Laser Cutting

Question 1

Problems with Nd-YAG laser?

Answer 1

Lower power

Somewhat reduced beam quality

Question 2

Benefits with Nd-YAG laser?

Answer 2

Lower wavelength makes some material absorb more energy (Al for example)

Question 3

Benefits with Fibre laser

Answer 3

Simple design (reliability, cost)
Lower losses
Easier to cool (high surface volume)
Good beam quality (Properties stays constant, partly because easy to cool)
Short wavelength: 1 μm

Question 4

TEM=?

Answer 4

Transverse Electromagnetic Mode

Question 5

Why do we have gas assistance?

Answer 5

Blows away molten material
Shields the cutting head
Air is one alternative
Can be inert (prevent oxidisation)
Oxygen provides additional energy in Fe-cutting

Question 6

Why do we use cooling?

Answer 6

To avoid so called “thermal lensing”; Diminish the altering of shape and material properties of the lens

Question 7

Which are the process parameters?

Answer 7

Emitted power
Continous/pulsed emission
Focal length
Focal point
Nozzle: Pressure, flowrate of gas
Nozzle: Workpiece distance
Gas: Nature and quality.

Question 8

Cutting speed?

Answer 8

P/(v*d)

Question 9

Al, stainl Steel, Mild steel, sort after max thickness to cut

Answer 9

Al

Question 10

Why cut using Oxygen?

Answer 10

The heated metal reacts with the oxygen in the kerf, it burns and oxidizes.

Higher cutting speeds are possible and greater material
thicknesses can be processed
Mainly for mild steel

Question 11

Disadvantage of cutting using oxygen?

Answer 11

An oxide film is formed on the cutting surface

Question 12

Why use shielding/inert gas to cut?

Answer 12

No reaction with molten metal.
Less exothermic reaction and oxidation may damage the material.
Used for alloyed steels and stainless.
O_2 can be used for piercing to diminish reflection

Question 13

Why do we use pulsed power?

Answer 13

Easy way to control power,
Freq= some hhz or some khz
avoids excessive heat in corners.

Question 14

Advantages of laser cutting?

Answer 14

Relatively small Heat Affected Zone
Narrow kerf
Perpendicular kerf and no/little burr
No mechanical force (just gas flow)
Very fast for thin shee

Question 15

Disadvantages of Laser cutting?

Answer 15

Difficult to cut reflective materials
Can produce hazardous gases
Low energy efficiency
Still some HAZ
Investment level

Question 16

How does EDM work?

Answer 16

A plasma channel is created (10Microm wide)
High temperatures are created(10000-20000°C) Material is melted &/ vaporised
the plasma turns to gas and then expands removes material. Material solidifies and is flushed away

Question 17

Olika Elektroder och för/nackdelar till edm?

Answer 17

Graphite Large electrodes, complex shapes.
Easily machines
High wear resistance, hard to melt.
-Fragile
CU: Quite easily machined
Ductile, good for thin sections and holes
CU-W: Wear resistant
-expensive

Question 18

Dielectric fluid functions?

Answer 18

1.
Insulates 
-
prevents spark to occur before correct distance and voltage
2.
Cools workpiece and tool
3.
Flushes material away, helps in the material removal

Question 19

Dielectric fluid ways of applying?

Answer 19

Open flushing
Interval 
flushing, retracting
the electrode at a given frequency
Through electrode (or workpiece) with 
certainpressure (”Pressure flushing”)

Question 20

which Dielectric fluid are used?

Answer 20

Aromatic Hydrocarbons(toxic)
Kerosene and vegetable oils
De-ionised water for wire edm

Question 21

EDM economics 101?

Answer 21

Low material removal rates
Long lead times for Ram-EDM since tool(s) need to be
produced
High tooling costs
Moving tools can diminsh costs and lead times
High degree of automation (+ unmanned)

Question 22

EDM Characteristics?

Answer 22

can cut all electrically conductive mtrls
Small deep holes: diam. 0,05 mm
No forces
Very complex geometries can be produced
Some HAZ