DE102015109183A1 - Method for joining two joining partners made of plastic - Google Patents

Abstract

The present invention relates to a method for joining two joining partners (01, 02) made of plastic. In this method, a first joint partner (01) and a second joint partner (02) are arranged in abutment so that the first joint partner (01) and the second joint partner (02) are arranged abutting one another in a joint region. Subsequently, the first joining partner (01) and the second joining partner (02) are heated in the joint area with a laser, whereby the first joining partner (01) and the second joint partner (02) at least partially melt in the joint area and flow into one another. Subsequently, the first joint partner (01) and the second joint partner (02) are cooled, whereby the first joint partner (01) and the second joint partner (02) solidify and form a welded joint in the joint area. According to the invention, the first joining partner (01) provided within a melting section (03) has a cross-section that tapers in the direction of the second joining partner (02), so that reservoirs (07) are formed laterally of the tapered cross-section. The reservoirs (07) are bounded by the second joining partner (02) arranged on impact and are filled with melt of the first joining partner (01) melted in the joint area.

Description

The present invention relates to a method for joining two joining partners made of plastic. In this method, a laser is used to form a welded joint between the joining partners.

Various methods for welding plastic by applying a laser are known in the prior art, and in the textbook of Klein, R .: "Laser Welding of Plastics", Wiley VCH Verlag, Weinheim, 2011 , described. The energy of a focused laser beam is brought into a joining zone between the joining partners to be joined, so that the plastic melts and, after cooling, forms a weld in the joining zone. In so-called laser transmission welding, one of the joining partners is irradiated with a laser beam which is absorbed by the other joining partner, for which purpose it has absorbent pigments. The two joining partners must have different optical properties. In most cases, one joining partner is optically transparent while the other joining partner appears colored. The laser transmission welding has the disadvantage that the energy distribution between the joining partners is usually uneven, so that the melting does not take place uniformly due to an uneven heat-affected zone. The sides of the absorbent joining partner facing away from the laser beam are not completely melted, so that, in particular in the case of butt joints, the joining partners are not completely connected and a notch effect is caused in the joining zone. In addition, the surface of the joining partners can be damaged in terms of transmission and absorption depending on the optical properties of the joining partners.

In the textbook of Ehrenstein, Gottfried W .: "Manual Plastics Connection Technology", Carl Hanser Verlag, Munich, 2004, ISBN 3-446-22668-0 , It is shown that the laser transmission welding requires, on the one hand, a precisely manufactured joining partner and, on the other hand, a guidance of the laser beam, by means of which both joining partners are uniformly heated. The greater the thickness of the joining partners, in particular in the case of butt joints, the more serious the disadvantages are. Another disadvantage is the long cycle times. The process control should be improved by a transparent cover, which should prevent the melt from escaping and cool the surface.

The DE 196 25 873 A1 shows a method for the connection of joining partners, in which first a frictional connection and then a welded joint are produced.

From the DE 44 32 081 A1 is a method for Schweißverbinden of plastic parts known in which the parts to be joined are held together by positive engagement or internal frictional connection.

From the EP 0 288 884 A1 is a method for welding plastic-coated sheets is known in which the sheets are pushed together tongue and groove interlocking.

The US Pat. No. 7,681,924 B2 teaches a method of fusion welding a tube that is shaped so that a bead or lip created during fusion welding does not interfere with the function of the tube.

The WO 2012/152790 A1 shows a method for welding objects with bevelled edges.

From the WO 2008/116981 A2 For example, there is known a method for producing a butt joint between two pipes in which closed ends of the pipes are heated and joined together.

The WO 89/10231 A1 shows a method for joining workpieces made of thermoplastic material with laser irradiation, in which a melting in the region of the joint is effected by energy absorption.

The DE 939 719 B shows a tube made of non-weldable plastic, which has at its ends lugs of weldable plastic.

The EP 0 662 389 A2 teaches a method for welding pipes of a thermoplastic material. The tubes each have at their ends two perpendicular to the axis arranged areas.

From the EP 0 882 543 A2 For example, an underwater welding method is known in which a water repellent powder is used.

The EP 0 997 261 A1 shows a laser joining method for joining workpieces made of plastic, in which a mask of laser-impermeable material is used.

In the EP 2 196 279 A2 is a Schmelzfügeverfahren for producing a fillet weld in Inneneckbereich two thin-walled, joined in the lap joint aluminum sheet metal parts described.

The JP H07-80940 A shows a method for diffusion bonding of pipes, in which the formation of a bead is prevented.

From the WO 02/070236 A2 For example, a method for welding pipe segments is known in which the use of insulating material is provided on a sleeve between the pipe segments.

The WO 2005/102671 A1 shows a method for the sterile connection of tubes by means of a laser beam.

The WO 95/26869 A1 teaches a method of laser welding plastic workpiece parts containing different levels of dye pigments to be differentially transparent to the laser beams.

The DE 10 2011 081 554 A1 shows a method for laser welding of two joining partners made of plastic, in which the laser power density is modulated during the welding process in the z-direction of the seam depth in the weld zone.

The object of the present invention, starting from the prior art, is to provide an improved laser welding method for joining two plastic joining partners.

The above object is achieved by a method according to the appended claim 1.

The inventive method is used to connect two joining partners made of plastic. As a result of the method, the two joining partners are permanently and firmly connected to each other by a welded joint and form a unit. Thus, the inventive method is a welding process.

In one step of the method according to the invention, at least one first joining partner made of a plastic and a second joining partner made of a plastic are provided, which are to be connected to one another. The joining partners are, in particular, workpieces.

In a further step of the method according to the invention, the provided first joining partner and the provided second joining partner are arranged in abutment, so that the first joining partner and the second joining partner are arranged abutting one another in a joint area. In the joint area later a welded joint is formed. The impact is in particular a butt joint. The two joining partners collide with their side surfaces without overlapping. The two joining partners are thus arranged together in one plane.

In a further step of the method according to the invention, the abutting first joining partner and the abutting second joining partner are heated directly or indirectly in the joint area with a laser, whereby the first joining partner and the second joint partner at least partially melt and flow into one another in the joint area. The laser is a focused laser beam generated by a device. The energy of the laser causes at least the plastic of the first joining partner to melt immediately.

In a next step of the method according to the invention, the previously heated first joining partner and the previously heated second joining partner are cooled, whereby the first joining partner and the second joining partner completely solidify again and form a welded joint in the joint area. The first joint partner and the second joint partner solidify insofar as they were previously melted, namely in particular in the joint area. The welded joint is formed, in particular, where the partially molten first joining partner and the partially molten second joining partner have merged into one another.

According to the invention, the first joining partner provided and arranged on impact has a cross section tapering in the direction of the second joining partner prior to heating within a melting section, so that reservoirs are formed laterally of the tapering cross section within the melting section. The tapered cross section is arranged perpendicular to the direction of the impact. This cross-section becomes smaller within the fusion section in the direction of the impact, with the cross-section preferably not tapering to a punk-shaped tip or to a straight edge, but tapered to a blunt end of the first joining partner. Consequently, the first joining partner within the fusion section becomes thinner in the direction of the second joining partner. The fusion section is an edge region of the provided first joining partner, which is melted or at least deformed by the heating. By becoming smaller in the direction of the second joining partner cross-section of the first joining partner empty spaces are present in the melting section, which form the reservoirs. The reservoirs are frontally limited by the provided and arranged on impact second joining partner. After the first joining partner and the second joining partner have been heated, the reservoirs fill at least with melt of the first joining partner melted in the joint area and possibly also with some melt of the molten second joining partner. Also, the reservoirs may shrink slightly due to the fact that the first mating partner in the Melting area plastically preformed; in particular that the first joining partner in the melting area is slightly thicker.

A particular advantage of the method according to the invention is that the two joining partners made of plastic can be absorbent and need not have any special optical properties with respect to the laser used. It is possible to use standard plastics as material for the joining partners, which are, for example, colored or contain other pigments. In addition, it is not necessary to use plastics with special additives or pigments for the application of the laser welding process. The method according to the invention allows a uniform melting of the joining partners, since the power density is controlled via the tapering cross section of the first joining partner. The inventive method allows the production of welded joints, which is a strength in the range of strength of the joint partners provided. The reservoirs allow the avoidance of a weld bead as far as possible.

In preferred embodiments of the method according to the invention, the provided first joining partner and the provided second joining partner are arranged in abutment such that a main extension plane of the first joining partner and a main extension plane of the second joining partner coincide, i. H. lie in one plane.

The tapering in the direction of the second joining partner cross-section of the abutting first joining partner tapers before heating within the fusion section preferably linearly in the direction of the second joining partner. Thus, the first joining partner is preferably linearly thinner in the direction of the second joining partner.

The relative amount of taper is preferably between 10% and 70%, ie. h., That the first joining partner in the fusion section due to the taper in the direction of the second joining partner preferably by 10% to 70% thinner. The relative degree of rejuvenation is more preferably between 20% and 50%.

In preferred embodiments of the method according to the invention, the cross-section of the abutting first joining partner prior to heating within the fusion section tapers on both sides of the main extension plane of the first joining partner in the direction of the second joining partner. Thus, in each case one of the reservoirs within the melting section is formed on both sides of the main extension plane of the first joining partner.

The cross section of the abutting first joining partner preferably tapers to a different extent on the two sides of the main extension plane of the first joining partner in the direction of the second joining partner. Thus, the two reservoirs on the two sides of the main extension plane of the first joining partner have different sizes. The larger of the two reservoirs is preferably facing the laser, since on the side of the first joining partner facing the laser, more melt is produced than on the other side of the main extension plane because of the greater heat. The different degrees of taper on the two sides of the main extension plane of the first joint partner can be given by the fact that the taper is steep on both sides. The different degrees of taper on the two sides of the main plane of extension of the first joining partner can alternatively or additionally also be given by the fact that the taper on these two sides at different distances from the second joining partner.

The cross section of the abutting first joining partner, which tapers in the direction of the second joining partner, preferably has the shape of a wedge before heating within the melting section. The wedge is preferably blunt, so it does not end with an edge, but with a narrower base. The wedge has two oblique side surfaces, each having an angle to a central axis of the wedge, the axis of the wedge being aligned in the direction of the impact and lying in the main extension plane of the first joining partner. The angles of the two side surfaces to the axis are preferably different sizes. They are preferably between 10 ° and 60 °; and more preferably between 30 ° and 50 °. The two side surfaces preferably have a different length in the direction of the second joining partner. The two side surfaces of the wedge limit the reservoirs. Since the two side surfaces of the wedge preferably have different angles to the axis and / or different lengths, the two reservoirs are preferably of different sizes. The laser is preferably directed to the larger of the two reservoirs, since the laser-facing side of the first joining partner is heated more and there more melt is formed.

The cross section of the abutting first joining partner, which tapers in the direction of the second joining partner, preferably has the shape of a trapezoid before heating within the melting section. The trapezoid is convex and not formed by a rectangle. The shorter of the two parallel bases of the trapezium abuts the second joining partner. The longer of the two parallel bases of the trapezium forms the transition from the melting section to the other first joining partner. The two legs of the trapezium bound the reservoirs.

The trapezoid preferably has base angles at the longer of the two bases between 30 ° and 80 °. The base angles are particularly preferably between 40 ° and 60 °.

The trapezoid is preferably unequal, so that the two base angles are not the same size. The longer of the two legs is preferably facing the laser.

In preferred embodiments of the method according to the invention, the first joining partner provided and arranged on impact has an abutment surface before heating, with which it abuts the second joining partner. The abutment surface is preferably flat. The abutment surface is preferably rectangular. The abutment surface is preferably aligned perpendicular to the direction of the impact. Thus, the abutment surface is preferably aligned perpendicular to the main extension plane of the provided and abutting first joining partner.

In preferred embodiments of the method according to the invention, the second joining partner provided and arranged on impact has a shock-limiting surface before heating, against which the first joining partner abuts. The first joining partner preferably abuts with its abutting surface against the impact limiting surface. The impact limiting surface also limits the reservoirs on the first joining partner.

The second joining partner preferably limits the reservoirs in the direction of the impact, i. H. in a plane that is perpendicular to the main extension plane of the first joining partner.

The impact limiting surface of the second joining partner limits the reservoirs preferably in the direction of the impact, d. H. in a plane that is perpendicular to the main extension plane of the first joining partner.

The impact limiting surface is preferably flat. The impact limiting surface is preferably rectangular. The impact limiting surface is preferably formed by a straight end of the second joining partner. The impact limiting surface is preferably formed on a cuboid conclusion of the second joining partner. The impact limiting surface preferably has a width which is equal to the thickness of the second joining partner. The impact limiting surface is preferably aligned perpendicular to the main extension plane of the second joining partner.

In preferred embodiments of the method according to the invention, the first mating partner provided and provided on the butt joint has the shape of a plate or a flat parallelepiped, apart from the melting section and the second joint mate- rial provided and provided on the joint. The two plate-shaped provided and arranged on joint joint partners are preferably together in a plane. In this case, the two plate-shaped joint members provided and arranged in abutment preferably abut one another with their narrow side surfaces.

The provided and arranged on impact first joining partner and the provided and arranged on impact second joining partner each have a thickness, wherein the thickness of the provided and arranged on impact first joining partner and the thickness of the provided and arranged on impact second joining partner is not more preferred than 20% differ. With particular preference, the first joining partner provided and arranged on the joint has the same thickness apart from the melting section as well as the second joining partner provided and arranged on the joint.

The abutting surface of the provided first joining partner preferably has, prior to heating, a width which is between 20% and 90% of the thickness of the first joining partner provided. The width of the abutment surface is particularly preferably between 50% and 80% of the thickness of the first joint partner provided.

In preferred embodiments of the method according to the invention, during and / or after the heating of the first joining partner and the second joining partner, the first joining partner and the second joining partner are moved toward one another, in particular displaced, over a joining path. In this case, the second joining partner is preferably at rest, while the first joining partner is pushed onto the second joining partner. This movement leads, in particular, to the fact that the reservoirs fill up with melt and possibly also fill or disappear by deformation. This movement also leads to the fact that the first joining partner is increasingly heated and melted by the laser in the melting section in a direction opposite to the second joining partner.

The joining path is preferably aligned parallel to the main extension plane of the provided and arranged on joint first joining partner. The joining path is preferably in the direction of the impact, i. H. aligned in the direction of the second joint partner.

The joining path is preferably shorter than the length of the taper of the cross section of the first Joining partners in the direction of the push. Thus, the joining path is preferably shorter than the extension of the fusion section in the direction of the impact. Thus, the joining path is preferably shorter than the height of the described trapezoid.

In preferred embodiments of the method according to the invention, the laser is directed to the tapered cross-section of the first joining partner, i. h., that the laser is directed to the fusion section. In this case, the laser is preferably aligned parallel to the abutment surface of the first joining partner. In this case, the laser is preferably aligned perpendicular to the main extension plane of the first joining partner. During the heating, the laser is preferably moved parallel and several times to the abutment surface of the first joining partner in order to heat the first joining partner along its main extension perpendicular to the direction of the impact. In these embodiments, the first joining partner is heated directly by the laser, while the second joining partner is heated by heat conduction directly from the heated first joining partner, so that the second joining partner is indirectly heated by the laser.

During heating, the laser preferably has a constant distance from the second joining partner, while the first joining partner and the second joining partner are shifted towards one another via the joining path. Consequently, the laser is preferably not moved in the direction of the impact to the second joining partner during heating.

In preferred embodiments of the method according to the invention, the plastic of the first joining partner and the plastic of the second joining partner are each thermoplastic.

The first joining partner and the second joining partner are preferably made of the same plastic. But they can also consist of different plastics.

The plastic of the first joining partner and the plastic of the second joining partner each have a transmission coefficient for the radiation of the laser, which is preferably less than 0.6; more preferably less than 0.4.

The plastic of the first joining partner and / or the plastic of the second joining partner are preferably reinforced with glass fibers and / or provided with flame retardants and / or with dyes.

In preferred embodiments of the method according to the invention, the welded joint formed by solidification completely fills the joint area. It is preferably formed a continuous heat affected zone.

In preferred embodiments of the method according to the invention, the reservoirs are completely filled and molded after solidification, so that the first joining partner no longer has the tapering in the direction of the second joining partner cross-section, but the weld has the same thickness as the first joining partner or only a small Bead is present.

In preferred embodiments of the method according to the invention, the laser has radiation with a wavelength between 0.7 μm and 2.5 μm.

The heating of the first joining partner and of the second joining partner in the joint region with the laser is preferably carried out by quasi-simultaneous welding, by simultaneous welding or by contour welding.

The laser can also be guided by a sweep over the joint area or over the melting section.

Further advantages, details and developments of the invention will become apparent from the following description of a preferred embodiment of the invention, with reference to the drawing. Show it:

1 two joining partners, which are arranged according to a preferred embodiment of a method according to the invention in shock;

2 : the two in 1 joining partners shown after they have been connected according to the invention;

3 : one of the two in 1 joining partner shown in a representation from the front;

4 : the in 3 joining partners shown in a perspective view; and

5 : the in 3 joining partners shown in a further perspective view.

1 illustrates a preferred embodiment of a method according to the invention, by which a first joining partner 01 on a plastic and a second joint partner 02 be connected from a plastic cohesively. In particular, a moment of the method sequence according to the invention is shown, in which the first joining partner 01 and the second joining partner 02 prepared and placed on butt joint. The two joining partners 01 . 02 are at the shown embodiment is generally plate-shaped formed with a same thickness and are arranged according to the invention in a plane. According to the invention, the shape of the first joining partner deviates 01 in a melting section 03 from the plate shape. In the melting section 03 the first mating partner tapers 01 in the direction of the impact to the second joint partner 02 , This is indicated by the first joining partner 01 in the melting section 03 Beveled edges so that it is in the melting section 03 wedge-shaped with two sloping wedge sides 04 . 06 is trained. However, the two wedge side surfaces 04 . 06 different sizes, since they are at different distances from the abutting end of the first joining partner 01 kick off. The two wedge side surfaces 04 . 06 each have an inclination of about 45 ° relative to the main extension plane of the first joining partner 01 on. Between the wedge side surfaces 04 . 06 and the second joint partner 02 are reservoirs 07 formed, which are two-sided limited cavities.

According to the invention, a laser (not shown) on the region of the joint between the joining partners 01 . 02 directed. The laser is especially focused on the melting range 03 of the first joining partner 01 directed. The laser is in particular on the first wedge side surface 04 of the first joining partner 01 directed, which is the larger of the two reservoirs 07 limited. The laser becomes perpendicular to the main plane of extension of the first joining partner 01 aligned and parallel to the joint between the joining partners 01 . 02 moved back and forth.

The energy of the laser melts the first joining partner 01 in its melting range 03 , The heat is also on the second joint partner 02 transferred, so this also in his first joining partner 01 contacting area melts. The molten portions of the two joining partners 01 . 02 flow into each other. At the same time, the first joining partner 01 continued in the direction of the second joining partner 02 postponed. This will fill the two reservoirs 07 with melt of the two joining partners 01 . 02 , Also disappear the two reservoirs 07 partly by a change in the external shape of the two joining partners 01 . 02 , The area of the melt of the two joining partners 01 . 02 then has a similar outer shape as the two joining partners 01 . 02 on. Subsequently, the heating is terminated by the laser, so that the melt of the two joining partners 01 . 02 cools and solidifies.

2 shows the two in 1 joining partner shown 01 . 02 after the melt of the two joining partners 01 . 02 cooled and solidified. This has a welded connection 11 between the two joining partners 01 . 02 trained, which are the two joining partners 01 . 02 firmly and permanently connects. The two joining partners 01 . 02 form a unit that the plate shape of the two joining partners 01 . 02 having. Only in the area of the welded connection 11 is a small weld bead 12 trained, but if necessary, also completely by a forming means such. B. a transparent plate (not shown) can be avoided.

3 shows the in 1 shown first joint partner 01 in a representation from the front. In this illustration, in particular, the two different sized reservoirs 07 illustrated by a dashed line.

4 shows the in 3 shown first joint partner 01 in a perspective view. Also in this illustration are in particular the two different sized reservoirs 07 illustrated by a dashed line.

5 shows the in 3 shown first joint partner 01 in a further perspective view.

LIST OF REFERENCE NUMBERS

01

first joint partner

02

second joint partner

03

melting section

04

Wedge face

05

06

Wedge face

07

reservoir

08

09

10

11

welded joint

12

weld bead

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely 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.

Cited patent literature

• DE 19625873 A1 [0004]
• DE 4432081 A1 [0005]
• EP 0288884 A1 [0006]
• US 7681924 B2 [0007]
• WO 2012/152790 A1 [0008]
• WO 2008/116981 A2 [0009]
• WO 89/10231 A1 [0010]
• DE 939719 B [0011]
• EP 0662389 A2 [0012]
• EP 0882543 A2 [0013]
• EP 0997261 A1 [0014]
• EP 2196279 A2 [0015]
• JP 07-80940A [0016]
• WO 02/070236 A2 [0017]
• WO 2005/102671 A1 [0018]
• WO 95/26869 A1 [0019]
• DE 102011081554 A1 [0020]

Cited non-patent literature

• Klein, R .: "Laser Welding of Plastics", Wiley-VCH Verlag, Weinheim, 2011 [0002]
• Ehrenstein, Gottfried W .: "Manual Plastics Connection Technology", Carl Hanser Verlag, Munich, 2004, ISBN 3-446-22668-0 [0003]

Claims (10)

Method for connecting two joining partners ( 01 . 02 ) made of plastic, comprising the following steps: - providing an initial joining partner ( 01 ) made of a plastic and a second joining partner ( 02 ) made of a plastic; - Arrange the first joining partner ( 01 ) and the second joining partner ( 02 ) on impact, so that the first mating partner ( 01 ) and the second joint partner ( 02 ) are arranged abutting one another in a joint area; - heating of the first joining partner ( 01 ) and the second joining partner ( 02 ) in the abutting area with a laser, whereby the first mating partner ( 01 ) and the second joint partner ( 02 ) melt at least partially in the abutting area and flow into one another; and - cooling the first joining partner ( 01 ) and the second joining partner ( 02 ), whereby the first mating partner ( 01 ) and the second joint partner ( 02 ) solidify and in the joint area a welded joint ( 11 ) train; characterized in that the provided and arranged on impact first joint partner ( 01 ) within a fusion section ( 03 ) in the direction of the second joining partner ( 02 ) has tapered cross-section so that reservoirs ( 07 ) are formed laterally of the tapered cross-section, of the provided and arranged on impact second joining partner ( 02 ) and after heating the first joining partner ( 01 ) and the second joining partner ( 02 ) with melt of the first joint partner melted in the joint area ( 01 ) to fill. Method according to claim 1, characterized in that the cross-section of the first joining partner ( 01 ) on both sides of a main extension plane of the first joining partner ( 01 ) in the direction of the second joining partner ( 02 ) rejuvenated. A method according to claim 1 or 2, characterized in that in the direction of the second joining partner ( 02 ) tapering cross-section of the first joining partner ( 01 ) the shape of a blunt wedge with two oblique side surfaces ( 04 . 06 ), wherein the two side surfaces ( 04 . 06 ) of the wedge in each case one of two of the reservoirs ( 07 ) limit. Method according to claim 3, characterized in that the two side surfaces ( 04 . 06 ) of the wedge have different angles to an axis of the wedge and / or different lengths in the direction of the second joining partner ( 02 ), so that the two of the side surfaces ( 04 . 06 ) limited reservoirs ( 07 ) are different in size, with the laser on the larger of the two reservoirs ( 07 ). Method according to one of claims 1 to 4, characterized in that the provided and arranged on joint first joint partner ( 01 ) has an abutment surface with which it at the second joint partner ( 02 ) abuts. A method according to claim 5, characterized in that the abutment surface has a width which is between 20% and 90% of a thickness of the first joining partner provided ( 01 ) is. Method according to one of claims 1 to 6, characterized in that during and / or after the heating of the first joining partner ( 01 ) and the second joining partner ( 02 ) the first joining partner ( 01 ) and the second joint partner ( 02 ) are moved towards each other over a joining path. A method according to claim 7, characterized in that the joining path is shorter than the length of the taper of the cross section of the first joining partner ( 01 ) in the direction of the second joining partner ( 02 ). Method according to one of claims 1 to 8, characterized in that the laser on the tapered cross-section of the first joining partner ( 01 ). Method according to one of claims 1 to 9, characterized in that the reservoirs ( 07 ) are completely formed and filled after solidification.

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