Segment 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 part and at least one litz wire of at least two strands of at least one wire and / or metal, in which both a material connection joint between the joining components and a material connection joint between the wires of the litz wire are formed during simultaneous compaction and deformation. [Background technology]

[0002] Evaluation of control parameters common today Resistance characteristic: the characteristic is calculated from the quotient of the measured voltage and the measured current. Since a direct measurement of the voltage in the joint zone is technically not feasible, the voltage measurement is inaccurate due to the contact resistance of the components and electrodes as well as the material resistance of the components and electrodes. However, a rough orientation is possible. Current and voltage characteristics: This is an issue when measuring resistance. Temperature characteristics: The temperature can only be measured from the outside. The temperature in the joining zone cannot be controlled directly. The measuring spot is usually too large and detects the components and the electrodes 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 the pressure characteristic. Submersion distance: The amount of electrode movement caused by the joining process. The entire interval is detected, so 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 any 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 disadvantages 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 be able to produce this quickly and at low cost. [Means for solving the problem]

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

[0005] [Figure 1] FIG. 2 is a diagram showing an example of the characteristics of a hot crimp process according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0007] 1 shows an exemplary possible profile 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 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 is started and ends when the switching height of segment 1 (6) is exceeded below. From the height difference between the thermal expansion stroke (5) and the start height of the hot crimp (4), the energy input in segment 1 (10) can be deduced. This initial energy results in the first joint construction (section a) in segment 1 (10). The current characteristic (2) is in this case divided into a ramped current characteristic during heating (18) and possibly a constant current characteristic during the hard soldering (19) here. The first joint construction here can start already in the heating phase (18) and end in segment 2 (11 or 12) without any restrictions. The temperature evolution in the joint zone depends greatly on the force characteristic (1), the current characteristic (2), the start height (4), the heat input in the pre-crimping phase (14), the position and duration of the switching height (6+7+8).

[0009] Upon reaching the first joint structure at segment 1 (10), further energy is supplied, but at a modified level, where 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).

[0011] The time profile of the crimp height (3) in each segment is 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 connection into several segments, each of which has a different set of parameters and acts differently metallurgically. The downward exceedance of a set cut-off height is used as the switching criterion for each segment. If reliable switching is not possible because the electrode is not immersed deep enough in one segment, the cut-off can also be performed when a defined duration is exceeded.

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

[0014] However, such short pauses usually result in further compaction of the litz wire, which leads to uncontrolled sinking of the electrodes, i.e. the predetermined breaking height of each segment can be used as the criterion for switching the segments, instead of the sinking distance during current flow.

[0015] The methods described herein can be applied to multiple metals and their alloys, such as, for example, copper, aluminum, iron, titanium, nickel, either by type or in admixture.

[0016] The most important welding parameters are current, pressure and duration. These main 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 section and the current source should 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, possibly assisted by the flow of electric current, between at least one forming member and a litz wire, followed by hot crimping. 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 which involves simultaneous mechanical deformation of at least two joining partners (the shaped member and the 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 joint 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 the properties of a diffusion barrier against the soft solder. However, the joining partners can also be used directly, e.g. structural elements made of copper, without coating them with the aluminum wire of the litz wire, possibly with partial melting of the litz wire wire in a subsequent diffusion. In the latter case, the litz wire wires are joined to one another.

[0023] At the same time, the compaction process results in the removal of the insulating layer both during the pre-pressing process and during the hot crimping process. The insulating layer here can be an oxide layer, a resist layer, an insulating layer or a contamination layer, as is known. The coating or solder can be applied galvanically (with and without electric 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 regulating parameters, i.e. current, pressure and duration of each segment, a parameter set consisting of current, pressure and cut-off height is proposed here. It has been found that due to the many influencing variables, a sufficiently reliable and reproducible hot crimping process cannot be achieved by time control.

[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] Different 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, whereas in two-shot, two equipments are used.

[0028] In two-shot, a first facility is used for pre-pressing and a second facility is used to carry out the hot crimp. During pre-pressing, pre-crimping is carried out by cold crimping (current-free compaction) and / or with the aid of a low pre-heating current in order to obtain a defined pre-crimp height and / or a defined electrode contact area. However, in cold crimping, the cold crimp height is determined essentially exclusively by the pressing force and the material properties and is therefore less suitable for higher quality in practice. Improvements can be achieved by additional height cut-off.

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

[0030] The structural elements preformed and fixed to one another in this way, 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] In the first segment, the energy required for the eutectic fusion bonding of the outer wire of the Litz wire with the shaped member is introduced. The most important adjustment parameters are the pressing force, the current and the interruption height as well as the energy or charge.

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

[0034] After a first joint structure has been obtained in the joint zone between the outermost wires of the litz wire bundle and the shaped component in segment 1, diffusion bonding and / or at least partial melting of the litz wire wires with each other takes place in the second segment and possibly further subsegments, 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 has been reached, the current is switched off and cooling begins with the newly adapted pressure.

[0036] This multi-step process control can prevent, 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 reduction in cross-sectional area.

[0037] Important quality criteria for monitoring the weld quality can be the measured expansion of the shaped parts and the litz wire as a result of the thermal expansion due to the introduced current and the detected duration of current flow or the energy or charge introduced into each individual segment.

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

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

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

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

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

[0043] For welding tasks, such as hot crimping, the invention has proven to be advantageous if the welding flow is divided into a number of 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 here is characterized by dividing the bonding process into a number of segments with optimal process parameters for each segment. Quality control is performed on monitoring the thermal compensation steps of each segment, on the actual individual segment duration and / or on the sinking speed and / or on 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, e.g. 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 the formation of joints and mechanically fixed bonds by material connections between identical or different metallic materials. In particular, the two-step method allows the joining of materials with melting points that are far apart from each other. If the method described here is not applied, the lower melting point material may transfer into the melt and subsequently form a joint between the joining partners.

[0047] Today, in parameter discovery, current strength and time must always be adjusted separately to determine the influence on the deformation and thus the sinking distance over a given time in the test. Furthermore, in the case of hot crimp, due to the high current demand, fluctuations in the power grid are to be expected, which make 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 segments of the hot crimp. The duration is adapted for each segment by a switching mechanism to the specific conditions of the structural member. In this way, variations in material properties, dimensions, current supply, electrode wear, etc. are compensated for independently for each individual structural member.

[0049] In association, this means a very high production quality level and the possibility of traceability and process optimization, whereby batch variations and / or equipment instabilities can be easily detected, automatically evaluated and intervention can be performed in an automated manner.

[0050] The physical properties of the materials, e.g., the 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] Additionally, thermal conductivity affects the heat dissipation from the contact zone for cooling, and specific gravity and specific heat capacity modify the heating behavior of the electrode according to the equation for adiabatic heating.

[0052] Adiabatic temperature rise = current 2 / area 2 *Specific resistance / specific gravity / non-thermal capacity*period observed, in addition to 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 when fixing the electrodes.

[0053] According to the concept of the invention, an application-specific optimization of dimensions and materials is proposed here 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 is preferably made of a more ohmic material than the opposing upper electrode and / or with a relatively small contact area. Such cases arise 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] When creating a joint between the profile and the litz wire with a long-term stable material connection, the process is divided into sections. This is important because the heat generation in the joint zone between the profile and the outer wire of the litz wire and inside the litz wire composite is controlled so that the melting temperature of e.g. aluminum is only partially reached. The particularly complete melting that occurs in resistance welding can lead to errors such as:

[0056] The compaction pressure required for the destruction of the non-conductive layers on the wires (oxide and / or resist layers) formed by the crimping process cannot be achieved. Conversely, the molten litz wire material (e.g. aluminum) is crushed and therefore only an insufficient contact area is formed between the litz wires. Furthermore, heat generation is mainly achieved by the current flowing through the electrodes and the forming members, rather than by the current flowing through the litz wire (self-heating).

[0057] After the outer wire is attached to the sleeve, only enough energy is supplied to keep the litz wire at the diffusion temperature as the deformation increases and the resulting enlarged contact area between the wire, the oxide layer and the insulation layer is removed by pressure and temperature, which could result in unacceptable melting of the litz wire in that section, which could lead to unacceptable melt flow-out and poor bonding of the wires to each other.

[0058] To form a melt, first the Joule heat is required to reach the melting temperature, then the heat of fusion. In addition, heat must be introduced, which flows through the electrodes and components. Typically, the heat of fusion is 9 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] In order to avoid the formation of an intensified melt, the whole process is divided into several sections, possibly into several subsections, so that a solid diffusion bond is formed at high pressure and for the longest possible duration, and no melt bond is formed inside the litz wire. In this case, different current adjustments or current flow times or sinking speeds for all the segments have proven useful. The switching between the segments can be preferably height-controlled and / or dependent 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 have point-like contacts with one another (asperities), small areas of which generate very high temperatures.

[0063] The first bond between the molded part and the litz wire wire occurs by eutectic melting between the litz wire material and the molded part. Since the two materials can be coated together on each side or on both sides, many other possible combinations are possible, such as, for example, the following combinations: A combination of blank profiles made of copper with blank Litz wire made of aluminum, Combining coated copper profiles with aluminum Branklitz wire, Combination of coated copper profiles with coated aluminium litz wires, 1. A combination of blank sections made of copper with coated aluminium litz wires, This 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 materials for the coating vary with the component material. The eutectic temperature is of importance.

[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 aluminium have a eutectic melting temperature of about 550°C, silver (if copper is silver coated) and aluminium have a eutectic melting temperature of about 570°C, and nickel (if copper is nickel coated) and aluminium have a eutectic melting temperature of about 640°C.

[0066] The idea of ​​the present invention contemplates a two-stage process sequence, which, unlike a resistance welded joint, includes an initial eutectic fusion bond between the litz wire and the shaped member (section a) and a diffusion process between the litz wire wires which forms a second joint (section b).

[0067] Sections (a) and (b) may naturally occur overlapping each other because the spatial extent of the contact and bonding zones results in different localized heating.

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

Claims

1. 1. A method for producing a hot crimp joint between a molded part and at least one litz wire of at least two strands of at least one wire and / or metal, in which a joint with a material connection between the joining components and a joint with a material connection between the wires of the litz wire are both produced during simultaneous compaction and deformation, It passes successively through the following metallurgically distinct sections: a) Segment 1: A first bond is formed between the shaped member 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 by compaction and / or pre-deformation proceeding in parallel in time, b) Segment 2: A diffusion bond and / or at least a partial fusion bond is formed between the inner wires of the Litz wire from which the insulation layer has been removed by compaction; c) Segment 3: Currentless cooling of the hot crimped composite is performed, in which the switching between at least two consecutive segments is performed after reaching a height position specific to the segment and / or after reaching the supplied energy or charge; A method comprising:

2. 2. The method according to claim 1, further comprising the step of shutting off the respective segment if a time period set depending on the segment is exceeded.

3. 3. The method according to claim 1 or 2, wherein the electrode current is controlled so that the distance-time trajectory of the electrode follows a sinking speed set depending on the segment and switching to the next segment occurs after passing below a height position specific to the segment and / or after reaching a predetermined energy or charge.

4. 4. The method according to claim 1, wherein the first joining of the segment 1 at section a is performed by a soldering process.

5. 4. The method according to claim 1, wherein the first joining of the segment 1 at section a is performed by a eutectic melting process of uncoated components.

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

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

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

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

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

12. 12. The method according to claim 1, wherein the contact areas of the electrodes with the structural member are different.

13. 13. The method according to claim 1, wherein a pre-deformation with height monitoring is carried out before the hot crimping.

14. 14. The method according to claim 1, wherein the pre-deformation and the hot crimping are carried out simultaneously or in direct succession in the same facility.

15. 15. The method according to claim 1, wherein the pre-deformation is carried out during heating within the segment 1.

16. 16. The method according to claim 1, wherein all process-relevant control and measurement variables are detected and assigned to individual structural components.

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