MACHINABILITY OF DUCTILE IRON CASTINGS

1 RESEARCH PROJECT No. 20 MACHINABILITY OF DUCTILE iron CASTINGS TESTING BY MACHINING RESEARCH, INC. REPORT PREPARED BY ROBERT J. CHRIST SOCIETY Issued by the DUCTILE iron Society for the use of its Member Companies - Not for General Distribution DUCTILE iron SOCIETY 28938 Lorain Road North Olmsted, Ohio 44070 21 6-734-8040 JULY 1993 DUCTILE iron Society Research Re ort Project No. f20 MACHINABILITY of DUCTILE iron CASTINGS Testin Done by Machining 53 esearch, Inc. Florence, Kentucky Re ort Prepared by fobert J. Christ introduction Summary of Findings Conclusions MACHINABILITY Test Results Investigational Procedure Material Sources MACHINABILITY Test Procedures Machine Tooling Cutting Tools Machining practices Metallurgical Studies Analyses of MACHINABILITY Data Face Milling Turning Drilling Metallurgical Evaluations General Observations Effect of Inclusions on MACHINABILITY Acknowledgements References Tables 1-5, Index Figures 1-69, Index Appendices A.

2 Tool Wear Data B. Representative Micrographs and EDS Inclusion Identification Plots MACHINABILITY of DUCTILE iron CASTINGS DIS Project P20 Tables and Figures Index Tables Topic Pages 1 Index, Tool Life vs. Cutting Speed for Various Feeds 4 2 Description of foundry Practices 13 3 Chemical Analyses of MACHINABILITY Bars 14 4 EDS-SEM Inclusion Analyses 58 5 Hardness of Inclusions in DUCTILE iron 59 1A - 3D Appendix A - Raw MACHINABILITY Data 70 - 83 Figures Topic Pages 1-25 Tool Life Curves - Face Milling 15 -39 26 - 32 Tool Life Curves - Turning 40 - 46 33 - 36 Tool Life Curves - Drilling 47 - 50 37 - 40 MACHINABILITY Test Bars 51 - 52 41 - 44 Machine Tooling Used in Investigations 53 - 54 45 - 46 Tool Wear

3 Characteristics 55 47 - 48 Examples of Ferritic Skin 56 - 57 49 - 58 Microstructures, Test Bars Used for Inclusion Analyses 60 - 69 B1 -B9 Appendix B - Additional Examples of Microstructures 84 - 93 B 10 - B 16 Appendix B - Typical SEM-EDS Inclusion Identification Plots 94 - 100 MACHINABILITY of DUCTILE iron CASTINGS DUCTILE iron Society Project P20 introduction The current study, which analyzes factors affecting MACHINABILITY of DUCTILE iron CASTINGS , is an extension of earlier studies. This earlier work was conducted at the Georgia Institute of Technology and is covered in DIS Research Report No.

4 P14 - October 1987. While the previous work showed how microstructure affects MACHINABILITY , and developed quantitative relationships to show tool wear rates versus pearlite content, graphite quality, and casting hardness, the study was limited to only turning operations. Additionally, this study was limited since it did not include an indepth assessment of all the factors affecting MACHINABILITY . In the current expanded study, MACHINABILITY data is developed which: Covers turning, milling and drilling operations.

5 Compares MACHINABILITY of the as-cast skin of CASTINGS , to sub-skin MACHINABILITY . Develops tool life data for pearlitic DUCTILE iron CASTINGS meeting ASTM Grade 80-55-06 and ferritic DUCTILE iron conforming to ASTM Grade 65-45-12, both produced in as-cast conditions. Covers irons cast in three different DIS member foundries identified simply as A, B, and C, to determine the relationship of production practice to MACHINABILITY . All irons were supplied and evaluated in the as- cast condition. Investigates the effect of microstructure and inclusions on tool life.

6 Results are presented in the form of curves that forecast tool life at different cutting speeds and tool feeds. This permits the user of this data to deterrmne trade-offs between maximum tool life and maximum rates of metal removal. Microstructures and inclusions are shown to be the major factors affecting MACHINABILITY in terms of tool life. foundry practice and process controls in a foundry determine what microstructures and degree of iron cleanliness are developed in any grade of DUCTILE iron , and hence, the machining characteristics.

7 This study demonstrates that MACHINABILITY of any grade of DUCTILE iron , whether in face milling, turning or drilling operations, is very much influenced by the total manufacturing and control practices of an individual foundry . Therefore, to use the data in this report to estimate the effect of variables on tool life, the user must equate particular CASTINGS to that of a similar product produced by one of the contributing foundries in the current study. Three DIS member foundries contributed the MACHINABILITY test CASTINGS , using their respective regular production practices.

8 There were two sources each of pearlitic and ferritic grades. MACHINABILITY tests were then conducted and analyzed by Machining Research, Inc., Florence, Kentucky, under a contract funded by the DUCTILE iron Society. Other contributors to completion of this work are listed in the Acknowledgements section of this report. SUMMARY OF FINDINGS The MACHINABILITY test results for all the metal cutting studies are plotted as tool life curves in Figures 1-36. The curves can be used to forecast MACHINABILITY at different cutting speeds and feed rates for ferritic and pearlitic type DUCTILE irons produced by processes similar to those used by the contributing foundries.

9 Throughout the study, the various investigators referred to 80-55-06 iron as "pearlitic" and the 65-45- 12 iron as "ferritic" and these terms are used throughout the report. However, the ferritic iron does contain some pearlite and the pearlitic, some ferrite. The as-cast ferritic irons at 156-163 Brine11 Hardness are typical of that grade. The pearlitic irons at 187 Brinell hardness and 223 Brinell hardness represent CASTINGS at the minimum and mid range for that grade. Face Milling As Cast Skin Significant observations and conclusions from the current study follow: General 1.

10 Tool life data for the as-cast skin was considerably more erratic than the core or sub-surface metal in both turning and face milling. This is due to large variations in microstructures between foundries, the CASTINGS in a single pour, and between the surface and near surface characteristics. There are variations in the degree and depth of the "as-cast skin," degree of embedded sand, if any, and a varying depth and intensity of the increased ferrite surface layer. A "ferritic skin" is common on many DUCTILE iron CASTINGS and one would expect a more ferritic material to have a higher MACHINABILITY .