Which Set Up is More Structurally Sound?

[sethro5hc]

This is a hitch attachment product for an automobile. We're increasing the angle that the hitch attaches by +3 degrees, the factory has informed us that they'd like to do it one of the following two ways.

1) change angle A
2) change angle B

changing angle B would likely be easier, but which would be most structurally sound. As a background, angle B would just be bent an additional 3 degrees, while angle A would mean cutting the parts on the left backwards and welding the part with its current 90 degree bend on at a 3 degree incline.

Changing angle B would leave the shearing on that weld having roughly the same effect but would change the forces on the bend shown at angle B, while changing angle A would change the forces on that weld.

That's a simplified version, but my question to you guys is which would be more structurally sound and would likely have the higher yield point? A, leaving the 90 degree bend but tilting the whole thing back at the weld, or B, just benging it up to an 87* bend rather than 90 and leaving the weld alone.

Any help is appreciated.

 

[ivymike]

I'm not seeing either one having any important effect.

Have you done an FEA of the baseline design? What happens if you change the design and re-run with the baseline loads?

 

[sethro5hc]

I haven't run any analysis, I'm fairly confident that the differences in these two changes will be insignificant for the application its used in, but a boss asked which would "maintain the overall strength/structure" of the part and I didn't want it to sound like I didn't know what was going on by saying....."um it really doesn't matter".

 

[desertfox]

Hi sethro5hc

Well I'd go for option B but only because its easier to make the modification.


desertfox

 

[ginsoakedboy]

Bending the plate to change angle B will require greater plastic deformation at the bend, which on one hand would work harden the L-section more but may also induce cracks and also it would be harder to maintain the angle of the bend at precisely 87°.

I would lean toward changing angle A but substantiate with strength analysis of the weld.

There is another option of welding a tapered shim on the L-section to change angle B.

I guess your 3 options are:

1. Additional bending to change angle B (probably cheapest, but IMHO not preferable)
2. Additional machining to change angle A (preferred)
3. Additional welding to change angle B using a shim (probably best, but not among your options)

 

[MadMango]

I would think changing the A would be the best, you want to keep your hitch tongue parallel with the road surface. B would be the easiest change, and at only 3deg, given suspension and uneven loading... parallelism probably isn't a huge factor.

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of these Forums?

 

[Ron]

Assuming rigidity of the part, changing angle A also changes angle B by the same amount. If you are considering that the current 90 degree angle should be changed, then only angle A should be changed. Angle B should remain parallel to the assumed road surface.

 

[unclesyd]

Watch the clearance for the ball receptor on the tongue.

My boat trailer has only about 1/16" clearance when making up the hitch.

 

[rstupplebeen]

If there has not been a simulation performed why would you increase it by 3deg? The consumer will probably just think you screwed up especially if you do it by method B. If you don't want to do a simulation build and break. Either one that fails above requirements is a viable solution and then choose the cheaper lighter one. I hope this helps.

Rob Stupplebeen

 

[rstupplebeen]

Is the 3deg to account for the car popping a wheelie under load?

Rob Stupplebeen

 

[ivymike]

maybe for deflection under load, to make the ball axis vertical?

 

[ebinnovate]

Hi, I guess from the date of this post you have already solved this problem. However, if you haven't, I wanted to say I think the answer depends partly on whether you believe the tensile force on this part (the load from the trailer) will be aligned with the changed part or be truly horizontal. If aligned, I would change B. If truly horizontal, you are introducing a bending moment at the curve, which will now have a slightly sharper angle and more stress concentration.

 

[dicer]

So are you saying the reciever for that hitch is not parallel to the road plane?

How thick is the ball plate/ L-plate? And what weight and trailer weight is it to take?