The core purpose of the drawing process of titanium wire is to gradually stretch the coarse diameter titanium wire rod or rod through a series of molds with specific pore diameters at room temperature or heating into wire products with finer diameters, precise dimensions, smooth surfaces, and mechanical properties that meet the requirements. This process is complex and sophisticated, and can be divided into three core stages: pretreatment, pulling operation, and post-processing.
Firstly, pre-treatment before pulling is a prerequisite to ensure successful pulling. Titanium has reactive chemical properties and is very easy to react with oxygen, nitrogen and other elements at high temperatures to form a hard and brittle surface layer, while its own strength is high and its plasticity is limited at room temperature, which brings great challenges to drawing. Therefore, pretreatment is crucial. The first step is surface preparation, which typically involves mechanical stripping, where the cortex rich in oxides and defects on the surface of the wire rod is removed with a lathe to obtain a fresh and clean metal surface. This is followed by cleaning and lubrication preparation, in order to effectively adhere to the lubricant, the titanium filament blank needs to be pickled to remove a slight oxide film, and may undergo surface transformation treatments, such as oxidation or phosphating, to form a porous, adhesive film on its surface, which can effectively store the lubricant and separate the titanium wire from the mold during the drawing process, reducing friction and adhesion.
Lubrication is the key to the success or failure of titanium wire drawing. Since titanium is prone to cold welding with the mold material, excellent lubrication is essential. Usually a combination of coating and lubricant is used, that is, a layer of soap (soap grease) or polymer coating is applied on the surface of the transformation treatment as a carrier, and then a special grease or polymer lubricant is used during drawing to form a high-pressure boundary lubricating film, which greatly reduces the pull-out force and frictional heat, and prevents surface scratches and breakage.
After the pre-treatment is completed, it enters the drawing operation stage. Depending on the material of the titanium wire (such as industrial pure titanium CP Grade 1-4 or alloys such as Ti-6Al-4V with higher strength) and the target diameter, choose a single draw or a continuous multi-pass draw. For finer wires, multiple passes of continuous drawing are more common. Each pass, the wire will pass through a mold hole slightly smaller than its own diameter, and will be stretched and thinned and lengthened by the pulling force. This process produces significant work hardening (or cold work hardening), where the strength and hardness of the titanium wire increase with the amount of deformation, but the plasticity and toughness decrease. When the accumulated amount of deformation makes the material too hard and brittle to proceed to the next draw, intermediate annealing is necessary. Annealing is the heating of titanium filament above the recrystallization temperature in an atmosphere furnace protected by vacuum or inert gas and holding it for a period of time, with the aim of eliminating work hardening and restoring its plasticity and toughness so that subsequent drawing reduction can be continued. This "pull-anneal-re-pull" cycle repeats until the final target size is reached.
Finally, post-processing. After drawing to the final size, according to customer requirements, the finished product may need to be annealed to obtain soft filament with low strength and good plasticity; Or no longer processed, delivered directly in a hard state. After that, it will also go through finishing processes such as shearing, straightening, and strict quality inspection, including dimensional accuracy measurement, surface defect inspection, mechanical property testing (such as tensile strength, elongation), and metallographic structure analysis, etc., to ensure that the product fully meets the specifications.
In conclusion, the drawing of titanium wire is far from a simple "stretch", it is a systematic process that integrates material science, surface engineering, heat treatment, and precision mechanical control. Through carefully controlled pretreatment, a clever combination of multiple draws and intermediate annealing, and precise post-treatment, tough titanium can be transformed into high-quality titanium filament with excellent performance and versatility, meeting the needs of a wide range of demanding applications, from aerospace and medical implants to high-end consumer goods.
