Mechanical Design Engineering Principles

This assignment delves into the core concepts of mechanical design engineering. It examines the importance of reliability in design processes and explores methods for incorporating it. The assignment also touches upon materials science, highlighting essential properties and considerations for mechanical design.

TWO-STAGE SPEED REDUCER
Executive summary
In this research study, a detailed analysis and evaluation of a two-stage speed reduced are
presented. The two-stage speed reducer is powered by means of an electric motor which moves
the rotating shaft. The major aim of this design project is to fully utilize the safety and the
efficiency of the input power of the electric motor. Besides, other designs of the speed reducers
have also been looked at and then a choice out of the best made depending on the optimum
operating performance. The research further presents some factors which help in determining
the choice of the best type of speed reducer. Some of this factor include couplings, shafts, gear
drives, machine housing among others (Benson, 2013).
These factors are arrived at considering various calculations as in the specifications
document. The calculations give a direction on the right choice of the material and sizes that
need to be applied in order to come up with the best design of the speed reducer.in order to
determine the optimum efficiency of the system, the internal components are analyzed
independently with regards to the power from the electric motor in the mechanical industry.
Usually, the electric motor is used while indoors as a result of the carbon oxide emissions and
also to ensure that minimum noise is produced (Shigley, 2011).
Introduction
This report presents elaborately the design of a gadget that will be applied while changing
the position of heavy objects in the conveyor belt. The conveyor belts have been in the past used
mostly in the manufacturing industries to move materials which are heavy as well as those that
need some packaging. While the conveyor belts are used for moving of objects , sometimes it

tends to experience some shocks resulting from the heavy loads and objects that it
transfers .nevertheless, the design provided in this report is such that all the shock loads that are
experienced by the conveyor belt are eliminated such that despite there generation, they are
never felt (Ramani, 2010). The design is a straight cut gear system which applies the belt as its
output.it focuses specific areas such as the smooth operation, reliability, low operation and
maintenance cost as well as the criteria for safety and performance.
Background
Over the past years, there has been an up growth in the demand for the efficient
powertrain components thereby also calling for more products to be produced. Conversely, the
engineers, in an attempt to offer solutions to most of the challenges, have also tried to come up
with some resolutions and in most case have settled to the idea of investing more on the
hardware parts of the components. For the engineers to come up with appropriate solutions, they
need to critically understand the performance criteria as well as the consumer needs of the
products.
The main aim of the speed reducer is to minimize the speed of the rotating shaft driven
by the electric motor while attempting to achieve a greater torque, hence, it is applied in
lessening the velocity of rotation. There are various designs of the sped reducer which are all
aimed at achieving some specific output configuration ratio that is desirable. Some of the various
designs of the speed reducers include the parallel shaft, worm gear, helical offset shaft, and
helical shaft among other types. The price of these types of speed reducers ranges from $400 to
$2000 depending on the costumer’s choice.

In most case, most of the customers' needs are not fully addressed when one is need of a
speed reducer and thus there are some features which define the speed reduces including the
mounting options, output replacement, the component life as well as the output ratio. One
common practice of the speed reducer is in the production line where it is applied in the
conveyor belt as result of the high demands of the products. The high demand for the products
calls for a production line design which will offer lower maintenance costs, longer lifetime and a
good performance quality. Apparently, the advancements in the manufacturing industry have
resulted in better ways of ensuring that materials of higher quality are produced.
Aim
The main of this research project is to come up with a two-stage speed reducer which can
be applied in the production industry with increasing efficiency and minimum requirements. The
designed speed reducer has to attain some characteristics such as being able to rotate the shaft by
the aid of a powered electric motor and then transfer of the power to various machine elements
after which it be able to minimize the speed of the output shaft while increasing the torque
Objective
The main objective of the task is to come up with a gear system that acts as a two-stage
speed reducer and at the same time be in line with the demands and specifications of the
manufacturing company. Described below are some criteria which must be met by the speed
reducer design
o Ensure safety while the system is in operation
o Reduced cost
o Development of prototype

o Cheaper maintenance costs
o Reduced noise and vibration
o Highly reliable
Performance criteria
In order to effectively come up with a design that will be able to meet up the requirements
and the demands of the customers, there are some performance criteria which must be adhered
to. These conditions include
 Product lifetime service of 10 years with 5 days weekly and 16 hours daily, time of
operation, thereby totaling to 4000hours
 The conveyor belts speed of 0.5m/s with a torque of 14ooNm and diameter of 350 mm
 Accuracy range of +-5%.
 Mechanical efficiency that is greater than 95%
 Couplings that are flexible to ensure the shaft is tightly fixed on the roller (Ajukumar,
2010).
 The ratio of the speed reduction to be not more than 3.53 and less than 3.46 in each of the
stages
For the two-stage speed reducer, the criteria of selection that must be adhered to is as follows
 Safety – safety of both the workers and in general the working environment must be an
apriority of the speed reducer
 Smooth operation
 High reliability
 Longer service life

 Reduced maintenance costs
 Compact size
When the above factors shall have been considered, the product will thus be worthy to be
disposed into the market as one of the highly competitive products
Conceptual design
There exists a variety of options in achieving the two-stage reduction design such as
helical gears, chains, worm gears, spur gears, belts as well as the bevel gears. They are applied
depending on the merits and preference (Wasson, 2015).
Belt and chain drive
A design of chain drive and belt can only regard as successful upon attaining the above
requirements. The composition of the speed reducer would involve two pairs of chains and
sprockets, 2 pairs of pulleys’, and a belt (Farber, 2011). The belt drives have not been included
while performing the design of the speed reducer due some reasons such as
 High maintenance cost since there is regular checking of belt tension
 The design of the belt drives is usually not compact hence failing to attain the design
requirements
 Rotational forces and the revolution per minute in the belt slippage thereby reducing the
efficiency of the system.
In addition, the chain drives have also been eliminated in the design of the two-stage speed
reducer as results;
 Compact failure in the design

 Noise factor from the chain driver
 Low efficiency
Spur gear drives
The reduction of the design spur gear drives is aimed at ensuring cost worthiness and
efficiency while attaining all the requirements of the design as stated by the manufacturing
company. Usually, these drives are applied to the parallel gear systems that have a greater
comparison with design criteria (Litzinger, 2013). It is great significance to consider the spur
gear drives while coming up with the design of speed reducer
Some of the advantages of the spur gear drives includes
 Cost effective as it involves cheaper production and maintenance costs
 Availability of separate gears thereby increasing the mechanical efficiency
 Presence of parallel set up that helps in attaining a compact design
 Longer product service life with reduced maintenance costs
Helical gear drives
The speed reducers of the helical gears are almost similar to the design of the spur gear.
The only difference is that the design of the helical gear drives generates less noise as well as
vibrations while in operation. In addition, they increase the efficiency of the machine. Despite
the helical gear drives being applied widely in the speed reduces that requires a higher rate of
revolutions per minute, they tend to meet the requirements of the client thereby enhancing the
overall efficiency of the design process (Mattheck, 2012).

Bevel gear drives
The main purpose of these gear drives is to perpendicularly transfer power and speed all
over the speed reducer. The bevel gears have same advantages as the helical and the spur gears.
The only difference is that for the perpendicular input, amount of power is required hence not in
line with the requirements of the manufacturing company (Goris, 2011).
Design analysis and decision making
The diagram shown below is a real model of what needs to be designed
Materials of choice
The materials that we have for the design of the two-stage speed reducer are below
 Three shafts
 Single rectangular key having a clip for connecting the gears
 Six bearings
There’s is a reduction in between the motor output and the pulleys and the input shaft gets
driven by the belt for the reason of attaining the required amount of power and torque ( Solis,
2010).

Gears
Its design was the major aim of the research alongside the speed reducer design .a greater
percentage of the minimized gears from the output of the electric motor gets completed t the
limits of the speed reducer with the aim of achieving a desirable output (Swierk, 2013). The final
ration of the gear is as per the manufactures wish list i.e. between 3.46 and 3.53. Thus, the
chosen ratio is 3.5
Lubrication
The lubrication plays a significant role while performing the design of the rotating shaft.
This is because it assists in attaining undisturbed operation of the machine and thus, a wet sump
system will be applied for the lubrication o the system and minimization of the friction in
between the moving parts (Larman, 2012).
Material selection
When coming up with the design of very crucial components, the materials selection is an
aspect that needs to be considered with a lot of care. There are characteristics that need to be
deliberated on such as the ductility, fatigue, creep, fracture toughness, impact hardness as well as
the creep .hence, it is greater need to consider all the components of the speed reducer in order to
a come up with a design that corresponds to the customer’s needs. To minimize the rotating
mass, the material that will be considered for the gear should be light in weight. This will also
help in enhancing the efficiency of the system besides, the gear materials should pose
characteristics such as reduced coefficient of friction, high tensile strength, and ease of
manufacturing (Yimin, 2010).

The minimized coefficient of friction plays a major role I the performance criteria
selection. This is because high coefficient of friction reduces the overall efficiency of the system
Various materials that been used while making the gears includes cast iron, alloy steel, carbon
steel and grey (Childs, 2013).
Shafts
The design of the shaft plays a significant role and it is obtained from mild steel. The
shafts are four in number and each of them is the case in the smooth running and they run
through the gear centres. In order to expect a smooth running, and eliminate incidences of
torques and stress, the shaft has reduced diameter of 40nm (Cianchetti, 2013).
Bearings
The design of the gearbox also applies the roller bearings for the purposes of smooth shaft
rotation thereby lessening the friction (Callister, 2011). Below are some of the reasons for
applying the roller bearings
 They are easily manufactured or purchased
 They are readily available
 When kept clean, they normally tend to last longer as compared to other parts of the
system
Motor selection
This factor is of great significance as it determines the service life of the product. The
motor selected should be of high quality in order to ensure that the service time is prolonged
(Xie, 2010). Besides, its speed should always be low such that it doesn’t overwork its

components which may end up destroying it. Currently, there are many electric motor designs
available in the market and the one that is selected should always be in line with the customer’s
needs (Ganesh, 2011).
Gearbox housing
The casing of the gearbox also is significant when doing the design and should be in a
position to counter the exerted stress while the gearbox is in motion. Considering the weight
factor, the chosen material or the housing of the gearbox is the cast iron as it will also help in
curbing the frictions (Huang, 2014).
Belt drive
The belt drive in this design plays just a smaller role. The chosen revolution per minute
of the design was 300 RPM and which has to be minimized by the belt drive to 95.5 RPM to
achieve the desired ratio of 3.14. Hence, the chosen design was a belt configuration as shown in
the below figure. This design only required the use of two belts and it ensures that the accuracy
of the length when manufacturing is able to minimize the efficiency of the belt drive (Ross,
2010).
Key
To come up with a design that locks the shaft and the gear while in the rotation, a power
locking mechanism has to be designed .while rotating in both of the directions i.e. axial and
rotational, the gear should be locked. The various means of locking the gears system includes
splines, welded press fitting, pins, and keys. The use of restraining rings helps in positioning the
axial movement. Hence, a key has to be designed for locking of the rotating gear and the shaft
(Kim, 2013).

Input calculation
To commence the design of the system, the revolution per minute was determined by the
use of provided torque, angular velocity and the output power. The angular velocity was taken to
nobble 2.85 radians per second while the output power 4000 Watt thereby giving a value of
27.215. For the system to be 99% efficient, the output power was calculated as 20130.44 W
while the angular velocity 9.9975 radians per second. Hence, the power to be inserted into the
system was determined as 4071.01 W and 34.92 radians per second
DETAILED GEAR DESIGN
The table below shows the detailed design of the gear
Components Dimension
Reduction ratio 3:5
Face width 1.2 nm
Diameter pitch 10 nm
Number of teeth gear 84
Number of teeth of pinion 24
Pinion and gear distance 5.4 nm
Teeth height 0.225nm
Thickness of rim 0.27nm
The second gear dimensions are same as those of the pinion as result of the identical reduction
ratio. The only values which are not similar in the two sets include the angular velocity and the
torques for the gears as well as the power input.

Design life
The design life of a product is of great significance in the design task since it acts as a
prerequisite of obtaining the maximum stress that is allowable for the system. The data below is
a list of the calculations which are determined for the design life of the product (Semini, 2011).
Design for x (DFX)
As mentioned earlier above, the design of any product should aim at ensuring that the design is
cost effective, made of high quality for maximum efficiency as well as environmentally friendly.
Otherwise, it will be difficult for the product to attract more customers in the market. A design
machine casing having a various bolt and half casings have been used in performing the design
for manufacturing. The design was as stated in order to ensure that the shaft is firmly fixed on
the grove with the bearings intact (Singh, 2013).
The assembly design is meant to minimize the time used while assembling the products as well
as the cost that is incurred. It has been enabled by the use of components that are easily
assembled with the help of basic tools such as pliers, hydraulic press, spanners among others
(Chang, 2010).
The environment design has been achieved by the inclusion of a drain plug at the bottom of the
casing to ensure that the oil will be easily drained from the system hence preventing the
incidences of leakage by the lubricants (Aijmer, 2014).
Conclusion and recommendation
The report provided has covered the design of a speed reducer which has in detail balanced the
performance constraints. Hence, it is imperative that all the engineering aspects are deliberated

upon to ensure that the final product produced is of a high standard. During the process of the
design, the theoretical knowledge has been put into practice and the project generally has offered
us with the perception of assessing the design and performance criteria which can be applied in
various workplaces. Moreover, the final overall design that has been deliberated meets up the
manufacturing company demands with the overall reduction speed ratio of 3.5 as well as other
requirements. The design hence, is environmentally friendly as the design for environment has
been incorporated where a drain plug has been installed to prevent any leakage of the lubricant as
well as cost-effective, highly efficient and compact

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