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Mechanical Design Mechanical Design Project Design of a Two-stage Speed Reducer Learning goals To narrow the gap between theory and practice of engineering by synergistically applying fundamentals of machine elements or components constructed in 300764 Mechanical Design to design a classic mechanical device – a two-stage speed reducer to perform a design practice and finish design loops in the assessment task – Mechanical Design Project. Design of two-stage speed reducer using gear drives A classical two-stage speed reducer using gear drives has been shown in Figure 1. Figure 1. Design of a classical two-stage speed reducer (Tudose, et al., 2008) 2 Figure 2. 92.1 / 93.1 Helical-Bevel Product Features (Tudose, et al., 2008) Design Requirements Overview For the design project, we assume a manufacturing company need a two-stage speed reducer which is required to install in their assembly line as depicted in Figure 3: 1) electric motor; 2) belt drive or chain drive; 3) gear driver-based speed reducer; 4) coupling; 5) roller; and 6) conveyor belt. Functions The functions of the gear type speed reducer are as follows: 1. To receive power from an electric motor through a rotating shaft. 2. To transmit the power through machine elements that reduces the rotational speed to a desired value. 3. To deliver the power at the lower speed to an output shaft, it ultimately drives the conveyor system. Working conditions  The components 5 and 6 are parts of a conveyor system, which is running 16 hr/day, 5 days per week, with a design life of 10 years. This is approximately 40,000 hours of operation and its operation is generally smooth.  The roller has a diameter of 350 mm and a torque of 1400 Nm is applied on it. The speed of the conveyor belt is 0.5 m/s, which is permitted to vary  5%.  The speed reduction ratio of the speed reducer should be controlled in a range of 3.46 to 3.53 for each stage.  A mechanical efficiency of greater than 95% is desirable.  Flexible couplings may be used to connect the output shaft directly to the shaft of the roller for the conveyor system. 3 (a) (b) Figure 3. Product development and design of a speed reducer for a company Selection Criteria 1. Safety: The speed reducer should operate safely and provide a safe environment for people near the machine. 2. Cost: Low cost is desirable so that the gearbox appeals to a large set of customers. 3. Size: compact design with a small size is preferred. 4. High reliability. 5. Low maintenance. 6. Smooth operation: low noise and vibration. 4 Methodology You will be allocated to a team of 2-3 students to achieve the design goal with creative ideas together and for equity, a peer-review report to evaluate each team member’s contribution is employed with the group slides and design report for submission at the end of the semester as required in the learning guide. In your team you should have a unified and clear target to design the two-stage speed reducer and its accessories including belt/chain drive to transfer the power and torque from the electrical motor to the input shaft of the speed inducer and a coupling to connect the output shaft of the speed reducer with the input shaft of the conveyor as required. The team members should have a discussion to allocate the design tasks evenly. Your design will involve in the following commonly-used machine elements:  Gear drives  Belt and Chain Drives  Keys, Couplings and Seals  Machine Housing  Shafts  Bearings The design will be mainly focused on gear drives, belt and chain drives, and couplings (components 1-4 of the system) according to the unit contents of 300764 Mechanical Design. Format for submission of Mechanical Design Project The design project report should be submitted electronically by uploading the necessary files into the appropriate assignment area in the vUWS site. The following important notes are highlighted: 1. All reports will be assessed by “Turnitin” in the vUWS site. “Turnitin” ensures the originality of your reports by comparing against a repository of previously submitted reports, current and archived internet contents, periodicals, journals and publications. 2. Submit all files for marking. In Solidworks, all part files used in the creation of an assembly must be submitted or else, the assembly cannot be opened. It is a good practice to keep all files for an assignment in a separate directory so that you do not miss any important files during the submission process. 3. Drawings can be submitted in e-Drawings format with all drawings in ONE file. Use the following checklist before you submit any drawings:  All drawings must use 3rd angle projection. 1st angle will not be accepted  All line types, arrow styles, dimensioning, sectioning, auxiliary views etc. must conform to the Australian Standards.  Use a Western U title block and sheet format for all drawings. 4. Make sure you retain a copy of all of your assignment files and create a back-up somewhere. If an assignment gets lost in the system this will help you to demonstrate that the assignment was completed by the due date and allow you to easily re-submit the files for marking. 5. Due date: 17:00 pm, Friday, 5th of October 2018, Week 14. 5 Marking Criteria for Mechanical Project Report Designers, according to Nigel Cross, Professor of Design at the Open University, produce novel, unexpected solutions, tolerate uncertainty, work with incomplete information, apply imagination and constructive forethought to practical problems, use drawings and other modelling mediums as a means of problem solving. The highest grades will be given to submissions that:  make clear statements about the design problem in terms of needs and goals;  show a high standard of analysis of the design problem;  show clear evidence of literature research, and evaluation of products already on the market by paying considerable attention to their benefits and shortcomings;  clearly document the design's development and show consideration of alternative approaches, methods or material considerations; and  provide a high-standard evaluation that demonstrates an understanding of the strengths and weaknesses in the final design through detailed analysis. The qualities described above are critical features central to good design practice. Consider the methodologies you devise in order to communicate the extent of your personal achievements of the above criteria as your first design challenge. A particular problem with design assignments is in how far to go with the final design. Students might be either afraid to do anything to an old design, or produce something that is impossible to manufacture or redefines the product so much that it cannot be considered to perform anywhere near the level of the original. Therefore, you must be careful not to fall for any of these problems. Essential Elements of the Project  Each Project has to have a clear, broad objective (task) to achieve: e.g. lift a man in a wheel chair on to a theatre stage; place caps on bottles on a conveyer belt; lift a heavy object and transfer it from one end of a warehouse to another; etc. Common to all these is a general intent or purpose the needs of which have to be met (engineered).  Given the task needing to be accomplished, it is necessary to provide specifications involving performance characteristics: 90-kg man, 2-m lift, 30 seconds, a 10-tone object, a 60-m long warehouse, 15 minutes, a 3-cm diameter, etc.  There is usually a number of ways to accomplish a given task. These should be identified and described.  One design should be chosen as the optimum – and this selection justified. This is an important part of the Design Process and great care should be paid as to the reasons for choosing a particular design – against all others that had been identified as possible solutions to the set problem.  A sketch of the chosen device/machine should then be made.  Main components should then be designed involving choice of material and application of analytical procedures, justification of sizes, types of member cross sections, types of loading, drives, gears, controls etc. This is the most important part of the project as it shows application of design principles to sizing of machine components, selection of drives and machine components which when all put together perform the desired task – a trademark of an engineer. You do have to be good at it – it is not a chore, it is what Engineering Professionals are made of.  Having sized all the machine components and selected any commercial items, the next task is to draw up an Assembly Drawing. It shows – usually in cross section – the whole machine with each part labelled (numbered). A parts list is given in the drawing (according to the Standard) – stating the part ID, material and the number needed (“number off” – or “no. off”). This is necessary for costing purposes, material purchase, manufacturing (machining) – and assembly. The drawing should be done in any CAD 6 you are familiar with. CAD proficiency is also expected of you in Industry – especially in your early years of employment. You should be practicing with the School’s Solid Works in any “free” time you may have – using given on-line tutorial guides. Individual machine parts should have an indicator of the surface finish required and each dimension should have a tolerance associated with it.  If there is any time left, produce a complete set of machine drawings “workshop ready”. All of the above items should be presented in its detailed form in the report, and in “highlights only” format in Power Point Slides presentation. Design report A design report would most likely contain the following items (separated by headings and subheadings): 1. Title page 2. Table of Contents page 3. Executive Summary 4. Introduction and Design Background – a short literature review on the design of speed reducer should be provided in this section. 5. Main body - The contents of this section (divided into suitably headed subsections) is subject to change, and it depends upon what is being examined. Typical contents would be analysis of initial object, redesign of object, assumptions made and analysis of redesign (discussion of why concept may or may not fail). No design is foolproof. In most cases, design is the art of compromise/trade-off. Typically, by making a change to an object, you will improve one characteristic of that object, but decrease another. These trade-offs should be recognised and discussed.  Aim and objectives  Performance criteria and design constraints  Conceptual design  Design analysis and decision making (Force, motion and stress analyses and CAD modelling, etc.)  Detailed design  Prototyping and design evaluation (optional) 6. Summary 7. Acknowledgments 8. References 9. Appendices – Peripheral information, including catalogues, technical drawings and calculations may be placed here or in the main body of the report depending upon its relevance (e.g. repetitive calculations should be left in the appendices, but you may wish to include a sample calculation within the body) ‘standard’ calculations would also be better in this section, rough sketches of rejected designs (including descriptions as to why they were rejected). 7 Outcomes of mechanical design project In either case, each student or a design team has to produce a  Power Point Presentation of the highlights of their Mini Design Project – particularly the aim and steps towards realising it, as well as how much in effect was accomplished in the time available for the exercise. The actual presentation should be made by each student involved in the project – and take no longer than 5 minutes.  You are also required to produce a written mini design report: one per Team. References 1. L. Tudose, O. Buiga, D. Jucan and C. Ştefanache (2008) Optimal design of two-stage speed reducer using two-phase evolutionary algorithm, INTERNATIONAL JOURNAL OF MECHANICS, Issue 3, Volume 2, pp. 55-66. 2. NORD Drivesystems Pty Ltd Australia (2014) 2 stage helical-bevel gearmotors & speed reducers (http://www5.nord.com). th 3. Mott LR (2006) Machine Elements in Mechanical Design (4 Edition) Pearson/Prentice Hall. 8

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Design of a two-stage Speed Reducer

TABLE OF CONTENTS
Introduction 2
Problem Statement 2
Conceptual Design 3
Belt Drive 3
Chain Drive 3
Spur gear drives 4
Helical gear drives 5
Worm gear drives 5
Bevel gear types 5
Input Calculations 6
Design Analysis and Decision Making 7
Initial design 7
Gear Design 8
Material Selection 12
Shaft Design 13
Key design 14
Bearing Design 15
Housing design 16
Lubrication 16
Detailed Design and CAD Modelling 17
Input Shaft 17
Speed Shaft 18
Output Shaft 18
Input Gear 19
Output Gear 19
Connecting Gear 20
Key 20
Housing Base 20
Housing Top 21
DFX Analysis 21
DFA (Design for Assembly) 21
DFM (Design for Manufacturing) 22
DFS (Design for Safety) 22
APPENDIX 23

Executive Summary
A manufacturing company needs a two-stage speed reducer to be assembled to their assembly line. The task is to design a two-stage speed-reducer with the speed reduction in each stage of the range of 3.46-3.53 and a mechanical efficiency greater than 95%. The design life of the speed-reducer should be approximately 40,000 hours.
For the design of the product, we first compared different ways in which this problem can be solved. After weighing the pros and cons of each design, a model was chosen. The detail design of the different components of the model was done using the theory of Machine Design. Standard components like bolts and bearings were also chosen for the design.

After the detail design, a CAD model was created in SolidWorks. Drawings were then prepared from this CAD model and the parts are ready to be manufactured. The next stage is prototyping.

Introduction
The aim of the project is to design a two-stage speed reducer which is to be installed in an assembly line. The customer wants the speed reducer to transmit power from an electric motor to drive a conveyer belt system at a reduced speed. A speed reducer, along with the connecting elements should be designed. The assembly line is shown below:
The first step of design is to define a clear problem statement by incorporating the requirements of the customer. Once the problem statement is created, several possible solutions should be considered. As no design is fool-proof, we should compare the pros and cons of different designs and finalize on one design.

The next step is the dimensioning of the design. This is performed by applying fundamentals of machine elements. The material selection is also performed in this stage. Subsequently the detail design of the system is performed and the assembly/part drawings are prepared.

In this report, we discuss about all these stages involved in the design of the speed reducer. The report is organized in the order as discussed above.

Problem Statement
By analysing the requirement of the customer, the problem statements can be written as:

• Design a speed reducer to transfer power between two shafts at different speeds
- Input Power: 5 hp
- Input Speed: 335 rpm
- Output Speed: 27.3 rpm
• Mechanical Efficiency: > 95%

The calculations performed to get the problem statement is detailed in the section “Input Calculations”

Conceptual Design
Multiple methods to realize the two-stage speed reducer were considered. The different options considered are listed below along with their features.

Belt Drive
A belt is a looped strip of flexible material used to mechanically link two or more rotating shafts. A belt drive offers smooth transmission of power between shafts at a considerable distance. Belt drives are used as the source of motion to transfer to efficiently transmit power.

The design candidate with a belt-drive consists of belts and pulleys, with different diameters as shown in the figure below. Two such drives can be connected in series to obtain a two-stage speed reducer.

Though belt drives are versatile, simple and economical with shocks and vibrations mostly absorbed by the drive that facilitates a smooth and noise free operation, it comes with a few primary concerns as listed below:

• Slippage at lower speeds due to increased tension in the belt leading to reduced mechanical power transfer.
• Reduced life due less than optimal belt speed requirements.
• Routine adjustment of centre distance and compensation required due wearing and stretching of belt.
• Non-safe design can lead to machine damage and hazardous operator conditions in the event of a belt failure or snap....

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