Case study of con rod(1)

CASE STUDY - An Analysis of the Relationship between Surface

Roughness and distribution of diameter measurements of the large

cylindrical feature of an Automobile Connecting Rod.

Abstract The automobile industry currently operates in a highly competitive environment where

innovation and performance are critical to enhanced market share and competitiveness. Thus

system design and optimal performance of the automobile parts are crucial elements that

enable a particular automobile brand to achieve sustainable competitive advantage. This

research examines performance parameters for the connecting rods of automobiles. Here the

surface roughness in relation to the diameter of the large cylindrical feature of the connecting

rod is examined. It is desirable that for optimum performance and low fuel consumption, the

surface roughness is as low as possible. This research also examines how Faro Arm and Vernier

callipers may be used to measure the diameter of the connecting rod and the methods for

evaluating surface roughness as well.

Keywords: Surface roughness; Surface texture; Surface roughness tolerance.

Introduction The Connecting Rod is a very important part of internal combustion engines that propel

automobiles. The connecting rod is fixed to the crankshaft of the automobile by a crank pin and

the other end of the rod gets connected to the piston through a piston pin. As the piston within

the internal combustion engine moves up and down, it is the connecting rod that transmits the

power thrusts so generated to the crank pin which in turn is transferred to the piston shaft in

the form of rotary motion (Walishaw, 2011). It is this motion that turns the wheels of the

vehicle generating movement. It may be inferred here that the efficiency of the engine is

dependent on how effectively or completely the connecting rod converts reciprocating motion

into rotary motion.

According to (Tlusty, Smith, & Winfough, 2013), it is very important that the connecting rod be

dimensionally correct in terms of weight and size so that no energy is lost due to vibrations in

the connecting rod. This specification assumes great significance given that the connecting rod

is invariably the most stressed out part of internal combustion engines (Smith, Winfough, &

Halley, 2012). These stresses are generated by the pressures exerted on the piston on the

crankshaft and can lead to failure of the connecting rod. In addition, the reciprocating load

generates its own set of pressures leading to alternate stretching and compression which can

lead to connecting rod failure called “throwing the rod” (Davies, Dutterer, & Pratt, 2014). (Pai,

2013) says that this failure is often catastrophic and irreparable. In recognition of this reality

much research has been conducted on how to design and manufacture connecting rods that

are light yet strong.

However an area that has been overlooked is the relationship between surface roughness of

the connecting rod and its dimensions. Surface roughness is a most important parameter that

impacts the productivity of machine parts such as connecting rods. This i s because low levels of

surface roughness ensures optimal tribological properties, increases resistance to fatigue and

possible failure, creates corrosion resistance surfaces and increases the aesthetic appeal of the

end product (Jeppsson, 2013). Surface roughness impacts precision of fits, the strength of

fastenings and friction between connecting rods and the crankshaft pins (Smith, S; Tlusty, J,

2013). Various parameters impact surface roughness including the speed of cutting and

machining, the feed rates of cutting spindles, the density of the metal in the work piece and the

rigidity of the machine tools (Serag, Sevien, Sheha, & El-Beshtawi, 2014). However it may be

noted here that these are processes that impact surface roughness at the end stage – which is

machining. What is also important is the beginning or the design stage to understand those

optimal dimensional measurements that impact surface roughness. One of these dimensional

measurements is the diameter of the small end of the connecting rod that interfaces with the

piston and the other is the diameter of the big end that connects with the crankshaft. However,

the study of relationship between the dimensional distribution and surface roughness is carried

out on the large cylindrical feature of the connecting rod.

This study is important because of the competitive business environment in which the

automobile industry operates today where the demand is for light weight, fuel efficient and

long lasting vehicles. This puts great pressure on research and development to develop critical

components – such as connecting rods – that function efficiently. On the basis of the

aforementioned introduction the following research questions and aims & objectives may be

formulated.

Research Question

What is the relationship between distribution of large cylindrical diameter measurements and

the corresponding surface roughness of an automobile connecting rod?

Aims & Objectives

To conduct an experiment using both Vernier scales and Faro Gage to measure diameter

of the large cylinder feature of automotive connecting rods and their corresponding

surface roughness.

To analyse the correlation of the surface roughness versus the diameter measurements

using statistical methods for each sample.

To understand whether the surface roughness characteristics have direct impact on the

distribution of measurement result for the cylinder diameter measurement.

To draw conclusions explaining issues related to feature dimensions and surface

characteristics at design, manufacturing and service stages .

Working Methodology

The method employed to analyse impact of dimensional measurement distribution on surface

roughness of connecting rods is shown below. This included the Define, Measurement,

Analysis, Understanding the correlations and results and conclusions.

Figure 1.Flow Chart of Methodology followed to Evaluate Surface Roughness Parameters and Dimensional Measurements.

Define This stage defines the nature of the experiment performed. The experiment is conducted on

five different connecting rods of varying geometry and surface roughness. These include low

carbon steel, aluminum silicate alloy (AlS) and MV 9 alloy. These represent the standard

materials used in the automobile industry for connecting rod manufacture. The below figure

shows the connecting rods used to conduct the experiment arranged in the order (a) Low

carbon steel connecting rod (b) MV9 alloy connecting rod (c) Aluminium silicate connecting rod

(d) Low carbon steel connecting rod and (e) MV9 alloy connecting rod.

i. Surface Roughness Parameter Measurement

Many surface roughness parameters can be used to define and analyze the surface of a

mechanically manufactured object which includes Average surface roughness (Ra), Maximum

height of the profile (Rt), Root mean square (Rq) etc. Out of this, the most common roughness

parameter employed to define a surface in many of the manufacturing industries is the average

surface roughness or Ra.

The average surface roughness is given by,

Where,

‘n’ is the number of evaluated points.

‘Yi’ is the absolute deviation of the profile line from the mean line.

The Ra value is measured using Taylor Hobson Surtonic-25 instrument.

ii. Dimensional Measurement

The dimensional measurement used in the experiment is the diameter of the large cylindrical

feature of the automobile connecting rod. The dimension measurement is initially observed

using a Mitutuyo Vernier Caliper and then measured using a FARO articulated arm CMM. The

later readings were observed with the aid of CAM2 Measure 10.2 software platform in a

computer system.

Measurement This stage explains the experimental procedure employed to measure the required surface

roughness parameter and the dimensional measurement of the connecting rod.

i. Surface Roughness Measurement

Prior taking the diameter dimensional measurements of the large cylindrical feature of the

connecting rods marked (a), (b) and (c), the Taylor Hobson Surtonic-25 equipment is calibrated

against a specimen of known surface roughness value of 6µm. On calibration an error of

0.02µm is found. Also, prior taking the diameter measurements of the large cylindrical feature

of the connecting rods marked (c) and (d), the Taylor Hobson equipment is calibrated against

the same specimen but an error of 0.26 µm is shown.

For the experiment all the connecting rods are individually held firmly on a working bench using

a mechanical G-clamp so that error due to vibration or misalignment of the connecting rod

while measuring can be avoided. The surface roughness values were taken at random points

from the periphery of the large cylindrical feature of the connecting rods marked (a), (b) and (c)

whereas in case of connecting rods marked (c) and (d), the roughness values of fixed marked

points were recorded. The observed surface roughness readings are as follows:

Marked Connecting

Rods

Observed Surface Roughness

value (µm)

Calibration

Error (µm)

Actual Surface

Roughness (µm)

a 0.38 0.26 0.38

b 0.66 0.26 0.66

c 1 0.26 1.26

d 0.16 0.02 0.18

e 0.28 0.02 0.30

The surface roughness value of connecting rod marked (c) could not be measured using Taylor

Hobson Surtonic-25 as its roughness value is beyond the measuring range of the instrument.

Due to the non-availability of other surface measuring instrument in the metrology laboratory a

roughness value above 1µm based on visual experience is assumed for the connecting rod (c).

ii. Dimensional Measurement

The dimensional measurement of the large cylindrical feature of the connecting rods marked

(a), (b), (c), (d) and (e) were initially measured using a Mitutuyo Vernier caliper. Before making

the diameter readings all the connecting rods were individually clamped to a work bench using

a mechanical G-clamp to avoid misalignment of the rod while measuring. The diameter

readings of the connecting rods marked (a), (b) and (c) are observed from random points on the

periphery of the large cylindrical part where as in case of connecting rods marked (d) and (e),

the diameter readings were taken corresponding to marked points on the periphery of the

cylindrical portion.

This was deliberately done to analyze how different measuring procedures can al ter the

accuracy of the measurement readings.

Similarly for all the connecting rod specimen’s diameter measurements were taken using FARO

arm CMM machine. As explained in the previous chapter, the FARO arm CMM gives much more

accurate measurements than Vernier caliper and this can be interpreted by following the below

procedure of diameter measuring.

(a) Before making the readings the FARO gauge arm CMM must be calibrated and verified

to avoid uncertainty in readings and to obtain precise and accurate readings. The FARO

gauge CMM is calibrated by placing the hard ball probe at the measuring arm of the

device in to a kinematic socket. The calibration process is achieved by making several

readings for different orientations of gauge arms and wrists without altering the

position of the probe from the socket. The device can be defined as accurate if all the

calibration readings are the same. One can easily assess the size of the sphere that

embodies all the points and utilize that at an indicator of the impact of the intensifying

errors of the angular encoders. The FARO arm CMM was calibrated, verified and

certified by the manufactures according to National Physical Standards before the

instrument was purchased (Laboratory, 2014).

(b) Measuring Procedure 1: The diameter readings of the connecting rods (a), (b) and (c)

were observed at random points on the top and bottom of periphery of the large

cylindrical portion of each connecting rods and random orientation of the articulated

arms of the FARO arm CMM with respect to each arm joints. The coordinates of the

origin was kept constant by placing the FARO CMM at fixed station.

(c) Measuring procedure 2: The diameter readings of the connecting rods (d) and (e) were

observed from marked points of the planes on the periphery of the large cylindrical part.

The appropriate number of uniformly spaced planes orthogonal to the cylinder axis

were obtained by the following equation (Flack, 2014).

Where,

‘n’c is the appropriate number of planes orthogonal to the cylinder axis.

‘N’ is the number of observations.

‘h’ is the height of the cylindrical feature.

‘r’ is the radius of the cylindrical feature.

The appropriate number of points to be marked on the planes is obtained by,

(Flack, 2014).

Where,

‘n’c is the appropriate number of planes orthogonal to the cylinder axis.

‘N’ is the number of observations.

Figure 2. Distribution of measuring planes and points on the cylindrical feature of the connecting rod (Flack, 2014).

Table 1 - the required number of planes and points for the successful measurement

Marked

connecting rods

Diameter of the

cylindrical feature,

D (mm)

Radius of the

cylindrical feature,

r (mm)

Appropriate

number of planes,

nc

Appropriate

number of points

on the planes, np

A 39 19.5 2.7 11

B 36 18 2.8 10.7

C 41 20.5 2.6 11.3

D 48 24 2.4 12.2

E 18 18 2.8 10.7

Also, the readings were observed from the FARO gauge instrument by keeping the following

angle of orientations for the instrument:

Angle of orientation at Wrist (1) at below 15° with respect to the fixed station.

Angle of orientation of the gauge arm 1 and gauge arm 2 at 30°.

Varying angle of orientation of the gauge arm 2 and gauge arm 3 since the orientation

will change according to the marked points.

The lengths of the gauge arms are fixed and the detailed specifications of the

instrument are described in the brochure of FARO arm CMM given by the manufacturer.

(See Appendix).

The working temperature is the room temperature (20°C). For the maximum accuracy

and portability, the temperature sensors incorporated in the instrument allows the

measuring arm to react to the thermal variations as described in the methodology of the

project.

Figure 3. Description of position and angle of orientation of FARO gauge arm.

The all the diameter readings and other measurement related details were assessed using

CAM2 Measure 10.2 software platform (See appendix).

Analysis

Descriptive statistics tool is employed to conduct the analysis of diameter and surface

roughness data’s of the large cylindrical feature of the selected connecting rods under

investigation. The statistical analysis is performed in Microsoft Excel to achieve accurate

analysis results. The statistical parameters considered in descriptive statistics included Mean,

Standard deviation, Maximum, Minimum and Range. The range between the maximum and

minimum numbers represents the Gaussian or normal distribution within which the average

values of diameters of the large cylindrical feature corresponding to varying surface roughness

and is diagrammatically represented in the form of a histogram. In the histogram, the x axis

represents the diameters of large cylinder feature of the connecting rods under examination

while the y axis represents the corresponding frequency values.

The descriptive statistical analysis is initially done for the diameter measurements obtained

from the two defined measuring strategies of the FARO arm CMM. The statistical analysis of

diameter measurements from Vernier calliper is also done to verify the results of the analysis.

Statistical Analysis of FARO arm measurements.

For each of the analysis, the band width of the bin of the histogram is theoretically calculated

for the optimum bin size and is given by the formula (Jenkinson, 2014),

ℎ = 3.5𝜎

𝑛1/3

Where,

‘h’ is the band width of the bin.

‘σ’ is the standard deviation.

‘n’ is the number of readings.

(a) Low Carbon Steel Connecting Rod

The table shows the descriptive statistical values for 30 sets of diameter readings of the large

cylindrical feature of the connecting rod made of low carbon steel and the surface roughness

value, Ra=0.38µm.

Mean 39.0084

Standard Error 0.005129271

Median 38.999

Mode 38.989

Standard Deviation 0.028094177

Sample Variance 0.000789283

Kurtosis -0.020582247

Skewness 0.800724163

Range 0.11

Minimum 38.974

Maximum 39.084

Sum 1170.252

Count 30

Table 2. Descriptive statistical analysis of diameter readings of the low carbon steel connecting rod.

From the descriptive statistical analysis, the maximum and minimum diameter reading of the

observation is 39.084mm and 38.974mm respectively. The difference between the maximum

and the minimum value is the range and is observed as 0.11mm. The mean diameter values is

approximately 39 and the standard deviation across the range from the mean value is 0.028.

The histogram depicting the frequency of occurrence of the diameter with in each range of

standard deviation is shown

Graph 1. Histogram of diameter readings of the low carbon steel connecting rod.

The greatest range of diameter reading occurrence is between the values 38.974mm and

39.005mm followed by 39.005mm and 39.036mm. By employing the statistical equations,

𝑈𝑝𝑝𝑒𝑟 𝑣𝑎𝑙𝑢𝑒 = 𝑀𝑒𝑎𝑛 + (𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑒𝑟𝑟𝑜𝑟 ∗ 𝑍) , and

𝐿𝑜𝑤𝑒𝑟 𝑣𝑎𝑙𝑢𝑒 = 𝑀𝑒𝑎𝑛 − (𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑒𝑟𝑟𝑜𝑟 ∗ 𝑍)

We can predict that 68% of observed diameter readings lies between the range 39.0033mm

and 39.0135mm, 95% of the diameter readings lies between the range 38.9982mm and

39.0186mm and 99.7% of the diameter readings lies between the range 38.9931mm and

39.0237mm.

(b) MV9 Alloy Connecting Rod


cylindrical feature of the connecting rod made of MV9 alloy and the surface roughness value,

Ra=0.66µm.

Mean 36.07006667


Median 36.063

Mode 36.059



Kurtosis -0.168587878

Skewness 0.60776998

Range 0.103

Minimum 36.029

Maximum 36.132

Sum 1082.102

Count 30

Table 3. Descriptive statistical analysis of diameter readings of the MV9 alloy connecting rod.

From the descriptive statistical analysis, the diameter readings fluctuates between 36.029mm

and 36.132mm with in a range of 0.103mm. The mean diameter values is 36.07 and the

standard deviation across the range from the mean value is 0.025.



Graph 2.Histogram of diameter readings of the MV9 alloy connecting rod.

From the Histogram, most of the observed diameter readings falls between 36.057mm and

36.085mm. The statistical analysis reveals that 68% of the observed diameter readings of the

connecting rod lies in the range 36.0649mm and 36.0751mm while 99.7% of the diameter

readings lies in the range 36.0547mm and 36.0853mm.

(c) Aluminium Silicate Connecting Rod


cylindrical feature of the connecting rod made of Aluminium Sil icate and the surface roughness

value, Ra=1.26µm.

Mean 41.12483333


Median 41.1315

Mode 41.146



Kurtosis 6.583775212

Skewness -1.82601957

Range 1.063

Minimum 40.421

Maximum 41.484

Sum 1233.745

Count 30

Table 4.Descriptive statistical analysis of diameter readings of the Aluminium silicate connecting rod.

From the descriptive statistical analysis, the minimum diameter reading is 40.421mm and the

maximum diameter reading is 41.484mm. The difference between the maximum and the

minimum value is the range and is observed as 1.063mm. The mean diameter values is

41.124mm and the standard deviation across the range from the mean value is 0.186.



Graph 3. Histogram of diameter readings of the Aluminium silicate connecting rod.


41.2714mm. The statistical analysis reveals that 99.7% of the observed diameter readings of

the connecting rod falls in the range 41.022mm and 41.226mm while 68% of the diameter

readings lies in the range 41.09mm and 41.158mm. 41.056mm to 41.192mm constitutes 95% of

the observed diameter readings.

(d) Low Carbon Steel Connecting Rod


cylindrical feature of the connecting rod made of Low carbon steel and the surface roughness

value, Ra=0.18µm.

Mean 48.1828


Median 48.1845

Mode 48.187





Range 0.05

Minimum 48.15

Maximum 48.2

Sum 1445.484

Count 30

Table 5. Descriptive statistical analysis of diameter readings of the Low carbon steel connecting rod.

From the descriptive statistical analysis, the minimum diameter reading and the maximum

diameter reading achieved is 48.15mm and 48.2mm respectively. The difference between the

maximum and the minimum value is the range and is observed as 0.05mm. The mean diameter

values is 48.1828mm and the standard deviation across the range from the mean value is

0.0135.



Graph 4.Histogram of diameter readings of the low carbon steel connecting rod.

From the Histogram, the highest frequency range of number of observations is 15 and it

corresponds to the range of diameter readings between 48.182mm and 48.198mm. The

statistical analysis reveals that 68% of the observed diameter readings of the connecting rod

falls in the range 48.1804mm and 48.1852mm while 99.7% of the diameter readings lies in the

range 48.1756mm and 48.1876mm. 95% of the diameter readings of the corresponding

connecting rod were observed between the range 48.178mm and 48.1876mm.

(e) MV9 Alloy Connecting Rod


cylindrical feature of the connecting rod made of MV9 alloy and the surface roughness value,

Ra=0.30µm.

Mean 36.01546667


Median 36.0115

Mode 36.008





Range 0.088

Minimum 36.001

Maximum 36.089

Sum 1080.464

Count 30


From the descriptive statistical analysis, the observed diameter readings of the large cylindrical

feature varies from 36.089mm to 36.001mm. The average diameter is found as 36.015mm and

the dispersion of the readings or standard deviation is 0.0162. The range over which the

diameter readings falls is 0.088.



Graph 5.Histogram of diameter readings of the MV9 alloy connecting rod.

From the Histogram, the most of the observed diameters lies in the range 36.001mm and

36.0186mm. From the statistical analysis we can predict that 68% of the observed diameter

readings of the connecting rod falls in the range 36.0121 and 36.0179 while 99.7% of the

diameter readings lies in the range 36.0063mm and 36.0208mm. 95% of the diameter readings

of the corresponding connecting rod were observed between the range 36.0092mm and

36.0208mm.

Statistical Analysis of Vernier Calliper Measurements

The statistical analysis of the diameter measurements from the Vernier calliper is performed to

assess whether the statistical analysis of FARO arm CMM reading for the same follows any

similar trend. For each of the analysis as of FARO arm, the band width of the bin of the

histogram is theoretically calculated for the optimum bin size and is given by the formula

(Jenkinson, 2014),

ℎ = 3.5𝜎

𝑛1/3

Where,

‘h’ is the band width of the bin.

‘σ’ is the standard deviation.

‘n’ is the number of readings.

(a) Low Carbon Steel Connecting Rod

The table establish the descriptive statistical analysis of the 30 sets of diameter readings of the

large cylindrical feature of the low carbon steel connecting rod with surface roughness, R a as

0.38µm.

Mean 38.83333333


Median 38.92

Mode 38.97



Kurtosis -0.679136819

Skewness -0.879469425

Range 0.52

Minimum 38.48

Maximum 39

Sum 1165

Count 30

Table 7. Descriptive statistical analysis of diameter readings of the low carbon steel connecting rod.

The descriptive analysis reveals that observed diameter readings falls in the range from

38.48mm to 39mm. The mean readings about which a standard deviation of 0.1704 occurs is

38.83mm. The range over which the 30 counts of readings fall is 0.52mm.



Graph 6. Histogram of diameter readings of the low carbon steel connecting rod

From the histogram we can anticipate that 68% of the observed diameter readings lies between

38.79 and 38.86 while 99.7% of the observed readings falls between 38.73 and 38.92. The

maximum frequency value is in the range 38.86mm and 39.05mm. From the shape of the

histogram it can be inferred that the diameter readings does not follow normal distribution like

FARO arm readings for the same connecting rod.

(b) MV9 Alloy Connecting Rod

The table establish the descriptive statistical analysis of the 30 sets of diameter rea dings of the

large cylindrical feature of the MV9 alloy connecting rod with surface roughness, R a as 0.66µm.

Mean 35.78433333


Median 35.81

Mode 35.53



Kurtosis -1.212139894

Skewness -0.343955533

Range 0.6

Minimum 35.42

Maximum 36.02

Sum 1073.53

Count 30


From the descriptive analysis, the maximum and minimum diameter reading is 36.02mm and

35.42mm respectively. The difference between the maximum and the minimum gives the range

and is found as 0.6. The mean of the observations is 35.78mm and the standard deviation is

0.184.



Graph 7. Histogram of diameter readings of the MV9 alloy connecting rod.



readings of the connecting rod falls in the range 35.67mm and 35.81 while 99.7% of the

diameter readings lies in the range 35.67mm and 35.88mm. 95% of the diameter readings of

the corresponding connecting rod were observed between the range 35.57mm and 35.84mm.

(c) Aluminium Silicate Connecting Rod



1.26µm.

Mean 40.74866667


Median 40.705

Mode 40.63



Kurtosis -0.260166927


Range 1.6

Minimum 40.09

Maximum 41.69

Sum 1222.46

Count 30

Table 9. Descriptive statistical analysis of diameter readings of Aluminium silicate connecting rod.

From the descriptive statistical analysis, the mean diameter reading for the range of

observations from a minimum of 40.09mm and maximum of 41.69mm is 40.74mm. The range

size is 1.6 and the corresponding standard deviation of the readings is 0.402.



Graph 8.Histogram of diameter readings of the Aluminium silicate connecting rod.


40.99mm followed by 40.9mm and 40.54mm. The statistical analysis reveals that 68% of the

observed diameter readings of the connecting rod lies in the range 40.66mm and 40.82mm

while 99.7% of the diameter readings lies in the range 40.52mm and 40.96mm. The shape of

the histogram depicts the shape of a flattened bell curve.

(d) Low Carbon Steel Connecting Rod



0.18µm.

Mean 48.03666667


Median 48.08

Mode 48.1



Kurtosis -0.572953373

Skewness -0.392874739

Range 0.53

Minimum 47.75

Maximum 48.28

Sum 1441.1

Count 30

Table 10.Descriptive statistical analysis of diameter readings of low carbon steel connecting rod.

From the descriptive analysis, the maximum and minimum diameter of the observations is

48.28mm and 47.75mm with mean value of 48.036mm. The difference between the maximum

and the minimum values gives the range of the diameter distribution and is observed as

0.53mm and the corresponding standard deviation is found as 0.133.



Graph 9. Histogram of diameter readings of the low carbon steel connecting rod.



readings of the connecting rod falls in the range 47.78mm and 48.27mm while 99.7% of the

diameter readings lies in the range 47.30mm and 48.75mm. 95% of the diameter readings of

the corresponding connecting rod were observed between the range 47.54mm and 48.52mm.

The shape of the histogram reveals a uniform probability distribution of diameter readings.

(e) MV9 Alloy Connecting Rod



0.30µm.

Mean 36.052


Median 36.08

Mode 36.08



Kurtosis

-

0.791917666


Range 0.5

Minimum 35.8

Maximum 36.3

Sum 1081.56

Count 30

Table 11. Descriptive statistical analysis of diameter readings of MV9 alloy connecting rod.

The descriptive statistical analysis reveals that the diameter of the MV9 connecting rod is

distributed over a range of 0.5mm with maximum and minimum observations 36.3mm and

35.8mm respectively. The mean across which the observations lie is 36.052mm and the

standard deviation is 0.139mm.



Graph 10. Histogram of diameter readings of the MV9 alloy connecting rod.


36.1mm. The statistical analysis reveals that 68% of the observed diameter readings of the

connecting rod lies in the range 36.02mm and 36.07 while 99.7% of the diameter readings lies

in the range 35.98mm and 36.13mm. The shape of the histogram depicts a perfect bell curve

graph.

Results and Discussions

The major objective of the investigation was to analyse the correlation of distribution of

dimensional measurements and surface roughness parameters. The descriptive statistical

analysis is the most suitable tool to quantitavely define the important features of collection of

information’s. Therefore, for the investigation the measurements of five different automobile

connecting rods of varying surface textures were statistically examined.

Results of correlation of the surface roughness and the dimensional

measurements

The correlation signifies how a particular quantity is depended on other parameters. With a

perfect relationship between two quantities helps to define one quantity in terms of the other.

From the analysis it is clear that surface roughness characteristics has an impact on the

distribution of measurement result for the large cylindrical feature diameter measurement of

the automobile connecting rod. This correlation can be revealed by plotting a graph of surface

roughness of the different connecting rod under investigation and the corresponding standard

deviation of the diameter measurements.

Graph 11. Surface roughness vs. Standard deviation of diameter measurements from FARO arm CMM.

The graph 11. Shows the correlation of surface roughness and the standard deviation of

diameter measurements of FARO arm CMM.

Graph 12.Surface roughness vs. Standard deviation of diameter measurements from Mitutuyo Vernier Calliper.

The graph 12. Shows the correlation of surface roughness and the standard deviation of

diameter measurements of Mitutuyo Vernier Calliper.

The nature of relationship between the surface roughness and dimensional distribution could

not be well established from the investigation since the graph showed a scattered output. But

the scattered graph revealed a strong correlation as the value of rate of dispersion of observed

dimensional measurements projected up with corresponding surface roughness parameter.

Plotting an imaginary line through the maximum points as shown in figure 11 and figure 12

would help to identify an improved correlation. The line obtained showed a direct relationship

between the variables for both the graphs. Hence, the investigation shows a linear relationship

of distribution of dimensional measurement and the surface roughness parameter. An

improved correlation data could be produced if more similar components were examined.

Also, the defined experimental methodology showed following results:

1. The Mitutuyo Vernier calliper observations showed a wide range of dispersion of

diameter readings of the large cylindrical feature of the automobile connecting rod

compared to FARO arm CMM. Also, the observations made from FARO gauge arm

produced a Gaussian bell curve which reveals that all the readings were uniformly

distributed across the mean reading. This may be due to high precision and accuracy of

FARO gauge instrument as defined in the methodology.

2. The methodology defined two different procedures for the dimensional measurement

of the connecting rods. This was deliberately done to verify the accuracy and

uncertainties in following different measuring procedures. Out of the two experimental

procedures, the experimental procedure followed to measure the diameter of the large

cylindrical feature of the connecting rods marked (c) and (d) as suggested by the

National Physical Laboratory- good practise guideline for CMM measurements gave an

healthy output for the analysis of the investigation.

3. A fluctuating histogram shape was noted during the analysis of dimensional

measurements. This may be due to varying profile of the surface roughness of the

examined cylindrical feature.

Conclusions

The paper looks at the relationship between distribution of large cylindrical diameter

measurements and the corresponding surface roughness of an automobile connecting rod. An

experiment was conducted experiment using both Vernier scales and Faro Gage to measure

diameter of the large cylinder feature of automotive connecting rods and their corresponding

surface roughness. We have analysed the correlation of the surface roughness versus the

diameter measurements using statistical methods for each sample and attempted to

understand whether the surface roughness characteristics have direct impact on the

distribution of measurement result for the cylinder diameter measurement.

We find that the relationship means how a specific quantity is relied on upon different

parameters. With an impeccable relationship between two quantities, it serves to characterize

one quantity regarding the other. From the investigation it is clear that surface roughness

qualities has an effect on the appropriation of estimation result for the large cylindrical feature

diameter width estimation of the auto associating pole. This connection can be uncovered by

plotting a chart of surface roughness of the distinctive interfacing bar under scrutiny and the

relating standard deviation of the measurement estimations.

The way of relationship between the surface roughness and dimensional dissemination couldn't

be settled from the examination since the chart demonstrated a scattered yield. However the

scattered diagram uncovered a solid connection as the estimation of rate of scattering of

watched dimensional estimations anticipated up with relating surface roughness parameter.

Plotting a graph through the greatest focuses as demonstrated in figure 11 and figure 12 would

help to recognize an enhanced connection. The line acquired demonstrated an immediate

relationship between the variables for both the diagrams. Henceforth, the examination

demonstrates a straight relationship of circulation of dimensional estimation and the surface

roughness parameter. Enhanced relationship information could be delivered if more

comparable parts were inspected. Additionally, the characterized exploratory strategy indicated

after results The Mitutuyo Vernier caliper perceptions demonstrated an extensive variety of

scattering of distance across readings of the huge tube shaped gimmick of the vehicles

associating bar contrasted with FARO arm CMM. Likewise, the perceptions produced using

FARO gage arm created a Gaussian chime bend which uncovers that all the readings were

consistently appropriated over the mean perusing. This may be because of high exactness and

precision of FARO gage instrument as characterized in the philosophy. The approach

characterized two separate methodologies for the dimensional estimation of the uniting bars.

This was deliberately done to confirm the exactness and instabilities in after diverse measuring

systems. Out of the two test methodology, the exploratory method took after to gauge the

width of the vast tube shaped diameter of the interfacing bars checked (c) and (d) as proposed

by the National Physical Laboratory- great practice rule for CMM estimations gave a sound yield

for the investigation of the examination. A fluctuating histogram shape was noted amid the

investigation of dimensional estimations. This may be because of fluctuating profile of the

surface roughness of the analyzed cylindrical diameter.

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