COLD FORMING
Slow speeds should be used when forming titanium. The degree to which a particular titanium grade or alloy can be formed at room temperature is dependent upon its uniform elongation in a tensile test. The uniform elongation dictates the minimum bend radius as well as the maximum stretch which the alloy can sustain without fracturing. In this respect, annealed TIMETAL 35A (Gr. 1) and TIMETAL 35A Pd12 (Gr. 11) exhibit maximum formability. These are followed by TIMETAL 50A (Gr. 2) and TIMETAL 50A Pd (Gr. 7), TIMETAL 50A Pd5 (Gr. 16), TIMETAL 65A (Gr. 3), TIMETAL Code-12 (Gr. 12), TIMETAL 75A (Gr. 4) and TIMETAL 6-4 (Gr. 5). Minimum bend radii for these alloys in sheet and plate product form, as defined by ASTM specifications (B265), are given in Table 18.

SPRINGBACK
A loss of 15 to 25 degrees in included bend angle must be expected, due to springback of titanium after forming. The higher the strength of the alloy, the greater the degree of springback to be expected. Compensation for springback is made by overforming. Hot sizing of cold formed titanium alloy parts has been successfully employed. This technique virtually eliminates springback when the hot sizing temperature is high enough to allow stress relief.

HOT FORMING
The ductility (bendability and stretch formability) of titanium increases with temperature. Thus, forming operations can be done at elevated temperatures which would be impossible at room temperature. The influence of elevated temperature on minimum bend radius of annealed TIMETAL 6-4 (Gr. 5) sheet is shown in Table 19.

The higher the temperature, the easier the forming. Unalloyed titanium, TIMETAL 35A Pd, 50A, 50A Pd and TIMETAL Code-12, are most readily hot formed in the 400-600 degrees F. range with no fear of thermal damage. Springback is virtually eliminated on forming TIMETAL 6-4 at 1200 degrees F. and mechanical properties are not affected. Oxidation of surfaces becomes a factor at temperatures exceeding 1100 degrees F., necessitating a descaling operation. Heating for hot forming can be accomplished by furnace, radiant heater or direct flame impingement (slightly oxidizing flame). Local chilling of heated metal should be avoided to prevent surface checking during forming operations. Allowances in tool design for thermal contraction of warm formed titanium parts may be necessary.

DRAWING
Unalloyed titanium is capable of being drawn to depths greater than those attainable with carbon steel. The TIMETAL 35A (Gr. 1) and TIMETAL 35A Pd12 (Gr. 11) alloys, which are most ductile, offer best drawability. Alloys, such as TIMETAL 6-4 (Gr. 5), which have lower ductility, are difficult to draw at room temperature.

Several factors need to be considered before drawing titanium:

1. Blanks should be deburred and edges carefully smoothed.

2. Tool surfaces should be polished and absolutely free of dirt.

3. Blanks should be clean and free of dirt and scale.

4. Proper lubrication should be applied to blanks.

5. The large springback of titanium may require modified die design.

6. Slow drawing speeds produce best results.

In practice, care must be taken in the drawing of titanium because of titanium's tendency to gall. Galling not only mars the surface of the titanium drawn part but may also cause failure of the part during the drawing operation. Precautionary steps, therefore, need to be taken to prevent any contact of the titanium with tools and dies by proper lubrication.

Conventional drawing lubricants generally are not acceptable for use with titanium. The most effective lubricants appear to be dry-film types incorporating anti-galling constituents. Polyethylene or polypropylene in dry-file or strippable form (0.003 inch thickness) have proven to be effective. A suspension of acrylic resin in trichloroethylene containing molybdenum disulfide and PTFE (polytetrafluoroethylene) coatings have also worked well and appear capable of surviving more than one draw. High-pressure grease-oil type lubricants may also be acceptable at room temperature for mild draws.

As with other forming operations, the springback characteristic of titanium needs to be recognized. Tools may have to be designed to compensate for springback, particularly if drawing is to be done at room temperature.

Deeper draws, lower loads and less distortion in the finished part are obtainable by drawing titanium hot. Temperatures in the range 400-600 degrees F. are best for unalloyed titanium. Titanium alloys, such as TIMETAL 6-4 (Gr. 5) which have low ductility and are difficult to draw at room temperature, often can be drawn hot, in the range of 900 to 1200 degrees F. Hot forming lubricants generally contain graphite or molybdenum disulfide and may be applied over zinc phosphate conversion coatings.

TUBE BENDING
Titanium tubing is routinely bent on conventional tube bending equipment. Mandrel benders are recommended particularly for tight bends. Wiper dies and mandrels should be smooth and well lubricated to minimize titanium's tendency to gall. Bending should be slow.

The minimum bend radii with mandrel for cold bent TIMETAL 50A (Gr. 2) tubing are given in Table 20. Bends made without mandrel require larger radii. If smaller radius bends than given in Table 20 are required, it may be necessary to bend the tubing at 400 to 600 degrees F. Consideration should be given to using heavier wall tubing for tight bends to compensate for thinning which takes place at the tubes outer periphery on bending.