Bolt made from upsetting vs machining 8

[jts20]

Working on a bolt compliant to MIL-S-1222, which requires wedge testing, which is more of a test of ductility than a confirmation of strength. We have a supplier that can make the bolt by either method, and the material (4340) coming in from the mill is produced with a reduction ratio of 15:1. Will anything be be gained by forging the head of these bolts vs. just machining from the bar?

 

My dated copy of Machinery Handbook devotes 450 pages to thread forms alone. That is before you even pick up a wrench to tighten a single nut.

Bolt failures is one of my most popular categories for post mortem investigations. I've found fastener science to be a nearly bottomless rabbit hole.


"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[mfgenggear]

if I was purchasing bolts from a supplier to ASTM specifications.
I would require the following regardless who manufactures them first tier or second tier.
would it cost more yes. you get what you pay for.
material certification
heat treat certification
forging times and temp certifications
grain flow and a spectral analysis of material certification
dimensional sampling plan
dimensional first article report
any critical dimensions inspected 100% eg threads or close diameters
and if coated or plated certifications.

but what the heck

 

mfgenggear,

What is the cost of failure?
I have taken a similar approach for refinery clients when their HX studs fail in sulphide stress cracking, recommending the following:

[li]for each heat/lot/size of fasteners, perform a complete mechanical and metallurgical workup as follows: macro exam; composition; actual tensile test; dimensional measurements; original CMTR. The measured yield strength feeds into an engineered torquing procedure[/li]
[li]treat a heat/lot/size of a batch of fasteners as a unique part number and segregate from other fasteners[/li]
[li]specify only A193 Grade 7M for ALL applications where A193-Gr7 is specified and purge Grade 7[/li]

No client has implemented these recommendations that I am aware of. But what the heck, failed studs put bread on my table.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[r6155]

I worked in nuclear service with 12.7mm bolts to M220mm x 2500mm stud (Reactor Pressure Vessel)
S.Steel bolts 12.7 with a final data book (5 kg of documents) was discovered at the nuclear plant that are not S. Steel !!

I worked in an inspection company and received reports of tensile test, bending test, charpy, ... etc. every day.
One day I went to witness a test of bending and Charpy for a plate. Many errors !!!.

Since then (year 1990) I have learned not to trust anyone !!.

My criteria to reduce risks:
I avoid bolts and use studs, as possible.
I avoid torque, I use elongation as possible

Regards