A solid rocket engine case outer member fillet weld CMT+P welding method

Abstract

A kind of CMT+P welding method for solid engine shell external corner weld, CMT+P welding process is divided into three stages, namely arc starting, normal welding and arc stopping, welding characteristic curve, so as to improve the surface forming and quality of corner weld in arc starting, arc stopping and normal welding position.Through the control of wire feed speed in arc starting stage, the height of fillet weld is made, the arc starting position and normal welding position are smoothly transitioned, and the unmelted defects in arc starting position are avoided;By controlling the normal wire feed speed, the height of fillet weld is kept at 3mm;By controlling the wire feed speed in arc stopping stage, the height of fillet weld is controlled, the arc stopping position and normal welding position are smoothly transitioned, and the crack defects and stress concentration in arc stopping position are avoided.The surface forming quality of external corner weld obtained by the present application is obviously better than that obtained by prior art.

Description

Technical Field

[0001] This invention relates to the field of CMT+P welding, specifically a CMT+P welding method for fillet welds on the outer components of a solid engine housing. Background Technology

[0002] Currently, manual tungsten inert gas (TIG) welding is the primary method for welding external components of solid rocket motor casings. However, TIG welding has a relatively high energy density and heat input when welding external components, resulting in significant post-weld deformation. This deformation becomes even more difficult to control when the casing wall is thin. Furthermore, manual welding requires a high level of welder skill, and defects such as cracks frequently occur after welding. Therefore, it is necessary to select a superior welding method to reduce heat input, deformation, and welding defects.

[0003] Cold metal transfer welding (CMT+P) is a welding method that combines cold metal transfer welding and pulsed MIG welding. CMT achieves short-circuit transfer by retracting the welding wire, bringing the molten droplet to near-zero short-circuit transfer current, based on MIG / MAG welding. CMT has low heat input, a small heat-affected zone, and minimal impact on the base metal properties. However, CMT generally has low arc stiffness, making it unsuitable for fillet welds. CMT+P, on the other hand, is a welding method combining cold metal transfer welding and pulsed MIG welding. Developed based on CMT, it allows for greater control over heat input and higher arc stiffness, making it suitable for fillet welds.

[0004] The paper "Research on Welding Process of Thin-Walled Stainless Steel Frame Based on CMT Technology" published by Yin Yayun et al. in February 2022 in Volume 51, Issue 3 of *Hot Working Technology* investigated the effects of arc length correction and pulse correction on the surface formation of fillet welds. However, this study did not examine the weld surface formation at the arc initiation and termination points, making it unsuitable for welding fillet welds on the outer components of solid rocket motor housings. The paper "Droplet Transfer Characteristics of CMT+P for SAF2507 Super Duplex Stainless Steel" published by Huang Hanchuan et al. in Volume 40, Issue 10 of *Welding Journal* in October 2019 investigated the droplet transfer characteristics of the CMT+P welding method. This study primarily focused on droplet transfer characteristics and did not examine the weld surface formation. The invention application with application number 202210655160.4 proposes a surface forming quality control method for CMT+P arc additive manufacturing. This method provides a contour forming path scanning method to control the stability of the molten pool, thereby improving the surface forming accuracy and quality of metal structural parts. However, this method is only applicable to additive manufacturing and not to fillet welds.

[0005] Currently available CMT+P welding technologies have not investigated the influence of welding characteristic curves on fillet weld formation. This invention, based on welding characteristic curves, provides a CMT+P welding process for fillet welds on the outer components of a solid engine casing. Summary of the Invention

[0006] To overcome the shortcomings of existing manual tungsten inert gas welding (TIG) for fillet welds on external components, which results in cracks and large welding deformation, this invention proposes a CMT+P welding method for fillet welds on external components of solid engine housings.

[0007] The specific process of this invention is as follows:

[0008] Step 1: Adjust the tilt angle of the welding torch.

[0009] The welding torch tilt angle is the angle between the welding torch and the axis of the solid rocket motor housing.

[0010] The welding torch is tilted at an angle of 45°±5°, ensuring that there is no interference between the welding torch and the solid-state engine and external components during the welding process, and that there is no arc blow phenomenon.

[0011] Step 2, set welding parameters:

[0012] The welding parameters include welding speed, wire feed speed, pulse correction, and inductance correction.

[0013] Switch the welding program to CMT+P welding program. Set the wire feed speed to 580–620 mm / min. -1 The welding speed is 3.5–4.5 m / min. -1 The pulse correction is +10% to +25%, and the inductance correction is 0% to 10%.

[0014] Step 3, set the welding characteristic curve parameters:

[0015] The welding characteristic curve parameters include normal wire feed speed WN, arc initiation wire feed speed WS, arc termination wire feed speed WE, arc initiation holding time TS, arc termination holding time TE, the time SI1 required for the arc initiation wire feed speed WS to linearly decrease to the normal wire feed speed WN, and the time SI2 required for the normal wire feed speed WN to linearly decrease to the arc termination wire feed speed WE.

[0016] In the set welding characteristic curve parameters, the arc initiation wire feed speed WS is 175–185 mm·min. -1 The normal wire feeding speed WN is 580–620 mm / min. -1 The arc initiation and holding time TS is 0s; the arc termination and wire feeding speed WE is 230~250mm·min. -1 The arc sustaining time TE is 0s; SI1 is 0.3s; SI2 is 0.1s.

[0017] Step 4, Preheating:

[0018] The temperature of the external components and the solid engine housing to be welded area is raised to 100-150°C.

[0019] Step 5, Welding:

[0020] Welding is performed according to the set welding characteristic curve parameters; the welding includes an arc initiation stage, a normal welding stage, and an arc termination stage.

[0021] Arc initiation stage. During arc initiation, the wire feeding speed WS is 175–185 mm·min. -1 The wire feeding speed increases linearly, reaching the normal wire feeding speed WN within 0.3 seconds; this normal wire feeding speed WN is 580–620 mm / min. -1 Entering the normal welding stage.

[0022] Normal welding stage. Normal welding wire feed speed is 580–620 mm / min. -1 This ensures that the weld leg height of the fillet weld is kept stable at 3mm.

[0023] During the arc-terminating phase, the wire feed speed decreases linearly from the start of the arc-terminating phase, ranging from 580 to 620 mm / min within 0.1 s. -1 The linear reduction is made to the winding wire feed speed WE. When the winding wire feed speed is reduced to 230–250 mm / min... -1 The welding process ends at that point.

[0024] Complete the CMT+P welding of the fillet welds of the outer components of the solid engine housing.

[0025] The fillet weld length of this invention is 20mm ± 1mm. Initially, lap tests were conducted on two substrates with a length of 180mm, resulting in fillet welds with suitable height and good surface formation. However, when the same parameters were applied to the fillet welds of the outer components of a solid rocket motor housing, it was found that the weld at the arc initiation point was too high, X-rays detected incomplete fusion at the arc initiation point, and cracks appeared at the arc termination point. The only difference between the tests on the substrates and those applied to the outer components of the solid rocket motor housing was the fillet weld length; everything else was identical. When the fillet weld length is too short, the influence of the arc initiation and termination points on the overall weld formation and quality cannot be ignored. Without controlling the welding parameters at the arc initiation and termination points, the weld at the arc initiation point is prone to excessive height and incomplete fusion defects, while the arc termination point is prone to cracks.

[0026] Based on this, the present invention divides the CMT+P welding process into three stages: arc initiation, normal welding, and arc termination, namely the welding characteristic curve, thereby improving the surface formation and quality of fillet welds at the arc initiation, arc termination, and normal welding locations.

[0027] The welding characteristic curve parameters during the arc initiation stage involve the arc initiation wire feed speed WS, arc initiation holding time TS, and SI1. Generally, the welding current during arc initiation should be greater than the welding current during normal welding. However, since the CMT+P welding parameters are unified parameters, the welding current and welding voltage are mainly adjusted by the wire feed speed. When the heat input during arc initiation is greater than the normal welding heat input, the arc initiation wire feed speed WS is greater than the normal wire feed speed WN. This will ultimately result in the fillet weld height at the arc initiation location being higher than the normal welding location. Therefore, WS must be less than WN. However, if WS is less than WN, the welding wire cannot be fully spread during arc initiation. Therefore, this invention heats the area to be welded on the external component and shell to 100-150°C before welding. Because WS is less than WN, the fillet weld filling is insufficient, and if the TS time is too long, the fillet weld height will be lower than the normal welding location. SI1 is the transition stage between the arc initiation location and the normal welding location. If it is too long, the fillet weld height will be too low; if it is too short, the transition between the arc initiation location and the normal welding location will be unsmooth.

[0028] The welding parameters during the arc-ending phase involve the arc-ending wire feed speed (WE), arc-ending duration (TE), and SI2. An excessively high WE will lead to excessive welding current, which in turn can cause cracks at the arc-ending point. Therefore, WE should be less than WN. Because WE is less than WN, the fillet wire filling is insufficient, and an excessively long TE will result in the fillet weld height being lower than other areas. SI2 is the transition phase between the arc-ending point and the normal welding area. An excessively long SI2 will result in a low fillet weld height, while an excessively short SI2 will result in an uneven transition between the arc-ending point and the normal weld area.

[0029] This invention adjusts the welding speed and wire feed speed to match the weld leg height of the fillet weld. Appropriate pulse correction and inductance correction parameters can prevent spatter during welding and ensure a smooth fillet weld surface, avoiding stress concentration.

[0030] Since the CMT+P welding parameters are unified, the welding current and welding voltage are adjusted by the wire feed speed. When the arc initiation wire feed speed WS is set greater than or equal to the normal wire feed speed WN, the weld leg height of the fillet weld at the arc initiation point will exceed that of the normal welding point. To avoid this phenomenon, a preheating step is added. To avoid arc termination cracks at the arc termination point, the arc termination wire feed speed WE is set less than the normal wire feed speed WN.

[0031] The welding process of this invention includes an arc-starting stage, a normal welding stage, and an arc-ending stage. The purpose of controlling the wire feed speed during the arc-starting stage is threefold: first, to control the leg height of the fillet weld; second, to ensure a smooth transition between the arc-starting and normal welding areas; and third, to prevent incomplete fusion defects at the arc-starting area through appropriate parameters. During the normal welding stage, the wire feed speed remains constant, stabilizing the leg height of the fillet weld at 3mm. The purpose of controlling the wire feed speed during the arc-ending stage is also threefold: first, to control the leg height of the fillet weld; second, to ensure a smooth transition between the arc-ending and normal welding areas; and third, to prevent crack defects at the arc-ending area through appropriate parameters.

[0032] Compared with existing manual tungsten inert gas welding for external components, the present invention has the following advantages and beneficial effects:

[0033] 1. This invention realizes the automated welding of fillet welds on external components. By adjusting the tilt angle of the welding torch and the welding parameters, the welding characteristic curve is further optimized to achieve CMT+P welding of fillet welds on the external components of solid rocket motor housings.

[0034] 2. This invention divides the CMT+P welding process into three stages: arc initiation, normal welding, and arc termination, i.e., the welding characteristic curve. By adjusting the parameters of the welding characteristic curve, a smooth transition between the arc initiation / termination stage and the normal welding stage is achieved, and welding defects during arc initiation / termination are avoided.

[0035] 3. The fillet welds of external components welded using the present invention have good surface formation and excellent internal quality, effectively solving the problem of easy cracking and large welding deformation in fillet welds of external components caused by manual tungsten inert gas welding.

[0036] Figure 3 and Figure 4 These are the fillet welds of external components obtained by the present invention and the existing CMT+P technology, respectively. Figure 3 This is a drawing showing the forming quality of fillet welds on external components that were not welded using the CMT+P method of this invention. Figure 4 This is a diagram showing the surface finish of the fillet weld on an external component welded using the CMT+P welding method of this invention. It can be seen that the surface finish of the fillet weld on the external component weld obtained by this invention is significantly better than that obtained by existing technologies. Attached Figure Description

[0037] Figure 1 This is the welding characteristic curve.

[0038] Figure 2 This is a schematic diagram of the welding torch tilt angle.

[0039] Figure 3 The diagram shows the forming quality of the fillet weld of an external component that was not welded using the CMT+P method of this invention.

[0040] Figure 4This is a diagram showing the forming quality of the fillet weld of an external component welded using the CMT+P welding method of this invention.

[0041] Figure 5 This is a flowchart of the present invention.

[0042] In the diagram: 1. Solid engine casing; 2. External components; 3. Welding torch. Detailed Implementation

[0043] This embodiment describes a CMT+P welding method for fillet welds on the outer components of a solid engine casing.

[0044] The solid engine housing has a wall thickness of 2.8 mm and is made of D406A material. The outer component 2 is made of 20# steel, with a fillet weld length of 20 mm ± 1 mm and a fillet weld leg height k = 3 mm.

[0045] The welding machine used was one with CMT (Continuous Metal-to-Mechanical) function. H10SiMnCrNiMoV welding wire was selected; the wire diameter was 1.2 mm, and the wire extension length was 11–13 mm. The shielding gas used in welding was a mixture of Ar and CO2; the molar ratio of Ar was 80%, and the molar ratio of CO2 was 20%; the shielding gas flow rate was 15–20 L / min.

[0046] Table 1 Process parameters selected in this invention

[0047]

[0048] The specific steps for welding are as follows:

[0049] Step 1: Adjust the tilt angle of the welding torch.

[0050] The welding torch tilt angle is the angle between the welding torch and the solid rocket motor axis, such as... Figure 2 As shown.

[0051] The welding torch tilt angle is adjusted to 45°±5° to ensure that there is no interference between the welding torch and the solid rocket motor housing 1 and the external component 2 during the welding process, and to prevent arc blow. Arc blow refers to the phenomenon that the electric arc deflects towards the solid rocket motor or external component during the welding process.

[0052] Step 2, set welding parameters:

[0053] Welding was performed using a Furniture welding machine.

[0054] The welding parameters are the welding speed, normal wire feed speed, pulse correction, and inductance correction of the welding machine.

[0055] When setting welding parameters, switch the welding program to CMT+P. Set the wire feed speed to 580–620 mm / min.-1 The wire feeding speed is 3.5–4.5 m / min. -1 The pulse correction parameter is increased by +10% to +25% from the original factory setting, and the inductance correction parameter is increased by 0 to 10% from the original factory setting. The welding speed and wire feed speed are adjusted to match the fillet weld leg height. Appropriate pulse and inductance correction parameters can prevent spatter during welding and ensure a smooth transition of the fillet weld surface, avoiding stress concentration.

[0056] The process parameters set in step 2 of Table 2

[0057]

[0058] Step 3, set the welding characteristic curve parameters:

[0059] The welding characteristic curve parameters include normal wire feed speed WN, arc initiation wire feed speed WS, arc termination wire feed speed WE, arc initiation holding time TS, arc termination holding time TE, the time SI1 required for the arc initiation wire feed speed WS to linearly increase to the normal wire feed speed WN, and the time SI2 required for the normal wire feed speed WN to linearly decrease to the arc termination wire feed speed WE.

[0060] The normal wire feeding speed WN is the same as the wire feeding speed in step 2.

[0061] The arc-starting wire feeding speed WS is 175-185 mm·min. -1 The normal wire feeding speed WN is 580–620 mm / min. -1 The arc initiation and holding time TS is 0s; the arc termination and wire feeding speed WE is 230~250mm·min. -1 The arc sustaining time TE is 0s; SI1 is 0.3s; SI2 is 0.1s.

[0062] Table 3. Welding characteristic curve parameters determined in step 3.

[0063] Example WS / mm min -1 ]] TS / s SI1 / s WN / mm·min -1 ]] SI2 / s TE / s WE / mm·min -1 ]] 1 175 0 0.3 580 0.1 0 230 2 180 0 0.3 600 0.1 0 240 3 185 0 0.3 620 0.1 0 250

[0064] Step 4, Preheating:

[0065] The temperature of the external components and the solid engine housing to be welded area is raised to 100-150°C.

[0066] Table 4 Process parameters for step 4

[0067]

[0068]

[0069] Step 5, Welding:

[0070] In this invention, welding is performed according to the parameters in Tables 1, 2 and 3.

[0071] Arc initiation stage. The arc initiation wire feed speed WS is 175–185 mm·min. -1 Increase to the normal wire feed speed WN within 0.3 seconds; this normal wire feed speed WN is 580–620 mm / min. -1 Entering the normal welding stage.

[0072] The purpose of controlling the wire feed speed during the arc initiation stage is threefold: first, to control the height of the fillet weld leg; second, to ensure a smooth transition between the arc initiation area and the normal welding area; and third, to avoid incomplete melting defects at the arc initiation area through appropriate parameters.

[0073] Normal welding stage. During the normal welding stage, the normal wire feed speed is 580–620 mm / min. -1 Because the wire feed speed remains constant during the normal welding phase, the height of the fillet weld leg is maintained at 3mm.

[0074] During the arc-terminating phase, the wire feed speed initially decreases linearly, from 580 to 620 mm / min within 0.1 s. -1 Reduced to 230–250 mm·min -1 When the wire feeding speed is reduced to 230–250 mm / min -1 At this point, the welding is complete. The CMT+P welding of the fillet welds on the outer components of the solid rocket motor housing is finished.

[0075] By controlling the wire feeding speed during the arc termination phase, the following objectives are achieved: first, to control the height of the fillet weld leg; second, to ensure a smooth transition between the arc termination area and the normal welding area; and third, to prevent crack defects from occurring at the arc termination area through appropriate parameters.

[0076] The surface morphology of the fillet weld after welding is as follows Figure 4 As shown, no grinding is required. The fillet weld surface has a smooth transition, a beautiful shape, and is free of spatter, cracks, and incomplete fusion defects.

Claims

1. A CMT+P welding method for fillet welds on the outer components of a solid engine housing, characterized in that, The specific process is as follows: Step 1: Adjust the tilt angle of the welding torch; The welding torch tilt angle is the angle between the welding torch and the axis of the solid engine housing; the welding torch tilt angle is 45°±5°. Step 2, set welding parameters: The welding parameters include the welding speed, wire feed speed, pulse correction, and inductance correction of the welding machine; Step 3, set the welding characteristic curve parameters: The welding characteristic curve parameters include normal wire feed speed WN, arc initiation wire feed speed WS, arc termination wire feed speed WE, arc initiation holding time TS, arc termination holding time TE, the time required for the wire feed speed to increase from the arc initiation wire feed speed WS to the normal wire feed speed WN SI1, and the time required for the wire feed speed to decrease from the normal wire feed speed WN to the arc termination wire feed speed WE SI2. In the set welding characteristic curve parameters, the arc initiation wire feed speed WS is 175~185 mm·min. -1 ; The normal wire feed speed WN is 580~620 mm·min -1 The arc initiation and holding time TS is 0s; the arc termination and wire feeding speed WE is 230~250 mm·min. -1 The arc sustaining time TE is 0 s; SI1 is 0.3 s; SI2 is 0.1 s; Step 4, Preheating: Heat the external components and the area of ​​the solid engine housing to be welded to 100~150℃; Step 5, Welding: Welding is performed according to the set welding characteristic curve parameters; the welding includes an arc initiation stage, a normal welding stage, and an arc termination stage; Arc initiation stage: During arc initiation, the arc initiation wire feeding speed WS is 175~185 mm·min. -1 The arc-starting wire feeding speed WS increases to the normal wire feeding speed WN within 0.3s; the normal wire feeding speed WN is 580~620mm / min; Entering the normal welding stage; Normal welding stage: The wire feed speed during this normal welding stage is 580~620 mm·min -1 ; To ensure that the weld leg height of the fillet weld is kept stable at 3mm; During the arc-terminating phase: The wire feeding speed begins to decrease linearly during arc-terminating, decreasing from 580 to 620 mm / min within 0.1 seconds. -1 Reduced to 230~250 mm·min -1 When the wire feeding speed is reduced to 230~250 mm·min -1 At that time, the welding was completed; Complete the CMT+P welding of the fillet welds of the outer components of the solid engine housing.

2. The CMT+P welding method for fillet welds of solid engine housing outer components as described in claim 1, characterized in that, Set the welding program of the welding machine to CMT+P welding program; set the welding speed to 580~620mm / min and the wire feed speed to 3.5~4.5m / min.

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