Review of metal cutting technologies: choice of method, waste minimization, typical mistakes

02/01/2019 Author: VT-METALL

Issues discussed in the material:

• What methods are there for cutting steel?
• What are the features of cutting steel with a guillotine?
• What are the advantages of punch cutting?
• What are the main advantages of laser cutting of steel?
• How to save money when cutting steel

The metallurgical industry is the basis of the economy of any state. The most common metal, used in almost all fields of activity, is steel. Cutting steel sheet profile metal is a special technological process used in the manufacture of metal structures. A competently performed operation with optimal arrangement of templates allows production to be achieved with the required number of workpieces, as well as saving the metal used.

Nowadays, there are many modern methods for cutting steel; advanced technologies have significantly expanded the range of operations offered, which allows you to choose an option for each type of rolled product. Let's figure it out and highlight the main methods of cutting steel.

Methods for cutting steel in scientific and technological progress

People who are used to making something at home are often faced with the question of how to more conveniently cut a metal workpiece. Depending on the specific case, they use a hacksaw, a grinder, special hand and electric scissors, or chop the workpiece using a regular chisel. In industrial conditions, when the volume of work is much higher, the most effective methods for cutting steel are used.

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Modern high-tech production makes it possible to cut metal with minimal losses, which has significantly increased the savings in raw materials. The equipment used for this makes it possible to fully provide metal structures for construction, machine and automotive manufacturing, medical and other areas of activity. Scientific and technological progress does not stand still, and now, when cutting metal, the most complex processing is carried out, and parts and products of non-standard configurations come off the assembly line.

Metal cutting is the very first operation that sets the contours of the future product. After performing a series of manipulations - punching, cutting, punching, cutting, trimming - the machine operator receives various parts and workpieces at the output. Cutting is carried out by the impact of the cutting tool on the material. There are several ways to cut steel. Let's take a closer look at them.

What will the cutting price depend on?

The cost of the service depends on several factors: - thickness of the material: the thicker and stronger the metal, the more power and time the master will need to process it; — quality of the cultivated material and equipment: high-quality carbide materials require processing on more expensive equipment; — complexity of the drawing/part: the laser cuts the products according to a given drawing, which is drawn up in advance by a master using a computer program; — work time: urgent work costs more.

Guillotine cutting as the most common method of cutting steel

Guillotine (guillotine shears) is the most common mechanical device designed for cutting metal. The design performs the operation using an oblique movable knife, which moves in one plane without changing the angle of inclination. The guillotine contains a special press with a mechanical or hydraulic drive, which allows you to hold the material during cutting. If you have a press (clamp), you can cut several sheets of metal at once.

The guillotine is designed for direct longitudinal and transverse cutting of sheet and strip material; cuts are not made with such a tool. The simplicity of using this design is that you do not need to exert much effort, since the pressure on the material being cut is not applied along the entire length of the cut. The operation is more reminiscent of chopping, which produces a neat cut, usually without jams or burrs.

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Cutting steel sheets with a guillotine allows you to virtually eliminate metal loss in the form of chips. This method is especially effective in mass production of sheet metal.

The advantages of cutting steel with a guillotine are obvious:

• cost-effective process with low energy intensity;
• minimal metal waste;
• high cutting accuracy, which does not require further processing of the part;
• simplicity of the work process;
• the small number of operations affects the cost of services, making them available to a large number of customers.

Among the disadvantages of the method are:

• impossibility of performing figured cutting;
• limitation in the type of metal and the thickness of the sheet being cut (for hydraulic machines, a maximum of 6 mm);
• low accuracy of the resulting strips, depending on the qualifications of the operator.

What is a line for cutting rolled metal?

Since cutting sheets using metal scissors is ineffective and inconvenient, in production cutting of rolled metals is carried out on special cutting lines. They allow you to cut rolled metal into pieces giving them different shapes (from square to diamond).

Cross cutting lines for rolled metal have the following technical characteristics:

• permissible width of steel roll – 0.16 m;
• maximum thickness of metal sheets – 0.4 cm;
• the minimum number of cut parts - from 18 or more, depending on the length of the sheet;
• the total power of the motors of all drives is 206 kW.

The line for cross cutting of rolled metal consists of the following elements - sheet shears with a knife installed at an angle, a control mechanism, a device for correct unwinding, a unit for folding cut parts, and a roller feed.

The functioning of the complex is carried out in accordance with a pre-established algorithm, depending on various parameters, including the initial and final dimensions of the workpieces, the length of the roll or sheet. Installations for cutting rolled metal can be fully automated or operator-controlled. In the first case, the equipment stops automatically after the unwinder runs out of material.

Let us dwell in a little more detail on the constituent elements included in the cutting line of rolled metal:

1. Straightening-unwinding device.

The purpose of this unit is to minimize the deformation of the sheets before they are threaded into the scissors. At the same time, special brushes remove residues of industrial contaminants, plaque and scale from the sheets. The apparatus is turned on if it is necessary to dissolve the hot-rolled metal into parts.

2. Scissors.

Automatic shears are similar to manual ones, the difference is that they are mechanically connected to the installation for cutting rolled metal.

If a problem occurs in the drive, the scissors will be turned off simultaneously with other elements of the installation. The cutting process is monitored using an image on a visual display. It should be borne in mind that the roll fixation error varies up to 0.4 mm in one direction or another. The error is significantly influenced by the characteristics of the source material.

Oxy-fuel cutting of steel

Oxygen gas cutting was started in 1840 by the German chemist D. Richmann, who invented the first apparatus capable of releasing hydrogen and subsequently producing a hydrogen flame in a burner. The device could weld and cut fusible metals. Until now, this method of cutting steel remains simple and the most affordable among thermal methods.

This technology is more suitable for cutting thick sheets, in particular for sheets with a thickness of more than 32 mm. Oxygen cutting occurs through the combustion of metal in a stream of technically pure oxygen, and the same flow removes the resulting slag from the cut.

Over the long period of use of this cutting method, scientists and engineers have developed and put into practice several varieties of it. The most commonly used ones are:

1. Propane.
   Suitable for low alloy alloys and steels with low carbon content. Steels containing more than 1% carbon can be cut in this way only with the addition of special powdered fluxes, which, when burned, release the missing heat.
2. Air-arc.
   When air-arc cutting, metal is melted by an arc burning between the product and a carbon electrode, its residues are removed with a stream of compressed air. Cutting is performed with direct current of reverse polarity. Power sources are standard DC welding converters or welding transformers. The surface at the cut site is flat and smooth. This method is widely used for cutting out defective areas of welds, cutting off rivets, punching holes, casting defects and other flaws. Easily cuts steel products up to 20–25 mm thick.
3. Oxygen-flux.
   High-alloy chromium steels are difficult to cut with oxygen alone. A refractory film of chromium oxides is formed, which covers the metal particles and prevents its combustion in a stream of oxygen. To facilitate the cutting process, powdered flux is continuously introduced, which, when burned, releases a large amount of additional heat, causing the film to melt and turn into slag. The cutting process proceeds at normal speed, and the cut surface is clean.
4. Spear.
   The cutting process is carried out due to the heat that is released during the combustion of the metal being cut, as well as additional heat from the combustion of the end of the steel spear tube. The tube is a consumable material that burns during cutting and has to be replaced from time to time.

   The slag formed during cutting with an oxygen lance is blown out through the gap between the tube and the walls of the hole formed under the influence of oxygen pressure.

   Holes are burned with an oxygen lance and parts of large thickness are cut. Usually cutting with a spear is combined with the work of a cutter, which is used to cut a slit, insert a spear into it and continue cutting. Using the combined operation of a cutter and a spear, it is possible to cut steel blanks up to 2 m thick.

This method of cutting steel has a number of advantages:

• the cut is made at any angle;
• allows cutting low-alloy and low-carbon steel, as well as structural steel;
• with relative simplicity of operations, the process is characterized by high productivity;
• Along with stationary machines, tools that are easy to transport are used;
• reasonable price of equipment, equipment and welding materials;
• availability of consumables;
• flame temperature control;
• low energy consumption.

The disadvantages of oxy-fuel cutting of steel usually include the fact that the method is not suitable for everyone, but only for metals with low thermal conductivity.

Sometimes, when cutting, sagging and scale form on the edges of parts, so additional processing is required. Also, this method of cutting steel is not very economical: metal losses occur due to the rather large width of the cut.

Waterjet cutting is the most common method for cutting steel.

In waterjet cutting, a jet of water (water and abrasive material) acts as a cutter, which is supplied under high pressure at high speed. When interacting with the workpiece being processed, natural erosion occurs.

People noticed the unique property of water under pressure to change the shape of objects a long time ago and gradually introduced it into industrial production. Active research by specialists from the USSR and the USA led to the fact that in 1979, engineers tried adding abrasive sand to a stream of water, due to which its cutting properties increased many times over.

In 1983, serial production of equipment and components for waterjet cutting began. This method of cutting steel is developing dynamically and is a serious competitor to traditional technologies.

The method is almost ideal, since when cutting the metal does not heat up or deform, and the amount of waste is minimal.

The advantages of this method of cutting steel also include:

• possibility of cutting metal sheets up to 200 mm;
• safety and environmental friendliness of the production process;
• possibility of non-standard and figured cutting;
• simultaneous cutting of several steel sheets.

But the following factors can be considered disadvantages:

• Low profitability of the machine, the same cutting speed for both thin and thick-walled materials.
• Deformation, appearance of taper (especially when processing thick-walled metals). The need for additional processing of the end of the part.
• Expensive equipment and maintenance.

Plasma arc cutting of steel

This method of cutting steel is carried out by a device called a plasma cutter, which creates a stream of high-temperature ionized air (plasma) that cuts the workpiece. An arc appears between the working metal surface and the electrode, locally heating the workpiece. In this case, the metal melts and a cut appears. The plasma temperature can reach +25,000…+30,000 °C. Particles of molten metal that appear on the surface of the workpiece being cut are blown away from it by a stream of air from the nozzle.

When using high temperature, the arc cuts into the material with lightning speed. Provided that the specialist has selected the optimal ratio of arc power and metal thickness, the cut occurs through the entire workpiece.

Plasma arc cutting is used in the production of parts with straight and shaped contours, cutting holes, cutting pipes and profiles.

The plasma cutting method, using a high-temperature arc, allows you to obtain a number of advantages over other methods of cutting steel, namely:

• high speed of the process;
• the ability to produce cuts of any shape, including geometric patterns and figured cutting of the highest complexity;
• high quality edges unlike other methods;
• speed and quality of work do not depend on the thickness of the workpiece;
• the ability to work at an angle, which helps to master wide sheets of metal;

• when working with painted surfaces, the appearance of the workpiece will not change, paint processing will be minimal;
• safe type of work from an environmental point of view with minimal release of harmful substances or pollutants into the air;
• the safety of the method, since there is no need to use explosive gas cylinders.

Like any other method of cutting steel, plasma cutting also has disadvantages:

• the limit of metal thickness for cutting is only 100 mm;
• complex equipment requiring highly qualified maintenance;
• a certain noise during the process, as compressed air or gas is supplied at high speed;
• high cost of devices and components for them.

Rapid wear of consumables can be caused by an incorrectly chosen angle of deviation from the perpendicularity of the cut. An acceptable deflection angle should not exceed 10–50°; if it is larger, a significant expansion of the cut occurs, which is undesirable when cutting steel.

Take into account this nuance: due to the rather complex equipment, it is impossible to connect two cutters to one device at the same time.

Common Mistakes

The main types of errors when cutting metal can be divided into calculation and technological. The first ones appear when the cutting pattern is formed incorrectly; the dimensions of the parts and the order of their arrangement on the sheet are not taken into account. These inaccuracies can be minimized using cutting programs. In paid versions, it is possible to organize stream production; business balances from previous cuttings are taken into account.

Examples of technological errors for various types of metal cutting:

• Plasma cutting. Incorrect operating mode will lead to the formation of defects. Additionally, there will be severe wear of the nozzle, the consequences of which are stretching the arc and widening the cut.
• Laser processing. Rapid passage of the beam can cause burrs to appear - hardening of beads on the edge. It is necessary to adjust the guide frame; its wear affects the accuracy of the cut.
• Mechanical cutting. A common cause of edge bending is a dull edge of a disk, guillotine or blade. Also, sheet fixation is important for machining.

To optimize the process and obtain high-quality workpieces, several cutting technologies can be used. This is relevant for the manufacture of complex-shaped products or for organizing constant flow production. The main advantage of this approach is the reduction of waste, which has a positive effect on product costs.

Punch cutting of steel

In industrial production and repair and construction work, coordinate punching of metal is very popular. Imagine, after such an operation, for example, a perforated sheet, necessary for the manufacture of all kinds of structures, as well as decorative elements. This method of cutting steel allows you to perform complex engineering tasks, implement all kinds of design ideas, but at the same time use metal blanks carefully and economically.

Processing of metal sheets by punch cutting of steel is used in the manufacture of:

• advertising structures and panels;
• various showcases;
• warehouse racks;
• fencing;
• elements of prefabricated building supports;
• some parts of machine tools and machinery.

Since dies for each operation are created individually, specialists are ready to make any, even non-standard holes according to customer requirements.

This method of cutting steel is a fairly fast operational process. The high speed of movement of the metal sheet makes it possible to punch a large number of products in a short time. Modern, highly efficient equipment punches holes whose smooth edges do not require additional processing.

Experts note multiple advantages of punch cutting of steel over stamping presses, equipment for laser and plasma cutting of metal:

• the ability to punch holes with complex contours in large volumes in a short period of time: from 1000 parts in one hour of working time;
• simple changeover, the ability to carry it out during work;
• performing incomplete punching and forming of parts;
• no heating of the metal, preservation of the original properties of steel in the finished part;

• creating holes of any shape and configuration;
• high accuracy;
• the ability to change the angle of the cutting tool;
• the ability to manufacture several products and parts in a single process from one sheet;
• minimal human costs;
• highly environmentally friendly process, since no slag, dust or combustion waste is formed.

However, there are problems that operations performed through punch cutting of steel do not solve completely or partially:

1. For example, jig presses cannot cope with 3D shaped parts or products with high or complex shapes. Limitations are caused by imperfect designs and tool dimensions.
2. You should be careful when choosing the thickness of the sheet you use. Despite the fact that the characteristics of the equipment are designed for large parameters, today few people fill the coordinate-punching press with a sheet thicker than 3 mm. This is dictated by the fact that otherwise it is necessary to apply more force at low moving speeds due to the large mass of the sheet. Accordingly, the stamping tool wears out much faster, and labor productivity decreases sharply.
3. It will also be problematic to make curved, non-repeating contours. To do this, it is necessary to use nibbling - a method of coordinate stamping, in which each blow is a cut of a small part of the metal, much smaller than the tool itself. Due to low productivity and high wear and tear of equipment, this method is only suitable for a single pilot production.

What equipment is used in the process

Laser cutting of metal products is carried out on special laser devices - machines. The equipment can perform large volumes of work and process surfaces made of different types of metal: stainless steel, steel, brass, aluminum, hard alloys. After laser cutting on the machine, the finished product has perfectly smooth edges and edges. There are two types of laser machines for metal processing: fiber and CO2 gas. The device consists of a coordinate table, a computer and the laser itself. Fiber machines are used for laser cutting of thin-sheet metal products.

Laser cutting as a modern method of cutting steel

Laser cutting is widely used throughout the world to process various types of materials, regardless of their thermophysical properties. A focused laser beam, usually controlled by a computer, delivers a high concentration of energy and produces the cut.

During the cutting process, the material of the cut area melts, ignites, evaporates, or is blown away by a stream of gas. Laser cutting of sheet metal involves high-precision processing of the sheet by heating the required area and its subsequent destruction by a laser beam.

Laser cutting of metal is an expensive operation, but it is still in great demand today and attracts with the quality of the cut and the high speed of the process. This method of cutting steel occurs with virtually no waste, because the thickness of the cut is very thin. Metal workpieces are not subject to deformation; the areas adjacent to the cutting zone are only slightly heated. In fact, with the help of laser cutting it is possible to produce a product that is ready for further use for its intended purpose.

Laser cutting is applied to any metal profiles: sheets, pipes, corners and others. Blanks can be made using different technologies: casting, stamping, rolling, and so on. The power of the laser used depends on the thickness of the workpiece. For example, a laser with a power of 0.5 kW will cut a part with a thickness of 4-5 mm. To cut a workpiece 12–15 mm thick, a more powerful 1.5 kW laser is required.

The advantages of using a laser are well known:

• laser processing is an expensive, but fairly accessible operation;
• Even the hardest metals can be cut;
• good cutting quality with fairly high productivity;
• lack of mechanical contact with the material, the ability to work with brittle metals that cannot be processed otherwise;
• making cuts along a contour of any complexity;

• dense arrangement of workpieces on the cutting sheet, economical consumption of material, reduction in the cost of the final product;
• no need for further processing of parts;
• easy control of laser beams, allowing you to cut material along a complex contour;
• thin cutting line - from 0.07 to 0.1 mm.

Among the negative reviews, the most common are the following:

• under thermal influence, changes occur in the structure of the material;
• narrow range of processed materials and their thickness;
• inability to cut light-transmitting materials;
• release of harmful chemicals into the atmosphere;
• high cost of equipment and its maintenance.

With this method of cutting steel, it is not recommended to use sheets with noticeable irregularities, or to cut rusty or corrosive metal.

When placing parts on the sheet, make sure that the distance between them is at least 5–10 mm, and from the edge - 10 mm.

To improve the external characteristics of parts, sheets with rounded corners are sometimes used. When laser cutting, the speed of the cutting head does not decrease due to this.

The higher cost of this method of cutting metal compared to others is due to the fact that the machine cuts into the material close to the line: the greater the number of contours and the more diverse their configuration, the longer the process.

Calculation of metal cutting, waste minimization

The first stage is the formation of a cutting map. This is a diagram of the location of the contours of parts (blanks) on sheet metal. This is done manually or using software packages. The latter option is preferable, since the cutting map is optimal. This is important for flow production when business balances need to be taken into account, which will reduce the amount of unrecoverable waste.

Principles of forming a metal cutting map.

1. Placing blanks of the same type allows you to use the material as efficiently as possible.
2. First, the dimensions of the long and wide parts are marked, then the remaining blanks fill the free space.
3. Aligns contours to optimize cutting, with fewer torch or laser head passes.
4. Technological cutting width. For heat treatment it is 3-5 mm from the actual width. It is not taken into account during mechanical cutting.
5. The larger the steel sheet, the higher the utilization rate. This is the ratio of the area of ​​the blanks to the area of ​​the sheet.

It takes into account which machine or other equipment is selected for cutting metal. The main parameter is the maximum and minimum cutting width, the ability to change this value. The basis for choosing technology is the quality requirements for the resulting workpiece. Thus, for high-precision production, the absence of a cut taper, or the minimum value of this parameter, is important.

Important: to produce parts of different thicknesses, it is recommended to draw up several maps, as well as calculate equipment parameters. This is necessary to optimize the process, increase processing speed, and product quality.

Savings when cutting steel

To reduce the cost of products, any enterprise is interested in reducing the consumption of materials. Even a small saving on one produced part can save several tens of tons of metal. However, any method of cutting steel inevitably generates waste. They are divided into technological and those that appear directly during cutting.

The first type of waste generated as a result of technological processing includes, for example, melting and scale when using gas cutting, chips removed from the surface of the workpiece during turning or milling, and metal filings. This part of the metal will no longer be used in further production.

Cutting waste is formed by that part of the metal that will not be used in a certain method of cutting steel.

Residues are obtained as a result of blank form waste and non-recycling waste. The first is considered to be that part of the metal that is located between the outer contour of one or several workpieces and the contour that limits the dimensions of the workpieces. Non-folding waste is generated when comparing sheet sizes and cutting workpieces. Unused metal residues appear if the dimensions of the sheet do not match the sum of the dimensions of the workpieces located along its sides.

When cutting, it is necessary to take into account the technological methods that will be used to divide the sheet into blanks; the selected cutting option directly depends on them. Thus, when gas cutting and cutting on disk and vibrating shears, any arrangement of workpieces is allowed. But with the guillotine, they should already be positioned so as to provide the possibility of through straight cuts along or across the sheet, or straight cuts at an angle.

The waste that remains during the production of individual parts, as a rule, is carefully sorted both by size and purpose, and then used for the manufacture of other parts.

The largest percentage of its use depends on the correct cutting of sheet material, so specialists choose the most rational of the various possible methods for cutting steel.

If it is necessary to produce large batches of various parts, it is very advisable to use a combined method of cutting rolled sheets, which allows you to cut out others of a smaller size from the waste of one part using the same stamp.

The essence of the combined method is to fit as many different blanks as possible into a minimally sized form.

If there are rectangular parts, it is better to place them with the smaller side along the strip, thus accommodating a larger number of them. This will save material when cutting sheets into strips and thereby increase the productivity of the combined method.

If the cutting efficiency is the same for different arrangements of parts on the strip, then it is better to choose the option with a wider strip.

It is rational to arrange round or polygonal parts in a checkerboard pattern in several rows. Sometimes, due to the high cost of multi-row dies, this method is abandoned, considering it economically unprofitable.

With the dimensional sequence cutting method, the workpieces are placed from largest to smallest.

To determine the cost-effective arrangement of parts with complex configurations, several templates made of thick paper are used. By placing them on a sheet of metal, the highest utilization rate of the material is selected.

Miter cutting is almost never used in various steel cutting methods due to the difficulties encountered in the design and manufacture of dies.

Economical cutting of metal and reduction of waste is an excellent path to highly efficient production and high-quality products.

What it is?

Metal cutting - marking parts on a metal sheet, and not just marking, but placing them with the greatest economy in order to use the sheet with a minimum amount of waste. The less waste, the cheaper the part is. They can be completely avoided only with products of the correct geometric shape; shaped blanks, as a rule, have a large number of uneven lines and curves.

Proper cutting of metal is one of the main ways to reduce the cost of manufacturing a metal product.