DE29922396U1 - Pressure welding device - Google Patents

Description

OJ DE-G-299 22 396.5

DESCRIPTION

Pressure welding device 5

The invention relates to a pressure welding device with the features in the preamble of the main claim.

Such pressure welding devices are known in practice in various designs. They have a plasticizing device for heating and melting the edge areas of the workpiece to be joined, a control system, a compression device and movable holders for the workpieces. Such pressure welding devices are known, for example, as friction welding devices or as

Magnetarc welding devices are designed with a magnetically moved arc. In the friction welding device, the plasticizing heat is generated by the frictional movement of the workpieces and in the Magn-tarc welding device, it is generated by the circulating arc between the workpieces.

The known pressure welding processes and devices are particularly suitable for similar workpieces. However, with different material pairings and in particular with very different physical properties of the workpieces, serious problems can arise. These become more serious the longer the heating and plasticizing process is. The workpieces can have differences in thermal conductivity, melting points, specific heat, radiation coefficients, etc. With the known pressure welding devices, a kc-LcJcte weld connection is often difficult or even impossible to achieve with such material pairings. The situation becomes even more difficult if one of the

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The workpieces to be joined must be in a liquid state at the front face at the latest at the moment of the upsetting process. This is the case, for example, with a friction weld between a cast material with globular graphite and steel.

In many welding processes, it is known from practice that certain materials need to be preheated when welding in order to avoid internal cracks or splits after welding. This heating is generally carried out before the actual welding process and outside the welding device, e.g. in the furnace.

US-A-5,240,167 and DE 691 02 165 T2 disclose a friction welding process for joining similar workpieces made of a nickel-based alloy, in which the joint is additionally heated by an inductor positioned centrally there. This is primarily used to form the structure after friction welding, with inductive reheating taking place over a considerable period of time and at high temperatures with slow cooling. This causes the hardenable phases in the nickel-based alloy to be separated. This must be done evenly in both workpieces. In addition, both workpieces are evenly inductively heated before or during the process in order to shorten the process time through additional heating. In the friction welding machine used, an axially adjustable inductor is positioned exactly in the middle above the joint and applies heat evenly to both workpieces. This friction welding machine cannot be used successfully in the intended design and function for friction welding very different material pairings.

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DE-A-23 28 653 deals with a method for joining plastic parts using inductive heating. DE-C 31 33 181 teaches the subsequent removal of a weld bead by machining after friction welding and a preceding heat treatment.

It is an object of the present invention to provide a pressure welding device which has a broader range of applications and is also suitable for critical material combinations.

The invention solves this problem with the features in the main claim.

The pressure welding device according to the invention has the advantage that the targeted additional heating of one of the workpieces in particular in the connection area enables a particularly reliable connection of dissimilar workpieces with very different physical properties and/or parameters. The heating of the workpieces is deliberately different and differs considerably, which is achieved by a targeted allocation and off-center positioning of the heating device during the process. This also makes it possible to pressure weld and in particular friction weld material combinations that could not previously be joined at all or only inadequately. This applies in particular to critical pairings such as steel with cast iron with globular graphite or other types of cast iron or titanium with steel or tungsten.

The additional heating device is preferably assigned to the workpiece with the higher thermal conductivity or generally with the higher heat requirement. This allows material-specific losses due to high heat dissipation, heat radiation, etc. to be compensated. In the particularly critical welding pairing of cast iron with globular graphite and steel, the additional

Heating device is assigned to the steel and compensates for its heat losses. Depending on the welding process and material combination, the additional heating device can not only compensate for the heat losses, but also deliberately heat one of the workpieces more strongly. In the interest of shortening the process times, both workpieces can alternatively be exposed to the additional heating device, although the heat supply to one workpiece is significantly greater than to the other.

The additional heating device enables balanced temperatures for the workpieces involved in the welding. This applies in particular to workpiece combinations where the formation of a melt is necessary to produce a good weld. The particular advantage here is that the balanced temperatures ensure significantly lower spatter formation.

In addition, the process times or the cycle times can be reduced overall, which is particularly the case with friction welding. Furthermore, post-heating reduces stresses or hardening that have arisen in the joint area as a result of the welding process.

The heat energy introduced at the joint can also be controlled and regulated independently of the heat energy generated during the pressure welding process by friction, arcing or the like, which can be done in particular depending on the temperature.

The pressure welding device according to the invention can basically be designed in any way depending on the process. It can be a friction welding device, a magnetarc welding device or the like.

The additional external heating energy can be introduced in different ways. The additional heating can be provided either from the inside or from the outside. The output of the additional heating device can also be controlled i;:^ and adjusted to the course of the process and, in particular, regulated according to the temperature or other parameters.

The additional heating device can be arranged in a fixed or movable manner, whereby it can be carried along with one of the moving workpieces during the upsetting stroke or equipped with an independent drive and then preferably arranged on the other side. A movable heating device can, for example, follow the shifting connection point or contact surface in a friction welding machine. However, it can also carry out any other movements and meet a wide variety of requirements and in particular process requirements. In particular, the movable heating device can be adapted to varying clamping positions of the workpieces. The temperature or power control can be location-dependent or location-independent.

The additional heating device can also be adjustable. This means that it can be adapted to workpieces of different sizes or shapes. If designed appropriately, it can also be opened and closed to insert and remove workpieces.

The additional heating device can be designed in any suitable manner. In the preferred embodiment, it is designed as an inductive heater and has at least one ring-shaped inductor. Further advantageous embodiments of the invention are specified in the subclaims.

The invention is illustrated by way of example and schematically in the drawings. In detail:

Figure 1: a friction welding machine with a

additional heating device in a schematic side view and

Figure 2: an enlarged and partially broken side view of the

Friction welding machine from Figure 1 with a modified additional heating device.

Figures 1 and 2 show a pressure welding device (1) in the form of a friction welding machine. Alternatively, it can also be a magnetarc welding machine or any other pressure welding device.

In pressure welding, at least two workpieces (2,3) are joined together under pressure. Before this, the area at the connection point (10) of both workpieces (2,3) is heated and, if necessary, plasticized. The axial connection is then made by a compression stroke in the direction of the axis (12), whereby one or both workpieces (2,3) are moved towards each other. In the friction welding machine (1) shown, the workpieces (2,3) are heated by rubbing. In a magnetarc pressure welding process, the heating is carried out by a magnetically driven arc that circulates between the two spaced workpieces (2,3).

The friction welding machine (1.) has a holder (6) for one workpiece (2,3), which is designed, for example, as a rotating chuck. The holder (6) is preferably fixed in the axial direction and can

by means of a drive (5). The drive (5) can be, for example, a speed-controlled spindle drive with a frequency-controlled three-phase motor. The other workpiece (2,3) is mounted in a second holder (7) and connected to a compression device (8). This holder (7) can, for example, be designed as a center clamp according to Figure 2 and can be attached to a slide (16) of the compression device (8). The two workpieces (2,3) are preferably arranged in alignment in the common axis of rotation (12).

The friction welding machine (1) has a control (9) which is suitably designed as a machine and process control and preferably has a computer or at least one microprocessor with one or more program and data memories, suitable interfaces and inputs and outputs for data and displays. The control (9) can have one or more programs for controlling and, if necessary, regulating the various process parameters. The latter can be calculated in the control (9) according to component specifications or selected from a stored technology database. The control (9) controls and regulates the drive (5) and the upsetting device (8) if necessary.

At the beginning of the friction welding process, the drive (5) is started with the workpieces (2,3) still at a distance and brings the holder (6) with one workpiece (2,3) to the desired speed. The two workpieces (2,3) are then brought into frictional contact with one another at their end faces by the upsetting device (8) and held in place. The contact surfaces are heated and, if necessary, plasticized by the relative rotational movement. This heating process is usually divided into a so-called friction phase and a friction phase, in which constant or different speeds and constant or varying contact forces or contact pressures prevail.

This depends on the respective material pairings and process conditions. As soon as sufficient plasticization is achieved, the rotary drive (5) is braked or switched off and simultaneously or with a time delay the upsetting device (8) is activated, which presses the two workpieces (2,3) axially together in an upsetting stroke, whereby the heated material is possibly displaced radially outwards from the connection area, which leads to the formation of a friction welding bead and to a

&iacgr;&ogr; can lead to component shortening.

The pressure welding device (1) has at least one additional heating device (11) which, at least during the pressure welding process, applies heat to and heats only one of the two workpieces (2,3) alone or at least with priority or intensification. For this purpose, the heating device (11) can preferably be arranged off-center and axially offset with respect to the connection point (10) of the workpieces (2,3). The workpieces (2,3) thus receive a significantly different additional heat supply. In friction welding, the connection point (10) is the frontal contact surface or friction surface of the workpieces (2,3). In magnetarc welding, it is the gap between the workpieces (2,3).

The heating device (11) can be arranged above the workpiece (2) directly adjacent to the connection point (10), as shown in Figure 1. However, it can also be arranged axially set back a little as shown in Figure 2 and at a distance from the connection point (10). In both cases, exclusively or essentially only one workpiece (2) is heated. In a variant not shown, the heating device (11) can be arranged slightly off-center to the connection point (10).

35. and both workpieces (2,3) overlap, but the center of gravity is on one workpiece (2). Both workpieces (2,3) are heated, whereby the

However, the degree of heating is deliberately different and one workpiece (2) is heated significantly more than the other.

Additional heat energy can be supplied via the heating device (11), particularly during the welding process, whereby the energy supply can take place on the inside and/or outside of the workpiece (2, 3) being treated, depending on the design of the heating device (11). The additional heat supply can also take place before the welding process in a preheating phase and alternatively or additionally after the welding process in a post-heating phase.

The pressure welding device (1) is designed to connect two workpieces (2, 3) made of different materials. The workpiece (2) is made of steel, for example, and the workpiece (3) is made of cast iron with globular graphite. The steel workpiece (2) has a higher thermal conductivity and accordingly greater heat losses at the contact surface or the friction welding zone during the friction welding process. These heat losses are compensated by the additional heating device (11) and the additional heat introduced. In this case, the heating device (11) is assigned to the steel workpiece (2).

Even with other different material pairings, it is recommended to assign the additional heating device (11) to the workpiece that has the higher heat requirement due to the process or its physical properties. With a material pairing of titanium and steel, the heating device (11) is also assigned to the steel workpiece. With a welding pairing of tungsten and titanium, the heating device (11) is assigned to the tungsten workpiece.

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In the embodiment shown, the additional heating device (11) is designed as an inductive heater, which heats the workpiece (2) inductively and without contact. The heating device (11) has, for example, an annular inductor (12), which can be designed in any suitable manner. In the embodiment shown, the inductor (12) is arranged on the outside around the workpiece (2) and, viewed in the axial direction, is located directly at or slightly set back behind the connection point (10).

The inductor (12) can consist of one or more parts and can be adjustable. In particular, the inductor (12) can be opened and closed for inserting and removing the workpieces (2, 3). The inductor (12) is connected to a suitable power source (not shown) which generates a preferably medium-frequency alternating current. The frequency range and the design of the power source can be selected as appropriate depending on the pressure welding process.

The inductor (12) can consist of a tube made of copper or another suitable current-conducting material and can have a circular, oval, prismatic or other cross-sectional shape. A coolant can be passed through the inductor (12). The inductor (12) can have a constant radial distance from the workpiece (2) to which it is applied and can thereby generate a locally constant magnetic induction in the workpiece (2). Alternatively, the magnetic induction can also be locally changed by locally changing the distance and/or position of the inductor (12) to the workpiece (2). When approaching, the magnetic induction increases and thus the energy input and heat influence on the workpiece (2). The same effect can be achieved alternatively or additionally by one or more locally attached to the inductor (12).

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Field concentrators (not shown) made of ferrite or coated transformer sheets can be used. A local change in induction can also be achieved by the targeted arrangement of several inductors (12) or inductor parts.

The heating power of the additional heating device (11) can be constant. In the preferred embodiment, it can be controlled and, if necessary, also regulated. The heating power is preferably matched to the pressure welding process and changes accordingly. For this purpose, the additional heating device (11) can have a control (15) which is arranged separately or which is assigned to the control (9) of the friction welding machine (1) and, if necessary, integrated into it.

is integrated. In particular, the additional heating device (11) can be switched on automatically via the control (9) as soon as the workpieces (2,3) are inserted into the holders (6,7) and access to the friction welding machine (1) is closed.

The additional heating device (11) can also be regulated. This is possible, for example, using a temperature sensor that is arranged at any suitable point on the workpiece (2, 3) or at another point and is connected to the control system (15). Figure 2 shows a variant with an infrared heat measuring camera (17) that is arranged at a distance from the connection point (10) and that measures the temperature without contact. Otherwise, any other measuring device can be used. The heating power can then be regulated based on the workpiece temperature. Otherwise, regulation can also be based on other criteria.

The additional heating device (11) can be arranged in a fixed or movable manner on the friction welding machine (1). In a fixed arrangement (not shown)

the position of the heating point on the workpiece (2) that is acted upon by the additional heating device (11) can change depending on the process progress. Depending on the workpiece pairing, for example,

axially displace the connection point (10). This relative change in location between the additional heating device (11) or the heating point and the connection area (10) or the friction welding plane can be achieved by changing the heating power and in particular

δ of the inductive current. The temperature or power control of the additional heating device (11) can basically be location-dependent or location-independent.

Figures 1 and 2 show a mobile arrangement of the additional heating device (11). In the embodiment of Figure 1, the heating device (11) is attached to the axially movable holder (7) via a boom and moves back and forth with this or with the carriage (16).

In the variant of Figure 2, the additional heating device (11) is arranged on the side of the other holder (6) and has its own drive (14).

This consists, for example, of an inductor carriage (13) that can move along the axis of rotation (12), to whose front end the inductor (12) is attached and whose rear end is connected to a suitable translatory drive, e.g. a spindle. In this embodiment, the additional heating device (11) can be moved axially independently. If necessary, mobility in other directions and axes can also be achieved depending on the design of the drive (14). The workpiece (2) being loaded can be clamped in the holder (6) as shown in Figure 2. However, it can also be in the opposite holder (7).

In a movable arrangement, the additional heating device (11) and its heating point can always be kept at the same distance from the connection point (10) of the workpieces (2, 3). Alternatively, however, any other movement can be carried out with respect to this connection point (10). In the carried arrangement of Figure 1, it is also advantageous if the additional heating device (11) is opened and closed at the same time as the center clamp (7).

The control (15) of the heating device (11) can be designed as a computer-aided and programmable controller. It can in particular contain a program. This can be used to run time- and/or process-dependent temperature profiles or power profiles of the additional heating device (11) as required. A temperature increase in the area of the connection point (10) can be very advantageous for process-technical reasons, particularly towards the end of the process. Likewise, different temperature ramps can be run depending on the course of the process.

After the friction welding process has been completed, the additional heating device (11) can remain switched on and ensure that the welded part is reheated. For this purpose, it can also carry out relative movements with respect to the clamped workpieces (2,3), e.g.

positioned centrally above the connection point (10). Subsequent heating reduces internal stresses in the welded part and reduces hardening in the connection area.

Modifications of the embodiment shown are possible in various ways. On the one hand, the additional heating device (11) can be designed and arranged in a different way. A different

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Strong heating of the workpieces can also be achieved by another heating device that acts on one side or has a reinforced effect on one side, whereby such a heating device can also be arranged centrally at the connection point if necessary. Instead of an induction heater, any other heating device with or without contact to the workpiece(s) (2,3) being heated can be used. This can be, for example, a resistance heater that is preferably applied to one of the two workpieces (2,3) and that transfers the heat conductively by contact. Heating can also be achieved by open flames, hot air streams or other similar carrier media. Tubular workpieces can also be heated from the inside.

The induction heating system shown can also be modified. It can contain more than one inductor (12) or an inductor with several loops, whereby the inductor(s) (12) can have different shapes. The inductor(s) (12) can also be plastically deformable. In particular, they can consist of several individual parts connected to one another by elastic lines, which are brought into the working position and into a largely closed ring shape relative to the workpieces (2, 3) by adjustable holders and are retracted into the rest position after the process, whereby the inductor (12) opens in this rest position.

The positioning devices for the additional heating device (11) are also variable. In a modification of the inductor slide (13) shown in Figure 2, any other adjustment device can also be present. In particular, the heating device (11) can also be arranged in a fixed position in the area of the holder (6) there.

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LIST OF REFERENCE SYMBOLS

1 pressure welding device, friction welding machine

2 Workpiece, steel part 3 Workpiece, cast part

4 Frame

5 Drive

6 Bracket, lining

7 Bracket, center clamp 8 Upsetting device

9 Welding machine control

10 Connection area

11 additional heating device

12 Inductor, coil 13 Inductor slide

14 Heating device drive

15 Heating system control

16 Slide compression device

17 temperature sensors, infrared heat measuring camera

Claims (9)

1. Pressure welding device for workpieces made of different materials with a plasticizing device for the workpieces ( 2 , 3 ), a control system ( 9 ), an upsetting device ( 8 ) and movable holders ( 6 , 7 ) for the workpieces ( 2 , 3 ), the pressure welding device ( 1 ) having an additional heating device ( 11 ), characterized in that the additional heating device ( 11 ) is arranged offset from the connection point ( 10 ) of the workpieces ( 2 , 3 ) and is assigned to one of the workpieces ( 2 ) for its priority heating. 2. Pressure welding device according to claim 1, characterized in that the additional heating device ( 11 ) is assigned to the workpiece ( 2 ) with the higher heat requirement, in particular the higher thermal conductivity and/or the higher heat radiation and/or the higher melting temperature. 3. Pressure welding device according to claim 1 or 2, characterized in that the additional heating device ( 11 ) is arranged to be axially movable. 4. Pressure welding device according to one of claims 1 to 3, characterized in that the additional heating device ( 11 ) has its own drive ( 14 ). 5. Pressure welding device according to one of claims 1 to 4, characterized in that the additional heating device ( 11 ) is designed to be adjustable. 6. Pressure welding device according to one of claims 1 to 5, characterized in that the additional heating device ( 11 ) has a control ( 15 ) for the heating power and/or the movements. 7. Pressure welding device according to one of claims 1 to 6, characterized in that the additional heating device ( 11 ) is designed as an inductive heater. 8. Pressure welding device according to one of claims 1 to 7, characterized in that the additional heating device ( 11 ) has a divisible annular inductor ( 12 ). 9. Pressure welding device according to one of claims 1 to 8, characterized in that the pressure welding device ( 1 ) is designed as a friction welding machine or as a magnetarc welding machine.