High-pressure Die Cast Cylinder Blocks Made of ... - KSPG AG

High-pressure Die Cast Cylinder
Blocks Made of Aluminium
Highly Efficient Solution Specifically
for Passenger Car In-line Engines

1. Aluminium cylinder blocks support light weight
design
Castings of aluminium are making an evermore significant
contribution to leveraging light construction potentials in
modern passenger cars. The heaviest individual component,
the cylinder block, has meanwhile taken on a key role. If we
consider the enormous number of in-line engines produced,
especially four-cylinder and three-cylinder engines, but increasingly
also six-cylinder engines in in-line and V arrangement,
the cost/benefit aspect must have absolute priority.
The replacement of grey cast iron with aluminium for cylinder
blocks therefore presupposes low-cost concepts.
2. Concept diversity for aluminium cylinder blocks
Contrary to the cylinder blocks produced so far, mostly made
from grey cast iron based on a uniform concept which already
incorporates the cylinder bore surfaces when a perlitic
structure configuration is chosen, there are many diverse
options in the case of aluminium. These relate to the concept
modules of type or cylinder block design, alloy, casting
method and cylinder bore surface, in which case manifold
incompatibilities have to be considered. The overriding aspect
is therefore the compatibility of the concept modules.
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Fig. 1: Highly efficient solution specifically for passenger car in-line engines
A further constraint for the concepts which are viable in principle
results for concrete engine development projects from
the targets and general specifications with respect to the engine
function, elemental engine characteristics (number and
arrangement of cylinders), annual outputs, costs of castings
and engine systems, optimization potential, environmental
aspects and recyclability. This situation has led to a large
number of marketable concepts.
3. Aluminium cylinder blocks and high-pressure
die casting method
3.1 Economic aspect
From the economic aspect, for mass produced engines, highpressure
die casting is mainly competing with the highly
automated sand core package process whose cycle time is
not bound to the solidification. In the highly competitive,
cost-sensitive market segment of the three-cylinder and
four-cylinder engines, however, high-pressure die casting is
unrivalled in cost-effectiveness thanks to outstanding productivity
based on appropriate component design. Currently,
worldwide large quantities of four-cylinder engine blocks of
aluminium are made by this method. The aluminium highpressure
die casting method is now also in the process of
establishing itself in the six-cylinder engine business.

Applying the latest high-pressure die casting technology,
aluminium cylinder blocks are produced whose properties
are hardly inferior to high-grade low-pressure die castings or
sand core castings and which boast a decisive cost benefit in
bulk production. Its attractiveness is the greater the smaller
the component and the higher the product output are. Innovative
approaches with new die concepts to increase the tool
life and further reduction of the cycle time, not least through
intensive die cooling, additionally contribute to curbing production
costs.
3.2 High-pressure die casting technology
As far as the frequently applied conventional high-pressure
die casting method is concerned, it should be mentioned
that in light of today’s constantly increasing requirements it
often fails to yield the necessary component quality. What
is more, conventional high-pressure die cast cylinder blocks
made of aluminium exhibit a relatively high degree of porosity
which prohibits the application of solution annealing and
of cylinder bore coating. To achieve the necessary static and
dynamic strengths, however, evermore refined high-pressure
die casting processes and new production processes
are essential. In order to remedy this situation, KS Aluminium-Technologie
employs techniques like an optimally degassed
melt, an efficiently evacuated high-pressure die as
well as residue-free lubricants for the shot plunger in the die
filling chamber. Further improvements are achieved through
innovations like optimized high-pressure die spraying technique
combined with wax-free spraying agent, long-life tool
coating as well as uniform, intensive cooling of the die. The
basic prerequisite for high strength and its enhancement is a
low degree of porosity at the quality level of low-pressure die
casting. In addition, this enables the cylinder bore surfaces
to be coated, in high-pressure die casting as well.
3.3 Design features
For cylinder blocks, the weight reduction potential inherent
in material substitution ranges from 35 %, expected of aluminium
used in passenger-car diesel engines as a minimum
requirement, appr. 50 %. High-pressure die casting allows
for extremely reduced wall thicknesses and thus offers especially
favourable conditions for light construction. In combination
with its near-net-shape benefits, the weight can be reduced
by eight to 15 % in comparison with low-pressure die
casting where no, or only a water jacket sand core is used.
For the conventional high-pressure die casting method,
mouldability in steel is a must and the open-deck design
is unavoidable therefore. But today, in general it is more
readily accepted for aluminium cylinder blocks. Distinctly
reduced water jacket depth and co-moulded cylinder bores
have created an option besides the conventional open deck
Fig. 2: Open-deck and closed-deck design, shown with one and the same high-pressure die cast aluminium cylinder block (left);
high-pressure die casting resistant water jacket sand core made by the warm-box process with the application of a special wash (right)
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which features a sufficiently stiff cylinder area even without
a closed deck, meeting the requirements of most in-line engines.
But the open-deck design limits the component thickness,
specifically in the upper cylinder area. For small highduty
engines – especially passenger-car DI diesel engines
– this handicap may potentially prevent the implementation
of low-cost high-pressure die-cast cylinder blocks and even
prompt a look back to grey castings.
In light of this situation, KS Aluminium-Technologie has for
many years already been studying ways to find suitable technologies
for producing lost water jacket sand cores which
can be used to implement a closed-deck design in a reliable
high-pressure die casting process (Fig. 1). On the one hand,
the core should be pressure-proof and also temperatureresistant
for a defined time and additionally cope with the
high flow velocity of the liquid metal. On the other hand, the
core removal should be unproblematic. Furthermore, lowcost
sands, binders and release agents are required which
should be easy to handle in order to warrant process stability.
This difficult trade-off has meanwhile been accomplished
satisfactorily on the basis of a “warm box” core with customized
release agents. It is viable now to offer the closed-deck
option in the high-pressure die casting mode at acceptable
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Fatigue strength [MPa]
140
120
100
80
60
40
20
0
Competitor data
R = -1: reversed stress
R = 0: tumescent tensile stress
Regular HPDC (as cast)
Vacuum support
incremental cost for specific series applications, e.g. for
boosting the performance of standard engines in open-deck
design.
3.4 Properties
The integral optimization of the influencing process steps
mentioned in 3.2 also enables extremely low-pore castings
to be produced by the high-pressure die casting method.
Thanks to intensive die cooling, the liquid aluminium will solidify
very fast, not only in the thin-walled areas but also in
the thick bulkheads. The application of high pressure makes
for very quick heat dissipation. Accordingly, the microstructure
is very dense, particularly near the surface. On account
of the quick gate freeze-off which is inherent in the principle
applied, the possibilities of supplementary feeding are limited,
however.
The cylinder blocks made by high-pressure die casting excel
by a highly fine-grained microstructure which, in combination
with low porosity, constitutes the basis for good strength
properties. These high-grade castings lend themselves to full
heat treatment. The attainable strength levels are very close
to those of low-pressure die and sand castings, even in regard
to their dynamic characteristics. (assuming local chill
moulds in the latter case!) (Fig. 2).
Vacuum
Vacuum + strength
increasing heat treatment
Fig. 3: Dynamic strength increasing steps in combination with suitable optimization measures for high-pressure die castings
Vacuum
+ optimized casting process
+ strength increasing
heat treatment

3.5 Cylinder bore surface
Reinforcing the cylinder bores is indispensable because the
hypoeutectic alloy options which are suitable for high-pressure
die casting lack the necessary tribological properties.
For this purpose, a multitude of liners are available (Fig. 3).
The lowest cost option consists in solving the cylinder bore
surface problem in the case of high-pressure die cast cylinder
blocks by means of cast-in liners may of grey cast iron.
However, the use of cylinder bore liners imparts on the cylinder
block a heterogeneous character. When liners are cast in,
with the high-pressure die casting method the smallest gaps
are produced between liner and overcast, which is reflected
in comparatively good equivalent thermal conductivity values.
According to the present state of the art, liners made of
suitable aluminium materials can anyway only be cast in by
high-pressure die casting as they have to rely on extremely
short solidification times because of the melting-through
risk. The outer face area fusion of aluminium liners or of aluminium-coated
grey cast liners with the aluminium overcast
can meanwhile be accomplished satisfactorily. A mechanical
interlock is feasible in combination with rough-as-cast liners
made of grey cast iron (BMI).
a b c d
e f g
Fig. 4: Cylinder bore liners of various designs for casting into
high-pressure die cast cylinders and for shrinking in or inserting
Cast-in liners are subject to residual stresses that are difficult
to control. Another problem is inhomogeneity as a result of
casting tolerances and deformation. So it takes substantial
development efforts to control multifactor-conditioned cylinder
bore distortion problems with potential functional drawbacks,
especially in long-term operation.
Monolithic and quasi-monolithic concepts with their inherent
advantages (see also product information brochure “Low-
pressure Die Cast Cylinder Blocks”, for example) are the only
option to readily comply with the frequent request for extremely
compact cylinder units (minimal land width between
cylinders = minimal cylinder spacing) or for maximum cylinder
bore at a given cylinder spacing.
With LOKASIL ® , KS Aluminium-Technologie has developed an
equivalent concept for the high-pressure die casting method
with local silicon concentration combined with a suitable
honing process for mechanical exposure of the silicon
grains. With PORSCHE as pilot customer, the series launch of
LOKASIL ® cylinder blocks was achieved with the engines
of Boxster and of the water-cooled 911 (identical cylinder
blocks in several bore/swept volume variants). The local
concentration of silicon particles in the cylinder bores with
MMC microstructure
Ceramic fiber –
particle preform
12.5 micron
Bulkhead / main bearing
reinforcement
Fig. 5: MMC bulkhead reinforcement with aluminium bedplate
and optionally also for an aluminium cylinder block
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LOKASIL ® is a substitute for the normally cast in massive
grey cast liners, thus contributing to weight reduction. The
quasi-monolithic component character offers a myriad of
benefits ranging from more compact longitudinal component
dimensions through more efficient thermal relief to reduced
cylinder distortion. With the LOKASIL ® Ib version, a low-cost
preform of silicon particles and certain ceramic fibres is
available which is competitive with grey cast liners (Fig. 4). It
ensures better infiltration and increases the strength of the
composite. Further decisive progress in process engineering
was achieved with the possibility to cast LOKASIL ® cylinder
blocks on real-time controlled high-pressure die casting machines
with absolute process reliability.
In order to meet the demand for advanced, downsized cylinder
blocks, it is indispensable from the technical aspect to
create outstanding tribological conditions. Internal friction
loss measurements have shown a clear advantage of ironcoated
bore surfaces compared to aluminium bore surfaces.
That is why for some years already KS Aluminium-Technologie
has focused on this issue and now resorts to a coating process
with preceding mechanical roughing up. The sprayed-on
iron coat is machined by means of a honing process purposeadjusted
to the individual cylinder block and its coating to
obtain the tribologically perfect piston running clearance.
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Temperature-related main bearing clearance
Increase of main bearing
clearance [%]
100
80
60
40
20
0
Aluminium
Modular inserts
Al/MMC
4. Bedplate
Fig. 6: Compensation of temperature-related increase of main bearing clearance (left)
Weight saving potential inherent in MMC bulkhead reinforcement (reight)
Cylinder blocks made of aluminium alloys are differentiated
according to various designs. Where stiffness is the most important
characteristic of a cylinder block, a bipartite design
is chosen. In this case, the cylinder block is split horizontally
at the level of the crankshaft bearing axis. The upper part
normally continues to be called cylinder block (more correctly
it would in this case have to be referred to as cylinder block
upper section) whilst the lower part is named bedplate.
If the bedplate is produced by high-pressure die casting, the
secondary alloy AlSi9Cu3 is used, in which case so-called
“bearing caps” made of nodular cast iron are integrally cast
in. The latter serve to control the main bearing clearance in
the operating temperature range (acoustics, oil pump delivery
rate/oil pump losses) and to stiffen the bulkhead system.
The cast-in inserts consist of two bosses with a bow-shaped
connector. In the case of V cylinder blocks, two bosses can
be arranged in parallel. To the side of the bosses and between
them underneath the bow, undercut and open-worked
anchors are arranged which provide for positive coupling
with the adjoining aluminium. As the main bearings are narrow,
the inserts are frequently cut free in large areas due to
the freewheeling of the crankshaft. That is why a solid anchor
system is of special importance. A crank scraper/oil separator
wall can be integrated into the bedplates, designed to
Weight saving potential
Weight saving potential [kg]
5
4
3
2
1
0
I4 I5 I6 V6 V8 V12
Engine design, amount of cylinders

oute the oil selectively from the crankcase to the oil sump
and to separate it at the same time from the crankcase in
order to minimize oil foaming.
The bearing caps made of nodular cast iron can also be replaced
by MMC bulkhead reinforcements for the purpose of
weight reduction. The gap-free composite with the adjoining
aluminium additionally prevents leaks in the lube oil supply
for the main bearings. The composite material is tailored
such that its coefficient of thermal expansion is only slightly
higher than that of the steel or nodular cast iron of the crankshaft.
As a result, this technology – which is ahead of the current
state of the art – can even achieve full compensation for
the significant thermal expansion of aluminium if the composite
material is also applied to the cylinder block (upper
part) (Figs. 5 and 6). In this way, bearing gap losses (oil pump
power loss) and noise excitation can be minimized thanks to
reduced main bearing clearances at operating temperature.
The unilateral application on the bedplate side has reached
commercial maturity whilst its application on both sides is
an option for the future.
Ongoing development efforts are made to be able to pay tribute
to customers’ demands for still greater stiffness (characterized
by the Young’s modulus). Using innovative ceramic
particles and the ceramic fibres already envisioned for this
application, meanwhile values in the upper range of lamellar
grey cast iron can be achieved.
5. Practical examples of implementation
Today, KS Aluminium-Technologie supplies the following
products made by the high-pressure die casting method
(Fig. 7):
Daimler four-cylinder blocks (gasoline engine in two versions
with cast-in grey cast liner and aluminium-coated
outside grey cast liner)
VOLVO five-cylinder block (gasoline engine with cast-in
grey cast liners, diesel engine with cast-in BMI liners)
PSA four-cylinder blocks (diesel engine: cast-in BMI
liners)
VW four-cylinder blocks (gasoline engine: cast-in grey cast
liners)
Volkswagen W12 Bedplate
Applying “classic” squeeze casting, the Porsche Boxer opposed
cylinder block halves were cast in series production
with LOKASIL ® cylinder bore surfaces.
Daimler 4 cyl. Volvo 5 cyl. VW 4 cyl.
Fig. 7: Current KS Aluminium-Technologie high-pressure die cast cylinder blocks
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KS Aluminium-Technologie GmbH · Hafenstraße 25 · 74172 Neckarsulm · GERMANY
Tel. +49 7132 33-1 · Fax +49 7132 33-4357 · www.kspg.com
Subject to alterations. Printed in Germany. A|IX|k