Material US Standard A286 4

[tkwricky]

We are using the A286 screws in Jetfoil repairing. Now we are going to look for substitution. We just have the material chemical composition and physical properties. Any material specialist can tell me the tips in process of machining, HOW can we check the quality in a easy way after machining?

Thank you!!

Jetfoil repairing

 

[TVP]

I am confused by your post. Do you mean that you are now trying to manufacture a screw from an alloy that is not A286? If so, what alloy are you proposing to use? Also, what parameters do you intend to monitor after machining? Physical dimensions like minor and major diameter, thread pitch, etc.? Or do you mean metallurgical properties like strength, hardness, grain size, decarburization, etc.? We will need information on these details in order to provide you anything useful.

 

[tkwricky]

Thank you for TVP's reply.
We are going to order the "SAME" A286 material (Chinese Standard GH2132) screws from China but we are worrying about the quality. So we are looking for a EASY "method" to check the quality.
Another issue is the machining process e.g. heat treatment or machining first. What is the correct process? Any reliable (manufacturer) with reasonable price recommend?

Thank you!
Ricky

 

[yates]

Ricky,
If your screws are to Aerospace standards then they will have to be headed, heat-treated, machined and thread-rolled in that order. If parts are to industrial specs, these may allow machined parts which is normally carried out in solution state before age heat treatment.

 

[TVP]

tkwricky,

There are a number of things that can be done to ensure good quality fasteners. First, require that raw material meets specifications like SAE AMS5726 or ASTM A 453. These standards have requirements for more than just the chemical composition and mechanical properties. Next, the manufacturer should routinely check for quality, both non-destructively and destructively. Non-destructive methods include visual examination using dye penetrant testing or magnetic particle inspection, as well as eddy current testing. The latter is usually part of a 100% inspection system, such as those provided by Mectron (

http://www.mectron.net/mectron.html).

Destructive testing involves mechanical testing for yield and tensile strength, wedge testing for head to shank integrity, and fatigue testing. Military and aerospace fastener standards usually require fatigue testing, whereas industry standards usually do not. Other destructive tests involve cross-sectioning the parts to observe for defects (cracks/laps/etc. in threads, folds in the underhead fillet), observe the microstructure (grain size, deformation due to forming and rolling), and find heat treating defects (alloy depletion, intergranular oxidation). Two excellent articles on this subject were published in Structure 30, 1996, which is the Struers Journal of Materialography. You can obtain it by contacting Struers (

http://www.struers.com).

Regarding manufacturing, yates provided the usual sequence for aerospace fasteners. I am not sure that this is the standard process for A 286 fasteners, though. A 286 is a precipitation hardening grade, not a martensitic grade like most steel alloys for fasteners, and as such, the precipitation reaction responds better after strain hardening. I believe that fasteners made from A 286 are made from wire that has already been solution annealed, which is subsequently cold formed to shape. Heads are sometime hot formed instead. The threads are then cold rolled, and then finally the bolts are subjected to a low temperature aging process. Perhaps someone else can confirm or deny this, possibly with reference to a standard.

 

[yates]

You are right TVP, A 286 responds to aging with a higher tensile strength as strain hardening increases up to the max. critical point, after which tensile strength drops off again. Aerospace fasteners in this material are cold headed (unless bolts are very big) from solution annealed wire which has different levels of cold working introduced by drawing, as a function of tensile strength required (usually 130, 160, 180 ksi classes)In this way the whole bolt has the required characteristics (double shear test on shank for example) rather than just enhanced (on bolt) tensile values due to cold work introduced during thread rolling. Specifications for aerospace bolts always prefer machining and thread rolling to be done in final heat treated condition. In this way any microcracks resulting from machining will not have the opportunity to propagate during heat treatment. Also thread rolling can be performed on a clean, newly-machined surface.
Alternatively, shank and to-be-rolled diameter may, if tolerances allow, be produced by extrusion of the blank through a die, thus introducing cold work into the blank rather than the raw material, before aging.
See specs. AS 7477, 7479

 

[tkwricky]

Thank you! I feel helpful!

 

[TVP]

yates,

Thanks for the additional information. I'll see if I can't track down a copy of the AS specs.