DE10355323B3 - Spot welding method used in the automobile industry comprises using a heating unit having an induction coil through which particles flow and are inductively heated - Google Patents

Abstract

Spot welding method comprises using a heating unit having an induction coil (20) through which particles (5) flow and are inductively heated.

Description

State of technology

The The invention relates to a method for drop welding Components, in particular joining partners, according to the preamble of claim 1.

In of production technology for For example, the automotive industry are methods of joining identical or dissimilar materials are important process steps. Among other things, temperature-resistant electrical connections needed for contacting sensors and actuators.

When thermal joining process for metallic Materials include laser beam welding and the arc welding known. In both cases becomes the welding necessary energy is converted directly into heat on the workpiece. But you want it without direct contact between heat source and workpiece a welding preferably small, thin and heat sensitive Achieve components, then the so-called "Droplet Welding" (drop welding) is the more suitable methods.

At the drop welding is at the end of a metallic wire by heat Melt drops formed, which on the joining partners to be joined falls and this connects. In fine and microtechnology, the "laser droplet welding" method and the "arc droplet welding" method are known. The to melt of the metal wire needed Energy becomes the welding process in the first case by a laser beam and in the second case by supplied an arc.

In the US 6,013,896 a drop welding method is presented by an arc, wherein the weld metal is arranged in the form of a wire as an electrode over a workpiece and by means of an electrical pulse, a molten droplet is formed at the end of the wire. The size of the drop initially increases in the growth phase, while at the same time the changing shape or the position of the drop at the wire end is constantly detected by a laser-optical system. After reaching the desired final size of the drop, the current at the electrode is lowered, so that the droplet is excited to oscillate back and forth in the direction of the workpiece. At a convenient moment, when the amplitude of the oscillation is large enough and the drop moves toward the workpiece, the current is again increased slightly, whereby the drop separates from the wire end and falls onto the workpiece.

Around perform the drop-weld process described above can, must be the release mechanism the drop of the wire to be known exactly. In particular, the must appropriate moment of separation during the oscillation of the drop by a time coincidence the increase the current strength on the one hand, and the cheap one On the other hand, the amplitude of the oscillation must be ensured ("phase match "). According to the above This document was experimentally found to be a too early or too late increase the current strength does not lead to a controlled droplet detachment.

Also was determined experimentally according to the above-mentioned document, that the frequency of the oscillation directly from the current difference between the higher Value in the growth phase and the lower value for stimulation of the drop depends on the oscillation. This is a derivative of the mass of the drop alone of the frequency the oscillation not readily possible. But varies the drop mass from drop to drop, is also the energy content of the drops and so that the welding spot quality fluctuations subjected.

A fundamental Difficulty in the above-mentioned drop welding process is that the detachment mechanism a drop of a wire must be precisely controlled. In addition to the The difficulties already mentioned influence the detachment mechanism also the drop direction of the drop, what the exact meeting of the joint difficult.

Out US 6,137,081 is another drop welding method is known in which the weld metal is present in already separated particles in spherical shape with a defined volume. This eliminates the described problems caused by the detachment mechanism of a drop from a wire. The pre-portioned balls are fed according to the teaching in the cited document via a guide of a heat unit through which the balls melt and impinge on workpieces in the molten state. For the effect of heat on the balls arc are provided.

Advantages of invention

The inventive method for drop welding of components with the characterizing features of claim 1 has the advantage of enabling a simple and inexpensive process, where the parameters of the heat unit in a simple way on the material and size of the particles or on the desired Final temperature of the drop can be adjusted.

The inventive method can be used in particular when contacting otherwise very difficult to weld, highly reflective materials. Also, the joining of dissimilar joining partners such as steel-brass, steel-copper, aluminum-steel or aluminum-copper is achieved by the method according to the invention allows.

advantageous Further developments of the method according to the invention are specified in the subclaims.

drawing

embodiments The invention will be apparent from the drawing and the description below explained in more detail. It demonstrate:

1 an arrangement for inductive droplet welding in a schematic representation and

2a to 2c a drop welding process by means of a positive connection without preheating the joining partners ( 2 B ) and with preheating of the joining partners ( 2c ).

description the embodiments

In 1 an arrangement for inductive droplet welding is shown schematically. The weld metal is not melted as a filler material from a continuously fed wire, but the filler material is already in the form of defined in particular in terms of their mass or volume, pre-portioned particles 5 in front. Particularly suitable shapes are balls, but also shapes of blocks, pieces of wire or plates are possible. Because of the particles 5 pre-portioned, the disadvantages of the fluctuating drop mass are eliminated. By a clever choice of the filler material with respect to the melting temperature, heat capacity or density, the drop welding process can be further adapted to the joining task.

Via a dosing unit 10 become the particles 5 dosed a heating unit 15 fed. Typically, the particles fall 5 in the lower heating unit 15 , but also by a heating unit 15 to be shot. The heating unit 15 includes an induction coil 20 through which the particles 5 fall through while being inductively heated. The particles 5 be due to the action of heat in the heating unit 15 brought to at least their melting temperature, causing the particles 5 melt and drop 25 form. These are the parameters of the induction coil 20 such as the length of the coil 20 or the fall distance in the coil 20 adapted to the material and the size of the particles 5 and to the desired final temperature of the drop 25 ,

After falling through the heating unit 15 meet the melted drops 25 on the components to be connected 30 . 31 , especially joining parts, and connect them. To further increase the impact accuracy of the particles 5 or the molten drops 25 is a guide 35 until just above the weld 40 intended. The leadership 35 is suitably a tube made of a high temperature resistant material. The suitable high temperature resistant material may be a ceramic, a glass or a metallic material.

Advantageously, the leadership 35 and / or the heating unit 15 be rinsed with a protective gas. This will oxidize the drops 25 avoided, whereby the joint quality is further improved and the welding process runs safer.

A particular embodiment of the method according to the invention is using a in the 2a to 2c illustrated arrangement explained.

2a shows a molten drop 25 , with which a positive connection between two joining partners 45 . 50 should be achieved. In this case, the one joint partner 50 an anvil-like extension 51 on, which through an opening 52 of the other joining partner 45 protrudes. To connect and bridge larger gaps, the drop must be 25 bring sufficient heat energy, so the drop 25 not before wetting the joining partners 45 . 50 is cold. In such cases, too rapid a cooling of the drop 25 on the weld 40 to avoid. In particular, when connecting thermally highly conductive materials such as copper or aluminum is in the drop 25 existing heat dissipates very quickly and leads to an insufficient connection of the joining partners.

Of course, in the process according to the invention also joining partners 45 . 50 conceivable with a different geometry than described above. Other possible designs are joining partners 45 . 50 in combination as a pin in a stamped grid or as a wire on a workpiece.

Also, the connection of a very small component with a large component with high thermal conductivity and heat capacity is problematic, since the heat flows very quickly into the large component and thus is no longer enough heat to establish a connection available. 2 B does not show optimally connected joining partners 45 . 50 ,

Finally is the bonding of non-metallic materials such as glass or ceramics with a metallic or non-metallic material in general problematic.

In order to achieve optimum welding quality even in the critical cases mentioned, the components are in the vicinity of the weld 40 by means of an additional heater 55 heated. The additional heating 55 , preferably a laser, can already bring the components to a high temperature before the process. This will make the liquid drop 25 on the weld 40 better tying conditions offered. The heat flow from the drop 25 is slowed down and, accordingly, the time in which the drop is prolonged 25 remains liquid.

In addition to the above-described thermal pretreatment of the joining partners 45 . 50 in the vicinity of the weld 40 can the cooling process of the drop 25 delayed by a reheating and extended. The reheating in particular prevents cracking. In addition, the external appearance of the weld improves 40 , Similar to the effect of preheating, larger gaps can be bridged by reheating before the drop 25 is cold. The known capillary action of a liquid drop 25 in which the drop is 25 Sucking into a gap when closing and closing it will help and last longer. The reheating by means of additional heating 55 can be done instead of or in addition to the thermal pretreatment.

Further, for process assurance, the temperature of the drop 25 and / or the weld 40 via a temperature control unit 60 such as a pyrometer, a camera system or a diode sensor are monitored. Suitable camera systems include thermal cameras, CCD cameras and CMOS cameras. By means of the temperature control unit 60 is the cooling behavior of the drop 25 or the weld 40 added. If the measured actual temperature deviates from the setpoint temperature, this is due to the additional heating 55 influenced accordingly, in particular online readjusted.

Alternatively, an insufficiently heated or overheated or deviating from the optimal trajectory drops 25 via a blow-off device 65 before hitting the weld 40 be removed or blown away.

Claims (9)

Method for drop welding, wherein a weld metal as a molten drop ( 25 ) on a weld ( 40 ) and components ( 30 . 31 ; 45 . 50 ), wherein the weld metal is in the form of pre-portioned particles defined in particular with regard to their mass or their volume ( 5 ) and via a dosing unit ( 10 ) doses a heating unit ( 15 ) and at least brought to the melting temperature of the weld metal, characterized in that the heating unit ( 15 ) an induction coil ( 20 ) through which the particles ( 5 ) and thereby inductively heated. Process according to Claim 1, characterized in that the defined, pre-portioned particles ( 5 ) have the shape of spheres, cuboids, pieces of wire or plates. Method according to claim 1 or 2, characterized in that the particles ( 5 ) about a guided tour ( 35 ) to just above the weld ( 40 ). Method according to claim 3, characterized in that the guide ( 35 ) is a tube made of high temperature resistant material. Method according to claim 3, characterized in that the guide ( 35 ) and / or the heating unit ( 15 ) is rinsed with a protective gas. Method according to one of claims 1 to 5, characterized in that the components ( 30 . 31 ; 45 . 50 ) in the vicinity of the weld ( 40 ) by an additional heating ( 55 ), in particular by a laser, preheated and / or reheated. Method according to one of claims 1 to 6, characterized in that for process assurance, the temperature of the drop ( 25 ) and / or the weld ( 40 ) via a temperature control unit ( 60 ) such as a pyrometer, a camera system or a diode sensor is monitored. Method according to claim 7, characterized in that the temperature of the drop ( 25 ) and / or the weld ( 40 ) by means of the additional heating ( 55 ) influenced, in particular online controllable, is. A method according to claim 7, characterized in that insufficiently heated or too hot or deviating from the optimal trajectory drops ( 25 ) via a blow-off device ( 65 ) before hitting the weld ( 40 ) are removed.