Shears for metal: working principle, characteristics, types

Scissors as driven and non-driven - grade separation equipment for metal forming.

They take their place in the park harvesting machinery engineering and metalworking industries, are widely used in construction.

Shears for metal used rescuers and small models of aggregates of data are available, even in home workshops. Portable Scissors are used for exterior use: fit the fence fragments of profiled sheeting, construction of steel roofing, etc.

The principle of operation and the function of scissors for metal

By dividing operations forming include:

• cutting - metal separation at open circuit, with the original and the workpiece is a sheet metal profile: channel bars, rods, tubes, etc.
• Nadrezka - A process comprising partial separation of one part from another blank. It is used if necessary forming the holes with a volumetric configuration integral sheet metal.
• cutting - separation operation preformed metal cards into two parts.
• punching - separating a portion of a metal blank from its rest part, wherein the detachable portion is a waste (at large amounts of waste it is used as a single-piece blank for the subsequent production of smaller parts sizes).
• Otrubka - the separation of bulk workpieces by introducing into them a wedge-shaped tool. V-blades often used when cutting pipes.
• felling - separating a portion of a metal blank from its rest part, wherein the detachable portion is a part.
• Punching or perforating - successive shaping of small holes having the same configuration in the strand (the tape roll, at least - band).

Some of these technological transitions are implemented and specialized stamping equipment - presses or machines, but in this case required the production of special stamps.

However, in the above situation requires stamps - a tool that includes at least two mandatory parts: core and cavity.

Stamps are not universal tooling (except group bystroperenalazhivaemyh stamps for group piecemeal or punching), and therefore their use negatively affects the final cost products. Especially if production - small series or single.

Therefore, modern design under consideration units are focused on maximum diversity of operations carried out by them dividing. It is believed that a tool for metal separation operations on scissors - knives - are easier to manufacture, commissioning and maintenance.

The sequence of separation of the metal to the cutter

Separation of metals into separate fragments by means of forming equipment is made only for a relatively ductile materials.

This parameter determines the power characteristics of the cutting process and the quality of the workpiece surface after separation.

When the deep cracks chipping quality cutting impossible or require special techniques that complicate maintenance of the separation equipment. This applies cutting- stockpiling facilities.

For various metals and alloys of the relative values ​​of introduction, depending on the thickness or diameter of the initial billet shown in the following table:

Metal / alloy	εmax, %
The deformable aluminum brand AD1	18…20
copper M1	13…14
Steels with a low content of carbon, tin	20…22
medium carbon steel	18…20
high-carbon steel	16…18
Alloy and stainless steels	14…16
ductility brass	19…21
Leaded brass, silicon bronze	12…14

Cutting of metals and alloys with εmax indicator relative ductility less than 11%, is not recommended in the usual scissors. The deformability of metals and alloys deteriorates with increasing percentage content of alloying elements and impurities: manganese, silicon, zinc, sulfur and carbon.

For maloplastichnyh steels or steels c increased hardness cold cutting to the desired quality can not therefore necessary to preheat the initial rolling to temperatures of 500... 600₀C. introducing into the heating apparatus equipment. Separation of metal is sequentially passing the following steps:

• surface collapse, during which the metal is pressed under the influence of the deformation effort. More split the workpiece does not occur, because the specific force does not exceed the shear strength of the metal.
• Implementations of the knife blank into a shared in which cutting begins.
• Cracking spalling, which is caused by the emergence of a metal workpiece of stress raisers. Cracks occur simultaneously on both surfaces, the propagation of which occurs on the shortest path to each other.
• Brittle workpiece along the surface of contact with the knives. During this phase separation does not operate knives and pushing a cut portion of the workpiece into the nip between the moving and the fixed tool.

A dramatic shift - the best option separation of materials with different indices of ductility. Conditions for the occurrence of shear deformations aimed specifically created in the construction of the separation instrument. In the separation zone are created compressive stresses.The surface of the cut blanks composed of the following zones:

• crumple zonesWhich visually manifested as sink marks on both sides of the deformable preform. Sink Mark - an unavoidable factor of cutting ductile metals and alloys. For high-speed equipment (pulse machines) it is due to inertia of the material being cut, is not present;
• shear zone ( "Brilliant girdle"), which dimensions are determined by the metal portion of the plastic deformation. With an increase in the area of ​​the brilliant cut surface of the girdle quality increases. The zone has the form of a crescent, and easily recognized by visual inspection of the workpiece;
• Zone brittleWhich starts from the cut zone by the movable knife and from the crumple zones - the part fixed. The macrostructure of this zone - is rough, since the metal fracture occurs in an uncontrolled manner at grain boundaries of its structure. By increasing the brittle fracture zone size cut surface quality deteriorates.

They are caused by errors in the cutting, blunting the cutting edges of the tool, as well as failure to comply with conditions for good separation of metals. How to use a pair of scissors for metalBefore the start of main sections at the shears (especially for bulk metal of - rods, wire, tubular blanks) is considered the establishment of proper gap dimensions: mechanical z_t and axial z_o.End (tangential) clearance is the distance between the working plane of the knives to be cut and the end of the workpiece in a direction perpendicular to the moving blade stroke.Axial (radial) gap is the distance between the working plane of the knives to be cut and the end of the workpiece in a direction parallel to the direction of travel of the movable knife. Its increase over and above the required value, adversely affects the quality of cut: crumple zones are formed, and for the rods and wire - and still further ovality final profile. The size of the end gap is determined by the quality of the original metal of (for hot metal value z_t always have to be increased), the state of the cutting edges of the tool setup characteristics, and the curvilinearity of cut sheet or rod. In processes that require special quality metal separation tip clearance is reduced using special technologies - cut-back bar, transverse compression of the workpiece separation roller blades and so forth.Appointment of radial clearance - reduction of the friction of the movable knife fixed blade, and prevent jamming of the tool during cutting. When optimum values ​​of the axial gap cleavage surface area decreases, and the cut surface, on the contrary, increased. Axial clearance is set before cutting, depending on the brand of metal, its plasticity, the cross-sectional dimensions and speed of movement of the movable knife.For constant values ​​of the axial clearance (for cutting long bars) using a shaped grinding tool or a workpiece at an angle of 3... 60 relative to the feed axis of the bar in the working zone equipment.The slope of the bar:

• It reduces the size of the cleaved zone;
• It reduces the force at the beginning of the introduction of the movable blade in the metal;
• Evenly wears knives.

It plays a special role in the inclination angle of the tubular cutting processes rolled. Minimum collapse after cutting the tubular blank is marked in those cases where the sharpening angle of the wedge knife edge is within ± 5 20.Vidy and purpose scissors metalAre classified according to the following criteria:Drive mind. Distinguish equipment manual (lever), or motorized drive. The latter, in turn, is a pneumatic, electromechanical and hydraulic.For technological purposes. Shears which cut the sheet metal, called leaf (there is an everyday name such units - "guillotine"). Cutting rods and wire are varietal.

By Application highlight key stockpiling equipment (it includes all of the above types of equipment), as well as accessories: skrapovye and alligator shears. They are used for cutting and processing of scrap metal on Vtorchermet enterprises.According to the degree of mechanization distinguish equipment with manual feed raw blanks and removal of the cut products, with automatic feed. In large plants are stockpiling systems operating with continuous rolled metal - roll or ribbon. Recent designs for longitudinal and cross-dissolve the roll, and are used mainly in the procurement departments of cold-stamping production.By type of actuator Scissors are the crank (the performance of the main mechanism pulling or pushing rods), lever and disc. The latter are used for slitting the roll on the tape. They are divided into single-disc and multi-disc.By type of cutting line: A straight line or a complex configuration (nibbling) .Parametry commercially available shears governed by the requirements of the relevant standards:

• Crank sheet with a canted cutter - GOST 6282,
• varietal - GOST 8248,
• Alligator - GOST 15032,
• Disc - GOST 8249,
• Hydraulic - GOST 12.2.118,
• Nibblers - GOST 16829,
• Combined - GOST 7355.

The choice of equipment is the size of the cross-section of metal to be cut. It is assumed, that the ultimate strength of the metal is 500 MPa (required to perform recalculation for other indicators). High-quality scissors are distinguished by the nominal force on the slide.For cutting the sheet using the cutting scheme, wherein the movable blade has a bevel 3... 6⁰But not more than the friction angle, i.e., 9⁰. That is why this equipment is called a scissors with raking knife. The design of such tool harder than knives with parallel cutting edges, but in this case the introduction of the tool into the metal takes place gradually. As a result of a suit deformation force is reduced. Reduced power consumption and operation, however less electric power installed for the drive. Cutting blades with parallel cutting edges has become popular in the schemes equipment that is designed for cutting narrow and thick strips of metals and alloys with low plasticity. At the initial instant of cutting, when introducing a metal knife, there occur reactions deformation resistance. This is expressed in the overturning and / or rotating portion of the preform under load. Therefore, in the structures necessarily present technique considered pressing mechanism. It has a mechanical (spring, for the thin sheet) or a hydraulic drive.

This is due to the need to reduce the inertia in the drive. Crank scissors with raking knife made with top or bottom drive. The first option is used in equipment designed for cutting sheets and wide strips of 3.15 mm thick. The units are compact, and the kinematics of their action determines high quality of the cut surface. In other cases the top drive.A typical design of such equipment includes the following components:

• Motor.
• V-belt transmission.
• Flywheel.
• Foster shaft.
• Gear (usually - open) transmission.
• switching system.
• The main shaft with two eccentrics or cranks.
• The blade beam.
• Backgauge.
• The front stop.
• Clamp.
• Desktop.
• lubrication system.
• Control block.
• The machine frame.
• Rail truck to collect the cut strips.

How it works: the torque from the electric motor (asynchronous motors are used in the designs of scissors AC squirrel cage) is transmitted through the V-belt transmission Foster shaft on which mounted flywheel.

As a result, the load on the actuator is reduced. When the motor is switched on and the brake flywheel rotates freely in the main bearings of the receiving shaft. Before switching on the equipment working stroke of the metal sheet to be cutting, it is set in the workspace. To do this manually or by means of the conveyor (automated complexes on the basis of the scissors) sheet is moved in the space between the upper and lower blades to a rear abutment which is pre-exposed to the desired width cut. After fixing the workpiece on the rear stop, the same procedure is done with the front focus. After that the clamping mechanism by means of which the sheet is securely pressed against the supporting surface of the table. Next to include stroke scissors. When this brake is released, it connects the clutch in receiving a working shaft, and the knife beam begins its downward movement.The operator's hands at this point support metal sheet, which is on the table. After making the working stroke of the knife beam is raised to the uppermost position where the brake is activated again, disconnecting the master actuator by operating the actuator. adjustable abutment portion is rotated, whereby the cut workpiece is released, and by gravity falls into the truck for the collection of finished strips. Subsequently the cycle repeats. Design features of individual nodesThe energy requirements of the cutting process is relatively small, so that the curve Torque has small square: the process begins and ends quickly, even at a considerable thickness to be cut preform. This is explained by the fact that already described previously cleaving zone starts after 25... 40% of the working stroke, and the further metal is degraded due to the appearance of internal stresses in it. At this point the work of deformation is zero.In older designs scissors generally occur with a rigid coupling inclusion, with the rotary key. Such equipment does not require a supply of compressed air, but operates unsatisfactorily at frequent (20... 25) inclusions per minute. Characteristic differences is the main actuator is considered equipment. All models feature a leafy circuit suspension on two rods. Thus, the main shaft is constructed either double- or two eccentrics. Unlike crank presses, sheet instruments with a mechanical drive to have the top or bottom location of the rods. In the first case we speak of the push drive, and the second - on pulling.Since the admissible voltage for the steel under compression greater than the tensile pulling the rods at the same effort they have menshny durability. Therefore aggregates with pulling rods produced small (1.5... 1 mm) sheet metal thicknesses. Connecting rods for all sizes of such equipment - unregulated, which explains the requirements of high stiffness. Moreover, when cut sheet is not necessary to change the course of the blade beam, as the metal thickness range for a scissors pattern varies slightly.knife beam - main element of shears. It established working knives. Because of its considerable length (width of cut sheet for devices with mechanically driven according to GOST reaches 3150 mm) made of a knife beam rolled plates of steel grades 45, 35X or 40HN.Dlya amplification longitudinal rigidity knife beam moves in a prismatic guide, are installed in C-frame. Left out of the guides - always adjustable. The knife beam is located pressing mechanism. It represents a collection of cylinders (for high-end models), or spring for pressing the cut of metal before cutting it.The blade set moving girder inclined blades. In large sizes shears blades perform sectional to facilitate tool change when worn or chipping of the cutting edges. For the manufacture of conventional stamps knives used U8A, U10 or alloy tool steel (9HS, 6HFS). Hardness knife - not less than 54... 56 HRC. To avoid accidents, the knives are covered with the front movable or fixed bars. In the rear part of the frame of equipment mounted rear stop mechanism. It is a hinged L-shaped plate, which rotates on two pivots under the influence of a cam mechanism that is associated with the blade beam. When the blade beam during down plate is placed in a position perpendicular to the axis of the sheet, and provides a reliable fixation of the material. During the return stroke plate pivots and freed from the contact metal strip under the action of its own weight falling in a rail carriage which, at its entry is removed from the frame.Overall dimensions of the section should not be less than 100 mm higher than the dimensions of the slab. For large equipment sizes table is equipped with a drive roller conveyor. Domestic models shears indexed designation H 3_ _ _ _. The first digit identifies the type of the subsequent drive (1- a top drive 3 - with the lower drive), and the last two indicate the limit value of the cut metal thickness (see. table) .For cutting of long productsSuch equipment for its construction like a closed single-crank presses. Scissors mechanical drive has an arrangement typical for this class of forging and stamping machines, except for the following features:

• The presence of one-piece, but because - rigid bed frame type.
• Mechanism pressing bar (which may be mechanical or hydraulic).
• Provision assembly of backwater cut portion of the workpiece, which prevents its folding at the final moment of the cut.
• Rear adjustable stop is provided, by which the volume is provided by cutting on the workpiece metal of a certain length.
• Actuator - mostly eccentric performance: it gives the host the necessary rigidity, and reduces the size of scissors.
• Connecting rod - a short, one-piece.
• Elongated rails, adjustable gap which is produced by an eccentric finger, placed on one side.

Principle of operation. When moving slider bracket located on it acts on the pressure plunger which opens the valve for supplying the working fluid, and it enters into the upper cavity of the impression cylinder. The rod is moved downward, and the fluid pressure force keeps the rod to be cut on the bias with an interval. At the beginning of the return stroke cam mechanism pushes up the valve, bracket raises the plunger and the oil goes free in the cylinder chamber. The composition of the complexes for cutting rolled necessarily included drive roller conveyor assembly which transports the rod to lock the scissors.Cutting the bulk metal cutting accuracy is much more important than the sheet. Therefore, modern high-quality execution of scissors designed for precise cutting of rolled. To this end, provides:

• Active transverse clamping rod before cutting differentiated type (with a different force on both sides of the bar)
• Additional components increase the rigidity of the frame.
• Remote-controlled focus.
• Simultaneous cutting of several bars, which more evenly distributes the force acting on the slider equipment.
• Increased performance metal separation are different automated systems (AC) on the basis of high-quality scissors. They include:
• Automated rack bars.
• Dispenser rod from the rack to the drive conveyor.
• Dispensing apparatus adapted for counting the number of workpieces cut.
• Node walking feed rod in the cutting zone.
• The mechanism of sorting workpieces, with rejection of off-gage rod ends in a separate container.
• Node aligning end portions of the rod before cutting.

Marking CIS production equipment is designated by a combination of H1 _ _ _. First following figure indicates the degree of cutting accuracy (3.8 - precision cutting, 5 - a conventional cutting), the other two indicate the rated force: with manual transmissionIn the practice of business activities of small enterprises and individual business, which is related to metal cutting processes, sometimes it is enough to have a pair of scissors, resulting in muscular force operator. In its structure, circuit and layout are reminiscent of the drive, but do not have a mechanism of inclusion, and the blade beam displacement is performed by means of a lever.

For small cutting efforts are applied single-lever manual execution units. With the growing amount of leverage cutting force increases to two or three. Stress is reduced, but the overall dimensions and the required displacement path of the lever increases. Performance of hand shears gives the drive unit, however small serial production of workpieces, lack of energy costs and compressed air makes them cost-effective type of equipment. Other types of drive devicesIn the small-scale production use scissors combined scales N14_ N52_ _ and _. Besides cutting strips, shapes, sections, they can also perform punching holes, cutting and editing contour. The peculiarity of these models - the direction of movement of the slide, which moves horizontally or at an angle of 45⁰. This makes it possible to cut the rolled workpiece fixing the qualitative stationary knife.Combination shears consist of the following components:

• Motor.
• V-belt transmission.
• Foster shaft.
• Spur gear.
• The crankshaft.
• Rod.
• Swing on the slide axis.
• Balance with the punching mechanism.
• Table for the fixed part of the tool.
• Frame.

Operating principle: cutting material to be prepared for the separation: the band is placed around the fence on the table, and metal products - by stops. The workpiece is set in the respective fixed knives which are arranged in the guiding slider.

To manage a punch unit of a private drive lever-type control of the main drive equipment - pedal. Scheme, similar to the above, and have alligator shears for cutting metal. All the above types of separating equipment, metal carry only straight cut.Nibbler - a kind of equipment which is capable of cutting metal figure. In addition, such techniques perform die cutting, molding, beading, flanging, is applied to the metal small corrugations. Distinctive features of die-cut patterns:

• High-speed transmission in which places without intermediate transfer.
• Urging the punch mechanism by which blanked significant inertial loads on the slider.
• The shaped guides by means of which is separated by a predetermined shirokopolosovoy metal circuit (a set includes a set of several guide).
• The lack of inclusion of the system - clutches and brakes, which is why starting and stopping of the equipment produced by the electric motor.
• Eccentric bushing to the main shaft, rotation of which changes the magnitude and stroke amount of the slide strokes per minute.

Manufacturers of scissors metalluLVD The Belgian company It produces a wide range of equipment and tools for sheet metal processing - produces drive scissors. ScanTool GroupOsnovnoe direction of the German company ScanTool Group - production of grinding and polishing equipment for metal, also makes the drive scissors. JouanelDeyatelnost French company Jouanel, (Russian representation Jouanel) - TOOLS and equipment for metal processing, this press brakes and sheet benders, Pressing machines, gilontiny for metal cutting tools, the product range also includes drive scissors. "Stroymash" OOO Company LLC "Stroymash" St. Petersburg is located in addition to the production of equipment for the metal working and processing raw material, designs, develops hardware, it also offers driving model scissors. JSC "Valley" The main direction JSC "Valley" located in Kuvandyk, Orenburg obl.proizvodstvo forging equipment, produce shears, as well as spare parts for equipment rezhushemu own production. Produce goods for municipal services - iron hatches for cable and manholes, for agro - cultivators, plows and the press.Popular brands:

• MetallMaster (Poland, produces hand guillotine)
• Makita (Japan, produces lever) – Russian representation Makita.
• Tapco (USA, manufactures and lever shears model)
• Bosch (Germany, produces a nibbler)
• Avalon (France, produces roller devices for slitting and strip).

Each firm is focused on the possibility of only its own equipment, so do not always heads for cutting, issued by one firm, suitable for power tools from another manufacturer. Fundamental differences of hand shears for metal is not from the driven equipment.

The thickness of the sheet metal, mm	1,6	2,5	4	6,3	10	12,5	16	20	25
standard size	12	14	16	18	20	21	22	24	26
The maximum rod diameter, mm	56	85…90	125…140	160	200	220
Nominal force. MN	1,0	2,5	6,3	10	16	25
standard size	30	34	38	40	42	44