PRODUCTION PROCESSES AND EQUIPMENT. Kristo Karjust. MET0180_Basic of Production Engineering . Cutting processes will divide:. Mechanical cutting processes; Electrical and chemical cutting processes; Thermal cutting processes. Mechanical cutting processes. Chip-removal operations .
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MET0180_Basic of Production Engineering
The turning process is characterized by solid work material, two-dimensional forming and a shear state of stress. The workpiece (W) is supported [clamped in a chuck (C) and supported by a center] and rotated (the primary motion R). Through the primary motion (R) and the translator feed (Ta =axial feed for turning and Tr = radial feed for facing) of the tool (V) the workpiece is shaped.
Turning is used primarily in the production of various cylindrical components with nearly unlimited number of external and internal axial cross-sectional shapes (including tapers, threads etc.). Facing is used for both regular and irregular shapes. Turning is the most extensively used industrial process, because it is quite cheap and easy.
In the turning process is important workpiece quality, for instance if we want to get surface quality IT6, then blank quality should be IT7. The material should not be too hard (HB<300) and should possess a minimum of ductility to confine deformation mainly to the shear zone. Generally turning provides close tolerances, often less than ± 0.01 mm. Tighter tolerances may be obtained. The surface roughness after turning is in the range 0.02 ≤ Ra ≤ 3.2 µm and quality at least IT6.
Tool geometry—external turning .
A wide variety of lathes are on the market: for instance, the engine lathe, the turret lathe, single- and multispindle screw machines, automatic lathes and NC lathes. In figure 188.8.131.52 is shown some lathes. Lathes are most frequently used machine in industry, because they are available in a wide range of sizes.
Horizontal lathe and vertical lathe
If heavy and large workpieces are to be machined, the horizontal lathe is impractical. Therefore, the vertical boring mill, which can be considered as a vertical lathe, has been developed .
The drilling process is characterized by solid work material, two-dimensional forming and a shear state of stress. The workpiece (W) is clamped on a table (B) and the tool (V) is given a rotation (the primary motion R) and translator feed (T). In drilling lathes, the workpiece is rotated and the feed is applied to the tool.
The drilling process is primarily used to produce interior circular, cylindrical holes. Through various tools (twist drills, combination drills, spade drills, etc.) different hole shape can be produced as cylindrical holes, drilled and counterbored, drilled and countersunk, multiple diameter holes, etc. drilling is an important industrial process.
Plants and equipment. Twist drills are manufactured in a wide variety of types and sizes. Various surface treatments such as cyaniding and nitriding are applied to high-speed-steel drills in order to increase the hardness of the outer layer of material. Special polishing and black oxiding are beneficial to minimize friction between the drill and the workpiece or the chips in the flutes.
The milling process is characterized by solid work material, two-dimensional forming (one dimensional forming may be used in a few cases) and a shear state of stress. The workpiece (W) is clamped on the table (B), which is given a translatory feed (T), that together with the primary motion (R) of the cutter (V) provides the many geometrical possibilities.
The milling process, through the various types of cutters and the wide variety of machines, is a versatile high-production process. Typical milling cutters like arbor-mounted cutters (a) and shank mounted (b) cutters. Milling cutters are usually made of hard alloys, sometimes also diamonds and metal ceramics. Hard alloy cutters permit roughness in steel Rz = 1...2 m and cast Rz = 4...7 m. Generally diamonds and metal ceramics cutters is used quit little, because they are slight .
2-he teraline sõrmfrees
Sõrmfrees – 2-he teraline soonfrees
3-me teraline sõrmfrees
There are: a - key-seating milling with disk cutters; b - slot milling with disk cutter; c - difficult contour cutting with different cutters (1,2,3,4,5); d – angle milling with angle cutter; e - T- slot milling with T-slot cutter; f- step milling with end mill; g – slot milling with T-slot cutter; h – two sided angle milling with angle cutter; i – incline surface milling with tool bit angle cutter. Generally the milling process comes close to turning in extensive industrial use, since the geometrical possibilities are enormous and the removal rate high .
Typical milling operations
Surface quality and accuracy. The hardness of the material should not be too high ( HB < 250 – 300) and a minimum of ductility is advisable. The obtained tolerances are ±0.05 mm, surface roughness is 3.2 ≤ Ra ≤ 6.3 µm and the quality IT7. Manufacturing depends on material structure and strength 
Cutting action in up-and-down milling .
Many different milling machines are on the market: for instance universal column-and-knee-type milling machines (plain column-and-knee-type milling machines supplied with a swivel on the saddle, enabling helices to be cut when swiveling the work table), ram-type milling machines and planer-type milling machines. Milling machines can also be used for drilling and boring. Milling machines are among the most important machine tools, as they can produce wide variety of machined surfaces .
Horizontal milling machine and plain column-and-knee-type milling machine
Reaming is a sizing or scraping operation in which the tool cuts slightly larger than its own diameter, usually direct proportion to the amount of stock to be removed. For efficient operation, reamers must be cutting at all times, which is possible only when they are being used in properly drilled holes. Removal of too much stock by reaming often causes oversize and rough holes.
Surface quality and accuracy. We can ream cylindrical and conical holes, different materials like steel, cast iron, colored metals and alloys. Accuracy is generally 5..6 IT and the surface roughness will normally be in the range 0,08 < Ra < 0,63 µm
Plants and equipment. A reamer is a rotary cutting tool, generally of cylindrical or conical shape, intended for enlarging and finishing holes to accurate dimensions. It is usually equipped with two or more peripheral grooves or flutes, either parallel to its axis or in a right-or left-hand helix as required. Those with helical flutes provide smooth shear cutting and produce a better finish. The flutes form cutting teeth and provide grooves for removing the chips.
Commercial types of reamers
Broaching is a high-production metal removal process that sometimes is required to make one-of-a-kind parts. Broaching is at its best in machining simple surfaces or complex contours. Properly used modern broaching processes can greatly increase productivity, hold tight tolerances, produce precision finishes and eliminate the need for highly skilled machine operators. The length of a broaching tool is determined by the practice by the amount of stock to be removed and limited by the machine stroke, bending moments, stiffness, accuracy and other factors. The length of an internal push broach should not exceed 25 times the diameter of the finishing teeth, a pull broach usually is limited to 75 times the finishing diameter.
The broaching tool may be pulled or pushed across a workpiece surface or the surface may move across the tool. Internal broaching requires a starting hole or opening in the workpiece for insertion of the broaching tool. The final shape may be a smoother, flatter surface, a larger hole or a complex splined, flanged, toothed, notched, curved, spiral or irregularly shaped section.
Possible workable shapes
Surface quality and accuracy. Generally any material that can be machined can be broached. Good tolerances can be obtained ( ± 0.1 mm ± 0.02 mm) and accuracy generally IT 7. The surface roughness will normally be in the range 0,8 < Ra < 2,0 µm .
The planning process is characterized by solid work material, two-dimensional forming (sometimes one-dimensional forming) and a shear state of stress. The workpiece (W) is clamped on the table (B), which is given a translatory primary motion (Tb) and the tool (V) is given a translator feed (Tv), providing the geometrical possibilities.
The hardness of the material should generally not exceed HB = 300 and a minimum of ductility is advisable. Planing depends on material structure and strength. Surface quality depends on cutting velocity and depths. The obtained tolerances are normally ± 0.05 to ± 0.10 mm and accuracy generally IT 3..4. The surface roughness is in the range 0.63 ≤ Ra ≤ 2.5 µm .
There are used straight and clinced planing cutters in planing machines. a – straight cutters; b – loop cutters; c – expansive loop cutters; d – edge cutters; e – slash cutters.
There are many different types of planing machines like pit-type planer, double housing planer, open-side planer, edge or plate planers.
The planing process is in general used to produce large horizontal, vertical, inclined flat surfaces, also T – slot and angle-shape grooves. Some planing examples are shown in figure, where: a – horizontal, vertical and incline surface planing; b – groove planing; c – T –slot planing; d – angle planing; e – dificult surface planing.
The grinding process is characterized by solid work material, two-dimensional forming (one-dimensional may occur) and a shear state of stress. The workpiece (W) is supported between centers (P) or clamped on a table (B) and given a rotary (R) and translatory (T) feed. The tool V (the grinding wheel) is given a rotary primary motion (Rv) and depending on the particular process, sometimes a feeding motion also.
Tolerances are around ± 0.001 mm and surface roughness is 0,04 µm < Ra < 0,32 µm. the surface accuracy should be at least IT 7 and in plain grinding IT 6. The grinding processes have a low material removal rate .
where a – straight profile plain wheel, which is used for cylindrical, internal, center less and surface grinding; b, c – conical profile plain wheels, which are used for thread, gear etc. grinding; d – opened hole plain wheels, which are used for cylindrical and surface grinding; e – sheet wheels (thickness 0.5 … 5 mm), which are used for cutting; f, g, h – band and pan wheels, which are used for flat grinding.
The grain size of the abrasive is an important factor in selecting the correct grinding wheel. Grain sizes are classified in accordance with an international mesh size in mesh/inch, ranging from 8 (coarse) to 1200 (super-fine).
In the case of diamond and boron nitride grinding wheels, European grinding wheel manufacturers indicate grain size by the diameter of the abrasive grains in microns
The most frequently used grinding tool is the grinding wheel used for cylindrical or plain grinding.
Grinding offers close dimensional control and fine surface finishes and has become extremely important in recent years, because of the increasing demands of high accuracy and surface quality.
Formerly grinding was used only for finishing operations, but rapid development is taking place with regard to roughing (high-speed) grinding, which may substitute for turning and milling .
The grinding processes are used primarily in finishing cylindrical or flat surfaces which have been produced by various other processes.
Different grinding operations.
Today roughing grinding including profile grinding at high cutting speeds, can sometimes substitute for turning, milling or planing.
Different grinding operations.
Honing is a low-velocity abrading process using bonded-abrasive stick for removing stock from metallic and nonmetallic surfaces. As one of the last operations performed on the surface of a part, honing generates functional characteristics specified for a surface and involves the correction of errors resulting from previous operations. Functional characteristics generated by honing include geometric accuracy, dimensional accuracy and surface character (roughness, lay pattern and integrity)
In honing the tolerances are around ± 0.001 mm and surface roughness is 0,08 µm < Ra < 0,32 µm. The surface accuracy should be at least IT 6 and in flat honing IT 4. [5, lk2900]
The most common application of honing is on the internal cylindrical surfaces. However, honing is also used to generate functional characteristics on external cylindrical surfaces, flat surfaces, truncate spherical surfaces and toroidal surfaces (both internal and external).
Honing operations: (A) internal cylindrical surface honing; (B) external cylindrical surface honing; (C) flat surface honing; (1) tool; (2) workpiece
Electrical-discharge machining (EDM) is a method of removing metal by a series of rapidly recurring electrical discharges between an electrode (the cutting tool) and the workpiece in the presence of a liquid (usually hydrocarbon dielectric). Minute particles of metal or “chips” (generally in the form of hollow spheres) are removed by melting and vaporization and are flushed from the gap between tool and work.
Basic components of an electrical discharge machine
The EDM tool electrode is the means by which electric current is transported to the work piece.
Shape of the electrode establishes a pattern whereby sparks will occur between the tool and work piece and the desired shape will be machined. Shapes machined are the opposite of the electrode shapes.
A requirement for any material used for an EDM electrode is that it be a conductor of electricity. Insulating materials are not usable.
A wide variety of materials are used in the manufacture of electrodes. Most used materials are graphite, copper, brass, copper tungsten, silver tungsten, carbide and zinc alloys.
The several methods of introducing dielectric fluid to the arc gap fall into four broad classifications: normal flow; reverse flow; jet flushing; immersion flushing.
Several methods of introducing dielectric fluid
Generally the surface roughness is Ra 1,6...3,2 µm, but it could be also 0,05...0,1 µm. Generally EDM provides close tolerances, often 50 µm and IT 7.. As a result, the smoothness of surfaces produced by EDM is generally limited more by economics than by the technological potential of the process.
Electrochemical machining (ECM) is important method of removing metal without the use of mechanical or thermal energy.
Electric energy is combined with a chemical to form a reaction of reverse plating. Direct current at relatively high amperage and low voltage is continuously passed between that anodic work piece and cathodic tool (electrode) through a conductive electrolyte.
At the anode surface, electrons are removed by the current flow and the metallic bonds of the molecular structure of this surface broken. These surface atoms proceed to go into solution as metal ions. Simultaneously positive hydrogen ions are attracted to the negatively charged surface and emitted at the cathode surface to form hydrogen atoms, which combine to form hydrogen molecules.
Dissolved material is removed from the gap between work and tool by the flow of electrolyte, which also aids in carrying away the heat and hydrogen formed.
Schematics of electrochemical machining (ECM) operations. (a) die sinking; (b) shaping of blades; (c) drilling; (d) milling; (e) turning; (f) wire ECM; (g) drilling of curvilinear holes; (h) deburring and radiusing.
A typical ECM machine consists of a table for mounting the work piece and a platen mounted on a ram or quill for mounting the cathode tool, inside an enclosure.
The work piece is mounted on the table and connected in a manner ensuring good electrical contact to the positive side of the power supply. The tool is mounted on the platen, with electrical connection to the negative side of the power supply.
Electrolyte is pumped under pressure between the work and tool. As the tool feeds into the work with current flowing, the electrolyte carries away machining products.
Electrochemical machining equipment schematic. (1) tool electrode; (2) finishing workpiece; (3) tank of electrolyte; (4) clamping system; (5) electrolyte supply system; (6) power supply. [6 ]
Materials used for ECM tools must have good electrical and thermal conductivity, be corrosion resistant and machinable, and be stiff enough to withstand the electrolyte pressures without vibrating or distorting. Copper, brass, bronze, copper-tungsten, stainless steel and titanium are most frequently used. Graphite can also be used, but it must be coated to prevent rapid erosion. The tools must be smoothly finished to assure uniform electrolyte flow and produce good surface finishes on the work.
Cathode accuracy directly affects product accuracy in ECM, because the product cannot be more accurate than the cathode tool whish produced it. Part accuracy is also affected by irregularities in electrolyte flow or current flow. Average surface finishes obtained range from 0,1 to 1,0 m and accuracy IT 7 .
Applications. Major advantages of the ECM process include stress and burr-free machining, no burning or thermal damage to workpiece surface and elimination of tool wear. Small thin disks are being consistently machined to tolerances within 0,007 mm on such machines. Die sinking is a major application with over cut throughout the surface being consistently maintained within 0,05 mm. Aircraft and aerospace components are frequently produced with this method because the high-strength, temperature resistant materials used are difficult to machine in other ways.
Electrochemical discharge grinding (ECDG), sometimes called ECDM grinding, is a combination of electrochemical grinding (ECG) and electrical discharge grinding (EDG), with some modifications.
Most of the stock is removed by ECG, with the oxides that from on the positively charged workpiece surfaces being removed by the intermittent spark discharges of EDG.
A bounded graphite wheel without any abrasive grains is used and the conductive electrolyte is generally a water solution of inorganic salts. Alternating current or a pulsing type d-c circuit at relatively high amperage and low voltage, is used to obtain random spark discharges.
No arc or spark suppressor circuit is required, since the work is held in direct contact with the wheel under low pressure. For profile grinding, the workpiece is traversed along the periphery of a performed wheel.
Wheel rotation is necessary in ECDG to introduce clean electrolyte through the gap and reduce the possibility of gap-spark information. Rotation also increases electrolyte pressure at the gap and helps to avoid electrolyte boiling.
Accuracy can be held to 0,01 mm under carefully controlled conditions and about 0,02 mm in normal operations (IT 5-6). A surface finish of 0,2 m can be obtained in grinding tungsten carbide with the ECDG process.
An advantage is the use of a low cost wheel. Application of this process, howerver, has been limited .
Metal can be chemically cleaned in numerous ways, including degreasing, pumice scrubbing, electro cleaning or chemical cleaning. The cleaned metal is coated with photographic material which, when exposed to light of the proper wavelength, will polymerize and remain on the panel as it goes through a developing stage.
This polymerized layer then acts as the barrier to the etching solution applied to the metal. After coating with resist, it is necessary to bake the panel prior to exposing it. This is used to drive off solvents in a simple drying operation.
The metallic coated panel is placed between sets of negatives (either film or glass) and is clamped by either vacuum or pressure. Certain resist require an additional baking operation following development. The next step is etching to remove the unwanted metal unprotected by the photo resist.
Process steps involved in the photographic-resist process of photochemical machining
Applications. The use of photochemical machining is generally limited to relatively thin materials, from 0,002 to 1,2 mm thick. The limit on material thickness is generally a function of the tolerance desired on finished parts. Photochemical machining has a number of applications wherein it provides unique advantages, for instance:
Ion beam machining
Ion-beam machining is a precise process. Because of the small beam diameter, tolerances of 0,001nmm can be held (IT 2-3). Surface roughness is normally in the range Ra 1 m .
The electron beam is formed inside an electron gun which is basically a triode and consists of cathode which is a hot tungsten filament emitting high-negative-potential electrons, a grid cup negatively biased with respect to the filament and an anode at ground potential through which the accelerated electrons pass.
EBM is generally limited to drilling extremely small holes and cutting narrow slots or contours in thin materials to close tolerances. There is no tool wear or pressure on the work. Stock removal rate is generally about 1,5 mm3/s. Using this process, it is possible to drill a cross-shaped hole, for example, through a piece of stainless steel 1 mm thick.
Extremely high energy density makes it possible to drill the hole while, a few thousandths of an mm away from the wall of the hole, the work piece remains at room temperature. We can make hole which diameter is 1,5 mm and length 10 mm. Any known material, metal or nonmetal that will exist in high vacuum can be cut.
Electron-beam machining is a precise process. Because of the small beam diameter, tolerances of 0,001 to 0,005 mm can be held (IT 2-3). Surface roughness is normally in the range Ra 5-20 m .
Many types of lasers exist which produce highly directive beams of optical or infrared radiation.
They can be classified as solid-state, gas or liquid. Solid-state units have laser rods made of any one of a number of a number of solid materials including ruby, neodymium-doped glass and neodymium-doped yttrium-aluminum-garnet (called YAG).
Gas units have glass tubes filled with CO2, helium-neon, cadmium gas or argon (figure 3.10.3). Only a few of the many types of lasers are practical for metalworking.
Ruby lasers produce the highest energy and peak power outputs, but they cost more. They generally used where a large amount of material must be removed with a single pulse. CO2 lasers are most efficient with respect to converting electrical energy to laser light energy.
They are generally used in a repetitively pulsed mode for metalworking and are sometimes assisted by air, inert gas or oxygen to facilitate coupling energy from the beam to the work piece.
CO2-, N2-, He- laser
To meet the basic requirements for industrial applications, the laser systems must meet the following specifications:
Machining of small holes in thin parts is a typical application.
The process is being used to pierce diamond wire-drawing dies and to remove metal from work pieces without stopping their rotation during dynamic balancing.
Other applications include hole drilling, resistor trimming and scribing of silicon wafers. It should be emphasized that laser is unlikely to replace any of the common drilling processes, but rather will continue to supplement them and enhance productivity. One of the present drawbacks in laser applications is cost.
Other limitations include low efficiency, slow repetition rate, limited durability and reliability, and the necessity for careful control and effective safety procedures.
Because of the laser’s ability to melt or vaporize any known metal and operate in any desired atmospheric environment, it is sometimes preferred over EBM.
Other advantage include the ability to machine areas not readily accessible and extremely small holes, the fact that there is no direct contact areas between the tool (laser) and the work piece, small heat affected zones, and easy control of beam configuration and size of exposed areas. 
To the sheet metal we can machine 60 … 240 holes/minute. Surface roughness is Ra 0,4...0,10 μm, which depends workable material and machining process. Structural changes could be in depth 1...100 μm .
Before ultrasonic can be used effectively, it is important to realize the following:
Workpieces to be cleaned are placed in the solution and the rapid oscillation of the solution resulting from the high-frequency sound waves creates minute vapor voids in the solution that implode against the workpiece and effectively clean its surfaces.
Mechanically held contamination is released from the surfaces, soluble materials are rapidly dissolved and oil and similar contaminants are easily emulsified.
Industrial ultrasonic cleaning systems are composed of three basic components: generator, transducer and tank containing the cleaning solution. The generator transforms standard line current of 50 or 60 Hz into desired higher frequency.
This high-frequency current is converted into sound waves (mechanical energy) of a corresponding frequency via a transducer, which radiates the waves into a cleaning solution in the tank.
There are two major types of ultrasonic cleaning units: integrated and modular. Integrated units have all components, including the tank for the cleaning solution in a single enclosure. Modular systems consist of a separate generator linked to either tanks equipped with transducers or immersible transducers.
The number of transducer elements per tank is determined by the tank volume and its designated power rating. It is important that the selected tank and generator have matched ratings for power and frequency, otherwise serious damage will result, usually the generator.
Tank heating is the common option for tanks with transducers and is specified by a majority of users to keep the cleaning solution at its best temperature for cavitations and cleaning effectiveness.
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