Janez Diaci

Expulsion detection system for resistance spot welding based on a neural network

Resistance spot welding is one of the most important welding procedures. Therefore, a strong emphasis is placed on the quality of the welds. One of the phenomena that causes the deterioration in quality is the eruption of molten material, the so-called expulsion. Expulsion can be avoided with appropriate parameter selection. The problem, however, lies in the fact that the best quality welds are made with parameters just below the expulsion area. Therefore, for any successful control scheme an efficient and dependable expulsion detection is needed. A linear vector quantization (LVQ) neural network system is proposed to achieve this goal. The network is analysed with different sensor combinations and different materials. The results show that the LVQ neural network is able to detect the expulsion in different materials. The experiment also points to the welding force signal as the most important indicator of the expulsion occurrence.

Overview of resistance spot welding control

Abstract This paper presents an overview of resistance spot welding control. The presentation of the physical background of the resistance welding process is followed by the description of the main problems concerning the appurtenant control theory. Solutions to these problems are presented primarily according to the measured signals used and to the type of control strategies.

Estimating the strength of resistance spot welds based on sonic emission

Abstract Audible sound signals detected during the resistance spot welding (RSW) of zinc coated steels were investigated in order to assess their suitability for estimating the strength of the weld. A new sonic emission indicator was introduced and compared to a commonly used emission count indicator. A new method of spot weld strength estimation based on the two indicators is presented. The advantage of the method is that it makes it possible to establish the stage when the electrode is worn out. The method enables the development of improved RSW process control algorithms.

A study of blast waveforms detected simultaneously by a microphone and a laser probe during laser ablation

We examine blast waves generated in air during irradiation of absorbing samples with Nd: YAG laser pulses of fluences exceeding the ablation threshold. Blast waves were detected simultaneously by a wideband microphone and a laser beam deflection probe. By a comparative analysis of both signals in the time and frequency domain we investigate characteristic features of their nonlinear waveform evolution. To explain the observed phenomena we employ the weak shock solution of the point explosion model.

Response functions of the laser beam deflection probe for detection of spherical acoustic waves

Detection of spherical acoustic waves by the laser beam deflection probe is examined. The probe is modeled as a linear system transforming acoustic wave form into transient angular deflection of the probe beam. Transfer and step response functions are derived assuming thin Gaussian laser beam and small deflection angle. It is demonstrated that the probe behaves as a half‐order differentiator when short acoustic transients are detected far from the source. Theoretical predictions are compared to the results of frequency analysis of optoacoustic signals detected by the deflection probe. Good agreement is found.

Influence of welding current shape on expulsion and weld strength of resistance spot welds

Abstract The present paper presents the influence of welding current shape on weld strength of resistance spot welds of zinc coated mild steel sheets. The influence is analysed at different levels of the electrode wear. Welding currents with different peak values and different RMS (root mean square) values were used in the experiment. The results show that welding current with high peak values implies higher weld strength.

Triangulation model taking into account light sheet curvature

This paper examines the problem of systematic measurement errors in optical triangulation when some light sheets that illuminate the measured surface exhibit non-negligible bending (curvature). The problem is demonstrated experimentally by triangulation measurement of two reference bodies whose geometry reveals systematic measurement errors due to light sheet curvature. To correct these errors a triangulation model is developed which assumes parabolic light sheet shape and allows exact solution of system equations. Test measurements show that the model successfully compensates for systematic measurement errors originating from the curvature of light sheets.

MULTIPLE-PASS LASER BEAM DEFLECTION PROBE FOR DETECTION OF ACOUSTIC AND WEAK SHOCK WAVES IN FLUIDS

We examine a novel laser beam deflection arrangement for detection of acoustic and weak shock waves in fluids. Novelty of the arrangement is folding of the probe beam by two parallel plane mirrors in such a way that the probe beam passes the wave propagation region several times before it reaches the deflection‐detecting photodetector. In this way the probed wave interacts with several segments of the probing beam in sequence. A single oscilloscope trace of the photodetector output thus gives us the possibility to study the evolution of the probed wave at several distances from the source. To demonstrate the potentials of the arrangement we present wave forms of spherical blast waves detected in air during laser ablation of solid samples. We also discuss a simple theoretical model that qualitatively explains the most characteristic features of this arrangement.

Optodynamic monitoring of the laser drilling of through-holes in glass ampoules

We present an accurate and reliable method for the detection of wall perforation during the excimer-laser micro-drilling of glass ampoules and vials. The method is based on the detection of shock waves generated in the air during the drilling process using a laser-beam deflection probe. An analysis of the detected optodynamic signals gives important information about the progress of the drilling process, and we take this as the basis for the presented online process-monitoring method. We show that a significant change in the signals amplitude is observed when the wall of a liquid-filled ampoule is perforated and the exit process point is in contact with the liquid, and that this signal change can serve as an indicator of wall perforation. We have verified this optodynamic method by examining the processed holes using optical and electron microscopy as well as with a non-destructive gas-leakage test method. The described method was employed for the production of test ampoules used for the adjustment of a high-voltage leak-detection device in a pharmaceutical production line. Holes with a diameter of less than 10 µm were produced in the walls of 0.5 mm thick glass ampoules using a XeCl excimer laser.

Measurement of energy conversion efficiency during laser ablation by a multiple laser beam deflection probe

We have developed a novel multiple-pass laser beam deflection (LBD) arrangement for detection of acoustic and weak shock waves in fluids. The arrangement gives us the possibility to acquire temporally resolved information (signal waveforms) on single and non-reproducible events in several points of space. We have applied the new arrangement to investigate spherical shocks generated during laser ablation of metallic targets in air. For each ablation event we determine shock transit times at several points in space and fit the data to the theoretical shock trajectory in order to determine the blast energy released in the shock wave. This multiple-point procedure improves the accuracy and reliability of blast energy measurement.