Production or assembly line method of spot welding

• US 20090084763A1
• Filed: 10/07/2008
• Published: 04/02/2009
• Est. Priority Date: 12/09/2005
• Status: Active Grant

• Current Assignee: Alcoa Incorporated (Howmet Aerospace, Inc.)
• Original Assignee: Alcoa Incorporated (Howmet Aerospace, Inc.)
• Inventors: Brockenbrough, John R., Spinella, Donald J., Fridy, Joseph M.
• Granted Patent: US 7,718,918 B2
• Time in Patent Office: Days
• US Class Current: 219/86.410
• CPC Class Codes: B23K 11/252 using digital means
• CPC Class Codes: B23K 11/253 the measured parameter being a displacement or a position

Abstract

The present invention provides a production line method of resistance welding comprising the steps of contacting a metal sheet with an electrode having an initial contact surface area at a force provide a pressure to the metal sheet; applying a current though the electrode to the metal sheet; measuring dimensional changes of the electrode; correlating dimensional changes in the electrode to changes in the initial contact surface area; and adjusting the force to compensate for the changes in the initial contact surface area of the electrode to maintain pressure to the metal sheet. The force may be adjusted by stepping the force to maintain pressure to the flaying surface of the metal sheet to be welded. By maintaining the pressure at the faying surface the life cycle of the electrodes may be increased without forming discrepant welds.

Claims

1. A production line method of spot welding comprising the steps of:

a. providing a pair of electrodes, wherein an electrode of the pair of electrodes comprises a tip, a tip surface area, a length, and a plurality of diameters along the length, wherein the electrode tip surface area is substantially proportional to a diameter of the plurality of diameters relative to the electrode length as the electrode tip erodes;

b. determining a pressure and a current for a weld cycle of a welding operation;

c. developing a relationship between an electrode force with the electrode length as the electrode tip erodes to substantially maintain the pressure for the weld cycle;

d. contacting a metal sheet with the electrode;

e. applying the electrode force associated with the length of the electrode to provide the predetermined pressure to the metal sheet;

f. measuring a stroke dimension of the electrode, wherein the stroke dimension is a distance from a reference point of the electrode to a contact surface of the metal sheet prior to applying the electrode current;

g. applying the electrode current through the electrode to the metal sheet to generate a weld, a new tip surface area of the electrode, a new electrode length, and a new contact surface of the metal sheet;

h. measuring a new stroke dimension, wherein the new stroke dimension is a distance from the reference point of the electrode to the new contact surface of the metal sheet;

i. determining the new electrode length, wherein the new electrode length equals the electrode length less the difference of the new stroke dimension and the stroke dimension; and

j. repeating steps d-i to substantially maintain the pressure for subsequent weld cycles until completion of the welding operation without increasing the current,

whereby, the electrode force is adjusted for each weld cycle to compensate for the change in the electrode tip surface area as the electrode erodes.

2. A weld controller operably connected to at least one pair of electrodes, each electrode of the at least one pair of electrodes having a tip and a length, the weld controller comprising:

an initialization program including an electrode type, an initial electrode length, a pressure, a current, a force, and a current stepper ratio 1;

1 without incremental increases in current;

a plurality of electrode length to force lookup tables for contact pressures and constant currents for a plurality of electrode types;

an electrode stroke distance program to determine a new length of the at least one pair of electrodes in response to a signal including an electrode stroke distance at each of a plurality of weld cycles; and

an electrode force program to access the plurality of electrode length to force lookup tables to determine a new force to be applied by the tips onto at least two workpieces to reproduce the pressure at the current.

3. The weld controller according to claim 2 further comprising an output signal transmitor to transmit the new force to the at least one pair of electrodes.

4. A method of welding comprising:

i. contacting a metal sheet with at least one electrode having all electrode tip with an electrode diameter at a force to provide a pressure to a contact surface of the metal sheet, wherein the electrode diameter has a starting position displaced from the contact surface by a stroke dimension, wherein the stroke dimension is equal to a difference in the starting position and a position of the electrode tip when the electrode tip makes contact to the contact mixture of the metal sheet;

ii. applying a current through the at least one electrode to the metal sheet;

iii. measuring a dimensional change off the stroke dimension;

iv. correlating the dimensional change in the stroke dimension to a subsequent force to maintain the pressure, and

v. applying the subsequent force to compensate for the dimensional change in the stroke dimension to maintain the pressure applied to the contact surface of the metal sheet.

5. The method according to claim 4 wherein the at least one electrode is a AWS Type B or a AWS Type E electrode and the subsequent force is detailed by the following algorithm:

Subsequent Force=Force×

Force Stepping Factor (y) given the electrode diameter;

Electrode Diameter, mm Force Stepping Factor Formula 4.0 y = 0.0278Δ

x² + 0.3333Δ

x + 1 5.0 y = 0.0331Δ

x² + 0.3636Δ

x + 1 6.0 y = 0.04Δ

x² + 0.4Δ

x + 1 7.0 y = 0.0494Δ

x² + 0.4444Δ

x + 1 8.0 y = 0.0625Δ

x² + 0.5Δ

x + 1 9.0 y = 0.0816Δ

x² + 0.5714Δ

x + 1 10.0 y = 0.1111Δ

x² + 0.6667Δ

x + 1 11.0 y = 0.16Δ

x² + 0.8Δ

x + 1 12.0 y = 0.25Δ

x² + Δ

x + 1

while Δ

x is the dimensional change in the stroke dimension.

6. The method according to claim 4 wherein the at least one electrode is a AWS Type A and the subsequent force is determined by the following algorithm:

Subsequent Force=Force×

Force Stepping Factor (y) given the electrode diameter,

Electrode Diameter, mm Force Stepping Factor Formula 4.0 y = 0.0833Δ

x² + 0.5774Δ

x + 1 5.0 y = 0.0533Δ

x² + 0.4619Δ

x + 1 6.0 y = 0.037Δ

x² + 0.3849Δ

x + 1 7.0 y = 0.0272Δ

x² + 0.3299Δ

x + 1 8.0 y = 0.0208Δ

x² + 0.2887Δ

x + 1 9.0 y = 0.0165Δ

x² + 0.2566Δ

x + 1 10.0 y = 0.0133Δ

x² + 0.2309Δ

x + 1 11.0 y = 0.011Δ

x² + 0.2099Δ

x + 1 12.0 y = 0.0093Δ

x² + 0.1925Δ

x + 1

wherein Δ

x is the dimensional change in the stroke dimension.