Type Of Turning Tool And How To Select The Right One?

Turning tool is the most widely used tool in metal cutting.

Turning tools are used on horizontal lathes, vertical lathes, turret lathes, automatic lathes and CNC machining centers to process the rotating surface of workpieces.

1. Classification of turning tools

(1) According to the surface type of machined workpiece

According to the type of workpiece surface, turning tools can be divided into cylindrical turning tools, inner hole turning tools and end face turning tools.

1. Cylindrical turning tool

The cylindrical turning tool is used for cylindrical turning to process the cylindrical surface of parts to obtain the required dimension, geometric tolerance accuracy and surface quality, as shown in Fig. 3-1.

cylindrical turning

Fig. 3-1 cylindrical turning

2. Inner hole turning tool

The inner hole turning tool is used for turning the inner hole, as shown in Fig. 3-2.

It is used to enlarge the inner hole of the workpiece or process the inner surface of the hollow workpiece by turning;

Most cylindrical turning processes can be used to turn the inner hole.

At this time, the tool is fixed (opposite to the direction of rotation of the boring tool in the machining center).

During cylindrical turning, the length of the workpiece and the size of the selected tool bar generally do not affect the tool overhang, so they can withstand the cutting force generated during machining.

When boring and turning inner holes, because the hole depth determines the overhang, the hole diameter and length of parts have certain restrictions on the selection of cutting tools.

inner hole turning

Fig. 3-2 inner hole turning

3. End turning tool

The end turning tool is used for end turning.

As shown in Fig. 3-3, the tool tip is always on a straight line intersecting with a point of the spindle axis, resulting in a plane or cone passing through the point and perpendicular to the spindle axis;

End turning tool refers to the tool whose main cutting edge can cut the end face of the workpiece.

end face turning

Fig. 3-3 end face turning

(2) According to the tool structure

According to the tool structure, turning tools can be divided into integral turning tools, welding turning tools, machine clamp turning tools, indexable turning tools and forming turning tools.

1. Integral turning tool

As shown in Fig. 3-4, the integral turning tool is made of the same kind of materials as the welding tool, or refers to a non detachable integral structure as compared with the indexable tool. Generally, the material commonly used for the integral turning tool is ordinary high-speed steel or high-performance high-speed steel.

The cutting tool has good rigidity.

The operator can grind the cutting part into straight surface, inclined surface and various forming surfaces according to the processing needs.

integral turning tool

Fig. 3-4 integral turning tool

2. Welding turning tool

As shown in Fig. 3-5, the welded turning tool is a turning tool that is used after machining a groove on the steel tool bar according to the requirements of the geometric angle of the turning tool, welding the high-speed steel or hard alloy blade in the groove with solder, and grinding according to the selected geometric parameters.

Due to the popularization and application of CNC lathes and compound machining machines, as well as the defects that welding turning tools are prone to micro cracks after welding and the performance of cemented carbide is reduced, they have been rarely used, but their overall rigidity is better than that of machine clamping turning tools and indexable turning tools.

After the tool is worn, it can be polished for many times, with high utilization rate.

welding turning tool

Fig. 3-5 welding turning tool

3. Machine clamp turning tool

As shown in Fig. 3-6, the machine clamp turning tool is a turning tool used to clamp the standard cemented carbide welding blade on the tool bar by mechanical clamping.

has the following characteristics:

(1) The blade is not welded at high temperature, which avoids the defects of blade hardness reduction and cracks caused by welding, and improves the service life of the tool.

(2) As the service life of the tool is increased, the service time is longer, and the tool change time is shortened, the production efficiency is improved.

(3) The tool bar can be reused, which not only saves steel, but also improves the utilization rate of the blade.

The blade is recycled and reproduced by the manufacturer, which improves the economic benefit and reduces the tool cost.

(4) After regrinding, the size of the blade will gradually decrease.

In order to restore the working position of the blade, an adjustment mechanism for the blade is often set on the turning tool structure to increase the regrinding times of the blade.

(5) The pressing plate end used to compress the blade can act as a chip breaker.

machine clamp turning tool

Fig. 3-6 machine clamp turning tool

4. Indexable turning tool

As shown in Fig. 3-7, the indexable turning tool is a machine clamp turning tool with indexable blades.

After a cutting edge is blunt, it can be quickly transposed and replaced with an adjacent new cutting edge, and then it can continue to work.

Until all cutting edges on the blade have been blunt, the blade can be scrapped and recycled.

After a new blade is replaced, the turning tool can continue to work.

Fig. 3-7 indexable turning tool

(1) The advantages of indexable turning tools mainly include the following:

1) Long tool life:

Because the blade avoids the defects caused by high temperature welding and grinding, the geometric angle of the tool is completely guaranteed by the blade and the tool bar groove, and the cutting performance is stable, thus improving the tool life.

2) High productivity:

As the machine tool operators no longer sharpen the tool, the auxiliary time such as stopping and changing the tool can be greatly reduced.

3) Conducive to the promotion of new technologies and processes:

The use of indexable cutters is conducive to the promotion of the use of coating, ceramics and other new cutting tool materials.

4) Helps to reduce tool costs:

Due to the long service life of the tool bar, the consumption and inventory of the tool bar are greatly reduced, the tool management is simplified, and the tool cost is reduced.

5) Stable chip breaking can be obtained:

The chip breaking groove is pressed and formed during the blade manufacturing, and the groove size is stable.

After selecting the appropriate chip breaking groove shape, the chip breaking is stable and reliable.

Because of the above advantages, indexable turning tool has been recognized as the preferred turning tool structure at home and abroad, and it is also the development direction of application.

(2) The clamping requirements for indexable turning tool blades mainly include:

1) It is required that the positioning accuracy of the cutter bar groove is high:

After the blade is rotated or replaced with a new blade, the change of the tool tip position shall be within the allowable range of the workpiece accuracy.

2) Reliable blade clamping:

Ensure that the contact surfaces of the blade, knife pad and knife bar are closely fitted, can withstand impact and vibration, the clamping force should not be too large, and the stress distribution should be uniform to avoid crushing the blade.

3) Smooth chip removal:

Ensure smooth chip discharge and easy observation.

4) Easy to use:

It is convenient and quick to change cutting edges and replace new blades.

The structure of small-size cutters should be compact.

When the above requirements are met, the structure shall be as simple as possible, and the manufacturing and use shall be convenient.

5. Forming turning tool

The forming turning tool is a special tool for machining the formed surface of the revolving body. Its blade shape is designed according to the contour shape of the workpiece.

It can be used to process the formed surface of the inner and outer revolving bodies on various lathes.

When machining parts with forming turning tool, the part surface can be formed at one time.

The operation is simple and the production efficiency is high.

After machining, the tolerance grade IT8~IT10 and the surface roughness value Ra6.3~Ra3.2μm can be achieved, and high interchangeability can be ensured.

However, the manufacturing of the formed turning tool is complex, the cost is high, and the working length of the cutting edge is wide, so it is easy to cause vibration.

Forming turning tools are mainly used to process small and medium-sized parts with forming surface in large batches.

2. Selection of turning tool

(1) Rational selection of cutting tools

In the actual cutting process, whether the turning tool is reasonable or not directly affects the tool life and machining efficiency, and also affects the machining cost.

The selection of turning tool should first select the best tool material according to the workpiece material to be machined, then select the blade shape, tool geometric angle, blade chip breaking groove shape, etc. according to the different machining forms in the actual cutting, and then adopt the reasonable cutting parameters to achieve the purpose of optimal use of turning tool.

(2) Selection of geometric parameters of turning tool

See table 3-1 ~ table 3-4 for recommended values of reasonable geometric parameters of common cemented carbide turning tools according to different workpiece materials.

Table 3-1 recommended reasonable rake angle of cemented carbide turning tool

Workpiece material Reasonable front angle y. (°)
Rough turning Fine turning
Low carbon steel Q235 20~25 25~30
Medium carbon steel 45 (normalized) 15~20 20~25
Alloy steel 40Cr (normalized) 13~18 15~20
Quenched steel 45 steel (45~50HRC) -15~-5
Stainless steel austenite (Crl8Ni9Ti) 15~20 20~25
Cast iron (continuous cutting) 5~10 10~15
Copper and copper alloys (brittle, continuous cutting) 5~10 10~15
Aluminium and aluminium alloys 30~35 35~40
Titanium alloy (Rm ≤ 1.17GPa) 5~10

Table 3-2 recommended reasonable back angle of carbide turning tool

Workpiece material Reasonable rear angle a0. (°)
Rough turning Fine turning
Low carbon steel Q235 3~6 8~11
Medium carbon steel 45 (normalized) 5~7 6~8
Alloy steel 40Cr (normalized) 5~7 6~8
Quenched steel 45 steel (45~50HRC) 12~15
Stainless steel (austenitic 1Crl8Ni9Ti) 6~8 8~10
Grey cast iron (continuous cutting) 4~6 6~8
Copper and copper alloys (brittle, continuous cutting) 4~6 6~8
Aluminium and aluminium alloys 8~10 10~12
Titanium alloy (Rm ≤ 1.17GPa) 5~10

Table 3-3 selection of main deflection angle of turning tool

Working conditions Main deflection angle x (°)
The system has good rigidity, small back feed, large feed and high workpiece material hardness. 10~30
The system has good rigidity (L/d<6), and it can process disc workpiece. 30~45
When the system rigidity is poor (L/d=6~12), the back cutting amount is large, or there is impact. 60~75
Poor system rigidity (L/d>12), turning step shaft, profiling turning, grooving and cutting. 90~93

Table 3-4 selection of turning tool pair deflection angle and blade inclination angle

Working conditions Secondary deflection angle Kt(°) Working conditions Blade inclinationλ s (°)
Fine turning 5~10 Finish turning outer circle and inner hole 0~4
Rough turning 10~15 Rough turning outer circle and inner hole -5~-10
Cylindrical turning tool 6~10 Finish turning nonferrous metals +5~+10
Grooving and cutting 1~3 Grooving and grooving 0
Cutting with intermediate cut 30~45 Intermittent turning with impact -10~-15
Wide blade turning tool and turning tool with polishing blade 0 Thin cutting with large inclination tool -45~75
Turning of high strength and high hardness materials 4月6日 Intermittent processing hardened steel -20~-30

(3) Selection of reasonable cutting parameters for turning

See table 3-5 for the selection of reasonable cutting parameters of turning tool.

Table 3-5 recommended cutting parameters of cemented carbide tools

Workpiece material Rough machining Finish machining
Cutting speed Vc/ (m/min) Feed rate f/ (mm/r) Back cutting amount ap/mm Cutting speed Vc/ (m/min) Feed rate f/ (mm/r) Back cutting amount ap/mm
carbon steel 220 0.2 3 260 0.1 0.4
low alloy steel 180 0.2 3 220 0.1 0.4
High alloy steel 120 0.2 3 160 0.1 0.4
cast iron 80 0.2 3 140 1 0.4
stainless steel 80 0.2 2 120 0.1 0.4
titanium alloy 40 0.3 1.5 60 0.1 0.4
Grey cast iron 120 0.3 2 150 0.15 0.5
Ductile iron 100 0.2 2 120 0.15 0.5
aluminium alloy 1600 0.2 1.5 1600 0.1 0.5

(4) Selection of tool bar and blade for turning tool with cylindrical end face

1. Selection of tool bar of cylindrical turning tool

The selection of turning tool bar needs to consider the factors such as machining shape, tool strength and economy.

(1) The cutter bar selection is mainly based on the processing form.

The turning position (excircle, end face, profiling, etc.) is different from the moving direction (forward or backward feed) of the turning tool, and the types of tool bars that can be used are also different.

(2) The corresponding machining shape of each tool bar is determined by the main deflection angle when installing the blade.

Generally, when 90 ° vertical cutting (right angle machining) is not required, if the turning tool bar with main deflection angle below 90 ° is selected, the tool bar with square blade can be selected, which is more economical.

When the end face is cut in the backward feed mode, due to the requirements of chip treatment, it is necessary to select the turning tool bar and blade with a main deflection angle of more than 105 °.

Chip handling is very difficult when the main deflection angle is below 95 ° and is not recommended.

Backward processing is not allowed when the main deflection angle is below 90 °.

Select the cutter bar with the main deflection angle of 45 ° ~ 60 ° in chamfering.

The negative secondary deflection angle is specially used for end face cutting.

2. Selection of turning tool blade for cylindrical end face

The selection of turning tool blade is as important as the selection of tool material, and the machining process, workpiece material, cutting conditions, etc. should be considered.

Selecting the best blade can improve the processing efficiency and reduce the processing cost.

(1) The selection of blade shape requires comprehensive consideration of machining shape, cutting edge strength, clamping strength, economy, etc.

CNC lathes are becoming more and more popular, and the blades that can process the outer circle and the end face at the same time are used most.

The 80 ° rhombic blade suitable for these processes can correspond to a wide range of areas from rough machining to finish machining.

The 55 ° diamond or 35 ° diamond blade is used for profiling.

Although the cutting edge strength is not as good as 80 ° diamond, it can correspond to the shape of the most widely machined shape.

Whether 55 ° or 35 ° is selected depends on the shape of the workpiece.

There are other blade shapes suitable for thread processing, grooving processing, cutting processing, etc.

(2) The larger the sharp angle of the blade, the higher the strength of the cutting edge, which is conducive to intermittent cutting, but it is easily restricted by the machining shape.

In stable cutting processes such as continuous cutting, it is more effective to use an equilateral triangle blade with slightly lower cutting edge strength but more cutting edges.

This defect can be remedied by selecting a triangular blade with unequal edges and unequal angles with a knife tip angle of 82 °.

When the back feed is small, it is also effective to use the hexagonal (80 °) blade with equal edges and unequal angles to ensure the strength of the cutting edge.

The circular blade has the best strength and is most suitable for use when a good machining surface is required.

Due to the large back force, it is easy to vibrate when machining slender and thin-walled workpieces, and it is difficult to manage when changing the edge angle.

The blade size is large and thick, or the vertical mounted blade has high clamping strength and is suitable for heavy cutting.

The cutting edge of the 80 ° diamond blade is long and can be positioned on both sides, so the clamping strength is large, which is conducive to intermittent cutting and heavy cutting.

(3) When using the negative angle blade, the square blade is the most economical, because the square blade can be used with 4 edges on one side and 8 edges on both sides, and the blade tip angle is 90 °, with high strength.

The second is an equilateral triangle blade with 3 blades on one side and 6 blades on both sides.

(4) The tip arc radius refers to the arc size of the blade tip.

The larger the arc radius of the tool tip, the higher the accuracy of the machined surface and the greater the strength of the tool tip, but it will increase the radial component force, which is easy to cause vibration and difficult to deal with chips.

In addition, the cutting edge position retreats and the machining diameter becomes larger.

On the contrary, when the arc radius of the tool tip decreases, the machining diameter decreases.

Generally, the tool tip arc radius used ranges from 0.4 to 1.2mm.

However, from the point of view of tool tip strength, a large tool tip arc radius should be selected for heavy cutting and a smaller tool tip arc radius for finishing machining.

(5) Selection of blade form in inner hole machining

The selection of the blade shape in the machining of inner hole is basically the same as that in the machining of outer circle.

However, when machining the inner hole, the tool overhang is large, so it is impossible to re cut, so it is almost unnecessary to consider the clamping strength of different shapes.

(1) With the increase of the arc radius of the tool tip, the back force component increases.

The component force in the back direction causes the cutter bar to bend and deform, and vibration must be prevented.

When the back feed is small, attention should be paid to the deterioration of chip handling and the change of chip removal direction caused by the increase of the arc radius of the tool tip.

When machining the inner hole, the chip must be discharged from the inside of the workpiece.

A small change in the direction of chip removal may cause difficulty in chip discharge.

(2) In order to prevent the interference between the blade and the inner wall surface during the machining of small-diameter inner holes, if the negative angle blade is used, a large negative front angle shall be selected.

This will increase the cutting force and easily cause high-frequency vibration, so the positive angle blade with back angle is usually used in inner hole machining.

If the machining diameter is large, it is more appropriate to use the negative angle blade from the economic point of view.

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