Manual felling is superseded by machining on metal-cutting machines (planing, milling), machining with an abrasive tool, and the use of mechanized hand tools and tools.

Handheld power tools include pneumatic and electric chipping hammers. In fig. 77 shows the device pneumatic chipping hammer RM-5 plant "Pneumatic". The hammer consists of a body, striker, spool and handle with a trigger. Compressed air from the shop line through a rubber hose and fitting 1 is supplied to the hammer handle. The locksmith takes the handle with his right hand, holds the barrel with his left, directing the movement of the chisel (Fig. 8, a, 6).

When you press the trigger 3 (see Fig. 77), the valve 2 opens and the air under pressure of 5-6 kgf / cm 2 from the line through the nozzle 7 enters the cylinder. Depending on the position of the spool 4, the air through the channels inside the body enters the chamber of working stroke 5 or into the chamber of reverse stroke 6. In the first case, the air interprets the hammer 7 to the right and it hits the shank of the working tool. At the end of the working stroke, the valve is displaced by air pressure, the air enters chamber 6 — a reverse stroke is performed. Then the cycle of work is repeated. The hammer is put into operation after the tool has been pressed on the surface to be machined.

As a tool for cutting with a pneumatic hammer, special chisels are used. Productivity of cutting with the use of mechanized tools increases 4 - 5 times. In fig. 78, a, 6 shows the operation of a pneumatic hammer.

In electric hammers, the rotation of the motor shaft mounted in the housing is converted into a reciprocating motion of the hammer, at the end of which a chisel or other tool is fixed.

Safety. When cutting metals, the following safety rules should be followed:

the handle of the manual hammer should be well secured and free from cracks;

goggles should be used when chopping with a chisel and cross cutter;

when cutting hard and brittle metal, it is imperative to use fencing: mesh, shield (Fig. 79, a);

to protect your hands from damage (during inconvenient work, as well as during training), you should wear a protective rubber washer on the chisel, and a protective visor on your hand (Fig. 79.6, c).

When working with a pneumatic hammer, you must:

before starting work, blow the pneumatic hammer with compressed air;

turn on the pneumatic tool only after installing the tool in the working position; tool idling is not allowed;

when connecting the hose, compressed air must be disconnected;

do not hold the air hammer by the hose or the working tool.

  Mechanization of metal cutting

TO  category:

Cutting of metal

Mechanization of metal cutting

Manual felling is superseded by machining on metal-cutting machines (planing, milling), machining with an abrasive tool, and the use of mechanized hand tools and tools.

Fig. 1. Processing of wide surfaces by chopping:

Fig. 2. Cutting through the lubrication grooves (a) and grooves (b) a - alignment of the grooves with a chassis grinder, 6 - chopping off the projections with a chisel

Fig. 3. Pneumatic chipping hammer RM-5

Handheld power tools include pneumatic and electric chipping hammers. In fig. 3 shows the device pneumatic chipping hammer RM-5 plant "Pneumatic." The hammer consists of a body, striker, spool and handle with a trigger. Compressed air from the shop line through a rubber hose and fitting goes to the hammer handle. The mechanic takes the right hand for the handle, the left holds the barrel, directing the movement of the chisel.

Pressing the trigger opens the valve and the air under pressure 5 -6. kgf / cm2 from the line through the nozzle enters the cylinder. Depending on the position of the spool, the air through the channels inside the housing enters the working stroke chamber or the return stroke chamber. In the first case, the air pushes the drummer to the right and he hits the shank of the working tool. At the end of the working stroke, the valve is displaced by air pressure, the air enters the chamber - the reverse stroke is performed. Then the cycle of work is repeated. The hammer is put into operation after the tool has been pressed on the surface to be machined.

As a tool for cutting with a pneumatic hammer, special chisels are used. Productivity of cutting with the use of mechanized tools increases 4 -5 times. In fig. 78, a, b shows the operation of a pneumatic hammer.

Fig. 4. Techniques for working with a chipping hammer: a - holding the tool, b-moment of work

Fig. 5. Safety devices used during chopping: a, b - safety covers, c - safety washer

In electric hammers, the rotation of the motor shaft mounted in the housing is converted into a reciprocating motion of the hammer, at the end of which a chisel or other tool is fixed.

Safety.

When cutting metals, the following safety rules should be followed:
   - The handle of the manual hammer should be well secured and free from cracks;
   - when chopping with a chisel and kreysmeysel it is necessary to use protective glasses;
   - when cutting hard and brittle metal, it is imperative to use fencing: mesh, shield;
   - to protect your hands from damage (during inconvenient work, as well as during training), a chisel should be worn on a chisel, and a protective visor should be worn on the hand.

When working with a pneumatic hammer, you must:
  1) before starting work with a pneumatic hammer, study the safety regulations: repeat the general techniques and methods of preparing pneumatic tools;
  2) to wipe the hole in the sleeve and the shank of the chisel; check the position of the sleeve, which should be tightly seated in the hole, and then install a chisel with a tight fit into the sleeve;
  3) blow a pneumatic hammer through with compressed air;
4) pour grease through a special hole in the body of the hammer, pull the trigger and insert grease into the inner working parts through the open hole;
  5) wear gloves and goggles; take working position; take the handle with the right hand, putting the thumb on the trigger, and cover the hammer body with the left hand;
  6) when cutting, set the chisel at an angle of 30 - 35 ° with respect to the surface to be treated. Cutting is carried out only by a sharply ground chisel;
  7) turn on the pneumatic tool only after installing the tool in the working position; tool idling is not allowed,
  8) when connecting the hose, compressed air must be disconnected;
  9) you can not hold a pneumatic hammer for a hose or a working tool;
  10) when transferring a pneumatic hammer, tension, looping and twisting of the hose must not be allowed;
  11) after work is finished, turn off the tap in the pipeline and disconnect the pneumatic hammer from the air line, remove the working tool, clean the hammer from dust, dirt and wipe; rewind the hose thoroughly.

The serviceability of a pneumatic tool is the basis of its high-performance and safe use. It is possible to keep the instrument for a long time and to have it always in working condition only with careful observance of the rules of operation and storage.

First of all, make sure that the tool is in good condition, i.e., check whether all the screws holding the individual components and parts are tightly tightened. Check the air hose; he should not have cracks and punctures. Before attaching the hose to a pneumatic tool, it is thoroughly blown with compressed air to remove dust and dirt, which, getting inside the tool, contribute to its wear. Then check the tool lubrication. The lubricant should not fall on the hose, as it causes damage to it. It is also necessary to check the serviceability of the insert tool (chisel, crosshead, groove, etc.) and the reliability of fixing its shank.

Pneumatic tools need to be held firmly and confidently in their hands. At first, it is recommended to test the instrument in operation, for which it is necessary to turn on the air 2-3 times and turn it off immediately. If the tool does not detect any abnormalities, it can be turned on to perform the required operation. Bending of the hose is not permitted, as this leads to a drop in pressure. We can not allow trolleys or cars to move through the hose, because of this the hose quickly fails. It is not recommended to tighten the hose, as this may lead to a break in the joints.

With continuous hard work, the insertion tool heats up, which can lead to jamming of the shank. Replace heated insert tools with another. For short breaks in operation, the pneumatic tool must be placed in a clean place. With a long break in work, close the air tap on the line, disconnect the tool from the hose, remove the insert tool and return it to the storeroom. Pneumatic tools can only be stored in a dry heated room.

The development of modern technology affects all areas of human activity. Especially actively introduced new methods in mechanical engineering, where every year the requirements for accuracy and quality of processing are increasing. Instead of the usual turning or milling machines used CNC machines, while the manual cutting, which is a time-consuming and complex process, replaces the mechanized.

Modern mechanized ways of cutting metal are a whole complex of operations, the main distinguishing feature of which is the use of a special tool. As a rule, mechanized cutting is performed by chisels equipped with pneumatic and electric drives. The main working tool in them are chisels, both with a narrow and wide blade. Also at large enterprises, mechanized cutting is not complete without special tools and devices, special machine equipment.

The advantages of mechanized logging

Today, using the features of mechanized methods for cutting metals, we can achieve a mass of unique advantages, among which are the following:

1. High cutting speed  metal blanks and chipping finished parts. The productivity of mechanized felling is almost 4-5 times higher than manual.
2. Increased accuracy metal billet in place log. Modern chisels and other tools for mechanized logging have a wear-resistant surface, and the equipment itself ensures the absence of scuffing and other defects.
3. Metal saving. Special equipment for cutting allows you to reduce the amount of waste, thereby reducing the cost of production of parts.
4. Versatility. With the help of mechanized tools and machines you can handle all kinds of metals, ranging from steel to non-ferrous alloys.
5. Security. Thanks to modern technology, the same pneumatic or electric hammers for cutting are as safe as possible for workers, which allows reducing the number of injuries at work.

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Manual chopping is a laborious and inefficient operation. It should be resorted to when it is impossible to apply machine processing (planing, milling, etc.).

For the mechanization of the cutting process using pneumatic or electric chipping hammers; special tools and devices; special machines on which the cutting operation is performed 8-10 times faster than manually.

When cutting, the pneumatic hammer is held with two hands: the right hand for the handle, and the left for the end of the barrel, guiding the chisel along the cutting line (Fig. 100). The hammer should be turned on after the tool has been pressed to the surface to be machined with a cutting edge.

Fig. 100. Chopping with a pneumatic hammer

As a tool for cutting with a pneumatic hammer, special chisels are used. Productivity of cutting with the use of mechanized tools increases 4-5 times.

In electric hammers, the rotation of the motor shaft mounted in the housing is converted into a reciprocating motion of the hammer, at the end of which a chisel or other tool is fixed.

Our industry produces various types of pneumatic chipping hammers. The MP-4 hammer is designed for easy chopping: the number of beats per minute is 3500, the power is 0.54 kW, the stroke of the hammer is 41 mm. MP-5 is used for average cutting: the number of beats per minute is 2200, the power is 0.43 kW, the stroke of the hammer is 71 mm. MP-6 is used for heavy logging: with the number of beats 1600, the stroke of the striker - 106 mm, power - 0.42 kW.

Safety rules

When cutting metals, the following safety precautions should be followed.

1. the handle of the hammer must be well fixed and should not have cracks;
2. when cutting with a chisel and crosshead, the locksmith must use safety glasses;
3. when felling hard and brittle metal, be sure to use fencing: mesh, shield;
4. to protect your hands from damage (during inconvenient work, as well as during training), you should wear a protective rubber washer on the chisel, and a protective visor on your hand.

Questions for self-test

1. How is the chisel and crossbridge for cutting different materials sharpened?
2. List safety instructions for chopping.
3. How does the sharpening angle, rear and front angles affect the cutting process?
4. What mechanized tools are used in your workshop when chopping?

Cutting is called an operation  removal of a layer of material from the workpiece, as well as cutting of the metal (sheet, strip, profile) into parts with cutting tools (chisel, cross-cutter, or groove with a hammer). The accuracy of processing when felling does not exceed 0.7 mm. In modern engineering, the process of cutting metal is resorted to only in cases where the workpiece, for one reason or another, cannot be processed on machine tools. The following works are being chopped down: removal of excess material layers from the surfaces of blanks (chipping of castings, welds, cutting of edges for welding, etc.); chipping of edges and burrs on forged and cast billets; cutting into pieces of sheet material; cutting holes in the sheet material; cutting through lubrication grooves, etc.

The cutting in a vice on a plate or on an anvil is made. Billets of large size when felling is fixed in a chair vice. Chipping castings, welds and tides in large parts is carried out on site. Manual cutting is a very difficult and time-consuming operation, so you need to strive to maximize its mechanization.

Cutting tools

The tools used for cutting are cutting, they are made of carbon tool steels of grades U7, U8, U8A. The hardness of the working part of the cutting tools after heat treatment must be at least HRC 53 ... 56 at a length of 30 mm, and the impact part - HRC 30 ... 35 at a length of 15 mm. The dimensions of cutting tools for cutting depend on the nature of the work performed and are selected from the standard range. Hammers of various sizes and designs are used as a percussion instrument during cutting. Most often, when cutting, use a flat hammer with a round striker of various weights.

The chisel (fig. 2.20) consists of three parts: working, middle, and impact. As with any machining, the cutting part of the tool is a wedge (Fig. 2.20, a).

The action of the wedge-shaped tool on the treated metal varies depending on the position of the wedge and the direction of the force applied to its base. There are two main types of wedge work during chopping:

The axis of the wedge and the direction of the force applied to it are perpendicular to the surface of the workpiece. In this case, the workpiece is cut into pieces (Fig. 2.20, b);

The axis of the wedge and the direction of the force applied to its base form an angle of less than 90 ° with the surface of the workpiece. In this case, chips are removed from the workpiece (Fig. 2.20, c).

The planes bounding the cutting part of the tool (see. Fig. 2.20, c) are called surfaces. The surface on which the chips come off during the cutting process is called the front, and the opposite surface, facing the surface of the workpiece, is called the rear. Their intersection forms the cutting edge of the tool. The angle between the surfaces forming the working part of the tool is called the sharpening angle and is denoted by the Greek letter b (beta). The angle between the front and machined surfaces is called the cutting angle and is denoted by the letter 8 (delta). The angle between the front surface and the plane through the cutting edge perpendicular to the cutting surface is called the front angle and is denoted by the letter y (gamma).

The angle formed by the back and machined surfaces is called the back angle and is denoted by the letter a (alpha).

The smaller the cusp angle of the cutting wedge, the less force must be applied when cutting. However, with a decrease in the cutting angle, the cross-section of the cutting part of the tool also decreases, and consequently, its strength. In this regard, the value of the sharpening angle must be selected taking into account the hardness of the material being processed, which determines the cutting force needed to separate the metal layer from the surface of the workpiece, and the impact force on the tool necessary to create a cutting force.

With an increase in the hardness of the material, it is necessary to increase the tapering angle of the cutting wedge, since the impact force on the tool is large enough and its cross-section should provide the cross-section area necessary for the perception of this force. The values ​​of this angle for various materials are approximately: cast iron and bronze - 70 °; medium hard steel - 60 °; brass, copper - 45 °; aluminum alloys - 35 °.

The back angle a determines the amount of friction between the back surface of the tool and the workpiece surface, its value ranges from 3 to 8. The back angle value is controlled by changing the chisel's tilt relative to the work surface.

Creutzmeisel  (fig. 2.21) differs from the chisel by a narrower cutting edge. Creutzmeisel is used for cutting grooves, cutting keyways and similar works. In order to prevent jamming of the crosshead during operation, its working part has a gradual narrowing from the cutting edge to the handle. The heat treatment of the working and impact parts, as well as the geometrical parameters of the cutting part and the procedure for determining the angles of tapering of the cutting part of the crossbutton are exactly the same as that of the chisel.

Trenchman(Fig. 2.22) is used for cutting out lubricant grooves in liners and bushes of plain bearings and profile grooves for special purposes. The cutting edges of the pan can have a rectilinear or semicircular shape, which is selected depending on the profile of the groove cut through. A fluke differs from a chisel and a crossbridge only in the shape of the working part. The requirements for heat treatment and the choice of sharpening angles for grooves are the same as for chisel and cross-cutter.

Hammers  (Fig. 2.23) are used when felling as a percussion instrument to create cutting forces and there are two types - with a round (Fig. 2.23, a) and square (Fig. 2.23, b) striker. The opposite end of the hammer is called a sock; it has a wedge-shaped shape and is rounded at the end. The hammer is fixed on the handle, which during operation is held in the hand, striking the tool (chisel, crossbody, gutter). For reliable holding the hammer on the handle and preventing it from jumping off during operation, wooden or metal wedges (usually one or two wedges) are used, which are hammered into the handle (Fig. 2.23, c) where it enters the hole of the hammer.

Small billet cutting  (up to 150 mm) of sheet material, wide surfaces of steel and cast iron billets of small size, as well as the cutting of grooves in the bearing shells are performed in a vice.

On the slab or on the anvil, cutting the blanks into pieces or cutting along the contour of the blanks of sheet material. Felling on the slab is used in cases where the workpiece is impossible or difficult to fix in a vice.

In order to give the working part of a chisel, a crutzmeisel or a groove, the necessary angle of sharpening, it is necessary to sharpen it.

Sharpening the cutting tool is carried out on sharpening machines (Fig. 2.24, a). The sharpened tool is installed on the handpiece 3 and with light pressure slowly moves it across the entire width of the grinding wheel. In the process of sharpening the tool is periodically cooled in water.

Sharpening a wedge surface  they alternate between one side and the other, which ensures evenness of sharpening and obtaining the correct sharpening angle of the working part of the tool. The grinding wheel during operation must be closed with a casing 2. Protection of eyes against ingress of abrasive dust is performed using a special protective screen 1 or safety glasses. The control of the taper angle of the cutting tool in the process of sharpening is carried out using a special template (Fig. 2.24, b).