WO2003045609A2 - Method for producing die-cast parts and a die casting device - Google Patents

Abstract

The invention relates to a method for producing die-cast parts, in particular wheel rims or wheels for vehicles, in addition to a die casting device therefor. To produce high quality wheel rims or wheels, the starting materials are heated in stages in a casting cell and are transferred in a semi-solid form to a die casting machine, where they are formed into die-cast parts.

Description

 Process for the production of die-cast parts and casting device

The invention relates to a method for producing die-cast parts, in particular parts made of aluminum or magnesium materials. The invention particularly relates to the manufacture of rims or wheels for the automotive industry.

Rims or wheels for vehicles, especially motor vehicles, are now manufactured from aluminum materials using the low-pressure casting process. These are mostly simply controlled low pressure casting machines with a high manual workload. Every machine needs an operator who is exposed to both the high temperatures of the molten metal and the exhaust gases from the casting process. The demolding of the cast parts is complex.

Many manual operations influence the part quality and the cycle time for casting a wheel is 7 to 12 minutes. Design changes require the production of new shapes.

The manufacturer (low-pressure casting machine) purchases the required aluminum alloy in ingot form and melts it in melting furnaces next to the low-pressure casting machine, i.e. the quality can also vary from machine to machine.

A process for the casting of motor vehicle wheels, made of aluminum, magnesium or the like.Light metals in low-pressure casting machines, which essentially consist of a crucible for keeping the melt warm, a casting mold arranged above the crucible, and a casting mold that extends from the casting mold and protrudes through the lid of the crucible DE-C-3619525 shows the riser pipe protruding into the melt, the metal consumed by the casting of the molded part being recharged into the casting machine. It is characterized in that, before each casting, a metal block (ingot) of a mass which essentially corresponds to the casting weight is introduced into the gas space above the bath level of the casting machine and before or after Pulling or ejecting the casting is introduced into the bath of the casting machine.

It is generally known to produce parts from aluminum or magnesium materials by die casting from the melt or also semi-solid, tailored bolts (SSM process or thixomolding). So far, however, it has not been possible to develop alternative processes economically for such highly stressed parts.

For example, DE-C-195 38 243 discloses a process for producing a semi-melted thixogiess casting material in which thixogiess material, which has an outer layer section with dendrites around an outer periphery of a main body section, is subjected to a heat treatment in order to to produce molten casting material with solid and liquid phases coexisting therein. Here, the dendrites, respectively. Dendrite fragments are transformed into spherical solid phases by increasing the temperature of the outer layer section with respect to the main body section, and the outer layer section is brought into a semi-melted state. The use of skin effects is intended to prevent the main body from heating up too quickly. Such a step-by-step method for heating is complex and requires several induction heating steps with different frequencies (powers).

The invention is therefore based on the object of developing a method for producing die-cast parts, in particular wheels or rims for vehicles, with which the disadvantages of the prior art can be overcome. In particular, high-quality wheels and the like should be able to be produced with reduced effort. The environmental impact should be noticeably reduced in connection with improved working conditions.

The object is achieved with the features of claim 1. Advantageous embodiments are disclosed in the subclaims.

Another object of the invention is to provide a casting device for carrying out the method. In a die casting cell known as such with supply and heating devices for the casting material, a die casting machine, handling devices and control devices, heating devices are integrated which enable the gradual heating of bolts made of aluminum materials (possibly also magnesium materials), which then come into contact without any significant contact with the ambient air reach the die casting machine. After die casting or pressure forming, the cast parts are cooled and stored in a special process, and much faster than usual. It is characteristic of the heating process that a high, constant energy input is started and the energy input is then reduced after reaching the thixotropic structure in the metal area.

Significant advantages of the method according to the invention are that it can be carried out fully automatically, there is no need to handle liquid metal, including the corresponding melting furnaces and potential hazards. Exhaust gases etc. do not come into direct contact with operators and the environment. The cycle time per wheel drops to approx. 1 minute.

The invention is described in more detail in an exemplary embodiment with reference to a drawing. In the drawing, the

Fig. 1 a casting cell. Fig. 2 a fixed mold frame in perspective. Fig. 3 a mold frame in partial section

The casting cell contains a die casting machine 1 with a mold, a converter for the heating system 2, a monitor 3, a removal robot 5 for parts removal with a control unit 5, a loading robot 6 for feeding the slug with control unit 7 and a spray robot 8 with control unit 9 Molding temperature control devices 10, cooling stations 11 and 13, electrical, for example inductive heating units 12 for heating slugs (bolts), a device for parts control in front of a conveyor belt 16 for the discharge of non-quality parts and a further conveyor belt 15 for the discharge of the good parts. A metal supply is also planned (Sluglager 17), an automatic cleaning station 18 and a manual cleaning station 20 for castings, a scale 19 and a repair area 21.

The die casting machine 1 is fed directly with slugs or bolts or portions that were previously heated in the heating units 12. They can be transferred directly and with no air into the casting chamber of die casting machine 1. When using magnesium materials (but also useful with aluminum materials), the heated slugs in closed containers are fed to the casting chamber of the die casting machine 1 by means of robots 6. The containers are closed with a lid, so that the slugs are already heated in them and can be fed from the heating unit 12 to the casting chamber without protective gas when the target temperature is reached. The container is provided with a lid which can be lifted off or which is articulated to the container. For the possible provision of molten portions, the lid or the bottom of the container can also be provided with an additional and closable opening for pressure or vacuum emptying. The container can be rather flat or tall and narrow. A complete adaptation of the container to the shape of the material portion is not necessary, although the smallest possible volume of air in the closed container is advantageous. In particular, there should only be a small air gap between the lid and the material surface (portion). A seal that can be achieved through the shape and weight of the lid is usually sufficient. With semi-solid materials, the container is simply emptied over the edge of the container. Alternatively, the bolts can also be fed directly from a heatable supply space / feed channel, which can also be connected directly to the casting chamber, if necessary, the temperature being able to be increased during the transfer if necessary. In the case of aluminum materials, for example, an alloy No. A357 (Al-Si7MgO, 6) is preferably used, which allows the cast parts to be quenched and stored in a shorter time (T5 treatment). The heating before pouring takes place gradually. This can be divided into three areas. A high-performance heating at the beginning, a "cooking" after reaching the thixotropic structure in the area of the stud and in a homogenization for the final adjustment of the globulithic structure in the primary material. Here, an AI bolt with a diameter of 5 to 6 "is first heated with constant high energy to approx. 550 to 570 ° C, whereby the difference in temperature inside the bolt is up to approx. 20 ° C. Then the energy input becomes very high short time drastically reduced, kept very short time ( "cook") and then increased again and held again until a temperature of approximately 585 ^C C is reached and the temperature difference has dropped to about 2 to 3 degrees. in stud to 4 "diameter, the procedure can be simplified to the extent that the step of lowering the energy input can take place more slowly and evenly over a longer period of time. The individual bolts can also be “wrapped” in foil before heating, preferably in an aluminum foil, in order to avoid oxide formation etc. Shielding gas can also be used to avoid oxide formation.

The starting material for the slugs is a homogeneously distributed, fine-grained material, which forms a uniformly distributed, globular microstructure with grain finenesses of approx. 50-100 μm due to the heating process. The latter is for e.g. high-quality wheels or rims, which are to be manufactured using an SSM process, are required.

There is no longer any liquid material to be handled. All exhaust gases are sucked off and the form spray is optimized so that no residual spray has to be disposed of. Smoke gas generation is almost impossible.

The molds and casting tools have a modular structure, so that cost-effective and easily exchangeable mold packages are available for each wheel type. A quick change for the respective shaping part of the forms is possible.

The shape in the die casting machine 1 is e.g. two-part or three-part and variable use. Since the rim base remains unchanged per wheel dimension, only two mold plates have to be adapted to different front designs. These can still contain inserts that are made of an inexpensive and less high-strength material. The service life of such inserts can thus be adapted to the required number of rounds and only the basic shape has to consist of high-strength material.

The mold plates can also contain slide inserts that allow adjustable heights and widths in the front design (depending on the tire and rim dimensions) in defined areas, so that an extra shape is not required for each dimension.

Special wipers enable easy demolding, even with complicated shapes or undercuts. These wipers are arranged in such a way that after a mold opening stroke, an ejection stroke moves upwards, le / slide can also move transversely to the demolding direction and can be detached from the cast part.

According to a further exemplary embodiment, the casting mold for producing a vehicle wheel from, for example, aluminum materials has a fixed molding frame 30 with a mold centering 31 as well as molded parts or slides 32 and cooling spirals. The fixed mold frame 30 is connected to the casting chamber 34 in a conventional manner. It also has part-specific core elements for bores in the hub 36 of the wheel 35, which can also serve as ejector elements of the wheel 35. This means that no additional ejectors are required, but functional parts are used that are already required for other tasks (here as the core element). The mold is filled from the hub 36 of the wheel 35 and between the hub surface and the gate 37 of the casting chamber 34, a filter or sieve 38 is arranged as an insert on the hub 36, which primarily serves to remove oxide skins of the SSM to be pressed in. Retain Bolzens, resp. to tear open and shred. The sieve 38 is a stamped part made of aluminum or steel and perforated as desired according to the hub surface. The bolts, not shown, are heated and fed with low O ₂ . The filling in the mold cavity is largely dry, ie without lubricant. Due to the sieve, there is no need for a shearing knife for the oxide skin of the bolt.

The casting chamber 34 and the casting piston of the die casting machine 1 preferably consist of a ceramic material in order to be able to dispense with lubricants and spraying agents as far as possible.

Compared to the previous direction of casting from the visible surface of the wheel 35, material return flows are significantly lower and the hub itself becomes a press residue. The remains of the sieve 38 are removed by machining the hub surface (if the sieve 38 is made of steel, the aluminum-steel chips can be used, for example, in the manufacture of steel). The visible surface of the wheel 35 is already cast to the final contour. The molded parts or slide 32 are provided with drives and guides (not shown) in order to ensure that the molded parts or slide 32 are retracted and extended.

Surfaces for locking the slide 32 are provided almost perpendicular to the support plane of the fixed mold frame 30. Furthermore, surfaces for locking the slide 32 are provided, which are arranged parallel to the abovementioned support plane on the slide 32 or the molded parts. Also almost perpendicular to the support plane mentioned, further surfaces for combined counter-locking and shape centering are provided.

Corresponding counter contours are formed in the movable mold frame 33.

The surfaces for locking the slide 32 are preferably on or in the fixed mold frame 30 and particularly preferably in a line. The surfaces for mold centering are circumferential regardless of the number of molded parts or slides 32.

The forces acting during casting are thus distributed in the fixed mold frame 30 to the surfaces for combined mold centering and counter-locking to the right and left of the slide 32 - force transmission and force transmission are thus approximately in line and are easier to control.

The molded parts or slides 32 are available for the common range of wheel sizes (for example from 13 "to 22") and can be arranged in only one set of molded frames 30, 33. reference numeral

die casting machine

inverter

monitor

removal robot

control unit

loading robot

control unit

spray robot

control unit

mold tempering

cooling station

heating unit

cooling station

parts control

conveyor belt

conveyor belt

Sluglager

cleaning station

Libra

cleaning station

Fixed mold frame repair area

guide

Slider movable mold frame

casting chamber

wheel

hub

bleed

scree

Claims

claims 1. Process for the production of die-cast parts, in particular wheels or rims for vehicles by casting, the starting materials being supplied and heated in the form of bolts or slugs, characterized in that the heated starting materials have a globulithic microstructure in the semi-solid form of a die-casting machine (1) fed and cast or formed using high pressures. 2. The method according to claim 1, characterized in that the heating of the starting materials takes place in stages. 3. The method according to claim 1 or 2, characterized in that the cooling takes place to at least 180 ° C and aging of the cast parts can be shortened (T5). 4. The method according to any one of claims 1 to 3, characterized in that the cycle time is approximately 1 minute. 5. The method according to claim 1, characterized in that the supply of the heated starting materials in the die casting machine (1) is carried out with largely air exclusion. 6. The method according to claim 2, characterized in that the bolt made of an aluminum material initially heated to a temperature with a high and constant energy input at which a thixotropic structure occurs in the jacket area then the energy input is drastically and quickly reduced and held for a short time thereafter the energy input is increased again and held until the temperature inside and in the jacket area is largely equalized. 7. Casting device for the production of die casting parts, in particular rims or wheels for vehicles with a casting device, heating devices for heating the starting materials and handling devices, in particular robots for handling the starting materials and die casting parts, characterized in that the casting device contains a die casting machine and is designed as an automated casting cell is. 8. Casting device according to claim 7, characterized in that it has variable shapes and inserts of the shapes. 9. Casting device according to claim 8, characterized in that the material of an insert is adapted to the required number of shots. 10. Casting device according to claim 8, characterized in that ejection elements are provided which are also functional elements during the casting process. 11. Casting device according to claim 8 or 10, characterized in that the mold comprises a fixed and a movable mold frame (1, 4) and molded parts or slides (3) arranged therein in guides and having a modular structure. 12. Casting device according to claim 8 or 10 or 11, characterized in that the molded parts or slide (3) for certain part sizes in the mold frame (1, 4) can be placed. 3. Casting device according to at least one of claims 1 to 12, characterized in that the casting chamber and piston of the die casting machine (1) consist of a ceramic material.