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Optimizing multi-item EPQ under defect and rework: A case in the plastic molding industry Nafisah, Laila; Sinaga, Rika Apriyanti Magdalena; Soepardi, Apriani; Salma, Melati; Irianto , Irianto
OPSI Vol 18 No 1 (2025): OPSI - June 2025
Publisher : Jurusan Teknik Industri, Fakultas Teknologi Industri UPN "Veteran" Yogyakarta

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.31315/opsi.v18i1.14740

Abstract

Product availability is a key indicator of service performance and is closely linked to production planning. Inaccurate decisions in lot sizing may lead to either overstock or stockout, resulting in substantial financial losses. Classical Economic Production Quantity (EPQ) models generally assume perfect quality and ignore real-world factor such as defects, rework, and backorders. This study proposes an extended EPQ model for multi-item production systems that integrates random defect rates, rework, and backordering within a single framework. Unlike previous studies that focus on single-item scenarios or deterministic defect rates, this model reflects a more realistic setting faced by companies by accounting for stochastic defects, the cost of crushing and rework, and customer backorder fulfillment. The model aims to determine the optimal lot size and production cycle that minimize the total inventory-related costs. The proposed model is validated using real case data from a plastic molding company. Results show that the model yields cost savings of 0.19% compared to the current company policy. Although modest, these savings are significant when scaled across production periods. More importantly, the model demonstrates strong adaptability to operational constraints and provides a practical decision-support tool for industries managing multiple products, quality variation, and uncertain demand.
Determining the International Hub Port on Sumatra Island Using the Integration of Geographic Information System and Analytical Hierarchy Process Methods Setijadi, Setijadi; Hartati, Verani; Fauzi, Muchammad; Salma, Melati
Spektrum Industri Vol. 23 No. 2 (2025): Spektrum Industri - October 2025
Publisher : Universitas Ahmad Dahlan

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.12928/si.v23i2.361

Abstract

Indonesia’s maritime trade development heavily depends on the effective utilization of its port infrastructure, particularly in Sumatra, which is strategically located along the Malacca Strait and near major ASEAN markets. However, trade and logistics activities remain concentrated in Java, creating regional imbalances and leaving western Indonesian ports underutilized. This study aims to identify the most strategic ports in Sumatra that can serve as international trade hubs by developing a spatially integrated, multi-criteria evaluation framework. Three main criteria, trade volume, global connectivity, and multimodal accessibility, were assessed using the Analytic Hierarchy Process (AHP) based on expert input from port management, logistics, and transport planning specialists. Geographic Information System (GIS)-based proximity analysis was applied to evaluate each port’s access to roads, railways, and industrial centers, producing a Multimodal Connectivity Index integrated into the AHP model. The findings reveal that Boom Baru (Palembang), Belawan (Medan), and Batu Ampar (Batam) rank as the top-performing ports, with final scores of 0.875, 0.855, and 0.800, respectively. These ports exhibit high trade volumes and superior multimodal connectivity, with Boom Baru and Belawan achieving the highest connectivity index (2.67 out of 3.00). In contrast, Pekanbaru and Tanjung Balai Karimun scored lower due to limited infrastructure and weaker integration. The study concludes that incorporating GIS-based spatial analysis into the AHP framework reduces subjectivity in port evaluation and provides a replicable, data-driven tool for regional infrastructure prioritization. This approach contributes a novel composite index and offers strategic insights for developing Sumatra’s role in Indonesia’s maritime trade network.