JPS6044077B2 - Quality determination method and device for flash welds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method and apparatus for determining the welding result of a product welded by flash welding without destroying the product.

As is well known, in the flash welding method, when butt-welding objects to be welded, the object to be welded is gripped by a fixed electrode and a moving electrode, and a voltage is applied between the two electrodes from a power source. By moving the moving electrode toward the fixed electrode using a speed pattern, electricity is repeatedly applied, melted, and scattered at the end face of the workpiece (flash process), and both electrodes are rapidly brought close together at an appropriate time (upset process). This is a method of welding. This flash welding method provides the best welding results among all welding methods and is known as a highly reliable welding method. Therefore, most of the products to be welded are used in parts that require high quality and high reliability. However, there has been no reliable and reliable method for inspecting the quality of welds produced by this type of welding method other than destructive testing. For this reason, in the production of parts that require absolute reliability, such as aircraft parts, anchor chains for ships, drill vibes for oil well drilling, etc., numerous tests and frequent sampling during actual welding (e.g. Currently, the quality is guaranteed by repeating destructive tests (once in every three welds) and statistically inferring the quality from these results. In order to implement such a quality control method. Many parts must be prepared for destructive testing, and a complete test takes a very long time, resulting in a large loss both economically and in terms of efficiency. For example, in the case of aircraft parts, we actually welded under welding conditions that are considered to be almost certain (according to the results of a large number of preliminary welding tests), and we extracted 113 samples out of these. Any point, e.g. tensile, bending, impact fatigue,
Various tests at low temperatures were conducted on each part of the welded product, and when all of the parts were found to be in good condition, the remaining products that were welded consecutively before and after the test were considered to be good products. However, it is easy to see that even for products that are found to be of good quality as a result of such strict quality inspections, the quality of the products themselves that are put into practical use is not truly guaranteed. Unlike the conventional quality control methods described above, the present invention focuses on the fact that flash welding results are greatly affected by the amount of heat input during welding, and monitors the amount of power supplied as the amount of heat input in each process of flash pad welding. We have proposed a method and device for determining the quality of flash welds, which makes it possible to reliably determine the quality of welds without the need for destructive testing. The following factors can be considered to affect the welding result in flash welding.

First, mechanical factors include fluctuations in the clamper, deviations in flash speed from the expected value, and wear and tear on the electrode shape.
There are changes due to scratches, etc. Electrical factors include fluctuations in the power supply voltage, welding current and voltage due to changes in the electrode surface condition and the surface condition of the welded object.Furthermore, as for the welding object itself, there are There are differences in the finishing condition and local non-uniformity of the material. These factors act in conjunction with each other, and although some act in an interpolative manner, they generally act in a direction that changes the welding result. By the way, no matter which of the above-mentioned variable factors are considered, changes appear in the welding voltage and current as a result. That is, when the clamp force decreases, the electrode slips against the workpiece during upset, and as a result, a sufficient upset operation is not performed, resulting in a decrease in the upset current. A faster flash speed will increase the flash current, and a slower flash speed will decrease the flash current. In addition, if the electrode wears out and the power supply point to the workpiece changes, the actual protrusion length from the electrode changes by that amount, and the impedance of the workpiece changes accordingly, resulting in a flash. Both current and upset current are greatly affected. Furthermore, in flash pad welding, in the flash process, a voltage is applied between the objects to be welded and the welded end surfaces of the objects to be welded are brought close to each other to repeatedly cause local short circuits, melting, and scattering to heat the objects. Since welding is carried out through an upsetting process in which the object to be welded is rapidly approached and pressed at the point where the object is welded, the supplied power is concentrated and stored in the welding area.
Of course, some of this supplied power is emitted to the outside with the flash, but the amount is commensurate with the amount of scattering and loss of the welded object determined as a flash allowance when selecting welding conditions, and the flash is generated stably. It can be considered that it remains almost unchanged as long as Therefore, when a difference occurs in the power supplied due to the various variable factors mentioned above, the amount of heat accumulated in the workpiece changes immediately, which directly affects the welding result. If these fluctuations can be controlled or monitored by some method, the quality of flash welding can be guaranteed rather than by analogy with destructive testing. By the way, flash welding involves completely different welding phenomena, the flash process and the upset process, and the heat supply mechanisms themselves are completely different, so it is necessary to control the state of heat input in both processes. It would be completely meaningless to implement heat input management only for a single phenomenon, as was done in welding.

Also, as used in the heat input management method in spot welding, it is also possible to add up the power supplied during the flash process, and when this total amount reaches a certain value, terminate the process and move on to the upset process. However, with this method, as described below, the flash distance, upset distance and other welding conditions cannot be defined, and good welding results cannot be obtained. That is, in flash pad welding, some of the welding conditions are (1) the length of the object to be welded protruding from the electrode before welding, (2) the length to be melted and scattered in the flash process (flash allowance),
(3) The length of the workpiece that is reduced during the upset process (upset allowance), and (4) the electrode spacing at the end of welding (final electrode spacing), and it is important to note that neither of these has a significant effect on the welding result. As is well known. Therefore, if we focus only on the power supplied during flashing and move to the upset process when it reaches a predetermined value (irrespective of the actual mechanical movement), each of the above conditions will not be satisfied, and it will be impossible to achieve a good result. It is not possible to obtain welding results.
Furthermore, in flash welding, not only the flash process and upset process each affect the welding result, but also the welding conditions in both processes act in conjunction with each other. Furthermore, the amount of power supplied in the flash process and the amount of power supplied in the upset process interpolate with each other, albeit within a certain range. For example, if the amount of power supplied in the flash process is less than the specified amount, that is, the amount of power under optimal welding conditions, and the amount of power supplied in the upset process is large, this shortfall in the flash process can be compensated for and the overall In some cases, a good weld can be made. Therefore, in the present invention, the amount of power supplied in the flash process and the amount of power supplied in the upset process are detected,
In addition to investigating whether each of these amounts of electricity is within the allowable range, we also investigate whether the sum of both amounts of electricity is within the allowable range, and when both of these are satisfied, Welding is judged to be good only when

On the other hand, the welding itself is carried out as usual under welding conditions selected through preliminary experiments. As mentioned above, both electric power amounts act in an interpolative manner to some extent, but their range is limited and it is not possible to completely compensate for a deficiency in the electric power amount by an excess in the other electric power amount. Therefore, it can be said that it is desirable to set the allowable range of the sum of both electric energies to be narrower than the allowable range of both electric energies. FIG. 1 is a schematic configuration diagram showing an example of an apparatus for implementing the determination method of the present invention.

In the same figure, the parts indicated by numerals 1 to 8 are determination devices to which the present invention is applied, and the parts indicated by numerals 11 to 17 schematically show the structure of a known flash welding machine. First, to explain the structure and operation of the flash welding machine, in Fig. 1, 11 is a fixed electrode fixed on the common base 15, and 12 is a movable electrode slidably placed on the soil of the common base 15. Both of these electrodes are connected to the workpiece 1.
3 and 13'' are held by a clamp mechanism (not shown).The movable electrode 12 is moved toward the stationary electrode 11 at a predetermined speed by an electrode drive cylinder 14 and a fluid pressure (not shown), such as a hydraulic power source. The electrode movement speed is determined by a known method, such as an exponentially increasing speed or a constant speed determined depending on the contact release state of the workpiece.Furthermore, the fixed side electrode 11,
Electric power is supplied to the moving electrode 12 from a secondary terminal of a welding transformer 16, and the primary terminal of the welding transformer 16 is connected to an AC power source (not shown) via a switching element 17 such as a thyristor or ignitron. Next, the determination device which is the subject of the present invention will be explained. In FIG. 1, 1 is a voltage detector that detects the voltage between the fixed electrode 11 and the movable electrode 12, and this voltage detector is for example shown in the figure. Transformer 1 for insulation from the welding circuit and level adjustment
01, a rectifier 10 that converts the output of the transformer 101 into direct current
2, and a variable resistor 103 for adjusting the output level.

Furthermore, if necessary, it can be provided with an amplification function or a filter circuit that bypasses unnecessary high frequency components. In addition, in order to more accurately measure the power supplied to the welding part, it is recommended to provide terminals on the objects to be welded 13, 13'' and introduce the voltage from there. 2 is a welding current detector, which is a welding transformer. The primary input current of the detector 16 is converted into a voltage by a current transformer 201 and a resistor 202, and a voltage output corresponding to the current is obtained by a circuit similar to that of the voltage detector 1.

In addition to the method using the current transformer shown in the figure, any method for detecting the current may be used, such as directly measuring the secondary current using a toroidal coil, using a Hall element, or using a shunt resistor. A multiplier 3 inputs the outputs of the voltage detector 1 and current detector 2 and outputs the instantaneous human power (power value) of the welding machine.

The output of multiplier 3 is supplied to integrator 4a or 4b via relay contact 8a or 8b. Integrators 4a and 4b
are connected to pushbutton switches PBl and P type for resetting these integrators 4a and 4b prior to welding quality determination. Relay contacts 8a and 8b are switched by an upset start signal during welding. It is something that
Before starting the upset, that is, during the flash process, the output of the multiplier 3 is guided to the integrator 4a by the normally closed contact 8b of the relay, and the integrator 4a integrates the flash power and outputs the flash power amount Pf. Here, multiplier 3 and integrator 4a
constitutes the flash j power integrator. When the welding progresses and the flash process ends, the relay contacts are switched by an excitation coil (not shown) at the start of the upset process, so that the normally closed contact 8b is opened and the normally open contact 8a is closed. As a result, the output of the multiplier 3 is led to an integrator 4b, and the integrator 4b outputs the integrated upset power Pu. Therefore, multiplier 3 and integrator 4
b becomes an upset power integrator. Integrators 4a and 4
The outputs Pf and Pu of b are led to comparator circuits 6a to 6d and also to an adder 5. Comparison circuit 6a
to 6d have comparators 601a to 601d and reference setters 602a to 602d, each of which has a maximum flash power amount Pfmaxl and a minimum flash power amount P.
fminl maximum upset power amount Pumaxl minimum upset power amount Punlln are set. here,
The comparison circuits 6a and 6b constitute a first discriminator, and the comparison circuits 6c and 6d constitute a second discriminator. Comparison circuit 6a
is (Pf-Pfmax), and the comparison circuit 6b is (Pfmi
n-Pf), and the comparator circuit 6c (Pu-Purnax)
and the comparison circuit 6d calculates (Pumin-Pu), respectively. Each of the comparators 601a to 601d may be one that outputs an r10 signal when the calculation result of each of the above equations is positive, and outputs a 10J signal when it is negative or zero. Further, the adder 5 combines the outputs of the integrators 4a and 4b and outputs the welding power amount (Pf+Pu). The output of adder 5 is supplied to comparison circuits 6e and 6f. Therefore, the multiplier 3, integrators 4a, 4b, and adder 5 become welding power integrator here.Comparators 601e, 601f and reference setters 602e, 602 are included in the comparison circuits 6e and 6f.
There is a maximum welding power amount POmax and a minimum welding power amount P in the reference setting devices 602e and 602f, respectively.
Omin is set. These comparators 6e and 6f become the third discriminator. The comparator 601e is (Pf+
Pu)-POmax, and the comparator 601f calculates POmin-
(Pf+Pu) and sends the result to the comparator 60 described above.
Similar to 1a to 601d, it is output as a logic signal 10 or RL. The outputs of comparison circuits 6a to 6f are input to logic circuit 7. When the input and output relationships of the comparators 601a to 601f are determined as described above, a NOR circuit is used as the logic circuit 7. In this case, when all the input signals of the logic circuit 7 are not 1, that is, Pf≦
Pfmax,. Pf≧Pfmjn. ．． Pu≦Punla
X. ．． pu≧Punllnl(Pf+Pu)≦POma
Only when all of xl(Pf+Pu)≧POmin are satisfied, signal 1 is output to the output terminal S, and is used as a good welding signal. Here, when the input and output relationships of the comparators 601a to 601f are opposite to those described above, that is, when the results of each of the above-mentioned arithmetic expressions are positive, RO! If the RlJ signal is set to be output when the signal is negative or zero, the AND
A circuit can be used. FIG. 2 is an example of a specific circuit diagram of the comparison circuits 6a to 6c used in the embodiment of FIG. 1.

In the figure, a comparison circuit 6a between the maximum flash power amount setting value Pfmax and the detected flash power Pf is shown as an example to avoid redundant explanation. In the same figure, El and E2 are DC power supplies, R1 is a variable resistor for setting the maximum flash power, R2 to Rl3 are resistors, 0P1, 0P2
is an operational amplifier, and Q1 to Q3 are transistors. In the figure, resistors R2 to R4 and operational amplifier 0P1 constitute an inverting addition counter, and this addition counter is connected to the DC power supply E
1 and the set value Pfm set by variable resistor R1
ax and the detected power Pf are added, but the set value Pfmax
Since the polarity of is opposite to the detected power Pf, (Pf-Pfm
ax). Since operational amplifier 0P1 has an inverted output, its output becomes (Pfmax-Pf), which is further connected to resistors R5, R6 and operational amplifier 0P2.
The signal is inverted to (Pf - Pfmax) and amplified as appropriate. Transistors Ql, Q2 and resistor R7
~Rll is a board forming the Schmitt trigger circuit. This Schmitt trigger circuit shapes the waveform of the output of operational amplifier 0P2, resulting in operational amplification? Only when a finite positive output appears at 0P2, that is, when Pf>Pfmax, transistor Q1 becomes conductive, and transistor Q2, which had been conductive until then, becomes conductive.
is cut off and a 1 is output at terminal e1. Conversely, when the output of operational amplifier 0P2 is zero or negative, transistor Q
2 remains conductive, and a 10-output appears at terminal e1. As mentioned above, when a NOR circuit is used for the logic circuit 7, the output e1 of this transistor Q2 may be used as is as the output of the discriminator, but when an AND circuit is used for the logic circuit 7, the output e1 is indicated by a broken line in the figure. Further resistor R
l. , Rl3 and a transistor Q3 to invert the output so that the RO output is obtained only when Pf>Pfmax, and the 01 output is obtained from the terminal when Pf≦Pfmax. A circuit similar to that shown in Fig. 2 is the comparator 6.
In addition to 01a, it can also be used in comparators 601c and 601e. On the other hand, comparators 601b and 601d
and 601f, the arithmetic expression is as described above (Pf
min-Pf), (PLllTlin-PU), POm
Since in-(Pf+Pu), the same result can be obtained by directly inputting the output of the operational amplifier 0P1 to the transistor Q1 without using the operational amplifier 0P2. Of course resistors R2~R4 operational amplifier 0P1,
A differential amplifier whose output is not inverted can be used in place of 0P2, and the Schmitt trigger circuit of transistors Ql and Q2 can be freely replaced with other known waveform shaping circuits. In the embodiment shown in Fig. 1, the detection signal is constantly integrated and discriminated, but in order to output the discrimination result only when necessary after welding is completed, the input and output terminals of each discriminator or the logic circuit are connected. Of course, a suitable switch can be provided on the output side.

In addition, as mentioned above, in flash welding, welding phenomena that occur for a while after welding starts, that is, welding phenomena at the beginning of the flash process, are simply caused by preheating the end surface of the workpiece to facilitate the generation of the flash necessary for welding. It is only effective for
In addition, since there are many unstable elements, indiscriminately integrating the initial data (input power amount detection value) of the flashing process often leads to erroneous judgments regarding the welding results.

Therefore, the flash power is not integrated over the entire flash process, but is calculated over a certain period just before the start of the upset after the flash phenomenon has stabilized (several seconds before the start of the upset or the number of electrode movements before the start of the upset). By integrating the amount of flash power consumed during the period (between the words) and comparing it with the corresponding allowable power amount range,
This allows for more accurate quality judgment. In the embodiment shown in FIG. 1, this situation is closed by a measurement start command between the voltage detector 1, the current detector 2, and the multiplier 3, or between the multiplier 3 and the integrators 4a and 4b. This can be easily realized by adding a switching element. As described above, according to the present invention, it is possible to judge the welding result without performing a destructive inspection on the welding result by the flash welding method.

Conventionally, quality was estimated from destructive tests using welded samples, which required an extra safety factor to be taken into consideration, but with the present invention, the safety factor can be reduced.
Furthermore, since the welding results can be handled numerically, the welding results can be reliably guaranteed, and the reliability of products produced by flash pad welding can be dramatically improved. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic configuration diagram showing an example of the configuration of an apparatus for carrying out the determination method of the present invention, and FIG.
FIG. 1 is a circuit diagram showing a specific example of a comparison circuit used in the embodiment of FIG.

1... Voltage detector, 2... Current detector, 3... Multiplier, 4a, 4b... Integrator, 6a to 6f... Comparison circuit , 7...logic circuit,
11... Fixed side electrode, 12... Moving side electrode.

Claims (1)

[Claims] 1. A workpiece to be welded is held by the fixed electrode and the moving electrode, and the moving electrode approaches the fixed electrode at a predetermined speed while supplying power from the power supply between the two electrodes. In a method for determining the quality of a welded part by flash welding in which a flash welding process and an upset process are performed, the amount of electric power Pf supplied during the flash process and the amount of electric power Pu supplied during the upset process are measured, respectively. , a maximum flash power amount Pfmax, a minimum flash power amount Pfmin, which separately defines an allowable range of the flash power amount Pf, a maximum upset power amount Pumax, a minimum upset power amount Pumin, and a minimum upset power amount Pumin, which define an allowable range of the upset power amount Pu. sum (Pf+
Determine the maximum allowable power amount P_0max and the allowable minimum power amount P_0min for Pfmin≦Pf≦Pfm
ax, Pumin≦Pu≦Pumax and P_
A method for determining the quality of a flash welded part, characterized in that it is determined that welding is good when 0min≦Pf+Pu≦P_0max. 2 The power amounts P_0min and P_0max are Pfmin+Pumin≦P_0min and Pfm, respectively.
The method for determining the quality of a flash welded part according to claim 1, wherein the method satisfies the following condition: ax+Pumax≧P_0max. 3. The method for determining the quality of a flash welded part according to claim 1 or 2, characterized in that the flash power is integrated only for a certain period of time including immediately before the start of upsetting. 4. The work to be welded is held by the fixed electrode and the moving electrode, and the moving electrode is brought closer to the fixed electrode at a predetermined speed while supplying power from the power supply between the two electrodes, thereby performing the flash process and In an apparatus for determining the quality of a welded part welded by flash welding that performs an upset process, a voltage detector detects the voltage between the two electrodes, a current detector detects the welding current, and the voltage detector and the current a flash power integrator that integrates the power supplied during the flash process from the output value of the detector; an upset power integrator that integrates the power supplied during the upset process from the output values of both the detectors; A first discriminator that determines whether the output of the power integrator is within a predetermined range, and a second discriminator that determines whether the output of the upset power integrator is within a predetermined range. and a third discriminator that determines whether the sum of the output of the flash power integrator and the output of the upset power integrator is within a predetermined range, and the first to third discriminators all detect 1. A flash welding quality determination device comprising at least a logic circuit that outputs a signal indicating that the welding is good only when outputting a signal in which the amount of electric power is within a predetermined range. 5 The above-mentioned first to third discriminators input the maximum and minimum allowable power amount setters that can be set independently, the output of each allowable power amount setter, and each detected power amount, and calculate the output of both input signals. 5. The flash welding quality determination device according to claim 4, further comprising a comparator that outputs a logic signal depending on the magnitude.