Process and apparatus for producing welded stamped parts

A process for producing at least two joined-together stamped parts stamps the two stamped parts in stamping operation of a stamping tool in a stamping press that retains the two stamped parts and welds the two stamped parts together at least at one location in the course of the stamping operation with the beam of a laser.

The present invention relates to a process for producing at least two 
joined together stamped parts, and an apparatus for carrying out the 
process. 
A known manner of joining two materials within a stamping machine is 
contact welding (e.g. the CONTRAP system). Hereby pre-stamped contacts are 
joined to parts separated from a profiled wire by means of resistance 
welding. This welding requires relatively much energy. The stamping cycle 
is limited to about 400 strokes per minute. 
A process of this kind is known by the term of FASTEC.RTM.; it has been 
developed by KURODA PRECISION Industries, LTD. With this process single 
stamped parts can be joined together in a stamping tool. The joining 
occurs by means of recesses (depressions) or the like so that the stamped 
parts fit into one another by being pressed or clutched. This process is 
used particularly for producing stacks of sheets, for example, for rotors 
and stators. A process of this kind is known from the German Application 
32 03 123. 
In these processes all operations are carried out within a multi-staged 
operation die, comprising a plurality of single dies. The processes are 
disadvantageous because 
the average stamping speeds at 3 to 400 strokes per minute are regarded as 
being low; 
the tool, which is required for producing such stamped parts, is 
complicated in design and expensive in production, and 
due to a locally limited joining of the stamped parts, they can deform so 
that they do not mate satisfactorily and, therefore, cannot be combined 
into a stack. 
Furthermore, it is known that in a multistage operation die there is 
provided a modulus for feeding parts and one for joining the stamped part 
to the part fed by means of laser welding in addition to the moduli for 
stamping, punching, bending, etc.. 
A disadvantage of this process resides in that the multistage operation die 
is burdened with operations not related to the stamping process. 
The object of the invention is to eliminate the aforestated disadvantages. 
It is an object of the invention to create a process for producing at least 
two joined together stamped parts, providing that the stamped parts are 
joined undetachably, cohesion is substantially increased, and the 
precision of measurement of the stamped parts joined together is improved 
toward one another. 
According to the invention, the object is achieved by means of the 
characterizing feature of claim 1. 
The advantages to be achieved are essentially seen in that the stamping 
speed can be increased, and the effect of the joint upon the form of the 
stamped parts can be reduced to a minimum. 
In a preferred embodiment of the process, in which the stamped parts are 
combined into a stack, adjacent stamped parts in the stack are welded 
together in an area of the superposed edge. 
The advantages resulting therefrom are seen in that the quality of the 
joint is improved, and the stacking in the stamping tool occurs in a 
precise superposed fashion, due to which separate known stackers drop out 
and the stamping cycle can be shortened. 
An apparatus for carrying out the process is characterized by claim 9. 
The advantages of the apparatus are seen in that the stamping tool is 
simplified and the stroke-frequency of the stamping press is increased.

In the process under discussion, the stamped parts are welded together 
within a stamping cycle by means of laser welding. The stamping cycle 
depends on the part to be stamped and, in the simplest case, it can 
consist of a single stamping operation. The succession of the stamping 
operation is predetermined by the stamping device, for example, by means 
of a shaft encoder coupled to the eccentric shaft of the stamping device. 
If two stamped parts are to be welded together, the welding occurs only in 
the second stamping operation, and the stamped parts must be in an 
off-position. 
FIGS. 1 to 4 show various forms of application of the process according to 
the invention; herein the same reference numerals are used for 
characterizing like elements. 
In the form of application, which is shown in FIG. 1, stamped parts 1 and 2 
have a recess 3 and can be welded together at the outer edge 4 and/or at 
edges 5 formed by recess 3 by means of laser beams 6 from laser-sources 7. 
Contrary to the form of application shown in FIG. 1, FIG. 2 shows a laser 
6, which is directed via a reflection means 8, for example, a mirror, to 
the area to be welded. 
FIG. 3 shows a form of application in which a punctiform welding of stamped 
parts 1 and 2 is carried out. 
FIG. 4 shows a form of application providing that two angle sections 9 and 
10 are welded together. 
In this context it will be pointed out that the process in not limited to 
the forms of application outlined. 
As FIG. 5 shows, an apparatus for carrying out the aforementioned process 
includes a stamping press comprising a slide 11 and a platen of a press 
12, a stamping tool 13, and a laser device 14 having a focusing device 15. 
The stamping tool 13 is mounted on a platen of the press 11 in a manner 
known pre se. The stamping tool 13 is developed in dependence on the part 
to be stamped and includes, as is well known, a lower part 16 of the tool, 
an upper part 17 of the tool, guide columns 18 for the upper part of the 
tool, which are mounted on the lower part of the tool, a holding plate 19 
comprising a stripper 20, which is directed along the guide columns, a 
pressure plate 21, a die 22, and a die holding plate 23, which is mounted 
on the upper part 17 of the tool, and also guide plates 24, 25 for the 
material, which is in the form of a tape (not shown), and a matrix 26 
mounted in the lower part 16 of the tool. 
An arrangement 31 for holding and adjusting the focusing device 15 of the 
laser device is disposed on the platen of the press 12. The focusing 
device 15 is connected to the laser device 14 via a light-guiding cable 
32. Advantageously, the laser device 14 is a pulsed laser, the radiation 
source of which is a glass rod or a YAG rod. In order to adjust the 
focusing device 15, arrangement 31 is provided with an adjusting member 
33. A laser, including a radiation divider, for welding in several 
locations, as, for example, it is shown in FIG. 2, is foreseen in the 
example described above. However, it is also possible to provide two 
welding apparatus 14, 15, which lie opposite each other, and are held, 
respectively, by arrangement 31. 
An observation device, which is coupled to the focusing device, is provided 
for adjusting a laser beam. In addition to the heretofore described 
separate arrangement of laser device 14 and focusing device 15, it is also 
possible to use a laser device having an integrated focusing device and 
observation device. 
The welding apparatus 14, 15 are controlled by a control instrument 34. The 
control instrument contains a shaft encoder, which is mechanically 
connected to the eccentric shaft of the stamping press, a scanner, which 
cooperates with the shaft encoder, and a control circuit, which receives 
signals from the scanner and transmits control signals for carrying out an 
appropriate function within an operation. 
Underneath matrix 26 there is mounted a brake 27, with which separate 
stamped parts can be delivered as a stack. 
As FIG. 6 shows, recesses 37 are provided in the matrix 26 and, 
consequently, also in the lower part of the tool, and holes 36 are 
provided in the die 22 in order to direct the laser beam 6 onto the 
stamped parts 1, 2 to be welded together. 
A preferred embodiment of the process concerns the production of stacks of 
sheets from electric sheets, for example, for rotors, stators and 
transformers. FIG. 7 shows the work cycle in this process in dependence on 
the rotation of the eccentric shafts. 
As FIG. 7 shows, the cutting operation I ends when the bottom dead center 
B.D.C. is reached. Subsequently there occurs an extension II of the die. 
In the area of the bottom dead center B.D.C. the laser beam 6 can be 
directed to the outer or inner edge 4 or 5 when the die 22 is provided 
with oblong holes 36,37. In the case a die 22 is not provided with oblong 
holes, a laser beam 6 is used at III. Subsequently a welding operation IV 
is carried out; it ends when the upper dead center U.D.C. is reached. Tape 
feed V begins immediately after the upper dead center; it is followed by a 
clamping operation VI. During the feeding of the tape V and the clamping 
VI there occurs a twisting of the stack VIII. After the clamping operation 
VI a cutting operation I is prepared by adjustment VII of a pilot pin, 
whereupon a new cycle begins. 
It is apparent from the above description that the process according to the 
invention offers a special advantage of carrying out a welding operation 
at the bottom dead center and the upper dead center. 
Thus, one can produce stacks of sheets which with regard to quality greatly 
surpass those produced according to prior art processes, and which also 
have much better operation characteristics and electrical properties; one 
would also have to pay special attention to the fact that work can be 
carried out at a high stamping speed, for example, 800 strokes per 
millimeter, and that the stamping tools undergo a substantial 
simplification.