Lesson Plan. Upon completion of this assignment, the student will be able to understand the basic welding circuit and its components.

Transcription

1 Course Title: Welding Session Title: Welding Circuit Lesson Plan Performance Objective: Upon completion of this assignment, the student will be able to understand the basic welding circuit and its components. Specific Objectives: Define basic terminology Label electrode negative and electrode positive diagrams Illustrate an alternating current Identify circuitry activity on a welding machine TEKS Correlations: Preparation This lesson, as published, correlates to the following TEKS. Any changes/alterations to the activities may result in the elimination of any or all of the TEKS listed. Welding: (c)(2)(F) demonstrate skills related to health and safety in the workplace, as specified by appropriate government regulations (c)(4)(A)(B)(C) use welding equipment according to safety standards; properly dispose of environmentally hazardous materials used in welding; and use appropriate personal protective equipment as needed to follow safety measures (c)(5)(A)(B)(C)(D)(E)(F) demonstrate knowledge of a welding blueprint; interpret blueprints, drawings, charts, and diagrams; analyze components of the welding symbol; analyze types of welding joints; analyze positions of welding; and 1

2 identify types of welds such as fillet, groove, spot, plug, and flanged. Interdisciplinary Correlations: English: (6)(A) Reading/word identification/vocabulary development expand vocabulary development through wide reading, listening, and discussing; Instructor/Trainer References: GTAW Student Material booklet Mid-America Vocational Curriculum Consortium (1984) Modern Welding (2004) Welding Principles and Applications (1999) Instructional Aids: 1. Welding Machine Basics PowerPoint Presentation 2. DCEN Handout 3. DCEN Worksheet 4. DCEP Handout 5. DCEP Worksheet 6. AC Handout 7. AC Worksheet 8. Ohm s Law Handout 9. Welding a Circuit Test 10. Welding a Circuit Test Key Materials Needed: Class copies of DCEN diagram Class copies of DCEP diagram Class copies of AC diagram Equipment Needed: Computer & monitor to support PowerPoint Overhead projector Learner The student should provide writing instrument and paper for note-taking. Introduction (LSI Quadrant I): Introduction A welding machine is powered by electricity. It is vital to have an understanding of how electric current plays an integral role in the function of the welding machine and in the process itself. 2

3 Outline Outline (LSI Quadrant II): I. Terminology (students take notes; this will serve as a Guided Practice activity) A. Electrons flow through a conductor from negative (-) to positive (+) B. Electricity flow of electrons (produces heat) C. Air gap space between the electrode and the work item D. Arc produced by electrons jumping across the air gap (produces great deal of heat) E. Voltage (V) measurement of electrical pressure (controls the maximum gap the electrons can jump to form an arc) *like pounds per square inch (psi), dealing with pressure (use the Ohm s Law transparency) F. Amperage (A) measurement of total number of electrons flowing (controls the size of the arc) *like gallons measures water G. Wattage (W) calculated by multiplying (V) x (A) is the measurement of the amount of electrical energy or power in the arc; the amount of watts being put into a weld per inch controls the width and depth of the weld bead H. Duty Cycle the amount of time a welding machine can be used continuously II. Currents (use transparencies for AC, DCEN, DCEP; students should have copies of the diagrams so they can label them; this will serve as a Guided Practice activity) A. AC (Alternating Current) electrons change direction every 1/120 of a second so that the electrode and work alternate thereby making a balanced work load evenly distributed B. DCEN (Direct Current Electrode Negative) electrode is negative, work is positive; produces high electrode melting rate C. DCEP (Direct Current Electrode Positive) electrode is positive, work is negative; produces the best welding arc characteristics III. Welding Machines A. Instructor should show PowerPoint presentation (students take notes) B. Complete Independent Practice activity over welding machine circuitry IV. Review V. Test Application Guided Practice (LSI Quadrant III): 3

4 Taking notes over terminology and labeling diagrams over currents Independent Practice (LSI Quadrant III): During the Independent Practice activity, small groups of students are sent out into the welding shop to look at the welding machines and gather information. Each group should come back from their assigned welding machine with the following information: 1. Is the machine AC or AC/DC? 2. What voltage does it run on? 3. What is the Duty Cycle of the machine? The groups should return with their information to be used in a full group discussion over the various machines in the shop. Review (LSI Quadrants I and IV): Summary Check for mastery/understanding by orally reviewing the students on the information. Answer any questions the class may have. Ask individual students to contribute one fact or principle he learned during the lesson. Make a list of these on the board or overhead. Informal Assessment (LSI Quadrant III): Evaluation Instructor should monitor student understanding throughout the lesson. If further explanation is needed on a given topic, instructor should elaborate or re-teach that portion of the lesson. Formal Assessment (LSI Quadrant III, IV): Mastery of at least 70% of objective test. Extension/Enrichment (LSI Quadrant IV): For those students who need remediation, a re-teach and review session will reinforce the topics of concern. The remediation will need to be tailored to the individual needs of the student. 4

5 ALTERNATING CURRENT (AC) HANDOUT 5

6 ALTERNATING CURRENT (AC) WORKSHEET 6

7 OHM S LAW HANDOUT 7

8 DCEN HANDOUT 8

9 DCEN WORKSHEET 9

10 DCEP HANDOUT 10

11 DCEP WORKSHEET 11

12 Welding Circuit Test Name: 1. Describe Voltage (V) 2. Describe Amperage (A) 3. Describe Wattage (W) 4. Explain the process of an AC (Alternating Current) 5. What is meant by a machine s Duty Cycle? 6. How much heat does the positive side get? 7. What are the common voltages welders run on? 8. Describe the difference between straight polarity and reverse polarity. 9. If you have 30 volts and 110 amps, what is your wattage? 10. What produces an arc in a welding current? 12

13 Welding Circuit Test KEY 1. Describe Voltage (V) Measurement of electrical pressure (just like psi is used for water pressure) 2. Describe Amperage (A) Measurement of total number of electrons flowing (same way gallons measures water flowing) 3. Describe Wattage (W) Measurement of amount of electrical energy 4. Explain the process of an AC (Alternating Current) Electrons change direction every 1/120 th of a second so that the electrode and work alternate. The rapid reversal of current causes the welding heat to be evenly distributed between the work and the electrode. The 50/50 distribution of heat gives the bead a balance between penetration and build-up. 5. What is meant by a machine s Duty Cycle? The percentage of time a machine can run continuously. (Example: 60% means 6 minutes running out of 10 minutes, with 4 minutes of rest time) 6. How much heat does the positive side get? - 75% 7. What are the common voltages welders run on? 110, 220, Describe the difference between straight polarity and reverse polarity. Straight polarity, the stinger is negative. Reverse polarity, the stinger is positive. 9. If you have 30 volts and 110 amps, what is your wattage? 330 watts 10. What produces an arc in a welding current? The electrons jumping the resistance of the air gap 13