Research on Machinability of Ti Alloy and Machining Tool Design
The dredge Suction Mouth is a Cutter Suction Dredger component positioned behind the cutter head of a CSD during extraction of non-cohesive material from the sea bottom.The suction mouth can be found on the front side of the Cutter Ladder. We have two designs available: a `smiley` cross section area to optimize the flow and a neutral cross section. Both designs are available in a welded or wear-resistant casted version. In combination with our cutter and pump performance, we will help you select and design the right suction mouth for your application.
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Titanium and titanium alloys are not only important structural materials for manufacturing aircrafts, missiles, rockets and other spacecraft, but also have become increasingly widespread in mechanical engineering, marine engineering, biological engineering, and chemical engineering. As in the manufacture of valves, stainless steel valves and titanium valves are used in acidic media at the same time. Titanium valves have a better service life.
The addition of alloying elements to titanium to form a titanium alloy significantly increases its strength and increases the σb from 350 to 700 MPa to 1200 MPa. Therefore, the significance of applying titanium alloys to the industry is even more important. Titanium alloys are generally classified into three types according to the tissue under use: α titanium alloys (expressed as TA), β titanium alloys, and (α+β) titanium alloys (expressed as TC). The most commonly used among the three titanium alloys is α. Titanium alloys and (α+β) titanium alloys. Due to the poor machinability of titanium alloys, it brings many difficulties to practical applications. The author starts from the study of the relative machinability of titanium alloys, and puts forward more practical tools based on years of production experience for reference by readers.
2. Research on Machinability of Titanium Alloy
If the machinability of the No. 45 steel is 100%, the machinability of the titanium alloy is about 20 to 40%, and the machinability thereof is inferior to that of the stainless steel, but slightly better than that of the high-temperature alloy. In titanium alloys, β-type titanium alloys, α+β-type titanium alloys, and α-type titanium alloys are gradually improved in machinability, while pure titanium has the best machinability. That is, under normal circumstances, the higher the hardness of the material, the more alloying elements added, the worse the machinability of the material. When machining titanium alloys, if the material hardness is less than HB300, there will be a strong sticking knife phenomenon, and when the hardness is greater than HB370 processing is extremely difficult, so it is best to make the hardness of titanium alloy material between HB300 ~ 370.
2.1 Research on the Cutting Mechanism of Titanium Alloys
(1) Influence of gas impurities
Various gas impurities have a great influence on the machinability of titanium alloys, the most notable being oxygen, hydrogen and nitrogen; the machinability of titanium alloys deteriorates as the content of gas in the titanium alloy increases.
Titanium has high chemical reactivity and strong affinity. It is easily combined with the impurities that are in contact. Titanium can work with oxygen in the atmosphere at temperatures above 600°C. When it exceeds 650°C, the effect of titanium increases with temperature. Oxides also diffuse on the surface of the surface while oxygen diffuses into the titanium. Above the allotropic transition temperature (882.5°C), oxygen diffuses particularly intensely in the titanium and forms an embrittlement layer, and its embrittlement layer thickness over time increases. As the number increases, the so-called "tissue alpha layer" is produced. This is the additional hardening of titanium caused by oxygen tarnish. The more oxygen in titanium, the harder it becomes. The oxidizing ability of hydrogen in titanium with increasing temperature, its diffusion is extremely strong, and the formation of interstitial solid solution, resulting in hydrogen embrittlement. At room temperature, nitrogen has no effect on titanium. At high temperatures, nitrogen and titanium strongly combine to form a hard and brittle titanium nitride (TiN).
It can be seen that in the titanium alloy, oxygen, hydrogen, and nitrogen impurities can make the titanium alloy brittle. These impurities also have abrasive properties, which can accelerate tool wear when machining titanium alloys; they can also be formed after forging and stamping. Harder and oxidized skin with much higher hardness than the original material. All these have greatly deteriorated the machinability of titanium and titanium alloys.
(2) Influence of material properties
From the viewpoint of machinability, the various physical-mechanical properties of titanium are very disadvantageous to the combination of cutting, because the presence of each property exacerbates the cutting difficulties caused by another property.
Titanium alloys have a low plasticity and therefore extremely significantly affect their plastic deformation during cutting. If the chipping shrinkage represents the deformation of the cut layer, the shrinkage coefficient of the titanium alloy chip is equal to 1 (even less than 1), while the shrinkage factor of the ordinary carbon steel chip is approximately equal to 3, the smaller value of the titanium alloy makes the chip After the main cutting edge cuts off, it immediately rolls up so that there is only a very small contact area (about 1/3 of the steel) between the chip and the rake face of the tool, so that the pressure and local temperature acting on the contact area of ​​the turning tool Increase
Due to the high strength limit of titanium alloys, the contact area is subjected to higher pressures and local temperatures; coupled with the low thermal conductivity of titanium alloys (only 1/5 of the iron, 1/10 of the aluminum, TC8 thermal conductivity λ = 7.955 W/mk), which greatly limits the cooling conditions of the tip; in addition, the highly active metal titanium is also easily combined with the tool to produce welding and sticking. Due to the combination of the above properties, under the same cutting amount, the cutting force per unit area of ​​the tool when processing the titanium alloy is much larger than that of the general steel and the cutting temperature is much higher, so the tool wears quickly, and the material The machinability deteriorated.
(3) Influence of carbon content
The machinability of titanium alloys is related to the carbon content. When the carbon content is more than 0.20%, hard carbides are formed in the alloy and the machinability is decreased. When the carbon content is less than 0.20%, the machinability is improved.
(4) Effect of work hardening
Work hardening is considered to be one of the reasons for the difficulty in processing titanium alloys. In order to determine its degree of influence, we conducted a test and found that the work hardening of titanium is much smaller than that of stainless steel in any processing situation, and it is also smaller than other kinds of steel that are easy to harden.
The severe hardening of titanium alloys is caused by the local high temperatures generated during the cutting process that make it easy for titanium to absorb the oxygen and nitrogen in the atmosphere to form a hard and brittle skin. Under normal cutting conditions, the hardening depth is 0.1 to 0.15 mm and the hardening degree is 20% to 30%.
2.2 Study on Relative Machinable Cutting Conditions of Titanium Alloy
(1) Tool Material
When processing titanium alloys, YT cemented carbide inserts should not be used. Because: 1YT carbide insert contains titanium, it will have affinity with the titanium alloy processing, stick out the tip. 2 When turning titanium alloy, the contact between the turning tool and the cutting swarf is much smaller than when machining the steel. The unit cutting burr on the turning area of ​​the turning tool is large. Because the YT carbide cutting blade is brittle, it is easy to chip.
In general production, YG-type inserts are used to process titanium alloys despite their poor wear resistance. The YG8 inserts are generally used for roughing and intermittent turning, YG3 inserts for finish turning and continuous turning, and YG6X inserts for general machining.
Practice has proved that the cemented carbide alloy YA6 (which belongs to the fine-grained tungsten-cobalt type cemented carbide) has a good effect. The addition of a small amount of rare elements improves the wear resistance of the blade and replaces the original YG6X. Both strength and hardness are higher than those of YG6X.
In low-speed cutting or cutting of complex surfaces, high-vanadium high-speed steel (W12Cr4V4Mo) and high-cobalt high-speed steel (W2Mo9Cr4VCo8) can be used. These are the best tool materials for machining titanium alloys, but due to their low cobalt resources and high prices, they are Should be used as little as possible to protect rare resources and reduce costs.
(2) Tool geometry
When cutting titanium alloy, turning angle α0 of turning tool is the most sensitive of all tool parameters, because metal elastic recovery under the cutting layer is large and the processing hardness is large. Generally, large relief angle can make the cutting edge easy to cut into the metal layer and reduce the back knife. The wear of the surface, but the back angle is too small (less than 15 °) will appear metal adhesion phenomenon; and the back corner is too large, the tool will be weakened, the blade is easy to disintegrate. Therefore, most turning tools for cutting titanium alloys use a 15° relief angle. From the viewpoint of tool durability, the α0 is less than or greater than 15°, which reduces the durability of the turning tool. In addition, the lathe blade with α0 of 15° is relatively sharp and can reduce the cutting temperature.
As the titanium alloy in the cutting process, with the air of oxygen, hydrogen, nitrogen, etc. to form a hard and brittle compound, resulting in tool wear (mainly occurs in the tool rake face), it should adopt a small value of the rake angle; In addition, titanium The plasticity of the alloy is low, and the contact area between the chip and the rake face is small. Therefore, a small value of the rake angle should also be selected. This can increase the contact area between the chip and the rake face, so that the cutting heat and cutting pressure are not excessively concentrated on the blade. Near the mouth, it is not only conducive to heat dissipation, but also strengthens the cutting edge to avoid chipping due to the concentration of cutting forces.
Therefore, when machining a (α+β) titanium alloy with a carbide tool, take the rake angle γ0=5° and grind the chamfer f (with a width of 0.05 to 0.1 mm), γf=0° to 10°, and the tool tip. Grind into a small radius of r = 0.5mm, and the blade inclination λ = +3°.
However, the research shows that the tool's durability is the best when the tool rake angle is in the range of 28° to 30°. Increasing the radius of the tool tip radius can also reduce the tool's avalanche.
General turning of titanium alloy turning tool geometric parameters: chamfer f = 0.3 ~ 0.7mm, γf = 0 °, γ0 = 8 ° ~ 10 °, α0 = 15 °, r = 0.5mm, λ = 0 °, κr = 45°, κ'r = 15°.
(3) Effect of cutting amount on cutting temperature
When turning titanium alloy TA2 with YG8 inserts, it can be seen from the relationship between the change of cutting parameters and the change of cutting temperature that the cutting temperature t increases sharply with the increase of cutting speed v. The increase of cutting amount f also increases the cutting temperature t. , but its impact is less than the increase in speed. The change in depth of cut has little effect on the cutting speed.
The high cutting speed at the time of machining causes the cutting tool to be abraded violently, and the titanium alloy has the ability to absorb oxygen and hydrogen from the surrounding atmosphere, generating so-called "pregelatinization of the structure" and strengthening the machined surface.
Usually when the cutting speed and cutting amount are selected, the cutting temperature is maintained at about 800°C. That is, when the cutting amount is f=0.11 to 0.35 mm/r, the cutting speed v is 40 to 60 m/min.
(4) Effect of cutting amount on surface roughness
Because titanium alloy is very sensitive to stress concentration, it will seriously reduce its fatigue strength in the presence of scratches or dents. Therefore, the quality of the surface quality of titanium alloy parts is greatly affected. From the processing of titanium alloy TC6 (velocity v = 40m/min, depth of cut ap = 1mm, ≤ ≤ 0.1mm after flank wear after h) the relationship between the amount of cutting and surface roughness of the surface has been known, in order to obtain the surface roughness For Ra1.6μm, the cutting amount f=0.16mm/r must be selected; if the cutting amount f=0.25mm/r, 0.35mm/r and 0.45mm/r, respectively, when machining, the corresponding surface roughness obtained is Ra 3.2 μm, Ra 6.3 μm, and Ra 12.5 μm.
When cutting titanium alloy, the surface roughness has nothing to do with the cutting speed, the influence of cutting depth is also very small, and the surface quality changes within the same surface roughness.
When finishing the titanium alloy, in order to get the surface roughness of Ra1.6μm, YG cemented carbide inserts should be used to grind the working surface of turning tool. The geometric parameters of the turning tool are: γf=0°, γ0=10°, α0. = 15°, r = 0.5 mm; the amount of cutting selected is: v = 50 ~ 70 mm/min, f = 0.1 ~ 0.2 mm/r, ap = 0.3 ~ 1.0 mm; after the tool wears h after ≤ 0.3 mm.
By increasing the arc radius r of the tool tip and reducing the amount f of the tool, the tool wear 0.15 mm after the tool wear is reduced. After the titanium alloy is continuously turned, the surface roughness Ra of 1.25 to 0.8 μm can be obtained.
3. Titanium alloy cutting and tool design
3.1 Turning
The elastic modulus of titanium alloy is small, such as TC4's elastic modulus E = 110 GPa, which is about half that of steel. Therefore, the elastic deformation of the workpiece caused by the cutting force will reduce the accuracy of the workpiece. Therefore, the processing system must be improved. rigidity. The workpiece must be clamped firmly so that the cutter moment on the workpiece support point is minimized.
The tool must be sharp, otherwise vibration and friction will occur, which will shorten the tool life and reduce the accuracy of the workpiece.
When cutting a titanium alloy, a built-up edge is formed only at a cutting speed of 1 to 5 mm/min. Therefore, when the titanium alloy is cut under normal production conditions, no built-up edge is generated. The coefficient of friction between the workpiece and the tool is not very large and it is easy to obtain a good surface quality. The use of cooling lubricating fluids has no effect on improving the micro geometry of the titanium alloy surface. The lower surface roughness of the machined titanium alloy is due to the absence of built-up edge on the tool.
However, in order to improve the cutting conditions, reduce the cutting temperature, increase the tool life, and to eliminate the risk of fire, it is necessary to use a large amount of soluble coolant during processing.
Usually titanium alloy parts are not burned during processing, but there is a flaming combustion phenomenon in the micro-cutting state. To avoid this danger, it should: 1 use a lot of coolant; 2 timely remove chips from the machine; There are fire extinguishing equipment; 4 timely replacement of blunt tools; 5 easy to cause sparks when the workpiece surface is contaminated, at this time must reduce the cutting speed; 6 compared to thin chips than thick chips are not easy to produce sparks, so to increase the amount of knife, plus The large amount of knife does not increase the temperature rapidly as the cutting speed increases.
The selection criteria for the cutting amount of titanium alloys to be processed: from the viewpoint of reducing the cutting temperature, a lower cutting speed and a larger cutting amount should be adopted. Due to the high cutting temperature, the titanium alloy absorbs oxygen and hydrogen from the atmosphere to cause the surface of the workpiece to be hard and brittle, which causes the tool to be heavily worn. Therefore, during the processing, the temperature of the tool tip must be maintained at an appropriate temperature to avoid excessive temperature.
When using a YG8 turning tool to cut a titanium alloy workpiece with a hard skin under intermittent cutting conditions, the recommended cutting amount is: v=15-28 m/min, f=0.25-0.35 mm/r, ap=1-3 mm.
When using a YG3 turning tool for a titanium alloy workpiece under continuous cutting conditions, the recommended cutting amount 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 available cutting amounts for turning titanium alloys.
Table 2. Cutting rates when turning titanium alloys
Process Properties - Titanium Alloy Material - Hardness - Cutting allowance (mm) - Cutting speed (mm/min) - Number of passes (mm/r)
Wild car - TA1 ~ 7, TC1 ~ 2 - soft -> oxide thickness -18 ~ 36-0.1 ~ 0.25
Wild car - TA8, TC3 ~ 8 - Medium -> Oxide skin thickness -12 ~ 27-0.08 ~ 0.15
Wild car -TC9 ~ 10, TB1 ~ 2 - hard -> oxide thickness -7.2 ~ 18-0.06 ~ 0.12
Roughing car - TA1 ~ 7, TC1 ~ 2 - soft -> 2-30 ~ 54-0.2 ~ 0.4
Roughing car - TA8, TC3 ~ 8 - medium -> 2-24 ~ 54-0.15 ~ 0.3
Roughing car - TC9 ~ 10, TB1 ~ 2 - hard -> 2-15 ~ 30-0.1 ~ 0.2
Precision car - TA1 ~ 7, TC1 ~ 2 - soft -0.07 ~ 0.75-37.5 ~ 60-0.07 ~ 0.15
Finishing car - TA8, TC3 ~ 8 - medium - 0.07 ~ 0.75-30 ~ 48-0.07 ~ 0.12
Finishing car - TC9 ~ 10, TB1 ~ 2 - hard - 0.07 ~ 0.75-18 ~ 36-0.05 ~ 0.12
The TC4 (hardness: HB320-360) was turned with a YG6X turning tool. The optimum cutting speed at ap=1mm and f=0.1mm/r was 60mm/min.
Based on this, the cutting speeds under different cutting amount and cutting depth are shown in Table 3.
Table 3. Cutting Speed ​​of Turned Titanium Alloy TC4
Ap-1mm-2mm-3mm
F (mm/r)-0.1, 0.15, 0.2, 0.3-0.1, 0.15, 0.2, 0.3-0.1, 0.2, 0.3
V(mm/min)-60,52,43,36-49,40,34,28-44,30,26
The typical turning tool for machining titanium alloys has the following characteristics: 1 The blade material is YG6X, YG10HT; 2 The rake angle is small, generally γ0=4°~6°, the strength of the Cutter Head is enhanced; 3 The negative torque is f=0.05-0.1mm. Edge, to enhance the strength of the blade; 4 large posterior angle, generally α0 = 14 ° ~ 16 °, in order to reduce the back of friction, improve tool durability; 5 generally not allowed to sharpen the sharp corner or transition edge, and grinding knife The sharp round r=0.5mm or so, roughing can reach r=1-2mm to enhance the strength of the cutting edge; 6When the precision turning or turning thin-walled parts, the main declination angle of the cutting tool is large, generally 75°～90°. .
Cutting amount:
Roughing car: v=40 to 50 m/min, f=0.2 to 0.3 mm/r, ap=3 to 5 mm.
Semi-finishing car: v = 40 ~ 45m/min, f = 0.2 ~ 0.3mm/r, ap = 1 ~ 2mm.
Finishing car: v = 50 ~ 55m/min, f = 0.1 ~ 0.15mm/r, ap = 0.2 ~ 0.5mm.
Emulsion cooling can effectively increase tool life. In the premise of guaranteeing the strength of the cutter head, making the cutter head with high wear resistance and hardness is the key to rational processing of titanium alloy. Therefore, the selected YG6X blade should be backed with diamond or silicon carbide whetstone (back chamfer) after sharpening, so as to eliminate the need for sharpening the saw blade and enhance the strength of the blade.
When irregular rough black leather workpieces are roughed, the blades are generally worn out at an angle of 3° to +5°; when the fine cars are finished, they generally have no cutting edge angles, and at this time, the tool wear is mainly kerf (adhesive) wear.
This typical turning tool can reasonably solve the problem that when the titanium alloy is processed, the material activity increases with increasing temperature and the thermal conductivity is poor, so the tool durability is greatly improved.
3.2 Drilling
Titanium alloy drilling process is more difficult, often in the process of burning knife and broken drill phenomenon, mainly due to poor grinding of the drill bit, chip removal is not timely, poor cooling and poor process system rigidity.
(1) Selection of drills: drills with a diameter of more than 5 mm are preferably made of hard alloy YG8 as the tool material; when processing holes smaller than 5 mm, high-speed steel drills with hardness greater than 63 HRC (such as M42 or B201) can be used; when the hole depth is less than For double diameters, a chute (short) drill is used; when the hole depth is more than twice the diameter, a twist drill is used. The geometry of the drill: λ = 0° to 3°, αc = 13° to 15°, 2φ = 120° to 130°.
In order to facilitate the formation of chips, reduce friction and improve the cutting ability of the drill, the width of the leading edge can be reduced to 0.1-0.3 mm according to the diameter of the drill bit, grinding the chisel edge to 0.1 D, and the double edge grinding angle 2φ=130°-140 °, 2φ = 70° to 80°. Table 4 lists the geometric parameters of the double-edge bit.
Table 4. Double front angle drill bit geometry
Drill diameter (mm) - apex angle 2φ - second apex angle 2φ0 - second edge edge relief angle α-b (mm) - c (mm)
>3 to 6-130 to 140 to 80 to 140 to 12 to 18 to 1.5 to 0.4 to 0.8
>6～10-130°～140°-80
° - 140 ° -12 ° -18 ° -1.5 - 2.5 - 0.6 - 1
>10 to 18-125 to 140 to 80 to 140 to 12 to 18 to 2.5 to 4-0.8 to 1
>18 to 30-125 to 140 to 80 to 140 to 12 to 18 to 4 to 6-1 to 1.5
(2) Cutting amount
Carbide drill: v = 9 ~ 15m/min, f = 0.05 ~ 0.2mm/r; high-speed steel drill v = 4 ~ 5m/min, f = 0.05 ~ 0.3mm/r.
(3) When drilling deep holes or small diameter holes, manual feed can be used. When drilling, you must periodically withdraw the drill from the hole to remove the chips. In order to avoid the strong wear of the drill bit, the drill bit cannot be stuck in the hole and the drill bit will rub the machining surface, which will cause work hardening and make the drill bit dull. Drilling must be well supplied with cooling lubricant. Soybean oil is generally used, and if necessary, French OLTIP drilling and tapping special oil can be added. As much as possible to improve the rigidity of the process system, the drill die is fixed on the workbench, and the drill die should be close to the machining surface to make the drill bit as short as possible.
Take the bit behind the bit after the wear h=0.4~0.5mm as the blunt standard for bit wear.
(4) Drilling example: Drilling is performed on α+β TC4 titanium alloy workpiece with molybdenum high-speed steel drill bit. The drill diameter is D=6.35mm and the hole depth is H=12.7mm. The selected cutting parameters were v=11.6m/min, f=0.127mm/r, and the emulsion cooling was used. The tool durability T is based on the wear width h=0.38mm, and 260 holes can be drilled per drill with excellent results.
Casting the dredge suction mouth in one piece allows the most intricate shapes, both external and internal that can be obtained to follow the shape of the flow and Competitive prices
The dredge suction mouth is produced with customized design for anti-wear resistance
The dredge suction mouth is produced with high accuracy and precise dimensions to fit in the cutter head and the Suction Pipe
The design of the dredge suction mouth is highly adaptable to the requirements of production allowing shorter delivery times
The dredge suction mouth is made of one cast piece. Its flange is cast together with the body of the dredge suction mouth By using only one cast piece eliminates many operations, such as machining, forging, welding and allows the most intricate shapes, both external and internal that can be obtained to follow the shape of the flow.
Materials of Dredge Suction Mouth
The dredge suction mouth is produced from Carbon Steel that allows easy welding and hard facing and casting. The other material, Carbon manganese steel increases the depth of hardening and improving strength and toughness. The Alloy steel is used to obtain higher performance in wear resistance.