Patent Description:
Furthermore, the invention relates to a welding torch for a non-melting electrode, especially a plasma welding torch, with a gas nozzle with an opening for the non-melting electrode, and with a device for mounting on a welding robot.

Finally, the invention relates to a method for teaching a welding path of a welding torch attached to a welding robot with an above mentioned teaching tool.

In robotic welding, especially for welding large workpieces, it is extremely difficult for operators to teach a weld because the sight from the welding nozzle is completely interrupted by the gas nozzle. As a result, it can not be judged whether the welding electrode is pointing to the weld joint or arc position and whether the distance between the nozzle and the workpiece is reasonable.

The present invention relates primarily, but not exclusively, to plasma welding wherein an arc is formed between a non-melting electrode and the workpiece. Plasma welding torches are relatively large, so visibility of the plasma gas nozzle during the teaching process is particularly limited or even blocked, making the teaching process very difficult. If the view of the welding torch is disturbed or even obstructed during the teaching process, it is not possible to judge whether the electrode is directed at the desired position on the welding track and whether the distance between the electrode or gas nozzle and the workpiece is suitable.

If the teaching process is performed with the normal welding torch with the non-melting electrode, there is also a risk of damaging the workpiece or parts of the welding torch, such as the gas nozzle or the electrode.

Special welding torches for use in the teaching process have become known from the prior art. For example,<CIT>describes a dummy contact tip which can be connected to the welding torch via screws. The dummy contact tip is made of elastic material and its dimensions correspond to those of the real electrode.

<CIT> describes a teaching tool for a welding torch according to the state of the art, whereby the connection with the welding torch or welding robot is not described in detail.

<CIT> discloses another teaching tool for an industrial robot.

Another teaching tool for a welding robot for MIG/MAG welding process is shown in <CIT>. The teaching tool is detachable screwed to the torch and contains a compressing spring or a rubber plate spring.

Known elements of this type for use in the teaching process of a welding torch often have a complex design or are complex to mount and dismount on the welding torch.

Therefore, the object of the present invention is to create a teaching tool for a welding torch with a non-melting electrode, especially a plasma welding torch, which can be mounted on and removed from the welding torch particularly easily and quickly, and which has a particularly simple and cost-effective design. A further object of the present invention is to provide a welding torch for a non-consuming electrode, in particular a plasma welding torch, and a method for teaching the welding path of a weld with such a welding torch, whereby the teach-in operation can be performed simply, safely and without risk of damage to the workpiece or parts of the welding torch. Disadvantages of known devices and methods are to be avoided or at least reduced.

The object of the present invention is solved, on the one hand, by a teaching tool mentioned above, in which the body comprises a connector arranged opposite the free end, which connector is formed by a truncated cone for tool-free fastening in the opening of the gas nozzle of the welding torch. The teaching tool consists of an elastic material, which on the one hand can prevent damage to the workpiece during the teaching process. On the other hand, the teaching tool can thus be attached to the welding torch and removed again particularly quickly and easily. The elastic material of the teaching tool and the corresponding dimensioning allow the teaching tool to be held in the gas nozzle by friction and no fastening elements and no tools are required for assembly and disassembly. The connector of the teaching tool is formed by a truncated cone. This design facilitates the placement of the teaching tool in the opening of the gas nozzle of the welding torch and the holding of the same by friction. The non-melting electrode of the welding torch does not have to be removed during the changeover for the teaching process, but can also just be moved inside the gas nozzle so that space is created for the teaching tool at the opening of the gas nozzle. The teaching tool is also particularly simple and thus inexpensive to manufacture.

Preferably an average diameter of the connector of the truncated cone is slightly larger than the diameter of the opening of the gas nozzle of the welding torch. Such dimensioning ensures that the teaching tool is held securely in the opening of the gas nozzle by friction. Preferably the average diameter of the truncated cone, is <NUM> to <NUM> % larger than the diameter of the opening of the gas nozzle of the welding torch.

If a flange with a larger diameter than the connector is arranged between the connector and the free end of the body of the teaching tool, it can be ensured that the teaching tool is attached to the gas nozzle in the desired position. On the one hand, the flange prevents the teaching tool from tilting relative to the gas nozzle and, on the other hand, a defined distance of the tip of the teaching tool from the end of the gas nozzle is always ensured. This ensures a proper Tool Center Point (TCP) during the teaching process.

Especially the body of the teaching tool is made in one piece. This allows the teaching tool to be produced very easily and cost-effectively.

If the elastic material of the body of the teaching tool contains graphitic carbon, in particular <NUM> to <NUM> volume percent, the wear resistance of the material can be increased and thus its service life. For a teaching tool made of common silicone rubber, the wear resistance will be greatly weakened after <NUM> times use. Adding some graphitic carbon to the silicone rubber matrix increases the lifetime of the teaching tool by <NUM> times or more. The graphitic carbon can be admixed to the silicone rubber matrix in form of a powder and/or in form of powder composites.

Advantageously, the elastic material of the body has a shore hardness of <NUM> to <NUM> Shore A, in particular <NUM> to <NUM> Shore A. Such hardness values are advantageous for the application of the teaching tool and the hold in the opening of the gas nozzle.

According to another feature of the invention, the elastic material of the body has an Elastic modulus of <NUM> to <NUM> MPa, in particular <NUM> to <NUM> MPa.

Suitable materials for the body of the teaching tool are rubber or rubber compounds, especially silicone rubber. Such materials with the above-mentioned features are used to match friction, hardness, wear resistance and elasticity. Silicone rubber shows an ideal performance of elasticity and heat resistance even at temperatures up to <NUM> and more. Furthermore, silicone rubber has a shore hardness of <NUM> - <NUM> degrees and an Elastic modulus of <NUM> MPa when the elastic hardness is <NUM> Shore A, therefore a little elastic deformation can generate an enough extrusion force, to obtain the friction between the teaching tool and the metal surface of the gas nozzle. The friction force is calculated by f = µ * N, wherein f is the friction, µ is the coefficient of friction (<NUM> between copper and silicon rubber) and N the normal force. As a result, the friction f is proportional to the normal force N and elastic deformation. In this case, a deformation of <NUM> - <NUM> of the silicone rubber is enough to generate the friction f to overcome the gravity.

If fluorescent particles are admixed to the elastic material or the body is at least partially surrounded with a fluorescent top or cover layer, the visibility of the teaching tool during the teaching process can be increased. The fluorescent teaching tool can be an advantage for the operator, especially in dark operating environments.

According to another feature of the invention, the free end of the body of the teaching tool has a rounding, in particular with a diameter of <NUM> to <NUM>. Such a radius has proven to be suitable in practice in terms of wear resistance of the tip.

The object of the present invention is also solved by a welding torch for a non-melting electrode, especially a plasma welding torch, with a gas nozzle with an opening for the non-melting electrode, and with a device for mounting on a welding robot, mentioned above, whereby a teaching tool described above is provided and fastened in the opening of the gas nozzle. Please refer to the above description of the teaching tool for the advantages achievable thereby.

Finally, the object of the present invention is also solved by an above-mentioned method for teaching a welding path of a welding torch attached to a welding robot with an above mentioned teaching tool, wherein the desired welding path is traversed with the welding torch on which the above described teaching tool is fastened. For the advantages that can be achieved by this method, please refer to the description of the teaching tool above.

Advantageously, a contact of the teaching tool with a workpiece is detected and the teaching of the welding path is corrected accordingly.

The contact of the teaching tool with the workpiece can be detected via a force detected at the welding robot or via an electrical measuring voltage at the teaching tool. The force acting on the teaching tool can be detected, for example, via a force measuring device usually present on the robot. In the latter case, a certain electrical conductivity of the teaching tool is required, which can be realized, for example, by adding conductive particles (for example, graphite, nickel-clad copper powder and/or silver powder) to the elastic material of the body of the teaching tool or by encasing the body of the teaching tool with an electrically conductive material. In a further embodiment, the body is at least partially surrounded by an electrically conductive cover layer. The electrically conductive cover layer can be applied by brushing, spraying, dipping or other coating methods.

The present invention is explained in more detail with reference to the appended figures.

<FIG> shows a welding torch <NUM>, especially a plasma welding torch <NUM> with a device <NUM> for mounting on a welding robot <NUM> (not shown) according to the prior art in simplified representation. The plasma welding torch <NUM> includes a gas nozzle <NUM>, having an opening <NUM>, and a non-melting electrode <NUM> usually made of tungsten. Based on the welding torch design the non-melting electrode <NUM> can protrude or not. The various electrical cables and cooling lines (not shown) are fed to the plasma welding torch <NUM> via a hose package S. In the figure above the plasma welding torch <NUM> is fed a filler material Z to the welding point P, with which the welding of a workpiece W along a welding path X is carried out. Before the welding process is carried out, a so-called teaching process is usually carried out, in which the movement of the welding robot <NUM> is determined so that the subsequent welding process is carried out along the desired welding path X. During the teaching process, there is a risk of damage to the workpiece W or to components of the plasma welding torch <NUM>, in particular to the non-melting electrode <NUM>, if the distance between the plasma welding torch <NUM> and the workpiece W is selected to be too small. This problem is to be eliminated by the present invention.

<FIG> shows a first embodiment of the teaching tool <NUM> in detail. The teaching tool <NUM> comprises a substantially circularly symmetric body <NUM> having a free end <NUM>, wherein the body <NUM> is formed of an elastic material, for instance rubber or rubber compound, especially silicon rubber. Further, the body <NUM> of the teaching tool <NUM> comprises a connector <NUM> arranged opposite the free end <NUM>, which connector <NUM> is designed for tool-free fastening in the opening <NUM> of a gas nozzle <NUM> of a welding torch <NUM> (see <FIG>). The connector <NUM> of the body <NUM> is formed by a truncated cone <NUM>, which makes it easier to fasten the teaching tool <NUM> within the opening <NUM> of a gas nozzle <NUM> (see <FIG>). The average diameter DA of the connector <NUM> (see <FIG>) is slightly larger than the diameter DG of the opening <NUM> of the gas nozzle <NUM> of the welding torch <NUM> so that the teaching tool <NUM> holds by friction only within the gas nozzle <NUM> (see <FIG>).

<FIG> shows a second embodiment of the teaching tool <NUM>, wherein a flange <NUM> with a diameter DF, which is larger than the maximum diameter DM of the connector <NUM> is arranged between the connector <NUM> and the free end <NUM> of the body <NUM>. By the flange <NUM>, which is a kind of limitation of the teaching tool <NUM>, it can be ensured that the teaching tool <NUM> is attached to the gas nozzle <NUM> in the desired position. The flange <NUM> prevents the teaching tool <NUM> from tilting relative to the gas nozzle <NUM> and a defined distance of the tip of the teaching tool <NUM> from the end of the gas nozzle <NUM> is always ensured.

<FIG> shows another embodiment of the teaching tool <NUM> with cylindrical connector <NUM> with an outer diameter DA, which is slightly, preferably <NUM> % to <NUM> %, larger than the diameter DG of the opening <NUM> of the gas nozzle <NUM>. This cylindrical connector <NUM> does not fall within the scope of protection of the present invention. The tip on the free end <NUM> of the body <NUM> shows a rounding <NUM>, in particular with a diameter of <NUM> to <NUM>.

<FIG> shows another embodiment of the teaching tool <NUM>, which corresponds in all other respects to the embodiment according to <FIG>. The connector <NUM> is formed by a truncated cone <NUM> whose average diameter DC is slightly larger than the diameter DG of the opening <NUM> of the gas nozzle <NUM>. In this embodiment, the body <NUM> of the teaching tool <NUM> is at least partially surrounded with a fluorescent top layer <NUM>. The fluorescent top layer <NUM> can be applied by brushing, spraying, dipping or other coating methods. Alternatively to a fluorescent top layer <NUM>, also fluorescent particles can be admixed to the elastic material of the body <NUM> of the teaching tool <NUM>. The fluorescent top layer <NUM> can improve the visibility of the teaching tool <NUM> during the teaching process.

<FIG> shows a sectional view of another embodiment of the teaching tool <NUM>, similar to the embodiment according to <FIG>. The only difference is a recess <NUM> on the connector <NUM> opposite the free end <NUM> of the body <NUM> of the teaching tool <NUM>, in which the tip of the non-melting electrode <NUM> of the welding torch <NUM> can be placed during the teaching process (see <FIG>). The recess <NUM> is correspondingly adapted to the shape of the tip of the non-melting electrode <NUM>.

<FIG> shows a sectional view of another embodiment of the teaching tool <NUM>. The angle of the recess <NUM> is smaller than that of the recess <NUM> according to <FIG>. If the elastic material of the body <NUM> of the teaching tool <NUM> contains graphitic carbon C, on the one hand, the wear resistance and thus service life of the teaching tool <NUM> can be increased. On the other hand, this or the addition of other conductive particles (like nickel-clad copper powder or silver powder) can make the teaching tool <NUM> electrically conductive. This means that contact between the welding torch <NUM> or the teaching tool <NUM> and the workpiece W can be detected by means of short-circuit detection. For this purpose, a measuring voltage UM is applied to the teaching tool <NUM> via the gas nozzle <NUM> and detected via a voltage drop when the free end <NUM> of the teaching tool <NUM> comes into contact with the conductive workpiece W. In case of a contact, an acoustically signal and/or a visually signal can be emitted.

<FIG> shows a partial sectional view of a gas nozzle <NUM> with a teaching tool <NUM> according to the invention according to the second embodiment as shown in <FIG>. The gas nozzle <NUM> has an opening <NUM> with a diameter DG. The non-melting electrode <NUM> can remain in the gas nozzle <NUM> during the teaching process and is merely moved backwards. This facilitates handling during the teaching process. The teaching tool <NUM>, whose maximum diameter DM of the connector <NUM> is slightly larger than the diameter DG of the opening <NUM> of the gas nozzle <NUM>, is inserted into the opening <NUM> of the gas nozzle <NUM>. Due to the elastic material of the body <NUM> of the teaching tool <NUM>, the teaching tool <NUM> can simply be inserted into the opening <NUM>, where it holds due to friction. The flange <NUM> prevents the teaching tool <NUM> from tilting relative to the gas nozzle <NUM> and ensures that the distance between the end of the gas nozzle <NUM> and the tip at the free end <NUM> of the teaching tool <NUM> is correct.

<FIG> shows a partial sectional view of another gas nozzle <NUM> with a teaching tool <NUM> according to the invention according to the second embodiment as shown in <FIG>. The arrows G show the path of the inert gas G inside the gas nozzle <NUM> during the welding process.

Finally, <FIG> shows a partial sectional view of another gas nozzle <NUM> with a teaching tool <NUM> according to the invention according to the embodiment as shown in <FIG>. Here, the tip of the non-melting electrode <NUM> can be arranged in the recess <NUM> on the connector <NUM> of the teaching tool <NUM> during the teaching procedure.

Claim 1:
Teaching tool (<NUM>) for a welding torch (<NUM>) with a gas nozzle (<NUM>) with an opening (<NUM>) for a non-melting electrode (<NUM>) with a tip (<NUM>), especially a plasma welding torch (<NUM>), used in case of teaching a welding path (X) along a workpiece (W) of the welding torch (<NUM>) attached to a welding robot (<NUM>), comprising a substantially circularly symmetric body (<NUM>) having a free end (<NUM>), wherein the body (<NUM>) is formed of an elastic material, characterized in that the body (<NUM>) comprises a connector (<NUM>) arranged opposite the free end (<NUM>), which connector (<NUM>) is formed by a truncated cone (<NUM>) for tool-free fastening in the opening (<NUM>) of the gas nozzle (<NUM>) of the welding torch (<NUM>).