Models for Component Commonality in Multistage Production

Use of common parts for different products (commonality) is important methods for managing product variety and preserving competitiveness in the age of mass customization and supply chain competition. In literature, the advantages of inclusion of common components in a product family are well established. Unfortunately, most of the works have been conducted via simulation or conceptual thinking. The mathematical models in the premises are not adequate for production, planning and control in multistage production. This paper focuses on the advancement of venerable manufacturing resources planning models by incorporating the part commonality concept in a multiproduct, multi-period and multistage manufacturing system under a deterministic situation. The models are validated with established MRPII models. The material requirement schedule for the basic MRP II and proposed models are compared. It is really a good matching shown between the two schedules. The later bearing additional information of the location where to be available the parts in a time frame. The effects of commonality on cost, capacity and requirement schedule are discussed based on the outcomes of the mathematical models executed with the available live data. Introduction The underlying ideas for commonality are not really new. As early as 1914, an automotive engineer demanded the standardization of automobile subassemblies, such as axles, wheels and fuel feeding mechanisms to facilitate a mix-and-matching of components and to reduce costs [1]. Commonality is the use of identical components in multiple/group of products in a product family. In manufacturing, component commonality refers to the use the same components for two or more products in their final assemblies. Commonality substantially lowers the costs of proliferated product lines, mitigate the effects of product proliferation on product and process complexity [2]. It reduces the cost of safety stock, decreases the setup time, increases productivity, and improves flexibility [3]. The required number of order (or setups) [4-5] pooling effect and lead time uncertainty are also condensed when part commonality is applied. Furthermore, it improves the economy of scale, simplify planning, scheduling and control, streamlines and speeds up product development process [6]. The details about the commonality, its measurements and models are narrated in Wazed et al.[7]. The commonality occurs in its own way in the system or can be planned for its preferred happening as well. Nowadays, manufacturing companies need to satisfy a wide range of customer desires while maintaining manufacturing costs as low as possible, and many companies are faced with the challenge of providing as much variety as possible for the market with as little variety as possible between the products. Hence, instead of designing new products one at a time, many companies are now designing families. Hence, the component commonality has wide scope to penetrate in the manufacturing and thereby might allow cost-effective development of sufficient variety of products to meet customers’ diverse demands. However, too much commonality within a product family can have major drawbacks. Consequently, there is a need of tradeoff between system performance and commonality within any product family. Applied Mechanics and Materials Vols. 110-116 (2012) pp 258-266 © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.110-116.258 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 202.185.100.21-03/10/11,11:48:19) MRP II is the widely used tool in the manufacturing. Even though the value of the MRP II that can bring to companies is clear, and a few will refuse its potential, numerous organizations have failed or are failing to apply effectively the advantages that this system can give. The same material requirement planning (MRP) logic is used in MRPII, enterprise resources planning (ERP) and extended ERP (ERP II) in their production-planning modules [8], thus their inability to cope and respond to uncertainty is still prevailing and the planned order release (POR) schedules are indifferent to those generated from an MRP system [9-10]. Enns [8] stated that MRP, MRPII or ERP is the ideal system within a batch-manufacturing environment. If resource loading and lead times are identical to those planned in the MRP systems, then the functions of such systems in planning and control will be ideal [11]. However, the production planning systems (viz. MRP, MRP II, ERP and ERP II) were designed and developed to operate within a stable and predictable batch manufacturing environment. Hence they are not capable of tackling uncertainty [12]. For details on the factors and sources of various uncertainties, the authors humbly like to refer the readers to Wazed et al. [13]. In earlier studies [2-4, 6-7, 14-20], the benefits of component commonality in the manufacturing systems associated with a decrease in inventory, lowers the costs of proliferated product lines, mitigate the effects of product proliferation on product and process complexity, reduce the cost of safety stock, decrease the set-up time, increase productivity, improve flexibility, permit greater operating economies of scale, facilitates quality improvement, enhance supplier relationship and reduce product development time, risk-pooling and lead time uncertainty reduction, simplify planning, schedule and control, streamline and speed up product development process, lowers the setup and holding costs, offer high variety while retaining low variety in operations, lower the manufacturing cost and design savings are obtained. However, the commonality issue is completely ignored in the existing manufacturing resource planning models. Furthermore, the analytical research on multistage manufacturing is very few in the present pool of knowledge. Hence, this article will advance the existing MRP II models by integrating component commonality concept. Component Commonality Model The component commonality models are developed from venerable MRP II models. This model is a useful starting point for further modeling. MRP II was inspired by shortcomings in MRP. The data requirements are nearly the same as for MRP. Using classic MRP II software, problem MRP II would not be solved directly. Instead, problem MRP would be solved and then the capacity constraint for the MRP II model would be checked. In other words, the result of solving problem MRP provides values for the decision variables. Once these values are known, they become data for subsequent processing. Direct solution of the optimization model is a much better idea. In practice, the problem is bigger and harder to solve than the simple MRP II models that have presented. However, MRP II provides us with a good jumping off point for more sophisticated models because it mimics a widely used planning tool. We can and will embed these constraints in a model that captures costs and constraints that are important to the manufacturing organization or the supply chain. Especially the dashing thought of component commonality is to be incorporated. Multistage Production Models in Deterministic Conditions In this section we introduce a class of models that is based on the simplest assumption: demand, lead time, quality and breakdowns are deterministic and stationary. We concentrate primarily on the case where the information of the factors is constant and not anticipated to change. Although the assumption of deterministic and stationary factors seems quite restrictive, models requiring that assumption are still important for the following reasons. First, many results are quite robust with respect to the model parameters, such as the demand rate and costs. Second, the results obtained from these simple models are often good starting solutions for more complex models. We consider an K -stage assembly/manufacturing line that produces ENDP products as illustrated in Figure 1 (aend product, bcomponent and cmanufacturing/assembly line). The production/assembly process of a product starts at stage 1. When a component moves along the line, Applied Mechanics and Materials Vols. 110-116 259