Titanium alloys are ideal materials for aircrafts and engines because of their high specific strength, good mechanical properties, and good corrosion resistance. However, due to their poor machinability, titanium alloys have restricted their application for a long time. With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of compressor parts, engine hoods, and exhaust devices for aircraft engines, as well as structural frames such as girder bulkheads for aircrafts. The titanium alloy parts of a new type of aero engine of our company account for about 11% of the total number of parts. This article is an experience summary of the titanium alloy material's cutting characteristics and the specific characteristics exhibited under different processing methods accumulated during the trial production of this new machine and the technical measures that should be taken.
1 Titanium Machinability and General Principles
Titanium alloys are divided into a phase, b phase, and a+b phase according to the metal structure, and their grades and types are represented by TA, TB, and TC, respectively. The materials used for a new type of engine in our company are TA and TC. General casting and forging adopt TA series, and bar uses TC series.
Features and Machinability
Titanium alloys have the following advantages over common alloy steels:
Stronger than the high: titanium alloy density is only 4.5g/cm3, much smaller than iron, and its strength is similar to ordinary carbon steel.
Good mechanical properties: The melting point of titanium alloy is 1660°C, which is higher than that of iron. It has higher thermal strength and can work below 550°C. At the same time, it usually shows better toughness at low temperature.
Good corrosion resistance: A dense oxide film is easily formed on the surface of titanium alloys below 550°C, so it is not easily oxidized and has high corrosion resistance to atmosphere, seawater, steam, and some acids, alkalis, and salts.
On the other hand, titanium alloys have poor machinability. The main reasons are: Poor thermal conductivity, resulting in high cutting temperatures and reduced tool life. At temperatures above 600°C, an oxidized hard layer forms on the surface and the tool has a strong wear effect. Low plasticity and high hardness make the shear angle increase, the contact length between the chip and the rake face is very small, the stress on the rake face is large, and the blade is prone to damage. The elastic modulus is low, the elastic deformation is large, and the springback amount of the workpiece surface near the flank is large, so the contact area between the machined surface and the flank surface is large and the wear is serious. These characteristics of the titanium alloy cutting process make it very difficult to process, resulting in low processing efficiency and high tool consumption.
The general principle of cutting processing According to the nature of the titanium alloy and the characteristics of the cutting process, the following aspects should be considered when processing:
Use carbide tools as much as possible, such as tungsten cobalt alloys and titanium alloys with low chemical affinity, good thermal conductivity, and high strength. The impact-resistant ultra-fine-grained hard alloy can be used for intermittent cutting at low speed, and high-speed steel with high-temperature performance can be used for forming and complex tools.
Use smaller rake angles and larger relief angles to increase the contact length between the chip and the rake face, reduce the friction between the workpiece and the flank, and use a circular blade to improve the strength and avoid sharp corner damage. And chipping. Sharp edges should be maintained to ensure smooth evacuation and avoid chipping. The cutting speed should be low to avoid excessive cutting temperature; moderate feedrate, too large easy-to-burn knife, too little wear due to blade working in the work hardening layer; cutting depth can be larger, so that the cutting edge is in the hardened layer The following work will help improve tool life.
Coolant must be fully cooled during processing.
When cutting titanium alloys, knife resistance is large, so the process system must ensure sufficient rigidity. Since the titanium alloy is easily deformed, the cutting and clamping force cannot be large, especially in some finishing processes, and if necessary, a certain auxiliary support can be used.
The above are the general principles that need to be considered when processing titanium alloys. In fact, there are different contradictions and problems and the focus of problem solving when using different processing methods and under different conditions.
2 Titanium alloy cutting and processing technology measures Turning titanium alloys easily obtains better surface roughness, and the work hardening is not serious, but the cutting temperature is high and the tool wears fast. In response to these characteristics, the following measures are mainly taken in terms of cutting tools and cutting parameters:
Tool material: Select YG6, YG8, YG10HT according to the existing conditions of the factory.
Tool geometry parameters: suitable tool front and rear corners, rounded corners.
Lower cutting speeds.
Moderate feed.
Deeper depth of cut.
The specific parameters used are shown in Table 1.
Table 1 Turning titanium alloy parameter table process tool rake angle go
° Turning angle
° Tool tip arc radius re
Mm Cutting speed v
m/min cutting depth ap
Mm feed amount f
Mm/r
Roughing car 5 6 ~ 10 1 ~ 2 40 3 0.2 ~ 0.3
Finishing car 5 6 to 10 0.5 60 0.2 to 0.5 0.1
Also note the following 3 points:
Cool enough.
The tip of the knife cannot be higher than the center of the workpiece when the outside is round, otherwise it is easy to tie the knife.
For precision turning and turning of thin-walled parts, the tool declination angle is large, typically 75 to 90°.
Milling titanium alloy milling than turning difficult, because the milling is interrupted cutting, and the chip is easy to bond with the blade, when the sticky teeth cut into the workpiece again, the sticky debris is knocked off and take away a small piece of tool material, forming The chipping greatly reduces the tool's durability. Therefore, three measures have been taken for titanium alloy milling:
Milling method: generally using milling.
Tool Material: High Speed ​​Steel M42.
Improves the rigidity of the process system from workpiece clamping and equipment.
Here we need to point out that the general machining of alloy steels does not use parallel milling. Due to the influence of machine screw and nut clearance, the milling cutter acts on the workpiece during the milling, and the force and feed in the feed direction. The same direction, easy to make the workpiece table gap turbulence, resulting in knife. In the case of Climb milling, when the blade starts to cut, it hits the hard skin and causes the tool to break. However, due to the fact that the counter-milling cuttings are thin to thick, the tool is susceptible to dry friction with the workpiece during the initial cutting, which increases the chipping and chipping of the tool. In the case of titanium alloys, the latter contradiction becomes even more pronounced.
In addition, for the smooth milling of titanium alloys, the following points should also be noted:
Compared to the universal standard cutter, the rake angle should be reduced and the back angle should be increased.
Milling speed should be low.
Use sharp-edged cutters as much as possible to avoid using spade cutters.
The tip should be transferred smoothly.
Use cutting fluid in large quantities.
In order to increase the production efficiency, the milling depth and width can be appropriately increased. The milling depth is generally 1.5 to 3.0 mm for rough machining and 0.2 to 0.5 mm for finishing.
Grinding
The common problem with grinding titanium alloy parts is that the sticky particles cause clogging of the grinding wheel and surface burns on the part. The reason for this is that the thermal conductivity of the titanium alloy is poor, resulting in a high temperature in the grinding zone, which causes the titanium alloy and the abrasive to bond, diffuse, and strongly chemical reactions. Sticking and wheel clogging cause a significant reduction in the grinding ratio. As a result of diffusion and chemical reactions, the workpiece is burned on the surface and the fatigue strength of the part is reduced. This is more noticeable in the grinding of titanium alloy castings. To solve this problem, the measures taken are:
Use the appropriate grinding wheel material: green silicon carbide TL.
Lower wheel hardness: ZR1.
Thicker wheel size: 60.
Lower wheel speed: 10 to 20 m/s.
Slightly smaller feed.
Cool thoroughly with the emulsion.
Drilling
Titanium alloy drilling is more difficult, often in the process of burning knife and broken drill phenomenon. This is mainly due to poor grinding of the drill bit, untimely chip removal, poor cooling, and poor rigidity of the process system. Therefore, the following points must be noted in the titanium alloy drilling process:
Tool material: high-speed steel M42, B201 or carbide.
Reasonable bit sharpening: increase the top angle, reduce the rake angle of the outer edge, increase the back angle of the outer edge, and add 2 to 3 times the inverted cone to the standard drill bit. Retract and timely remove chips, pay attention to the shape and color of the chips. For example, when the feathering or color change occurs during the drilling process, it indicates that the drill bit has become blunt and should be changed in time.
Adding cutting fluid: Soybean oil is generally used, and if necessary, French OLTIP drilling and tapping special oil can be added.
Improve the rigidity of the process system: The drilling die should be fixed on the workbench, and the drilling die guide should be close to the machining surface, and the short bit should be used as far as possible.
It is also worth noting that when the manual feed is used, the drill bit must not retreat in the hole, otherwise the drill edge rubs the machining surface, causing work hardening and making the drill bit dull.
Reaming titanium alloy cutting tool wear is not serious, the use of carbide and high-speed steel reamers can be. The factory commonly used W18Cr4V, M42, YW1, YG8, YG10HT and so on. When using a carbide reamer, a process system like drilling is used to prevent the reamer from chipping. The main problem that arises when the titanium alloy is reamed is that the reaming is not light, and the following solution can be taken: the width of the hinge blade is narrowed with whetstone to avoid the adhesion of the land and the hole wall, but sufficient strength is ensured, and the blade width is generally 0.1 ~0.15mm is better.
The transition between the cutting edge and the calibration part should be a smooth arc, which should be repaired in time after wear and require uniform arc sizes.
If necessary, increase the calibration part of the inverted cone.
Reamed twice. Rough hinge allowance 0.1mm, precision hinge allowance is generally less than 0.05mm.
Spindle speed 60r/min.
When the retracting knife is finished, the hand hinge cannot be reversed and the machine hinge should not stop to exit the reaming knife.
Tapping of titanium alloys with tapping, especially tapping with M6 mm or less, is quite difficult. Mainly because of the small chip, easy to bond with the blade and the workpiece, resulting in a large surface roughness and torque. Improper selection and improper operation of taps during tapping can easily cause work hardening. The processing efficiency is extremely low and there is a phenomenon of tapping. The solution is as follows:
Priority is given to a bit of tapping teeth in the tap, the number of teeth should be less than the standard tap, generally 2 to 3 teeth. Cone angle should be large, taper part is generally 3 to 4 thread length. In order to facilitate chip evacuation, it is also possible to grind negative angles in the cutting cone. Try to use short taps to increase tap rigidity. The inverted cone portion of the tap should be increased more than the standard to reduce the friction between the tap and the workpiece.
When the bottom hole of the thread is processed, the rough drill is first used and then the hole is used to expand the hole to reduce the work hardening of the bottom hole. For threads with a pitch of 0.7-1.5 mm, the bottom hole size can be machined to the standard deviation of the standard threaded bottom hole specified by the national standard and allow an additional 0.1 mm.
If it is not limited by the position of the screw hole and the shape of the workpiece, use the machine attack as much as possible to avoid the work hardening caused by uneven feed and tapping in the manual tapping.
Titanium alloys are ideal materials for aircrafts and engines because of their high specific strength, good mechanical properties, and good corrosion resistance. However, due to their poor machinability, titanium alloys have restricted their application for a long time. With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of compressor parts, engine hoods, and exhaust devices for aircraft engines, as well as structural frames such as girder bulkheads for aircrafts. The titanium alloy parts of a new type of aero engine of our company account for about 11% of the total number of parts. This article is an experience summary of the titanium alloy material's cutting characteristics and the specific characteristics exhibited under different processing methods accumulated during the trial production of this new machine and the technical measures that should be taken.
1 Titanium Machinability and General Principles
Titanium alloys are divided into a phase, b phase, and a+b phase according to the metal structure, and their grades and types are represented by TA, TB, and TC, respectively. The materials used for a new type of engine in our company are TA and TC. General casting and forging adopt TA series, and bar uses TC series.
Features and Machinability
Titanium alloys have the following advantages over common alloy steels:
Stronger than the high: titanium alloy density is only 4.5g/cm3, much smaller than iron, and its strength is similar to ordinary carbon steel.
Good mechanical properties: The melting point of titanium alloy is 1660°C, which is higher than that of iron. It has higher thermal strength and can work below 550°C. At the same time, it usually shows better toughness at low temperature.
Good corrosion resistance: A dense oxide film is easily formed on the surface of titanium alloys below 550°C, so it is not easily oxidized and has high corrosion resistance to atmosphere, seawater, steam, and some acids, alkalis, and salts.
On the other hand, titanium alloys have poor machinability. The main reason is:
Poor thermal conductivity, resulting in high cutting temperatures, reduces tool life.
At temperatures above 600°C, an oxidized hard layer forms on the surface and the tool has a strong wear effect.
Low plasticity and high hardness make the shear angle increase, the contact length between the chip and the rake face is very small, the stress on the rake face is large, and the blade is prone to damage.
The elastic modulus is low, the elastic deformation is large, and the springback amount of the workpiece surface near the flank is large, so the contact area between the machined surface and the flank surface is large and the wear is serious.
These characteristics of the titanium alloy cutting process make it very difficult to process, resulting in low processing efficiency and high tool consumption.
General principles of cutting
According to the nature of the titanium alloy and the characteristics of the cutting process, the following aspects should be considered when processing:
Use carbide tools as much as possible, such as tungsten cobalt alloys and titanium alloys with low chemical affinity, good thermal conductivity, and high strength. The impact-resistant ultra-fine-grained hard alloy can be used for intermittent cutting at low speed, and high-speed steel with high-temperature performance can be used for forming and complex tools.
Use smaller rake angles and larger relief angles to increase the contact length between the chip and the rake face, reduce the friction between the workpiece and the flank, and use a circular blade to improve the strength and avoid sharp corner damage. And chipping.
Sharp edges should be maintained to ensure smooth evacuation and avoid chipping.
The cutting speed should be low to avoid excessive cutting temperature; moderate feedrate, too large easy-to-burn knife, too little wear due to blade working in the work hardening layer; cutting depth can be larger, so that the cutting edge is in the hardened layer The following work will help improve tool life.
Coolant must be fully cooled during processing.
When cutting titanium alloys, knife resistance is large, so the process system must ensure sufficient rigidity. Since the titanium alloy is easily deformed, the cutting and clamping force cannot be large, especially in some finishing processes, and if necessary, a certain auxiliary support can be used.
The above are the general principles that need to be considered when processing titanium alloys. In fact, there are different contradictions and problems and the focus of problem solving when using different processing methods and under different conditions. Machine attack, to avoid the manual hardening caused by uneven tapping and halfway pauses.
1 Titanium Machinability and General Principles
Titanium alloys are divided into a phase, b phase, and a+b phase according to the metal structure, and their grades and types are represented by TA, TB, and TC, respectively. The materials used for a new type of engine in our company are TA and TC. General casting and forging adopt TA series, and bar uses TC series.
Features and Machinability
Titanium alloys have the following advantages over common alloy steels:
Stronger than the high: titanium alloy density is only 4.5g/cm3, much smaller than iron, and its strength is similar to ordinary carbon steel.
Good mechanical properties: The melting point of titanium alloy is 1660°C, which is higher than that of iron. It has higher thermal strength and can work below 550°C. At the same time, it usually shows better toughness at low temperature.
Good corrosion resistance: A dense oxide film is easily formed on the surface of titanium alloys below 550°C, so it is not easily oxidized and has high corrosion resistance to atmosphere, seawater, steam, and some acids, alkalis, and salts.
On the other hand, titanium alloys have poor machinability. The main reasons are: Poor thermal conductivity, resulting in high cutting temperatures and reduced tool life. At temperatures above 600°C, an oxidized hard layer forms on the surface and the tool has a strong wear effect. Low plasticity and high hardness make the shear angle increase, the contact length between the chip and the rake face is very small, the stress on the rake face is large, and the blade is prone to damage. The elastic modulus is low, the elastic deformation is large, and the springback amount of the workpiece surface near the flank is large, so the contact area between the machined surface and the flank surface is large and the wear is serious. These characteristics of the titanium alloy cutting process make it very difficult to process, resulting in low processing efficiency and high tool consumption.
The general principle of cutting processing According to the nature of the titanium alloy and the characteristics of the cutting process, the following aspects should be considered when processing:
Use carbide tools as much as possible, such as tungsten cobalt alloys and titanium alloys with low chemical affinity, good thermal conductivity, and high strength. The impact-resistant ultra-fine-grained hard alloy can be used for intermittent cutting at low speed, and high-speed steel with high-temperature performance can be used for forming and complex tools.
Use smaller rake angles and larger relief angles to increase the contact length between the chip and the rake face, reduce the friction between the workpiece and the flank, and use a circular blade to improve the strength and avoid sharp corner damage. And chipping. Sharp edges should be maintained to ensure smooth evacuation and avoid chipping. The cutting speed should be low to avoid excessive cutting temperature; moderate feedrate, too large easy-to-burn knife, too little wear due to blade working in the work hardening layer; cutting depth can be larger, so that the cutting edge is in the hardened layer The following work will help improve tool life.
Coolant must be fully cooled during processing.
When cutting titanium alloys, knife resistance is large, so the process system must ensure sufficient rigidity. Since the titanium alloy is easily deformed, the cutting and clamping force cannot be large, especially in some finishing processes, and if necessary, a certain auxiliary support can be used.
The above are the general principles that need to be considered when processing titanium alloys. In fact, there are different contradictions and problems and the focus of problem solving when using different processing methods and under different conditions.
2 Titanium alloy cutting and processing technology measures Turning titanium alloys easily obtains better surface roughness, and the work hardening is not serious, but the cutting temperature is high and the tool wears fast. In response to these characteristics, the following measures are mainly taken in terms of cutting tools and cutting parameters:
Tool material: Select YG6, YG8, YG10HT according to the existing conditions of the factory.
Tool geometry parameters: suitable tool front and rear corners, rounded corners.
Lower cutting speeds.
Moderate feed.
Deeper depth of cut.
The specific parameters used are shown in Table 1.
Table 1 Turning titanium alloy parameter table process tool rake angle go
° Turning angle
° Tool tip arc radius re
Mm Cutting speed v
m/min cutting depth ap
Mm feed amount f
Mm/r
Roughing car 5 6 ~ 10 1 ~ 2 40 3 0.2 ~ 0.3
Finishing car 5 6 to 10 0.5 60 0.2 to 0.5 0.1
Also note the following 3 points:
Cool enough.
The tip of the knife cannot be higher than the center of the workpiece when the outside is round, otherwise it is easy to tie the knife.
For precision turning and turning of thin-walled parts, the tool declination angle is large, typically 75 to 90°.
Milling titanium alloy milling than turning difficult, because the milling is interrupted cutting, and the chip is easy to bond with the blade, when the sticky teeth cut into the workpiece again, the sticky debris is knocked off and take away a small piece of tool material, forming The chipping greatly reduces the tool's durability. Therefore, three measures have been taken for titanium alloy milling:
Milling method: generally using milling.
Tool Material: High Speed ​​Steel M42.
Improves the rigidity of the process system from workpiece clamping and equipment.
Here we need to point out that the general machining of alloy steels does not use parallel milling. Due to the influence of machine screw and nut clearance, the milling cutter acts on the workpiece during the milling, and the force and feed in the feed direction. The same direction, easy to make the workpiece table gap turbulence, resulting in knife. In the case of Climb milling, when the blade starts to cut, it hits the hard skin and causes the tool to break. However, due to the fact that the counter-milling cuttings are thin to thick, the tool is susceptible to dry friction with the workpiece during the initial cutting, which increases the chipping and chipping of the tool. In the case of titanium alloys, the latter contradiction becomes even more pronounced.
In addition, for the smooth milling of titanium alloys, the following points should also be noted:
Compared to the universal standard cutter, the rake angle should be reduced and the back angle should be increased.
Milling speed should be low.
Use sharp-edged cutters as much as possible to avoid using spade cutters.
The tip should be transferred smoothly.
Use cutting fluid in large quantities.
In order to increase the production efficiency, the milling depth and width can be appropriately increased. The milling depth is generally 1.5 to 3.0 mm for rough machining and 0.2 to 0.5 mm for finishing.
Grinding
The common problem with grinding titanium alloy parts is that the sticky particles cause clogging of the grinding wheel and surface burns on the part. The reason for this is that the thermal conductivity of the titanium alloy is poor, resulting in a high temperature in the grinding zone, which causes the titanium alloy and the abrasive to bond, diffuse, and strongly chemical reactions. Sticking and wheel clogging cause a significant reduction in the grinding ratio. As a result of diffusion and chemical reactions, the workpiece is burned on the surface and the fatigue strength of the part is reduced. This is more noticeable in the grinding of titanium alloy castings. To solve this problem, the measures taken are:
Use the appropriate grinding wheel material: green silicon carbide TL.
Lower wheel hardness: ZR1.
Thicker wheel size: 60.
Lower wheel speed: 10 to 20 m/s.
Slightly smaller feed.
Cool thoroughly with the emulsion.
Drilling
Titanium alloy drilling is more difficult, often in the process of burning knife and broken drill phenomenon. This is mainly due to poor grinding of the drill bit, untimely chip removal, poor cooling, and poor rigidity of the process system. Therefore, the following points must be noted in the titanium alloy drilling process:
Tool material: high-speed steel M42, B201 or carbide.
Reasonable bit sharpening: increase the top angle, reduce the rake angle of the outer edge, increase the back angle of the outer edge, and add 2 to 3 times the inverted cone to the standard drill bit. Retract and timely remove chips, pay attention to the shape and color of the chips. For example, when the feathering or color change occurs during the drilling process, it indicates that the drill bit has become blunt and should be changed in time.
Adding cutting fluid: Soybean oil is generally used, and if necessary, French OLTIP drilling and tapping special oil can be added.
Improve the rigidity of the process system: The drilling die should be fixed on the workbench, and the drilling die guide should be close to the machining surface, and the short bit should be used as far as possible.
It is also worth noting that when the manual feed is used, the drill bit must not retreat in the hole, otherwise the drill edge rubs the machining surface, causing work hardening and making the drill bit dull.
Reaming titanium alloy cutting tool wear is not serious, the use of carbide and high-speed steel reamers can be. The factory commonly used W18Cr4V, M42, YW1, YG8, YG10HT and so on. When using a carbide reamer, a process system like drilling is used to prevent the reamer from chipping. The main problem that arises when the titanium alloy is reamed is that the reaming is not light, and the following solution can be taken: the width of the hinge blade is narrowed with whetstone to avoid the adhesion of the land and the hole wall, but sufficient strength is ensured, and the blade width is generally 0.1 ~0.15mm is better.
The transition between the cutting edge and the calibration part should be a smooth arc, which should be repaired in time after wear and require uniform arc sizes.
If necessary, increase the calibration part of the inverted cone.
Reamed twice. Rough hinge allowance 0.1mm, precision hinge allowance is generally less than 0.05mm.
Spindle speed 60r/min.
When the retracting knife is finished, the hand hinge cannot be reversed and the machine hinge should not stop to exit the reaming knife.
Tapping of titanium alloys with tapping, especially tapping with M6 mm or less, is quite difficult. Mainly because of the small chip, easy to bond with the blade and the workpiece, resulting in a large surface roughness and torque. Improper selection and improper operation of taps during tapping can easily cause work hardening. The processing efficiency is extremely low and there is a phenomenon of tapping. The solution is as follows:
Priority is given to a bit of tapping teeth in the tap, the number of teeth should be less than the standard tap, generally 2 to 3 teeth. Cone angle should be large, taper part is generally 3 to 4 thread length. In order to facilitate chip evacuation, it is also possible to grind negative angles in the cutting cone. Try to use short taps to increase tap rigidity. The inverted cone portion of the tap should be increased more than the standard to reduce the friction between the tap and the workpiece.
When the bottom hole of the thread is processed, the rough drill is first used and then the hole is used to expand the hole to reduce the work hardening of the bottom hole. For threads with a pitch of 0.7-1.5 mm, the bottom hole size can be machined to the standard deviation of the standard threaded bottom hole specified by the national standard and allow an additional 0.1 mm.
If it is not limited by the position of the screw hole and the shape of the workpiece, use the machine attack as much as possible to avoid the work hardening caused by uneven feed and tapping in the manual tapping.
Titanium alloys are ideal materials for aircrafts and engines because of their high specific strength, good mechanical properties, and good corrosion resistance. However, due to their poor machinability, titanium alloys have restricted their application for a long time. With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of compressor parts, engine hoods, and exhaust devices for aircraft engines, as well as structural frames such as girder bulkheads for aircrafts. The titanium alloy parts of a new type of aero engine of our company account for about 11% of the total number of parts. This article is an experience summary of the titanium alloy material's cutting characteristics and the specific characteristics exhibited under different processing methods accumulated during the trial production of this new machine and the technical measures that should be taken.
1 Titanium Machinability and General Principles
Titanium alloys are divided into a phase, b phase, and a+b phase according to the metal structure, and their grades and types are represented by TA, TB, and TC, respectively. The materials used for a new type of engine in our company are TA and TC. General casting and forging adopt TA series, and bar uses TC series.
Features and Machinability
Titanium alloys have the following advantages over common alloy steels:
Stronger than the high: titanium alloy density is only 4.5g/cm3, much smaller than iron, and its strength is similar to ordinary carbon steel.
Good mechanical properties: The melting point of titanium alloy is 1660°C, which is higher than that of iron. It has higher thermal strength and can work below 550°C. At the same time, it usually shows better toughness at low temperature.
Good corrosion resistance: A dense oxide film is easily formed on the surface of titanium alloys below 550°C, so it is not easily oxidized and has high corrosion resistance to atmosphere, seawater, steam, and some acids, alkalis, and salts.
On the other hand, titanium alloys have poor machinability. The main reason is:
Poor thermal conductivity, resulting in high cutting temperatures, reduces tool life.
At temperatures above 600°C, an oxidized hard layer forms on the surface and the tool has a strong wear effect.
Low plasticity and high hardness make the shear angle increase, the contact length between the chip and the rake face is very small, the stress on the rake face is large, and the blade is prone to damage.
The elastic modulus is low, the elastic deformation is large, and the springback amount of the workpiece surface near the flank is large, so the contact area between the machined surface and the flank surface is large and the wear is serious.
These characteristics of the titanium alloy cutting process make it very difficult to process, resulting in low processing efficiency and high tool consumption.
General principles of cutting
According to the nature of the titanium alloy and the characteristics of the cutting process, the following aspects should be considered when processing:
Use carbide tools as much as possible, such as tungsten cobalt alloys and titanium alloys with low chemical affinity, good thermal conductivity, and high strength. The impact-resistant ultra-fine-grained hard alloy can be used for intermittent cutting at low speed, and high-speed steel with high-temperature performance can be used for forming and complex tools.
Use smaller rake angles and larger relief angles to increase the contact length between the chip and the rake face, reduce the friction between the workpiece and the flank, and use a circular blade to improve the strength and avoid sharp corner damage. And chipping.
Sharp edges should be maintained to ensure smooth evacuation and avoid chipping.
The cutting speed should be low to avoid excessive cutting temperature; moderate feedrate, too large easy-to-burn knife, too little wear due to blade working in the work hardening layer; cutting depth can be larger, so that the cutting edge is in the hardened layer The following work will help improve tool life.
Coolant must be fully cooled during processing.
When cutting titanium alloys, knife resistance is large, so the process system must ensure sufficient rigidity. Since the titanium alloy is easily deformed, the cutting and clamping force cannot be large, especially in some finishing processes, and if necessary, a certain auxiliary support can be used.
The above are the general principles that need to be considered when processing titanium alloys. In fact, there are different contradictions and problems and the focus of problem solving when using different processing methods and under different conditions. Machine attack, to avoid the manual hardening caused by uneven tapping and halfway pauses.