Module. 02.pptx of manufacturing processes 2

manufacturing process 2 about metullergy

1. MANUFACTURING PROCESSES-II Engr. Umair Ahmed Rajput

2. What is Manufacturing? The word manufacturing is derived from two latin words, manus (hand) and factus (make), the combination means made by hand. Manufacturing, in its broadest sense, is the process of converting raw materials into products. Manufacturing can be defined two ways, one technologic and other economic. Technologically, manufacturing is the application of physical and chemical processes to alter the geometry, properties and appearance of a given starting material to make parts or products; manufacturing also includes assembly of multiple parts to make products. Economically, manufacturing is the transformation of materials into items of greater value by means of one or more processing and/or assembly operations. Production vs Manufacturing Production engineering is a complete cycle as it involves procurement of raw material, storing that raw material as inventory, conversion of raw into semi finished or finished goods, dispatching, sales forecasting etc. but manufacturing is a part of production engineering which just involves in the value addition of raw materials (conversion of raw into semi finished or finished goods).

3. Chapter No. 02 Cutting Tools

4. Cutting Tools Methods of Machining Basically , there are two methods of metal cutting, depending upon the arrangement of the cutting edge with respect to the direction of relation of work tool motion Orthogonal cutting or two dimensional cutting Oblique cutting or three dimensional cutting

5. Cutting Tools Methods of Machining

6. Cutting Tools Tool Geometry (Tool-in-hand Nomenclature ) Cutting tool is a device with which a material could be cut to the desired size, shape or finish. So a cutting tool must have atleast a sharp edge. We can take a blade or a knife, as simple examples of cutting tools having only one thin cutting edge. But in the industry where a work piece say of steel is be shaped on a lathe, (i.e. to be given a surface of revolution), a cutting tool of proper size, shape and length is essential. A cutting tool shown in figure has an edge ab, which cuts the work piece. This edge is called cutting edge. We said earlier that the tool can have one or more than one cutting edges. The tool having only one cutting edge is called single point tool. Examples are shaper tool, lathe tool, planer tool etc. The tool having more than one cutting edge is called multi point cutting tools. For example drills, milling cutters, broaches, grinding wheel honing tool etc. We shall restrict our discussion to single point cutting tool only.

7. Cutting Tools Tool Geometry (Tool-in-hand Nomenclature)

8. Cutting Tools Basic Cutting Geometry Depending upon the number of cutting edges the cutting tools used in metal cutting are classified as follows, Single point cutting tool Multi point cutting tool . Single point cutting tool This type of tool has an effective cutting edge and removing excess material from the work piece . The cutting edge of the single point cutting tool is of the following types. Ground type, Forged type, Tipped type, Bit type

9. Cutting Tools Basic Cutting Geometry In Ground type, the cutting edge is formed by grinding the end of piece of tool . Where as in forged type the cutting edge is formed by rough forging before hardening and grinding. In tipped typed cutting tool the cutting edge is in the form of a small tips made of high grade material, which is welded to shank made up of low grade material. In bit type, a high grade material of a square, rectangular or some other shape is held mechanically in a tool holder. Single point tool are commonly used in Lathes and Shapers, Planers and boring machines.

10. Cutting Tools Basic Cutting Geometry Single point cutting tool One cutting edge Turning uses single point tools Point is usually rounded to form a nose radius. Turning Tool

11. Cutting Tools Basic Cutting Geometry Multi point cutting tool They have more than one effective cutting edge to remove the excess material from the work piece. Milling cutters, drills, reamers and grinding wheels are multi point cutting tools. Motion relative to work usually achieved by rotation. Drilling and milling use multiple cutting edge tools. Multipoint Cutting Tools Milling tool Drilling tools

12. Meaning of Tool Life Every equipment or tool has functional life. At the expiry of which it may function, but not efficiently. So it is true with a cutting tool also. In course of use, tool loses its material, i.e. it gets worn out. As the wear increases, the tool looses its efficiency. So its life has to be defined and on expiry of its life, it should be reground for fresh use. The tool life is defined as the time elapsed between two successive grindings. This definition assumes that as soon as the tool is ground, it is used till its life is over. So according to this definition the tool life means the actual cutting time after a grinding. Cutting Tools Tool Life

13. There are other ways also of expressing the tool life, such as : Machine Time: According to this definition the tool life is the total time of operation of this machine tool. The tool may be cutting intermittently during this period. Consider shaping operation for example say the tool requires regrinding after 30 minutes of cutting i.e. after 30 min. machine run. During this run, we know this tool does not cut on both to and fro strokes 2. Actual cutting time: According to this definition the tool life is the time elapsed during which the tool is actually cutting, between two successive grindings Cutting Tools Tool Life

14. 3. Volume of metal removed: According to this after a certain volume of metal is removed, the life of the tool is assumed to be over. As is obvious, in this method, different volume of metal for different work material and tool material are to be specified. This criteria of tool life is seldom used in practice . 4. Number of pieces removed: According to this the number of work pieces decides the tool life. This criteria is also not used widely as the number of pieces is dependent on the diameter, length and hardness of work piece. Say with a high speed steel tool, if 5 numbers of mild steel work pieces of 5 cm dia. and 25 cm length for example are machined, then the tool should be reground before the further machining is done. That is the tool life is five such work pieces. With any change in the dimension or quality of the work piece the number will change. Taylor tool life equation: where v = cutting speed, m/min (ft/min); T = tool life, min; and n and C are parameters whose values depend on feed, depth of cut, work material, tooling(material in particular), and the tool life criterion used. Cutting Tools Tool Life

15. Operator’s tool life Tool life is measured by : Visual inspection of tool edge Tool breaks Fingernail test Changes in cutting sounds Chips become ribbony, stringy Surface finish degrades Computer interface says - power consumption up - cumulative cutting time reaches certain level - cumulative number of pieces cut reaches certain value Cutting Tools Tool Life

16. There are three possible modes by which a cutting tool can fail in machining: Fracture failure. This mode of failure occurs when the cutting force at the tool point becomes excessive, causing it to fail suddenly by brittle fracture. Temperature failure. This failure occurs when the cutting temperature is too high for the tool material, causing the material at the tool point to soften, which leads to plastic deformation and loss of the sharp edge. 3. Gradual wear . Gradual wearing of the cutting edge causes loss of tool shape, reduction in cutting efficiency, an acceleration of wearing as the tool becomes heavily worn. Fracture and temperature failures result in premature loss of the cutting tool. These two modes of failure are therefore undesirable. Cutting Tools Tool Failure

17. Gradual wear occurs at two principal locations on a cutting tool: the top rake face and the flank. Accordingly, two main types of tool wear can be distinguished: crater wear and flank wear, illustrated in Figures. Crater wear , consists of a cavity in the rake face of the tool that forms and grows from the action of the chip sliding against the surface. High stresses and temperatures characterize the tool–chip contact interface, contributing to the wearing action. The crater can be measured either by its depth or its area. Flank wear occurs on the flank, or relief face, of the tool. It results from rubbing between the newly generated work surface and the flank face adjacent to the cutting edge. Flank wear is measured by the width of the wear band. Cutting Tools Tool Failure

18. The mechanisms that cause wear at the tool–chip and tool–work interfaces in machining can be summarized as follows: Abrasion. This is a mechanical wearing action caused by hard particles in the work material gouging and removing small portions of the tool. it is a significant cause of flank wear. Adhesion. When two metals are forced into contact under high pressure and temperature, adhesion or welding occur between them. These conditions are present between the chip and the rake face of the tool. As the chip flows across the tool, small particles of the tool are broken away from the surface, resulting in attrition of the surface. Diffusion. This is a process in which an exchange of atoms takes place across a close contact boundary between two materials . In the case of tool wear, diffusion occurs at the tool–chip boundary, causing the tool surface to become depleted of the atoms responsible for its hardness. As this process continues, the tool surface becomes more susceptible to abrasion and adhesion. Diffusion is believed to be a principal mechanism of crater wear. Chemical reactions. The high temperatures and clean surfaces at the tool–chip interface in machining at high speeds can result in chemical reactions, in particular, oxidation, on the rake face of the tool. Plastic deformation. Another mechanism that contributes to tool wear is plastic deformation of the cutting edge. The cutting forces acting on the cutting edge at high temperature cause the edge to deform plastically. Plastic deformation contributes mainly to flank wear. Most of these tool-wear mechanisms are accelerated at higher cutting speeds and temperatures. Diffusion and chemical reaction are especially sensitive to elevated temperature. Cutting Tools Tool Failure

19. Requirements: The cutting tool materials must possess a number of important properties to avoid excessive wear, fracture failure and high temperatures in cutting, The following characteristics are essential for cutting materials to withstand the heavy conditions of the cutting process and to produce high quality and economical parts : H ardness at elevated temperatures (so-called hot hardness) so that hardness and strength of the tool edge are maintained in high cutting temperatures. T oughness : ability of the material to absorb energy without failing. Cutting if often accompanied by impact forces especially if cutting is interrupted, and cutting tool may fail very soon if it is not strong enough . W ear resistance : although there is a strong correlation between hot hardness and wear resistance , later depends on more than just hot hardness. Other important characteristics include surface finish on the tool, chemical inertness of the tool material with respect to the work material, and thermal conductivity of the tool material, which affects the maximum value of the cutting temperature at tool-chip interface. Cutting Tools Cutting Tool Material

20. Cutting tool materials: Carbon Steels It is the oldest of tool material. Carbon steels have been used since the 1880s for cutting tools. However carbon steels start to soften at a temperature of about 180 o C. This limitation means that such tools are rarely used for metal cutting operations. Plain carbon steel tools, containing about 0.9% carbon and about 1% manganese, hardened to about 62 HRC, are widely used for woodworking.   Cutting Tools Cutting Tool Material

21. High-speed steel (HSS) HSS tools are so named because they were developed to cut at higher speeds. Developed around 1900s.They are highly alloyed with vanadium, cobalt, molybdenum, tungsten and chromium added to increase hot hardness and wear resistance. Can be hardened to various depths by appropriate heat treating up to cold hardness in the range of HRC 63-65. HSS tools are tough and suitable for interrupted cutting and are used to manufacture tools of complex shape such as drills, reamers, taps, dies and gear cutters. Tools may also be coated to improve wear resistance. HSS accounts for the largest tonnage of tool materials currently used. Typical cutting speeds: 10 - 60 m/min . Cutting Tools Cutting Tool Material

22. Carbide Also known as cemented carbides or sintered carbides were introduced in the 1930s and have high hardness over a wide range of temperatures, high thermal conductivity making them effective tool and die materials for a range of applications.  The two groups used for machining are tungsten carbide and titanium carbide, both types may be coated or uncoated.  Tungsten carbide particles (1 to 5 micro-m) are bonded together in a cobalt matrix using powder metallurgy. The powder is pressed and sintered to the required insert shape . A wide range of grades are available for different applications.  Sintered carbide tips are the dominant type of material used in metal cutting.  Cutting Tools Cutting Tool Material

23. Coatings  Coatings are frequently applied to carbide tool tips to improve tool life or to enable higher cutting speeds. Coated tips typically have lives 10 times greater than uncoated tips. Common coating materials include titanium nitride, titanium carbide and aluminum oxide, usually 2 - 15 micro-m thick. Often several different layers may be applied, one on top of another, depending upon the intended application of the tip. The techniques used for applying coatings include chemical vapour deposition (CVD) plasma assisted CVD and physical vapour deposition (PVD ). Ceramics Ceramic materials are composed primarily of fine-grained, high-purity aluminum oxide ( Al 2 O 3 ), pressed and sintered with no binder. Two types are available: white , or cold-pressed ceramics, which consists of only Al 2 O 3 cold pressed into inserts and sintered at high temperature. black, or hot-pressed ceramics, commonly known as cermet (from ceramics and metal). This material consists of 70 % Al 2 O 3 and 30% TiC. Both materials have very high wear resistance but low toughness, therefore they are suitable only for continuous operations such as finishing turning of cast iron and steel at very high speeds. There is no occurrence of built-up edge, and coolants are not required. Cutting Tools Cutting Tool Material

24. Cubic boron nitride (CBN) and synthetic diamonds Diamond is the hardest substance ever known of all materials. It is used as a coating material in its polycrystalline form, or as a single-crystal diamond tool for special applications, such as mirror finishing of non-ferrous materials. Next to diamond, CBN is the hardest tool material. CBN is used mainly as coating material because it is very brittle. In spite of diamond , CBN is suitable for cutting ferrous materials. Cutting Tools Cutting Tool Material

25. 1. In high speed machining of steels the teeth of milling cutters may fail by (a) mechanical breakage (b) plastic deformation (c) wear (d) all of the above 2. Tool life in turning will decrease by maximum extent if we double the (a) depth of cut (b) feed (c) cutting velocity (d) tool rake angle 3. In cutting tools, crater wear develops at (a) the rake surface (b) the principal flank (c) the auxiliary flank (d) the tool nose 4. To prevent plastic deformation at the cutting edge, the tool material should possess (a) high fracture toughness (b) high hot hardness (c) chemical stability (d) adhesion resistance

26. Introduction to Cutting Fluids: Cutting fluid(coolant) is any liquid or gas that is applied to improve tool life, reducing work piece thermal deformation, improving surface finish and flushing away chips from the cutting zone .A very few cutting operations are performed dry, i.e., without the application of cutting fluids. Practically all cutting fluids presently in use fall into one of four categories: Straight oils are non- emulsifiable and are used in machining operations in an undiluted form. They are composed of a base mineral or petroleum oil and often contains polar lubricants such as fats, vegetable oils and esters. Synthetic Fluids contain no petroleum or mineral oil base and instead are formulated from alkaline inorganic and organic compounds along with additives for corrosion inhibition. Synthetic fluids often provide the best cooling performance among all cutting fluids. Soluble Oil Fluids form an emulsion when mixed with water. The concentrate consists of a base mineral oil and emulsifiers to help produce a stable emulsion. They are widely used in industry and are the least expensive among all cutting fluids. Semi-synthetic fluids are essentially combination of synthetic and soluble oil fluids and have characteristics common to both types. The cost and heat transfer performance of semi-synthetic fluids lie between those of synthetic and soluble oil fluids.   Cutting Tools Cutting Fluid

27. Cutting fluids serve three principle functions : To remove heat in cutting : the effective cooling action of the cutting fluid depends on the method of application, type of the cutting fluid, the fluid flow rate and pressure. The most effective cooling is provided by mist application combined with flooding. Application of fluids to the tool flank, especially under pressure, ensures better cooling that typical application to the chip but is less convenient. To lubricate the chip-tool interface : cutting fluids penetrate the tool-chip interface improving lubrication between the chip and tool and reducing the friction forces and temperatures . To wash away chips : this action is applicable to small, discontinuous chips only. Special devices are subsequently needed to separate chips from cutting fluids. Cutting Tools Cutting Fluid

28. Methods of application: Manual application Application of a fluid from a can manually by the operator. It is not acceptable even in job-shop situations except for tapping and some other operations where cutting speeds are very low and friction is a problem. In this case, cutting fluids are used as lubricants. Flooding In flooding, a steady stream of fluid is directed at the chip or tool-work piece interface. Most machine tools are equipped with a recirculating system that incorporates filters for cleaning of cutting fluids. Cutting fluids are applied to the chip although better cooling is obtained by applying it to the flank face under pressure : Cutting Tools Cutting Fluid

29. Mist applications Fluid droplets suspended in air provide effective cooling by evaporation of the fluid. Mist application in general is not as effective as flooding, but can deliver cutting fluid to inaccessible areas that cannot be reached by conventional flooding. Jet Application of Fluid A jet of cutting fluid is applied on the work piece directed at the cutting zone. Coolant-fed tooling Some tools, especially drills for deep drilling, are provided with axial holes through the body of the tool so that the cutting fluid can be pumped directly to the tool cutting edge. Cutting Tools Cutting Fluid

30. Environmental issues Cutting fluids become contaminated with garbage, small chips, bacteria, etc., over time. Alternative ways of dealing with the problem of contamination are: replace the cutting fluid at least twice per month, machine without cutting fluids (dry cutting ), use a filtration system to continuously clean the cutting fluid . Disposed cutting fluids must be collected and reclaimed. There are a number of methods of reclaiming cutting fluids removed from working area. Systems used range from simple settlement tanks to complex filtration and purification systems. Chips are emptied from the skips into a pulverize and progress to centrifugal separators to become a scrap material. Neat oil after separation can be processed and returned , after cleaning and sterilizing to destroy bacteria. Cutting Tools Cutting Fluid

31. Cutting Fluid Selection Criteria The principal criteria for selection of a cutting fluid for a given machining operation are: Heat transfer performance Lubrication performance Chip flushing Fluid mist generation Fluid carry-off in chips Corrosion inhibition Fluid stability (for emulsions) Process performance Cost Performance Environmental Performance Health Hazard Performance Cutting Tools Cutting Fluid