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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