Method for the automated manufacture of wound electrical components by contacting thin insulated wires to terminal elements on the basis of laser welding

In a method for automated manufacture of wound electrical components by contacting thin insulated wires to terminal elements on the basis of laser welding, only the terminal element is melted by direct laser irradiation to form a welding spot at the location provided for the welding. The wire is subsequently embedded into the welding spot as soon as the welding spot has cooled to such an extent that the wire subsequently only melts superficially. During the course of continuous winding of winding carriers, the insulated winding wire is wound into the welding spot produced on the respective terminal element, and is thereby pressed by the winding tension into the melt which solidifies to form the welded connection.

BACKGROUND OF THE INVENTION 
The invention is directed to a method for the automated manufacture of 
wound electrical components by contacting thin insulated wires to terminal 
elements on the basis of laser welding. 
A method of this type wherein the laser welding is undertaken indirectly by 
irradiation of a lamina placed onto the wire is disclosed by German 
Published Application 33 07 773, incorporated herein. 
In electrical components such as, for example, in relays, coils, 
transformers and other components, the induction coils employed therein 
are becoming smaller and smaller within the framework of a continuing 
miniaturization. This means that the winding wires thereby utilized have a 
smaller and smaller diameter, this makes the contacting of the coil 
terminals more difficult. For example, the lacquer-insulated winding wires 
can have a diameter in the range from 30 through 100 .mu.m (0.03 through 
0.1 mm). 
Up to now, lacquer-insulated winding wires were usually contacted to coil 
terminals by resistance, ultrasound or laser welding. The softening of 
wire and terminal during the welding process is thereby a function of the 
temperature that is produced by energy application, heat capacity, and 
heat elimination. The various welding processes particularly differ in how 
the energy is supplied to wire and terminal. Heat capacity and heat 
elimination of wire and terminal, by contrast, are independent of the 
welding process--in a first approximation--and are respectively lower at 
the winding wire than at the terminal. 
In resistance welding wherein both electrodes contact the winding wire, the 
heat generating occurs in the winding wire and not in the terminal onto 
which the heat is transmitted by thermal conduction. The chronologically 
earlier heating of the winding wire in comparison to the terminal is 
therefore caused by earlier application of energy to the winding wire, 
lower heat capacity, and lower heat elimination. The earlier heating and, 
thus earlier softening of the winding wire and the pressing power of the 
electrodes then lead to great deformation of the winding wire given little 
deformation of the terminal. In resistance welding, moreover, the 
electrodes in the case of miniaturized components such as, for example, 
SMD coils, must have such small dimensions that their service life is too 
short for automated manufacture. Further, the contamination of the 
electrodes by lacquer residues deriving from the winding wire is 
disturbing. 
In ultrasound welding, the sonotron pressure not only produces the welding 
pressure but simultaneously causes the friction that generates the heat. 
Due to the lower heat capacity and the lower heat elimination, the wire 
softens earlier than the terminal. The ultrasound oscillation acting on 
the softened wire deforms the winding wire to an even greater degree than 
does resistance welding. In ultrasound welding of lacquer-insulated wires 
having a diameter below 0.4 mm, an additional cover lamina is welded on 
(sandwich technique) for mechanically reinforcing the weld, or the weld is 
covered with glue (see European Patent 0 200 014, incorporated herein). 
The mechanical reinforcement of the weld is required since the wire 
deforms greatly during welding and its mechanical stability thereby 
decreases. The electrical reliability of the winding contacting is 
likewise diminished due to the deformation. 
In laser welding, German Published Application 33 07 733, incorporated 
herein discloses that copper wire microfinish enamel cannot be directly 
welded to the terminal element. Given direct irradiation of the winding 
wire by the laser beam, the wire would also have to absorb the energy that 
is required for softening the terminal. The wire, however, thereby melts 
or evaporates before the terminal softens, so that a usable winding 
contacting does not result. In order to avoid this, the laser energy is 
not directly supplied to the joining zone but to the surface of a lamina 
that covers the wire and the terminal (sandwich technique). In laser 
welding with a sandwich technique, the cover material softens first, then 
the winding wire and, finally, that part of the terminal to be contacted. 
The cover material is melted, flows over the wire to the terminal contact, 
completely dissolves the wire, and forms a welded bridge between wire and 
terminal. Analogous to a soldered connection, the boundary surface between 
melt and non-melted wire is critical for the contacting. Since the wire 
fully dissolves in an undesirable fashion, the boundary surface has 
approximately the size of the wire cross section. There is the risk of 
embrittlement at this boundary surface and the risk of an increase in the 
electrical resistance as a consequence of oxygen enhancement, pore 
formation, inadequate recrystallization, etc. The relatively small 
boundary surface yields a lower mechanical and electrical stability of the 
laser-welded connection in comparison to a soldered connection wherein the 
wire is embedded in the solder with an unmodified cross section. 
Also included in the problem area of laser welding is that the lacquer of 
solderable copper lacquer wires (for example, on a polyurethane basis) 
does not complicate the welding or even assists it in that it acts as a 
fluxing agent, but the lacquer of the copper lacquer wires which are 
difficult to solder (for example, on a polyamide basis) and that are 
required for SMD coils, leads to poor welding results. By contrast to 
resistance and ultrasound welding, laser emission ultimately exerts no 
mechanical pressure onto the members to be welded. The members to be 
welded, however, must touch one another since a gap between the members to 
be welded deteriorates the welding results. 
SUMMARY OF THE INVENTION 
An object of the present invention is to specify an improved method of the 
type initially cited that, in particular, leads to a 
high-temperature-resistant contacting with improved mechanical and 
electrical stability on the basis of reduced wire deformation, and also 
leads to miniaturized dimensions of components manufactured without a 
sandwich technique by using direct joining of wire and terminal elements. 
For achieving this object, the method of the invention of the type 
initially cited is characterized in that only the terminal element is 
melted to form a welding spot by direct laser irradiation at the location 
provided for welding, the wire being subsequently embedded thereinto as 
soon as the welding spot has cooled to an extent that the wire 
subsequently melts only superficially. 
In energy application by direct laser irradiation, the melted terminal 
material is heated far above the melting point. The invention is based on 
the perception that the energy stored in the melt is adequate in order to 
heat the relatively minute wire material indirectly and without further 
direct or indirect laser irradiation to such an extent as needed for the 
welding process. This opens up the possibility of not melting the wire 
during welding in that the unheated wire is only dipped into the melt of 
the terminal material when the melt has lost so much energy due to heat 
elimination that the energy remaining in the melt is just adequate to 
superficially melt the wire. 
An especially advantageous development of the method of the invention 
derives during the course of continuous, particularly standstill-free 
winding of winding carriers of electrical components in that the insulated 
winding wire is wound into the welding spot produced on the respective 
terminal element of the winding carrier and is thereby pressed by the 
winding tension into the solidifying melt to form the welded connection. 
Further advantageous developments of the invention are the subject matter 
of additional claims.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIG. 1 shows the sandwich technique when Welding with a laser beam 2 that 
is known from the prior art. As indicated in FIG. 1, it is thereby 
provided that a cover lamina 4 presses the wire 1 down onto the provided 
welding location of the terminal element 3. In the known method, the wire 
1 can also be removed from direct irradiation by, for example, overlapping 
material of the terminal element that serves as a covering, instead of 
being protected by a separate cover lamina 4. In any case, this requires 
additional work steps and leads to larger dimensions of the contacted 
component. 
FIG. 2 shows a convex part 5 of the terminal surface 6 of a terminal 
element 3, whereas FIG. 3 shows a sectional surface 8 of a terminal 
element 3. It is advantageous to produce a welding spot 7 with the laser 
beam 2 either in a convex part 5 or at a section surface 8 of the 
respective terminal element 3, as shown in FIGS. 2 and 3, so that the 
welding pressure is produced, for example, by the forces exerted onto the 
winding wire by the winding tension instead of being produced, as 
previously, by dies and mechanical pressure. 
The laser welding method of the invention enables the welding of a copper 
microlacquer wire that is difficult to solder and is heat resistant. The 
energy that is required for the melting or carbonization of the wire 
lacquer is supplied to the lacquer in the joining zone, not from the wire, 
but from the welding spot. The removal of the lacquer insulation that is 
critical for the quality of the contacting can therefore occur with a 
defined energy application. Added thereto is that the afore-mentioned 
welding pressure reduces the gap formation and promotes the break-out or 
channelling by the carbonized residues of the wire lacquer that is 
difficult to solder and that is required for an electrically stable welded 
connection. A general advantage of the welding method of the invention is 
also comprised therein that the wire surface that is only superficially 
melted enlarges the critical boundary surface between the wire and the 
melt. The energy application, moreover, can unproblematically occur with, 
for example, a pulsed solid-state laser (Nd-glass or Nd-YAG laser). 
The method of the invention can be employed in the course of continuous 
winding of winding carriers of electrical components, whereby the winding 
carriers are supplied sequentially and step-by-step to a winding mechanism 
with a conveyor means, are wound and conveyed further, and whereby the 
wire is respectively welded fast at the terminal elements of the winding 
carriers and the winding wire is separated between successive electrical 
components. Such a winding method is inherently known from German 
Published Application 35 18 651. In this case, the insulated winding wire 
is wound into the welding spot produced on the respective terminal element 
and is thereby pressed by the winding tension into the melt that 
solidifies to form the welded connection. The time between the production 
of the welding spot and the wound introduction of the winding wire into 
the solidifying melt is set by the parameters defining the winding process 
(for example, start of winding, winding length, winding rate, etc.) which 
are particularly dependent on the wire diameter and on the wire 
lacquering, in such a way, that winding wire only superficially melts, but 
does not entirely melt. By selecting the geometrical position of the 
welding spots on the terminal elements moreover, a simple variation of the 
length of the winding wire, and thus an unproblematical setting of the 
corresponding nominal induction value of an electrical coil, is possible. 
This helps in meeting the tolerances required by the customers. 
For illustrating the contacting during the course of continuous winding of 
winding carriers, FIG. 4 shows respective double terminal elements 10 
designed in U-shaped fashion which are respectively secured at end faces 
to two neighboring winding carriers 9 having a rectangular cross section. 
These double terminal elements 10 serve as system carriers for the winding 
carriers 9 during the work steps of winding, extrusion-coating, etc. 
Subsequently, the double terminal elements 10 are parted in the middle 
into terminal elements belonging to different winding carriers 9. Welding 
spots 11 and 12 produced according to the method of the invention are 
respectively indicated at the section surfaces of the two U-shaped legs of 
the double terminal elements 10 which are directed to the upper side of 
the winding carrier 9, but project there beyond. Thus, ultimately deriving 
during manufacture is a wound coil whose winding wire is respectively 
welded fast directly by laser irradiation, and is welded to the two 
terminal parts projecting beyond the carrier member without cover lamina 
or the like. 
Compared to the method disclosed by German Published Application 35 18 651 
that provides a (multiply coated) high-grade metallic carrier band having 
arms applied thereto at an angle as an additional system carrier, the 
inventive manufacture of surface mountable coils without a system carrier 
makes an elimination of terminal material possible that corresponds to 
approximately 20% of the material costs of the component. Given 
standstill-free winding--by contrast to German Published Application 35 18 
651, however, the carrier members 9 cannot be brought through the orbit of 
the winding fingers into a winding position. Instead, the carrier members 
9 are situated in the axis perpendicularly and centrally relative to the 
orbit and are also brought into a winding position by being conveyed in 
the direction of this axis, whereby the carrier members 9 are conveyed in 
unwound fashion through the axis of the supply reel for the winding wire. 
Before the winding, the double terminal elements 10 must be joined to the 
carrier members 9, for example with glue. Until the glue hardens, the 
former would therefore have to be held in gluing position; this can be 
carried out on the basis of specific holding mechanisms. These, however, 
can deteriorate the appearance and the solderability of the surface of the 
terminal elements. The advantageous employment of the double terminal 
element 15 shown in FIG. 5 thereby lies at hand within the framework of 
the method of the invention, wherein the two U-shaped legs of this double 
terminal element 15 have window-like recesses 16 which accept the 
correspondingly shaped end faces 14 of the neighboring winding carriers 
13. Thus, the double terminal element 15 is secured to the winding 
carriers 13 with glue and is carried during the hardening of the glue by 
the winding carriers 13 held by a conveyor mechanism. Potential auxiliary 
mounts are thus superfluous and an easier handling in the manufacture of 
the wound components results overall. 
Although various minor changes and modifications might be proposed by those 
skilled in the art, it will be understood that I wish to include within 
the claims of the patent warranted hereon all such changes and 
modifications as reasonably come within my contribution to the art.