Force required to dimple metal with sharp tip
Force required to dimple metal with sharp tip
(OP)
What formula or method would you use to determine the force required to push the sharpened tip of a round shaft a certain distance into a very thick piece of metal (magnesium in my case, but I assume the formula would be the same using the proper E or Fy or something for whatever material)? To be specific, I want to push a sharpened steel shaft (45° point) 1/2" into a piece of magnesium that is 30" thick and 18" x 18" square. How do I calculate the axial force required to do that?





RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
TTFN
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RE: Force required to dimple metal with sharp tip
I am a structural guy so for steel there are bearing calculations that are essentially 1.8 x Fy x Bearing Area to theoretical failure (which is quite a bit less than the 3xFy stated above by CoryPad), but it doesn't seem quite right to call this a bearing surface area failure.
RE: Force required to dimple metal with sharp tip
TTFN
I can do absolutely anything. I'm an expert!
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RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
You are driving a cone into the large diameter "log" so the initial penetration starts with a near-zero-area point touching a near-zero area tangent wall on the side of the log. Then, as this point goes in, the contact area increases as two things happen: Unlike a shear punch through a flat metal, the contact area increases proportional as all three of the depth of the cone AND the angle of the cone AND the depth of the side of the log increase, while the shear force of the flat metal remains the same all of the time as the diameter of the punch.
So I expect your initial pressure and initial torque to be very low, and initial penetration depth starts very low then increases to some "stall point".
RE: Force required to dimple metal with sharp tip
je suis charlie
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
In the end, I still think that all of that information (except maybe the flat face bit) is not required to answer the question, if there is an answer. It doesn't matter why I want to do it this way or how the shaft is driven, I just want to know if there is an equation that describes the normal force required to drive a shaft into a material. MintJulep gave a good resource, but as others have clarified, it only works in the elastic range. Does anyone have a reference for an equation in the plastic region?
RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
NO... How’s that for an answer without any questions or discussion?
If you don’t want to discuss your problem, we don’t really give a damn what you do, or why, or how. There is a lot of engineering knowledge and experience here on E-Tips, and many people more than willing to waste their time on you problem and to try to be of help. But, with your attitude, who cares. I just deleted the page of thoughts and comments I had started for you to consider, since I don’t have a quick formula.
RE: Force required to dimple metal with sharp tip
http://www.sciencedirect.com/science/article/pii/S...
RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
As an experiment, you might try using a cutting tip, like the end of a big drill, instead of your 45 degree anvil. It might be a lot easier to drive it. You might have to experiment with the pitch of the driving thread. As a SWAG, maybe use a 3/4"-16 thread? Maybe use a ball screw to minimize driving force as well.
Maybe use a 3/4-16 rod with an adaptor, threaded at one and and a socket for a 5/8 or 3/4 stubby drill at the other. Drive the same, back it out, and snug a bolt into the new hole.
RE: Force required to dimple metal with sharp tip
I would caution you against making assumptions about what is, or isn't, a critical detail. Often, there are trivial constraints that could have monumental effects, had someone been made aware of them.
To wit, the fact that the shaft is turning raises issues not only about friction, but also the possibility of galling. While magnesium is supposedly "resistant" to galling, applying that much pressure to it could change the dynamic.
TTFN
I can do absolutely anything. I'm an expert!
homework forum: //www.engineering.com/AskForum/aff/32.aspx
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RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
Sensibly, if the material is already near the melting point, the force required lessens.
At each increment in depth there will be a volume of material intersected by the cone, so divide the energy required for that incremental amount by the distance required to get the force required for that increment. Since the volume incrementally displaced is the cube of the depth, the forces should be increasing at least as the cube of the depth with some factor for increasing friction; simple enough to test with a small setup and more limited depths.
The inaccuracy to this is that it doesn't account for residual strength in the displace material, and it doesn't include material outside the cone volume that is also displaced. It also avoids the contribution of elastic deformation outside the plastic zone and the friction between the cone and the material being displaced. Accounting for torque applied and thread friction is a separate issue.
I don't imagine the amounts from these contributors are equal to the initial volumetric displacement, so doubling the values from melting should be representative.
Altogether I would not expect a simple formula.
I would probably pre-drill the indentation, although since similar amounts of material are displaced, one could look at the power absorbed during the process to also make an estimate similar to melting the material.
RE: Force required to dimple metal with sharp tip
In this case, the volume of the cone is pushed INTO the base metal around the cone (no metal is removed at all) and so the plasticized volume is 2x the conic volume. First you have to displace the base metal from the cone, then you have to push it through the base metal that surrounds the final cone.
RE: Force required to dimple metal with sharp tip
racookpe1978, for indentation, the metal would flow in the opposite direction of the cone, up the sides of the indenter and create a "pile up" on the surface around the indenter.
RE: Force required to dimple metal with sharp tip
I went out and we tested the torque it would take to drive the point in and found that the turning tip embeds slightly further than the fixed tip on the opposite side. A 5/8" embedment of the turning tip (which embedded the fixed tip about 9/16") required 925 ft-lbs of torque. We got the same results with four tests. We didn't have any way to test for a smaller indentation because the torque wrench we had had a minimum setting of 50 ft-lbs and our torque multiplier was 18.5:1. So we basically just torqued it until we hit the minimum 50 lbs of torque on the torque wrench (which using the multiplier was 925 ft-lbs) and that gave us the 5/8" embedment. This was quite a bit less than was reported to me originally but they said they were going off memory from doing this several years ago, so they probably just remembered wrong.
I wanted to keep playing with it for science, but the plant operations guys said they had better things to do so the experiment was ended. I can't get any of the mathematical models I tried to match the experimental results. The closest I got was about 4x more than the experimental results with a model based on delta = PL/AE. But I didn't feel like that was the model I would have expected to be the most accurate. Oh well, time to move on to something more productive I guess.
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
another day in paradise, or is paradise one day closer ?
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
je suis charlie
RE: Force required to dimple metal with sharp tip
I am amazed at the small difference turning vs plunge.
Cheers
Greg Locock
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RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
RE: Force required to dimple metal with sharp tip
from the OP ... "The shaft diameter is 2.25" and I am only trying to push the tip in about 5/8", ..."
another day in paradise, or is paradise one day closer ?