Fabrication Schedule Research Articles

Locating algorithm of steel stock area with asynchronous advantage actor-critic reinforcement learning

Abstract In the steel stockyard of the shipyard, the sorting work to relocate the steel plates already stacked to retrieve the target steel plate on the fabrication schedule is labor-consuming work requiring the operation of overhead cranes. To reduce the sorting work, there is a need for a method of stacking the steel plates in order of fabrication schedules when the steel plates arrive at the shipyard from the steel-making companies. However, the conventional optimization algorithm and heuristics have limitations in determining the optimal stacking location of steel plates because the real-world stacking problems in shipyards have vast solution space in addition to the uncertainty in the arrival order of steel plates. In this study, reinforcement learning is applied to the development of a real-time stacking algorithm for steel plates considering the fabrication schedule. Markov decision process suitable for the stacking problem is defined, and the optimal stacking policy is learned using an asynchronous advantage actor-critic algorithm. The learned policy is tested on several problems by varying the number of steel plates. The test results indicate that the proposed method is effective for minimizing the use of cranes compared with other metaheuristics and heuristics for stacking problems.

Rotation cycle time and delivery decision for a multi-item producer-retailer integrated system featuring overtime and random scrap

A multi-item producer-retailer integrated system featuring overtime and random scrap is studied. The objectives are to jointly decide the most economic rotation fabrication cycle time and distribution of products. In order to meet the increasing demands of diversified end items, production managers today need to plan a multiproduct fabrication schedule and to expedite both manufacturing and transportation times so that they can meet product demands as quickly as possible. Also, due to potential uncontrollable reasons, scrap items are generated randomly in a real fabrication process. To address the aforementioned issues, this study examines a multi-item producer-retailer integrated system featuring overtime and random scrap. We build a mathematical model to interpret the proposed multi-item producer-retailer integrated system which incorporates shipping and retailer’s holding cost. The Hessian matrix equations are used for solving the optimality of the system. Diverse important system information can now be exposed to backing managerial decision makings, which includes individual and combined influences of variations in particular system factor(s) (such as scrap rate and overtime related parameters) on the specific system performance.

A multi-item manufacturing system with an outsourcer and random defective items

This study examines a multi-item manufacturing problem with a single machine, an outsourcer, and random defective items. To cope with the increasing multi-product demands from global markets, modern manufacturing firms must make an efficient production plan to satisfy customer’s needs with quality goods and smooth the in-house fabrication schedule and utilization. Outsourcing is an effective option to avoid machine overloads and smooth fabrication schedules. Further, the fabrication of random defective products is inevitable because of unanticipated factors in real manufacturing environments. These products must be identified, separated and discarded to retain the desired quality of the finished lot. To address the above-mentioned concerns, this study develops a mathematical model to represent a hybrid stock refilling system, employs mathematical derivations to find long-run average system expenses, and uses an optimization technique to derive a closed-form common rotation time for this hybrid system. The results of this study show the individual and combined impacts of variations in outsourcing percentages and scrap rates on optimal rotation time and diverse core system parameters (such as machine utilization, specific cost component, etc.) to facilitate planning, controlling, and decision making in such a particular hybrid fabrication system.

Multi-Item Production Lot Sizing with Postponement, External Source for Common Parts, and Adjustable Rate for End Products

This study considers a multi-item production lot-size problem incorporating postponement, an external source for common parts, and an adjustable-rate for end products. Dealing with product variety, timely requirements, and limited in-house capacity has led production managers to seek manufacturing schemes and utilization-reduction strategies that can help them meet customer needs, smoothen fabrication schedules, and lower overall manufacturing expenses. We propose a two-stage manufacturing scheme. The first stage produces common parts for multiproduct incorporating a partial supply from an outside contractor to reduce utilization/uptime. Stage two fabricates all end products using an adjustable-rate to reduce the uptime further. We build a model to characterize the problem’s features and use optimization methods to derive the optimal rotation cycle time in order to help managers make cost-effective lot-size decisions and allow manufacturers to gain competitive advantages. A numerical illustration validates the model’s capability and applicability. This study makes two important contributions: (1) It offers a decision-support model for studying such a particular batch-size problem and deciding the optimal rotation cycle time, and (2) it identifies the individual/collective influence of dual uptime-reduction strategies on the operating policy and various performance indexes to help facilitate managerial decision-making.

Studying the effect of stochastic breakdowns, overtime, and rework on inventory replenishment decision

This study investigates the effect of stochastic breakdowns, overtime, and rework on the inventory replenishment decision. The overtime capacity and inevitable situations during the manufacturing process, such as the production of imperfect items and random breakdowns, are often considered in advance by production manager to smoothen fabrication schedules, maintain the desired quality, and reduce the impact from undesirable interruptions. This study builds a model to characterize these real features of a manufacturing process and derive the total relevant expenses of the system. Although a closed-form solution is unobtainable, a recursive algorithm is proposed to help find the optimal runtime for the batch fabrication plan. A numerical illustration shows how the proposed procedure and algorithm function. It also demonstrates the ability of the proposed model to reveal diverse crucial information regarding the individual and combined influences of deviations in overtime factors, the mean-time-to-failure, and rework- related variables, on the optimal replenishment runtime, total operating expenses, and different cost contributors. The research results will facilitate better decision-making aimed at increasing the competitive advantages of a manufacturing firm.

The Collective Influence of Component Commonality, Adjustable-Rate, Postponement, and Rework on Multi-Item Manufacturing Decision

The present study explores the collective influence of component commonality, adjustable-rate, postponement, and rework on the multi-item manufacturing decision. In contemporary markets, customer demand trends point to fast-response, high-quality, and diversified merchandise. Hence, to meet customer expectations, modern manufacturers must plan their multiproduct fabrication schedule in the most efficient and cost-saving way, especially when product commonality exists in a series of end products. To respond to the above viewpoints, we propose a two-stage multiproduct manufacturing scheme, featuring an adjustable fabrication rate in stage one for all needed common parts, and manufacturing diversified finished goods in stage two. The rework processes are used in both stages to repair the inevitable, nonconforming items and ensure the desired product quality. We derive the cost-minimized rotation cycle decision through modeling, formulation, cost analysis, and differential calculus. Using a numerical illustration, we reveal the collective and individual influence of adjustable-rate, rework, and postponement strategies on diverse critical system performances (such as uptime of the common part and/or end products, utilization, individual cost factor, and total system cost). Our decision-support model offers in-depth managerial insights for manufacturing and operations planning in a wide variety of contemporary industries, such as household merchandise, clothing, and automotive.

A hybrid finite production rate system featuring random breakdown and rework

To reduce the order response time or achieve optimal utilization, manufacturers often include an outsourcing alternative in their production plans. Further, undesirable machine breakdowns and nonconforming items produced during the in-house processes must also be effectively managed/corrected to adhere to the fabrication schedules and meet the desired quality level. This study addresses the aforementioned concerns by examining a hybrid finite production rate (FPR) system featuring: breakdown that follows the Poisson distribution, and rework/repair of all the nonconforming goods produced. A portion of the batch size is outsourced to an external supplier, who guarantees quality but at a higher unit cost than that incurred in-house. A mathematical model is explicitly built to represent the features of the proposed hybrid FPR system. We use the optimization approach and an algorithm to determine the optimal replenishing runtime that minimizes total costs; results are demonstrated through a numerical example and sensitivity analyses. Diverse crucial system information available to assist manufacturers in production planning includes the individual and joint influence of rework, outsourcing, and breakdown on: (a) variable rework cost; (b) the optimal runtime; (c) total system cost; (d) utilization; (e) detail of system's cost elements; and (f) other important system parameters.

Experiments of double curvature plate bending with induction heating and processing parameters investigation by computational analysis

plate bending with double curvature is an essential procedure in shipbuilding, which is also a bottleneck problem to restrict the fabrication schedule and dimensional accuracy. With the induction heating technology, plate bending with double curvature as saddle and sail types, was conducted experimentally. Meanwhile, due to the rated output power of induction heating, heat input as well as moving speed of induction heating coil has a significant influence on maximal temperature and final bending deformation. In addition, out-of-plane bending deformation with different patterns can be observed and their magnitudes were also measured by three-coordinate measuring machine (TMM). Computational analysis with thermal elastic plastic (TEP) and elastic FE approaches was then employed to investigate processing parameters of induction heating. Computed out-of-plane bending deformations have a good agreement with measurement about not only deformed shape but also magnitudes. Elastic FE computation with bending moment as input loading has much more obvious efficiency comparing to conventional TEP FE computation without loss of computational accuracy. Moreover, generation mechanism of bending deformation with different patterns was also examined and clarified with in-plane plastic strains caused by induction heating, which will be converted to shrinkage force and bending moment for plate bending.

Preliminary investigation on plate bending with multiple-line induction heating

Plate forming is an essential procedure in shipbuilding, which will influence the dimensional accuracy and fabrication schedule. Due to the advantages of induction heating for plate forming such as precision controlling, high level of automation, an experimental investigation for plate forming with multiple linear induction heating was carried out at first. With advanced 25 kW induction heating equipment and additional water cooling system, thermal cycles of several examined points during plate forming with induction heating was measured, and the influence of moving speed of induction heating coil on highest temperature of examined points was also investigated. Applying different heating pattern, plate with 6 mm in thickness will buckle as saddle shape due to the multiple-line heating in longitudinal direction and its generated large enough compressive force. Moreover, thermal elastic plastic (TEP) FE and elastic FE computational approaches were proposed and employed. Predicted out-of-plane bending deformations both have good agreement with measurement. Elastic FE computation with bending moment caused by induction heating as input load has effective advantage and high accuracy comparing to conventional thermal elastic plastic FE computation.

Research into the process of loading wood assortments by a tractor-mounted hydraulic manipulator of a tractor-trailer train

In order to gain competitive advantages, managers of present-day supply chain systems need to achieve critical operation goals, such as keeping flexible fabrication schedule, retaining product quality, maintaining timely delivery, and lowering overall operating costs. Inspired by these factors, this study developed a decision model for managers to investigate the joint impacts of quality-assured issues, overtime, and multi-shipment plan on optimal fabrication-shipment policy and on diverse system parameters of the economic production quantity (EPQ)-based supply chain system. An imperfect fabrication process producing perfect quality, repairable, and scrap items is assumed in the proposed system, along with assumptions of a flexible overtime schedule to partially expedite fabrication rate and a discontinuous multi-delivery policy for distributing end products. With a help from mathematical modeling and optimization method, the closed-form optimal fabrication-shipment policy is derived. A numerical example was employed to demonstrate applicability of our result and to expose critical managerial information of the system for supporting decision-making.

A BIM-based Supply Chain Integration for Prefabrication and Modularization

Prefabrication and modularization helps to reduce cost and schedule time for on-site activities. The use of Building Information Modeling (BIM) helps to improve collaboration and improve the construction process. The improved installation precision provided by BIM Model-Driven Prefabrication can decrease on-site labor time and increase productivity. Prefabrication, Modularization, and off-site construction transfers activities that would have been performed on site to earlier stages of the supply chain. The implementation of Just-In-Time (JIT) delivery transfers the costs and risks associated with inventory to the supplier. Construction Supply Chain Integration can help reduce cost and waste across the supply chain particularly for large and complex buildings. This paper presents a methodology that utilizes a BIM based construction supply chain integration to reduce cost and waste in the construction and offsite manufacturing processes. It utilizes the integration of BIM with the on-site schedule and the manufacturing or fabrication schedule of the different supply chain members. The methodology utilizes the onsite schedule, lead times of prefabricated elements or modules and the transportation logistics to help reduce cost across the supply chain. The information, material and cash flows as well as the transportation logistics is utilized in generating an optimized just-in-time delivery schedule for large and complex buildings. The optimized delivery schedule takes into account the variations in the on-site and off-site schedules to forecast delivery dates of precast elements or fabricated modules.

Dry-Machining of Aerogel Foams, CH Foams, and Specially Engineered Foams Using Turn-Milling Techniques

A new method has been developed to dry-machine foams. Most of these foams are at the lower end of what is considered machineable because of their density or foam composition. Excluding aerogel foams, the foams traditionally required a wax-fill process before surviving any machining forces. This new dry-machining method uses a technique called turn-milling and replaces the old wax-fill method that added several weeks to the fabrication schedule and uncertainty in the quality of the final part. The new method utilizes a computer numerical control gang-tool–style lathe that is set up with electric live-tooling spindles. The foams are dry-machined with the lathe main spindle turning in the opposite direction of the live-tooling spindle. This turn-milling technique reduces tool pressure and can accommodate heavier roughing cuts that produce much faster cycle times. With this new dry-machining method we are able to machine the entire foam target component in one operation, eliminating the need for another machining operation for finishing the backside.

조선소 WPS/PQR 관리 DB시스템 개발에 관한 연구

WPS/PQR is the essential documents for shipbuilding welding. WPS is the document containing the information related to welding procedure and PQR is the record of approval for welding procedure. Both documents should be approved by the ship owners and the classification societies. It is very important to manage these documents because the welding procedure using these documents could not be carried out before they are approved. Database is an useful tool to manage these documents. It can manage a number of documents and show the processing status of WPS/PQR documents. In this study, all documents related to WPS/PQR documents were investigated and analyzed in the viewpoint of DB. An appropriate DB system was designed for WPS/PQR and the related documents on the basis of CBD methodology. The DB system could make WPS/PQR documents easily and shortly. The grasp of the processing status of WPS/ PQR could help the good management of fabrication schedule in shipbuilding.

A study on degradation of germanium coating on Kapton used for spacecraft sunshield application

Sunshield membranes made of germanium‐coated black polyimide (GBP) or Kapton are often used on the reflector/transmitter antenna of satellites for thermal control applications. However, the germanium top layer is prone to degrade during ground storage and implementation. Hence, vacuum/inert gas‐sealed packaging is required for storing the membranes, followed by a staggered fabrication schedule as the shelf‐life of the GBP is identified as only ~6 months. In the present study, microstructural, thermo‐optical, and electrical properties along with X‐ray photoelectron spectroscopy (XPS) studies for evaluating oxidation states of the as‐received and degraded GBP films have been investigated thoroughly. The radio frequency (RF) loss behavior of both the films has also been studied for S band (2.5–3.5 GHz), Ku band (10.5–14.5 GHz), and Ka band (30–35 GHz). Copyright © 2015 John Wiley & Sons, Ltd.

Densification behaviour and two stage master sintering curve in lithium sodium niobate ceramics

The Master Sintering Curve (MSC) has received much attention in recent years due to its ability to predict sintering behaviour of a given powder and green body process regardless of its thermal history. In this paper MSC, based on the combined stage sintering model is constructed for one of the most important lead-free piezoelectric viz. lithium sodium niobate, Na1-xLixNbO3 (x=0.12, LNN-12), ceramic using shrinkage data. The present study has been carried out to understand and control the densification behaviour during pressureless sintering. Two distinct stages of densification have been observed en route to the upper limit to sintering temperature. The activation energies of densification for the two temperature ranges viz. 800–1150°C and 1150–1300°C were found to be 365kJ/mol and 2530kJ/mol, respectively, through the construction of MSC. The MSC should be useful in predicting the densification behaviour and the final density and for designing a reproducible fabrication schedule for the LNN-12 ceramics.

Assessment of Weld Embrittlement in A516 Steel Due to Multiple Repair Welds

A 3-million gallon petroleum storage tank was fabricated in the Midwest using A516 steel. The initial fabrication schedule had become compressed; welders worked hurriedly and did not produce good welds. Numerous welds had to be repaired via grinding and rewelding. The quality of the steel near the welds were questioned regarding their ductility; it was thought that the material had become embrittled and would fail prematurely in a catastrophic manner and be more susceptible to poor performance during the winters (−25 °F) because of welds being repaired up to six (6) times. The contracting company requested that the repair welds be evaluated and compared to the base metal and the original welds. The repair welds could not be removed from the structure. Therefore, the welding vendor was requested to provide mock-up welds and mock-up repair welds that simulated the welding process used during fabrication. The welding vendor provided base metal, mock-up of in-service weld, and mock-up of in-service repair weld for metallographic evaluation and mechanical testing. The vendor also provided hardness data for in-service weld and in-service repair weld along with hardness data for mock-up of in-service weld and mock-up of in-service repair weld. The mock-up welds adequately represent the production welds (original welds and repaired welds). All the test results indicate that the repaired welds are of similar quality as the original weld.

Development and characterization of advanced 9Cr ferritic/martensitic steels for fission and fusion reactors

This paper presents the results on the physical metallurgy studies in 9Cr Oxide Dispersion Strengthened (ODS) and Reduced Activation Ferritic/Martensitic (RAFM) steels. Yttria strengthened ODS alloy was synthesized through several stages, like mechanical milling of alloy powders and yttria, canning and consolidation by hot extrusion. During characterization of the ODS alloy, it was observed that yttria particles possessed an affinity for Ti, a small amount of which was also helpful in refining the dispersoid particles containing mixed Y and Ti oxides. The particle size and their distribution in the ferrite matrix, were studied using Analytical and High Resolution Electron Microscopy at various stages. The results showed a distribution of Y 2O 3 particles predominantly in the size range of 5–20 nm. A Reduced Activation Ferritic/Martensitic steel has also been developed with the replacement of Mo and Nb by W and Ta with strict control on the tramp and trace elements (Mo, Nb, B, Cu, Ni, Al, Co, Ti). The transformation temperatures ( A c1, A c3 and M s) for this steel have been determined and the transformation behavior of the high temperature austenite phase has been studied. The complete phase domain diagram has been generated which is required for optimization of the processing and fabrication schedules for the steel.

Design optimization and experimental testing of the High-Flux Test Module of IFMIF

The design of the High-Flux Test Module of the International Fusion Material Irradiation Facility has been developed continuously in the past few years. The present paper highlights recent design achievements, including a thorough state-of-the-art validation assessment of CFD tools and models. Along with design related analyses exercises on manufacturing procedures have been performed. Recommendations for the use of container, rig, and capsule materials as well as recent progress in brazing of electrical heaters are discussed. A test matrix starting from High-Flux Test Module compartments, i.e. segments of the full module, with heated dummy rigs up to the full-scale module with instrumented irradiation rigs has been developed and the appropriate helium gas loop has been designed conceptually. A roadmap of the envisaged experimental activities is presented in accordance with the test loop facility construction and mock-up design and fabrication schedules.

Passive microelectrode arrays for recording of neural signals: A simplified fabrication process

A new process for the fabrication of microelectrode arrays is developed that is fully compatible with standard integrated circuit fabrication schedules. The process involves two innovations: the use of initially thin silicon substrates (50 μm), and the use of sputtered SiO2 as a plasma etching mask. The finished electrode array consists of a very thin silicon substrate (<20 μm) that provides a mechanically stable carrier for the electrodes. The electrode metal conductors are sandwiched between two layers of polyimide films that adhere firmly to the substrate. Small electrode interface and contact windows are made with lithographically limited minimum feature sizes. Dry plasma etching is employed both to open the windows and to thin the substrate. For the former, we have determined the appropriate etching conditions and thicknesses necessary for SiO2 to be a viable mask in this step. For the latter step, the electrode profile is first etched to the final desired substrate thickness from the front (with the same oxide as the mask), and the wafer is then turned over and fully etched until the electrodes separate. Using initially thin wafers simplifies considerably this final etch.

Earing Control and Deformation Processing of Aluminium Alloys

The production of ear free aluminium flat rolled products highly depends on the ability to balance the deformation and recrystallization textures at the final gauge. A model based on the concept of earing diagram is proposed, which enables the process-texture-earing relationships to be assessed in a fairly simple way. It is shown that such a predictive tool can be used for the definition of optimized fabrication schedules leading to ear free material. Such earing control is achieved by a control of both the microstructural evolution as well as the position of the recrystallization steps along the complete fabrication sequence.