Arc welding basics

ARC WELDING BRIEF DESCRIPTION


hi friends today i am giving information of ARC welding process.
generally i post about Welding and fabrication because i am working in that field from 3 years and have good knowledge and hands on knowledge of welding field.
arc welder,welding processes knowledge

Table of contents(click on content to get details)

WHAT IS FULL FORM OF ARC?

The ARC is not acronym it don't have any full form.
it is a word.

electric arc = "a lightened discharge of current that is formed when a strong current jumps in a gap in  a circuit between two electrodes."

Temperature of arc welding

arc welding temperature is 3000 to 20,000 degree celsius


What is ARC welding?Definition.

arc welding is process of fusion welding in which the heat required for  welding  is created through electric arc struck between the work(base metal) and electrode(filler metal).
what is arc

PRINCIPLE OF ARC WELDING?

"ARC welding is the process used to join two similar or dissimilar metals by using electrical power to create enough heat to melt metal and after cooling cause binding of the metal."

"ARC welding is type of welding that uses a welding power supply to create an electric arc between the electrode and the base material to melt the metal at welding point."

TYPES OF CURRENTS USED IN ARC WELDING PROCESS?

  • AC = flows half the time in one direction and other half in another direction
  • DC = flows in one direction only.
arc welding used with both DC and AC modes.
mostly DC is used.

WHAT IS POLARITY IN ARC WELDING?
polarity word come because electric circuit have positive and negative poles.
polarity in welding

Polarity in ARC welding machines
when the work is connected to positive terminal of machine and electrode is connected to negative terminal the it said to be have straight polarity.also called as electrode negative
and
When the work is connected to the negative terminal of DC  machine and electrode is connected to the positive terminal then the setup is said to be Reversed polarity.also called as electrode negative.

Effects of polarity on welding?

with few exceptions
electrode positive means reverse polarity is used for deeper penetrations.

while

electrode negative means straight polarity is used for more melting rate of electrode  means more Deposition rates.

"for proper penetration,uniform bead appearance,and good welding results proper polarity is important when welding with any metallic electrode"
"if polarity used is not correct then it results in overheating,rapid burning of electrode,excessive spatter,irregular bead shape,poor penetration,excessive spatter,difficulty in controlling ARC.


TESTING/CHECKING POLARITY IN WELDING?

Determine polarity by using metallic electrode
How to set correct polarity?

STEPS FOR CHECKING POLARITY
  1. clean base metal and keep it flat.
  2. set current or amperage to the 130 to 150A.(for 5/32 inch electrode).
  3. set on either polarity.
  4. start welding arc and run a bead with normal arc length and standard angle.
  5. carefully listen the sound of arc.right polarity with right parameters and angles create regular crackling sound on other hand using incorrect polarity will create irregular crackling and popping sound and create unstable arcs.
  6. Check results of this polarity inspect bead and appearance.
  7. Now change the polarity and repeat welding with same parameters.and check bead.
  8. clean weld runs and examine .with wrong polarity you will get bad weld beads.
  9. repeat same process until you get good quality weld bead and stick to that polarity.

POWER SUPPLIES IN ARC WELDING

  • constant current power supply
  • constant voltage power supply
in arc welding voltage is directly relates to arc length and current relates to heat input.
  • constant current power supply
constant current power supply's used in mostly manual weldings like GTAW and SMAW.
because they maintain constant current even voltage varies.this is because in manual welding the electrode cannot be held with constant arc length which causes variation in voltage.
  • constant voltage power supply
constant voltage power supplies holds the voltage constant and current varies.thatswhy is mostly used in automation welding 
such as GMAW,SMAW,SAW.
here arc length kept constant so any change in distance between the torch and base metal is quickly corrected by large change in currents.


  METHODS USED IN ARC WELDING

  1. consumable electrode method
  2. non-consumable electrode method
  • in consumable electrode method electrode used is have properties of getting melted and form weld with base metal.so it is called consumable electrode method like in SMAW,GMAW,SAW,FCAW.
  • in non consumable electrode method electrode is used to only melting the job.and filler provided externally. like in                   GTAW,AHW,CAW,Electro slag welding,electro gas welding,Plasma arc welding.

TYPES OF ARC WELDING 

  1. CAW ( Carbon arc welding)........note aw refers to arc welding for all below types
  2. SMAW (shielded metal AW) also called MMAW(manual metal aw)
  3. SAW (submerged AW)
  4. GTAW (gas tungsten AW)also called TIG(tungten inert gas welding)
  5. GMAW(gas metal AW) also called MIG(metal inert gas welding)
  6. Electroslag welding                                                                      
  7. Electrogas welding                                                                   
  8. Plasma arc welding
  9. Arc spot welding
  10. Stud welding

DUTY CYCLE IN ARC WELDING MACHINE

definition of duty cycle

definition 1
"The amount of time for which you can weld continuously without worrying about overheating of welding machine."

definition 2
"The duty cycle is rating that indicate how much time the welding machine used to its maximum current without affecting welding machine."

definition 3
"duty cycle is welding equipment specification that defines the no of time within the 10 minutes period during which given welder safely produce given weld current.

Duty cycle based on 10 minute working cycle.

Example of duty cycle
if a welding equipment have 200A/60% duty cycle that means after welding for 6 minutes with given amperage rating welding machine needs 4 minutes rest. 

how to calculate duty cycle/formula

take example above neglect current.60% duty cycle means

60% means
60 divided by 100 and multiplied by 10 minutes

answer = 6 minutes.(duty cycle)


arc welding safety equipments

Safety equipment's and precautions take in arc welding.

 safety is very important in welding and also everywhere.

dangers while welding are 
  • arc of welding have very high intensity so its dangerous to eyes.
  • fumes and smoke created during welding also have dangerous gases which are dangerous to health.
  • spatters get on sides of welder there are chances of fire because welder not able to see what happening besides him.
  • burning of hands,skin. 
Safety equipment's and precautions
  • Use welding helmet to avoid affecting eyes with high intensity arc light by using din glass use 11 to 13 din glass according to application.
  • use eye goggle for avoiding eye and fumes contacts
  • use nose mask to avoid fumes and smoke going into lungs.
  • wear leather hand gloves,boiler suit.

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arc welding pdf types of arc welding arc welding basics arc welding temperature arc welding rods arc welding machine principle of electric arc welding arc welding ppt
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