A Complexity Code for Manufacturing Systems

A new coding system is introduced to classify manufacturing systems and capture the characteristics of the various pieces of equipment and the relationships among them within a manufacturing system, which contribute to their structural, time-independent inherent complexity. The manufacturing Systems Complexity Code (SCC) consists of fields representing equipment, such as machines, buffers and transporters, as well as their layout. Each field contains a string of digits, the value of which depends on the degree of structural, control, programming and operation complexity of theses entities. The developed coding system has many applications including manufacturing systems design, comparison and planning, assessment of their complexity and evaluation of redesign alternatives and trade-offs. The new coding system is described along with its applications and demonstration examples.

Modeling and Assessment of Porosity Effects on Mechanical Properties of Tissue Scaffolds

Mechanical properties of scaffolds are important for fabricating engineered tissues. However, localized mechanical properties of scaffold cannot be directly obtained from experiments. This study provides a solid modeling approach to simulate mechanical behaviors of alginate scaffolds with different porosity. A scaffold micro-domain has been modeled as made of sub-units, arranged in a sphere-based pore architecture. An expression to calculate porosity was also derived for the scaffold architecture. Finite element simulations of compressing alginate scaffolds were performed to evaluate the effect of porosity on quasi-static mechanical behavior. The developed FEA model is capable of computing scaffold strength and predicting localized mechanical behavior without destructive materials testing.

Overview of a Distributed Process Planning Approach Targeting Manufacturing Uncertainty

This paper presents an overview of our DPP (distributed process planning) approach, covering DPP concept, generic machining process sequencing using enriched machining features, process plan encapsulation in function blocks, and process monitoring enabled by the function blocks. A two-layer structure of Supervisory Planning and Operation Planning is proposed in DPP to separate generic data from machine-specific ones. The supervisory planning is only performed once, in advance, at shop level, whereas the operation planning is carried out at runtime at machine level. This dynamic decision-making is facilitated by a set of resource-driven algorithms embedded in the function blocks. The internal structures of typical function blocks are also introduced in the paper. The DPP approach and algorithms are further verified through a case study before drawing conclusions. It is expected that the new approach can largely enhance the dynamism of fluctuating job shop operations.

Three-Dimensional Finite Element Modeling of Drilling Processes

The three dimensional (3D) finite element modeling (FEM) and experimental validation of drilling are presented. The Third Wave AdvantEdge machining simulation software is applied for the FEM. It includes fully adaptive unstructured mesh generation, thermo-mechanically coupling, deformable tool-chip-workpiece contact, interfacial heat transfer across the tool-chip boundary, and constitutive models appropriate for process conditions and finite deformation analyses. The workpiece is modeled with a predrilled cone-shape blind hole to enable the early full-engagement of the whole drill point region to reduce the simulation time. Drilling experiments are conducted on the Ti-6Al-4V using a twist drill geometry. The calculated cutting force and torque are compared with the results of experiments with good agreement. Effects of process parameters on the stress and temperature distributions of the drill and workpiece are investigated in detail using the FEM.

Molding of Three-Dimensional Microcomponents

Traditional micromanufacturing has been developed for semiconductor industry. Selected micro electrical mechanical systems (MEMS) have been successfully developed and implemented in industry. Since current MEMS are designed for manufacture using microelectronics processes, they are limited to two-dimensional profiles and semiconductor based materials. Such shape and material constraints would exclude many applications that require biocompatibility, dynamic stress, and high ductility. New technologies are sought to fabricate three dimensional microcomponents using robust materials for demanding applications. To be cost effective, such microdevices must be economically mass producible. Molding is one of the promising replication techniques to mass produce components from polymers and polymer-based composites. This paper presents the development of a micromolding process to produce thermoplastic microcomponents. Mold design required precision fitting and was integrated with a vacuum pump to minimize air trap in mold cavities. Nickel and aluminum mold inserts were used for the study; their cavities were fabricated by combinations of available micromachining processes like laser micromachining, micromilling, micro electrical discharge machining, and focused ion beam sputtering. High and low density polyethylene, polystyrene polymers were used for this study. The effects of polymer molecular structures, molding temperature, time, and pressure on molding results were studied. Simulation of stress in the microcomponents, plastic flow in microchannels, and mold defects was performed and compare with experimental data. The research results showed that a microcomponent can be fabricated to the minimum size of 10 ± 1μm (0.0004 inch) with surface roughness <10 nm Rt. Molding of micro-size geartrains and orthopedic meso-size fasteners was completed to illustrate the capability of this process.

Effect of Substrate Temperature on Properties of Nano-Scale Functionally Graded Calcium Phosphate Coatings

The effect of substrate temperature and processing parameters on microstructure and crystallinity of calcium phosphate coatings deposited on heated substrates in an Ion Beam Assisted Deposition (IBAD) system are being studied. The experimental procedures include mechanical testing and film thickness measurements using bonding strength and profilometery. Cross-sectional scanning transmission electron microscopy (STEM) with energy dispersive X-ray spectroscopy (EDX) through the thickness of the film as well as scanning electron microscopy (SEM) with EDX at the top surface of the film was performed to evaluate the microstructure of the film. The coating crystallinity was studied through X-ray diffraction (XRD). The information gained from current analysis on the set temperature coatings will be used to refine the processing techniques of the Functionally Graded Hydroxyapatite (FGHA) coating.

A New Approach to G1 Biarc Approximations for Making Smooth, Accurate, and Non-Gouged Profile Features Using CNC Contouring

Extensive research on G1 biarcs fitting to free-form curves (i.e., Bezier, B-spline, and NURBS curves) has been conducted in the past decades for various purposes, including CNC contouring to make smooth, accurate profile features such as pockets, islands, and sides. However, all the proposed approaches only focused on the approximation errors and the biarc number, not on the radius of the individual fitting arc; so it could be smaller than the cutting tool, which would cause gouging during machining. This work, based on the tool radius pre-determined by the minimum size of the concavities of the design profile, proposes a new approach to approximating the profile with a G1 biarc curve in order to make smooth, accurate, and non-gouged profile features using CNC contouring. The significant new contribution of this work is a new mechanism that ensures all the concave arcs of the fitting curve are larger than the pre-determined tool and the fitting errors meet the specified tolerance. This approach can promote the use of G1 biarc tool paths in the manufacturing industry to make high precision profile features.

Radio Channel Characteristics of Zigbee Wireless Sensors in Machine Shop for Plant Floor Process Monitoring

Wireless sensors are envisioned to be useful for plant floor process monitoring with unprecedented flexibility and low costs, where data can be relayed via a wireless network formed among the sensors. Factory environments, however, are known harsh for radio communications. For sensor radios engineered with extremely low power and simple circuitry, the sensor radio channel characteristics must be identified for optimal network design and reliability assessment. In this paper, a preliminary radio channel measurement study was performed based on the wireless sensor pairs in normal communication at the 2.4 GHz Industrial, Scientific and Medical (ISM) band to assess the sensor radio channel properties in a university machine workshop. The effect of both stationary and moving (forklift) obstacles on the radio propagation in terms of the received signal power, bit error and packet error rates was studied. The effect of stationary obstacles was further analyzed against a simple path loss model to find the path loss exponent. A spectrum analyzer was also used to capture the noise backgrounds in free space and the machine shop, which shows significantly different radio activities among the investigated scenarios. The proposed channel measurement methodology through directly utilizing the sensor platforms will help future radio channel characterization studies in manufacturing plant floor environments.

Fault Failure Diagnosis for Compliant Assembly Structures Using Statistical Modal Analysis

This paper develops a new diagnostics methodology for N-2-1 fixtures used in assembly processes with compliant parts. The developed methodology includes: (i) the predetermined CAD-based dimensional variation fault patterns model; (ii) data-based dimensional variation fault model; and (iii) the fault mapping procedure isolating the unknown fault. The CAD-based variation fault pattern model is based on the piece-wise linear bi-partitioning of compliant part into deformed (faulty) and un-deformed regions. Data-based dimensional variation fault models are based on the statistical modal analysis (SMA) which allow to model part deformation with varying number of deformation modes. It is proved in the paper that these independent deformation modes are equivalent to the CAD-based faults models obtained in (i). The fault mapping procedure allows to diagnose the unknown fault by comparing the unknown fault variation pattern obtained from the SMA model with one of the predetermined CAD-based fault patterns. One industrial case study from an automotive roof framing assembly illustrates the proposed method.

Simultaneous Scalable-Reconfigurable Manufacturing System Design and Inventory Control Policy Decision Making

Scalable reconfigurable manufacturing systems (scalable-RMS) consist of standardized modular equipment that can be quickly added or removed to adjust the production capacity. Each modular machine, referred to as a scalable reconfigurable machine tool (scalable-RMT), is composed of identical modules that can be added to, or removed from the machine depending on its required throughput. In previous work, conceptual scalable-RMTs have been described. Additional scalable-RMTs are presented in this paper to highlight the applicability of this concept in manufacturing. As an extension to existing scalable-RMS literature, this paper incorporates multiple products in the system configuration design. Specifically, this paper proposes an integer programming based iterative algorithm for finding the minimum cost configuration of a multi-product system. It is shown that the proposed algorithm converges to the optimal solution under the majority of practical conditions. Then, a mathematical formulation to minimize the system investment and operational costs in a multi-product scalable-RMS is presented. A numerical example compares the solution obtained using the traditional approach of determining the system design and then the inventory control policy versus the proposed simultaneous approach. It is concluded that the simultaneous approach yields significant improvement over the traditional (decoupled) approach.