Note: Descriptions are shown in the official language in which they were submitted.
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SI/cs 050969wo
09 February 2007
METHOD FOR MOUNTING A MOULD FOR CASTING A CAST PART FROM A
METAL MELT
The invention relates to a method for mounting a mould
composed of mould parts for casting a cylinder block of an
internal combustion engine from a metal melt, in which at
least one chill, which forms at least one part section of
the inner surfaces of a cylinder space of the cylinder
block, is positioned and retained at a wall of one of the
mould parts.
Such methods and devices are used on a large technical
scale, for example in the motor vehicle industry, in order
to manufacture the cylinder blocks of internal combustion
engines in large numbers. In this situation, there is a
particular requirement, especially in the area of cylinder
barrels, for a fine-grain, metallurgical microstructure to
be constructed which will guarantee a high load-bearing
capacity. As an example of another location at which a
particularly fine-grain, rapidly solidifying and tough
casting microstructure is required is the area of a
cylinder block in which the bearings for the crankshafts
are formed.
In order to obtain rapid solidification in the casting
microstructure, in particular in the casting of light metal
melts, metal inserts are introduced into the mould,
referred to as "chills", which consist of a highly heat-
conductive material and as such represent a heat sink, by
means of which comparatively large volumes of heat are
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drawn within a short period of time from the melt coming
into contact with the metal inserts. Accordingly, during
the casting of cylinder blocks made of aluminium casting
material, chills are arranged in such a way, for example,
that they form the cylinder barrels in the block which is
being cast. The casting material coming into contact with
the chills arranged in this way then cools very much more
rapidly than the melt present in the mould which is further
away from the chills, with the result that the desired
solidification, characterised by a fine-grain
microstructure takes place in the area of the barrels.
One example of how metal inserts are introduced into moulds
as chills is provided in DE 195 33 529 C2. In this patent
publication, a method for casting an engine block made of
aluminium is described, in which the engine block is cast
into a sand mould and its cylinder cavities are formed by
chills inserted into the sand mould, these chills
consisting of a brass material, wherein the brass material
has a coefficient of thermal expansion of more than 18 x
6 K-~, adjusted to suit the coefficient of thermal
expansion of the aluminium melt being cast in each case.
Even if this method allows for the desired microstructure
to be specifically created in the finished cast component,
despite the adaptation of the behaviour of the chills when
being heated to the coefficient of thermal expansion
behaviour of the aluminium melt, it has in practice proved
difficult, in certain application situations, for the
chills to be removed from the completed casting after
solidification of the casting material.
Due to its direct effect on the shape retention of the
individual casting, however, the positioning of the metal
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inserts must in practice always be exact, even under the
rough conditions of a casting plant. This has often proved
to be an elaborate procedure if the mould as a core package
is composed of several mould parts and metal inserts. The
term "core packages" is given to casting moulds which are
composed of several casting cores. Casting moulds can be
easily assembled from core packages, with which even
complex and filigree mould cavities and therefore castings
can be formed.
A further problem in connection with the use of metal
inserts is derived if, as in the example given in DE 195 33
529 C2, the mould is what is referred to as a "lost mould"
which is composed of parts manufactured from a mould
material and must be destroyed after the solidification of
the melt in order to release the finished casting from the
mould. In order to be able to position the metal inserts
used for cooling in such moulds in a reliable manner and
keep them in position, it is necessary for them to be
clamped to the moulds, with the mould material surrounding
them, with the result that after solidification of the
melts they can only be released from the casting with
difficulty.
In order to render the release of the metal inserts easier,
it has been usual hitherto to provide the metal inserts
with a ceramic powder coating, with the intention of
reducing the risk of damage to the metal inserts when they
are removed from the finished casting. As well as the
additional effort and expenditure involved with the
application of the coating, this arrangement has the
disadvantage that the heat transfer between the casting
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metal and the insert is impaired, and therefore also the
cooling effect.
In addition to the prior art referred to heretofore, aimed
directly at the assembly of moulds from mould parts and
cores, a method and device are known from the German Patent
Specification 719 454 for the manufacture of cores or mould
parts for moulds made of a core compound or mould compound,
which allow for a chill to be retained in the individual
mould or core box in such a way that it stands reliably in
the position intended for it in the individual core or
mould part to be produced in each case. For this purpose,
the individual chill is initially positioned in the empty
mould or core box, wherein in this position it is in
contact in each case with an outer wall of the mould or
core box. By means of an electromagnet, which is located in
a cut-out formed from the outside into the wall concerned
of the mould box and exerts its effect through the wall
section present between it and the chill, the chill is
thereafter held in this position. Once the filling of the
core compound or mould compound has been completed, the
excitation current circuit of the electromagnet is switched
off, with the result that the individual mould part or core
can be removed from the box with the chill incorporated in
it.
The invention is based on the object of providing a method
of the type referred to in the preamble, by means of which,
in a simple and nevertheless reliable manner, moulds can be
mounted for casting cylinder blocks with metal inserts
provided in the mould cavity.
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This object is resolved according to the invention by the
method described in Claim 1. Advantageous embodiments of
the method according to the invention are described in the
claims referring back to Claim 1.
The method according to the invention is suitable in
particular for casting light metal melts, in particular
aluminium-based melts.
According to the invention, the individual chill, which may
also be designated hereinafter as a "metal insert", is held
in a simple manner by magnetic forces, which are exerted by
at least one magnet arranged in a suitable manner, in the
position in the mould provided with regard to its mounting.
The only precondition for this is that the chills are
themselves magnetically sensitive. Accordingly, as the
material for the chills, consideration can be given in
particular to ferromagnetic materials, such as iron and its
alloys. In particular, chills used according to the
invention can be manufactured from economical and wear-
resistant materials such as cast iron.
With the method according to the invention, the magnet body
exerting the retaining forces on the individual chill
during the mounting procedure is arranged in such a way
that it does not interfere with the casting of the metal
melt or other mounting procedures. This is achieved
according to the invention in that the magnet is arranged
behind the wall at which the metal insert is positioned in
such a way that its magnetic forces penetrate through the
wall and hold the insert without a direct contact between
the insert and the magnet.
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In the method of operation according to the invention it is
no longer necessary to embed the chills in a mould part in
order to hold them. In fact, the chills can be handled
separately from the mould parts so that when mounting the
mould they can be handled like a mould part. This leads to
a distinct simplification of the whole production process.
Since the chills in the method according to the invention
do not have to be firmly embedded into a mould part or into
the respective cast part any more, when removing a mould
produced according to the invention there is also no longer
the problem of damage caused to the chills or the cast part
when demoulding. Therefore, the chills do not have to be
coated and the amount of preparation can be reduced.
Instead, chills according to the invention held by magnetic
forces can be removed easily from the cast part and the
mould parts of the mould after casting. This advantage is
evident particularly when casting cylinder blocks of
internal combustion engines, in the technical language also
referred to as "engine blocks", in which the chills
represent the contact surfaces of the cylinders.
Embedding the chills required according to the prior art as
early as during production of the mould parts by
surrounding them with mould material in a mould is not
required with the method according to the invention. Due to
the fact that the chills are handled separately when the
mould is assembled and are held in their position by
magnetic forces exerted by an individual retaining device,
it is possible, in the case of the use of moulds mounted
from mould parts formed from mould material, to dispense
with the need to coat the chills with a finish, as is
required with the conventional procedure in order to
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guarantee optimum separation of the individual chill from
the cast part produced in each case.
A further advantage of the invention lies in the fact that
it can be easily integrated into already existing systems.
The method according to the invention therefore makes
possible the manufacture of cast components in a simpler
and more economical manner than with the prior art. The
invention is particularly well-suited for casting light
metal melts, in particular aluminium melts.
The mould parts from which a mould is composed according to
the invention are preferably manufactured from a mould
material which is mixed from a mould basic material and a
binder. As basic materials in this situation, consideration
can be given, for example, to sands containing quartz or
free of quartz, while as binders use can be made of both
inorganic as well as organic binders. The invention proves
to be particularly advantageous if the mould is formed in a
known manner as a core package.
The positioning and retaining of a chill in the mould can
be carried out with the method according to the invention
independently of any specific preparation of the particular
location at which it the metal part is to be arranged.
Accordingly, the positioning of the metal part can in each
case be carried out at a time which is determined solely by
the optimum operational sequence in each case on mounting
the individual mould. The only decisive factor in this
situation is that the magnet required for the retention can
be arranged in such a way in the area of the chill which is
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to be retained that the forces exerted by it will reliably
secure the chill.
In order to guarantee a particularly reliable effect of the
magnet provided to retain the magnetic insert, an opening
may be formed in the mould part at the wall of which the
chill is positioned, into which the magnet is introduced.
With this arrangement of the wall of the individual mould
part, the magnet used to retain the chill can be moved into
close proximity to the chill in order to facilitate the
mounting process. In particular, when casting engine blocks
of which the barrels are represented by chills, it can be
of advantage for this reason if the mould part is designed
in a mandrel shape with a blind hole aperture, into which
the magnet is introduced. With this formation of the mould
part concerned, a plurality of chills can be arranged next
to one another on the outer surface of the mould part, so
that they form in common the inner shape of the individual
cylinder and are held jointly by a magnet arranged in the
central blind hole aperture.
Another variant of the invention of importance for
practical application is characterised in that the chill is
held in its position by means of the magnet until a further
mould part is arranged which then holds the chill in its
position, by positive and/or non-positive fit. With this
embodiment of the invention, the chill is held in its
position by mould parts mounted after its positioning
without magnetic forces being required for this. A further
advantage of this method is that the position of the chill
in the mould can be exactly defined by the other parts of
the mould which come into contact with it either in
positive and/or non-positive fit. The retention of the
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chill according to the invention by magnetic forces
therefore serves, in this embodiment of the invention, only
for as long as needed to bridge a situation, undefined with
regard to the retaining of the chill in the mould, until
the individual chill is held in its position by a further
mould part, without the need for any further retention
forces to be exerted by a separate retaining device.
In principle, all magnets are suitable for the application
of the magnetic forces used for the retaining of the chill
according to the invention which can produce a sufficiently
strong magnetic field. Thus, for example, for a
particularly simple, economical, and practical embodiment
of the invention, permanent magnets can be provided in
order to apply the retaining forces in the manner according
to the invention onto the individual chills.
However, if particularly powerful forces are to be applied,
and at the same time a particularly precise control of the
magnetic retaining forces achieved, then an electromagnet
is particularly well-suited. Electromagnets not only allow
for an exact adjustment of the strength of the magnetic
field generated by them in each case, but it is also
possible with them, in a simple manner, by switching the
electric power on and off, to determine precisely the time
period within which the magnetic forces are applied on the
individual chill in the manner according to the invention.
For this purpose, consideration can be given, for example,
to electromagnets manufactured on the basis of coils. The
magnetic field from such electromagnets can be controlled
proportionally to the strength of the current conducted
through the coils.
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As already mentioned, the invention is particularly well-
suited to the manufacture of a cylinder block of an
internal combustion engine made of a light metal melt, such
as an aluminium or magnesium melt, wherein at least one
part section of the inner surfaces of the individual
cylinder space of the cylinder block can be formed by one
or more chills.
The invention is particularly well-suited for application
in a fully-automatic device for assembling a mould in which
devices such as robots are provided for the handling of the
mould parts. With the application of the invention these
devices can also position the chill with no problem at all,
since the retention of this metal insert in its particular
position by the magnet is assured, and no integral joining
of the chill to one of the mould parts is required.
The invention is described in greater detail hereinafter on
the basis of drawings representing embodiments. These show
in diagrammatic form:
Fig. 1 A first mould part in a section along the section
line A - A incorporated in Fig. 3,
Fig. 2 The mould part represented in Figure 1 in a side
view, and
Fig. 3 The mould part represented in Figures 1 and 2 in
a section along the section line B - B
incorporated in Figure 2.
The mould part 1 formed as a single piece is a constituent
part of a mould not further represented here for casting a
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cylinder block for a combustion engine from a melt which is
formed from an aluminium casting alloy. It is manufactured
in an inherently known manner from a mould material which
is mixed from a mould sand as the basic mould material and
a binder and has a basic section 2, which carries a mandrel
section 3 projecting upwards and essentially cylindrical in
shape.
The mandrel section 3 has a casing surface 4, which is
subdivided by four radially projecting ribs 5 into four
part sections. In the area of the transition of the mandrel
section 3 into the basic section 2 of the mould 1 is a
circumferential groove 6, formed into the upper face
surface 7 of the basic section running around the mandrel
section 3 aligned essentially at right angles to the
circumferential surface 4 of the mandrel section 3.
According to a variant not represented here, the mandrel
section can also have a casing surface, which is divided by
radially projecting ribs into two, three, or more part
sections. In addition, the ribs can be designed, in
contrast to the shape having parallel side walls
represented here, conically in cross-section tapering or
broadening out. According to a further conceivable
embodiment, the mandrel section can also have a casing
surface which is not subdivided by additional ribs. In this
case, the casing surface is entirely surrounded by the
chill which is to be accommodated in each case.
With the embodiment represented in the Figures, a blind
hole aperture 9 is additionally formed into the casting
part 1, going outwards from the lower face surface 8 of the
basic section 2, opposite the upper face surface 7, this
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blind hole aperture 1 extending from the face surface 8 of
the basic section 2 as far as the closure wall 10 of the
mandrel section 3, forming the face side of the mandrel
section 3. The diameter of the blind hole aperture 9 in
this situation is adapted to the outer diameter of the
mandrel section 3 in such a way that only one wall 11 with
a low wall thickness is present between the inner faces of
the blind hole aperture 9 and the casing surface 4, this
wall 11 being sufficient to guarantee the required shape
stability of the mandrel section 3.
Inserted into the blind hole aperture 9 is an electromagnet
12, which is secured to the free end of a rod 13. The rod
13 with the electromagnet 12 is part of a device, not
further represented, for the retaining of metal parts 14,
15, 16, 17, which are put into use as chills by a device
not represented here for positioning at the casing surface
4 of the mandrel section 3.
The rod 13 with the electromagnet 12 can be moved from a
position of rest by means of an adjustment device likewise
not represented, in which the electromagnet 12 is outside
the blind hole aperture 9, into the operational position
represented in Fig. 1, in which the electromagnet 12 is
fully introduced into the blind hole aperture 9. The supply
of the electromagnet 12 with electrical energy is effected
by a control device, likewise not represented, which
supplies electrical energy to the electromagnet 12 when the
chills 14 - 17 are positioned, in order to retain them in
their position.
The height of the chills 14 - 17 is adapted to the height
of the mandrel section 3. In this context the chills in
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each case have on their upper and lower narrow sides a web
18, 19, projecting upwards and downwards respectively, of
which the lower web 18 engages in the groove 6, so that the
chills 14 - 17 are held in that location in positive fit.
At the same time, the chills 14 - 17 are cambered in such a
way that they are located flush with the section of the
casing surface 4 of the mandrel section 3 allocated to them
in each case. At the same time, the width of the chills 14
- 17 is adjusted to the width of the sections of the casing
surface 4 in such a way that the sections of the casing
surface 4 are filled completely by the chills 14 - 17
located flush with them.
The chills 14 - 17 are cast as grey cast iron from a cast
iron alloy, known under the designation GG20 (as per DIN
1691).
As soon as the chills 14 - 17 are positioned in the
sections of the casing surface 4, the electromagnet 12 is
charged with electrical energy. The magnetic field which is
then generated by the electromagnet 12 acquires the chills
14 - 17, and holds them in their position at the casing
surface 4 of the mandrel section 3.
Next, the other parts, not shown here, of the mould,
likewise not shown, are mounted. One of the mould parts,
not shown, has a groove-shaped mounting into which, after
positioning of the mould part concerned, the rib 19
engages, formed at the upper end of the chills 14 - 17,
such that the chills 14 - 17 are then also held in positive
fit at their upper end. As soon as this state has been
attained, the energy supply to the electromagnet 12 can be
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switched off and the rod 13 with the electromagnet 12 can
be withdrawn from the blind hole aperture 9.
On casting the cylinder block in the mould, assembled by
using the mould 1 and the chills 14 - 17, the chills 14 -
17 form the barrels of one of the cylinders of the cylinder
block. In this case, the chills 14 - 17 form a heat sink,
by means of which it is ensured that the aluminium melt
coming into contact with the chills 14 - 17 solidifies
rapidly and forms a fine-grain microstructure.
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REFERENCE FIGURES
1 Mould part
2 Basic section
3 Mandrel section
4 Casing surface of the mandrel section 3
Ribs of the mandrel section 3
6 Groove
7 Upper face surface of the basic section 2
8 Lower face surface of the basic section 2
9 Blind hole aperture
Closure wall of the mandrel section 3
11 Wall of the mandrel section 3
12 Electromagnet
13 Bar
14-17 Chills
18, 19 Webs
