Transcript Document
Physics of Welding Continued Physics of Welding Continued Lesson Objectives When you finish this lesson you will understand: • Wire melting modes • Power Supply Characteristics • Interactions between the arc and the power supplies • Principles of Magnetic Arc Blow Learning Activities 1. Look up Keywords 2. View Slides; 3. Read Notes, 4. Listen to lecture 5. View Hi-speed Videos 6. Do on-line workbook 7. Do Excel Tutorial Keywords Metal Transfer, Short Circuit Transfer, Pulsed Arc, Power Supply Characteristics, Open Circuit Voltage, Closed Circuit Current, Constant Voltage Power Supply, Constant Current Power Supply, Drooping Characteristic, Self Regulating Arc,Magnetic Arc Blow Physics of Welding • Heat Input Concepts • Energy Sources • Arc Characteristics • Wire Melting Gas Metal Arc Welding GMAW Modes of Metal Transfer Spray Globular Short Circuiting Pulsed Spray Ave I Pulsed Arc Tandom Arc View the Arc Welding High Speed Videos from the Video Web Page on the WE300 Website Turn to the person sitting next to you and discuss (1 min.): • From the chart showing the effect on metal transfer by changes in shielding gas it is seen that an addition of 2% oxygen to tan argon GMAW using DCEP caused the arc to stop wandering and have good spray transfer. Can you explain from a physical point of view what might have happened? Welding Arcs and Machines Open-Circuit Voltage V CC Voc Hot Start Arc CV Voc I Short-Circuit Current V CC Arc Force or Dig CV Arc I Isc Isc (1000's) Electrical Stability of the Arc V Unstable Rs Stable Arc will operate here Arc Source I Manual Arc Control F F F B h B h B=F B h F>B F = Feed Rate B = Burn-Off Rate B>F Manual Arc Control Inputs Vary I V I V Power Source Power Source Vary h Arc Arc h I Vary Current I Current Varies Self-Regulation of the Arc Wire Spool or Reel Feed Rolls V I=F/k1 Contact Tube or Tip F CV Power Source I Vm Wire Feeder B arc too long CV V arc too short h F=constant, I varies current drops B<F current rises B>F I Processes Using Constant Current • SMAW • GTAW • PAW • Processes where humans control arc length by hand Processes Using Constant Voltage • GMAW • FCAW • SAW • Processes that use constant velocity wire feeding Turn to the person sitting next to you and discuss (1 min.): • In the V-I Characteristic Curves, there are two places where the Arc current and voltage are the same as the power supply current and voltage, one point is stable and the other is unstable. Why is the unstable point unstable? Magnetic Arc Blow Magnetic Flux Concentration Next Class Period You will Have a Homework Assignment which will require the use of an Excel Spreadsheet. You should review your knowledge of Excel or click on the digging deeper tutorial. Excel Tutorial