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DETERMINATION OF INVENTORY PERIODIC REVIEW POLICY (R, s, S) USING POWER APPROXIMATION METHOD FOR MINIMIZE TOTAL INVENTORY COST IN PT. OPQ Wia, Ratna; Aurachman, Rio; Kenaka, Saskia Puspa
International Journal of Innovation in Enterprise System Vol 3 No 01 (2019): International Journal of Innovation in Enterprise System
Publisher : School of Industrial and System Engineering, Telkom University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.25124/ijies.v3i01.108

Abstract

PT. OPQ is a company engaged in the automotive manufacturing industry. The company produces bolts for the safety area, it is related to the lower body of the four-wheeled vehicle. PT. OPQ was established in 2014 and today has already been the supplier for several major automotive companies in Indonesia. The demand of PT OPQ that must be fulfilled is increasing as the amount of consumer is increasing too. Due to the high demand, so the raw material stockout occurs. This make the company's service level is below the standard. This study involved 48 sku of material raw materials that have normal distributed demand. Inventory policy applied in this research is periodic review (R, s, S) with the aim to minimize total cost of inventory and improve service level of company. The result of this research was found to decrease total inventory cost by 15% with the value of existing inventory cost Rp1.100.879.479,- to Rp 936.061.349,- . In addition, service level at PT. OPQ has increased with the value of existing conditions 85% to 99%.  
Comparison Study of Neighborhood Structures in Local Search for Vehicle Routing Problem with Multiple Trips and Time Windows Kenaka, Saskia Puspa; Suprayogi, Suprayogi
Jurnal Teknik Industri: Jurnal Keilmuan dan Aplikasi Teknik Industri Vol. 23 No. 2 (2021): Dec 2021
Publisher : Institute of Research and Community Outreach - Petra Christian University

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.9744/jti.23.2.161-170

Abstract

This paper deals with the vehicle routing problem with multiple trips and time windows (VRPMTTW). The problem combines two features to the basic vehicle routing problem (VRP): multiple trips and time windows. The basic VRP and its variants fall into hard combinatorial optimization problems. Therefore, many heuristics have been developed to solve large problems. Local search (LS) is one of the heuristics using a neighborhood structure in order to find a better solution. This paper focuses on the comparative study of neighborhood structures applied in LS for the VRPMTTW. Two classes of neighborhood structures are compared: Tour-based and permutation-based neighborhood structures. The tour-based neighborhood structures are the neighborhoods in which the moves are performed on the solution represented by a set of tours. The permutation-based neighborhood structures are the neighborhood structures in which the moves are carried out on the solution represented by a permutation of customers. Comparing the performance of the neighborhood structures uses two responses: (1) relative improvement in the objective function value and (2) computation time. The first response is used to measure effectiveness, while the second is used as efficiency. Based on the computational experiment results, it is generally revealed that the permutation-based neighborhood structures used in LS are more effective than the tour-based neighbourhood structures. However, the permutation-based neighborhood structures are less efficient because they give higher computation times.