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Objectives
The MONCERAT project aims the research in
the development of ceramic materials that can optimally be machined by
EDM. The uniqueness of this project is to work on the
development of the material as well as on the development of the EDM
machining process. The materials to be developed should fulfil
functional requirements such as mechanical properties (strength,
toughness,...) as well as requirements related to the machineabilty by
EDM. Further, the project aims to study how material properties of
ceramics produced by EDM can be integrated into the design phase.
The development of a proper EDM technology (generator, machining
strategy,...) for ceramics requires a good knowledge of the
material removal mechanisms. It is known that in case of steel
and cemented carbides (WC-Co), the material removal is based on melting
and evaporation. When machining ceramics melting and evaporation still
may occur. However, other material removal mechanisms could occur as
well, such as sublimation or removal of solid particles due to thermal
shocks and fall out of structural elements due to melting of the binder
phase. Different material removal principles can occur at the same
time. Whether the one or the other mechanism is more dominant depends
on the material (microstructure,...) and the EDM process conditions
(generator settings, type of dielectric, ...). The exact material
removal mechanism is not known for all the materials envisaged in this
project. Therefore, research is required in order to understand the
relation between the ceramic material and the EDM process. This basic
understanding will allow to define an optimal EDM process strategy for
the machining of existing materials and to develop both new materials
and related EDM process technology for newer ceramic materials.
The MONCERAT project will focus on three major classes
of materials, non-oxide ceramics with none or a minor addition of
sinter additives, ZrO2-containing electro-conductive ceramic matrix
composites and non-oxide-based cermets with a metal binder.
The three classes of material will span a range of hardness, toughness,
density and strength. The role of the mechanical properties will be
variable depending on the envisaged industrial application. For
example, pure non-oxide ceramics are not expected to perform well as
punching tools because of their lower strength and toughness, whereas
the zirconia-containing ceramics on the other hand should perform well
from a strength and fracture toughness point of view. In addition, it
is also important to consider a range of chemistries for the EDM
material removal mechanism and the corrosion resistance.
How the microstructure of the ceramic material influences
the EDM process (and vice versa) has to be studied in detail within the
MONCERAT project. The microstructure is strongly influenced,
not only by the composition of the ceramic material (influenced by type
of powders, powder properties, additives,...) but also by the sintering
process (temperature cycle) and how the powders are produced. Further,
the EDM process has on his turn a strong influence on the surface and
sub-surface quality. The high temperatures (due to the EDM discharges)
influences the metallurgical structure of the upper-layers. For
example, it is known that the use of nano-powders for carbide material,
which initially increases the strength of the ceramic material, can
result in a higher chance for crack formation during the EDM process,
finally resulting in a shorter life time of the ceramic component. How
the EDM process influences the surface and sub-surface quality of
ceramic materials has to be studied in detail within this research
project. The production of non-oxide ceramics without binder requires
different temperature cycles during sintering (much higher temperatures
will be needed). These higher temperatures can again influence the
grain growth during sintering which is not beneficial for the strength
of the ceramic material. Research to understand the metallurgical
phenomena is needed and is an important objective of this project.
The project aims further to study the SHS process (Self
propagating High temperature Synthesis) for the economic
production of high quality nano-powders. The SHS process, for the
production of powders, has not been studied in detail at this time.
This technique offers great potential and lots of possibilities for the
production of non oxide ceramic powders which can be used pure or as a
binder material for other - non conductive- ceramic materials. By this,
electro-conductive ceramic grades can be attained. The principle of SHS
reactions is the elaboration of materials using very exothermic
chemical reactions, which are auto-propagated without supplying
external energy. The combustion reaction is initiated by supplying a
short intense burst of energy, like an electrical spark or a laser
beam, at the reactant mixture. The propagation of the combustion
reaction is generally comprised between 10-4 and 0.15 m/s and local
temperatures can reach values between 1800-3700°C in the reaction zone.
Looking to the end-users, there is need to have more advanced
software systems for the design of ceramic components. The MONCERAT
project aims to investigate how these design systems can take the
realistic properties of the ceramic material machined by EDM into
account. This means that the influence of the EDM process on for
example the strength and the tool life of the ceramic component has to
be taken into account.
The scientific objectives can be summarised as
follows:
·
Study of the sintering parameters, powder
material and additives on the final properties of the ceramic material
(strength, toughness, ...) as well as the machineability by EDM (by
Milestone 3)
·
Detailed investigation of the SHS process with
respect to the production of high quality nano-powders. (by Milestone
3)
·
To have a better understanding on the EDM
removal mechanism active in the machining of ceramic material. It is
aimed to find relation ships between the removal mechanism and the
microstructure of the ceramic material. This knowledge is essential for
the development of "ideal" ceramic materials and the
development of a proper EDM technology. (by Milestone 3)
·
Study of new generator technologies (different
pulse shapes, higher currents,...) for the machining of ceramic
material. (by Milestone 2)
·
A strong research co-operation between
developers of ceramic material and EDM machine builders. (whole of the
project)
·
Study on how to integrate the properties of
ceramic components made by EDM in the design phase. (by Milestone 2)
The technological objectives (quantifiable and
measurable) of the project are as follow:
·
Development of novel ceramic materials that
meet the end-users requirements of strength, toughness,... and which
can be machined by EDM. (non-oxide ceramics by Milestone 2; non-oxide
based cermets and ceramic matrix composites by Milestone 3)
·
More economical production of high quality
nano-powders using the SHS process. (nitride powders by Milestone 2;
carbide powders by Milestone 3)
·
Development of a prototype EDM generator for
the machining (wire EDM, die sinking,...) of ceramic material. (by
Milestone 3)
·
Development of a software tool for the design
of ceramic components taking the properties of ceramic material
machined by EDM into account. (by Milestone 2)
·
Design of the correct interfaces between the
ceramic part and its metal surroundings. (by Milestone 2)
Finally, the uniqueness of the MONCERAT project
is the strong co-operation between ceramic material producers, EDM
machine builders and potential users of ceramic materials in order to
extend the fundamental knowledge, needed to developed the ceramic
materials of the future, that optimally can be shaped by EDM.
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