A STUDY OF THE TURNING OF AUSTEMPERED DUCTILE IRON (ADI) GRADES WITH COATED CARBIDE TOOLS

Open Access
Author:
Ting, Pei Long
Graduate Program:
Industrial Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
December 16, 2016
Committee Members:
  • Robert Carl Voigt, Thesis Advisor
  • Edward Demeter, Committee Member
  • Janis P Terpenny, Committee Member
Keywords:
  • ADI
  • Turning
  • Cutting speed
  • Surface finish
  • Chip formation
  • Tool life
Abstract:
Austempered Ductile Iron (ADI) is a relatively new material with the highest hardness and strength of any material in the cast iron family. Through the unique heat treatment - austempering, the “ausferrite” microstructure of ferrite and carbon-stabilized austenite along with graphite nodules is formed. Multiple strength levels can be produced by varying the austempering temperature or time. In general, ADI has a high strength-weight ratio, good toughness, and very high wear resistance compared to other ductile iron grades. In addition, the density of ADI is lower than steel but with approximately the same strength. These unique properties make ADI as an ideal material for manufacturing products requiring light weight but with high strength and toughness. On the other hand, ADI is difficult to machine because of its high hardness. This has impeded the application and the growth of market applications of ADI. The primary objective of this study was to evaluate the machinability of different grades of ADI (GR900, GR1050, GR1200) during high speed turning with coolant. Comprehensive turning experiments were conducted under a range of different machining conditions. The influence of cutting speed on tool life, surface roughness, and chip formation were analyzed during turning with coated carbide tools. The turning experiments were conducted on large diameter commercially produced, pre-machined cylinder castings at a constant feed rate of 0.012 ipr and depth of cut of 0.06 inches. The cutting speed was varied for the different grades of ADI, from 250-1000 fpm and tool wear was measured at various time intervals. A Taylor tool life model was developed by measuring the tool life for a range of cutting speeds. This model was then used to generate general turning guidelines for the various grades of ADI based on tool life. Lastly, in order to benchmark the turning of ADI with other materials, turning studies with conventional Ductile Iron grade 100-70-03 were also investigated under similar cutting conditions. The chip formation for all grades of ADI and DI 100-70-03 were discovered in the form of discontinuous c-shaped chips. As expected increasing cutting speeds accelerated the rate of tool wear. The surface roughness trend when machining GR900 and GR1050 are similar – decreased cutting speed improved surface finish but a very low cutting speeds the surface finish of grade 1200 ADI also decreased.