Laser welding method

To weld a filter made of a laser beam-transmittable fiber material to a case made of a laser beam-nontransmittable resin material by a laser beam the filter is first placed on the case; subsequently, the filter is pressurized by a jig to increase the fiber density of a welding portion; and then the welding portion is irradiated by the laser beam. In the step of increasing the fiber density, a periphery of the welding portion is pressurized by the jig to increase the fiber density of the filter in a larger area than the welding portion. Accordingly, the laser beam transmitting through the filter melts a part of the case, and the melted resin material permeates through gaps between the fibers constituting the filter, thereby welding the welding portion to the case.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a laser welding method for welding a fiber filter to a resin base member by a laser beam.

2. Description of Related Art

Some of conventional methods for welding a nonwoven filter made of fibers to a base member made of resin are disclosed in, for example, Japanese patent unexamined publications No. Hei 8-229312 and No. 2000-186635. These welding methods include a first step of placing a nonwoven filter made of polyester fibers onto a base member made of nylon (trade name), a second step of partially melting the base member, thereby allowing the melted material to permeate through the gaps between the fibers constituting the filter to weld the filter to the base member.

Each related art mentioned above adopts an ultrasonic welding method or a vibrational friction welding method. For instance, in the ultrasonic welding method, an ultrasonic oscillator is disposed near a filter and caused to emit ultrasonic waves to melt a base member, so that the melted material of the base member permeates through the gaps between fibers of the filter and cured therein. Likewise, in the friction welding method, an oscillator is disposed near a filter. It therefore can be said that the friction welding method includes similar steps to those in the ultrasonic welding method.

The conventional welding methods, however, need a step of moving the oscillator or others toward or away from the filter. It would take some time by just that much to complete welding.

In this regard, there is a laser welding method using a laser beam as the method which can eliminate the need for moving the oscillator or other devices toward a work or reduce a moving distance of the devices. In this welding method, even where a laser emission device is placed apart from a work to be irradiated, the laser beam can reach a welding portion of the work if only the laser emission device is operated to emit a laser beam to the welding portion. If this welding method is used to weld a filter to a base member, consequently, it would be possible to omit or reduce a moving time of the emission device, thereby shortening the time required for the completion of welding.

However, there is no conventional example heretofore proposed for welding a filter to a base member by use of a laser beam. It is also conceivable that the welding by the laser beam will cause problems in securing welding strength or in preventing defects such as scorches or holes in the work. Consequentially, the proposal of a practical laser welding method has been desired.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances and has an object to overcome the above problems and to provide a laser welding method capable of adequately welding a filter to a base member while enhancing welding strength and preventing defects such as scorches and holes.

To achieve the purpose of the invention, there is provided a laser welding method for welding a fiber filter to a resin base member by a laser beam, the method including the steps of: placing the filter made of a laser beam-transmittable fiber material on the base member made of a laser beam-nontransmittable resin material; increasing the fiber density of a welding portion of the filter; and irradiating the laser beam to the welding portion; wherein the base member will partially be melted by the laser beam transmitting through the filter and a melted material of the base member will permeate through gaps between the fibers constituting the filter so that the welded portion is joined to the base member.

According to another aspect of the invention, there is provided a laser welding method for welding a fiber filter to a resin base member by a laser beam, the method including the steps of: placing the filter formed of a nonwoven fabric made of a laser beam-transmittable fiber material on the base member made of a laser beam-nontransmittable resin material; pressurizing a welding portion of the filter by a jig having a slit to increase the fiber density of the welding portion; and irradiating the laser beam to the welding portion through the slit of the jig; wherein the base member will partially be melted by the laser beam transmitting through the filter and a melted material of the base member will permeate through gaps between the fibers of the filter so that the welded portion is joined to the base member.

Furthermore, according to another aspect, the present invention provides a canister provided with the base member and the filter welded by any one of the laser welding methods described above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A detailed description of a first preferred embodiment of a laser welding method embodying the present invention will now be given referring to the accompanying drawings. In the present embodiment, this laser welding method is adopted for the manufacture of a canister.

FIG. 1is a sectional view of a canister1in the present embodiment. This canister1is provided with a substantially cylindrical case2and a cover3which covers the case2. The case2contains a first filter4, charcoal5, a second filter6, a plate7, and a spring8.

The case2, which corresponds to a base member of the invention, is made of a laser beam-nontransmittable resin material. In the present embodiment, for example, “PA66 (trade name: 66-nylon)” is used as the laser beam-nontransmittable resin material. The melting point of PA66 is 265° C. The case2includes an upper opening2a, an inside shoulder2b, a lower opening2c, and a plurality of female screw holes2darranged around the lower opening2c. A flange2eis also formed on the periphery of the upper opening2a.

The cover3is set to cover the upper opening2aof the case2and has a circumferential welding portion B1which is laser-welded to the flange2e.The cover3includes a pipe joint3a.The cover3is made of a laser beam-transmittable resin material. In the present embodiment, for example, “PA66” is used as the laser beam-transmittable resin material.

The first filter4, which corresponds to a filter of the invention, is made of a laser beam-transmittable fiber material. This laser beam-transmittable fiber material in the present embodiment is for example a mixture of “polyester” fibers and “rayon” fibers which are formed in intertwining relation into a nonwoven fabric. With regard to the polyester fibers, the fiber diameter is 10 μm to 15 μm, the melting point is 270° C., and the polyester content in the mixture is 54%. With regard to the rayon fibers, the fiber diameter is 10 μm to 40 μm, the melting point is 180° C., and the rayon content in the mixture is 46%. The first filter4has a circumferential welding portion B2which is laser-welded to the inside shoulder2bof the case2.FIG. 2is a table showing a comparison of the material characteristics of the case2and the first filter4.

The charcoal5is used to adsorb evaporated fuel of gasoline. In the present embodiment, “BAX1100” is used as the material of charcoal5. The charcoal5is put in layers having a predetermined thickness on the first filter4.

The second filter6is formed of a nonwoven fabric which is thicker than the first filter4. This nonwoven fabric in the present embodiment is for example “urethane foam”. The second filter6is set on the charcoal5.

The plate7is placed on the second filter6. This plate7in the present embodiment is made of for example “punching metal”. The spring8is arranged between the cover3and the plate7to press the plate7with the urging force against the charcoal5. The spring8is made of for example “SWPA”.

The canister1having the above structure is manufactured in accordance with the following steps. At first, the first filter4is laser-welded to the inside shoulder2bof the case2and fixed to the case2.

Secondly, the charcoal5is put in layers on the first filter4and then the second filter6is placed on the charcoal5.

In the next step, the plate7is put on the second filter6, and then the cover3is set on the second filter2after the spring8is placed between the plate7and the cover3.

After that, the flange2eof the case2and the circumferential portion of the cover3are laser-welded to fix the cover3to the case2. Consequently, the canister1shown inFIG. 1is completed.

Next, the laser welding method for welding the first filter4to the inside shoulder2bof the case2will be explained in detail.

FIG. 3is a schematic structural view of a laser welding apparatus11used for this laser welding method. This apparatus11is provided with a work table12, a robot13, and a compression unit14, the robot13and the compression unit14being installed on both sides of the table12.

The work table12is used for setting thereon the case2as a work. The robot13includes a multi-articulated arm15. At an end of this arm15, a laser emission device16is attached. This emission device16is internally provided with an optical system for emitting energy (a laser beam LB) delivered from an energy generator (a laser source) not shown through an optical fiber17to a work (the case2) on the work table12. As this energy generator, for example, a diode laser (a semiconductor laser) is used. In the present embodiment, the laser beam LB to be emitted through the emission device6is an infrared laser beam of 500 W and the spot diameter of the laser beam LB is set at for example about 3 mm to about 4 mm.

The compression unit14is used to press the first filter4against the inside shoulder2bof the case2. This unit14includes a hydraulic or pneumatic cylinder18having a cylinder rod18a, and a jig19attached to an end of the cylinder rod18a. Expansion and contraction of the cylinder rod18acauses the jig19to move toward or apart from the work table12. As shown inFIG. 5, the jig19is used to apply pressure on the periphery of the welding portion B2of the first filter4. The jig19is formed with a slit19athrough which the laser beam LB is irradiated to the welding portion B2. This slit19ais designed to have a smaller width, e.g., 2 mm, than the spot diameter of the laser beam LB.

The laser welding of the first filter4to the inside shoulder2bof the case2is conducted in the following steps by use of the above mentioned laser welding apparatus11.

In a first step, the case2is first put and fixed on the work table12, as shown inFIG. 4.

In a second step, the first filter4is placed on the inside shoulder2bof the case2, as shown inFIG. 5. At this time, the jig19of the compression unit14is disposed above the case2.

In a third step, as shown inFIG. 6, the jig19of the compression unit14is moved downward onto the first filter4and pressurized to press the periphery of the welding portion B2of the first filter4against the inside shoulder2b, thereby compressing the welding portion B2and its periphery to increase the fiber density of the first filter4. That is, the fiber density of the first filter4is increased in a slightly larger area than the welding portion B2. In the present embodiment, the jig19is operated to compress the first filter4so that the filter thickness of 3 mm is reduced to 0.5 mm.

In a fourth step, sequentially, the laser beam LB is irradiated from the emission device16to the welding portion B2of the first filter4. At this time, the first filter4is continuously compressed in the same manner as in the third step. In the present embodiment, by universal manipulation of the arm15of the robot13, the laser beam LB from the laser emission device16can circumferentially be irradiated to the first filter4.

It is to be noted that the emission device16illustrated inFIG. 6is positioned near the jig19, but it is merely for drawing convenience. Actually, the emission device16is disposed relatively apart from the jig19. The position of the emission device16is adjustable by selection of a condensing lens of the optical system.

In the third step, as shown inFIG. 7, a slightly larger area in the first filter4than the welding portion B2is pressurized to increase the fiber density. More specifically, the periphery of the welding portion B2is compressed against the inside shoulder2bby the jig19so that the welding portion B2is indirectly compressed. Thus, the welding portion B2and its periphery in the first filter4are compressed and therefore the fiber density of the welding portion B2of the first filter4is increased as shown inFIG. 8.

As shown inFIGS. 6 and 7, when the laser beam LB passing through the slit19aof the jig19transmits through the first filter4, the surface of the inside shoulder2bof the case2is thereby heated and melted. The melted material of the case2is allowed to permeate through the gaps between fibers constituting the welding portion B2of the first filter4, thereby welding the welding portion B2to the inside shoulder2b.

According to the above mentioned laser welding method, the first filter4is put on the inside shoulder2bof the case2and then the fiber density of the welding portion B2of the filter4is increased. Accordingly, the thermal conductivity of the welding portion B2is increased, which enhances the heat dissipation property of the filter4. The contact area of the welding portion B2with the melted material of the case2is also increased. This can enhance the welding strength of the first filter4to the inside shoulder2bof the welding portion B2. The increased fiber density of the welding portion B2of the first filter4can improve the thermal conductivity of the fibers of the welding portion B2, thereby enhancing the heat dissipation of the welding portion B2. Consequently, it is possible to prevent the filter4from being scorched or holed by the melting heat of the inside shoulder2b. Furthermore, the first filter4itself is made of a laser beam-transmittable fiber material, which can transmit the laser beam LB. Accordingly, the fiber itself is not heated during transmission of the laser beam, so that the filter4can be prevented from being scorched or holed by the laser beam LB. In other words, the first filter4can adequately be welded to the inside shoulder2bof the case2while the welding strength can be enhanced and the defects such as scorches and holes can be prevented.

The above operations and effects can result from the pressurization and compression of the welding portion B2of the first filter4by the jig19. For instance,FIG. 9shows a comparative example in which a jig29having a relatively larger slit29ais used to press a filter24against a case22. In this case, the periphery of a welding portion B2is not compressed. As shown inFIG. 10, accordingly, the fiber density of the welding portion B2is not increased and the fibers constructing the welding portion B2remain rough. When the laser beam LB is irradiated to the welding portion B2in this state, the welding portion B2will be scorched or holed because of the low thermal conductivity. In this case, furthermore, the contact area of the fibers with the melted material of the case22is small and therefore the welding strength of the filter24to the case22is low. These disadvantages can be avoided according to the laser welding method in the present embodiment.

In the present embodiment, the fiber density of the first filter4is increased in a slightly larger area than the welding portion B2, which makes it possible to reduce a thermal influence on the portion other than the welding portion B2, namely, the portion having a low fiber density. It is consequently possible to surely prevent the portions other than the welding portion B2from being scorched or holed.

In the present embodiment, the welding portion B2and the periphery thereof in the first filter4are pressurized and compressed against the inside shoulder2bof the case2, thereby increasing the contact area of the welding portion B2and its periphery with respect to the inside shoulder2b. Consequently, the joining strength between the first filter4and the inside shoulder2bcan further be enhanced.

FIG. 11is a graph showing a relationship between each filter welding method and the joining strength. InFIG. 11, the lateral axis indicates the types of welding methods and the vertical axis indicates the peel strength related to the joining strength. In the lateral axis, there are shown the laser welding examples shown inFIG. 9(the comparative example) andFIG. 7(the present embodiment) respectively and the ultrasonic welding example.

Measurements of the peel strength were carried out in the following manner. Specifically, samples were prepared by welding the filters to the cases according to the above three types of welding methods. In each sample, as shown inFIG. 12, the filter is pressed by a piston from the lower opening side of the case (namely, from above inFIG. 12). The conditions of measurements were that the inner diameter of the opening O (corresponding to the lower opening2cinFIG. 1) of the case was 38 mm, the outer diameter of the piston was 36 mm, and the pressing speed of the piston was 5 mm/min.

As shown inFIG. 11, the peel strength in the laser welding shown inFIG. 9was about 20 g/cm, that in the laser welding shown inFIG. 7was about 100 g/cm, and that in the ultrasonic welding was about 1200 g/cm. In the ultrasonic welding, the melted resin of the case permeated in the filter throughout the thickness, so that the peel strength was determined at a high value approximately equal to the strength of the filter itself. In the laser welding, on the other hand, the melted resin permeated in the filter at only a portion (about 100 μm) near the contact surface with the melted resin, so that the peel strength was lower than that in the ultrasonic welding. However, the laser welding in the present embodiment shown inFIG. 7could provide the peel strength (welding strength) sufficient to be practically used.

In the present embodiment adopting the laser welding method, there is no need to move the emission device16toward and apart from the welding portion B2before and after the step of irradiating the laser beam LB to the welding portion B2. In other words, differently from the conventional ultrasonic welding method in which the oscillator was needed moving toward and apart from the filter during welding, the present invention can eliminate the need for moving the laser emission device16. Thus, it is possible to reduce the time needed for completing the welding by just that much.

Next, the laser welding of the case2and the cover3is explained below. In the present embodiment, the case2is made of a laser beam-nontransmittable resin material and the cover3is made of a laser beam-transmittable resin material. Accordingly, as in the case of the case2and the filter4, the laser welding can be adopted for laser-welding the cover3to the case2.

More specifically, as shown inFIG. 13, the laser beam LB is irradiated to the cover3placed on the flange2eof the case2along the circumference of the cover3so that the surface of the flange2eis partially melted by the laser beam LB transmitting through the cover3. The melted resin of the flange2eis then joined to the cover3, thereby welding the welding portion B1of the cover3to the flange2eof the case2.

In the present embodiment, by universal operation of the arm15of the robot13, the laser beam LB can be irradiated along the circumference of the cover3. In the present embodiment, following the welding between the case2and the first filter4, the laser welding is further adopted for the welding between the case2and the cover3. Consequently, for the manufacture of the canister1, the laser welding can be adopted for all the welding operations, so that manufacturing equipment and manufacturing steps can be simplified and the necessary time can be reduced as compared with the case where plural welding methods of various types are adopted.

In the present embodiment, the above mentioned laser welding method is adopted for the manufacture of the canister1and therefore this manufactured canister1is provided with the case2and the first filter4welded according to the above method. The canister1can accordingly have the operations and effects according to the above laser welding method. Consequentially, the first filter4can be held in a securely welded state to the case2for a long time and in this connection the durability of the canister1can be improved. Furthermore, the time needed for completing the laser welding can be reduced, thereby reducing the time needed for manufacturing the canister1.

Next, explanation is made on a second embodiment of the laser welding method of the present invention, which is adopted to manufacture a canister.

It is to be noted that like elements in each of the following embodiments to those in the first embodiment are given like numerals and the explanation thereof is omitted. The following embodiments are explained with a focus on differences from the first embodiment.

A different point of this second embodiment from the first embodiment in relation to the laser welding of the case2and the first filter4is in that a protrusion2fis provided on the surface of the inside shoulder2bof the case2in correspondence with the welding portion B2of the first filter4as shown inFIG. 14.

More specifically, in a step of increasing the fiber density of the first filter4according to the laser welding method in the second embodiment, the periphery of the welding portion B2is pressurized and compressed against the inside shoulder2bof the case2by means of the jig19, thereby indirectly compressing the welding portion B2while directly pressurizing and compressing the welding portion B2from the case2side by the protrusion2fof the inside shoulder2b.

According to the laser welding method in the second embodiment, the welding portion B2and its periphery are pressurized and compressed against the inside shoulder2b, so that the contact area of the welding portion B2and its periphery with respect to the inside shoulder2bis increased. Since the welding portion B2is directly compressed from the case2side, the joining degree between the welding portion B2and the inside shoulder2bis also increased. Consequently, the laser welding method in the second embodiment can more largely increase the joining strength between the first filter4and the inside shoulder2bas compared with that in the first embodiment. In other words, the laser welding method in the second embodiment can reduce output energy (output power) of the laser beam to be emitted from the emission device16to about one-fifth the output energy in the first embodiment in order to provide the joining strength substantially equal to that in the first embodiment. Thus, energy consumption can be reduced. Other operations and effects are similar to those in the first embodiment.

Next, explanation is made on a third embodiment of the laser welding method of the present invention, which is adopted to manufacture a canister.

A different point of this third embodiment from the first and second embodiments in relation to the laser welding of the case2and the first filter4is in that a groove2gis provided in the case2at a corner of the inside shoulder2bin correspondence with the welding portion B2of the filter4as shown inFIG. 15and the peripheral edge of the first filter4is wedged in the groove2g. More specifically, in a step of increasing the fiber density of the first filter4in the laser welding method in the third embodiment, the welding portion B2and its periphery are inserted in a tucked state into the groove2gof the inside shoulder2bof the case2so that the welding portion B2and its periphery are compressed inside the groove2g.

In the third embodiment, since the welding portion B2and its periphery are compressed in the groove2gof the inside shoulder2b, the contact area of the welding portion B2and its periphery with respect to the inside shoulder2bcan be increased without the use of the above mentioned jig19and others. Thus, the third embodiment can provide the same effects as in the case of the compression by the jig19and others in the first embodiment.

In the third embodiment, the tucking operation is performed after the case2is set on the work table12. Alternatively, the peripheral edge of the first filter4may be previously inserted (folded) in a tucked state into the groove2gof the inside shoulder2b.

The present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For instance, the following alternatives can be adopted.

In the first and second embodiments, the jig19is partially formed with the slit19ain correspondence with the welding portion B2of the first filter4to allow the laser beam LB to pass through the slit19a. As an alternative, the jig itself may be made of a laser beam-transmittable material and the slit may be omitted so that the jig directly presses the welding portion of the filter. In this case, the joining strength of the welding portion can be more increased.

In the first and second embodiments, the jig19may be made of a material having good thermal conductivity to promote heat dissipation of the first filter4. In this case, the cooling effect of the first filter4can be enhanced, which makes it possible to surely prevent the filter4from being scorched or holed by heat of the laser beam.

In the first and second embodiments, the step of increasing the fiber density of the welding portion B2of the first filter4is provided as a pre-step of the laser irradiation step. Alternatively, under condition that the welding portion of the filter is previously constructed with a higher fiber density than other portions, a step of placing and lightly pressing the filter on the inside shoulder of the case by the jig may be provided as a pre-step of the laser irradiation step. Furthermore, the step of increasing the fiber density of the welding portion as compared with other portions may be achieved by compressing and hardening only the welding portion of the filter. Alternatively, the filter may be constructed to entirely have a uniform thickness with only the welding portion previously having the higher fiber density than other portions. These cases can also produce the same operations and effects as those in the first and second embodiments.

In each of the above embodiments, the laser welding method of the present invention is adopted to manufacture the canister1by welding the case2and the first filter4. The present invention can be adopted to not only the manufacture of the canister but also manufactures of various devices if a filter made of a fiber material is welded to a base member made of a resin material by a laser beam.