Citation: Bugaric, U.; Tanasijevic, M.; Djenadic, S.; Ignjatovic, D.; Jankovic, I. Development of the Cost-Based Model for Monitoring the Lifetime of the Earth Moving Machines. Machines 2022, 10, 995. https:// doi.org/10.3390/machines10110995 Academic Editor: Ahmed Abu-Siada Received: 20 August 2022 Accepted: 26 October 2022 Published: 29 October 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). machines Article Development of the Cost-Based Model for Monitoring the Lifetime of the Earth Moving Machines Ugljesa Bugaric 1 , Milos Tanasijevic 2, * , Stevan Djenadic 2 , Dragan Ignjatovic 2 and Ivan Jankovic 2 1 Faculty of Mechanical Engineering, University of Belgrade, 11120 Belgrade, Serbia 2 Faculty of Mining and Geology, University of Belgrade, 11120 Belgrade, Serbia * Correspondence: milos.tanasijevic@rgf.bg.ac.rs; Tel.: +381-11-3219-155 Abstract: This paper presents the model for the identification of reference points on the lifetime curve of engineering systems. This curve commonly represents the increase and decline of failure in relation to time. A direct correlation between failure rate and costs is assumed in this paper, therefore, statistical and empirical analysis of costs provided reference points. This approach is used for positioning stages of the engineering system’s lifetime with a minimal number of failures and costs, regardless of whether these are acceptable or not. The following three stages are usually identified: the beginning, the stationary part and the end of life. The boundaries between them are recognized on the basis of minimum total lifetime costs and on economic lifetime costs. Model is tested on the dozers, machines frequently used in the mining industry for the earthmoving operations, and which are characterized by high operating and maintenance costs. Keywords: lifetime curve; failures; costs; dozer 1. Introduction Successful management of an engineering system’s lifetime has the task of reducing costs and maximizing profit while achieving required production rates and preserving the status of equipment and machines. Equipment is passed through several stages of its lifetime during the operation, which can be defined according to different criteria in function to the purpose of the equipment. In function of time, equipment is inevitably getting old, with an increasing number of failures and decreasing availability. Reduced availability is generating additional operational and maintenance costs, reducing the profit further [1]. The relation between increasing costs and time, i.e., the age of equipment, is evident [2]. It is important for the owner of the equipment to identify the reference points between the lifetime stages of the engineering system or the machine. The property of these stages is the level of cost, which can be minimal, acceptable, or unacceptable [3]. The major task here is to determine the maximal profit and to establish an acceptable level of cost for the owner, i.e., to identify the specific period of the machine’s lifetime [4]. The International Electrotechnical Commission (IEC) presented the Dependability management: Application guide—Life cycle costing (IEC 60300-3-3:2017 and 2018) standard [5]. The purpose of this standard is to provide basic guidelines for the assessment of dependability and costs, including cost determination in relation to the quality of service [5] of the engineering system. The systemic approach is necessary to define the ownership and operational costs, which include acquisition, maintenance, operation, overhaul, etc. This approach also requires a certain balancing level between the costs and the residual value of the machine [2]. This balance is achieved by assessing the dependability trend against costs induced by the analyzed system at any given time of its life [1]. In general, there are several lifetime stages of an engineering system or equipment [1]. A technical lifetime is a period during which the equipment meets the designed criteria Machines 2022, 10, 995. https://doi.org/10.3390/machines10110995 https://www.mdpi.com/journal/machines