JP2015202499A - Estimation method of nugget diameter of resistance spot welding - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an estimation method of a nugget diameter of resistance spot welding capable of predicting a weld lobe under a condition of requiring consideration of a distributary of an electric current, on a desk, by using the weld lobe of already acquired single point welding.SOLUTION: In an estimation method of a nugget diameter of resistance spot welding, kof I=k×Iis determined by using a thickness (t) of a welding object material, an electric current Iflowing between electrodes for sandwiching the welding object material, an electric current Iflowing in a welding point, a distance (b) between the welding point and an already dotted point, a nugget diameter dof the welding point in the case of single point welding, a nugget diameter dof the welding point and the already dotted point when welded under the same welding condition as the single point welding, specific resistance ρof a welding part and specific resistance ρof a distributary part, and the determined kis substituted in a relational expression of dand d, and the nugget diameter in the already-known weld lobe of the single point welding is substituted in dof the relational expression, so that the nugget diameter is estimated when having the already dotted point corresponding to a current condition.

Description

  The present invention relates to a method for estimating a nugget diameter in resistance spot welding. More specifically, the present invention relates to a method for estimating a nugget diameter of resistance spot welding under a condition in which a current flowing through a welding point to be welded by resistance spot welding is diverted to an already welded spot existing in the vicinity of the welding point.

  As one method for joining materials in various industrial members such as automobiles, resistance spot welding is used. In resistance spot welding, two or more workpieces to be joined are sandwiched between electrodes, and electricity is applied while pressing the workpieces with these electrodes. Thereby, a part of contact interface of the to-be-welded two or more to-be-welded materials is fuse | melted and joined.

  As a technique regarding such resistance spot welding, for example, Non-Patent Document 1, p. FIG. 4 of 11 shows a typical nugget growth process in spot welding. Here, a diagram (for example, FIG. 5 of Non-Patent Document 1, p. 87) in which an appropriate welding range is displayed two-dimensionally by combining current and pressure, or current and welding time as variables, and combining them. The expression “weld lobe” is generally used for a curve described on a coordinate plane called “weld lobe” and having a current on the horizontal axis and a nugget diameter on the vertical axis.

Edited by the Light Welding Society of Japan, “Resistance spot welding of thin steel plates and aluminum alloy plates”, p. 11, 87

  In resistance spot welding, when the interval between welding points is narrow, the current applied to the welding point is diverted to the hitting point in the vicinity, delaying the formation of the melted part (nugget), or a sound nugget cannot be obtained. is there. On the other hand, from the viewpoint of improving the rigidity of the parts, it is required to arrange spot welding points at appropriate positions. In some cases, it is effective to narrow the spot welding point interval (to reduce the pitch). Under such conditions where shunting is unavoidable, it is difficult to determine the appropriate welding conditions from the weld lobe obtained by laboratory single-point welding. It is necessary to collect a weld lobe according to the (divided flow rate). However, since there are a large number of materials to be welded that can be welded by resistance spot welding, an experiment that considers the diversion is performed for each combination according to the distance between the welding point and the hit point, and the weld lobe is Collecting is extremely difficult from the viewpoint of working time and the like.

  If the weld lobe can be predicted on the desk using the already obtained single-point welding weld lobe without considering the split flow, and if the weld lobe is collected by conducting an experiment It is considered that the required weld lobe can be obtained in a shorter time. However, no such prediction technology has been reported so far.

  Therefore, the present invention uses the already obtained single-point welding weld lobe to estimate the resistance lobe welding nugget diameter in which the weld lobe in a condition that requires consideration of current shunting can be predicted on a desk. It is an object to provide a method.

  As a result of intensive studies, the inventor of the present invention has made a welded lobe at the time of single-point welding, which is usually taken in a laboratory for two-layered plate sets of the same thickness, the same thickness, and the different thickness. If there is a single spot near the weld point, and if there are two spot hits on the straight line including the weld point at the same distance on both sides near the weld point, consider the effect of diversion It was found that the welded lobe can be easily predicted on a desk. It was also found that the appropriate welding conditions (appropriate current conditions) can be easily estimated by comparing the predicted weld lobe and the required nugget diameter. The present invention has been completed based on such findings. The present invention will be described below.

The first aspect of the present invention considers that the current flowing through the welding point to be welded by resistance spot welding is shunted to the already welded hit point existing at a predetermined distance from the welding point. When the weld lobe, which is the relationship between the energizing current and the nugget diameter at the welding point, is estimated, the thickness of each of the two workpieces to be welded by resistance spot welding is t [mm], Welding in the case of single point welding where the current flowing between the electrodes sandwiching the welding material is I ₀ [kA], the current flowing through the welding point is I _a [kA], the predetermined distance is b [mm], and there is no hit point. The nugget diameter of the point is d ₀ [mm], the nugget diameter of the weld point and the hit point when the welding is performed under the same welding conditions as the single point welding is d _a [mm], and the average specific resistance of the weld is ρ _a [Ω ・ m], average ratio of shunt Anti the ρ _b [Ω · m], that when, in the case of already hitting point 1 _{point, k a} of _{I a =} k _a · I ₀ is represented by the following formula (X), already hitting point two points _{If, k a} of _{I a =} k _a · I ₀ is represented by the following formula (Y), to represent a _{k a,} represented by a function of the nugget diameter _{d a} and _k a _{(d a),} is already RBI In the case of one point, in a known weld lobe, which is a combination of kugget diameters d _{0 and k} obtained for _k current conditions I _{0 and k} in single-point welding (k is an integer greater than 1), respectively. the d _{0, k} is substituted into _{d 0} of the formula (Z), and, by substituting _{k a} represented by the following formula (X) to _k a _{(d a)} of the following formula (Z) The nugget diameter da _{, k} when there are already hit points corresponding to the current conditions I _{0, k} is estimated, and when there are 2 hit points, k types (k The a _{d 0, k} at a known weld lobe is a combination of nugget diameter _{d 0, k} respectively obtained with respect to the current condition _{I 0, k} of an integer greater than 1) to _{d 0} of the formula (Z) assignment was, and, by substituting _{k a} represented by the following formula (Y) to _k a _{(d a)} of the following formula (Z), corresponding to the current condition _{I 0, k,} having already RBI This is a method for estimating the nugget diameter of resistance spot welding, which includes a nugget diameter estimation step of estimating the nugget diameter da _{, k} in the case.

Here, in the first aspect of the present invention and the other aspects of the present invention, “current” means effective current in the case of alternating current. In addition, the “welded portion” means that a current starting from one electrode constituting a pair of electrodes sandwiching two materials to be welded passes through _a joining interface having _a diameter da to be welded, to the other electrode. This refers to a substantially cylindrical energized region. In addition, the “diversion portion” refers to a region in which a current starting from one electrode constituting a pair of electrodes sandwiching two materials to be welded passes through to the other electrode via a hit point. . That is, the sum of the currents passing through the “welded part” and the “diversion part” is the amount of current passed between the two electrodes. The “average specific resistance” represents the time average of the specific resistance change of the part, which changes with the temperature change in the welded part and the shunt part from the start to the end of welding. More specifically, included in the formula (X) or formula (Y), a concept has been introduced to provide a time average in the form of (ρ _{b /} ρ _a), the specific resistance [rho _a current-carrying part is typically the When considering a steel sheet that is rapidly heated to a temperature at which the weld is melted and the present invention is intended, it is considered that it gradually increases as the temperature rises above the Curie point (about 770 ° C.), and the ratio of the flow-dividing part resistance [rho _b, the temperature rise diverter is relative to the conductive portion is the slow, be considered also again gradually increases changes that for that reason the temperature rises, i.e., even in the energizing unit, specific resistance in shunt unit Since both increase gradually, the time change of the ratio (ρ _b / ρ _a ) is small, meaning that it can be roughly handled as an almost uniform average value for each combination of materials to be welded. Also, the nugget diameter of the welding point and already RBI, both have a d _a (approximate) because, usually, in the proximity RBI enough diversion affects, of course, the plate pairs also believed the same, the same This is because the plate assembly is expected to have the same nugget diameter for quality control and is considered to be practically acceptable.
In the first aspect of the present invention, using a known weld lobe in the case of single-point welding, the nugget diameter d of the welding point corresponding to the current condition I _{0, k} when the number of hit points is one or two points. _{a, k} are estimated. By estimating the nugget diameter of the welding point corresponding to each of a plurality of current conditions, it is possible to estimate the weld lobe when the number of hit points is one or two. Therefore, by adopting such a configuration, when two workpieces having the same thickness are to be resistance spot welded, current splitting of current can be performed using a welded lobe of single point welding already obtained. It is possible to provide a resistance spot welding nugget diameter estimation method capable of easily predicting a weld lobe in a condition requiring consideration on a desk.

The second aspect of the present invention considers that the current flowing through the welding point to be welded by resistance spot welding is shunted to the already welded hit point existing at a predetermined distance from the welding point. When the weld lobe, which is the relationship between the energizing current and the nugget diameter at the welding point, is estimated, the thicknesses of the first and second welded materials to be welded by resistance spot welding are t ₁ [mm], respectively. And t ₂ [mm], I ₀ [kA] as the current flowing between the electrodes sandwiching the first and second welded materials, I _a [kA] as the current flowing through the welding point, and b as the predetermined distance [Mm], the nugget diameter of the welding point in the case of single-point welding where there is no hit point d ₀ [mm], and the nugget diameter of the welding point and the hit point in the case of welding under the same welding conditions as the single point welding is d _a [mm], of the weld Hitoshiteki a resistivity ρ _a [Ω · m], the average resistivity of the diverter ρ _b [Ω · m], the ρ _b / ρ _a relative first workpieces (ρ _b / ρ _{a) 1} , ρ _b / ρ _a for the second workpiece is (ρ _b / ρ _a ) _2, and t ₁ , t ₂ , (ρ _b / ρ _a ) ₁ , and (ρ _b / ρ _a ) ₂ when the _{[rho ab,} the value represented by the following formula (W) by using, in the case of already hitting point 1 _{point, k a} of _{I a =} k _a · I ₀ is represented by the following formula (X) ' , if already hitting point 2 _points, I _{a =} k _{k a} of a · _{I 0} is represented by the following formula (Y) ', a _{k a,} represented by a function of the nugget diameter _{d a k a (d a} ), When the number of hit points is one point, the nugget diameters d _{0 and k} obtained for _k current conditions I _{0 and k} (k is an integer larger than 1) by single-point welding, respectively. A known weld draw that is a combination The _{d 0, k} at blanking substituted into _{d 0} of the formula (Z), and, substituting _{k a} represented by the following formula (X) 'to _k a _{(d a)} of the formula (Z) Thus, the nugget diameter da _{, k} when there are already hit points corresponding to the current conditions I _{0, k} is estimated, and when there are two hit points, k types (k is 1) by single-point welding. the d _{0, k} is substituted into d ₀ of the formula (Z) in an integer greater than) the known weld lobe is a combination of nugget diameter d _{0, k} respectively obtained with respect to the current condition I _{0, k} of In addition, by substituting k _a represented by the following formula (Y) ′ into k _a (d _a ) in the following formula (Z) _, there is an already hit point corresponding to the current condition I _{0, k} Nugget diameter estimation of resistance spot welding having a nugget diameter estimation step for estimating the nugget diameter da _{, k} It is a regular method.

In the second aspect of the present invention, the current condition I _0, using a known weld lobe in the case of single-point welding of the first welded material having the thickness t _{1 and} the second welded material having the thickness t _{2 ,} The nugget diameter da _{, k} of the welding point when the number of hit points corresponding to _k is 1 or 2 is estimated. By estimating the nugget diameter of the welding point corresponding to each of a plurality of current conditions, it is possible to estimate the weld lobe when the number of hit points is one or two. Therefore, by adopting such a configuration, even when two materials to be welded having different plate thicknesses are resistance spot welded, current splitting of current can be performed by using the already obtained single-point welding weld lobe. Therefore, it is possible to provide a method for estimating the nugget diameter of resistance spot welding, in which a weld lobe in a condition that needs to be considered can be easily predicted on a desk.

In the first aspect of the present invention and the second aspect of the present invention, the energization time during which the nugget diameter d ₀ is obtained under welding conditions in which the current I _{0 is} passed by the single point welding is τ _e , When the current flowing through the point is shunted to the previously hit point, the same pressure and energization time τ _e as those under the welding conditions in which the nugget diameter d ₀ is obtained by flowing the current I ₀ over the energization time τ _e by single-point welding. When the current required to obtain the nugget diameter d ₀ is I ₀ ^* , a current estimation step for estimating the current I ₀ ^* using the following formula (V) may be further included.

Here, “k _a (d ₀ )” is k _a expressed as _a function of the nugget diameter d ₀ .
By adopting such a configuration, when the current that should flow through the welding point is shunted to the hit point, the current I ₀ ^* necessary for obtaining the same nugget diameter d ₀ as in the case of single point welding is easily predicted. It becomes possible.

  According to the present invention, the resistance of the spot welding nugget diameter can be predicted on the desk using the already obtained single-point welding weld lobe, in which it is possible to predict the weld lobe in a condition that requires consideration of current shunting. An estimation method can be provided.

It is a figure explaining the estimation method of the nugget diameter of resistance spot welding of this invention. Is a diagram illustrating a current I ₀ ^* interpolation. It is a figure explaining the derivation process of a shunt evaluation numerical model. It is a figure which shows the conductors 1, 2, and 3 attached to the line by the space | interval b. It is a figure which shows the cross section of an electricity supply part typically. Fig.5 (a) is a figure which shows typically the cross section of the electricity supply part of single point welding, and FIG.5 (b) is a figure which shows typically the cross section of the electricity supply part of shunt welding. It is a figure which compares the weld lobe of the condition 1 estimated by this invention with the weld lobe of the condition 1 calculated | required by experiment. It is a figure which compares the weld lobe of the condition 2 estimated by this invention with the weld lobe of the condition 2 calculated | required by experiment. It is a figure which compares the weld lobe of the condition 3 estimated by this invention with the weld lobe of the condition 3 calculated | required by the three-dimensional finite element method analysis. It is a figure which compares the weld lobe of the condition 4 estimated by this invention with the weld lobe of the condition 4 calculated | required by the three-dimensional finite element method analysis. It is a figure which compares the weld lobe of the condition 5 estimated by this invention with the weld lobe of the condition 5 calculated | required by the three-dimensional finite element method analysis. It is a figure which compares the weld lobe of the condition 6 estimated by this invention with the weld lobe of the condition 6 calculated | required by the three-dimensional finite element method analysis.

  Embodiments of the present invention will be described below. In addition, the following description is an illustration of this invention and this invention is not limited to the form illustrated below.

1. Configuration of the Present Invention FIG. 1 is a diagram for explaining a nugget diameter estimation method S10 of resistance spot welding according to the present invention. The present invention shown in FIG. 1 includes a nugget diameter estimation step (S1) and a current estimation step (S2). Of the configurations (i) to (v) described later, (i) to (iii) are descriptions relating to the nugget diameter estimation step, and (iv) is a description regarding the current estimation step. Moreover, (v) is an explanation regarding a case where the thicknesses of the two welded materials (steel plates) to be welded are different.

1.1. Nugget diameter estimation process (S1)
(I) When two steel plates of the same material with a thickness of t are stacked and resistance spot welding is performed between the electrodes through an energization amount I ₀ , (A) When there is one hit point at a distance b from the welding point And (B) When there are two hit points, the current I _a flowing through the welding point is represented by I _a = k _a · I ₀ , and k _a is the following formula for the condition (A): It is given by (1), and for condition (B), it is given by the following equation (2).

Here, d _a is the nugget diameter of the weld point and the hit point, and (ρ _b / ρ _a ) is _a material parameter that can be experimentally determined for each plate set (steel plate material), for example, JSC270D and JSC590R. Then, it is the value of Table 1. A method for determining (ρ _b / ρ _a ) will be described later.

(Ii) When the nugget diameter in single-point welding is d ₀ , there is a hit point at a distance b from the welding point under the same welding conditions (same pressure, current value, energization time) as the single-point welding. nugget diameter d _a obtained in welds case,

Is given as a solution. However, k _a (d _a ) is given by Equation (1) when the number of hit points is one, and by Equation (2) when the number of hit points is two.

(Iii) A combination (so-called weld lobe) of nugget diameters d _{0 and k} obtained for each of _k current conditions I _{0 and k} (k is an integer greater than 1) in single point welding is known. By using d _{0, k} for d ₀ in equation (3) described in (ii) above, the nugget diameter d _{a, k} when there is a hit point corresponding to the current condition I _{0 , k} , that is, It is possible to estimate the weld lobe when there is a hit point.

1.2. Current estimation step (S2)
(Iv) It is assumed that the nugget diameter d ₀ is obtained by single-point welding under the welding conditions of current = I ₀ and energization time = τ _e . On the other hand, the current required to obtain the nugget diameter d ₀ (target nugget diameter) with the same pressure and energization time in the shunt welding in which the current is diverted to the hit point is I ₀ ^* . At this time, in the single point welding, if the weld lobe d _{0, j} (j = 1 to N) for N current conditions I _{0, j} (j = 1 to N) is known from the experiment, the above (iii) Therefore, the weld lobe d _{a, j} (j = 1 to N) at the time of shunt welding corresponding to I _{0, j} can also be predicted immediately, so that d _{a, 1} ≦ d ₀ ≦ d _{a, In} the case of _N , I ₀ ^* can be obtained from the equation (4) by linear interpolation.

However,
d _{a, j} ≦ d ₀ ≦ d _{a, j + 1} (j = 1, 2,..., N−1)
It is.
By the way, when d ₀ > d _{a, N} , I ₀ ^* cannot be obtained by interpolation from known points as described above. In this case, it is only necessary to approximate the weld lobe of single-point welding from the actual measurement result and extrapolate d ₀ in the high current region (> I _{0, N} ). For example, a known weld lobe (I _{0, j} , d _{0, j} ; j = 1 to N) is obtained using a function f

When can be approximated as, nugget diameter _d ^{0 *} is for any current _I ^{0 *,}

It can be obtained more. On the other hand, when the current required to obtain a nugget diameter _{d 0} during shunting the welding is to be _I ^{0 *,} and change the _{d a} to _{d 0} in equation (3), and changes the _{d 0} to _d ^{0 *} Further, the following relational expression is obtained by applying the relation of the expression (6) to d ₀ ^* .

By solving Equation (7) for I ₀ ^* , the current to be obtained is expressed as:

Of course, this procedure can also be applied to the cases of da _{, 1} ≦ d ₀ ≦ da _{, N} , so if there are enough measured points (current levels) in the weld lobe in single point welding, the target nugget it can be applied regardless of the size of the diameter d _0.

(V) The techniques described in (i) to (iv) above can be extended to two-plate assembly welding with different thicknesses regardless of different materials and the same materials. Now, a material to be welded first plate thickness t _1, the plate thickness is considered to be welded material 2 t _2. The welded material 1 and the welded material 2 may be the same material or different materials. In this case, the _{k a} of formula (1) and (2), by setting the respective following equations (9) and (10), the techniques described above (i) ~ (iii), of different thickness It can be used as it is for double plate welding.

Here, when (ρ _b / ρ _a ) for the workpiece 1 and the workpiece 2 are (ρ _b / ρ _a ) ₁ and (ρ _b / ρ _a ) ₂ respectively, the equation (9) Ρ _ab in the equation (10) is represented by the following equation (11).

2. Derivation of Formula Consider a modeling of a current-carrying path during shunt welding for a two-ply plate set of the same material and the same thickness handled in the present invention. 3A shows a case where there is one hit point at a position b from the welding point, and FIG. 3B shows a case where there are two hit points on both sides of the welding point at a position b from the welding point. FIG. 5 is a diagram schematically showing an energization path when energizing each of the two steel plates while being sandwiched between a pair of electrodes.

The electrical resistance between the electrodes is considered for each of the models (A) and (B) shown in FIG. Assuming that the current-carrying diameter (diameter) of the welding point and the hit point during welding is constant at d _a (= 2r) and the contact resistance between the plates is ignored, the resistance R _a of the welded portion per plate And the resistance R _{b of the} shunt portion is expressed by the following equations (12) and (13) in the case of the model (A), and in the following equations (14) and (15) in the case of the model (B). expressed.

Here, ρ _a and ρ _b are the average specific resistance [Ω · m] of the welded portion and the diverted portion, b is the distance [mm] between the weld point and the hit point, and t is the plate thickness [mm], respectively. is there. As shown in FIG. 3, the resistance R _a of the energization part is approximated by the resistance of a cylinder having a thickness t and a cross-sectional area of πr ² . On the other hand, the resistance _Rb of the flow dividing portion is derived as follows, for example, in the case of the model (B) (when there are two hit points).

Now, as shown in FIG. 4, consider attaching one conductor 3 of the cylindrical radius r ₀ of the (1,2,3), in a row so that each interval thin steel plate having a thickness of t is b . However, it is assumed that t << r ₀ << b. Considering the case where the specific resistance of the conductor is sufficiently larger than the specific resistance ρ of the steel sheet, the potential of the conductor is constant over the entire length, and can be considered as an approximate electrostatic problem when determining the electric field. Assume that the line charge densities q ₁ , q ₂ , and q ₃ on the conductors 1, 2, and 3 shown in FIG. 4 are q ₁ = 2q and q ₂ = q ₃ = −q, respectively. According to Gauss's theorem, the electric field strengths E ₁ , E ₂ , and E ₃ created by the conductors ₁ , ₂ , and ₃ are expressed as follows: r is the distance from the conductor axis, and ε ₀ is the dielectric constant of the vacuum.

It is. Therefore, the potential difference between conductor 1 and conductor 2 (and conductor 3) is

Can be written. Here, from b >> r ₀ , considering that the potential near each conductor does not depend on the charges on the other conductors, assuming that the current density j is constant regardless of the thickness of the steel sheet, the current flows from the conductor 1. The following equation holds for all currents.

Therefore, the following equation (20) is obtained as the resistance between the conductor 1 and the conductor 2 (and the conductor 3).

In Equation (20), r ₀ is rewritten as d _a / 2 and ρ is expressed as ρ _b , which is the resistance R _b (Equation (15)) of the shunt portion in the model (B) shown in FIG. Similarly, the resistance R _b (formula (13)) of the flow dividing portion in the case where the number of hit points is one (model (A) shown in FIG. 3) can also be derived.

After all, considered Synthesis and resistor R _b of the resistance between the electrodes and the resistance R _a weld diverter becomes parallel resistance, the ratio (power ratio) of the current flowing through the weld of the total current energized k _a Is calculated, the equation (1) is obtained when the number of hit points is one, and the equation (2) is obtained when the number of hit points is two.

  Next, a method for predicting the weld lobe at the time of the shunt welding from the nugget growth curve (weld lobe) of the single-point welding will be described in consideration of more proactive use of the shunt evaluation numerical model shown in FIG. First, focusing on the amount of heat generated in single-point welding and shunt welding, the basic logic for predicting the weld lobe during shunt welding is derived by setting some simplifications and assumptions.

For single-point welding and shunt welding, nugget diameters obtained under the same welding conditions (current I ₀ , welding time τ _e ) are d ₀ and d _a , respectively, and the following approximation is set.
-Under the same conditions of plate assembly, electrode shape, and applied pressure, the current-carrying area S (volume of the current-carrying part) is the same (Fig. 5).
And thermal diffusion of the conductive portion (heat conduction), and the specific resistance [rho _a of-energizing portion time variation negligible current ratio k _a constant and uniform and can be regarded (temperature of the conductive portion is approximate to Curie point)
- with or without diversion, this time nugget shape is three-dimensionally similar, the calorific value Q ₀ and Q _a in the conductive portion of the single-point welding and shunt welding, as follows referring to FIG. 4, respectively You can write

Here, when it is assumed that the ratio of the calorific values represented by the equations (21) and (22) is equal to the volume ratio of the nugget to be formed,

The following relationship is obtained. By solving the above equation for k _a, the following important formula (24) is obtained.

Here, ka is a function of the plate thickness t, the hitting point distance b, the nugget diameter d _a , and ρ _b / ρ _a , and when t and b are known, the function is only d _a and ρ _b / ρ _a. It becomes. This expression is nothing but Expression (3).

Next, ρ _b / ρ _a included in the equations (1) to (3) is identified. The basic idea is that the nugget diameter d ₀ at the single point welding obtained from the experiment (or numerical analysis that can predict the nugget diameter at the time of spot welding: hereinafter simply analysis) and the shunt welding obtained from the experiment (or analysis) For the set of nugget diameters d _a of {d ₀ , d _a }, the results are prepared under several welding conditions, and ρ _b / ρ _a is determined so that these satisfy Expressions (1) to (3). To do. At this time, as _{a way} of selecting {d ₀ , d _a }, preparation is made under as many conditions (levels) as possible with respect to the plate thicknesses t and b included in the expressions (1) and (2). preferable.

Now, for the steel sheet M, combinations of the respective nugget diameters d ₀ and d _a obtained under the same welding conditions (pressing force, current, energization time) in single point welding and shunt welding (the hitting point distance b is arbitrary) {d _When N _{, 0, k} , da _{, k} } are known (k = 1, 2,..., N), the parameter (ρ _b / ρ _a ) _M for the steel plate _M is the following minimization problem: It can be obtained as a solution of

For example, the values specifically obtained for the two materials JSC270D and JSC590R are as shown in Table 1 above.

  In the said description regarding this invention, although the form which has a nugget diameter estimation process and an electric current estimation process was illustrated, this invention is not limited to the said form. The present invention may be configured without the current estimation step. However, from the viewpoint of making it possible to grasp the current value necessary for obtaining the same target nugget diameter at the time of single-point welding at the time of shunt welding, it is preferable to have a form having a nugget diameter estimation step and a current estimation step.

<Example 1>
For condition 1 and condition 2 shown in Table 2, the weld lobe during shunt welding was compared between the experimental result and the predicted result according to the present invention. Specifically, the weld lobe of single-point welding obtained from an experiment is used as d ₀ in equation (3), and the predicted weld lobe d _a ^Pred at the time of the diverted welding is obtained as the measured weld lobe d _a ^Exp . Compared. The results for Condition 1 are shown in Table 3 and FIG. 6, and the results for Condition 2 are shown in Table 4 and FIG. The condition 1 is a condition for welding two JSC270D having a thickness of 1.4 mm, and the condition 2 is a condition for welding two JSC590R having a thickness of 1.0 mm. The superscript “Exp” means an experimental result, and the superscript “Pred” means a prediction result according to the present invention.

As shown in Table 3 and FIG. 6 and Table 4 and FIG. 7, the weld lobe at the time of shunt welding can be predicted with good accuracy in both conditions 1 and 2, so that the present invention enables shunt welding. Can be predicted on the desk.

<Example 2>
Weld lobes at the time of shunt welding were predicted using the present invention for four plate assemblies having different thicknesses (conditions 3 to 4) and different thicknesses (conditions 5 to 6) including JSC270D and JSC590R. Here, the nugget diameter at the time of single-point welding obtained from the two-dimensional finite element method (2D FEM) analysis was used as d ₀ in Equation (3). Also, the nugget diameter d _a of at shunt welding comparing the predicted results of the invention, using a three-dimensional finite-element method, instead of the experimental results (3D FEM) results of the analysis. Specific analysis conditions are shown in Tables 5 and 6, and the results are shown in FIGS. Condition 3 is a condition for welding a 1.0 mm thick JSC270D and a 1.0 mm thick JSC590R. Condition 4 is a 1.4 mm thick JSC270D and a 1.4 mm thick JSC590R. Condition 5 is a condition for welding JSC270D having a thickness of 0.7 mm and JSC590R having a thickness of 2.3 mm, and condition 6 is JSC590R having a thickness of 0.7 mm and a thickness of 2.3 mm. Of JSC270D.

  As shown in FIGS. 8 to 11, it can be said that the weld lobe predicted by the present invention is in good agreement with the result of the three-dimensional finite element method analysis in any plate assembly. From these results, it is possible to predict the weld lobe at the time of the shunt welding according to the present invention even for the different material different thickness plate assembly.

Claims (3)

Considering that the current flowing through the welding point to be welded by resistance spot welding is diverted to the already welded spot existing at a predetermined distance from the welding point, When estimating the weld lobe that is related to the nugget diameter,
The thickness of each of the two workpieces to be welded by resistance spot welding is t,
I ₀ , the current flowing between the electrodes sandwiching the two materials to be welded,
I _a , the current flowing through the weld point,
The predetermined distance is b,
The nugget diameter of the welding point in the case of single-point welding where there is no existing spot is d ₀ ,
The nugget diameter of the welding point and the already dotting when welded under the same welding condition as the single point welding d _a,
The average specific resistance of the weld is ρ _a ,
When the average specific resistance of the shunt is ρ _b ,
Wherein if already hitting point of 1 _{point, k a} of _{I a =} k _a · I ₀ is represented by the following formula (X),
Wherein if already hitting point two _{points, k a} of _{I a =} k _a · I ₀ is represented by the following formula (Y),
When the k _a expressed as _a function of the nugget diameter d _a is expressed as k _a (d _a ),
When the hit point is 1 point,
K as a single point welding (k is an integer greater than 1) below the d _{0, k} at a known weld lobe is a combination of nugget diameter d _{0, k} respectively obtained with respect to the current condition I _{0, k} of By substituting into d _{0 of the} formula (Z) and substituting k _a represented by the following formula (X) into k _a (d _a ) in the following formula (Z), current conditions I _0, corresponding to _k, and estimates a nugget diameter d _{a, k} when having already RBI
When the hit points are 2 points,
K as a single point welding (k is an integer greater than 1) below the d _{0, k} at a known weld lobe is a combination of nugget diameter d _{0, k} respectively obtained with respect to the current condition I _{0, k} of By substituting into d _{0 of the} formula (Z) and substituting k _a represented by the following formula (Y) into k _a (d _a ) in the following formula (Z), current conditions I _{0, A} method for estimating the nugget diameter of resistance spot welding, which includes a nugget diameter estimation step for estimating the nugget diameter da _{, k} in the case of having a hit point corresponding to _k .
Considering that the current flowing through the welding point to be welded by resistance spot welding is diverted to the already welded spot existing at a predetermined distance from the welding point, When estimating the weld lobe that is related to the nugget diameter,
The thicknesses of the first workpiece and the second workpiece to be welded by resistance spot welding are t ₁ and t ₂ , respectively.
I ₀ , the current flowing between the electrodes sandwiching the first welded material and the second welded material,
I _a , the current flowing through the weld point,
The predetermined distance is b,
The nugget diameter of the welding point in the case of single-point welding where there is no existing spot is d ₀ ,
The nugget diameter of the welding point and the already dotting when welded under the same welding condition as the single point welding d _a,
The average specific resistance of the weld is ρ _a ,
The average specific resistance of the shunt is ρ _b ,
Ρ _b / ρ _a for the first workpiece (ρ _b / ρ _a ) ₁ ,
Ρ _b / ρ _a for the second work piece is (ρ _b / ρ _a ) ₂ ,
When t ₁ , t ₂ , (ρ _b / ρ _a ) ₁ and (ρ _b / ρ _a ) ₂ are used and the value represented by the following formula (W) is ρ _ab ,
Wherein if already hitting point of 1 _{point, k a} of _{I a =} k _a · I ₀ is represented by the following formula (X) ',
Wherein if already hitting point two _{points, k a} of _{I a =} k _a · I ₀ is represented by the following formula (Y) ',
When the k _a expressed as _a function of the nugget diameter d _a is expressed as k _a (d _a ),
When the hit point is 1 point,
K as a single point welding (k is an integer greater than 1) below the d _{0, k} at a known weld lobe is a combination of nugget diameter d _{0, k} respectively obtained with respect to the current condition I _{0, k} of By substituting into d _{0 of the} formula (Z) and substituting k _a represented by the following formula (X) ′ into k _a (d _a ) in the following formula (Z), the current condition I _{0 , K} , and estimate the nugget diameter da _{, k} when having hit points,
When the hit points are 2 points,
K as a single point welding (k is an integer greater than 1) below the d _{0, k} at a known weld lobe is a combination of nugget diameter d _{0, k} respectively obtained with respect to the current condition I _{0, k} of substituted into _{d 0} of the formula (Z), and, by substituting _{k a} represented by the following formula (Y) 'to _k a _{(d a)} of the following formula (Z), the current condition _{I 0 , K} , and a nugget diameter estimation step for estimating the nugget diameter da _{, k} in the case of having already hit points.
The energization time during which the nugget diameter d ₀ is obtained under welding conditions in which the current I _{0 is} passed in the single point welding is represented by τ _e ,
When a current required to obtain the nugget diameter d ₀ under the welding conditions and the energization time τ _e when the current flowing through the welding point is shunted to the hit point is I ₀ ^* ,
The resistance spot welding nugget diameter estimation method according to claim 1, further comprising a current estimation step of estimating the current I ₀ ^* using the following formula (V).