Patent ID: 12233491

DETAILED DESCRIPTION OF THE EMBODIMENT(S)

The invention will now be described in greater detail and in an exemplary manner using embodiments and with reference to the drawings. The described embodiments are only possible configurations in which, however, the individual features as described herein can be provided independently of one another or can be omitted.

Referring toFIG.1, a schematic three-dimensional view of a thermistor or a thermocouple200connected to a stranded wire300by a welded connection100according to an embodiment is shown. The thermistor200has a connecting part202that is connected to the stranded wire300. The stranded wire300and the connecting part202are arranged linearly; the stranded wire300and the connecting part202have a common longitudinal axis. The welded connection100surrounds an end of the connecting part202and an end of the stranded wire300. The stranded wire300may also be referred to as a first connector300and the thermistor200may also be referred to as a second connector200.

The welded connection100is shown in greater detail inFIG.2.FIG.3is a schematic ofFIG.2used to explain the main characteristics of the welded connection100in greater detail.

The welded connection100, as shown inFIGS.2and3, connects the first connector300to the second connector200. A weld102connects the first connector300and the second connector200. The weld102is formed by melting an end section of the first connector300. The weld102surrounds a second end220, indicated by a broken line inFIG.3, of the second connector200. The first connector300and the second connector200extend in opposite directions from the weld102.

The first connector300has a first diameter310and the second connector200has a second diameter210. As shown inFIG.3, the first diameter310is larger than the second diameter210. In an exemplary embodiment, the first connector300has a diameter310of greater than or equal to 0.25 mm and less than or equal to 2.0 mm, or greater than or equal to 0.65 mm and less than or equal to 0.85 mm, and the second connector200has a diameter210of greater than or equal to 0.1 mm and less than or equal to 0.5 mm, or greater than or equal to 0.15 mm and less than or equal to 0.25 mm. According to the present application, a diameter is the diameter of a circle or the diagonal of a polygon, in particular the diameter of a rectangle.

As shown inFIGS.2and3, a face104of the weld102forms has convex shape, approximately forming an ellipsoid. A symmetry axis of the weld102is formed by a common longitudinal axis of the first connector300and the second connector200, which indicated by dashed line1400inFIG.3.

As further shown inFIG.2, the face104is only approximately an ellipsoid. The ellipsoidal shape indicates that the molten material has formed a drop, which indicates a strong cohesion of the weld102in the liquid phase, and thus, results in a strong connection of the weld102and the second end220. Notably, the shape of the weld102deviates from the theoretical ellipsoidal shape by the protrusions caused by the second end220. However, these protrusions do not influence the overall convex shaped face104of the weld. In particular, a convex shape is an indication of cohesion.

As shown inFIGS.2and3, the weld102has a first toe110, also referred to as first meniscus110, and a second toe120, also referred to as second meniscus120, wherein the shape of the both toes110,120deviate from the ellipsoidal shape of the face104. In more detail, the toes110,120are concave shaped regions, which are also referred to as meniscus. Concave meniscus occurs when the particles of the liquid are more strongly attracted to the solid, i.e. the second connector200and the stranded wire300, (adhesion) than to each other (cohesion), causing the molten material to climb the walls of the connectors200,300. The formation of menisci is used in surface science to measure contact angles and surface tension. In a contact angle measurement, the shape of the menisci is measured e.g. optically with a digital camera. Menisci are a manifestation of capillary action, by which surface adhesion pulls a liquid up to form a concave meniscus.

As shown inFIGS.2and3, the contact angles of the toes110,120are less than 90° indicating that the liquid molecules of the molten material are strongly attracted to the solid molecules of the connectors200,300, and thus, the molten material spread out on the solid surface. Notably, the contact angles of the toes110,120are extremely sensitive to contamination; values reproducible to better than a few degrees are generally only obtained under laboratory conditions with purified liquids and very clean solid surfaces.

As shown inFIG.2, the weld has face104that has a convex shape and a first and second toe110,120that have a concave shape. As further shown inFIG.3, the face104is approximately a prolate spheroid and the common longitudinal axis1400is the symmetry axis of the weld102. In an embodiment, an equatorial radius140of the weld has a diameter of 1.5 times the first diameter310of the first connector300. Such a shape ensures that a second connector200with a thinner radius, such as a dumet wire250, can be completely confined by the weld102.

A welding method for connecting the first connector300to the second connector200will now be described with reference toFIGS.4to8.

FIG.4shows a schematic view of a first step of the welding method according to an embodiment. Firstly, the second connector200is provided. The second connector200has a second diameter210. The second connector200defines a second longitudinal axis indicated by dash-dotted line240and is aligned in respect to an electrode400. The electrode400is aligned along a main axis indicated by dash-dotted line410. The energy is dissipated along the main axis410from the electrode400. The electrode400is spaced apart from the second connector200. In an embodiment, the distance between the second connector200and the electrode400is a first distance310, which is equal to the first diameter310of the first connector, and a predetermined distance420of 0.5 mm. In the shown embodiment, the main axis410of the electrode400is perpendicular to the second longitudinal axis240.

A second step of the welding method is described inFIG.5, wherein the first connector300is provided. The first connector300defines a first longitudinal axis indicated by dash-dotted line340and is aligned in respect to the electrode400. In an embodiment, the first connector300is aligned parallel to the second connector200. Notably, the first and second step of the method may be interchanged.

The first connector300has a first end and the second connector200has a second end, the second end for being welded to the first end. In an embodiment, the first end has a length of at least one diameter310of the first connector300, and in the embodiment shown inFIG.5, the first end has a length320of two times the diameter310. In other embodiments, the length320is at least three times the diameter310, or is greater than three times and less than four times the diameter310. The first end of the first connector300overlaps a second end of the second connector200. In other words, the lateral surfaces of the ends are connected by a lap joint, i.e. the lateral surfaces are abutting, and the base surfaces of the ends of the two connectors200,300are facing opposite directions.

A central section of first end is aligned with respect to the main axis410of the electrode400. Thus, a length322of the end section of the first end shown inFIG.5has a length less than the length320of the first end. In an embodiment, the length322of the end second is less than one diameter310of the first connector300. Additionally, a second end section of the second connector200overlaps with the first end of the first connector. In an embodiment, a length222of the second end section is less than or equal to one diameter310of the first connector300.

As shown inFIG.5, the central section of the first end is arranged in the middle of the axial extension direction of the first connector300. In other words, an overlapping region of the first end and the second end is mirror symmetrical with respect to the main axis410of the electrode400. A cathode430is connected to the first connector300.

In a third step of the welding method, as shown inFIG.6, a heat shield500is provided, the heat shield500covering, during the heating, at least partly the end section of the first end. The second end of the second connector200and the heat shield500are arranged on opposing sides of the lateral surface of the first end of the first connector300. In other words, the second end of the second connector200, the first end of the first connector300, and the heat shield500are arranged on the main axis410of the electrode400with decreasing distance to the electrode400, respectively. The lateral surface of the first connector300is the area of all the sides of the object, excluding the area of its base and top; such a configuration optimally employs the adhesive effects. The heat shield500can be made of a ceramic material.

The heat shield500influences adhesive forces. In more detail, adhesive effects influence the shape of the melted material. In more detail, in surface science, the term adhesion refers to dispersive adhesion. In a typical solid-liquid-gas system (such as a drop of liquid, i.e. the melted material on a solid, i.e. the first connector300and the second connector200surrounded by air or an welding gas) the contact angle is used to evaluate adhesiveness indirectly. Generally, cases where the contact angle is low are considered of higher adhesion per unit area. This approach assumes that the lower contact angle corresponds to a higher surface energy. By embedding the second connector200, tipping the melt of the first connector300around the second connector200, the joint becomes insensitive to peel forces. The quality of the joint can be seen from the contact angle. The contact angle is also referred to as wetting angle. Furthermore, the heat shield500influences the tensile strength by protecting the second connector200against notching.

The contact angle of the three-phase system is a function not only of dispersive adhesion (interaction between the molecules in the liquid and the molecules in the solid) but also the presence of the heat shield500. In other words, the dissimilar materials and surfaces of the melted material and the heat shield500increases the wetting of the weld to the connectors200,300. Wetting is the ability of a liquid, i.e. the molten material, to maintain contact with a solid surface, i.e. the first and second connector200,300, resulting from intermolecular interactions when the two are brought together. Thus, by cooling down the molten material a particularly strong connection is realized.

A schematic view a fourth step of the welding method is described inFIG.7, showing the contactless heating of the central section of the first end. In the shown embodiment, the central section is heated using an arc440. Additionally, an inert gas450is protecting the welding area. Contactless welding enables a fast process which is easily automated, and thus, making the process highly productive.

The heat is contactless transferred via process such as an arc welding process, for example a gas tungsten arc welding process, or an energy beam welding process, for example a laser beam or an electrode beam. Tungsten inert gas (TIG) is useful for welding thin materials, this method is characterized by a stable arc and high quality welds, but it requires significant operator skill and can only be accomplished at relatively low speeds. In particular, a follow rate of the inert gas, e.g. argon, allows to be adapted so that the surface appearance of the weld102can be improved. Energy beam processes are extremely fast, and are easily automated, making them highly productive. The primary disadvantages are their very high equipment costs and a susceptibility to thermal cracking.

FIG.7shows the heat flux in the first connector300. The heat is conducted by the first connector300. The heating of the central section of the end section allows an asymmetric heat dissipation with regard to opposing directions of the first connector300. A first part600of the heat is conducted to the end section. As the end section is short, the heat is confined and the end section is heated up until the end section is melting. During heating, the end section transforms from a solid to liquid having an ellipsoidal shape. A second part610of the heat is conducted to a main section of the first connector300, the main section is the part of the first connector300opposing the end section. The length322of the end section is shorter, and in an embodiment negligible, compared to the length of the main section of the first connector300. Thus, the second part610of the heat is not sufficient to melt the main section of the first connector300. The overall heat capacity of the first connector300is large compared to the heat capacity of the end section. The molten mass confines additionally the second end of the second connector200. Thus, by overlapping the first end and the second end in an axially orientated direction before heating, a particularly space saving arrangement is realized.

In an embodiment, the first connector300has a higher thermal conductivity than the second connector200. Therefore, only little heat can be dissipated via the second connector200and the end section heats up faster than the main section. Additionally or alternatively, the first connector300has a lower melting temperature than the second connector200. Thus, the end section of the first connector300melts first.

A schematic view a fifth step of the welding method is described inFIG.8, showing the welded connection100after melting the end section. The method includes the step of cooling the first end and the second end so that the molten mass hardens. The weld102, which is hardened by the phase transition from liquid to solid, connects then the first connector300and the second connector200. According to the present invention, the first connector300and the second connector200extend in opposite directions from the weld102. Such a connection enables an axial orientation of the welding partners without bending one partner after cooling down the weld. The welded connection100is the same as described above with regard toFIGS.2and3and a detailed description thereof is omitted. In addition toFIGS.2and3, the side view ofFIG.8shows that the first longitudinal axis340and the second longitudinal axis240are not collinear. This, however, does not influence the convex shape of the face104and the concave shape of the first and second toe110,120.

The welded connection100makes a bending step of one connector in order to achieve axial orientation after welding unnecessary. Additionally, such a welding connection is a particularly strong and the operating temperature in an application using such a connection100can be more than 180° C.

FIG.8shows the heat shield500and the power source400. The close arrangement of the heat shield500supports the forming of the convex shape of the face104and the concave shape of the second toe120. Thus, a particularly strong connection can be realized. Further, the heat shield500improves the melting process by efficiently confining the heat.

FIG.9shows a cross-sectional schematic view of a dumet wire250used for forming the second connector200. Dumet is a portmanteau of “dual” and “metal,” because it is a heterogeneous alloy, usually fabricated in the form of a wire with an alloy core and a copper cladding. These alloys possess the properties of electrical conductivity, minimal oxidation and formation of porous surfaces at working temperatures of glass and thermal coefficients of expansion which match glass closely. These requirements allow the alloys to be used in glass seals, such that the seal does not crack, fracture or leak with changes in temperature. The dumet-wire250is a copper clad wire252with a core254of nickel-iron alloy. A component body256is encapsulated with glass. The core254has a low coefficient of thermal expansion, allowing for a wire with a coefficient of radial thermal expansion which is slightly lower than the linear coefficient of thermal expansion of the glass, so that the glass-to-metal interface is under a low compression stress.

FIG.10shows a cross-sectional schematic view of a stranded wire350that can be used as the first connector300. The stranded wire250is composed of a number of small wires352bundled or wrapped together to form a larger conductor. The small wires352are cladded by an insulation layer354, e.g. a high temperature fluoropolymer. Alternatively, a lead frame or a massive wire may be used instead as first connector300.

In an embodiment, the welded connection100may by be used to connect a connecting terminal of a thermocouple200to a connecting terminal of a connector300.

The welding connection100optimally uses the installation space and provides a particularly robust connection that can used at operation temperatures higher than 180° C. The connection100can be fabricated at low costs. Additionally, the connection100enables an easy visual inspection and can be used to connect elements that have different material compositions and geometrical dimensions. Such dimension allows a strength of the weld connection100that is larger than the strength value of the second connector200, i.e. the second connector200would crack first.