What Is a Cutter Bar?

CNC tool

Overview of CNC tools

NC tool is a tool used for cutting in mechanical manufacturing, also known as cutting tool. In the broadest sense, cutting tools include both tools and abrasives. At the same time, in addition to cutting blades, "NC tools" also include accessories such as tool holders and tool holders!

NC tool attribute classification

According to the tool structure, it can be divided into:

Integral type: the cutter is a whole, manufactured from a blank, without splitting;

Welding type: Welding method is used to connect the cutter head and cutter rod;

Machine clamp type: Machine clamp type can be divided into non-indexable and indexable two types; usually CNC tool uses machine clamp type!

Special types: such as compound tools, shock-absorbing tools, etc.

According to the materials used to make the tool, it can be divided into:

High speed steel cutter

Cemented carbide cutters;

Diamond tool

Cutting tools of other materials, such as cubic boron nitride cutting tools, ceramic cutting tools, etc.

From the cutting process can be divided into

Turning tools, including external, internal, thread, cutting, grooving tools, etc .;

Drilling tools, including drills, reamer, taps, etc .;

Boring tool

Milling tools, etc.

Development of CNC tools

The development of knives occupies an important position in the history of human progress. As early as the 28th to 20th century BC, copper tools such as brass cones and copper cones, drills, and knives appeared. In the late Warring States Period (third century BC), due to mastering carburizing technology, copper knives were made. The drills and saws of the time were somewhat similar to modern flat drills and saws.

However, the rapid development of knives came in the late 18th century with the development of machines such as steam engines. In 1783, Rene first produced milling cutters in France. In 1792, Mozley produced taps and dies. The earliest literature about the invention of twist drills was in 1822, but it was not produced as a commodity until 1864.

At that time, the tools were made of solid high-carbon tool steel, and the allowable cutting speed was about 5 m / min. In 1868, the British Musherte made tungsten-containing alloy tool steel. In 1898, Taylor and the United States. White invented high-speed steel. In 1923, Schlettler of Germany invented the cemented carbide.

When using alloy tool steel, the cutting speed of the tool is increased to about 8 m / min. When using high-speed steel, it is more than doubled. When using hard alloy, it is more than twice as high as using high-speed steel. The surface quality and dimensional accuracy of the workpiece are also greatly improved.

Due to the high price of high-speed steel and cemented carbide, tools have welding and mechanical clamping structures. Between 1949 and 1950, the United States began to use indexable inserts on turning tools, and soon it was applied to milling and other tools. In 1938, the German company Degussa obtained a patent on ceramic tools. In 1972, General Electric produced polycrystalline synthetic diamond and polycrystalline cubic boron nitride inserts. These non-metallic tool materials allow the tool to cut at higher speeds.

In 1969, the Sandvik Steel Plant in Sweden obtained a patent for the production of titanium carbide-coated carbide inserts by chemical vapor deposition. In 1972, Bangsa and Lagulan in the United States developed a physical vapor deposition method, coating a hard layer of titanium carbide or titanium nitride on the surface of a carbide or high-speed steel tool. The surface coating method combines the high strength and toughness of the base material with the high hardness and wear resistance of the surface layer, so that this composite material has better cutting performance.

Tools can be divided into five categories according to the form of the workpiece machining surface. Tools for processing various external surfaces, including turning tools, planers, milling cutters, external surface broaches and files, etc .; hole processing tools, including drills, reamers, boring tools, reamers and internal surface broaches, etc .; thread processing Tools, including taps, dies, automatic opening and closing thread cutting heads, thread turning tools and thread milling cutters, etc .; gear processing tools, including hobs, shapers, shavers, bevel gear processing tools, etc .; cutting tools, including inserts Tooth circular saw blades, band saws, hacksaws, cutting tools, saw blade milling cutters, etc. In addition, there are combination tools.

According to the cutting movement mode and the corresponding cutting edge shape, the cutting tools can be divided into three types. General-purpose tools, such as turning tools, planers, milling cutters (excluding formed turning tools, forming planers and forming milling cutters), boring tools, drills, reamers, reamers and saws, etc. It has the same or nearly the same shape as the processed workpiece, such as forming turning tools, forming planers, forming milling cutters, broaches, conical reamer and various thread processing tools; the forming tools are used to process gears by the forming method Tooth surface or similar workpieces, such as hobs, gear cutters, shavers, bevel gear planers and bevel gear milling cutters.

The structure of various tools is composed of a clamping part and a working part. The clamping part and the working part of the integral structure cutter are made on the cutter body; the working part (tooth or blade) of the insert structure cutter is mounted on the cutter body.

There are two types of tool clamping parts: holed and shank. The tool with holes relies on the inner hole to be set on the spindle or spindle of the machine tool, and transmits the torsional moment by the axial key or the end key, such as a cylindrical milling cutter, a sleeve face milling cutter, and the like.

There are three types of shank tools: rectangular, cylindrical and conical. Turning tools, planers, etc. are generally rectangular shanks; conical shanks bear axial thrust by taper and transmit torque by friction; cylindrical shanks are generally suitable for smaller twist drills, end mills and other tools. The resulting friction forces transmit torsional moments. The shank of many shank tools is made of low-alloy steel, and the working part is made by welding two parts with high-speed steel.

The working part of the tool is the part that generates and processes the chip, including the cutting edge, the structure that breaks or rolls the chip, the space for chip removal or storage, and the channel of the cutting fluid. The working part of some tools is the cutting part, such as turning tools, planers, boring tools, milling cutters, etc .; the working part of some tools includes the cutting part and the calibration part, such as drills, reamers, reamers, inner surface pulls, etc. Knives and taps. The function of the cutting part is to remove the chips with the cutting edge, and the function of the calibration part is to polish the cut machining surface and guide the tool.

The structure of the cutter working part has three types: integral type, welding type and mechanical clamping type. The overall structure is to make cutting edges on the blade body; the welding structure is to braze the blade to the steel blade body; there are two types of mechanical clamping structures, one is to clamp the blade on the blade body, and the other The brazed cutter head is clamped on the cutter body. Hard alloy cutting tools are generally made of welded structure or mechanical clamping structure; porcelain cutting tools all adopt mechanical clamping structure.

The geometric parameters of the cutting part of the tool have a great influence on the level of cutting efficiency and the quality of the machining. Increasing the rake angle can reduce the plastic deformation of the rake face when the cutting layer is squeezed, and reduce the frictional resistance of the chips flowing through the front face, thereby reducing the cutting force and cutting heat. However, increasing the rake angle will reduce the strength of the cutting edge and reduce the heat dissipation volume of the cutter head.

When choosing the angle of the tool, the influence of various factors needs to be considered, such as workpiece material, tool material, processing properties (rough, finishing), etc., which must be reasonably selected according to the specific situation. Generally speaking, the tool angle refers to the marked angle for manufacturing and measurement. In actual work, the actual working angle and the marked angle are different due to the different installation positions of the tool and the cutting movement direction, but the difference is usually small. .

The materials used to make the tools must have high high-temperature hardness and abrasion resistance, necessary bending strength, impact toughness, and chemical inertness, good processability (cutting, forging, and heat treatment, etc.) and are not easy to deform.

Generally, when the hardness of the material is high, the wear resistance is also high; when the bending strength is high, the impact toughness is also high. However, the higher the hardness of the material, the lower its bending strength and impact toughness. Because of its high bending strength and impact toughness, as well as good machinability, modern high-speed steel is still the most widely used tool material, followed by cemented carbide.

Polycrystalline cubic boron nitride is suitable for cutting high-hardness hardened steel and hard cast iron; polycrystalline diamond is suitable for cutting non-ferrous metals, and alloys, plastics and glass steel; carbon tool steel and alloy tool steel are now only used For tools such as files, dies and taps.

Cemented carbide indexable inserts are now coated with titanium carbide, titanium nitride, alumina hard layers or composite hard layers by chemical vapor deposition. The physical vapor deposition method under development can be used not only for carbide tools, but also for high-speed steel tools such as drills, hobs, taps, and milling cutters. The hard coating acts as a barrier against chemical diffusion and heat conduction, which reduces the wear rate of the tool during cutting, and the life of the coated blade is about 1 to 3 times longer than that of the uncoated one.

Due to the high-temperature, high-pressure, high-speed, and parts working in corrosive fluid media, more and more difficult-to-machine materials are applied, and the level of automation of cutting and the requirements for machining accuracy are getting higher and higher. In order to adapt to this situation, the development direction of tools will be the development and application of new tool materials; further development of the vapor deposition coating technology of tools, deposition of higher hardness coatings on high toughness and high strength substrates, and better solutions The contradiction between the hardness and strength of the tool material; further development of the structure of the indexable tool; improving the manufacturing accuracy of the tool, reducing the difference in product quality, and optimizing the use of the tool.

Tool materials are roughly divided into the following categories: high-speed steel, cemented carbide, cermets, ceramics, polycrystalline cubic boron nitride, and polycrystalline diamond.

Here we mainly mention ceramics. Ceramics were used for cutting tools earlier than cemented carbide, but due to their brittleness, they have developed slowly. But since the 1970s, it has developed relatively quickly. There are two main types of ceramic tool materials, namely alumina and silicon nitride. Ceramic as a tool has the advantages of low cost, high hardness, good high temperature resistance, etc., and has good prospects.