Preamble: Titanium alloy has a small elastic modulus of elasticity. For example, the modulus of elasticity of TC4 is E = 110 GPa, which is about half the modulus of elasticity of steel. Therefore, the large elastic deformation of the workpiece caused by the cutting force reduces the accuracy of the workpiece, so it is necessary to improve the rigidity of the machining system. The workpiece must be very tightly secured and the tool moment to the workpiece support point of the tool is minimized. The tool must be sharp. Otherwise, vibration and friction will occur, the tool will be less durable and the workpiece will be less accurate.
When cutting titanium alloys, tumor-forming tips can only be in the range of cutting speeds of 1-5 mm / min. When cutting titanium alloys Therefore, under general manufacturing conditions, no chip tumor will be present. The coefficient of friction between the workpiece and the tool is not very large and good surface quality can be easily obtained. The use of cooling lubricants has no effect on improving the fine shape of the titanium alloy surface. The lower surface roughness of machined titanium alloys is due to the tool’s lack of build-up edges. The use of cooling lubricants has no effect on improving the fine shape of the titanium alloy surface. The low roughness of the machined surface when cutting titanium alloys is due to the absence of tip tumors on the tool.
However, in order to improve cutting conditions, reduce cutting temperature, increase tool life and eliminate the risk of fire, it is necessary to use a large amount of soluble coolant during the process.
Normally, there are no ignition and combustion phenomena in the machining of titanium alloy parts, but there are ignition and combustion phenomena in the micro cutting process. To avoid this danger, you need to use a lot of coolant. Remove chips from the machine tool in time. Fire extinguishing equipment is available. Replace the blunt cutter in time. If the surface of the work is dirty, sparks are likely to occur. At this time, it is necessary to reduce the cutting speed. Thick chips are not as easy to generate sparks as thin chips, so you need to increase the cutting volume so that the temperature does not rise immediately when you increase the cutting speed.
Titanium machining selection criteria: From the viewpoint of lowering the cutting temperature, it is necessary to slow down the cutting speed and increase the cutting amount. Due to the high cutting temperature, titanium alloys absorb oxygen and hydrogen from the atmosphere, making the surface of the workpiece hard and brittle, and severely wears the tool. Therefore, it is necessary to keep the tooltip temperature at an appropriate temperature during machining to avoid excessive temperature.
When turning a sclerite titanium alloy parts with a YG8 turning tool under intermittent cutting conditions, the recommended cutting parameters are: v = 15 to 28 m / min, f = 0.25 to 0.35 mm / r, ap = 1 to 3 mm.
When using the YG3 turning tool to finish titanium alloy workpieces under continuous cutting conditions, the recommended amount of cutting is: v = 50 to 70 m / min, f = 0.1 to 0.2 mm / r, ap = 0.3 to 1 mm. Table 2 shows the amount of cutting available for turning titanium alloys.
Amount of cutting when turning titanium alloy
Procedure Properties-Titanium Alloy Material-Hardness-Cutting Allowance (mm) -Cutting Speed (mm / min) -Tool Walking
- Oxide film thickness
- Roughing: TA1 ~ 7, TC1 ~ 2-Soft->
- Roughing: TA8, TC3-8-Medium->
- Roughing: TC9-10, TB1-2-Hard->
- Turning finish: TA1-7, TC1-2-soft
- Turning finish: TA8, TC3-8-in
- Turning finish: TC9-10, TB1-2-Hard
TC4 (hardness HB320-360) is turned with a YG6X turning tool, and for ap = 1mm and f = 0.1mm / r, the optimum cutting speed is 60mm / min. Based on this, Table 3 shows the cutting speeds at different cutting amounts and cutting depths.
Cutting speed of titanium alloy TC4
Common turning tools for machining titanium alloys have the following characteristics:
The material of the blade is YG6X, YG10HT. The rake angle is small, usually γ0 = 4 ° to 6 °, which increases the strength of the cutter head. There is a negative chamfer of f = 0.05-0.1mm to increase the strength of the blade. Rear friction is high, typically α0 = 14 ° to 16 °, reducing back friction and improving tool durability. In general, it is not possible to polish sharp corners or transition edges. In addition, the rounded corners of the polished edge are r = 0.5 mm, and rough cutting reaches r = 1-2 mm to increase the strength of the cutting edge. When turning or turning thin-walled parts, the main deviation angles of the tool are large, typically 75 ° to 90 °.
- Roughing: v = 40 to 50 m / min, f = 0.2 to 0.3 mm / r, ap = 3 to 5 mm.
- Semi-finishing turning: v = 40 to 45 m / min, f = 0.2 to 0.3 mm / r, ap = 1 to 2 mm.
- Finening: v = 50 to 55m / min, f = 0.1 to 0.15mm / r, ap = 0.2 to 0.5mm.
- Cooling with an emulsion can effectively improve the durability of the tool.
The high abrasion resistance and hardness of the cutter head under the premise of ensuring the strength of the cutter head are the keys to the rational machining of titanium alloys. Therefore, the selected YG6X blade should be sharpened (chamfered on the back) and then ground with a diamond or SiC grindstone to eliminate the sharpening of the incisions and increase the strength of the blade.
When rotating irregular black leather workpieces roughly, the blades are typically ground with a blade tilt of 3 ° to + 5 °. In the case of fine lathes, there is generally no blade tilt, the tool wear at this time is the bonding of the main rake face.
Such a general turning tool can reasonably solve the problem that the activity of the material increases as the temperature rises, the thermal conductivity decreases when the titanium alloy is processed, and the durability of the tool is greatly improved. increase.
Drilling holes in titanium alloys is difficult. Burns and drill damage often occur during the drilling process. The main reasons are poor grinding of the drill bit, untimely chip removal, poor cooling and lack of rigidity of the process system.
(1) Drill selection
For drills larger than 5 mm in diameter, it is best to use cemented carbide YG8 as the tool material. For drilling holes smaller than 5 mm, high speed steel drill bits with hardness greater than 63 HRC (such as M42 and B201) can be used. If the hole depth is less than twice the diameter, a bit (short type) bit is used. If the hole depth is more than twice the diameter, a twist drill is used. Geometric parameters of the drill bit: λ = 0 ° to 3 °, αc = 13 ° to 15 °, 2φ = 120 ° to 130 °.
It reduces friction and improves the cutting capacity of the drill bit to promote chip formation.
The width of the guide edge band can be reduced to 0.1-0.3 mm depending on the diameter of the drill bit, and the cross edge can be ground to 0.1D. In addition, the apex angle of double-edged grinding can be 2φ = 130 ° to 140 ° and 2φ = 70 ° to 80 °.
Double-edged bit geometric parameters
Bit diameter (mm)-Vertex angle 2_-2nd vertex angle 2_0-2nd edge back angle a
- 3 to 6-130 ° to 140 ° -80 ° to 140 ° -12 ° to 18 °-
- > 6 ~ 10-130 ° ~ 140 ° -80 ° ~ 140 ° -12 ° ~ 18 °-
- > 10-18-125 °-140 ° -80 ° -140 ° -12 ° -18 °-
- > 18 ~ 30-125 ° ~ 140 ° -80 ° ~ 140 ° -12 ° ~ 18 °-
Carbide drill bit: v = 9 to 15 m / min, f = 0.05 to 0.2 mm / r; High speed steel drill bit v = 4 to 5 m / min, f = 0.05 to 0.3 mm / r.
Manual feed is possible when drilling deep holes or small diameter holes.
The drill must be regularly pulled out of the hole during drilling to remove chips. To avoid strong wear on the drill bit, the drill bit should not be allowed to stay in the hole, and the drill blade causes work hardening, making the drill bit dull and rubbing the surface. Cooling lubricant must be properly supplied during drilling. In general, if desired, you can add French OLTIP drilling, tap special oils and use soybean oil. To improve the rigidity of the process system, to secure the drill die to the work bench, the drill die should be close to the machined surface in order to make the bit as short as possible.
The wear rate of the rear corner of the bit is 0.4-0.5 mm, which is used as a measure of drill dullness.
Example of drilling
Drill an α + β TC4 titanium alloy workpiece using a molybdenum high speed steel drill. The diameter of the drill is D = 6.35 mm and the depth of the hole is H = 12.7 mm.
The cutting parameters v = 11.6 m / min and f = 0.127 mm / r were selected and cooled using the emulsion.
The durability T of the tool is based on the wear width h = 0.38 mm, and each drill can drill 260 holes for excellent results.