DE102018200509A1 - Method of making coils - Google Patents

Abstract

The application relates to a process for producing metallic coils, as well as the coils produced in the process. The method comprises the following steps: providing a helical cavity (1.1) in an injection mold; Filling the cavity (1.1) with a molding material containing a powder of a sinterable material; Producing a green part (2) by solidification of the molding compound; Removing the green part (2) from the injection mold; Debindering the green part (2); Sintering of the green part (2).

Description

The application relates to a method of metal powder injection molding for producing metallic coils.

Metallic coils, such as coils or springs, are made in the prior art by winding wire, such as round or profiled wire. In industrial manufacturing, the winding process is automated especially for simple coils and for large quantities and is carried out on special winding machines. However, for example, for small filigree coils, coils with a high degree of filling or special rigidity requirements, automated winding systems can only be used to a limited extent, which results in high costs and high production costs.

The object of the application is to produce metallic coils in a metal powder injection molding process. This is achieved by a method according to claim 1. Possible embodiments emerge from the subclaims as well as from the description and the figures.

To produce a metallic coil in a method according to the application, a helical cavity is provided in an injection mold.

The cavity is filled with a molding material containing a powder of a sinterable material. By solidification of the molding compound, a green part is produced, which is then removed from the injection mold. Subsequently, the green part is debinded and sintered.

The helical cavity may be formed by a mold of the injection molding tool. However, it may also be formed by one or more inserts provided in the mold or formed by one or more inserts together with the mold of the injection mold.

To prepare the helices, a powder-filled molding compound is prepared which contains a binder, for example an organic binder, and a powder of a sinterable material, for producing a sintered molding. For example, metal powders may be used to make a metallic molding, and in particular, copper powder, aluminum powder, steel powder, titanium powder and / or noble metal powder such as platinum powder may be used. In one embodiment, high purity copper powder can be used. Powders of metallic alloys, such as aluminum alloys, may also be used to make molded articles of alloyed materials. For the preparation of molded parts from alloyed materials, pre-alloyed powders may be used or a combination of elemental powders may be provided. In another embodiment, it is also possible to use a master alloy to which one or more elemental powders are added.

In one embodiment, powder mixtures of metallic and ceramic powders are used for the production of metal-ceramic structures.

The organic binders in one embodiment contain at least one thermoplastic polymer. In one embodiment, the organic binders may further contain a plasticizer that can be selectively dissolved out, and / or a second polymer that can be selectively decomposed. For example, the second polymer may be thermally or catalytically decomposable.

The organic binders may also contain other components in various embodiments, such as surfactants, phase mediators, wetting aids, oligomers, short-chain polymers and / or other plasticizers.

The composition of the organic binders depends on the composition of the powder in different embodiments in order to avoid a chemical reaction of the binder with the powder and, for example, to effect a wetting which is commensurate with the powder.

Due to the composition of the molding composition, different material properties, such as a certain conductivity or spring hardness, can be achieved.

The powder-filled molding compound is mixed, for example, and then preferably homogenized under high shear forces. This can be done by using a shear roller or an extruder, for example by using a twin-screw extruder. However, the mixing and / or the homogenization of the molding composition can also be done by kneading or by a combination of kneading and extrusion.

The molding compound may include, for example, a steel powder in one embodiment, for the production of steel springs.

In one embodiment, the molding compound may contain a copper powder, for example of highly conductive copper, for the production of copper coils.

By producing the helixes as a cast body in an injection molding process, increased flexibility in the helix geometry can be achieved.

The possible use of inserts, the flexibility is further increased.

The cavity, which is filled with the molding compound and predetermines the shape of the desired helical cast body, can have a complex geometry. Below are some examples of such complex geometries. These can be combined with each other. Other geometries are also possible and arise for the skilled person from the desired use of the helix.

Coil parameters or helix parameters such as, for example, pitch and number of turns per length can be set in a targeted manner by means of a correspondingly shaped cavity.

An inner cavity bounded by the helix or turns of the helix may have a complex cross-sectional area in a plane orthogonal to a longitudinal direction of the helix. In particular, the inner cavity may have a cross-sectional area which is difficult or impossible to reach by winding. The inner cavity delimited by the turns of the cast helix may have a round or non-circular cross-sectional area and / or a cross-sectional area that varies along the longitudinal direction of the helix. The cross-sectional area can have a constant or variable radius, or a constant or variable side length, and can be, for example, round, oval, rectangular or polygonal.

The outer helical dimensions in the plane orthogonal to the longitudinal direction can also be adjusted by the proposed method. The outer coil dimensions may, for example, have a round, oval or rectangular shape. In the plane orthogonal to the longitudinal direction, an extension of the helix may for example be between 0.5 cm × 0.5 cm and 10 cm × 10 cm. For example, a rectangular coil may have external dimensions of between 1cm x 3cm and 3cm x 8cm. Larger and smaller dimensions in both directions are also possible.

The metallic coil may also have a complex winding cross-section profile. With a winding cross section, the cross section of the material itself is referred to, corresponding to the wire cross section of a wire used, for example, in wound coils. For example, the winding cross section profile may be rectangular, which would make winding difficult or impossible, but has no negative effect on the manufacture of the coil in the method presented here. The winding cross-sectional profile can also be polygonal or oval, have indentations and / or bulges and / or be variable along its length.

A pitch of the helix and / or a winding direction of the helix may be variable along the longitudinal direction.

The proposed manufacture of the helix may combine the described potentially variable complex turns or surface cross sections of the inner cavity, the potentially variable outer helix dimensions, and the possibly variable coil parameters. For example, a rectangular winding cross-sectional profile can be realized along the helix of variable side length with an angled course and a variable pitch along the longitudinal direction of the coil.

To set a desired spring hardness, for example, certain materials or alloys for the metal powder can be selected and the desired pitch or winding thickness or winding cross-sectional geometry of the spring can be adjusted.

Coils produced by the proposed method may have, for example, turns of between 0.1 mm and 2 mm.

In one embodiment, coils with turns of less than 200 μm, preferably less than 150 μm, are produced.

A filling factor of the coils produced in this way is for example over 65%, preferably over 75%, particularly preferably over 85%. In one embodiment, the fill factor is over 90%, for example 95%.

In one step of the method, the cavity is filled with the metal powder-filled molding compound by injecting the molding compound into the cavity. In one embodiment, the injected molding compound has a temperature of at least 50 ° C, preferably at least 100 ° C, more preferably at least 120 ° C and a temperature of at most 300 ° C, preferably at most 250 ° C, more preferably at most 200 ° C.

Subsequently, a green part is produced by solidification of the molding material. The solidification of the molding material is typically carried out by cooling the molding material. The green part forms, if one or more inserts are present together with the one or more inserts an intermediate product. The intermediate product is removed from the injection mold.

If inserts are present, the one or more inserts will be removed in a subsequent step. The inserts are typically destroyed.

In one step, the binder is removed by debindering the green part, for example by chemical, catalytic and / or thermal debindering.

In one step, the molding is compacted by sintering, wherein the molding can get its intended final shape.

In one embodiment, first the one or more inserts are removed and the green part is subsequently debinded and sintered. If there are no inserts, the green part is removed in one embodiment from the cavity of the injection mold, optionally post-processed, debindered and sintered.

In one embodiment, removal and debinding are done in the same step. In one embodiment, the one or more inserts may be removed during burnout thermal debinding.

In one embodiment, in a step subsequent to the removal of the one or more inserts, the green part is mechanically rinsed to remove residue of the one or more inserts on the green part.

In one embodiment, the green part is mechanically reworked before or after removal of the one or more inserts, but preferably before sintering. Thus, for example, burrs, sprue structures or other unwanted parts of the green part can be removed mechanically or a surface of the green part can be machined on the comparatively easily workable green part. It is thus an economical removal of, for example, ridges or edges and reworking possible and it can be a high tool life and a greater tolerance in the tool production and the production of inserts are achieved. The removal of the burrs or sprue structures or other unwanted parts can be done manually, for example with a knife, a utility knife or a scalpel.

Preferably, the inserts for use in a method according to the application are designed so that they do not deform under the pressure of the injected molding compound and due to the heat input of the injected molding compound. Therefore, a difficulty is to provide inserts that can withstand the mechanical and thermal stresses on the one hand, on the other hand, but are removable.

The inserts can be subjected to a material test for this purpose.

The inserts can be made of water-soluble or decomposable by aqueous media materials.

For this purpose, inserts can be produced, for example, from a thermosetting polymer, in particular from a thermosetting polymer having hydrolytically cleavable functionalities, such as, for example, esters, anhydrides or carbamates.

The inserts may also be made of a thermoplastic composite, for example a composite containing water-soluble materials. In particular, a water-soluble thermoplastic polymer having particulate inclusions, for example inclusions of ceramic particles or salt particles, may be used.

In another embodiment, inserts made of salt can be used.

Also, inserts of a thermoplastic polymer such as PMMA, or inserts of a composite comprising such a thermoplastic polymer may be used.

The possible inserts can be made for example by casting, injection molding or reactive injection molding. The inserts can also be made in an additive manufacturing process, such as stereolithography, direct light processing or digital light processing, selective laser sintering, selective laser melting, fused deposition modeling or fused filament fabrication, multijet modeling, binder jetting or laminated object molding. The inserts can also be manufactured or reworked by subtractive manufacturing processes, such as machining or milling.

Furthermore, several inserts can be made by the same or different methods described above and releasably or permanently connected to each other, or assembled into a single insert. The inserts then taken together and optionally together with the mold of the injection mold, the cavity.

In one embodiment, inserts are manufactured in additive processes as individual parts to avoid combining multiple inserts and to increase the economics of the process.

Due to the different possible manufacturing methods for the possible inserts, as well as the combination of these manufacturing methods a special flexibility in the production of moldings is achieved. Even complex geometries can be achieved, such as geometries with undercuts, holes, channels, or openings. In addition, different materials can be used, which are removable in different ways.

The inserts may be formed such that the mold of the injection molds used, in which the inserts are used, partially contribute to the shape of the molding, for example by the mold dictates the outer boundary or also predetermines other parts of the mold. But the inserts can also be designed so that the mold of the injection mold has no effect on the shape of the molding, but the shape is determined only by the inserts. The inserts are, for example, designed so that their outer boundary is adapted to the mold of the injection mold. In one embodiment, contact of the molding compound with the injection mold is avoided in order to avoid sticking of the molding compound to the injection mold. The inserts and / or the casting mold have areas or openings into or through which the molding compound can be injected into the cavity.

The manufacturing methods described above for the inserts and the use of the inserts in injection molds, which need not have a special shape, allow economical production of small and pilot series in low quantities.

If present, the one or more inserts may be removed by placing the intermediate in an aqueous medium to dissolve the one or more inserts. However, the one or more inserts may also be decomposed by acid or base based catalysis or by hydrolysis. The one or more inserts can also be removed by burning out in another embodiment.

In one embodiment, the insert undergoes swelling upon initiation, and an elastic binder for the powder-filled molding compound is used that will tolerate deformation of the insert or inserts and resume its original shape upon removal of the insert.

In one embodiment, in the process, spirals, ie, helical bodies, such as coils or springs, are manufactured by designing the one or more inserts such that the one or more inserts and optionally the injection mold in which the inserts are arranged, a helical cavity is given. Thus, coils can be produced with any cross-sectional geometries or variable cross-section, which can not be produced by winding. In particular, coils can be produced with non-circular winding profiles.

For example, in one embodiment, the inserts include handles, protrusions, recesses, or other geometries that do not contribute to the shape of the cavity and that facilitate handling of the intermediate product. For example, the intermediate can be gripped and moved by hand or with the aid of a tool on such a handle or geometry.

The method according to the application allows the production of castings with different geometry by making different inserts that can be used in the same injection mold. The inserts can be made such that their cavities have a different profile, but their outer contour is the same, so that the different inserts fit into the injection mold.

• 1 Ein Einlegeteil zur Verwendung im Metallpulverspritzgießen in einem Spritzgießwerkzeug;
• 2 Ein Zwischenprodukt, das Einlegeteil aus 1 und ein Grünteil umfassend; und
• 3 Das Grünteil aus 2 nach Entfernen des Einlegeteils.

Exemplary embodiments are shown in the figures. Show it:

• 1 An insert for use in metal powder injection molding in an injection mold;
• 2 An intermediate product, the insert part 1 and a green part comprising; and
• 3 The green part off 2 after removing the insert.

In 1 is a possible insert 1 shown. The insert 1 has a helical cavity 1.1 on, for producing a coil for an electric motor, for example for a pedelec engine. The insert 1 is manufactured in one piece from a thermosetting polymer by digital light processing. The insert 1 can be used in an injection mold (not shown), so that the injection mold, the insert 1 encloses. Together with the mold of the injection mold, the insert forms a helical cavity which corresponds to the desired spiral geometry. In this helical cavity, a molding compound can be injected.

2 shows an intermediate product, which is the insert 1 out 1 and a helical green part 2 from one in the helical cavity 1.1 comprises solidified molding material. The molding compound contains a highly conductive copper powder and an elastic organic binder. In other embodiments, the molding compound may also contain another metal powder, such as, for example, steel powder, aluminum powder or titanium powder, or contain powders of alloys. The intermediate product is removed from the injection mold. In a next step, the insert part 1 in which it is decomposed by hydrolysis. An expansion or deformation of the insert 1 during decomposition, the elastic organic binder tolerates the molding compound and the green part 2 takes after the insert 1 completely decomposed again is the shape of the helical cavity 1.1 on.

3 shows the helical green part 2 out 2 , wherein the insert part 1 was removed. The green part 2 has the desired geometry for the molding. On the relatively easy to work green part 2 In post-processing steps, unwanted sprue structures, edges or burrs can be easily removed mechanically. Subsequent debindering removes the organic binder and then densifies the component by sintering, whereby the component contains its final shape. By producing the helical green part in an injection molding process, the green part can have a rectangular winding cross section profile 2.1 as well as an angled course 2.3 which is unreachable by winding.

Claims (12)

Method for producing metallic coils, comprising the following steps: - Providing a helical cavity (1.1) in an injection mold; - filling the cavity (1.1) with a powder containing a sinterable material containing molding material; - Producing a green part (2) by solidification of the molding material; - Removing the green part (2) from the injection mold; - debindering the green part (2); - Sintering of the green part (2). Method according to Claim 1 in which the helical cavity (1.1) is formed by a casting mold of the injection molding tool and / or by one or more inserts (1). Method according to one of the preceding claims, wherein the molding composition contains a steel powder for the production of steel springs. Method according to one of the preceding claims, wherein the molding composition contains a copper powder for the production of copper coils, preferably high-purity copper for the production of highly conductive copper coils. Metallic coil made in a process according to any one of the preceding claims. Metallic helix after Claim 5 wherein the coil is a copper coil or aluminum coil or a coil of a copper alloy or an aluminum alloy. Metallic helix after Claim 5 , wherein the coil is a steel spring. Metallic coil after one of the Claims 5 to 7 , characterized in that one of the turns of the cast helix limited inner cavity (2.2) has a non-round cross-sectional area. Metallic coil after one of the Claims 5 to 8th , characterized in that the inner cavity (2.2) delimited by the turns of the cast coil has a cross-sectional area which is variable along a longitudinal direction 3 of the coil. Metallic coil after one of the Claims 5 to 9 , characterized in that it has a non-circular winding cross-section profile (2.1). Metallic coil after one of the Claims 5 to 10 , characterized in that it has a variable winding cross section profile (2.1). Metallic coil after one of the Claims 5 to 11 , characterized in that it has a variable pitch and / or winding direction along the longitudinal direction (3).

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