Lift Lug Punched or Machined??
Lift Lug Punched or Machined??
(OP)
Can you punch the center hole on lifting lugs, or must they be machined (ex: with a MagDrill)??
I want to speed up production and reduce cost, so punching would the obvious choice, but I am concerned with the metallurgical changes that occur during punching. Would punching greatly reduce the structural integrity of the lug?
MAterial is 1/2" M.S. Plate.
Center diameter hole is 1.75", with 1.25" of material from edge of hole to edge of plate all around.
Thanks in advance.
I want to speed up production and reduce cost, so punching would the obvious choice, but I am concerned with the metallurgical changes that occur during punching. Would punching greatly reduce the structural integrity of the lug?
MAterial is 1/2" M.S. Plate.
Center diameter hole is 1.75", with 1.25" of material from edge of hole to edge of plate all around.
Thanks in advance.





RE: Lift Lug Punched or Machined??
RE: Lift Lug Punched or Machined??
RE: Lift Lug Punched or Machined??
I would not laser or waterjet the hole, because of fatigue issues caused by having the direction of the machining marks in the wrong orientation. You will want to have any microscopic grooves left by machining to be tangential, as opposed to axial.
Some of this was in a post a few months back:
http://www
Engineering is not the science behind building. It is the science behind not building.
RE: Lift Lug Punched or Machined??
RE: Lift Lug Punched or Machined??
I have the same aversion any cutting nicks in the hole on the axis of the pin as EngineerTex does. The pl. thickness, and thus the pin bearing length and bearing stress, and the stresses in the pl. are still outstanding, as are the welding details.
RE: Lift Lug Punched or Machined??
The lifting lugs are welded 1/4" fillet all around.
We do have access to a waterjet table, but the waterjet is expensive to run and cutting 1/2" steel would take some time, and use more consumables. Thats why I was thinking punching would be much faster.
Line bore sounds like it would be easy, fast and cost effective. That or cut them on the waterjet and allow for some left over material, and clean up the hole afterwards. like dhengr said.
RE: Lift Lug Punched or Machined??
it is one of the easiest & cheapest manufacturing methods.
it would be cheaper than milling/boring.
with out a drawing & it's requirements it hard to discuss what is a viable manufacturing method would be.
punching would be cheaper if the the material thickness to punch diameter ratio will allow it. however halve of the hole lenth is deformed and not cut.
if the hole is critical the boring is an option as said before.
RE: Lift Lug Punched or Machined??
Regards,
Mike
RE: Lift Lug Punched or Machined??
RE: Lift Lug Punched or Machined??
RE: Lift Lug Punched or Machined??
My friends in the GOM oil patch insist on bored and reamed holes and full penetration welds on all lifting lugs.
Mike Halloran
Pembroke Pines, FL, USA
RE: Lift Lug Punched or Machined??
You may get by with this design because it's only used once, or a few times in its life; or the actual load is fairly light and those are the only shackles the end user has. But, that doesn't make this good design, or indicate a real understanding of the problem.
RE: Lift Lug Punched or Machined??
Drop a skid in the dirt next to a landborne rig, and you get to dust it off and maybe unbend a few things.
Drop it next to a drilling platform, and somebody pays millions a day while you fish it out of the water or build a replacement. I'm guessing that something like that happened once a long time ago, and everyone decided that full-pen welds are cheaper than delay.
Not my rule. To tell the truth, my (now former) fab crew just flat refused to build skids any other way. ... and had finished building my first skids before I had finished reading the specs we were to meet. I'll miss those guys.
Mike Halloran
Pembroke Pines, FL, USA
RE: Lift Lug Punched or Machined??
3-3.3.3 Fatigue Loading
"Pin holes in connections designed for Service Classes
1 through 4 shall be drilled, reamed, or otherwise finished
to provide a maximum surface roughness of 500 micro-in. (12.5 micro-m) around the inside surface of the hole."
Commentary:
"Pin holes in lifting devices used in construction
(Service Class 0) are at times flame cut. Experience
shows that this is acceptable practice for devices not
subject to cyclic loading. Connections in devices
designed for Service Classes 1 through 4 shall be
machined as required to avoid the notches that result
from flame cutting."
3-3.3.5 Pin-to-Hole Clearance.
when the diameter of the pin hole is greater than 110% of the diameter of the, the effect of the clearance shall be taken into account when determining the strength of the connection.