A method for optimizing process parameters of plasma arc welding of 301 stainless steel sheet

Abstract

The present application relates to the technical field of welding, in particular to a kind of 301 stainless steel sheet plasma arc welding process parameter optimization method, the method is first prepared with the same batch same specification 0.6mm thickness 301 stainless steel sheet base metal, set initial process parameter range including welding current, with welding current as only debugging variable first round welding test is carried out, control ion gas flow, shielding gas flow and welding speed constant, obtain the weld surface topography under different current;Screening good current interval, prepare multiple sets of parallel samples in the interval for room temperature tensile test, determine the highest tensile strength current as the optimal welding current;The present application is optimized by hierarchical progressive strategy, combined with topography observation and mechanical property test, avoids the uncertainty of traditional experience method, realizes the collaborative optimization of weld forming quality and mechanical property, significantly improves the accuracy and efficiency of parameter determination, and can be applied to other sheet welding process development.

Description

Technical Field

[0001] This invention relates to the field of welding technology, specifically a method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates. Background Technology

[0002] 301 stainless steel, a metastable austenitic stainless steel, is widely used in aerospace, cryogenic engineering, and pressure vessel manufacturing due to its excellent cold work hardening ability, good formability, and high strength. Particularly in aerospace tank manufacturing, thin-walled 301 stainless steel structures have become the preferred material for key components such as propellant tanks and gas cylinders due to their significant weight reduction effect. With the increasing demands for lightweight spacecraft, tank wall thicknesses are continuously decreasing, and ultra-thin 301 stainless steel plates with a thickness of 0.6 mm are now being used in certain specific tank structures. Plasma arc welding, as a high-energy beam welding method, has advantages such as high energy density, narrow heat-affected zone, small welding deformation, and good arc stability, making it particularly suitable for welding thin-plate materials. Compared with traditional tungsten inert gas (TIG) welding, plasma arc welding has a higher arc column temperature and more concentrated energy, which can minimize the heat-affected zone and welding deformation while ensuring penetration.

[0003] However, determining the plasma arc welding process parameters for ultra-thin 301 stainless steel plates with a thickness of only 0.6 mm still faces many technical challenges. First, the 0.6 mm ultra-thin plate is extremely sensitive to heat input; even small fluctuations in heat input can lead to significant changes in weld formation quality. Insufficient heat input can easily result in incomplete penetration and insufficient penetration depth, leading to discontinuity on the back side of the weld. Excessive heat input can easily cause burn-through, collapse, spatter, or poor weld formation. Second, 301 stainless steel has unique thermophysical properties, with a low thermal conductivity and a high coefficient of linear expansion, making it prone to generating significant residual stress and deformation during welding. Third, the presence of metastable austenite in 301 stainless steel makes the influence of welding thermal cycles on microstructure evolution more complex, and the selection of welding parameters directly affects the mechanical properties and service reliability of the joint.

[0004] Currently, the determination of process parameters for plasma arc welding of thin plates relies heavily on empirical formulas or extensive trial-and-error experiments, lacking a systematic experimental optimization method. Traditional parameter adjustment methods typically employ single-factor rotation, which consumes a large amount of materials and time, and makes it difficult to guarantee the consistency of weld joint strength and forming quality. Furthermore, existing technologies often separate the selection of welding parameters from the evaluation of joint performance, resulting in well-formed joints but not necessarily optimal mechanical properties. Therefore, in view of the above situation, there is an urgent need to develop an optimization method for plasma arc welding process parameters of 301 stainless steel thin plates to overcome the shortcomings in current practical applications. Summary of the Invention

[0005] The purpose of this invention is to provide a method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates, so as to solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates includes the following steps:

[0008] S1: Prepare the 301 stainless steel sheet base material to be welded, and select the base material of the same batch and specification.

[0009] S2: Set the initial welding process parameter range, which includes at least the welding current. Determine the adjustment range of the welding current, and keep the other process parameters constant throughout the entire test.

[0010] S3: Conduct the first round of welding tests with welding current as the only debugging variable, keep the other process parameters constant, and obtain and record the surface morphology of the weld under different welding currents.

[0011] S4: Select the welding current range with good weld formation according to the preset weld formation standard, prepare multiple sets of parallel specimens for the weld joints corresponding to each welding current in the range, and conduct room temperature tensile tests. Take the average value of the tensile strength of each set of specimens as the representative value of the tensile strength under the corresponding current.

[0012] S5: Compare the representative values ​​of tensile strength of welded joints under different welding currents, and determine the welding current with the highest tensile strength as the optimal welding current.

[0013] As a further aspect of the present invention: in step S1, the base material is cut and surface cleaned pretreatment to remove oil, oxide film and impurities from the weld area and its sides.

[0014] As a further aspect of the present invention: in step S2, the set welding current adjustment range fully covers the three heat input areas of incomplete penetration, good forming and weld penetration.

[0015] As a further aspect of the present invention: in step S3, the observation of the weld surface morphology includes the weld width uniformity, reinforcement height, fish scale pattern uniformity, back penetration, and whether there are defects such as undercut, weld beads, depressions, and spatter.

[0016] As a further aspect of the present invention: in step S4, the tensile specimen is cut along the direction perpendicular to the weld, and the weld is located at the center of the parallel segment of the specimen.

[0017] Prepare at least 3 parallel samples for each welding current.

[0018] As a further aspect of the present invention: in step S3, a micro-beam plasma arc welding machine with a current accuracy of not less than ±0.1A is used for welding, and the deviation between the actual welding parameters and the set values ​​during the welding process does not exceed ±2%.

[0019] As a further aspect of the present invention: in step S2, the process parameters kept constant include ion gas flow rate, shielding gas flow rate, and welding speed.

[0020] As a further aspect of the present invention, it also includes a verification step for the optimal welding current:

[0021] Using the same base material, equipment, and constant process parameters as in steps S1-S3, the welding current is set to a determined optimal value, and multiple parallel test plates are welded.

[0022] The weld formation quality of the test plate was verified, and tensile specimens were prepared for room temperature tensile tests. The dispersion of tensile strength data was statistically analyzed.

[0023] As a further aspect of the present invention: the 301 stainless steel sheet base material is a 301 stainless steel cold-rolled sheet with a thickness of 0.6mm.

[0024] As a further aspect of the present invention: the room temperature tensile test was conducted at 23±2℃, using constant strain rate control, with a strain rate of 1×10⁻⁶. -3 s -1 .

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention scientifically determined the optimal welding current for plasma arc welding of 0.6mm thick 301 stainless steel sheets by systematic welding current gradient experiments, combined with weld surface morphology observation and room temperature tensile mechanical property testing. This avoids the uncertainty of traditional empirical methods, achieves synergistic optimization of weld formation quality and mechanical properties, and significantly improves the accuracy and efficiency of welding process parameter determination.

[0027] This invention employs a hierarchical optimization approach. First, it filters for suitable current ranges based on surface morphology, eliminating obviously unacceptable welding parameters and narrowing down the scope of subsequent tests. Then, it uses mechanical property testing to precisely compare the selected parameters and determine the optimal current. This progressive optimization strategy ensures both comprehensive evaluation and controlled experimental workload.

[0028] This invention uses macroscopic forming quality and mechanical properties as comprehensive evaluation indicators to ensure that the determined welding parameters can guarantee both the appearance quality of the weld and the optimal load-bearing capacity. This optimization method is also applicable to the development of welding process parameters for thin plates of other thicknesses or materials, and has good promotional value. Attached Figure Description

[0029] Figure 1 This is a flowchart illustrating the optimization method for plasma arc welding process parameters of 301 stainless steel thin plates in an embodiment of the present invention.

[0030] Figure 2 These are comparative photographs of weld surface morphology under different welding currents in embodiments of the present invention.

[0031] Figure 3 This is a room temperature tensile stress-strain curve of the welded joint under different welding currents in an embodiment of the present invention. Detailed Implementation

[0032] 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 some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] The specific implementation of the present invention will be described in detail below with reference to specific embodiments.

[0034] Please see Figures 1-3 The present invention provides a method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates, comprising the following steps:

[0035] S1: Prepare the 301 stainless steel sheet base material to be welded, and perform pretreatment operations such as cutting and surface cleaning on the base material. Select base material of the same batch and specification to eliminate the influence of material batch differences on the test results.

[0036] S2: Set the initial welding process parameter range, which includes at least the welding current. Determine the adjustment range of the welding current and make it cover the three heat input areas of incomplete penetration, good formation and burn-through. Other process parameters such as ion gas flow rate, shielding gas flow rate and welding speed are kept constant throughout the entire test.

[0037] S3: Conduct the first round of welding tests with welding current as the only debugging variable, keep other process parameters constant, obtain and record the surface morphology of the weld under different welding currents, and observe the weld width, reinforcement height, uniformity of fish scale pattern, back penetration, and whether there are surface defects such as undercut, weld beads and spatter.

[0038] S4: Select the welding current range with good weld formation according to the preset weld formation standard, prepare multiple sets of parallel specimens for the weld joints corresponding to each welding current in the range, and conduct room temperature tensile tests. Take the average value of the tensile strength of each set of specimens as the representative value of the tensile strength under the corresponding current.

[0039] S5: Compare the representative values ​​of tensile strength of welded joints under different welding currents, and determine the welding current with the highest tensile strength as the optimal welding current.

[0040] This method employs a hierarchical, progressive optimization strategy. First, it rapidly screens and eliminates obviously unqualified welding parameters through macroscopic morphology. Then, it precisely determines the optimal parameters through quantitative mechanical property testing, thereby achieving synergistic optimization of weld formation quality and mechanical properties.

[0041] Example 1: Preliminary setting of welding process parameters and first round of welding tests

[0042] This embodiment is used to complete the welding current gradient test and the preliminary screening of weld formation quality. The specific implementation process is as follows:

[0043] First, the base material preparation step was carried out, using 0.6mm thick 301 stainless steel cold-rolled sheet as the test material. To eliminate the influence of batch differences on the test results, all test plates were taken from the same batch and heat number of raw materials, and the surface was free of defects such as oil stains, rust, and scratches that would affect welding quality. The base material was uniformly cut into rectangular test plates of 160mm × 100mm, which facilitates subsequent welding operations and standardized preparation of tensile test specimens. Before welding, the surface of the weld area and 20mm on both sides was wiped with acetone to remove oil stains, oxide film, and other impurities. After wiping, it was allowed to air dry naturally. This pretreatment step can effectively avoid defects such as porosity and inclusions during welding, ensuring the consistency of weld quality.

[0044] Following this, welding equipment debugging and basic parameter settings were performed. Welding tests were conducted using a micro-beam plasma arc welding machine, which possesses precise current control capability with an accuracy of ±0.1A, meeting the stringent heat input control requirements for welding 0.6mm ultra-thin plates. The welding torch was vertically fixed above the welding worktable, with the distance between the torch nozzle and the workpiece surface adjusted to 2–3mm, and the tungsten electrode extension length controlled to 1–2mm. These parameters are standard settings for micro-beam plasma arc welding of 0.6mm thin plates and remained constant throughout the tests. The welding worktable is equipped with a high-precision servo-driven guide rail system, enabling stepless adjustment and stable control of the welding speed.

[0045] The following constant welding process parameters were set: argon gas with a purity ≥99.99% was used as the ionizing gas, with a flow rate of 0.65 L / min; argon gas with a purity ≥99.99% was used as the shielding gas, with a flow rate of 6.5 L / min; and the welding speed was set to 250 mm / min. These parameters remained constant throughout the entire welding experiment to ensure that the welding current was the only experimental variable, eliminating the interference of fluctuations in other parameters on the experimental results.

[0046] Welding current was set as the debugging variable, with a total of eight discrete current gradient values: 13A, 15A, 16A, 19A, 20A, 21A, 22A, and 23A. This current range fully covers the three heat input intervals of incomplete penetration, good weld formation, and complete weld penetration, allowing for comprehensive observation of the influence of welding heat input changes on weld formation. Two parallel test plates were welded for each current parameter to improve the reliability of the test results.

[0047] The welding process employs an automatic arc ignition method. After successful arc ignition, the welding torch remains stationary, while the worktable moves the workpiece at a set speed of 250 mm / min to complete a 120 mm long straight weld. During the welding process, the welding machine's monitoring system collects arc voltage and welding current data in real time to ensure that the deviation between the actual welding parameters and the set values ​​does not exceed ±2%, thus guaranteeing the consistency of the test conditions.

[0048] After welding, the test plate was allowed to cool naturally to room temperature in the air before the weld surface morphology was observed and recorded. Visual inspection combined with 5x industrial camera photography was used to observe the formation of the weld on both the front and back sides, with a focus on checking the weld width uniformity, fish scale pattern, surface defects, and back penetration.

[0049] The observation results can be divided into three categories:

[0050] Welded joints under currents of 13A, 15A, 16A, and 19A: Insufficient heat input and low molten pool temperature resulted in incomplete penetration of the plate thickness. This manifested as a narrow weld width on the front side, unclear fish-scale pattern, and only slight localized oxidation discoloration on the back side, lacking continuous penetration and exhibiting obvious incomplete penetration defects. The incomplete penetration was most severe at 13A and 15A, while the penetration at 16A and 19A showed slight improvement, but the back side penetration remained discontinuous, failing to meet application requirements.

[0051] Welded joints under 23A current: Excessive heat input and high molten pool temperature lead to molten pool collapse. This manifests as a significant increase in the width of the weld face, a depression in the center of the weld, and undercut defects at the edges; excessive melting penetration on the back of the weld results in obvious weld beads and spatter, with some areas showing burn-through, which is an unacceptable weld quality.

[0052] Welded joints under currents of 20A, 21A, and 22A: The heat input is well matched with the 0.6mm plate thickness. This is characterized by a uniform width on the weld front, clear and regular fish-scale pattern, smooth and flat surface, and no surface defects such as undercut, weld beads, dents, or spatter; the weld back has continuous and uniform penetration, slight oxidation, and meets the criteria for good weld formation.

[0053] Based on the above morphological observations, the optimal welding current range of 20A to 22A was selected, and welded joints within this range were then tested for mechanical properties. This step, through rapid screening based on macroscopic morphology, eliminated 75% of the unqualified parameters, significantly narrowing the scope of subsequent experiments and improving optimization efficiency.

[0054] Example 2: Room Temperature Tensile Test and Determination of Optimal Welding Current

[0055] This embodiment is used to evaluate the mechanical properties of welded joints within a well-formed region and determine the optimal welding current. The specific implementation process is as follows:

[0056] First, tensile specimens were prepared. Using wire EDM (Electrical Discharge Machining), tensile specimens were cut perpendicular to the weld direction from each test plate welded at currents of 20A, 21A, and 22A in Example 1. Plate-shaped tensile specimens were prepared according to GB / T228.1-2021 standard, with a parallel section length of 50mm and a width of 12.5mm, ensuring the weld was centered within the parallel section to ensure uniform tensile stress in the weld area during tensile testing. Three parallel specimens were prepared for each welding current, for a total of nine specimens. After specimen preparation, the cut edges were progressively sanded with 400# to 1200# fine sandpaper to remove the heat-affected zone and micro-cracks generated during wire EDM, ensuring a smooth specimen surface, preventing premature fracture due to edge defects, and guaranteeing the accuracy of the test results.

[0057] Tensile tests were conducted on an electronic universal testing machine equipped with an extensometer of accuracy grade 0.5 for precise measurement of the specimen strain. The tests were performed at room temperature (23±2℃) using a constant strain rate control method, with the strain rate set to 1×10⁻⁶. -3 s -1 The strain rate meets the general standard requirements for room temperature tensile testing of austenitic stainless steel. During the test, the computer automatically collects load, displacement, and strain data and plots stress-strain curves. When the specimen fractures, the test automatically stops, and key mechanical properties such as tensile strength are extracted from the collected data.

[0058] The tensile strength values ​​of three parallel specimens for each welding current were calculated, and the arithmetic mean was taken as the representative value of the tensile strength of the welded joint under that current. At the same time, the standard deviation was calculated to assess the dispersion of the data.

[0059] The experimental results show that welded joints under different welding currents exhibit similar deformation behavior, all undergoing elastic, yielding, and strengthening stages, but with significant differences in strength levels. The average tensile strength of the 20A welded joint is the highest, followed by the 21A welded joint, and the 22A welded joint has the lowest average tensile strength. Within the well-formed range of 20A to 22A, the tensile strength of the welded joint gradually decreases with increasing welding current, reaching a peak at 20A.

[0060] Based on the above experimental results, 20A was determined as the optimal welding current for plasma arc welding of 0.6mm thick 301 stainless steel sheets. This step, through quantitative mechanical property testing, selected the parameters with the best mechanical properties from the parameter range with good form, avoiding suboptimal selections that might be caused by relying solely on appearance and ensuring the load-bearing capacity of the welded joint.

[0061] Example 3: Verification Test of Optimal Welding Current

[0062] This embodiment is used to verify the reliability and stability of the determined optimal welding current. The specific implementation process is as follows:

[0063] Using the same base material, equipment, and welding process parameters as in Example 1, with the welding current set to the optimal value of 20A determined in Example 2, the ion gas flow rate of 0.65L / min, the shielding gas flow rate of 6.5L / min, and the welding speed of 250mm / min kept constant, five parallel test plates were re-welded.

[0064] After each test plate was welded and allowed to cool naturally to room temperature, the weld surface morphology was observed according to the same standards as in Example 1 to check the weld formation quality. The results showed that the welds of all five test plates exhibited good forming characteristics consistent with those of the 20A current in Example 1: the weld width on the front side was uniform, the fish scale pattern was regular and clear, and there were no surface defects; the back side had continuous and uniform penetration, slight oxidation, and stable and consistent forming quality.

[0065] Three tensile specimens were cut from the weld area of ​​each verification test plate, for a total of 15 specimens. Room temperature tensile tests were conducted according to the same test methods and conditions as in Example 2. Statistical analysis was performed on the tensile strength data of all 15 specimens, and the mean, standard deviation, and coefficient of variation were calculated.

[0066] Statistical results show that the tensile strength data of the 15 samples are distributed within a small range, and the average value is highly consistent with the average tensile strength of the 20A welded joint in Example 2, with a standard deviation of less than 10 MPa and a coefficient of variation of less than 1.5%. These results indicate that a 20A welding current can stably produce high-strength welded joints with good process repeatability and high reliability, making it suitable for practical production applications.

[0067] It should be noted that, in this invention, although the specification describes the embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates, characterized in that, Includes the following steps: S1: Prepare the 301 stainless steel sheet base material to be welded, and select the base material of the same batch and specification. S2: Set the initial welding process parameter range, which includes at least the welding current. Determine the adjustment range of the welding current, and keep the other process parameters constant throughout the entire test. S3: Conduct the first round of welding tests with welding current as the only debugging variable, keep the other process parameters constant, and obtain and record the surface morphology of the weld under different welding currents. S4: Select the welding current range with good weld formation according to the preset weld formation standard, prepare multiple sets of parallel specimens for the weld joints corresponding to each welding current in the range, and conduct room temperature tensile tests. Take the average value of the tensile strength of each set of specimens as the representative value of the tensile strength under the corresponding current. S5: Compare the representative values ​​of tensile strength of welded joints under different welding currents, and determine the welding current with the highest tensile strength as the optimal welding current.

2. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, In step S1, the base material is cut and surface cleaned to remove oil, oxide film and impurities from the weld area and its sides.

3. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, In step S2, the set welding current adjustment range fully covers the three heat input areas: incomplete penetration, good forming, and burn-through.

4. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, In step S3, the observation of the weld surface morphology includes the weld width uniformity, reinforcement height, fish scale pattern uniformity, back penetration, and whether there are defects such as undercut, weld beads, depressions, and spatter.

5. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, In step S4, the tensile specimen is cut along the direction perpendicular to the weld, and the weld is located at the center of the parallel segment of the specimen. Prepare at least 3 parallel samples for each welding current.

6. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, In step S3, a micro-beam plasma arc welding machine with a current accuracy of not less than ±0.1A is used for welding, and the deviation between the actual welding parameters and the set values ​​during the welding process does not exceed ±2%.

7. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 3, characterized in that, In step S2, the process parameters that are kept constant include the ion gas flow rate, the shielding gas flow rate, and the welding speed.

8. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, It also includes a verification step for the optimal welding current: Using the same base material, equipment, and constant process parameters as in steps S1-S3, the welding current is set to a determined optimal value, and multiple parallel test plates are welded. The weld formation quality of the test plate was verified, and tensile specimens were prepared for room temperature tensile tests. The dispersion of tensile strength data was statistically analyzed.

9. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 1, characterized in that, The base material for the 301 stainless steel sheet is a 0.6mm thick 301 stainless steel cold-rolled sheet.

10. The method for optimizing the process parameters of plasma arc welding of 301 stainless steel thin plates according to claim 5, characterized in that, The room temperature tensile test was conducted at 23±2℃ using a constant strain rate control of 1×10⁻⁶. -3 s -1 .

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