Wear electrode for resistance projection welding of bolts

Abstract

Wear electrode for resistance projection welding of bolts (9), with - an electrode body (5) which has an opening (12) for inserting a bolt (9), - a receptacle (24) formed in the electrode body (5), - wherein a sleeve (6) is received in the receptacle (24), characterized in that - that the sleeve (6) has a first section (17) in which the outer diameter of the sleeve (6) tapers towards the opening (12).

Description

[0001] The invention relates to a wear electrode for resistance projection welding of studs. The wear electrode has an electrode body with an opening for inserting a stud and a receptacle formed in the electrode body in which a sleeve is received. The sleeve serves to center the inserted stud.

[0002] Methods for resistance projection welding of studs onto a workpiece – usually a sheet metal part – are well known in the art. These methods utilize a welding electrode with a top electrode and a bottom electrode. The bottom electrode features a wear electrode with a standard electrode body.

[0003] Before welding, the sheet metal is placed on the consumable electrode. The stud is then inserted through an opening in the sheet metal into the opening of the electrode body. This opening defines the position where the stud is to be welded to the sheet metal. The sleeve serves to center the stud and also provides insulation.

[0004] For welding, the upper electrode moves down onto the stud and presses the stud onto the sheet metal. This creates an electrical connection between the upper electrode, the stud, the sheet metal, and the lower electrode. Due to the voltage drop between the stud and the sheet metal, a significant amount of heat is generated, causing the stud to melt and thus weld to the sheet metal.

[0005] A typical bolt has a head and a pin. The head serves as a bearing surface on the sheet metal and is welded to it. The pin can be smooth or have an external or internal thread. The term "projection welding" derives from one or more projections arranged on the underside of the head, i.e., the side facing the sheet metal. Prior art describes bolts with several individual projections arranged on the underside of the head. A projection ring is also known. The at least one projection protrudes from the underside of the bolt head and melts during the welding process.

[0006] Resistance welding has proven its worth, particularly in the automotive industry, but also in other sectors. Over several welding cycles, residues from the molten material can lead to wear of the electrode. Furthermore, the electrode is subjected to significant heat stress due to the high welding temperatures and pressure from the contact pressure of the top electrode. Over time, this results in a depression forming on the electrode. When the electrode loses its shape and / or the contact surface is no longer sufficiently electrically conductive, it is replaced. From both a cost and quality perspective, the longest possible service life for the electrodes is desirable.

[0007] A wear electrode of this type is known from EP 3 412 398 B1. The wear electrode has an electrode body with an opening through which the bolt is inserted. The electrode body has a receptacle for receiving a cylindrical sleeve. As previously described, the sleeve serves to center the inserted bolt.

[0008] The well-known wear electrode has generally proven its worth. However, contamination of the thread can sometimes occur with this type of wear electrode.

[0009] The invention is based on the objective of further developing the known wear electrode in such a way that the bolt is better protected.

[0010] The problem is solved by a wear electrode having the features of claim 1.

[0011] The wear electrode according to the invention has an electrode body with a receptacle in which a sleeve is received. As in the prior art, the sleeve serves to center a bolt. The sleeve has a first section in which the outer diameter of the sleeve tapers towards the opening. The sleeve thus tapers towards its free end.

[0012] The invention is based on the understanding that slag and weld spatter can enter through the opening of the electrode body. These become lodged on the thread, thereby impairing its performance. The metallic weld spatter can cause an electrical short circuit, which is undesirable and leads to melting in unwanted areas.

[0013] To remedy this, the invention provides that the outer diameter of the sleeve tapers towards the opening. This allows the sleeve to extend further towards the opening than is known from the prior art. At the same time, it is advantageous if the receptacle also tapers so that it supports the sleeve in the region of the first section.

[0014] The invention has several advantages. Firstly, the tapered design allows the sleeve (in the case of a vertical welding electrode) to be pulled further upwards. This allows the thread to be covered, thus preventing it from becoming contaminated during the welding process. Secondly, unwanted electrical short circuits are avoided.

[0015] The invention has a further significant advantage. The tapering allows the electrode body (in a lateral sectional view) to become thinner towards the opening in the area of ​​the first section. However, the sleeve supports the electrode body in the area of ​​the tapering, which is considered very advantageous in itself. Despite the thinner wall thickness of the electrode body in the area of ​​the tapering, the invention therefore still provides excellent stability. Furthermore, the tapering enables an advantageous current flow between the wear electrode and the at least one boss of the bolt. This is because sufficient electrode body material is located below the bolt head.

[0016] Preferably, the sleeve has a through-opening. The pin can pass through this opening. Advantageously, the through-opening of the sleeve is aligned with the opening of the electrode body.

[0017] Within the scope of the invention, the tapering can, in principle, be carried out in stages. For example, the tapering has at least one stage.

[0018] However, it is considered particularly advantageous if the sleeve tapers conically in its first section. The conical shape allows for a ceramic-compatible manufacturing process for a ceramic sleeve, which is considered beneficial. In addition to good insulating properties, the ceramic material also offers the advantage of good abrasion resistance, which is particularly advantageous for the sharp threads of a bolt-pin.

[0019] The conical taper also allows for optimal current flow. This is because the current flows advantageously along the shortest possible path from the wear electrode through the workpiece to the bolt (or vice versa). The current flow therefore does not have to take any "detour".

[0020] Preferably, in a lateral sectional view, the electrode body extends over the first section. The receptacle of the electrode body, in which the sleeve sits, thus tapers towards the opening. This advantageously provides the electrode body with a large contact surface for the workpiece. At the same time, it supports the receptacle. Conversely, the sleeve also supports the electrode body in this area, as has already been advantageously described above.

[0021] An advantageous embodiment of the invention is characterized in that the sleeve extends into the opening. In this case, the sleeve is advantageously positioned in the opening between the electrode body and a bolt inserted into the wear electrode. This embodiment has the advantage that the thread of an inserted bolt is largely protected. Electrical short circuits and / or contamination of the thread are effectively prevented. In the prior art, it was sometimes the case that the opening narrowed progressively over the service life. This is related to the high pressure that the upper electrode exerts on the bolt and the workpiece, and thus also on the lower electrode. The material of the electrode body was therefore increasingly displaced in the area of ​​the opening, resulting in both an (undesirable) indentation and an (equally undesirable) reduction in the size of the opening.Furthermore, in some cases, the component, which should have been lying flat on the support surface at this point, was pressed into the recess during welding. This resulted in a so-called "distortion" of the component, which could lead to its rejection. Because the sleeve extends all the way into the opening, this disadvantage can be avoided.

[0022] In a further development of the invention, it is proposed that the electrode body has a flat bearing surface for supporting a workpiece that is to be welded to the bolt, wherein the bearing surface forms a bearing plane, and wherein the distance between the sleeve and the bearing plane is less than 2 mm, preferably less than 1 mm. In particular, it can be provided that the sleeve essentially terminates in the bearing plane defined by the bearing surface. Here, "essentially" means that, advantageously, the sleeve can theoretically extend exactly to the bearing plane. However, due to tolerance deviations, in practice the sleeve will only extend just to the bearing plane to prevent the workpiece from resting solely on the sleeve. This ensures that both the shank of the bolt and the electrode body of the wear electrode are covered.

[0023] As mentioned above, the sleeve not only provides shielding for the bolt pin but also supports the electrode body. Therefore, it is considered advantageous if the electrode body rests against the sleeve over a flat surface in the first section. This flat contact allows the sleeve to provide maximum support. This is especially true if the receptacle has a tapered, particularly conical, contact surface against which the sleeve rests, as is considered advantageous in itself.

[0024] Also, with regard to good support of the electrode body in the contact area by the sleeve, it is considered advantageous if the sleeve rests against the contact surface with preload. This allows it to counteract the pressure of the upper electrode to a beneficial degree.

[0025] An advantageous embodiment of the invention is characterized in that the receptacle has a cylindrical receiving section in which the sleeve is guided for longitudinal displacement. This allows the sleeve to be inserted into the receptacle particularly well. With additional clamping, as described in more detail below, the sleeve slides in the cylindrical receiving section until it abuts the aforementioned contact surface.

[0026] Alternatively or additionally, it is advantageous for the sleeve to have a cylindrical guide section that allows the sleeve to be guided longitudinally within the electrode body, particularly within the receptacle. A cylindrical guide section gives the sleeve a simple yet very stable shape, making it robust for its intended use.

[0027] In a further development of the invention, it is proposed that the sleeve is pre-tensioned towards the opening. The sleeve is thus clamped during operation of the welding electrode. The pre-tension ensures that the electrode body can withstand significant forces from the upper electrode.

[0028] In one embodiment, the wear electrode has a clamping element that engages in the threads of the electrode body and holds the sleeve in the receptacle. Tightening the clamping element increases the preload on the sleeve. The clamping element also has the further advantage that the wear electrode according to the invention can be supplied pre-assembled. The assembly consists of the electrode body, the sleeve, and the clamping element. This is particularly advantageous because wear electrodes must be replaced regularly, as already described. Therefore, according to the invention, a complete assembly can be provided.

[0029] Preferably, the clamping element is designed as a clamping sleeve that engages with an internal thread in the electrode body via an external thread. The clamping sleeve offers two advantages. Firstly, it can at least partially accommodate the bolt, enabling a compact design. Secondly, the clamping sleeve can be easily pre-tensioned by rotating it. The pre-tension can be selected depending on the tightening torque.

[0030] Preferably, the clamping element has a through-opening. Depending on its length, the pin of the bolt can pass through this opening.

[0031] In particular, the through-hole allows the use of compressed air, as is used with some welding electrodes. In known welding processes, compressed air is used to blow weld spatter away from the lower electrode.

[0032] An advantageous embodiment of the wear electrode according to the invention is characterized in that the sleeve has a second section in which the diameter of the sleeve tapers away from the opening. While the sleeve tapers towards its first free end in the first section, it tapers towards its second free end in the second section. This distributes the force on the electrode body particularly advantageously. This is especially true if the second section tapers conically. The conical shape is also advantageous with a ceramic material, since a ceramic sleeve is particularly well able to absorb compressive forces.

[0033] The sleeve preferably has a first and a second section, each tapering outwards in opposite directions, particularly conically. This is especially advantageous because, when the first section wears out, the sleeve can be removed and used in reverse, so that the second – unworn – section can perform the support function described above.

[0034] For these reasons, it is also considered advantageous if the clamping element has a support surface with which it rests against the second section of the sleeve. If the second section of the sleeve is conical, a conical support surface is advantageous.

[0035] The protection of the present invention is not limited to a wear electrode. The scope of protection also includes a lower electrode with a wear electrode according to the invention, as well as a welding device with an upper electrode and a lower electrode comprising a wear electrode according to the invention.

[0036] The invention will now be explained in more detail with reference to preferred embodiments in conjunction with the attached drawing. The drawing shows: Fig. 1 an expanded representation of a component with a wear electrode according to the invention; Fig. 2 the component after Fig. 1 in a sectional view; Fig. 3 an enlarged view of a detail from Fig. 2; Fig. 4 a sectional view of an electrode body of the wear electrode according to Fig. 1; Fig. 5 a second embodiment of a component with a wear electrode according to the invention in an expanded view; Fig. 6 the component after Fig. 5 in a sectional view; Fig. 7 a welding device according to the invention with a third embodiment of a wear electrode; and Fig. 8 the wear electrode after Fig. 5 as an enlarged detail.

[0037] Fig. Figure 1 shows a component for a welding fixture. The component has a base 1 and a wear electrode 2. The base 1 can be screwed onto a welding fixture (not shown) and has a thread 3 for this purpose. Reference numeral 4 indicates a pneumatic connection.

[0038] The wear electrode 2 has three components: an electrode body 5, a sleeve 6, and a clamping element 7. Preferably, the outer cross-sectional shape of the sleeve 6 is round. In particular, the sleeve 6 can be rotationally symmetrical.

[0039] Advantageously, the clamping element 7 clamps the sleeve 6 in the electrode body 5.

[0040] The welding device can be used to weld a sheet metal 8 and a bolt 9 together. Before the welding process, the sheet metal 8 is placed on the wear electrode 2. For this purpose, the electrode body 5 has a contact surface 10, which in this case is flat.

[0041] Before the welding process, the bolt 9 is inserted into an opening 11 in the sheet metal 8 and further into an opening 12 in the electrode body 5. The sleeve 6 has a through-opening 13 into which a threaded pin 14 of the inserted bolt 9 engages. During the welding process, the bolt 9 is pressed towards the sheet metal by an upper electrode (not shown) until the head 15 of the bolt 9 rests on the sheet metal. A projection 16 extends from the underside of the head 15; in this case, it is designed as an annular projection and melts upon contact with the sheet metal 8, thus welding it together.

[0042] The principle of resistance projection welding of bolts onto sheets is generally known and does not need to be explained in detail here.

[0043] Furthermore, how it looks Fig. As can be seen from Figure 1, the sleeve 6 has a first section 17 in which the outer diameter of the sleeve 6 tapers towards a free end 18. In this case, the sleeve 6 tapers conically, which is considered particularly advantageous. The sleeve 6 has a second section 19 in which the sleeve 6 also preferably tapers conically. The taper extends towards the other free end 20 of the sleeve 6. Between the first section 17 and the second section 19, the sleeve has a cylindrical guide section 21.

[0044] The sleeve 6 is inserted into the electrode body 5 for assembly. The clamping element 7 has a thread 22 by means of which the clamping element 7 can be screwed into the electrode body 5. The clamping element 7 can pre-tension the sleeve 6, as will be explained in more detail below.

[0045] The electrode body 5 also has a thread 23. It can be screwed into the base 1.

[0046] The following will refer to the Fig. 2 and Fig. Reference is made to Figure 3, which shows the component, in particular the wear electrode 2, in a sectional view in its assembled state. Fig. For clarity, bolt 9 and sheet metal 8 have been omitted.

[0047] The sleeve 6 sits in a receptacle 24. Preferably, the receptacle 24 tapers towards the opening 12 in a section 25, which is considered advantageous in itself, especially if the receptacle 24 tapers conically.

[0048] Section 25 forms a preferably conical contact surface for the sleeve 6. The first section 17 of the sleeve 6 rests against section 25. This allows the sleeve 6 to support the electrode body 5 in section 25 under pressure on the support surface 10. Despite the wall thickness in section 25 decreasing towards the opening 12, the sleeve 6 thus enables stabilization of this area. This is particularly true when the sleeve 6 is preloaded in the receptacle 24. For this purpose, the clamping element 7 is screwed into the electrode body 5 and rests against the sleeve 6 with preload.

[0049] Preferably the receptacle 24 has an internal thread into which the clamping element 7 is screwed.

[0050] Reference numeral 26 designates a cylindrical receiving section in which the sleeve 6 is guided for longitudinal displacement. When the clamping element 7 is screwed into the electrode body 5, the sleeve 6 moves towards the opening 12 until it abuts the section 25. The section 25 thus advantageously serves as a stop for the sleeve 6. The clamping element 7 has a preferably conical support surface 27 with which it abuts the second section 19 of the sleeve 6.

[0051] Preferably, the sleeve 6 extends into the opening 12. The opening 12 is advantageously formed by the non-tapering portion of the electrode body 5. It can, for example, be drilled. In that case, the opening 12 is cylindrical. Because the sleeve 6 extends so far upwards, the thread of an inserted bolt (see Fig. 2) be covered so that there is no risk of damage from weld spatter or other contamination. At the same time, the electrode body 5 extends to below the hump (see Fig. 2), so that an advantageous current flow is ensured.

[0052] Fig. Figure 4 shows an electrode body 5 in isolation. Image 24 and opening 12 are more clearly visible in this image. Advantageously, the electrode body 5 does not taper at opening 12.

[0053] The Fig. 5 and Fig. Figure 6 shows a second embodiment, which differs from the first embodiment in that the first section 17 of the sleeve 6 has steps 28 for forming the taper. As can be seen from Fig. If section 6 results, then section 25 is also designed in stages. Furthermore, this embodiment is intended to demonstrate that the second section 19 of the first embodiment can also be omitted. In this case, the sleeve 6 has an end 20 with a cylindrical termination. The clamping element 7 is adapted accordingly. For further details, please refer to the description of the first embodiment.

[0054] Fig. Figure 7 shows a third embodiment of the invention. Here, the wear electrode 2 is mounted on a lower electrode 30 by means of a union nut 29. The design and function of the lower electrode 30 (with the exception of the wear electrode 2) are essentially prior art and do not require further explanation.

[0055] Fig. Figure 8 shows an enlarged view of a detail from Fig.7. It is clear from this that, in contrast to the first embodiment, the electrode body 5 does not have an external thread, but rather inclined support surfaces 31 which are engaged by the union nut 29 to secure the electrode body 5 to the lower electrode 30. For further details, please refer to the description of the first embodiment.

[0056] For the sake of clarity, the above description has used some of the same reference symbols for different embodiments, even if the corresponding components have a slightly different design. Reference symbol list 1 Base 2 Wear electrode 3 threads 4 Pneumatic connection 5 electrode bodies 6 sleeve 7 clamping element 8 sheets 9 bolts 10 contact surface 11 Opening (sheet metal) 12 Opening (electrode body) 13 Passage opening 14 Threaded pin 15 heads 16 humps 17 first section 18 End 19 second section 20 End 21 Leadership section 22 threads 23 threads 24 recordings Section 25 (electrode body) 26 Recording section (electrode body) 27 Support surface (clamping element) 28 steps 29 Union nut 30 Lower electrode 31 Support surface QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] EP 3 412 398 B1

[0007]

Claims

[1] Wear electrode for resistance projection welding of bolts (9), with - an electrode body (5) which has an opening (12) for inserting a bolt (9), - a receptacle (24) formed in the electrode body (5), - wherein a sleeve (6) is included in the receptacle (24), characterized by , - that the sleeve (6) has a first section (17) in which the outer diameter of the sleeve (6) tapers towards the opening (12). [2] Wear electrode according to claim 1, characterized by , that the outer diameter of the sleeve (6) tapers conically in the first section (17). [3] Wear electrode according to claim 1 or 2, characterized by , that the electrode body (5) extends over the first section (17). [4] Wear electrode according to any one of claims 1 to 3, characterized by that the sleeve (6) extends into the opening (12). [5] Wear electrode according to any one of claims 1 to 4, characterized by , that the electrode body (5) has a flat support surface (10) for supporting a workpiece which is to be welded to the bolt (9), wherein the support surface (10) forms a support plane, and wherein the distance between the sleeve (6) and the support plane is less than 2 mm, preferably less than 1 mm. [6] Wear electrode according to claim 5, characterized by , that the sleeve (6) essentially terminates in the support plane defined by the bearing surface (10). [7] Wear electrode according to any one of claims 1 to 6, characterized by , that the electrode body (5) lies flat against the sleeve (6) in the area of ​​the first section (17). [8] Wear electrode according to any one of claims 1 to 7, characterized by that the electrode body (5) has a preferably conical contact surface against which the sleeve (6) rests. [9] Wear electrode according to claim 8, characterized by , that the sleeve (6) rests against the contact surface with preload. [10] Wear electrode according to any one of claims 1 to 9, characterized by , that the receptacle (24) has a cylindrical receiving section (26) in which the sleeve (6) is guided longitudinally displaceably and / or that the sleeve (6) has a cylindrical guide section (21) with which the sleeve (6) is guided longitudinally displaceably in the electrode body (5). [11] Wear electrode according to any one of claims 1 to 10, characterized by , that the sleeve (6) is biased towards the opening (12). [12] Wear electrode according to any one of claims 1 to 11, characterized by a clamping element (7) which engages in the thread with the electrode body (5) and holds the sleeve (6) in the receptacle (24). [13] Wear electrode according to claim 12, characterized by, that the clamping element (7) is designed as a clamping sleeve which engages with a thread (22) in an internal thread of the electrode body (5). [14] Wear electrode according to any one of claims 1 to 13, characterized by , that the sleeve (6) has a second section (19) in which the outer diameter of the sleeve (6) tapers away from the opening (12). [15] Wear electrode according to claim 14, characterized by , that the second section (19) tapers conically. [16] Wear electrode according to claim 12 or 13 and 14 or 15, characterized by that the clamping element (7) has a preferably conical support surface (27) with which the clamping element (7) rests against the second section (19) of the sleeve (6). [17] Wear electrode according to any one of claims 1 to 16, characterized by , that the sleeve (6) is made of an electrically insulating material, in particular ceramic. [18] Wear electrode according to any one of claims 1 to 17, characterized by , that the sleeve (6) supports the electrode body (5) in the area of ​​the narrowing. [19] Lower electrode with a wear electrode according to any one of claims 1 to 18.

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