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"End forming of needle"


Dear Sir,

We are interested in forming hemispherical closed end of hypodermic needle of 20 G i.e.0.9 mm OD and 0.7mm ID.

Material Type: Stainless Steel 304, 316 or 316L

Condition : Hard and preferably should be maintained

We are attaching drawings for your reference and suggestions to us.


Please reply by your earliest.

Thanking you,

Amrut Patel
- Ahmedabad, India



My first suggestion would be for you to go to a local 'pipe bending Company' for some advice ... although you can be l00% sure they would have never 'bent' something so small !

Bend radius! If you cold bend your needle, either it will break or it will flatten out. The absolute min. bend radius I would consider is 6 x diameter and that's using heat to form over(i.e., around) a mandrel. Maybe start off @ 8. The larger the radius, the better (quality) the bend.

You state that the needle's end(s)are closed. In the metal pipe bending field in order to make perfect bends, they use a 'rosin' which is heated up to well under 100 °C but, upon cooling, becomes solid. This allows for excellent bends to be made in certain materials (copper) without heat.

Somehow that sure doesn't seem feasible for you. Summary... use heat (to red hot), use a large bend radius.... and cross your fingers!

freeman newton portrait
Freeman Newton [dec]
(It is our sad duty to advise that Freeman passed away
April 21, 2012. R.I.P. old friend).



I understand your drawing to show a section of the tube, with the end closed. I see nothing in your query or sketch about bending. I think Freeman has mis-read the situation.

Assuming you need a gas/liquid-tight closure, you'll probably be able to get it done by a company that manufactures thermocouples. The usual way of closing the end of the metal sheath of mineral-insulated thermocouples is by TIG welding. This is on tubing down to a couple of mm inside diameter. It's a small TIG-welding setup! For a tube as small diameter as yours, you wouldn't need any filler metal.

Probably, electron-beam welding would also do the job OK, but might be a problem accommodating the tube in the vacuum chamber. I'd go for the TIG.

Bill Reynolds
Bill Reynolds [dec.]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.


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