Setup adjustment for discrete-part manufacturing processes with asymmetric cost functions

This paper presents a feedback adjustment rule for discrete-part manufacturing processes that experience errors at the setup operation which are not directly observable due to part-to-part variability and measurement error. In contrast to previous work on setup adjustment, the off-target cost function of the process is not symmetric around its target. Two asymmetric cost functions—constant and quadratic functions—are considered in this paper. By introducing a bias term in the feedback adjustment rule, the process quality characteristic converges to the optimal steady-state target from the lower cost side of the cost function. This minimizes the off-target loss incurred during the transient phase of adjustment. A machining application is used to illustrate the proposed adjustment procedure and to demonstrate the savings generated by the proposed feedback adjustment rule compared to an adjustment rule due to Grubbs and to an integral controller. It is shown that the advantage of the proposed rule is significant when the cost of the items is high, items are produced in small lot sizes and the asymmetry of the cost function is large.     

Product complexity and design of inspection strategies for assembly manufacturing processes

In the manufacturing field, the assembly process heavily affects product final quality and cost. Specific studies, concerning the causes of the assembly defects, showed that operator errors account for high percentage of the total defects. Also, models linking the assembly complexity with the operator-induced defect rate were developed. Basing on these models, the present paper proposes a new paradigm for designing inspection strategies in case of short-run productions, for which traditional approaches may not be carried out. Specifically, defect generation models are developed to get a priori predictions of the probability of occurrence of defects, which are useful for designing effective inspection procedures. The proposed methodology is applied to a case study concerning the assembly of mechanical components in the manufacturing of hardness testing machines.     

Inspection procedures in manufacturing processes: recent studies and research perspectives

Quality inspections are performed in almost every production system to prevent nonconforming products from reaching final customers or end users. Quality inspections are typically performed referring to specific inspection procedures, depending on the production process. Two general inspection paradigms may be identified: online inspection and offline inspection. These are differentiated by the way in which inspections are made. The paper presents a recent survey on new studies on inspection procedures for both paradigms. The main novelty of the study is the identification of new research perspectives in such a highly explored field. New schemes of analysis allow highlighting the research areas which are not adequately covered by the literature. A brief examination of some bibliometric aspects is also proposed.     

A quasi-optimal inspection strategy for leased equipment

This paper presents a quasi-optimal inspection policy for equipment that is leased for a given period and whose failures can be detected only through inspections. Maintenance including inspections and replacements is entrusted to the lessor. Whenever inspection reveals that the equipment is in failed state, it is replaced (or restored to a state as good as new). In case the average downtime between failures and their detection exceeds a contractual pre-specified duration, a penalty is incurred by the lessor. The proposed mathematical model and numerical algorithm allow finding a quasi-optimal sequence of inspection instants (θ₁*, θ₂*,?…?, θ_N*) which minimises the expected total cost incurred by the lessor over the lease period L. A numerical example is presented and the obtained results are discussed. We investigate numerically the effect of the variation of the downtime penalty cost, the inspection cost, the lease period length, and the equipment reliability on the quasi-optimal inspection policy to be adopted by the lessor.     

Allocating solder-paste printing inspection in high-volume electronics manufacturing

The paper describes an optimization model for allocating solder-paste printing inspection that explicitly considers the economic tradeoff between board yield and inspection accuracy. The paper also shows that the use of a heuristic solution method for solving the post-printing inspection allocation model is effective and efficient for high-volume electronics manufacturing. The model has been developed using real production and visual inspection data provided by a high-volume electronics manufacturer located in Huntsville, AL. In addition, randomly generated problems are used to evaluate the performance of the proposed heuristic. Results from a large case study show that when compared with a full post-printing inspection, the heuristic approach provides a solution that can increase the total expected gains by 15%.     

Optimization and validation of manufacturing processes

Validation in the definition adopted by a Joint FIP Committee means that every essential operation in the development, manufacture and control of pharmaceutical products is reliable, reproducible and capable of providing the desired product quality if stipulated production instructions and control procedures are followed.

A pre-requisite for, and an integral part of process-validation is that people, premises and equipment should be qualified. In other words, validation activities rely upon the check of technical and physical parameters when measuring devices are being calibrated, equipment is being qualified as well as on chemical, physical and biological parameters when processes are being Validated.

As we know, validation starts with planning a new plant, a new machine or equipment as well as with the development of a new or changed product.

This way of development from the laboratory trial and the clinical trial until the production phase has to guarentee the manufacture of products conforming to the desired profile.

According to a new draft guideline prepared by the FDA this year, drug products which are produced for clinical trials have to comply with the GMP - regulations. For example, the drug product must be produced in a qualified facility and the process must be validated. This means that manufacturing processes for clinical trials should be validated at the end of the development phase, as soon as processes are at least partially optimized, even if scaling up has not yet been completed.

The results of all development studies i.e. the use of equipment, the tolerances of physical parameters in the manufacturing process and the approved specification of starting materials being summarized in such a validations-report, the latter mostly seems to be an optimization-report. This can be of special value when scaling up in the production facility is completed.

As far as a sufficient number of clinical trials batches are manufactured according to an approved procedure this process can be validated prospectively. The results of this validation as well as the Know-how gained during optimization provide the basis for the validation of production conditions.

The organization of our validation activities in the manufacture of sterile and nonsterile drug products will be described in this presentation and some examples of process-validation will be given.     

Robust manufacturing inspection and classification with machine vision

This paper presents and compares methods for inspecting products using machine vision systems. This research compares the Mahalanobis Taguchi System (MTS) with a method based on principal component transformation and multi-modal overlap methods, and which is called the Principal component Feature overlap Measure (PFM). In an example application, the PFM achieves significantly higher Signal/Noise-ratios (+80 dB) and equal or better classification performance than MTS with a lower number of classification features (-75%).     

Optimization and validation of manufacturing processes

Abstract

Validation in the definition adopted by a Joint FIP Committee means that every essential operation in the development, manufacture and control of pharmaceutical products is reliable, reproducible and capable of providing the desired product quality if stipulated production instructions and control procedures are followed.

A pre-requisite for, and an integral part of process-validation is that people, premises and equipment should be qualified. In other words, validation activities rely upon the check of technical and physical parameters when measuring devices are being calibrated, equipment is being qualified as well as on chemical, physical and biological parameters when processes are being Validated.

As we know, validation starts with planning a new plant, a new machine or equipment as well as with the development of a new or changed product.

This way of development from the laboratory trial and the clinical trial until the production phase has to guarentee the manufacture of products conforming to the desired profile.

According to a new draft guideline prepared by the FDA this year, drug products which are produced for clinical trials have to comply with the GMP - regulations. For example, the drug product must be produced in a qualified facility and the process must be validated. This means that manufacturing processes for clinical trials should be validated at the end of the development phase, as soon as processes are at least partially optimized, even if scaling up has not yet been completed.

The results of all development studies i.e. the use of equipment, the tolerances of physical parameters in the manufacturing process and the approved specification of starting materials being summarized in such a validations-report, the latter mostly seems to be an optimization-report. This can be of special value when scaling up in the production facility is completed.

As far as a sufficient number of clinical trials batches are manufactured according to an approved procedure this process can be validated prospectively. The results of this validation as well as the Know-how gained during optimization provide the basis for the validation of production conditions.

The organization of our validation activities in the manufacture of sterile and nonsterile drug products will be described in this presentation and some examples of process-validation will be given.     

Theory and practice of manufacturing strategy

This paper first proposes a methodology for manufacturing strategy development based on a critical review of the theory of manufacturing strategy. The methodology captures the essential factors that must be considered, and the steps that must be taken, by a firm attempting to design a viable manufacturing strategy. An exploratory study of the process of formulating and implementing manufacturing strategy practised by three firms is conducted. Their experiences in the manufacturing strategy process are reported and analysed. While the practice of each firm is different, the process of manufacturing strategy formulation seems to be in line with the conceptual models discussed in the literature. Our findings offer some evidence that manufacturing is slowly shedding its image as the ‘missing link’ in corporate strategy. While managers of the studied firms are fully aware of the competitive advantages that manufacturing can provide, they are not totally committed to articulating a manufacturing strategy because of concerns about its successful implementation. It is proposed that further research on manufacturing strategy focus on such implementation issues as the infrastructure, corporate culture, performance measurements, decision-making and managerial styles.     

A coordination strategy for distributed multi-agent manufacturing systems

This paper proposes a distributed multi-agent approach for dynamic part routing in automated manufacturing systems. In particular, each part in the system is associated to an intelligent software agent that must select its next destination autonomously (i.e. ignoring the actions of the other agents) and in real time (i.e. at each time it completes an operation on a workstation). Differently from other existing approaches, we overcome the typical myopia of negotiation algorithms based on dispatching rules by allowing the part agents to take decisions not only about the imminent operation, but also for the subsequent ones. The anticipated decisions are transmitted to workstation agents, which are also designated to detect and resolve conflicts by modifying part agents’ decisions. To describe the single agents and their interaction schemes in a formal way, we take advantage of DEVS discrete-event modelling tools, which also allow us to develop a detailed simulation platform for our multi-agent system. The simulation experiments obtained on a detailed model of a manufacturing system derived from the literature confirm the effectiveness of the proposed approach.     

A freeform surface manufacturing approach by integration of inspection and tool path generation

Freeform surfaces have been widely used in various engineering applications. Increasing requirements for the accuracy of freeform surfaces have led to significant challenges for the manufacturing of these surfaces. A method for manufacturing of freeform surfaces is introduced in this paper by integrating inspection and tool path generation to improve manufacturing quality while reducing manufacturing efforts. Inspection is conducted by comparing the digitised manufactured surface with the design surface to identify the error regions. In this new inspection technique, the areas on the manufactured surface that are beyond the design tolerance boundaries are used as the objective function during the localisation process, in order to minimise post-inspection machining efforts. The tool path generation methods are then selected based on the geometric characteristics of the identified error regions, for creating tool paths to remove the errors. Computational efficiency, machining efficiency, and quality are considered in this integrated method.     

A heuristic approach to the formulation of manufacturing strategy

In this paper an attempt is made to define and analyse the critical subsystems relationships within a manufacturing strategy. For this purpose the whole production function is described as a pressurized Venturi system in an effort to clarify complex input-output and control relationships within a typical batch manufacturing environment. The value of scheduling methods is also discussed with attention directed towards critical value added stages and throughput time in the manufacturing process.     

A strategy for the risk-based inspection of pressure safety valves

The purpose of a pressure safety valve (PSV) is to protect the life and safety of pressure vessels in a pressurized system. If a weakened PSV fails to function properly, a catastrophic event might occur if no other protective means are provided. By utilizing the as-received test data and statistical analysis of the aging conditions of PSVs in lubricant process units, a risk-based inspection (RBI) system was developed in this study. First of all, the characteristics of PSV were discussed from the practical viewpoint of engineering inspection and maintenance. The as-received test data, which shows obvious PSV damage, will be separated from the data used in the following statistical analysis. Then, the relationship between the aging conditions and the corresponding PSV parameters was analyzed by using the statistical technique—analysis of variance (ANOVA). Finally, a strategy for semi-quantitative RBI is proposed. Also, a definitive estimated inspection interval for every PSV is suggested. The outcome indicated most of the risks result from a few PSVs, for which the corresponding inspection intervals will be shorter than the 2 years in accordance with relative standards and local government regulations.     

Group inspection of dependent binary processes

We consider serially dependent binary processes, how they occur in several fields of practice. If such a process cannot be monitored continuously, because of process speed for instance, then one can analyze connected segments instead, where two successive segments have a sufficiently large time‐lag. Nevertheless, the serial dependence has to be considered at least within the segments, i.e. the distribution of the segment sums is not binomial anymore. We propose the Markov binomial distribution to approximate the true distribution of the segment sums. Based on this distribution, we develop a Markov np chart and a Markov exponentially weighted moving average (EWMA) chart. We show how average run lengths (ARLs) can be computed exactly for both types of chart. Based on such ARL computations, we derive recommendations for chart design and investigate the out‐of‐control performance. A real‐data example illustrates the application of these charts in practice. Copyright © 2008 John Wiley & Sons, Ltd.     

A survey of the application of gamma processes in maintenance

This article surveys the application of gamma processes in maintenance. Since the introduction of the gamma process in the area of reliability in 1975, it has been increasingly used to model stochastic deterioration for optimising maintenance. Because gamma processes are well suited for modelling the temporal variability of deterioration, they have proven to be useful in determining optimal inspection and maintenance decisions. An overview is given of the rich theoretical aspects as well as the successful maintenance applications of gamma processes. The statistical properties of the gamma process as a probabilistic stress-strength model are given and put in a historic perspective. Furthermore, methods for estimation, approximation, and simulation of gamma processes are reviewed. Finally, an extensive catalogue of inspection and maintenance models under gamma-process deterioration is presented with the emphasis on engineering applications.     

Neuro-fuzzy control of complex manufacturing processes

A scheme for intelligent optimization and control of complex manufacturing processes is presented. The underlying nonlinear process is modelled by artificial neural networks and process control is performed by fuzzy logic. Fuzzy rules are automatically generated from the trained neural networks through a novel rule generation mechanism and fuzzy control is performed by Mamdani implication. Simulation results show that the proposed approach can provide a robust and accurate way of controlling complex processes without comprehensive models or knowledge about the process.     

制造业发展中的问题及对策

通过对制造业发展中的一些问题分析,依据制造业的发展规律,探索和研究制造业发展的策略。     

Modelling robustness in serial multi-stage manufacturing processes

The study of robustness in single-stage manufacturing has been explored by a large number of researchers and practitioners. However, modelling of robustness in multi-stage manufacturing using multivariate data is seldom used. The aim of this paper is to develop a methodology to model process robustness in a serial multi-stage manufacturing system. Combining statistical regression, Taylor series expansion, the root-sum-squares method and a variation model, the methodology proposes a measurement system for robustness. The resulting metric, while quantifying robustness, measures absorbed and transmitted variations across the stages of a manufacturing process. Using the methodology in a serial two-stage worm gear manufacturing process, the levels of robustness and both absorbed and transmitted variations are determined, thus identifying significant variations across manufacturing stages. The details of this application with the types of corrective actions as required for minimisation of process performance deterioration are presented.     

An optimization model for selective inspection in serial manufacturing systems

This paper describes an optimization model for allocating inspection efforts at each stage in a serial multi-stage assembly line. The model explicitly considers the economic tradeoff between product yield and inspection accuracy. The paper also shows that the use of a heuristic solution method, simulated annealing, is effective and efficient for solving the inspection allocation model. Problem instances have been developed using real production and visual inspection data provided by a local high-volume electronics manufacturer. In addition, randomly generated problems are used to evaluate the performance of the proposed heuristic.