Spot resistance-welding electrode; contact tip for such an electrode; machine for exchanging these tips

A machine for exchanging contact tips on electrodes wherein each electrode comprises an electrode body mounted on a support arm and connected to a high intensity welding current source as well as to a cooling water supply circuit and a welding cap securely fastened to an end of said body, said cap having (a) a consumable contact tip which is a distinct component of the cap and whose role is to ensure contact with metal sheets to be welded and to transmit to the sheets a welding current pressure and welding current intensity, and (b) a brazing which connects said cap to said tip which is produced by passing a current necessary for melting the brazing from said welding current source, said machine comprising:

• a loading station for loading new contact tips;
• a revolving platter and a stepwise drive motor means coupled to said platter for driving said platter in rotation, said platter comprising at least one loading cell for receiving a new contact tip when said platter stops opposite said loading station;
• a brazing-unbrazing station for brazing-unbrazing new and worn contact tips respectively, said brazing-unbrazing station comprising a resistive plate on which said contact tip rests and which allows the passage of the brazing or unbrazing current through this contact tip;
• at least one pair of jaws suitable for grasping a contact tip during unbrazing;
• and
• an automatic sequential control means for controlling said loading station, said revolving platter and said drive motor means, said brazing-unbrazing station, and said at least one pair of jaws and for ensuring that an operation for loading new contact tips at said loading station is carried out during an operation for unbrazing worn tips at said brazing-unbrazing station, and wherein said loading cell, equipped with at least one new contact tip, then comes, by a rotation of said platter, into the vicinity of said brazing-unbrazing station, so that said new tip is brazed onto the electrode which has previously had the worn contact tip removed.

A method for changing a distinct contact tip of a spot resistance-welding electrode wherein the electrode comprises (a) an electrode body connected to a high intensity welding current source as well as to a cooling water supply circuit and (b) a welding cap securely fastened to an end of the body to which the contact tip is attached by a brazing between the cap and the contact tip, the contact tip being consumable and acting to ensure contact with metal sheets to be welded and to transmit to the sheets a welding current pressure and welding current intensity, said method comprising the steps of:

• melting the brazing by passing a current necessary for melting the brazing from the welding current source through the contact tip;
• removing the contact tip from the cap while the brazing is melted;
• positioning a new contact tip with a new brazing material adjacent the welding cap;
• and
• melting the new brazing material by passing a current necessary for melting the new brazing material from the welding current source through the new contact tip, whereby the new contact tip is attached to the welding cap by a new brazing.