Biuletyn Instytutu Spawalnictwa No. 01/2012

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ination of its power and width (duration). Therefore, these radiation beam parameters cannot be shaped freely, as one cannot freely define the duration and emission frequency of a pulse for the assumed value of the average power of a radiation beam. The energy of a pulse cannot exceed the maximum value defined for a given resonator. The average power of laser radiation in pulsed mode is defined as the product of the average power of the radiation of one pulse P i , the duration of this pulse t i and the number of pulses per a second expressed through the frequency of emission f. For a given average power there is a number of combinations of the selection of pulse energy and pulse repetition frequency. P śr = P i × t i × f = E i × F (1) The frequency of a pulse emission is a parameter closely related to the period of their occurrence expressed in the following relation: A weld produced by a laser beam emitted in pulsed mode is composed of a number of overlapping spot welds. The degree of overlapping of individual pulses expressed in percentage, i.e. the so-called overlap, represents the degree at which the area of a material molten by a single pulse overlaps a similar area produced by the previous pulse. By means of a specific overlap one can control the amount of heat supplied to a material being welded, as well as influence the homogeneity of the structure of a weld. The overlap is defined by the rate of the welding process appropriately selected in relation to the frequency of pulses. In turn, the frequency of pulses depends on the pre-defined power of a pulse and its duration. If an area molten by a single pulse of a laser beam takes an elliptic shape (as a result of the pro- 1 ⎡ 1 ⎤ T = f ⎢ s = ⎣ Hz ⎥ ⎦ (2) The average energy of laser radiation for the pulsed operation mode is defined as the product of the average radiation power and radiation beam action time. E śr =P śr × t [J] (3) In the case of single pulse spot welding, an important parameter is the density of pulse power. GP i Pi Ei = = A t × A i ⎡ J ⎢ ⎣s ⋅ m (4) where A represents the focusing area of a radiation beam. In the case of a pre-defined average power of a radiation beam P śr , the density of the power supplied to the area unit, i.e. the average 2 ⎤ ⎥ ⎦ area power density, is determined by means of the following quotient: GP śr = P śr A ⎡ W ⎢ ⎣m 2 ⎤ ⎥ ⎦ (5) The quotient of the area power density GP śr and radiation beam action time determines the average area power density: GEśr = GPśr × t ⎡ J ⎢ ⎣m (6) The quantities defined above are presented in Figure 1. Fig. 1. Graphic interpretation of average power of pulse P i , average power of radiation beam P śr , pulse energy E i , pulse duration t i , pause time t p pulse period T 2 ⎤ ⎥ ⎦ 6 BIULETYN INSTYTUTU SPAWALNICTWA NR 01/2012
cess being carried out at a specific rate), the longer axis of the ellipse is designated as the dimension S, whereas the shorter one as the dimension D (Fig. 2,3) Fig. 2. Scheme of process of laser welding with radiation beam emitted in pulsed mode Degree of overlapping of pulses is defined by the following relation: [ ] % ' S − S Z = × 100 (7) S where: S = D + v × t (8) i S’ = v× T (9) After transformation of relations 7, 8, 9, the overlap Z is the following: ⎡ v × T ⎤ Z = ⎢1 − ⎥ ×100% (10) ⎣ D + v × t i ⎦ Effective penetration depth is conditioned by the overlap Z (Fig. 3). Welding with laser radiation beam emitted in pulsed mode The miniaturisation in many areas of technique has almost become a trend, stimulating the development of micro-machining (including micro-joining) of various structural materials. In relation to miniature structural elements and modules, as well as a variety of miniature components and devices, today’s manufacturing techniques and classical joining technologies in particular meet technical limitations preventing the efficient use of the former. In many applications the only solution is the laser, regarded as one of the most innovative tools of modern industry. Operating a laser in pulsed mode enables the precise production of welded joints of elements made of technologically advanced materials and having minute dimensions. A joint of this type is obtained through the melting of a very small amount of metal by a single pulse of a laser beam and its immediate crystallisation. A continuous weld is formed as a result of the proper selection of welding rate and pulse repetition frequency. Pulsed laser welding is applied where one needs to join ready-made electronic components in a tight housing, thin-walled elements (membranes) with massive cases, thin-walled housings, medical equipment elements (housings of cardiac pacemakers, endoscopes, medical implants, surgical instruments and others). Fig. 3. Graphic interpretation of overlap of pulses of laser radiation beam: v – welding rate, t i – pulse duration, D – diameter of area of focusing of radiation beam, T – pulse period [1,3] NR 01/2012 BIULETYN INSTYTUTU SPAWALNICTWA 7
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Page 3 and 4: Summaries of the articles J. Dworak
Page 5: Jerzy Dworak Research Impact of las
Page 9 and 10: pulses up to several dozen millisec
Page 11 and 12: ectangular pulse, P i max =702 W, p
Page 13 and 14: ectangular pulse, P i max =1752 W s
Page 15 and 16: Antoni Sawicki Modified Habedank an
Page 17 and 18: 1 dr r dt - in the resistance form
Page 19 and 20: The conditions of the selection of
Page 21 and 22: Similarly as previously (37), one c
Page 23 and 24: Eugeniusz Turyk, Agnieszka Żydzik-
Page 25 and 26: gical weldability, confirmed by the
Page 27 and 28: Damage was also caused to the welde
Page 29 and 30: Initial selection of method for wel
Page 31 and 32: Fig. 19. Assembly table with fixed
Page 33 and 34: Agnieszka Kiszka, Tomasz Pfeifer Va
Page 35 and 36: Fig. 4. Course of changes in curren
Page 37 and 38: extreme, the process was less stabl
Page 39 and 40: Fig. 13. Macrostructure of T-shaped
Page 41 and 42: L=1 mm, I=25 A L=1 mm, I=50 A L=1 m
Page 43 and 44: case of TIG welding (for similar we
Page 45 and 46: Other, equally important research i
Page 47 and 48: tion of a function connected with t
Page 49 and 50: The intensity of arc radiation was
Page 51 and 52: On the basis of calculations (Table
Page 53 and 54: NR 01/2012 BIULETYN INSTYTUTU SPAWA
Page 55: INSTYTUT SPAWALNICTWA The Polish We

Biuletyn Instytutu Spawalnictwa No. 01/2012

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