DE19846705A1 - Soldering of low melting point highly conductive thin sheet components, especially stud soldering to a sheet, is effected using a solder deposit of low melting solder and high electrical resistance high melting solder - Google Patents

Abstract

Soldering of low melting point, highly conductive thin sheet components (1,2), using a solder deposit of low melting solder and high electrical resistance high melting solder, is new. Thin sheet components are soldered, according to the parent patent application DE19714755.0, by depositing a solder powder on one of the components by means of solder sintering using conductive resistance heating preferably at the particle surfaces, positioning the components so that the solder deposit is located between the components and then locally heating and cooling the assembly between electrodes. In the present invention, the thin sheet components are soldered together by loosely placing a low melting solder powder, mixed with 30-70 % of a high melting solder with a high electrical resistance and a particle size of less than 30 microns , on one of the components or on a lower electrode prior to carrying out the process of the parent patent.

Description

The invention relates to a method for the punctiform and linear connection of sheet metal components from thin sheets by soldering using conductive resistance heating using pul deformed solders. The invention further relates to a method preferably for connecting Bolts with components by soldering using powdered solders and suitable devices for the production of filler metal deposits on the end faces of bolts. The registration is a Addendum to the main patent application 197 14 755.0.

As already stated in the application 197 14 755.0, it is known to use sheet metal components To combine a large number of process variants of resistance spot welding (Krause, M .: Resistance spot welding, German publishing house for welding technology, Düsseldorf, 1993). This The disadvantage of this method is that electrodes of the same type are usually used on both sides when joining partners of the same type there are impressions that usually require reworking on visible surfaces. By using electrodes with larger working surface diameters on the visible side to prevent the electrode impression. Because the melting volume generated during spot welding Always shrinking when it solidifies is a surface indentation in the Area of the welding lens inevitable and therefore usually a reworking, albeit minimized required.

It is also known, as described in the main patent application, by means of projection welding To connect sheet metal parts. Due to the large-area current input typical of the process the problems here are generally less than with spot welding. Hump welding However, it has significant restrictions with regard to the realizable component size, since in general all partial welds mean (must) be created at the same time.

The methods mentioned are often not suitable for joining different materials, because brittle intermetallic phases form when welding different combinations.

In the main patent application, reference was also made to a known method by means of con structural resistance heating to produce solder connections (ZIS-Mitt., Halle 29 (1987) 4, p. 367-374). The disadvantage is that so far either a third part (solder foil, solder wire, solder paste or similar) to be positioned immediately during the joining process or a part with a coating must be provided. When using galvanic coatings as solder, that must  complete component must be coated. The choice of the applicable solders is then strong limited.

In the main application it was therefore proposed to use a bed of solder powder on one of the parts to be connected, on partial surfaces, i.e. h Sub-areas that correspond to the later bonding areas are to be created by means of conductive resistance heating and after placing the second sheet thereon also by means of conductive resistance heating to produce punctiform solder connections. However, there is a problem with the use of this method in certain cases:
When connecting sheets made of materials with high electrical conductivity and low melting point, e.g. B. Al, it was found that it is not possible to use the existing solders to produce connections without melting the base materials, which means that due to the small difference in melting points, melting of the base materials cannot be avoided.

The creation of solder deposits, in order to then make point-like solder connections, as in the The main patent application described should be emphasized in another aspect. It has been shown that these depots are also suitable for soldering connections between egg to produce a component and a bolt end face. However, this has the disadvantage that to educate on the bolt side, the connections of the depot diameter are very good on the bolt diameter knife must be matched and the bolt must be positioned exactly on the depot.

In addition, it must also be stated that when connecting the end face of bolts with sheets or massive metal parts known to be different variants of arc welding come to turn (Trillmich, Welz: stud welding, specialist book series welding technology, vol. 133, DVS publishing house Düsseldorf, 1997). However, all of these process variants have disadvantages.

So welding with tip ignition has the advantage that there is very little heat flow zone arises and thus bolts can be attached to sheets of only 1 mm thick nen without this being visible from the back. The disadvantage is the high vulnerability of the Process for surface contamination.  

This disadvantage is avoided by the drawn-arc or short-term drawn-arc variants. However, this can cause problems when welding on solid steel parts due to hardening in follow high cooling speeds or when welding different materials Emergence of brittle phases occur.

Especially when welding studs to sheet thicknesses that are small compared to the stud diameter, there is a risk of pore formation. Therefore, limit values for ver Ratio of bolt diameter to sheet thickness, namely max. 4: 1 for drawn arc or 8: 1 for short-term drawn arc ignition (DVS leaflet 0902 stud welding with drawn arc ignition).

Based on the main patent application, according to which a soldering process and a corresponding one Device for generating solder deposits on sheet metal surfaces has been proposed and knows thereafter assuming that the lot depots also correspond to the main patent application other metal components can be placed, it is the task of the additional application, especially to enable the soldering of materials with high conductivity and low melting point (here especially from the point of view of joining thin sheets) and spot soldering with the help of the depot to modify it so that it meets the special conditions of the Bol zenbefestigungsstechnik adapted and this is thus further developed.

According to the invention the object is achieved as follows, with regard to the basic inventions derische thoughts on the main claim 1 and the secondary claims 4 and 7 is referred. In the further embodiment according to the invention, dependent claims 2, 3, 5 and 6 referred.

Further explanations are required for the invention.

For connecting components consisting of materials with high conductivity and low This becomes the melting point, especially for the point and line-shaped joining of thin sheets Solder powder with high conductivity mixed with a proportion of poorly conductive powder. In connection the solder depot is then created as described in the main patent application.

When soldering bolts, the process of creating solder deposits according to main pa Modified tent registration so that the solder deposit is created on the bolt end.  

The method for bolt fastening is carried out analogously with the devices, as in the main patent application for the production of the point-shaped solder deposits be proposed. For certain bolt shapes, the devices for production Lot depots represent expedient modifications to the main patent application.

With regard to the connection of components especially for the point and line-shaped connection of highly conductive sheet metal components, preferably made of thin sheets using solder deposits, the method includes the following steps:

• - A powder mixture (powdered solder) consists of a special solder powder mixture, this solder powder mixture on a component or on one located under the component Electrode is placed. The solder powder mixture consists of a portion of low melting Solder and a proportion of higher melting solder with high electrical resistance. The higher melting solder with a grain size of <30 µm with a share of 30-70% mixed with the low melting solder.
• - The further steps up to the connection of the components result from the main pa tent registration.

Reference is made to claim 1 of the main patent application.

The metal powder mixture required to carry out the method according to the invention represents a novelty for the special application. For this purpose, claim 3 referred.

When applying bolts to components such as sheets, rails or the like by punctiform soldering, the following procedure is proposed:

• - Creation of a solder depot by resistance heating; with it sintering process of the powder grain ner with each other and at the same time diffusion process between the powder bed and the Bolt face that is to be connected to a component.
• - Subsequent soldering process using
  Resistance heating
  Arc heating
  inductive heating
  or other point heat sources,
  by positioning the end face of the bolt and the component in relation to one another and making the connection under point heating and force in accordance with the main patent application.

In this regard, reference is made to the auxiliary claim 4.

An expedient arrangement of a solder deposit and the design of a device result themselves from subclaims 5 and 6 to subsidiary claim 4.

The generation of a so-called solder tablet is another useful embodiment of the Main patent. In this regard, reference is made to the auxiliary claim 7.

The invention will be explained below using several exemplary embodiments.

In the accompanying drawings:

Fig. 1 section through the arrangement of two sheets for soldering according to the main patent application

Fig. 2 section through a connection of 2 Al sheets using commercially available AlSi 12-solder powder.

Fig. 3 section through an aluminum sheet connection, which was generated according to the invention.

Fig. 4 to 6 The procedure according to the invention for the production of solder-deposits on bolt ends.

Fig. 7 An arrangement according to the invention for establishing a solder connection between the end face of a bolt and a sheet.

Fig. 8 modifications of solder deposits to 9 two bolts according to the invention at the end faces for the utilization of an arc as an energy source for bolt soldering.

Fig. 10 A solder depot generation according to the invention on a stud which is provided for soldering by means of arc heating.

Fig. 11 arc soldering.

With reference to FIGS. 1 and 2, the experiences that have been made in the application of the method steps according to the main patent application will be explained when it comes to the connection of sheets made of materials of high electrical conductivity and low melting point, eg. B. to connect aluminum sheets. An aluminum sheet with a melting point of 659 ° C was provided with a solder depot 5 made of Al-Si 12 powder with a melting range around 580 ° C in accordance with the main patent application. The aluminum sheet 1 with the solder deposit 5 was also positioned in accordance with the main patent application with an aluminum sheet 2 between the lower electrode 3 and the upper electrode 4 of a spot welding machine. In the subsequent process step of joining, due to the very close melting points of solder depot 5 or aluminum sheet 1 and 2, it is not possible to prevent the sheets 1 , 2 from melting in the desired manner. By melting the solder deposit 5 and melting the aluminum sheets 1 , 2, a common melt is formed, which solidifies into a melting lens 6 at the end of the process.

The modification of the process according to the invention consists in first producing a powder mixture of the solder AlSi 12 and a higher-melting metal powder with a high specific resistance. A NiCrBSi solder powder was used and a mixing ratio of 1: 1 was chosen. With this powder mixture, a solder deposit is created on the aluminum sheet in accordance with the main patent application. In the subsequent process step of producing the connection, the current can be significantly reduced, so that melting of the aluminum sheets is avoided. Due to the admixture of the poorly conductive NiCrBSi powder, the average resistance of the solder depot is almost twice as high as before, so that the AlSi 12 solder is melted despite the low current. The NiCrBSi particles also heat up, but are not melted and remain trapped in the solder joint. Fig. 3 shows a section from the solder joint after solidification of the solder. The two sheets 1 , 2 were connected without melting by the AlSi 12 solder 7 . The NiCrBSi particles 8 are unaffected in the solder. The initially used NiCrBSi powder with a particle size range of 20-60 µm provided a relatively brittle fracture behavior when the shear tensile test of the connection. A repetition with a finer powder with a grain size range of 10-20 µm brought about the retention of the above-mentioned effect in the joining process, but an improvement in the fracture behavior.

Referring to Figs. 4 to 6, the generation of solder depot is described on bolt end faces below.

The bolt 9 , which is to be provided with a solder deposit on its end face 10 , is tensioned in the upper electrode of a spot welding machine designed as a tension electrode 11 such that its end face 10 and the end face of the lower electrode 12 are parallel to one another. A solder powder bed 13 is located on the end face of the lower electrode 12 . The clamping electrode 11 and the lower electrode 12 are connected in a known manner to the secondary winding 14 of the welding transformer. After actuation of the spot welding machine, the upper clamping electrode 11 with the bolt 9 moves downward in accordance with the main patent application and a force effect is generated between the bolt 9 and the lower electrode 10 . The current flow that then takes place in the powder bed 13 initially heats and then sinters the powder grains with one another and at the same time a diffusion process between the powder bed 13 and the bolt end face 10 .

FIGS. 5 and 6 show the state at the end of this process stage before or after the lifting of the clamping electrode 11. A solder depot 15 was created on the bolt end face 10 . The excess powder 16 remains in a ring around the bolt or on the lower electrode 12 . The solder depot 15 is now securely fastened to the bolt end face 10 and can be used to produce a solder connection between the bolt and a sheet metal.

According to FIG. 7, the production of a solder connection using the conductive resistance heating is to be explained.

The bolt 9 with a solder deposit 15 is clamped in the upper electrode of a spot welding machine designed as a clamping electrode 11 . The sheet 1 on which the bolt 9 is to be fastened lies on the large-area lower electrode 12 . The upper and lower electrodes are connected to the secondary winding 14 of the welding transformer.

After actuation of the spot welding machine, power build-up, current flow and the heat generation associated therewith run in a known manner. Here, between the sintered particles of the solder depot 15 and the surface of the sheet 1 , microscopic relative movements still take place, which favor the bonding process. The solder deposit increases in diameter while its thickness decreases. At the end of the process, after the current has been switched off, repressing takes place in a known manner, so that the formation of the connection is completed under pressure and a punctiform soldering is produced between the end face of the bolt 9 and the sheet metal 1 . The surfaces of the bolt 9 and sheet 1 are not melted.

The generation of the soldered connection between the bolt 9 and a sheet metal surface is, however, not restricted to a specific heating process. Rather, all processes that allow point heating are suitable for this.

In the following, the heating by means of an arc will be described with reference to FIG. 8.

The modified geometry of a bolt 9 is explained with solder depot 15 for soldering with conventional stud welding technique based on Fig. 8.

For stud welding with drawn arc or short-term drawn arc, studs are usually used which are provided on the end face with a very obtuse taper angle of α = 166 °. According to the invention, this cone is provided with a solder deposit 15 . The device required for generation will be discussed later.

Fig. 9 shows a modification of the solder depot generation according to the invention to the requirements of the welding with a rotating arc, to which is also known device technology can be used.

Referring to the FIG. 10 will be discussed on the apparatus which is proposed for the production of solder-deposits on front sides of bolts 9, when the end faces of the pins are provided with a taper angle of α = 166 ° 9. The device has a conical shape 17 with the angle α = 166 °. The conical shape 17 is approximately filled with a powder fill 13 . Analogous to the description of FIGS. 4 to 6, the solder depot is generated in the conical shape 17 .

Fig. 11 shows the soldering process by means of short cycle in the heating phase. The solder drips off the bolt 9 and wets the sheet. The dripping solder is provided with the position symbol 18 . In the second, final phase, the bolt 9 is pressed onto the liquid solder (analogous to the known short-time drawn arc welding process).

Furthermore, it was found that by heating solder powder between two Cu electrodes the solder powder particles can be sintered into a solder tablet.  

Reference list

1

,

2nd

- Al sheet

3rd

- lower electrode

4th

- top electrode

5

- Lot depot

6

- Melting lens

7

- Lot

8th

- Grains of a higher melting metal

9

- Bolt face

11

- clamping electrode

12th

- lower electrode

13

- powder spill

14

- secondary winding of the welding transformer

15

- Lot depot

16

- excess powder

17th

- conical elaboration

18th

- dripping solder

Claims (7)

1. Soldering method for connecting sheet metal components made of thin sheets, consisting of materials with high conductivity and low melting point, according to patent application 197 14 755.0, characterized in that a powder bed ( 13 ) consisting of a solder powder mixture of a low melting solder and a higher melting one Solder with high electrical resistance, with the higher melting solder being mixed with 30-70% of the lower melting solder and the higher melting solder having a grain size of <30 µm, on one of the parts to be connected or on an electrode which is located underneath one of the parts to be connected, is placed loosely and the process steps according to patent application 197 14 755.0, claim 1, are carried out further by the metal powder filling by means of conductive resistance heating on one of the parts to be connected, preferably on partial areas which correspond to the later binding areas, by means of Solder-sintering is deposited in a transport-safe manner, the parts to be connected are brought into the desired position, the solder depot partial surfaces being between the parts to be connected and the local heating of the parts to be connected and the solder, the formation of the connection and the cooling under the influence of the electrodes. 2. Soldering method according to claim 1, characterized in that the powder fill ( 13 ) using devices for producing linear filler material depots according to patent application 197 14 755.0, claims 6, 7, is used. 3. Powder filling according to claim 1, characterized in that the powder filling ( 13 ) consists of a solder powder mixture, namely from a proportion of powder mixture with a low melting point, preferably the solder AlSi 12 and a proportion of powder mixture with a higher melting point with high electrical resistance, preferably the solder NiCrBSi, the solder solder NiCrBSi has a grain size <30 µm and the proportion of NiCrBSi solder in the solder powder mixture is 30-70%. 4. Soldering method preferably for connecting the end faces of bolts or pins with sheet metal components using powdered solders according to patent application 197 14 755.0, characterized; that the powdered solder is placed as a powder bed ( 13 ) on a lower electrode ( 12 ), the powder bed ( 13 ) is deposited safely by means of resistance heating on the bolt end face ( 10 ) by means of solder sintering, and then a positioning between the bolt end face ( 10 ) and the component takes place and now the bolt surface ( 10 ) and the component are connected under point heating, preferably by press soldering, that is to say with simultaneous application of force. 5. Soldering method according to claim 4, characterized in that the solder depot on the sheet metal part is soldered on. 6. The device according to claim 4, characterized in that a device as a lower electrode has a conical shape ( 17 ) with an angle which corresponds to the angle which the conical end face of a bolt ( 9 ), wherein the bolt ( 9 ) during manufacture of the conical solder depot ( 15 ) represents the upper electrode. 7. Method for producing solder tablets using commercially available solder powder and commercially available resistance welding machines with electrodes made of commercially available copper Alloys according to patent application 197 14 755.0, characterized in that Introducing the solder powder between the two electrodes in the welding program known sequence pressure build-up current flow pressure reduction takes place and thereby a sintering process takes place between the individual solder powder particles, so that a tablet-shaped Solder molding is created.