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?

 

[EdStainless]

If you are working a lower strength then maybe not. If you are pushing to higher strength then likely yes.
We had high alloy (not steel) high strength bolts that were headed and rolled vs machined. The machined ones never came close even with good surfaces and generous radius.

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[jts20]

That's interesting. We are targeting a relatively low yield of 115ksi. What sort of condition did the material start out in, in your case?

 

[Tomg212]

Forming a larger diameter bolt or screw head through the hot, upset forging method reorients the straight/parallel material grain flow into a radial flow at the head-to-shank juncture. This radial flow vastly enhances the fatigue resistance at that highly stressed area. In any bending load or wedge effect under the head, this also provided resistance to head failure; the stresses must cause a failure path across the grain, rather than between/with the grain, as it would in a machined-from-bar product. The wedge tensile test confirms that the head forming has been done properly (no overheating of the forging billet) and that the dimensional characteristics of the head are correct (radius, head thickness, depth of engagement of a socket, etc.).

 

[EdStainless]

We had bolts custom made in K500, 625, and 718. They were all formed from rod, warm headed and thread rolled.
I have had issues with temp control in heading, head to shank radius, and final HT control. All of these have caused serious problems (bolt head falling off).
You want the grain flow around the corners where the shank meets the head that you get with heading (cold, warm, or hot). These bolts will have better strength at the junction.
So you are going to HT to 150ksi UTS or so, probably a 1100-1150F temper temperature.
How well do you know the supplier? Have you visited? Audited?


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P.E. Metallurgy, consulting work welcomed

 

[Tomg212]

Unfortunately, a significant number of bolt manufacturers are not actually competent to manufacture bolting. This is a serious matter. Any company purchasing critical-service bolting should have his subject matter expert qualify the technical competence of their chosen bolt supplier before any purchasing is done. Usually the damage done to the material through incorrectly applied processing (poorly produced raw material, over heating during forging, poor heat treatment, bad machining processes, bad thread rolling, bad plating, etc.) can't be discovered through inspection. You learn how bad your bolt supplier is when the parts fail in the field. Usually the bolt supplier outsources much of the processing ... forging, heat treatment, machining, thread rolling, plating ... to the lowest cost supplier. The fastener industry is woefully unregulated and full of incompetence.

 

[mfgenggear]

Quote" Unfortunately, a significant number of bolt manufacturers are not actually competent to manufacture bolting. This is a serious matter. Any company purchasing critical-service bolting should have his subject matter expert qualify the technical competence of their chosen bolt supplier before any purchasing is done. Usually the damage done to the material through incorrectly applied processing (poorly produced raw material, over heating during forging, poor heat treatment, bad machining processes, bad thread rolling, bad plating, etc.) can't be discovered through inspection. You learn how bad your bolt supplier is when the parts fail in the field. Usually the bolt supplier outsources much of the processing ... forging, heat treatment, machining, thread rolling, plating ... to the lowest cost supplier. The fastener industry is woefully unregulated and full of incompetence. "un quote

In the aircraft business most suppliers have to be ISO9001 or NADCAP approved. strict requirements, and all materials, heat treat, NDT & processes have to be certified.
very expensive but it prevents the above issues, as well an audit of the facilities that their quality requirements are in compliance.
when the the above is followed there has been very rare issues. It has been my experience unless there is very high shear and tensile requirements, it is much faster and cheaper to mfg from
raw wrought bar stock.

 

[Tomg212]

I originally believed that ISO9001 would be a great solution for ensuring quality of bolt manufacturers, as well. Unfortunately, that's just not the case. Correctly applied and verified through audit, that standard does a great job of determining whether the company has written procedures and whether they are appropriately followed. ISO 9001 does not, however, assess the procedures to determine whether they are appropriate for the desired outcome. You can follow totally incorrect procedures and be awarded ISO certification because you did what you said you were going to do. There are other specifications available for supplier audit, but none can replace a technical assessment done by a qualified subject matter expert. Quality audits just don't have the scope to determine the competence of a manufacturing company; only whether they are following a process.
As to the statement that; "it is much faster and cheaper to mfg from raw wrought bar stock," that is totally dependent on the type, size (diameter and length) and quantity of parts being made. If your output is to be 3 pieces, machining from bar might be appropriate (although, perhaps still technically inferior). On the other hand, if you are making 3,000 (or 300,000) that is not the case. Forming, either hot or cold (depending upon many factors, such as material type, configuration, etc.) would absolutely be the correct process.

 

[mfgenggear]

Tomg212

I should of and you caught it for small lots and expedited schedule, and I should have added that as there needs to be specific specifications for the quality of material, heat treat, and processes. in addition to iso or nad cap. far as the process of which process is economically feasible. there are machines for the quantity. standard lathe with twin chucks with live tools can easily do 1000 parts, there are multi spindle machines that can handle 1000-100000 parts. depending on the type of forging process would also determine the cost. But I disagree that ISO9001 would not be a viable solution. it has to be supplemented by each type of product and quality required on the engineering drawings.

 

[Tomg212]

mfgenggear

I appreciate your viewpoint and I understand that everyone has their own experienced-based opinion. My experience happens to be explicitly in this arena. I've been in the hot-forged, high-integrity, critical-service bolting industry since 1972 ... 49 years. I can't argue with your experiences, but I do understand mine well. My experiences lead me to make no assumptions and to take nothing for granted.

 

[mfgenggear]

Tomg212

I gave you a star my friend. we have about equivalent experience in years, I do listen and I am constantly learning. I done mostly job shop

 

[SwinnyGG]

I disagree that ISO9001 would not be a viable solution

ISO certifications are only valuable if the processes being audited are valuable- I've worked for multiple companies which frequently touted their various ISO specifications- none of which meant anything because the people in charge made sure the processes were vague enough that 'following them' had little effect on anyone's actual methods of performing the work, or any real effect on the end result.

 

[EdStainless]

I tore someone apart in an audit recently because they had no quantitative verification that operators knew the procedures, could follow them, and that the results were correct.
The old days of training being that you attended a class are gone, the current wording requires verification of everything.

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P.E. Metallurgy, consulting work welcomed

 

[SwinnyGG]

Verification against the established processes - but not verification that the processes make good quality product. Big difference.

 

[EdStainless]

But if the process is wish-washy then actual verification becomes impossible.
There is now a way to fight people that are following bad procedures, ask to see the measured results.

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P.E. Metallurgy, consulting work welcomed

 

[SwinnyGG]

Right, but ISO auditors cannot possibly be experts on everything.

I've worked for more than one company that had perfect ISO audits and made bad product every day of the week.

 

[mfgenggear]

maybe I simplified a little. the key with any company is a well trained staff and employees and keeping up with training. and a management that is proactive in training new employees. passing on the experience of the journeymen and engineering staff.. a well established company that are experts in their field is invaluable. no amount of procedures will work unless the engineering and the factory are well trained and experienced.
in addition there are well thought procedures, as well as suppliers that have the same key procedures and experience. I too have seen were corporations tried to make their own highly complexed parts and failed because not having the above. and takes years of having key people who are experienced. as said tho all inclusive the right procedures have to be in place.

 

[Tomg212]

My industry, Bolting, typically offers few barriers to entry. Anyone with a cell phone and a little basic knowledge of the industry language (do you know the difference between a bolt and a nut?) can go into the business of buying and selling fasteners. You don't need an office full of people or a warehouse full of inventory. You don't need any engineers, any metallurgists, any quality professionals, any subject matter experts, any books of product specifications and standards. You don't even have to know how to correctly manufacture bolting or have any industry experience. You only need to know who you can buy from and who you can sell to. If you buy at a lower cost than you can sell for you can be in the bolt business. Most fastener companies start that way. Within a couple of years, you decide you can make more money by cutting out the middle man and start "manufacturing" yourself. You buy a saw, a hammer and a set of die stamps to mark a "B7" on the studs you are now cutting from threaded rod imported from a low-cost country. If you're really successful, you buy a forging press and start hot forging. Or, you go to a forging source (the lowest cost forger you can find) and buy forgings you then send to the cheapest heat treater. Cut some threads on those and ship 'em! YOU DON'T HAVE TO UNDERSTAND A SINGLE THING ABOUT ANY OF THE PROCESSES!!!!! If you price is lowest, you can sell your product. If you follow your written procedures, you can hang an ISO certificate on the wall, no matter how incomplete, inaccurate or incorrect the procedures are. Just make sure you follow them.

 

Tomg212,
Excellent summary of not just your business but the metal selling industry in general.
It's become franchise owners and call centres and a general loss of technical and industry knowledge.

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

 

[SJones]

Interesting discussion. People do lose sight of the fact that ISO 9001 is a quality management system certification, and not a product certification. The oil and gas industry has had many issues with fastener quality that has got the US BSEE and National Academy Of Science involved, prompting API to issue API Specs 20 E and F. These specs demand product manufacturing qualification, not just quality management system certification. Then it boils down to @Tomg212's point: "none can replace a technical assessment done by a qualified SME." So, the target shifts - what constitutes a trustworthy qualification? Does the purchaser believe a qualification dossier stamped by some individual from an inspection agency, or do they undertake the expensive qualification exercise themselves using someone with verified qualifications and experience?

Steve Jones
Corrosion Management Consultant

http://www.linkedin.com/in/drstevejones

All answers are personal opinions only and are in no way connected with any employer.