International Journal for Quality Research 11(3) 627–642 ISSN 1800-6450 627 Fulufhelo Ṋemavhola 1 Kemlall Ramdass Article info: Received 31.03.2017 Accepted 03.06.2017 UDC – 005.6:621.8 DOI – 10.18421/IJQR11.03-09 USING STATISTICAL PROCESS CONTROL AND SIX SIGMA TO CRITICALLY ANALYSE SAFETY OF HELICAL SPRINGS: A RAILWAY CASE STUDY Abstract: The paper exhibits the examination of life quality evaluation of helical coil springs in the railway industry as it impacts the safety of the transportation of goods and people. The types of spring considered are: the external spring, internal spring and stabiliser spring. Statistical process control was utilised as the fundamental instrument in the investigation. Measurements were performed using a measuring tape, dynamic actuators and the vernier caliper. The purpose of this research was to examine the usability of old helical springs found in a railway environment. The goal of the experiment was to obtain factual statistical information to determine the life quality of the helical springs used in the railroad transportation environment. Six sigma advocacies were additionally used as a part of this paper. According to six sigma estimation examination only the stabilizers and inner springs for coil bar diameter met the six sigma prerequisites. It is reasoned that the coil springs should be replaced as they do not meet the six sigma requirements. Keywords: statistical process control, helical springs, railway industry engineering, six sigma 1. Introduction 1 Suspensions are the imperative machine component of rail vehicles which absorb the shocks and vibration during driving, bending and further secure the axle drive. The helical compression sort of spring is utilized to permit axle bending and further afford some parallel bending at curvature (Kumbhalkar, Bhope, & Vanalkar, 2015; Schiehlen & Iroz, 2015; Zhu, Wang, & Huang, 2014). Railroad vehicles are among the most broadly utilized strategies for transporting travelers and 1 Corresponding author: Fulufhelo Ṋemavhola email: masitfj@unisa.ac.za products (Shabana, Zaazaa, & Sugiyama, 2007). The rationale energy to a train is administered by means of the suspension structure (bogie). In the railroad environment, helical coil springs and stabiliser springs are utilised to facilitate a comfortable ride in respect of both the trains and the wagons and to delay the lifespan administration of different segments (Ahmadian & Yang, 1998; Lóránt & Stépán, 1996; Xu, Liang, Li, & Yang, 2015). Helical coil springs are used as part of the suspension of rail vehicles to provide dynamic active supporting capacities