Why it is difficult to cut sheet metal with blunt scissors

Metal cutting faults and work safety

The main reasons of defective cutting are as follows: oblique cutting of metal, failure to comply with the specified dimensions as a result of incorrect marking or cutting not in line, damage to the workpiece being cut because of incorrect clamping in a vice, etc.

When working with a handheld hacksaw, you must clamp the workpiece securely in a vise. The blade in the hacksaw should be stretched not too tight and not too weak. In both cases the possibility of blade breakage and accidental injury of workers increases. At the end of the cut, release the pressure on the hacksaw and support the part to be cut so that it does not fall on the legs.

When cutting thin sheet metal with hand scissors, it is easy to injure your left hand with both the sharp edges of the material being cut and the scissor blades. That’s why the material to be cut should be held with the left hand and a grip on it. Do not use blunt scissors that do not cut as much as crumple the metal. Never use scissors with loosened hinge.

Lever scissors must be provided with a counterweight or other devices to prevent spontaneous lowering of the moving blade.

When cutting metal with a guillotine shears you must carefully control the proper feed of the metal and prevent it from jamming. Install the deflector bar or safety clamp. Foot pedal of guillotine shears must be securely fenced.

When working on circular shears, circular knives must be protected with special shields to prevent the worker’s fingers from getting under the knives.

Band saws must also be guarded except for that part of the band which is involved in the cutting process. High-speed band saws must be equipped with breakage breakers to stop the band in case of a breakage.

Do not touch two live electrodes at the same time when cutting metal in anode-mechanical and electric-spark machines. Work in protective goggles and rubber gloves.

When cutting metal with swarf removal, swarf should be removed with a hairbrush rather than blown away or removed by hand to avoid eye injury or hand trauma.

Before you start cutting machines, please read the safety instructions and strictly follow them while working with this equipment.

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Metal cutting with hand shears is widespread in metalworking and tinsmithing workshops. With the help of shears it is possible to cut very thin sheet and strip material, as well as workpieces of complex configuration.

Cutting sheet and strip metal with scissors is carried out without removing chips. shearing. The essence of the shearing process is the separation of a part of the metal under the pressure of a pair of cutting blades along the mowing line of their direction.

During the operation the plate to be cut is placed between the knives. Upper knife lowers and presses down on metal, pressing it to the lower knife. Both blades press into the metal surface and then break it up with the resulting shear cracks. Angle of sharpening p at the cutting part of scissors varies from 65 ° to 80 °, depending on the hardness of the cut metal; for soft metals (copper, etc.) it is equal to 65 °, for metals of medium hardness. 70-75 °, for hard metals. 80 °. In order to reduce friction of the knives in the process of work, the rear angle a of 2-3° is created on their cutting surfaces.

In order to obtain a clean cut, the correct choice of the gap m between the upper and the lower blade is essential. When the gap is small, the direction of the shear cracks does not match the direction of the shear, and the surface will be rough, “torn”. If the gap is too big, the shearing surface will have a big burr.

The size of the gap between the knives depends on the thickness of the cut metal, but should not be more than 0,5 mm. With handheld shears, this gap is usually no more than 0.1 to 0.2 mm.

In order to decrease effort, consumed at cutting, cutting blades are installed at an angle Ф one to another. The more this angle is, the less the cutting force is. However, a large angle of inclination of the blade increases its travel and creates a force that pushes the sheet from under the blades. Steering by these considerations, angle Ф is accepted equal to 7-12°.

Depending on the device of cutting blades (blades), hand scissors are divided into straight scissors. with straight cutting blades, intended mainly for cutting material along the straight mowing line and along the circle of large radius; curved scissors. with curved cutting blades and finger scissors. with thin and narrow cutting blades, used for cutting holes and surfaces with small radiuses in sheet material.

Hand scissors are subdivided into right-hand and left-hand shears according to cutting blade location. Bevel of lower blade on right side of right shears and bevel on left side of left shears.

Hand shears are made of carbon steel of U7 grade. Blades of scissors are hardened and tempered to hardness HRC 52-60. Cutting edges of scissors must be straight, without cracks and blockages. Length of cutting blades up to rotation axis usually makes up 55 to ПО mm, general length of scissors is 200 to 400 mm. The most used scissors are 250-320 mm long.

Metal cutting with hand scissors.

When cutting manually, the scissors are held with right hand. The thumb is placed on the upper handle of the scissors, and the index, middle and ring fingers grip the lower handle. Keep your little finger between the handles and use it to move the scissors apart as you cut. Some locksmiths prefer to do this with their index finger, but this method is not quite convenient. Use the left hand to feed the sheet of paper, lifting it slightly to make it easier to move the scissors.

Do not open the scissor blades wide during cutting, because when they are open wide the blades will push out instead of cutting through the metal. The scissor blades must be open about 2/3 of their length.

To prevent notches and burrs when moving the scissor blades forward along the marking line, it is necessary that the planes of the blades pressed against the plane of the cut and followed the marking. The cutting edges of the blades must be well sharpened, and the cutting surfaces (planes) must be properly adjusted and secured on the axle. Scissors are usually checked by cutting paper: well sharpened and adjusted scissors should cut paper. The marked sheet must be cut so that the cutting line is in the line of sight. Therefore, cutting sheet metal in a straight line and on a curve (circles and curves) without sharp turns is made with the right scissors.

Cutting a sheet along a curved contour or cutting circular disks is best done with a pair of scissors with curved cutting blades. When cutting out apertures and curved inner contours, it is necessary to chisel a hole in the material for the scissor blades to pass through, and then cut along the line. To cut holes it is better to use finger scissors.

Quality of the cut depends on how well the workpiece is positioned relative to the cutting edges of the scissors. There must be a right angle between the cutting plane and the workpiece, otherwise the scissors will spring and jam the workpiece, the dent will appear on the workpiece and it will be much harder to cut it. Hand scissors can cut sheet and strip steel up to 0,3 mm thick, roofing iron up to 1 mm thick, copper and brass sheets up to 2 mm thick.

Cutting metal with a pair of lever scissors. Manual cutting of metal is also performed with lever shears: chair, flywheel, toothed rack (bar type) and other types.

Unlike manual scissors the chair scissors are made in larger sizes. They have one curved handle with a sharpened end for fastening to a thick board or workbench, and the second, elongated handle for working by hand. Chair scissors are stable in operation and give considerable freedom to the hands of the locksmith. They are used for cutting 2-3 mm thick sheets.

Lever-arm scissors consist of vertical cast iron supports and a metal table.on them a metal table. In the right longitudinal lateral plane of the table the lower cutting blade is fixed the upper blade is mounted on the hand lever, seated on an axle. There is a counterweight at the tail end of the arm to prevent its self-lowering.

Cutting sheet metal on the Type I-37 Lever-arm Shears can be performed according to the marking and stop. For cutting along the marked line a sheet is placed on the table so that the marking risk coincides with the blade of the lower knife. After pressing the sheet against the clamping plate, the lever with the upper blade is moved down firmly and is pressed down until the desired cut length has been reached. When cutting sheet along the stop (without marking) the width of the cut sheet can be adjusted by moving stop bar.

The sheet length which can be cut with the shears can be quite long, because the shears allow moving the sheet along the blades. Length of cutting blades of this type of shears is 1050 mm, angle of blade inclination f=712°, thickness of cut sheet. up to 2.5 mm.

Lever scissors with a toothed rack are used for cutting steel sheets up to 3 mm thick, thin rods and small section metal. They consist of a base frame in the lower part of which a shear blade is fixed. When the lever is lowered, the force transmitted through the toothed overdrive, the shackle and the slide with the blade fixed on it ensures the cutting of metal of permissible cross-sections.

Movement of the slider with the upper knife is carried out with the help of the handle through the toothed gear and the lever.

Lever scissors blades are made of tool steel U8. Knife blades are hardened and tempered to the hardness of HRC 52-60. Angle of sharpening of cutting surfaces of the blades P = 75-t-80°. With a smaller angle of sharpening knives are blunted or cut off quicker; with a larger angle of sharpening they are more durable, but require considerable cutting effort.

Hand-operated bar shears of H-911 and HA-913 models are used for cutting long products of round, square, angle, strip, channel and T-beam sections (Fig. 4,б). These scissors allow cutting steel of different cross-sections: round. 25 mm diameter, square. up to 22X22 mm, strip. 550 mm, angle. 65658 mm and T-joint. 355 mm.

Cutting metal with electric and pneumatic shears. In order to mechanize the relatively heavy and time-consuming process of cutting sheet metal with hand shears, electric and pneumatic hand shears are used. Straight and curved cuts with smallest curvature radius of about 20 mm can be made easily with these scissors, and use a template, which also improves cutting performance considerably.

Domestic industry produces several sizes of electric shears. Thus, electric shears brand I-31 are designed for cutting sheet steel up to 2.7 mm thick. They consist of a housing in which an electric motor rated at 370 W is installed, and a knife head housing. The motor armature rotates the eccentric shaft via a worm pair. The crank arm is seated with the upper head on this roller and the lower head is connected to the upper blade lever pin. The lower blade is mounted on a shackle.

During operation the crank, making reciprocating motion and forcing the blade lever with the upper blade to swing, makes metal cutting. Knife gap is regulated by moving the clamp in the knife head casing. The gap is set depending on the thickness of the metal to be cut. The scissors can be suspended or supported by the upper handle for ease of operation. I-31 electric shears productivity. up to 3 m/min.

At the Kolomna Textile Machinery Plant on the proposal of G.M. Ovchinnikova, the shears were developed and put into operation on the factory’s premises. Е. Electromagnetic vibrating hand shears for cutting thin metal sheets with thickness of 0,5-1,5 mm were produced by Dr. Morgunov Institute of Cybernetics and introduced into production. Cutting shears represent an electromagnet with a coil and an anchor, mounted inside the body on the base. Fixed knife is attached to the same base and movable knife is attached to the axis. The right arm of the blade is fixed to the electromagnet armature with a shackle. A spring presses the blades one against the other.

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Knives are made of U8A steel grade. The electromagnetic shears work on the principle of conventional shears. They are light, compact and easy to work with.

Electromagnetic scissors of VEN model are used for cutting cardboard gaskets.0 Jl design. М. Sytykh and V. А. Ovchinnikova. The principle of their work is similar to that described above. Fixed knife is attached to the coil core, and the movable knife is attached to the vibrating armature. The shears are actuated by pushing on the switch. Change of cutting speed is regulated by screw. They are connected to 220 V mains, and if the coil is designed for 36 V, then the connection is made through a transformer.

Shears have high cutting speed (up to 3 m/min) and low weight of 350 g. Short cutting length of 3 mm in one stroke makes it suitable for cutting gaskets of complex shape.

Pneumatic shears are designed for cutting of sheets up to 1,5 mm thick. They have small dimensions and weight (1.5 kg), so they are convenient to use for metalwork and assembling works and in all cases when it is impossible to use stationary scissors.

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Manual scissors are used for cutting of steel sheet of thickness 0,5. 1,0 mm and of non-ferrous metals up to 1,5 mm. Hand scissors are made with straight and curved cutting blades,

Hand scissors are subdivided into right- and left-handed according to cutting edge location.

Right-handed scissors are scissors with the bevel on the right side of the cutting part of each half. Right-handed scissors cut along the left edge of the piece in a clockwise direction.

difficult, sheet, metal, blunt, scissors

Left-handed scissors are scissors with the bevel on the left side of the cutting part of each half. These scissors cut counterclockwise along the right edge of the piece.

When cutting a sheet with right-handed scissors, you can always see the risk on the metal being cut. When working with left-hand scissors, in order to see the risk, you have to bend the cut metal with your left hand, moving it through the right hand, which is very inconvenient. That’s why straight and curved sheet metal (circles, curves) are cut with the right scissors without any sharp turns.

Hold the scissors in the right hand, wrap four fingers around the handles and press them to the palm; put the little finger between the scissor handles.

Clenched index, ring and middle fingers unclench, straighten the little finger and with its effort move the lower scissor handle to the desired angle. Holding the sheet with the left hand (fig. 2, b), feed it between the cutting edges, directing the upper blade exactly in the middle of the marking line, which should be visible during cutting. Then, squeezing the handle with all fingers of the right hand except for the little finger, perform the cutting.

In Fig. 2, c, d shows the techniques of working with scissors.

For rectilinear cutting of metal of small thicknesses the hand scissors are used, one handle of which is clamped in a vice.

Chair notebooks differ from manual notebooks in their larger size and are used when cutting sheet metal up to 3 mm thick. The lower handle is firmly clamped in a bench vice or nailed (hammered in) to a table or other rigid base. For cutting sheet metal up to 3 mm thick chair scissors with a stationary fixture are used (fig. 3, в).

Chair scissors are inefficient, they require a lot of effort, so they are not used for cutting large amounts of sheet metal.

Hand-held small power note-takers. Novator A. Н. Small-size power scissors were designed by Vasiliev to cut sheet steel up to 2,5 mm thick, rods, bolts (studs) up to 8 mm in diameter. These scissors have the same dimensions as standard hand scissors For cutting the handle is fixed in a vice and the handle (working handle) is actuated. The working handle is a system of two levers connected in series. The first lever, on one arm of which the blade is mounted, is connected to the handle with a screw.

The second arm of the lever, which is the handle in conventional scissors, is made shortened and ends with a hinge, or the scissor handle itself. Handle is connected to the handle with a double-hinge link. This lever system increases the cutting force to about twice that of a conventional scissor of the same size. The scissor blades are replaceable and attached to the levers on countersunk rivets.

These shears also have a cutting attachment for bars up to 8 mm in diameter. The attachment has discs with holes attached to the scissor arms and is an ordinary scissor, but with specially shaped knives (hardened sleeves). These blades are replaceable and can be inserted into the slot of the discs. For cutting screws (saws). there is a thread sleeve on one of the discs, which protects the bolt threads when cutting the saw blades.crush-resistant cuts.

Small-sized power scissors provide good quality of cut.

Lever scissors are used to cut sheet steel up to 4 mm thick, aluminum and brass up to 6 mm thick. The upper hinged knife is lever-operated. The lower blade is stationary.

Blades are made of U8 steel and hardened up to hardness HR.C 52. 60. Angles of sharpening of cutting edges 75-85°.

Before operation check if all rubbing parts are lubricated, if the lever moves smoothly, if there is no gap between cutting edges.

When cutting metal the right hand grips the lever handle and smoothly moves it to the up position with the upper knife 3 moving upwards. Then lay the sheet so that the left hand holds it horizontally and the cutting line is in sight and coincides with the blade of the upper knife. Use your hand to push the lever with the blade downward until part of the metal has been cut, then push the lever upward. Then the sheet 4 is lifted slightly with the left hand, moved along the cutting edge of the upper knife and the cutting method is repeated until a full cut is achieved. The scissors ensure that the cut is free of dents, edge cuts and sufficiently accurate.

Hand scissors are widely used for cutting sheet metal of thickness 1,5-2,5 mm with tensile strength 450. 500 MPa (45. 50 kgf/mm2) (steel, duralumin, etc.). д.). Metal of considerable length can be cut with these scissors. Lever scissors have a cast-iron frame and table, the lower fixed blade is built into the table, and the upper movable blade with a curved cutting edge is fixed in the knife holder. Upper moving blade has counterweight that balances blade holder with blade.

The size of the cut pieces is either pre-marked or limited by an adjustable stop, for which the stop is first set at the desired distance from the cutting edge of the lower fixed blade. During cutting, the sheet is pressed firmly with the side edge against the stop and the other edge against the spring stop. After that, turning the handle away from yourself the sheet is pressed tightly on top of the pressure bar and, lowering the top nose with a knife-holder 6, cut the workpiece.

The knife holder rests against the spring stop when lowered. The stop is repositioned by means of a handle.

Shears with angled (guillotine) knives allow to cut sheet metal with thickness up to 32 mm, sheets with dimensions of 1000. 3200 mm, less often strip, as well as non-metallic sheet materials.

Why is it difficult to cut sheet metal with blunt scissors?

Cutting thin sheet metal with scissors

Thin sheet metal can be cut with special scissors.

Hand scissors consist of two halves. Each half is made as one unit and combines the blade and handle. The halves are screwed together. Hand scissors are subdivided in accordance to position of cutting blades into left-handed (fig. left (a) and right (fig. left b). When viewed from the knife side, the left-hand scissors have the upper knife on the left-hand side, the right-hand scissors on the right-hand side.

Cutting blunt shears are shaped like straight ones (fig. right a-d) and curved scissors (e).

Lever-arm scissors are used to reduce the effort required to cut through tough material (see “Lever-arm scissors”).fig. left).

Cutting edges of knives must be well sharpened, and cutting planes must adjoin tightly to each other and be well fixed with a screw.You can check the quality of scissors sharpening by how good or bad they cut paper.

Thin sheet metal can be cut in two ways. The first way. the scissors are taken with the right hand. The thumb is placed on the upper handle, and the index, middle, and ring fingers are placed on the lower handle. the little finger is placed between the handles: when cutting, it moves the handles of the scissors apart (see “Plunge cut”).Figure. on the right). If the handles of the scissors are tight, you can use your index finger instead of your little finger. In this case it is placed between the handles of the shears.

The second way of cutting thin sheet metal is to clamp one handle of the scissors (the one at the bottom) in a vice, and hold the other handle with the fingers of your right hand (see the.figure. on the left). The material is fed with the left hand in both cases. This method makes it possible to significantly increase the pressure between the knives and to cut harder material. the workpiece is slightly lifted and fed toward you, and the blade is guided precisely along the mark.

After cutting, the workpiece is straightened, burrs are removed from the edges, sharp corners are blunted and the quality of cutting is checked with a ruler and square.

The methods of cutting a sheet of metal with scissors along a straight line are somewhat different from those of cutting along a circle or other curve, but in any case it is necessary that the cutting line is always visible in the process of cutting.

When cutting along the curve of the mowing line (see.Fig. The trailer is made for the right side of the shears, which creates difficulties in the advancement of the shears, because in the place of curvature the cut part of the metal is curved worse and interferes with the work of the shears.

To avoid this when cutting, for example, a circle from a square sheet of tin, the corners are first cut in straight lines, and then the circle is cut out by cutting a short strip of tin (see Fig.Figure. left).

Do not open the scissors fully, but open them just enough so that they grip the sheet. If you open the shears too wide you will have to push the sheet out instead of cutting it.

When cutting thin sheet metal with scissors the cut part is curved strongly and the edges of the sheet are very sharp at the place of cut. That’s why it is necessary to put on mittens on your left hand, which supports the sheet.The left hand should not be on the cutting line. When cutting a sheet of sheet metal over a long cut line, the knives must not be fully squeezed, as this can cause cracks or even tearing of the edges of the material on the cut line.Clamping of scissors in a vice must be firm and reliable, because it is possible to hurt your hands on the jaws of the vice if they break.Do not touch the cut edges of the workpiece with your bare hands.Feed the scissors with the handles away from you, and put them in reverse.

In factories thin sheet metal is cut on special shearing machines. There is a difference between mechanical scissors. guillotine and circular shears.

Guillotine shears come in two types: parallel and inclined. The former have their blades parallel to each other, the latter have them at a slight angle.

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In circular scissors, sheet metal is cut by the sharp edges of the rotating discs (see the “Circular scissors”).Fig. left).

For shape cutting cutters are used, the upper blade of which is rotated around its axis, while the lower one is stationary.Fig. right).

Workpieces are cut at the factory by metal cutters. They must have a good knowledge of the properties of various metals and the construction of industrial shears, and be able to mark up workpieces.

Recently, metal cutting by laser beam, high-pressure water jet have become widespread in production. These methods are highly productive and precise.

Metal cutting with hand tools and cutting machines

As you know, metal can be cut with hand tools and machines.

Depending on the material and size of the workpiece, a distinction is made between metal cutting without chip removal (shearing) with scissors, wire cutters and chip removal.

a cutting; b curved cutting; c cutting; d hole cutting.

All other methods connected with metal layer removal (chopping, sawing, cutting with a hacksaw, drilling, turning, milling, planing), performed both with hand tools and on machines, are cutting with chip removal.

  • What are the ways of metal cutting?
  • What kinds of work can be carried out with a pair of scissors??
  • Which tools are used for chip removal cutting??

Cutting sheet metal with hand shears

It is possible to cut sheet metal into separate parts, to cut holes in parts, to make parts with curved contours, and to perform other similar works with hand shears. Depending on location of the cutting edge of the scissor blade (to the right or to the left of the lower blade) they are called right-handed (Fig. 47, a) or left (Fig. 47, б). Hand scissors are made with straight (fig. 47, a, b) and curved (Fig. 47, c) cutting blades.

Hand scissors with straight cutting blades are used to cut sheets, strips and strips of steel up to 0.7 mm thick and non-ferrous metals up to 1.5 mm thick in straight lines. Scissors with curved cutting blades are used when cutting sheets, strips and bands from steel with thickness up to 0,6 mm, and from non-ferrous metals with thickness up to 1,2 mm along curved lines or when cutting details with combination of curved and straight lines.

GOST 7210-54 Hand scissors are made in lengths of 200, 250, 320 and 400 mm, in which case the width of the outer edge of the handles in closed state correspondingly to total length is 40, 40, 50, 55 mm.

Scissors consist of two halves, which are manufactured as one-piece or compound with welding blades. Solid halves of scissors are made of carbon steel 65, 70. Handles of welded scissors are made of carbon steel of Sta grade or higher. 2, and blades. from tool carbon steel U7 with heat treating them to hardness of HRC 52-58. The cutting edges of the blades are sharpened at an angle of 70-75° (fig. 47,(3). Blades and surfaces of scissors must be free of burrs, wrenches, burrs, cavities, hairs, nicks and cracks.

Blades of scissors in closed state shall overlap mutually, and overlap at the ends shall not exceed 2 mm. Both halves must be connected by a screw and nut and ensure a tight fit of the halves without warping or backlash. The scissors must cut with any part of the cutting edges; their WHEEL should move smoothly without jolting.

In Fig. 47, d shows hand scissors that differ from conventional scissors in the shape of the blades. The lower blade is straight upper one is bent toward the cutting edge. The bottom knife is equipped with a special flanging, thanks to which the cut part of the sheet is bent and the scissors freely pass along the scythe line of the marking along the whole cut sheet. Due to the shape of the blades, less effort is required to cut with these shears. These scissors have handles at a 30° angle to the cutting plane, which eliminates the possibility of hand cuts. sheet metal is cut in half as fast with these scissors as with standard hand scissors.

Sheet metal is cut with hand scissors, as a rule, according to marking lines that are pre-drawn on the surface of the sheet metal.

When cutting sheets into wide strips, bend away the cut strips with your left hand without making any sharp bends (fig. 48, а). This will make it easier for the scissors to move while cutting and protect the right hand from being cut.

When cutting a sheet with left-handed scissors (fig. 48, b) on narrow workpieces make sure they bend forward.

When cutting sheet metal along a curved contour, e.g. when cutting a circle with left-hand scissors, cut in the clockwise direction, positioning the scissors so that they do not cover the cutting line’s blade with the marking (Fig. 48,в).

Parts with curved outlines are cut with the right scissors counterclockwise (Fig. 48, г).

When cutting, open the scissors to about 2/3 of the blade length, so that they could grasp the metal well and cut without much effort. The strongly opened blades do not cut, but thrust the metal out.

Make sure that the cutting plane is perpendicular to the sheet to be cut, because tilting of the scissor leads to metal crumpling on the cut edge, jams and burrs formation.

When moving the scissors forward, they are pressed tightly against the end of the cut, otherwise burrs are inevitable. Cut holes in the parts with curved cutting blades (Fig. 48, д).

Cutting with hand scissors

Hand scissors cut thin sheet material: steel 0.5. 0.7 mm, roofing iron, non-ferrous metals up to 1.5 mm thick. The scissors have two short blades (knives) and two long handles. Both parts of the scissors are hinged together. Scissors length varies from 200 to 400 mm.

Cutting sheet and strip metal with scissors is performed without chip removal by plastic deformation method. The essence of this process is to separate part of the metal under pressure of a pair of cutting knives along the mowing line of their direction (Fig. 7.7). Both blades press into the surface of the metal and then cut it apart. In order to obtain a clean cut, the gap between the upper and the lower blade must be correctly set. A small gap will cause a rough, “torn” cut surface. With a large clearance, the cutting surface will have more burrs. The size of the gap between the blades depends on the thickness of the metal being cut. In hand scissors, this clearance is usually less than 0.1. 0,8 mm.

Fig. 7.7. The process of cutting with scissors

In cross-section the cutting part of the scissors has a wedge shape with an angle of sharpening ?3 = 70° (Fig. 7.8). A large angle of sharpening is taken so that when cutting the blades do not chip out. To reduce friction, rear angle os take equal to 1. 2°.

Fig. 7.8. Hand shears:

а. right; б. left; в. with a curved cutting blade

From the equality of a ?3 y= 90°, the value of the rake angle y varies from 18 to 19°. The blades of the cutter blades must be straight and sharpened.

Hand scissors are made with straight (fig. 7.8, a, b) and curvilinear (fig. 7.8, в) cutting blades.

Hand scissors can be right-handed and left-handed according to the cutting edge. Right are called scissors which have the bevel on the lower blade on the right side during cutting, left. scissors with the bevel on the left side. Right-handed scissors cut along the left edge of the piece in clockwise direction (fig. 7.9, а), and left-handed scissors. along the right edge of the piece counterclockwise (fig. 7.9, б). The right scissors are mostly used, because the marking risk is always visible when cutting.

When cutting, the scissors are held in the right hand (fig. 7.10). The thumb is placed on the upper handle, three fingers wrap around the lower handle, and the index finger or little finger is placed between the handles (to spread them apart).

Fig. 7.9. Cutting techniques with scissors: а. right grip; б. left

The least cutting force will be when the material is pushed deeper into the shed of the scissor blade. However, with a large opening of the blades, the horizontal component of the cutting force (Fig. 7.11) increases so much that the scissors don’t cut, but push out the metal. At an opening angle of about 30°, the frictional forces and the force of the left hand of the worker can counteract the ejection force. This angle should be considered the most favorable for cutting metals with hand shears. Scissors set perpendicular to the surface to be cut (otherwise they will crumple the metal) and move along the marking line, firmly pressed against the kerf. To keep the strip of metal being cut out of the way, it is bent out of shape. Only ductile metals and alloys are cut with scissors. Sheet metal up to 2 mm thick can be cut with hand shears as shown in Fig. 7.12. Scissors lower handle is fixed in a bench vice, the left hand feeds the workpiece in the blade slot, and the right hand creates the cutting force and unclamping scissors. Do not hit the top handle with a hammer, as this may cause the shears to break.

Fig. 7.11. Schematic of the cutting forces with scissors

Fig. 7.12. Cutting with scissors in a bench vice

For cutting sheet steel up to 2.5 mm thick use power scissors (Fig. 7.13). When working, the handle 8 (with notch) is clamped in a vise, and the handle 1 (the working one with a plastic tip) is gripped with the right hand. Work handle 1 is a system of two arms connected in series. First lever 3 ends with a knife 5 and connected with a twist 6 through a washer 4 with the handle 8. This lever system increases the cutting force to about twice that of a conventional scissor of the same dimensions. Scissor blades are replaceable and fixed on levers by countersunk rivets. These scissors have a special device for cutting bars up to 8 mm in diameter.

1,8. handle; 2,7. levers with spring ; 3. lever; 4. washer; 5. cutting blade; 6. screw

For cutting metal with thickness up to 2 mm use chair scissors. clamp the lower handle in a parallel bench vice (fig. 7.14) or fixed on a table or other rigid base. These scissors are low-productive, requiring considerable effort when working, so they are used for cutting small batches of parts.

Rice. 7.14. Cutting with chair shears

For cutting sheet metal up to 4 mm thick use the lever scissors (fig. 7.15). Bottom blade 1, Sharpened at an angle of 90°, fixed on the base of the shears rigidly. Top knife 3 the curved blade is moved with a lever 2. Metal to be cut 4 place it on the lower blade so that the marking line is positioned under the upper blade. Downward movement of the lever causes the sheet to be cut. The lever is then withdrawn, the workpiece is moved along the marking and the process is repeated many times until it is completely cut.

In Fig. 1.Figure 11 shows another lever scissor design for cutting sheet metal, round rods, and metal angles with dimensions of 35 x 35 x 5 mm. Their construction and operating methods are described in § 1.2.

For cutting pipes without removing chips, the pipe cutters. Cutting with a pipe cutter is more productive than with hacksaws. Pipe cutters are made in three sizes:. 2, 3 for cutting of pipes of 1/4 diameter respectively. 3/4″, 1. 2,5″ и 3. 4″. Three-roller pipe saw (fig. 7.16) has two sharpened cutting discs (rollers) 2, mounted on fixed

axis in the body 1, and a movable roller 4, installed in the movable jaw 5. The pipe is clamped in the pipe clamp 3. The pipe cutter is put on it and by turning the screw 6, press a roller into the metal. Spin pipe cutter around the pipe and cut along the marking, periodically pressing roller. The place of cutting is lubricated with machine oil.

Manual metal cutting

In metalwork and tin fitting shops widespread use of the Metal cutting with hand shears (fig. 11.49). It is possible to cut very thin sheet and strip material, as well as workpieces of complex configuration with the help of scissors.

Cutting of sheet and strip metal with shears is performed without removing chips. by shearing. The essence of the process shear cutting consists in separating a part of the metal under the pressure of a pair of cutting knives along the mowing line of their direction.

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In the process of work the cut sheet 2 (fig. 11.49, а) is placed between the knives 1 и 3. The upper blade lowers and presses the metal against the lower blade. Both blades crush the surface of the metal by indenting and then break it up by the resulting shear cracks. Angle of sharpening (3) of the cutting part of the scissors varies from 65° to 80° depending on the hardness of the cut metal; for soft metals (copper, etc.) the angle of sharpening is 80°.) it is 65°, for metals of medium hardness. 70. 75°, for hard metals. 80°. In order to reduce friction of the knives in the process of work, a back angle a of 2 is created on their cutting surfaces. 3°.

In order to obtain a clean cut, it is necessary to choose the right gap т between upper and lower knives (Fig. 11.49, б). With a small gap, the direction of shear cracks does not coincide with the direction of the cut and its surface will be rough, “torn”. With a larger clearance, the cutting surface will have a larger burr.

The size of the gap between the knives depends on the thickness of the cut metal, but should not be more than 0.5 mm. With hand shears, this gap is usually less than 0.1. 0.2 mm.

To reduce the power required for cutting, the cutting blades are installed at an angle Ф one to the other (Fig. 11.49, а). The larger this angle, the lower the cutting force. A larger blade angle, however, increases blade travel and creates a force that pushes the sheet out from under the blades. Guided by these considerations, the angle f is taken equal to 7. 12°.

Depending on the device of the cutting knives (blades), hand shears are divided into straight shears (Fig. 11.50, а). with straight cutting blades, designed mainly for cutting material in a straight mowing line and on a circle of a large radius; scissors

curves. with curved cutting blades (fig. 11.50, б, в) и finger scissors with thin and narrow cutting blades (Fig. 11.50, г), used for cutting small radius holes and surfaces in sheet material.

According to the arrangement of the cutting blades, hand shears are divided into right-hand and left-hand. У right-handed scissors the bevel of the cutting part of the lower blade is on the right-hand side, and on the left-hand side the left-hand. left side.

Hand scissors according to GOST 7210-59 are made of 45, 65 and 70. Scissor blades are hardened and tempered to hardness HRC 52. 58. Cutting edges of scissors must be straight, without cracks and blockages. Length of cutting blades up to rotation axis is usually from 55 to 130 mm, total length of scissors. from 200 to 400 mm. The most common scissors with a length of 250 m and a length of 50 m are. 320 mm.

When cutting manually, the scissors are held with the right hand. Place your thumb on the top handle of the scissors (fig. 11.51, o), and use your index, middle, and ring fingers to grasp the lower-

While cutting you should not open the scissor blades to a large angle, as with a large opening the blades will push out, but not cut the metal. The scissor blades should be open about 2/3 of their length.

In order to prevent notches and burrs when moving scissor blades forward along the marking line it is necessary that the planes of blades pressed to the cutting plane and follow the marking. The cutting edges of the blades must be well sharpened, and the cutting surfaces (planes) must be properly adjusted and secured on the axle. Scissors are usually checked by cutting paper: well sharpened and adjusted scissors must cut through paper. The marked sheet should be cut in such a way that the marker is in the field of view. Therefore, cutting sheet metal in a straight line mowing line and along the curve (circles and roundings) without sharp turns is made with the right scissors (Fig. 11.52, a, b, d).

It is most convenient to cut a sheet along a curved contour or to cut a circular disk with a pair of curved cutting blades. When cutting out bores and curved contours inside the material, it is necessary to chisel a hole in the material for the scissor blades to pass through, and then cut along the line (fig. 11.52, c, e). Finger scissors are better for cutting out holes.

The quality of the cut depends on how properly the workpiece is positioned relative to the cutting edges of the scissors. There must be a right angle between the cutting plane and the workpiece, otherwise the scissors will spring and jam the workpiece, an indentation will appear on the workpiece and it will be much harder to cut it. Sheet and strip steel up to 0,8 mm thick, roofing iron up to 1 mm thick, copper and brass sheet up to 2 mm thick can be cut with hand scissors.

Manual cutting the metal is also made on lever scissorsChair scissors, hand scissors, toothed rack and other types of scissors.

Chair scissors (fig. 11.53, а) unlike manual scissors are made of large size. They have one curved handle with a sharpened end for fastening to a thick board or workbench, and a second, elongated handle for working by hand. Stool scissors sturdy-

Lever arms hand scissors (fig. 11.53, б)are made up of vertical cast iron columns 1 and the metal table mounted on them 2. In the right longitudinal lateral plane of the table the lower cutting knife is fixed 9upper knife 5 is mounted on flywheel 4, seated on axle 7. There is a counterweight mounted on the tail end of the arm to prevent automatic lowering 6.

Cutting sheet metal on the lever-arm scissors of I-37 type can be performed according to marking and stop. To cut by marking, the sheet is placed on the table so that the marking risk coincides with the blade of the bottom knife. After pressing a sheet with a clamping plate 3, lower the lever with the upper blade with violent movement and “press” it until the required part of the sheet is cut. When cutting along the stop (without marking) the width of the strip to be cut is adjusted by the adjustable stop bar 8.

The sheet length the shears can cut can be quite long as they allow movement of the sheet along the blades. Length of cutting blades of this type of shears is 1050 mm, angle of inclination of blades is 1. 12°, thickness of cut sheet up to 2.5 mm.

Lever scissors toothed shears are used to cut sheet metal up to 3 mm thick, thin rods and small section metal. They consist of a base frame with a fixed blade on the underside. When lowering the lever, the force transmitted through the gear, the shackle and the slide with the blade fixed on it, ensures the cutting of metal of the allowed cross-sections. Knives for lever shears are made of tool steel U8. Blades of knives are hardened, then tempered to hardness HRC 52. 60. Corner angles of the cutting surfaces of knives p = 75. 80°. Smaller sharpening angles blunt or shear out more quickly, larger ones are more durable but require more cutting force.

For cutting bar stock of round, square, angular, strip, channel and T-beam sections use manual section shears models Н-911 and НА-913 (fig. 11.53, в). These scissors allow you to cut steel of various sections: round. 25 mm diameter, square up to 22 x 22 mm, strip 5 x 50 mm, angle 65 x 65 x 8 mm and T-beam 35 x 5 mm. The movement of the slider with the upper blade is carried out by means of a handle through a toothed gear and a lever.

Exercise 1.Metal cutting with hand shears

Take the scissors in your right hand, place your thumb on the upper handle of the scissors, with your index, middle and ring fingers grasp the lower handle from below, and place your little finger between the scissor handles (it serves to move them apart during the cutting) and spread the scissor blades about on ¾ their length; with the left hand take the metal sheet to be cut and put it between the scissor blades so that it is perpendicular to them; when squeezing the scissor handles during cutting take care that the blades do not converge completely, because it causes tearing of the metal at the end of the cut; when opening the scissor move the sheet “toward you” gently hold the sheet with the left hand to avoid cutting your hands on the sharp edges it is recommended to wear mittens

Mark a circle and cut a circle piece with a straight cut with an allowance of 5-6 mm.

Rotating the workpiece clockwise, cut a circle on the scythe line of the marking, positioning the scissors so that they do not cover the lines of the marking with their blade

Observe all the rules mentioned above when cutting the circle.

Exercise 2.Cutting metal with a pair of lever scissors

Cut a sheet of metal with a pair of lever scissors.

Note. Lever scissors cut sheet metal from 1.0 to 2.5 mm thick and only cut in a straight line.

Remove the locking pin and raise the lever to the up position.

Insert the sheet to be cut between the blades so that the line of the marking converges exactly against the edge of the top of its blade and the sheet is perpendicular to the blade.

Hold the sheet vertically with your hand and use your right hand to lower the lever down without allowing the blades to completely compress 4 to 5 mm.

Raise the lever up, push the plate to be cut “away from you” and continue cutting all the way through.

Observe the following work safety rules:

Hold the sheet carefully with your left hand to avoid cutting your hands on the sharp edges (use mittens recommended).

Finish the cut with gentle pressure on the lever.

After the cut, secure the lever arm with the locking pin in the down position.

Exercise 3.Cutting metal with electric vibrating shears

Cut the sheet metal with the electric scissors.

difficult, sheet, metal, blunt, scissors

Connect the lead wire to the mains and, by pressing the button on the handle, check the operation of the electric vibrating shears at idle speed.

Hold the scissors by the handle with your right hand and bring the blades to the mowing line of the cut.

Start the motor and make cuts as per the marks by sliding the electric shears forward.

Strictly obey the rules of electrical safety while working ,

Checklists for instruction card 10

“Cutting metal with scissors”

How to organize your workstation when cutting sheet metal with scissors?

2.How thick sheet metal can be cut:

3.How to cut sheet metal in a straight line with hand scissors?

4.Why do hand scissors sometimes “crumple” metal when cutting sheet metal rather than cut it?? How to avoid it?

5.Why it is not advisable to move the scissor blades completely when cutting sheet metal?

6.Is the cutting force when cutting metal with hand scissors the same?

How to cut a circle out of sheet metal with hand scissors?

STOP DOING THIS WRONG! How To Use Aviation Snips The RIGHT WAY

8.How to cut sheet metal with lever scissors?

How to cut sheet metal with electromagnetic shears?

What safety rules should be observed when cutting sheet metal:

BUDGETARY PROFESSIONAL EDUCATIONAL INSTITUTION OF THE ORYOL REGION

“ORYOL TECHNICAL COLLEGE OF AGRIBUSINESS AND SERVICE”

The cycle methodical deputy director for educational work. director for educational work

the commission _ Pavlikova L.Н.

Minutes № “_” _2012015

Instruction card 1 for MKT:

“Locksmithing and technical measurements.”

mastering of the working position while filing.

Mastering of the working movements for filing.

Tools: flat blunt-nose files with a notch and 2 250-300 mm long.

Fixtures: Parallel vise, training devices or channel.

Date of addition: 2018-06-27 ; views: 1492 ; We will help in writing your paper!