Method for evaluating a weld joint formed during a welding process

• US 20060260403A1
• Filed: 12/11/2003
• Published: 11/23/2006
• Est. Priority Date: 12/18/2002
• Status: Active Grant

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Waschkies, Eckhard
• Granted Patent: US 7,373,822 B2
• Time in Patent Office: Days
• US Class Current: 73/588
• CPC Class Codes: B23K 11/252 using digital means
• CPC Class Codes: B23K 15/02 Control circuits therefor
• CPC Class Codes: B23K 26/03 Observing, e.g. monitoring, the workpiece
• CPC Class Codes: B23K 31/125 Weld quality monitoring
• CPC Class Codes: B23K 9/095 Monitoring or automatic control of welding parameters
• CPC Class Codes: G01N 2291/0252 Melting, molten solids
• CPC Class Codes: G01N 2291/0421 Longitudinal waves
• CPC Class Codes: G01N 2291/0422 Shear waves, transverse waves, horizontally polarised waves
• CPC Class Codes: G01N 2291/048 Transmission, i.e. analysed material between transmitter and receiver
• CPC Class Codes: G01N 2291/102 one emitter, one receiver
• CPC Class Codes: G01N 2291/2677 Lapp welding
• CPC Class Codes: G01N 29/07 by measuring propagation velocity or propagation time of acoustic waves
• CPC Class Codes: G01N 29/42 by frequency filtering or by tuning to resonant frequency

Abstract

Disclosed is a method for evaluating, during a welding process, a welded joint as it is forming between at least two parts of a joint using at least one ultrasonic transmitter sound penetrating the region of the forming welded joint with ultrasonic waves and at least one ultrasonic receiver, which registers the changes in sound transmittance of the ultrasonic waves penetrating the region of the forming welded joint in order to evaluate the welded joint.
The invention is distinguished by sound being transmitted with longitudinal (l) and transverse(t) ultrasonic waves into the region of the welded joint, the time-dependent changes in sound transmittance D_l(t), D_t(t) of the longitudinal ultrasonic waves (l) and the transverse ultrasonic waves (t) being registered separately, and using the ratio of D_l(t) to D_t(t), the time point t_s at which a molten mass forms in the region of the welded joint being determined and serving as a basis for evaluating the welded joint.

Claims

1. A method for evaluating, during a welding process, a welded joint as it is forming between at least two parts of a joint using at least one ultrasonic transmitter penetrating the region of the forming welded joint with ultrasonic waves and at least one ultrasonic receiver, which registers the changes in sound transmittance of the ultrasonic waves penetrating the region of the forming welded joint in order to evaluate the welded joint, wherein sound is transmitted with longitudinal (l) and transverse(t) ultrasonic waves into the region of the welded joint, the time-dependent changes in sound transmittance D_l(t), D_t(t) of the longitudinal ultrasonic waves (l) and the transverse ultrasonic waves (t) are registered separately, and using the ratio of D_l(t) to D_t(t), the time point t_s at which a molten mass forms in the region of the welded joint is determined and which serves as a basis for evaluating the welded joint.

2. The method according to claim 1, wherein the time point t_s at which a molten mass forms in the region of the welded joint between the parts of the joint is determined by the time point of the time-dependent ratio function of D_l(t) to D_t(t), at which the ratio function indicates a big leap in rising, is determined.

3. The method according to claim 1, wherein the at least one ultrasonic transmitter transmits ultrasonic waves into a first part of a joint via a contact area and the at least one ultrasonic receiver registers ultrasonic waves transmitted into the region of the welded joint via a contact area of a second part of the joint, the following time-dependent ratio function is utilized to evaluate the welded joint:

$\frac{D_l<br><br>\left(t\right)}{D_t<br><br>\left(t\right)}=\frac{{\left(\mathrm{EB}\right)}_l<br><br>\left(t\right)·<br><br>{\left(\mathrm{BB}\right)}_l<br><br>\left(t\right)·<br><br>{\left(\mathrm{BI}\right)}_l<br><br>\left(t\right)·<br><br>{\left(\mathrm{BE}\right)}_l<br><br>\left(t\right)}{{\left(\mathrm{EB}\right)}_t<br><br>\left(t\right)·<br><br>{\left(\mathrm{BB}\right)}_t<br><br>\left(t\right)·<br><br>{\left(\mathrm{BI}\right)}_t<br><br>\left(t\right)·<br><br>{\left(\mathrm{BE}\right)}_t<br><br>\left(t\right)}\approx <br><br>\frac{{\left(\mathrm{EB}\right)}_l^2<br><br>\left(t\right)·<br><br>{\left(\mathrm{BB}\right)}_l<br><br>\left(t\right)}{{\left(\mathrm{EB}\right)}_t^2<br><br>\left(t\right)·<br><br>{\left(\mathrm{BB}\right)}_t<br><br>\left(t\right)}\approx <br><br>\frac{{\left(\mathrm{BB}\right)}_l<br><br>\left(t\right)}{{\left(\mathrm{BB}\right)}_t<br><br>\left(t\right)}$

with (EB)_{l or t} (t)≡

sound transmittance of longitudinal waves or transverse waves at the sound coupling—

in area on the first part of a joint

(BB)_{l or t}(t)≡

sound transmittance of longitudinal waves or transverse waves at the contact between the parts of a joint

(BI)_{l or t}(t)≡

sound transmittance of longitudinal waves or transverse waves inside the parts of a joint

(BE)_{l or t}(t)≡

sound transmittance of longitudinal waves or transverse waves at the sound couplingout area on the second part of a joint

with (Bl)²_{l or t}(t) and (EB)²_{l or t}(t) of the longitudinal waves and the transverse waves being largely the same provided that frequencies are low and the transmission paths are short.

4. The method according to claim 3, wherein the evaluation of the welded joint is based on the size of the forming molten mass which is determined from the degree of difference in the rise of the ratio function at the time point t_s.

5. Amended) The method according to claim 1, wherein the welding is conducted as part of a resistance welding process in which contact electrodes are placed on the parts of the joint, the contact electrodes forming contact areas with the parts of the joint via which the ultrasonic waves are coupled in, respectively coupled out.

6. The method according to claim 1, wherein the welding process is conducted as part of a noncontact welding process in which the ultrasonic transmitter and the ultrasonic receiver are brought in direct contact with the respective part of the joint.

7. The method according to claim 6, wherein laser beam, electron beam or ion beam welding is used as the noncontact welding process.

8. The method according to claim 1, wherein piezoelement probes or EMUS probes are used as the ultrasonic transmitter and the ultrasonic receiver

9. The method according to claim 1, wherein standard values are generated by means of an online evaluation of the forming welded joint which influence the welding process.