Turn or mill this part? (or machine as two pieces and join somehow)

[dubc4]

I'm looking to make a small aluminum cup style hydraulic cylinder. (single acting)

I can't seem to figure out the best way of going about making the "body" of the cylinder. I've attached a picture of the basic shape (cross section). There are some dimensions on there in mm, but they are just rough figures. I do not know yet what they will be, but I do know the depth of the cup will be approximately 50mm.

Since there will be seals on the piston that run along the inner faces, the finish and tolerances will have to be pretty good (have to get it hard anodized after). I'm wondering if it is practical to have this shape turned? I was told that it will be pretty tough to do at that depth... Then I considered milling, but it seems that the inner sleeve might be too tall. Having a relatively small diameter end mill reach that far would probably lead to deflection and poor surface finish / tolerance.

I've also considered making it two pieces and having the inner sleeve welded to the outer sleeve from the backside. However, this only welds them at the back and I'm concerned about the integrity of the whole piece and warpage from the heat.

Would love to hear everyone's thoughts.

Thank you!

 

[MikeHalloran]

It can be made in a lathe with a trepanning tool, or probably three tools; one to rough plunge, one to finish the ID, and one to finish the (OD).

Getting the chips out without them forming 'birds nests' will be a bitch. It will be easier with a free machining alloy like 2024-T4 or similar, _IF_ you can get enough spindle speed to break up the chips into small flakes and make them fly out. I'm thinking at least 3000 rpm for the 70mm and 90mm diameter cuts, more if you can get it. Trying to cut slower will just jam up the chips and break tools. Machinists who 'baby' their tools so they last forever will not be able to make the part successfully. It's a 'balls to the wall' part.

You will need modest radii at the 'corners' of the recess, or you will spend a lot of money replacing the cutters.














Mike Halloran
Pembroke Pines, FL, USA

 

[CoryPad]

How many do you need?

Impact extrusion can make similarly shaped parts, although I think the depth:diameter ratio would make it difficult to make in one piece.

A two-piece design made from wrought parts (tubes, forgings, extrusions) could be welded by multiple techniques, although friction stir welding appears to be the best choice based on tolerances and distortion.

Either of these options would be expensive unless the required numbers of pieces are high.

 

[ornerynorsk]

Mike is spot on. You can actually use a roto-broach to rough it out, then come back and finish with trepanning tool. This is definitely a lathe piece. Anodizing is going to present a challenge. The current density is going to be very low on the inside feature, and will probably require some special fixturing or anodes made to accommodate the part.

Good luck.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[dubc4]

Thanks to all for the replies.

Gives me some ideas in the meantime.

At my work we actually have a similar piece being made from AISI 4340 in Asia. I might be able to have this made there (easier in Al.? ) since they have the tooling.

Thanks again!

 

[MikeHalloran]

Do not ask your Asian vendor to run the part in aluminum.

In all probability, the machine they use for steel can't get anywhere near the RPM required to make friable chips in aluminum. They will fill the cavity with long birdcaged chips and break the cutting tool.



Mike Halloran
Pembroke Pines, FL, USA

 

[Bugie]

Tyrn it for sure

Regards
Greg

 

[jthornhill]

Just wondering why something like this couldn't be done? I'm assuming your piston is moving in the annular space between the barrel sections.

 

[dubc4]

I'm assuming the ring on the bottom is to be welded in place.

I did have a similar two piece design drawn up that would require welding. I'm not opposed to it, but I was hoping there was an elegant (and cost effective solution) that could produce the part in one piece.

 

[jthornhill]

Yes, I've sketched it as 3 pieces: inner barrel, outer barrel and ring.

Honestly, depending on how many you are making and your timeframe, welding may well be a good and cost-effective solution. It shouldn't require any special tooling on the part of the machinists unless you wish to skim the barrel after welding.

Is there any particular reason you've chosen to go with aluminum for this cylinder? What kind of pressure are you expecting?

 

[silveringchap]

Depending on the batch size, one method would be to rough turn the part first omitting the groove. Then chain drill the groove and then finish turn. The chain drilling should break up the swarf. If it was a large batch then I would knock up 2 or 3 grooving tools.

 

[dicer]

2 parts and EB weld it.