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Standard Test for Machinability of Cast Iron |
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Coordinator
Finn Metalworking & Cutting Solutions
Metallurgical release parameters such as hardness, mechanical strength and microstructure do not fully explain differences in machinability encountered by users of cast iron. Poor machinability complaints may be related to factors that cannot be characterized by the foundry with standard tests. The complaints may also be related to tooling or machining variables that are not selected nor controlled by the foundry. A standard machinability test would provide cast iron producers with an additional measurement tool to detect material and processing concerns affecting machining.
In many cases the foundry is blamed for a machining problem, yet further investigation revealed that the problem was related to factors other than the metallurgical quality of the material. Before discovering that the machining system is not optimized, an extensive amount of time and money is spent on chemical, tensile and microstructure rechecks of the castings. The standard machinability test would be used to:
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Compare material of the same grade from different lots made in the same foundry
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Qualify material of the same grade to a benchmark material
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Qualify material of the same grade from different foundries
The test would initially be used for comparative references only. As the popularity of the machinability test increases, a database may be compiled to enable adaptation of the test as a specification like hardness or mechanical properties. The 5-J Committee suggested adapting the ISO 3685-E Specification for face turning by selecting and verifying the most effective tooling and machining parameters (speed, feed, depth of cut). The principle investigator selected feed and speed from the Machining Data Handbook for a five to sixty minute wear test for each grade of cast iron. He also chose to measure flank wear of the cutting tool insert until it reaches 0.015 in. and record the corresponding time
Members of the AFS Cast Iron Committee (5-J) suggested that the measurable observation of the test would be the V30 Value based on a tool life database for each grade of cast iron. The V30 Value is the maximum cutting speed for a thirty-minute cutting tool life. The members envisage that the in-house or contracted testing laboratory would run the machinability test on a representative disc for thirty minutes at the V30 Value (specified speed) for that grade of cast iron. The cutting tool (insert) would be removed and measured for flank wear. The heat or lot of cast iron would pass the machinability test, if the flank wear did not exceed the "end-of-test" criterion.
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