Question

True or False

1. High rake angles produce high shear strain. 2. Chip gets thicker when rake angle is decreased. 3. Thrust can be negative if rake angle is high. 4. Flank wear is major function of cutting temperature as opposed to crater wear. 5. Diamond cutting tools have low hot hardness. 6. Trepanning can be used to cut through long cylindrical billets. 7. Drill breakage can be occur due to ineffective chip clearance. 8. Down cut milling has greater Workholding pressure than Up-cut milling. 9. Feed marks in face milling can be affected by feed rate. 10. Hobbing to make gears can achieve high production rates. 11. Surface hardening is often a common finishing operation for gears. 12. Friability of abrasive particles (grains) can influence life of a grinding wheel. 13. The total specific energy for grinding processes is lower than other typical machining operations. 14. Grinding wheel can wear due to attrition (mechanical wear), grain fracture or bond fracture. 15. It is better to use soft grade wheels (softer bond material) to cut soft (low hardness) workpieces. 16. Centerless grinding between two rolls pulls the workpiece in due to friction. 17. Lapping can be used to get good surface finish for spherical parts. 18. In electrical discharge machining the tool material is also removed or lost i.e. in a way the tool gets machined as well. 19. Chemical machining can produce really small feature size (for eg hole diameters can be in microns or even nm) 20. Water jet machining has a limitation on thickness of sheets it can cut through.

Answer 1

1) High rake angles produce high shear strain.

Answer: True; A high rake angle is considered to be a negative rake as it's greater than 90°. An effective rake angle is negative, result in a substantial increase in shear strain.

2) Chip gets thicker when the rake angle is decreased.

Answer: True; As the lead angle decreased, the thickness of the chip becomes thicker and decreases in length.

3) Thrust can be negative if the rake angle is high.

Answer: False; The Thrust force is slowly increased or positive as the rake angle change to more negative or high.

4) Flank wear is a major function of cutting temperature as opposed to crater wear.

Answer: True; Flank wear decays the surface quality and extent the contacted surface area, thus resulting in increased generation of heat or Cutting temperature. on the other hand, The crater wear can increase the working rake angle and reduce the cutting force.

5) Diamond cutting tools have low hot hardness.

Answer: False; Diamond cutting tools having a very high hot hardness. Diamond is the hardest material and used to cut hard materials including other diamonds.

6) Trepanning can be used to cut through long cylindrical billets.

Answer: True; Trepanning is a manufacturing process used to produce holes and it can be used to cut through long cylindrical billets by using large lathe deep hole drilling systems.

7) Drill breakage can occur due to ineffective chip clearance.

Answer: False; Chips are easily removed through flutes present in the drill bit. Large deflection causes the drill bit to break at the end of the flute and Twisted large toque broke it from the middle of the flute.

8) Down cut milling has greater work holding pressure than up-cut milling.

Answer: True; In down milling, the cutter rotates in the same direction of feed of workpiece. thus, More tool deflection is encountered hence greater the work holding pressure.

9) Feed marks in face milling can be affected by feed rate.

Answer: True; Feed marks are spiral profile on the machined surface produced by the tool in turning operation, Increasing or decreasing the feed rate may vary the feed marks.

10) Hobbing to make gears can achieve high production rates.

Answer: True; Gear hobbing is a fast and continuous process hence lower production cycle time or production rate.

11) Surface hardening is often a common finishing operation for gears.

Answer: False; The common surface finishing processes are done after hardening.

12) Friability of abrasive particles (grains) can influence the life of a grinding wheel.

Answer: True; High friability makes the abrasive particles (grains) soft that they become quite fragile, Low friability prevents the abrasives from breaking and sharpening themselves again, thus increases grinding wheel life.

13) The total specific energy for grinding processes is lower than other typical machining operations.

Answer: True; Specific energy can be obtained by power divided by MRR (material removal rate) hence the MRR of grinding is low. thus the specific energy of grinding is relatively high. The specific energy for unit material removal in grinding is very high.

14) The grinding wheel can wear due to attrition (mechanical wear), grain fracture, or bond fracture.

Answer: True; The common factors to wheel wear is grain fracture, Attritious wear or progressive wear, bond fracture, or the brittle fracture of the adhesive bonds between the grains.

15) It is better to use soft grade wheels (softer bond material) to cut soft (low hardness) workpieces.

Answer: False; Soft grade wheel is used to grind hard materials such as hard tool steels & carbides.

16) Centerless grinding between two rolls pulls the workpiece in due to friction.

Answer: True; In centerless grinding, the workpiece is held between two grinding wheels, rotating in the same direction at different speeds. One wheel is fixed and the other is regulatory, the fixed one performs the grinding action, and the regulating wheel is positioned to apply lateral pressure and has either a rough or rubber bonded abrasive to trap the workpiece by friction.

17) Lapping can be used to get a good surface finish for spherical parts.

Answer: False; Lapping can be used to get a good surface finish for spherical parts as well as flat surfaces and cylindrical surfaces.

18) In electrical discharge machining, the tool material is also removed or lost i.e. in a way the tool gets machined as well.

Answer: True; In EDM machining the tool act as a cathode and workpiece as anode held in a dielectric liquid without physical contact, when the voltage between the two electrodes is increased, the electrodes becomes greater than the strength of the dielectric, which breaks down, allowing current to flow between the two electrodes. As a result, the material is removed from the electrodes.

19) Chemical machining can produce really small feature size (for eg. hole diameters can be in microns or even nm)

Answer: False; ECM can produce holes range from 0.3mm to 3mm in diameter. Micro-ECM produces such small holes which measure in microns or nanometer.

20) Water jet machining has a limitation on the thickness of sheets it can cut through.

Answer: False; There is no such real limit. to cut a sheet, as the major applications are between 3 - 100 mm, the remainder are special cases, outside of this range – 180 mm concrete plates and 400 mm Steel parts can be cut through water jet.