Paolo Salini

A decision model for selecting parts feeding policies in assembly lines

Purpose – The purpose of this paper is to develop an optimization model allowing the choice of parts feeding policy to assembly lines in order to minimize total cost. Design/methodology/approach – An integer linear programming mathematical model is developed to assign the optimal material feeding policy to each part type. The model allows choice between kitting, line stocking and just in time delivery policies. Findings – The choice of assembly lines feeding policy is not trivial and requires a thorough economic comparison of alternatives. It is found that a proper mix of parts feeding policies may be better that adopting a single material delivery policy for all parts. Research limitations/implications – The model is aimed at single-model assembly lines operating in a deterministic environment, but can be extended to the multi-model line case. While relevant quantitative cost drivers are included, some context-related qualitative factors are not included yet. The model assumes that information about prod...

Planning models for continuous supply of parts in assembly systems

Purpose – The purpose of this paper is to develop analytical planning models to compare just-in-time (JIT) delivery and line storage (LS) alternatives for a continuous supply of materials to assembly lines. Design/methodology/approach – A mathematical model is developed to size resources and to determine total system costs. Findings – The choice of assembly lines feeding policy requires a thorough economic comparison of alternatives. However, the existing models are often simplistic, neglecting many critical factors which affect the systems’ performances. As a consequence, industries are unsure about which system is best for their environment. This model allows to compare the cost and suitability of two major continuous-supply alternatives in any specific industrial setting. Results of the model application are case-specific and cannot be generalized. Research limitations/implications – The model is aimed at single-model assembly lines operating in a deterministic environment. Although relevant quantitati...

Impact of accidents risk on hydrogen road transportation cost

Purpose – The purpose of this paper is to estimate delivered hydrogen cost including both transport and expected accidents cost comparing compressed gas or liquid hydrogen road transport. The model allows to determine whether, in a given context, the risk of accidents is an influencing variable in the selection of the hydrogen transport mode. It also helps to select the lowest cost transport mode and route.Design/methodology/approach – Transportation cost models are developed and integrated with a risk analysis model to determine expected accidents cost so that an overall delivered hydrogen cost can be computed. Alternative transport modes are compared on the basis of hydrogen demand, delivery distance and route type.Findings – While safety cost in many cases can be considered negligible with respect to overall hydrogen transport cost, there are cases (high flow rate, long distance) where accident cost is relevant, especially in routes through densely populated areas. In such cases, factoring in accidents...

Modeling errors in parts supply processes for assembly lines feeding

Purpose The purpose of this paper is to develop a quantitative model to assess probability of errors and errors correction costs in parts feeding systems for assembly lines. Design/methodology/approach Event trees are adopted to model errors in the picking-handling-delivery-utilization of materials containers from the warehouse to assembly stations. Error probabilities and quality costs functions are developed to compare alternative feeding policies including kitting, line stocking and just-in-time delivery. A numerical case study is included. Findings This paper confirms with quantitative evidence the economic relevance of logistic errors (LEs) in parts feeding processes, a problem neglected in the existing literature. It also points out the most frequent or relevant error types and identifies specific corrective measures. Research limitations/implications While the model is general purpose, conclusions are specific to each applicative case and are not generalizable, and some modifications may be required to adapt it to specific industrial cases. When no experimental data are available, human error analysis should be used to estimate event probabilities based on underlying modes and causes of human error. Practical implications Production managers are given a quantitative decision tool to assess errors probability and errors correction costs in assembly lines parts feeding systems. This allows better comparing of alternative parts feeding policies and identifying corrective measures. Originality/value This is the first paper to develop quantitative models for estimating LEs and related quality cost, allowing a comparison between alternative parts feeding policies.

Influence of Preventive Maintenance Frequency on Manufacturing Systems Performances

Preventive maintenance (PM) is often scheduled in order to minimize the maintenance cost or to comply with production planning requirements. However, maintenance interruptions affect process time variability and resource utilization, thus causing adverse effects on the operational performance of the manufacturing system such as Work in Process (WIP) and cycle time. In this paper some approximate queueing models are utilize to asses the impact of PM interval on WIP. It is shown that maintenance intervals corresponding to a minimum maintenance cost or minimum WIP can be quite different thus asking for trade-off decisions by plant managers.

Modelling human errors and quality issues in kitting processes for assembly lines feeding

Abstract In this paper a quantitative model is developed to assess errors probability and errors correction costs in kit preparation and delivery processes feeding parts to assembly lines. Error trees and event trees are adopted to keep track of unwanted events and error correction opportunities during the entire logistic process, starting from material picking in the warehouse to kit delivery at workstations and parts assembly. A numerical example is included to show the method application and assess the contribution of each potential error to the overall quality cost in kitting systems. The method is aimed at quantifying the economic consequences of errors in the parts feeding logistic process, and identifying the major error sources. This allows to better compare kitting systems to alternative parts feeding policies and identify corrective measures.

Selection of assembly lines feeding policies based on parts features and scenario conditions

This paper explores the impact of parts features, i.e. unit size and cost, as well as scenario variables on the total delivery cost of materials to assembly lines workstations, according to different materials feeding processes (kitting, line storage and just-in-time delivery). After building cost models based on parts features explicitation, a sensitivity and parametric analysis is carried out in order to justify the cost-effectiveness of each feeding policy and understand whether economic break-even points exist among available feeding alternatives on the basis of the values assumed by relevant attributes of parts. This allows to map areas where each feeding policy is more convenient and also allows a quick method to choose the best feeding policy for each part on an economic basis.