FIELD OF THE INVENTION

The present invention relates to a method for assembly of a lighting device, and in particular to a method for final assembly and a lighting device thereof. BACKGROUND OF THE INVENTION

Many different types of lighting device exist today thanks to the broad development within the field. Besides from different types of light sources, lighting devices may also comprise further parts such as control electronics, optical elements such as diffusers, light altering coatings or elements and heat control elements such as heat sinks and heat spreaders. The parts may be arranged together in a shell of the lighting device for protection against damage and moreover for protecting the user from accessing the inner parts of the lighting device.

By an increased number of parts included in a lighting device, the assembly and logistic costs and material cost for manufacturing of the lighting device increase. Further, matching of coefficient of thermal expansion (CTE) of the different parts gets more difficult with the increasing number and the design freedom becomes more restricted. Altogether, this leads to a higher manufacturing cost for the lighting device.

Development of different parts of the lighting device may alleviate this problem. New better or cheaper materials and addition of more functionality to the lighting device are examples of solutions which may lower the cost or increase the value for the end customer. Also the development of standards of different parts or materials may make the production more efficient.

As apparent from the above, there exists a need for improvement of the manufacturing of a lighting device.

SUMMARY OF THE INVENTION

It is an object of the present invention to overcome the above mentioned problems, and to provide an improved manufacturing process for a lighting device in order to decrease production costs and increase production efficiency. A further object is to increase the design freedom in order to improve the overall function of the lighting device.

According to a first aspect of the invention, this and other objects are achieved by a method for final assembly of a lighting device, the method comprising: providing a plurality of parts to be included in the lighting device in a mold, and casting a mechanically supporting body partly or fully enclosing the plurality of parts by introducing a casting material in the mold, wherein the plurality of parts includes a collimator and wherein the mechanically supporting body is provided with, in view of an edge portion of the collimator, a lower portion and an upper portion such that the collimator is fixated by the mechanically supporting body.

In a conventional lighting device, parts need to be designed with not only function in mind, but also with care taken to the interaction with other parts. Properties such as coefficient of thermal expansion (CTE) and shape need to be carefully considered. The design of a conventional lighting device is therefore limited in that function needs to be balanced with integration and also with production efficiency. The present invention provides a solution which alleviates this problem, and which may also decrease the number of required parts and may add functionality to the lighting device. The solution according to the present invention decreases the assembly cost by replacing numerous steps of fitting parts to each other with a single step. Moreover, by casting a mechanically supporting body partly or fully enclosing the plurality of parts of the lighting device a high Ingress Protection ratio (IP-ratio) will be gained. Hence, moisture, dust or dirt is hindered from entering the lighting device and reaching live/corrosive parts. Accordingly, the lighting device will be more easy to use in outdoor environments as compared with conventional light sources. Furthermore, by casting a mechanically supporting body partly or fully enclosing the plurality of parts of the lighting device a better protecting against electrical shock may be achieved. For example, by using a suitable casting material it would be possible to achieve a flammability rating of V0, enabling to make use of an electrical non-insulated driver instead of an insulated one (the non- insulated driver is cheaper and more efficient than the insulated one).

The casting may replace some parts and/or components of a conventional lighting device. A simpler design in the form of fewer parts may decrease material costs, logistics cost and may increase the freedom of design.

The mechanically supporting body may in addition provide functional properties to the lighting device. The method may for this purpose comprise electing the casting material based on a functional property selected from the group consisting of: heat spreading, flame-retardation, electrical insulation, emissivity, reflectivity and thermal conductivity. Thereby, functions such as better heat transmission between an integrated driver and an end cap of the lighting device may be provided.

Alternatively, or in addition, the mold may be configured to provide the body with a functional form. The functional form may be selected from the group consisting of: a reflecting portion and a part of or a whole bulb. Thereby, functions of e.g. a reflector may be provided by the mechanically supporting body thus reducing the number of parts.

The method may further comprise, preceding said casting, forming a subassembly of some of or all of the plurality of parts. The sub-assembly simplifies handling and arranging of the parts in the mold. Moreover, the use of a sub-assembly increases the control of the positioning of the parts such that dislocation of the parts during the casting process is counteracted.

The casting may be performed by means of a low pressure casting method selected from the group consisting of: transfer molding, vacuum molding, and liquid silicone injection molding. A low pressure casting method decreases the risk of damaging the parts in the mold during the casting process.

The configuration with a casted mechanically supporting body allows for easy disassembly of the lighting device. Silicone materials are preferred casting materials in view of this aspect. These materials typically have a low resistance against tear and will disassemble more easily than e.g. polymers like polybutylene terephthalate (PBT), or die-cast aluminum parts. Other preferred casting materials includes mineral, plaster like, materials which are brittle and will easily break off parts, such as the PCB, during shredding.

In one embodiment, the plurality of parts includes a printed circuit board (PCB), at least one light emitting diode mounted on said printed circuit board, and a plate collimator. For such a configuration, the method may further comprise, preceding said casting, arranging the plate collimator on the printed circuit board. Thereby, the light emitting diodes are protected against casting material during said casting.

In another embodiment, the plurality of parts includes a collimator. For such a configuration, the mechanically supporting body may be provided with, in view of an edge portion of the collimator, a lower portion and an upper portion such that the collimator is fixated by the mechanically supporting body. Thus, no further fixating means are required. Other parts of the lighting device may be fixated by the mechanically supporting body as well. According to a second aspect of the invention, the above mentioned and other objects are achieved by a lighting device comprising a plurality of parts and a mechanically supporting body partly or fully enclosing the plurality of parts, wherein the mechanically supporting body is casted.

The casting material may be selected based on a functional property such as heat spreading, flame-retardation, electrical insulation, emissivity, reflectivity and thermal conductivity.

The body may be provided with a functional form selected from the group consisting of: a reflecting portion and a part of or a whole bulb.

It is noted that the invention relates to all possible combinations of features recited in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

This and other aspects of the present invention will now be described in more detail, with reference to the appended drawings showing embodiments of the invention.

Fig. 1 is an exploded view of a lighting device.

Fig. 2 is a perspective view of a lighting device according to an embodiment of the present invention.

Figs. 3 and 4 are perspective views of cross-sections of lighting devices according to different embodiments of the present invention.

Fig. 5a is an exploded view of a lighting device.

Fig. 5b is a cross-sectional view of the lighting device of figure 5a.

Fig. 5c is a perspective view of the lighting device of figure 5a.

Fig. 6a is a cross-sectional view of an assembled lighting device. Fig. 6b is a perspective view of the assembled lighting device of figure 6a.

Fig. 7 illustrates a method according to one embodiment of the present invention.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which currently preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

The detailed description will refer to a lighting device comprising a light emitting diode (LED). However, the present invention may, within the scope of the appended claims, be applied to lighting devices based on other types of light sources as well.

Figure 1 illustrates parts which are typically included in a LED lighting device 1. The lighting device 1 comprises light emitting diodes 10 mounted on a printed circuit board (PCB) 11. A thermal interface element 12 is arranged in connection to the PCB 11 for heat dissipation.

The lighting device 1 further comprises an integrated driver 13. The driver 13 may provide functionality, such as voltage control or suppression of harmonics or distortions in the mains supply, to the lighting device 1.

The lighting device 1 further comprises a heat sink 18 for dissipating heat generated within the lighting device 1.

Remote phosphor optics 17 is provided in connection to the LEDs 10. A light bulb 16 comprising secondary optics, such as a diffuser, is arranged to enclose and protect the remote phosphor optics 17 and the LEDs 10.

A shell body 14 is provided for forming an interface between the heat sink 18 and an end cap 19. The shell 14 comprises a thermal potting member 15 for increased heat control.

The end cap 19 is provided for connecting the lighting device 1 to a power supply.

The lighting device 1 is manufactured by firstly producing and/or pre- assembling each part, and thereafter arranging the parts together to form the lighting device 1. Some of the parts may be arranged in a protective shell, which the heat sink 18 and the shell body 14 provide examples of.

Each part needs to be elected with the interaction with other parts in mind, not only its function. When designing the lighting device 1 as a whole, the parts have thus been elected or designed in view of not only their function but also so as to match each other with respect to e.g. coefficient of thermal expansion (CTE) and shape. The overall design of the lighting device is therefore limited in that the function of each part needs to be balanced with integration and further with production efficiency.

The present invention provides a solution which alleviates this problem, and which may decrease the number of required parts and add functionality as well. Figure 2 illustrates a lighting device 2 which has been manufactured according to one embodiment of the present invention. The lighting device 2 comprises a mechanically supporting body 20. The body has a lower portion 20a and an upper portion 20b.

According to the present invention, the mechanically supporting body 20 is casted during final assembly of the lighting device 2. Instead of fitting each part together with other parts to form the lighting device 2, the parts are arranged in a mold cavity of a mold in which the supporting body is thereafter casted. The body 20 encloses the parts in full or in part. Some or all of the parts of a lighting device, such as the one illustrated in figure 1 , may be arranged in the mold and enclosed by the mechanically supporting body.

This solution decreases the assembly cost by replacing a complex assembly process of fitting parts to each other, which often requires manual handling, with a simple casting process which may be automated. Further, the mechanically supporting body may replace some parts and/or components such as the shell body 14 or the thermal potting member 15 of figure 1. A simpler design in the form of fewer parts may decrease material costs, logistics cost and may increase the freedom of design.

Different molding techniques are possible, including injection molding, transfer molding, vacuum molding and liquid silicone injection moulding (LIM). LIM is similar to transfer molding but the silicone rubber material is supplied through an injection nozzle and is injected into the mold cavity. A low pressure casting method is preferred for decreasing the risk of damaging the parts during casting.

The casting may be performed in a single step, thus providing a simple and time-efficient final assembly, or in a plurality of steps for e.g. the use of different materials (with different properties and/or functions) or for forming complex shapes.

Different casting materials are possible. For example, the casting material may comprise a plaster, cement, concrete, Polyurethane (optionally filled), rubber, filled resin systems, or a silicon material such as a liquid silicone rubber or thin coat silicone. It is appreciated that several types of materials, besides those mentioned here, are known to have both thermally, optically and mechanically satisfying properties to allow for the mechanically supporting body. Moreover, a combination of different casting materials is possible.

A collimator 22 is arranged on a PCB (not shown) comprising LEDs (not shown). Alternatively, the LEDs may be arranged on a lead frame. The positions of the collimator 22 and other parts are fixated by means of the mechanically supporting body 20. Thus, there is no need for fixating the parts to each other. In order to further simplify the final assembly step, a group of or all of the parts may be arranged in a sub-assembly. For example, a separately injection molded frame, in e.g. a plastic material, provided with snap-features allows for easy assembly of some or all of the parts before arranging the parts inside the mold.

Alternatively, instead of providing a separate frame structure, the frame may be formed in one or more casting steps and in a casting material. One or more casted frames and sub-assemblies thereof may be formed inside the mold before casting the mechanically supporting body. Thus, there is no need for additional structures for mechanical fixation of parts in the mold.

As an example, lighting devices such as the ones illustrated in figures 2-4 may be casted in two steps. A first casting step forms a sub-assembly of a first portion of the mechanically supporting body together with input pins. The second casting step forms the rest of the mechanically supporting body in which a PCB and a collimator are fixated to the sub-assembly, filling up the gaps between the first portion of the mechanically supporting body and the electronic parts for heat spreading/heat sinking means. This procedure may be advantageous during assembly of some constructions, such as a construction in which the PCB needs soldering to the input pins. The soldering may thus be performed as an intermediate step between the step of casting of the first portion of the mechanically supporting body and the step of casting the rest of the mechanically supporting body.

As another example, the sub-assembly may be a lead frame or a PCB assembly. The lead frame may be overmolded in a subsequent casting step, wherein the casting material may be chosen with a specific functionality, such as forming a reflective surface on the lead frame.

The sub-assembly simplifies handling and arranging of the parts in the mold. Moreover, the use of a sub-assembly increases control of the positioning of the parts such that dislocation of the parts during the casting process is counteracted.

As mentioned above, the sub-assembly may be formed during one of a plurality of casting steps forming the mechanically supporting body. Such an embodiment may improve curing times. This method allows for different casting materials with different properties to be used. The method also allows for cavities or other complex structures to be formed with a minimized use of material.

The configuration with a casted mechanically supporting body 20 allows for easy disassembly of the lighting device 2. Disassembly of the lighting device 2 is for example desirable when recycling where the different parts of the lighting device 2 are separated and taken care of differently. Silicone materials are preferred casting materials in view of this aspect. These materials typically have a low resistance against tear and will disassemble more easily than e.g. polymers like polybutylene terephthalate (PBT), or die-cast aluminum parts. Other preferred casting materials includes mineral, plaster like, materials which are brittle and will easily break off parts, such as the PCB, during shredding.

Another embodiment of a lighting device according to the present invention is illustrated in cross-section in figure 3. The lighting device comprises a mechanically supporting body 30. The shape of the body 30 differs from the one illustrated in figure 2, however the body 30 has the same purpose and is created in the same manner.

The lighting device comprises parts in the form of a L2 type PCB 35 with

LEDs 34 and other components mounted thereon. Power supply connectors 33 extend from the PCB 35 to the outside of the mechanically supporting body 30, where the connectors 33 may be arranged in an end cap (not shown) such as an Edison E27 end cap.

A collimator 32, corresponding to the collimator 22 in figure 2, is arranged on the PCB 35 comprising the LEDs 34. The collimator 32 is configured such that the LEDs 34 are located in air pockets between the collimator 32 and the PCB 35. This configuration with air pockets counteracts that casting material gets between the LEDs 34 and the optics of the collimator 32 during the casting process.

The mechanically supporting body 3 comprises a lower portion 30a and an upper portion 30b. By that the lower portion 30a and the upper portion 30b are arranged at the lower and upper side, respectively, of an edge portion 32a of the collimator 32, the collimator 32 is fixated by the body 30. The lower portion 30a and the upper portion 30b are connected to each other by an intermediate portion 30c.

Yet another embodiment of a lighting device according to the present invention is illustrated in cross-section in figure 4. This lighting device also comprises a mechanically supporting body 40, a PCB 45 with LEDs 44 mounted thereon, a connector 43 and a collimator 42. Driver parts such as an electrolytic capacitor 46 and an inductor 47 are arranged to form a driver which is integrated with the PCB 45. The electrolytic capacitor 46 and the inductor 47 are in this embodiment completely enclosed by the mechanically supporting body 40.

The casting material may be elected so as to provide the body with a functional property. Non-limiting examples of functional properties are heat spreading, flame-retardation, electrical insulation, emissivity, reflectivity and thermal conductivity. Thus, the body does not only provide mechanical support, it also functions as e.g. a heat dissipating element for the driver parts 46, 47 and the PCB 45.

Moreover, the mold may be configured to provide the body with a functional form. By functional form is meant a form or portion of the body which provides a function to the lighting device. For example, the mold may be configured such that the body is provided with a reflecting portion. Another example is that the mold may be configured such that the body forms a part of or even a whole bulb of the lighting device.

By electing a suitable material and a suitable form, the mechanically supporting body may thereby complement or even replace parts of the lighting device, such as the shell body 14 or the heat sink 18 of figure 1. The mechanically supporting body may thus form and function an integrated housing, an interface between a heat sink and an end cap, a heat sink, a heat spreader, a reflector and even partly (or wholly) an outer bulb, depending on its properties. Moreover, a combination of different casting material with different material properties, such as high reflectivity combined with high thermal conductivity, may be elected to optimize the functionality of the mechanically supporting body.

Another embodiment of a lighting device will now be disclosed with reference to figures 5a-5c and figures 6a-6b. Figures 5a-5c illustrate a conventional lighting device 5 in different views. The lighting device 5 has been manufactured and assembled according to the conventional method of mounting different parts to each other. Figures 6a and 6b illustrate a lighting device 6 according to an embodiment of the present invention. The lighting device 6 forms a further development in view of the conventional lighting device 5 of figures 5a-5c. The lighting device 6 in figures 6a-6b are manufactured and assembled according to the method of the present invention.

Starting with the conventional lighting device 5, figure 5 a illustrates the different parts included therein. The lighting device 5 comprises an L2 type PCB 50 on which light emitting diodes are mounted, a mixing chamber 51, and a driver 53 comprising different driver components. The lighting device 5 further comprises a supporting member 54 for the PCB 50, a heat spreader 59 and a thermal pad 55. A housing 58 encloses the parts of the lighting device 5. A lens 56, here in the form of a Fresnel lens, is arranged in a light exit aperture of the housing 58. These parts or equivalents thereof are common in lighting devices. Figure 5b is a cross-sectional view illustrating the inside of the lighting device 5. The different parts illustrated in figure 5 a have been mounted to each other in a series of assembly steps.

Figure 5 c illustrates a perspective view of the lighting device 5 in its assembled and final form.

The lighting device 6 in figure 6a is a further development of the lighting device 5 of figures 5a-5c. Instead of mounting the different parts of the lighting device to each other and enclose them in the housing 58, different parts have been arranged in a mold in which a mechanically supporting body 60 has been casted, according to the method of the present invention. Different variations of the method as disclosed in connection to other embodiments herein apply also to this embodiment.

By the inventive method, several parts which are present in the conventional lighting device 5 may be omitted. In this example, the mechanically supporting body 60 replaces the function of the housing 58, the mixing chamber 51, the thermal pad 55 and the supporting member 54 for the PCB 50.

As mentioned earlier in connection to other embodiments, the mechanically supporting body 60 may be casted in a plurality of casting steps such that different casting materials may be utilized. For example, the portion of the mechanically supporting body 60 replacing the thermal pad 55 may be casted in a material with enhanced conduction properties for providing a desired heat conduction. Other portions of the mechanically supporting body 60 may be formed by casting materials with other properties, also as mentioned before, such as reflective properties for the portion replacing the housing 58.

As can be seen when comparing figures 5c and 6b, there is no essential difference in appearance between the conventional lighting device 5 and the inventive lighting device 6. However, as recognized by the above, the manufacturing and assembling of the lighting devices are essentially different. Thus, the invention may not only improve the manufacturing process with respect to both costs and time, but the end product may be provided with the same appearance as its conventional counterpart. This is advantageous both in view of marketing, where customers may tend to buy products with an appearance which they are already familiar with, and in view of the exterior design of the lighting device which may be restricted by standards or other compliance requirements.

As exemplified above, the mechanically supporting body may have many different forms. The form of the body is determined by the configuration of the mold with its mold cavity, thus there are almost endless possibilities for designing the body. In figure 7, the method of final assembly of a lighting device according to any of the above disclosed or other embodiments is illustrated. The method comprises a first step of providing 701 a plurality of parts in a mold. The plurality of parts may be sub-assembled. The method further comprises casting 702 a mechanically supporting body by introducing casting material in the mold. The mechanically supporting body encloses the parts partly or in full. The mechanically supporting body may fully enclose one or more parts and partly enclose other one or more parts.

The person skilled in the art realizes that the present invention by no means is limited to the preferred embodiments described above. On the contrary, many modifications and variations are possible within the scope of the appended claims. For example, the lighting device parts presented above constitutes non-limiting examples, thus variations of these or other types of lighting device parts are feasible as well.

Additionally, variations to the disclosed embodiments can be understood and effected by the skilled person in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measured cannot be used to advantage.