Reducing Material Rejects at the Warehouse–Production Interface: A Fishbone Root Cause Analysis and Quality Improvement Strategy in a Manufacturing Company

Abstract

Material rejects at the interface between the warehouse and the production line raise rework, delay production schedules, and waste materials. This study analyzes the causes of material rejects in PT. ABC, a manufacturing company, and formulates improvement strategies to reduce them. A descriptive qualitative design was applied. Data were collected through direct observation, semi-structured interviews with quality control and production personnel, and a review of inspection records and reject reports during an industrial internship. The causes were classified with a fishbone (Ishikawa) diagram based on the 5M+1E framework (man, method, material, machine, measurement, and environment) and analyzed through data reduction, data display, and conclusion drawing. Two reject cases dominated: defective wire components that passed incoming inspection and required rework of about 50–100 production units per week, and Lexan sheets damaged during storage, about 5–10 sheets per week (20–40 per month). The causes were concentrated in four categories. Method and man were dominant, namely inconsistent application of the inspection procedure and high workload, followed by unsuitable packaging of fragile materials and poor warehouse organization; no dominant cause was recorded under machine or measurement. The proposed strategy combines stricter procedure compliance at incoming inspection, competency training for quality control personnel, workload balancing during peak periods, standardized protective packaging, 5S workplace organization, and periodic warehouse audits. The study shows that reject prevention should begin at material receiving and storage, not at the assembly line.