EP3164235B1 - Device and method for generating at least one metallic component - Google Patents

Description

The invention relates to a device for producing at least one metallic component by injecting flowable metallic material into at least one cavity of a multi-part mold, in particular for casting magnesium or magnesium alloys in the thixotropic state, comprising a conveyor device for the flowable metallic material, at least one nozzle arranged downstream of the conveyor device and the mold with the at least one cavity, wherein the conveyor device is connected to a distributor unit with several nozzles, via which the flowable metallic material can be injected under pressure into the at least one cavity in order to fill the at least one or more cavities simultaneously via individual nozzles, wherein channels of the distributor unit are formed free of corners with a right angle and wherein the distributor unit has straight sections which lead from a branching point to the nozzles.

The invention further relates to a method for casting at least one metallic component, wherein flowable metallic material, in particular magnesium or a magnesium alloy in the thixotropic state, is guided from a conveyor device via a distributor unit to several nozzles for forming the at least one component and is injected via these under pressure into at least one cavity of a multi-part mold, after which the at least one component is allowed to solidify in the mold, whereupon the mold is opened and the at least one component is removed, after which the mold is closed and the next component is created and the flowable metallic material is guided via channels of the distributor unit, which are free of corners with a right angle, from a branching point of the distributor unit to the nozzles without deflection, wherein the flowable metallic material is guided from the branching point to the nozzles in a branching manner along straight sections of the distributor unit.

In many areas of technology, attempts are being made to replace components or parts with higher density with those with lower density. The basic idea is usually that additional advantages can be achieved by using components with lower density and the associated weight reduction. One example is current developments in automotive engineering, where components or parts traditionally made of steel are being or have been partially replaced by those made of light metals.

Simply optimizing weight by using a light metal to replace components made of steel or other materials with a higher density is not enough. The substitute light metals must of course also have the required mechanical property profiles, which can be compensated for by slightly stronger design of the components without losing the advantage of weight savings.

Aluminium and aluminium alloys are primarily used as lightweight materials for the purposes mentioned. In recent times, however, magnesium and magnesium-based alloys, i.e. those that predominantly contain magnesium, have attracted attention. Magnesium is significantly lighter than aluminium, which is why components made of magnesium or magnesium-based alloys can potentially achieve significantly greater weight savings. In addition, they also have sufficient mechanical properties for many areas.

Magnesium and magnesium alloys can be processed by casting in molds, just like aluminum and aluminum alloys. If a mold has recesses corresponding to a component to be produced, this can be produced close to the final dimension.

Magnesium and magnesium alloys can be processed using die casting, for example, whereby flowable metallic material is injected into a mold under high pressure. The disadvantage of die casting, however, is that components can only be cast with certain dimensions. The production of thin components with wall thicknesses of, for example, 1 mm is currently hardly possible using die casting. Another disadvantage of die casting is the limited flow path during production. The longer the flow path, the more likely it is that premature solidification will occur locally and the more likely there will be inhomogeneities in the final component.

The problems of die casting are avoided with a thixomolding process. Thixomolding is a technology that was developed in the 1980s. This technology processes magnesium in the temperature range of the solid-liquid transition; alloys are processed in the area of the phase diagram between the solidus line and the liquidus line, i.e. in the semi-solid state. In these temperature ranges, fine crystallites are present in the surrounding melt during processing. Such flowable material can be easily injected into molds and can be molded into components with thin walls of around 1 mm and above all leads to components with high material homogeneity and thus ultimately also good material behavior in use.

Thixomolding uses devices that have a conveyor (so-called barrel) that houses a screw in a steel casing. Metallic granulate is fed in via a filler neck, brought to the desired temperature in the barrel and homogenized. A nozzle is connected to the barrel, through which the material is injected by axially moving the screw. The nozzle is held in a first part of a mold, whereby this part of the mold is held in position throughout the entire cycle from injection to component removal and reclosure of the mold. A second part of the mold, however, is designed to be movable and is pressed against the first part of the mold with a closing pressure to create a component. One or more cavities are provided in the inserted or second part of the mold, in which the component or components are molded by injecting the flowable metallic material in the thixotropic state. After the mold has been injected and cooled, the second part is retracted so that the product created can be removed. After applying a release agent, the second part of the mold is put back in place or pressed and the next cycle begins.

In known thixomolding devices, injection is carried out via a single nozzle. This means that the flowable metallic material must fill the entire volume starting from the so-called connection point, where the filling of one or more cavities begins. In order to achieve this as quickly as possible with a single cavity, a sprue is provided. This branches off from the connection point to different areas of the component to be created. This ensures that the component is molded as quickly as possible with a single cavity and thus the cycle time is kept to a minimum. If several cavities are planned to produce several identical components in a single operation, a sprue is essential because the flowable material must move at the same speed from the connection point to several cavities with the same mold.

If injection is carried out using a single nozzle, there are several disadvantages. First of all, waste is always produced. The component(s) must be separated from the material which solidifies in the area of the sprue. In addition, the projected area increases with the sprue and thus the additional volume to be filled, which is why a higher closing pressure must be set. In addition, the material must flow along the sprue, which leads to longer flow paths, which in turn can be the starting point for material inhomogeneities. Finally, after injection, the material in the area of the sprue must also be brought into a solid form, which is associated with a higher cooling capacity.

To solve these problems, attempts have already been made to use a device with several nozzles, whereby the thixotropic material is fed from the barrel or a conveyor device to several nozzles via a distribution unit. In contrast to plastics, which can be processed relatively easily at low temperatures, this is extremely difficult with magnesium and magnesium alloys in the thixotropic state. This may be because magnesium shrinks particularly large during solidification (around 10%), but at the same time complete filling of possibly several cavities must be achieved, high pressures are used, the processing temperatures are much higher and, with the desired complete cavity filling, the process must still be carried out in a temperature-sensitive manner so that no material escapes from the nozzles when the mold is open, which could lead to burn-off.

The previous solutions can consist of a distribution unit with several nozzles, whereby distribution arms with at least largely identical sections lead to individual nozzles. A corresponding device is available in the US 2007/0199673 A1 However, devices of this type do not prove to be operable for series production with cycle times of less than 40 seconds in continuous operation.

The document US 2003/0222121 A1 discloses an injection molding device, wherein sprue channels are provided downstream of a nozzle in order to introduce casting material into the sprue channels with the nozzle and to introduce it into a cavity via the sprue channels.

The document US 2004/0151799 A1 discloses an injection molding apparatus, wherein a distribution unit is provided with rectangular channels whose corners are slightly rounded.

The documents US 2007/0181280 A1 , US 2007/0131376 A1 and WO 2007/065246 A1 disclose casting devices, wherein a distributor device provides a right-angled deflection of casting material.

The object of the invention is to provide a device of the type mentioned at the outset, with which multiple firing via several nozzles is possible with a high level of process reliability.

A further aim is to provide a suitable procedure for this purpose.

The object is achieved according to the invention if, in a device of the type mentioned at the outset, the distributor unit has straight sections which lead from a branching point to the nozzles.

Within the scope of the invention, it was recognized that a design of a distributor unit according to the prior art, which has right angles in individual sections, can be the starting point for a lack of process reliability. Due to the right angles, the flowable metallic material has to be strongly deflected under the given high pressures of several hundred bar, which results in high pressure peaks and also makes the conveying of the flowable metallic material more difficult. In contrast, according to the invention, the distributor unit in the area from a branching point of the channels to the nozzles does not have any corners that enclose a right angle. This avoids the aforementioned pressure peaks, which prevent a homogeneous material flow. Obtuse angles can at most be present in the channels. Ultimately, this protects the conveying device or the barrel.

In particular, it can be provided that the distributor unit is designed without corners. This means that the material from a branching point within the distributor unit or a connection point to the conveyor device or the barrel up to an outlet has no corner around which the castable metallic material is to be guided. According to the invention, for the reasons mentioned, it is provided that the distributor unit has straight sections which lead from a branching point to the nozzles. The branching point is on a front side or within the The distribution unit is positioned and is fed with material via one end of the barrel. At the branching point, the material fed in this way is distributed into the individual sections of the distribution unit and ultimately reaches the nozzles, via which injection can take place. It is particularly advantageous if the channels of the distribution unit branch off from the branching point at an angle of maximum 50°, preferably maximum 45°, in particular 20° to 40°. The corresponding angle refers to an axis of the conveyor, usually a horizontal axis of a barrel. In order to achieve the smoothest possible material flow, this angle should on the one hand be a maximum of 50°, preferably a maximum of 45°. On the other hand, when the sections are designed in a straight line, the smaller the angle, the longer the distribution unit and thus ultimately a first part of the mold has to be for a given component size, since the smaller the angle, the less spreading is. In this respect, it is advantageous if a lower threshold value for the angle of 20° is not undercut.

In principle, the distribution unit can have any number of channels. The minimum is two channels. However, it is preferred that the distribution unit has at least three channels.

The distribution unit is integrated in a first part of the mold. At least one heating element is provided around the distribution unit in order to be able to heat the distribution unit. It goes without saying that the distribution unit with the heating element can be further surrounded by thermal insulation in order to be able to set and maintain a temperature in the distribution unit as best as possible.

It is advantageous to provide a heating device for each individual nozzle. Individual heating devices on the nozzles allow the temperature on or in them to be adjusted, which can prove to be a great advantage during a cycle. For this purpose, a control system for the heating devices can be provided in particular, which variably controls a temperature on or in the nozzles depending on the status of a cycle. This means that a temperature on a nozzle can be kept high during injection, but lowered during the subsequent component cooling and removal and then increased again for the next cycle to create a component.

The individual heating devices for the nozzles are preferably designed as resistance heaters, which not only provide high performance but also enable good control.

The individual nozzles are preferably made of steel, in particular hot-work steel, in order to be able to permanently withstand the sometimes high operating temperatures of 500 °C to 800 °C.

In order to achieve a rapid temperature adjustment at the nozzles within a cycle of less than 40 seconds, the heating devices are preferably soldered to the nozzles. For this purpose, the nozzles can have recesses on the outside into which the heating devices are soldered and run in a spiral.

The further aim is achieved if, in a method of the type mentioned at the beginning, the flowable metallic material is guided from a branching point of the distribution unit to the nozzles without deflection, wherein the flowable metallic material is guided from the branching point along straight sections of the distribution unit to the nozzles.

One advantage achieved with a method according to the invention is that pressure peaks and thus ultimately uncontrollable process uncertainties are avoided when the flowable metallic material is fed to several individual nozzles. The method is therefore particularly suitable when using a device according to the invention to produce large components, possibly with low wall thicknesses, by filling a cavity from several points. The same applies if, in order to produce several components, several cavities are filled at the same time via the feed through the nozzles at individual points.

In accordance with the advantages described, it is provided that the flowable metallic material is guided from the branching point to the nozzles by branching along straight sections of the distributor unit. A favorable material flow can be achieved in particular if the flowable metallic material is guided from the branching point to the nozzles by branching at an angle of maximum 50°, preferably maximum 45°, in particular 20° to 40°.

In order to be able to simultaneously fill a large cavity from several points or, if necessary, to fill cavities of the same size at individual points to create several identical components without pressure peaks or defects such as cavities or porosity occurring, the individual nozzles should open simultaneously when the mold is opened. This can be achieved by heating the nozzles while the mold is open in order to at least soften any plugs that have formed in the nozzles before the next component is created. While the mold is cooling to solidify the component(s), a plug forms in the individual nozzles due to the good heat conduction of the cast material. This plug is definitely desirable because it temporarily seals a nozzle and thus prevents material from flowing out when the mold is open. When the mold is opened again in the next cycle However, this plug represents an obstacle that must be overcome, which is taken into account according to the state of the art by applying high pressure when shooting, so that the plug is shot out and caught in a so-called plug catcher. When using a distribution unit with several nozzles, however, this could lead to all nozzles no longer opening simultaneously if the pressures are partially too low. In addition, correspondingly high pressures would also be required for the simultaneous shooting of several plugs. However, if the nozzles are heated in such a way that the plugs formed at least soften, preferably melt, before the next component is created, the plugs that were initially desired but later became a hindrance are no longer effective, so that simultaneous injection can take place at several points via several nozzles. In this context, the preferred procedure is that after the mold has been opened and the component(s) removed, a heating output on the nozzles is set so that the plug softens without flowable metallic material entering at least one cavity. In other words, the plug that breaks off at one end when the component is removed is already softened when the mold is still open. This does not pose a safety risk because the material does not escape when the pressure is off, even if the solid plug has turned into a softened thin film. Then, when the mold is closed again, the heating power at the nozzles can be increased to create the next component. Ideally, this will dissolve the last remnants of the plug or the thin film, so that each individual nozzle is available for a shot at the same time.

However, since the plugs in the nozzles are required as explained above, the heating power at the nozzles is preferably reduced when the component is allowed to solidify, so that the temperature falls below a level that would allow plugs to form in the nozzles. Together with the temperature control measures described above, this results in dynamic control of the temperature at or in the nozzles, which during a cycle encompasses starting or injecting, mold and component cooling, mold opening and component removal, application of a release agent to the opened mold, closing the mold to create the next component, which is optimally adapted to the respective step of the (production) cycle.

• Fig. 1 eine Vorrichtung zum Erstellen von Bauteilen in einem Thixomoldingverfahren;
• Fig. 2 eine Verteilereinheit;
• Fig. 3 einen Ausschnitt gemäß III aus Fig. 2;
• Fig. 4 ein Teil einer Form mit einer Kavität und einem Anschusspunkt;
• Fig. 5 ein Teil einer Form mit einer Kavität und mehreren Anschusspunkten;
• Fig. 6 einen Verfahrensablauf;
• Fig. 7 eine schematische Darstellung des Materialverhaltens in einer Düse während des Verfahrensverlaufs gemäß Fig. 7.

Further features, advantages and effects of the invention will become apparent from the following explanation thereof. In the drawings, to which reference is made here, show:

• Fig.1 a device for producing components using a thixomolding process;
• Fig. 2 a distribution unit;
• Fig.3 an excerpt according to III from Fig.2 ;
• Fig.4 a part of a mold with a cavity and a connection point;
• Fig.5 a part of a mold with one cavity and several connection points;
• Fig.6 a procedure;
• Fig.7 a schematic representation of the material behavior in a nozzle during the process according to Fig.7 .

In Fig.1 a device 1 is shown which is designed for thixomolding components 2 made of magnesium or a magnesium alloy. The device 1 comprises a container in which the material 3 to be processed is kept in granulate form. Material 3 is conveyed from the container into a filler neck via a suction conveyor or another conveying element. The material 3 passes through the filler neck into a conveyor device 6 or a barrel which is provided with a screw with a corresponding drive. The barrel is kept at a suitable temperature by a heater so that the material 3 assumes a thixotropic state or is transported in this state to a nozzle 7 arranged downstream. The nozzle 7 is integrated in a first part 11 of a mold 5. A second part 12 of the mold is opposite the first part 9 of the mold 5 and can be moved horizontally so that the mold 5 can be opened, for example in order to remove components 2 produced by means of a robot arm.

In Fig. 2 a distribution unit 8 is shown which is used in a device 1 according to the invention. The distribution unit 8 has several channels 10 which extend from a branching point 15 in the distribution unit 8. In Fig. 2 a cross-section of a distribution unit 8 is shown, which has a total of four channels 10. The channels 10 are formed in sections 9 that run straight. In principle, the sections 9 can also be curved or designed in another form, as long as corners are avoided around which flowable metallic Material 3 can only be diverted with difficulty or with the build-up of local pressure peaks, particularly in the barrel. The distribution unit 8 is built into the first part 11 of the mold 5 and is connected to an inlet on the conveyor device 6 or the barrel. The barrel is only pressed against the distribution unit 8 in the connection area. In order to maintain a seal in this area, through which the material 3 flows at a temperature of 600 °C, for example, the contact surfaces are surrounded by a steel ring cooled with compressed air. Although small gaps form between the three elements barrel, distribution unit 8 and ring, any metallic material 3 that enters these solidifies immediately, so that a self-seal is created, so to speak.

The sections 9 with the straight channels 10 connect to a central feed 16, which represents an axial extension along a preferably horizontal axis of the conveyor device 6 or the barrel, from the branching point 15 preferably at the same angle α. An angle α should be between 20° and 50°, preferably 20° and 40°. This results in a gentle flow away from the distribution point towards individual nozzles 7, which are positioned at the end in the area of the sections 9 on the distribution unit 8.

A nozzle 7 is closer in Fig.3 shown. The nozzle 7 connects to a channel 10 of a section 9. The nozzle 7 can be permanently attached to the section 9 or formed integrally with it. It is also possible for the nozzle to be detachably attached to the section 9, for example by a screw connection. This allows the nozzle 7 to be replaced if necessary. The nozzle 7 is surrounded on the outside by a heating device 13. The heating device 13 is designed as a resistance heater. A heating coil extends along the nozzle 7 in a spiral around it. For good heat transfer and thus rapid adjustment of the temperature on or in the nozzle 7, the heating device 13 is preferably connected to the nozzle 7 in a material-locking manner, in particular by soldering. Although a resistance heater is provided in the exemplary embodiment, an inductive or other type of heating can also be provided. In an end region 7, from which the flowable metallic material 3 ultimately exits the nozzle 7 at the connection point into a cavity 4, the nozzle 7 is tapered in some areas. Due to the tapering, after the component(s) 2 have solidified and the mold 5 has been opened, the actual casting can be easily removed in the area of the Plug 14 can be broken off, leaving a part of a plug 14 in the nozzle 7.

In Fig.4 a cavity 4 with a connection point and a sprue 17 is shown. As can be seen, a cross has to be filled with the flowable metallic material 3 from the connection point to the cavity 4 before the cavity 4 is reached. This means that there is initially a high proportion of waste that accumulates in the area of the sprue 17. This waste can be recycled, but this is complex. In addition, longer distances have to be covered, which has to be taken into account in the process management. The closing pressures for the mold 5 or its first part 11 and its second part 12 are also higher because the projected cross-sectional area is larger.

In Fig.5 is schematically a spraying with a distribution unit according to Fig. 2 The cavity 4 can be filled simultaneously at each of the connection points via four sections 9 with channels 10, allowing flowable material 3 to enter.

So as for Fig.5 explains a simultaneous connection in several different points with a distribution unit 8 according to Fig. 2 dynamic temperature control at the nozzles 7 is advisable. This can be seen from Fig.6 and 7 explained in more detail. In Fig.6 First, the processes during a (production) cycle are shown. When the mold is closed, the material 3 is injected via the barrel into the downstream nozzle 7 into one or more cavities 4, which are present in the second part 12 of the mold 5. When the cavities 4 are completely filled, the component is cooled. Then the mold 5 is opened, the component(s) 2 are removed and the mold 5 is cleaned within a few seconds and treated with a release agent so that one or more components 2 created in the next cycle can be easily removed. Then the mold 5 is closed, which ends the cycle. The next cycle begins again with the injection of material 4. A cycle as in Fig.6 shown is common in thixomolding processes.

The nozzles 7 of the device 1 are expediently subjected to a temperature program that leads to lower pressure peaks in the conveyor 6 or the barrel without extending the cycle time and thus significantly increases its service life. The variable temperature control at or in a nozzle 7 is in Fig.7 for a Production cycle shown. When injecting into the closed mold, the nozzle 7 is subjected to maximum heating power so that the material 3 can flow freely through the nozzle 7. This corresponds to state A. As soon as one or more cavities 4 are filled and the component 2 is cooled, the heating power can be reduced in a first section of the nozzle 7, which is closer to a sprue point, as shown by a changed hatching in the heating device 13. This corresponds to state B. A plug 14 then forms in the nozzle 7 in the area that is at the beginning of the nozzle 7. Cooling may be useful for plug formation, but does not necessarily have to be implemented. Since the mold 5 is cooled to solidify the component(s) 2 and magnesium has good thermal conductivity, the plug 14 can in principle also form with further, albeit possibly reduced, heating of the nozzle 7. When the mold 5 is opened and the component 2 is removed, the plug 14 breaks off in the area of the nozzle 7, but essentially remains intact. This corresponds to state C. The mold 5 is still open, but the heating device 13 can already operate at higher power to soften the plug 14. This corresponds to state D. As soon as the mold 5 is closed again, the heating device 13 can be operated at full power so that the plug 14 ideally melts completely. This corresponds to state E. This means that the nozzle 7 is completely free during the next cycle or injection, so that pressure peaks in the conveyor 6 or the barrel are eliminated or at least reduced. The targeted softening and subsequent melting of the plug 14 can be carried out within the usual time for a production cycle of less than 40 seconds.

Claims (16)

1. A device (1) for producing at least one metallic component (2) by injecting flowable metallic material (3) into at least one cavity (4) of a multipart mould (5), in particular for casting magnesium or magnesium alloys in the thixotropic state, comprising a conveying device (6) for the flowable metallic material (3), at least one nozzle (7) downstream of the conveying device (6) and the mould (5) with the at least one cavity (4), wherein the conveying device (6) is adjoined by a distributor unit (8) with a plurality of nozzles (7), via which the flowable metallic material (3) can be injected under pressure into the at least one cavity (4) in order to fill the at least one or more cavities (4) simultaneously via individual nozzles (7), wherein channels (10) of the distributor unit (8) are constituted free from corners with a right-angle, characterised in that the distributor unit (8) comprises rectilinear sections (9) which lead from a branching point (15) to the nozzles (7).
2. The device (1) according to claim 1, characterised in that the channels (10) of the distributor unit (8) are constituted free from corners.
3. The device (1) according to claim 1 or 2, characterised in that the channels (10) of the distributor unit (8) branch off from the branching point (15) at an angle (α) of at most 50°, preferably at most 45°, in particular 20° to 40°.
4. The device (1) according to any one of claims 1 to 3, characterised in that the distributor unit (8) comprises at least three channels (10).
5. The device (1) according to any one of claims 1 to 4, characterised in that the distributor unit (8) is integrated in a first part (11) of the mould (5).
6. The device (1) according to any one of claims 1 to 5, characterised in that a heating device (13) is provided for each nozzle (7).
7. The device (1) according to claim 6, characterised in that a control is provided for the heating devices (13) which variably controls a temperature at or in the nozzles (7) depending on the status of a cycle.
8. The device (1) according to claim 6 or 7, characterised in that the heating devices (13) are constituted as resistance heaters.
9. The device (1) according to any one of claims 1 to 8, characterised in that the nozzles (7) are formed from a steel, in particular a hot working steel.
10. The device (1) according to any one of claims 6 to 9, characterised in that the heating devices (13) are soldered to the nozzles (7).
11. A method for casting at least one metallic component (2), wherein the flowable metallic material (3), in particular magnesium or a magnesium alloy in the thixotropic state, for forming the at least one component (2) is guided from a conveying device (6) via a distributor unit (8) to a plurality of nozzles (7) and is injected via the latter under pressure into at least one cavity (4) of a multipart mould (5), after which the at least one component (2) is allowed to solidify in the mould, after which the mould (5) is opened and the at least one component (2) is removed, after which the mould (5) is closed and the next component (2) is produced, characterised in that the flowable metallic material (3) is guided via channels (10) of the distributor unit (8), which are free from corners with a right-angle, from a branching point (15) of the distributor unit (8) without deflection to the nozzles (7), wherein the flowable metallic material (3) is guided from the branching point (15) branching off along rectilinear sections (9) of the distributor unit (8) to the nozzles (7).
12. The method according to claim 11, characterised in that the flowable metallic material (3) is guided from the branching point (15) at an angle (α) of at most 50°, preferably at most 45°, in particular 20° to 40°, branching off to the nozzles (7).
13. The method according to any one of claims 11 or 12, characterised in that the nozzles (7) are heated when the mould (5) is opened in order at least to soften plugs (14) formed in the nozzles (7) before the production of the next component (2).
14. The method according to any one of claims 11 to 13, characterised in that, after opening of the mould (5) and removal of the component or components (2), a heating power at the nozzles (7) is set in such a way that the plug (14) softens without entry of flowable metallic material (3) into the at least one cavity (4).
15. The method according to claim 14, characterised in that the heating power at the nozzles (7) is increased after mould (5) is closed in order to produce the next component (2).
16. The according to any one of claims 13 to 15, characterised in that the heating power at the nozzles (7) is reduced when the component is allowed to solidify, so that a temperature for a plug formation in the nozzles (7) is fallen short of.

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