Cutting mode for milling. Types of milling cutters, calculation of cutting speed

One of the ways of finishing materials is milling. It is used for processing of metal and non-metallic blanks. The work process is controlled by cutting modes.

The essence of the process

Milling is carried out for the purpose of deep roughing and finishing, forming a certain profile of the surface (grooves, grooves), cutting teeth on gears, adjusting the shape, artistic engraving of patterns and inscriptions.

The working tool - the milling cutter - makes the main rotating motion. Auxiliary is the progressive feed of the workpiece relative to its stroke. This process is intermittent. Its most important feature, which differs from turning and drilling, is the fact that each tooth works separately. In this regard, it is characterized by the presence of shock loads. To reduce their influence is possible taking into account a rational assessment of the situation and the selection of regimes.

Basic concepts of the work of milling machines

Depending on the method of locating the spindle and fixing the milling cutter in it, from the types of operations performed and from the control methods, the main types of milling equipment are distinguished:

• Horizontal;
• Vertical;
• Universal;
• Milling machines with numerical control.

The main nodes of the vertical milling machine:

1. The frame in which the speed box is located, which regulates the rotation of the vertically mounted spindle and the milling cutter fixed on it.
2. A table that includes a console with transverse slides for fastening and moving the workpiece and a feed box that controls the feed movements.

In horizontal milling machines, the tool is fixed horizontally. A universal has several varieties.

There is a universal horizontal equipment, which is characterized by the presence of table turnover and, thus, the expansion of the range of possible work to be performed. In addition, there is a wide-universal, having in its structure both spindles and allowing to carry out all types of milling.

CNC milling machines are distinguished by the availability of software and computer control. They are designed for artistic processing of blanks, including in 3D format.

Classification of cutters

Cutters are tools for cutting. The basic physical parameters with which they are evaluated are: height, diameter, chamfer and backsight, circumferential pitch. There is a huge variety of them, distributed according to various signs:

• By the type of surfaces that are processed (for wood, plastic, steel, non-ferrous metals, etc.);
• In the direction of rotation - right-handed and left-handed;
• Depending on the design features - solid, napaynye, collapsible (have inserted knives), welded;
• In shape: conical, cylindrical, disk;
• Depending on the operating conditions and requirements for the cutting part, can be made of different materials. These include: carbon tool and high-speed steel (alloyed, with increased content of tungsten), hard alloy (strong - for roughing, wear-resistant - for finishing). Versions are common when the body is made of carbon or high-speed steel, and the knives are plug-in hard-alloy ones;
• Depending on the purpose: cylindrical, end, end, slotted, cut-off, shaped.

The most informative signs are: cutting edge material and purpose.

Types of milling for flat surfaces

For the purpose of removing layers of material on horizontal, vertical or inclined planes, cylindrical and end mills are used.

The instrument of the first type can be either integral or with knife blades. Large solid milling nozzles are designed for roughing, and small ones for finishing. Insertable knives for folding cutting heads can be made of high-speed steel or equipped with hard-alloy plates. Carbide tipped cutters have greater productivity than those made of alloyed steel alloy.

The end is used for elongated planes, its teeth are distributed on the end surface. Large folding ones are used for wide planes. By the way, for the removal of chips from difficult to process refractory metals, the presence of carbide knives is mandatory. For the application of these groups of milling devices, a considerable width and length of the product is needed.

Types of tools for artistic milling

To impart a certain profile to the material, to apply the pattern, to form narrow grooves, end and disc milling nozzles are used.

The end or groove cutter is common for cutting grooves, narrow and curved planes. All of them are solid or welded, cutting part of high-speed alloy steel, it can be hard- alloyed , and the body is made of carbon steel. There are low-voltage (1-3 spirals) and multi-hop (4 or more). Used for machine tools with numerical control.

Disk - this is also a milling cutter. It is applicable for grooves, grooves, teeth cutting on gear wheels.

Artistic milling is carried out on wood, metal, PVC.

Types of cutters for edge processing

Removal of chips from corners, giving them a rational shape, modeling, separation of the workpiece into parts can be realized with the help of slotted, angular and shaped milling attachments:

1. Cutting and splined has the same function as the disk, but is more often used for cutting and separating excess parts of the material.
2. Angle is required for the edges of parts and corners. There are single-angle (only one cutting part) and two-corner (both conical surfaces are cutting).
3. The shape is used for complex designs. Can be semicircular or concave. It is often used for tapping the profile of taps, countersinks, spiral drills.

Practically for all types it is possible to have a solid steel construction or a folding one, with the presence of insert carbide knives. Carbide cutters have qualitatively higher performance and its duration for the tool as a whole.

Classification of milling types

There are several classification features, according to which the types of milling are divided:

• By the method of locating the spindle and mill, respectively, on the horizontal and vertical;
• In the direction of motion, on the oncoming and passing;
• Depending on the tool used, on the cylindrical, end, shaped, end.

Cylindrical machining is applicable for horizontal planes, carried out with the help of appropriate milling machines on horizontal machines.

End milling can be considered universal. It is applicable for all types of horizontal, vertical and inclined planes.

The end trim ensures the formation of the required profile with curved grooves, drills and instruments.

Shaping is carried out for surfaces with a complex configuration: corners, edges, grooves, cutting teeth for gears.

Regardless of the type of work and materials being processed, the result should be high smoothness of the finish layer, absence of jags, precision of finish. In order to obtain a clean treated surface, it is important to control the feed rates of the workpiece relative to the tool.

Counter and passing milling

When the milling of the counter-type metal is performed - the workpiece is fed to the rotational movements of the nozzle. In this case, the teeth gradually cut into the processed metal, the load increases directly proportional and evenly. However, before plunging the tooth into the part, it slides for a while, forming a hard work. This phenomenon accelerates the output of the milling cutter from the working state. Used for roughing.

When performing a passing type - the workpiece is fed along the rotational movements of the tool. Teeth work shockfully under heavy loads. The power is 10% lower than with counter milling. It is carried out at finishing parts.

The basic concept of milling operations on CNC machines

They are characterized by a high degree of automation, precision of the working process, high productivity. Milling on a CNC machine is carried out most often with the help of end or end mills.

The latter are the most widely used. In this case, depending on the material being processed, the type of chip forming, the specified parameters of the software, different end mills are used. They are classified according to the number of spiral passes that ensure the presence of cutting edges and the ditching of chips.

Materials with wide shavings are advisable to be milled using instruments of a small number of visits. For hard metals with characteristic fracture shear, it is necessary to choose milling devices with a large number of spirals.

Use of milling cutters for CNC machines

CNC milling cutters can have from one to three cutting edges. They are used for wood, plastics, composites and soft compliant metals, requiring rapid removal of wide chips. Used for roughing blanks, to which high requirements are not put. This tool has a small performance, low rigidity.

With the help of single-pass, artistic milling of aluminum is carried out.

Widely used are two- and three-end ones. They provide stiffness of higher values, qualitative chip removal, allow working with metals of medium hardness (for example, with steel).

Multi-thread milling cutters for CNC have more than 4 cutting edges. They are used for metals of medium and high hardness, which are characterized by small chips and high resistance. They are characterized by significant performance, they are relevant for finishing and semi-finishing and are not designed to work with soft materials.

In order to choose the right tool for CNC machines, it is important to take into account the cutting mode for milling, as well as all characteristics of the machined surface.

Cutting Modes

To ensure the required quality of the milled layer, it is important to correctly identify and maintain the necessary technical parameters. The main indicators describing and regulating the milling process are the operating modes.

Calculation of cutting modes for milling is performed taking into account the main elements:

1. Depth (t, mm) - the thickness of the metal ball, which is removed in one working stroke. Select it based on the allowance for processing. Rough work is carried out in one pass. If the allowance is more than 5 mm, the milling is carried out in several passes, while the last one is left about 1 mm.
2. Width (B, mm) - the width of the machined surface in a direction perpendicular to the feed motion.
3. Feed (S) is the length of the workpiece movement relative to the tool axis.

There are several interrelated concepts:

• Feed per tooth (S _z , mm / tooth) - change the position of the part when turning the cutter a distance from one working tooth to the next.
• Feed per revolution (S _о , mm / rev) - movement of the structure with one complete revolution of the milling nozzle.
• Feed per minute (S _min , mm / min) is an important cutting mode for milling.

Their relationship is established mathematically:

S _min = S _ob * n = S _z * z * n,

Where z is the number of teeth;

N is the spindle speed, min ^-1 .

The amount of feed is also affected by the physical and technological properties of the treated area, the strength of the tool and the operating characteristics of the feed mechanism.

Calculation of cutting speed

As a nominal design parameter take the degree of rapid rotation of the spindle. The actual speed V, m / min, depends on the diameter of the mill and the frequency of its rotating movements:

V = (π * D * n) / 1000

The rotational speed of the milling tool is determined by:

N = (1000 * V) / (π * D)

With the information about the minute feed, you can determine the required time for the workpiece c of length L:

T ₀ = L / S _min

Calculation of cutting modes during milling and their installation is actual to be performed before setting up the machine. The establishment of rational preset parameters, taking into account the characteristics of the tool and the material of the part, ensures high productivity of the work.

Tips for defining modes

It is impossible to choose the cutting mode perfectly when milling, but you can follow the basic principles:

1. It is desirable that the diameter of the milling cutter corresponds to the depth of processing. This will ensure the cleaning of the surface in one pass. Here the main factor is the material. For too soft, this principle does not work - there is a risk of removing chips that are thicker than necessary.
2. Shock processes and vibrations are inevitable. In this regard, an increase in feed rates leads to a decrease in speed. It is optimal to start work with a feed to the tooth equal to 0.15 mm / tooth, and in the process - to regulate.
3. The speed of the tool should not be as high as possible. Otherwise, there is a risk of reduced cutting speed. Its increase is possible with an increase in the diameter of the cutter.
4. Increasing the length of the working part of the mill, the preference for a large number of teeth reduces the productivity and quality of the processing.
5. Approximate speeds for different materials:

• Aluminum - 200-400 m / min;
• Bronze - 90-150 m / min;
• Stainless steel - 50-100 m / min;
• Plastics - 100-200 m / min.

It is better to start with an average speed, and in the process to adjust it to a smaller or larger side.

The cutting mode for milling is important to determine not only mathematically or using special tables. To correctly select and set the optimal parameters for the machine and the tool you need to operate with certain features and personal experience.