Extrusion-Based Systems
This chapter deals with AM technologies that use extrusion to form parts. These technologies can be visualized as similar to cake icing, in that material contained in a reservoir is forced out through a nozzle when pressure is applied. If the pressure rem
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Extrusion-Based Systems
6.1
Introduction
This chapter deals with AM technologies that use extrusion to form parts. These technologies can be visualized as similar to cake icing, in that material contained in a reservoir is forced out through a nozzle when pressure is applied. If the pressure remains constant, then the resulting extruded material (commonly referred to as “roads”) will flow at a constant rate and will remain a constant cross-sectional diameter. This diameter will remain constant if the travel of the nozzle across a depositing surface is also kept at a constant speed that corresponds to the flow rate. The material that is being extruded must be in a semi-solid state when it comes out of the nozzle. This material must fully solidify while remaining in that shape. Furthermore, the material must bond to material that has already been extruded so that a solid structure can result. Since material is extruded, the AM machine must be capable of scanning in a horizontal plane as well as starting and stopping the flow of material while scanning. Once a layer is completed, the machine must index upwards, or move the part downwards, so that a further layer can be produced. There are two primary approaches when using an extrusion process. The most commonly used approach is to use temperature as a way of controlling the material state. Molten material is liquefied inside a reservoir so that it can flow out through the nozzle and bond with adjacent material before solidifying. This approach is similar to conventional polymer extrusion processes, except the extruder is vertically mounted on a plotting system rather than remaining in a fixed horizontal position. An alternative approach is to use a chemical change to cause solidification. In such cases, a curing agent, residual solvent, reaction with air, or simply drying of a “wet” material permits bonding to occur. Parts may therefore cure or dry out to become fully stable. This approach may be more applicable to biochemical applications where materials must have biocompatibility with living cells and so choice of material is very restricted. However, industrial applications may also exist,
I. Gibson, D.W. Rosen, and B. Stucker, Additive Manufacturing Technologies, DOI 10.1007/978-1-4419-1120-9_6, # Springer ScienceþBusiness Media, LLC 2010
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6 Extrusion-Based Systems
perhaps using reaction injection molding-related processes rather than relying entirely on thermal effects. This chapter will start off by describing the basic principles of extrusion-based additive manufacturing. Following this will be a description of the most widely used extrusion-based technology, developed and commercialized by Stratasys, USA. Bioplotting equipment for tissue engineering and scaffold applications commonly use extrusion technology and a discussion on how this differs from the Stratasys approach will ensue. Finally, there have been a number of interesting research projects employing, adapting, and developing this technology, and this will be covered at the end of the
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