MECH3600 9660 Quiz 1 CNC 2016 Solution

MECH3660 9660 Manufacturing Engineering QUIZ 1 2016 Solution Do NOT place your name on this quiz paper

Place your SID only on this line: The total of Part 1 is worth 10.0% of the assessment for MECH3660 9660 The total of Part 2 is worth 10.0% of the assessment for MECH3660 9660

Part 1 CNC Machining Multiple-choice (0.25 marks each) Answer all questions Circle the most correct answer 1. Select one method of improving the finish on a CNC part? 1. Using a long series slot drill cutter at a high feed rate and a very slow spindle speed. 2. Machining without the use of coolant. 3. Using the G54 command after a G40 to initiate tool compensation. 4. Immersing the machining process in a bath of non-corrosive salts. (For st ress relief) 5. Running the CNC program twice.

2. What would occur during a machining cycle if the G54 command was not included in the program? 1. If there are no limit switches, life would go on. You can always repair the damage caused. OR 4. 2. If the feed rates are ar e also converted to –ve values, the program would run successfully. 3. No tool changing would take place. 4. Machining would take place at the Machine Coordinate System. 5. Program Zero would also need to be relocated by using the G19 command.

3. The G80 command is used for what purposes? 1. Allows for the alignment of a rotating spindle in preparation for a tool change. 2. Allows for easy repetition of a program once it has run. 3. Allows for the cancellation of any canned cycles such as drilling routines. 4. Aligns the height offset with the tool offset. 5. Allows for the conversion between up and down cut milling.

4. What is the main advantage of using a Slot Drill cutter? 1. Slot Drill cutters enable the drilling of very small (< 0.1mm) hole diameters. 2. Slot Drill cutters are able to take traversing cuts and drill holes. 3. Slot Drill cutters enable very large traversing cuts to be made. 4. Slot Drill cutters are able to machine complex surfaces on 3 axis mills. 5. Slot Drill cutters require little if any lubrication during the cutting process.

5. You would use a G17 command if you were machining on a: 1. XY plane. 2. XZ plane. 3. YZ plane. 4. A carousel machining bed. 5. A disinclined XZ-YZ plane.

6. Which of the following options is not a suitable hold down option? 1. Using strong double sided tape between the bed and very thin (< 3mm) sheets of soft material. 2. Using T-bolts and a machine bed with matching T-slots machined along its length. 3. Using a magnetic bed on mild steel work pieces. 4. Using a modular fixture style bed when larger work pieces need to be s ecured. 5. Using a vice to tightly grip a thin sheet of material between its long axis.

7. Which is the control code M09 used for? 1.Turning the spindle off. 2.Setting the units to metric. 3.Turning the coolant on. 4.Turning the coolant off. 5.Removing any reference to incremental programming.

8. What is the main advantage of using a 4 axis instead of a 3 axis CNC mill for a milling operation. 1.A 4 axis mill is cheaper in purchase price than 3 axis mill. 2.A 4 axis mill can carry more tools in its magazine than a 3 axis mill. 3.A 4 axis mill us the full flank of a tool during a complex surface milling operation. 4.A 4 axis mill is able to use a faster range of spindle speeds than a 3 axis mill. 5.A 4 axis mill has a larger bed than a 3 axis mill for machining work.

9. Why are the leadscrews on a CNC machine preloaded? 1. To provide servo drive and control cable redundancy. 2. To minimize tool deflection. 3. To remove the average error. 4. To remove the backlash error. 5. To minimize the level of dust entry.

10. Does the T command actually perform the tool change in a CNC program? 1. Yes, T is a modal command. 2. Yes, but only when combined with a H command. 3. Yes, but only when a value between 1 to 4 is used for both the T and H c ommands. 4. Yes, but only when the correct T number is used. 5. No, the T command only rotates the carousel in preparation for the tool change.

Written solutions (0.5 mark each) Answer all questions WHERE APPLICABLE ILLUSTRATE YOUR ANSWERS WITH CLEAR SKETCHES

1. Give only two reasons why it is good practice when moving in free air to move the cutter in the XY plane independent of a movement in the Z direction. e.g.? G00 X100.0 Y50.0 G43 Z50.0 H1 G00 Z15.0 To avoid collisions with fixtures. (0.25 mark) To avoid accidentally damaging the workpiece. (0.25 mark)

2. Name only two main sources of error in CNC machine’s accuracy and repeatability? Provide a solution for each of these. Tool Deflection: Use a short series tool where ever possible. (0.25 mark) Thermal Error: Use Cutting Fluids and Internal A/C systems. (0.25 mark)

3. Name only one reason why you would end your CNC program with a M30 command instead of a M02? To allow repetition of the program or words to effect of manufacturing the piece more than once. (0.5 mark)

4. “Machining Plastics is very easy with HSS (High Speed Steel) cutters.” Is this statement true or false? Give only one reason to explain your answer. False. (0.25 mark) Machining plastics is difficult due to heat buildup. Plastics are not conductive. or words to the effect. (0.25 mark)

5. Name only one function that position transducers / encoders have on each axis of an AC or DC servo motor CNC machine? To provide position feedback or words to the effect. (0.5 mark)

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Analytical (5 marks in Total) Answer all questions Using the CNC code below; (a) Sketch and dimension the final shape of the object that is being machined. (3.0 marks) (b) The path of the tool using dashed lines. (2.0 marks)

A 10mm Slot Drill is used as the cutting tool and the material being cut is 200mm x 200mm x 10mm thick Perspex. Please use the graph paper provided and ignore any fixture requirements. •

The Plunge Feed rate is equal to 70 mm/min

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The Traverse feed rate is equal to 170 mm/min

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The Rapid Traverse rate is equal to 6000 mm/min

 N1  N2  N3  N4  N5  N6  N7  N8  N9  N10  N11  N12  N13  N14  N15  N16  N17  N18  N19  N20  N21  N22

G90; Tool Dia 10mm M03; G00 X0 Y0 Z25; G00 Z1; G00 X-35 Y-35; G01 Z-7 F70; G01 Y35 F170; G01 X35; G01 Y-35; G01 X-35; G00 Z1; G00 X-20 Y-20; G01 Z-1 F70; G01 X0 Y20 F170; G01 X20 Y-20; G00 Z1; G00 X0 Y-10; G01 Z-1 F70; G00 Z1; G00 X0 Y0 Z25; M02; M05;

Perspex 200mm x 200mm

Correctly Drawn Object (2.0 marks) Dimensioning of Key Features (1.0 mark) Correct Tool Path using Dashed Lines (2.0 marks)

THIS IS THE END OF PART 1 OF THE QUIZ