Raw Material Control Before Drawing
Titanium alloy wire supplies aerospace fasteners, consumer electronics frames, spectacle frames, automotive components, medical devices and welding consumables. Almost all of it is finished by cold drawing, and the process usually starts from a wire or rod whose diameter is 30% to 40% larger than the finished product so that sufficient deformation is available to reach the final size and properties.
Because cold drawing gives the material little opportunity to forgive defects, incoming quality decides the outcome. Chemical composition must be controlled tightly, particularly hydrogen, oxygen, nitrogen, iron and silicon. Hydrogen is the most damaging: once it exceeds the specification limit the wire becomes susceptible to hydrogen embrittlement, and a fastener or a medical component can fail long after it has passed a dimensional check. Surface condition matters just as much, since cracks, folds, laps and scars open up and propagate during drawing, reducing strength or causing a break. Raw material is therefore inspected and pretreated, with pickling, descaling and, where necessary, grinding applied before the coil reaches the draw bench.
| Element | Grade 2 (typical max) | Grade 5 (typical max) |
|---|---|---|
| Hydrogen | 0.015% | 0.015% |
| Oxygen | 0.25% | 0.20% |
| Nitrogen | 0.03% | 0.05% |
| Iron | 0.30% | 0.30% |
| Carbon | 0.08% | 0.08% |
Annealing Cycles and Work Hardening
Titanium alloy work hardens rapidly, so a drawing schedule is really an annealing schedule with drawing in between. Three separate treatments are normally involved: a pre-treatment anneal that conditions the incoming rod, intermediate anneals that soften the wire between drawing blocks, and a final anneal that sets the delivered properties. Recrystallisation annealing of alpha-beta wire is carried out in vacuum or an inert atmosphere, typically in the region of 700 to 750 °C, and the soak time is matched to the coil mass so that the whole cross section is treated.
A shortcut in the anneal is expensive later. Insufficient softening leaves residual work hardening that causes breakage at the next pass, and an over-long or overheated cycle coarsens the grain and reduces the elongation the customer needs for forming. Controlled cooling after the anneal also matters, because it influences residual stress in the finished coil.
Die Material and Die Geometry
Drawing dies for titanium wire are made from cemented carbide or diamond. Carbide dies are the general-purpose choice for the larger sizes because they combine high hardness with good wear resistance at reasonable cost. Diamond dies are preferred for fine and ultra-fine wire: the cost and the difficulty of processing the die are higher, but the hardness and wear resistance give better size stability over a long production run.
Geometry is at least as important as material. Arc-shaped and conical entry profiles suit different wire diameters and reduction ratios, and the bore is built from distinct zones: the entrance cone that guides and carries lubricant, the approach or working cone where the reduction actually happens, the sizing land that fixes the final diameter, and the back relief or exit cone that limits friction on the way out. Bearing length is a balancing act, since too long a land generates friction and heat while too short a land gives up size control and die life.
Pass Deformation, Total Reduction and Drawing Speed
Room-temperature tensile plasticity of titanium alloys is relatively low, so pass deformation has to be controlled rather than maximised. Area reduction per pass is kept modest, and the reduction sequence is increased gradually so that the microstructure is refined step by step and tensile strength climbs in a predictable way. Force that is applied too aggressively in a single pass shows up as surface tearing, internal cracking or a break.
Total deformation plays a different role from pass deformation. Raising the total reduction increases wire strength, but it also increases work hardening and lowers toughness, so the optimum is decided by the balance of strength and ductility that the application demands. Drawing speed acts on productivity and on heat. Higher speed improves output and saves energy, yet it also raises die temperature and wear rate, which eventually shows up as poor surface finish, excessive pick-up or a wire break. Speed is therefore tuned together with lubricant and reduction rather than set independently.
Lubrication, Cleaning and Final Inspection
Lubrication carries the drawing load away from the die surface. Dry-film lubricants and drawing compounds are selected for the reduction and speed in use, and the wire is cleaned between passes and before every anneal, because burnt lubricant residue contaminates the surface and can raise carbon content at the surface of the finished wire.
| Parameter | Typical target | Why it matters |
|---|---|---|
| Straight wire diameter | 0.1 mm to 5.0 mm, tolerance about +/-0.05 mm | Fits the customer forming and welding operation |
| Coiled wire diameter | 0.1 mm to 5.0 mm, spool diameter about 300 mm | Controls feeding and pay-off behaviour |
| Anncal temperature | About 700 to 750 °C in vacuum | Sets ductility versus strength in the delivered wire |
| Surface finish | Polished, pickled or oxide free | Affects fatigue life and downstream coating adhesion |
| Hydrogen content | Within the grade specification limit | Prevents hydrogen embrittlement in service |
Final inspection closes the loop: diameter and ovality measurement, surface examination, tensile and, where required, torsion or bend testing, plus a certificate that records composition and mechanical properties so the wire can be traced back to its heat. Straight and coiled formats are supplied to suit the downstream machine, from fastener heading lines to welding wire feeders.
Frequently Asked Questions
Q: Why does titanium wire need a larger starting diameter?
Cold drawing requires surplus cross section, and the starting wire is usually 30% to 40% larger than the finished product so the target size and strength can be reached.
Q: Which elements are most closely controlled in titanium alloy wire?
Hydrogen, oxygen, nitrogen, iron and silicon, because they govern embrittlement risk, strength and ductility; hydrogen is the most critical of them.
Q: What is the purpose of intermediate annealing?
It removes the work hardening accumulated during drawing, restores elongation and plasticity, and prepares the wire for the next reduction without cracking.
Q: Which die material is used for titanium wire drawing?
Cemented carbide dies are standard for larger diameters, while diamond dies are chosen for fine and ultra-fine wire where size stability and wear life dominate.
Q: How much deformation can be taken in one drawing pass?
Pass reductions are kept modest and increased progressively, because the low room-temperature plasticity of titanium alloys makes aggressive single-pass reduction risky.
Q: Does higher drawing speed improve quality?
Not by itself. Higher speed raises throughput but also die temperature and wear, so it is balanced against lubricant performance and pass reduction.
