RESISTANCE-WELDING ELECTRODE ADAPTER

FIELD OF THE INVENTION

The present invention relates to a resistance-welding electrode adapter.

PRIOR ART

Resistance welding involves applying a resistance-welding elec- trode onto a work piece, and heating the work-piece to a welding temperature by letting a large current pass through the material of the work piece, so that the material melts and creates a weld. A resistance welding apparatus according to the prior art generally comprises a current generator, a replaceable resistance- welding electrode adapter arm adapted to be cooled internally, and a replaceable resistance-welding tip adapted to be in contact with, and to transfer the current to the work piece. The electrode adapter arm is adapted for conducting large currents with low resistance, meaning that the adapter arm has a large diame- ter and is made in a metal having high electric conductivity. The adapter arm is also usually cooled internally by circulating water.

The resistance-welding electrode tip is subjected to heavy wear, and is therefore replaceably attached onto the adapter arm. One problem with the adapter arm is that even though the adapter arm is cooled the adapter arm is also worn out after a period of use, after which the arm needs to be replaced. Due to the demands of low resistance, the resistance welding adapter arm is both heavy and large, due to the necessity of a large diameter, and is made in expensive, low resistance materials, such as

copper alloys. Hence the replacement of the adapter arm is very expensive.

SUMMARY OF THE INVENTION

One object of the present invention is to alleviate the high costs involved with the resistance welding apparatus of the prior art.

According to a first aspect of the invention this object is achieved with a resistance welding electrode adapter arm according to claim 1 , and according to a second aspect of the invention this object is achieved with the resistance welding electrode adapter tip according to claim 9.

By letting an adapter arm comprise an adapter tip adapted to be fastened to and released from the adapter arm, so that the adapter tip is replaceable, which adapter tip is further adapted to allow replaceable attachment of a resistance-welding tip, only the part that is heavily worn of the adapter arm during usage needs to be replaced periodically instead of the entire arm. Hence the cost for replacing the adapter arm decreases drastically, especially due to the high price and large amount of the material in the adapter.

The electrode adapter arm and adapter tip are adapted to conduct an electric welding current to a welding tip. The welding tip has a contact surface adapted to be applied against and to transfer the welding current to the work piece. A complete resistance-welding electrode according to the invention hence com- prises an attachment for an adapter arm, an adapter arm, an adapter tip, and a welding tip. The electrode is usually movable so as to allow being applied to the surface of the work piece. Normally, the resistance welding equipment comprises two electrodes jointly forming a nip between their respective welding tips. The welding tips may be provided with different kinds of contact surfaces having different shapes, such as male or fe-

male contact surfaces. Hence the same welding tip may be used for several different welding applications by simply changing the welding tip.

Preferably the adapter arm is adapted to be cooled internally. Preferably the adapter arm comprises an inner channel adapted to allow a coolant to flow inside the adapter arm. Preferably the adapter tip is also adapted to be cooled internally. Preferably the adapter tip also comprises an inner channel adapted to allow a coolant to flow inside the adapter tip. By cooling the adapter tip and the adapter arm internally the adapter tip and adapter arm may be held at a lower temperature during the welding, so that the lifetime of the adapter arm and tip increases.

According to one embodiment the adapter arm has a length that is at least 6 cm, preferably at least 10 cm, and most preferably at least 20 cm. Hence the slender adapter arm will provide a sufficient distance between the work piece and the more bulky resistance welding apparatus to allow agile welding of different kinds of work pieces.

According to one embodiment the adapter tip has a length that is smaller than or equal to 6 cm, preferably smaller than or equal to 5 cm, and most preferably smaller than or equal to 4 cm. Such a length for the adapter tip is in most applications sufficient for the functionality of the adapter tip, wherein the savings in material costs is large. Preferably the adapter tip has a length that is at least 2 cm. Hence it is ensured that the adapter tip has sufficient length to allow a secure fastening to the adapter arm, as well as to allow other functions necessary for the adapter tip as described below.

According to one embodiment the adapter tip also has a weight less than or equal to 200 grams, preferably less than or equal to 150 grams, and most preferably less than or equal to 100 grams. Preferably, the adapter tip has a weight greater than or

equal to 20 grams. Preferably the adapter arm has a weight that is at least 200 grams, preferably at least 250 grams, and most preferably at least 400 grams. Preferably the adapter arm has a weight that is less than 5 kg. Preferably, the adapter tip has a weight that is less than 80 % of the weight of the adapter arm, preferably less than 50 %, and most preferably less than 25 %. Correspondingly, the adapter arm has a weight that is at least 1 .25 times larger than the weight of the adapter tip, preferably at least 2 times larger, and most preferably at least 4 times lar- ger than the adapter tip. Hence the adapter tip is sufficiently small relative the adapter arm so as to make savings in material costs to balance the cost of manufacturing the new adapter arm and tips.

According to one embodiment the adapter arm is shaped with a bend, and the adapter tip is adapted to be fastened to the arm in a position after the bend. Hence the adapter tip automatically will be directed in a correct direction after being fastened to the adapter arm. Preferably the adapter tip is shaped straight. If the adapter tip would be curved, the adapter tip would otherwise be in the risk of being directed in different directions after fastening to the adapter arm, depending on its angular rotation.

According to one embodiment the adapter tip comprises a threading adapted for fastening the adapter tip to the adapter arm. Correspondingly, the adapter arm comprises a threading adapted for fastening the adapter tip to the adapter arm. A threading allows easy fastening and releasing of the tip from the adapter arm. Furthermore, a threading provides for a secure fas- tening of the adapter tip, so that it does not change its position in relation to the adapter arm during a welding operation.

According to one embodiment the threading is flat. By providing a flat threading there is no uncertainty about at which distance the adapter tip will be securely fastened to the adapter arm, thus

decreasing the variation of the difference in tip position after replacement of the adapter tip.

According to one embodiment the adapter tip is shaped with a shoulder arranged next to the threading and having a larger diameter than the threading. Preferably, the adapter arm comprises a sleeve-portion internally fitted with said threading, wherein the end of the sleeve is adapted to interact with the shoulder arranged on the adapter tip in order to provide a stop for the adapter tip, so that the location of the contact surface is the same for different adapter tips.

According to one embodiment one surface of the shoulder is adapted to interfere with a sleeve-portion of the adapter arm, and is angled outwardly towards the sleeve-portion. By arranging such an angled surface interfering with the sleeve-portion a watertight seal is achieved. By arranging a watertight seal between the adapter tip and the adapter arm it is possible to provide the adapter arm and adapter tip with an internal coolant flowing between the adapter arm and the adapter tip.

According to one embodiment the adapter tip and the adapter arm is made in a precipitation hardened metal. A precipitation hardened metal has both a high conductivity and a high me- chanical strength, due to the precipitated particles inside the metal matrix. Since the particles are at least partly precipitated the particles do not interfere greatly with the conductivity of the more pure metal matrix, while the particles still interfere sufficiently to reduce slip and mechanical deformation. Preferably the adapter tip and adapter arm are made in a copper alloy alloyed with aluminium oxide.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now to be described as a non-limiting example of the invention with reference to the attached drawings.

Fig. 1 a shows a resistance-welding adapter arm in cross-section provided with a resistance welding adapter tip according to one example of the invention.

Fig. 1 b shows the resistance-welding adapter tip shown in fig. 1 a.

Fig. 1 c is an elevation of the adapter arm and the adapter tip in figs. 1 a-b.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Fig. 1 a and 1 c show a resistance-welding electrode comprising a resistance welding electrode adapter arm 1 , a resistance welding electrode adapter tip 3, and a resistance-welding tip 29 according to one example of the invention. In fig. 1 b the adapter tip 3 is shown in more detail, and in fig. 1 c the welding adapter arm 1 and adapter tip 3 are shown in elevation. During actual welding a work piece is placed in a nip between a welding tip arranged on the adapter tip 3, and a second welding tip mounted on another, similar electrode. The two electrodes are then moved so as to close the nip, a current is applied and conducted into the work piece through the welding tips, wherein the work piece is heated by the current and welded.

The adapter tip 3 is adapted to be fastened to and released from the resistance welding adapter arm 1 , so that the adapter tip is replaceable. Correspondingly the resistance welding adapter arm 1 is adapted to allow fastening and releasing of a replaceable resistance welding electrode adapter tip 3 to one end 5 of the adapter arm 1 . Hence it is possible to replace the tip 3 when the tip is worn out, instead of having to replace the entire adapter arm 1 . The adapter arm 1 is likewise replaceable from its resistance welding apparatus, and the resistance-welding tip 29 is replaceable from the adapter tip 3.

The adapter arm 1 has a length that is at least 10 cm, preferably at least 15 cm, and most preferably at least 20 cm. In this example the adapter arm 1 has a length of 22 cm. Furthermore, the adapter arm 1 has a length that is shorter than 1 .5 m. Furthermore, the adapter arm has a weight that is at least 200 grams, preferably at least 250 grams, and most preferably at least 400 grams. Preferably the adapter arm 1 has a weight that is less than 5 kg. In this example the adapter arm 1 has a weight of 2.5 kg.

The adapter tip 3 in turn has a length that is smaller than or equal to 6 cm, preferably smaller than or equal to 5 cm, and most preferably smaller than or equal to 4 cm. Furthermore, the adapter tip 3 has a length that is at least 2 cm. In this example the adapter tip 3 is 3.4 cm long. The adapter tip 3 also has a weight less than or equal to 200 grams, preferably less than or equal to 150 grams, and most preferably less than or equal to 100 grams. Furthermore, the adapter tip 3 has a weight greater than or equal to 20 grams. In this example the adapter tip 3 weighs 100 grams. Hence the adapter tip 3 weighs only 4% of the weight of the adapter arm 1 . Hence the adapter tip 3 is very small relative the adapter arm 1 , so that large savings in material costs is made by only replacing the adapter tip instead of the entire adapter arm.

The adapter arm 1 is shaped with a bend 1 1 , which is adapted to facilitate the formation of a nip between a welding tip and a corresponding welding tip of another electrode. In this example the bend 1 1 is only slightly curved, but the bend may be also be made in a sharper angle, such as at a right angle. The adapter tip 3 is fastened to the adapter arm 3 in the end 5 of the adapter arm directed towards the work piece, and after the bend 1 1 . Hence it becomes easier to replace the adapter tip 3, since there is no need to consider a correctly oriented bend 1 1 .

The adapter arm 1 comprises a wall 7 made in a highly conductive material, and adapted to carry the welding current to the adapter tip 3. The wall 7 is shaped to enclose an inner channel 9, adapted to allow a flow of coolant to and from the adapter tip 3. The coolant, which in this example is water, cools the adapter tip 3 to prevent it from melting and to increase the life-time of the adapter tip 3. The adapter tip 3 further comprises a channel 21 for conducting the coolant inside the adapter tip 3. At the end of the channel 21 the water is turned so as to flow back through the channel 21 and 9, and out of the electrode. In another example the water may instead be passed on to and into the welding tip.

The wall 7 of the adapter arm 1 further comprises a sleeve- portion 13, adapted to allow fastening of the adapter tip 3. In this example the sleeve-portion is internally fitted with a threading 15, adapted for fastening the adapter tip 3 to the adapter arm 1 . The adapter tip 3 correspondingly comprises a threading 17, adapted for fastening the adapter tip 3 to the adapter arm 1 . The adapter tip 3 is further shaped with a shoulder 19, arranged next to the threading 17, which shoulder 19 has a larger diameter than the threading 17. The outermost end of the sleeve- portion 13 is adapted to interact with the shoulder 19, arranged on the adapter tip 3, in order to provide a stop for the adapter tip 3 when screwing the adapter tip into the sleeve-portion 13.

The threading 15 and the threading 17 are in this example flat, so as to prevent different adapter tips 3 to be screwed into the sleeve-portion 15 with different lengths, which might happen if the threadings had been tapered. The flat threads 15, 17 in combination with the stop provided by the shoulder 19 and the sleeve-portion 13, function to ensure that every new adapter tip is screwed into the arm 1 with equal distance. It is important that the distance between the adapter tip 3 and the adapter arm 1 is constant, so as to allow swift replacement of adapter tips without a need for lengthy calibration processes.

The shoulder 19 is further shaped with a surface 23 adapted to interfere with the sleeve-portion 13. The surface 23 is angled outwardly towards the sleeve-portion 13, wherein the surface 23 and the sleeve 13 achieves a water-tight seal, so that the coolant flowing inside the channel 9 remain inside the electrode.

The adapter tip 3 is further provided with a tapered thread 25, ending in a surface 27, adapted for allowing fastening of a weld- ing tip to the adapter tip 3. The surface 27 is in this example circular with a diameter between 13 mm and 25 mm. The design of such surfaces and tapered threads are known in the art of previous adapter designs.

The adapter arm 1 and the adapter tip 3 are in this example made in a precipitation hardened metal. It is preferred that at least the adapter tip 3 is made in a precipitation hardened metal, since it is the adapter tip 3 that will be subjected to the most of the stress during welding. A precipitation hardened metal comprises an alloy having an alloying element that precipitates and forms particles inside the metal matrix. The particles thus both strengthen the metal mechanically, and allow for high electric conductivity. The precipitation hardened metal alloy is in this example a copper alloy alloyed with aluminium oxide.

The invention is not limited to the example and embodiments indicated above, but may be varied freely within the framework of the following claims. In particular, a man skilled in the art of fastening technology may devise different methods or construc- tion for fastening the adapter tip to the adapter arm, and the welding tip to the adapter tip.