DE102018213372A1 - Method and device for ultrasonic spot welding - Google Patents

Abstract

The invention relates to a method for ultrasonic spot welding, in which fiber-reinforced plastic components (4, 5) are brought together between a sonotrode (2) and an anvil (3) and are welded to one another by applying a longitudinal vibration. At the welding point, sound impulses are coupled into the components (4, 5) by means of the anvil (3) and the echo signals (10, 11, 12) of the sound pulses are recorded and evaluated to determine the quality of the welding spot. A device for ultrasonic spot welding is also specified.

Description

The invention relates to a method and an apparatus for ultrasonic spot welding.

In ultrasonic spot welding, the components to be welded are overlapped at the joint and fixed between a sonotrode and an anvil. The sonotrode is used to apply mechanical vibrations with an ultrasound frequency, accompanied by a static force, which is also referred to as welding force, to the components to be welded, the anvil serving as a counterbearing. The direction of vibration in plastic ultrasonic welding is perpendicular to the welding surface. Absorption of the vibrations in the material of the components creates heat through interfacial and molecular friction. The heat leads to plasticization of the material. The simultaneous pressurization with subsequent cooling results in a material connection between the components to be welded.

The welding of thermoplastic fiber composites has proven to be extremely delicate. The fiber composite material has a plastic matrix and reinforcing fibers embedded therein. These can e.g. as directional fibers in the form of fabrics or scrims or undirected, e.g. present as a fleece. If fiber composite materials are spot welded using ultrasound, the weld spot strength fluctuates greatly from weld to weld, even with identical welding parameters. The optimum joining temperature is often not reached or exceeded. As a result, there is an incomplete weld spot or pore formation in the weld zone. This is attributed to the fiber material in the components, which is distributed inhomogeneously, so that there are different requirements at each welding point. As a result, to ensure process reliability, it is desirable to be able to reliably assess the quality of all welding spots.

Devices and methods for ultrasonic testing are known for assessing the quality of metallic welding spots, an example is given in the document DE 102 30 587 A1 directed.

Against this background, the object of the present invention is to provide a possibility of how the welding quality of ultrasonic spot welds on fiber composite components can be reliably checked in a simple and inexpensive manner. Another task is to provide a possibility for large-scale production of how fiber composite components can be securely welded.

The object is achieved by a method according to patent claim 1 and a device according to patent claim 6. Further advantageous configurations result from the subclaims and the following description.

A method for ultrasonic spot welding is specified in which fiber-reinforced plastic components are brought together between a sonotrode and an anvil and are welded to one another by applying a longitudinal vibration.

According to the invention, sound impulses are coupled into the components at the welding point by means of the anvil and the echo signals of the sound impulses are recorded and evaluated to determine the quality of the welding spot.

Furthermore, a device for ultrasonic spot welding is specified with a sonotrode and an anvil. The ultrasonic spot welding device also has a transmitter / receiver unit and an evaluation device. The transmitting / receiving unit is set up to transmit sound pulses and to receive echo signals of the sound pulses, and the evaluation device is set up to evaluate the echo signals with regard to the quality of the spot weld connection. It is of central importance for the invention that the transmitter / receiver unit is integrated in the anvil so that the sound pulses can be coupled into the components by means of the anvil.

In other words, the welding spot quality is checked using the pulse-echo method, the checking still being carried out in the welding device itself. This type of inline inspection has the advantage that the weld seam quality can be determined immediately after welding while the components are still clamped. There is no need for an additional test station. The time-consuming and error-prone subsequent localization of the welding spots is also eliminated, since the ultrasound probe is automatically correctly positioned. Possibly. a faulty weld can still be "saved" by a welding correction.

In the pulse-echo method, ultrasound signal pulses are injected into the components to be tested by an ultrasound probe, which includes a transmitter and receiver unit. At signal interfaces, each signal pulse is partially reflected and returned to the test head as an echo signal. The echo signal is detected there. If the echo time, that is to say the time between the transmission of the signal pulse and detection of the echo signal, is also detected, the distance of the Determine the interface to the test head and thereby the position of the detected interfaces.

For assessing the quality of the welded connection, it is particularly advantageous if the sound pulse is coupled in coaxially with the direction of vibration of the sonotrode. Accordingly, the transmitter / receiver unit can be aligned accordingly. The pulse signal thus strikes the interface between the components or the welding lens perpendicularly, which improves the signal quality of the echo signals. The test head or the transmitter / receiver unit preferably do not come into direct contact with the components, but are integrated into the anvil in such a way that they couple their vibrations into an anvil contact part. The anvil contact part is the part of the anvil that comes into direct contact with the component during welding.
The anvil contact part is then used on the one hand as a delay line for the ultrasonic welding and on the other hand as a spacer for the ultrasonic test head. The length of the anvil contact part is preferably chosen such that the focal point of the transmitting unit is below the welding point. Such an integration of an ultrasound test head into a welding device represents a particularly simple and inexpensive solution which at the same time enables a precisely positioned and thus very reliable measurement.

In a preferred embodiment, it is provided that the amplitudes of the echo signals are evaluated in order to determine the weld spot quality. The amplitudes of the echo signals allow simple conclusions to be drawn about the type and nature of the interface from which they are reflected. The clearer the interface, the higher the amplitude of the reflected signal.

In one configuration, the reflections of the sound pulses are divided into first, second and third echo groups based on the return time of the echo signals. The echo signals of the first echo group are signals which are reflected at the interface of the first component facing the transmitter unit. This interface has the shortest distance to the transmitter unit and thus the shortest echo time. The echo signals of the second echo group are signals which are reflected back at the interface between the two components, ie where the welded connection is created. The third echo group contains signals which are reflected by the interface of the second component with the sonotrode. The evaluation unit checks whether the amplitude of the second reflection group is below a first predetermined limit value and the amplitude of the third reflection group is above a second predetermined limit value. If this is the case, the weld is to be assessed as OK and a corresponding evaluation signal can be output. In all other cases, the weld is not in order and an error signal can be issued.

The evaluation device is set up in order to be able to carry out the evaluation described above. The limit values can e.g. can be determined by reference measurements.

For a reliable assessment of the weld seam quality, it has proven to be advantageous if the sound impulses are coupled in immediately after the weld. It is preferable to wait until the weld has cooled down before checking. This can take a few seconds. It should therefore be considered immediate if the sound impulses are coupled in a few seconds after the welding is completed. This has the advantage that a statement about the quality of the welding spot can be made in the welding device directly after the welding.

The ultrasonic spot welding device can be a stationary system. With regard to high working speeds, however, it is advantageous if the ultrasonic welding device in one configuration is a robot-guided welding device. For example, the sonotrode and anvil can be attached to an industrial robot and can be positioned and operated by means of this.

The device for ultrasonic spot welding is set up to carry out the method described above and, as such, achieves the same technical effects and advantages.

Further advantages, features and details of the invention emerge from the following description, in which exemplary embodiments of the invention are described in detail with reference to the drawings. The features mentioned in the claims and in the description can each be essential to the invention individually or in any combination. If the term "can" is used in this application, it is both the technical possibility and the actual technical implementation.

• 1 eine Ultraschallschweißvorrichtung in schematischer Darstellung und
• 2A bis D beispielhafte Signalbildverhalten

Exemplary embodiments are explained below with reference to the accompanying drawings. In it show:

• 1 an ultrasonic welding device in a schematic representation and
• 2A to D exemplary signal pattern behavior

1 shows an exemplary ultrasonic spot welding device 1 in a schematic representation. The ultrasonic spot welding device 1 has a metallic sonotrode 2 and a metallic anvil 3 on, between which two components 4 and 5 are clamped in the form of thin-walled thermoplastic fiber-reinforced plastic components. An ultrasound frequency is generated via a generator, not shown, which is passed on to an oscillation system. The oscillation system can consist, for example, of a converter, an amplitude transformation piece and a sonotrode, wherein in 1 only the sonotrode 2 is shown. The converter converts the high frequency of the generator into mechanical vibrations. The vibration is passed on to the sonotrode and from there to the components via the amplitude transformation piece 4 and 5 transfer. The direction of the ultrasonic vibration U is perpendicular to the welding interface between the component flanges and specifies a joining axis. Furthermore, by means of the sonotrode 2 a static welding force is applied to the components. The components are placed between the sonotrode and anvil 3 added with an anvil contact part 6 comes into contact with the component. The anvil contact part 6 is articulated as a compensation ball in the anvil part 7 held.

In the anvil 3 is still a transmitter / receiver unit 8th integrated in the form of an ultrasonic probe. The test head 8th is about a feather 9 to the anvil contact part 6 pressed to ensure the coupling of the sound waves. The anvil contact part 6 lies between the components 4 . 5 and the ultrasonic probe 8th and acts as a vibration damper. The ultrasonic probe 8th is a nominal probe that sends longitudinal waves into the components perpendicular to the surface. In addition to the transmitter unit required for this, the test head also has a receiver unit. This receives the echo signals reflected at the component interfaces 10 . 11 and 12 , Here are the amplitudes A of the echo signals 10 . 11 and 12 a measure of the size of the existing reflectors. Furthermore, the time t between sending the sound pulse and receiving the echo signal 10 . 11 and 12 measured. The position of the reflectors can be determined from this echo propagation time t. The transmitter / receiver unit is equipped with an evaluation device for evaluating the signals 13 in an active connection, which is set up to evaluate the echo signals in the manner described below with regard to the quality of the welded connection.

There are now three notable echo groups for the weld site to be examined: a first echo group I with echo signals 10 by the interface between anvil 3 and the first component 4 be reflected, a second echo group II with echo signals 11 by the interface between the two components 4 . 5 be reflected and a third echo group III with echo signals 12 that at the interface of second component 5 to the sonotrode 2 be reflected.

In the method, the received echo signals 10 . 11 and 12 due to their individual echo run times t assigned to one of these three groups. Based on the amplitudes AII . AIII The quality of the spot welding is then assessed in the second and third echo groups.

Here, the invention is based on the consideration that when an optimal welding lens is formed, the interface between the two components 4 . 5 largely disappears through fusion of the plastic parts of the components. Consequently, with good weld spot quality in the second echo group II only echo signals with very low amplitude are reflected. For the second group II therefore becomes a limit GII specified, which is below for an optimal weld.

At the same time is the third echo group III a measure of overheating of the plastic material. The more the plastic material is burned, the more the amplitude of the echo signals in the third echo group drops. For the third echo group III therefore becomes a limit GIII specified that must be exceeded for an optimal weld.

The amplitudes are now used to evaluate the weld spot quality A of the echo signals evaluated to determine whether the first limit GII undershot and the second limit GIII is exceeded. In this case, the welding result is assessed as OK. In all other cases, the weld is to be regarded as not in order.

The 2A to 2D each show a representation of the amplitudes of the echo signals 10 . 11 and 12 over time t for four different welding results. In 2A no weld spot was formed. The echo signals 11 the second group II are far above the first limit GII and the echo signals 12 the third group III below the second limit GIII , 2 B shows an echo distribution for an incomplete weld spot. The amplitude A of the echo signals 11 the second group II are reduced, but are still above the first limit GII , In the third echo group III lies the amplitude AIII of the echo signals 12 below the second limit GIII , 2C shows an echo distribution for an optimal Spot weld. The first limit GII is from the echo signals 11 the second group II falls below and the second limit value is exceeded by the echo signals of the third group. 2D shows an echo distribution for a weld with heavy combustion. Both the amplitudes AII in the second echo group II and AIII in the third echo group III are very small. In the third echo group III however becomes the second limit GIII below.

The level of the first and second limit GII and GIII is preferably determined by tests on reference measurements.

LIST OF REFERENCE NUMBERS

1

Ultrasonic spot welder

2

sonotrode

3

anvil

4, 5

components

6

Anvil contact member

7

Ambossachsteil

8th

Transmit / receive unit

9

feather

10, 11, 12

echo signals

13

evaluation

A, AII, AIII

Amplitudes of the echo signals

I, II, III

echo group

GII, GIII

limits

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 10230587 A1 [0004]

Claims (9)

Method for ultrasonic spot welding, in which fiber-reinforced plastic components (4, 5) are brought together between a sonotrode (2) and an anvil (3) and are welded to one another by applying a longitudinal vibration, characterized in that at the welding point by means of the anvil (3) sound impulses are coupled into the components (4, 5) and the echo signals (10, 11, 12) of the sound impulses are recorded and evaluated to determine the weld spot quality. Procedure according to Claim 1 , in which the sound pulses are coupled coaxially to the direction of vibration (U) of the sonotrode (2). Method according to one of the preceding claims, in which the amplitudes (A) of the echo signals (10, 11, 12) are evaluated in order to determine the weld spot quality. Method according to one of the preceding claims, in which the echo signals (10, 11, 12) of the sound pulses are divided into first, second and third echo groups (I, II, III) on the basis of the return time of the echo signals, and a check is carried out to determine whether the amplitude ( All) of the second echo group (II) is below a first predetermined limit value (GII) and the amplitude of the third echo group is above a second predetermined limit value. Method according to one of the preceding claims, wherein the coupling of the sound pulses takes place immediately after the welding. Device for ultrasonic spot welding with a sonotrode (2) and an anvil (3), a transmitting / receiving unit (8) integrated in the anvil (3), which is set up for transmitting sound pulses and for receiving echo signals (10, 11, 12) of the sound pulses, and an evaluation device (13) which is set up to evaluate the echo signals (10, 11, 12) with regard to the quality of the spot weld connection. Ultrasonic welding device after Claim 6 , in which the sound pulses can be coupled coaxially to the direction of vibration (U) of the sonotrode (2). Ultrasonic welding device after Claim 6 or 7 , in which the evaluation device (13) is set up to divide the echo signals (10, 11, 12) into a first, second and third echo group (I, II, III) based on their return time (t) and to check whether the amplitude the second echo group (II) is below a first predetermined limit value (GII) and the amplitude of the third echo group (III) is above a second predetermined limit value (GIII). Ultrasonic welding device according to one of the Claims 6 to 8th which is a robotic welding device.

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