Patent Application
20100244653
The present invention relates to a method for producing a contact pin for use as an electric contact element of a fluorescent tube according to the preamble of claim 1.
Moreover, the present invention relates to a contact pin such as can be produced in particular using the inventive method.
Known fluorescent tubes feature end caps respectively provided at the axial ends thereof, wherein the end caps are respectively provided with two contact pins. Said contact pins serve as electric contact elements with which the fluorescent tube is fastened and electrically contacted in base brackets. In generic contact pins, a recess is provided which extends along the longitudinal axis and into which a connection wire of the fluorescent tube can be inserted, by means of which connection wire the fluorescent tube is supplied with a voltage. The connection wire is electrically contacted with the contact pin subsequent to insertion into the recess of the contact pin, which can be performed in particular by sleeving. The outer wall of the contact pin has a cylindrical contact region which is electrically contacted in the base bracket when the fluorescent tube is activated. Moreover, an annular collar protruding beyond the cylindrical contact region is disposed on the outer wall of the contact pin. Said collar serves as a form-fitting stopper in order to readily enable assembly and fixing of the contact pin in the end cap. The end cap has a recess for each contact pin, the diameter of the recess being somewhat larger than the diameter of the cylindrical contact region of the contact pin. During assembly of the contact pin, one end of the contact pin is inserted into the recess of the end cap until the formed collar rests against the end cap.
For producing the known contact pins, a semi-finished metal product which is made of a brass material is used. Contact pins of the generic type are small parts to be manufactured in mass production, so that large quantities have to be produced in the shortest possible time. However, by using brass as a basic material for manufacturing the contact pins, the attainable maximum production speed is limited, since brass can only be processed at a limited production speed using known production processes.
Hence, it is an object of the present invention to suggest a novel method for producing contact pins for use in fluorescent tubes, which enables to further increase production speed. It is another object of the present invention to suggest a novel contact pin which can be produced at maximum possible production speeds, in particular using the novel method.
These objects are attained by a method and a contact pin according to the teaching of the two independent main claims.
Advantageous embodiments of the present invention are the subject-matter of the dependent claims.
The inventive method is based on the fundamental idea that a semi-finished metal product composed of an aluminum alloy is used for producing the contact pin. Another essential aspect of the inventive production method is that the shaping of the contact pin subsequent to cutting to length the semi-finished metal product is performed in principle in two separate process steps. In the first process step, the cut-to-length part of the semi-finished metal product is initially deformed, wherein, as a result of said deformation, at least the collar protruding beyond the diameter of the contact region is formed. By means of deforming the semi-finished metal product it is possible to form the protruding collar at the semi-finished metal product, so that a semi-finished metal product having a diameter corresponding to the diameter of the cylindrical contact region can be used as a basic material. In this way metal abrasion at the outer circumference of the contact pin can substantially be dispensed with.
In order to form the recess in the interior of the contact pin, the contact pin is then machined in a subsequent second process step.
By means of the combined deformation and machining of the semi-finished metal product made of an aluminum alloy, extremely high production speeds can be attained. Moreover, by means of the inventive method contact pins of supreme quality and with excellent electrical properties can be produced. In this context, in semi-finished metal products it is particularly advantageous to use a wire, since wires are available at a low cost with accordingly well-dimensioned diameters. Moreover, the essentially endless semi-finished wire product enables quasi-continuous processing and production of the contact pins.
The type of deformation process employed for forming the collar protruding at the outer circumference of the contact pin is basically optional. Cold deformation processes have proven to be particularly suitable. In particular upsetting the cut-to-length semi-finished metal product is very well suited for forming the protruding collar.
In order to ensure good machinability of the contact pin during assembly at the end cap and during contacting at the base bracket, the protruding collar should be deformed preferably on one side with a conical flank and on the opposite side with a planar flank or else with a second conical flank. By means of the planar flank, reliable positioning of the contact pin is ensured when the collar rests against the wall of the end cap.
In order to avoid twisting of the contact pins relative to the end cap, whereby the contact wires of the fluorescent tube may twist off, a form-fitting and force-fitting engagement should be provided between the planar flank of the collar at the contact pin and the opposite wall of the end cap. In order to allow for this aspect, protruding teeth can be readily formed at the planar flank of the collar by means of the deformation process. In the light of the fact that the formation of the protruding teeth is performed in the course of the deformation process of the aluminum alloy material, no considerable additional costs are incurred as a consequence.
The material removed from the semi-finished metal product as a result of the machining process can only be further utilized as metal waste and is thusly practically useless. In order to reduce the amount of chip waste produced as a result of the machining process, according to a preferred method variation, a part of the recess cannot be produced by machining but rather by deforming. This means that in the course of the production step for deforming the semi-finished metal product not only the protruding collar at the outer surface of the cut-to-length semi-finished metal product is formed, but likewise at least a part of the recess extending along the interior of the longitudinal axis of the contact pin is produced with the aid of material extrusion. In particular by using backward extrusion, at the frontal surfaces of the initially still massive semi-finished metal product one or two cups can be created by deformation.
In order to attain the desired production efficiencies, upon completion of the deformation of the semi-finished metal product, a drilling process should be performed to form the recess. The drilling process enables very high production efficiency, especially when the drilling process is performed at a rotational speed of more than 10,000 r/min, for instance at a rotational speed of 12,800 r/min. During machining, the material should be cooled and lubricated using a lubricant, in particular a nano lubricant.
In order to ensure that the bore precisely extends along the longitudinal axis of the contact pin and to prevent the drill from laterally drifting away during the drilling process, it is particularly recommendable to drill the recesses starting from both frontal surfaces. The bore can thereby be created in a gradual fashion. This means in other words that the bore is gradually widened with the aid of different drills having increasingly larger diameters.
In order to be able to readily insert the connection wire of the fluorescent tube into the recess, a particularly large diameter of the recess is desirable. Conversely, it is advantageous if the recess in the contact region between contact pin and connection wire has the smallest possible diameter, since in this way, a very low deformation degree will already suffice for establishing the electrical contact between connection wire and contact pin. In order to fulfill both requirements with respect to a contact pin, the bore of the one axial end of the contact pin should have a diameter larger than that of the bore extending from the opposite frontal surface. As a result, a recess is created in the contact pin, said recess having a region with a larger diameter and a region with a smaller diameter. The region with the larger diameter faces towards the fluorescent tube subsequent to assembly at the fluorescent tube and thusly enables easier insertion of the connection wire. The portion with the smaller diameter faces away from the fluorescent tube and serves for contacting the connection wire in the contact pin.
In order to ensure easy insertion of the connection wire from the section with the larger diameter into the section with a smaller diameter, a conical transition zone should be drilled between the two cylindrical bores using a drill bit. At the conical inner wall of said transition zone, the end of the connection wire can then be inserted into the region of the bore with a smaller diameter starting from the bore with a larger diameter.
The geometry of the conical transition zone between the two bore sections is basically optional. An opening angle of 60° has proven to be particularly suitable, so that in the formation thereof, a drill bit ground at an opening angle of 60° should be employed.
In order to be able to readily fasten the contact pin at the end cap, the bore with the larger diameter should form a wall thickness which can be deformed, in particular riveted, in the region of the one axial end of the contact pin. For assembly of the contact pin at the end cap, said axial end is then inserted into the recess of the end cap and is moved forwards until the protruding collar rests against the wall of the end cap. Subsequently, the end of the contact pin protruding at the inner surface of the end cap is deformed, for example riveted, and the contact pin is thereby fixed at the end cap. Insofar as the outer edges of the contact pin are supposed to be chamfered in order to thusly avoid for instance injuries on the part of the user and to facilitate assembly by means of the insertion chamfer, the outer edges should be chamfered in the course of the machining step by means of a metal-cutting process.
In order to be able to make optimum use of the potentials of the inventive method, in particular with respect to high production efficiency, where for instance a quantity of 135 to 155 items/min is required, a material optimally adapted to the requirements of the production process has to be utilized. Moreover, said material needs to satisfy the requirements in terms of electrical conductivity and in terms of mechanical stability. In order to attain optimum production efficiencies, comprehensive trials with a large variety of different aluminum alloy materials have been carried out. Materials inter alia conforming to designations nos. A199.5 (AW 1050), AlMn1 (AW 3103), AlZn5.5 MgCu (AW 7075) and similar aluminum alloys have been examined. The various examined materials all failed to fully satisfy the necessary requirement profile.
In the course of the trials it has proven that optimal product requirements and an optimal compromise with respect to material costs, electrical properties and mechanical properties can be attained by using aluminum alloys, in particular aluminum wrought alloys, insofar as said aluminum wrought alloys have a minimum aluminum content of 90%, a minimum copper content of 4.5% and/or a minimum magnesium content of 0.5%. Said requirements can be satisfied in particular using aluminum wrought alloys from series 2000 (Al—Cu), aluminum wrought alloys from series 5000 (Al—Mg) or else aluminum wrought alloys from series 6000 (Al—Mg—Si). Insofar as the various material contents are indicated in percent in the present invention, said designations are supposed to refer to weight percent.
The aluminum content of the aluminum alloy should preferably be in the range of 93% to 94%. The copper content in turn should preferably be in the range of 5% to 6%, in particular in the range of 5.4% to 5.6%.
Another enhancement of the machinability of the aluminum alloy material in the two-step processing with a deformation step and a machining step is attained if the aluminum alloy additionally contains bismuth. In the German language bismuth is sometimes also referred to as “Wismut”.
In this connection, the bismuth content should be in the range of 0.1% to 0.9%, in particular in the range of 0.2% to 0.6%. Optimum results are attained with a bismuth content of 0.45% to 0.55%.
In the context of the material trials, in particular one aluminum alloy, the quality thereof conforming to material designation AlCu6Bi, has been identified as being particularly suitable.
Moreover, the aluminum alloy should preferably also have a lead content. The lead content should preferably be in the range of 0.2% to 0.6%, in particular in the range of 0.2% to 0.4%.
Insofar as the aluminum alloy composed of aluminum, copper and bismuth additionally also contains lead, the aluminum alloy should conform to a quality in line with material designation AlCu6BiPb. In addition to the indicated contents (aluminum, copper, bismuth, lead), the aluminum alloy may additionally also contain trace amounts of silicon, iron, manganese, magnesium, chromium, zinc and/or titanium.
From the wrought aluminum alloys from series 2000 (Al—Cu), in particular the aluminum alloy conforming to the quality of material designation no. EN AW 2011 is perfectly suited for producing the contact pins with the inventive method. Quality standard designation no. EN AW 2011 contains for instance 5.5% copper, 0.48% bismuth, 0.51% lead, 0.06% silicon, 0.13% iron, 0.01% manganese, 0.01% magnesium, 0.01% chromium, 0.03% zinc and 0.03% titanium. The remainder of the aluminum alloy is formed by aluminum. The aluminum alloy in line with material designation number EN AW 2011 in particular is also specified in Eurocode No. EN 573-3. The aluminum alloy in line with material designation number EN AW 2011A having the somewhat lower minimum copper content of 4.5% is equally well suited.
Alternatively thereto, from the wrought aluminum alloys from series 5000 (Al—Mg), the aluminum alloys in line with material designation numbers EN AW 5019 (AlMg5), EN AW 5754 (AlMg3), EN AW 5154A (AlMg3,5(A)) or else EN AW 5083 (AlMg4,5Mn0,7) are very well suited for producing the contact pins using the inventive method.
Among the aluminum alloys from series 6000 (Al—Mg—Si), the aluminum alloy in line with material designation number EN AW 6082 (AlSi1MgMn) is very well suited for producing the contact pins using the inventive method.
Various aspects of the present invention are schematically illustrated in the drawings and will be exemplarily specified herein below, wherein:
The two contact pins 01 each have a recess 06 continuously extending along the longitudinal axis 05 thereof from one axial end to the other axial end. In said recesses 06 a connection wire of the fluorescent tube is respectively inserted and electrically contacted by crimping the contact pins 01. The recess 06 has a region 06a with a large diameter, a region 06b with a small diameter and a conical transition zone 06c. The connection wire of the fluorescent tube is inserted into region 06b and is electrically contacted therein.
For fastening the contact pins 01 at the frontal cap 04, the axial ends 07 which face towards the fluorescent tube and which have an outer and inner diameter initially corresponding to the outer and inner diameters in region 06a are riveted. In order to ensure fastening of the contact pins 01 by means of the riveting process, a collar 08 is additionally formed at the outer circumference, the collar 08 resting against the outer surface of the frontal cap 04. With the aid of the collar 08 and the riveted axial end 07, the contact pin 01 is fixed in the recess of the frontal cap 04 in a form-fitting manner.
For producing the recess 06 with regions 06a, 06b and 06c thereof, the semi-finished metal product 13 is subsequently machined in eight process steps. In the first three machining steps, bores 15 and 16 are formed at axial ends 07 and 11 in a gradual fashion with the aid of fast rotating drills.
Subsequent to the first three steps for producing recess 06 by means of bores 15 and 16, the axial edges 07 and 11 are chamfered and the edges are fractured. Then, the bore 15 is deepened in three further process steps, wherein different drills each with gradually decreasing outer diameters are employed. In the ultimate processing step, using a drill with a drill bit ground at an opening angle of 60° the inner contour is finish-drilled and the conical transition zone 06c is thereby formed by the drill bit.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 049 531.7 | Oct 2007 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/DE08/01278 | 8/8/2008 | WO | 00 | 4/9/2010 |
