A STUDY OF MACHINABILITY IN MILLING OF AUSTEMPERED DUCTILE IRON (ADI) ADI 900, ADI 1050, AND ADI 1200 WITH CARBIDE TOOLS

Open Access
Author:
Sinlah, Abibu I
Graduate Program:
Industrial Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Chris Saldana, Thesis Advisor
Keywords:
  • Machinability
  • milling
  • Austempered Ductile Iron (ADI)
  • AISI/SAE 4340 steel
  • tool life
  • surface roughness
  • cutting stiffness
Abstract:
Austempered Ductile Iron (ADI) is a relatively new and high strength material produced from Ductile Iron (DI) by means of a unique heat treatment, austempering. The heat treatment produces a uniform microstructure of acicular ferrite and carbon-stabilized austenite, known as “Ausferrite,” with graphite nodules. ADI exhibits grade material properties including a high strength-weight ratio, good ductility and toughness, high fatigue strength, and wear resistance. It is also approximately 10% less dense than steel with similar strength levels and three times stronger than aluminum at only 2.5 times the mass. These material properties make ADI an attractive alternative for applications that require light weight flexible designs, where density matter and the maintaining of high strength and toughness are important. However, the difficulties experienced when machining ADI remain one of the major restricting factors in the growth of the market for ADI. In many cases, because of the high strength and hardness values, manufacturers have deemed ADI un-machinable. The main objective of this study was to assess the machinability of ADI grades 900, 1050, and 1200 (GR900, GR1050, GR1200) in order to establish cost-effective processing conditions for the machining of ADI. This was accomplished by conducting face and end milling studies for a range of machining conditions. More specifically, the effects of cutting speed on tool life and surface roughness in face milling were investigated as well as the effects of chip load on cutting force and cutting stiffness during end milling. The face milling operations were carried out on 25 mm thick plates using the following cutting conditions with a three tooth, 80 mm face milling tool: constant chip load of 0.08 mm/tooth and depth of cut of 1 mm, with varying cutting speed of 120-360 m/min, 240-480 m/min, and 240-480 m/min for GR1200, GR1050, and GR900, respectively. A Taylor tool life model was also developed, using the five cutting speeds, for the GR900, GR1050, and GR1200. In addition, end milling operations were carried out on 25 mm thick plates using the following cutting conditions with a single tooth 19 mm end milling tool: constant cutting speed of 15 m/min and depth of cut of 1 mm, with varying chip load of 0.05-0.15 mm/tooth. In addition to the analysis of machinability of the grades of ADI, the machinability was compared to that of AISI/SAE 4340 steel (S-4340), under similar cutting conditions. The cutting stiffness of the grades of ADI were found to be generally in the expected cutting stiffness range for hardened steels, such as S-4340, during conventional milling. Empirical testing also showed that high cutting speeds accelerate the rate of tool wear, decreasing tool life and increasing surface roughness when machining ADI. In general, GR900 exhibited the best tool life, surface finish, and cutting stiffness with higher machinability than the higher strength grades of ADI. Furthermore, Taylor tool life models were developed that represented 95%, for GR1200 and GR1050, and 85%, for GR900, of the tool life data collected.