MMA Welding Principle of Operation

 

MMA Welding Principle of Operation

MMA welding

 

MMA Welding (Manual Metal Arc) welding, also known as stick welding, operates by creating an electric arc between the workpiece and a consumable electrode rod. The rod melts and forms the weld joint as it is deposited onto the workpiece, while the heat from the arc also melts the workpiece, creating a fused joint.

Main features:
• Shielding provided by decomposition of flux covering
• Electrode consumable
• Manual process
Welder controls:
• Arc length
• Angle of electrode
• Speed of travel
• Amperage settings

Manual Metal Arc Basic Equipment

 

Manual Metal Arc Basic Equipment

MMA Welding Plant

Welding Transformer:
• Changes mains supply voltage to a voltage suitable for welding.
Has no moving parts and is often termed a static plant.
Welding  Rectifier:
• Changes a.c. to d.c., can be mechanically or statically achieved.
Welding Generator:
• Produces welding current. The generator consists of an armature
rotating in a magnetic field, the armature must be rotated at a
constant speed either by a motor unit or, in the absence of
electrical power, by an internal combustion engine.
Welding Inverter:
• An inverter changes d.c. to a.c. at a higher frequency.

 

MMA Welding Variables

Welding Voltage
• The arc voltage in the MMA process is measured as close to
the arc as possible. It is variable with a change in arc length
Welding O.C.V.
• The open circuit voltage is the voltage required to initiate, or
re-ignite the electrical arc and will change with the type of
electrode being used e.g 70-90 volts
Welding Current
• The current used will be determined by the choice of
electrode, electrode diameter, and material type and
thickness. Current has the most effect on penetration.
Welding Polarity
• Polarity is generally determined by operation and electrode
type e.g DC +ve, DC –ve, or AC

 

Constant Current Power Source

 

Drooping Characteristic

MMA welding parameters

 

Travel speed

Manual Metal Arc welding parameters

Welding Current

Arc length

 

Type of Welding current:
• voltage drop in welding cables is lower with AC
• inductive losses can appear with AC if cables are coiled
• cheaper power source for AC
• no problems with arc blow with AC
• DC provides a more stable and easy-to-strike arc, especially
with low current, better positional weld, thin sheet applications
• welding with a short arc length (low arc voltage) is easier with
DC, better mechanical properties
• DC provides a smoother metal transfer, less spatter

Polarity: DCEP generally gives deeper penetration

 

MMA Electrode Holder

MMA electrode holder

 

MMA Covered Electrodes

The three main electrode covering types used in MMA welding

• Cellulosic – deep penetration/fusion
• Rutile – general purpose
• Basic – low hydrogen

(Covered in more detail in Section 14)

 

MMA welding typical defects

 

Most welding defects in MMA are caused by a lack of welder
skill (not an easily controlled process), the incorrect settings
of the equipment, or the incorrect use, and treatment of
electrodes

Typical Welding Defects:

•Slag inclusions
•Arc strikes
•Porosity
•Undercut
•Shape defects (overlap, excessive root penetration, etc.)

 

Manual Metal Arc Welding Advantages and Disadvantages

 

Advantages	Disadvantages
Field or shop use	High welder skills required
Range of consumables	High levels of fume
All positions	Hydrogen control (flux)
Portable	Stop/start problems
Simple equipment	Comparatively uneconomic when compared with some other processes i.e MAG, SAW and FCAW

 

MMA Welding Safety Precautions

 

Protective Clothing and Equipment:

• • Wear appropriate protective clothing, including flame-resistant coveralls or leather aprons, to protect your skin from sparks, molten metal, and UV radiation.
  • Use welding helmets with the appropriate shade of lens to shield your eyes from harmful UV rays and flying debris.
  • Wear welding gloves to protect your hands from heat and electrical shock.
  • Wear safety shoes with steel toes to protect your feet from falling objects and electrical hazards

Proper Ventilation:

• • Ensure adequate ventilation in the welding area to remove fumes and gases generated during the welding process.
  • Use local exhaust ventilation systems or respiratory protective equipment (RPE) to minimize exposure to harmful fumes.

Electrical Safety:

• • Inspect welding equipment regularly for any damage or defects, especially electrical cables and insulation.
  • Ensure proper grounding of the welding machine and workpiece to prevent electrical shock.
  • Never touch live electrical parts with bare hands or wet gloves.

Fire Prevention:

• • Keep a fire extinguisher nearby and ensure it is easily accessible in case of emergencies.
  • Clear the welding area of any flammable materials, such as solvents, oils, and rags.
  • Be cautious of sparks and hot slag that can ignite nearby combustible materials.

Eye Protection:

• • Always wear welding helmets or goggles with the appropriate shade of lens to protect your eyes from intense light, sparks, and flying debris.
  • Never look directly at the welding arc without proper eye protection.

Safe Handling of Electrodes:

• • Store electrodes in a dry and cool place to prevent moisture absorption.
  • Use only electrodes that are in good condition and free from damage.
  • Discard damaged or wet electrodes to avoid potential hazards.

Post-Welding Safety:

• • Allow the welded metal to cool down completely before handling or touching it.
  • Be cautious of sharp edges and burrs on the welded metal, which can cause cuts and injuries.