed along the weld direction to complete the welding of the entire weld seam, finishing at the arc-end plate area. The keyhole is then led out of the base material, ensuring stable welding parameters throughout the process.

[0033] Step S4: Post-weld treatment. After welding, keep the tooling clamped until the workpiece cools to room temperature. After unclamping, perform food-grade surface finishing on the weld. Then, perform a comprehensive cleaning and performance test on the finished product tray. After passing the test, the food-grade tray is obtained.

[0034] In step S4, the surface finishing process involves polishing both sides of the weld with a food-grade scouring pad or non-woven fabric. The weld surface roughness Ra is lightly polished with a food-grade scouring pad to ensure it is ≤0.8μm, consistent with the surface finish of the base material, and free of burrs and flash. The entire tray is then ultrasonically cleaned with a food-grade neutral detergent to remove residual impurities, rinsed with water, and dried. The finished tray undergoes performance testing: visual inspection reveals uniform weld formation, free of defects such as porosity, cracks, and incomplete penetration. The weld meets 96% of the base material standard value, and the fracture location is within the base material area. The test is passed, and the food-grade tray is obtained.

[0035] A welding fixture for friction stir welding of food-grade material trays includes a fixture base 1, a positioning component 2, a rigid clamping mechanism 3, a weld back support bushing 4, and an anti-deformation support component 5. The fixture base 1 is a high-strength steel platform that can be detachably fixed to the worktable of a friction stir welding machine. The surface of the fixture base 1 is provided with an array of T-slots for flexible installation and position adjustment of the other components. The positioning component 2 includes side positioning blocks and end positioning blocks, which can be detachably installed on the fixture base 1 to limit the sides and ends of the material to be welded 6, respectively, to ensure the accuracy of the joint alignment. The rigid clamping mechanism 3 includes several sets of independent clamping units, which are evenly distributed at equal intervals along the length of the weld. The clamping force of the clamping unit is independently adjustable. The clamping end of the clamping unit is covered with a food-grade silicone layer to prevent scratching the surface of the sheet material. The weld back support bushing 4 is positioned directly below the joint. The weld back support bushing 4 is detachably connected to the tooling base 1. The top surface of the weld back support bushing 4 is fully in contact with the back of the sheet material 6 to be welded. The top surface of the weld back support bushing 4 has a zero-gap forming groove corresponding to the joint to suppress weld collapse and back flash. The anti-deformation support component 5 is positioned in the non-welding cavity area of ​​the sheet material 6 to be welded. The anti-deformation support component 5 is detachably connected to the tooling base 1. The top surface of the support is fully in contact with the back of the sheet material 6 to be welded to suppress warping deformation of the sheet material 6 during welding. The weld back support bushing 4 is made of H13 mold steel or tungsten steel.

[0036] Therefore, the present invention adopts the above-mentioned stirring friction welding process and welding tooling for a food-grade tray to solve the problems of porosity, sand holes, insufficient welding strength, micro-cracks and failure to meet food hygiene and safety standards in the fusion welding process, while achieving precise control of welding deformation and improving production efficiency and product consistency.

[0037] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A friction stir welding process for food-grade material trays, characterized in that, Includes the following steps: Step S1: Pre-welding preparation. Select food-grade austenitic stainless steel sheet as the base material. Complete the material cutting and precision machining of the welding edges according to the material tray drawing. Perform food-grade cleaning treatment on the welding area. Select a stirring head that matches the thickness of the base material and complete the installation, leveling, and functional debugging of the special welding fixture. Step S2, clamping and positioning: Place the pre-treated plate to be welded on a special welding fixture, complete the precise alignment of the seam through the positioning component, start the rigid clamping mechanism, clamp the plate to be welded evenly along the length of the weld, and at the same time ensure that the back of the weld is completely in contact with the back support bushing of the weld of the fixture. Step S3: Friction stir welding. Set the friction stir welding process parameters, start the equipment to make the stirring head rotate at the set speed and press down to the preset depth. After holding the pressure and preheating, move at a constant speed along the weld direction to complete solid phase welding. During the welding process, high-purity inert gas is used to protect the welding area from oxidation. When welding to the end of the weld, the welding key hole is led out to the outside of the base material through the arc-retracting plate to avoid welding defects in the base material area. Step S4: Post-weld treatment. After welding, keep the tooling clamped until the workpiece cools to room temperature. After unclamping, perform food-grade surface finishing on the weld. Then, perform a comprehensive cleaning and performance test on the finished product tray. After passing the test, the food-grade tray is obtained.

2. The friction stir welding process for a food-grade material tray according to claim 1, characterized in that, In step S1, the base material is austenitic stainless steel.

3. The friction stir welding process for a food-grade material tray according to claim 1, characterized in that, In step S1, the stirring head includes a shoulder and a stirring pin, and the stirring head is made of tungsten-rhenium alloy, nickel-based high-temperature alloy or cubic boron nitride.

4. The friction stir welding process for a food-grade material tray according to claim 1, characterized in that, In step S2, the clamping force of the rigid clamping mechanism is set according to the thickness of the plate.

5. The friction stir welding process for a food-grade material tray according to claim 1, characterized in that, In step S3, the welding process parameters are set according to the thickness of the plate.

6. The friction stir welding process for a food-grade material tray according to claim 1, characterized in that, In step S4, the surface finishing process involves polishing both sides of the weld using a food-grade scouring pad or non-woven fabric.

7. The welding fixture for the friction stir welding process of a food-grade material tray as described in any one of claims 1-6, characterized in that, The system includes a tooling base, positioning components, a rigid clamping mechanism, a weld seam back support bushing, and an anti-deformation support component. The tooling base is a high-strength steel platform with an array of T-slots on its surface. The positioning components include side positioning blocks and end positioning blocks. The rigid clamping mechanism includes several independent clamping units, which are evenly distributed along the weld seam length. The clamping ends of the clamping units are covered with a food-grade silicone layer. The weld seam back support bushing is positioned directly below the weld seam and is detachably connected to the tooling base. The top surface of the weld seam back support bushing is fully fitted to the back of the plate to be welded, and the top surface of the weld seam back support bushing has a zero-gap forming groove corresponding to the weld seam. The anti-deformation support component is positioned in the non-welded cavity area of ​​the plate to be welded and is detachably connected to the tooling base.

8. The welding fixture for friction stirring welding of a food-grade material tray according to claim 7, characterized in that, The back support bushing of the weld is made of H13 mold steel or tungsten steel.

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