Cost of cast titanium for a gearbox case or bellhousing.....

[grano123]

I'm doing a project feasibility study, and wondered if anyone knows the ballpark costing for casting a gearbox casing or bellhousing in titanium, as opposed to magnesium?

I'm assuming the patterns would be similarly constructed, but I'm not sure...........any help would be appriciated.

Thanks.

[Scuderia Nuvolari]

Is this what you are asking about?

http://www.crptechnology.com/sito/it/ra ... ducts.html


If you can perform services like this, you can pretty much name your price.

[WhiteBlue]

I'm no expert but you can find some things quickly on the net.

http://www.p2pays.org/ref/34/33110.pdf

Thin wall castings from titanium alloys are rare. The aircraft parts that you see are generally machined from a block or a forged part. I understand that porosity is the main problem.

http://www.ml.afrl.af.mil/stories/MLL/asc_04_0162.html

some military applications with alloys have apparently succeded but I guess they would still be hugely more expensive than magnesium.

Magnesium parts in large automotive quantities may cost close to 15-20$/kg. For single items that can probably go up to 100 times.

Since some years you can injection mould magnesium in the thixomolding process. That may be more conveniant than die casting and reduce scrap rate and cost.

http://www.thixomat.com/docs/newsletter.pdf

[scarbs]

Grano,
CRP as mentioned in the previous link are the people you need to contact. they are surprisingly open and have a forum on their site where you post the question and get a reasonably quick answer.

Can you do one thing for us here, post the answer here when you find it...!

Scarbs

[Scuderia Nuvolari]

"The casting structure is formed of an aggregate of grains or polyhedral crystallites which produce isotropy compensation, while in a solid metal they are anisotropic: it is obvious that isotropy has great advantages, for instance, FEM calculations are very close to the real behaviour of the part thanks to the isotropy of the piece."


Thats right, they have a forum but I'll be doggoned if I can grasp thier proven methodology. It must be in the grain crystals.

[WhiteBlue]

That is a simple thing. The metal forms crystaline structures. Isotropic means the crystals have a similar structure in each xyz directions in the cast product. It means load bearing and other properties are not displayed with a preferred direction by freezing under stress. In the solid metal due to some manufacturing influences there is obviously a directional influence. They say it is easier for computation if the properties are the same in all directions which is making life easier for the CAD guys.

[bazanaius]

I understand this, but I'm jsut wondering whether they havn't got it the wrong way around?

Surely they should be focussing on making the FEA more accurate on anisotropic materials, unless the isotropy is materially beneficial? I'd say using a material just because you can model it is bad - there's probably something out there that a would be a better material, even if the modelling is less accurate. Why not just do some physcial tests?!

[WhiteBlue]

It is not the modelling that is bad. It is the way you manufacture in casting. You have no control over anisotropy in the flow proces. It is different with composites. There you can use the manufacturing process by conciously placing anisotropic strength into directions that benefit. In a flow process the geometric properties of the flow path determine by shear stress where you end up with anisotopies. That only applies if the material is subject to shear due to its viscosity. It is good that is does not, being liquid enough for die casting.

If you want to learn about CFD of mold flow click here.

[bazanaius]

I am not questioning the difference between isotropic and anisotropic materials. I'm saying that the company claims that isotropic materials are better because they're easier to model in computer packages (you say it makes the CAD guys life easier). I'd say that this isn't a selling point - it just highlights the problems with the computer package.

I think we might be getting confused about the use of the word 'model' tho. I'm referring to something like FEA where the designed part is tested in a computer before it's built - the accuracy of the solution is dependant of the software, which is inherently slightly innacurate due to necessary assumptions (discretisation of the mesh for example).
i think you might be referring to the mold design, which can be modelled in a computer and may well provide good insight using cfd to model the material flow properties. I guess that this would be used to try and make the mold produce an isotropic material when it is wanted.

I think it's the difference between 'using an isotropic material because it's easier to model in a computer' and 'using a computer to design the mold so that the material is isotropic (as far as possible)'.

My point refers to the first statement, because I think that selecting a material because it is easy to simulate is not a valid design process. you choose the best material you can and model it in the most accurate way you can, with consideration for the accuracy of your model. Making the CAD guys jobs easier is not the correct way to do things!

[WhiteBlue]

The CFD of viscous fluids in a mold is well known. So what you can do is predicting the unisotropies. The problem arises where you have no control over locating the stronger direction. Most often you end up with the highest stresses lined up with the lowest strength. Predicting properties is not consitent with controling them. This is why isotropic materials are better in processes which produce uncontrollable shear stresses. One should not forget that other aspects are more damaging. The frozen in stresses can relax under heat and lead to deformations. also the parts shrink and warp with less control when you cool them down if the material is anisotrop. bad for maintaining close tolerances.

[bazanaius]

I agree - in the majority of cases (particularly casting) isotropic materials are better than anisotropic for the reasons you mention. THIS is a selling point of the material.
'Making it easier for the CAD guys' is not. Unless by this you mean that it is easier for the CAD guys to design the mold because they don't have to worry anisotropy?

Just trying to clarify what you mean

[riff_raff]

grano123,

Casting a gearcase in titanium (typically an alpha-beta 6Al-4V alloy) has lots of advantages over magnesium or aluminum for an F1 chassis. It has a higher M of E than magnesium or aluminum, it has a CTE that closely matches the transmission's steel gears, bearings and shafts, it has high fatigue limits, it has excellent strength at high temperatures, and it can be attached directly to carbon composite parts without galvanic corrosion problems.

Its drawbacks are that it is a very expensive metal (40 or 50 dollars US per pound), it has a very high melting temperature (over 3000degF) and it is highly reactive to oxygen in a molten state. The only practical way to cast titanium is using a vacuum furnace and a ceramic investment mold. Investment casting is capable of producing very fine details, thin lightweight walls, and very high dimensional accuracy. But the process is very labor intensive and the tooling costs are very high.

http://www.pccstructurals.com/locations ... tanium.php

http://www.alcoa.com/howmet/en/about/br ... /index.asp