CDA360 Brass alternative?

[quizzical1]

Hi Guys,

We manufacture parts that must be machined into a cup shape (.500" OD x .400" ID x .500" Lng - .06" thk wall on bottom). The bottom gets "bumped" after assembly with a .25"R spherical nose tool, dimpling the part into shape.

Problem is, while the part machines perfectly, the cold forming "bump" process causes cracking. The suspect parts and bar stock were checked and found to be 75B Rockwell which I believe is the spec for Annealed state.

Question: Is there a better copper alloy (e.g. CDA353 Brass) that both machines well, cold forms well and is readily available in 1" dia bar stock?

 

[TVP]

UNS C36000 free-cutting brass that has been annealed will be closer to 20 HRB than 75 HRB; that hardness corresponds to bar/rod that has been cold worked ~ 20%. I did a quick search and could not find any copper alloys other than 353 or 360 reasonably available off-the-shelf in bars. 353 would be a little better in terms of workability due to its reduced Pb content. UNS C26000 (cartridge brass) has excellent workability, but is only available in bar/rod from producers like Ansonia, and not generally from service centers. One question: why not cold form/extrude the part first using a grade like 260 and then just clean up the necessary dimensions in a secondary machining operation?

 

[EdStainless]

I am glad that you said it first TVP, it didn't make sense to me.
This sounds like a stamped/drawn part, not machined from bar. A 1:1 draw ratio is nothing for these grades. Look at cartridges.
And annealed brass should be a lot softer than RB75.

= = = = = = = = = = = = = = = = = = = =
Rust never sleeps
Neither should your protection

http://www.trent-tube.com/contact/Tech_Assist.cfm

 

[quizzical1]

Thanks guys...I really appreciate the help.

TVP - You are correct - the best way would be stamping / drawing the cup out of 260, but unfortunately we are in a situation where everthing revolves around CNC machined parts and tooling up for stamping isn't an option (qty's are too low to justify the expense).

 

[TVP]

Using annealed material appears to be one solution to this problem. Either the initial bar stock should be annealed, or you can anneal the CNC-machined blank prior to forming.