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structure dimension
5

structure dimension

structure dimension

(OP)
could some one tell me how to work out the minimum wall thickness that can be used without causing any deformation.  please refer to the file attached for furthur info.

RE: structure dimension

Is this school work?

RE: structure dimension

(OP)
no this for work project, i'm desiging a base frame for a welding manipulator, the base frame will be made out of mild steel.  i've looked for information all over the web but struggled to find what i'm looking for so if you can help i'l be very greatful

RE: structure dimension

3
Change your file to a .jpg.  I (and probably most people on here with sense) don't open zip files.  

When you talk about deformation, are you talking about permanent deformation?  Or are you looking for something that doesn't deflect at all?  (If so, then you you should use a tempered alloy that was quenched in unicorn tinkle.)  

Without looking at your model, you probably need to look at http://www.roymech.co.uk/Useful_Tables/Beams/Beam_theory.html

I assume you have some sort of tube (rectangular, round or square) that is holding *something* and you need to know how thick to make the wall.  If that's the case, then you really need to contact someone in your organization that is capable of doing this.  Even consider an outside consultant.  Nothing wrong with asking, but I think you will find a lot of people responding to your post with the very wise advice of seeking professional help on this one.  My big concern for this is that you're talking about a manipulator which can/may(?) impose some very serious dynamic loads on whatever type of base that you're trying to design.  Merely taking into account weights and offset loads can end up killing people.  That means YOU go to jail.  

As I said, I didn't look at your file, but I think you are in over your head.  Get someone to help you on this.  

 

Engineering is not the science behind building.  It is the science behind not building.   

RE: structure dimension

You need to specify what is causing the deformation. Machining, welding, normal in-use loads, etc.

ISZ

RE: structure dimension

How is it going to be held to the ground?

In the detail you show there, it appears that the upper horizontal member is butted up against the two vertical members and furthermore, the two vertical members extend higher than the horizontal support.  

Because of this, you do not have an adequate moment connection between the members.  If you assumed this as having restrained ends, you would get a certain amount of fixity between the two parts, but in reality, the vertical member would "oilcan" *out* at the upper weld and *in* at the lower weld of the connection of the horizontal support.  So, unless you change that portion of the detail, you should probably calculate it as a simply supported beam with a load in the center.  

What kind of steel are you making this out of?  If it is 40mm sq tubing, then you're probably building this in Europe.  If that's the case, then assume a simply supported beam, add any torsion due to offset of load, determine your required section modulus (including the correct safety factor) and find your corresponding tube size from the tables here:

http://www.corusconstruction.com/file_source/StaticFiles/Business_Units/Corus_Tubes/Corus%20SHS%20Hybox.pdf

The tubes you can obtain most easily in western Europe should conform to EN 10210:S355.   

Engineering is not the science behind building.  It is the science behind not building.   

RE: structure dimension

(OP)
the frame will be made out of a 40 mm steel plate and the profile will be cut using a cnc so it will require any weld.  how can i find the minimum wall thickness using simply supported beam equation?

RE: structure dimension

For the top horizontal beam only, you can calculate shear, moment, and torsion (if any) using beam formula, then check it against the allowable stresses for the metal in construction. The most straight forward method is to assume an initial wall thickness to obtain relevant member properties, calculate stresses, and perform iterations to get minimum thickness required to satisfy the stress limitations.

After you get the wall thickness, you can use beam formula to calculate displacement under the force. You can get all formula from an engineering handbook, or from the web.

RE: structure dimension

Hi ash1982

Are you intending to make the whole frame out of plate and fabricate box sections?
How do you attach your device to the structure assuming its all fabricated box section?

I would suggest if you want to fabricate sections then fabricate small "I" beams see attached sketch.
Analyse as a simple beam and you can take proportions of plate thickness for flanges and webs from standard beam sections found at this site:-

http://www.roymech.co.uk/Useful_Tables/Sections/steel_section_index.htm

also you can calculate the stresses from the beam theory from the same site but a different link:-

http://www.roymech.co.uk/Useful_Tables/Beams/Beam_theory.html

Your going to have to guess a size for your "I" beam in terms of depth and width and run some calculations, if it doesn't work try again with a different section.
I suppose one difficulty might be the 40mm width unless you can change it.

RE: structure dimension

You've also got to take into account buckling on the vertical members.  

desertfox, there will be no welding on this.  What you see in the .jpg is just a single piece of 40mm plate, cut out on a cnc.  The term "wall thickness" should actually be "member depth."  

ash1982, I would suggest you look around a parking lot at the rear bumpers of a lot of larger vehicles.  You will see 50mm x 50mm square tube being used as the structural member of receiver hitches.  I have attached a picture.  It's the part in black.  

Look at that picture, remember that these items are designed to pull 5000 pounds and handle heavy acceleration, braking, potholes, overloaded trailer tongue weights and severe abuse by a generally uninformed public and still hold up.  This is a 50mm x 50mm section that is hollow in the middle.  Take that for what it is -- an observation -- and try to extrapolate it into your application.  

Beyond that, I don't think I can help.   

Engineering is not the science behind building.  It is the science behind not building.   

RE: structure dimension

The OP states that the sketch is for a base frame.
Is this just a frame (base) to hold single column manipulator?

If not the above and just looking at initial and subsequent sketches, I think the use of the phrase welding manipulator is misapplied as the frame depicted would  be more suitable for a welding positioner.  All welding manipulators that I'm acquainted with are composed of single column with a radial arm or gantry  to carry the welding head.  If this is indeed for a positioner the loadings would be very high and complex.

Welding manipulators>
 
http://www.mitrowskiwelding.com/weld-manipulators-c-2.html
 

RE: structure dimension

Has anyone here heard of a structure that doesn't deflect when loaded?  Please tell us and explain.  There is no simple beam in the pictures or sketches shown.  Does anyone here think it's strange that we are trying so hard to respond to a question which is so ill asked that we don't know what to suggest.  Does anyone other than EngineerTex (2JAN10, 17:07) and me think this guy could kill someone, and we are helping, aiding and abetting him.  What he should do is get a good strength of material text and a good structural design text and learn his trade so he can at least ask a less dangerous question.

RE: structure dimension

(OP)
a lot of appreciation to everyone who tried to help me solve the matter.  I'm really sorry about the unclear explaintion of what is required.
dhenger i'm not looking for a structure that does not deflect when loaded, i'm looking for a mimiumum structure that can take the vertical load without any permenant deformation (Plasticity) thanx for you concern anyway.
 

RE: structure dimension

Hi ash1982

It would help if you can tell us exactly what this frame is going to have attached to it.
A 40mm wide structure as we see it doesn't look very stable on its own.
Can you tell us how the frame will be held vertical and why its only 40mm wide, also how do you intend to fasten anything to it.
We are trying to point you in the right direction is there anyone you work with that could help you also?

desertfox

RE: structure dimension

H ash1982

Thanks for the pic it does help but how is the frame attached to the other parts ie bolted, welded?
Also the geen coloured structure that rests on the frames are the attached in anyway and are they running at the centre of the frame or to either side of centre.

desertfox

RE: structure dimension

(OP)
Thanks desertfox for your intreset. The frame is bolted to the manipulator via 12 mm bolt. The Green coloured structure (Boom) sits on the center of the frame  between the two vertical members of the frame. the Boom will also be secured down to the frame by the use of adjustable block.

RE: structure dimension

ash1982, this is far worse than I thought.  Just looking at your sketch, it looks like the structure (boom) that you're supporting is a very heavy (400kg) and quite unbalanced load.  

Think about this for a second: when you stand on a diving board, the support next to the pool is in compression and the support farthest from the pool is in tension.  Apply that to your model: one of your supports is likely to be loaded to well over 400kg and the other one will probably be in tension.  You need to figure out the center of gravity of your boom and apply that information to your structure.  

Furthermore, it appears that a portion of the assembly rotates.  Is that correct?  Does it rotate about the axis of the centers of the two supports?  This fact makes it much more complicated than you first stated.  What happens when you turn the boom through a few degrees and the loading is now bending your "vertical" members?  Are you sure that the base is fixed to the ground well enough to prevent overturning of the entire assembly?  

You ABSOLUTELY MUST call an outside consultant.   

Engineering is not the science behind building.  It is the science behind not building.   

RE: structure dimension

(OP)
engineerTex, i've already made sure that the Center of gravity of the Boom is located in the center of the fixture to make sure that the load is balanced, this is why i stated that the height of the supporting frame has to be (264 mm. thanks for your guidance and i'l have to consult some one about it.

RE: structure dimension

ash1982:

Assume a simply support beam loaded on mid-span with a concentrate load:

L = beam length between center of verticals (say 300 mm)
P = applied load (200 kg + assumed/estimated beam weight)
b = frame/member width (40 mm)
h = member depth to be determined
va = allowable shear stress (0.4*fy, fy = yield strength, mpa)
fa = allowable flexural stress (0.6*fy)

From above we derive two relationships:

P <= 2*va*b*h
-->   h >= P/(2*b*va)       (1)
M = P*L/4
S = section modulus = b*h^2/6
M <= fa*S
-->   h >= [6*M/(fa*b)]^0.5     (2)

The larger h from above satisfys strength requirement. Now check performance of service:

D = deflection
E = modulus of elasticity
I = moment of inertia (b*h^3/12)

D (max) = P*L^3/(48*E*I), at center of the beam
Select a bigger size beam if deflection is too large, and repeat the steps. The result would be conservative for a statically loaded beam.

You may wish to check the vertical members:

1. Assume column simply supported on both ends, k=1.
2. Find allowable stress for respective k*L/r
   L = column length
   r = radius of gyration (of the weak axis)
3. Check compression stress (P/(2*b*h)) against the allowable. Repeat steps 2 & 3 if necessary.

Finally, check the bottom beam use the same approach as for the top beam. However, P = 200 kg + weight of all 4 members. So the bottom member shall be bigger than the top as the result.

Check my formulations for correctness. Good luck.

RE: structure dimension

Hi ash1982

I have uploaded a file which gives a formula for the depth of the top member making the assumption that the top member is a simply supported beam in truth of course its far from it but it might get you started.
I got the formula by manipulating the standard bending stress formula ie

σ= M*y/(I)          I= b*d^3/12

                             y = d/2    
                            

                             where b= beam width 40mm
                                   M= bending moment
                                  
                                 I = second moment of area

You need to check the vertical legs as suggested cntw1953.

Also if your profiling this plate I would put large radius on all the internal edges, square corners as you have them in your model will give rise to large stress concentrations which might cause you problems.
Seriously you need to get some help from someone your working with as we cannot see or know all the issues.
Personally I would do some ballpark calculations and ask the stress guys to model it to finalise the design.
  
  

RE: structure dimension

ash1982.

Is there going to be any rotation of the manipulator once the boom is placed inside it?

RE: structure dimension

Very good point on the trailer hitch EngineerTex.   

"I came, I saw, I made it better."
-Ode to Industrial Engineers
Will ChevronTexaco Corp.

RE: structure dimension

Things you need to do:
1. You need to come up with a free-body-diagram to solve for the weight distribution (which will include finding the CG). If parts can move, you may have to consider several different orientations. You may also need to think about other possible loads on your parts.

2. Determine exactly what material you will be using and what it's properties and capabilities are - then knock the capabilities down at least by half (you should probably have an even larger factor of safety for something like this - it looks like something that might end up being beat to crud)

3. Once you know the weight distribution and the material specifications, you'll have to look at buckling and yielding in your structure for your worst case load condition. If there's any question about which case is the worst case, you should calculate it for all the cases that look like they might be the worst. Pay special attention to stress concentrations in areas such as holes, fillets, and larges changes in net section. Welds are an area of special concern because the material properties of a weld are often lower than that of the parent material. In addition, welds are often at the same locations as stress concentrations. Check literature for information on analyzing weld joints (Shigley's Mechanical Engineering Design is good for basic analyses)

4. You'll have to determine what an acceptable deflection for your part is and make sure the cross section of your supports. You should calculate the deflection your parts under worst case loading. If there's any question about what is the worst case, calculate all cases in question.

5. If your structure fails to meet your requirements in any of the calculations you performed, change your geometry (or material) and iterate until you have a design that works.

If you don't have experience with the types of analysis that I mentioned above, you may need to go get outside help. It looks like you're dealing with some pretty heavy parts, and that a failure could end up hurting someone. You could always try your own hand at an analysis, then hire a consultant to check your work.
 

RE: structure dimension

I just looked at this thing again and you mentioned that it's a "manipulator". I assume that this means it's moving in some way. Make sure that you understand both the dynamic and static loads on the part, as they're both important. Understanding the loading can sometimes be a very challenging part of the analysis.

RE: structure dimension

let's start at the beginning ...
can you solve the reactions of a beam ?  that's what the green arm looks like to me.  if you can, consider the two extremes on position of the arm.  this will give you the load into the grey frames (that you're designing).  hint, if someelse is designing the green arm, you could ask for their reactions.)

once you've got the load applied, the frame divides into beams and columns; each can be analyzed in turn.

point to ponder ... consider lateral load, what looks to be your x-direction, along the green arm ... the grey supports are not very effective in this direction.

each of your frames will be supporting something like 200 kg (mass, i assume) = 2000N ... not a heck of a lot.  what safety factor will you apply ? 2?, 4??

btw ... rant removed ('cause i couldn't be bothered to type it a 2nd time)

RE: structure dimension

ash1982,

   I agree with EngineerTex.  If you have to ask questions like this, you should not be doing the job.  Even if we do provide useful help on your wall thickness, that is not the only thing that might cause a catastrophic failure.  

   Even if people are not hurt, you could still be producing something that will not work.  Your company will be embarrassed.  You will be embarrassed.  Your customer will be pissed off.  

               JHG

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