A laser welding set up with dual focal lens for laser welding of dissimilar materials

Abstract

The invention relates to a laser welding setup (100) with a dual focal lens (115) for welding dissimilar metals. The laser welding setup comprises two different laser cavities (110) and (111) which act as the laser sources. The laser sources follow the basic mechanism of CO2 laser. The laser beams generated in those cavities are guided by two metallic mirrors (102) and (103); and incident on the top surface of the dual focal lens (115) which is a specially designed positive Meniscus lens. The dual focal lens has a conical top surface and a concave bottom surface. The laser beams incident on either side (left or right inclination) of the inclined conical surface (201) and (202) and move vertically in the lens medium. Further, after refraction in the concave surface (204), the laser beams converge toward two different focal points. The welding edges of the materials to be welded are kept at the focal point and heat is generated at the welding edges. Due to heating and melting, the materials are welded. The intensities of the laser beams are different; and consequently, the heat generated at the welding edges is different based on their melting points. Thus, two dissimilar metals can be welded accordingly using this technology.

Description

FIELD OF THE INVENTION:The present invention relates to a laser welding set up with dual focal lens for laser welding of dissimilar metals. More particularly the invention relates to a laser welding set up having a dual focal lens with multiple laser sources.BACKGROUND OF THE INVENTION & PRIOR ARTS:The demand of welding of dissimilar metals is growing expeditiously in modern manufacturing. However, it is a challenging technology owing to varying thermal and electrochemical properties of both the materials. Especially the difference between melting point, thermal expansion, and thermal conductivity for both the metals to be joined created severe problem in the welding phenomenon. For varying melting points and other thermal properties, the heat generated at the weld bid should be different for both materials. This phenomenon restricts the application of fusion based welding processes for dissimilar metals. Therefore, researchers have gone for non-fusion mechanical welding process for dissimilar metals such as friction welding or friction stir welding.Murr et al. (1998) performed friction stir welding of dissimilar aluminium and copper alloys. In this phenomenon a rotating friction stir tool moved along the joining of both the metals. Consequently, due to friction plastic flow of material has been taken place from one metal to another under the solid state. Therefore, dynamic recrystallization has been taken place at the joining interface and welding occurred.Meshram et al. (2007) performed friction welding for various pairs of metals which include iron and titanium, copper and titanium, iron and copper, iron and nickel, copper and nickel. Some of the metals have a large difference in melting point as well. All the pairs of metals were subjected to huge forging load under rotational conditions. Therefore, plastic deformation occurred at the joining interface of the pairs of metals due to rapid friction. Due to plastic flowof metals, they were joined with each other. Due to rapid strain hardening under this situation, the hardness of weld bid was much higher.Bang et al. (2012) performed a hybrid welding process incorporating gas tungsten arc welding with friction stir welding for joining aluminium and stainless steel. The preheating was performed at the joining line using GTAW technology and further welding was performed using friction stir tool. The preheating technique initiated the plastic deformation process which was further accelerated by friction and recrystallization occurred. This hybrid technique was able to improve the elongation and joining strength in weld bid.Meanwhile, laser welding technology is a fusion based welding process which uses a focused laser beam. This technology has been adopted in many industries due to its high precision. The energy for welding is generated by a high-performance laser. The laser beam is able to generate localized heat at the welding interface. Therefore, this phenomenon is suitable for materials and components that are to be welded at high speed with a narrow weld seam and low thermal distortion. As a result, laser welding is used for high-precision applications in a wide range of industries, including the automotive, aerospace and medical sectors. However, varying melting points have restricted the application of laser welding for dissimilar metals. It can be possible to utilize laser welding for dissimilar metals if the intensities of the laser beam are varied at the joining interface of both materials in accordance with their melting point. Therefore, using multiple laser sources with varying intensities can be a solution to that problem. Due to localized heating, the chance of heat flow from one metal to another is very less in case of laser welding. However, it is required to focus two different laser beams at two different locations which are the welding edges of both the metals. A specially designed dual focal lens can be introduced for this purpose.Korean Patent KR102184105B1 disclosed a welding method of two or more flat workpieces having different contours applicable for vehicle body in motor vehicle industries. This technology followed a method of butt welding of sheet metal by laser welding. The process was divided in two subcategories which included formation of gap between the welding edges andmeasuring and monitoring the gap before the welding process. A twin spot rotating lens has been utilized in this process.Korean Patent KR20090032222A disclosed a laser welding system using a scanning mirror to improve the welding efficiency by proper radiation of the laser beam according to the shape of a base material and adjusting the vibration or width of the laser beam. The laser welding system comprised of multiple laser beam nozzles, a scanning mirror positioned between the laser beam nozzle and base materials, a vibrating device connected to the scanning mirror to control the vibration, and a focusing lens positioned between the scanning mirror and the base materials. In this technology, multiple laser beams were oscillated at variable frequency and amplitude which was controlled by the scanning mirror; and focused on a certain spot through the focusing lens in such a way that the focus was varied accordingly with the frequency and amplitude.Chinese Patent CN109954969B disclosed a flexible switching method for laser deep melting welding and laser modification welding. In this case, a diffraction optical lens was inserted between a focusing lens and an anti-splash lens on a laser welding head. The function of the diffraction optical lens was to change the shape of a light spot and the energy distribution of the light beam without changing the height between the laser welding head and the welding plane. This helped to modify the shape and the energy distribution mode of the laser beam when the process changed from deep laser melting welding to modification welding. Thus, the laser modification welding quality was enhanced.Russian Patent RU2711996C2 demonstrated a laser welding system for patterned welding by providing oscillatory movement to the laser beam. The laser welding system comprised of movable mirrors which provided oscillatory motion to one or multiple laser beams within a relatively small scanning zone. The laser welding head consisted of a diffractive optical element to provide a definite shape to the movable laser beam.United States Patent US10668565B2 disclosed a laser welding system with a controller which controlled the scanner to move the laser beam with respect to the metal surface to multiple focussed spots. This phenomenon caused formation of multiple melt pools in one metal and heat stakes in the second metal. The distance between the focal spots was small enough such that the melt pools overlapped over each other; however, the extreme ends of the heat stakes were distinct from each other.Russian Patent RU2700723C2 disclosed a laser based optical technology where multiple laser beams of controlled radiation came from multiple sources and incident on one optical component. This system comprised multiple fibre laser systems, multiple output fibres, and volumetric optical element. Each laser beam exhibited a different characteristic. The optical element created separate beams of output radiation of fibre laser substantially at distance from each other. This technology was able to generate incoherent laser beams with controlled radiation.United States Patent US 7302181B2 a disclosed optical communication device having multiple light sources under a single lens. The lens was optically coupled to the two light sources and shaped to direct light from the two light sources towards an axis of the lens. Another light source was located below the approximate center of the lens. The function of the lens was to direct all the lights coming from different sources in a single direction.Taiwanese Patent TWI627451B disclosed a near-eye display and a near-eye binocular display system. The near-eye display system incorporated a multi-beam diffraction grating display for providing different visual images, and an optical system to transmit those images to different positions in the eye area. On the other way, the binocular near-eye display system incorporated a pair of multi-beam diffraction grating displays and a binocular optical system to provide and transmit a pair of stereoscopic images which presented a 3D scene to a corresponding pair of laterally-shifted suitable eyes area. This invention fitted multiple images from an image to different positions of eye-fitting area and thereby providing a depth of focus prompt to a user.However, focusing the laser beams coming from multiple sources to different points using a single lens was not disclosed in previous studies; especially for laser welding applications. Eventually, the application of laser welding for dissimilar metals was still unknown.OBJECTS OF THE INVENTION:In view of the foregoing limitations inherent in the state of the art, some of the objects of the present disclosure, which at least one embodiment herein satisfy, are listed herein below.Therefore it is an object of the invention to propose a dual focal lens for laser welding of dissimilar metals.Another object of the invention is to propose a laser welding set up with dual focal lens for laser welding of dissimilar metals having a welding set up with two laser sources with different intensities.A further object of the invention is to propose a laser welding set up with dual focal lens for laser welding of dissimilar metals to focus two laser beams having different intensities in two different locations.A still another object of the invention is to propose a laser welding set up with dual focal lens for laser welding of dissimilar metals to generate variable heat at the welding edges of two different metals in contact.A still further object of the invention is to propose a laser welding set up with dual focal lens for laser welding of dissimilar metals having different melting points.Another object of the invention is to propose a laser welding set up with dual focal lens for laser welding of dissimilar metals welding multiple metals at a time.These and other objects and advantages of the present invention will be apparent to those skilled in the art after a consideration of the following detailed description taken in conjunction with the accompanying drawings in which a preferred form of the present invention is illustrated.SUMMARY OF THE INVENTION:This summary is provided to introduce concepts related to a laser welding setup having a dual focal lens and multiple laser sources for welding dissimilar metals. The concepts are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.The present disclosure relates to a dual focal lens technique for laser welding of dissimilar metals. The laser welding setup comprises two laser sources and a dual focal lens. The number of laser sources can be further enhanced depending on the requirement. Two different laser sources emit laser beams of varying intensities. The laser sources follow the basic mechanism of CO2 laser. The laser beams emitted from the laser sources incident on a dual focal lens which is a specially designed positive Meniscus lens. The top surface of the lens is conical in shape with its apex on the top. The bottom surface of the lens is concave in shape. The dimensions of the lens are proposed based on the distance from the laser sources and the workpiece. The metal mirrors used in the laser source are kept at an angle such that the laser beams incident on the conical surfaces of the dual focal lens and move vertically in the lens medium. Further, the laser beams refract from the concave surface and converge toward the welding edge. Two laser beams having different intensities incident on two different sides of the conical surface and refract from the concave surface. These two laser beams focus on each welding edge of the dissimilar metals to be welded which is placed at the focal length. Due to varying intensities, the heat generated at the welding edges is different; and consequently, the edges of the dissimilar metals melt and join accordingly.Other objects, features and advantages of the present disclosure will become apparent from the following detailed description. It should be understood, however, that the detailed description and the specific examples, while indicating specific embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS:While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter that is regarded as forming the present subject matter, it is believed that the present disclosure will be better understood from the following description taken in conjunction with the accompanying drawings, in which:Fig. 1 is a schematic view of the laser welding setup 100 having multiple laser sources with a dual focal lens for welding dissimilar metals, in accordance with an embodiment.Fig. 2A is the front view of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment.Fig. 2B is the top view of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment.Fig. 3 is the schematic view of the working principle of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment.Fig. 4 is the schematic view of the laser welding performed in the laser welding setup 100 using the dual focal lens 115, in accordance with an embodiment.DETAILED DESCRIPTION OF THE INVENTION:The detailed description of various exemplary embodiments of the disclosure is described herein with reference to the accompanying drawings. It should be noted that the embodiments are described herein in such details as to clearly communicate the disclosure. However, the amount of details provided herein is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present disclosure as defined by the appended claims.It is also to be understood that various arrangements may be devised that, although not explicitly described or shown herein, embody the principles of the present disclosure. Moreover, all statements herein reciting principles, aspects, and embodiments of the present disclosure, as well as specific examples, are intended to encompass equivalents thereof.The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises", "comprising", "includes", "consisting" and / or "including" when used herein, specify the presence of stated features, integers, steps, operations, elements and / or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and / or groups thereof.It should also be noted that in some alternative implementations, the functions / acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may, in fact, be executed concurrently or may sometimes be executed in the reverse order, depending upon the functionality / acts involved.Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which example embodiments belong. It will be further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.Referring to the Fig. 1, disclosed is a schematic view of the laser welding setup 100 with a dual focal lens for welding dissimilar metals, in accordance with an embodiment. The laser welding setup comprises two laser sources which can be increased depending on the requirement. The laser sources follow the basic mechanism of CO2 laser. The laser welding setup comprises a pumping source 101. Further, the laser welding setup 100 comprises two different metallic mirrors 102 and 103 which are used to govern the direction of two different laser beams in particular directions. The laser welding setup comprises of two different laser cavities 110 and 111 as laser sources. The laser cavities contain a mixture of carbon di-oxide, helium, and nitrogen gas which generates the laser beam after ionization. These are used to generate two laser beams of varying intensities. 104 is the partial reflector of the laser cavity 110. While 105 is the partial reflector of the laser cavity 111. Further, 108 is the full reflector of the laser cavity 110. While 109 is the full reflector of the laser cavity 111. The laser cavity 110 comprises two electrodes 112 used for generating high voltage. The laser cavity 111 comprises two electrodes 113. Due to high voltage generation, discharge takes place in the laser cavities which ionized the gas the mixtures and produce laser beams. 106 is the ionization in the laser cavity 110. While 107 is the ionization in the laser cavity 111. The laser beam generated in the cavity 110 passes through the partial reflector 104 and is guided by the metallic mirror 102 toward the dual focal lens 115. Similarly, the laser beam generated in the cavity 111 passes through the partial reflector 105 and is guided by the metallic mirror 103 toward the dual focal lens 115. A shielding gas source 114 is used in the laser welding setup 100 which supplies inert gas surrounding the laser beams. The laser beam 116 generated from the laser cavity 110 refracts by the dual focal lens 115 and focuses on the welding edge of metal A. Similarly, the laser beam 117 generated from the laser cavity 111 refracts through the dual focal lens 115 and focuses onthe welding edge of metal B. As high velocities ions strike the edges of the metals, rapid heat generates which melts the welding edges of both the metal and welding takes place. The intensities of both the laser beams 116 and 117 are different. Therefore, the heat generated at the edges of both materials A and B are different. This is favorable as the melting points of both the metals are different. Thus, welding of dissimilar metals can be performed using the laser setup 100.Fig. 2A is the front view of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment. The dual focal lens is specially designed positive Meniscus lens for refracting and focusing two different laser beams into two different locations which are closed to each other. The dual focal lens 115 comprises three surfaces. The top surface of the dual focal lens 115 is conical in shape with the apex at the top. 201 indicates the right inclination of the top conical surface in the dual focal lens 115. 202 indicates the left inclination of the top conical surface in the dual focal lens 115. The side surface 203 of the dual focal lens 115 is cylindrical in shape. The bottom surface 204 of the dual focal lens is concave in shape.Fig. 2B is the top view of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment. The dual focal lens 115 is basically a circular lens. 205 indicates the apex of the top conical surface of the dual focal lens 115.Fig. 3 is the schematic view of the working principle of the dual focal lens 115 used in the laser welding setup 100, in accordance with an embodiment. The laser beams incident on the conical surface of the dual focal lens 115. The designed dual focal lens is functioned as a combination of two Plano concave lens. The angle of inclination of the conical plane with horizontal is 0. One of the laser beam incidents on the right inclination 201 of the conical surface. Similarly, another laser beam incidents on the left inclination 202 of the conical surface. The incident angle of the laser beam on the conical surface is considered i. Let the angle of refraction is R. According to Snell's law, (n1 sin i = n2 sin R). Here, n1 and n2 are the refractive index of the laser medium and lens medium respectively. Meanwhile, the laser beam refracts in the top surface and moves vertically in the lens medium. Therefore, the angle of refraction becomes 0. Therefore, theinclination angle (0) of the conical surface of the dual focal lens is such that, (sin 0 = ni sin i / n2). The diameter of the dual focal lens is d, and this is at least twice the diameter of the laser beam coming from the metallic mirrors (102, 103). Further, the two laser beams refract from the concave surface 204 of the dual focal lens 115 and converge toward the focal points. X and Y are the two focal points of laser beam 116 and 117 respectively. The distance of the focal points from the principal plane of dual focal lens (Effective focal length, EFL) is f. Therefore, the welding edges of both the workpiece are required to be placed at point X and Y respectively. The vertical thickness of the dual focal lens, t is selected based on the ISO standard. The curvature radius of the concave surface 204 of the lens 115 is determined according to the lensmakers formula, (f ^ rJ) , where Ri and R2 are the radius of curvature of thelens and n2 is the refractive index of the lens material.Fig. 4 is the schematic view of the laser welding performed in the laser welding setup 100 using the dual focal lens 115, in accordance with an embodiment. A welding edge is prepared at both the workpieces (A and B) to be welded. The workpiece A contains a top surface 301 and a welding edge 303. The workpiece B contains a top surface 302 and a welding edge 304. Both the workpieces placed together and aligned Horizontally. Further they are placed in such a way that the welding edge 303 is positioned at the focal point X of laser beam 116 and the welding edge 304 is positioned at the focal point Y of laser beam 117. Both these edges are at a distance of effective focal length (f) from the dual focal lens 115. The laser beams coming from the metallic mirror 102 and 103 create an angle (0 + i) with the horizontal. Therefore, the metallicmirrors 102 and 103 are tilted at angle of (45° - with the horizontal plane. The laserbeams 116 and 117 coming from the metallic mirrors 102 and 103 incident on the inclined conical plane 201 and 202 of the dual focal lens 115. Further, they refract from the concave surface 204 and converge toward two different focal point X and Y which are situated on the welding edges 303 and 304. Therefore, heat is generated at the welding edges which melts the edge sections of both the work piece A and B. As the intensities of laser beams 116 and 117 are different, the heat generation is also different. The intensities of the laser beams are selected based on the melting points of materials A and B. The laser beams are then traversed along the joining of the material A and B. The heat transferred vertically downward along the contactedges of material A and B. Due to melting, welding occurs between A and B. Thus, two dissimilar metals A and B can be welded using this technology. A separate material can be placed in between the two materials A and B to be welded if they have different electrochemical properties. This material can act as a transition material which restricts the noble metals from pulling out electrons of the basic metals. In addition, the third material can also act as a barrier to heat flow from one material A to another material B. Thus, undesirable malting of the metals can be restricted. After welding, the top surface 301 and 302 of materials A and B can be slightly damaged due to heat transfer in the transverse direction. Therefore, a machining operation afterward the welding can be performed to clean the top surfaces.The proposed laser welding setup 100 with dual focal lens 115 can be used for any pair of materials having different melting points even when the difference between the melting points is very high. Depending on the melting point of the metals, the intensities of the laser beams need to be modified. This technology can be useful for welding two or more dissimilar metals at a time by combining more laser sources with only one dual focal lens. In addition, this technique can be utilized for any laser setup other than CO2 laser by incorporating multiple laser sources with the same dual focal lens.TECHNICAL ADVANTAGE:The present invention proposes (a) a laser welding set up with dual focal lens having two laser sources;(b) to focus two laser beams having different intensities in two different locations;(c) to generate variable heat at the welding edges of two different metals having contact;(d) to weld two different metals having different melting points;(e) to weld multiple metals at a time using more laser sources and only one dual focal lens.

Claims

1. A laser welding set up (100) with dual focal lens (115) for laser welding of dissimilar materials, the said laser welding set up (100) comprising; a pumping source (101); two different laser cavities (110) and (111) to effect as laser sources adapted as to effectively generate two laser beams of varying intensities; two different metallic mirrors (102) and (103) adapted to govern the direction of two laser beams in particular direction a partial reflector (104) in the laser cavity (110); a partial reflector (105) in the laser cavity (111); a full reflector (108) in the laser cavity (110); a full reflector (109) in the laser cavity (111); two electrodes (112) in laser cavity (110) disposed to effectively generate high voltage; two electrodes (113) in laser cavity (111) disposed to effectively generate high voltage; characterized in that, the laser beams generated by the ionized gas mixture in the said cavities (110, 111) passes through the partial reflector (104) and (105) to be effectively guided by the mirrors (102) and (103) respectively toward the dual focal lens (115), wherein the laser beam (116) generated from the laser cavity (110) effectively refracts by the dual focal lens (115) to focus on the welding edge of metal A and the laser beam (117) generated from the laser cavity (111) effectively refracts by the dual focal lens (115) to focus on the welding edge of metal B, wherein high velocity, ions strike the edges of metal A and B causing rapid heat generation to effect melting the welding edges of both the metal causing welding of the metals.

2. The laser welding set up as claimed in claim 1, wherein a shielding gas source (114) is arranged in the laser welding set up (100) which supplies inert gas surrounding the laser beams.

3. The laser welding set up (100) as claimed in claim 1, wherein the dual focal lens (115) is specially designed positive meniscus lens consisting three surfaces, the top surface being conical in shape with the apex (205) at the top, wherein the conical surface has right inclination (201) and left inclination (202) and the side surface (203) is cylindrical in shape and bottom surface (204) is concave in shape.

4. The laser welding set up (100) as claimed in claim 3, wherein the angles of right and left inclination (201) and (202) of the conical surface of the dual focal lens (115) are adapted to effect the laser beams (116) and (117) incident on the conical surfaces moves vertically within the lens medium.

5. The laser welding set up (100) as claimed in claim 3, wherein the diameter of the dual focal lens is at least twice the diameter of the laser beams coming from the metallic mirror (102) and (103).

6. The laser welding set up (100) as claimed in claim 4, wherein the laser beams (116) and (117) refracted from the dual focal lens (115) converge towards two different focal point X and Y.

7. The laser welding set up (100) as claimed in claim 1, wherein the laser beams (116) and (117) have different intensities based on the melting points of material A and B.