Purpose – The purpose of this paper is to systematically and critically review the literature related to process design and modeling of fused deposition modeling (FDM) and similar extrusion-based additive manufacturing (AM) or rapid prototyping processes. Design/methodology/approach – A systematic review of the literature focusing on process design and mathematical process modeling was carried out. Findings – FDM and similar processes are among the most widely used rapid prototyping processes with growing application in finished part manufacturing. Key elements of the typical processes, including the material feed mechanism, liquefier and print nozzle; the build surface and environment; and approaches to part finishing are described. Approaches to estimating the motor torque and power required to achieve a desired filament feed rate are presented. Models of required heat flux, shear on the melt and pressure drop in the liquefier are reviewed. On leaving the print nozzle, die swelling and bead cooling are considered. Approaches to modeling the spread of a deposited road of material and the bonding of polymer roads to one another are also reviewed. Originality/value – To date, no other systematic review of process design and modeling research related to melt extrusion AM has been published. Understanding and improving process models will be key to improving system process controls, as well as enabling the development of advanced engineering material feedstocks for FDM processes.

Purpose -The purpose of this paper is to critically review the literature related to dimensional accuracy and surface roughness for fused deposition modeling and similar extrusion-based additive manufacturing or rapid prototyping processes. Design/methodology/approach -A systematic review of the literature was carried out by focusing on the relationship between process and product design parameters and the dimensional and surface properties of finished parts. Methods for evaluating these performance parameters are also reviewed. Findings -Fused deposition modeling ® and related processes are the most widely used polymer rapid prototyping processes. For many applications, resolution, dimensional accuracy and surface roughness are among the most important properties in final parts. The influence of feedstock properties and system design on dimensional accuracy and resolution is reviewed. Thermal warping and shrinkage are often major sources of dimensional error in finished parts. This phenomenon is explored along with various approaches for evaluating dimensional accuracy. Product design parameters, in particular, slice height, strongly impact surface roughness. A geometric model for surface roughness is also reviewed. Originality/value -This represents the first review of extrusion AM processes focusing on dimensional accuracy and surface roughness. Understanding and improving relationships between materials, design parameters and the ultimate properties of finished parts will be key to improving extrusion AM processes and expanding their applications.

Additive manufacturing and specifically metal selective laser melting (SLM) processes are rapidly being industrialized. In order for this technology to see more widespread use as a production modality, especially in heavily regulated industries such as aerospace and medical device manufacturing, there is a need for robust process monitoring and control capabilities to be developed that reduce process variation and ensure quality. The current state of the art of such process monitoring technology is reviewed in this paper. The SLM process itself presents significant challenges as over 50 different process input variables impact the characteristics of the finished part. Understanding the impact of feed powder characteristics remains a challenge. Though many powder characterization techniques have been developed, there is a need for standardization of methods most relevant to additive manufacturing. In-process sensing technologies have primarily focused on monitoring melt pool signatures, either from a Lagrangian reference frame that follows the focal point of the laser or from a fixed Eulerian reference frame. Correlations between process measurements, process parameter settings, and quality metrics to date have been primarily qualitative. Some simple, first-generation process control strategies have also been demonstrated based on these measures. There remains a need for connecting process measurements to process models to enable robust model-based control.

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The elastic properties of polishing pads critically affect polishing results during chemical mechanical polishing ͑CMP͒ of integrated circuit substrates. The ability of water to plasticize polishing pads and the resulting effects on pad performance were investigated. Water is hypothesized to penetrate the surface of the polishing pads, disrupting hydrogen bonds between adjacent polymer molecules within the pads and altering the pad elastic modulus. Infrared spectra obtained using an attenuated total reflection technique were used to confirm the effect of water on the polishing pad structure. Contact with deionized water reduced the pad elastic modulus due to the formation of a hypothesized soft layer on the pad surface. Removal of the soft layer from the pad, as occurs during conditioning, increased observed CMP removal rates. Experiments on a commercial dual-axis polisher using a noncommercial process showed decreased oxide removal rates as the duration of the pad exposure to water increased. A pad asperity-wafer contact model was developed. This model indicates that if the surface of the pad asperities is softened by the penetration of water compared to the bulk pad, then the asperities will deform to a greater degree under the applied load than in the absence of the softening. As a result, the effective pad-wafer contact area for a given applied load will increase and the average pad-wafer separation will decrease, causing the applied load to be carried by a larger number of asperity-wafer contacts and reducing the local load on the wafer surface. The reduced local loads will contribute to reduced polishing rates, consistent with experimental observation. The maximum depth of penetration of water into the pad surface was estimated to be ϳ20 m.Chemical mechanical polishing ͑CMP͒ has become an essential step in the manufacturing of advanced integrated circuits ͑ICs͒. During CMP, material is removed from the surface of a wafer when the wafer is rubbed against a polymeric polishing pad coated with aqueous slurry. Although this technology has developed rapidly in recent years, understanding of the fundamental chemical and mechanical processes involved in polishing is still developing. In this work, the effects of water penetration into the pad are considered, including effects on the pad physical properties and the resulting polishing performance.A combination of mechanical and chemical processes during polishing results in material removal from the surface of both the wafer and pad. It has been observed that as the number of wafers polished by a pad increases, pad morphology is altered by wear and glazing. 1,2 Pad glazing occurs as debris from the pad and wafer accumulates in the pad pores and as the pad surface is smoothed by the polishing. 3 In the absence of steps to counteract wear and glazing, material removal rates decrease compared to the original removal rate with increases in the number of wafers polished by a pad. 4 To maintain stable removal rates over the life of the pad, pad conditioning is widely uti...