Titanium Hot Forming 2

[Bradbury]

A little Help Required.

I am looking to hot form sheet titanium of thickness 0.7mm and 0.9mm,

I am currently forming parts (around 200/anum)with a press brake. This is time consuming and due to material chemical composition for each material batch, spring back is varied.

Thus programming the press brake is not an option - unless someone developes some super software that lets you enter the material composition and the press break works out the spring back and tells the operator which tool radii to use at each forming stage.

The part profile is of aerofoil form - thus many radii.

As you can imagime forming each part is very labour intensive.

Hot forming may reduce labour skill and improve product repeatability, however cost effectiveness could be the deciding factor. (male and female tooling with press operation)

Spring back is eliminated at 450 deg C.

My question is what material would be most suited to thermal cycles and be suitable to press titanium?.

How many cycles could this material see before tool degridation sets in?.

I envisage that the tool would have its own heating elements with thermostatic control.

If anybody has more information or has the design capacity and would be interseted to develope tooling please let me know.

 

[TVP]

For hot forming at elevated temperatures, tool steels like H11 or H13 can be used. Heat resistant alloys (Cobalt, Nickel, or Iron-based alloys like A286 or Waspaloy) can also be used. A high temperature lubricant is required, usually a graphite suspension or a slurry containing boron nitride. Molybdenum disulfide is also used. MoS₂ is preferred due to its ease of application and removal, and better lubricity.

Forming should be done in heated dies in a press with a slow, controlled motion that can dwell in the position needed during the press cycle. Hot forming can be performed in dies that are heated by the press platens. Press platens heated to ~ 650 C can transmit enough heat to keep the working faces of the die at ~ 425-480 C.

 

[knobhead]

I'd be curious to know how you get on; I've machined with Ti, but never done any sheet metal work.

I'd be interested to know if you have any problems with movement of the material following forming? (Not springback, just a 'relaxing' of the form over time as the internal stresses come out) Do you need to stress relieve or do you think the heat from the forming process means you don't need to?
What about hydrogen embrittlement?

I know I'm supposed to help not ask more questions, but I'm interested in this one!

Excessive accuaracy is a sign of poor breeding. -Socrates.

 

[Bradbury]

Further Responce.

Titanium fabrication is by no means 100% documented, only a handful of companies undertake such fabrications mainly due to the cost of development and production scrap or rework. Therefore information is scarce. I will need to carry out many trails.

However IMI have published sound information.

QUOTE: 'Titanium can also be contaminated by atmospheres containing either free hydrogen or hydrogen compounds. The rate of absorption varies with temperature and partial pressure; it also depends on surface cleanliness, and increases rapidly above 400 deg C. Heat treatment ("in my case hot forming&quot of thin sections is therefore best carried out in electric furnaces.' (I may need to create a vacuum with the pressing space).

However if hydrogen embritalment is a problem it can be removed in a vacuum furnace at 800 deg C. It will be however my goal to avoid such pickup in the first place by controlling the furnace (hot forming process) atmosphere.

Upon completion of forming - relaxing over time could be an issue - the tooling may need to be modified to allow for this.

Research has informed me that Commercially Pure Titanium (TA1 or ASTM grade 1)should not required stress relieving. However this will be reviewed after forming.

Paul.

 

[TMJ]

Paul,

If the form you intend to achieve requires a high degree material deformation, you may want to consider Super Plastic Forming (SPF) of Titanium.

The forming temperature is higher (around 980 deg C) and the material is formed by gas pressure (usually argon) inside a cavity tool, but the degree of form that can be achieved is very dramatic in comparison to hot forming.

At these temperatures it is also possible to 'diffusion bond' (DB) titanium fittings to the formed sheets, the process results in a migration of atoms across the joint line giving homogeneous joint with no stress concentrations (combined with Super Plastic Forming this is SPF/DB).

Trevor

 

[yates]

Bradbury,
I would not have too many concerns about hydrogen embrittlement at 450°C. In the fastener world, bolts in Ti6Al4V are hot headed at about 750°C and also have a requirement for a max 80 ppm H2 content in the finished product (to be checked on every batch) Testing over the years has shown no (or insignificant) increase in H2 content between the mill cert figure and the finished part figure. Almost all hot heading on Ti alloys is done using MoS2 as a lubricant. Sorry I can't help you with the springback prediction, it's bad enough for us and probably a lot worse in sheet metal forming !

yates

 

[Gerryy]

Hello Bradbury,

On the aircraft program I am working on, we are currently having a titanium sheetmetal wing to fuselage drag angle manufactured by hot forming. The drag angle has a "S" cross-section and is actually two 0.063 sheets formed together. Material is 6AL-4V Titianium. Our supplier is Parsons Precision Products of Parsons, Kansas. You may want to contact them for further info.

Regards,
Gerryy

 

[n8scstm]

I work for a company that specializes in titanium sheet forming. Frequently, we use a hydroform, it works great. You might want to look into that. OUr website is

http://www.klune.com.

 

[n8scstm]

sorry that link doesnt work. This one will.

http://www.klune.com

 

[fooksan]

I was wondering if anyone here has information on dertermining diffusion cycles of aluminide coatings, in particular Alseal 625.

 

[aerodog]

This is an old thread, but since other users may refer to it from time to time, some clarification is in order.

While Klune may be cold forming commercially pure titanium, 6AL4V needs to be hot formed.

The process typically uses matched male/female dies, 304 stainless works fine for the dies although a scale adjustment is required to account for the difference in Cte between titanium and stainless.

For super plastic forming, only one side of the tool is required. The sheet metal is brought in contact with the die using vacuum. Cast ceramic makes an inexpensive SPF tool.

Spring back is not required for TI hot forming, dies are net.

It does not take much pressure to form the parts. One company used to heat the dies with cartridge heaters and just use the weight of the dies and a few fire bricks to form the parts.

Forming temperature is around 700 C.

The part is held at temperature for around 20 minutes.

Some process specs require the part to be formed in a gas that displaces air (argon or nitrogen if my memory serves).

Parts are trimmed after forming.

Due to costs of tooling and complexity of the forming process, titanium parts are expensive and generally only used in areas exposed to elevated temperatures.