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Directed Energy Deposition (DED) is a metal additive manufacturing process where feedstock (metal powder in this study) is delivered to a meltpool on the surface of a metallic part simultaneously with an energy source (a laser in this study) that causes the local melting. DED process productivity is measured using the Material Addition Rate (MAR) which is a measure of the amount of material that is added to the part per interval of time, while process efficiency is measured with the powder catchment efficiency which is the ratio of powder deposited into the part and powder fed through the nozzle during the deposition cycle. If clad geometry can be maintained while deposition head feed rate is increased, then MAR is increased. As DED functionality has been integrated into industrial CNC machining centers published deposition head feed rates in literature have not kept up with machine feed rate capabilities. This research demonstrates a method of using energy and powder fluence into the meltpool to scale up deposition head feed rate in a DED equipped CNC machining center to improve MAR while maintaining part quality and geometric accuracy.

The efficiency of powder-based directed energy deposition (DED) nozzle is dependent on its ability to direct the pneumatically conveyed powder into the meltpool. Computational fluid dynamics (CFD) with discrete phase modeling (DPM) has been used to investigate the optimization of DED nozzle geometry and DED parameter selection, however, the effect of material choice for nozzle fabrication has not been fully investigated. To explore the effects of the nozzle material on powder efficiency a CFD DPM model was created and analyzed in ansys fluent. Various nozzle materials were simulated using statistical models for the coefficient of restitution (COR) between the powder and nozzle wall from the literature. The results of the CFD DPM model aligned well with experimental data for a 316L stainless steel prototype nozzle. CFD DPM results indicated that using a material with a lower mean COR value improved the powder efficiency of the nozzle. Powder efficiency improved because the component of powder velocity normal to the direction of gas flow was reduced in nozzles made from materials with lower COR values, which in turn led to fewer impacts between the particles and the nozzle walls.

Successful and efficient hybrid manufacturing consisting of Directed Energy Deposition (DED) followed by milling as a postprocess requires that material deposited during the DED step be geometrically consistent and slightly larger than the desired final, machined dimensions. DED clad width is directly correlated to meltpool energy, while powder fluence directly correlated to DED clad cross-sectional area. Due to heat accumulation into the DED part during deposition, meltpool energy does not remain constant without modification of DED process parameters over the deposition cycle. Meltpool energy is typically managed by decreasing the laser power to reduce the energy fluence into the meltpool – though this technique limits DED productivity. If the working distance and laser optics within the deposition head are static, energy fluence reduction can also be achieved by increasing deposition head feedrate. Modifying powder mass flowrate through the deposition nozzle to maintain powder fluence into the meltpool allows for both the clad geometry to be maintained while also increasing the productivity of the DED process. Numerical simulation of the heat flow in a DED thin wall part was used to derive laser energy fluence values to maintain a constant meltpool energy. Derived values were tested using both the laser power and feedrate to moderate energy fluence into the meltpool. Results are compared to a thin wall deposited without meltpool energy control. Clad geometry variation and cycle time are both shown to reduce when using a feedrate-based meltpool energy control method as compared to laser power-based meltpool energy control or no meltpool energy control, increasing the geometric accuracy for postprocess machining and productivity.

In order to achieve high accuracy of computer numerical controlled (CNC) machine tools, various error compensation functions are implemented in the CNC control system. However, these error compensations are not designed to track the dynamic change in accuracies, such as thermal distortion or aging deterioration, during a machining process. To compensate for the dynamic change in accuracy, a built-in automatic measurement and compensation system based on dual linear scales was proposed, and its performance requirement was analyzed. Based on the analysis, a physical prototype was developed, and its feasibility was investigated by a series of experiments. The results showed that the measurement with the linear scale system agreed with a conventional measurement method within the uncertainty estimated at the design stage. In a subsequent experiment, the accuracy compensation was performed based on the measurement value. With compensation, the maximum accuracy deterioration was successfully suppressed from 22 to 3 μm.

Directed energy deposition (DED) is an additive manufacturing (AM) process where a laser is used to fuse a metal powder onto a substrate. The powder is deposited in a layer-by-layer fashion, and each deposited track is referred to as the clad. Large thermal gradients that occur during DED can cause changes in the clad geometry as well as deformation of the substrate and final part. Thermal behavior of DED manufactured parts and mitigation of thermal distortion has been addressed in the literature, but these studies mainly focused on material properties while neglecting the effect of thermal distortion on part geometry. One of the mitigation strategies that has been widely tested and accepted is substrate preheating. This study uses analytical and experimental models to observe changes in clad geometry when energy input to the part is varied by adjusting process parameters and preheating the substrate. A method to quantify substrate energy, or the amount of heat energy the substrate holds, is found as well as a relationship between the substrate energy and clad geometry. The geometry of the clad can be controlled by controlling the total energy added to the clad.

The directed energy deposition (DED) process enables the production of near net shape parts in the starting form of either powder or wire melted by a focused energy source, such as laser. The target geometry is then built layer by layer. In theory, engineering components with complex shapes can be fabricated with a single setup using a hybrid CNC machine tool, which has capabilities of both DED and traditional subtractive machining processes. However, the issue of inaccurate DED deposited geometry and insufficient material deposition results in the repetition of the hybrid process to achieve the goal geometric dimension. This paper presents a generalized strategy for different materials that plan DED toolpath for the planar geometric feature to achieve its required final geometric dimension by using only a single hybrid manufacturing cycle based on simulated results and validate the strategy experimentally by using a hybrid CNC machine.

In this work, we present a model for origami-based sheet metal (OSM) folding that can predict the required bending force. OSM folding is enabled by introducing bending features along the bending line, named material discontinuity (MD). Firstly, the introduced analysis in this work developed a bending setup for OSM that does not require a die then introduced a method to analytically derive the bending force for a regular sheet without any added folding features. The analytical approach is followed using an experimental setup identical to the developed OSM bending configuration. Secondly, the OSM bending experiment is conducted to measure the required bending force and to identify which parameters influence the OSM bending force significantly. Finally, an empirical model is proposed considering the analytical force in the first step and the influencing parameters defined in the second step. Regression analysis is carried out using one portion of experimental force measurement to determine the coefficients of the proposed empirical model. The other measurement set is used to validate the prediction model. The validation results of the proposed prediction model show good agreement between the developed prediction model and the experiment results. The prediction model provided a shape factor that represents the topology of each bending feature, as well.

A dynamic powder splitting system (DPSS) was developed to overcome a slow powder flow rate (PFR) response in conventional powder delivery systems used in the Directed Energy Deposition (DED) additive manufacturing process. Complementary to the main powder delivery system, the DPSS uses a custom valve to split powder flow and cyclone separator to redirect powder flow that is not used in the cladding process. Its potential applications are compensation for clad height inconsistencies caused by machine feed rate errors and increase of powder usage efficiency via a powder recycling system. Various tests were performed to verify performance and cladding.

Directed energy deposition (DED) is often utilized to coat metallic part with complex geometries in a variety of anti-corrosion materials or high-temperature materials. Computer-controlled scanning patterns always affect the grain morphology in coating, which can further influence coating’s mechanical properties. In this study, a Kinetic Monte Carlo (KMC) Potts model is applied to predict the grain morphology under two different frequently-used laser scanning patterns: unidirectional and bidirectional raster patterns. Then the predicted grain morphologies in coatings with these two scanning patters were quantified and analyzed respectively. The simulated results were verified with an electron backscatter diffraction (EBSD) image of SS304 DED part reported by a literature. It was found that the primary grain morphology in coating was columnar shape. Some fine equiaxed grains appeared near the center line of scanning path. However, the columnar grains had crescentic shapes under unidirectional pattern, which was different from the linear shape of columnar grains under bidirectional pattern.

Directed energy deposition (DED) is an advanced additive manufacturing process which can deposit or fabricate a part with complex and nontraditional geometries in many kinds of engineering structural materials, high-temperature materials, and anti-corrosion materials. The fed metallic powder is melted by a laser beam with highly concentrated energy on the substrate surface. In this manufacturing process, different laser transverse speeds can significantly affect the microstructural morphology of the deposited layer. Some microstructural morphologies observed in DED may appear in classic solidification processes. However, the effect of mobile heat sources which vary with time and location can result in significant microstructural heterogeneity. In order to investigate the laser transverse speeds’ effects on the microstructural morphology in DED processes, a Kinetic Monte Carlo (KMC) Potts model was utilized to exactly predict the grain evolvement under different laser transverse speeds in this study. Three increasing transverse speeds, 450 mm/min, 600 mm/min, and 1000 mm/min, were chosen and then investigated. The predicted microstructural morphology in depositions with these three different laser transverse speeds was quantified and analyzed. The processing parameters in the KMC Potts model were cited from a previous reference and have been validated with experimental EBSD microstructural images.

Directed energy deposition (DED) is an additive manufacturing technology where a moving energy source creates a meltpool on the surface of a substrate into which feedstock material is deposited to form the final part geometry. Maintenance of the meltpool during deposition requires very high intensity energy flux to overcome thermal losses to the surroundings and substrate. Trochoidal toolpaths are investigated using numerical simulation and DED experiments as a means of increasing the efficiency of the DED process. Trochoidal laser motion during DED was found to increase the material addition rate by 17% and powder catchment efficiency by 15%.

Medical screws are a common mass-produced implantable medical component made of Titanium. To machine the threads of these types of components, thread whirling with carbide tools is typically used. However, tool wear and low cutting speed limit the productivity and increase the manufacturing cost of such medical parts. In this study, a direct motor driven thread whirling unit for an advanced Swiss-type CNC lathe was developed and it was used with advanced tool materials such as low binder content Cubic boron nitride (CBN) and Polycrystalline diamond (PCD) to find a cost-effective and more productive alternative to carbide tools.

Gray cast iron (GCI) is highly anisotropic at the microscale consisting of stochastically distributed and orientated graphite flakes within a ferric matrix. The anisotropy of the microstructure endows gray cast iron with favorable damping characteristics which makes it a common material for machine tool structural components. However, the microstructure inhibits the formation of a finished surface of sufficient quality for use as a slideway when milled with a defined cutting edge. The mechanisms of irregular surface formation during the machining of GCI were investigated using both a 3-D finite element cutting simulation and milling experiments. Investigation of simulation and machining tests indicates that the interaction of the primary shear zone in front of the cutting edge and graphite flakes is the cause of microcavity formation on the machined surface.

An innovative injection mold making and cooling approach using a hybrid additive and subtractive machine tool is proposed in this paper. Approximated mold geometry is quickly formed using prefabricated blocks. Directed Energy Deposition (DED) followed by finish milling is then used to form the continuous free-form surface of the mold cavity. The innovative technique enables quick fabrication of a mold with a conformal cooling channel resulting in a dramatic improvement in cooling performance of the mold. A mold prototype was fabricated and the performance was evaluated compared to a mold fabricated by the traditional subtractive machining method.

A new vision-based system is designed for the identification of chatter vibration. Chatter vibration is a major obstacle in CNC machining as it causes bad surface finishes and increases tooling damage and costs. This research proposes the use of machine vision for the detection of chatter vibration frequencies during high-speed milling operations. The vision system utilizes digital image processing and texture analysis to determine the frequencies of the chatter marks on the surface of a machined workpiece. The developed system provides a solution to machinists at ease without any expensive measuring equipment. The vision system was verified and compared with other chatter detection methods by identifying and creating tests based on the dynamics of a machine tool.

Currently, linear sliding guideways are fabricated using machining centers for roughing and drilling while grinding machines are used for finishing operations. As a consequence, large and heavy machine tool castings must be transferred back and forth multiple times between the different equipment. In an effort to eliminate workpiece transfers and reduce production costs, an alternative manufacturing process that utilizes hard milling followed by fine-finishing with a spindle mounted abrasive filament tool is proposed. The goal of the current paper is to determine process settings for the filament tool optimized for sliding friction coefficients between PTFE slider and cast iron slideway. Areal function parameters Sk, Spk, Svk and load bearing ratio were used to evaluate the surface texture after polishing with various filament tools. A two-level partial factorial experiment with five factors was conducted friction coefficients were measured to calculate the significant main effects and second-order interactions. The dynamic sliding performances of five types of surfaces (ground, milled, milled + polished) were tested at sliding speeds from 80 to 2000 mm/s. It was found that the filament tools with the largest grit and thickest bristles have the greatest impact on surface quality, the alternative polishing method results in lower static and dynamic friction coefficients and the new process is not expected to increase machining time based on theoretical cycle time analysis.

In order to expand the regional production of machine tools which utilize precision machined sliding guideways, cubic boron nitride (CBN) hard milling may be implemented as an alternative finish process instead of conventional surface grinding. While higher material removal rates can be achieved with a milling strategy, the use of a defined cutting edge leads to surfaces with asperities. These sharp peaks quickly wear down during sliding contact, resulting in unacceptable changes in the load bearing surface of the guide. Therefore, a post process to milling must be implemented to mitigate these features. This paper investigates the use of a spindle mounted abrasive disk filament tool for producing a functional surface similar to the ground surfaces. The optimal process parameters were investigated using 2D profile measurements, followed by comparison using areal analysis of ground, milled, and polished surfaces. It was found that polishing reduces both the height and volume of asperities on the milled surface, leading to contact characteristics which were more similar to those of the conventional ground surfaces currently used for sliding guideways.

Sliding guideways for machine tools require smooth, consistent surface texture for optimal performance. An excessively smooth surface causes adhesion between the moving components, while a rough surface accelerates wear. Conventional guideway fabrication uses large, expensive grinding machines. To reduce manufacturing costs while maintaining functional performance, cubic boron nitride (CBN) milling followed by abrasive surface polishing has been proposed. This study investigates the use of an abrasive filament tool to correlate the effect of polishing with lubricated static/dynamic friction coefficients. The results are compared with the sliding performance of milled and ground hardened grey cast iron samples. It was found that polishing had the largest effect on surfaces that were previously milled at higher feed rates and, if realized by industry, could increase productivity.

Sliding guideways are often used as the foundation for linear motion in computer numerical control (CNC) machine tools due to their high damping capabilities especially for heavy duty machining applications. However, the traditional manufacturing process with grinding is time-consuming, and the product’s sliding performance has not been optimized nor clearly understood. In order to increase productivity, a machining center based manufacturing method with cubic boron nitride (CBN) milling tools was introduced and tested by researchers. While greatly reducing manufacturing time and cost, a rougher milled surface, in comparison to traditional grinding, is a possible concern for the performance as well as the life of sliding guideways. In this study, a novel planar honing process was proposed as a postprocess of CBN milling to create a finish surface on hardened cast iron sliding guideways used for CNC machine tools. A design of experiment (DOE) was conducted to statistically understand significant factors in the machining process and their relationship with surface topography. Effective planar honing conditions were discovered and analyzed with three-dimensional (3D) and two-dimensional surface parameters.

Robotic total hip arthroplasty is a procedure in which a milling operation is performed on the femur followed by insertion of a prosthetic implant. Although surgeons operate the robots, they do not control the choice of robotic tools and cutting strategies of the robot. Toolpath parameters, such as feedrate, tool geometry, and spindle speeds, govern the cutting forces of the robot. This research covers a methodological approach for finding optimal parameters such that cutting forces and surgical times are reduced. Many different types of orthopedic surgical burs were retrofitted into an advanced computer numerically controlled (CNC) machine, and the characteristics of each tool were evaluated. A simulation cutting model was then developed to find the parameters that could remove the most material in the fastest amount of time without violating any of the safety constraints of surgery. The new methodology proposed not only finds the theoretical optimal parameters but also expedites the process of finding sufficient parameters for orthopedic surgery.

Sliding guideways have received renewed interest in recent years as machine tool linear motion guides, due to a demand for machine tools to have good dynamic performance, which is of vital importance when machining difficult-to-cut materials. While the traditional fabrication approach of the sliding surface is grinding, this paper investigated the possibility of an alternative cubic boron nitride (CBN) milling-based manufacturing approach while utilizing Al and Mg additives in the cast iron material for better machinability and productivity. Machining results have shown a dramatic improvement in machinability especially in terms of tool wear at certain cutting conditions with the refined hardened cast iron and a CBN tool. It was found by the post experimental analysis that oxide films of the Al and Mg additives were generated at the cutting edge of the CBN tool to protect the tool from wear. Because of suppression of tool wear, a very constant surface roughness can also be achieved. A case study has also demonstrated the effectiveness of the CBN milling-based manufacturing approach with the refined cast iron and the found high-speed cutting conditions.

To improve efficiency and cost performance of cast iron machine tool component fabrication, an alternative process must be developed in order to replace the grinding process, which often causes a bottleneck in production. As an alternative manufacturing approach, this research applies cubic boron nitride (CBN) hard milling operations to eliminate the grinding process in order to improve the overall manufacturing process. A variety of hardened cast iron materials with Al and Mg additives and CBN tool types were prepared and tested based on a design of experimentation (DOE) to observe their effect on surface quality and tool life. Al and Mg were added to raw cast iron to achieve generation of oxide layers at the cutting edge during milling to protect the tool from wear. By executing the DOE, the optimal cutting conditions for achieving the best surface quality were introduced. Also, additional machinability tests were conducted with the optimal conditions in order to evaluate tool wear characteristics and surface quality of the machined workpieces. Based on the observation of the used tool by electron probe micro-analyzer (EPMA), a protective oxide layer of additives was observed at the cutting edge. Hardened cast iron with Al and Mg additives is found to show preferable wear and surface quality characteristics.

A milling operation is inherently an intermittent material removal process where cutter engagement and disengagement is repeated until the end of the material removal process. During the process, the cutter receives multiple impacts and mechanical and thermal vibrations which eventually damage the cutting edge. The optimum rigidity and damping of the spindle motor for the least tool damage highly depends on the cutter and workpiece material properties and the cutting application. This paper introduces the concept of flexible rotational rigidity control using a high performance Permanent Magnet Synchronous Motor (PMSM) which is used as a direct spindle drive. With the PMSM spindle, the spindle rotational characteristics can be adjusted for optimizing the cutting process in order to prevent tools from unwanted premature damage. Simulation models of the spindle motor drive system are presented, which show that a very stiff spindle can be realized by fully utilizing the potential capability of the PMSM and a spindle with the same dynamic properties of a conventionally used induction motor can be realized with a single PMSM spindle. The system prototype and feasibility studies are also presented in this paper. The experimental results show that the PMSM spindle characteristics behave differently depending on the controller setting, and the spindle motor drive system rotational characteristics greatly affect the cutting process, which confirms the importance of the flexible motor control concept.

In order to develop highly stable machining processes in heavy duty milling applications, a study on the development of a high torque–high power spindle system has been conducted. The study includes the design of a new permanent magnet synchronous motor, drive system and spindle system with the designed motor, prototype of the spindle system with the designed motor and experimental evaluation of the entire system by conducting heavy duty milling of a titanium alloy. The results of the experiments show that the spindle has a high rotational rigidity under heavy duty intermittent cutting processes.

BACKGROUND Robot-assisted joint replacement surgery is becoming increasingly more common worldwide, therefore it is important to characterize and improve the bone-cutting mechanics of surgical tools. METHODS Linear coefficients relating cutting force and chip thickness were derived for a surgical spindle. The cutting coefficients were integrated into an analytical simulation which calculated cutting forces, torque, and power consumption. An optimization experiment was performed. High speed video was taken at various tool parameter settings. RESULTS Varying machining parameters resulted in lower cutting forces. The surgical spindle stalled at the current spindle speed used in surgery, but did not for the new, optimized conditions. Multiple anomalies were identified in the videos that confirmed observations from the cutting force data. CONCLUSIONS Improved surgical performance and accuracy were achieved using slower spindle speeds, decreased cutting depth, and increased feed rates, as well as improving motor torque to ensure a smooth cutting process.

In order to create a higher torque spindle system for productive milling operations, rotational speed stability against the torque disturbance has been studied with respect to the spindle mechanical design parameters, actuator types and spindle control algorithms. The study showed a remarkable difference in the spindle rotational speed stability against torque disturbance between a spindle system equipped with an induction servo motor and a permanent magnet synchronous servo motor. The results of this study have been obtained by theoretical analysis, numerical simulation and physical experiments, and the experimental study showed that the hybrid actuation spindle achieves longer tool life.

Gene Tsudik proposed a Trivial RFID Authentication Protocol (YA-TRAP), where a valid tag can become incapacitated after exceeding the prestored threshold value and is thus vulnerable to DoS attack. Our scheme solves the problem by allowing a tag to refresh its prestored threshold value. Moreover, our scheme is forward secure and provides reader authentication, resistance against timing, replay, tracking attacks. We show the use of aggregate hash functions in our complete scheme to reduce the reader to server communication cost. The reader uses partial authentication to keep the rogue tags out of the aggregate function.

A compact multi-purpose spindle for multi-tasking machine tools has been developed such that it can provide high power and torque for lower speed ranges while it rotates at high speeds for light duty machining. The innovative design based on the dual direct drive concept has been adopted such that the size of the spindle can stay the same as a conventional spindle of its class. For optimizing the design process, a method based on the complete virtual approach using 3D solid models has been studied and developed. Machining performance has been verified through a physical prototype.

An Attribute-Based Encryption (ABE) is an encryption scheme, where users with some attributes can decrypt ciphertexts associated with these attributes. However, the length of the ciphertext depends on the number of attributes in previous ABE schemes. In this paper, we propose a new Ciphertext-Policy Attribute-Based Encryption(CP-ABE) with constant ciphertext length. Moreover, the number of pairing computations is also constant., Proceedings of the 5th International Conference, ISPEC 2009 Xi’an, China, April 13-15, 2009.

Robotic total hip arthroplasty is a procedure in which milling operations are performed on the femur to remove material for the insertion of a prosthetic implant. The robot performs the milling operation by following a sequential list of tool motions, also known as a toolpath, generated by a computer-aided manufacturing (CAM) software. The purpose of this paper is to explain a new toolpath force prediction algorithm that predicts cutting forces, which results in improving the quality and safety of surgical systems. With a custom macro developed in the CAM system’s native application programming interface, cutting contact patch volume was extracted from CAM simulations. A time domain cutting force model was then developed through the use of a cutting force prediction algorithm. The second portion validated the algorithm by machining a hip canal in simulated bone using a CNC machine. Average cutting forces were measured during machining using a dynamometer and compared to the values predicted from CAM simulation data using the proposed method. The results showed the predicted forces matched the measured forces in both magnitude and overall pattern shape. However, due to inconsistent motion control, the time duration of the forces was slightly distorted. Nevertheless, the algorithm effectively predicted the forces throughout an entire hip canal procedure. This method provides a fast and easy technique for predicting cutting forces during orthopedic milling by utilizing data within a CAM software.