Lec9

Question 1

Broaching MRR

Answer 1

Rise per tooth (Rt) * Number of roughing teeth in contact with a part (Nrt) width of a broach tool

Question 2

3 types of saw blades

Answer 2

hacksaw
bandsaw blade
circular saw cold saw

Question 3

Hacksaw blade properties

Answer 3

straight rigide and of limited length with teeth on one side

Question 4

Bandsaw blade properties

Answer 4

flexible enough that a long length can be formed into a continuous band with teeth on one edge

Question 5

What are bandsaw used for

Answer 5

cutting irregular or curved shapes but also straight cuts uniform cutting action result due to evenly distributed load

Question 6

Circular saw

Answer 6

rigid disk with teeth on the periphery

Question 7

Saw blade material

Answer 7

tungsten or molbdenum high speed steel high tensile strength alloy steel

Question 8

Saw blade tooth spacing

Answer 8

proper tooth spacing is required to ensure chips drop off from this space after cutting

Question 9

saw blade; Blade thickness or gauge

Answer 9

wider and thicker blades desirable for heavy duty work

Question 10

saw blade; tooth set

Answer 10

refers to the manner in which the teeth are offset
from the centreline in order to make the kerf wider
than the gage
permits the saw to move more freely in the kerf
and reduces frictions and heating

Question 11

Cutting speed influence on tool life

Answer 11

50% increase in speed 90% decrease in tool life

Question 12

Feed influence on tool life

Answer 12

50% increase in feed = 60% decrease in tool life

Question 13

depth of cut influence on tool life

Answer 13

50% increase in depth of cut = 15% decrease in tool life

Question 14

How to extend tool life

Answer 14

increase feed and depth of cut

but increaseing cutting speed increases productivity and profitiability

Question 15

Factors to consider when increasing cutting speed

Answer 15

decreases machine time
tools wear out faster and must be replaced
not making money when replacing tool
down time cost incurred

Question 16

Costing normally based on?

Answer 16

per unit or per batch

Question 17

factors that affect cost

Answer 17

1 machine tools - suppliers automation working enviroment
2 cutting tools - required performance life operating parameters
3 labour skilled or unskilled
4 overhead - rent electricity
5 machine setup time - for each batch during normal operation
6 loading and unload time - for each unit or batch
7 depreciation and residual values of equipment expressed in unit timer
original cost - residual cost operating life

Question 18

Non cuttting time percentage total time spent machining

Answer 18

5% - of that incut less than 30% rest position loading gaging idle etc

Question 19

Machine hourly rate

Answer 19

how much the machine costs to run per hour regardless of the nature of operations
MHR = Depreciation + staff costs + overhead

Question 20

Fixes cost

Answer 20

cost that is fixed per batch

fixed costs = tooling + setup time x MHR

Question 21

Variable costs

Answer 21

cost taht varies with batch size expressed per unit

Variable cost = material req + (processing time x MHR)

Question 22

Total cost

Answer 22

= fixed costs + variable costs x number of units

Question 23

Trades off are required between

Answer 23

capital cost of machines and tooling
cost per piece or batch
eg CNC more expensive but make products to certain quality much quicker

Question 24

Compareing raw machining costs

Answer 24

used for selecting new supplier forcutting tools so per per performance
C = non productive cost + machining costs + tool change cost + cost of cutting tools

Question 25

high efficiency machining range

Answer 25

minimum total cost per piece cutting speed and minimum time per piece cutting speed

Question 26

Other factors to consider while costing

Answer 26

have to cost and deal with waste, if producing tonnes of waste every year very expensive very quickly

Question 27

Adv of cutting fluids

Answer 27

coolant
lubricant
carry away chips and reduce friction 
reduce temperature maintains tool hardness
removal of heat

Question 28

cutting fluids maintains tool hardness

Answer 28

extends tool life or allows increase in cutting speed

Question 29

Removal of heat cutting fluids

Answer 29

reduces thermal distortion of the workpiece - improved dimensional control

Question 30

Effectiveness of coolant

Answer 30

thermal capacity and conductivity of the fluid used

Question 31

Issues with water as cutting fluid

Answer 31

very effective in reducing temperature

but causes rust and poor lubricant

Question 32

Oils as cutting fluid

Answer 32

less effective coolant capacity than water
better lubricant
dont cause rust

Question 33

Normal coolant used

Answer 33

combination of oil and water or water and wax or just water used

Question 34

Ideal use of cutting fluid

Answer 34

collect and reuse it - good recycling retain 99% of cutting fluid

Question 35

Economics of machining

Answer 35

majority of time not profitable

Question 36

A good cutting fluid

Answer 36

helps increase cutting speed