Cost of machining aluminum versus steel

[John2004]

Hello,

I would like to ask if anyone could please tell me (in general) the difference in cost for machining an aluminum versus a steel part?

I am interested in learning the general difference in machining-time for aluminum (7075-T7) versus a basic free machining steel.

I am also interested in learning the general difference in cost of material, but I am guessing that the increased machining-time for steel is what will really make the difference.

The question relates to fairly small parts, (something that could be cnc machined out of a 2" cube).

Aluminum "seems" strong engough in tests, but I am much more confident with the strength of steel. Strength would be the only advantage of steel. The advantage of aluminum is easier machining, and the fact that I do not have to put a finish on the aluminum part. If I use steel I will have to use a black oxide finish or some comparable finish (the more cost effective the better).

I would appreciate any suggestions or feedback.

Thanks
John

 

[mrainey]

If you know a little bit about machining and cutting tools, the following free program might help you to instantly compare the difference in machining time for a specific operation.

http://dl.winsite.com/bin/downl?14500000037133

 

[cncprogrammer]

John,

It would help to know a little more about your part. There are grades of aluminum that are stronger than steel but also costly i.e. AL 7075 which has more tensil strength that cold roll through 17-4 SS. You can machine cold roll, hot roll and other mild steels at or near the same rates as AL with proper tools and equipment.

David

 

[griffengm]

John2004,
One advantage you might realize from the aluminum is to have it cast near-net and minimize machining.
Since you do not say whether this is a temperature sensitive application, steel, on the other hand, might give less problems. Think Raytheon gaskets.

Griffy

 

[John2004]

Hello everyone,

Thank you for your reply to my question.

To David:

If I could find a steel that would machine almost as easy as 7075-T7 aluminum, but offer more strength than the aluminum, that would be great. Can you or anyone else please recommend a type(s) of steel that would allow me to increase strength over aluminum as much as possible, while keeping machining time, plus material cost, as close to aluminum as possible? I will also have to put a black oxide finish on the steel part.

The part basically comprises a very small aluminum shank perpendicular to a small aluminum bearing housing. The shank and housing are machined out of one piece of aluminum.

The shank has a 0.375" outside diameter and I will be pressing a stock hardened steel connection socket into the shank with loc-tite retaining compound. A 6" lever is connected to the steel socket that allows the bearing housing to be rotated by hand (at times fairly aggressively, with possibly around 50 pounds of force maximum).

The steel connection socket is strong, but the aluminum "wall" left in the shank after machining the hole for the stock hardened steel socket is small (only 0.030"). If using loc-tite can make the steel socket and aluminum shank as "one piece" then it should be strong enough, as long as the loc-tite bond is strong enough and will not work loose over time.

I would appreciate any feedback from you or anyone else on the effectiveness of bonding steel to aluminum with loc-tite. I have had experience with bonding steel to steel with loc-tite and it is very strong, but I have not had experience with bonding aluminum to steel, (I just don't know if I can trust it in the long run).

If I can make the part from steel, loc-tite the steel socket into it, and put a black oxide finish on the part at a price that is reasonably close to making the part from aluminum without the finish, I would rather just go with that option and eliminate the worry.

To Griffy:

This is not a temperature sensitive application. Although at this stage I am mainly interested in comparing machining costs, you make a point about the possibility of making the part as a casting. I think it would be some time down the road before production would get high enough to warrant a casting, but I like to think ahead.

In general, how does the price of casting an aluminum part compare to casting a steel part? If I cast with aluminum, can I make the casting as strong as the machined 7075-T7 aluminum part ? What aluminum alloy would I use for a casting? I know a few alloys cannot be cast (possibly 7075)?

To Mrainey:

Thanks for the link to the software. I am not a machinist but I just downloaded the software and I will try it out. I have the CAD files for the part and I heard there is software that can estimate machining time based on a CAD file, but I have not seen any freeware software that does this.


Thanks again everyone, I would appreciate any further feedback.
John