Title of Invention

“A METHOD OF MATERIAL JOINING TECHNIQUE FOR AN ELECTRICALLY CONDUCTIVE PURE NICKEL TAB”

Abstract

A method of materials joining technique for an electrically conductive pure nickel tab onto an electrically non-conductive sintered/impregnated porous nickel electrode comprising fabricating substrate selected from nickel fibre mat and nickel plated steel grid; applying nickel oxide slurry coating on said mat or grid; impregnating said coated mat or grid with Ni/Cd hydroxide; sintering impregnated porous Ni electrode upto a thickness of 0.7 to 0.8 mm characterized by; controlled heat input by square wave pulses of laser beam spot welding and using solid state Nd:YAG, subjecting the sintered impregnated electrode to laser welding, the step of impregnation is conducted prior to welding in the process sequence.

Full Text

FIELD OF INVENTION The present invention relates to a method of materials joining technique for an electrically conductive pure nickel tab onto an electrically non-conductive sintered/impregnated porous nickel electrode. The present invention particularly relates to materials joining technique for an electrically conductive pure nickel tab onto an electrically non-conductive sintered/impregnated porous nickel electrode employed in the manufacture of batteries using solid state Nd : YAG (Niodymium Yttrium Alumina Garnet) laser spot welding process. PRIOR ART The sintered/impregnated porous nickel electrode and the pure nickel tab is used an positive and negative terminals in the electrical component fabrication, such as the manufacturing of high energy batteries. The present manufacturing method refers to the following : 1. The said porous nickel electrode is manufactured from the nickel fibre, known as mat or from a nickel plated steel grid, known as grid. 2. This substrate is subsequently coated with Ni oxide slurry and allowed to dry for a specific period of time under a controlled atmosphere. At this point, the said component is known as porous nickel electrode. 3. After obtaining a satisfactory coating, the mat / grid is then subjected to sintering process at a controlled temperature and atmosphere. The sintered porous nickel surface is electrically conductive. At this point, the said component is known as sintered porous nickel electrode. The thickness of such electrodes ranges between 0.7 to 0.8 mm. 4. The pure nickel tabs are resistance spot welded onto the above sintered porous nickel electrodes. 5. The resistance spot welded electrodes are then impregnated using nickel hydroxide / cadmium hydroxide. The impregnated surface is electrically non-conductive. At this point, the above component is known as sintered / impregnated porous nickel electrode. During the impregnation process, the nickel tab adjoining the sintered porous nickel electrode portion also gets contaminated with nickel / cadmium hydroxide. This contamination is manually removed using chemical and mechanical cleaning. During this cleaning process, more than 30% of the electrodes are damaged. DESCRIPTION OF PRIOR ART With the present manufacturing process, resistance spot welding is applied prior to impregnation, since the impregnated layer is active and non-conductive. During impregnation, dis-colouration on the Ni tab, adjoining the sintered/impregnated porous nickel electrode occurs. Also, tear off between Ni electrode and Ni tab during and after impregnation is a problem faced in the manufacturing process. To overcome these problems, the applicant has developed a new manufacturing method. STATEMENT OF INVENTION According to this invention there is provided a method of materials joining technique for an electrically conductive pure nickel tab onto an electrically non-conductive sintered/impregnated porous nickel electrode comprising: i) fabricating substrate selected from nickel fibre mat and nickel plated steel grid; ii) applying nickel oxide slurry coating on said mat or grid; iii) impregnating said coated mat or grid with Ni/Cd hydroxide; iv) sintering impregnated porous Ni electrode upto a thickness of 0.7 to 0.8 mm characterized by; controlled heat input by square wave pulses of laser beam spot welding and using solid state Nd:YAG, v) subjecting the sintered impregnated electrode to laser welding, vi) the step of impregnation is conducted prior to welding in the process sequence. DESCRIPTION OF THE INVENTION The present invention is described hereinbelow in detail with reference to the drawings accompanying this specification, wherein Fig. 1 shows the flow sheet diagram of the known method of manufacture of sintered/impregnated porous Nickel (Ni) electrodes used in nickel batteries: Fig.2 shows new manufacturing sequence for sintered / impregnated porous nickel electrodes using laser spot welding according to the invention. Fig.3 shows an arrangement for laser spot welding of pure Ni tab to sintered / impregnated porous nickel electrode. The manufacturing process for sintered / impregnated porous nickel electrode using the proposed laser spot welding route is as follows (Fig.2): 1. The porous nickel electrode is manufactured from the nickel fibre, known as mat or from a Nickel plated steel grid, known as grid. 2. This substrate is subsequently coated with Ni oxide slurry and allowed to dry for a specific period of time under a controlled atmosphere. At this point, the said component is known as porous nickel electrode. 3. After obtaining a satisfactory coating, the mat / grid is then subjected to sintering process at a controlled temperature and atmosphere. The sintered porous nickel surface is electrically conductive. At this point, the said component is known as sintered porous nickel electrode. The thickness of such electrodes range between 0.7 to 0.8 mm. 4. The sintered porous nickel electrodes are then impregnated using nickel / cadmium hydroxide. The impregnated surface is electrically non-conductive. At this point, the above component is known as sintered / impregnated porous nickel electrode. 5. The pure nickel tabs are then laser spot welded onto the sintered / impregnated porous nickel electrodes using a solid state Nd : YAG laser machine. The arrangement for laser spot welding of pure Ni tab to sintered / impregnated porous nickel electrode is shown in Figure 3. 6. Laser spot welding parameters like mean power, peak power, dwell time, frequency and spot arrangement is given Table 1 below : Table 1 Laser Spot Welding Procedure For Nickel Battery Components MATERIAL SPECIFICATION a) Pure Nitab, 0.2 mm thick b) Ni hydroxide coated / impregnated electrode ( Grid / Mat), 0.7 mm thick JOINT TYPE Spot welding Spot size Pitch distance Line distance 2 mm max 5 mm 8 mm (Table Removed) 7. Quality assessment of laser spot welded locations are done employing the same electrical resistance measurement method used in assessing the resistance spot welding practiced in manufacturing at present. The results are given in Table 2 below : Table 2 MEASUREMENT OF ELECTRICAL RESISTANCE USING MICRO OHM METER (Table Removed) Note: The maximum acceptable limit for the electrical resistance value is 120micro Ohm centimeter specification of Laser System employed for developing the spot welding technology Capacity : 2000 watt Type of source : Continuous wave solid state Nd : YAG laser Beam modulation : Square and Sine, max freq 500 Hz Integrated with CNC work station for programmable welding sequence LASER SPOT WELDING METHODOLOGY Laser sport welding was carried out using a special fixture designed for this purpose, where the electrodes are inserted and clamped prior to welding for achieving programmed spot welds in three lines. Square wave beam modulation with 400-500 Hz frequency with a base power of 200-220 watts of beam power was employed (refer Table 1). All the laser spots were subjected to electrical resistivity measurement as per the acceptance criteria (refer Tab 2). The measurements were found to give a consistent value of electrical resistance reinforcing the consistency of the laser spot welding technology. WE CLAIM; 1. A method of materials joining technique for an electrically conductive pure nickel tab onto an electrically non-conductive sintered/impregnated porous nickel electrode comprising: i) fabricating substrate selected from nickel fibre mat and nickel plated steel grid; ii) applying nickel oxide slurry coating on said mat or grid; iii) impregnating said coated mat or grid with Ni/Cd hydroxide; iv) sintering impregnated porous Ni electrode upto a thickness of 0.7 to 0.8 mm characterized by; controlled heat input by square wave pulses of laser beam spot welding and using solid state Nd:YAG, v) subjecting the sintered impregnated electrode to laser welding, vi) the step of impregnation is conducted prior to welding in the process sequence.

Documents:

1318-DEL-2004-Abstract (8-1-2010).pdf

1318-DEL-2004-Abstract-(13-01-2011).pdf

1318-del-2004-abstract.pdf

1318-DEL-2004-Claims (8-1-2010).pdf

1318-DEL-2004-Claims-(13-01-2011).pdf

1318-del-2004-claims.pdf

1318-DEL-2004-Correspondence Others-(08-11-2011).pdf

1318-del-2004-Correspondence Others-(26-12-2012).pdf

1318-DEL-2004-Correspondence-Others (8-1-2010).pdf

1318-DEL-2004-Correspondence-Others-(13-01-2011).pdf

1318-del-2004-Correspondence-Others-(15-07-2013).pdf

1318-del-2004-correspondence-others.pdf

1318-DEL-2004-Description (Complete) (8-1-2010).pdf

1318-DEL-2004-Description (Complete)-(13-01-2011).pdf

1318-del-2004-description (complete).pdf

1318-del-2004-description (provisional).pdf

1318-del-2004-drawings.pdf

1318-del-2004-form-1.pdf

1318-del-2004-form-18.pdf

1318-DEL-2004-Form-2 (8-1-2010).pdf

1318-del-2004-form-2.pdf

1318-del-2004-form-3.pdf

1318-del-2004-form-5.pdf

1318-DEL-2004-GPA-(13-01-2011).pdf

1318-del-2004-gpa.pdf