Clamping force calculation

[SteviegtrParticipant @steviegtr]

Have you guys never heard of a mig welder. Job done. Son why have you brought your welding mask into school again. Student. Because your question is flamin stupid.

Well it is Saturday night lock up. Like doing Porrige.

Steve.

[Jeff DaymanParticipant @jeffdayman43397]

I think it is someone's homework.

+ 1 for powered bellcrank or toggle clamps, used commercially made ones for years in fixture design in industry. No sane tool designer would use a clamp like the OP's sketch. If the V block is supposed to centralize the workpiece as they usually are used, putting a big force vector on it to one side is not a good thing. The part or the V block will likely deform in some sort of bad way if high forces are applied at angles as the OP's sketch.

Good commercial bellcrank / toggle clamp at link below just FYI

**LINK**

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, if the link is pivoted at both ends, as the drawing suggests, then the top bar will still move to the left and maybe even bend the piston rod if the cylinder isn't pivoted at either the top or on the base. If the link is fixed to the top bar, then the cylinder will have to be pivoted or the piston rod will bend. It is a bad design/idea. See my rough & ready sketches below assuming the link is pivoted at both ends and the cylinder is fixed.

Regards Nick.

P.S. I also think the cylinder is at a mechanical disadvantage, the "link" would be better if it is closer to the work, but you would need a longer travel for the cylinder piston/rod.

Edited By Nicholas Farr on 03/05/2020 08:38:52

[SillyOldDufferModerator @sillyoldduffer]

Just out of interest I wondered what Fusion 360 would do with this problem. Created a model clamp, dimensions correct but omitted the cylinder & piston in favour of simulating a 9815N up pull on the end of the lever.

Running the simulation doesn't answer the exam question! At least, not in the local solver. (The paid solver in the cloud might do more, but I'm too mean to try it out of interest.)

Rather than produce actual stress values it colours the model to show where the stress is, going from RED (will break) to BLUE (no problem),

My safety simulation goes red on the axle pin, which I modelled as 10mm diameter mild-steel. (The whole model is mild steel apart from the job, in Brass, cause I like shiny things!

The displacement analysis below shows the lever arm bending but the exciting axle problem is hidden from view. The thin end of the 20 degree arm is going orange, indicating that this too is bending too much for comfort.

Not sure at all I've modelled this correctly, because the arm has penetrated the job but – without having to do complicated maths – the pretty colours tell me the axle must be beefed up considerably and that the arm needs attention too, especially at the angled end.

So Fusion 360 looks good for checking the strength of designs whilst being no good for doing homework needing numeric answers! Though I'm confident Duncan can do the sums, Fusion doesn't help me confirm or refute his answer.

Dave

[duncan webster 1Participant @duncanwebster1]

The stress in the pin may well be too high (in fact I think it is if using EN3) but if SOD's FE program is anything like the one we had at work, red just indicates the highest stress, not necessarily that it is too high. Many Chief Engineers could not get their heads round this, red = danger to them

[Roger BestParticipant @rogerbest89007]

Posted by duncan webster on 03/05/2020 18:38:34:

The stress in the pin may well be too high (in fact I think it is if using EN3) but if SOD's FE program is anything like the one we had at work, red just indicates the highest stress, not necessarily that it is too high. Many Chief Engineers could not get their heads round this, red = danger to them

Good joke, I laughed as this has been my experience too.

The wife asked why I laughed, I said "CAD joke".

That required extensive explanation.

[Author]

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