WO2022063982A1

WO2022063982A1 - Method and device for welding plastic parts

Info

Publication number: WO2022063982A1
Application number: PCT/EP2021/076353
Authority: WO
Inventors: Steffen BOEHLER; Guenter BOEHLER
Original assignee: Gmb Kunststoffteile Gmbh
Priority date: 2020-09-28
Filing date: 2021-09-24
Publication date: 2022-03-31
Also published as: DE102020125290B4; DE102020125290A1; DE202021101884U1

Abstract

The invention relates to a method and a device for welding plastic parts (10), in which two plastic parts (10) to be welded to each other are welded to each other by means of two mutually facing joining faces (14), wherein at least one of the two joining faces (14) is heated, and the two plastic parts (10) are then welded to each other by pressing the joining faces (14) against each other, wherein the at least one joining face (14) is subjected to and heated by a hot gas flow, which is directed onto the at least one joining face (14) through a recess (38) in a gas-guiding block (26), said recess extending along the joining face (14).

Description

Process and device for welding plastic parts

The invention relates to a method for welding plastic parts, in which two plastic parts to be welded to one another are welded to one another by means of two joining surfaces facing one another, with at least one, preferably both, of the joining surfaces being heated and the two plastic parts then being joined together by pressing the joining surfaces together are welded, with the joining surfaces being flown and heated by means of a hot gas stream.

The invention also relates to a device suitable for carrying out the method for welding plastic parts.

A method and a device for welding plastic parts are known from DE 100 19 300 A1. Here, a tool consisting of a heating plate with welding blocks attached to the top and bottom is used, with the tool being inserted between the plastic parts to be joined, the plastic parts being heated by radiant heat with the aid of the tool without contact, while at the same time a hot stream of inert gas is applied is guided to the workpiece area to be welded. The plastic parts are heated to a temperature above the softening point so that they become doughy and can be pressed together and thus welded after the tool has been removed.

[0004] In principle, plastic parts can be welded to one another without contact using such a welding process. Since the welding is contact-free, sticking of radiators is avoided. By using radiant heat and an additional stream of hot inert gas to heat the plastic parts should result in accelerated heating and good heat distribution should be achieved.

In practice, however, it has been shown that welding plastic parts along the joining surfaces requires a considerable heating-up time for each of the plastic parts.

Since such plastic parts are often used in large series, for example in automobile construction, particularly short cycle times are of considerable importance.

Furthermore, it is known from use in the prior art to heat the joining surfaces of the plastic parts to be welded together by means of a hot gas stream, which is emitted from a distributor via a large number of tubes arranged essentially parallel to one another, the outlet openings of which are approximately uniformly spaced in front the joint surfaces end, is directed to the joint surfaces.

Although this enables relatively uniform heating of the joining surfaces, there are still considerable heating-up times for the plastic parts to be welded.

It is known from WO 2020/164978 A1 to arrange mutually parallel angles on a surface facing the joining surface in order to form a channel into which the hot gas is introduced via a line. This should result in a shorter heating-up time for the plastic parts to be welded.

However, this arrangement is also in need of improvement. In particular, it is not possible to realize a curved or complex-shaped duct for guiding the hot gas by means of angles.

[0011] DE 3828728 A1 discloses a device and a method for welding multi-layer webs of thermoplastic material as they run over a deflection roller is known. The device consists of a housing that can be set against the deflection roller, is curved approximately concentrically to it and encloses it over part of its circumference when it is set, which is provided with a longitudinal hot air duct curved in the same direction, which has an inlet for blowing in warm air and in its the housing wall facing the deflection roller has a multiplicity of outlet bores.

The known device and the known method can be used specifically for welding multi-layer webs of plastic, but are not suitable for welding together dimensionally stable plastic parts.

Finally, EP 3453 522 A1 discloses a device and a method for welding hybrid parts or plastic parts, the joining surfaces to be welded to one another being heated by means of hot gas nozzles. However, large distances between the hot gas nozzles and the joining surfaces to be heated result in high thermal losses, so that long cycle times are required and high energy losses occur.

Against this background, the invention is based on the object of specifying a contactless method for welding plastic parts, in which two plastic parts to be welded to one another are welded to one another by means of two joining surfaces facing one another and the joining surfaces are heated to the desired target temperature in takes place in as short a time as possible. In this case, it should preferably also be possible to weld curved or complicatedly shaped joining surfaces in a simple manner.

[0015] Furthermore, a device is to be specified which is suitable for carrying out this method.

[0016] This object is achieved by a method for welding plastic parts, in which two plastic parts to be welded to one another are joined by means of two joining surfaces facing one another, which are preferably designed to be complementary to one another. are welded to one another, with at least one of the two joining surfaces being heated and the two plastic parts then being welded to one another by pressing the joining surfaces together, with the at least one joining surface being heated by means of a stream of hot gas which flows through a channel-shaped recess extending along the joining surface of a gas guide block is directed onto the at least one joining surface, the hot gas stream being supplied through a plurality of supply channels in the gas guide block opening out at an angle into the recess, and the gas guide block being formed at least in segments in one piece with the channel-shaped recess.

The object of the invention is also achieved by a device for welding plastic parts along joining surfaces to be welded to one another with a heating block from which hot gas can be fed to the joining surface of at least one of the plastic parts, with a gas guide block extending along the joining surface has a channel-shaped recess in the form of a channel extending along the joint surface, a plurality of supply channels for supplying hot gas being provided in the gas guide block, which feed channels open at an angle into the channel-shaped recess, the gas guide block being formed in one piece with the channel-shaped recess, at least in segments.

The object of the invention is completely solved in this way.

According to the invention, the joining surface is heated by means of a hot gas stream which is directed through a recess in a gas guide block extending along the joining surface onto the at least one joining surface. As a result, the hot gas flow is concentrated on the joint surface, which leads to a considerable reduction in the heating-up time and enables energy-saving operation.

[0020] Due to the concentration of the hot gas stream on the joining surface that is actually to be heated, unintentional heating of surrounding parts is significantly reduced, so that the risk of damage is reduced. Since the gas guide block together with the channel-shaped recess according to the invention at least consists of one piece in segments and can be machined in a suitable manner by milling and/or drilling, the feed channels through which the hot gas is conducted into the recess can be arranged precisely on the gas guide block, with complexly shaped joining surfaces also being able to be realized.

Overall, this results in a significantly simplified and more reliable construction and a significantly reduced heating time, even if the joining surfaces are complicated in shape.

In a preferred development of the method according to the invention, the bottom of the recess has a concavely curved shape towards the outside.

[0023] As a result, the supply of the hot gas is further concentrated in the direction of the joining surface to be heated.

In a preferred development of the invention, the recess has a substantially U-shaped cross section.

[0025] This results in particularly good adaptation to the part to be heated and thus particularly rapid heating.

According to a further embodiment of the invention, the recess is three-dimensionally curved.

In this way, heating of three-dimensionally curved joining surfaces can be achieved.

For this purpose, first bore sections can be provided in the gas guide block, which essentially extend in an extension of the axial direction of the opening tubes and which are connected to the recess of the gas guide block via second bore sections extending at an angle thereto. In this way, the supply of hot gas in a three-dimensionally curved recess of the gas guide block is made possible in a simple manner.

In a further embodiment of the invention, the guide block consists of aluminum or an aluminum alloy and the heating block consists of an iron alloy, preferably steel.

Since in the recess of the gas guide block a temperature that is about half as high (e.g. in the range of about 200° C.) as in the area of the heating block from which the hot gas is supplied (e.g. about 400° C.) can be applied to this In this way, the thermal expansion of the different materials (aluminum or steel) can be adjusted, since the coefficient of expansion of aluminum is about twice that of steel. In addition, aluminum is a particularly good conductor of heat and thus supports uniform heating of the joint surface to be heated.

In a further embodiment of the invention, the heating block is connected to the supply channels in the gas routing block via a plurality of tubes, the tubes preferably extending essentially parallel to one another.

[0033] This enables a simplified construction.

[0034] If tubes used for gas supply are not precisely aligned with associated bores in the gas guide block, this can be tolerated to a certain extent.

In addition, it is avoided that the direct supply of hot gas via tubes to the joining surfaces used up to now in the prior art has to be adjusted by hand by bending the tubes in order to compensate for errors, as was previously necessary in the prior art. In the prior art, manual bending of the tubes resulted in tubes that were imprecise and sometimes wavy in the area of their mouths. According to a further embodiment of the invention, the tubes are attached to the heating block and preferably engage in the supply channels of the gas flow block with play.

[0037] On the one hand, this ensures that the hot gas is guided reliably into the gas guide block and into the channel-shaped recess. On the other hand, the addition of a clearance (e.g. an increase in diameter by about 0.2 mm) ensures sufficient tolerance to allow easy assembly without manual bending of the tubes.

According to a further embodiment of the invention, the bottom of the recess has a concave shape with respect to the joining surface.

According to a further embodiment of the invention, the recess has an essentially U-shaped cross section.

[0040] These measures result in a particularly good adjustment for a concentration of the hot gas for rapid heating of the joining surface.

In an additional development of the invention, individual segments extend over a length of up to approximately 150 mm, preferably up to approximately 100 mm, in the direction of the at least one joining surface.

In this way, thermal stresses can be compensated for by small gaps between adjacent segments if such remain as a result of remaining differences between the thermal expansion coefficients of the materials and not completely precise matching in the different expansion coefficients.

[0043] According to a further embodiment of the invention, the recess is three-dimensionally curved, first bore sections being preferably provided in the gas routing block, which are essentially in an extension of the axial direction. extending in the direction of the opening tubes and which are connected to the recess of the gas guide block via the second bore sections extending at an angle thereto.

In this way, three-dimensionally curved joining surfaces can also be heated in a simple manner via three-dimensionally appropriately adapted recesses in the gas routing block.

It goes without saying that the features of the invention mentioned above and those yet to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the invention.

Further features and advantages of the invention result from the following description of preferred exemplary embodiments with reference to the drawing. Show it:

1 shows a partial cross-section through a plastic part which consists of two individual parts which each have joining surfaces running in the circumferential direction, the two individual parts being placed one on top of the other with their mutually complementary joining surfaces along which welding is to take place;

FIG. 2 shows a partial cross-section through a plastic part according to FIG. 1, in which the joining surfaces are formed in a sawtooth-like manner for the purpose of enlarging the surface;

FIG. 3 shows a partial cross section through a plastic part according to FIG. 1 , in which the joining surfaces are corrugated for the purpose of enlarging the surface;

4 shows a longitudinally sectioned perspective view through a device for heating a plastic part, which is here arranged at a distance from the device; 5 shows a partial cross-section through the gas routing block with an associated heating block and an associated plastic part to be heated, and FIG

6 shows a partial cross section through a modified embodiment of the device according to the invention, the gas routing block being three-dimensionally curved in order to be able to heat a plastic part with a three-dimensionally curved joining surface.

Fig. 1 shows a partial cross-section through a plastic part, which consists of two individual parts 10, 12, each having a peripheral joint surface 14, 16 on which welding can take place. The two joining surfaces 14, 16 are designed to be complementary to one another. For welding, both joining surfaces are heated on a heating device until they become doughy and can then be welded to one another by pressing them together.

2 and 3 show alternative designs of the joining surfaces with a sawtooth-shaped structure for the plastic parts 10a, 12a according to FIG. 2 and with wavy shaped joining surfaces 14, 16 for the plastic parts 10b, 12b according to FIG. 3.

[0049] Compared to a planar joining surface according to FIG. 2, the outer surface in this area is enlarged by a factor of about 2. In some cases, such configurations of joining surfaces are used in order to bring about a reduction in the heating-up time.

4 shows a device according to the invention for heating the joining surface of a plastic part by means of hot gas and is denoted overall by the number 20 .

An associated plastic part 10, whose joining surface 14 can be heated with this device 20, is shown at a distance from it. This is an oval plastic part, only the first plastic part 10 being shown here. which is to be welded together with the second plastic part 12 complementary thereto.

It goes without saying that the joining surfaces of the plastic parts 10, 12 or 10a, 12a or 10b, 12b to be welded together can have any shape, in particular can be three-dimensionally curved.

The elevations and depressions of the joining surfaces then preferably extend along the longitudinal direction of the joining surfaces, so that mutually complementary structures result in elevations or depressions facing one another, which intermesh when the heated plastic parts are subsequently joined.

According to the invention, the joining surface on each of the plastic parts is heated by means of a stream of hot gas which is directed from the associated device in a targeted manner onto the joining surface. According to the invention, a gas routing block is used for this purpose, in which a recess is provided which extends along the joint surface and through which the hot gas flow is concentrated onto the joint surface, as will be explained in more detail below with reference to FIG.

The device 20 has a heating tool 34 which can be heated by means of electrical heating elements 30 . A plate 36 in which cavities 28 are provided is arranged on the heating tool 34 . Lines 32 run through the cavities 28 and are provided with radial outlet openings from which supplied compressed air can escape into the cavities 28 . Furthermore, there is a quartz sand filling in the cavities 28, through which the heat transfer surface for heating the compressed air is further increased.

The plastic part 10 to be heated is placed on the device 20 by means of a handling device and can then be heated to the target temperature in a short time by hot air. Heated compressed air passes from the cavities 28 into a circumferential annular distribution channel 29 which is formed in a heating block 22 placed thereon. From the distribution channel 29, the hot gas goes directly into the tube 24 and flows from there into a gas guide block 26 with a U-shaped recess 38, as will be explained in more detail below with reference to FIG.

According to FIG. 5, the gas guide block 26 is made in one piece from a block and preferably consists of an aluminum alloy. A recess 38 with a preferably U-shaped cross section is provided in the gas routing block 26 and extends along the joining surface 14 to be heated. The plastic part 10 to be heated can preferably protrude with its joining surface 14 into the recess 38 during the heating process.

The gas routing block 26 is screwed to the heating block 22 via spacers 41 (not shown in FIG. 4). The assigned tubes 24, which are held in the heating block 22 and are supplied with hot gas from the distribution channel 29, end directly at the gas routing block 26. In the gas routing block 26, assigned bores 39 are provided, through which the hot gas flows from the tubes 24 into the recess 38. The bores end at an angle, preferably essentially at right angles, in the recess 38.

The contour of the gas guide block 26 and the recess 38 provided therein is adapted to the course of the joining surface 14 of the plastic part 10 to be heated, so that the hot air supplied directly onto the joining surface to be heated

14 is concentrated.

Due to the shape of the recess 38 and the relatively small gap between the recess 38 and the joining surface 14, the heating time can be significantly reduced compared to conventional heating by means of hot air escaping from tubes, for example from 25 seconds when using tubes to less than

15 seconds using the gas guide block according to the invention. The heater block 22 is typically made of steel, while the gas guide block 26 is typically made of an aluminum alloy. The temperature of the distribution channel 29 is significantly higher than the temperature in the area of the recess 38 of the gas routing block 26. While the temperature in the distribution channel 29 is, for example, about 400° C., the temperature of the gas routing block 26 in the area of the recess 38 is, for example, about 200° C. The different materials - aluminum for the gas guide block 26 and steel for the heating block 22 - are used to compensate for these temperature differences. Since the expansion coefficient of aluminum is about twice as high as that of steel, at twice the temperature in the area of the heating block, the thermal expansion of the heating block on the one hand and of the gas routing block 26 on the other is about the same. Shifts in the tubes 24, which are fixed in the heating block 22 and engage in the associated bores 39 in the gas routing block 26 with a play of 0.2 mm, for example, are minimal in this way and can be tolerated.

If larger plastic parts are to be heated, the gas guide block 26 is composed of several segments. In this case, individual segments preferably have a size of up to approximately 100 mm and are then joined to the next segment in each case via a small gap. The gaps allow further compensation for different thermal expansions.

If three-dimensionally curved plastic parts with three-dimensionally curved joining surfaces are to be heated, this is also possible using the device according to the invention. The gas routing block 26 is correspondingly provided with a three-dimensionally curved recess 38 which is adapted to the three-dimensionally curved joining surface of the plastic part to be heated.

As shown in FIG. 6, the small tubes 24 provided for supplying the hot gas run at a uniform distance from the hot gas block. The bores in question, from which the hot air supplied via the tubes 24 reaches the recess 38, are advantageously composed of two bore sections. In this case, a first bore section 42 runs in the axial direction of an associated tube 24, while a second one arranged at an angle thereto Bore portion 44 opens into the recess 38 at the desired location. This is preferably done approximately at right angles.

In this way, three-dimensionally curved joining surfaces can also be heated via a suitable gas guide block 26 .

Claims

Method for welding plastic parts (10, 12; 10a, 12a; 10b, 12b), in which two plastic parts (10, 12; 10a, 12a; 10b, 12b) to be welded together are joined by means of two joining surfaces (14, 16) facing each other. , which are preferably designed to be complementary to one another, are welded together, with at least one of the two joining surfaces (14, 16) being heated and the two plastic parts (10, 12) then being welded together by pressing the joining surfaces (14, 16) together, with the at least one joining surface (14, 16) is heated by means of a hot gas stream which is directed through a channel-shaped recess (38) of a gas guide block (26) extending along the joining surface (14, 16) onto the at least one joining surface (14, 16). , wherein the hot gas stream is fed through a plurality of supply channels (39; 42, 44) opening at an angle into the recess (38) in the gas guide block (26), and wherein the gas guide block (26) is at least t is formed in one piece with the channel-shaped recess (38) in segments. Method according to Claim 1, in which the hot gas stream is fed into the feed channels (39; 42, 44) in the gas guide block (26) via a plurality of small tubes (22). Method according to Claim 1 or 2, in which the hot gas stream is supplied via a gas guide block (26) in which the recess (38) has an outwardly concavely curved shape at its base (40). Method according to Claim 3, in which the hot gas stream is supplied via a gas guide block (26) in which the recess (38) has a substantially i-shaped cross section. Method according to one of the preceding claims, in which the hot gas stream is supplied via a gas guide block (26) in which the recess (38) is three-dimensionally curved. Method according to Claim 5, in which the hot gas stream is supplied via a gas guide block (26) in which first bore sections (42) are provided which extend essentially in an extension of the axial direction of tubes (24) over that extending at an angle thereto second bore sections (44) are connected to the recess (38) of the gas guide block (26). Device for welding plastic parts (10, 12; 10a, 12a; 10b, 12b) along joining surfaces (14, 16) to be welded to one another, which are preferably designed to complement one another, with a heating block (22), from the hot gas to the joining surface (14, 16) at least one of the plastic parts (10, 12; 10a, 12a; 10b, 12b) can be fed, with a gas guide block (26) extending along the joining surface (14, 16) having a channel-shaped recess (38) in Has the form of a channel extending along the joining surface (14, 16), a plurality of supply channels (39; 42, 44) for supplying hot gas being provided in the gas guide block (26) and opening at an angle into the channel-shaped recess (38), wherein the gas routing block (26) is formed in one piece with the channel-shaped recess (38), at least in segments. Device according to Claim 7, in which the heating block (22) is connected to the supply channels (39; 42, 44) in the gas guide block (26) via a plurality of tubes (22), the tubes (22) preferably being substantially parallel to one another extend. Device according to Claim 7 or 8, in which the gas guide block (26) together with the channel-shaped recess (38) is produced at least in segments from one block, preferably as a milled part and/or drilled part. Device according to one of Claims 7 to 9, in which the gas guide block (26) consists of aluminum or an aluminum alloy and the heating block (22) consists of an iron alloy, preferably steel. 16 Device according to one of Claims 8 to 10, in which the small tubes (22) are fastened to the heating block (22) and preferably engage with play in the feed channels (39; 42, 44) of the gas guide block (26). Device according to one of Claims 7 to 11, in which the recess (38) has an outwardly concavely curved shape at its base (40), the recess (38) preferably having a substantially U-shaped cross section. Device according to one of Claims 7 to 12, in which the individual segments extend over a length of up to about 150 mm, preferably of up to about 100 mm. Device according to one of Claims 7 to 13, in which the recess (38) is three-dimensionally curved. Device according to Claim 14, in which first bore sections (42) are provided in the gas guide block (26), which essentially extend in an extension of the axial direction of the small tubes (42) that open out, and the second bore sections (44) extending at an angle thereto with the Recess (38) of the gas guide block (26) are connected.