Manufacturing Processes UES102 PDF

Thapar Institute of Engineering & Technology, Patiala Manufacturing Processes UES102  MATERIAL REMOVAL PROCESSES The MATERIAL REMOVAL PROCESSES are a family of SHAPING OPERATIONS in which excess material is removed from a starting work-part so t...

Thapar Institute of Engineering & Technology, Patiala Manufacturing Processes UES102  MATERIAL REMOVAL PROCESSES The MATERIAL REMOVAL PROCESSES are a family of SHAPING OPERATIONS in which excess material is removed from a starting work-part so that what remains is the desired final geometry. The most important branch of the family is conventional machining, in which a sharp cutting tool is used to mechanically cut the material to achieve the desired geometry. 2  MATERIAL REMOVAL PROCESSES The three principal machining processes are turning, drilling, and milling. TURNING DRILLING MILLING Image source: http://home.iitk.ac.in/~jrkumar/download/Lecture-2.pdf 3  MACHINING PROCESSES Machining is important commercially and technologically for several reasons: – Variety of work materials. – Variety of part shapes and geometric features. – Dimensional accuracy. – Good surface finishes. 4  MATERIAL REMOVAL PROCESSES On the other hand, certain disadvantages are associated with machining and other material removal processes: – Wasteful of material – Time consuming 5  MATERIAL REMOVAL PROCESSES Machining is generally performed after other manufacturing processes such as casting or bulk deformation (e.g., forging, bar drawing). The other processes create the general shape of the starting work-part, and machining provides the final geometry, dimensions, and finish. 6  CUTTING TOOL A CUTTING TOOL has one or more sharp cutting edges and is made of a material that is harder than the work material. The cutting edge serves to separate a chip from the parent work material. 7  SINGLE POINT CUTTING TOOL A SINGLE-POINT tool has one cutting edge and is used for operations such as turning. In addition to the tool features shown in Figure (next ppt), there is one tool point from which the name of this cutting tool is derived. During machining, the point of the tool penetrates below the original work surface of the part. The point is usually rounded to a certain radius, called the nose radius. 8  SINGLE POINT CUTTING TOOL 3-D VIEW Image source: Cutting tool technology, 9 (https://www.egr.msu.edu/~pkwon/me478/cuttingtool.pdf)  MULTI-POINT CUTTING TOOL MULTIPLE-CUTTING-EDGE TOOLS have more than one cutting edge and usually achieve their motion relative to the workpart by rotating. Drilling and milling use rotating multiple-cutting- edge tools. Figure shows a helical milling cutter used in peripheral milling. Although the shape is quite different from a single point tool, many elements of tool geometry are similar. 10  MULTI-POINT CUTTING TOOL Direction of Rotation Cutting Edges 11 Image source: https://encrypted-tbn0.gstatic.com/images?q=tbn%3AANd9GcTUrHMdTdjfdwAvIh- fMb7NQCwD0zOz3Xba4A&usqp=CAU MULTI-POINT CUTTING TOOL: Milling cutters 12 Source: https://madhavuniversity.edu.in/images/milling-cutters.jpg MULTI-POINT CUTTING TOOL: Drill bits Image source: https://www.the-diy-life.com/which-drill-bit-to-use/ 13 MULTI-POINT CUTTING TOOL 14 SINGLE POINT CUTTING TOOL 3-D VIEW 15 SINGLE POINT CUTTING TOOL 3-D VIEW Side Flank End Flank 16 SINGLE POINT CUTTING TOOL 3-D VIEW Side Cutting Side Flank Edge 17  SINGLE POINT CUTTING TOOL 3-D VIEW End Cutting Edge End Flank 18 SINGLE POINT CUTTING TOOL 3-D VIEW End Flank Nose / Corner / Tip 19  SINGLE POINT CUTTING TOOL PHOTOGRAPH RAKE FACE End Cutting Edge End Flank Side Cutting Side Flank Edge 20  RAKE FACE Rake face is the surface over which the chip , formed in the cutting process, slides. EF 21  FLANK FACE Flank face is the surface(s) over which the surface, produced on the workpiece, passes. EF 22  CUTTING EDGE Cutting edge is a theoretical line of intersection of the rake face and the flank surfaces. EF 23  CUTTING WEDGE Cutting wedge is the tool body enclosed between the rake and the flank faces. EF 24  WEDGE ANGLE Wedge angle is defined as the angle between flank and rake face. Side Wedge Angle End Wedge 25 Angle  SHANK Shank is the part of the tool by which it is held. EF 26  CUTTING TOOL ANGLES 2 1 3 4 7 5 6 27  CUTTING TOOL ANGLES End Cutting Edge Angle (µe) RAKE FACE SHANK Side Cutting Edge Angle (µs) EF 28  SIDE CUTTING EDGE ANGLE(µs) End Cutting Edge Angle (µe) RAKE FACE SHANK Side Cutting Edge Angle (µs) Side cutting angles may vary from 10° to 20°, depending on the material cut. If this angle is too large (over 30°), the tool will tend to chatter. 29  END CUTTING EDGE ANGLE(µs) End Cutting Edge Angle (µe) RAKE FACE SHANK Side Cutting Edge Angle (µs) End cutting edge angle may vary from 5° to 30°, depending on the type of cut and finish desired. 30  NOSE RADIUS Nose Radius SHANK EF The nose is the part of the tool bit which forms the corner between the side cutting edge and the end cutting edge. The nose radius is the rounded end of the tool bit. 31  CUTTING TOOL ANGLES Back Rake Angle (αb) SF End Relief /Clearance Angle EF (βe) 32 END RELIEF (CLEARANCE) ANGLE(βe) Back Rake Angle (αb) End relief (clearance) angle is the angle ground below the nose of the tool, which SF permits the cutting tool to be fed into the work. End Relief /Clearance It is generally 10° to Angle 15° for general-purpose (βe) tools.  END WEDGE ANGLE (γe) End wedge angle is defined as the angle between end flank and rake face. End Wedge Angle EF End Wedge 34 Angle  BACK (TOP) RAKE ANGLE (αb) The back (top) rake angle is the backward slope of the tool face away from the nose. The back rake angle is generally about 20°. Back rake permits the chips to flow away from the point of the cutting tool. Two types of back or top rake angles are provided on cutting tools and are always found on the top of the tool bit. 35  POSITIVE RAKE Positive rake, where the point of the cutting tool and the cutting edge contact metal first and the chip moves down the face of the toolbit. Positive Rake Angle FLANK 36  POSITIVE RAKE Generally, positive rake angles: – Make the tool more sharp and pointed. This reduces the strength of the tool, as the small angle in the tip may cause it to chip away. – Reduce cutting forces and power requirements. – Helps in the formation of continuous chips in ductile materials. – Can help avoid the formation of a built-up edge. – Are suitable for lower cutting speeds. – Are suitable for ductile materials. 37  POSITIVE RAKE High-speed steel-cutting tools are almost always ground with positive rake angles. HSS has good strength and toughness, so that the thinner cross section of the tool created by high positive rake angles does not usually cause a problem with tool breakage. 38  POSITIVE RAKE NOTE Because there is less strength at the point of positive rake angle tools than with negative-rake tools, tool failure is more likely with large positive rake angles at high cutting speeds or with intermittent cuts. 39  NEGATIVE RAKE Negative rake, where the face of the cutting tool contacts the metal first and the chip is forced up the face of the toolbit. Negative Rake Angle FLANK 40  NEGATIVE RAKE Negative rake angles are generally preferred for ceramic, diamond, and cubic boron nitride tools (Brittle in nature). As a group, these materials have higher hardness and lower toughness. In other sense these materials are strong in compression but are relatively weak in tension because of their brittle nature. 41  NEGATIVE RAKE Cemented carbides, for example, are used with rake angles in the range from -5° to -10°. Ceramics have rake angles between -5° to -15 °. 42  NEGATIVE RAKE Negative rake angles also provide greater strength at the cutting edge and better heat conductivity. The surface finish is usually poorer with negative rakes, although they can have good finish at higher speeds. 43  NEGATIVE RAKE Generally, negative rake angles : – Make the tool more blunt, – increasing the strength of the cutting edge – Causes high compression – Increase the cutting forces. – Can increase friction, resulting in higher temperatures. – Are suitable for higher cutting speeds. – Are suitable for hard brittle materials. 44  NEGATIVE RAKE NOTE Negative-rake tools are most likely to produce a built-up edge with a rough continuous chip and a rough finish on the work, especially at lower cutting speeds and with soft ductile materials. Better finishes with negative rake can be obtained at high speeds with hard brittle materials. 45 RAKE ANGLES 46  CUTTING TOOL ANGLES Side Wedge Angle (γ ) s Side Rake Angle (αs) EF Side Relief /Clearance EF Angle (β ) s 47  SIDE RELIEF (CLEARANCE) ANGLE (βs) Side Wedge Angle Side relief (clearance) (γs) angle is the angle Side Rake Angle ground on the flank of (αs) the tool below the cutting edge. EF This angle is generally 6° to 10°. Side Relief /Clearance Angle (β ) s 48  SIDE WEDGE ANGLE (γS) Side wedge angle is defined as the angle between side flank and rake face. Side Wedge Angle Side Wedge Angle 49  SIDE RAKE ANGLE (αs) Positive Side Rake Angle Negative Side Rake Angle The side rake angle is the angle at which the face is ground away from the cutting edge. For general-purpose tool bits, the side rake is generally 14°. 50  TOOL SIGNATURE Convenient way to specify tool angles by use of a standardized abbreviated system is known as tool signature or tool nomenclature. It indicates the angles that a tool utilizes during the cut. The seven elements that comprise the signature of a single point cutting tool can be stated in the following order: 51  TOOL SIGNATURE Tool signature 0-7-6-8-15-16-0.8 1. Back rake angle (0°) 2. Side rake angle (7°) 3. End relief angle (6°) 4. Side relief angle (8°) 5. End cutting edge angle (15°) 6. Side cutting edge angle (16°) 7. Nose radius (0.8 mm) 52  2 1 3 4 7 5 6 53 References: M. P. Groover, Fundamentals Of Modern Manufacturing: Materials, Processes, and Systems, Wiley (2010), 4th edition. Degarmo, E. P., Kohser, Ronald A. and Black, J. T., Materials and Processes in Manufacturing, Prentice Hall of India (2008) 8th ed. Kalpakjian, S. and Schmid, S. R., Manufacturing Processes for Engineering Materials, Dorling Kingsley (2006) 4th ed. 54