Multi-objective Production Planning Considering Partner Selection for Networked Manufacturing① Zhi-xiang Chen1 , Li Li2 1 Department of Management Science, Sun Yat-sen University, Guangzhou, China 2 International Business, Sun Yat-sen University, Zhuhai, China (mnsczx@mail.sysu.edu.cn, Li_whileblue@163.com ) Abstract – This paper studies an integrated optimization model of production planning with partner selection in a networked manufacturing system. An integrated multiobjective programming model is proposed and a numerical example is illustrated. The result shows the effectiveness and feasibility of the model. The model is suitable for the decision of production planning in networked manufacturing environment Keywords – Production planning, partner selection, multi-objective programming, networked manufacturing I. INTRODUCTION Production planning is a core decision problem in a manufacturing system. Traditional production planning is assumed that the production resource is limited within a manufacturer, or relative external resources are determined. With the globalization and wide application of information technology, more and more companies are outsourcing their non-core business to other collaborative partners. This new economic environment is leading up to the emergence of collaborative business (Niehaves and Plattfaut, 2011). Networked manufacturing, or distributed manufacturing, is one kind of new collaborative business pattern in the era of IT, which not only changes the traditional business mode but also changes the business process. It links the business processes of different partners (e.g., OEM (Original Equipment Manufacturer), CM (contact manufacturers) and other partners) together and forms a strategic alliance to respond to the customer demand. Under this new business environment, the production planning decision mechanism is different from the traditional production planning. Therefore, it is important to discuss the decision methods of production planning for networked manufacturing system. There are some authors have researched the problem of production planning for distributed and networked manufacturing. Gnoni et al (2003) deal with lot sizing and scheduling problem of a multiple-site manufacturing system with capacity constraints. Similarly, Leung, Wu and Lai (2003) study the multi-site aggregate production planning with multi-objective using goal programming approach. Jolayemi and Oloruniwo (2004) develop a deterministic model for planning production and transportation quantities in multi-plant and multiwarehouse environment with extensible capacities. Ling et al (2006) study the distributed production planning with supplier selection using Analytical Target Cascading ① This paper is funded by NSFC (70972079) method. Dudek and Stadtler(2005) study a negotiationbased production planning between supply chains partners .Boulaksil and Fransoo (2009) study one OEM manufacturing firm which outsources some of its production activities to a contract manufacturer. Lin and Lin (2009) study an interactive meta-goal programming based decision method of collaborative manufacturing. In the study, decision participate can interactively make decision with other partners during the decision, and each partner can consider his (her) own individual local objective and preference, finally, a global optimization result is reached. Chung et al (2010) apply genetic algorithm (GA) to study the multi-factory production planning problem. In the model, different factories with capacity constraints and precedence relationships are involved, and order completion time, i.e., makespan is taken as objective of the model. Jung (2011) studies a fuzzy AHP-GP approach for integrated production planning considering manufacturing partners. In the model, decision is made to allocate production tasks to partners. In this paper, we study a multi-objective programming method for networked manufacturing considering partner selection. The model can concurrently decide the production lot size and partner selection. This method is especially suitable for the OEM driven networked manufacturing system, in which, collaborative partners are selected when make production planning and allocate production tasks to different partners. II. FORMULATION OF THE PROBLEM A. assumptions and notations Assumptions Our model will be formulated based on the production networked shown in figure 1. In order to formulate the problem, the following assumptions will be needed. (1) OEM company acts as the decision maker of the production planning; (2) Demand of products in periods is known; (3) Production planning decision concurrently considers the supplier or contract manufacturer selection; (4) All demand in each period should be satisfied and no shortage and backlog is allowed (5) Transaction cost is supplier dependent but is not dependent on variety and quantity of the products. (6) Holding cost of products is product dependent. The system of the integrated inventory model is shown as figure 1. Contract manufacturers OEM and products Customers CM1 Product 1 CM2 Product 2 ┋ ┋ Proudct M CM N Fig.1 Production network of OEM driven manufacturing Notations The following notations will be used in the model. Indices: i (=1,…, M) Index of products j (=1,…, N) Index of contract manufacturers t (=1, …, T) Index of time periods Parameters: Dit Demand of product i in period t. (units/period) C ij Per unit price of product i supplied by contract manufacturer j. ($/unit) H i Holding cost of product i per period and per unit ($/unit/period) O j Transaction cost for contract manufacturer i. ( $/per time) wi Storage space of product i ( m3/per unit) W Total storage space (m3) Bt Budget in period t q ij Quality level of product i offered by contract manufacturer j S j Service level of contract manufacturer j B Model formulation of the problem In this paper, the problem can be described as: there is a networked manufacturing system consisting of one OEM and multiple CMs (contract manufacturers), in which OEM is responsible for the product sale, market development and customer service, while CMs are responsible for the production of products. In order to meet customer demand, OEM needs concurrently decide which product will be assigned to which CM to produce, to maximize the total profit, total product quality level and customer service level. The three objective functions are expressed as follows, Objective functions: M Per unit transportation cost of contract manufacturer j Decision variables X ijt The quantity of product i purchased from contract manufacturer j in period t. Y jt =1 if contract manufacturer j is selected in period, 0, otherwise. Intermediate variable I it Inventory level of product i in period t N i t t 1 M { N T - j 1 N T Cij X ijt + O j Y jt + i 1 j 1 t 1 M j 1 t 1 T t N t H i ( X ijk Dik ) + i 1 t 1 M N k 1 j 1 k 1 T f i 1 j 1 t 1 j X ijt } Pi ,t Sell price of product i in period t fj T max TP Pit X ijt M max TQ (1) N T q X ij i 1 j 1 M N t 1 ijt (2) T X i 1 j 1 t 1 ijt N 1 T max TS T t 1 S Y j 1 j (3) N Y j 1 jt jt The first objective is to maximize the total profit; the second objective is to maximize the total quality level of all products and the last objective is to maximize the total service level. Constraints t N t I it X ijk Dik 0 for all i and t. (4) k 1 j 1 k 1 T Dik Y jt X ijt 0 k t for all i , j, and t. (5) t N t w X i ijk Dik W for all t. (6) i 1 k 1 j 1 k 1 Because the model is a multi-objective programming problem, so, in order to solve it, it is necessary to convert the multi-objective programming model into single-objective programming model. There are different methods for converting multiobjective programming model into single-objective programming model. In this paper, we use the following method. . max P M N i 1 j 1 M N ijt Cij Bt T M for all t. i 1 j 1 t 1 T (8) i 1 t 1 Y jt ={0,1} for all j and t. (9) X ijt 0 for all i ,j, and t (10) TQ TS S TQmax TS max (11) objectives of total profit, total quality and total service respectively. The TPmax , TQmax and TS max are the (7) X ijt Dit TPmax Q s.t. constraints (4)-(10) In above model, P , Q , S are the weights of the M X TP Constraint of (4) describes that all requirements must be filled in the period in which they occur and shortage or backlog is not allowed. Constraint (5) describes that there is not an order without charging an appropriate transaction cost. Constraint (6) means that storage space is limited and constraint (7) means that total purchasing cost is not exceed the budget. Constraint (8) restricts the total supply equal to the total demand. The last two constraints (9) and (10) are variable constraints respectively for supplier selection and purchasing quantity. optimal values of TP(total profit), TQ(total quality) and TS(total service) under their own individual single objective model without considering other objectives respectively. There are different methods can be used for weight assignment, such as AHP (Analytical Hieratical Process). For the sake of convenience and saving pages, in this paper, we first automatically give out the weights of objectives. The weights are 0.30, 0.40, and 0.30 for total profit, quality and service respectively. The solution procedure is described as : Step 1: Initialization and data setting for the model Step 2: Solve the three single-objective programming models of total profit, total quality and total service respectively to obtain TPmax , TQmax , TS Max . Step 3: Solve weighted multi-objective programming model (11) to obtain solution. Ⅲ NUMERICAL EXAMPLE In this section we use an example to show the effectiveness of the model. Data are listed out in table 1 II SOLUTION PROCEDURE Table 1 parameters of model Product Demand/price of OEM Period 1 Period 2 A 12/100 15/120 B 20/200 21/240 C 20/150 19/170 Transaction cost ($) Service level Transportation cost ($/unit) Price/quality level of CM Period 3 Period 4 Period 5 17/130 22/210 18/140 20/120 23/240 17/160 13/110 24/210 16/155 CM1 CM2 CM3 C q C q C q 30 32 45 110 0.95 6 0.97 0.95 0.98 33 35 43 80 0.90 5 0.95 0.97 0.96 32 30 45 102 0.97 7 0.95 0.97 0.95 Holding cost Storage space 1 2 3 10 40 50 Note: CM=contract manufacturer, total storage space S=200. C=supply price of CM, q=quality level of CM. Use the data, we first solve each objective independently using Lingo11, and obtain the maximum objective value as. TPmax 35433.07 , TQmax 0.9718051 TS max 0.964 Then we solve model (11), obtain the objective value The production plan and contract manufacturer TP= 35334.83, TQ= 0.9658604, TS= 0.9580000 selection result is shown in table 2. Table 2 solution result t t=1 t=2 t=3 t=3 t=4 t=5 Xijt Yjt Iit Xijt Yjt Iit Xijt Yjt Iit Xijt Yjt Iit Xijt Yjt Iit Xijt Yjt Iit A(i=1) 20 13 CM1(j=1) 12 0 0 0 0 0 0 1 15 1 37 1 CM2(j=2) 0 0 0 0 0 0 CM3(j=3) 0 0 0 0 13 0 B(i=2) 1.8 2.2 CM1(j=1) 0 0 19.8 0 0 0 CM2(j=2) 0 0 0 0 0 0 CM3(j=3) 20 1 23.2 1 0 0 24.8 22.3 C(i=3) CM1(j=1) 0 19 0 18 0 0 CM2(j=2) 20 1 0 0 0 0 0 CM3(j=3) 0 0 0 0 1 1 17 16 From the result we can see that, when use multipleobjective model, the optimal value of each objective in the integrated mode will be less than the objective value in single-objective model. This reveals the trade-off relationship, i.e., when consider multiple objectives in the decision model, each objective can only be sub-optimal When there are more objectives, this relationship will be more significant. V CONCLUSIONS The increasing global competition is changing the business mode. More and more companies are seeking cooperation with other companies and forming a strategic alliance to compete with competitors. Under this business background, production planning decision is different from that of traditional manufacturing system. This paper studies an integrated optimization model of production planning with partner selection in a networked manufacturing system. An integrated multi-objective programming model is proposed and a numerical example is illustrated. The result shows the effectiveness and feasibility of the model. The model is suitable for the decision of production planning in networked manufacturing environment Further research can be made to extend the work based on this paper. First, it can be considered multiple transportation alternatives in the model. Second, it also can be considered the demand characteristics of customers, e.g., different customer orders have different preference for selecting partner. 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