DE102015209203B4 - Method of lift-arc welding and use - Google Patents

Abstract

Method for the arc welding with direct current, in which a welded part (100) is welded to a workpiece (200) at a joint (300), wherein initially in a pre-flow phase over a Vorstromzeitraum (tV) by means of a Vorstroms (IV) an arc between the welded part (100) and the workpiece (200) is formed and in a subsequent main flow phase, the bias current (IV) is increased to a main current (IH) for a main flow period (tH), the workpiece (200) is operated as an anode, characterized in that the Vorstromzeitraum (tV) and / or the amount of the bias current (IV) are adjusted so that the workpiece (200) is heated during the Vorstromphase in the region of the joint (300) at least until the plastic deformability.

Description

The invention relates to a method for Hubzündungschweißen with DC according to claim 1 and a use according to claim 8.

When Hubzündungschweißen a welded part, such. B. a bolt, welded to a workpiece at a joint. For this purpose, the welding part is placed on the joint on the workpiece. In a first phase, the pre-flow phase, a low bias current is applied, which flows through the welding part and the workpiece. The welding part is removed up to a predetermined distance from the workpiece. This leads to the formation of a weak arc. This is followed by the main flow phase, in which the pre-flow is increased to a main flow (welding current). The resulting welding arc requires at least partial melting of the materials of the welding part and the workpiece. To end the process, the welding part is lowered onto the workpiece or immersed in the workpiece by a small distance and the current is switched off. The melted materials cool.

In direct current spark-ignition welding, the flow direction of the stream is not changed during the process.

Direct current DC spark-ignition welding is an unstable and difficult-to-control process, especially when welding aluminum-containing workpieces or welded parts. It often comes to spattering by explosion of the melt or to strength problems due to blowing effect or insufficient penetration into the workpiece.

To improve the welding quality in DC-DC welding, it is from the publication DE 10 2012 107 702 A1 It is known to already start the main flow phase while the welding part is still being moved away from the workpiece. This is to prevent emigration of the arc and a uniform melting can be achieved.

Furthermore, from the document DE 36 11 823 A1 a control circuit for the Hubzündungschweißen known, wherein from the ignited Vorstromlichtbogen a control voltage is derived, which represents the resistance value of the Vorstromlichtbogens. To achieve perfect welds even under different welding conditions, a correction voltage for a switching power supply is derived from the control voltage, and the switched-mode power supply adjusted according to the control voltage, so that the output current of the switching power supply is adapted to the resistance of the Vorstromlichtbogens.

The publication DE 10 2007 039 308 A1 further shows a stud welding method in which the heat input into the joint is optimized by the welding arc is interrupted by an intermediate short circuit briefly. For this purpose, the bolt is moved in the direction of the workpiece and then moved back to draw again a welding arc.

The object of the present invention is to provide a process for DC-DC welding with which the quality of the welded joint can be further improved.

The object of the invention is achieved by a method according to claim 1.

According to the invention, the workpiece is operated as an anode and the amount of the bias current and the duration of the pre-current phase are selected such that the workpiece heats up during the pre-current phase in the joining region at least up to plastic deformability. In experiments, it has been shown in this process procedure that, in particular, the heat input on the workpiece side can be increased by a larger energy input in the pre-flow phase, whereby the quality of the welded connection is increased.

While in conventional methods, the pre-flow phase is only used to form the arc, now during the pre-flow phase, a significant heating of the workpiece in the joint is desired. For this purpose, a higher pre-flow and a longer pre-flow time is used compared to the conventional pre-flow phase. Due to the higher energy input into the base material, a deeper penetration with a better joining zone between the welding part and the workpiece is realized in the welding result. Surprisingly, it has been found that the tendency to spatter is also significantly reduced. The reason for this is assumed to be improved surface cleaning due to the stronger or longer-lasting pre-arc.

The method according to the invention therefore provides for increasing the amount of the pre-flow and / or the duration of the pre-flow phase compared with the known lift-and-strike welding methods. As a result, the energy input is increased in the pre-current phase, so that the main current can be reduced in the subsequent main current or welding phase. Advantageously, this results in a reduced melting of the weldment and a quieter melt and reduced bead ejection.

The method has proved to be particularly effective when a significant proportion of the introduced electrical energy is introduced within the pre-current phase. As a result, the base material is better melted at the same time reduced melting of the weldment. Thus, in one embodiment, at least 30% of the electrical energy should be introduced in the pre-flow phase, preferably at least 50%, and more preferably at least 60%. The introduced energy E _{GES is} determined according to equation 1. E _GES = E _V + E _H , Eq. 1 wherein, in simplified terms, the energy introduced in the Vorstromzeitraum period E _V as the product of bias current I _V , arc voltage U _V in the Vorstromphase and Vorstromzeit t _V (equation 2), and introduced in the main flow period energy E _H as a product of main current I _H. , Arc voltage U _H in the main current phase and main current time t _H (equation 3). E _V = I _V · U _V · t _V Eq. 2 E _H = I _H · U _H · t _H Eq. 3

Depending on the materials used and component dimensions, different process parameters are necessary to achieve the desired effect. Pre-flow and pre-flow time are chosen in particular so that, although there is a significant heating in the workpiece, but not yet to a melting at the weldment. This takes place only in the subsequent main flow or welding phase, for which purpose the main flow or the main flow time are selected accordingly.

Experiments have shown that a welded connection of particularly high quality can be achieved if the pre-flow period or the pre-flow time in one embodiment has at least seven times the duration of the main flow period or the main flow time, preferably eight to ten times the duration. In addition, it is advantageous if, in this embodiment, the amounts of pre-flow and main flow are selected such that the ratio of pre-flow to main flow is in a range of 0.3 to 0.5, preferably in a range of 0.35 to 0, 45th

To terminate the process, the welding part is lowered onto the workpiece and the welding current is switched off. To increase the process stability of the welding current is switched off in one embodiment, as soon as a ground contact between the welding part and the workpiece is produced.

A further reduction of weld spatter and a higher strength of the welded connection can be achieved in an embodiment in which the immersion, ie the lowering of the welding part on or into the workpiece, at a reduced speed of 0.11 m / s or less, and preferably of 0.1 m / s or less.

The method described above is particularly suitable for applying T-bolts and threaded bolts (with external or internal thread), preferably with a diameter in the range of 3 mm to 9 mm. However, other types of bolts, such as. As ball pins, etc., and bolts of other dimensions are applied to a workpiece with this method.

The method is particularly suitable for welding bolts on thin sheets having a thickness in the range of 0.5 mm to 3 mm. The process achieves particular advantages in the welding of aluminum-containing workpieces or welded parts and in the welding of workpieces which are provided with an anticorrosion layer, eg. As zinc or aluminum coated sheets. Here is achieved by the extended Vorstromphase a good surface cleaning. However, the method is not limited to the aforementioned workpieces and weldments.

In other words, as compared with a conventional arc ignition process, an increase in the bias current and the bias current time while reducing the main current. In addition, the immersion speed is reduced, whereby the melt stably impacts the base material.

The inventive method with novel welding characteristic results in the following advantages. The base material is better melted, at the same time the bolt is not so much melted, resulting in a high connection strength. Due to the low immersion speed, the melt remains calm until it comes to the connection. Thus, spatter is minimized and the melt is not over-expelled. This results in a higher lower head size and very low spatter formation, bead formation and a very high strength tensile test or Scherzugbelastung in the assembly.

With a sibling claim, the solution of the problem also extends to a use of a welding device for carrying out the method according to the invention.

A welding device for carrying out the method described above has a conventional holder for receiving a welding part. Furthermore, the welding device to a DC power source and a control and regulating device by means of a direct current between the welding part (cathode) and a workpiece (anode) can be applied, to form an arc between the welding part and the workpiece. The control and regulating device is suitable for carrying out the method described above, for example, the parameters bias current, bias current, main current, main current time, immersion speed, immersion delay in the control and regulating device in the required value range adjustable or stored as a characteristic.

Further advantageous embodiments of the invention will become apparent from the dependent claims.

The above-described characteristics, features, and advantages of this invention, as well as the manner in which they are achieved, will become clearer and more clearly understood in connection with the following description of the embodiments. If the term "can" is used in this application, it is both the technical possibility and the actual technical implementation.

Embodiments will be explained below with reference to the accompanying drawings. Show:

1 a characteristic curve for the exemplary representation of process parameters according to an embodiment of the invention,

2 a schematic representation of a welding device for Hubzützschweißen.

1 shows a characteristic of a DC stud welding process according to an embodiment of the invention.

A 5 mm diameter T-bolt was applied to a workpiece in the form of a hot-dip galvanized aluminum plate (DX54D Z100) with a thickness of 0.7 mm to 0.8 mm.

In 1 the course of the current I, the resulting voltage U and the lift-off movement s of the welding bolt over time for the embodiment is shown. The dashed auxiliary lines along the time axis t each indicate time intervals of 30 milliseconds. The dashed lines in the y-direction scale, depending on the reference size, in steps of 100 A, 10 V or 1 millimeter.

At the beginning of the process, after contacting the bolt with the workpiece surface, a bias current I _V of 100 A was switched on for a pre-current period t _V of 0.1 s (100 milliseconds). The bolt was raised 1.4 mm from the workpiece at a speed of 0.127 m / s. After expiration of the pre-current time t _V , the current was increased to a main current I _H of 270 A for a welding time t _H (main current period) of 0.012 s (12 milliseconds).

To complete the process, the bolt was lowered and slightly lowered into the plate at a speed of 100 mm / s.

Compared to the process parameters of a conventional method of lift-and-strike welding of this material combination, the pre-flow time t _{V has been} extended. Thus, the pre-flow phase lasts more than eight times as long as the subsequent welding phase. Furthermore, the amount of the bias current I _{V was} increased and the main current I _H reduced. Vorstrom I _V and main current I _H are in this embodiment in a ratio of 0.37. At the same time, the dipping speed was reduced.

Table 1 shows a comparison of the control parameters according to the embodiment and the conventional method: TABLE 1 embodiment Conventional procedure bias 100 A (60 A effective) 60 A (36 A effective) Bias-time 100 milliseconds 70 milliseconds main power 270 A 370 a Mainstream time 12 milliseconds 11 milliseconds Immersion speed 100 mm / s 127 mm / s

In 1 It can be seen that during welding only minor fluctuations in the course of the current and the voltage occur. The extended pre-flow phase with higher pre-flow and reduced main flow creates a quiet melt with reduced bead ejection. Slowly lowering the weldment to the workpiece at the end of the process further reduces spattering.

The method can be implemented by simple means in a plant for Hubzündungschweißen. 2 shows a schematic representation of the essential components of a Hubzündungsschweißanlage for performing the method according to the invention. The welding device 10 has a holder 20 on, for receiving and holding a welding part 100 in the form of a bolt. Opposite the bolt 100 is a workpiece 200 arranged on which the bolt 100 at a joint 300 to be welded on. The welding device 10 also has a DC power source 30 on, by means of wires 32 . 34 a welding circle with the bolt 100 as the cathode and the workpiece 200 as an anode forms. A control and regulating device 40 is via electrical lines 42 . 44 into the device 10 integrated, and designed so that the necessary for the process described above welding and process parameters can be implemented. In particular, the control and regulating device 40 be formed via an interface, not shown, for inputting the desired parameters or it may be z. B. one or more corresponding characteristics in the control and regulating device 40 be deposited.

The embodiments are not to scale and are not restrictive. Modifications in the context of expert action are possible.

LIST OF REFERENCE NUMBERS

10

welder

20

bracket

30

DC power source

32, 34

cables

40

Control and regulating device

42, 44

cables

100

weldment

200

workpiece

300

joint

I

electricity

I _V

bias

I _H

main power

s

Abhubstrecke

t _V

Preweld current (space)

t _H

Main current time (space)

U

tension

Claims (8)

Method for DC-DC welding in which a welded part ( 100 ) with a workpiece ( 200 ) at a joint ( 300 ) is welded, wherein first in a Vorstromphase over a Vorstromzeitraum (t _V ) by means of a bias current (I _V ) an arc between the welded part ( 100 ) and the workpiece ( 200 ) is formed and in a subsequent main flow phase, the bias current (I _V ) is increased to a main current (I _H ) for a main flow period (t _H ), the workpiece ( 200 ) is operated as an anode, characterized in that the Vorstromzeitraum (t _V ) and / or the amount of the bias current (I _V ) are set so that the workpiece ( 200 ) during the pre-flow phase in the area of the joint ( 300 ) is heated at least until plastic deformability. Hubzündungschweißverfahren according to claim 1, wherein at least 30% or at least 50% or at least 60% of the introduced electrical energy is introduced in the pre-flow phase. Stroke ignition welding method according to claim 1 or 2, wherein the Vorstromzeitraum (t _V ) has at least seven times the duration of the main flow period (t _H ) or eight to ten times the duration and the amount of the bias current (I _V ) and the amount of the main current ( I _H ) are chosen to have a ratio of bias to main flow in a range of 0.3 to 0.5 or in a range of 0.35 to 0.45. Stroke ignition welding method according to one of the preceding claims, in which the welding part ( 100 ) on or in the workpiece ( 200 ) is lowered and the main current (I _H ) is turned off as soon as a ground contact between the welding part ( 100 ) and workpiece ( 200 ) will be produced. Stroke ignition welding method according to one of the preceding claims, in which the welding part ( 100 ) at a rate of 0,11 m / s or less, or 0,1 m / s or less, onto or into the workpiece ( 200 ) is lowered. Method according to one of the preceding claims, wherein the welded part ( 100 ) is a bolt and is welded to a thin sheet. Method according to claim 6, wherein the thin sheet is a galvanized aluminum sheet. Use of a welding device for connecting a welding part ( 100 ) and a workpiece ( 200 ) at a joint ( 300 ) by means of reciprocating welding with a holder ( 20 ) for receiving the welding part ( 100 ), a DC power source ( 30 ) and a control device ( 40 ), by means of a direct current (I _V , I _H ) between the welding part ( 100 ) and the workpiece ( 200 ) can be applied to form an arc, for carrying out the method according to one of the preceding claims.

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