Failure of hydraulic lathe chuck assembly

• Published in: Engineering failure analysis 2022-03, Vol.133, p.106001, Article 106001
• Main Authors: Sondar, Pavankumar R, Gurudath, B, Ahirwar, Virendra, Hegde, Subray R
• Format: Article
• Language: English
• Subjects: Cryogenic Treatment; Fractography; Hydraulic Chuck; Jaw Carrier; Plunger
• ISSN: 1350-6307; 1873-1961
• DOI: 10.1016/j.engfailanal.2021.106001

•Chuck assembly suffered fracture of the plunger and jaw carrier during the service.•Cracks initiated at the mating parts of plunger and jaw carrier.•Plunger failed by fatigue and jaw carrier failed because of overstressing.•Presence of sharp corners and improper heat treatment are the causes of failure.•Design modification and introduction of proper cryogenic treatment are recommended. Present work provides a detailed failure investigation of a hydraulic lathe chuck assembly that comprises a plunger, three jaws, and three jaw-carriers that are made of carburized, tempered and sub-zero treated EN36C steel. The chuck assembly suffered premature failure of the plunger and one of the jaw carriers during the service in a CNC lathe. The investigation comprises a detailed metallurgical failure analysis involving: visual inspection, fractography, metallography, and hardness measurements. The analysis concludes that plunger failed first by fatigue fracture that is originated at a sharp corner of a T-slot. The mating jaw-carrier failed in the next event due to instant misalignment and overstressing during the lathe operation. The investigation concludes that design flaw and improper heat treatment cycle as the reasons for the premature failure of the assembly. Through experimental simulation of the heat-treatment cycles using EN36C specimens, the work suggests that carburizing, cryogenic treatment and then tempering is the proper sequence for achieving the best combination of mechanical properties that should extend the service life of the chuck-assembly.