6AL4V Titanium stress relief? 1

[BrendanP]

Hi,

Wondering if anyone has any experience with stress relief on 6AL4V?

We machine some .090''sheet 8'' diameter, once machining is complete we may have .010'' -.015'' of distortion. Is it feasible to stress relive this post machining to flatten it back out, If so what we be the process?

Thanks in advance!

BP

 

[tbuelna]

Can you describe the machining operations performed? Usually better to change your machining process so that it does not produce unacceptable distortion rather than trying to flatten the part after the fact.

 

[BrendanP]

The 8'' diameter has a continuous spline around the outside, there is 29 holes is this sheet ranging from .200 to 1.5''.

All holes larger that .315, are pre drilled then end milled,we have optimized feeds and speeds to reduce cutting loads. First opp is to drill all holes then it is bolted in 16 positions before milled.

The residual material left is approximately 60% of the 8'' stock , so I feel whilst the machining process can be improved upon there will still be a lot of stress due to the material removal.

 

[EdStainless]

What is the heat treat condition of the material? Go back and read the AMS spec that this was purchased to.
If you want to stress relive before machining you will need a way to hold the piece flat while doing it. The best way would be to hold uniform radial tension on it while heating.
The only way to flatten it after machining is to cold flatten it.
Why do you think that a piece of thin sheet can be machined and stay flat in the first place?

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P.E. Metallurgy, Plymouth Tube

 

[DavidHansen]

My pal says you can get it hot rolled on a plate mill, flatten it, and then treat it. As far as stress reliving the post machining, I don't see why not. Have you googled it and looked through tutorials? It seems like there's a video for just about anything on YouTube. Good luck.

 

[Maui]

You can find the information on stress relieving Ti-6Al-4V here:

https://www.atimetals.com/Documents/ati_6-4_tds_en_v1.pdf

Annealing at 1,700-1,900°F (927 - 1,038°C) is done where high hardness, tensile and fatigue strength are desired.
ATI 6-4™, Grade 5 Alloy can be heat treated in several ways.
1. Anneal: 1,275 -1,400°F; (691 - 760°C), ½ to 2 hours, air or furnace cool
2. [bold]Stress Relief Anneal: 1,000 -1,200°F; (538 - 649°C), 1 to 8 hours, air or furnace cool[/bold]
3. Solution Heat Treatment: 1,675 -1,750°F; (913 - 954°C), 1 hour, water quench
4. Aging Treatment: 975 -1,025°F; (524 - 552°C), 4 to 8 hours - air cool
The very best of properties in the solution treated and aged condition are obtained in small cross sections that are rapidly
quenched. Larger sections sizes and/or a quench delay may cause properties to be lower than the optimum values.

Maui

 

[EdStainless]

But the key is, has the sheet been aged?
If so they would need to stay below 950F so that they don't screw up the properties.
On the other hand if the sheet is annealed (or annealed and stress relieved) they can use the 1100F SRA, but they need to cool quickly or they will also be aging the material.

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P.E. Metallurgy, Plymouth Tube

 

[tbuelna]

BrendanP-

Here's some information on creep flattening/straightening of titanium:

http://www.nssmc.com/en/tech/report/nsc/pdf/6208.pdf

http://www.totalmateria.com/Article97.htm

"Creep straightening may be readily accomplished during the annealing and/or aging processes of most titanium alloys. However, if the annealing/aging temperature is below about 540 to 650°C (1000 to 1200°F), depending on the alloy, the times required to accomplish the desired creep straightening can be extended. Creep straightening is accomplished with rudimentary or sophisticated fixtures and loading systems, depending on part complexity and the degree of straightening required.

Creep flattening consists of heating titanium sheet between two clean, flat sheets of steel in a furnace containing an oxidizing or inert atmosphere. Vacuum creep flattening is used to produce stress-free flat plate for subsequent machining. The plate is placed on a large, flat ceramic bed that has integral electric heating elements. Insulation is placed on top of the plate, and a plastic sheet is sealed to the frame."