DMV30203 CHAPTER 4 PROCESS PLANNING

Define process planning.

• The process of cutting tools selection for machining operations.

• The development of CNC part programs, involving machine selection, fixturing, machining strategy, and tool selection.

• The process of selecting suitable cutting fluids for CNC machining.

• The evaluation of the material properties before machining.

Describe how cutting speed and feedrate are calculated for a milling operation.

• Cutting speed is calculated using chip load, and feedrate is determined using spindle torque.

• Cutting speed uses diameter and spindle speed, and feedrate uses chip load, number of teeth, and spindle speed.

• Cutting speed is measured directly on the machine, and feedrate depends on coolant flow rate.

• Both cutting speed and feedrate are calculated based on material hardness alone.

Discuss how improper feedrate settings can affect both the tool life and the quality of the finished part.

• Improper feedrate does not impact tool life but only affects part aesthetics.

• Incorrect feedrate leads to tool breakage without affecting surface finish.

• Improper feedrate can cause premature tool dulling, burning, or chipping, affecting both tool life and part quality.

• It only affects the machine's power consumption without impacting the tool or part quality.

Explain advantages and disadvantages of HSS over Carbide.

• HSS is more brittle but cheaper than Carbide.

• HSS cannot be re-sharpened, unlike Carbide tools.

• HSS is less expensive, less brittle, and easier to re-sharpen than Carbide, but it cannot handle high temperatures or hard materials as well.

• Carbide tools are always preferable as they have no disadvantages compared to HSS.

State the critical factors in selecting a CNC machine for a specific part program during process planning.

• Machine's color, availability of digital display, and tooling capacity.

• Programmer's experience, machine availability, part requirements, and suitability for lathe or milling operations.

• Only the cost and power consumption of the machine.

• The brand of the machine and its warranty period.

State the steps involved in selecting the right cutting tool for CNC machining during process planning.

• Check the material, the machine used, and coolant type.

• Evaluate tool availability, machining strategy, order quantity, blueprint tolerances, and machine specifications.

• Only focus on tool sharpness and rigidity.

• Select based on visual inspection of the tool.

An aluminium alloy (grade 7075) workpiece is to be milled by using a flat HSS endmill. The endmill is 14.0 mm in diameter with three flutes. Cutting speed (CS) = 220 mm/min, chip load (R) = 0.02 mm/tooth. Find the spindle speed and feedrate.

• 3000 rpm, 180 mm/min

• 4000 rpm, 250 mm/min

• 5001 rpm, 300.07 mm/min

• 6000 rpm, 350 mm/min

An aluminium alloy (grade 7075) workpiece is to be milled using a flat HSS endmill with a 16.0 mm diameter and four flutes. Cutting speed (CS) = 250 mm/min, chip load (R) = 0.02 mm/tooth. Find the spindle speed and feedrate.

• 4000 rpm, 300 mm/min

• 4974 rpm, 397.89 mm/min

• 6000 rpm, 500 mm/min

• 7000 rpm, 600 mm/min

An aluminium alloy (grade 7075) workpiece is to be milled by using a flat HSS endmill. The endmill is 20.0 mm in diameter with two flutes. Cutting speed (CS) = 350 mm/min, chip load (R) = 0.02 mm/tooth. Find the spindle speed and feedrate.

• 5000 rpm, 200 mm/min

• 5500 rpm, 220 mm/min

• 5572 rpm, 222.87 mm/min

• 6000 rpm, 250 mm/min

An aluminium alloy (grade 7075) workpiece is to be milled using a flat HSS endmill with a 10.0 mm diameter and four flutes. Cutting speed (CS) = 275 mm/min, chip load (R) = 0.02 mm/tooth. Find the spindle speed and feedrate.

• 8500 rpm, 650 mm/min

• 8753 rpm, 700.26 mm/min

• 9000 rpm, 750 mm/min