EAT309 – MECHANICAL DESIGN AND MATERIAL SELECTION
Torque Limiting Clutch for an Hydraulic Winch
This is an individual assignment. Students may draw on information and knowledge gained in the sessional assessment but work towards this submission should be entirely the students own work and must NOT have input from other group members.
After the successful introduction of the safety clutch to the Hydraulic Winch, the technical director would like some further changes to be studied. The changes still require the design of a retro fit clutch which will limit the load capacity of the winch to 1.6 tonnes. Our stress engineers have looked into this and have advised that the skid base frame is capable of safely supporting this increase in SWL provided that some means of ensuring the new load capacity cannot be exceeded. To achieve this it has been decided that a friction clutch will be included as an upgrade grade kit and located between the gearbox and the winch drum. A schematic of this arrangement is shown in the diagram below.
Figure 1: Schematic Arrangement of Hydraulic Winch with Torque Limiting Friction Clutch.
As with the previous designs the winch will be used at disaster sights and most often will be lifted to the site by helicopter. Once on site it may be assumed that the winch will need to be hand carried to the point of use and that this may involve carrying it over uneven ground in locations which are difficult to access. To this end the original winch was designed to be ‘two person portable’ which for our purposes means using only one hand per person and to ensure that this is still possible with the upgrade kit the clutch needs to be designed to be as light as possible. Please note that your scope of supply is limited to the clutch assembly (including the connecting shaft to the winch drum) and that the new hydraulic motor needed for the increase in load has already been specified. A tolerance of -0 to +5% has been suggested by our stress engineers on the clutch’s torque capacity in order to prevent any risk of damage to the skid base framework.
The existing winch drums have an effective diameter of 260mm and an overall efficiency of 92%. Based on the number of winches sold to date it is estimated that the demand for the retro fit upgrade will be around 40 units per annum for the next five years.
SCOPE OF SUPPLY.
You are required to prepare a design proposal for the arrangement of the clutch system. Any bought in components used in the arrangement must be accurately specified by manufacturer’s name, type and size and the selection of the components used is to be backed by calculation. All calculations must be in SI units. Calculations in imperial units will not be marked.
Your design report is to contain the following sections:
- A design specification for the clutch system. (Please note that this is a design specification and therefore needs to provide details of what it is you are required to design. Your specification must therefore be written in the future tense. Your specification must include all limitations imposed upon the design by the conditions described or implied above, as well as any further details you deem relevant. It should not include irrelevant details and must not be written as a product specification, i.e. NOT as a document which provides details of an already existing product)
(15%)
- Identify a suitable friction material currently available in the market. All relevant material properties must be given and the units used MUST be SI units. If the manufacturer of the material has listed the properties in imperial units it is your responsibility to convert these into SI units for presentation in your report. References need to be cited in this submission and copies of manufacturers’ web pages (cut and pasted) are to be included in the appendix to your report. The properties must at least include the coefficient of friction of the material, with either cast iron or steel as the mating material, and the maximum compressive strength of the material. The material presented must be commercially available in the market and be a proprietary product. Generic materials found in text books, such as ‘woven’ or ‘moulded’ (‘molded’) will not count and will not accrue any marks. The material you have chosen must be accompanied by a justification and the reasons you deem this a suitable material.
(15%)
- Calculations to determine the torque that the clutch is required to transmit, taking account of the efficiency of the winch drum. Based on the material selected in section 2) above determine the required dimensions of the clutch and the clamping force needed. In the notes provided there are two sets of formulae given and these are based on two different assumptions. You need to state clearly which of the two you have used and give relevant reasons for your choice. All calculations must be in SI units. Use of imperial units is not permitted and will incur penalties by marks being deducted.
(20%)
- A written review, not exceeding 1500 words of three different materials you believe might be used to manufacture the shaft connecting the clutch to the winch drum. From the three materials you review you need to select the one you deem most suitable for the intended application. This should be done in the form of a discussion listing the advantages and disadvantages of each material and by developing and comparing performance indices based on the conditions and requirements your group set out in your design specification as well as those listed or implied in the brief. Your discussion must take account of the relevant service conditions, cost considerations and most importantly ethical and environmental considerations. While it is expected that you will rely on CES to assist with your selection, the output from the software on its own is insufficient. The software output if used, MUST be accompanied by and supported with a clear explanation of the method and the findings of the analysis. A weighted Objectives Method is NOT required for this part of the exercise.
(20%)
- Using the material selected in 4) determine the required diameter(s) for the shaft connecting the clutch to the winch drum based on the torque it is required to transmit. You may assume that the total length of the shaft is 160mm. All other assumptions made in your calculations must be clearly stated and you must select an appropriate factor of safety that you use in these calculations and provide a suitable rationale for your choice.
Please note that when determining the shaft diameter(s), STANDARD sized bought in components such as bearings and seals MUST be available to suit your design and so the diameters you calculate may need ‘rounding’ to a standard dimension. It is your responsibility to demonstrate that standard sized bought-in components are available for this. Failure to take account of this may result in significant loss of marks. Please note that all calculations and material properties MUST be shown in SI units only.
(20%)
- An overview of the manufacturing methods that might be employed in the manufacture of the connecting shaft from the raw material. In this case ‘raw material’ refers to the material as supplied by the material stockholders. It does not mean manufacturing from the ore. Your manufacturing plan must cover all features included in the shaft required to achieve the drive between the clutch and the winch. Please note! No description of the manufacturing processes is required; you are simply expected to suggest the methods and the sequence of operations by which the gearbox casing might be finish machined to the required standard. All processes, including any finishing processes, involved in the production of the connecting shaft should be included and your reasons for selecting them given.
(10%)
As in the real world of engineering design it is important to provide exactly what the customer has asked for. You need only provide answers to the questions asked. Additional answers to questions not asked will not be marked and will therefore not be awarded any marks. If you are in any doubt as to what has been asked for then please make further enquiries to obtain clarification.
Finally, please be aware that the customer has a right to amend any of the details provided within this brief, at any time during the course of the “contract”. All changes will be notified to the teams as soon as possible and may be subject to an increase or a decrease in the costs associated with the completion of the “contract”.
Submission Details and Dates
What and how you are required to submit
You are required to submit one report/portfolio which must contain all of the above sections.
All submissions are to be made via Canvas and submitted via ‘Turnitin’. Submitting in this way will generate a report which checks for cases of plagiarism. The report submission is required as a single document in Word format set out in the order shown above, i.e. numerical order from the list above. To help with identification of your work, you MUST include your name and student ID on the fornt page of your report and adopt the following file format.
FamilynameInitialEAT342refassignment.doc
Please Note! No other filenames or file format than those specified above can be accepted. A marks reduction penalty will be applied if you do not use the required filename or file format.
Avoiding Plagiarism Accusations
Please note that whilst some notes and materials will be provided to support this task it is expected that you will carry out your own research and use a variety of information sources to complete the task. However, all of your work must be presented in your own words and not taken directly from any other source. All sources you have used in your search must be clearly and appropriately referenced using the Harvard referencing system and a list of references included in the back of each submission. Using sources which have not been appropriately referenced or taking any data directly from any source which you include in your work will be regarded as plagiarism and may result in you failing this part of the report or even the whole module. It is acceptable to use quotes, photographs and/or diagrams from other sources, where appropriate, but these must be properly referenced. Any quotations you wish to use from external sources must be less than 200 words in total for any submission of your report and again must be cited and referenced correctly. All quotations must be shown within quotation marks.
Submission Date:
You are required to upload your work by Midnight on Friday, 26 January 2018.
Marking Criteria
70-79% 3 of the following, 80-89% 4 of the following, 90% and above 5 of the following
- Thorough understanding of all key points and distinguishing features and factors
- Reasons given for all decisions, all aspects understood, very clearly explained and correct
- All calculations correct, clearly explained and presented
- A clear structure used and good critical analysis
- Demonstration of thorough knowledge across substantive areas
- All issues/aspects addressed thoroughly and clearly
55-69%
- A good understanding of most key points and distinguishing features and factors
- Reasons given for most decisions, most aspects understood, clearly explained and correct
- Most calculations correct, clearly explained and presented
- A clear structure used and evidence of critical analysis
- Demonstration of a good depth of knowledge across substantive areas
- Majority of issues/aspects addressed thoroughly and clearly
40-54%
- An understanding of most key points and distinguishing features and factors
- Reasons given for some decisions, most aspects understood, explained and correct
- Basis of all calculations correct but containing some errors
- A reasonable structure used and some evidence of reasonable critical analysis
- Evidence of some knowledge across substantive areas
- Most issues/aspects addressed but some not addressed thoroughly or clearly
F – 39% or less
- Little evidence of understanding of the essential features and factors
- Reasons seldom given for decisions, few aspects understood, explained or correct
- Basis of some calculations incorrect and some/all containing errors
- A poor structure used and little evidence of any reasonable critical analysis
- Little evidence of knowledge or understanding across substantive areas
- Irrelevant, unrelated and muddled material.