Tightning torque aluminium? 1

[SteelAndSteel]

Hi

I have an aluminium detail with some helicoil holes (M6, M8, M10 and M12). The material is EN 5052 T5, which is an aluminium alloy which has Rp0,2 on 60 MPa, which isn't that much. The bolts is 8,8

What tightening torque should i use? There r tabels for 8,8 screws, but the strength of the alloy is only 60 MPa so i wonder if i should use less?

 

[ctopher]

I think the torque listed on the HeliCoil spec should be sufficient.

Chris, CSWA
SolidWorks 13
ctopher's home
SolidWorks Legion

 

[SteelAndSteel]

Ok, if we look at page 7 on the following document

http://www.collycomponents.se/wp-content/uploads/2013/05/Helicoil-Plus.pdf

In the first row in the table it says for M12 15.5 Nm on 1st screwing-on; but what is the rows below about? 1st screwing-off, min and 5th screwing-off, min ???

 

[Tmoose]

For charts of what UNBRAKO felt in 1996 were reasonable tapped hole thread strength (achieved by length of engagement) to consider for a quality socket head capscrew ("stronger than the 8.8 fastener you described ) into brass, aluminum, cast iron and mild steel, look at page 66/68 here.

http://www.dalecompany.com/pdf/UNBRAKO.pdf

Generally helicoiled holes are considered even stronger than holes tapped directly in the material.

Plenty of machine design books would offer the 1.5X diameter rule to develop full strength of the fastener in generic aluminum.

 

[tbuelna]

With regards to your specific question "How much tightening torque should I use?", it all depends on the requirements of your design. Why torque and preload your fasteners more than the application requires? If you wish to know what the axial load limit of the helicoil insert is when installed in a given substrate, the product literature will usually provide a total root shear value for the external thread of the insert. You can then multiply that number by the shear strength of the substrate material to get an approximate value.

 

[Tmoose]

"Ok, if we look at page 7 on the following document

http://www.collycomponents.se/wp-content/uploads/2...

In the first row in the table it says for M12 15.5 Nm on 1st screwing-on; but what is the rows below about? 1st screwing-off, min and 5th screwing-off, min ??? "

I believe that table is just for inserts with deformed threads to provide a degree of self locking.
So the "screwing off" values are likely the minimum prevailing torque expected of an insert in good condition when the mating fastener is removed and installed repeatedly.

 

[Screwman1]

If your goal is just to get the maximum clamp load on the joint safely, then a decent approach is to take a number of assemblies (using all new parts each time) up to failure, and then set your seating torque at 65% of the average failure torque. You have to be aware of the standard deviation in the failure torques, but this is a rough and dirty method that has worked well for many, many years.

 

[ameyerrenke]

I have used the same procedure as Screwman1 in the past.

 

[Ron]

Agree with screwman1...this procedure should work for any metal. We generally use 70% for steel, but galling is less of an issue for steel than aluminum.

 

[yoshimitsuspeed]

If you are running helicoils and any decent depth on them and the screws I'd bet money on your bolts failing before the holes.
Personally I'd think torquing it to the spec of the bolt would be fine but it can't hurt to test the theory.