1. Types and uses of turning tools
Turning tools are the most commonly used single-edged tools. It is also the basis for learning and analyzing different types of cutting tools. Turning tools are used on various lathes to process outer circles, inner holes, end faces, threads, grooves, etc. According to the structure, turning tools can be divided into solid turning tools, welding turning tools, machine collet turning tools, indexable turning tools and forming turning tools. Among them, indexable turning tools are increasingly used, and their proportion in turning tools is gradually increasing.
1. Carbide welding turning tool
The so-called welded turning tool is a turning tool that is used after cutting a slot on the carbon steel tool holder according to the geometric angle requirements of the tool, welding the carbide blade into the slot with welding and sharpening it according to the selected geometric parameters knife.
2. Machine Collet Turning Tool
Machine clamped turning tools are turning tools that use ordinary blades and use mechanical clamping to clamp the blades onto the tool holder. This type of knife has the following characteristics:
(1) The blade does not undergo high temperature welding, which avoids defects such as decrease in blade hardness and cracks caused by welding, and improves the durability of the tool;
(2) Due to the improved durability of the tool, the use time is longer, the tool change time is shortened, and the production efficiency is improved;
(3) The tool holder can be reused, which not only saves steel but also improves the utilization rate of the blade. The blade is recycled and reconditioned by the manufacturer, which improves economic benefits and reduces tool costs;
(4) After the blade is resharpened, the size will gradually become smaller in order to restore the working position of the blade, a blade adjustment mechanism is often provided on the structure of the turning tool to increase the number of blade resharpening;
(5) The end of the pressure plate used to compress the blade can function as a chip breaker.
3. Indexable turning tool
Indexable turning tools are machine clamped turning tools that use indexable inserts. Once a cutting edge is dull, it can be quickly replaced with a new adjacent cutting edge, and work can continue. The blade is only discarded when all the edges of the blade have been dull. After replacing the new blade, the turning tool can continue to work. Compared to welding turning tools, indexable tools have the following advantages:
(1) Long lifespan. Since the blade avoids defects caused by high welding and sharpening temperatures, the geometric parameters of the tool are fully guaranteed by the grooves of the blade and tool holder, and the cutting performance is stable, thus increasing the life of the tool;
(2) High production efficiency. Since machine tool operators no longer need to sharpen tools, auxiliary times such as downtime for tool changes can be significantly reduced;
(3) It is conducive to the promotion of new technologies and new processes. Indexable knives promote the use of new tool materials such as coatings and ceramics;
(4) Helps reduce tool costs. Due to the long service life of the tool holder, the consumption and inventory of the tool holder are greatly reduced, the tool management is simplified, and the tool cost is reduced;
Features and clamping requirements of indexable turning tool inserts:
(1) High positioning precision. After the blade is indexed or replaced with a new blade, the change in position of the tool tip must be within the allowable range of workpiece accuracy;
(2) The blade is tightened reliably. It should be ensured that the contact surfaces of the blade, tool holder and tool holder are in close contact and can withstand shock and vibration, but the clamping force should not be too large and the stress distribution must be uniform to avoid crushing the blade;
(3) Chip removal is gentle. It is best not to place any obstacles in front of the blade to ensure smooth chip discharge and easy observation;
(4) Easy to use. It is convenient and quick to change the blade and replace it with a new one, and the structure of small-sized tools should be compact. When meeting the above requirements, the structure should be as simple as possible and easy to manufacture and use.
4. Forming turning tool
The forming turning tool is a special tool for processing the forming surface of the rotating body. Its blade shape is designed according to the profile of the workpiece. It can be used on various lathes to process the forming surfaces of internal and external rotating body. . When processing workpieces with a forming turning tool, the surface of the workpiece can be formed in one go. It is easy to operate and has high productivity, it can reach tolerance level IT8~IT10, the roughness is 10~5μm. , and it can guarantee high interchangeability. However, the manufacturing of forming turning tools is complicated and expensive, and the working length of the cutting edge is large, so it is easy to cause vibration. Forming turning tools are mainly used to process large batches of medium and small sized parts with formed surfaces.
In order to make good cuts on a lathe, it is very important to prepare and use the tool correctly. Different situations require different shapes of turning tools, and cutting different materials requires the cutting edge to have different angles. There is also a certain relative relationship between the position and speed of the turning tool and the workpiece. The turning tool itself must also have sufficient hardness, strength, wear resistance and heat resistance. Therefore, when selecting turning tool materials, the tool angle, etc. should be taken into consideration. are all important considerations.
2. Classification and application of turning tool materials
The improvement and development of tool materials is one of the important topics in the current development of metal processing, because good tool materials can not only do the cutting work efficiently and quickly, but also maintain tool life. Commonly used turning tool materials include:
1. High carbon steel
High carbon steel turning tools are a type of carbon steel with a carbon content of 0.8% to 1.5%. They are used after quenching and hardening. Due to friction when cutting, they are easily quenched and softened and are replaced by other tools. like high speed steel. Generally only suitable for cutting soft metal materials, commonly used ones include SK1, SK2, SK7, etc.
2. High speed steel
High speed steel is a steel-based alloy commonly known as blank turning tool. It is made of carbon steel with carbon content of 0.7% to 0.85% by adding alloying elements such as W, Cr, V and Co. For example, high speed steel 18-4- 4 contains 18% tungsten, 4% chromium and 4% vanadium. The frictional heat generated when cutting high-speed steel turning tools can reach 6000°C. It is suitable for thread turning speeds below 1000 rpm. Generally, high speed steel turning tools such as SKH2, SKH4A, SKH5, SKH6, SKH9, etc. are commonly used.
3. Cast Alloy Cutting Tools
It is an alloy of cobalt, chromium and tungsten. Because it is difficult to cut and process, it is made by casting, so it is also called superhard cast alloy. The most representative is the stellite. Its toughness and wear resistance are excellent. At 8200℃, its hardness remains unchanged, its heat resistance is much higher than that of high speed steel, and it is suitable for high-speed and deeper cutting work.
4. Sintered Carbonized Cutting Tools
Carbide tools are powder metallurgy products. The main component of tungsten carbide tools is 50-90% tungsten, with titanium, molybdenum, tantalum, etc. added as a binder and cobalt powder as a binder, then heated and sintered. The hardness of carbonized tools is higher than other materials and is suitable for cutting harder metals or stones. Because the material is brittle and hard, it can only be made into sheets and then welded to a strong handle when the blade becomes dull or cracked. , You can replace another cutting edge or a new blade. This type of turning tool is called disposable turning tool.
According to the different cutting properties of the international standard (ISO), carbonized tools are divided into three categories: P, M and K, and are marked with three colors: blue, yellow and red:
Grade P is suitable for cutting steel. There are six categories: P01, P10, P20, P30, P40 and P50 is a high-speed fine turning tool with small number and high wear resistance. coarse turning tool with large number and high toughness, the handle is painted blue for identification;
Type K is suitable for cutting brittle and hard materials such as stone and cast iron. There are five types: K01, K10, K20, K30 and K40 is high speed fine turning tool and K40 is low speed fine turning tool. rough turning tool. These tool handles are painted red to identify them;
Type M is between Type P and Type M and is suitable for cutting tougher materials. This type of tool holder is painted yellow to identify it.
5. Ceramic Turning Tools
Ceramic turning tools are made from aluminum oxide powder, adding a small amount of elements, and then sintered at high temperature. Its hardness, heat resistance and cutting speed are higher than those of tungsten carbide. However, because they are fragile, they are. are not suitable for discontinuous or heavy turning. They are only suitable for discontinuous or heavy turning. Suitable for high speed finishing.
6. Diamond cutter
For advanced surface treatment, round or industrial diamonds with surface edges can be used for light treatment. It can achieve a smoother surface and is mainly used for precision turning of copper alloys or light alloys. High speed should be used during filming, with a minimum speed of 60-100m/min, usually 200-300m/min.
7. Boron oxide
Cubic boron oxide (CBN) is a material that has been promoted in recent years. Its hardness and wear resistance are second only to diamond. This tool is suitable for processing hard and wear-resistant alloys of the iron family, nickel-based alloys and cobalt. base alloys.
3. Shape and use of turning tools
1. Generally, the following types of turning tool tips are used:
(1) Rough turning tool: It is mainly used for cutting large and redundant workpieces to make the workpiece diameter close to the required size. Surface finish is not important in rough turning, so the tip of the tool can be ground to a sharp point, but the tip usually needs a slight roundness to prevent breakage .
(2) Fine turning tool: This blade can be sharpened with a whetstone to produce a very smooth surface. Generally speaking, the round nose of fine turning tools is larger than that of rough turning tools.
(3) Round Nose Turning Tool: This is a commonly used turning tool that can be used for many different types of jobs. It can be used for turning left and right when grinding the top surface, and can also be used for turning brass. This turning tool can also form an arc surface on the shoulder angle and can also be used as a precision turning tool.
(4) Cutting turning tool: only the end is used to cut the workpiece. This turning tool can be used for cutting materials and turning grooves.
(5) Screw turning tool (dental tool): used for turning screws or nuts. According to the shape of the thread, it is divided into 60 degree or 55 degree V-shaped tooth tool, 29 degree trapezoidal tooth tool. and a square-toothed tool.
(6) Boring turning tool: used for turning drilled or cast holes. The goal is to obtain photometric dimensions or truly straight hole surfaces.
(7) Side turning tool or side turning tool: used for turning the end face of the workpiece. The right turning tool is generally used at the end of the finishing turning shaft, and the left turning tool is used to finish turning the left side. of the shoulder.
2. Different shapes of blades are used due to different workpiece processing methods, which generally can be distinguished as follows:
(1) Right-hand turning tool: from right to left, turn the outer diameter of the workpiece.
(2) Left turning tool: from left to right, turn the outer diameter of the workpiece.
(3) Round nose turning tool: The blade is arc-shaped and can be turned in left and right directions. It is suitable for turning rounded corners or curved surfaces.
(4) Right turning tool: turn the right end face.
(5) Left turning tool: turn the left end face.
(6) Cutting knife: used for cutting or grooving.
(7) Inner hole turning tool: used for turning inner holes.
(8) External thread turning tool: used for turning external threads.
(9) Internal thread turning tool: used for turning internal threads.
4. Names and functions of each part of the turning tool
Turning tools are single-edged tools. They come in several types due to the different shapes of the turning part, but the names and functions of each part are the same. A good turning tool should have a stiff handle and a sharp blade. The blade angle of the turning tool directly affects the turning effect. Different turning tool materials and workpiece materials have different blade angles. Turning tools for lathes have four important angles, namely front clearance angle, side clearance angle, back bevel angle and side bevel angle.
1. Front clearance angle
The tilt angle from the nose of the tool to the inside of the tool is the front clearance angle. Due to the front draft angle, a space is formed below the work surface and the tip of the tool, so that the cutting action is concentrated on the work surface. tool nose. If the angle is too small, the tool will rub on the surface and produce a rough surface. If the angle is too large, the tool will vibrate easily, causing the tool nose to break and become impossible to polish. When installing a turning tool with a tilted center tool holder to grind the front clearance angle, the tilt angle of the tool holder must be considered. This angle is approximately 8 to 10 degrees for high speed steel turning tools and 6 to 8 degrees for carbide turning tools.
2. Side clearance angle
The angle at which the side of the knife slopes from the edge toward the inside of the knife is the edge clearance angle. The edge clearance angle forms a space between the work surface and the side of the tool, allowing the cutting action to be concentrated on the cutting edge, improving cutting efficiency. The angle of high speed steel turning tools is about 10 degrees to 12 degrees.
3. Back Bevel
The angle of inclination from the top surface of the knife, from the nose to the handle, is the back bevel. This angle is mainly used to guide chip removal and reduce chip removal resistance. For cutting general metals, high-speed steel turning tools typically have a tilt angle of 8 to 16 degrees, while carbide turning tools have a negative or zero degree tilt angle.
4. Beveling the edges
The top surface of the tool is inclined from the cutting edge to the other side, and the angle between this inclined surface and the horizontal plane is the edge bevel angle. This angle is the angle at which the chips are separated from the workpiece, making chip removal easier and enabling efficient turning. The angle of high speed steel turning tools is about 10 degrees to 14 degrees, while carbide turning tools can have positive or negative tilt angles.
5. Knife end angle
The vertical angle between the front end of the blade and the handle. This angle is used to maintain a space between the front end of the blade and the workpiece to prevent the blade from rubbing against the workpiece or scratching the machined surface.
6. Cut corners
The vertical angle between the front end of the blade and the handle allows you to change the thickness of the cutting layer. At the same time, the cutting angle can also change the force direction of the turning tool, reduce the resistance of the cutting tool, and increase the tool life. Therefore, in general, in rough turning it is advisable to use a turning tool with a. Larger cutting angle to reduce cutting tool resistance and increase cutting speed.
7. Tool nose radius
The highest point of the blade is the arc radius of the blade. The tool nose radius is large and strong and is used for large cutting depths, but it is subject to high frequency vibration.
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