This paper examines a new paradigm in the world of manufacturing—distributed manufacturing based on desktop manufacturing (DM)2. The evolution of (DM)2 began in the last decade of the 20th century and its technological development is well underway, as is evidenced by a World Technology Evaluation Center study (www.wtec.org). However, as managers begin to assess the competitive advantages of moving to this manufacturing model it will be important to consider the social and environmental implications of this paradigm shift as well as issues related to materials and energy utilization. The factors that now appear to be driving the need for radical departures from the more traditional manufacturing paradigms have been broadly articulated but the longer-term future of this manufacturing model is less clear. Several scenarios are proposed and discussed that suggest how manufacturing will shift to a more distributed model via the concept of desktop manufacturing (DM), which will coexist with the centralized manufacturing model but likely take on a greater and greater share of the total manufacturing market worldwide. Spurred on by the rapid emergence of miniaturization technologies, the development and refinement of these desktop manufacturing scenarios needs to be examined in the context of a number of important socioeconomic, environmental, and materials and energy utilization issues as (DM)2 continues to evolve as a transforming paradigm for the world of manufacturing. Scientific, technical, and economic barriers and challenges are identified and discussed.

Carbon nanotubes (CNTs) are an ideal reinforcement phase for composite applications at the micro-scale. These include specific use in the areas of biomedicine, electromechanical actuators and electrically-conductive polymers. The objective of this paper is to highlight the importance of developing a knowledge base that will enable the design of CNT composites to meet both the micro-scale engineering and manufacturing/machining requirements. To this end, significant results from recent experimental and modeling research on the machining of CNT composites are presented. CNT loading, alignment, dispersion and the interfacial bonding between the CNTs and the matrix have a strong influence on the functionality and machinability of CNT composites. Micro/meso-scale machining studies reveal that an increase in CNT loading improves the machinability of the composite. Misco-elastic/plastic deformation of the polymer-phase plays a significant role while machining the composite with 1.75% CNT loading, whereas for CNT loadings >= 5%, the CNT distribution and interface failure effects were found to be important. Microstructure-based CNT composite machining model is presented and model predictions are discussed. This model serves as a design tool to identify critical microstructural parameter combinations of CNT loading, alignment and dispersion that result in favorable machining results. These results were then used to show how the morphology of the machined surface could be harnessed to produce the next generation of micro-fluidic devices with self-mixing capabilities.

The machinability of carbon nanotube (CNT)-reinforced polymer composites is studied as a function of CNT loading, in light of the trends seen in their material properties. To this end, the thermomechanical properties of the CNT composites with different loadings of CNTs are characterized. Micro-endmilling experiments are also conducted on all the materials under investigation. Chip morphology, burr width, surface roughness, and cutting forces are used as the machinability measures to compare the composites. For composites with lower loadings of CNTs (1.75% by weight), the visco-elastic/plastic deformation of the polymer-phase plays a significant role during machining, whereas, at loadings ≥5% by weight, the CNT distribution and interface effects dictate the machining response of the composite. The ductile-to-brittle transition that occurs with an increase in CNT loading results in reduced minimum chip thickness values and burr dimensions in the CNT composite. The increase in thermal conductivity with the increase in CNT loading results in reduced number of adiabatic shear bands being observed on the chips and reduced thermal softening effects at high cutting velocities. Thus, overall, an increase in CNT loading appears to improve the machinability of the composite.

Membrane microfiltration is a promising technology that has been shown to extend metalworking fluid (MWF) life by eliminating contaminants while allowing the fluid to stay in use. However, the efficacy of this technology is compromised by the clogging of the filter pores in a process known as membrane fouling. In this paper the fouling issue is addressed by the development of a semi-synthetic MWF specifically designed to not foul microfiltration membranes. The composition of the designed MWF is discussed and compared with a commercial MWF. Cross-flow microfiltration fouling tests were carried out in low-pressure, high-velocity conditions on ceramic α-alumina membranes. Several common MWF components are shown not to be factors of membrane fouling on these membranes. The flux of the designed fluid was found to reach an immediate steady state at about twice the value of the steady-state flux of the tested commercial fluid. Scanning electron microscope imaging was used to further evaluate membrane fouling by each fluid. The machining capabilities of the designed fluid were examined in terms of cutting forces and machining temperature.

In micromachining, the uncut chip thickness is comparable or even less than the tool edge radius and as a result a chip will not be generated if the uncut chip thickness is less than a critical value, viz., the minimum chip thickness. The minimum chip thickness effect significantly affects machining process performance in terms of cutting forces, tool wear, surface integrity, process stability, etc. In this paper, an analytical model has been developed to predict the minimum. chip thickness values, which are critical for the process model development and process planning and optimization. The model accounts for the effects of thermal softening and strain hardening on the minimum chip thickness. The influence of cutting velocity and tool edge radius on the minimum chip thickness has been taken into account. The model has been experimentally validated with 1040 steel and Al6082-T6 over a range of cutting velocities and tool edge radii. The developed model has then been applied to investigate the effects of cutting velocity and edge radius on the normalized minimum chip thickness for various carbon steels with different carbon contents and Al6082-T6.

An oblique cutting model is developed to predict the thrust and torque created by the chisel edge of a drill with an arbitrary point geometry. The chisel edge geometry is modeled using a mathematical representation of the flank grinding parameters and the flute geometry. The varying cutting angles at the chisel edge are determined and used to calculate the force contribution of each element using a mechanistic modeling approach. The model is validated for three commercial point geometries—the conical, helical and Racon® drill points. Model simulations match experimental data well for the geometries tested and show a marked improvement over the orthogonal cutting model.

The machinability of a polycarbonate nanocomposite containing multiwalled carbon nanotubes is investigated and contrasted with its base polymer and with a conventional carbon fiber composite. The material microstructures are characterized using transmission electron and scanning electron microscopy methods. Micro-endmilling experiments are conducted on the three materials. Chip morphology, machined surface characteristics, and the nature of the cutting forces are employed as machinability measures for comparative purposes. Polycarbonate chips are seen to transition from being discontinuous to continuous as the feed-per-tooth (FPT) increases, while, at all FPT values the nanocomposite is seen to form comparatively thicker continuous chips. The nanocomposite and the carbon fiber composite are seen to have the lowest and the highest magnitudes, respectively, for both the surface roughness and cutting forces. Shearing along the nanotube-polymer interface and better thermal conductivity are speculated to be the mechanisms responsible for the observations seen in the nanocomposite.

In this paper, a dynamic model that considers the vibrations of both the workpiece and fixture elements in order to accurately predict the friction damping over a wide range of clamping forces has been developed. The model is established based on the theory of variational inequality and solved via a nonlinear FEM. It is shown that the model is capable of predicting the system dynamics over a wide range of clamping forces. It is also demonstrated that the increasing then decreasing trend of the damping ratio caused by “interface locking” is due to the relative velocity change at the contact interface. With multiple contact interfaces, the “locking” occurs sequentially. Finally, the model is used to study the influence of friction damping on machining process stability.

A model to predict the dynamics of a workpiece-fixture system has been developed based on the equivalency of the dynamic frictional contact problem with a nonlinear friction law to that of a variation inequality problem. Nonlinear finite element method has been employed to solve the problem. A series of experiments under various fixture configurations were conducted on a modular fixture test-bed to determine the dynamic characteristics of the workpiece-fixture system. Model predictions of the dynamic characteristics have been compared to those obtained from the experiments and are found to be in good agreement. It was found that frictional sliding contact at the workpiece-fixture interfaces provides damping to the system and that the nature of this contact and level of damping are highly dependent on contact forces developed through clamping. Clamping sequence was also found to be important in determining dynamic characteristics.

A model to predict the full biaxial surface and subsurface residual stresses from the turning process is presented. The model formulation includes thermomechanical coupling, plastic heating, frictional heating, convection, conduction, thermal softening and strain hardening. Calibration and validation of the model are undertaken. The predictive model stands as a tool both to optimize the turning process based on the resulting residual stresses and also to gain an in-depth understanding of the physics of residual stress development from the turning process. In addition, thorough analysis of the experimental results reveals insight into the effects of feed and depth of cut on the surface and subsurface machining-induced residual stresses.

Controlled orthogonal and controlled oblique machining of annealed AISI 4340 have been undertaken in a design of experiments framework to investigate the machining-induced residual stresses resulting from these processes. The experimentation demonstrates significant simplifications in the machining-induced residual stress problem when the stresses are expressed in a coordinate system fixed in the tool and also indicates that the directions along the cutting edge and normal to the cutting edge of the tool are principal directions of the machining-induced residual stresses. Based on the experimental results, a plane strain thermoelastoplastic model of metal flow under the flank of a cutting tool is developed to predict the full in-plane biaxial residual stress profiles existing at and beneath the newly created surface. Calibrated results show favorable agreement with the experimental machining-induced residual stresses in annealed AISI 4340. [S1087-1357(00)00201-X]

A new analytical model to predict the chatter stability of variable spindle speed machining is presented. This model is based on transforming the linear differential equations with time varying delay to the solution of an infinite order characteristic equation. The model has been validated using the results of numerical time domain simulations and through experimentation. The analytical model employs normalized parameters which permits its use in studying the stability of variable spindle speed machining systems with a wide range of parameters without having to solve the complex system of differential equations. The analytical model is also used to design optimal variable spindle speed machining parameters in the presence of known fixed or varying machining dynamics. [S1087-1357(00)01402-7]

A mechanistic model is developed to predict the forces for arbitrary drill point geometry. The cutting lips are divided into elements and the elemental forces are determined from a fundamental oblique cutting model. A method is developed to parametrically define the cutting lip in three-dimensional space and to determine the oblique cutting parameters (cutting angles and chip thickness) at each element on the cutting lip. The model does not require calibration experiments for each point geometry. The conical drill is used to determine the model coefficients for a tool and workpiece material combination and these are used for other drill point geometry. Model simulations match experimental data very well for four commercial drill point geometry—the Racon, Helical, Bickford and Double angle drill points.

Under normal machining conditions, the cutting forces are primarily due to the bulk shearing of the workpiece material in a narrow zone called the shear zone. However, under finishing conditions, when the uncut chip thickness is of the order of the cutting edge radius, a ploughing component of the forces becomes significant as compared to the shear forces. Predicting forces under these conditions requires an estimate of ploughing. A slip-line field is developed to model the ploughing components of the cutting force. The field is based on other slip-line fields developed for a rigid wedge sliding on a half-space and for negative rake angle orthogonal cutting. It incorporates the observed phenomena of a small stable build-up of material adhered to the edge and a raised prow of material formed ahead of the edge. The model shows how ploughing forces are related to cutter edge radius — a larger edge causing larger ploughing forces. A series of experiments were run on 6061-T6 aluminum using tools with different edge radii — including some exaggerated in size – and different levels of uncut chip thickness. Resulting force measurements match well to predictions using the proposed slip-line field. The results show great promise for understanding and quantifying the effects of edge radius and worn tool on cutting forces.

In this paper, a summary of work performed in the area of modeling of the dynamic metal cutting process is presented. A general view of evolution of the dynamic cutting process models is depicted. Specifically four modeling approaches including analytical, experimental, mechanistic and numerical methods are critically reviewed. A brief assessment of future research needs is also given.