Machining technology of titanium parts
The machining technology of titanium parts includes: turning, milling, tapping, reaming, drilling, grinding
1. Turning titanium parts
Turning titanium alloy products can easily obtain better surface roughness, and the work hardening is not serious, but the cutting temperature is high and the tool wears quickly. In view of these characteristics, the following measures are mainly taken in terms of tools and cutting parameters:
Tool material: The existing plant conditions selected YG6, YG8, YG10HT.
Tool geometry parameters: suitable front and rear angles of the tool, tool tip rounding.
Low cutting speed, moderate feed rate, deep cutting depth, sufficient cooling, the tool tip cannot be higher than the center of the workpiece when turning the outer circle, otherwise it is easy to stick the tool. When fine turning and turning thin-walled parts, the leading angle of the tool should be large, generally 75-90 degrees.
2. Milling titanium alloy
Milling of titanium alloy products is more difficult than turning, because milling is an intermittent cutting, and titanium chips are easy to bond with the milling cutter edge. When the teeth of the sticky titanium chips cut into the workpiece again, the sticky titanium chips are knocked off and a small piece of tool material is taken away, and the tool has a chipped edge. Greatly reduce the durability of the tool.
Milling method: generally adopt down milling.
Tool material: high-speed steel M42.
Generally, down milling is not used in the processing of titanium alloy steel, due to the influence of the ball screw and nut clearance of the machine tool. During down milling, the milling cutter acts on the workpiece, and the component force in the feed direction is the same as the feed direction. It is easy to cause intermittent movement of the workpiece table and cause the tool to hit. For down milling, the cutter tooth hits the hard titanium skin at the beginning of the cut, causing the cutter to break. However, because up-milling chips vary from thin to thick, the tool is prone to dry friction with the workpiece during the initial cutting, which increases the sticking and chipping of the tool. In order to make titanium alloy milling smoothly, it should be noted that the rake angle should be reduced and the back angle should be increased compared to the general standard milling cutter. The milling speed should be low, try to use the sharp tooth edge milling cutter, avoid using the shovel tooth edge milling cutter.
3. Tapping of titanium parts
Tapping titanium alloy products, because of the small chips, and the work is easy to bond with the blade, causing surface roughness value larger parts, high torque. When tapping, improper selection of taps and improper operation can easily cause work hardening, extremely low processing efficiency and sometimes tap breaks.
The skip-tooth tap must be selected first, and the number of teeth should be less than that of the standard tap, generally 2 to 3 teeth. The cutting taper angle should be large, and the taper part is generally 3 to 4 thread lengths. In order to facilitate chip removal, a negative inclination angle can also be ground on the cutting cone. Try to choose short taps to increase the rigidity of the taps. The inverted taper part of the tap should be appropriately enlarged compared to the standard to reduce the friction between the tap and the workpiece.
4. Reaming titanium alloy
The tool wear is not serious when titanium alloy reaming, and cemented carbide and high-speed steel reamer can be used. When using cemented carbide reamer, the rigidity of the process system similar to drilling should be adopted to prevent the reamer from chipping. The main problem in the reaming of titanium alloys is the poor finish of the reaming. Whetstone must be used to narrow the width of the reamer blade to prevent the blade from sticking to the hole wall, but sufficient strength must be ensured. Generally, the blade width of the cutter is preferably 0.1～0.15mm. The transition between the cutting edge and the calibration part should be a smooth arc, and it should be sharpened in time after being worn, and the size of the arc of each tooth should be the same; If necessary, the inverted cone of the calibration part can be enlarged.
5. Drilling titanium alloy
It is difficult to drill titanium alloys, and the phenomenon of burning tools and broken drills often occurs during the processing. This is mainly caused by several reasons such as poor sharpening of the drill bit, delayed chip removal, poor cooling and poor rigidity of the process system. Thus, in the titanium alloy in drilling drill grinding it should be noted that reasonable, large apex angle, reduced rake angle outer edge, the outer edge of the corner increases, inverted cone was added to 2 to 3 times the standard drill bit. Withdraw the knife frequently and remove the chips in time, paying attention to the shape and color of the chips. When plumes such as chips or a color change occurs during drilling, indicate that the drill has been blunt, it is timely sharpening tool change.
The drilling jig should be fixed on the worktable, and the guiding face of the drilling jig should be close to the processing surface. Use a short drill bit as much as possible. Another noteworthy problem is that when manual feeding is adopted, the drill should not advance or retreat in the hole, otherwise the drill blade will rub against the machined surface, causing work hardening and dulling the drill.
6. Grinding of titanium alloy parts
The common problems in grinding titanium alloy parts are sticky debris causing blockage of the grinding wheel and burns on the surface of the parts. The reason is the poor thermal conductivity of the titanium alloy, which causes high temperature in the grinding area, so that the titanium alloy and the abrasive material bond, diffuse and have a strong chemical reaction. Sticky chips and blockage of the grinding wheel lead to a significant decrease in the grinding ratio, the result of diffusion and chemical reactions. The surface of the workpiece is burned by grinding, resulting in a reduction in the fatigue strength of the parts, which is more obvious when grinding titanium alloy castings.
1. Turning titanium parts
Turning titanium alloy products can easily obtain better surface roughness, and the work hardening is not serious, but the cutting temperature is high and the tool wears quickly. In view of these characteristics, the following measures are mainly taken in terms of tools and cutting parameters:
Tool material: The existing plant conditions selected YG6, YG8, YG10HT.
Tool geometry parameters: suitable front and rear angles of the tool, tool tip rounding.
Low cutting speed, moderate feed rate, deep cutting depth, sufficient cooling, the tool tip cannot be higher than the center of the workpiece when turning the outer circle, otherwise it is easy to stick the tool. When fine turning and turning thin-walled parts, the leading angle of the tool should be large, generally 75-90 degrees.
2. Milling titanium alloy
Milling of titanium alloy products is more difficult than turning, because milling is an intermittent cutting, and titanium chips are easy to bond with the milling cutter edge. When the teeth of the sticky titanium chips cut into the workpiece again, the sticky titanium chips are knocked off and a small piece of tool material is taken away, and the tool has a chipped edge. Greatly reduce the durability of the tool.
Milling method: generally adopt down milling.
Tool material: high-speed steel M42.
Generally, down milling is not used in the processing of titanium alloy steel, due to the influence of the ball screw and nut clearance of the machine tool. During down milling, the milling cutter acts on the workpiece, and the component force in the feed direction is the same as the feed direction. It is easy to cause intermittent movement of the workpiece table and cause the tool to hit. For down milling, the cutter tooth hits the hard titanium skin at the beginning of the cut, causing the cutter to break. However, because up-milling chips vary from thin to thick, the tool is prone to dry friction with the workpiece during the initial cutting, which increases the sticking and chipping of the tool. In order to make titanium alloy milling smoothly, it should be noted that the rake angle should be reduced and the back angle should be increased compared to the general standard milling cutter. The milling speed should be low, try to use the sharp tooth edge milling cutter, avoid using the shovel tooth edge milling cutter.
3. Tapping of titanium parts
Tapping titanium alloy products, because of the small chips, and the work is easy to bond with the blade, causing surface roughness value larger parts, high torque. When tapping, improper selection of taps and improper operation can easily cause work hardening, extremely low processing efficiency and sometimes tap breaks.
The skip-tooth tap must be selected first, and the number of teeth should be less than that of the standard tap, generally 2 to 3 teeth. The cutting taper angle should be large, and the taper part is generally 3 to 4 thread lengths. In order to facilitate chip removal, a negative inclination angle can also be ground on the cutting cone. Try to choose short taps to increase the rigidity of the taps. The inverted taper part of the tap should be appropriately enlarged compared to the standard to reduce the friction between the tap and the workpiece.
4. Reaming titanium alloy
The tool wear is not serious when titanium alloy reaming, and cemented carbide and high-speed steel reamer can be used. When using cemented carbide reamer, the rigidity of the process system similar to drilling should be adopted to prevent the reamer from chipping. The main problem in the reaming of titanium alloys is the poor finish of the reaming. Whetstone must be used to narrow the width of the reamer blade to prevent the blade from sticking to the hole wall, but sufficient strength must be ensured. Generally, the blade width of the cutter is preferably 0.1～0.15mm. The transition between the cutting edge and the calibration part should be a smooth arc, and it should be sharpened in time after being worn, and the size of the arc of each tooth should be the same; If necessary, the inverted cone of the calibration part can be enlarged.
5. Drilling titanium alloy
It is difficult to drill titanium alloys, and the phenomenon of burning tools and broken drills often occurs during the processing. This is mainly caused by several reasons such as poor sharpening of the drill bit, delayed chip removal, poor cooling and poor rigidity of the process system. Thus, in the titanium alloy in drilling drill grinding it should be noted that reasonable, large apex angle, reduced rake angle outer edge, the outer edge of the corner increases, inverted cone was added to 2 to 3 times the standard drill bit. Withdraw the knife frequently and remove the chips in time, paying attention to the shape and color of the chips. When plumes such as chips or a color change occurs during drilling, indicate that the drill has been blunt, it is timely sharpening tool change.
The drilling jig should be fixed on the worktable, and the guiding face of the drilling jig should be close to the processing surface. Use a short drill bit as much as possible. Another noteworthy problem is that when manual feeding is adopted, the drill should not advance or retreat in the hole, otherwise the drill blade will rub against the machined surface, causing work hardening and dulling the drill.
6. Grinding of titanium alloy parts
The common problems in grinding titanium alloy parts are sticky debris causing blockage of the grinding wheel and burns on the surface of the parts. The reason is the poor thermal conductivity of the titanium alloy, which causes high temperature in the grinding area, so that the titanium alloy and the abrasive material bond, diffuse and have a strong chemical reaction. Sticky chips and blockage of the grinding wheel lead to a significant decrease in the grinding ratio, the result of diffusion and chemical reactions. The surface of the workpiece is burned by grinding, resulting in a reduction in the fatigue strength of the parts, which is more obvious when grinding titanium alloy castings.
