Laser cutting for metal: technology, equipment, modes, advantages. Choice of cutting modes when working on milling and engraving equipment Gas cutting modes

When performing flame separation cutting, the requirements for cutting accuracy and the quality of the cut surface must be taken into account. The preparation of the metal for cutting has a great influence on the quality of the cut and cutting performance. Before cutting, the sheets are fed to the workplace and laid on linings so as to ensure unhindered removal of slag from the cutting zone. between the floor and the bottom sheet should be at least 100-150 mm. The metal surface must be cleaned before cutting. In practice, scale, rust, paint and other contaminants are removed from the metal surface by heating the cutting zone with a gas flame, followed by cleaning with a steel brush. The parts to be cut are marked with a metal ruler, scriber and chalk. Often the sheet to be cut is fed to the cutter's workplace already marked.

Before starting oxygen cutting, the gas cutter must set the required gas pressure on the acetylene and oxygen reducers, select the required numbers of the outer and inner mouthpieces, depending on the type and thickness of the metal being cut.

The process of oxygen cutting begins with heating the metal at the beginning of the cut to the ignition temperature of the metal in oxygen. Then they start cutting (continuous oxidation of the metal occurs throughout the thickness) and move the cutter along the cut line.

The main parameters of the oxygen cutting mode are: the power of the preheating flame, the pressure of the cutting oxygen and the cutting speed.

Heating flame power characterized by the consumption of combustible gas per unit time and depends on the thickness of the metal being cut. It should provide rapid heating of the metal at the beginning of cutting to the ignition temperature and the necessary heating during the cutting process. For cutting metal up to 300 mm thick, a normal flame is used. When cutting thicker metal, the best results are obtained by using a flame with an excess of fuel (carburizing flame). In this case, the length of the visible flame (and the closed oxygen valve) must be greater than the thickness of the metal being cut.

Choice of cutting oxygen pressure depends on the thickness of the metal being cut, the size of the cutting nozzle, etc. oxygen purity. As the pressure of oxygen increases, its consumption increases.

The purer the oxygen, the lower its consumption per 1 linear meter. m cut. The absolute value of the oxygen pressure depends on the design of the cutter and mouthpieces, the resistance values ​​in the oxygen supply fittings and communications.

Torch travel speed should correspond to the burning rate of the metal. The stability of the process and the cut parts depend on the cutting speed. A low speed leads to melting of the cut, and a high speed to the appearance of sections of the cut that have not been cut to the end. The cutting speed depends on the thickness and properties of the cut sections. The cutting speed depends on the thickness and properties of the metal being cut. When cutting steels of small thickness (up to 20 mm), the cutting speed depends on the power of the preheating flame. For example, when cutting steel with a thickness of 5 mm, about 35% of the heat comes from the preheating flame.

a - cutting speed is low, b - optimal speed, c - high speed

Figure 1 - The nature of the release of slag

The speed of oxygen cutting is also affected by the cutting method (manual or machine), the shape of the cut line (straight or figured) and the type of cut (blank or finish). Therefore, the permissible cutting speeds are determined empirically, depending on the thickness of the metal, the type and method of cutting. With a correctly selected cutting speed, the cut line lag should not exceed 10-15% of the thickness of the metal being cut.

Figure 1 schematically shows the nature of the ejection of slag from the cut. If the speed of oxygen cutting is low, then the deflection of the spark beam in the direction of cutting is observed (Fig. 1, a). At an overestimated cutting speed, the deflection of the spark beam occurs in the direction opposite to the cutting direction (Fig. 1, c). The cutting speed is considered normal if the spark beam comes out almost parallel to the oxygen jet (Fig. 1, b).

The width and cleanliness of the cut depend on the cutting method. Machine cutting produces cleaner and narrower cuts than hand cutting. The greater the thickness of the metal being cut, the greater the roughness of the edges and the greater the width of the cut. Depending on the thickness of the metal, the approximate width of the cut is.

The basic principle of the CNC milling machine

Milling of workpieces occurs when the cutting tool interacts with the material. The degree of entry of the cutter teeth into the material depends on the taper angle. The smaller the angle, the lower the cutting force.

The choice of cutter diameter is determined by the width and depth of milling. Both parameters are set in the drawings and correspond to the size of the workpiece. If it is necessary to manufacture several blanks, the parameters are multiplied by the number of required parts.

While working on CNC milling machines, the cutter performs rotational movements, gradually removing the necessary layers of material from the workpiece, which, in turn, performs translational motion relative to the cutter. Depending on the design of the machine, either the table moves in relation to the cutter, or the cutter in the second is the cutter in relation to the table.

Two elements are involved in the production process - a cutter and a workpiece. However, all manipulations are performed by a cutter. Management is carried out using a computer or other computing device.

Main Modes

Milling machines have several basic operating modes, the parameters of which are adjusted depending on the material. The main modes of operation include: cutting, sampling and engraving.

The indicated mode of operation is used for cutting blanks and shaping the product. Work in this mode is performed using a helical 1-start or 2-start cutter.

Engraving involves the application of drawings or inscriptions to the surface of the material using an engraver.

Cutter selection

For successful work, you need to choose the right cutter. The choice of cutter is determined by two parameters - the depth and width of the milling of the cutting surface. Usually these parameters are indicated in the drawings for blanks and depend on the planned size of the parts.

Depth of cut - an indicator that determines the thickness of the material removed by the cutter in one pass. When processing hard materials, the cutter makes several passes, then the surface of the material is smoother. However, at shallow depths, the cutter only makes one pass. Milling width - measured by the size of the workpiece. Both parameters are set in the drawings.

Cutting speed refers to the path that the cutter travels during operation for one minute. The path is usually indicated in meters. The optimal speed is calculated based on the circumference of the cutter and the number of teeth. The total circumference of the cutter is multiplied by the number of teeth and the number of revolutions per minute. To obtain a metric result, the resulting value must be divided by 1000, by the number of millimeters in meters.

The optimal speed for different materials is determined according to the reference tables. The cutting speed during the operation of the machine depends on the reliability of the cutter, therefore the tables show the maximum allowable machine revolutions at which the cutter cannot be damaged.

Spindle movement

The cutter moves in three directions, according to the coordinate axis, where X - corresponds to the transverse movement of the spindle, Y - longitudinal, and Z - vertical direction.

The main cutting parameters are the feed rate and spindle rotation. One minute feed refers to the amount of movement that the spindle makes in one minute. This value is measured in millimeters. It is calculated based on the number of teeth of the cutter and the revolutions per minute. Thus, one minute feed is equal to the feed per tooth of the cutter multiplied by the number of teeth and revolutions per minute.

Operating mode selection

The choice of processing mode depends on the materials, machine power, and processing speed. The higher the power of the machine, the higher the speed of obtaining the part, which is reflected in the intensity of production. But too high a speed reduces the quality of processing, so the choice of speed is determined by the properties of the material and the presence of a cooling system for the machine and chip removal, as well as the type of cutter. Basic data regarding cutting and milling feed rates and depths are contained in the accompanying tables. The table indicates the maximum allowable values ​​for the indicated types of materials, since a value exceeding the indicated number can lead either to damage to the cutter or to the workpiece.

The processing of metal and other surfaces with the help has become an integral part of everyday life in the industry. Many technologies have changed, some have become simpler, but the essence remains the same - correctly selected cutting conditions during turning provide the desired result. The process includes several components:

• power;
• rotation frequency;
• speed;
• processing depth.

Key manufacturing points

There are a number of tricks that must be followed while working on a lathe:

• fixing the workpiece in the spindle;
• turning with a cutter of the required shape and size. The material for metal-cutting bases is steel or other hard-alloy edges;
• the removal of unnecessary balls occurs due to different revolutions of rotation of the caliper incisors and the workpiece itself. In other words, an imbalance of speeds between the cutting surfaces is created. Surface hardness plays a secondary role;
• the use of one of several technologies: longitudinal, transverse, a combination of both, the use of one of them.

Types of lathes

For each specific part, one or another unit is used:

• screw-cutting lathes: a group of machines that are most in demand in the manufacture of cylindrical parts from ferrous and non-ferrous metals;
• carousel-turning: types of units used for turning parts. Especially large diameters from metal blanks;
• frontal lathe: allows you to grind parts of cylindrical and conical shapes with non-standard dimensions of the workpiece;
• : production of a part, the workpiece of which is presented in the form of a calibrated pond;
• - numerical control: a new type of equipment that allows you to process various materials with maximum accuracy. Specialists can achieve this with the help of computer adjustment of technical parameters. Turning takes place with an accuracy of micron fractions of a millimeter, which cannot be seen or verified with the naked eye.

Selection of cutting conditions

Operating modes

The workpiece from each specific material requires the appropriate cutting mode for turning. The quality of the final product depends on the correct selection. Each specialist in his work is guided by the following indicators:

• The speed at which the spindle rotates. The main emphasis is on the type of material: rough or finishing. The speed of the first is slightly less than the second. The higher the spindle speed, the lower the cutter feed. Otherwise, melting of the metal is inevitable. In technical terminology, this is called "ignition" of the treated surface.
• Feed - is selected in proportion to the spindle speed.

Cutters are selected based on the type of workpiece. Turning with the help of a turning group is the most common option, despite the availability of other types of more advanced equipment.

This is justified by low cost, high reliability, long service life.

How speed is calculated

In an engineering environment, the calculation of cutting conditions is calculated using the following formula:

V = π * D * n / 1000,

V - cutting speed, calculated in meters per minute;

D - the diameter of the part or workpiece. Indicators should be converted to millimeters;

n - the value of revolutions per minute of the time of the processed material;

π - constant 3.141526 (table number).

In other words, the cutting speed is the length of the path that the workpiece travels per minute.

For example, with a diameter of 30 mm, the cutting speed will be 94 meters per minute.

If it becomes necessary to calculate the value of revolutions, subject to a certain speed, the following formula is applied:

N = V *1000/ π * D

These values ​​and their interpretation are already known from previous operations.

Additional materials

During manufacture, most specialists are guided as an additional benefit by the indicators below. Strength factor table:

Material strength factor:

Tool life factor:

The third way to calculate speed

• V actual = L * K*60/T cutting;
• where L is the length of the canvas, converted into meters;
• K is the number of revolutions per cutting time, calculated in seconds.

For example, the length is 4.4 meters, 10 revolutions, the time is 36 seconds, total.

The speed is 74 rpm.

Video: The concept of the cutting process

The main indicators of the cutting mode are the pressure of the cutting oxygen and the cutting speed, which depend (for a given chemical composition of the steel) on the thickness of the steel being cut, the purity of the oxygen and the design of the cutter.

Cutting oxygen pressure is of great importance for cutting. With insufficient pressure, the oxygen jet will not be able to blow the slag out of the cut and the metal will not be cut through to the full thickness. With too much oxygen pressure, its consumption increases, and the cut is not clean enough.

It has been established that a 1% decrease in oxygen purity reduces the cutting speed by an average of 20%. It is not advisable to use oxygen with a purity below 95% due to a decrease in the speed and quality of the cut surface. The most expedient and economically justified use, especially in machine oxygen cutting, is oxygen with a purity of 99.5% or more.

The cutting speed is also influenced by the degree of mechanization of the process (manual or machine cutting), the shape of the cut line (straight or figured) and the quality of the cut surface (cutting, blanking with a machining allowance, blanking for welding, finishing).

In addition to the table, manual cutting speed can also be determined by the formula

where δ is the thickness of the cut steel, mm.

If the cutting speed is low, then edge melting will occur; if the speed is too high, gaps will form due to the backlog of the oxygen jet, cutting continuity will be broken.

The modes of machine finishing cutting of parts with straight edges without subsequent machining for welding are given in Table. 20. For shape cutting, the speed is taken within the limits indicated in the table for cutting with two cutters. In blank cutting, the speed is assumed to be 10 - 20% higher than indicated in the table.

The data in the table take into account that the purity of oxygen is 99.5%. With lower purity, the consumption of oxygen and acetylene increases, and the cutting speed decreases; these values ​​are determined by multiplying by a correction factor equal to:

When cutting sheets with a thickness of ∼ 100 mm, it is economically justified to use a preheating flame with excess oxygen to heat the metal surface as quickly as possible.

Oxygen cutting is based on the combustion of metal in a jet of commercially pure oxygen. During cutting, the metal is heated by a flame, which is formed during the combustion of a combustible gas in oxygen. Oxygen that burns heated metal is called cutting oxygen. During the cutting process, a jet of cutting oxygen is supplied to the cutting site separately from the oxygen used to form a combustible mixture for heating the metal. The process of combustion of the metal being cut extends over the entire thickness, the resulting oxides are blown out of the cut by a jet of cutting oxygen.

The metal subjected to cutting with oxygen must meet the following requirements: the ignition temperature of the metal in oxygen must be lower than its melting point; metal oxides must have a melting point lower than the melting point of the metal itself, and have good fluidity; metal should not have high thermal conductivity. Good for cutting low carbon steels.

Combustible gases and vapors of combustible liquids are suitable for oxygen cutting, giving a flame temperature when burned in a mixture with oxygen of at least 1800 g. Celsius. Oxygen purity plays a particularly important role in cutting. For cutting, it is necessary to use oxygen with a purity of 98.5-99.5%. With a decrease in oxygen purity, cutting performance is greatly reduced and oxygen consumption increases. So, with a decrease in purity from 99.5 to 97.5% (i.e., by 2%), the productivity decreases by 31%, and the oxygen consumption increases by 68.1%.

Oxy cutting technology. When parting cutting, the surface of the metal being cut must be free of rust, scale, oil and other contaminants. Separation cutting usually starts at the edge of the sheet. First, the metal is heated with a heating flame, and then a cutting jet of oxygen is launched and the cutter is evenly moved along the cut contour. The cutter must be at such a distance from the metal surface that the metal is heated by the reducing flame zone, which is 1.5-2 mm away from the core, i.e. the highest temperature point of the heating flame. For cutting thin sheets (thickness no more than 8-10 mm), batch cutting is used. In this case, the sheets are tightly stacked one on top of the other and compressed with clamps, however, significant air gaps between the sheets in the package impair cutting.

On machines MTR "Crystal" the cutter "Effect-M" is used. The peculiarity of the cutter is the presence of a fitting for compressed air, which, having passed through the internal cavity of the casing, expires through the annular gap above the mouthpiece and creates a bell-shaped curtain, which localizes the spread of combustion products and protects the structural elements of the machine from overheating.

Parameters of cutting modes of mild steel are shown below in Table 1:

1. Thickness of the metal being cut
5. Oxygen pressure
6. Cutting speed
7. Oxygen consumption
8. Propane consumption
9. Cutting width
10. Distance to sheet

Air plasma cutting

The process of plasma cutting is based on the use of a direct-current air-plasma arc (electrode-cathode, cut metal - anode). The essence of the process lies in the local melting and blowing of the molten metal with the formation of a cut cavity when the plasma cutter moves relative to the metal being cut.

To excite the working arc (the electrode is the metal being cut), with the help of an oscillator, an auxiliary arc is ignited between the electrode and the nozzle - the so-called duty arc, which is blown out of the nozzle by starting air in the form of a torch 20-40 mm long. Pilot arc current 25 or 40-60 A, depending on the source of the plasma arc. When the torch of the duty metal arc touches, a cutting arc arises - a working one, and an increased air flow is switched on; the standby arc is automatically switched off.

The use of the air-plasma cutting method, in which compressed air is used as a plasma-forming gas, opens up wide opportunities for cutting low-carbon and alloy steels, as well as non-ferrous metals and their alloys.

Advantages of air-plasma cutting in comparison with mechanized oxygen and plasma cutting in inert gases are the following: simplicity of the cutting process; the use of inexpensive plasma-forming gas - air; high cleanliness of cut (when machining carbon and low-alloy steels); reduced degree of deformation; more stable process than cutting in hydrogen-containing mixtures.

Rice. 1 Scheme of connecting the plasma torch to the device.

Rice. 2 Phases of working arc formation
a - the origin of the duty arc; b - blowing out the duty arc from the nozzle until it touches the surface of the sheet being cut;
c - the appearance of a working (cutting) arc and penetration through the cut of the metal.

Air plasma cutting technology. To ensure a normal process, a rational choice of mode parameters is necessary. The mode parameters are: nozzle diameter, current strength, arc voltage, cutting speed, distance between the nozzle end and the workpiece, and air consumption. The shape and dimensions of the nozzle channel determine the properties and parameters of the arc. With a decrease in the diameter and an increase in the length of the channel, the plasma flow rate, the energy concentration in the arc, its voltage and cutting ability increase. The service life of the nozzle and cathode depends on the intensity of their cooling (water or air), rational energy, technological parameters and the amount of air flow.

During air-plasma cutting of steels, the range of cut thicknesses can be divided into two - up to 50 mm and above. In the first range, when process reliability is required at low cutting speeds, the recommended current is 200-250 A. An increase in current to 300 A and above leads to an increase in cutting speed by 1.5-2 times. Increasing the current strength to 400 A does not give a significant increase in the cutting speed of metal up to 50 mm thick. When cutting metal with a thickness of more than 50 mm, a current of 400 A and above should be used. As the thickness of the metal being cut increases, the cutting speed drops rapidly. The maximum cutting speeds and currents for various materials and thicknesses, made on a 400 amp machine, are shown in the table below.

Air plasma cutting speed depending on the thickness of the metal: table 2

Modes. table 3

Modes of air-plasma cutting of metals. table 4

Rice. 3 Areas of optimal metal cutting modes for an air-cooled plasma torch (current 40A and 60A)

Rice. 4 Areas of optimal modes for an air-cooled plasma torch (current 90A).

Rice. 5 Dependence of the choice of the nozzle diameter on the plasma current.

Rice. 6 Recommended currents for hole punching.

The speed of air-plasma cutting, in comparison with gas-oxygen, increases by 2-3 times (see Fig. 7).

Rice. 7 Cutting speed of carbon steel depending on metal thickness and arc power.
The sloping bottom line is oxy-fuel cutting.

Good cut quality when cutting aluminum, using air as a plasma gas, can be achieved only for small thicknesses (up to 30 mm) at currents of 200 A. Deburring from thick sheets is difficult. Air-plasma cutting of aluminum can only be recommended as a separating process for the preparation of parts that require subsequent machining. Allowance for processing is allowed at least 3 mm.