Non-linear Process Plans Research Articles

Multi-objective optimisation in flexible assembly job shop scheduling using a distributed ant colony system

This paper studies the production scheduling problem in a flexible manufacturing system with two adjacent working areas, whose products are incorporated with flexible non-linear process plans and assembling operations. The basic parts are produced in one area before they are transported to the other area for assembly. The assembling structures of products are either flat or multi-levelled. Sequence-dependent setup times of operations and transition times of jobs between machines are considered separately from processing times. Lot streaming is considered beforehand such that each job represents a basic part instead of a batch of identical parts. Identical subassemblies are shared by all possible assembling operations, instead of being pre-associated with any product. Makespan, total tardiness and total workload are taken as objectives to be optimised. We propose a distributed ant colony system to solve the problem and explore the Pareto front. The approach is first compared with other methods, using several sets of hypothetical test cases with different sizes and complexities; then, it is applied to solve a ball valve production scheduling problem under different scenarios. We show that the proposed approach outperforms most of the other methods for the tested problems, especially for large-scale instances, making it a valuable and competitive approach for solving practical production scheduling problems.

Flexible Assembly Job-Shop Scheduling With Sequence-Dependent Setup Times and Part Sharing in a Dynamic Environment: Constraint Programming Model, Mixed-Integer Programming Model, and Dispatching Rules

This paper studies the flexible assembly job-shop scheduling problem in a dynamic manufacturing environment, which is an exension of job-shop scheduling with incorporation of serveral types of flexibilies and integration of an assembly stage. Each product is assembled from several parts with nonlinear process plans with operations involving alternative machines. Setup times are sequence dependent and serparately considered from processing times. Part sharing is fully allowed such that they can be used for the assembly of any possible product, rather than being preassociated to a specfic product. We employ constraint programming and mixed-integer linear programming to formulate the problem. Besides, several dispatching rules with machine feedback machanism are developped. Experimental studies are conducted based on test case problems with different scales and complexities. It is found that constraint programming is the most efficacious approach, whose solution fitness outperforms mixed-integer linear programming as well as all dispatching rules in both static and dynamic cases. On the other hand, dispatching rules are simple to implement, among which the “earliest completion time” rule is the most favourable. A real-time scheduling/rescheduling system has been constructed for the implementation of the proposed approaches to solve practical problems in production.

Cloud-based adaptive process planning considering availability and capabilities of machine tools

Disturbances on manufacturing shop-floors and the increasing number of product variants necessitate adaptive and flexible process planning methods. This paper proposes a service-oriented Cloud-based software framework comprising two services. The first service generates non-linear process plans using event-driven function blocks and a genetic algorithm. The second service, gathers data from shop-floor machine tools through sensors, input from operators, and machine schedules. An information fusion technique processes the monitoring data in order to feed the process planning service with the status, specifications, and availability time windows of machine tools. The methodology is validated in a case study of a machining SME.

Network part program approach based on the STEP-NC data structure for the machining of multiple fixture pallets

The adoption of alternative process plans, that is, process plans that include alternative ways of machining a workpiece, can improve system performance through a better management of resource availability. Unfortunately even if this opportunity is deeply analysed in literature, it is not frequently adopted in real manufacturing practice. In order to fill this gap, this article presents the network part program (NPP) approach for the machining of multiple fixture pallets. The NPP approach is based on the STEP-NC data structure which supports nonlinear sequences of operations and process flexibility. In the NPP approach, a machining system supervisor defines the machining sequences and generates the related part programs just before the execution of the pallet. This article provides an approach with high scientific value and industrial applicability based on the integration of new and existing process planning methods. A real industrial case study is considered in order to show that in real applications the final quality is unaffected by the change of the sequence of the operations due to the employment of nonlinear process plans. Since the results appear very encouraging, the proposed approach is a possible solution to accelerate the adoption of nonlinear process planning in real manufacturing practice.

A novel function block based integration approach to process planning and scheduling with execution control

In today's decentralised business environment, manufacturing enterprises are implementing advanced distributed manufacturing planning and control strategies to adapt to and win the fluctuating global market. Within the context, this paper presents a novel approach to the integration of process planning, scheduling and execution in dynamic machining shop floors. Based on the concept of distributed process planning (DPP), function blocks are adopted as information carriers to optimise and specialise the nonlinear process plans (NLPP) progressively throughout the three planning stages: supervisory planning, execution control and operation planning, with scheduling functionality integrated seamlessly. Architecture of DPP and function block based integration are proposed, followed by a system functional design using IDEF0 methodology. The advantages of adopting function block technology are demonstrated and recent research results as well as future directions are pointed out in this paper.

Elaboration and validation of AND/OR graph-based non-linear process plans for shop floor control

Feature-based process planning has been popular in academia and industry owing to its ability rigorously to integrate design and manufacturing. In spite of this benefit, feature-based process planning has been difficult to implement because it is not easy to extract even simple features from the design data automatically and efficiently. Furthermore, it is even more difficult to construct the temporal precedence relationships among the extracted features with regard to plan alternatives and sequence options. The objective here is to present elaboration and validation methodologies for AND/OR graph-based non-linear process plans that help users construct, validate or modify a controller-friendly process plan easily and efficiently. An elaborated process plan created by a CAPP or an experienced process planner should be validated with respect to various validation criteria, such as the shape of a finished part, feature interaction, feature interference, feature manufacturability and flexibility for shop floor control. For each validation criteria, the invalid indicator matrix proposed here can quantify the degree of invalidity of the process plan. The invalid indicator matrix will help the process planner fix and refine rapidly the elaborated process plan. The methodologies proposed will save cost and time in the production of a controller-friendly process plan. Initial results are promising.

A Schema for Flexile Equipment Control in Manufacturing Systems

In this work a methodology is proposed for increasing the flexibility of the control software of Flexible Manufacturing Systems (FMSs). This greater flexibility is required due to factors such as uncertain product demand, uneven distribution of shop load, and machine or cutting tool unavailability. In the proposed framework the following modules were developed: (a) an automated process planning module which generates non-linear process plans for a given part, considering the shop floor resource availability; the non-linear plans include both material handling and material processing information; (b) a planning module that linearises the process plan aiming at minimising the total manufacturing time of the parts; (c) a NC program generation module, which generates the NC program for the chosen CNC machine(s). In order to increase the flexibility of the control software even more, a resource model was devised and implemented, which provides the necessary resource information for the above modules. Each of these modules is described within this paper, and details about the part and process plan representation necessary for this implementation are also given. A case study is presented in order to show the capability of the methodology.

Methods to improve the response time of a CAPP system that generates non-linear process plans

Feature-based Computer Automated Process Planning applications often suffer from exponential growth of the search space and thus CPU time, with increasing complexity of a part. This paper will explain some methods that were used to improve the response time of a newly developed CAPP system that is capable of generating net-shaped process plans, called non-linear process plans, containing several alternatives. One method to improve the performance is called Opportunistic process planning. The approach consists of dividing the features into two sets: one set, called the important features, is used to generate a process plan; the other features, called non-important features, are added to the process plan afterwards. This generation method highly resembles the reasoning pattern of a human process planner. Another innovative method for performance improvement is called Feature grouping. This method combines features that have strong resemblance, and considers them as only one feature during the process plan generation. Other reasoning methods, described in this paper, are: combined variant/generative planning and constraint-based search. All of the above-mentioned methods allow us to reduce the search space significantly. The developments have been carried out in the framework of the Esprit project 6805, COMPLAN (Concurrent Manufacturing Planning and Shop Control for small batch production). The COMPLAN CAPP system is able to cover a wide workpiece spectrum (customizable towards specific needs). It has been intensively tested for three workpiece families (i.e. hydraulic valves, bending tool-knives and prismatic parts) of a pilot end-user, a producer of sheet metal machinery. The system can be easily extended towards other part spectra. Also the embedded process-planning knowledge is easy to configure or alter.

A collaborative process planning and scheduling system

Traditionally, process planning and scheduling have been rather separate activities within a company. Nowadays, the need for more flexible production and shorter production lead times urges for a close collaboration between these activities as a first step towards simultaneous engineering. This article describes the results of the ESPRIT project COMPLAN, which aims at the implementation of an integrated automatic process planning and scheduling system based on the concept of non-linear process plans. In addition to the use of NLPP for flexible load balancing and reactive rescheduling, a new collaborative approach is presented that is based on production constraints as a means to realize a feedback from scheduling to process planning. A process-planning kernel is described that integrates this concept of production constraints.

A CAPP System for Nonlinear Process Plans

Abstract Non-linear process plans are process plans which comprise different manufacturing alternatives Such non-linear process plans increase the flexibility of scheduling activities and allow to remedy quickly to disturbances in the workshop They are represented by Petn nets The automatic generation of a non-linear process plan is realised m different steps: - the feature based workpiece description is transformed into a non-linear sequence of operation steps: - the resources capable to manufacture : he specified operation steps, are determined. - the non-linear sequence is converted into a non-linear process plan which is directly usable for scheduling The developed CAPP system has been rested ‘or hydraulic components