Removing an inside weld line in a pipe

[Amir Sedieqy]

What is the best and fastest way to remove the inside weld line of pipes with 16mm outside diameter and 1m thickness so a piston can reciprocate easily inside it? I have two options in mind. one is to have the inside of LSAW pipes machined, which might be laborious. The other option is to cold draw ERW pipes (I think cold drawing LSAW pipes would not result in smooth and accurate enough inside surface). I'm not sure whether either of these methods works. Is there a better way to to this? The end product is 12cm Cylinders which will be produced at least 1000 in quantity per day.

 

[Lnewqban]

Welcome

How long is the stroke?
What are the materials?
What type of seal?
What fluid?

 

[Amir Sedieqy]

Thank you.
The stroke is 12cm, but I buy them as 6m or 3m steel pipes. They will be filled with nitrogen under 6bar pressure, so the seals are for gas.

 

[jrmichler]

Can you use a reamer? Something like this: https://www.mscdirect.com/product/details/81136251. Possibly followed by a honing operation depending on your requirements for surface finish. Reamers are also available in custom sizes if you cannot find a catalog size that works.

A twist drill could also work if you can tolerate a much rougher surface than that from a reamer.

 

[Lnewqban]

There is no economic or practical way to machine that welded seam for 16 mm x 14 mm x 120 mm, keeping a perfectly round shape in my opinion.
Could you go with seamless steel or brass tube of dimmensions close to this welded pipe?

Please, see:
https://www.grainger.com/product/GRAINGER-APPROVED-6-ft-Seamless-1010-Carbon-3CCJ8

 

[Baluncore]

Get tube with known outside dimension.
Mount tube in a jig that clamps and supports the entire length of outer wall.

Draw a lubricated circular broach through the bore, to remove internal variation and cut the final bore dimension.

Internal surface is then finished, with cutter lines on the surface in the same direction as piston travel.

The tapered broach would be made for the job, with several cutting edges, ground from tool steel stock.

 

[DaveE]

So, in production you are thinking of buying something like 3km/month of this pipe? Unless you are only worried about prototypes/pre-production then you are definitely asking the wrong people here. You need to be speaking with high volume manufacturers of this sort of thing. They (each) know what they can do most effectively better than anyone else.

edit: You need to move past what you can buy from normal distributors or have machined at normal fabricators. This high volume sort of production is all about suppliers and tooling. You are thinking about your product design, which is ok at first, but you will need to be thinking about building a manufacturing facility or negotiating with large turn-key manufacturers to make this really work.

 

[Amir Sedieqy]

Can you use a reamer? Something like this: https://www.mscdirect.com/product/details/81136251. Possibly followed by a honing operation depending on your requirements for surface finish. Reamers are also available in custom sizes if you cannot find a catalog size that works.

A twist drill could also work if you can tolerate a much rougher surface than that from a reamer.

I can use a reamer, but I'm not sure whether it is the most efficient way to do this at large-scale or not.

 

[Amir Sedieqy]

There is no economic or practical way to machine that welded seam for 16 mm x 14 mm x 120 mm, keeping a perfectly round shape in my opinion.
Could you go with seamless steel or brass tube of dimmensions close to this welded pipe?

Please, see:
https://www.grainger.com/product/GRAINGER-APPROVED-6-ft-Seamless-1010-Carbon-3CCJ8

Unfortunately, It would not be economical to use either seamless steel or brass for large-scale production.

 

[Lnewqban]

Unfortunately, It would not be economical to use either seamless steel or brass for large-scale production.

Machining is going to be more expensive in the long run, I believe.
Consider that you only have 1 mm of wall to play with.
Holding the tube for machining may introduce radial deformations to that wall, unless fabricating and adjusting special jig, as explained by @Baluncore above.

Either of the tools mentioned above will work on removing metal from the seam, but they may remove some softer material from the thin wall that is located opposed to the seam.
I would run some practical test prior embarking in massive production.

 

[jrmichler]

Look into DOM (Drawn Over Mandrel) tubing. It has a smooth surface finish on both the inside and outside, and tight tolerances on diameter and wall thickness. You might not need any inside surface preparation. It's welded construction, but the weld line disappears after the drawing operation. And the wall thickness is much more consistent than with seamless tubing.

 

[Lnewqban]

Setting and centering the parts in the tool and the process of machining are also time consuming: 1000 pieces per day means 2 per minute for a normal shift of 8 hours, which seems almost impossible to achieve with a shop tool such as a broaching machine.

Please, see:
https://en.wikipedia.org/wiki/Broaching_(metalworking)

 

[Baluncore]

Setting and centering the parts in the tool and the process of machining are also time consuming: 1000 pieces per day means 2 per minute for a normal shift of 8 hours, which seems almost impossible to achieve with a shop tool such as a broaching machine.

For quantity production go for drawn tube that does not require weld bead removal or surface machining. If you cannot do that for a prototype run then I suggest a circular broach because;

1. It is the fastest process available that will remove an internal weld and finish the surface, while avoiding tool marks that may damage the piston seals. That satisfies the OP weld bead removal in the fastest possible way.

2. Tool cost is significantly lower than expected since the broach tool can be made in a lathe or cylindrical grinder. It can be sharpened easily as required, without loss of profile.

3. The jig needed to hold the workpiece tube is also very simple to make. It can operate like a collet, that clamps the tube while the broach pulls the workpiece against a low end step in the jig.

4. Pulling will self centre the broach in the tube. If you have not used a broach before then you will not appreciate what can be achieved, or the elegance of the solution.

5. If throughput or reliability was a problem then, two machines with a shared pool of 5 broach cutters, would provide sufficient redundancy to maintain production.