Manufacture of Microcantilever Sensors

Mechanical micro machining is an emerging technology with many potential benefits and equally great challenges. The push to develop processes and tools capable of micro scale fabrication is a result of the widespread drive to reduce part and feature size. One important factor that contributes to the ability to machine at the microscale level is the overall size of the machine tool due to the effects of thermal, static, and dynamic stabilities. This paper explores the technical feasibility of miniaturized machine tools capable of fabricating features and parts on the micro scale in terms of depth of cut and part form accuracy. It develops a machine tool and examines its capabilities through benchmarking tests and the making of precision dies for the injection molding of microcantilever parts. The design and configuration of a miniaturized vertical machining center of overall dimension less than 300 mm on a side is presented and the component specifications discussed. The six axis machine has linear positioning resolution of 4 nm by 10 nm by 10 nm, with accuracy on the order of 0.3 μm, in the height, feed, and cross feed directions. The work volume as defined by the ranges of axes travel are 4 mm by 25 mm by 25 mm in the height, feed, and cross feed and 20 degrees in the rotational space. To quantify the performance capability of the miniaturized machine tool as a system, a series of evaluation tests were implemented based on linear and arch trajectories over a range of feed speed and depth of cut conditions. Test results suggest that micro level form accuracy and sub-micron level finish are generally achievable for parts with moderate curvature and gradient in the geometry under selected machining parameters and conditions. An injection mold was made of steel with this machine and plastic microcantilevers fabricated. Plastic microcantilevers are appropriate for sensing applications such as surface probe microscopy. The microcantilevers, made from polystyrene, were 464 to 755 μm long, 130 μm wide and only 6–9 μm thick. They showed very good uniformity, reproducibility, and appropriate mechanical response for use as sensors in surface force microscopy.

Variation Simulation of Fixtured Assembly Processes for Compliant Structures Using Piecewise-Linear Analysis

While variation analysis methods for compliant assemblies are becoming established, there is still much to be done to model the effects of multi-step, fixtured assembly processes statistically. A new method is introduced for statistically analyzing compliant part assembly processes using fixtures. This method yields both a mean and a variant solution, which can characterize an entire population of assemblies. The method, called Piecewise-Linear Elastic Analysis, or PLEA, is developed for predicting the residual stress, deformation and springback variation resulting from fixtured assembly processes. A comprehensive, step-by-step analysis map is presented for introducing dimensional and surface variations into a finite element model, simulating assembly operations, and calculating the error in the final assembly. PLEA is validated on a simple, laboratory assembly and a more complex, production assembly. Significant modeling issues are resolved as well as the comparison of the analytical to physical results.

Retrieving Assembly Part Design Using Case-Based Reasoning and Genetic Algorithms

Artificial intelligence (AI) approaches have been successfully applied to many fields. Among the numerous AI approaches, Case-Based Reasoning (CBR) is an approach that mainly focuses on the reuse of knowledge and experience. However, little work is done on applications of CBR to improve assembly part design. Similarity measures and the weight of different features are crucial in determining the accuracy of retrieving cases from the case base. To develop the weight of part features and retrieve a similar part design, the research proposes using Genetic Algorithms (GAs) to learn the optimum feature weight and employing nearest-neighbor technique to measure the similarity of assembly part design. Early experimental results indicate that the similar part design is effectively retrieved by these similarity measures.

Numerical Investigation of Heat Partition in the Primary Shear Zone in Metal Cutting

The fraction of heat generated in the primary shear zone that is conducted into the workpiece is a key factor in the calculation of the shear plane temperature and in calculating the cutting forces based on material flow stress. Accurate analytical, numerical, or experimental determination of this heat partition coefficient is not available to date. This study utilizes a new approach to obtain the heat partition coefficient for the primary shear zone using results for strain, strain rate, and temperature distribution obtained from a coupled thermo-mechanical finite element analysis of machining. Different approaches, using strain rate and equivalent strain, are used for calculating the total plastic power in the primary shear zone and the heat generated by plastic deformation below the plane of the machined surface. The heat carried away by the workpiece is obtained by calculating the heat flow by convection in regions where the conduction is expected to be small. We have used an elastic perfectly plastic material model and constant thermal properties to mimic the assumptions used in analytical models. The fraction of the total heat generated in the primary shear zone that is conducted into the machined workpiece is found and compared to the prediction of different analytical models. It is found that for most of the cutting conditions, the values of heat partition coefficient are closest to those provided by Weiner’s model.

Particle Dampers for Workpiece Chatter Mitigation

It is well known that the chatter stability of a machining process can be improved by increasing the structural damping of the system. To date this approach has been effectively used on various components of the machining system, for example boring bars, milling tools, and the machine structure itself. Various damping treatments have been proposed, including tuned vibration absorbers, active methods, and impact dampers. However, to date there has been little or no work to investigate the issue of particle dampers for this application. This special class of damper comprises a container of thousands of small granular particles which dissipate energy by friction and impact when the container vibrates. The resulting behaviour is highly nonlinear but can provide very high levels of damping across a wide frequency range. In the present study, particle dampers were applied to a workpiece to mitigate chatter during milling, and the limiting critical depth of cut was increased by an order of magnitude. This article gives an overview of the particle damper’s behaviour and key design parameters. Cutting trials employing the device are then described.

Computer-Integrated Design and Manufacturing of Packaging Machines

Automated packaging machines must be constantly redesigned to accommodate ever changing packing. There is little time to make these changes and no room for error. In this work, computer-integrated design and manufacture of a packaging machine has been conducted. A knowledge base system has been developed, which checks for errors in user input, updates all assemblies per the user input, checks for part interferences in the assembly, holds the new design to accepted design standards, and sends warning messages to the user’s computer screen in the event of a problem. The knowledge base then creates new intelligent part numbers. These part numbers provide the informational link from Engineering to Production as they contain all the new part information needed to make the parts. These part numbers are entered into a program that automatically creates the new tool paths for the CNC mill. The entered part number is automatically milled into the part to insure the correct part was entered. The cost of design and manufacture is then reduced substantially. This knowledge base also extends into sales for quoting and for new job creation which expedites the entire process.

Eliminating Redundant Operations While Improving Part Quality by Modeling Machining Errors

A methodology to predict part quality was applied to the perpendicularity quality of the bell face and main axis of a transmission case. By modeling the quality of different processing sequences, we were able to show that the quality of the part - perpendicularity of critical features - does not improve significantly by performing two-pass machining process instead of a single-pass. This application of our quality methodology required the modeling of additional system errors which were not developed in the earlier version and which were needed to predict certain types of form errors. In addition to improved part quality, changing the existing line to a single-pass process eliminated a bothersome job-setting procedure and tooling costs at the second-pass and increased productivity of a rebalanced line.

Tool Selection and Path Control for Automated Anterior Teeth Coronal Canal Treatment Preparation

This paper represents a part of research plan of “Advanced Endodontic Technology Development”. In order to aid endodontic treatment a 3-D computer model of root canals has been created which shows the geometrical characteristics. The extent of work needed for root canal treatment is obtained from this 3-D model. The objective of this paper is to convert the geometrical characteristics into automatic treatment procedure planning. This computer-aided process planning for endodontic treatment determines tool selection and process method. It also calculates tool path and optimum tool movement distance. The output of this planning system is a numerical controlled program. Because of paper size limitation, only tool selection and path control during coronal canal treatment preparation for anterior teeth are discussed in the paper. The computer-aided treatment procedure planning system provides transformation from a 3-D canal model to a machine-controlled program that will yield a treated root canal ready for filling. It serves as a bridge between design (3-D canal model) and manufacturing (canal treatment). Unlike conventional methods for root canal treatment, the computer-aided treatment process planning system emphasizes a non-destructive internal tooth geometry examination and less invasive access preparation.

Superplastic Forming Formula for Aluminum Channel Panels

A parametric study was conducted to determine how the design features and forming parameters affect part thinning and forming time in the Superplastic Forming Process (SPF). Explicit formulas, describing the maximum percent thinning and the forming time for channel parts formed by the SPF process as a function of eight designs and forming parameters, were derived. The formulas are good approximations of those obtained by finite element simulation analyses and physical experiments. Thinning of the channels was influenced most by the component aspect ratio (height versus width) and entry radius at top of the channel forming tool. The forming time was most influenced by strain rate, aspect ratio and tool bottom radius. A design domain can be established to avoid excessive thinning. The Taguchi design-of-experiment method was applied to select parameter combinations, and the MARC finite element code was used to conduct sectional analysis for various combinations.

Massive Parallel Laser Shock Peening: Simulation, Verification, and Analysis

Laser shock peening (LSP) is a surface treatment process to improve the surface integrity of metallic components. The nearly pure mechanical process of LSP results in favorable surface integrity such as compressive residual stress and improved surface material properties. Since LSP is a transient process with laser pulse duration time on the order of 40 ns, real time in-situ measurement of laser/material interaction is very challenging, if not impossible. A fundamental understanding of laser/material interactions is essential for LSP planning. Previous finite element simulations of LSP have been limited to a single laser shock location for both two and three dimensional modeling. However, actual LSP are performed in a massively parallel mode which involves almost simultaneous multi-laser/material interactions in order to induce uniform compressive residual stress across the entire surface of the workpiece. The massively parallel laser/material interactions have a significant compound/interfering effect on the resulting surface integrity of the workpiece. The numerical simulation of shock pressure as a function of time and space during LSP is another critical problem. The purpose of this paper is to investigate the effects of parallel multiple laser/material interactions on the stress/strain distributions in the workpiece during LSP of AISI 52100 steel. FEA simulations of LSP in single and multiple passes were performed with the developed spatial and temporal shock pressure model via a subroutine. The simulated residual stresses agree with the measured data in nature and trend, while magnitude can be influenced by the interactions between neighboring peening zones and the locations of residual stress measurement. Design-of-experiment (DOE) based simulations of massive parallel LSP were also performed to determine the effects of laser intensity, laser spot size, and peening spacing on stresses and strains. Increasing the laser intensity increases both the stress magnitude and affected depth. The use of smaller laser spot sizes decreases the largest magnitude of residual stress and also decreases the depth affected by LSP. Larger spot sizes have less energy attenuation and cause more plastic deformation. Spacing between peening zones is critical for the uniformity of mechanical properties across the surface. The greatest uniformity and largest stress magnitudes are achieved by overlapping of the laser spots.