Plasma Arc Cutting

Lesson 10 Plasma Arc Cutting

Name Date Class Instructor

Learning Objective You will be able to identify equipment and supplies used in the plasma arc cutting and gouging process. You will also be able to describe the principles used in this process.

Instructions Carefully read Headings 10.1 through 10.8 of the text and study the related ﬁ gures. Then answer the following questions.

1. Free electrons in plasma conduct _____. 1. electricity

2. Plasma arc welding power supplies are constant _____ machines. 2. current

3. Label the parts of the plasma arc cutting torch shown. Torch body A. A Electrode B. F Constricting nozzle C. E D. Heat shield E. Swirl ring B F. Valve pin C D

4. List two ways cutting torches can be cooled. They can be cooled by the plasma gas or liquid- cooled (water-cooled).

5. Which of the following is used as an electrode material? 5. D A. Mild steel B. Stainless steel C. Aluminum D. Hafnium

Ch10.indd 183 8/7/2012 10:51:04 AM 6. The plasma gas and arc travel through a hole in which part of the torch? The constricting nozzle. Note: An answer of just “nozzle” is not clear, since there is also an outer gas nozzle used to direct the shielding gas.

7. What polarity is the electrode in plasma arc cutting? 7. negative

8. Name the two purposes of gases used in PAC. Plasma gas and shielding (secondary) gas

9. The most common gas used for manual plasma arc cutting is 9. air _____.

10. What plasma gas is recommended for cutting aluminum that is 1.0″ (25mm) thick? 65% argon and 35% hydrogen

11. What minimum number lens should be worn during plasma 11. Number 9 arc cutting?

12. What can be worn to protect a person from the loud noises 12. Earplugs or earmuffs that can occur during plasma arc cutting?

13. True or False? If the proper current setting is not known, it is 13. False better to set the current lower than needed prior to cutting.

14. A pilot arc is between the _____ and the _____. 14. electrode, constricting nozzle

15. Which type of arc erodes the electrode and constricting nozzle 15. a nontransferred arc more—a transferred arc or nontransferred arc? ° 16. Describe how to pierce using the PAC process. Hold the torch at a 60 angle, pointing away from the welder and other workers. As the pierce begins, rotate the torch toward perpendicular.

17. What causes dross that is difﬁ cult to remove from the base metal? Traveling too fast or too low a current.

18. During plasma arc cutting, a proper cutting speed is indicated 18. 20 when sparks exit from the bottom of the base metal and point rearward by about _____°.

19. Plasma arc gouging requires _____. 19. A A. a greater voltage than plasma arc cutting B. a smaller constricting nozzle oriﬁ ce than plasma arc cutting C. the torch to be held perpendicular to the base metal D. All of the above.

20. List three shielding gases used for plasma arc gouging. Any order: argon, nitrogen, air.

184 Modern Welding Lab Workbook Copyright by The Goodheart-Willcox Co., Inc.

Ch10.indd 184 8/7/2012 10:51:05 AM Job 10-1 Piercing and Cutting Using the Plasma Arc Cutting Process

Name Date Class Instructor

Learning Objective In this job, you will pierce and cut various materials using the PAC process.

1. Obtain pieces of 1/4″ (6.4mm) mild steel, stainless steel, and aluminum that are 3″ (75mm) wide and 10″ (250mm) long. 2. Refer to Figures 10-11, 10-15, 10-16, and 10-17 in the text and answer the following questions. To cut the mild steel: A. What polarity is suggested for cutting or piercing? DCEN B. What current setting is suggested? 40 amps–80 amps C. What low-cost plasma gas will produce a good-quality cut? air ″ ″ D. What is the recommended cutting speed? 40 /min–100 /min To cut the stainless steel: A. What polarity is suggested for cutting or piercing? DCEN B. What current setting is suggested? 40 amps–80 amps C. What low-cost plasma gas will produce a good-quality cut? air ″ ″ D. What is the recommended cutting speed? 33 /min–100 /min To cut the aluminum: A. What polarity is suggested for cutting or piercing? DCEN B. What current setting is suggested? 40 amps–80 amps C. What low-cost plasma gas will produce a good-quality cut? air ″ ″ D. What is the recommended cutting speed? 50 /min–130 /min

Ch10.indd 185 8/7/2012 10:51:06 AM 3. Mark each piece of metal as shown on the following drawing.

″ ½ Pierce Cutting line 4 holes 10.0

1.0

3.0

1.0

1.5 2.75 1.5 1.5 1.5

4. Pierce four holes approximately 1/2″ (13mm) in diameter along the line drawn in the middle of each piece.

5. Cut the 3″ (75mm) pieces in two places as shown on the drawing.

Inspection The edges of the holes and the edge of the cut metal should be smooth. The top and bottom edges should be free of dross.

Instructor’s initials:

186 Modern Welding Lab Workbook Copyright by The Goodheart-Willcox Co., Inc.

Ch10.indd 186 8/7/2012 10:51:06 AM Job 10-2 Cutting a Shape Using the Plasma Arc Cutting Process

Name Date Class Instructor

Learning Objective In this job, you will cut a shape on plain carbon steel, stainless steel, and aluminum using the PAC process.

1. Obtain pieces of 1/4″ (6.4mm) mild steel, stainless steel, and aluminum that are 2″ (50mm) wide and 6″ (150mm) long.

2. Using soapstone, draw the shape shown in the following diagram on each piece of base metal.

Mark circles tangent .75R at these points Cut line

1.0

1.25

2.75

4.25

3. Using the variables listed in Job 10-1, cut along the lines drawn on each piece of base metal.

4. What action needs to be taken if there is hard-to-remove dross on the bottom edge of the metal? Reduce travel speed.

Inspection The edges of the shape you cut should be square and fairly smooth. The surfaces should be free of dross. The shape should be cut as close to the drawn line as possible.

Instructor’s initials:

Ch10.indd 187 8/7/2012 10:51:06 AM 188 Modern Welding Lab Workbook Copyright by The Goodheart-Willcox Co., Inc.

Ch10.indd 188 8/7/2012 10:51:07 AM