There are no particular differences between the formability of titanium and stainless steel. Grade 1 or Grade 2 titanium can be formed employing the same equipment, tools and techniques used for standard stainless steel.
Cutting and Shearing
Standard metal cutting techniques are used for titanium – hand cutting, electric shear cutting, shearing, saw cutting and punching. No post-shearing protection is required.
Formability
Titanium can be subjected to forming such as bending, press forming and roll forming in the same manner as stainless steels. Due attention should be paid to the larger spring-back of titanium, resulting from the modulus of titanium which is half of stainless steel.
Bending
Bending of a titanium sheet is accomplished using standard equipment: 3-roll bender, folding machine or press. The ability to bend varies with the grade, hardness and thickness of the sheet. Grade 1 is the preferred titanium for architecture as it is softer and has less springback than other grades. Springback is a factor of utmost importance in dimensional accuracy of a bent metal. Every metal that is elastically deformed tends to return to its original shape due to its elasticity when the bending force is removed. This phenomenon is called springback. The amount of springback increases with a decrease in gauge thickness and an increase in the strength of the sheet. In bending operations, the amount of springback increases in direct proportion to the radius and angle of bend and in inverse proportion to the die opening. A greater allowance for springback (over-bending) must be provided. Example: When bending a titanium sheet to a 90° angle using a brake press, the die opening should be set at 87° or 88° to obtain the intended 90° angle.
Press Forming
Press forming processes include deep drawing, stretch flanging, bulging and bending. One of the important considerations in press forming is to prevent the piece being formed from sticking to the die by using a suitable lubricating oil or covering the titanium with PVC. Grade 1 titanium should be utilized for this process as it can be press-formed as easily as stainless steel or mild steel.
Roll Forming
Roll forming means threading a coil through the gaps between several sets of rotating forming rolls aligned in series to be gradually bent into a desired shape. This method is used for long sheets while short sheets can be formed using a brake. Roll forming is a continuous forming process that is excellent in terms of productivity and economy (example: standing seam roof application.)
Machining
Various machining operations can be performed on commercially pure titanium (Grade 1 or Grade 2) as easily as stainless steel can be machined. For milling, a high-speed milling cutter or cemented carbide milling cutter can be used.
Joining Titanium
Titanium sheets are joined together using the following methods: welding, mechanical joining and adhesive bonding. Titanium is readily weldable, using several processes described below. Properly made welds are ductile and, in most environments, are as corrosion resistant as the base metal. Techniques and equipment used in welding titanium are similar to those required for stainless steel and other high-performance metals.
Seam Welding
Titanium sheets are joined together by a seam welder to form a waterproof layer or shingle of a roof. Seam welding provides excellent waterproofing and is suitable for the fabrication of a roof having intricate and curved contours. The lock seam is sandwiched between the two electrodes of the seam welder and electrical-resistance welded. This can be performed in the atmosphere because it takes only a short time to complete a joint and the high-temperature (molten) zone is shielded from the atmosphere by the material being welded. Seam welders generally used for stainless steel can be used titanium with the same welding current level.
Spot Welding
Spot welding is employed to partially join or reinforce a clip or channel, or to join the drop plate of a gutter prior to seam welding the entire roof assembly. Spot welding can also be performed in the atmosphere. The bond strength of the weld increases with increasing depth and penetration and size of the weld, which are in proportion to the amperage and duration of the welding current applied.
TIG Welding
TIG welding is principally employed for joining titanium sheets and plates and uses a tungsten electrode while melting filler wire in an inert gas-shielded atmosphere. The hardness of titanium increases and the toughness decreases upon absorption of even the smallest amounts of oxygen, nitrogen and hydrogen at elevated temperature. Therefore, titanium needs to be shielded by an inert gas such as argon or helium during welding. This and the high activity and fluidity of titanium dictate special precautions in designing and preparing the groove, tack welding, designing the method of shielding, and observing the surface appearance of weld beads. The filler rod or welding wire must be made of titanium in the same grade as the sheet, and be fully degreased in order to prevent entry of oxygen and other impurities.
Resistance Stud Welding
Resistance stud welding is one of the methods used to quickly fix a threaded stud to a titanium panel for mechanical attachment. It is performed by charging a large capacitor from a relatively small capacity AC power supply and instantly discharging a weld between the stud and the base metal. Again, in this case, the stud should also be titanium.
Adhesive Bonding
Adhesive bonding has previously been used for lightweight materials or in applications where low bond strength is required. Many new and improved types of adhesives are now available for use with titanium. This joining practice offers many advantages over other methods, including:
• Better ease of joining (minimal preparation)
• No stress concentration because of surface-to-surface bonding
• Dissimilar metals can be joined together and isolated from each other
• Joints are inconspicuous from the viewpoint of design
Pressure-sensitive double-sided adhesive tape has excellent adhesion, weathering resistance, absorption capacity of repetitive expansion/contraction cycles, and a very high level of immunity to deterioration proved by a series of accelerated deterioration tests.
