Significant Reduction In Cycle Time Research Articles

Effect of In-trough and Out-of-trough fixturing in vibro-polishing

Advanced compressor design with superior aerodynamic and fatigue life performance demands superior surface quality, typically Ra≤0.25 µm. Vibro-polishing is media finishing technology which is commonly employed to mass finish aerospace engine components such as blisks. Frequency of vibration, location, and orientation of workpiece, media size, lubrication etc. are known tuneable knobs to optimize the performance of Vibro-polishing. However, longer cycle times in vibro-polishing still pose a challenge. In this study, effect of In-trough (IT) and Out of trough (OOT) fixturing at various depths of immersion into the media is studied. Workpiece used was made of Ti-6Al-4V with a geometry representative of a blisk blade. OOT fixturing was observed to yield better surface quality than IT fixturing irrespective of the depth of immersion. Further, a very low Ra of about 0.10 µm was achieved with 1 h of processing at highest depth of immersion into the media in OOT fixturing, resulting in significant reduction in cycle time to reach aerospace component surface roughness of Ra≤0.25 µm. Further, uniform vibro-polished surface topography with no alterations in the as received microstructure was observed in both IT and OOT fixturing.

Comparison of Conventional and Conformal Cooling Channels in the Production of a Commercial Injection-Moulded Component

Cooling channels are critical in injection mould tooling as cooling performance influences component quality, cycle time, and overall process efficiency. Additively Manufactured moulds allow the incorporation of cooling channels conforming to the shape of the cavity and core to improve heat removal. These conformal channels can reduce the cycle time, reduce mould temperature, and enhance the temperature uniformity on the mould's surface, leading to improved quality of the moulded components and reduced wastage in the production. The design of such channels is more challenging than conventional channels; thus, Computer-Aided Engineering (CAE) has a significant role within the design process. In this paper, a novel design for conformal cooling channels for the production of a commercial component from an industrial partner is investigated. This component had issues of high cycle time and a high defect rate due to residual stresses, resulting in component shrinkage. First, the existing conventional drilled cooling channels in the mould were simulated in Autodesk Moldflow Insight to evaluate temperature distribution and cycle time. Based on the temperature distribution, conformal cooling channels were designed in Solidworks, addressing the problem areas. Next, a simulation of fluid flow in the conformal channels was conducted in ANSYS-Fluent to ensure equal flow distribution in the entire circuit, iteratively arriving at an optimal configuration. Finally, the results of the new conformal channels, including mould temperature and cycle time, were compared with conventional cooling channels in simulation. The results showed a significant reduction in cycle time and improvement in the temperature distribution, thereby minimising residual stresses and shrinkage.

Minimizing backtracking distance for networked operations in smart manufacturing

ABSTRACT A novel integer programing (IP) model is developed to assign various operations of product variants to candidate machines and select the best place for each machine among the candidate locations. Product variants are considered to have operation sequence flexibility which are optimized for each product variant. The objective is to minimize the total backtracking distance by considering the production volume of each variant. Backtracking occurs when the production flow is upstream. Minimizing backtracking will improve forward production flow and reduces unnecessary distance travelled by parts which can lead to significant reduction in cycle time and improve machine utilization and total system throughput. In the literature, backtracking problem has been addressed in generalized flow line (GFL) problems, and flexible manufacturing systems. There is no work in the literature considering product variants with networked operation sequence as well as machine selection for each operation. A non-linear mathematical model is first formulated, then converted to an equivalent integer programing (IP) model and solved. A family of engine cylinder blocks is used as a case study for demonstration. The obtained results reveal that minimizing backtracking can significantly improve the total throughput and reduce the total traveling distance (33.33% and 27.78%, respectively, in the case study).

Optimal Scheduling of Complex Multi-Cluster Tools Based on Timed Resource-Oriented Petri Nets

Complex multi-cluster tools have been extensively used in semiconductor manufacturing. It is crucial to increase their productivity by their effective operation. With structural complexity, multiple robots, and the interaction among individual tools, it is very challenging to schedule a tree-like multi-cluster tool. This paper investigates the scheduling problem of such a tool whose bottleneck individual tool is process-bound. The system is modeled by well-known discrete-event models, i.e., resource-oriented Petri nets. Based on the models, for the first time, this work develops necessary and sufficient conditions under which a one-unit (wafer) periodic schedule exists and shows that an optimal one-unit periodic schedule can always be found. Algorithms with polynomial complexity are presented to find the optimal cycle time and the one-unit periodic schedule. Industrial examples are used to illustrate the proposed method, and they show that a significant reduction in cycle time can be obtained in comparison with the existing method.

Modelling and analysis of a multi-stage system involving batch processors with incompatible job families

Batch processors can concurrently process more than one job, and are commonly used in complex manufacturing systems such as wafer fabrication facilities (wafer fabs). Previous work has shown that there can be a significant reduction in cycle time when the control of the upstream serial processor is dependent on the batch processor. We wish to determine whether this is also true when the upstream processor is also a batch processor, with smaller capacity. We model a two-stage system with an upstream batch processor and a downstream batch processor under differing simple control policies as a continuous time-discrete state Markov chain. In doing so, we show that the concept of constraining the production of the upstream processor in accordance to the anticipated needs of the downstream batch processor can similarly reduce mean system cycle time when the upstream processor is a smaller batch processor. We also perform simulation experiments, using parameters close to those found in wafer fabs, and confirm that the strategy of prioritising the formation of larger batches for the downstream batch processor typically results in substantial cycle time reductions for the two-stage system.

The effect of copper alloy mold tooling on the performance of the injection molding process

AbstractThe performance of copper alloy mold tool materials in injection molding has been examined with respect to cycle time, part quality and energy consumption using in‐process monitoring techniques. A mold insert manufactured from conventional tool steel was compared to four identical inserts made from beryllium‐free copper alloys with copper contents ranging from 85 to 96%. Injection molding trials using high density polyethylene and polybutyl terepthalate were performed using a highly instrumented injection molding machine. Results showed that copper alloy mold tools exhibited cooling rates up to 29% faster than conventional tool steel and that cooling rate was related to thermal conductivity of the alloy. Lower cycle times were achievable with copper alloy than for tool steel before part quality deterioration occurred. The results suggest that copper alloy tooling has the potential to achieve significant reductions in cycle time without detriment to the process or product quality. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

Designing an optimal turnover-based storage rack for a 3D compact automated storage and retrieval system

Compact, multi-deep (3D) automated storage and retrieval systems (AS/RS) are becoming increasingly popular for storing products. We study such a system where a storage and retrieval (S/R) machine takes care of movements in the horizontal and vertical directions of the rack, and an orthogonal conveying mechanism takes care of the depth movement. An important question is how to layout such systems under different storage policies to minimize the expected cycle time. We derive the expected single-command cycle time under the full-turnover-based storage policy and propose a model to determine the optimal rack dimensions by minimizing this cycle time. We simplify the model, and analytically determine optimal rack dimensions for any given rack capacity and ABC curve skewness. A significant cycle time reduction can be obtained compared with the random storage policy. We illustrate the findings of the study by applying them in a practical example.

Rotational molding cycle time reduction through surface‐enhanced molds, Part B: Experimental study

AbstractRotational molding is a process used to manufacture hollow plastic products, and has been heralded as a molding method with great potential. Because of long production cycle times, which are limited by the time required to heat‐up and cool‐down the mold and the product, its productivity is hampered. To address this issue, exterior mold modification techniques (i.e. the application of extended and rough surfaces) have been employed to enhance heat transfer to and from molds, ultimately reducing cycle times. Extended surfaces have the potential to enhance heat transfer by increasing the surface area. Roughness elements are utilized in conjunction with turbulent flows, also producing significant increases in heat transfer rates. Experimental results presented here demonstrate very significant cycle time reductions through the use of surface‐enhanced molds. The experimental savings are in the order of 18 and 28%, whereas the predicted cycle time reductions are around of 21 and 32% for roughness‐enhanced and pin‐enhanced molds, respectively. Although the prediction methods have been unable to forecast the exact experimental cycle times very accurately, they have proved to be useful for predicting the approximate cycle time reductions and the relative rankings of the plain and the surface‐enhanced molds. POLYM. ENG. SCI., 47:1420–1429, 2007. © 2007 Society of Plastics Engineers

Project Manager’s Decision Aid for a Radical Project Cycle Reduction

Currently there are no formal decision tools or guidelines to assist owners and managers in choosing delivery systems and strategies that would allow significant reductions in the cycle time. The development of a decision aid that would allow a manager to prioritize and apply cycle reduction techniques would be a valuable tool for achieving cycle time reduction in projects. This paper presents a new high performance delivery system called project manager's game planner PMGP designed to assist a decision maker in identifying and utilizing an optimal set of radical reduction techniques RRTs with the greatest potential for success in achieving cycle time reduction. Additionally, the PMGP can assist the user in identifying the top RRTs during any of the five phases: preproject planning, design, material management, construction, and start-up. Most projects can utilize this PMGP to improve the performance whether to achieve significant cycle time reduction or to simply achieve effective execution.

Curing of composite components by ultraviolet radiation: A review

AbstractCuring of polymer matrices by ultraviolet (UV) irradiation can be applied to a variety of processes in the production of composite components, as long as the component can be directly irradiated. Wet lay‐up techniques, vacuum infusion type processes with UV‐transparent membranes, filament winding, and prepreg processes have been adapted to UV curing. Unlike in thermal curing, the curing time is in the order of magnitude of minutes rather than hours, which means a significant reduction in cycle time. The radiation can be generated by a variety of sources suitable for various specific applications and different curing strategies. The most frequently used radiation sources are mercury arc lamps. Because of the absorption of radiation passing through matter, the thickness of laminates for efficient application of UV curing is limited. The curing mechanism is either radical polymerization for acrylate‐based resins or cationic polymerization for epoxies and vinyl ethers. The properties of the UV‐cured polymer matrix are determined by the cross‐linking density. This depends on the type and concentration of the photoinitiator and of the (optional) diluents, the intensity and the duration of the irradiation, and the temperature at which the curing process takes place. POLYM. COMPOS., 27:119–128, 2006. © 2006 Society of Plastics Engineers.

ACHIEVING REDUCED CYCLE TIMES IN SEMICONDUCTOR MANUFACTURING VIA EFFECTIVE CONTROL OF THE P-K EQUATION FACTORS

In the current environment of flash semiconductor market, competitive cycle times are the key to success. Cycle Time (CT) reduction can be achieved by process time elimination and/or equipment performance improvement, but also by optimizing on the WIP management policy. In this paper, we discuss how significant CT reductions are attained via the effective change of parameter values of the governing WIP management policy of a semiconductor factory. A full factorial Design of Experiments (DOE) was performed, and several parameters were examined. The impact on the coefficient of variability of departure rate (CDR) and CT was evaluated. Results have clearly shown that by changing the values of these parameters, significant cycle time reductions can be achieved.

Dramatically reducing cycle times through flash development

The reduction of cycle time has emerged as a fundamental element of new product development strategy. Many companies look solely at speed enhancement and increase the human, capital and technical resources allocated to development projects. However, additional resources do not guarantee significant reductions in cycle time. As well as speed enhancement activities, there exist two other sets of activities that are key to shortening the development cycle: those that act to prevent delays ( friction) in the development process and those that define the scope of the final outcome ( direction). This paper describes flash development as an alternative approach to reducing product development cycle times. Flash development works by creating a process that focuses on speed, friction and direction. The process is illustrated through an analysis of the Galileo Project at Nortel Networks.

An optimal boundary for two class-based storage assignment policy in carousel system

Abstract This paper examines the effects of 2-class-based turnover assignment policy on the throughput performance of the carousel system in which a storage/retrieval machine performs pickup/discharge operations. Two alternative configurations in class boundary shape are considered. For each alternative, the expected cycle time is developed for single and dual command cycles based on the continuous analytical models. It is shown that with 2-class-based turnover assignment policy(C2) significant reductions in cycle time are obtainable over randomized storage assignment policy. The effects of the system parameters such as the skewness of the inventory distribution, the shape factor and the pickup/discharge time are studied on the optimal boundary.

Class-based storage assignment policy in carousel system

The carousel storage system is an automated warehousing system which has been widely used in a broad range of applications. This paper examines the effects of storage assignment policy on the throughput performance of the carousel system in which a storage/retrieval machine performs pickup/discharge operations. For 2-class-based storage assignment policy, the expected cycle time models are developed for single and dual command cycles. It is shown that with 2-class-based storage assignment policy significant reductions in cycle time are obtainable over randomized storage assignment policy. The effects of the system parameters such as the skewness of the inventory distribution, the shape factor and the pickup/discharge time are studied on the optimal boundary.

Knowledge-Based Expert System for Ballscrew Grinding

This paper discusses the ballscrew grinding process and provides a newly structured knowledge-based expert system (KBES) developed to automate the process based on fuzzy pattern recognition techniques for shape control with recommendations for further optimization considering practical machining constraints. The KBES offers several advantages including the use of semiskilled operators who can monitor several machines simultaneously, the consistent production of high quality parts, and the significant reduction in cycle time due to automatic adjustment of steadies. A new stepper motor steady design and in-process measuring system are also described.