The machining of aluminum alloy parts in the aerospace industry has high requirements for the knife. The tool must be cost-effective and must meet the requirements of high-quality machining. Due to the extremely sharp cutting edge and groove shape of the solid carbide tool, it has a small cutting force in aluminum alloy finishing, and has the advantages of large chip space and smooth chip removal. Therefore, the whole cemented carbide tool has gradually replaced the traditional one. High speed steel cutter.
In addition, the modulus of elasticity of cemented carbide is about three times that of steel, which means that the solid carbide tool has a deformation of only one-third of the indexable tool under the same load. The solid carbide end mill can also be made into a spiral edge, so that the cutting and cutting can be smoothly performed, and the chip removal is smooth and smooth, which helps to reduce the fluctuation of the cutting force and thus suppress the resulting Vibration trend.
The indexable insert tooling system offers potential advantages for aluminum roughing and finishing, especially when using medium to large diameter tools from 25 to 100 mm. The indexable end mills for aluminum alloy machining require no re-grinding for superior safety, versatility and higher metal removal rates for unparalleled performance. However, in many cases the finishing cannot reach the required level. However, now Sandvik Coromant's CoroMill790 can achieve this with new cutting edges, inserts, inserts and clamping technology.
Improvements in CoroMill790
When developing a new end mill concept for aluminum alloy machining, a series of parameters can be modified to achieve a critical breakthrough in radial milling with indexable inserts. The main technical difficulties include: smooth cutting action; good chip formation; extremely high material removal rate; low power consumption; good surface roughness and minimum tooling trace; ensuring tool safety at high speeds.
Machining of aluminum alloys, especially in the finishing of small-volume cutting, the edge of the indexable insert is usually blunt, often resulting in the "ploughing" effect, the cutting edge is also easy to cut into the workpiece, causing a sudden increase in cutting force . A sudden increase in cutting force results in excessive knife size and high power requirements. The above problems are further complicated by the demand of the cutting edge, and a sharp positive rake cutting edge must be used for finishing, and the cutting edge is required to have sufficient strength to ensure metal removal rate during roughing. Therefore, in view of cutting forces, cutting edge incision, chip formation, stability, and blade positioning and clamping, a new approach is needed to use indexable inserts.
Cutting force generated on the cutting edge
When the cutting edge of the milling tool cuts into the workpiece, a sudden impact will cause the tool to vibrate. The resulting cutting force is primarily dependent on the chip thickness, which is proportional to the feed. The initially induced tool vibration will change the subsequent chip thickness, which may then continue to increase as the cutting force changes, which in turn causes the vibration of the processing system to increase. The direction and variation of the cutting force largely determine the vibration trend. Such regenerative vibration is also called flutter. If it is not suppressed, the variation of the cutting force will increase, which will reduce the surface roughness after cutting, resulting in the attachment of the knife, and even the cutting edge and the tool damage. Detrimental effects on the machine tool spindle.
For this reason, it is necessary to suppress the sharp fluctuation of the cutting force at the start of cutting to suppress the vibration tendency, which is also the main reason for using the vibration-proof cutter. However, in many cases this is achieved by optimizing the blade structure parameters.
Establishing a desirable model (capable of accurately calculating and predicting cutting forces) is one of the main reasons for developing a new insert geometry. Later, advanced FEM simulations demonstrated many answers, including the combined design of the edge line, rake angle and chip breaker, and the development and optimization of new cutting edge features on the flank of the insert. This is largely based on the vibration waveform calculated from the measured modal parameters.
Edge factor
It is well known that when milling cast iron, the wear of the flank faces a certain degree of vibration damping. The worn area of ​​the flank faces rubs against the machined surface, absorbing vibrational energy, resulting in amplitude attenuation. Logically, this effect should also be used to suppress other types of milling vibrations. The difficulty with this technology is how to reasonably use a specially designed flank wear strip as the primary flank. In order to achieve the correct damping effect, its position on the insert, its angle, its width, and its extent on the cutting edge need to be fairly accurate and should have the correct relationship to other design factors on the insert.
If this technique is applied properly, the cushioning flank can inhibit the increase in tool deformation and thus control chip thickness and radial cutting force. The secret of Sandvik Coromant's patented new blade design is that when the blade has a tendency to deviate from the workpiece, its land will contact the corresponding formed surface on the workpiece at the moment the tool begins to bend backwards - thus Prevents an increase in tool amplitude during machining. This means that the blade has a constant stabilizing effect, which is also part of the cutting action. The occasional brief contact between the specially designed main back rake and the workpiece is very gentle and does not have any effect on tool cutting performance, wear development or burr formation. As a result, the radial cutting force changes considerably.
The key to the success of this technology is the size and position of the main rear corner land relative to the blade geometry and tool diameter. The combined forces of the cutting forces, chip formation, and stress levels in the blades were then evaluated by finite element analysis with simulation of the cutting process.
Diameter factor
For the influence of radial cutting force, the small to medium diameter tool is not good in rigidity, and it is easy to be skewed, while the large diameter tool is relatively stable, and their requirements for anti-vibration are different. It has also been found that the feed rate is not the main factor affecting the radial cutting force. The radial cutting force is only slightly different between the different feeds of the tool (usually 0.25 mm and 0.35 mm per tooth feed). Variety. For a typical 25 mm diameter aluminum alloy end mill, the land on the insert is 1°, 0.1 mm wide and perfectly matches the curved cutting edge.
Aluminum alloy is a material with good machinability. The material has a cutting force of about one-third of that of steel and a melting point of 625 degrees. This low melting point means that no matter how high the cutting speed is, the temperature in the cutting zone will not exceed 625 degrees. Cemented carbide inserts can withstand high temperatures before excessive wear and no effect on the strength of the cutting edge.
Higher cutting speeds also increase power requirements. In fact, a common problem in high-speed machining of aluminum alloys is the need for large machine power, which tends to result in low metal removal rates per unit of power consumption. Therefore, it is usually required that the machine tool can provide the largest possible output power at high rotational speeds - it is very beneficial to reduce the required power due to the improvement of the tool when machining the aluminum alloy at high speed.
From a tool point of view, the main cutting force has a decisive influence on the power demand. The power required to reduce the amount of material removed has a significant positive impact on aluminum milling applications, as shown in the higher production efficiency of each process and the greater machine tooling capacity. In addition to determining whether the cutting is brisk, the rake angle also affects the main cutting force. The new blade design minimizes cutting forces by increasing the rake angle while matching the rest of the blade geometry, greatly reducing power requirements with the new CoroMill 790 blade design.
Easy to cut in
In the milling process, in order to prevent a sharp increase in the initial cutting force, the cutting edge needs to be cut into the workpiece as much as possible (such as stepwise cutting along the spiral of the solid carbide end mill), which will affect the radial cutting force. , direction, and growth rate, and thus affect the tool deformation and the shape error of the workpiece.
Sandvik Coromant found that by designing the new CoroMill 790 insert geometry, it can be cut at greater speeds and depths, resulting in a beneficial cut-in extension effect - significantly slowing the impact of entry, thus making the part The tooling error of the radial milling face is minimized. In addition, the axial cutting force can be greatly reduced, which means that the pressure exerted by the tool on the machined surface becomes smaller, which is a factor to be considered when processing thin-walled parts.
By deepening the chipbreaker on the rake face of the insert, the cutting force is reduced, and chip formation and chip removal are optimized - flying out and away from the cutting zone and the workpiece surface. This grooved blade-to-chip contact surface is smaller, has lower friction and smoother cutting action, and allows for greater depth of cut.
Although the cutting edge of the insert appears to be more fragile due to its sharper and deeper chipbreaker, its stress level is not higher than the relatively blunt cutting edge. With a more systematic design method, more sophisticated calculations, simulation and testing methods, a more reasonable blade structure can be developed, with better cutting performance and safety.
In addition, the modulus of elasticity of cemented carbide is about three times that of steel, which means that the solid carbide tool has a deformation of only one-third of the indexable tool under the same load. The solid carbide end mill can also be made into a spiral edge, so that the cutting and cutting can be smoothly performed, and the chip removal is smooth and smooth, which helps to reduce the fluctuation of the cutting force and thus suppress the resulting Vibration trend.
The indexable insert tooling system offers potential advantages for aluminum roughing and finishing, especially when using medium to large diameter tools from 25 to 100 mm. The indexable end mills for aluminum alloy machining require no re-grinding for superior safety, versatility and higher metal removal rates for unparalleled performance. However, in many cases the finishing cannot reach the required level. However, now Sandvik Coromant's CoroMill790 can achieve this with new cutting edges, inserts, inserts and clamping technology.
Improvements in CoroMill790
When developing a new end mill concept for aluminum alloy machining, a series of parameters can be modified to achieve a critical breakthrough in radial milling with indexable inserts. The main technical difficulties include: smooth cutting action; good chip formation; extremely high material removal rate; low power consumption; good surface roughness and minimum tooling trace; ensuring tool safety at high speeds.
Machining of aluminum alloys, especially in the finishing of small-volume cutting, the edge of the indexable insert is usually blunt, often resulting in the "ploughing" effect, the cutting edge is also easy to cut into the workpiece, causing a sudden increase in cutting force . A sudden increase in cutting force results in excessive knife size and high power requirements. The above problems are further complicated by the demand of the cutting edge, and a sharp positive rake cutting edge must be used for finishing, and the cutting edge is required to have sufficient strength to ensure metal removal rate during roughing. Therefore, in view of cutting forces, cutting edge incision, chip formation, stability, and blade positioning and clamping, a new approach is needed to use indexable inserts.
Cutting force generated on the cutting edge
When the cutting edge of the milling tool cuts into the workpiece, a sudden impact will cause the tool to vibrate. The resulting cutting force is primarily dependent on the chip thickness, which is proportional to the feed. The initially induced tool vibration will change the subsequent chip thickness, which may then continue to increase as the cutting force changes, which in turn causes the vibration of the processing system to increase. The direction and variation of the cutting force largely determine the vibration trend. Such regenerative vibration is also called flutter. If it is not suppressed, the variation of the cutting force will increase, which will reduce the surface roughness after cutting, resulting in the attachment of the knife, and even the cutting edge and the tool damage. Detrimental effects on the machine tool spindle.
For this reason, it is necessary to suppress the sharp fluctuation of the cutting force at the start of cutting to suppress the vibration tendency, which is also the main reason for using the vibration-proof cutter. However, in many cases this is achieved by optimizing the blade structure parameters.
Establishing a desirable model (capable of accurately calculating and predicting cutting forces) is one of the main reasons for developing a new insert geometry. Later, advanced FEM simulations demonstrated many answers, including the combined design of the edge line, rake angle and chip breaker, and the development and optimization of new cutting edge features on the flank of the insert. This is largely based on the vibration waveform calculated from the measured modal parameters.
Edge factor
It is well known that when milling cast iron, the wear of the flank faces a certain degree of vibration damping. The worn area of ​​the flank faces rubs against the machined surface, absorbing vibrational energy, resulting in amplitude attenuation. Logically, this effect should also be used to suppress other types of milling vibrations. The difficulty with this technology is how to reasonably use a specially designed flank wear strip as the primary flank. In order to achieve the correct damping effect, its position on the insert, its angle, its width, and its extent on the cutting edge need to be fairly accurate and should have the correct relationship to other design factors on the insert.
If this technique is applied properly, the cushioning flank can inhibit the increase in tool deformation and thus control chip thickness and radial cutting force. The secret of Sandvik Coromant's patented new blade design is that when the blade has a tendency to deviate from the workpiece, its land will contact the corresponding formed surface on the workpiece at the moment the tool begins to bend backwards - thus Prevents an increase in tool amplitude during machining. This means that the blade has a constant stabilizing effect, which is also part of the cutting action. The occasional brief contact between the specially designed main back rake and the workpiece is very gentle and does not have any effect on tool cutting performance, wear development or burr formation. As a result, the radial cutting force changes considerably.
The key to the success of this technology is the size and position of the main rear corner land relative to the blade geometry and tool diameter. The combined forces of the cutting forces, chip formation, and stress levels in the blades were then evaluated by finite element analysis with simulation of the cutting process.
Diameter factor
For the influence of radial cutting force, the small to medium diameter tool is not good in rigidity, and it is easy to be skewed, while the large diameter tool is relatively stable, and their requirements for anti-vibration are different. It has also been found that the feed rate is not the main factor affecting the radial cutting force. The radial cutting force is only slightly different between the different feeds of the tool (usually 0.25 mm and 0.35 mm per tooth feed). Variety. For a typical 25 mm diameter aluminum alloy end mill, the land on the insert is 1°, 0.1 mm wide and perfectly matches the curved cutting edge.
Aluminum alloy is a material with good machinability. The material has a cutting force of about one-third of that of steel and a melting point of 625 degrees. This low melting point means that no matter how high the cutting speed is, the temperature in the cutting zone will not exceed 625 degrees. Cemented carbide inserts can withstand high temperatures before excessive wear and no effect on the strength of the cutting edge.
Higher cutting speeds also increase power requirements. In fact, a common problem in high-speed machining of aluminum alloys is the need for large machine power, which tends to result in low metal removal rates per unit of power consumption. Therefore, it is usually required that the machine tool can provide the largest possible output power at high rotational speeds - it is very beneficial to reduce the required power due to the improvement of the tool when machining the aluminum alloy at high speed.
From a tool point of view, the main cutting force has a decisive influence on the power demand. The power required to reduce the amount of material removed has a significant positive impact on aluminum milling applications, as shown in the higher production efficiency of each process and the greater machine tooling capacity. In addition to determining whether the cutting is brisk, the rake angle also affects the main cutting force. The new blade design minimizes cutting forces by increasing the rake angle while matching the rest of the blade geometry, greatly reducing power requirements with the new CoroMill 790 blade design.
Easy to cut in
In the milling process, in order to prevent a sharp increase in the initial cutting force, the cutting edge needs to be cut into the workpiece as much as possible (such as stepwise cutting along the spiral of the solid carbide end mill), which will affect the radial cutting force. , direction, and growth rate, and thus affect the tool deformation and the shape error of the workpiece.
Sandvik Coromant found that by designing the new CoroMill 790 insert geometry, it can be cut at greater speeds and depths, resulting in a beneficial cut-in extension effect - significantly slowing the impact of entry, thus making the part The tooling error of the radial milling face is minimized. In addition, the axial cutting force can be greatly reduced, which means that the pressure exerted by the tool on the machined surface becomes smaller, which is a factor to be considered when processing thin-walled parts.
By deepening the chipbreaker on the rake face of the insert, the cutting force is reduced, and chip formation and chip removal are optimized - flying out and away from the cutting zone and the workpiece surface. This grooved blade-to-chip contact surface is smaller, has lower friction and smoother cutting action, and allows for greater depth of cut.
Although the cutting edge of the insert appears to be more fragile due to its sharper and deeper chipbreaker, its stress level is not higher than the relatively blunt cutting edge. With a more systematic design method, more sophisticated calculations, simulation and testing methods, a more reasonable blade structure can be developed, with better cutting performance and safety.
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