FORM TP m a y /ju n e 2010

Transcription

1 TEST CODE FORM TP m a y /ju n e 2010 CARIBBEAN EXAMINATIONS COUNCIL SECONDARY EDUCATION CERTIFICATE EXAMINATION MECHANICAL ENGINEERING TECHNOLOGY Paper 02 - Technical Proficiency 2 j hours 05 MAY 2010 (a GENERAL DIRECTIONS: 1. This paper consists of THREE sections. You MUST answer a total of FIVE questions. SECTION A: You must answer the COMPULSORY question from this section. SECTION B: You must answer THREE questions from this section. SECTION C: You must answer ONE question from this section. 2. In addition to the 2 - hours, you are allowed 10 minutes to read through the paper. Writing MAY begin during tle 10-minute period. 3. Write your answers in the answer booklet provided. 4. Use sketches when necessary to support your answers. 5. Silent electronic calculators may be used. DO NOT TURN THIS PAGE UNTIL YOU ARE TOLD TO DO SO /F 2010 Copyright 2008 Caribbean Examinations Council. All rights reserved.

2 -2- This paper is divided into THREE sections - A, B and C. You MUST answer the question from Section A, THREE questions from Section B and ONE question from Section C. This paper contains metric dimensions only. You should work your answers in the metric system. SECTION A You are allowed to use freehand sketches or rule-assisted sketches to answer this question which is based on Module B8 of the syllabus - Engineering Design. The question is worth 40 marks. You are advised NOT to spend more than 50 minutes on this question. 1. Figure 1, on page 3, shows an incomplete elevation and plan for a pressure juicer designed for squeezing the juice from fruits. The cylinder and plunger are made from stainless steel while the column and base are made from aluminium alloy. The arm of the mechanism should be attached to the column and plunger and should be able to move up and down as indicated by arrow A-B. The arm is pulled down towards B to squeeze the juice and returns to the top of the arc when it is at rest. The cylinder is to be supported by a bracket that is attached to the column and should allow for easy removal of the cylinder to dispose of the pulp after each squeeze. Use sketches to show clearly the following: A means of attaching the plunger to the arm at point C so that they move up and down together. ( 8 marks) A means of attaching the arm to the column at point D and allowing the arm to move up and down. ( 8 marks) A bracket supporting the cylinder. ( 8 marks) A means of attaching the bracket securely to the column at E while allowing the cylinder to be removed easily to dispose of pulp. ( 8 marks) (e) A mechanism for lifting the arm back in the raised position after each squeeze. ( 8 marks) Total 40 marks

3 -3 - BASE PLAN Figure 1 m Q K m n / c o m n

4 SECTION B You are required to answer any THREE questions from this section. EACH question is worth 20 marks. Figure 2 shows a component to be made from a piece of 30 mm diameter mild steel bar 120 mm long. The threaded portion of the figure should be done by hand with an M12 x 1.7 die. Figure 2 List the steps of procedure to produce the component. (6 marks) (ii) With the aid of a sketch, explain the procedure you would follow when producing the threaded end to ensure the thread is started squarely. (4 marks) (e) Briefly explain the difference between a rake and a clearance angle as used on a lathe cutting tool. ( 2 marks) Calculate the spindle speed that is to be used to produce the 20 mm diameter if the cutting speed for mild steel is given as 30 metres per minute. ( 4 marks) State TWO ways in which the work on a centre lathe may be secured and driven. (1 marks) List TWO safety precautions that should be observed when using the centre lathe.

5 3. The template shown in Figure 3 is to be produced from a piece of mild steel stock 3 mm thick by 160 mm long by 120 mm wide. The material is prepared and ready to be marked out o <N If i N O Figure 3 ^ List the steps of the procedure for marking out the template. (6 marks) (ii) 4 Identify the tools to be used for marking out the template. ( 3 marks) List the correct sequence of the operations to be performed at the bench in cutting out the slot at A. ( 4 marks) (ii) Name the tools to be used for cutting out the slot. ( 3 marks) List TWO precautions that should be observed when cutting out the slot to ensure it is done accurately. ( 2 marks) State TWO safety precautions that should be observed when using laying-out tools. \

6 4. The slot in the component shown in Figure 4 is to be produced on the horizontal milling machine Figure 4 Sketch and name a milling cutter that could be used to produce the slot. ( 3 marks) The slot is to be produced using conventional or up cut milling. With the aid of a sketch indicating the direction of the feed, and the rotation of the cutter, outline the steps of the procedure for producing the slot. ( 7 marks) The operation for cutting the slot is to be performed using a 100 mm diameter cutter. If the cutting speed for the material is 30 m/min, calculate the required spindle speed for carrying out the operation in revolutions per minute. ( 3 marks) Explain briefly what is likely to happen in EACH of the following cases: (ii) Spindle speed is too fast. Feed is too fast. (iii) Work is not securely fastened for machining operation. (iv) Arbour nut is tightened without arbour support in place. ( 4 marks) (e) State THREE precautions that should be taken while working on the milling machine. (3 marks)

7 -7-5. Figure 5 shows the outline of a baking pan that is to be produced from sheet metal and the edge secured with a piece of 3 mm wire. Figure 5 List TWO different types of sheet metal that could be used to make the baking pan. List FOUR properties that the materials named in would be expected to have. (4 marks) (ii) Explain why any TWO of the properties listed in b are important. ( 2 marks) Make a sketch of the development of the pan indicating the allowances for the seams and wired edge. ( 4 marks) With the aid of sketches, describe the procedure necessary to produce the pan. (6 marks) (e) State TWO safety precautions that should be observed when working with sheet metal.

8 Illustrate with a neat diagram EACH of the following: A permanent joint (ii) A temporary joint ( 4 marks) Outline TWO circumstances under which hard soldering or brazing would be preferred to soft soldering. ( 2 marks) State the approximate tin-lead composition of the following soft solders that would be used for general sheet metal work (ii) soldering electrical components. ( 2 marks) State the difference between an active soldering flux and a passive soldering flux. (e) Give an example of EACH type of flux named in above. ( 2 marks) (f) With the aid of sketches list the steps of the procedure for completing the following types of joints using snap head rivets. Double-strap butt joint (ii) Double riveted lap joint ( 8 marks)

9 - 9 - SECTION C You are required to answer ONE question from this section. EACH question is worth 20 marks. EITHER 7A. Figure 6 shows two cylinders, A and B, which are to be welded together using oxy-acetylene welding. Cylinder A has a hole that is 30 mm in diameter, while cylinder B has one that is 20 mm in diameter. Both holes are to be aligned when the parts are welded together. B DIA 60 MM DIA 30 MM Figure 6 With the aid of sketches: Indicate the preparation that should be made for welding the pieces together, showing clearly how they will be held together during the welding process. (3 marks) (ii) Outline the procedure for welding the pieces together. (4 marks) With the aid of a sketch explain the leftward method of welding using the oxy-acetylene torch. ( 3 marks) During the welding process some common problems that may affect the operation can arise. Copy the table below in your answer booklet and complete it to show a cause and the method of correction for EACH of the problems shown. Problem Cause Correction Poor fusion Torch backfires Torch will not stay lit Flame gives off soot (8 marks) State TWO safety precautions that should be observed while doing oxy-acetylene welding. ( 2 marks) n 1 o o c a ^ a /T? o r v i r\

10 OR 7B. Figure 6 shows two cylinders, A and B, which are to be welded together using electric arc welding. Cylinder A has a hole that is 30 mm in diameter, while cylinder B has one that is 20 mm diameter. Both holes are to be aligned when the parts are welded together. B DIA 60 MM DIA 30 MM Figure 6 With the aid of sketches: Indicate the preparation that should be made for welding the pieces together, showing clearly how they will be held together during the welding process. ( 3 marks) (ii) Outline the procedure for welding the pieces together. (4 marks) State TWO purposes of the electrode coatings used in the arc welding process. During the welding process some common defects occurred. Copy the table below in your answer booklet and complete it to show a cause and the method of correction for EACH of the defects shown. Defects Cause Correction Incomplete penetration Poor fusion Slag inclusion Excessive splatter (8 marks) With the aid of a sketch briefly describe the procedure for striking and maintaining the arc during the welding process. ( 3 marks)

11 Illustrate with a neat diagram EACH of the following forging processes: (ii) Upsetting the end of a bar Bending a right angle (iii) Drawing down a piece of round stock to a point ( 6 marks) State TWO major advantages of forging a component to shape rather than machining it from the solid. ( 2 marks) Describe with the aid of neat diagrams how you would harden and temper the point of a centre punch made from 0.6% carbon. ( 4 marks) Explain the difference between the following: Hardening and tempering ( 2 marks) (ii) Normalizing and annealing ( 2 marks) (e) Explain the difference between sand casting and die casting. ( 2 marks) (ii) Give an example of when die casting is preferred to sand casting. As the new laboratory technician in a high school machine shop you are responsible for maintenance of all machines. Copy the table below in your answer booklet and complete it by indicating the different maintenance activities which you will perform with respect to EACH machine for EACH of the periods specified. MACHINE SHOP MAINTENANCE SCHEDULE Machines Daily Weekly Monthly Annually Drill Press Lathe (8 marks) List THREE reasons why it is important to have a preventive maintenance schedule. (3 marks)

12 State the difference between preventive maintenance and corrective maintenance. Name TWO different types of lubricants commonly used in the school workshop. ( 2 marks) State THREE ways in which lubricants can be applied to machines in the workshop. (3 marks) Outline the procedure for applying the lubricant in any ONE of the situations stated in (e) above. END OF TEST /F 2010