RU2229382C1 - Method of ultrasonic welding of thermoplastics - Google Patents

Abstract

FIELD: plastics welding. SUBSTANCE: the invention presents a method of plastic welding, in particular the method of welding of thermoplastic polymeric materials, that may be used in aircraft industry at manufacturing belts, halyards, shroud lines, etc. out of capron straps and cords, at manufacturing mats and brushes out of synthetic monofilaments, in production of plastic household goods and consumer goods. The method of ultrasonic welding of thermoplastics provides, that before squeezing of welded pieces they switch on and start to measure a counter movement of a waveguide and a support with respect to each other. The measurement is going on in a period of the pieces squeezing between the waveguide and the support by an increasing pressure of squeezing. At reaching by the counter movement of the given value this movement is fixed and the pressure of squeezing is removed. Then the ultrasonic oscillations and welding pressure are switched on and the welding cycle is ended in the given mode. The invention ensures an increase of quality of welded joints at the expense of provision of permanence of the beginning of the process of welding with stationary from a cycle to a cycle parameters by a strict differentiation of a material squeezing process and process of a welding, and also differentiation of parameters of squeezing and a welding. EFFECT: the invention ensures an increase of quality of the welded joints. 1 dwg

Description

The invention relates to the field of welding of plastics, namely thermoplastic polymeric materials, and can be used in the aviation industry in the manufacture of belts, halyards, slings, etc. from kapron tapes and cords, in the manufacture of mats and brushes from synthetic monofilaments, in the production of household and consumer goods from plastics.

It is known that in order to obtain a high-quality welded joint, it is necessary to accurately dose the mechanical energy introduced into the materials to be joined, and for this it is necessary to have a stable reference point for this dose (see the book: Volkov S.S., Chernyak B.Ya. Plastics welding with ultrasound. 2- ed. revised and supplemented. - M .: Chemistry, 1986, 256 pp .; pp. 30-31).

A known method of ultrasonic welding of thermoplastics (AS USSR No. 304139, class B 29 from 27/08, 1970), including squeezing the parts with the simultaneous inclusion of ultrasonic vibrations. However, due to the unsteady process of compression of the materials being welded and, accordingly, their inhomogeneous density in the sub-waveguide zone, the initial heat generation is uncertain at the place and time and can occur directly on the contact surface of the waveguide with the material, and only then at the material interface. This uncertainty makes it difficult to ensure a constant amount of mechanical energy introduced into the joints and leads to a decrease in the quality and quality stability of the welded joint.

In another known method for ultrasonic welding of thermoplastics (AS USSR No. 669591, B 29 from 27/08, 1979) during the exposure of the materials to be joined under pressure, the compressive strain rate of the materials is measured, and ultrasound is turned on when the compression strain rate is constant. However, this method also does not guarantee quality and quality stability for several reasons. Firstly, the concept of “compression deformation” is not a definite concept, because for woven and non-woven fibrous materials, this can be a different degree of compaction, for “soft” polymers during compression, a waveguide is introduced along with the compaction of materials, for “hard” polymers with complete adherence of surfaces, compression can cause wrinkling, and for uneven surfaces with compression parts are deformed to ensure fit in the contact area. Secondly, the constancy of the strain rate of compression does not indicate the end of the stage of compaction of materials and cannot serve as the end or the beginning of any process, thirdly, the equality of the strain rate to zero can only indicate the equality of the internal resistance of the materials to compressive (and in the known method, equal to it, but not optimal welding) pressure, but not about the end of material compaction.

The last remark is eliminated in the prototype method of ultrasonic welding of thermoplastics (AS USSR No. 1497032, V 29, 65/08, 05/29/87), in which the compression of parts is carried out by monotonously increasing pressure until the compression strain rate reaches a constant or zero value after which the pressure is kept constant.

The end of the compression process, as follows from the prototype, can occur at different pressure values, therefore, the start of the welding process can occur at different supported constant values of the welding pressure, i.e. welding process parameters vary from cycle to cycle and lead to instability in the quality of welded joints.

The technical result of the claimed invention is to improve the quality and quality stability of welded joints of thermoplastics by ensuring the possibility of a constant start of the welding process with parameters that are constant from cycle to cycle by strictly distinguishing between the compression process of materials and the welding process, as well as between the parameters of compression and welding.

The technical result is achieved by the fact that in the known method of ultrasonic welding of thermoplastics, which includes compression of parts by increasing pressure.

The peculiarity is that, before compression, the oncoming movement of the waveguide and supports relative to each other is turned on and measured, the measurement is continued while the parts to be welded are compressed by increasing pressure between the waveguide and the support, when the oncoming movement reaches the set value, this movement is fixed to prevent movement in the opposite direction, the compression pressure is removed, ultrasonic vibrations and welding pressure are turned on, and the welding cycle is completed in the set mode.

Before starting compression, the inclusion and the beginning of the measurement of the opposite movement of the waveguide and the support relative to each other allows you to set a reference point independent of the thickness of the material for all welding cycles, the reference point of movement of the waveguide to the support or vice versa - supports to the waveguide, depending on the design of the welding machine, and increasing pressure eliminates possible interference in the movement.

Continuation of the measurement of the opposed movement of the waveguide and the support during compression of the parts to be welded is accompanied by an increasing compression pressure, which overcomes the increasing resistance of the compressible material until the counter-movement of the waveguide and the support reaches a predetermined value.

Fixing the movement to prevent the movement in the opposite direction allows you to fix constantly the same independent relative to the internal resistance of the materials the specified relative position of the waveguide and the support, which is maintained after removing the increasing compression pressure.

Removing the increasing compression pressure ensures the completion of the compression process, as well as the possibility of applying the welding pressure to an optimal predetermined value, which may differ from the achieved value of the increasing compression pressure of the material before welding. Fixation of movement does not allow the waveguide and support to “disperse” in opposite directions.

Thus, in the aggregate, all the signs ensure the achievement and fixation of a given rigidly constant initial and final position of the waveguide and the support relative to each other at the beginning and after the completion of the compression stage of parts, which eliminates the influence of the parameters of this first stage of the welding process on the stability of the amount of mechanical input during welding energy into the welded parts. This increases the average value of the strength of the welded joint, i.e. quality stability, what is achieved by the technical result.

The analysis of the prior art by the applicant, including a search by patent and scientific and technical sources of information, and the identification of sources containing information about analogues of the claimed invention, made it possible to establish a set of significant distinguishing features in relation to the applicant's technical result in the claimed method set forth in the claims.

Therefore, the claimed invention meets the condition of "novelty."

To verify the compliance of the claimed invention with the condition “inventive step”, the applicant conducted an additional search for known solutions in order to identify signs that match the distinctive features of the claimed method from the prototype. The search results showed that the claimed invention does not follow explicitly from the prior art for a specialist, since the influence of the transformations provided for by the essential features of the claimed invention on the achievement of a technical result is not revealed from the prior art as defined by the applicant, in particular, the following transformations are not provided for by the claimed invention:

- addition of a known product by any known part (s) attached to it (by) according to known rules, in order to achieve a technical result with respect to which the effect of such an addition is established;

- replacement of any part (s) of a known product with another known part to achieve a technical result, in respect of which the influence of such a replacement is established;

- the exclusion of any part (element, action) of the product with the simultaneous exclusion of the function due to its presence and the achievement of the usual result for such exclusion (simplification, reduction of mass, dimensions, material consumption, increased reliability, reduced process time, etc.);

- an increase in the number of elements of the same type, actions, to enhance the technical result due to the presence in the tool of precisely such elements, actions;

- the implementation of a known tool or part (s) of a known material to achieve a technical result due to the known properties of this material;

- the creation of a tool consisting of known parts, the choice of which and the relationship between them are based on known rules, recommendations, and the technical result achieved in this case is due only to the known properties of the parts of this tool and the relationships between them.

The described invention is not based on a change in a quantitative characteristic (s), the presentation of such signs in relationship, or a change in its appearance. This refers to the case when the fact of the influence of each of these characteristics on the technical result is known, and new values of these signs or their relationship could be obtained on the basis of known dependencies and patterns.

Therefore, the claimed invention meets the condition of "inventive step".

The drawing shows a block diagram of a laboratory installation on which the proposed method was carried out.

The installation consists of a waveguide 1, a support 2, a welding head 3, a pneumatic actuator 4 with electro-pneumatic valves 5 and 6, a displacement sensor 7 with an indicator 8, a ratchet mechanism 9 with an pneumatic actuator 10, switches 11, 12 and 13, a pressure regulator 14, and receivers: 15 - compression pressure, 16 - welding pressure, 17 - lifting pressure of the welding head 3, welding process control unit 18, ultrasonic generator 19, item 20 indicates the material to be welded.

When performing the proposed method, the operator places the material to be welded 20 between the waveguide 1 and the support 2, the switch 13 sends a signal to the electro-pneumatic valve 6, which connects the receiver 15 through the regulator 14 to the electro-pneumatic valve 5, with the switch 12, the operator turns on the electro-pneumatic valve 5 and supplies air to the upper chamber of the pneumatic actuator 4 from receiver 15, i.e. turns on the compression pressure, switching on the compression pressure starts moving the waveguide 1 towards the support 2, which is recorded and measured by the sensor 7 and visually controlled by the operator according to indicator 8, if necessary, in case of braking the movement by the resistance of the material being welded 20, the operator increases the compression pressure by the pressure regulator 14, providing further movement of the waveguide 1, at the moment of reaching the displacement value of the set value, which is observed by indicator 8, the operator switch 11 This turns the actuator 10 causes actuator 10 to engage the ratchet 9 than captures moving waveguide 1 in the opposite direction of the original, a switch 12 via the operator electropneumatic 5 overlaps air supply from the receiver 15, and the upper chamber of the pneumatic cylinder actuator 4 connects with the atmosphere, i.e., switches off the compression pressure, then, through the welding process control unit 18, turns on ultrasonic vibrations from the generator 19, a switch 13 connects the welding pressure receiver 16 through an electro-pneumatic valve 6 to an electro-pneumatic valve 5, and a switch 12 through an electro-pneumatic valve 5 disconnects the upper chamber of the pneumatic actuator pneumatic cylinder 4 from the atmosphere and connects to the receiver 16, i.e. turns on the welding pressure, after reaching the specified parameters of the welding process, the welding control unit 18 turns off ultrasonic vibrations, and then sends a signal to the operator about the need to remove the material being welded 20, the switch 11 sends a signal to the pneumatic actuator 10 and turns off the ratchet mechanism 9, then the switch 12 through the electro-pneumatic valve 5 connects the upper chamber of the pneumatic actuator pneumatic cylinder 4 with the atmosphere, and the lower one with the lift pressure receiver 17, which moves the waveguide 1 to the initial one to start the process th position.

For comparison, 100 samples were welded from a nylon strip LTK 44-1600 (MRTU 17-711-69), 2.7 mm thick. After welding, samples were tested on a tensile testing machine R-10. The specified parameters of the welding mode: welding pressure - 5.0 MPa, the oscillation amplitude of the working end of the waveguide - 50 μm, the oscillation frequency - 17.9 kHz. Specified by the claimed method, the movement of the waveguide towards the support was 7.4 mm, which ensured the inclusion of ultrasonic vibrations with a distance between the waveguide and the support of 2.0 mm. When welding by a known method, ultrasonic vibrations were switched on when the compression strain rate reached zero, while the value corresponding to this moment of the compression pressure was measured, which was subsequently kept constant. The measurement results are as follows: the average value of the compression pressure at the moment of switching on the ultrasonic vibrations is 4.6 MPa, the standard deviation is 0.3 MPa, the coefficient of variation is 6.52%. The test results of the welded samples are as follows: the average breaking load is 605 kN, the standard deviation is 105.4 kN, and the coefficient of variation is 17.42%. When welding according to the claimed method, the achievement of a given waveguide displacement was ensured by compression pressure with an average value of 5.2 kN, welding was carried out at the specified mode parameters (see above), test results: average breaking load - 640 kN, standard deviation - 64 kN, coefficient variations - 10%. A comparison of the test results confirms the achievement of the proposed method of the claimed technical result.

Claims (1)

A method of ultrasonic welding of thermoplastics, including compression of parts by increasing pressure, characterized in that before compression they turn on and begin to measure the opposed movement of the waveguide and supports relative to each other, the measurement is continued while compressing the parts to be welded between the waveguide and the support, when the set value reaches the opposite movement this movement is fixed, the compression pressure is removed, ultrasonic vibrations and the welding pressure are turned on, and the welding cycle is completed in the set mode.