Guides / Process

Ten Drawing Decisions That Decide What Your Titanium Part Costs

Most of what a titanium part costs is decided on the drawing, before anybody programs it. Here are the ten decisions that move the number most, roughly in order of how much they matter.

1. Start from the right stock

Titanium bar costs several times more per kilo than aluminium, so material waste is a real line in the quote, not a rounding error.

Ask, for every part: is this a bar part, a plate part, a tube part or a forging part? The buy to fly calculator shows how much of the bar you are paying to turn into swarf. A bracket cut from a solid block might leave 80 percent of the bar on the floor. The same bracket from plate, or from a near net forging on a repeating order, can change the quote more than any cycle time saving you could negotiate.

2. Open the internal corners

Every internal vertical corner needs a radius, and that radius sets the smallest cutter that can reach it. A small cutter in titanium means low feed, low depth, poor tool life and a long cycle.

Target roughly a quarter of the pocket depth as a corner radius. In practice, anything under 3 mm in a pocket deeper than 15 mm is worth a second look.

3. Do not draw the wall thinner than the part needs

Wall thickness drives fixturing. Above roughly a 5 to 1 height to thickness ratio the shop starts adding passes, and above 10 to 1 it starts adding fixtures. Half a millimetre of extra wall often costs nothing in weight and removes a whole problem.

4. Tolerance only what has to be toleranced

This is the most common expensive habit. A tight block tolerance applied to every dimension on the drawing prices the whole part at the level of its hardest feature.

Do this instead: a general tolerance that is genuinely adequate, usually ISO 2768-m, plus two or three specific features called out tighter. Now the shop knows where to spend the finishing passes and the inspection time.

Approach	What the shop has to do
Tight tolerance on every dimension	Finish pass and inspect everything
General tolerance plus called out features	Rough to size, finish and inspect the features that matter

5. Keep hole depths reasonable

Up to about 5 times diameter is routine. Past that the chips have trouble clearing and the drill heats, so the shop pecks, or uses through spindle coolant, or reaches for a gun drill.

If a deep hole is unavoidable, say what it is for. Sometimes a through hole plugged at one end is cheaper than a deep blind hole, and only you know whether that is acceptable. The drilling guide covers why titanium holes are the hardest single feature to price.

6. Avoid titanium on titanium threads with no treatment

Titanium galls against itself. Threads seize, sliding faces pick up. This is a design issue, not a machining defect.

Fixes to put on the drawing: an anti-seize compound, a Type II anodize to AMS 2488, a stainless or bronze insert at the interface, or a mating part in a different material.

7. Think about how the part is held

A part with no flat, no clampable boss and no square face needs a fixture built for it. That fixture is designed, machined and paid for once, which is fine at 200 pieces and painful at one.

If you can leave a sacrificial clamping boss or a flat that is removed in a second operation, say so on the drawing. Shops will use it.

8. Say what the surface finish actually needs to be

A default Ra on every surface is expensive in titanium because the finishing pass is slow. Call out the finish where it matters, functional faces and sealing surfaces, and leave the rest as machined.

If the part is going to be anodized, remember that anodizing does not hide tool marks. The machined finish is what you will see through the colour.

9. Decide the certificates early

Mill certificate to EN 10204 3.1, heat lot traceability, first article inspection report, material standard such as AMS 4928 or ASTM F136. Each one is real work and real cost.

Ask for exactly what your customer requires. Asking for everything narrows your supplier list and raises the price. Asking for nothing and then needing a certificate after the parts are cut usually means cutting them again.

10. Say whether the part repeats

Programming and fixturing are paid once per order. On a quantity of one they can be most of the price. If you will need this part again, or if this is the prototype for a run of 200, say so on the RFQ. Shops quote differently when they know a repeat is coming, and some will amortise the fixture across the releases.

A short pre release checklist

Before you send the drawing out:

• Is the stock form the cheapest one that works?
• Is every internal corner radius at least a quarter of its pocket depth?
• Is any wall above a 10 to 1 height to thickness ratio, and does it need to be?
• Is the general tolerance as loose as it can be, with the tight ones called out separately?
• Is any hole deeper than 5 times its diameter?
• Are there titanium on titanium threads with no treatment specified?
• Is there somewhere to clamp it?
• Is surface finish called out only where it is needed?
• Are the certificates listed, and are they all genuinely required?
• Does the RFQ say whether the part repeats?

Ten questions, maybe fifteen minutes. On a titanium part that is usually the highest paid fifteen minutes in the project.

Frequently asked questions

Keep reading

• Drilling Titanium: Speeds, Heat and Why Holes Fail First
• Welded Titanium Assemblies and the Alpha Case Problem