Features of titanium processing

One of the most common materials used in mechanical engineering, and not only, is titanium.According to the ISO classification of materials, it corresponds to group S. This is a difficult-to-process material. Its properties complicate the cutting process even in comparison with the processing of materials such as cast iron and stainless steel. However, with the use of tools/tooling optimized for titanium processing, it is possible to turn the specific properties of this material into an advantage. 

Many of the properties that make titanium an attractive material have an impact on its machinability.

• high strength-to-weight ratio, and its density is, as a rule, only 60 percent of the density of steel

• it has a lower modulus of elasticity and is more malleable than steel

• it has a higher resistance to corrosion than stainless steel,

• low thermal conductivity.

Such qualities of titanium and titanium alloys are widely in demand and have found their application in various industries – shipbuilding, aircraft construction, aerospace, chemical, gas, oil, food, medical industry and many other areas. Both technically pure titanium and titanium alloys are used to produce critical parts of machines and devices.

Titanium alloys are divided into three classes depending on the structure and composition of alloying elements. The content of alloying elements is reflected in the designation of the alloy. 

1. Alpha alloys are alloyed with Al, O and/or N, which are predominantly α-stabilizers. 

2. Beta alloys are alloyed with Mb, Fe, V, Cr and/or Mn, which are β-stabilizers. 

3. α+β alloys are alloys having a two–phase structure. Most of the alloys that are currently used are α+β alloys.

Alloying elements have a direct effect on the physical and chemical properties of alloys, as well as temperature characteristics and machinability. Technical titanium is well processed by pressure, sheets, forgings, pipes, wire, etc. are made of it. It is well welded by argon arc welding and other types of contact welding. But as for cutting processing, titanium shows poor characteristics, in a word — it is poorly cut. Titanium sticks to the cutting edge of the tool, which leads to its rapid wear.

Due to the characteristics of the material, titanium processing must be carried out with a specially designed tool. Many tool manufacturers have special solutions for working with titanium in their line. The tool itself undergoes wear during the working process: abrasive, adhesive and diffuse. With diffuse wear, mutual dissolution of the material of the cutting tool and the titanium workpiece occurs. These processes are particularly active at a temperature of 900 — 1200 ° C. The main mechanisms of wear during titanium processing are hole formation and plastic deformation. Under the influence of the main angle in the plan, the nature of wear does not change, only the degree of wear changes. The intensity of wear and the efficiency of the cutting process as a whole depend very much on the amount of heat generated. The temperature in the cutting zone can be controlled by changing the speed, chip thickness and cutting depth. Thus, it is possible to influence the wear of the tool by changing the shape of the plate or the angle in the plan.

If the tool and cutting modes are selected correctly, as well as with good machine rigidity and reliable workpiece fixing, the titanium processing process will be highly efficient. Many of the problems that traditionally arise when processing titanium can be avoided.

The main recommendations when working with titanium will be:

• Choose пластины with polished cutting edges, it increases tool durability and reduces cutting forces
  
• When processing, also keep in mind that the metal is very viscous and when turning it using of the lathe, it gets very hot, which leads to the sticking of titanium waste on the cutting tool
  
• Titanium has a low thermal conductivity, which requires a specially selected cutting tool
  
• Processing of titanium workpieces is carried out with the obligatory supply of a special emulsion cooling the tool under pressure to ensure normal temperature conditions.
  
• When using a deeper cut, it is necessary to reduce the processing speed of titanium by changing the operating modes
  
• When milling titanium, keep a small contact area. One of the features of this metal is poor thermal conductivity. While working with this metal, the main percentage of heat is transferred to the working tool
  
• Use milling cutters with a large number of teeth. This will eliminate the need to reduce the feed to the tooth, and increase productivity