PENGEMBANGAN MODEL MATEMATIKA UNTUK PENJADWALAN PENGIRIMAN PASOKAN BAHAN BAKU PADA STRATEGI MULTI-SUPPLIER

In order to increase the competitiveness, a company has to fill the customer�s satisfaction by meeting the demand properly, including the quality, the quantity, and the time. For this purpose, supply chain department gives the contribution by controlling the inventory. Going along with the development of the industry, the strategy of the company in looking for raw material is also developed, by changing from single-supplier into multi-supplier strategy. In multi-supplier strategy, the problems are about determining the order portion for each supplier and scheduling and determining the quantity of the order. The problems become more complex because of the different parameters of each supplier, such as the lead time, quantity of order, and lot size of each order, and the constraint of the company, such as warehouse capacity and minimum inventory. So, the purposes of this research are to evaluate the minimum inventory level in order to avoid the stock out and to develop mathematical model to determine the time and quantity of the order from each supplier. In this research, PT Sarihusada Generasi Mahardhika, as a company using multi-supplier strategy, is become the object. The research is done by developing mathematical model to determine the time and quantity of the order, in order to minimize the inventory cost, by considering the parameters value of each supplier and the constraints of company. The model was transformed using software LINGO 9.0. The verified and validated model is used to optimize the level of safety time and schedule the order to get the minimum inventory cost. The optimization gives the result that the level of safety time for raw material A, B, and C are 10, 11, and 10 days. For the schedule of the order, the inventory cost for raw material A is Rp 921,125,869,823.35, for raw material B is Rp 145,401,633,136.82, and for raw material C is Rp 566,216,302,570.24. Based on this research, it has got the optimum safety time of each raw material, considering the fluctuation of demand and deterministic shipping lead time. This research also has developed a mathematical model to determine the arrival time and quantity of the order in multi-supplier strategy, considering the parameters of each supplier and the contraints of the company