Paper ID #29741

Teaching Assembly Planning Using AND/OR Graph in a Design andManufacture Lab Course

Dr. Khalifa H Harib, United Arab Emirates University

Khalifa H. Harib joined the United Arab Emirates University in 1997. Currently he serves as associateprofessor of mechanical engineering. He obtained his B.Sc. degree from UAE University in 1986, and hisM.Sc. and Ph.D. degrees from the Ohio State University in 1993 and 1997, all in mechanical engineering.His research and teaching interests include robotics, mechatronics, dynamics and control, and computeraided manufacturing.

Dr. Sangarappillai Sivaloganathan, United Arab Emirates University

Dr Sangarappillai Sivaloganathan – Siva is a Srilankan by birth and a citizen of the United Kingdom. Hisexperience in Sri-lanka started with an year’s post-graduate apprenticeship in the manufacturing shops ofthe Government Railway and nine years in the Cement Industry. He graduated as a Mechanical Engineerfrom University of Srilanka, and obtained his Masters from the University of Aston and PhD from CityUniversity of London, both in the UK. He started his career in the UK as the Senior Research Assistant atthe SERC Engineering Design Centre. He joined Brunel University in 1995 where he worked for 18 yearsbefore joining United Arab Emirates University in August 2011. During his stay at Brunel he has workedwith many British industries. Dr Sivaloganathan is a keen researcher in Design and was the Convenor forthe International Engineering Design Conferences in 1998 and 2000. He has been a regular participant ofthe ASEE annual conference during the past few years. He has published more than 85 papers in reputedjournals and conferences.

Mr. Hayder Zulafqar Ali, United Arab Emirates University (UAEU)

Hayder Ali is an instructor in the Mechanical Engineering Department at United Arab Emirates University(UAEU). Before joining UAEU, he received training on a long term technology transfer (plastic moldmaking) project between government of Pakistan and government of Japan. He holds a master’s degreein Mechatronics Engineering and a bachelor’s in Mechanical Engineering, both from the University ofEngineering and Technology, Lahore, Pakistan. He has extensive teaching and industrial experience.

Dr. Bobby Mathew, United Arab Emirates University, Mech. Engineering Department

Dr. Mathew is an assistant professor with the mechanical engineering department at United Arab EmiratesUniversity, UAE. He started at UAEU in 2016. His teaching interests include heat transfer and fluidmechanics.

c©American Society for Engineering Education, 2020

Teaching Assembly Planning Using AND/OR Graph in a Design and Manufacture Lab Course

Sangarappillai Sivaloganathan, Khalifa Hareb, Bobby Mathew and Hayder Ali

United Arab Emirates University PO Box 15551

AlAin United Arab Emirates

Key Words: AND/OR Graph, Systematic Assembly Planning Abstract: This paper describes how AND/OR graph has been introduced as a systematic assembly sequence planning to senior mechanical engineering students at United Arab Emirates University. The students were introduced to AND/OR graph through Matrix Manipulations. They were then given hands on experience in the assembling of a bearing puller. A practical mid-term examination in the assembly planning of a Three-pin plug was given as the examination task. The results were excellent in that 43 out of 51 scored more than 90%. The encouraging results suggest that AND/OR graph is a suitable method for assembly planning. 1. Introduction Manufacturing in general can be divided into two classes of activities: fabrication and assembling. In fabrication, constituent parts are produced using the basic and advanced manufacturing processes. Assembling on the other hand views the product as a set of fabricated parts linked together through joints during the assembly process and each joint is made using an assembly technique. Assembly Planning aims to identify and evaluate the different ways of constructing a mechanical object from its components. Mechanical products often have multiple assembly sequence plans, due to the complexity and the multiplicity of their components, and therefore some assembly sequence plans are more efficient than others [1]. The requirement of fixtures at different stages, makes it essential to look at multiple assembly plans to choose the optimum one. An AND/OR graph is a representation that contains the solution of a problem that can be solved by decomposing it into a set of smaller problems until all of them are solved. In assembling, a product is the combination of sub-assemblies, the sub-assemblies are combinations of sub-sub-assemblies and they in turn are combination of parts. Therefore, assemblies can be represented by AND/OR graphs and the representation can have the OR node showing a choice between possible assembly path and the AND node representing a given assembly path. The motivation for the inclusion of this assignment came from the observation of struggling students in their capstone projects, where assembly planning would have helped them. This paper describes how assembly planning principles and their implementation at the product level, is taught to senior mechanical engineering students through the Design and Manufacture Lab course, so that they can use assembly planning in their capstone projects. 2. The Methodology The methodology consists of two steps and an assessment through a practical question in the midterm examination. In the first step a lecture on AND/OR graph explaining how it is used in a matrix manipulation case and a mechanical assembly case was given. The matrix manipulation is seen as an easy way to introduce the AND/OR graph. In the second step the students were given a hands-on experience with a bearing puller. Finally, they were given a

practical examination in the assembly planning of a 3-pin plug. The following sub-sections describe them. 2.1 Matrix Manipulation Explaining AND/OR Graph Consider the situation where there are three matrices ["]!×#, [$]#×$ and [%]$×%and the product ["$%] is needed. This can be achieved in two different ways. Way 1 - A(BC): ["] pre-multiplies the product [$%] to get ["$%] Way 2 – (AB)C: The product ["$] pre-multiplies [%] to get the product ["$%]. When two conformable matrices [&]&×' and [']'×( are multiplied the number of multiplications needed is equal to the product of the dimensional numbers ()*. If this number of multiplications is taken as the cost of the multiplication then The cost of Way 1 would be = Cost of product BC + Cost of product A and (BC) = 4 × 6 × 1 + 3 × 4 × 1 = 24 + 12 = 36 Similarly, the cost of Way 2 would be = Cost of product AB + Cost of product (AB) and C. = 3 × 4 × 6 + 3 × 6 × 1 = 72 + 18 = 90 These are represented in the AND/OR Graph shown in Figure 1. Node 1 represents the goal, which is to get the product of the matrices, ABC. Way 1 which is A(BC) is shown in the left-hand side branch and the Way 2 which is (AB)C is shown in the right-hand side branch. Since way 1 and way 2 are alternative ways of getting the result, node 1 is an OR node. In the next level node 2 shows how the product A(BC) is achieved. It is achieved by multiplying a 3 × 4 matrix and a 4 × 1 matrix. Since this combines two branches it is an AND node and an arc is placed to show that it is an AND node. The next level node, i.e. node 5, produces the product (BC) and this would incur a cost of 4 × 6 × 1 = 24. The costs are shown in double brackets at the corresponding nodes. A similar approach is taken to prepare the graph on the right-hand side that shows the Way 2. The branch with the low cost is marked with an additional line next to the branches showing the chosen operations. From the graph it can be seen that all branches that emanates from a node remain marked or unmarked (consider nodes 2 connecting 4 or 5). But only one branch emanating from the OR gate is marked (consider node 1, connecting to 2 and 3).

Figure 1: AND/OR Graph of Matrix Multiplications

3.0 The Bearing Puller and the assembly Process The bearing puller shown in Figure 2 has five component groups including the fasteners as shown in Table 1. The cross arm carries a nut that is driven by the forcing screw to generate the pull forces. The claw legs engage the bearing, the forcing screw engages the shaft at the centre as shown in Figure 2. The applied torque creates a force and resulting movement of the bearing upwards.

Figure 2: Bearing Puller at work (Adapted from the net [2,3])

Table 1: Component Groups in a Bearing Puller Assembly

Component Group Name Notation Number in Product

1 Cross Arm A 1 2 Beam Pairs B 3 3 Claw legs C 3 4 Forcing Screw D 1 5 Nuts and bolts (Fasteners) 6

The assembly process starts with the first component, called the base component, onto which other components are attached. The assembly can be started with the arm or the forcing screw. The assembling sequence for both processes is given in the first two columns of Table 2. The third column shows the sequence when using pre-assembled sub-assemblies consisting of the beam pair and the claw leg. This was included after constructing the AND/OR graphs for the first two sequences. The students assembled the piece by holding the base part and the resulting additions in one hand, while using the other hand to assemble parts. In the option of using the ‘Forcing Screw’ as the base part, a bench vice was found to be useful to hold the screw freeing both hands. For mass production, this process was found to be uncomfortable and the students developed a fixture to hold the arm. This actually resulted in the method with pre-made sub-assemblies described in column 3. This method of pre-made sub-assemblies can be used with either arm or forcing screw as the base component. A fixture would be needed if large quantities are to be assembled. In this case, if forcing screw is the base component, vice is the fixture. On

the other hand, if arm is the base component a fixture has to be made. Figure 3 shows the assembling process with the fixture for using arm as the base component, and Figure 4 shows a typical AND/OR chart formed by the students for this method.

Table 2: Some Possible Assembling Sequences Arm as Base Component Screw as Base Component With sub-assemblies

Arm Forcing Screw Arm Beam Pair 1 Arm Beam pair claw assembly 1 Beam Pair 2 Beam Pair 1 Beam pair claw assembly 2 Beam Pair 3 Beam Pair 2 Beam pair claw assembly 3 Claw leg 1 Beam Pair 3 Forcing Screw Claw leg 2 Claw leg 1 Claw leg 3 Claw leg 2 Forcing Screw Claw leg 3

Figure 3: Assembling with the Fixture

Figure 4: AND/OR Graph for the Assembling Process

4.0 Examination with the Three-Pin Plug The students’ ability was tested in the midterm examination of the Design and Manufacture Lab course where they were given three-pin plugs as assembled pieces and disassembled components. Together with two optional fixtures where they could (a) use a bench vice or (b) a purpose-built fixture. The use of fixtures is shown in Figures 5 and 6 and the parts of the plug are shown in Figure 7. Most of the students chose both options. They were asked to construct the AND/OR graph for assembling process. The bench-vice process starts with a sub-assembly with the earth pin and base, assembled by hand. The earth-pin is used as the base part to hold in the vice for the rest of the process until the cable grip is assembled. Then the assembly is taken on hand to tighten the cable grip and to place the cap. The cap screw is tightened and the instruction paper is placed completing the assembly process. The process with the purpose-built fixture starts with placing the base in the fixture and continues adding component after component. The assembly is taken in hand after just installing the cable grip. The screws were tightened after turning the assembly upside down and placing the cap. The process is complete with installing the instruction paper. Figure 8 shows the combined AND/OR chart for easy reading and comprehension.

Figure 5: The Bench Vice as the Fixture

Figure 6: The Purpose-Built Fixture

Figure 7: Three-Pin Plug and Components

Figure 8: Typical AND/OR Chart by Students (Combined)

5.0 Analysis and Discussion The results of the examination show that the students have got a clear grasp of the process. Out of the 51 students nearly half (49%) got full marks while another 35.3% got more than 95%. As an assignment in a lab course, consisting of five assignments and a project, it is a worthwhile experience for the students.

Table 3 Range of Marks M No of

Students Percentage

= 100 25 49.0 95 ≤ $ < 100 7 13.7 90 ≤ $ < 95 11 21.6 80 ≤ $ < 90 7 13.7

<80 1 2.0 The useful feature of the AND/OR graph representation of the assembling process is that it portrays all possible assembly plans. It shows the assembly tree from the node containing the final assembled product to the single parts, and traverses through the intermediate sub-assemblies. This fact has been realized well by the students. Informal discussions with the students highlighted the following:

• It gave an opportunity to think about the assembling process which they never did. • It provided all the possible assembly plans to choose the best. • It provides an opportunity to identify weak spots in new designs with respect to

assembling. • It provides an opportunity to identify areas where jigs and fixtures can improve the

process. • Can be very useful when building their prototypes for their capstone projects.

5.1 Students’ Feedback It is customary at United Arab Emirates University to get students’ feedback on Course Learning Outcomes, the CLOs. For the particular Learning Outcome covering the AND/OR chart assignment 38 students returned the survey. Their ratings on 5 to 1 scale where 5 is the highest are given in Table 4.

Table 4: Students’ Feedback on CLO Rating No of

Students Percentage

5 22 57.9 4 12 31.6 3 3 7.9 2 1 2.6 1 0 0

6.0 Conclusions This assignment is the first introduction of the assembly planning for the students in the Mechanical Engineering undergraduate program at authors’ university. The results are very encouraging towards leading them to think and plan the assembling process while the design is still in the development stage. It has been recognized that the AND/OR graph is a systematic method of assembly planning. The assignment has initiated the students to think about

assembling in a serious way when it comes to their capstone projects. These are the generic effects of the assignment. On the specific assessment of the assignment and examination, the results are convincing or encouraging. In particular, the identification of the pre-assembled beam-pair-claw leg sub-assembly by the students, was very encouraging. It proves that the students had started thinking on complexity reduction of the assembling process. A majority of the students were assembling the plug for the first time. But they were able to grasp the process and produce the AND/OR graph. The fact that nearly half of them got it fully correct, suggests that more complex products can be offered to enrich the learning experience. References 1. An Automated Assembly Process Planning System. Available from (accessed Feb 01

2020): https://www.researchgate.net/publication/302922047_An_Automated_Assembly_Process_Planning_System [].

2. https://www.wonkeedonkeetools.co.uk/media/wysiwyg/10P-Pulleys-Sam/8P/10P-8-5.jpg 3. https://www.aceuae.com/en-AE/suki-3-jaw-gear-puller-15-

cm/930249.html?gclid=EAIaIQobChMItNzL24_G5wIVEtreCh0HegxsEAQYAyABEgK7zPD_BwE