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Machining Gray Iron vs. Ductile Iron

Machining Gray Iron vs. Ductile Iron

Machining Gray Iron vs. Ductile Iron

I have been asked by a customer to give them a new quote on machining a casting that is currently cast in 65-45-12 ductile. They want to know what the cost savings would be if it was machined from Class 30 Gray Iron. Is there a rule of thumb for quickly figuring a new time? I'm thinking in the way of a percentage factor such as adding or subtracting a certain percentage of the machine time to obtain a new time to go by.

RE: Machining Gray Iron vs. Ductile Iron

Please don't take this as criticism of your skill, but if you do not have any experience machining gray iron, then you should use an arithmetic method for determining the appropriate machining time.  I'm sure you already know this, but the tool suppliers will have extensive data on appropriate inserts, materials/coatings, feeds, speeds, etc. for machining gray iron and other materials.

RE: Machining Gray Iron vs. Ductile Iron

Gray iron has better machinability compared to ductile iron.Both feed and speeds can be higher for gray iron compared to ductile iron.

I am unable to quantify the benefit,but I am certain that it will be substantial.

Why is the component being down graded from ductile iron to gray iron?

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RE: Machining Gray Iron vs. Ductile Iron

How much machine time is there on the current casting?
You should see some decrease in the machining time, but unless the numbers are high enough, is it worth the effort?
Consider these items:
1) requote the job - quantity of parts per year
2) retool the job - machining time and machine operation type, milling, turning or drulling, etc.


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RE: Machining Gray Iron vs. Ductile Iron

I haven't machined ductile iron but I have machined gray cast iron.  It machines nice but is a real mess. Be prepaired for messy dust all over your machines.

RE: Machining Gray Iron vs. Ductile Iron

Ductile iron is very abrasive and will ruin your machines in a very short time. Cover all ways and precision surfaces and clean up immediately after the job is finished. i have seen companies that didn't want the liabilities of machinin
g ductile iron on their equipment, so they would job it out to other shops. You should see about a 20 % decrease in time but an increase in time for clean up. I have been in the machining business for about 36 years now and ductile iron is one of the most messiest and abrasive materials i have used. It will ruin your equipment unless you stay on top of cleaning up and taking precautions to protect your equipment

RE: Machining Gray Iron vs. Ductile Iron

The answer to this depends on the respective grade of Gray Iron and Ductile.  The most common grade of Gray is Cl 30 and the most common grade of Ductile is 65-45-12.

Machinery's Handbook (25thEd) list cutting speeds for these as follows for the respective cutter type:

Gray BHN 190-220; HSS 80 fpm / Carbide 275 fpm
Ductile BHN 140-190; HSS 100 fpm / Carbide 450 fpm

The dust comes primarily from the flake graphite in gray iron which also acts as a lubricant (ways in machine bases are made from gray iron).  The abrasion is probably coming from sand which has adheared to the outside or inside of the casting.  Advise the foundry to use proper cleaning methods.


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