RESISTANCE SPOT WELDING METHOD

• US 20160271720A1
• Filed: 12/22/2014
• Published: 09/22/2016
• Est. Priority Date: 12/27/2013
• Status: Active Grant

• Current Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Original Assignee: JFE Steel Corporation (JFE Holdings Incorporated)
• Inventors: SAWANISHI, Chikaumi, OKITA, Yasuaki, IKEDA, Rinsei
• Granted Patent: US 9,821,404 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: B23K 11/115 by means of two electrodes placed opposite one another on both sides of the welded parts
• CPC Class Codes: B23K 11/24 Electric supply or control circuits therefor
• CPC Class Codes: B23K 11/241 Electric supplies B23K11/248 takes precedence
• CPC Class Codes: B23K 2103/04 Steel or steel alloys
• CPC Class Codes: B23K 35/02 characterised by mechanical features, e.g. shape
• CPC Class Codes: B23K 35/0205 Non-consumable electrodes; C-electrodes

Abstract

In a resistance spot welding method, test welding and actual welding in which a current pattern is divided into two or more steps are performed. In the test welding, a constant current of a different value is passed in each step, and a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume are stored as a target value. In the subsequent actual welding, when a time variation amount of an instantaneous amount of heat generated per unit volume deviates during any step from the results of the test welding, a current passage amount is controlled to compensate for the difference during a remaining welding time in the step. In the test welding, 0.3×I_x≦I_a<I_x, where I_a is the current in the first step, and I_x is the current in second and subsequent steps.

Claims

1. A resistance spot welding method to join parts to be welded by squeezing and pressing the parts between a pair of electrodes and passing current, the parts being a plurality of overlapping metal sheets, the method comprising:

performing test welding and actual welding in which a current pattern is divided into two or more steps, wherein

in the test welding, a constant current of a different value is passed in each step, and a time variation of an instantaneous amount of heat generated per unit volume and a cumulative amount of heat generated per unit volume that are calculated from an electrical property between electrodes when forming an appropriate nugget are stored as a target value,

in the subsequent actual welding, welding is started using, as a standard, a time variation curve of the instantaneous amount of heat generated per unit volume obtained by the test welding,

when a time variation amount of an instantaneous amount of heat generated per unit volume deviates during any step of the actual welding from the time variation curve by a difference, a current passage amount is controlled in order to compensate for the difference during a remaining welding time in the step so as to match a cumulative amount of heat generated per unit volume in the actual welding to the cumulative amount of heat generated per unit volume that is determined in advance in the test welding, and

in the test welding, 0.3×

I_x≦

I_a<

I_x, where I_a is a current in a first step, and I_x is a current in second and subsequent steps.

2. The method of claim 1, wherein current is passed in the first step to secure a current path between the metal sheets or in the second and subsequent steps to obtain a predetermined nugget diameter.