CNC Machining Questions
Section 1: Introduction to Computer Numeric Control
1. Explain what you understand by the term ‘numerical control’?
2. What are the factors that contributed to the development of numerical control?
3. Briefly explain the functions that are expected to be served by numerical control in machine tools.
4. Explain the principle of numerical control.
5. Show schematically the different forms of numerical control, viz., open-loop and closed loop control
systems.
6. What are the applications where numerical control is most suitable?
7. Give the advantages and disadvantages of numerical control of machine tools.
8. What is the difference between NC and CNC?
9. Explain the advantages to be gained by using CNC compared to NC.
Section 2: CNC Hardware Basics
1. What are the requirements of structure in the case of CNC machine tools?
2. What are the design criteria to be used in designing CNC machine tools?
3. What are the various types of materials used in the construction of CNC machine tools?
4. What factors should be kept in mind during the design of spindles for CNC machine tools?
5. Briefly describe about the type of electric drives used in CNC machine tools.
6. Why is a recirculating ball screw universally used in the actuation system in CNC machine tools?
7. List different types of nut arrangements used in recirculating ball screws. Give a comparative
evaluation.
8. State the advantages of recirculating ball screws compared to the conventional Acme screws.
9. Give a brief description of the linear motion elements as used in CNC machine tool slides.
10. What are the requirements of feedback devices in CNC machine tools?
11. Give a comparison of the encoder and linear scale as a feedback device for displacement in CNC
machine tools.
12. Give a brief write-up on encoders used in CNC machine tools.
13. Briefly explain the basis of designating the coordinate axes in CNC machine tools.
14. Examine the following CNC machines (Fig.10.32) and show the axes designation as per the ISO
standard. Justify your choice.
Section 3: CNC Tooling
1. What are the types of cutting-tool materials used in CNC machine tools?
2. How do you select the carbide grade for a given machining application?
3. Write a small note on coatings used in cutting tools.
4. What are the requirements for using ceramics in machining?
5. Briefly explain the ISO coding system used carbide-tool bits.
6. Briefly explain the ISO coding system used carbide-turning tool holders.
7. What are the advantages of modular tooling units in CNC turning?
8. What are the requirements of tool pre-setting in CNC machining?
9. Give a brief description of any one of the tool pre-setter you are familiar with.
10. What are the various types of tool magazines used in CNC machine tools? Give their relative merits.
11. How does a tool change occur in a typical automatic tool changer?
12. What are the work-holding methods suitable for CNC machining centres?
Section 4: CNC Machine Tools and System Controls
1. Give a brief description of the CNC machining centres.
2. How do you select a CNC machining centre for machining the following components?
(a) Aircraft fuselage section
(b) Compressor rotor
(c) Gearbox housing of an automobile
3. What are the ways in which 5-axes can be realised in CNC machining centres (vertical axis as well as
horizontal axis)?
4. Briefly describe the automatic pallet changer as used in CNC machining centres.
5. Give a brief description of CNC turning centres.
6. Explain the reasons why turn mill centre is preferable to a 2-axis CNC turning centre?
7. Explain some of the multiple-axis (more than 2-axes) turning centres with applications.
8. What are the differences between horizontal- and vertical-axis CNC turning centres? Give their
applications.
9. What are the variations available in vertical CNC turning centres? Give their applications.
10. How do you distinguish between high-speed machining and conventional machining?
11. What are the applications of high-speed machining?
12. What are the advantages to be gained by the use of high-speed machining?
13. What are some of the benefits achieved by the modern CNC controllers compared to the pre
microprocessor era controllers?
14. What are the various sub-systems present in a modern CNC controller unit?
15. Explain adaptive control as it pertains to numerical control.
16. What is adaptive control optimisation? How is it used in CNC machines?
17. What is adaptive control with constraints? How is it used in CNC machines?
18. Give a brief description of some of the support systems found in CNC machine tools.
19. Give a brief note on the touch-trigger probes.
20. Give a brief description of the data transmission method between the touch-trigger probe and the CNC
controller. Give their relative advantages.
21. What are all the applications where the touch trigger probes can be used in the shop floor? Give a
brief description.
22. Write a short note on digitising using touch trigger probes.