Design for manufacturing - Assembly design 1

MIG WELDING AND TIG WELDING:

- they are part of the arc welding but for manufacturing

MIG welding → metal inert gas

the electrode is the same as the filler metal → same material

- inert gas → does not react with the metal → no corrosion → argon, helium

- or carbon dioxide → to protect the join against corrosion

- base metal and welding gun are connected with the welding machine that provide

electric power

the electrode is in wire that passes between the electric power tool →

- there are some rollers that drive the wire to the welding machine →

originally the wire is on a spool

- advantages:

the rollers can control feed and speed of the wire automatically →

- the arc distance is automatically captured by the settings and does

not change during the process → it is more precise because is up to

the welding machine and not the human

welding machine can be set with lower power because dìthere is a

- lower risk of losing the arc because of the distance → is a great

advantage

another advantage → the wire is automatically given by the

- machine and there is no need to replace it → we do not lose time

we have a tank with shielding or inert gas → connected with the

- welding machine → the gas goes out from the welding gun just

around the arc → this protect the arc and we have less defect

- lower heat

- more precise and regular geometry

- for steels, aluminium, titanium (wide range)

- relatively fast

- thickness between 0.5 and 6 mm

6 mm because of the shielding gas that expands getting cooler → it cools

- the base metal → only on one side → the back side remains hot →

difference of temperature create thermal stress that can bring to breakage

- optimum quality on carbon steels

- 30-40 cm per minute

TIG welding → tungsten inert gas

we have a tungsten electrode → very high melting temperature 3000

- degree → refrattario → if we have a tungsten electrode → can be heated to

2000 degrees → it gets hotter so the arc can be kept on at a lower electric

current power

- filler metal is provided by an additional stick

- we have in some cases a source of cooling water that goes into the welding gun and

cools the tungsten electrode so it is not overheated

- thickness 0.2 to 3 mm

- slower than mig

better quality than mig on al and ti → no discolouration → so good for

- aesthetic

- same alloys as mig

- we use a lower current

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welding jig is a sort of bench where there are metal blocks that keeps the part in the right

position

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sometimes:

first → mig welding → MIG tack welds = saldature a punti → purpose of the

- tack is to avoid distortion and deformation and create a first joint → mig

because is faster

- then we use TIG to have complete welds

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mig and tig create visible welds → after grinding and polishing

(levigatura/smerigliatura e lucidatura) we improve the look of the welds → they

are finishing operations that requires little time

we can obtain the same result without finishing operation with:

Laser-beam welding:

laser beam is an high energy light (heat source) → generated by a laser

- source and is focused using lenses on a very narrow spot 0.1 or 0.2 mm

- when the light hits the parts, they absorb the light and converts the light into heat

the base metal change the frequency of the light, turning it into heat → it

- heat the metal and we have melting and then solidification of the weld

- we do not have filler metal because the concentration of the light allows to do not

have gaps on the base metal

- advantages:

extreme concentration of the light → high speed and very good

- quality

- disadvantages:

- expensive equipment

2 main application:

- continuous joint with very high quality

- spot welds in a very small size

Resistance spot welding (saldatura a punti):

- spot means on a single point

resistance → we heat the material using the electric current of the material

- → dissipated and converted into heat → Joule effect

- used for lap joint

- 2 copper electrodes connected to an electric power source

- between them there are the 2 metal parts

the current when the copper electrode clumps the parts with a force →

- they heat the material

- the base metal melts, then solidifies and creates a spot weld

- one spot is not enough so there are more spots on the same surface

- advantages:

- very fast

- steels and aluminium and titanium

for steel → thickness < 15-20 mm, up to 3-4 layers

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- disadvantages:

we do not have a continuous welding → we have gaps → not for

- liquids or gas etc

- alternative:

seam welding → saldatura a rulli:

- - copper electrodes are disks that rotate in opposite directions and

create a continuous weld (multiple spot weld one just after the other)

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spot welding:

manual spot welding machine → the operator moves the base metal

- robotic welding line → for higher production volume → mechanical arms

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