1



UNIT 26

Applications of Computer Numerical

Control in Engineering

ASSIGNMENT ONE

|ASSESSMENT CRITERIA |COMPLETE (Y/N) |FEEDBACK |

|P1 |Describe the principles on which a | | |

| |machine tool operates when controlled | | |

| |by a CNC system | | |

|P2 |Describe, with the aid of suitable | | |

| |diagrams, the structure of a given CNC | | |

| |machine type (Lathe and/ or Milling | | |

| |Machine) | | |

CNC Principles and Machines

Student declaration

I declare that all the work submitted for this assignment is my own work or, in the case of group work, the work of myself and the other members of the group in which I worked, and that no part of it has been copied from any source

I understand that if any part of the work submitted for this assignment is found to be plagiarised, none of the work submitted will be allowed to count towards the assessment of the assignment

Signed ………………………………………………………………… Date …………………………………………

Unit 26 – Applications of Computer Numerical Control in Engineering

Assignment 1

On completion of this assignment you should understand the principles of computer numerical control (CNC) and machine structures

As part of your assessment material you are required to reflect on your tutorial sessions, your practical hands on and site visits to produce a written report of 1000 words that includes the following:

P1 Describe the principles on which a machine tool operates when controlled by a CNC system

Headings and Topics you must include (in bold) in your written report with examples of research areas

1. System

a. Draw a system diagram of a typical CNC machine.

(Include the machine control unit, safety switches, input devices, output devices, axis amplifiers, drive motors, encoders, spindle interface, spindle amplifier, spindle motor, rotary encoder)

b. How is a G&M program usually transferred to the machine control unit. What methods are available or have been used historically. (USB, CDROM, Wifi, DNC, punched tape)

c. Explain what is the purpose of the machine control unit?

d. Explain how the Machine Control Unit will interpret the G&M program in order to move the machine in the X and Z axis.

e. How is the position of the axis known by the machine control unit? What is the purpose of the linear encoders on the axis?

f. Describe how the spindle speed is maintained when the program is running.

g. What happens when a tool change is requested by the G&M program?

2. Machine Parameters

a. Draw a diagram of a CNC machine and identify where the following Datum points are:-

i. Machine datum (home position, absolute X0, Z0)

ii. Component datum (x=0, Z=0)

iii. Tool Datum

iv. Start Position / Tool change position

a. Produce an explanation of common G and M code parameters that are used by the CNC programmer,

i. M05, M06, M08, M09, M12, M13

ii. G00, G01, G02, G03, G20, G21

3. CNC process

a. How would a CNC programmer know which machine to choose before preparing to write a program?

b. How would the programmer know which tooling is available on the machines? This would include cutting tools and clamping devices

c. How would the programmer decide on the machining sequence to manufacture a part?

d. What is the benefit of using 'point data' on operation sheets?

e. What methods are used to calculate positional coordinates? What is the difference between absolute and relative datum positions?

f. How would a programmer calculate spindle speeds?

g. How would a programmer calculate feedrate?

h. describe what methods of programming are available (graphical CAD/CAM method and the G&M programming method)

i. What is post-processing?

j. What would a CNC programmer prepare for the machine operator to help to setup, verify and edit, store a program for future use?

P2 Describe, with the aid of suitable diagrams, the structure of CNC machine types

1. Types of CNC Machines

Perform some research then describe with the aid of suitable diagrams or photographs , the structure of a range of CNC machines. (you could use machines at college, at a workplace, industrial visit, internet research) Include:-

a. CNC lathe

b. CNC Machining Centres. (3, 4, and 5 axis)

c. CNC drilling machines (for Electronic Circuit Boards)

d. laser cutting machine

e. water jet cutting machine

For each machine shown include some labelling to show the Designation of axes

2. Axis, Spindle Motor and Drive Units / Methods

a. What is a 2 axis machine?

b. What is a 3 axis machine?

c. What is a 4 axis machining centre?

d. What is a 5 axis machining centre?

e. Show an explain an example of a typical axis amplifier and axis stepper motor

f. Show an example of a spindle motor

g. Show and describe an example of a reciprocating ball screw as a method for accurately moving the axis. How do they eliminate backlash in comparison to a normal thread?

3. Positional / Speed Feedback Transducers

How does the physical position / speed of the machine feedback to the machine control unit?

Research into the following types of encoders:-

a. Linear

b. Rotary

c. Digital

d. Optical

4. Types of Tooling

Show a range of tool types for the lathe and milling machines.

a. Lathe Knife tool, Parting off tool, drills, boring bars

b. Milling Slot drills, End mills, Facing cutters

c. Modular Tipped cutters - Advantages of interchangeable tips

d. Quick change tooling Interchangeable chucks / tool holders

e. Automatic turret Examples of auto tool change arms / mechanisms

5. Methods of Cutting Tool transfer

a. Automatic turret Examples of auto tool change arms / mechanisms

b. Chain Magazine On large CNC machines (Makino / Mazak / Mitsui)

c. Circular Magazine

6. Work holding

Show examples of the different methods of securing the material to the machine or work holding.

a. Pallets Multiple machine tables set up whilst machine in cycle

b. Sub tables (fixtures) Fixtures to hold complex components or forgings

c. Rotary work changer Cube on the 4th axis

d. Grid plate (matrix plate) For locating and bolting material to the machine table

7. Swarf removal

Describe examples of methods to remove swarf from machines. (Chutes, chip controllers, conveyors)

8. Work piece /Tool Cooling

a. What methods are used to keep the cutting tool and metal cool during machining?

b. Show an example of tool chatter. Describe why it happens and what can be done to prevent it.

9. Computer hardware devices

a. Describe what functions are available on the machine control panel.

b. Why is it important to be able to manually 'jog' the machine

c. What feedback is shown to the operator (on the screen)

10. Computer software

a. Name a typical CNC Programming language

b. What is meant by the term CAD/CAM?

c. What are the benefits of using a CAD CAM method of programming?

d. Why is it important to be able to write / modify / edit a G&M program?

e. Why is there a need to export files from CAD systems as a ‘dxf’ file (data translation)

11. Safety

What systems are available to avoid overloading the cutting tool?

What are the purpose of machine guards?

Why do some machines use light barriers? (Flow Water jet)

What is a machine interlock?

What other features are on CNC machines to keep an operator safe?

Useful Sources of information

Wikipedia - Numerical control

Boxford Resource Manuals (on School Network)

(downloads – product specifications)

(CNC Structure/ principles /diagrams)





Makino Machine Tools

Mitsui Seiki - UK distributor



(Definition of a CNC machine) (Also available in P:\Technology\6th Form Eng\MODULE SPECS\Year_12\Unit_26_CNC\Handouts_5_Definition_of_a_CNC)

P:\Technology\6th Form Eng\MODULE SPECS\Year_12\Unit_26_CNC\Handouts_1_CNC Machine_Configuration\Unit_20_CNC_Tutorial_1_Understanding_of_CNC_Lathe.ppt



P:\Technology\6th Form Eng\MODULE SPECS\Year_12\Unit_20_CNC\e_books\CNC-Information-Site-eBook.pdf



(Google – moiré fringes cnc)

Important Information

If you use any information extracted from websites then it must have a comment to reference where the source of the information came from. You must not copy from any source.

Submission

Your assignments must include a header containing the Unit information / Course / and Student Name.

The assignment must be written on A4 paper, printed and suitably bound.

The ‘first draft’ Submission date is ___________________

Final Submission date is____________________

HOW WILL THE ASSIGNMENT BE ASSESSED

Your report should be presented in an appropriate format in order that it can be read by both your assessor and any others, who may wish to read your work,

* The assignment should be either word processed or written on A4 paper

* A front cover sheet must be included with the following information, student name, date, unit and assessment number.

* Correct use of spelling and grammar.

* Clear and legible writing or font/font size.

* Page numbers.

* Clear indication of the tasks being completed.

* Appropriate text and web based sources should be used to research your assignment.

Your work must be your own. Any websites or books used to obtain information must be referenced in a bibliography at the end of your assignment.

It is important that your assignment is handed in on or before the ‘hand in date’ stated on the front cover sheet. Late assignments will only be assessed if the reasons for the lateness have been discussed with both yourself and the assessor. Any work handed in after the hand in date without prior agreement with the assessor will not be assessed.

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