Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2002-05-21
2004-10-12
Aftergut, Jeff H. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S293000, C156S294000
Reexamination Certificate
active
06802929
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to a process for transmission laser welding of plastic parts.
BACKGROUND OF THE INVENTION
Electrical devices often comprise a plastic housing, in which the electrical components are accommodated. Such housings are generally made of a plurality of plastic parts, which are put together during the assembly of the electrical device, and often a solid connection between the housing parts is desired.
In order to solidly connect these housing parts together, various techniques may be employed. For example, ultrasonic welding is a technique which allows to hermetically seal plastic housings. However, it is disadvantageous since solder connections on the electrical components and also the components themselves may be destroyed on account of the ultrasonic vibrations, ultimately making the electrical device unusable.
When the housing parts have a rotational symmetry, it is possible to use a friction welding process. This technique is however constraining, as the arrangement of the electrical components within the housing must be such as to avoid any rubbing of an electrical component against a moving housing part during the welding process. This means that some air gaps must be provided at some locations, which in some cases, depending on the type of electrical device, may be disadvantageous. For example, in the case of a magnetic sensing device, it is desirable that the magnetic sensor be in close contact with the housing wall for sensitivity reasons.
In U.S. Pat. No. 5,893,959 a method for sealing a housing of an electrical switch by means of transmission laser welding is described. The housing is composed of two housing parts such as a pot-shaped housing base and a housing cover. The housing base has an annularly surrounding shoulder on which the housing cover is placed, whereby a continuous annular joining zone exists between the housing base and the housing cover. The housing cover is essentially transparent for the spectrum of the laser source whereas the housing base is essentially absorbent for the spectrum of the laser source. In order to seal the housing, a laser beam is directed to impinge on the shoulder of the housing base, through the housing cover, along the annular joining zone to form a weld.
Such a method of transmission laser welding is not damaging to the electrical components and does not require a special arrangement of the components with regard to the housing parts. However, it shall be noted that the housing parts being welded must be in close contact with each other. Therefore, it is preferable to apply a pressure onto the joining zone, in particular for avoiding the formation of voids. As described in U.S. Pat. No. 5,893,959, it is possible to use clamping means which are transparent to the laser beams, with the result that the action of pressure can be brought to bear directly in the region of action of the laser beams. The use of such clamping means however complicates the welding process, as it must be installed and removed for each housing to be welded. Furthermore, the use of clamping means is particularly inconvenient when welding together parts having a non-planar geometry.
OBJECT OF THE INVENTION
The object of the invention is to provide a process of transmission laser welding of plastic parts, wherein a good quality weld can be achieved without clamping means, also with plastic parts having a non planar geometry. This is achieved by a process of transmission laser welding as claimed in claim
1
.
SUMMARY OF THE INVENTION
According to the invention, a process of transmission laser welding is proposed, in which a first plastic part and a second plastic part that can be at least partially received in the first plastic part are welded together. It shall be appreciated that the first plastic part and the second plastic part are formed in such a way that upon introduction of the second plastic part into the first plastic part, they are connected by means of an interference fit. Accordingly, the first and second plastic parts are thus first connected by at least partially inserting the second plastic part into the first plastic part, whereby at least one contact zone between the second plastic part and the first plastic part is formed as a result of the interference fit. According to an important aspect of the invention, a laser beam is then directed to impinge on the second plastic part, through the first plastic part, along the at least one contact zone to form a weld.
A great advantage of the process of the invention is that at the contact zone pressure forces due to the interference fit exist, which cause an outer surface portion of the second plastic part and an inner surface portion of the first plastic part to be pressed against each other. Hence, an action of pressure exists directly in this inner contact zone where the welding is to be effected and there is no need for external clamping means for pressing the two plastic parts against each other during the welding process. Moreover, these pressure forces at the contact zone will generally increase during the welding, due to thermal expansion of the plastic materials. As a result, an intimate contact is ensured at the contact zone, during the whole welding process, thereby avoiding the formation of voids in the weld. It follows that high quality welds can be obtained, whereby the welds may also provide an airtight and watertight sealing. Besides, the present process allows to assemble and adjust the plastic parts in their final positions with precision, before the laser welding step. Indeed, the interference fit keeps the two plastic parts in place, without specific hold means. This obviously simplifies the welding process. Furthermore, in case the surfaces in the contact zone are not exactly complementary, as well as in case of burrs on these surfaces, the interference fit will tend to cause the plastic parts to adapt to the shapes of each other. This effect as well as plastic expansion at the weld allow to obtain a uniform weld.
The present method thus provides a process which allows to obtain good quality welds without clamping means. Further benefits of the present process are: (1) precise and contactless heat transmission with improved control of temperature in the heated zones; (2) high and economically interesting welding speeds; (3) possibility of welding parts with different stiffnesses and viscosities.
As the laser beam has to penetrate through the first plastic part to reach the contact zone and heat up the second plastic part, it is clear that the first plastic part should be more transmitting, respectively less absorbing, than the second plastic part for the spectrum of the laser beam, at least in the regions touched by the laser.
In a preferred embodiment, the first plastic part comprises a tubular shell and the second plastic part comprises an insert element that can be at least partially inserted into the tubular shell. Moreover, the insert element and the tubular shell are formed in such a way as to provide the interference fit connection, whereby the at least one contact zone is formed between the insert element and the tubular shell. Hence, the welding is carried out by directing the laser beam to impinge on the insert element, through the tubular shell, along the at least one contact zone.
In such a case, the interference fit connection may result from different types of shapes of the plastic parts. A first possibility is that the tubular shell has a circular cross-section and the insert element has a cylindrical outer shape with a diameter which is superior to the inner diameter of the tubular shell.
Another way of creating an interference fit is to provide an annular rib either on the outer surface of the insert element or on the inner surface of the tubular shell, the rib having a thickness such that it interferes with the other part. In such a case, the tubular shell preferably has a circular inner cross-section and the insert element has a cylindrical outer shape with a diameter inferior to the inner diameter of
Aftergut Jeff H.
Delphi Technologies Inc.
Funke Jimmy L.
Haran John T.
LandOfFree
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