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In assembly process control and design optimization, it is critical to establish a mathematical model that describes the relationship between the dimensional quality of the final product and the various process parameters (e.g., the fixture layout and locator position deviation). This article presents a surrogate modeling methodology for multistage assembly processes to characterize the relationship between fixture layout and product dimensional quality. The mathematical structure of the model is derived from a physical analysis based on first principles and then the parameters of the model are identified using data horn computer experiments. The resulting surrogate model can enable fixture layout optimization in process planning. A comprehensive case study of a multistage assembly process is also presented to demonstrate the effectiveness and high fidelity of the developed method. Keywords: Surrogate modeling, variation propagation, multistage assembly, Notation [t.sub.i] = coordinates of the ith locator in a reference co-ordinate system; [v.sub.i] = small deviations of the ith locator from its nominal positions; U = the small tolerance [...]

This paper presents a 3D finite element (FE) model of a thread forming screw assembly process based on the ABAQUS 6.5.4 Explicit software program. The model consists of two principal elements: an M10 x 12 thread forming screw and a lower 4 mm plate into which the screw taps its threads. The aim was to develop a robust industrial dimensioning tool; the model can be extended to establish the preload and investigate other types of assemblies. A 45 deg sector, which represents 1/8 of the joint, was modeled to maintain a good compromise between calculation time and an accurate representation of the thread forming process. The intent of the study was to analyze the material flow throughout the thread forming process; a parametrical study was also conducted to identify the most influential process parameters. To validate the model, FE numerical simulation results are compared with published experimental results. The study shows that the lead hole diameter has an important influence on the screwing torque. [DOI: 10.1115/1.3160377] Keywords: thread forming screws, finite element simulations, chipless assembly, tapping

Based upon basic drivers for the flow time, a lumped parameter model for a manufacturing line has been derived by using Kingman's approximation. The lumped parameter model for the flow time consists of a workstation and delay time. The workstation is characterized by the effective process time of the bottleneck workstation and the weighted sum of the coefficients of variation of all workstations. The delay time is determined by the sum of all effective process times of the nonbottleneck workstations. The advantage of the application of the lumped parameter model is that the variability of the total line is determined by a measurement at the operating point of the actual manufacturing line. This variability depends upon the operating point. Examples show that this dependency is not too strong for lines with a distinct bottleneck workstation in the actual line. From the derivation of the lumped parameter model it can be concluded that an improvement of the effective process time of the bottleneck workstation of the line results in an increase of the total variability of the line. This variability can be reduced by either reducing the variability of all workstations or the effective process times of the nonbottleneck workstations. Index Terms--Lumped parameter model, manufacturing systems, performance, variability.

Much of the previous research on unpaced production lines with variable processing times has addressed either the issue of the allocation of work to the stations or the allocation of storage space to the buffers between stations. Our focus is instead on the simultaneous optimization of the workload allocation and the buffer allocation. We use a basic cost-based model that includes both revenue per unit of throughput and cost per unit of buffer space. Using both exponential and Erlang processing times, exact numerical results are obtained for the underlying Markov chain for cases where the number of states range up to over 2000 000. We investigate how the bowl phenomenon for workload allocation and the storage bowl phenomenon for buffer allocation interact when performing both allocations simultaneously. We also find counterexamples to a conjecture previously published in the literature that a balanced buffer allocation is optimal when the total number of buffer spaces is an integer multiple of the number of buffers., 1. Introduction Because of the fundamental role of unpaced production (or assembly) lines in modern industry, considerable research has been conducted on how to improve their efficiency. Much of the [...]

A mechanistic model for the micro-endmilling process is developed that explicitly accounts for the different phases while machining heterogeneous materials. It is shown that frequencies in the cutting force signal higher than those that can be explained by the kinematics of the process can be explained by considering the multiple phases in the material. Experiments are performed on two compositions of ductile iron, pure ferrite and pearlite workpieces. These experiments show that the nature of the variation in the ductile iron cutting force signals can be attributed to the mixture of the phases. Additionally, simulation studies show that the frequency component of the variation is related to the spacing of the secondary (ferrite) phase and the magnitude of this component is determined by the size of the secondary phase particles. [DOI: 10.1115/1.1556402]

Flexibility is evaluated in terms of production and operations and across hierarchical service levels. The measure developed to evaluate flexibility is characterized by an ordinal scale and general application to account for various flexibility factors and also integrates loss of goodwill. For multi-criteria situations, such a measure must consider both short- and long-term costs that depend on the expressed level of flexibility.

A stochastic, single-stage, single-product functioning under a Materials Requirements Planning (MRP) control is studied. MRP was traditionally based on a deterministic production system. In the fixed MRP system, production and inventory is done at a fixed basis so that a single-stage production occurs. Replacement of products is done only after one is finished. However, in the stochastic environment, production and inventory is done at random, replacement is done only when deemed necessary.

In this paper, a system-theoretic approach to bottlenecks in Markovian production lines is introduced and analyzed. The approach is based on the sensitivity of the system production rate to machines' reliability parameters. Using this approach, definitions of bottlenecks are introduced, methods for their identification are developed, and their implications for production automation and preventative maintenance are discussed. Index Terms - Markovian statistics of breakdowns, production bottlenecks, production systems, unreliable machines.

Understanding bottom-hole assembly (BHA) dynamic phenomena remains a critical drilling systems issue due to the cost of potential failures. Many studies have provided useful insight into drillstring dynamics. This study extends previous efforts by providing a novel BHA model which accounts for several critical response factors and can be augmented to address a variety of other effects; new data from an experimental study regarding damping are presented. The proposed model represents the transfer function of the drillstring in terms of its natural modes and properly incorporates several factors critical to BHA dynamic response prediction, including frequency-dependent fluid added mass, and nonlinear wellbore constraints. Results from pertinent numerical studies are presented.

An assembly sequence planner is a system which, given a description of an assembly to be manufactured, identifies subassemblies and generates high-level plans for the construction of the each subassembly, including the final assembly. Previous research has shown that feasible plans can be efficiently produced for large assemblies, but the generation of good plans has met with less success. Not only are there difficulties in defining "good plans," but all published methods for finding good plans have computational complexities that make them unlikely to be practical for large assemblies. This paper shows that representing an assembly as a hierarchy of assembly structures can overcome many of these difficulties. A planner is described which uses the structure hierarchy both as a framework for structure-dependent definitions of a good plan, and as a tool for finding good plans more rapidly by using high-level expert advice, by reusing subplans for repeated substructures, and by not fully optimizing the plan. Analytical and experimental results are presented to demonstrate the effectiveness of the approach.

The characterization of production lines and transfer lines by queueing network models is considered. Specifically, the queueing network models in the literature are classified according to their assumptions into exact results, approximate, continuous part flow models. Exact result models may be of the closed-form, state or holding time type, depending on the approach. Likewise, approximate models may be obtained via the phase-type and generalized expansion method.

An approximation method is developed for computing the the average throughput of a K-station production line with exponential service times, manufacturing blocking and no intermediate buffers between adjacent stations. The holding time model method is utilized. The applicability of the method is due to its capacity to handle the case of workstations with different mean processing times. By applying the method to the balanced lines case, a simple formula can be used to provide very good results.

This paper deals with models for flow management problems in flexible assembly systems (FAS's). The system consists of a set of machines that must perform the assembly of a number of parts, possibly of different types. Each part type requires a set of operations; the precedence relations among the operations are specified by an assembly tree. Machines are provided with limited-capacity tool magazines and a finite buffer for holding parts. Each machine can be tooled to perform only a particular subset of the operations required by the whole process. One problem is that of finding a feasible assignment of operations to machines and a feasible schedule of the subassemblies in order to minimize the completion time of all of the parts. In this paper, the problem is analysed as a case of pipelined assembly, i.e., when the FAS is characterized by a serial transportation system (flow line) and there exists a dominating path in the assembly tree. Typically, this happens when there is a main pallet and all of the other components are assembled directly on it in a given sequence. We present polynomial-time dynamic programming algorithms for solving the problem for both single-type and multi-type production. The approach is more general than typical ALB algorithms.

The three-station serial line is a fundamental building block of many complex production systems. In this paper we develop methods for predicting the throughput of unbalanced three-station serial lines. We model the variability of processing times using a variety of probability distributions that spans the range of variabilities encountered in practice. We develop procedures for approximating throughput, for any allocation of total mean processing time, based on the throughput of a small number of easily analyzed cases.

From the concept of designing for automation, a system modeled from simple part-mating is proposed for helping automating the fine motion control phase of assembly operations. The proposed system consists of three subsystems. The first subsystem is a part-mating model categorized from different mating geometric constraints of simple parts. The second subsystem is a coding system, named Structured Assembly Coding System (SACS), that codes different part-mating tasks with different levels of geometrical constraints. From this coding system, specific part-mating types can be identified for different tasks of assembly operations. Conversely, constraint configurations for each part-mating task can also be generated from the proposed part-mating model. After constraint configurations are identified for an assembly operation, the third subsystem is to automate an assembly operation by deducing the compliance control strategies. The proposed system is demonstrated through a case study of pump assembly. The actual implementation of such an automated assembly will be our future work.

We present a novel method for "what's next" scheduling of semiconductor manufacturing lines based on the deterministic fluid network model of Chen and Yao [2]. By "what's next" scheduling we mean specifying the order in which jobs are processed at each tool group. The approach we take here is first to determine how to allocate tool capacity among competing job types by solving a series of linear and quadratic programming problems related to the fluid model and then to specify a "What's next" scheduling algorithm designed to track these capacity allocations. The primary advantage of our approach is that it gives rise to a dynamic schedule which is based on global rather than local state information and which is responsive to stochastic changes in the line including tool incapacitation events and operator unavailability. This is in contrast to many other scheduling rules, such as first come first served and closest to completion which are essentially static rules based on local information. In addition to describing the scheduling algorithm, we present some theoretical results about the fluid model that have important implications in the context of semiconductor manufacturing as well as some preliminary simulation results comparing the fluid model to other scheduling policies.

This article examines the use of cladistic analysis in historiography, focusing on an evolutionary model of automobile manufacturing factories. Topics include the history of automotive production strategies and how automation enabled large-scale production.

The objective of this paper is to develop a methodology for customizing pull control systems, replacing traditional control systems such as Kanban, Conwip, and Base Stock. The basic principle is to start with a pull control system that connects each stage of a given production line with each preceding stage; next, the optimization of the corresponding simulation model shows which of these potential control loops are actually implemented. The result of this methodology may be one of the traditional systems, but it may also be one of the following three new types: (1) the total line may be decomposed into several segments, each with its own classic control system, (2) the total line or its segments may combine different traditional systems, or (3) the line may be controlled through a new type of control system. Indeed, these three systems are found in a simulation experiment with a set of twelve production lines. These twelve lines are selected through a statistical design with ten factors that characterize production lines. Keywords: production control systems; heuristic optimization; simulation

An important aspect in recycling and reuse for environmentally conscious manufacturing is disassembly. Although disassembly systems contain the same basic elements as assembly systems, the disassembly problem differs significantly from the assembly problem due to the fact that the incoming disassembly product is not controlled. In addition, complete dismantling of products is not necessarily required for disassembly, whereas assembly builds a product completely. This paper describes a model for automated disassembly that accounts for workcell interaction and used product constraints. The model provides an essential means to determine, in real-time, the next component for disassembly using the knowledge of the product design and sensor feedback minimizing the steps to remove goal components. Sets of components for removal were resolved by minimizing setup time for disassembling the component. Given the model, a controller for product disassembly is defined that can account for missing and known replacement components. The controller can recover from unknown replacement components and jammed components when alternate removal sequences exist to meet the cell goal. Two case study examples are presented and experimentally simulated. Simulation results based on real product, vision sensor measure, and process input are presented and discussed. It is expected that the concepts demonstrated through these case studies can provide useful insights into other mechanical assemblies. Index Terms--Assembly system, disassembly, product modeling, supervisory control, workcell programming.

The relevant issues pertaining to the system design of electronic assembly lines in printed circuit board manufacturing environments were examined using a mathematical programming model. The proposed algorithm considers the operational trade-offs associated with the principal design components of such assembly lines, namely, mini-line, flexible flow line and hybrid line designs. A set of managerial guidelines for choosing the appropriate design for electronic assembly lines is presented.

Markovian models of discrete materials flow production systems were studied, particularly the transient properties of a production line. Specifically, mean and variance of the number of parts produced in a given time period conditioned on an arbitrary initial condition were determined by applying a Markov reward model. Closed-form expression for the variance of the output from a single unreliable station was derived to demonstrate the process. Then, variance of the output from a general two-station production line with a finite buffer was determined through a set of recursive equations that take advantage of the special structure of the probability matrix.