阅读说明：本技术 一种焊接保护气最小用量的计算方法 (Method for calculating minimum consumption of welding shielding gas ) 是由 裴宏杰 陈钰荧 刘成石 王贵成 于 2019-08-05 设计创作，主要内容包括：本发明提供一种焊接保护气最小用量的计算方法,包括以下步骤：以喷嘴末端中心为坐标原点建立的保护气扩散的空间坐标系。通过分析熔池形貌,确定出有效保护范围,建立有效保护范围与侧风速度和靶距的关系。进而,根据通过有效保护范围的界定,确定出有效保护范围的临界点坐标。最后,选择连续喷射点源的建模方向,结合气体扩散理论模型,建立有侧风环境下的保护气体扩散的数学模型。并根据气体有效保护范围的界定、通过保护气体扩散的理论模型、流量与源强的关系等,确定出保护气体的最小用量的数学表达式。根据各工况取值可推导出保护气最小使用流量的理论参考值,为焊接保护气的用量及研究提供了理论支持。(The invention provides a method for calculating the minimum consumption of welding shielding gas, which comprises the following steps: and a space coordinate system of the protective gas diffusion is established by taking the center of the tail end of the nozzle as a coordinate origin. And determining an effective protection range by analyzing the appearance of the molten pool, and establishing the relation between the effective protection range and the crosswind speed and the target distance. And determining the critical point coordinates of the effective protection range according to the definition of the effective protection range. And finally, selecting the modeling direction of the continuous jet point source, and establishing a mathematical model of protective gas diffusion in the crosswind environment by combining a gas diffusion theoretical model. And determining a mathematical expression of the minimum dosage of the protective gas according to the definition of the effective protective range of the gas, a theoretical model of the diffusion of the protective gas, the relationship between the flow and the source intensity and the like. The theoretical reference value of the minimum use flow of the shielding gas can be deduced according to the values of all working conditions, and theoretical support is provided for the use amount and research of the welding shielding gas.)

1. A method for calculating the minimum consumption of welding shielding gas is characterized by comprising the following steps:

establishing a gas diffusion space coordinate system: establishing a space coordinate system of the diffusion of the shielding gas by taking the center of the tail end of the nozzle as a coordinate origin, and expressing the gas concentration of a certain point (x, y, z) in a gas diffusion range by C (x, y, z), and assuming that the shielding gas flowing in the air of the lower layer belongs to a turbulent state, obtaining the following formula according to the concentration change differential equation of the gas diffusion:

in the formula I: c is gas instantaneous jet concentration, kg/m³；

t is the jet gas diffusion time, s;

u is wind speed, m/s;

K_x,K_y,K_zthe coefficients of turbulent diffusion m in the directions of the x, y and z axes, respectively²/s；

And (3) defining the effective protection range: analyzing the appearance of the molten pool, and determining the effective protection range:

d_g＝d_mp+d_ha+d_wformula II

In the second formula: d_mpIs the width of the molten pool, d_haWidth of the fusion zone, d_wThe width is reserved for resisting the cross wind,

determining the coordinate of a critical point of the effective protection range by defining the effective protection range, combining a gas diffusion space coordinate system, wherein the origin of the coordinate is positioned at the center of the tail end of the nozzle, the height of the nozzle from the plane of a welding workpiece is represented by j, and then z is equal to j; since the effective protection range is similar to a cone shape in three dimensions, when y is 0 at the critical point, x is dg/2; if y is not equal to 0, x²+y²＝(dg/2)²(ii) a Where the wind speed u is equal to v_cwA side wind speed;

mathematical model of diffusion of shielding gas under crosswind conditions:

in the eighth formula, Q is the source strength of the gas in the nozzle, Kg/s; setting the flow rate of gas in the nozzle as q, L/min; the relationship between the flow rate of gas in the nozzle and the source intensity can be expressed as:

in the ninth formula, rho is the density of the protective gas;

calculating the minimum flow of the protective gas:

according to the definition of the effective protection range of the gas and through a protection gas diffusion mathematical model, the minimum dosage of the protection gas is expressed as:

in the formula ten: x, y, z coordinates satisfy

2. The method of claim 1, wherein the width d of the weld zone is calculated as the minimum amount of weld shielding gas used in the method_haIs 1 mm.

3. The method of claim 1, wherein the weld puddle width d is calculated as the minimum quantity of weld shield gas_mpThe relation with the calculated thickness of the welding seam is shown as the formula III:

d_mpphi x B type III

In the third formula, phi is the width-thickness ratio of the welding seam, and B is the calculated thickness of the welding seam.

4. The method for calculating the minimum consumption of the welding shielding gas according to claim 3, wherein the calculation formula of the width-thickness ratio phi of the welding seam is as follows:

φ＝R/(H+w)

wherein w is the weld reinforcement; r is the width of the weld, ignoring the shrinkage variation of the weld, in which case the width R of the weld may be approximately equal to the width d of the weld pool_mp。

5. The method of claim 1, wherein the weld puddle width d is calculated as the minimum quantity of weld shield gas_mpThe upper surface of the molten pool is equivalently replaced by a circle in an effective protection range calculated by the surface area of the molten pool, and then the upper surface of the molten pool is equivalent to the circleWherein S is the upper surface area of the molten pool.

6. Method for calculating the minimum quantity of welding protection gas according to claim 1, characterized in that said pre-set width d for resisting crosswind_wThe relationship with the target distance and the crosswind speed is shown as the following formula:

in the formula IV, d_wWidth reserved for resisting crosswind, H is target distance, H is maximum nozzle height value specified in industry, v_cwIs the crosswind velocity.

7. The method of claim 1, wherein the shielding gas concentration C is 95%.

Technical Field

The invention belongs to the technical field of welding, and particularly relates to a method for calculating the minimum consumption of welding shielding gas.

Background

Gas shielded welding is a welding method using heat of an arc generated between electrodes as a melting heat source and a shielding gas as a medium. On one hand, the protection gas can protect the stability of the internal arc combustion, on the other hand, impurities in the air can be isolated in the welding process, the quality of a welding seam is guaranteed, and splashing is reduced. The welding effect is superior to other welding methods, and the welding method becomes the most widely applied welding mode in the current industrial production.

However, the current gas is basically used for empirical rough gas supply, and during actual welding, a small amount of gas can play a role in protection, a large amount of protective gas is wasted, so that the pollution to the atmospheric environment is also aggravated while the resource consumption is increased. The main factors influencing the dosage of the protective gas have three aspects, namely the ambient crosswind speed, the target distance and the width of a molten pool. The ambient crosswind speed, when the protective gas is sprayed on the surface of the workpiece, the diffusion speed towards the periphery is higher than the crosswind speed. The target distance, which is the distance from the lower surface of the nozzle to the surface of the molten pool, is too large, so that the protection effect and the production efficiency are reduced. The width of the molten pool and the area of the stamping plate from the protective gas to the surface of the workpiece should be fully coated on the molten pool, the coating amount is too small, the protection is insufficient, and the protective gas is wasted due to too large coating amount. How to determine the minimum amount of shielding gas to be used according to the effective protection range of the gas is one of the important points of research in the field of welding.

Disclosure of Invention

Aiming at the situation that the shield gas consumption is larger based on experience determination in the traditional gas shielded welding, a new calculation method of the minimum amount of the shield gas consumption is provided. In the welding process, the working process of the protective gas in the gas shielded welding can be equivalently understood as gas diffusion movement coupled with factors such as source intensity, cross wind, temperature and the like. The method firstly establishes a space coordinate system of the protective gas diffusion by taking the center of the tail end of the nozzle as a coordinate origin. And determining an effective protection range dg by analyzing the appearance of the molten pool, and establishing a relation between the effective protection range dg and the crosswind speed and the target distance h. And determining the critical point coordinates of the effective protection range according to the definition of the effective protection range. And finally, selecting the modeling direction of the continuous jet point source, and establishing a mathematical model of protective gas diffusion in the crosswind environment by combining a gas diffusion theoretical model. And determining a mathematical expression of the minimum dosage of the protective gas according to the definition of the effective protective range of the gas, a theoretical model of the diffusion of the protective gas, the relationship between the flow and the source intensity and the like. The theoretical reference value of the minimum use flow of the shielding gas can be deduced according to the values of all working conditions, and theoretical support is provided for the use amount and research of the welding shielding gas.

The invention is realized by the following scheme: a method for calculating the minimum consumption of welding shielding gas comprises the following steps:

establishing a gas diffusion space coordinate system: the working process of the protective gas in the gas shielded welding is equivalent to gas diffusion movement, a space coordinate system of protective gas diffusion is established by taking the center of the tail end of a nozzle as a coordinate origin, the gas concentration of a certain point (x, y, z) in a gas diffusion range is represented by C (x, y, z), and if the protective gas flowing in the lower-layer air belongs to a turbulent flow state, a differential equation can be obtained according to the concentration change of the gas diffusion:

in the formula I: c is gas instantaneous jet concentration, kg/m³；

t is the jet gas diffusion time, s;

u is wind speed, m/s;

K_x,K_y,K_zthe coefficients of turbulent diffusion m in the directions of the x, y and z axes, respectively²/s；

And (3) defining the effective protection range: analyzing the appearance of the molten pool, and determining an effective protection range dg, wherein:

d_g＝d_mp+d_ha+d_wformula II

In the second formula: d_mpIs the width of the molten pool, d_haWidth of the fusion zone, d_wThe width is reserved for resisting the cross wind,

determining the coordinate of a critical point of the effective protection range by defining the effective protection range, combining a gas diffusion space coordinate system, wherein the origin of the coordinate is positioned at the center of the tail end of the nozzle, the height of the nozzle from the plane of a welding workpiece is represented by j, and then z is equal to j; since the effective protection range is similar to a cone shape in three dimensions, when y is 0 at the critical point, x is 0dg/2; if y is not equal to 0, x²+y²＝(dg/2)²(ii) a Where the wind speed u is equal to v_cwA side wind speed;

mathematical model of diffusion of shielding gas under crosswind conditions:

in the eighth formula, Q is the source strength of the gas in the nozzle, Kg/s; setting the flow rate of gas in the nozzle as q, L/min; the relationship between the flow rate of gas in the nozzle and the source intensity can be expressed as:

in the ninth formula, rho is the density of the protective gas;

calculating the minimum flow of the protective gas:

according to the definition of the effective protection range of the gas and through a protection gas diffusion mathematical model, the minimum dosage of the protection gas is expressed as:

in the formula ten: x, y, z coordinates satisfy

In the above-mentioned embodiment, the width d of the fusion zone_haIs 1 mm.

In the above scheme, the width d of the molten pool_mpThe relation with the calculated thickness of the welding seam is shown as the formula III:

d_mpphi x B type III

In the third formula, phi is the width-thickness ratio of the welding seam, and B is the calculated thickness of the welding seam.

Further, the calculation formula of the width-thickness ratio phi of the welding seam is as follows:

φ＝R/(H+w)

wherein w is the weld reinforcement; r is the width of the weld, neglecting the shrinkage variation of the weld, thisThe width R of the weld may be approximately equal to the width d of the weld pool_mp。

In the above scheme, the width d of the molten pool_mpThe upper surface of the molten pool is equivalently replaced by a circle in an effective protection range calculated by the surface area of the molten pool, and then the upper surface of the molten pool is equivalent to the circleWherein S is the upper surface area of the molten pool.

In the above scheme, the reserved width d for resisting crosswind_wThe relationship with the target distance and the crosswind speed is shown as the following formula:

in the formula IV, d_wWidth reserved for resisting crosswind, H is target distance, H is maximum nozzle height value specified in industry, v_cwIs the crosswind velocity.

In the above embodiment, the shielding gas concentration C is 95%.

Compared with the prior art, the invention has the beneficial effects that: the method has a simple model, can deduce a theoretical reference value of the minimum use flow of the shielding gas according to values of various working conditions, and can properly adjust the use flow according to the theoretical reference value and in combination with the welding effect in the actual welding work, thereby avoiding excessive use, reducing resource consumption, reducing manufacturing cost and providing theoretical support for the use amount and research of the welding shielding gas.

Drawings

FIG. 1 is a coordinate system of shielding gas diffusion in a crosswind environment according to an embodiment of the present invention.

FIG. 2 is a schematic view of a molten bath and a gas shield according to an embodiment of the present invention.

Detailed Description

The invention will be further described with reference to the following figures and specific examples, but the scope of the invention is not limited thereto.

A method for calculating the minimum consumption of welding shielding gas comprises the following steps:

establishing a gas diffusion space coordinate system:

fig. 1 shows a coordinate system for shielding gas diffusion in a crosswind environment according to the present invention. The protective gas is sprayed from the end of the nozzle and is diffused under the influence of cross wind and the atmospheric environment, which is equivalent to the spraying and diffusing process of the leakage gas when the sealed container leaks in the atmospheric environment. Because the atmosphere is a semi-infinite medium, even if the motion change is weak, the atmosphere can have a large Reynolds number to achieve a turbulent flow state. Therefore, the welding protective gas flowing in the lower layer of air is assumed to be in a turbulent flow state, and the working process of the protective gas during welding is equivalent to the diffusion movement of the leaked gas of the sealed container coupled with factors such as cross wind, temperature and the like under the condition of strong continuous source. Therefore, a spatial coordinate system of the diffusion of the shielding gas is established with the center of the nozzle tip as the origin of coordinates, and as shown in fig. 1, C (x, y, z) represents the gas concentration at a certain point (x, y, z) in the gas diffusion range, and assuming that the shielding gas flowing in the air in the lower layer belongs to a turbulent state, the differential equation of the concentration change of the gas diffusion can be obtained:

in the formula I: instantaneous C-gas injection concentration, kg/m³；

t-jet gas diffusion time, s;

u-wind speed, m/s;

K_x,K_y,K_z-coefficient of turbulent diffusion in x, y, z directions, m²/s。

And (3) defining the effective protection range:

FIG. 2 is a schematic diagram of the molten pool and the gas protection range established by the present invention, analyzing the molten pool morphology, determining the effective protection range dg, establishing the effective protection range dg and the crosswind speed v_cwAnd target distance h.

The effective protection range of the gas shielded welding mainly comprises a molten pool width, a fusion zone width and a reserved width for resisting crosswind, and can be expressed by a formula: ,

d_g＝d_mp+d_ha+d_wformula II

In the formula II, d_gFor the effective protection range of gas-shielded welding, d is a numerical value_gDistance in cross section of effective protection range of gas shielded welding, d_mpIs the width of the molten pool, d_haWidth of the fusion zone, d_wReserving width for resisting crosswind.

The relation between the width of the molten pool and the calculated thickness of the welding seam is shown as the formula III:

d_mpphi x B type III

Wherein phi is the width-thickness ratio of the welding seam, and B-the thickness of the welding seam is calculated.

The boundary area of the welding seam and the base metal is a welding fusion area with the width d_haIt is generally narrow, typically about 1 mm.

Reserved width d for resisting crosswind_wThe relation between the target distance and the crosswind speed is shown as the formula IV

In the formula IV, d_wWidth reserved for resisting crosswind, H is target distance, H is maximum nozzle height value specified in industry, v_cwIs the crosswind velocity.

According to the formulas two, three and four and the schematic diagram of the protection range of the molten pool and the gas, the critical point coordinate of the effective protection range in the graph 1 can be determined. By defining the effective protection range, the origin of the coordinate is positioned at the center of the tail end of the nozzle, the height of the nozzle from the plane of the welding workpiece is represented by j, and z is equal to j; since the protection range is approximately conical in three dimensions, as shown in fig. 1, x is dg/2 when y is 0 at the critical point; if y is not equal to 0, x²+y²＝(dg/2)²(ii) a Where the wind speed u ═ v_cwThe side wind speed.

Mathematical model of diffusion of shielding gas under crosswind conditions:

the leakage point source of gas diffusion mainly comprises a transient source and a continuous source, and in the case of gas shielded welding, gas is continuously sprayed out of a nozzle, and the source intensity type of the gas shielded welding belongs to the continuous source.

In an environment with side wind, the model of the shielding gas diffusion is feathered, and in the wind direction, the total amount of shielding gas in the y-z space is the source intensity Q, i.e., the

In the case that the flow field is relatively stable, then the concentration of the shielding gas at a certain coordinate point in space is a constant value and does not change with time, so under the crosswind condition, it can be obtained:

through simplification, the formula six is:

initial conditions in environmental variables: when x is y is 0, C → ∞; boundary conditions: x, y, z → ∞ time, C → 0. According to the gaussian model, the concentration equation of the protective gas diffusion in the presence of crosswind is:

in the eighth formula, Q is the source strength of the gas in the nozzle, Kg/s; setting the flow rate of gas in the nozzle as q, L/min; the relationship between the flow rate of gas in the nozzle and the source intensity can be expressed as:

in the formula nine, rho is the density of the protective gas.

Calculating the minimum flow of the protective gas:

according to the definition of the effective protection range of the gas and the theoretical model of the diffusion of the protection gas, the minimum dosage of the protection gas can be expressed as follows:

in the formula ten: x, y, z coordinates satisfy

According to the above study, d_g＝d_mp+d_ha+d_wWherein d is_mpOn one hand, phi is R/(H + w), w is the weld reinforcement, and changes such as contraction of the weld are ignored, and the width R of the weld can be approximately equal to the width of the molten pool; on the other hand, the width d of the molten pool_mpCan be calculated by the surface area of the molten pool, and the upper surface of the molten pool can be equivalently replaced by a circle within the effective protection range, and then the upper surface of the molten pool is equivalent to the circleAnd S is the upper surface area of the molten pool. Where C ═ C (x, y, z) represents the concentration of the gas at a certain point coordinate within the effective protection range. According to related researches, the protective effect can be achieved only when the protective gas concentration around the molten pool reaches more than 95% in the welding work, so that the concentration in the effective protection range is more than or equal to 95%, and the protective gas concentration C at the critical point is 95%. In the formula, K_x、K_yThe diffusion coefficient of the plume diffusion model can be selected according to the Pasquill-Gifford model method, as shown in table 1. Through calculation verification, the stability grade is generally selected to be the urban condition grade D when gas shielded welding is carried out under the crosswind condition of 0.5 m/s.

TABLE 1 diffusion coefficient of Passell-Gifford plume diffusion model

The present invention is not limited to the above-described embodiments, and any obvious improvements, substitutions or modifications can be made by those skilled in the art without departing from the spirit of the present invention.