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vapor pockets. Alternatively, when the pores are partially open, the capillary forces resist distortion as the binder softens. Thus, progressive stepwise removal of the binder is
mandatory to hold the component shape.
Final step involved in MIM process is sintering, which take place at high temperatures in order to bond the particles together. Sintering is a thermal treatment for bonding the
particles into a coherent, predominantly solid structure via mass transport events that often occur on the atomic scale German, 1996. The binder in the molded part that
produces via injection molding process is removed through the solvent extraction prior to the thermal pyrolisis. The thermally debound part or the brown part still can retain the
shape due to the friction among the powder particles even though all the binder has been removed at the earlier stage. Hence, this part is very fragile and needs to be handled
carefully for the next sintering process which later performs to achieve desired final mechanical, physical and chemical properties. High final density is important for the
optimization of the desired attributes. The final properties of the product can be further improved with additional heat and mechanical treatments.
1.2 Problem Statements
Numerous research efforts in the metal injection molding MIM are related to the physical and mechanical properties investigation. Selection of powder and binder system
will affect these properties significantly. Binder system in MIM processing is the important key consideration which provides powder with good flowability and
formability that necessary for the molding operation Klar and Samal, 2007. It is important and possible to develop a new binder system that could be used in the MIM
processing which exhibit economical and environmental friendly characteristics for the application in automotive, tooling, medical and hardware component. The mixture of
powder and binder is termed the feedstock. In the feedstock mixture, it is expected that each powder particle, should be enveloped by a very thin film surface of the binder and
has a tight contact with each other. At the same time, pores between the powder particles
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are homogenously filled with the binder. However, it is very difficult to get that kind of homogenous ideal powder and binder mixture condition Li et al., 2007. Usually, the
method for removing the binder is by thermal debinding that is a major controlled step in the MIM process. However, the great quantity of gas is produced by the evaporation and
degradation of the binder which later produces many defects, such as bubbles and cracks in the molded parts. Thermal debinding process also consumes quite a long duration of
operation Li et al., 2003. Besides, the other aspect that should be considered is related to the component shrinkage and warpage. They are very low during the injection
molding step and increases significantly during the debinding and sintering steps. As a result, the components may be out of design tolerances or, in the worst case; it may be
cracked, excessively warped or chemically incorrect with a very poor density Heaney and Spina, 2007. In view of that, a new binder system which is thermoplastic waste
rubber TPWR will be developed as to improve these processes and to encounter major drawbacks of this process. The uses of waste rubber as novel binder system in the MIM
processing to replace natural rubber is receiving great attention, due to the advantage of renewability, thermal stability and high shear viscosity. These waste rubber outstanding
properties such as very weak adhesion between the waste rubber and polymer is due to the crosslinked structure of the waste rubber Tan et al., 2008. Therefore, in this study,
waste rubber will be utilized, formulates and evaluates as a new binder system for the MIM processing due to their above mention advantageously.
1.3 Objectives
