Tailoring the porous microstructure of MIM flow restrictors Kaline Furlan 1 , Renan Schroeder 1,2 , Fernando Torres 2 , Vinicius G Calcagni 1 , Cristiano Binder 1 , Aloisio N. Klein 1 1 Materials Laboratory – Mechanical Engineering Dept., Federal University of Santa Catarina Florianopolis, SC, Brazil; 2 Whirlpool / Embraco Unit, Joinville, SC, Brazil; E-mail: furlan@labmat.ufsc.br Abstract Despite being known by its ability in the production of nearly full dense sintered parts, Metal Injection Molding (MIM) allows also tailoring porous microstructures for special applications such as small-size flow restrictors. In other words, through simple modifications in the sintering parameters, an interconnected porous microstructure with the capability of control the gas flow rate from a high to low pressure region can be obtained. In this work, the effect of sintering temperature and time is addressed over two parameters: i- the microstructure evolution of the stainless steel parts and ii- the gas flow behavior in each component under different upstream pressures. Therefore, the parts were characterized in terms of porosity and shape factor by image analysis while a nitrogen flow test apparatus was used to elucidate the gas flow conditions. The results show that production of tailor- made flow restrictors is feasible by MIM. Introduction Porous components are an important class of materials where the pores have a certain role in the engineering application and are somehow responsible for the properties of these parts. The pores characteristics such as amount, size distribution, tortuosity and interconnectivity might, under different combinations, result in diverse final microstructures and therefore this characteristics must be set according to the final use of the porous component. Among the industries and applications for which this kind of materials are use, one can include: filters in beverage production, acoustic absorbers in aircrafts, lubricant reservoir in oil- impregnated bearings, biomedical components with improved tissue growing behavior, heat isolators in civil engineering, lightweight parts in automotive, gas flow restrictors in medical devices like breathing apparatus and many others [1]. The focus of the current study is on gas flow control applications, particularly flow restrictors, in which the function of pores is to measure or limit the flow of a certain gas from a high pressure region to a low pressure region in a controlled rate (Figure 1). If the goal is to have always the same flow rate, it is necessary to keep constant the upstream and downstream pressure condition as well as the fluid temperature [2]. For such a kind of application, the gas flow rate must be well known, precise and consistent in order to keep the same result in every single use of the system. Therefore, the characteristics of pores are very important and must be accurate controlled during processing. Figure 1: Illustration of a porous flow restrictor [2]. There are several methods of producing metallic porous components from processes using solid, liquid and vapor metal or metal ion solution [1]. Powder metallurgy has been one of the most traditional and economic processes to manufacture these special parts, as soon as pores are intrinsic from sintered products [3]. By controlling mainly the powders characteristics, the green density of the parts and the sintering parameters, it is possible to give special features to the pores hence to reach specific properties into the sintered part. Some studies have been made [2,4-7] focusing on the influence of raw materials, such as characteristics of metallic powders or space holder compounds, however there is a lack of studies focusing on the influence of processing parameters in the properties of porous parts, specially the fluid flow behavior of porous parts.