Tow Trains Research Articles

Design and simulation of assembly line feeding systems in the automotive sector using supermarket, kanbans and tow trains: a general framework

A growing number of manufacturers are adopting the so-called supermarket strategy to supply components to the production system. Supermarkets are decentralized storage areas used as intermediate warehouses for parts required by the production system (typically assembly lines). Such a feeding system is widely used in the automotive industry where assembly stations in multiple mixed-model assembly lines are usually refilled by means of a systematic part replenishment driven by Kanban systems, adopting small trucking vehicles towing some wagons (tow trains). The aim of this paper is to provide a simple but robust framework in order to design the supermarket/feeding system dedicated to complex multiple mixed-model assembly lines. This framework proposes an integrated approach both for long-term (static analytical model) and short-term (dynamic simulation) problems dealing with Kanban and Supermarket systems dedicated to assembly lines, and the tow train fleet sizing and management. This proposed methodology is applied to a case study derived from the Italian automotive industry, and the results highlight the high interrelation between the long and the short term variables that can be evaluated only by an integrated approach that considers both static and dynamic aspects of the problem. The results of this study are then presented and widely discussed.

Just-in-Time supermarkets for part supply in the automobile industry

In the automotive industry, a supermarket is a decentralized in-house logistics area for intermediately storing parts in direct vicinity of the assembly line consuming these parts. In a supermarket, tow trains—consisting of a small towing vehicle and a few waggons—are loaded with parts, which then successively visit the stations of the line according to a periodical schedule exchanging empty with filled part bins. This emerging logistics concept enables a reliable and flexible small-lot delivery of parts in line with the basic Just-in-Time (JIT) philosophy. This paper describes the supermarket concept in detail and surveys the literature on the elementary decision problems arising when implementing the supermarket concept. Finally, interfaces with other basic business functions are characterized.

Optimally loading tow trains for just-in-time supply of mixed-model assembly lines

In today's mixed-model assembly production, there are two recent trends—namely, increasing vertical integration and the proliferation of product variety—that shift focus to an efficient just-in-time part supply. In this context, many automobile manufacturers set up decentralized logistics areas referred to as supermarkets. Here, small tow trains are loaded with parts and travel across the shop floor on specific routes to make frequent small-lot deliveries that are needed by the stations of the line. This article investigates the loading problem of tow trains, which aims at minimizing inventory near the line while avoiding material shortages given the limited capacity of the tow trains. An exact polynomial-time solution procedure is presented and interdependencies with production planning, that is, the sequencing problem of product models launched down the line, are investigated in a comprehensive computational study.

Optimally routing and scheduling tow trains for JIT-supply of mixed-model assembly lines

In recent years, more and more automobile producers adopted the supermarket-concept to enable a flexible and reliable Just-in-Time (JIT) part supply of their mixed-model assembly lines. Within this concept, a supermarket is a decentralized in-house logistics area where parts are intermediately stored and then loaded on small tow trains. These tow trains travel across the shop floor on specific routes to make frequent small-lot deliveries which are needed by the stations of the line. To enable a reliable part supply in line with the JIT-principle, the interdependent problems of routing, that is, partitioning stations to be supplied among tow trains, and scheduling, i.e., deciding on the start times of each tow train’s tours through its assigned stations, need to be solved. This paper introduces an exact solution procedure which solves both problems simultaneously in polynomial runtime. Additionally, management implications regarding the trade-off between number and capacity of tow trains and in-process inventory near the line are investigated within a comprehensive computational study.

Optimally locating in-house logistics areas to facilitate JIT-supply of mixed-model assembly lines

Abstract In modern-day production systems, ever-rising product variety poses a great challenge for the internal logistics systems used to feed mixed-model assembly lines with the required parts. As an answer to this challenge many manufacturers especially from automobile industries have identified the supermarket-concept as a promising part feeding strategy to enable flexible small-lot deliveries at low cost. In this context, supermarkets are decentralized in-house logistics areas in the direct vicinity of the final assembly line, which serve as intermediary stores for parts. Small tow trains are loaded with material in a supermarket and deliver parts Just-in-Time to the stations lying on their fixed route. This paper discusses the general pros and cons of the supermarket-concept and treats the decision problem of determining the optimal number and placement of supermarkets on the shop floor. A mathematical model is proposed, an exact dynamic programming algorithm presented, and the validity of the proposed approach for practical purposes as well as the trade-off resulting from fixed installation and maintenance cost is investigated in a comprehensive computational study.

THE USE OF PATTERN RECOGNITION ALGORITHMS IN AN AUTOMATIC VEHICLE IDENTIFICATION SYSTEM

Apart form reading vehicle numbers passed at a given point the Automatic Vehicle Identification (AVI) system employed by Spoornet is required to build a record of the train consist and requires identification of the vehicle types, such as wagons and locomotives. This must be accurate even if electronic tags are missing or damaged on some of the vehicles, or when the train speed or direction changes while being measured. In many cases clearance between tracks on a double line section prohibit the installation of reader antennas between the lines. Under these conditions it is required that the train consist shall not be corrupted while tow trains pass on a double line at the same site. In order to ensure reliable performance in accordance with these requirements different pattern recognition algorithms had to be implemented on the system. This paper presents the algorithms employed, some of the operational problems experienced as well as unique developments undertaken to solve these problems.