Segmental control of position-dependent welding parameters

Abstract

It would be desirable to improve the method for forming a hot crimp joint so that it is possible to form a long-term stable electrical connection between an electrical conductor and an electrical terminal with as few qualitative variations as possible.To achieve this goal, it is proposed to pass through successive metallurgically distinct sections: Segment 1: A first joint is formed between the molded part and the outer layer of the wire and / or the outer layer of the litz wire by a complete and / or partial eutectic melting process of the outer wire, the insulation of which has been removed by compaction and / or pre-deformation, which proceeds in parallel in time; Segment 2: A diffusion and / or at least partial melting joint is formed between the inner wire of the litz wire, the insulation of which has been removed by compaction; Segment 3: Currentless cooling of the hot crimped composite, in which switching between at least two successive segments takes place after reaching a segment-specific height position and / or after the supplied energy or charge has been reached.

Description

[Technical Field]

[0001] The present invention relates to a method for forming a hot crimp joint between a molded element and at least one litz wire of at least two strands of at least one wire and / or metal, wherein the simultaneous compaction and deformation results in both a material connection between the joining components and a material connection between the wires of the litz wire. [Background technology]

[0002] Evaluation of control parameters common today Resistance characteristic: This characteristic is calculated from the quotient of the measured voltage and the measured current. Since direct measurement of the voltage in the joint zone is technically impractical, the voltage measurement is subject to errors due to the contact resistance of the components and electrodes as well as the material resistance of the components and electrodes. However, a rough estimation is possible. Current and voltage characteristics: This is an issue when measuring resistance. Temperature characteristics: The temperature can only be measured externally. The temperature in the bonding zone cannot be controlled directly. The measuring spot is often too large and detects the structural member and the electrode as if they were in the same area. For optical systems, the correction factors are difficult to determine and are not constant. A thermocouple measures the electrode temperature in the area of ​​the cooling zone. Pressure characteristic: An additional measurement quantity for controlling pressure characteristics. Submergence distance: The amount of electrode movement caused by the joining process. Since the entire section is detected, no information is available about the time characteristics of the movement. Final End Height: Customer-specific control. If the start height is not detected, the measurement will not deliver information about the actual overall sinking distance. Summary of the Invention [Problem to be solved by the invention]

[0003] The object of the present invention is to avoid the above-mentioned drawbacks and to form a long-term stable electrical connection between an electrical conductor and an electrical terminal with as few qualitative variations as possible, and further to make it possible to produce it quickly and at low cost. [Means for solving the problem]

[0004] This problem is solved by the method steps set forth in claim 1. Further method steps are set forth in claims 2 to 16. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a diagram illustrating an example of the characteristics of a hot crimp process according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0006] The present invention will be described in detail with reference to the drawing (Fig. 1), which shows an example of the characteristics of the hot crimping process according to the present invention.

[0007] 1 shows an exemplary possible configuration of a hot crimp process (15) with an immediately preceding preforming or pre-crimping phase (14), which here consists of a cold crimping phase (16) and a hot crimping phase (17). The hot crimping phase (15) here consists of the following sections: Segment 1 (10), Segment 2a (11), Segment 2b (12), and Segment 3 (13).

[0008] In segment 1 (10), the detection of the start height 4 begins and ends when the switch height of segment 1 (6) is exceeded. The energy input in segment 1 (10) can be estimated from the height difference between the thermal expansion stroke (5) and the start height of the hot crimp (4). This initial energy results in the first joint formation (section a) in segment 1 (10). The current characteristic (2) is divided in this case into a ramped current characteristic during heating (18) and, optionally, a constant current characteristic during hard soldering (19). The first joint formation here can begin as early as the heating phase (18) and end in segment 2 (11 or 12) without any restrictions. The temperature evolution in the joint zone depends heavily on the force characteristic (1), the current characteristic (2), the start height (4), the heat input in the pre-crimping phase (14), and the position and duration of the switch heights (6+7+8).

[0009] Upon reaching the first bond structure at segment 1 (10), further energy is supplied, but at a modified level, whereby the current (2) and force (1) are adapted to the requirements of forming a diffusion bond and / or partial fusion bond when the switching height (7+8) is reached at segment 2a+2b (20+21).

[0010] When the final switching height in segment 2, here switching height (8), is exceeded, the current is interrupted (22) and cooling (23) in segment 3 (13) begins in relation to the further depression of the crimp height (electrode follow-up).

[0011] The time characteristics of the crimp height (3) in each segment are determined primarily by the position of the switching height (here 6, 7, 8), the current (2), the pressing force (1), and the preheating in the preceding segment.

[0012] The claimed method divides the joining process with material connections into several segments, each with a different set of parameters and acting differently metallurgically. The switching criterion for each segment is exceeding a set cutoff height. If reliable switching is not possible because the electrode is not immersed deep enough in one segment, the cutoff can also occur after a defined time period.

[0013] Since the force should be switchable segment by segment, preferably no current flows for the duration of the force regulator's transient response process, thereby avoiding overheating of the electrodes and / or structural members due to an excessively small force in the event of a force undershoot.

[0014] However, such short pauses usually result in further compaction of the litz wire, which leads to uncontrolled electrode subsidence, so that the predetermined breaking height of each segment can be used as the criterion for switching the segments, rather than the subsidence distance during current flow.

[0015] The methods described herein are applicable to multiple metals and alloys thereof, such as, for example, copper, aluminum, iron, titanium, nickel, either individually or in admixture.

[0016] The most important welding parameters are current, pressure, and duration. These parameters depend on the dimensions of the components and electrodes to be joined, as well as the material properties (type and thickness) of the components, electrodes, and coatings.

[0017] Additionally, the cooling element and the current source must be considered. In the case of current sources, AC / DC, phase difference, pulse width or similar quantities, current direction and control type (constant current, constant voltage or constant power) are important.

[0018] In hot crimping, the mechanical and physical processes, i.e. deformation and joining, are interlinked.

[0019] More generally, cold crimping herein refers to mechanical deformation (subsequent hot crimping) between at least one forming element and a litz wire, possibly assisted by the flow of electric current. Also referred to herein as pre-pressing or pre-forming or pre-crimping.

[0020] Hot crimping is understood here to be at least a two-stage joining process involving simultaneous mechanical deformation of at least two joining partners (molded element and Litz wire).

[0021] Essentially, during hot crimping, one or more wires and / or round or shaped wires, typically Litz wires, are joined to shaped components such as cable shoes, sleeves, tabs, plug-in connectors, butt connectors, thereby achieving a permanent mechanical and metallurgical material connection between these structural components.

[0022] This process is roughly divided into two parts: pre-pressing or pre-deformation to form a defined and enlarged electrode contact area, and the actual hot crimp. The latter can be further divided into complete or partial melting of the solder, where the hard solder has diffusion barrier properties against the soft solder. However, joining partners, for example, structural components made of copper, can also be used directly without coating the aluminum wire of the litz wire, possibly with partial melting of the litz wire in a subsequent diffusion step. In the latter case, the litz wires are joined to each other.

[0023] At the same time, the compaction process removes the insulating layer both during the pre-pressing and during the hot crimping process. The insulating layer here can be an oxide layer, a resist layer, an insulating layer, or a contaminant layer, as is known. The coating or solder can be applied galvanically (with and without current), physically (by sputtering), as a molded insert, or in a rolling technique.

[0024] Studies have shown that the pressing force and current of each segment as well as the achievable sinking distance of each segment are crucial to the weld quality.

[0025] Unlike the typical adjustment parameters, i.e., current, pressure, and duration of each segment, a parameter set consisting of current, pressure, and cutoff height is proposed here. It has been found that time control cannot achieve a sufficiently reliable and reproducible hot crimping process due to the many influencing variables.

[0026] The energy or charge delivered to each segment can be used as an additional or alternative criterion for switching to the next segment.

[0027] Various variants of hot crimping are proposed: in one-shot, the pre-pressing and the actual hot crimping are carried out in the equipment without temporarily removing the component, while in two-shot, two equipments are used.

[0028] In two-shot welding, one device is used for pre-crimping, and the second device is used for hot crimping. During pre-crimping, pre-crimping is performed by cold crimping (currentless compaction) and / or with the aid of a low preheating current, with the aim of achieving a defined pre-crimp height and / or a defined electrode contact area. However, in cold crimping, the cold crimp height is essentially determined exclusively by the pressing force and material properties, and therefore is less suitable for practically higher quality. Additional height cutoff can be achieved.

[0029] Therefore, preferably, the cold-pressing process is directly followed by hot-pressing with height monitoring, which results in a defined pre-pressing height and also in a substantially identical contact area for the electrodes in the same step.

[0030] The structural elements thus preformed and fixed to one another, i.e. the Litz wires with the shaped elements, are joined to one another by a material connection in a subsequent hot crimping step.

[0031] This step is similarly divided into segments.

[0032] The first segment introduces the energy required to form a eutectic fusion bond between the outer wire of the Litz wire and the molded part. The most important control parameters are the pressing force, current, breaking height, and energy or charge.

[0033] After exceeding the maximum spread above, a switchover to segment 2 is subsequently made if a switchover height and / or energy or charge specifically defined for segment 1 is exceeded below.

[0034] After a first joint structure is obtained in the joint zone between the outermost wires of the litz wire bundle and the shaped element in segment 1, diffusion bonding and / or at least partial melting of the litz wires to one another takes place in the second segment and possibly further sub-segments, again with the parameters of pressure, current and interruption height and / or energy or charge being determined separately for each segment.

[0035] After the final switching threshold is reached, the current is switched off and cooling begins with the newly adapted pressure.

[0036] This multi-stage process control prevents, for example, low-melting point Litz wire from migrating into the melt in unacceptable amounts, thereby weakening the overall joint strength through alloy changes and cross-sectional area reduction.

[0037] Important quality criteria for monitoring the welding quality can be the measured expansion of the formed element and the Litz wire as a result of thermal expansion due to the introduced current, as well as the detected current flow duration or the energy or charge introduced into each individual segment.

[0038] One-shot combines the pre-pressure and hot crimp processes into one overall process.

[0039] In another configuration, the pre-pressurization phase may be incorporated into the heating phase of segment 1.

[0040] To control the joining process non-destructively, resistance characteristics, current or voltage characteristics, temperature characteristics, pressing force characteristics, sunk distance or final finish height are usually used.

[0041] Destructive testing according to DIN or customer specifications can be carried out in batches.

[0042] The objective of the control is to ensure a joint with a stable material connection between the structural members or weld partners over the long term.

[0043] For welding tasks, such as hot crimping, the present invention has proven advantageous to divide the welding flow into several segments, each of which usually has a different set of parameters, so that the various metallurgical transformations during the joining process are better taken into account and further measurement quantities become available for assessing the quality of the welded connection.

[0044] The bonding method is characterized by dividing the bonding process into multiple segments with optimal process parameters for each segment, and quality control is performed by monitoring the thermal compensation process of each segment, the actual individual segment duration, and / or the sinking speed, and / or the supplied energy or charge, or current duration.

[0045] The measurement data and adjustments of each individual structural member are stored in a database. Individual labeling is performed, as is known, by applying a data code, such as a bar code, a data matrix code, etc., to one of the components. Limited traceability is also achieved by using LOS cards and time stamps.

[0046] Importantly, such multi-step joining techniques allow for the formation of material connections and mechanically fixed bonds between identical or dissimilar metallic materials. In particular, two-step methods allow for the joining of materials with melting points that are significantly different from each other. Without applying the methods described herein, the lower-melting-point material may transition into the melt and subsequently form a bond between the joining partners.

[0047] Today, in parameter discovery, current strength and time must always be adjusted separately to determine their influence on the deformation and thus the sinking distance over a given time in the test. Furthermore, in the case of hot crimping, fluctuations in the power grid are expected due to the high current demand, which makes parameter discovery in the definition phase and stable production quality in the production phase even more difficult.

[0048] The solution to this problem is the height-dependent and / or supplied energy or charge-dependent switching of individually optimized hot crimp segments. The duration is adapted for each segment by a switching mechanism to the specific conditions of the structural element. In this way, variations in material properties, dimensions, current supply, electrode wear, etc. are compensated for independently for each individual structural element.

[0049] In association, this means a very high level of production quality and the possibility of traceability and process optimization, which makes it easy to detect and automatically evaluate batch variations and / or equipment instabilities and to intervene in an automated manner.

[0050] The physical properties of the materials, e.g., electrodes, determine the temperature characteristics of the intrinsic heating between the three sections a, b, and c. Highly ohmic materials, e.g., tungsten, result in stronger intrinsic heating than low-resistivity materials, e.g., copper.

[0051] Furthermore, thermal conductivity influences the heat dissipation from the contact zone for cooling, and specific gravity and specific heat capacity change the heating behavior of the electrode according to the equation for adiabatic heating.

[0052] Adiabatic temperature rise = current 2 / area 2 *Resistivity / Specific gravity / Non-thermal capacity*Period observed, besides the material selection, the area of ​​the contact zone and the contour of the contact zone (flat, concave or convex) may also play an important role in fixing the electrode.

[0053] According to the concept of the invention, an application-specific optimization of dimensions and materials is now proposed in order to control the heat flow in the shaped element and in the litz wire in the required manner.

[0054] For example, if the application requires a stronger heat generation, for example, on the lower electrode, this heat generation is preferably made of a more ohmic material than the opposing upper electrode and / or with a relatively small contact area. This occurs in molded parts where the litz wire in the contact zone on the lower "tongue" side must be heated more than the litz wire in the contact zone on the upper "tongue" side. A current change or duration change will only result in identical electrode heating on both sides.

[0055] To create a long-term, stable material connection between the profile and the litz wire, the process is divided into sections. This is important because the heat generation in the joining zone between the profile and the outer wire of the litz wire, as well as the heat generation within the litz wire composite, is controlled so that the melting temperature of, for example, aluminum, is only partially reached. The complete melting that occurs in resistance welding can lead to errors such as:

[0056] The compaction pressure required to break the non-conductive layer on the wire (oxide and / or resist layer) formed by the crimping process cannot be achieved. Conversely, the molten litz wire material (e.g., aluminum) is crushed, resulting in an insufficient contact area between the litz wires. Furthermore, heat generation is primarily due to the current flowing through the electrodes and forming elements, rather than through the current flowing through the litz wire (self-heating).

[0057] After the outer wire is attached to the sleeve, the increased deformation, and the resulting increased contact area between the wire, the oxide layer, and the insulating layer, is removed by pressure and temperature, and only enough energy is supplied to keep the litz wire at the diffusion temperature. If enhanced melting of the litz wire occurs in this section, this can result in unacceptable melt flow and poor bonding of the wires to each other.

[0058] To form a melt, first Joule heat is required to reach the melting temperature, then the heat of fusion. Additional heat must be introduced, which flows through the electrodes and components. Typically, the heat of fusion is nine times higher than the Joule heat.

[0059] In contrast, diffusion bonding requires high pressure, high temperatures but below the melting temperature, and long durations.

[0060] To prevent the formation of an intensive melt, the entire process is divided into sections, possibly subsections, so that a solid diffusion bond is formed at high pressure and for as long a time as possible, without forming a fusion bond inside the litz wire. Different current adjustments, current flow times, or sinking speeds for all segments prove useful. Switching between segments is preferably controlled by height and / or can be performed depending on the supplied energy or charge.

[0061] What helps ensure a diffusion process instead of a melting process is the physical property that the heat demand to form a melt is about nine times higher than Joule heating.

[0062] Local, often point-like, melting occurs between the wires because, during deformation, some of the wires come into point-like contact with one another (asperities), small areas of which generate very high temperatures.

[0063] The first bond between the molded element and the litz wire occurs by eutectic fusion between the litz wire material and the molded element. The two materials can be coated on each side or both sides together, so that many other possible combinations are possible, such as, for example: a combination of blank shaped components made of copper and blank Litz wire made of aluminum; Combination of coated copper profiles with aluminium Branlitz wires, a combination of a profiled element made of coated copper and a litz wire made of coated aluminum; a combination of blank profiles made of copper and coated aluminum litz wire; occurs.

[0064] Known soft solders for coating are tin and zinc, while hard solders are available as aluminum hard solders according to DIN, or eutectic solders with favorable diffusion barrier properties, such as nickel or silver. The material for the coating varies depending on the component material. The eutectic temperature is crucial.

[0065] Important for the hot crimp joining technique is the requirement that the joining partners have a eutectic melting temperature lower than the melting temperature of the litz wire material, for example copper and aluminum have a eutectic melting temperature of about 550°C, silver (if copper is silver coated) and aluminum have a eutectic melting temperature of about 570°C, and nickel (if copper is nickel coated) and aluminum have a eutectic melting temperature of about 640°C.

[0066] The concept of the present invention contemplates a two-stage process sequence that differs from resistance welding bonding and includes an initial eutectic fusion bond between the litz wire and the formed member (section a) and a diffusion process between the litz wire wires that forms the second bond (section b).

[0067] Sections (a) and (b) may naturally overlap because the spatial extent of the contact and bonding zones results in different local heating.

[0068] An optimal sinking speed can be set for each segment. During this process, the sinking speed is continuously calculated within each segment based on the sinking distance achieved and the required duration for this sinking distance. The resulting trajectory is compared with the target trajectory, and the current is controlled accordingly using a control technology algorithm. Switching to the next segment occurs when the switching height is exceeded and / or when the segment reaches a preselected energy or charge.

Claims

1. 1. A method for forming a hot crimp joint between a molded element and at least one wire and / or at least one litz wire consisting of at least two wires made of a metal, the hot crimp joint being formed using a hot crimping device having at least two spaced apart electrodes, wherein compacting the at least one wire and / or at least one litz wire and deforming the molded element simultaneously results in both a material connection between the joining components and a material connection between the wires of the litz wire, It passes through successive metallurgically distinct sections: Section a) Segment 1: A first bond is formed between the shaped element and the outer layer of the wire and / or the outer layer of the litz wire by a complete and / or partial eutectic melting process of the outer wire from which the insulation layer has been removed through compaction and / or pre-deformation proceeding in parallel in time, Section b) Segment 2: A diffusion bond and / or at least a partial fusion bond is formed between the inner wires of the Litz wire, the insulation layer of which has been removed by compaction; Section c) Segment 3: currentless cooling of the hot crimp joint is performed, wherein switching between at least two consecutive segments is performed after reaching a height position specific to the segment and / or after the supplied energy or charge reaches a predetermined amount of energy or charge; A method characterized by:

2. 2. The method according to claim 1, wherein a blocking of the respective segment is performed if a period set depending on the segment is exceeded.

3. 3. The method of claim 1, wherein the electrode current is controlled so that the electrode's distance-time trajectory follows a sinking speed set depending on the segment, and switching to the next segment occurs after the height position specific to the segment has been exceeded and / or after a predetermined energy or charge has been reached.

4. 2. The method of claim 1, wherein the first joint at the segment 1 is made by a soldering process.

5. The method of claim 1 , wherein the first bonding at the segment 1 is performed by a eutectic melting process of uncoated components.

6. 2. The method of claim 1, wherein the shaped member is coated with a metal that is identical to or metallurgically very similar to the material of the litz wire.

7. The method of claim 1 , wherein the section a and / or the section b and / or the section c are divided into a plurality of further segments.

8. The method of claim 1 , wherein for each segment, a force, a current characteristic, a current level, a sinking rate, a maximum duration, an energy or charge, and a switching height are set.

9. The method according to claim 8 , wherein an electrode movement distance is set as a switching criterion instead of the switching height.

10. 2. The method according to claim 1, wherein the duration and / or the distance traveled and / or the sinking velocity and / or the energy or charge for the thermal expansion stroke and each individual segment are used as quality criteria.

11. The method of claim 1 , wherein the materials for the at least two opposing electrodes are different materials.

12. The method described in claim 1, wherein each of the at least two electrodes is configured to contact the molded member with a different contact area from the other.

13. The method of claim 1 , wherein pre-deformation with height monitoring is performed before hot crimping.

14. The method of claim 1 , wherein the pre-deformation and hot crimping are performed simultaneously or in direct succession in the same equipment.

15. The method of claim 1 , wherein the pre-deformation is performed during heating within the segment 1 .

16. 2. The method of claim 1, wherein all process-related adjustments and measurements are detected and associated with individual forming members.

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