Technical Field of the Invention
[0001] The present invention relates to a device and a method for obtaining semi-solid sludges
applicable in the metallurgical industry and more specifically in the field of manufacturing
metal parts by means of any semi-solid state injection process in which closed vessels
are used for preparing materials, preferably for preventing them from having a non-dendritic
structure.
Background of the Invention
[0002] The shaping of materials by means of semi-solid state injection can be considered
a process that is half-way between shaping by molding and solid state shaping. The
semi-solid state shaping of aluminum alloys is a process comprising elements of several
classic shaping techniques, such as high-pressure injection, squeeze casting and forging.
[0003] The advantages of semi-solid state shaping include the fact that it allows a great
deal of freedom in the design of the mold and a high production rate, as well as high
metallurgical quality and mechanical properties that are better than those from permanent
mold casting or high-pressure injection casting.
[0004] The interest of these semi-solid state shaping techniques is based on the need to
produce new parts and components with fewer defects and at a lower cost, and it is
based on the thixotropy of certain materials whereby the rheological properties of
the materials when a liquid phase and spheroidal solid phase coexist allow low viscosity,
even with solid fractions, of 0.6 (expressed as per unit) depending on the material
deformation rate, hence its name rheocasting.
[0005] Several processes for semi-solid state manufacturing are known today which, unlike
the forging or casting process, allow obtaining a non-dendritic material structure
which yields a material with thixotropic characteristics. Different technologies have
been developed for this purpose, including the following with should be pointed out:
- Passive agitation.
- SRC (Shearing Cooling Rolling) process.
- Ultrasonic treatment.
- Electric discharge treatment.
- Rapid solidification processes such as the Osprey process.
- Air SlipTM.
- SIMA (Strain Induced Melt Activated).
- RAP (Recrystallization and Partial Melting).
- Electromagnetic agitation (MHD).
- New RheoCasting (NRC).
- HITACHI Metals.
- Semi-solid Rheocasting (SSR™).
- Continuous Rheoconversion Process (CRP).
- Direct Thermal Method (DTM).
- Sub Liquidus Casting (SLC™).
- Swirl Enthalpy Equilibration Device (SEED).
- SLC developed by THT Presses.
[0006] In several of these technologies, agitation makes it necessary to pour the liquid
into a crucible or cylindrical or frustoconical vessel, and after reaching the non-dendritic
semi-solid structure, the slug, i.e., the semi-solid mass, also called semi-solid
sludge, must be extracted. At this point of the process different problems arise which
have a negative consequence of generating oxides on the surface, entrainments or material
which remains adhered on the surface of the vessel. It must be taken into account
that aluminum alloys oxidize almost immediately upon contact with the air.
[0007] One of the processes using vessels for handling material is the SEED (Swirl Enthalpy
Equilibration Device) process mentioned above which is used below as the basis for
the description of the problems of any process needing a closed vessel for preparing
the material in a non-dendritic structure, especially in the case of cylindrical or
frustoconical vessels.
[0008] The features of the semi-solid SEED injection process are as follows:
- It is based on a liquid material (rheocasting).
- It requires a lesser degree of control compared to other techniques.
- It offers a relatively wide process window.
- It reduces the tendency of the material to adhere to the mold.
- The slug has a broad weight range (2-8 kg).
- A wide range of alloys can be used:
- Casting alloys: 319, 356, 357, 514, 206.
- Forging alloys: 6061.
[0009] A schematic sequence of the current SEED process for manufacturing semi-solid sludges
(slugs) used in aluminum injection cells for obtaining customized slugs has been depicted
in Figure 1 and comprises the following sequential steps.
- a) Melting aluminum by means of traditional methods: melting and pouring on a holding
furnace, also referred to as a metering unit. Next, pouring the aluminum into monobloc
cylindrical recipients referred to as crucibles. Each crucible is tipped to favor
pouring and to reduce the generation of gases, as can be seen in the crucible of the
prior art depicted in Figure 2.
- b) Shaking the crucibles, usually on a vibration table, and cooling the aluminum until
it reaches a suitable globular structure. The solid fraction will make up about 50%
as a function of the percentage of Si, depending on the proximity to the eutectic
point.
- c) Optionally, after step b) the obtained semi-solid sludge can be drained prior to
demolding.
- d) Removing the crucible from the vibration table and transporting it with the slug
therein to the container of high-pressure injection HPDC (High Pressure Die Casting)
equipment, hereinafter the HPDC injector. Next, longitudinally extracting the slug,
for example in automated equipment by means of an abrupt movement of the robot or
by means of an auxiliary piston, and depositing it in the container of the HPDC injector.
At this point it must be taken into account that the slug cannot be broken so as to
prevent the generation of oxides.
- e) Pushing the slug or semi-solid sludge with the piston of the HPDC injector in order
to fill the steel mold.
[0010] In addition to these sequential steps depicted in Figure 1, it is necessary to verify
that no aluminum residues remain in the crucible and if necessary they must be cleaned
as vigorously as possible to remove them. These aluminum residues can be oxides which
deteriorate the following part to be obtained in the process. Standard crucible preparation
steps must also be taken which comprise their cleaning, heating, etc. On the other
hand, it is necessary to mount and secure the crucible on the vibration or shaking
table and lubricant, usually boron nitride, must be sprayed on the crucible.
[0011] An auxiliary crucible preparation process should also be performed which comprises
applying a lubricant on the crucibles with a brush or spray gun in a manner similar
to how the paint is applied, and it is subsequently dried in a furnace. Depending
on the lubricants, there will be between 3 and 5 application layers, and the application
frequency logically varies depending on the applied layers.
[0012] As mentioned above, all these steps and the time and cost they entail are aimed at
preventing the generation of oxides on the surface of the sludges and the crucibles
or vessels, as well as entrainments or material that remains adhered on the surface
of the vessels.
Description of the Invention
[0013] A first aspect of the present invention relates to an equipment for manufacturing
metal injection parts as defined in claim 1.
[0014] A second aspect of the invention relates to a method for obtaining semi-solid sludges
as defined in claim 4.
[0015] In processes for manufacturing semi-solid sludges of the prior art the molten aluminum
is poured into a monobloc cylinder or crucible which is a recipient made of a refractory
material used for melting a material at a very high temperature, while according to
the invention the crucible is formed by two parts or shells which are preferably semi-cylindrical
molten metal injection molds in which metal objects are melted, i.e., the invention
proposes a crucible with two halves. The semi-solid or slug is therefore demolded
transversely rather than longitudinally. The risks of the slugs breaking during demolding
are thus eliminated and the slug is prevented from remaining completely or partially
adhered to the crucible. Crucible cleaning processes are also significantly reduced.
[0016] The crucible according to the invention comprises two half-shells or parts, a half-shell
fixed to the vibration table and a movable half-shell. Fixing means have been provided
for fixing the moveable part to the fixed part and to the vibration table which allow
configuring the crucible for pouring and solidification and logically allow separating
the moveable part for demolding. According to a preferred embodiment, the fixing means
are made up of a tiltable grip assembled in an articulated manner on the vibration
table which can be coupled onto a perimetric flange of the movable half-shell. This
is obviously a specific embodiment but this fixing could be done in many ways.
[0017] When demolding, the moveable shell is separated from the fixed shell and the slug
is in the moveable shell that is displaced to the piston of the injector. This movement
can be performed by means of a robot or any other type of automated installation.
Description of the Drawings
[0018] To complement the description that is being made and for the purpose of aiding to
better understand the features of the invention according to a preferred practical
embodiment thereof, a set of drawings is attached as an integral part of said description
in which the following has been depicted with an illustrative and non-limiting character:
Figure 1 shows a schematic view of the sequence of operations comprising a semi-solid
state injection process of the prior art.
Figure 2 shows an elevational view of a crucible of the prior art that can be used
in the process depicted in Figure 1.
Figure 3 shows a schematic view of the sequence of operations comprising an embodiment
of the method for obtaining semi-solid sludges according to the invention.
Figure 4 shows an elevational detail of a double-shell crucible comprising a fixed
part and a moveable part, comprising an embodiment of the device for obtaining semi-solid
sludges of the invention.
Preferred Embodiment of the Invention
[0019] In view of the mentioned drawings, it can be seen how in one of the possible embodiments
of the invention one of the processes using vessels for handling the material is the
process referred to as SEED (Swirl Enthalpy Equilibration Device) mentioned above
which is the basis for the description of an embodiment of the invention; however,
the invention is extensive and can be applied to any process needing closed vessels
for preparing the material in a non-dendritic structure, especially cylindrical or
frustoconical vessels.
[0020] The invention comprises a crucible recipient in two halves which can be used in manufacturing
metal parts by means of any semi-solid state injection process (e.g. SEED) using closed
vessels for preparing materials, preferably with a non-dendritic structure.
[0021] The differences between the two types of monobloc and double-shell crucibles are
the following:
The double-shell recipient must have uniform thicknesses in order to assure a balanced
heat discharge, guaranteeing the uniformity of the globular structure throughout the
slug. There are clear geometric differences between both types of recipients because
the double-shell recipient needs spaces for implementing securing systems between
half-shells, securing with the shaking table and support-grip for handling the movable
half-shell.
[0022] With this new recipient (crucible) architecture, one of the half-shells is permanently
secured to the vibration (shaking) table and the other one will be moveable. The moveable
one will have three positions:
1st position: Secured to the table and to the other half-shell at the time of pouring.
2nd position: It is then released, transporting and depositing the slug on the container
of the HPDC injector.
3rd position: Cleaning and preparing for the next cycle.
[0023] The movable half-shell has a type of grip plate which allows grabbing it and handling
it by means of robot, manipulator or manually. Taking into account that the thicknesses
must be uniform in the recipient, an insulator is introduced between the movable half-shell
and the grip plate. This grip plate must ideally be located in the upper part of the
recipient, at a height which the liquid aluminum/slug never reaches.
[0024] The bottom of the half-shells coming into contact with the shaking table can be open
or closed, whichever is appropriate, because the drain hole is not required.
[0025] The cleaning process is much simpler in the double-shell system because the movable
half-shell is brought closer to the cleaning-lubricating head which is always accessible
and in the same position.
[0026] The double-shell system does not require much lubrication because the transverse
demolding of the semi-crucibles is very easy due to the fact that it already has natural
demolding. As less lubrication is needed, the thickness of the oxide layer enveloping
the slug is less and the risk of displacing said oxides to the part when filling the
mold is lower.
[0027] The resulting process is as follows:
- A) Melting aluminum by means of traditional methods: melting and pouring on holding
furnace (also referred to as metering unit).
- Pouring the aluminum on double-shell cylindrical recipients (crucibles). The crucible
is tipped to favor pouring and to reduce the generation of gases.
- B) Shaking the double-shell crucibles (on a vibration table) and cooling the aluminum
until it reaches a suitable globular structure. The solid fraction will make up about
50% as a function of the percentage of Si (proximity to the eutectic point).
- C) Turning the crucible until it is horizontal and separating the movable half-shell
such that the slug remains therein to be transported to the container of the HPDC
injector.
- D) Depositing the slug on the container is reduced to turning the half-shell and letting
the slug fall by rolling-gravity. Pushing the semi-solid slug with the piston of the
HPDC injector to fill the steel mold.
[0028] The process also comprises the following auxiliary steps:
- Standard crucible preparation process: cleaning, heating and lubricating.
- Operation for mounting and securing the crucible on the vibration (shaking) table.
[0029] The crucible recipient in two halves (half-shells) allows the transverse demolding
of the slug and accordingly:
- Simplifies the lubrication process and reduces the thickness of the oxide layer generated
on the skin of the slug.
- Eliminates the risks of the slugs breaking.
- Eliminates the risks of the skin of the slug being adhered to the recipient. It increases
the quality of the parts and reduces deterioration.
[0030] By eliminating the longitudinal extraction of the slug, the risk of the slug adhering
to the crucible (completely or partially) is reduced, reducing interruptions caused
by insufficient lubrication. In addition to the interruptions, the recipient cleaning
processes are significantly reduced, especially when the skin remains adhered to the
crucible.
[0031] The transport and pouring of the slug into the container of the HPDC injector is
simplified and the risks of the slug breaking are reduced. This advantage will be
more important as the size of the slugs increases.
[0032] An important part of the crucible lubrication and preparation processes is eliminated.
The process becomes more linear and more efficient, and it provides a prior verification
that no residues are left in the crucible with the subsequent need to eliminate them.
1. Equipment for manufacturing metal injection parts, comprising a vibration table, a
high-pressure injection equipment (5) and a device for obtaining semi-solid sludges,
characterized in that the device for obtaining semi-solid sludges comprises a crucible (1, 2) comprising
at least one fixed part (1) which is fixed to the vibration table, and at least one
moveable part (2) which can be attached to the fixed part (1) through fixing means
(3).
2. Equipment according to claim 1, wherein the fixing means (3) consist of an articulated
clamp which allows fixing the moveable part (2) to the fixed part (1).
3. Equipment according to any of the preceding claims, comprising a fixed part (1) and
a moveable part, both being semi-cylindrical.
4. Method for obtaining semi-solid sludges, characterized in that it comprises using the equipment according to any of claims 1 to 3.
5. Method according to claim 4, which comprises:
A) melting aluminum and pouring said molten aluminum into the crucible formed by at
least one moveable part (2) and at least one fixed part (1), tipping the crucible
to favor pouring and to reduce the generation of gases,
B) shaking the crucible and cooling the aluminum,
C) turning the crucible until it is horizontal and separating the moveable part (2)
such that an obtained solid mass (4) is housed in said moveable part (2) for transport
to high-pressure injection equipment (5), and
D) depositing the semi-solid mass (4) on the container of the high-pressure injection
equipment (5) by means of turning the moveable part (2), letting said semi-solid mass
(4) fall due to the effect of gravity, and pushing the semi-solid mass (4) with the
piston of the high-pressure injection equipment (5).
6. Method for shaping materials which comprises obtaining semi-solid sludge by means
of the method according to any of claims 4 and 5.
1. Vorrichtung zum Herstellen von Metallspritzgussteilen, aufweisend einen Vibrationstisch,
eine Hochdruckspritzeinheit (5) und eine Vorrichtung zum Erhalten halbfester Schlämme,
dadurch gekennzeichnet, dass die Vorrichtung zum Erhalten halbfester Schlämme einen Schmelztiegel (1, 2) aufweist,
der zumindest einen festen Teil (1), der fest mit dem Vibrationstisch verbunden ist,
und zumindest einen beweglichen Teil (2) aufweist, der an den festen Teil (1) mittels
Befestigungsmitteln (3) angebracht werden kann.
2. Vorrichtung nach Anspruch 1, wobei die Befestigungsmittel (3) aus einer gelenkigen
Klammer gebildet werden, die das Befestigen des beweglichen Teils (2) an das feste
Teil (1) ermöglichen.
3. Vorrichtung nach einem der vorangegangenen Ansprüche, aufweisend ein festes Teil (1)
und ein bewegliches Teil, wobei beide halbzylindrisch sind.
4. Verfahren zum Erhalten halbfester Schlämme, dadurch gekennzeichnet, dass dieses das Verwenden der Vorrichtung nach einem der Ansprüche 1 bis 3 aufweist.
5. Verfahren nach Anspruch 4, welches aufweist
A) Schmelzen von Aluminium und Gießen des geschmolzenen Aluminiums in den Schmelztegel,
welcher durch zumindest ein bewegliches Teil (2) und zumindest ein festes Teil (1)
gebildet wird, Kippen des Schmelztiegels, um das Gießen zu erleichtern und die Bildung
von Gasen zu reduzieren,
B) Schütteln des Schmelztiegels und Abkühlen des Aluminiums,
C) Drehen des Schmelztiegels bis dieser horizontal ist und Abtrennen des beweglichen
Teils, derart, dass eine erhaltene erstarrte Masse (4) in dem beweglichen Teil 2 für
den Transport zur Hochdruckspritzeinheit (5) aufgenommen ist, und
D) Ablegen der halbfesten Masse (4) auf dem Container der Hochdruckspritzvorrichtung
(5) mittels Drehen des beweglichen Teils (2), Fallenlassen der halbfesten Masse (4)
aufgrund der Schwerkraft und Pressen der halbfesten Masse (4) mit dem Kolben der Hochdruckspritzvorrichtung
(5).
6. Verfahren zum Materialformen, welches das Erhalten halbfester Schlämme mittels des
Verfahrens nach einem der Ansprüche 4 bis 5 aufweist.
1. Équipement de fabrication de pièces d'injection de métal, comprenant une table vibrante,
un équipement d'injection haute pression (5) et un dispositif pour l'obtention de
boues semi-solides, caractérisé en ce que le dispositif pour l'obtention de boues semi-solides comprend un creuset (1, 2) comprenant
au moins une partie fixe (1) qui est fixée à la table vibrante, et au moins une partie
mobile (2) qui peut être fixée à la partie fixe (1) par l'intermédiaire d'un moyen
de fixation (3).
2. Équipement selon la revendication 1, dans lequel le moyen de fixation (3) est constitué
d'une pince articulée qui permet de fixer la pièce mobile (2) à la partie fixe (1).
3. Équipement selon l'une quelconque des revendications précédentes, comprenant une partie
fixe (1) et une partie mobile, les deux étant semi-cylindriques.
4. Procédé d'obtention de boues semi-solides, caractérisé en ce qu'il comprend l'utilisation de l'équipement selon l'une quelconque des revendications
1 à 3.
5. Procédé selon la revendication 4, qui comprend :
A) fondre de l'aluminium et verser ledit aluminium fondu dans le creuset formé par
au moins une partie mobile (2) et au moins une partie fixe (1), incliner le creuset
pour favoriser le versement et réduire la génération de gaz,
B) secouer le creuset et refroidir l'aluminium,
C) faire tourner le creuset jusqu'à ce qu'il soit horizontal et séparer la partie
mobile (2) de telle sorte qu'une masse solide (4) obtenue soit logée dans ladite partie
mobile (2) pour être transportée vers un équipement d'injection haute pression (5),
et
D) déposer la masse semi-solide (4) sur le récipient de l'équipement d'injection haute
pression (5) en retournant la pièce mobile (2), laisser tomber ladite masse semi-solide
(4) sous l'effet de la gravité, et pousser la masse semi-solide (4) avec le piston
de l'équipement d'injection haute pression (5).
6. Procédé de façonnage de matériaux qui comprend l'obtention des boues semi-solides
au moyen du procédé selon l'une quelconque des revendications 4 et 5.