Plastic workpiece and process for producing it

The present invention relates to a method of welding a workpiece, particularly a housing of an electric switch according to the preamble of claim 1, and a workpiece portion according to the preamble of claim 7.

The plastic housing of the electric switch can accommodate electrical components such as fixed contacts, switch contacts, and other components. The housing is generally formed from a plurality of housing portions having a complex spatial shape. The housings are assembled when the switch is assembled, and the housings often must be securely connected. Since such a connection must be made in line with the contour of the housing portion, it has the shape of a three-dimensional space.

It is known that housing portions are connected to each other by ultrasonic welding, especially when the housing needs to be sealed from the outside. In this case, there is a problem that the solder connection of the electric component and the electric component itself are destroyed by the ultrasonic vibration, and the switch becomes unusable. Therefore, there is a need for a method of welding the housing portion of the electric switch without adversely affecting the electrical components.

It is well known from German Patent Publication 3621030 that plastic films are welded together by a laser beam. For this purpose, the plastic films are stacked in layers. Next, the focused laser beam passes through the film, and the film is heated at the joint portion so as to be in a molten state, cooled, and then fixed at the joint portion.

Since the film is a thin part, it is possible to heat the entire joint part when the laser beam passes through it. This usually results in an acceptable welded connection between the films. For thick workpieces, such as electrical switch housings, however, only the surface of the workpiece can be heated by well-known joining methods, making it impossible to achieve a usable welded connection between the two workpieces. Especially in the case of the housing part of an electric switch for design reasons, the joint is often provided inside the housing. Such inner welded connections are clearly not possible with well-known joining methods.

Furthermore, the method of welding a plastic sheet by a laser beam is well known from EP-A2-0159169. In the case of this method, a second sheet is provided on the first sheet and is adapted to absorb the laser beam by using an additive in the plastic. Black dyes, often carbon black, are used as additives. Since the plastic of the second sheet does not contain additives, the second sheet allows the laser beam to pass through considerably.

Next, the laser beam acts on the second sheet, and after passing through the second sheet, it is absorbed by the first sheet, and as a result, the contact surfaces of the two sheets adjacent to each other are melted, and then They are combined with each other in the cooling process of.

In this method, since the second sheet cannot contain additives, it cannot be colored and is milky white, while the first sheet is colored with a black dye. The workpieces produced thereby are therefore formed from parts of very different colors, which impairs the overall visual impression. However, in the case of an electric switch housing, the entire housing needs to give a uniform visual impression, especially with respect to color. Further, the sheets shown in the publication form a plane that is welded to each other on the plane. However, in general, the housing portion is not limited to one surface because it has a complicated shape, especially in the case of an electric switch or the like, and the joint portion to which the housing portions are connected to each other must follow this shape. Nothing is said in the specification of the publication regarding the manufacture of joints in complex spaces. Therefore, well-known methods are not particularly suitable for welding the housing portion of an electric switch.

<p> The present invention designs a workpiece formed from a plurality of workpieces such that the workpieces can be connected to each other by a laser beam, especially at the junction in the inner three-dimensional space, and such a workpiece. Based on the purpose of specifying the manufacturing method of.</p>

<p> This object is achieved by a workpiece belonging to the feature of claim 1 and a method belonging to the feature of claim 7. In the present invention, the laser beam passes through the first workpiece portion substantially unimpeded at the position closest to the laser beam source and is significantly absorbed by the second workpiece portion, thereby causing two at the junction. Based on the concept that the workpiece is melted. For this purpose, the first workpiece portion is made to transmit the laser beam considerably, at least in the part where the laser beam is in contact, and the second workpiece portion is considerably laser beam by adding an additive at an appropriate ratio. Is made to absorb. Therefore, the first workpiece portion has a higher transmission coefficient and a lower absorption coefficient than the second workpiece portion. That is, the first workpiece portion has a higher transmission coefficient than the second workpiece portion, and the second workpiece portion has a higher absorption coefficient than the first workpiece portion. However, since both workpieces contain additives, they have the advantage of being opaque to light in the visible range of the human eye, thereby giving a substantially uniform impression. After welding, the individual workpieces are virtually indistinguishable visually.</p><p> Further improvements of the present invention are the gist of the dependent terms. In particular, the second workpiece can be configured to absorb the laser beam on the surface so that it can only pass through the second workpiece only slightly. Therefore, even low laser power gives good results during welding. The permeability coefficients of the two workpieces indicate the degree of transmission and the absorption coefficient indicates the degree of absorption, which can be adjusted by adding, for example, a pigment additive to the plastic. The first workpiece part is adjusted to a transmittance T of 60% or more and an absorption rate A of 30% or less, and the second workpiece part is adjusted to an absorption rate A of 90% or more, especially a very slight transmittance T. It was found to be convenient.</p><p> Especially for workpieces of complex shape, the joints are provided in a three-dimensional space, even inside the workpiece, so that the workpiece can be optimized for each intended use. In order to sufficiently seal the inside of the workpiece, the walls of the workpieces adjacent to each other can be overlapped, so that the critical parts such as corners and through holes are separated by a laser beam at the joint. It can be sufficiently joined by welding. The workpieces to be connected to each other can have overlapping joints of various shapes at the joint.</p><p> The degree of bonding of the joint can be further increased by applying pressure to the joint until it has cooled. The pressure preferably acts along the focal point of the laser beam, so that the transmission of the laser beam through the workpiece is not impeded. However, pressure can be made to act directly on the area of action of the laser beam by using a clamping means that allows the laser beam to pass through. Preferably, the pressure acts to track the movement of the laser beam along the junction. Such movement of the laser beam can be easily achieved in a spatially programmable manner, for example when a robot or multi-axis processor is used. In particular, segmental welding can be easily performed at individual positions of the workpiece. Further, the manufacturing method can be optimized by automatically controlling the operating parameters of the laser beam source by a method corresponding to the measurement process parameters at the junction such as pressure and temperature.</p><p> High quality welding is achievable by the present invention, especially when welding into overlapping or adjacent shapes by a laser beam, especially even thick wall workpieces, at least partially welded inside. The advantage of being done is achieved. Unlike conventional ultrasonic welding, the shape of the weld can be freely adapted to the design requirements. That is, spatial welding is possible in the housing if desired. Since the welding path can be formed by programming the beam path of the laser beam and moving the workpiece, it is possible to manufacture a variety of workpieces. The work piece portion can be welded only by heating, and no additional additive is required in actual welding. Waste is avoided, especially in the manufacture of electrical switches, as there is no need to worry about the destruction of electrical components.</p>

Preferred embodiments of the present invention are described in detail below and are shown in the drawings. FIG. 1 shows an outline of an apparatus for welding a workpiece portion by a laser beam by the method according to the present invention. The device comprises a laser beam source 1, eg, an Nd: YAG laser, a light outlet connected to the optical system 3 by a flexible light guide 2, so that the laser beam source 1 can be located in the desired spatial position. it can. The optical system 3 is provided on the workpiece holder 4 and can be moved by a control device by a drive device, for example, as indicated by the direction arrow 5 in FIG. Of course, the optical system 3 can also be designed to be movable.

The workpiece holder 4 is preferably provided with workpiece portions to be welded to each other, that is, parts of the housing 6, and the housing 6 is the housing of the electric switch in this embodiment. The housing 6 includes two housing portions, that is, a pot-shaped housing base 7 forming the second workpiece portion and a housing cover 8 which is the first workpiece portion. Both the housing base 7 and the housing cover 8 are made of plastic, preferably a thermoplastic. As shown in detail in FIG. 2, the housing base 7 has a shoulder 9 that surrounds it in an annular shape, on which the housing cover 8 is mounted. At the shoulder 9, the housing cover 8 is welded to the housing base 7 by a laser beam along a joint 10 that continuously surrounds the ring, so that the housing 6 of the electric switch is hermetically sealed, especially from dust. Has been done.

Further, as can be seen from FIG. 1, the housing cover 8 and the housing base 7 are heated by the laser beam 11. The laser beam is radiated from the optical system 3 to the housing 6 along the junction 10 so that the housing base 7 and the housing cover 8 are in a molten state at the junction 10. As a result, the housing base 7 and the housing cover 8 are joined at the joint portion 10 and solidified in the next cooling step to form a weld. Then, if necessary, annealing can be performed to reduce the welding stress at the joint portion 10. By moving the workpiece holder 4 and / or the optical system 3 or the laser beam source 1, a joint portion 10 is formed in the housing 6 which surrounds the housing 6 in an elongated ring shape. Where appropriate, the housing 6 can also be welded at individual locations, resulting in a non-contiguous but segmented cross-section joint. Preferably, in the case of sectional welding, since the welding stress is low, it is not necessary to perform annealing next.

By relatively moving the laser beam source 1 or the optical system 3 and the workpieces 7 and 8, the joint portion 10 can be provided in a three-dimensional space that can be arbitrarily oriented in the housing 6. For this purpose, for example, the workpiece holder 4 is designed as a multi-axis processor that is three-dimensionally movable according to arrow 5. Similarly, a robot can be used, or the optical system 3 can be moved. Since the desired spatial movement of the workpiece holder 4 is programmable, joint portions 10 each having a corresponding spatial shape are formed during welding. Preferably, particularly in the case of the electric switch housing 6, the complex shaped joint portion 10 can be formed to be easy to handle and flexible.

In particular, as shown in FIG. 2, for design reasons, the joint portion 10 is located inside the housing 6, and the joint portion 10 overlaps the shoulder 9 and has a joint. In a further embodiment shown in FIG. 4, adjacent overlapping joints 17 are formed on the housing cover 8 and the housing base 7. In the embodiment shown in FIG. 5, the housing base 7 and the housing cover 8 have a wedge-shaped overlapping joint 18. In these examples as well, the joint portion 10 is provided at least partially inside the housing 6.

In the embodiment shown in FIG. 6, a shoulder-shaped overlapping joint 19 is further provided. Workpieces 7 and 8 have shoulders 20 and 20 ́ protruding from the actual wall, respectively, and the joint 10 is provided at the transition between the protruding shoulders 20 and 20 ́. The laser beam 11 acts approximately perpendicular to the projecting shoulder 20 ́ on the opposite side of the projecting shoulder 20 ́ in this embodiment. Other shapes of shoulder-shaped joints are shown in Figures 7 and 8. In the case of the shoulder-shaped joint 21 of FIG. 7, the workpiece portion 7 is provided with a stepped receiving portion, and the wall of the workpiece portion 8 is inserted into the stepped receiving portion. Finally, in FIG. 8, the corresponding wall of the workpiece portion 8 is inserted into the staircase-shaped receiving portion provided in the workpiece portion 7 so as to form a shoulder-shaped joint 22.

Finally, the groove-shaped overlapping joint 23 shown in FIG. 10 also exhibits an excellent sealing effect as a labyrinth seal against the intrusion of dust into the housing 6. For this purpose, a ridge 25 provided corresponding to the wall of the workpiece portion 7 is fitted in the groove 24 formed in the wall of the workpiece portion 8. The laser beam 11 contacts the surface of the workpiece portion 8 approximately perpendicularly in the region of the groove 24, thereby forming a joint portion 10 between the ridge 25 and the groove 24 on the side of the workpiece portion 8 facing this surface. Will be done.

As shown in the cross-sectional view of the somewhat intricately designed workpiece portion 6 of FIG. 9, the outer shell of the wall 26 in three-dimensional space is adapted for each intended use. Such a complex housing 6 is used, for example, in an electric switch of an electric tool, in which an empty body 27 is defined by a wall 26 of a workpiece portion 8 to accommodate a functional portion of the electric switch. In order to protect the empty body 27 from dust, the ridge 25 of the workpiece portion 7 is fitted into the groove 24 provided in the wall 26 as described with respect to FIG.

Further, as shown in FIG. 9, since the groove 24 is provided with the sectional joint portion 28, the two workpiece portions 7 and 8 are welded on the surfaces connected to each other. The compartmentalized joint 28 has a hook-shaped or zigzag-shaped path, which is formed by moving the laser beam 11 and the workpieces 7, 8 relative to each other in a programmable three-dimensional space. The joint 28 does not consist of continuous spaces, but individual compartments. These are especially the corners of the wall 26 or the bends where the direction of welding suddenly changes. Further, the segmented joint portion may be provided in a region such as a penetrating portion or the like where, for example, a shaft, a push rod, or the like, which is not shown, rushes into the empty body 27 of the housing 6 from the outside. Such areas need to be specifically sealed, but are securely sealed by the compartmentalized joints 28.

The individual compartments of the joint 28 are simply linear and do not need to be sealed in a very complicated way. In this case, it is sufficient to overlap the groove 24 and the ridge 25 on the wall 26 of the workpieces 7 and 8 without welding, and a sealing groove is formed. In order to support this, by further providing a snap connection 29 or the like between the sections of the joint portion 28, the connection surfaces of the walls 26 of the two workpiece portions 7 and 8 are sealed to each other in these regions. Be pressed. In this embodiment, since only the partitioned joint portion 28 is provided, the time required for welding the workpiece portions 7 and 8 is reduced.

In order to sufficiently heat the junction 10, the housing base 7 and the housing cover 8 differ in their properties with respect to the spectrum of the laser beam 11 at least in a small area. For example, the transmission coefficient of the laser beam 11 is larger in the housing cover 8 than in the housing base 7, while the absorption coefficient is larger in the housing base 7 than in the housing cover 8. The two workpieces, the housing base 7 and the housing cover 8, and the optical system 3 of the laser beam source 1 are lasered at the first coupling portion 12 opposite the junction portion 10 as shown in FIG. The beams 11 are located relative to each other so that they hit the housing cover 8. The first workpiece portion, that is, the housing cover 8, has a high transmission coefficient, so that the spectrum of the laser beam 11 is transmitted at least partially in the region from the first coupling portion 12 to the bonding portion 10. As a result, at least a part of the laser beam 11 passes through the housing cover 8. As shown in FIG. 3 at the second coupling portion 13, the transmitting portion of the laser beam 11 penetrates into the second workpiece portion, that is, the housing base 7. As shown, the first coupling portion 12 and the second coupling portion 13 are substantially located on the straight line formed by the laser beam 11. In particular, this straight line is almost perpendicular to the connecting portions 12 and 13.

Due to its high absorption coefficient, the housing base 7 is adapted to absorb the spectrum of the laser beam 11 at least partially in the region of the second coupling portion 13 of the junction portion 10. As a result, the housing base 7 is heated in the absorption region 14 by at least a portion of the laser beam 11 in contact with the second coupling portion 13. In this example, the wavelength of the laser beam 11 that is made or used so that the housing base 7 absorbs on the surface of the second coupling portion 13 is such that the laser beam 11 is slightly, preferably only a few microns, on the housing base 7. It suffices if it is selected to penetrate, so that the absorption region 14 is formed only on the surface of the housing base 7 as shown in FIG. Since heat is transmitted from the absorption region 14 to the adjacent housing cover 8, the housing cover is similarly heated in the heat conductive region 15. By heating the absorption region 14 and the heat conduction region 15, the plastic is melted, whereby the joint portion 10 solidified after cooling is formed in common with these two portions 14, 15.

As mentioned above, the housing 6 is made of plastic. The use of styrene-acrylonitrile copolymers, polyamides, etc. has been proven to be particularly suitable as housings for electrical switches in this example. Pigments, glass fibers, etc. are used in plastics to adjust the partial permeability of the housing cover 8 and the partial absorption of the housing base 7 with respect to the spectrum of the laser beam 11, ie, the transmission coefficient and the absorption coefficient. In this case, the adjustment is performed by making the ratio of the additive in the two workpiece portions 7 and 8 different. The ratio is selected so that the reflectances of the two workpieces 7 and 8 with respect to the spectrum of visible light are substantially the same. In particular, it was found that it is preferable to increase the absorption coefficient of the housing base 7 with a black pigment. By testing the plastics of the molds described above, 1% to 2% of the pigment was added to the partially absorbent plastic of the housing base 7, while a lower percentage of the pigment was added to the plastic of the partially permeable housing cover 8. Or, in special cases, it has been shown that it is convenient not to add pigments. Therefore, the two workpieces 7 and 8 are substantially impermeable to visible light and are colored black to give a nearly uniform visual effect. Therefore, fortunately, the two workpieces 7 and 8 of the housing 6 give the same visual impression, and it is not visible that the adjustment is changed for each plastic.

The advance speed of the housing 6 with respect to the optical system 3 was tested at 3 m / min with a 10 W output Nd: YAG laser that emits a laser beam at a wavelength of about 1.06 μm, which is particularly suitable for the plastics of the type described above. It was found that good welding results can be obtained by maintaining the above parameters. For the spectrum of the Nd: YAG laser beam, the housing cover 8 must have a transmittance T of 60% or more, an absorption rate A of 30% or less, and a reflectance R of 20% or less if necessary. .. In addition, the housing base 7 must have an absorption rate of 90% or higher, in particular a negligible transmittance T and, if necessary, a reflectance R of 10% or lower. This percentage relates to the laser beam 11 in contact with the coupling portions 12, 13 in the case of this example. In each case, T + A + R = 100% It should also be emphasized that the proportion of laser beam 11 reflected by each of the joints 12 and 13 does not have much effect on the heating of the joint 10 and should be kept as low as possible by adjusting the plastic. There must be.

To improve the quality of the weld, pressure can be applied to the joint portion 10 when or after the joint portion 10 is heated and melted by the laser beam 11. For this purpose, the pressure roller 16 acts on the top of the housing cover 8 in the region of the joint 10 as shown in FIG. The pressure roller 16 is adapted to track the laser beam 11 as the workpiece holder 4 advances in the direction arrow 5'. Therefore, the pressure of the pressure roller 16 acts until the joint portion 10 cools, thereby preventing the escape of dissolution from the joint portion 10 and preventing the risk of forming voids in the joint portion 10. As shown in FIG. 1, this pressure acts along the focal point of the laser beam 11 so that the laser beam 11 is unobstructed at the coupling portion 12 of the housing cover 8.<u style="single">I.</u>

Weld quality is further positively affected in that the operating parameters of the laser beam source 1 are continuously and automatically controlled as a function of the process parameters of the joint portion 10. These process parameters are temperature, pressure, etc. The operating parameters of the laser beam source 1 are continuously measured, and if there is a deviation from the set value, it is changed according to the deviation until the desired set value is reached again.

The present invention is not limited to the examples described and illustrated. Rather, it includes all development by those skilled in the art within the scope of the invention concept. For example, the present invention is not only used in the manufacture of electric switches, but can also be used in any desired workpiece, housing, etc. made of plastic for, for example, household items, packaging, etc.

<figref num="1">Schematic of a welding device for an electric switch housing.</figref><figref num="2">Longitudinal sectional view of the housing.</figref><figref num="3">Enlarged view of part X in Fig. 1.</figref><figref num="4">Longitudinal sectional view of a portion of the housing of a further embodiment.</figref><figref num="5">Longitudinal sectional view of a portion of the housing of a further embodiment.</figref><figref num="6">Longitudinal sectional view of the wall of the housing of another embodiment.</figref><figref num="7">Longitudinal sectional view of the wall of the housing of yet another embodiment.</figref><figref num="8">Longitudinal sectional view of the wall of the housing of another embodiment.</figref><figref num="9">Sectional view of the housing in a complex space design.</figref><figref num="10">Sectional view along line 10-10 in Figure 9.</figref>

Code description

1: Laser beam source 2: Light guide 3: Optical system 4: Workpiece holder 5, 5 ́: Direction arrow 6: Housing 7: Housing base (second workpiece part) 8: Housing cover (first workpiece part) 9: Shorda 10: Joint 11: Laser beam 12: First joint part 13: Second joint part 14: Absorption area 15: Heat conduction region 16: Pressure roller 17: Adjacent overlapping joint (further shape) 18: Wedge-shaped joint (further shape) 19: Shoulder-shaped overlapping joint (further shape) 20, 20 ́: Protruding shoulder 21: Shoulder-shaped joint (further shape) 22: Shoulder-shaped joint (further shape) 23: Grooved overlapping joint 24: Groove 25: Ridge 26: Wall 27: Empty body 28: Partitioned joint 29: Snap connection