Hydraulic Cylinder Casing Turning?

[Moparmatty]

Is anyone on the forum currently building hydraulic cylinders on cnc lathes. We are currently looking at simplifying/increasing our cylinder production. Just looking for feed back on what equipment you are currently using.

Thanks,

[307startup]

What are you looking for exactly? I have some questions that might help me give you better answers. Are your porting through the rod and buttplate? Are you welding your buttplates on before machining? Are you welding your NPT ports on before machining?

[RICHARD ZASTROW]

What sizes are the cylinders in question?

Dick Z

[Moparmatty]

Cylinder sizes are 3" - 6" o.d. tubes with lengths from 8.5" - 65".

NPT ports are currently welded on a head of time and cylinder caps with porting are welded on afterwards.

We currently do all of the tube/casing work on manual machines. Pistons, glands, heads, caps are done on cnc and manual set-ups.

Any other info needed?

[307startup]

I'm assuming these are the normal weld on bungs that are approximately .75" tall?

I'm also assuming these are using threaded glands?

I would consider facing and beveling the tubing for buttplate on the manual machine, weld on the butt plate, then send to the CNC for threading.

As you know, welding does cause some distortion to the bore. By doing ALL of your welding processes before machining, you minimize any risk of your thread going out of round.

I prefer machining the buttress threads after the buttplate is welded on due to the fact that the tubing is less of a resonant structure with an end cap and is less likely to stress crack if using a four-jaw chuck for workholding (due to overtightening...which isn't hard)

If you are looking for the CNC equipment to do the job, I would strongly suggest looking for a large-bore hollow spindle cnc lathe. We have a Haas at work that does similar jobs. You're going to want a machine that has a bore AT LEAST 1" over your largest cylinder you manufacture. This is to allow for loading the part from the rear of the bore on your longer parts as well as allowing for adequate clearance for your ports. This way you can grab aft of the ports on the front chuck....not the most rigid setup, but the one that provides the least amount of distortion to your bore at the thread.

Dual chucks are fantastic for these longer parts as they cut down on any axial misalignment from gravitational forces pulling on the cantilevered load. If you decide to forego the dual chuck option, consider making some kind of end-cap "booty" that will fit over the welded buttplate reasonably snug and hold the tube centered in the bored of the lathe. Makes dialing in easier as well as providing for less stress on the machines bearings from a long unsupported load on the singular chuck.

Have any other questions, I'll be happy to answer them.

[Moparmatty]

I'm interest in doing the tubes between centers using expanding mandrels in both ends of the tubes. Doing it this way would allow machining of both ends at the same time, no dial indicating needed.

[307startup]

Gotcha...didn't realize this was an external thread with a thread-on gland rather than thread-in gland.

Even with an expanding mandrel, unless there is a definite gauge point on them, some indicating will be necessary in order to adjust axially...too loose or too tight on the adjusting rod will have them swapping high/low spots from center. Not to mention the catastrophic failure that could arise were the expanding mandrels not expanded sufficiently.

I suppose it would be possible to mount a pneumatic/hydraulic operated mandrel in the chuck end and also on the tailstock using the ram to engage. That would be the ultimate bang for your buck. But dang...the engineering and fine tuning. Not to mention developing a process with rigidly defined protocol for absolute repeatability. Because you will need that in order to train an operator correctly. No ifs, and or buts about it. Liability is a *****, and having an operator say "but so & so showed me to do it this way" with no proven and documented company policy or procedure allows for them to collect Unemployment Insurance at best, or Workers Compensation and/or a lawsuit at the worst, should that employee press the Go button and all is not kosher with the workholding setup. Not to mention machine damage. Gives me the willies thinking about it.


Why not simply use appropriately sized live centers mounted at both ends? Seems overly complicated to use expanding mandrels when proper programming and appropriate tooling selection for clearance would allow you to use off-the shelf bullnose centers.

That is a significant amount of travel you will need. Daewoo, Haas, Okuma and I'm sure other machine manufacturers make extended-travel versions of their slant-bed lathes.

The only question I have is....why such an expensive machine to do something you can or are probably already doing on your manual lathes? Basically you will only be using two tools...hardly worth the expense of a turret equipped machine. Which would then allow you to look at some of the flat-bed offerings from such machine manufacturers.

Which again begs the question...how much cycle time can you trim going from the manual setup to the CNC setup? What's your ROI? Wouldn't outfitting your manual lathes with scales/DROs and air-kickouts be a quicker proposition as well as much less expensive?

[Moparmatty]

Expanding mandrels would be used for doing the internal threads as well. We have some guys the used to work at Parker and that's how their older VDF lathes were configured. The mandrels were set in say 5" from each end of the tube and the tooling was configured to allow machining of both ends in one set-up.

Not sure if there is any cost justification at all. This is what I am trying to figure out.

http://www.bardonsoliver.com/

This is another option I am looking at.

[RICHARD ZASTROW]

You might find the Seneca Falls center drive lathes interesting.

Dick Z

[Moparmatty]

Thanks Richard.