Claims:The scope of the invention is defined by the following claims:

Claim:
1. A welding fixture comprising:
a. A back up member (Fig. 1a, Fig. 2a, Fig. 4) is the platform for all the parts attached for the welding of thin foil (Fig. 1d, Fig. 2d).
b. A Backing plate (Fig.1b, Fig. 2b and Fig. 3) is mounted on the back up member which provides the pathway for the inert gas from the back side of the foil (Fig. 1d, Fig. 2d).
c. A welded foil (Fig. 1d, Fig. 2d) is kept on a glass fibre mat/sheet (Fig 1.c, Fig. 2c).
d. The welded foil (Fig. 1d, Fig. 2d) is pressed by a heat conductive plate (Fig. 1e, Fig. 2e). The heat conductive plate is bonded with the perforated silicon rubber mat/sheet (Fig. 1f, Fig. 2f).
e. The hold down plate (Fig. 1g, Fig. 2g and Fig 5) members presses the welded foil (Fig. 1d, Fig. 2d) through a silicon rubber mat/sheet using head less bolts (Fig. 2h) and holds the assembly.
2. As mentioned in the claim 1, the perforated copper backing plate (Fig.1b, Fig. 2b and Fig. 3) is used to dissipate the heat produced during welding and provide back shielding of the foil (Fig. 1d, Fig. 2d) to be welded.
3. As per the claim 1, the glass fiber mat/sheet (Fig 1.c, Fig. 2c) is used to eradicate the chilling effect and to permit sufficient movement of the foil work to release thermal strains and prevent hot cracking during welding. The process of thin foil welding using glass fiber mat/sheet (Fig 1.c, Fig. 2c) is useful to reduce or prevent cracking either in the welds, or adjacent to the welds, in those materials having higher susceptibility to such cracking under the thermal strains of welding.
4. As per the claim 1, the hold down plate (Fig. 1g, Fig. 2g and Fig 5) members to press the welded foil at their respective place without distortion. The members are placed fairly distant so that welding torch can easily move.
5. As per the claim 1, 2, the perforated copper backing plate (Fig.1b, Fig. 2b and Fig. 3) is detachable, which can be used for welding of different materials.
6. As per the claim 1, the combined assembly (Fig. 1) is used for defect free welding of thin foil of thickness 0.008 inch. , Description:Field of Invention
The present invention pertains to arc welding and more specifically to gas tungsten arc welding of thin metal foil where high heat input and lower penetration and hence distortion, low welding speed and porosity have to be eradicated. The invention incorporates the use of a fixture to provide effective support and heat dissipation to the foils that are being joined.
Background of the Invention
The aim of this invention is concerned with fabrication of a fixture for fusion welding of thin foils below 0.008-inch thickness and eradicate the ill effects of high heat input and lower penetration during welding.
In the welding of metal foils, conventionally they are placed over or in-contact with each other at the intended location and weldment is completed. Alternately, the foils are held in position by using suitable fixtures or jigs. The purpose of the fixture is to press the welding members against each-other or as close to the line of joint as possible in case of lap and butt configuration respectively.
The welding of thin foils can be accomplished through less complicated and less expensive welding processes and hence is suitable for commercial practices. The electrically operated arc welding processes like gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), shielded metal arc welding (SMAW) and submersible arc welding (SAW) are those kinds of processes. In all of the above-mentioned welding processes GTAW possess special attention because of cost effectiveness, shop floor friendliness and control over weld and hence has wide application in fabrication and service repairing of mechanical parts to produce clean, precise and high-quality joints. However, the problems like distortion, slower welding speed and porosity generally encountered due to high heat input and lower arc penetration especially in the case of thin foil limits its application.
Several previous patents aimed at successfully developing a fixture for joining of thin foils have been attempted. Examples of such patents include U. S patent No. 3,082,318, U. S patent No. 3,458,683, U. S patent publication No. 2004/0245233 and copious other patents have accomplished various techniques to join thin foils.
In all the published patents although the fixture has been successfully fabricated to weld the foil but very little care has been taken into consideration to dissipate the heat generated and chilling effect during welding. For example, in U. S patent No. 3,082,318, the authors have used copper as backing plate to dissipate heat at a high rate but there is no perforation in the plate to increase it further according to the requirement.
In light of above, in the present investigation, focus is not only on holding the foil but also to dissipate the heat rapidly and eradicate the chilling effect. For the same, the backing plate used was of copper material (high thermal conductivity) with perforation. Copper being high in thermal conductivity will dissipate heat rapidly. additionally, perforation in the copper plate will allow shielding gases to pass through and hence further increment in heat dissipation through convection. To overcome the chilling effect and hence the need for pre-heat a mat/sheet of glass fibre was placed on the top. On the top of the foil to be welded, a thin copper sheet (3 mm thick) along with perforated silicon rubber sheet was also used.
There are three prime objectives that are aimed to be achieved through this invention: i) To provide an apparatus to hold the foil, dissipate heat and omit the need of pre-heat so that the effect of high heat input and lower penetration can be eradicated ii) The apparatus should be handy and reliable for performing welding. iii) The apparatus must be flexible enough to be used for different materials in various weld configuration.
Summary of the Invention
The aforesaid objectives have all been achieved in present invention. The present invention pertains to arc welding and more specifically to gas tungsten arc welding of thin metal foil where high heat input and lower penetration and hence distortion, low welding speed and porosity have to be eradicated. The invention incorporates the use of a fixture to provide effective support and heat dissipation from the foils that are being joined.
Brief Description of Drawings
The invention will be described in detail with reference to the exemplary embodiments shown in the figures wherein:
Figure 1 Pictorial representation of GTAW welding process.
Figure 2 Pictorial representation of all the parts
Detailed Description of the Invention
The invention provides suitability for arc welding of thin foils made up of stainless steel, aluminum, tungsten, Inconel etc. At the bottom of the apparatus a highly conductive material (copper) in plate form with perforation was used as backing plate to dissipate the heat at a fast rate. On the top of the backing plate a glass fiber mat is used to eradicate the chilling effect. On the top of the foil to be welded, a thin sheet of copper of thickness 3 mm was used to remove the excessive heat generated from the arc side. To maintain the uniformity of heat accumulated on the copper sheet, a perforated silicon rubber mat was also used. The perforation in the rubber mat was to maintain its dimension throughout the process. The rubber mat may be mounted with the sheet for a production setup. The hold down plate is used to press the foil through the silicon rubber. The hold-down members are equally placed and fairly distant so that welding torch can easily move.
Fig. 1 is cross-sectional view of the apparatus illustrating the invention. Fig. 2 is an exploded 3D view of the fixture. As shown in Fig. 2 f, a perforated silicon rubber sheet of 3 mm thickness is placed above the metal foil (Fig. 2 d) to be welded. The silicon sheet is on the same side of the torch above the supporting copper plate (Fig. 2 e). Copper plate is for heat dissipation purpose. Both butt and lap type weld joints may be made; for butt joint the edges of the foil to be welded need to be turned sharply upward at right angle (Fig. 1). The hold down clamps (Fig. 2 g and Fig. 5) (especially made from non-magnetic materials i.e., plastics, austenitic steel etc. to eradicate the arc blow due to electromagnetic force) are sufficiently apart so that the welding torch can move freely. These hold down clamps are used to fix the thin foil at the right place which is being welded. The fixing is performed in such a way that each attached bolt (Fig. 2 h) exerts equal amount of pressure to the silicon rubber so that thin foil cannot be distorted due to clamping.
A glass fibre mat/sheet is placed under the foil being welded, as shown in Fig. 2 c. The reason for using glass fibre mat/sheet is to reduce the chilling and to permit sufficient movement of the foil to release thermal strains and prevent hot cracking during welding. Such activity is generally practice to reduce or prevent cracking either in the welds, or adjacent to welds, particularly in those materials which are susceptible to such cracking under the thermal strains of welding. Further, it will eliminate the need for preheating the welding fixtures. The back-up shielding gas or back purging will be required for highly reactive materials. Hence, the backing plate (copper) were drilled so that a suitable inert gas may be delivered through to protect the underside of the joint being welded from the ambient air (Fig. 3). The back-up non-magnetic bulk member which is connected with the either pole of the current for the welding is shown in Fig. 2 a and Fig. 4. This back-up section contains grooves and slots for the flow of inert gas from the gas cylinder to the copper backing plate. The torch is provided shielding from the upper section (Fig. 1). It also contains a purging cup for extra shielding which is preferably suitable for Ti and its alloys. Fig. 1 illustrates the relative physical relationship of the parts found necessary for obtaining good quality welds.
6 Claims & 2 Figures