Identify metal parts to be refinished; determine the materials, preparation, and refinishing procedures
Lesson Plan for
CRT 150-1Painting and Refinishing I
Course HS Title: / PAINT & REFINISH / Program:KCTCS Courses included in HS Title: (Lesson is prepared for course highlighted.)
KCTCS Course No. / KCTCS Course Title
Introduction/Context / This lesson will instruct students on the proper procedures needed to identify metal parts to be refinished, plus determine the materials, preparation, and refinishing procedures needed for proper repair. Knowledge of these techniques and the skills required to correct problems associated with this task are necessary for a student to acquire if they wish to compete for high paying, high skilled jobs in an automotive repair facility. Entry level technicians need to be able to perform this task to 100% accuracy. Incorrectly performing this task can lead to safety problems, incorrect repair, or create customer satisfaction issues.
Prepared By / School / Date:
Grade Level / No. Students / No.IEP's: / Lesson Length:
Task
Identify metal parts to be refinished; determine the materials, preparation, and refinishing procedures.
No. / Objective
1 / Given the proper tools and instructions from a vehicle manufacturers shop manual or automotive computer software program, students will be able to identify aluminum/metal parts to be refinished, determine the materials, preparation, and refinishing procedures needed, and pass a written exam on the task with 100% by the end of the course.
Connections:
New Common Core:RST 11-12-2
RST 11-12-3
Skills Standards:
OC002
EG011
New Common Core Technical
TD-SYS-1
TD-OPS-3
INSTRUCTIONAL MATERIALS/TECHNOLOGY
Textbooks and Workbooks
James Duffy / Auto Body Repair Technology / 5th / Delmar / 345-346
James Duffy / I-CAR Professional Automotive Collision Repair / 2001 / Delmar / 200
Tobalt/Richardson / Auto Body Repairing and Refinishing / Goodheart/Wilcox / 80-81
Content/Presentation/Demonstration Outline
Instruct students that high-strength, low-alloy steel (HSLA) has replaced mild steel for many exterior body panel applications. HSLA is also used for structural components, such as front and rear rails, rocker panels, door hinges, pillars, and other reinforcements. Let them know that HSLA has two to three times the yield strength of mild steel. Explain that yield strength is the stress required to produce a certain amount of permanent strain (elongation) in a piece of steel. Since HSLA is stronger than mild steel, tell students that thinner, lighter sections of this material can be used to produce a structurally sound vehicle. Unfortunately, let them know that HSLA is more brittle than mild steel. Instead of stretching or deforming smoothly, it tends to kink and crack.
Tell students that high-strength steels (HSS) include a number of different types of high tensile strength steels. Explain that tensile strength is the metal’s ability to withstand being pulled apart. Let them know that HSS is often used for suspension components, door side guards, and bumper reinforcements. Inform students that ultra-high-strength steel (UHSS) may have a tensile strength that is almost ten times that of mild steel. Tell them that UHSS is used for door beams, bumper reinforcements, hinges, and other structural components.
Instruct students that internal stresses in high-strength steels are commonly relieved by applying a pulling force or by spring hammering. Let them know that spring hammering is a process that involves lightly striking the ridge of a dent with a bumping hammer while holding a spoon firmly against the back of the damaged area. The pressure and rebound energy from the spoon helps to straighten the dent. Explain that The vibrations from the light hammer blows help to relieve pressure by rearranging the molecular structure of the metal.
Instruct students that Aluminum is used for a variety of automotive panels, such as hoods, fenders, and roof panels. Inform students that a few passenger cars have their entire unibody made of an aluminum alloy. Aluminum's natural resistance to rusting and corrosion is its primary advantage. Let students know that the repair of aluminum panels requires much more care than working steel panels. Aluminum is much softer than steel, yet it is more difficult to shape once it becomes badly bent and work hardened. It also melts at a lower temperature and readily distorts when heated.
Instruct students that aluminum panels are usually thicker than today's HSS (high strength steel) panels. Tell them it is important to keep in mind that aluminum body and frame parts are usually 1.5 to 2 times as thick as steel parts. When damaged, let students know that aluminum feels harder or stiffer to the touch because of work hardening. Make them aware that these characteristics must be considered when working damaged aluminum panels.
Inform students that the hammer-on-dolly method is generally recommended for aluminum panel straightening. Because aluminum is less ductile (less capable of being shaped or molded) than steel, students should know it does not readily bend back to its original shape after being buckled by an impact. Therefore, let them know that aluminum does not respond well to off-dolly hammering. Tell students that care must also be exercised to avoid additional damage when attempting to lower ridges with hammer and dolly blows.
Instruct students that aluminum alloys bend much more quickly when the panel is sandwiched between the hammer and dolly, as with the hammer-on-dolly method. When it is necessary to hammer on dolly, inform students that hammering too hard or too much can stretch the soft aluminum panel. Tell them it is better to use many light strokes than a few heavy blows.
Teach students that shrinking hammers used for working steel should not be used with aluminum, because they can cause cracking. Let them know that separate sets of tools should be used on steel and aluminum.
When hammer picking aluminum, remind students to work slowly and methodically. Inform students that raising small dents with a pick hammer or pry bar is an excellent way to repair aluminum panels. Tell them to be careful not to raise the panel too far, stretching the soft aluminum. Also, let them know that spring hammering with hammer and spoon is an excellent way to unlock stresses in high-pressure areas in aluminum. Tell them that the spoon distributes the force of the blow over a wider area of the soft aluminum, minimizing the possibility of creating additional dents in any unyielding buckles.
Instruct students that because aluminum is so soft, they should reduce hand pressure on the body file when marking high and low spots. Tell them to use a file with rounded edges to avoid scratching and gouging the metal. Soft aluminum cuts much more easily than steel.
Grinding must be done very carefully on aluminum panels. Inform students that a coarse grit disc on a high-speed grinder can quickly burn through the soft metal. The heat from the grinding operation can also quickly warp the panel. Inform them that they can use a #36 grit open coat disc, but grind carefully in order to remove only paint and primer, not the metal. Instruct students to make two or three passes. Then, quench the area with a wet rag to cool the metal and minimize heat gain. Tell students that grinding small areas and featheredging should be done with a dual-action sander or an electric polish machine that rotates at less than 2,500 rpm. Let them know too use #80 or #100 grit paper and a soft, flexible backing pad.
Instruct students that there is one major difference with straightening aluminum by heat shrinkage. With steel, tell them too use heat only when the metal is stretched and cannot be straightened by other means. With aluminum, tell them heat must be used to restore the flexibility that was reduced by work hardening. Without the use of heat, let students know that the aluminum may crack when straightening force is applied. Inform students that before attempting to straighten aluminum, heat the damaged metal with a torch. Remind them that it is easy to apply too much heat, because aluminum does not change color with high temperatures. Aluminum melts easily, so let students know that careful heat control is very important. Tell them to use a temperature-sensitive paint or a heat-sensitive crayon made to change color at about 750'F (417'C).
Have students follow these steps for properly using the heat-sensitive crayon: Tell students to apply a temperature-sensitive paint or crayon in a circular pattern around the area that will be exposed to the flame. Inform them that aluminum does not glow cherry-red like steel does right before it melts. Have them heat the area, moving the flame constantly. Tell them to stop heating when the paint or crayon color changes. Instruct students that the surface temperature at the center of the heated area will be between 750° and 800°F, which is a safe margin from aluminum's melting point. Let them know that a lack of caution will result in a melted panel. Also, tell students that the shrink spot must be very slowly quenched to avoid distorting the panel by excessive contraction.
Applications/Practice
Evaluation and feedback Prior to Testing or Lab Work
STUDENT ASSESSMENT:(Assess student progress with performance criteria.)
IMPACT--Reflection/Analysis of Teaching and Learning: (How did students’ progress in relation to the state objectives? Was the instruction successful? Analyze samples of student work particularly that which is unsatisfactory, for the purpose of planning further instruction.)
REFINEMENT--Lesson Extension and Follow-up: (To be filled in as the lesson is modified during initial planning and/or during the teaching learning process.)