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;
- - numeric program control: the new kind equipment that allows to process various materials with maximum accuracy. Specialists can achieve this with the help of computer adjustment 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
Laser metalworking is a technology in which the material is heated in the processing zone, followed by destruction by a beam flux. This process is used for mass production as well as in private workshops. The use of laser cutting has made it possible to modernize the production of many parts. It is used for processing almost all types of metal products and is ordinary, artistic and curly. This diversity makes it possible to make objects of a very unusual shape. For different metal products, appropriate equipment is used, taking into account the characteristics of the material. Thanks to this, products of the required configuration are produced, and marriage is excluded.
Despite the fact that the technology belongs to expensive processes, it is in high demand due to its capabilities. High quality cut and speed of the procedure is carried out with virtually no waste. Metal edges are obtained almost perfectly even, requiring no additional machining. This allows you to get the output ready product, fully suitable for further use by appointment. The photos below show laser cutting of various metals.
Technology
In special devices for cutting metals with a laser, the main organ is a beam installation. The metal region is destroyed under the influence of high energy flux density. The technology of metal laser cutting is to use the properties of this beam. It has constant wavelengths as well as frequencies (monochromaticity), which ensures its stability. In addition, a small beam can be easily concentrated in a small area.
This is the basis for the system of laser cutting of metal, the principle of which is to influence the material with a bunch of energy. At the same time, the flow power increases tenfold due to special types of oscillations that cause resonance. The treated area is heated to the melting temperature of the metal product. For a short time period, the melting process increases and passes to the main thickness of the object. With a significant increase in the temperature value, the material may begin to evaporate.
The technology of cutting metal in production is carried out by two methods: melting and evaporation. In this case, the second method is accompanied by increased energy costs, which is not always justified. As the thickness of the material increases, the quality of the cut surface deteriorates. The most widely used melting when working with metal products.
Cutting equipment
Installations in which laser cutting of metal is actively used contains several basic elements:
- energy source;
- block of special mirrors (optical resonator);
- the working body that creates the ray flux.
According to the power of the working body, the installations themselves are divided:
- up to 6 kW - solid-state lasers for metal cutting;
- over 6 and up to 20 kW - devices of the gas principle of operation;
- from 20 to 100 kW - gas-dynamic type devices.
Solid state units use ruby or specially treated glass containing calcium fluorite as an additive component. A powerful energy impulse is created in a fraction of a second, and the work is carried out both in a continuous cutoff mode and in an intermittent one.
Gas laser metal cutting equipment uses electric current to heat the gas. The composition includes nitrogen, as well as carbon dioxide, helium.
Gas-dynamic devices use carbon dioxide as the basis. It heats up and, passing through a narrow nozzle, expands and immediately cools. In this case, a huge amount of thermal energy is released, capable of cutting metal products of great thickness. High power provides the highest cutting accuracy with minimal beam energy consumption.
Devices that perform laser cutting of steel, as well as other metal materials, are among the most advanced and high-tech equipment. Using special machines, high-quality and very accurate cuts are obtained, which absolutely do not require additional machining. These machines have a very high cost and are used in reputable enterprises that perform precise processing of various metal products. Equipment using a laser for cutting is not intended for use in small private workshops, as well as for household work.
At the same time, it can be pointed out that occasionally this technique is used to perform engraving and other work that requires a minimum error, the accuracy of laser cutting of metal is at the highest level. These machines provide the ability to cut according to pre-specified parameters. After preliminary setting by the operator, the further process switches to automatic mode.
Installations for cutting products of any configuration are capable of cutting depressions, as well as milling according to specified values. In addition, these universal devices are capable of performing artistic engraving on a wide variety of surfaces. Their cost directly depends on such indicators as functionality, laser power for cutting metal, as well as the brand of the manufacturer.
Machines of this type are equipped with a special software requiring preliminary training of the operator. Having mastered the course of work on this technique, managing the process itself will not be difficult at all. The sale of installations of this type is carried out in specialized stores that work with complex equipment.
Cutting modes
Laser processing of metal products is carried out on special equipment operating in one of three modes:
- evaporation;
- melting;
- combustion.
Evaporation
Laser cutting of metal by evaporation requires a high beam intensity. This is necessary to minimize heat loss from thermal conduction. For this, special solid-state installations are used, which use a pulsating mode for operation. At this method the material in the treated area is completely melted, after which it is removed using a special process gas (argon, nitrogen or others). This mode of metalworking is used very rarely.
Melting
With this method, the material does not burn out, and the melt is carried away from the area of processing by a gas jet. This method is used to work with aluminum and its alloys, as well as with copper. This is achieved by creating alloys of a refractory type with active interaction with oxygen. These metals can only be cut with a high power beam.
Combustion
This mode uses intense oxidation, which absorbs laser radiation and increases the locality of the treated area. With this method, the waste is removed evenly. The combustion mode is divided into controlled and autogenous, in which combustion metal surface occurs throughout the site of oxygen exposure. This mode does not allow you to get a smooth cut and they try to avoid it.
These modes of laser cutting of metals are selected according to the parameters of the material and the required processing accuracy. It should be remembered that the quality of the process directly depends on the thickness of the product and the speed of metalworking.
Processed materials
Laser metalworking is used to process aluminum, as well as its many alloys, bronze, titanium, stainless steel, copper and other materials. At the same time, aluminum, titanium, stainless steel products have good reflectivity, which negatively affects the speed of their processing. sheet metal parts up to 6 mm it is better to process with a nitrogen plant.
For metal alloys, the cutting quality directly depends on their thickness. Black steel items have a maximum processing thickness of 20 mm, stainless steel 15 mm, copper 5 mm, and aluminum 10 mm.
Brass processing is carried out both automatically and manually. There are no special features or difficulties. The machine itself is programmed very quickly and allows you to get the details of the required configuration.
Benefits of laser cutting
Devices in which special laser cutting of metal is used allows processing objects of almost any thickness. These machines work with both simple metal parts and stainless steel, as well as a variety of aluminum alloys. The absence of direct mechanical contact retains the shape of the product and does not cause damage or deformation of the surface. Automated system works through control programs that provide the ability to perform cutting with the highest precision.
The installations operate not only in automatic mode, but also in manual mode, in which the laser cutting process is performed by the operator himself at high speed. These machines have high functionality and versatility. For them, there is no need to use a variety of molds, as well as molds, which significantly reduces costs. The high speed of operation significantly increases the productivity of the process, in which consumable used with minimal waste.
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 steel) on the thickness of the steel being cut, the purity of the oxygen, and the design of the torch.
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.
where D is the nominal cutter diameter.
Milling order
1. According to the cutter diameter, milling width, depth of cut and feed per tooth, the cutting speed and minute feed are determined. The special conditions of a particular milling should be taken into account: the presence or absence of cooling, the design features of the cutter, etc.
2. Adjust the spindle speed.
3. Adjust the spindle feed.
Tool wear
The higher the cutting speed, the more heat is generated and the more the cutter teeth heat up. When a certain temperature is reached, the cutting edge loses its hardness, and the cutter stops cutting. The temperature at which the cutter stops cutting is different for different cutters and depends on the material from which the cutter is made.
During operation, the cutter becomes dull. Cutter dulling occurs due to wear caused by the friction of the descending chips on the front surface of the tooth and the friction of the back surface of the cutter tooth on the work surface. Friction also causes an increase in the temperature of the cutting tool, which in turn reduces the hardness of its blade and contributes to faster wear. During operation, the cutter goes through three stages of wear:
1. New, sharp cutter - serviceable.
Signs: the presence of factory lubrication, normal surface color (no scale), even one-time sharpening.
2. Cutter with normal wear - it is irrational to use the cutter further, it is better to sharpen it.
Signs: the onset of vibration, the appearance of an uneven (torn) surface of the processing and excessive heating due to increased friction.
3. Cutter with catastrophic wear - recovery of the cutter is almost impossible.
Signs: it is visually seen that the working edge of the cutter is destroyed.
Cutting modes used in practice, depending on the material being processed and the type of cutter
The table (below) contains reference information for cutting data taken from practice. It is recommended to start from these modes when processing various materials with similar properties, but it is not necessary to strictly adhere to them.
It should be taken into account that the choice of cutting conditions when machining the same material with the same tool is influenced by many factors, the main of which are: the rigidity of the Machine-Device-Tool-Part (AIDS) system, tool cooling, machining strategy, the height of the layer removed per pass, and the size of the processed elements.
It is best to mill plastics obtained by casting, because. they have a higher melting point.
- When cutting acrylic and aluminum, it is desirable to use a lubricating and cooling liquid (coolant) to cool the tool, ordinary water or WD-40 universal grease (in a can) can act as a coolant.
-When cutting acrylic, when the cutter is seated (blunted), it is necessary to lower the speed until a sharp chip comes out (be careful with feed at low spindle speeds - the load on the tool increases and, accordingly, the likelihood of breaking it).
- For milling plastics and soft metals, the most suitable are single-flute (single-toothed) cutters (preferably with a polished flute for chip removal). When using single-thread milling cutters, optimal conditions are created for chip removal and, accordingly, heat removal from the cutting zone.
- When milling, it is recommended to use such a machining strategy in which there is a continuous removal of material with a stable load on the tool.
-When milling plastics, to improve the quality of the cut, it is recommended to use up-cutting.
-To obtain an acceptable surface roughness, the step between the cutter / engraver passes must be equal to or less than the working diameter of the cutter (d) / engraver contact patch (T).
-To improve the quality of the machined surface, it is advisable not to process the workpiece to the full depth at once, but to leave a small allowance for finishing.
- When cutting small elements, it is necessary to reduce the cutting speed so that the cut elements do not break off during processing and are not damaged.
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 below 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.
For oxygen cutting combustible gases and vapors of combustible liquids are suitable, giving a flame temperature when burned in a mixture with oxygen of at least 1800 gr. 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, flows out 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:
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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. Maximum speeds cutting and amperage for various materials and thicknesses, performed on a 400 amp machine, are shown in the table below.
Air plasma cutting speed depending on the thickness of the metal: table 2
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Modes. table 3
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Modes of air-plasma cutting of metals. table 4
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Rice. 3 Regions optimal modes metal cutting for 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.
