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Assignment 2
Solid modelling project
Due date: 19 October 2020
Value: 750 of the 1000 marks for this course
Background
Figure 1 shows the arrangement of a gear pump. The following design considerations and modifications are to be implemented.
1. It has been determined that there is a market for a variety of similar pumps but with reduced pumping capacity. This can be achieved by fitting ‘thinner’ gears. The same housing can be utilised but with a reduced depth of the machined cavity to suit the ‘thinner’ gears. The current design shows 19 mm wide gears but future designs must cater for any gear width from 15 mm to 19 mm.
2. The single groove pulley shown is to be replaced by a double-groove pulley. More information on this pulley and how it is to be attached to the pump shaft is given in item 6 below and later in this document.
3. The ¼” pipe thread is to be replaced by a M12 x 1.5 thread.
4. The gears are to be metric with the following specifications:
• number of teeth 13
• pitch diameter 32.5 mm
• outside diameter 37.5 mm
• pressure angle 20O
• module 2.5 mm
5. It has also been decided to supply an assembled kit equipped with two gear pumps, connected in series, driven by an electric motor. The pumps and the motor are to be mounted on a specially designed and fabricated steel base. The general arrangement is depicted in Figure 3.
6. Drive from the motor to one of the pumps is by V-belts running between two double-groove pulleys. Each pulley is keyed to its respective shaft using 4mm keys. (Do not use the taper pin shown in Figure 1.)
7. The electric motor, refer to Figure 5 for the basic dimensions, runs at a constant 1440 rpm but the gear pumps need to operate at 900 rpm ± 20 rpm.
8. Two different length drive belts could be used depending on supply availability 450 mm and 500 mm pitch lengths. Both belts are classified as type ‘Y’ section.
9. The second pump is driven by the first through a flexible drive coupling – see Figure 4.
The Project
Your task is to:
1. Create parametric feature-based solid models for all the components of the gear pump as shown in Figure 1 - but with a suitable double-groove pulley instead of the single-groove pulley represented.
2. Create an assembled model of a single pump showing all parts in their working positions and with the 19 mm wide gears fitted.
3. Set up a parametric relationship to automatically update the housing cavity depth and other parts, features and dimensions affected by the gear width change as mentioned in item 1 of the Background section (i.e. a simple dimension edit to the width of the driving gear model should automatically change the sizes and / or shape of the effected mating parts and features.)
4. Produce a model of a double-groove pulley for the electric motor.
5. Design and model a base to support the motor and two pumps. The base should be designed to allow positional adjustability of the motor so that the belts can be tensioned as well as accommodating the different length V-belts - as mentioned in the Background section, item
8.
6. Create a second assembled model. This time the model should show the spatial arrangement of the motor, pumps and base. You will need to include the pulleys, coupling and all other associated drive components e.g. keys, belts, couplings. You should also show all the fasteners – bolts, nuts, washers, screws etc.
7. Produce two separate engineering assembly drawings - one of the overall assembly as in 6 above and the second of a single pump as in 1 and 2 above. In addition to the orthographic views the drawing should also include a perspective view, title block, parts lists, and other information generally associated with assembly drawings.
8. Produce fully dimensioned engineering detail drawings for the parts listed below:
• housing
• housing cover
• gear
• gear stud
• shaft
• mounting base
• drive and driven pulleys
Specify appropriate surface finish requirements, general tolerances, and other information normally shown on a detail drawing. In addition to the orthographic views each drawing should also include a perspective view of the part.
9. Nominate and justify suitable fits and tolerances, on a separate A4 sheet, for the following mating parts / features:
(a) driven gear and gear stud
(b) housing and gear stud
(c) driving gear and shaft
List the basic size and dimension tolerances for each fit on the sheet. The specific tolerances should also be shown in the detail drawings.
Guidance on the Project
Some of the diagrams provided show limited details and in many cases the dimensioning of the details is incomplete or missing. Therefore, you will be expected to combine some research with sound practical judgement to obtain all the missing information necessary to complete the design.
Before commencing this assignment you should think about the function of each feature and each part and how the individual components might be made. Also consider the physical assembly process, i.e. how the parts actually fit together, the order in which the components might be put together and the use of sub-assemblies. Your model creation process should reflect this wherever possible. Some guidance is given in the instructions for the Roller Bracket exercise you completed as part of assignment 1.
Gears
You may simplify the gear tooth profile to that shown in Figure 2. (Normally, the profile of the tooth face is that of an involute and not of a constant radius arc as shown.)
Keys
There is information regarding keys and keyways in the text by Boundy. You should use the nominal dimensions given there. Pulleys and belts
For the V-belts you should use a ‘Y’ section belt.
You will need to determine suitable pitch diameters for both the motor pulley and the pump pulley to satisfy the requirements in item 7 of the Background section.
For a list of pulley sizes to choose from and for critical pulley, groove and belt dimensions you should refer to the tables and related information at the end of this document.
Base frame
Use 30 x 30 x 3 mm mild steel angle iron for all elements of the base frame. You may use Figure 3 as a guide to your design. Angle iron sizes can be found in the Onesteel Hot Rolled and Structural Steel Products 7th edition catalogue which you should be able to access on the internet.
Fasteners
Use M6 bolts and nuts for securing the motor and pumps to the base. Use M4 threads for fixing the pulleys and coupling. There is no need to include the actual thread features on these fastener models or their mating threads.
Threads
Model the M20 and M12 threads on the Housing and Housing cover as helical sweeps. Boundy shows the thread form geometry. For the other pump threads use the cosmetic thread feature. Pipes, hoses and their fittings Do not include these.
What you need to submit:
Your assignment is to be submitted online through USQStudyDesk in a compressed (zipped) folder. Do not submit the files individually.
In the zipped folder include:
• Part ‘.prt’ files and assembly ‘.asm’ files of all the Creo models*
• ‘.pdf ‘ files for all the working drawings listed in 7 and 8 of The Project section – i.e. you will need to ‘save as’ or ’export’ the Creo 6.0 drawings (.drw) to .pdf before submitting. Do not submit Creo 6.0 .drw files.
• A ‘.pdf’ electronic copy of an A4 sheet or sheets (created from a word document) with:
• a listing of the file names you used for each part and each assembly
• fits and tolerance justifications as requested in item 9 of The Project section
• instructions on how to test the parametric relationship between the Gears and other components.
Important - check that your files open correctly from the zipped folder before submitting your assignment. A marks penalty will apply if the files cannot be opened or easily accessed by the markers.
• Creo only to be used in this assignment.
Marking this assignment
The following sample marking sheet has been included to indicate the criterion to be assessed and the relative marking for each criteria.
MEC2304 Assignment 2 – marking sheet
Semester 2, 2014
Student name:
Marker’s name : Total mark / 750
Models
Criterion Your mark Out of
1. completeness – all parts modelled and all features included 100
2. accuracy of parts and assembly, functionality and practicality of the Base, Pulleys and general arrangement designs 175
3. presentation / creation of computer models, part and / or assembly relations 175
total 450
Assembly drawing
Criterion Your mark Out of
1. completeness – all parts shown and clearly identified; title block / parts lists 50
2. presentation / clarity – view selection and layout 50
total 100
Detail drawings
Criterion Your mark Out of
1. completeness – all parts drawn and submitted; title block / notes 60
2. presentation / clarity – view selection and layout 60
3. accuracy – dimensioning / tolerances / surfaces finishes 80
total 200
Figure 1: Gear pump
(Source: Luzadder & Duff 1989, Fundamentals of engineering drawing, 10th edn, Prentice Hall, p. 440.)
Figure 2: Gear tooth profile
Figure 3: General arrangement
Figure 4: Flexible coupling parts
Figure 5: Electric motor – basic dimensions
V-belts and V-groove pulleys
The follow information relates to the sizes and dimensions associated with V-belts and Vgroove pulleys.
To calculate the centre distance between the pulleys:
C = A + where and
C = centre distance
D = pitch diameter of larger pulley d
= pitch diameter of smaller pulley L = pitch length of belt
(SAA HB61999)
MEC2304 – Solid modelling
( SAA HB61999 )
(SAA HB61999)
MEC2304 – Solid modelling
(SAA HB61999)
Reference
SAA HB61999, Design standards for mechanical engineering students, 4th edn, Standards Australia,

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