Laser micro welding pdf

Laser welding tests were performed for various qualities of stainless steel of type X Cr — Y Ni — Zmo. The probes, made of stainless steel 18 Cr — 8 Ni, having a high percentage of carbon 0. The most frequent defects of the weld are presented in continuation, the causes of their apparition being specified as well.

Welding by superposition of two L stainless steel sheets Fig. The presence of impurities in a weld obtained by end-to-end welding of two stainless steel plates L The same causes lead to the defects that can be noticed in fig. The measures to be taken to avoid such defects regard the correlation among the energy of laser pulses, their frequency and the displacement speed of probes in front of the focused laser beam.

All probes feature a very good quality of the weld and a reduced thermal influenced area compared to other weld procedures able to be used for this range of assemblies and materials to be welded.

The hardness of laser welds was established using a Vickers micro-hardness testing machine with a load of grams. The results are synthesized in fig. These results will be presented in another paper. Dontu, a. Carosena M. Zhang Li. Download PDF. Tamaki et al. Watanabe et al. The possibility of femtosecond laser welding of borosilicate glass substrates in the high repetition-rate regime using 1-MHz, fs, nm laser pulses has been recently reported [ 8 , 9 ].

However, there has been no quantitative evaluation of the resulting joint strength in the high repetition-rate regime. In this paper, we demonstrate the laser micro-welding of materials by a localized heat accumulation effect using an amplified femtosecond Er-fiber laser system with a wavelength of nm and a repetition rate of kHz.

We report on welding of non-alkali glass substrates and demonstrate that the resulting joint strength was 9. We also succeeded in welding a non-alkali glass substrate and a silicon substrate using nm laser pulses, at which wavelength silicon is transparent.

We could obtain a joint strength as large as 3. Figures 1 a , 1 b , and 1 c show the laser micro-welding procedure using femtosecond laser pulses. Two substrates Sample 1 and Sample 2 were carefully cleaned, stacked one on another [ Fig. In this experiment, the pressing lens was made of fused silica. In order to weld two substrates, femtosecond laser pulses were focused at the interface between the two substrates [ Fig. The focal region was elongated along the optical axis due to nonlinear propagation, such as filamentation.

The filamentary propagation of femtosecond laser pulses bridges the two substrates along the laser propagation axis z -axis [ 11 , 12 ]. This filamentary propagation creates a liquid pool due to localized melting, and the liquid pool at the interface then resolidifies, welding the two substrates.

Filamentary propagation is superior for laser welding because the elongated liquid pool means that it is not necessary to translate the focal spot along the z -axis.

Table 1. Figures 2 a and 2 b show schematic diagrams of the welding volumes. Schematic diagram of laser micro-welding of two substrates. Schematic diagram of welding volumes a in the xy -plane and b in the yz -plane. To estimate the joint strength, we performed a simple tensile test after welding the substrates. A schematic diagram of the tensile tester is illustrated in Fig.

The front face of Sample 1 was joined to a string and the rear face of Sample 2 was joined to a base with an adhesive. The load was increased by adding weights until the welded sample was cleaved into two substrates. When the sample was cleaved, we determined the joint strength by dividing the load by the welding areas. Schematic diagram of a tensile tester. The optical setup used for structural modification inside the non-alkali glass was almost the same as that used in Refs.

It should be noted that the repetition rate was set at kHz. The pulse duration was fs. The sample was mounted on a two-dimensional translation stage with nm resolution Physik Instrumente V The pulse energy was controlled by rotating a half-wave plate in front of a Glan-laser polarizer.

The maximum input energy was 0. Images of the structural modification produced in the non-alkali glass were observed in the xy -plane and in the xz -plane by optical transmission microscopes with white-light illumination. In order to investigate the heat accumulation effect, femtosecond laser pulses were focused with static exposure for various exposure times. In this experiment, we set the input pulse energy at 0. Figure 4 a shows optical images of the refractive-index change in the xy -plane when increasing the exposure time the number of pulses from 1 to s by factors of Figure 4 b shows the dependence of the diameter on the exposure time.

The size of the refractive-index change in the x -direction was larger than the focal spot size approximately 2. The 1. Furthermore, the size of the refractive-index change increased as the number of laser pulses increased, and the optical images in Fig. We confirmed that the heat accumulation effect was induced at the repetition rate of kHz.

Optical images of the refractive-index change in the xy-plane as a function of exposure time. We investigated the laser micro-welding of transparent materials using a femtosecond fiber laser at nm based on the heat accumulation effect.

These experiments were performed at room temperature in an air atmosphere. First, we demonstrated the laser welding of non-alkali glass substrates. The laser welding was performed in accordance with the procedure described in Section 2. The normal force W , the average contact pressure P mean , and the maximum contact pressure P max between non-alkali glass substrates were calculated using Eq.

The radius of curvature of the pressing lens was 6. By substituting these values into Eq. The input energy was 0. Figure 5 a shows that the welding volume was formed by the refractive-index change. Figure 5 b shows that the welding volume was formed around the interface between the non-alkali glass substrates.

Dashed line in b shows the welding volumes. In the regime where heat accumulation occurs, we first welded the non-alkali glass substrates and then evaluated the joint strength. The joint strengths were measured to be 9. The joint strengths were weaker than that in Ref. The possible reason of weaker joint strength is attributed to a total fluence, which is determined by multiplying the single-pulse fluence by the number of pulses in the focal spot.

In our experiments, the maximum pulse energy at a repetition rate of kHz is 0. Laser systems with higher output energy will increase the joint strength. Another possibility is repulsion that is released when the sample holder is set aside. The released repulsion may decrease the joint strength.

To verify that this technique can be extended to semiconductor materials, we demonstrated the welding of a silicon substrate with a non-alkali glass substrate. Silicon is transparent in the wavelength range of 1. Note that non-alkali glass and silicon are both transparent at nm.

The coefficient of thermal expansion of silicon 2. The welding procedure was the same as that used between the non-alkali glass substrates. That is, the non-alkali glass substrate was first mounted on the silicon substrate, and femtosecond laser pulses were then focused at the interface between the substrates. The joint strength was 3.

We investigated the morphology of the cleaved surfaces of the two substrates after laser welding. Observation using an optical microscope revealed that the silicon adhered to the non-alkali glass substrate only in the welding volume. For femtosecond laser welding of glass substrates, previous reports used a 1-kHz Ti:sapphire laser at a wavelength of nm [ 2 , 3 ].

Compared with the Ti:sapphire laser, the fiber laser we used has some advantages, such as i stable output power, ii high repetition rate, iii excellent beam quality, iv high conversion efficiency of optical energy ratio of excitation light to output light , v compactness, and vi ease of handling.

As a result, the fiber laser will be an important tool for laser welding in industrial applications. In the repetition-rate regime higher than kHz, we expect that the processing speed will be greatly improved. Conventional laser joining techniques require that one of the substrates to be joined be transparent at the wavelength of the laser, and that the other substrate be absorbing at that wavelength.

For example, because a Nd:YAG laser wavelength, nm has an absorption band only in silicon, silicon-glass joints have conventionally been performed by the following process [ 20 , 21 ]: i the laser beam is transmitted through the transparent material glass , and ii is absorbed at the surface of the opaque material silicon.

Alternatively, the welding of transparent materials can be performed by using a light-absorbing intermediate layer between the substrates. In our experiments, the wavelength of the fiber laser was 1. At this wavelength, both the silicon substrate and the non-alkali glass substrate are transparent; the welding of the silicon substrate and the non-alkali glass is thus performed by nonlinear absorption in the materials without introduction of an intermediate layer.

When welding the silicon substrate and non-alkali glass substrate, the surface of the silicon substrate is melted by an optically-excited electron-hole plasma [ 22 ]. The melting of the silicon substrate at the interface eliminates the gap between the substrates. Although further investigation of the welding mechanism is the subject of future work, this welding technique using 1. We believe that our technique can be applied to the welding of dissimilar transparent materials, such as silicon substrate and fused silica, whose coefficients of thermal expansion are different.

Tight focusing using a high-NA objective increases the intensity in the focal volume, thus compensating for the limited output energy of the laser pulses 0. High-NA objectives produce shorter filaments, resulting in reduced welding volume and thus increased intensity. In addition, they have shorter working distances, meaning that they can be used to weld only samples of limited thickness because the laser pulses must propagate through the first sample to the interface.

On the other hand, low-NA objectives produce longer filaments, resulting in increased welding volume and thus reduced intensity. However, they have longer working distances and can thus be used to weld thicker samples. Therefore, it is necessary to select an objective of suitable NA to weld the samples. Kumawat for carrying out the tensile testing of the welded specimens. Valuable discussions with R. Singh and D. Sathe are also acknowledged. This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

You can also search for this author in PubMed Google Scholar. Correspondence to Aniruddha Kumar. Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Reprints and Permissions. Kumar, A. Lasers Manuf. Download citation. Accepted : 02 April Published : 18 April Issue Date : 15 June Anyone you share the following link with will be able to read this content:. Sorry, a shareable link is not currently available for this article. Provided by the Springer Nature SharedIt content-sharing initiative.

Skip to main content. Search SpringerLink Search. Abstract Joining of materials is an essential process step in manufacturing industry. References 1. Woodhead publishing in materials, Cambridge Google Scholar 4. Springer, Heidelberg Google Scholar Woodhead Publishing, Cambridge Google Scholar Acknowledgements The authors would like to acknowledge Nagendra Kumar for his help in carrying out the radiography of the welded specimens and B.

Biswas Authors Aniruddha Kumar View author publications. View author publications. Rights and permissions Reprints and Permissions.