School of Mechanical, Materials, Mechatronic and Biomedical Engineering
MECH215 Mechanical Engineering Design 1
Assignment 2 – Gearbox Design - 2018
This is an individual assignment to be completed independently.
Part 2B – Design and Analysis of Gearbox Output Stage
OVERVIEW Purpose:
The purpose of this assignment is to allow you, or cause you to apply many of the concepts addressed in the lecture program to a typical mechanical engineering design problem. In particular:
1. Mechanical arrangements: Shafts and shaft components
2. Gears General including force analysis
3. Strength under static and variable loading
4. FEA
5. Rolling-contact bearing selection and sizing
6. Shafts and shaft components – Limits and fits, keys and pins
It also allows you to detail a mechanical component ready for manufacture.
BASIC DESIGN TASK
You are required to detail the design of the output shaft assembly in the a single-stage bevel gearbox which is similar to the one that you designed for Assignment 2A. The parameters relevant to the gearbox will be supplied to you in a separate document: Gearbox Design – Individual Parameters. Numerous parts of the gearbox are provided as Creo Parametric models as part of Assignment 2A. A new input shaft assembly and a gear assembly will be provided consistent with your individual parameters.
Set out your work methodically on design sheets utilising the task statements as headings. For each task, set out: 1. Task statement; 2. Inputs and data, 3. approach, 4. Options where relevant; 5. Analysis;
6. Selection; 7. Verification and 8. Conclusion. The use of spreadsheets is strictly prohibited.
SUBMISSION
Make a copy of your assignment before you submit it.vThere are 3 parts to the submission:
1. Workbook: Submit to EIS Central* in hard copy with coversheet:
a) Title page and table of contents.
b) Summary sheet: proforma provided separately.
c) Part drawing of the final shaft;
d) Assembly drawing of the gearbox;
e) Design sheets for each of the tasks;
2. Creo Parametric files: ZIP file: 200Mb maximum file size, including all: part; assembly and drawing files used for this assignment Submitted through a separate link provided on eLearning. Ensure no erroneous files are included.
* Not this supersedes instructions in the Subject Outline
TASKS
1. OUTPUT SHAFT ASSEMBLY DESIGN
1.1 SELECT THE BEARINGS FOR THE OUTPUT SHAFT
Establish suitable bearing types and arrangement: a. establish the requirements for these bearings; b. identify 3 options for bearing types and arrangements; c. select a combination that is different from that used for Assignment 2A: i.e. different bearings and/or different arrangement. Select specific bearings by first determining the gear forces and resulting reactions at the bearing locations. Now identify the relevant features of the bearing shaft journal and housings, including the endcaps and record the relevant bearing data: fits, geometry and surface finishes required (refer to separate advice on how to proceed with this as provided within the rolling-contact bearing selection and sizing lecture and tutorial).
Bearing selection must be done manually, based on the ISO basic life rating.
Note you need to be prepared to iterate given that the span of the shaft depends on the width and position of the bearings thus affecting the forces applied to the bearings.
1.2 SELECT A COUPLING FOR THE OUTPUT SHAFT
Establish 3 options for suitable coupling types given that the gearbox is to drive a belt conveyor in a mine application. Choose one of these types and select a specific coupling from a catalogue.
Choose a suitable fit for the coupling.
1.3 SHAFT FORM DESIGN, PRELIMINARLY SIZING
Again in your design sheets, design the output shaft to suit the bearings selected to support the output gear. Include the design of the keys and keyways required to couple the gearwheel, and to couple the output coupling half: utilising the British Standard guidelines to determine the profile and strength considerations to determine the required length for the key. The fit for the gear should be H7/r6. .
Select a suitable seal.
1.4 MODIFY GEARBOX COMPONENTS
Duplicate and rename your project folder from Assignment 2A to
FamilyName_Initials_MECH215_Assignment_2B-CreoFiles_Project_Folder. Copy new parts and assemblies provided for Assignment 2B to your new project folder. Download CAD models in Creo format for the bearings and coupling if available. If not then develop basic part models. Seek advice if necessary.
Model or modify the resulting parts and assemblies in order to create your gearbox assembly for Assignment 2B.
. Delete the existing input shaft assembly and assemble the new input shaft using the existing bearings. Make any modification to the design of the input shaft and bearing arrangements you consider necessary (optional).
CONTINUED OVER
2. CHECK STRESSES INDUCED INTO THE OUTPUT SHAFT
2.1 ANALYTICAL ANALYSIS
Calculate the von-Mises (equivalent) stress and Factor of Safety for fatigue failure, at the maximum torque, using the modified Goodman criteria for the critical section: advised to be the outboard (coupling) end of the gear journal. For this you are required to investigate 2 different materials: AISI4130 Q&T 650C and AISI4340 Q&T 315C. You must use the properties for these materials as defined in the text. From your analysis, specify the shaft material and finalise the shaft details.
For this analysis you are required to use the basic theory as set out in Chapter 5 and 6 of the text. You are forbidden from using the approach given in Chapter 7 or other direct shaft analysis algorithms.
2.2 NUMERICAL ANALYSIS
Perform a FEA of the output shaft designed and compare the output to your analytical results. Include a brief discussion on the reasons for the differences in the results. Suggest any actions that could be taken to reduce the stress in the shaft but do not redesign the shaft.
Your design sheets should include: the inputs to your FEA (model, forces, joints used, meshing strategy) and the output: picture of meshed shaft; comparison of the bearing reactions and coupling torque to the theoretical values; picture of the shaft with von Mises (equivalent) stress field.
Take care to identify the maximum stress indicated in the FEA and to consider which analytical results should be compared with the FEA result.
3. PRODUCE THE DRAWINGS
3.1 PART DRAWING FOR THE OUTPUT SHAFT
Produce a detailed shaft drawing-sheet from your shaft model using Creo Parametric such that the shaft can be manufactured from this drawing. Ensure that all details are provided such that the shaft could be manufactured from the drawing: include all dimensioning and geometric tolerances.
3.2 ASSEMBLY DRAWING
Produce an assembly drawing for the gearbox.
REFERENCE
Text: Budynas, R.G and Nisbett, J.K. Shigley’s Mechanical Engineering Design (in SI Units) 10th Ed, McGraw-Hill Book Company, New York. Chapters 5 and 6.
Bearing, Seal and Coupling catalogues.
Various standards.
MARKING GUIDE
Task Mar k
/100 Mar k Details of Requirements for each Section
1.1 SELECT THE BEARINGS FOR THE OUTPUT SHAFT
Bearing arrangement design 5 Appropriate bearings types and arrangements selected from the 3 feasible options.
Gear Forces 2.5 Forces calculated accurately using the relevant approach.
Bearing Forces 2.5 Forces calculated accurately using the relevant approach.
Bearing Specification 10 Bearing sized correctly.
Fits, geometry and surface finishes identified. 5 Tolerances identified correctly.
1.2 SELECT THE COUPLING FOR THE OUTPUT SHAFT
Coupling type 5 Selection from 3 feasible options.
Coupling selection 5 Coupling sized correctly.
1.3 SHAFT FORM DESIGN, PRELIMINARLY SIZING
General form of shaft 5 Journals and abutments appropriate having regard for stress and assembly.
Key Design 5 Key profile and length appropriate.
Seal Selection 5 Appropriate seal selected and shaft journal details required are noted: surface finish, geometric tolerances
2.1 ANALYTICAL
ANALYSIS 20 Accurate analysis done.
2.2 NUMERICAL
ANALYSIS, FEA 10 Appropriate FEA analysis and correct interpretation of results. Insightful comparison to analytical results.
3.1 PART DRAWING FOR THE OUTPUT
SHAFT 10 Drawing appropriate for manufacture activity.
3.2 ASSEMBLY DWG 5 Drawing appropriate for assembly activity
PRESENTATION 5 Overall presentation throughout design sheets is logical.
TOTAL