What Is a Mill File?

CNC milling cutters are rotary tools with one or more teeth for milling. During the work, each cutter tooth intermittently cuts off the remaining amount of the workpiece. Milling cutters are mainly used for machining processes such as steps, grooves, forming surfaces and cutting workpieces.

CNC milling cutter

CNC

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.

Integral

The blade body and the teeth are made into one body.

Integral welding tooth

For tooth

The size is not accurate enough: Solution:

1.Excessive cutting reduces the depth and width during low cutting

2. Machines or fixtures lack accuracy to repair machines and fixtures

3. The machine or fixture lacks rigidity. Change the machine \ fixture or cutting setting.

4. Too few edges use a multi-edge end mill

Milling cutters are developing very fast. They are called rotary cutters in the industry.

Clamping of milling cutter

Most of the milling cutters for machining centers accept the spring clamp set clamping method, which is in a cantilever shape when used. Being

Common milling cutters on CNC machine tools:

First, the face milling cutter, the circumferential surface and the end surface of the face milling cutter have cutting edges, and the end cutting edge is a secondary cutting edge. Face milling cutters are mostly made of nested tooth structure. The cutter teeth are high-speed steel or hard alloy. The cutter body is 40Cr.

Second, end mills, both the cylindrical surface and the end face of the end mill have cutting edges, they can be cut simultaneously or separately. The cutting edge on the cylindrical surface of the end mill is the main cutting edge, and the cutting edge on the end face is the secondary cutting edge. Note that it is not possible to perform axial feed because there is a groove in the middle of the end face of the end mill.

Third, the mold milling cutter, his structure is characterized in that the ball head or the end face is covered with cutting edges, the circumferential edge and the ball head edge arc connected, can be used for radial and axial feed.

Fourth, the keyway milling cutter, it has two teeth, the cylindrical surface and the end face have cutting edges, the end face edge extends to the center. When machining, first feed axially to the groove depth, and then mill the entire length of the keyway in the direction of the keyway.

5. For drum milling cutters, his cutting edges are distributed on a circular arc surface with a radius of R, and the end faces have no cutting edges. The upper and lower positions of the tool are controlled during processing, and corresponding oblique angles from negative to positive can be cut on the workpiece corresponding to the cutting position of the cutting edge of the face. The smaller R is, the wider the range of bevels that the drum milling cutter can process.

6. Forming cutters are generally specially designed and manufactured for specific workpieces or processing contents.

There are some general-purpose milling cutters, but because the spindle taper is different, a transition sleeve and a pull stud must be prepared

Now several types of milling cutters that are commonly used are described in terms of their applications.

(A) single-edged milling cutter

The tool has high processing efficiency, uses high-quality hard alloy as the tool body, generally adopts sharp-edged grinding technology, and high-capacity chip removal, so that the tool has non-stick chips, low heat generation and high smoothness during high-speed cutting. It is widely used in crafts, electronics, advertising, decoration and wood processing industries, suitable for factory batch processing and demanding products.

(Two) two-blade end mill and four-blade end mill

This type of tool generally adopts an overall alloy structure, which is characterized by strong stability. The tool can work stably on the processing surface, so that the processing quality can be effectively guaranteed. Wide range of applicable materials, such as carbon steel, mold steel, alloy steel, tool steel, stainless steel, titanium alloy, cast iron, suitable for general mold and mechanical parts processing.

(Three) thread milling cutter

With the development of China's CNC machine tools , thread milling cutters have been more and more recognized. Its good machining performance has become a powerful machining tool that reduces the cost of thread processing, improves efficiency, and solves thread processing problems. Because the current thread milling cutter is made of hard alloy, the processing line speed can reach 80 200m / min, while the processing speed of the high-speed wire cone is only 10 30m / min, so the thread milling cutter is suitable for high-speed cutting and processing threads. The surface finish is also greatly improved. High-hardness materials and high-temperature alloy materials, such as titanium alloys and nickel-based alloys, have always been a difficult problem. The main reason is that when high-speed wire cones are used to process the threads of the above materials, the tool life is short, and the carbide thread milling is used. Tool-to-hard material thread processing is an ideal solution. Machinable hardness is HRC58 62. For thread processing of high-temperature alloy materials, the thread milling cutter also shows very excellent machining performance and a longer life than expected. For threaded holes with the same pitch and different diameters, taps require multiple tools to complete, but if a thread milling cutter is used, only one tool is required. After the tap is worn and the processed thread size is less than the tolerance, it can no longer be used and can only be scrapped. When the thread milling cutter is worn and the processed thread hole size is less than the tolerance, the necessary tool radius compensation can be adjusted by the CNC system, and then it can be continued. Machining a thread of acceptable size. Similarly, in order to obtain a high-precision threaded hole, it is much easier to adjust the tool radius with a thread milling cutter than to produce a high-precision tap. For the processing of small diameter threads, especially in the processing of high hardness materials and high temperature materials, the taps sometimes break, blocking the threaded holes, and even scrapping the parts. With thread milling cutters, the diameter of the tool is smaller than the processed hole, even if it is broken. Does not block threaded holes, is very easy to take out, and does not cause parts to be scrapped. With thread milling, compared with taps, the cutting force of the tool is greatly reduced. This is particularly important when processing large diameter threads, which solves the excessive load on the machine tool. The problem that the tap cannot be driven normally.

Thread milling cutter, as a tool that uses CNC machine tools to process threads, has become a widely used practical tool type. ^[1-4]