Relevance

All kinds of machining are used for manufacturing of structures and parts from titanium alloys: grinding, turning, drilling, milling, polishing.
One of the important peculiarities of machining parts from titanium and titanium alloys is that it is necessary to ensure the resource and especially the fatigue characteristics that largely depend on the qualities of the surface layer that is formed during cold machining. Because of the low thermal conductivity and other specific properties of titanium, it is difficult to carry out grinding as the final machining stage. During grinding, burns can very easily form, defective structures and residual stresses and tensions can arise in the surface layer, which significantly influence the reduction of fatigue strength of products. Therefore, grinding of titanium parts is necessarily performed at reduced speeds and, if necessary, can be replaced by blading or abrasive machining with low-speed methods. In case of grinding, it should be performed with strictly regulated modes, with subsequent control of the part surface for burnt and accompanied by improvement of the part quality through hardening by surface plastic deformation (SPD).

Challenges

Due to its high strength properties, titanium is poorly machinable. It has a high yield strength to tensile strength ratio of about 0.85-0.95. For example, for steel, this ratio does not exceed 0.75. As a result, machining of titanium alloys requires high forces, which, due to the low thermal conductivity, entails a significant increase in temperature in the surface layers of the cut and makes it difficult to cool the cutting zone. Because of the strong adhesion, titanium accumulates on the cutting edge, which greatly increases the friction force. In addition, titanium welding and adhesion at the contact points of the surfaces causes changes in tool geometry. Such changes, which alter the optimal configuration, entail a further increase in machining forces, which consequently leads to an even higher temperature at the point of contact and accelerated wear. The increase in temperature in the working zone is most affected by the cutting speed, to a lesser extent it depends on the tool feed force. The depth of cutting has the least influence on the temperature increase.

Under the influence of high temperatures during cutting, the titanium chips and the work piece are oxidized. This subsequently poses a disposal and remelting problem for the chips. A similar process for the workpiece can subsequently lead to a degradation of its performance characteristics.

Comparative analysis

The process of cold working of titanium alloys is 3-4 times more labour-intensive than the one for carbon steels, and 5-7 times more difficult than the one for aluminum. According to the information of MMPP Salyut, titanium alloys BT5 and BT5-1 as compared to carbon steel (with0,45% C), have the coefficient of relative machinability 0,35-0,48 and for alloys BT6, BT20 and BT22 this parameter is even less and is 0,22-0,26. It is recommended when machining to use low cutting speed with a small feed, using a large amount of coolant for cooling. When machining products from titanium, cutting tools of the most wear-resistant high-speed steel are used, preference is given to hard alloy grades. But even if all the prescribed conditions for cutting are met, speeds should be reduced by at least 3-4 times compared to steel machining, which should ensure acceptable tool life, especially important when working on CNC machines.

Optimizing

The temperature in the cutting zone and the cutting force can be significantly reduced by increasing the hydrogen content in the alloy, vacuum annealing and appropriate machining. Conducting alloying of titanium alloys with the help of hydrogen ultimately gives a significant reduction of temperature in the cutting zone, makes it possible to reduce the cutting force, increases the durability of the carbide tool up to 10 times, depending on the nature of the alloy and the mode of cutting. This method makes it possible to increase the machining speed by 2 times without loss of quality, as well as to increase the force and depth during cutting without reducing the speed.

For machining parts from titanium alloys the technological processes are widely used, which allow combining several operations into one due to the use of multi-tool equipment. It is most expedient to perform such technological operations on multitool machines (machining centers). For example, to manufacture power parts from forgings machines MA-655A, FP-17SMN, FP-27S are used; parts of "bracket", "column", "casing" types are used.column", "casing" of shaped castings and forgings - machines Horizont, Me-12-250, MA-655A, sheet panels - machine tool VFZ-M8. Principle of "maximum" completeness of machining in one operation is realized on these machines for majority of parts processing. It is reached due to consecutive machining of a part from several sides on one machine by means of several installed on it attachments.

Milling

Due to high forces requirement, for machining titanium alloys large machines are usually used (FP-7, FP-27, FP-9, VFZ-M8, etc.). Milling is the most labor-intensive process during production of parts. Particularly high volume of such work falls on manufacturing of power parts of airplane framework: ribs, ribs, beams, spars, crossbars.

Several methods are used in the milling of "traverse", "beam" and "rib" type parts. 1) By means of special hydraulic or mechanical copiers on universal milling machines. 2) By copying on copy-milling hydraulic machines. 3) With CNC machines like MA-655C5, FP-11, FP-14. 4) Using three-axis CNC machines. For this purpose the following tools are used: special assembly cutters with angle changed during machining; shaped concave and convex cutters of radial profile; end mills with table face brought to cylindrical surface of a part at a required angle.

Machines

For machining of aviation materials in our country many machine tools were created, which are not inferior to the world standards, and some of them have no analogs abroad. For example, CNC machine VF-33 (longitudinal-milling three-spindle three-axis) which purpose is simultaneous processing by three spindles of panels, monorails, ribs, beams and other such parts for heavy and light aircrafts.
2FP-242 V machine with two movable gantries and CNC (three-spindle four-axis longitudinal-milling machine) is designed for machining of dimensioned side members and panels for heavy and wide-bodied aircrafts. FRS-1 machine, equipped with movable column, 15-axis CNC horizontal-milling and boring machine is designed for machining of centerplane and wing joint surfaces of wide-bodied airplanes. SGPM-320, flexible production module, which includes a lathe, CNC AT-320, a magazine with 13 tools, an automatic manipulator for removal and installation of parts for CNC. Flexible production unit ALK-250, designed for production of precision parts for hydraulic unit bodies.

Tools

To provide optimum cutting conditions and high quality of parts surface it is necessary to observe strictly geometric parameters of hard alloys and high-speed steels tools. Cutters with inserts made of hard alloys ВК8 are used for turning forged blanks. The following geometrical parameters of cutters are recommended during machining on gas-saturated crust: main angle in plan φ1 =45°, auxiliary angle in plan φ =14°, front angle γ = 0°; back angle α = 12°.At the following cutting conditions: feed s = 0,5 - 0,8 mm/rev, depth of cut t not less than 2 mm, cutting speed v = 25 - 35 m/min. For finishing and semi-finishing continuous turning it is possible to apply tools from hard alloys ВК8, ВК4, ВКбм, ВК6 etc. at depth of cutting 1-10 mm, cutting speed makes v = 40-100 mm/min, and the feed should make s = 0,1-1 mm/rev. Tools from high-speed steel (Р9К5, Р9М4К8, Р6М5К5) can be applied as well. For cutters made of high-speed steel the following geometrical configuration is developed: radius at apex r = 1 mm, back angle α = 10°, φ = 15°. Permissible cutting modes when turning titanium are achieved with depth of cut t = 0,5-3 mm, v = 24-30 m/min, s <0,2 mm.

Hard alloys

The milling work with titanium makes it difficult to adhere titanium to the cutter teeth and to knock them out. Hard alloys VK8, VK6M, VK4 and high-speed steel R6M5K5, R9K5, R8MZK6S, R9M4K8 and R9K10 are used for milling cutter working surfaces. For titanium milling by cutters with ВК6М alloy plates it is recommended to use the following cutting mode: t = 2 - 4 mm, v = 80 - 100 m/min, s = 0,08-0,12 mm/tooth.

Drilling

Drilling of titanium makes it difficult for chips to adhere to the working surface of the tool and to get them in the outlet grooves of the drill, which leads to an increase in cutting resistance and rapid wear of the cutting edge. To prevent this, it is recommended that the tool be periodically cleaned of chips during deep drilling. The tools made of high-speed steel R12P9K5, R18F2, R9M4K8, R9K10, R9F5, F2K8MZ, R6M5K5 and hard alloy ВК8 are used for drilling. Thus the following parameters of drill bit geometry are recommended: for helical groove inclination angle 25-30, 2φ0 = 70-80°, 2φ = 120-130°, α = 12-15°, φ = 0-3°.

COOLANT

To increase the productivity in the machining of titanium alloys and to increase the service life of the tools used use fluids such as RZ SOJ-8. They relate to galloid-containing lubricating-cooling. Workpiece cooling is carried out by abundant sprinkling. Application of halide-containing fluids during processing leads to the formation of a salt crust on the surface of titanium parts, which, taking into account the heating and the simultaneous action of stress, may cause salt corrosion. To prevent it after machining with RZ SOJ-8 the parts undergo an etching treatment, during which the surface layer with thickness up to 0,01 mm is removed. During the assembly operations the use of RZ SOJ-8 is not allowed.

Grinding at .

The machinability of titanium alloys is significantly affected by their chemical and phase composition, type and microstructure parameters. It is most difficult to machine titanium semi-finished products and parts having rough lamellar structure. This kind of structure is present in shaped castings. In addition, shaped titanium castings have a gas-saturated crust on the surface, which greatly affects tool wear.

Grinding of titanium parts is difficult because of the high tendency for contact sticking during friction. The oxide surface film is easily destroyed during friction under the action of specific loads. During friction, active material transfer from the workpiece to the tool ("setting") takes place at the points where the surfaces come into contact. Other properties of titanium alloys also contribute to this: lower thermal conductivity, increased elastic deformation with a relatively low modulus of elasticity. Due to heat generation, the oxide film on the rubbing surface thickens, which in turn increases the strength of the surface layer.

When machining titanium parts, belt grinding and grinding with abrasive wheels are used. For industrial alloys, the most common use of abrasive wheels of green silicon carbide, which has great hardness and brittleness with stable physical and mechanical properties with higher abrasive than black silicon carbide.

Buy, price

Evek GmbH sells rolled metal products at the best price. It is formed taking into account LME (London metal exchange) rates and depends on the technological features of production without including additional costs. We supply semi-finished products from titanium and its alloys in wide assortment. All batches have quality certificate for compliance with standards requirements. With us you can buy in bulk the most various products for large-scale productions. The wide choice, exhaustive consulting of our managers, reasonable prices and timely delivery determine the face of our company. There is a system of discounts for wholesale purchases

Relevance

All kinds of machining are used for manufacturing of structures and parts from titanium alloys: grinding, turning, drilling, milling, polishing.
One of the important peculiarities of machining parts from titanium and titanium alloys is that it is necessary to ensure the resource and especially the fatigue characteristics that largely depend on the qualities of the surface layer that is formed during cold machining. Because of the low thermal conductivity and other specific properties of titanium, it is difficult to carry out grinding as the final machining stage. During grinding, burns can very easily form, defective structures and residual stresses and tensions can arise in the surface layer, which significantly influence the reduction of fatigue strength of products. Therefore, grinding of titanium parts is necessarily performed at reduced speeds and, if necessary, can be replaced by blading or abrasive machining with low-speed methods. In case of grinding, it should be performed with strictly regulated modes, with subsequent control of the part surface for burnt and accompanied by improvement of the part quality through hardening by surface plastic deformation (SPD).

Challenges

Due to its high strength properties, titanium is poorly machinable. It has a high yield strength to tensile strength ratio of about 0.85-0.95. For example, for steel, this ratio does not exceed 0.75. As a result, high forces are required when machining titanium alloys, which, due to the low thermal conductivity, entails a significant increase in temperature in the surface layers of the cut and makes it difficult to cool the cutting zone. Because of the strong adhesion, titanium accumulates on the cutting edge, which greatly increases the friction force. In addition, titanium welding and adhesion at the contact points of the surfaces causes changes in tool geometry. Such changes, which alter the optimal configuration, entail a further increase in machining forces, which consequently leads to an even higher temperature at the point of contact and accelerated wear. The increase in temperature in the working zone is most affected by the cutting speed, to a lesser extent it depends on the tool feed force. The depth of cutting has the least influence on the temperature increase.

Under the influence of high temperatures during cutting, the titanium chips and the work piece are oxidized. This subsequently poses a disposal and remelting problem for the chips. A similar process for the workpiece can subsequently lead to a degradation of its performance characteristics.

Comparative analysis

The process of cold working of titanium alloys is 3-4 times more labour-intensive than the one for carbon steels, and 5-7 times more difficult than the one for aluminum. According to the information of MMPP Salyut, titanium alloys BT5 and BT5-1 as compared to carbon steel (with0,45% C), have the coefficient of relative machinability 0,35-0,48 and for alloys BT6, BT20 and BT22 this parameter is even less and is 0,22-0,26. It is recommended when machining to use low cutting speed with a small feed, using a large amount of coolant for cooling. When machining products from titanium, cutting tools of the most wear-resistant high-speed steel are used, preference is given to hard alloy grades. But even if all the prescribed conditions for cutting are met, speeds should be reduced by at least 3-4 times compared to steel machining, which should ensure acceptable tool life, especially important when working on CNC machines.

Optimizing

The temperature in the cutting zone and the cutting force can be significantly reduced by increasing the hydrogen content in the alloy, vacuum annealing and appropriate machining. Conducting alloying of titanium alloys with the help of hydrogen ultimately gives a significant reduction of temperature in the cutting zone, makes it possible to reduce the cutting force, increases the durability of the carbide tool up to 10 times, depending on the nature of the alloy and the mode of cutting. This method makes it possible to increase the machining speed by 2 times without loss of quality, as well as to increase the force and depth during cutting without reducing the speed.

For machining parts from titanium alloys the technological processes are widely used, which allow combining several operations into one due to the use of multi-tool equipment. It is most expedient to perform such technological operations on multitool machines (machining centers). For example, to manufacture power parts from forgings machines MA-655A, FP-17SMN, FP-27S are used; parts of "bracket", "column", "casing" types are used.column", "casing" of shaped castings and forgings - machines Horizont, Me-12-250, MA-655A, sheet panels - machine tool VFZ-M8. Principle of "maximum" completeness of machining in one operation is realized on these machines for majority of parts processing. It is reached due to consecutive machining of a part from several sides on one machine by means of several installed on it attachments.

Milling

Due to high forces requirement, for machining titanium alloys large machines are usually used (FP-7, FP-27, FP-9, VFZ-M8, etc.). Milling is the most labor-intensive process during production of parts. Particularly high volume of such work falls on manufacturing of power parts of airplane framework: ribs, ribs, beams, spars, crossbars.

Several methods are used in the milling of "traverse", "beam" and "rib" type parts. 1) By means of special hydraulic or mechanical copiers on universal milling machines. 2) By copying on copy-milling hydraulic machines. 3) With CNC machines like MA-655C5, FP-11, FP-14. 4) Using three-axis CNC machines. For this purpose the following tools are used: special assembly cutters with angle changed during machining; shaped concave and convex cutters of radial profile; end mills with table face brought to cylindrical surface of a part at a required angle.

Machines

For machining of aviation materials in our country many machines were created, which are not inferior to the world standards, and some of them have no analogs abroad. For example, CNC machine VF-33 (longitudinal-milling three-spindle three-axis) which purpose is simultaneous processing by three spindles of panels, monorails, ribs, beams and other such parts for heavy and light aircrafts.
2FP-242 V machine with two movable gantries and CNC (three-spindle four-axis longitudinal-milling machine) is designed for machining of dimensioned side members and panels for heavy and wide-bodied aircrafts. FRS-1 machine, equipped with movable column, 15-axis CNC horizontal-milling and boring machine is designed for machining of centerplane and wing joint surfaces of wide-bodied airplanes. SGPM-320, flexible production module, which includes a lathe, CNC AT-320, a magazine with 13 tools, an automatic manipulator for removal and installation of parts for CNC. A flexible production unit ALK-250, designed for production of precision parts for hydraulic unit housings.

Tools

To provide optimum cutting conditions and high quality of parts surface it is necessary to observe strictly geometric parameters of hard alloys and high-speed steels tools. Cutters with inserts made of hard alloys ВК8 are used for turning forged blanks. The following geometrical parameters of cutters during machining on gas-saturated crust are recommended: main angle in plan φ1 =45°, auxiliary angle in plan φ =14°, front angle γ = 0°; back angle α = 12°.With the following cutting conditions: feed s = 0,5 - 0,8 mm/rev, cutting depth t not less than 2 mm, cutting speed v = 25 - 35 m/min. For finishing and semi-finishing continuous turning it is possible to apply tools from hard alloys ВК8, ВК4, ВКбм, ВК6 etc. at depth of cutting 1-10 mm, cutting speed makes v = 40-100 mm/min, and the feed should make s = 0,1-1 mm/rev. Tools from high-speed steel (Р9К5, Р9М4К8, Р6М5К5) can be applied as well. For cutters made of high-speed steel the following geometrical configuration is developed: radius at apex r = 1 mm, back angle α = 10°, φ = 15°. Permissible cutting modes when turning titanium are achieved with depth of cut t = 0,5-3 mm, v = 24-30 m/min, s <0,2 mm.

Hard alloys

The milling work with titanium makes it difficult to adhere titanium to the cutter teeth and to knock them out. Hard alloys VK8, VK6M, VK4 and high-speed steel R6M5K5, R9K5, R8MZK6S, R9M4K8 and R9K10 are used for milling cutter working surfaces. For titanium milling by cutters with ВК6М alloy plates it is recommended to use the following cutting mode: t = 2 - 4 mm, v = 80 - 100 m/min, s = 0,08-0,12 mm/tooth.

Drilling

Drilling of titanium makes it difficult for chips to adhere to the working surface of the tool and to get them in the outlet grooves of the drill, which leads to an increase in cutting resistance and rapid wear of the cutting edge. To prevent this, it is recommended that the tool be periodically cleaned of chips during deep drilling. The tools made of high-speed steel R12P9K5, R18F2, R9M4K8, R9K10, R9F5, F2K8MZ, R6M5K5 and hard alloy ВК8 are used for drilling. Thus the following parameters of drill bit geometry are recommended: for helical groove inclination angle 25-30, 2φ0 = 70-80°, 2φ = 120-130°, α = 12-15°, φ = 0-3°.

COOLANT

To increase the productivity in the machining of titanium alloys and to increase the service life of the tools used use fluids such as RZ SOJ-8. They relate to galloid-containing lubricating-cooling. Workpiece cooling is carried out by abundant sprinkling. Application of halide-containing fluids during processing leads to the formation of a salt crust on the surface of titanium parts, which, taking into account the heating and the simultaneous action of stress, may cause salt corrosion. To prevent it after machining with RZ SOJ-8 the parts undergo an etching treatment, during which the surface layer with thickness up to 0,01 mm is removed. During the assembly operations the use of RZ SOJ-8 is not allowed.

Grinding at .

The machinability of titanium alloys is significantly affected by their chemical and phase composition, type and microstructure parameters. It is most difficult to machine titanium semi-finished products and parts having rough lamellar structure. This kind of structure is present in shaped castings. In addition, shaped titanium castings have a gas-saturated crust on the surface, which greatly affects tool wear.

Grinding of titanium parts is difficult because of the high tendency for contact sticking during friction. The oxide surface film is easily destroyed during friction under the action of specific loads. During friction, active material transfer from the workpiece to the tool ("setting") takes place at the points where the surfaces come into contact. Other properties of titanium alloys also contribute to this: lower thermal conductivity, increased elastic deformation with a relatively low modulus of elasticity. Due to heat generation, the oxide film on the rubbing surface thickens, which in turn increases the strength of the surface layer.

When machining titanium parts, belt grinding and grinding with abrasive wheels are used. For industrial alloys, the most common use of abrasive wheels of green silicon carbide, which has great hardness and brittleness with stable physical and mechanical properties with higher abrasive than black silicon carbide.

Buy, price

Evek GmbH sells rolled metal products at the best price. It is formed taking into account LME (London metal exchange) rates and depends on the technological features of production without including additional costs. We supply semi-finished products from titanium and its alloys in wide assortment. All batches have quality certificate for compliance with standards requirements. With us you can buy in bulk the most various products for large-scale productions. The wide choice, exhaustive consulting of our managers, reasonable prices and timely delivery determine the face of our company. There is a system of discounts for wholesale purchases