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Flashcards in Lec6 Deck (55)
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1

4 types of chips

continuous
built up edge
serrated
discontinous

2

Types of wear

Flank: adhesive
Abrasive; Crater

3

What is machining

Machining is a process of removing unwanted
material from a workpiece in the form of chips

4

Basic terms: speed

The primary cutting motion that relates velocity of a cutting tool relative to a workpiece (represented as solid arrows)
metre/min. or metre/sec. or rev./min.

5

Feed or feed rate

The distance a tool travels per unit revolution of a workpiece (represented as dashed arrows) mm/rev or inch/rev

6

Depth of cut

mm or in pretty self explanatory

7

Diagram of two dimensional cutting process

chip
rake angle
tool face
tool
shear plane
shear angle
workpiece
flank
relief or clearance angle

8

Purpose of relief angle

ease cutting operation

9

What happens during cutting

shearing takes place
material underneath the shear zone not removed
everything above the shear zone converted into chips

10

Where does shearing take place

Along the shear plane which is at angle theta called the shear angle with the workpiece

11

What happens above the shear plane

Chip is already formed and moving up the face of the tool as cutting progresses

12

What can chip thickness (tc)be determined from

by knowing depth of cut (to) rake angle (alpha) and shear angle (theta)

13

What velocity does shearing take place at

Vc

14

What is the cutting ratio

r = to/ tc = sin(theta) / cos (theta - alpha)
theta = shear angle
alpha = rake angle

15

What is the compression ratio

reciprocal of r, measures how thick the chip has become compared to the depth of cut

16

What is shear strain

shear strain material undergoes = cos (theta) + tan (theta - alpha)
theta = shear angle
alpha = rake angle

17

Effect of shear angle

influences chip thickness, force and power requirements and temperature

18

Large shear strains are due to?

small shear angles and small or negative rake angles

19

equation relating cutting velocity and chip velocity

V (cutting velocity) * depth of cut (to) = Vc (chip velocity) * tc (chip thickness)
or Vc = V * r
Vc = V * sin(theta)/cos(theta - alpha)

20

What is the cuttting force

Acts in the direction of the cutting speed V and supplies energy req for cutting

21

What is the thrust forcce

acts in the direction normal to the cutting velocity (perpendicular to the workpiece)

22

Importance of thrust force and the balance between machine tool

too high tool will be pushed away from the surface - reduced depth of cut
machine tool, tool holder work holding devices must be sufficiently stiff to minimise deflections caused by force or same thing will happen

23

What are forces measured

Using dynamometeres or force transducers mounted on the machine tool or
forces can be computer from power consumption during cutting if efficiency of the machine tool is known

24

Importance of chips

Influence the surface finish produced and overall cutting operations (tool life, vibrations and chatter)

25

how are continuous chips formed

formed with ductile materials at high cutting speeds and or large rake angles
deformation takes place along primary shear zone

26

Adv and disadv of continuous chips

Produce good surface finish but not always desirable for automated machines operations need to be stopped to remove chips

27

Solutions to continuous chips

chip breakers, change machine parameters cutting speed feed cutting fluids

28

If continous chips produce secondary shear plane where would this be and due to what

zone at tool chip interface caused by friction

29

Where are build up edge chips (BUE) formed

tip of tool during cutting

30

What do build up edge chips (BUE) consist of

Layers of material from the workpiece that are gradually deposited on the tool