EP0912276A1

EP0912276A1 - Thixoforming device

Info

Publication number: EP0912276A1
Application number: EP97917232A
Authority: EP
Inventors: Kurt Detering; Jörg Detering
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-23
Filing date: 1997-02-21
Publication date: 1999-05-06
Also published as: JP2000504632A; DE19606806A1; DE19606806C2; WO1997030806A1

Abstract

The invention concerns a thixoforming device which comprises at least two casting fittings to ensure that, when the mould gravure is filled, no regions are produced in which the flow of material stops spontaneously and then continues on its path at random, which might result in the mould gravure being filled incompletely.

Description

Device for thixoforminα

In addition to forging and other forming techniques, casting techniques can also be used to manufacture molded parts. The latter come into question when very complicated, possibly thin-walled parts have to be produced, which cannot be produced by forging. The material is viscous when forging, which is why certain minimum cross sections must not be undercut in view of reasonable pressures.

When pouring, however, the material is comparatively very thin. The thin material can flow through narrow gaps in the engraving of the casting mold and easily fill complicated spaces.

In so-called "sand or permanent mold casting", the liquid material flows into the mold from a pouring funnel due to gravity. Solidification may only start when the mold is completely filled. The cycle times are correspondingly long and it is only possible to produce molds which do not involve the risk of premature cooling in sections. The cold spots would result in casting errors.

The cycle times can be increased if, as with die casting, these boundary conditions do not have to be met.

The arrangement for die casting consists of a divisible casting mold, the mold halves of which contain the mold engravings. A casting set is connected to the casting mold, which includes a fan-shaped casting run, which widens in the direction of the shape engraving and has its smallest cross-section in the casting chamber, which holds the liquid metal. During the casting process, the liquid metal contained in the casting chamber is injected through the casting barrel into the mold engraving with the aid of a piston which is movable therein. The flow velocities for the pressure greeting are 40 m / sec and can reach up to 60 m / sec. These high flow speeds lead to a turbulent flow in the jet and to the rupture of the metal jet in the casting run and the engraving. As a result, like in an aerator at a tap, the air contained in the casting mold and the pouring barrel is mixed into the thin-bodied metal. After cooling, the air pockets in the finished casting form tiny cavities that adversely affect the strength.

So that the liquid metal cannot flow out of the press chamber in an uncontrolled manner, the casting chamber must be arranged under the die. Due to the arrangement and the high flow rate, the engraving fills from the end of the engraving which is furthest away from the casting run or the casting chamber; the engraving fills, so to speak, against the direction of influence of the material.

Although very thin-walled parts can be produced in principle with die-casting technology, the parts produced in this way do not meet the requirements of, for example, car body parts be put. The die-cast component does not reach the necessary elongation and strength values with sufficient certainty, which is due on the one hand to the material to be used and on the other hand to the air pockets which are unavoidable in die-casting technology.

For this reason, attempts have already been made to evacuate the die before the metal is injected in order to avoid the bubbles in the workpiece. The equipment required for this is extremely high.

Another disadvantage associated with die casting technology is the fact that the metal only has to be handled in completely liquid form. This presupposes either melting the solid material completely at the point of use or making it in the form of a liquid melt from the production site, for example the aluminum works, to the foundry.

In this respect, the so-called "thixoforming" is much cheaper. In thixoforming, an alloy is used which, in a temperature range dependent on the material used, occupies an intermediate position between solid and liquid. It is believed in the professional world that the material at this temperature has a still firm but deformable structure with liquid components embedded therein. About 50% to 60% of the material is liquid during thixoforming, while the rest 20% is still in the solid state.

In thixoforming, a bolt heated to the thixoforming temperature, the volume of which corresponds to the finished workpiece plus overflow, is placed in a press chamber. The thixotropic material is pressed into the mold using a casting piston. Since the thixoforming material is not flowable by itself, the position of the casting chamber is irrelevant. The material cannot run out of the casting chamber on its own. Thixoforming has already proven itself quite well for the production of elongated, approximately rod-shaped parts. The air pockets that occur during die casting are completely avoided because the material flow is so viscous that the air that is in the mold is displaced by the material without being able to penetrate the material. The temperatures during thixoforming are comparatively lower, which means an energy reduction and, in addition, the casting chambers are filled with qusi solid bolts which can be handled safely. Thixoforming does not require the dangerous transport of hot melt by truck across the street to the place of use.

An attempt was therefore made to transfer the thixoforming to flat, thin-walled parts by using the casting sets common in die casting technology. However, the desired success has not materialized.

Proceeding from this, it is an object of the invention to provide a device for thixoforming with which it is possible to also produce flat parts.

It was recognized by the inventor that material which is suitable for thixoforming apparently spontaneously and accidentally comes to a standstill when it flows through the casting run of a die casting mold. The pushing material is not able to liquefy such a section which has come to a standstill and is forced to flow around this point, with cavities or unforeseen flow directions in the shadow of these stuck material areas. against the material. Both have an adverse effect on the filling of the engraving. The partial solidification of the material flow is promoted by the fan-shaped shape of the casting run during pressure casting. The casting run during die casting extends from the casting chamber to the gate and accordingly the flow rate decreases. A flow rate that is too low can lead to spontaneous solidification.

The use of at least two casting runs makes it possible to avoid such a spontaneous solidification in the case of flat parts. The shape of the casting runs is selected such that each generates a material flow, the material flow front of which, alone or together with another material flow, essentially completely fills the cross section of the engraving at the respective location of the material flow front.

These currents can either flow towards one another, welding occurring at the joint, or they can flow through the mold in synchronism if a correspondingly large width has to be covered. Finally, it is conceivable to use both filling processes at the same time, always striving to achieve material flows that are inevitably guided by the wall of the engraving or the casting run, so that there are no places where the flow rate may be so low that spontaneous solidification can occur.

For the rest, further developments of the invention are the subject of subclaims.

In the drawing, an embodiment of the object of the invention is shown. Show it:

1 is a highly schematic die casting machine according to the prior art, with the mold open,

2 shows the casting machine according to FIG. 1 in a longitudinal section,

3 is a schematic representation of the invention modern device for thixoforming, in a plan view with the engraving open, and

Fig. 4 shows the device of the invention according to fig. 3 in a longitudinal section at right angles to the engraving gap.

For a better understanding of the invention, the prior art given by die casting technology will first be explained with reference to FIGS. 1 and 2.

For die casting, a die 1 is used, which consists of a lower and an upper mold half 2, 3, which abut each other at a flat engraving gap 4. On the two abutting sides of the two mold halves 2, 3, a mold engraving 5, 6 is formed, which represents the negative of a workpiece to be created. In the present case, it is assumed that the finished workpiece is a rectangular plate, which is delimited by four mutually parallel narrow sides 7, 8, 9, 11 of the shape engraving 5, 6 and two flat sides.

At the lower end of the die 1, a single casting set is shown in a highly schematic manner

12, which is composed of a casting chamber 13 with a casting plunger 15 movably guided therein and a casting casting run 16 which widens in a fan shape. The casting drive for moving the casting piston 15 via its casting rod rod 17 is not shown for the sake of simplicity.

In the interior of the casting run 16, as is customary in the case of die casting machines, there is a slot-shaped channel 18 which extends in a fan shape from an outlet 19 of the casting chamber

13 extended to the wide narrow side 7 of the workpiece. In the direction perpendicular thereto, the channel 18 tapers, starting from the outlet 19, in the direction of the engravings 5, 6. The channel 18 opens at a so-called gate 21 into the cavity defined by the two engravings 5, 6.

As can be seen, the channel 18 contained in the casting run 16 merges into the cavity of the die 1 via a throttle point. For die casting, the casting chamber 13 is filled with the molten metal. After being poured into the casting chamber 13, the metal is injected into the casting mold 1 under high pressure using the casting piston 15. The molten material, like a fountain, shoots from below in a more or less compact jet 22 of liquid metal through the channel 18 upwards into the cavity of the casting mold 1 until it hits the opposite edge 9. The subsequently injected liquid metal keeps the previously injected material pressed against the wall 9 due to the inherent kinetic energy.

During die casting, the mold cavity gradually fills from top to bottom, ie against the direction of flow of the injected metal, as is indicated schematically by material fronts 23a, 23b and 23c. The material front 23a forms before the material front 23b is formed.

The shooting in of the metal continues until the channel 18 in the casting run 16 is filled.

The bullet speed for the metal is between 40 and 60 m / s. At this high speed, turbulence occurs in the metal jet, in particular also caused by the taper at the gate 21, as a result of which the metal jet mixes with air contained in the casting mold 1, which forms finely distributed cavities in the solidified metal.

3 and 4 show a highly schematic device 31, which is provided for thixo-forming, in order to produce relatively large-area parts in this way by means of primary shaping. For this purpose, a thixotropic metal alloy is used which has thixotropic properties above a temperature which is dependent on the material, insofar as part of the metal, approx. 40% - 50%, physical state, while the rest is still in the solid state. Such a thixotropic alloy exhibits a viscosity behavior in which the viscosity decreases with increasing shear stress.

The device according to the invention consists of a casting mold 32, to which a plurality of casting sets 33a, 33b, 33c are connected.

The casting mold itself consists of a lower mold half 34 and an upper mold half 35, which assembles between them an engraving 36, consisting of a mold engraving 37 in the upper mold half 35 and a mold engraving 38 in the lower mold half 34. The necessary mold clamping unit is not shown because it is not necessary for an understanding of the invention.

To explain the invention it is assumed that the workpiece to be produced, as the plan view in Fig. 3 shows, should have approximately a trapezoidal shape, and laterally by edges 39, 41, 42 and 43 of the engraving 36 and by imaginary dashed lines 44, 45 and 46 is limited, which should also symbolize the location of the gates.

The casting sets 33a ... 33c are identical to one another, which is why the same reference numerals are used for the individual components, each supplemented by a corresponding letter.

The casting set 33a includes a casting barrel 47a, the channel 48a of which connects a casting chamber 49a to the engraving 36. The pouring run 48a mentally ends at the dashed line 44, i.e. the dashed line 44 corresponds to what is referred to in the die casting technique as a gate.

In the casting chamber 49a, a casting piston 51a is slidably guided, which is driven via a casting piston rod 52a. The casting piston drive is not shown further, since it is also not necessary for an understanding of the invention.

As can be seen from the sectional illustration in FIG. 4, the channel 48a merges into the engraving 36 without any appreciable restriction. In addition, the channel 48a is provided with essentially parallel side flanks 53 and 54, its width in the present case corresponding to the length of the gate 44.

In the case of the two casting sets 33b and 33c, the cross-sectional dimension of the associated channel 48b and 48c, viewed in the longitudinal direction of the gate, is smaller than the length of the relevant edge of the workpiece to be produced. The wall 41, which is part of the two engraving halves 37 and 38, rises between the two channels 48b and 48c. However, even with these casting sets 33b and 33c, the channels 48b and 48c in the casting runs 47b and 47c are practically non-divergent in the direction of the mold engraving 36.

Within the casting mold 32, the two engravings 37 and 38 form an overflow 56, the position of which results from the following functional description:

For casting, the casting chambers 49a ... 49c are opened and they are charged with a hot bolt made of a thixotropic alloy and dimensioned in volume. The casting chambers 49a ... 49c are then closed.

Simultaneously or before the bolts are poured into the casting chambers 49a ... 49c, the movable mold half, that is to say the mold half 34 or the mold half 35, is pressed onto the fixed mold half 34, 35 by the mold clamping unit (not illustrated). The casting drives for the casting pistons 51a ... 51c, which are also not shown, are then started essentially simultaneously in order to press the material out of the casting chambers 49a ... 49c at a flow rate between 4 m / sec and 15 m / sec. The material emerging from the casting chamber 49a forms a material flow, the foremost front 57 of which fills the entire cross section of the channel 48a and moves from the casting chamber 49a in the direction of the engraving 36. The shape of the channel 48a and the position of the gate 44 are selected such that the material flow front 57 does not lose contact with the boundary wall of neither the channel 48a nor the engraving 36 at any point, and that the material remains flowing at all points on the material flow front .

The material flow coming out of the casting chamber 49 moves in the direction of an arrow 58 in the direction of the center of the engraving 36. Lines 57a ... 57c are intended to indicate various temporarily occurring positions of the material flow front.

Since the casting drives for the two casting sets 33c and 33b were also started at the same time, a material flow also emerges from their casting run 47b and 47c, the material flow fronts 51 and 61 of which at practically every point also have the cross section of the relevant channel 53b and 53c to complete.

As soon as the material flow fronts 59 and 61 have exceeded the gates 45 and 46, the material flow fronts 59, 61 run along the wall 41 until they touch each other, as a result of which the two material flows coming from the channels 48b and 48c , weld together. They then form a common material flow front 62 which moves towards the material flow front 57. The flow directions of the material flows from the channels 48b and 48c are symbolized by arrows 63 and 64. The material flow fronts 57 and 62 meet below the overflow 56 and also weld there. Since the only free space which is not yet filled is the overflow 56, the now combined material flows will flow into the T-shaped overflow 56, with which the engraving 36 is completely and completely filled.

The position of the gates 44, 45 and 46 as well as the geometry of the channels 48a ... 48c in connection with the shape of the shape engraving 36 are selected so that an inevitable flow movement without danger at all points of the material flow fronts 57, 59, 61, 62 stagnation is maintained. Such a condition is preferably met if the material flow fronts 57, 59, 61, 62 do not come into a position in which mushroom heads form and the material flow front comes to a standstill at any point on the wall or within the engraved shape 36.

The comparison of the casting using the thixoforming and the new device with the die casting shows that in the die casting, the engraving is filled against the inflow direction of the molten metal, while in the thixo molding the engraving is filled in the direction of the material flow . Thus, in die casting, the first shot material lies at the edge of the engraving, while in thixo forming, the first pressed material comes to lie more towards the center of the engraving, depending on where the material flows meet in opposite currents.

It is understandable that FIGS. 3 and 4 only represent the basic principles and that in this way any complicated flat-shaped structures, such as, for example, the cross member (dashboard support) of a car or the B pillar, can be produced by a correspondingly large one Number of cast fittings 33 is used to achieve the above properties fulfill. It is irrelevant whether the material flows in the direction of rotation completely fill the engraving 36, as is shown by way of example for the material flows from the casting sets 33b and 33c, or whether the material flows strive in opposite directions to one another or whether, as shown, a combination of all possible flow directions is used. Also, the channels 48 do not have to have a strictly constant cross section, but can also expand slightly as long as the flow conditions mentioned above are observed.

It is also important to note that the channels 48 open into the shape engraving as freely as possible, i.e. in the area of the gates 44, 45, 46, no unnecessary artificial changes in cross-section may occur. The consequence of this is that the finished workpiece in the area of the gate has almost the same thickness as the sprue residue present at this point, so that the sprue must generally be separated by cutting processes. The advantage, however, can be seen in the fact that unnecessary undercuts which are difficult to fill with the thixotropic mass are avoided.

In a departure from the exemplary embodiment shown, the material can also flow into the mold engraving perpendicular to the engraving division if the casting set is arranged accordingly. Depending on its position, the metal flows into the engraving in one or in opposite directions depending on its location, i.e. after the first cut, the material flow is divided into two material flows.

In a device for thixo-forming, at least two casting sets are provided to ensure that that when the form engraving is filled there are no areas in which the material flow spontaneously comes to a standstill and then takes an arbitrary course which may lead to incomplete filling of the form engraving.

Claims

claims

1. device (31) for thixoforming,

with two mold halves (34, 35) which delimit a mold engraving (36) corresponding to a workpiece to be produced,

with at least two casting runs (47), each of which is designed in such a way that it generates at least one material flow of flowable material which forms a material flow front (57, 59, 61, 62) at its head, each material flow front (57, 59, 61, 62) fills essentially the entire cross-section of the mold engraving (36) at their respective location, the material flows essentially move on one another and each material flow fills its part of the mold engraving (36) in the state of forward-heating until the material flows meet, and

with at least one filling chamber (49) which feeds at least one of the casting runs (47).

2. device (31) for thixoforming,

with at least two casting runs (47), each of which is designed in such a way that a material flow is produced from flowable material which forms a material flow front (57, 59, 61, 62) at its head, the at least two material flow fronts (57,59,61,62) on hers each place jointly fill essentially the entire cross-section of the mold engraving (36), the material flows move in synchronism and each material flow fills its part of the mold engraving (36) in the state of forward heating, and

3. Apparatus according to claim 1 and 2, characterized gekenn¬ characterized in that at least three casting runs (47) are present such that they produce at least two material flows flowing in unison and at least one material flow flowing counter to the at least two material flows in unison.

4. Apparatus according to claim 1 or 3, characterized gekenn¬ characterized in that it has at the point where the material flows meet at least one overflow (56).

5. Apparatus according to claim 1 or 2, characterized gekenn¬ characterized in that each casting run (47) is assigned its own casting chamber (49).

6. The device according to claim 1 or 2, characterized gekenn¬ characterized in that a plurality of casting runs (47) is assigned a common casting chamber (49).

7. The device according to claim 1 or 2, characterized gekenn¬ characterized in that the casting run (47) is arranged such that the material flow flows parallel to the engraving in the mold engraving (36).

8. The device according to claim 1 or 2, characterized gekenn¬ characterized in that the casting run (47) is arranged such that the material flow flows perpendicular to the engraving in the mold engraving (36).

9. The device according to claim 1 or 2, characterized gekenn¬ characterized in that the material flow forms a laminar flow.

10. The device according to claim 1 or 2, characterized gekenn¬ characterized in that the casting run (47) opens into the shape engraving (36) without restriction.

11. Tixoforming process,

in which a device (31) is provided which comprises:

two mold halves (34, 35) which delimit a mold engraving (36) corresponding to a workpiece to be produced,

at least two casting runs (47), each of which is designed in such a way that it generates at least one material flow of flowable material which forms a material flow front (57, 59, 61, 62) at its head, each material flow front (57, 59 , 61, 62) fills essentially the entire cross section of the mold engraving (36) at their respective location, the material flows essentially move on one another and each material flow fills its part of the mold engraving (36) in the state of forward heating until the Material flows meet, and

at least one filling chamber (49) which feeds at least one of the casting runs (47); and

in which flowable material from the filling chamber is pressed into the casting runs and from there into the mold engraving.

12. Tixoforming process, in which a device (31) is provided which comprises:

at least two casting runs (47), each of which is designed in such a way that a material flow is produced from flowable material which forms a material flow front (57, 59, 61, 62) at its head, the at least two material flow fronts (57, 59, 61, 62) at their respective location together essentially fill the entire cross section of the mold engraving (36), the material flows move in synchronism and each material flow fills its part of the mold engraving (36) in the state of forward heating, and

13. The method according to claim 11 and 12, characterized gekenn¬ characterized in that at least three casting runs (47) are seen vor¬ such that they produce at least two material flows flowing in synchronism and at least one at least two co-flowing material flows counter-flowing material flow .

14. The method according to claim 11 or 13, characterized gekenn¬ characterized in that it has at the point where the material flows meet at least one overflow (56).

15. The method according to claim 11 or 12, characterized gekenn¬ characterized in that each casting run (47) is assigned its own casting chamber (49).

16. The method according to claim 11 or 12, characterized gekenn¬ characterized in that a plurality of casting runs (47) is assigned a common casting chamber (49).

17. The method according to claim 11 or 12, characterized gekenn¬ characterized in that the casting run (47) is arranged such that the material flows parallel to the engraving in the Form¬ engraving (36).

18. The method according to claim 11 or 12, characterized gekenn¬ characterized in that the casting run (47) is arranged such that the material flows perpendicular to the engraving in the Form¬ engraving (36).

19. The method according to claim 11 or 12, characterized gekenn¬ characterized in that the material flows a laminar.

20. The method according to claim 11 or 12, characterized gekenn¬ characterized in that the casting run (47) opens into the shape engraving (36) without restriction.

21. The method according to claim 11 or 12, characterized gekenn¬ characterized in that the engraving is filled in the direction of the inflowing material flowing into the engraving.