1. TITLE Surface Roughness Measurement 2. OBJECTIVE IVE a)
To obta obtain in the the value alue of roug roughn hnes ess s of a spec specim imen en by the the CENT CENTER ER LINE LINE AVER AVERAG AGE E (CLA (CLA)) or ROUG ROUGHN HNES ESS S AVER AVERAG AGE E (Ra) (Ra) meth method od by usin using g a Computerized Roughness Measuring Machine.
b) To compare compare the value value of roughnes roughness s of a specimen specimen by the Center Center Line Line Average Average (CLA) and average roughness (Ra) method. c) To study the the causes of different different value of of roughness roughness of a specimen specimen between between CLA CLA and Ra method. d)
To study the necessary precaution needed for this experiment .
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3. INTR INTROD ODUC UCTI TION ON
Figure 1: Sketch depicting how a probe stylus travels over a surface
Roughness is a measure of the texture of a surface. A surface can never be perfectl perfectly y smooth smooth and will will always always have have two compone components nts of surface surface texture texture namely namely roughness and waviness as shown in figure above. They may vary from fine to coarse accor accordin ding g to the the mach machine ine proce process ss used. used. Rough Roughne ness ss is quan quantif tifie ied d by the the verti vertical cal deviations deviations of a real surface from its ideal form. If these deviations deviations are large, the surface is rough; if they are small the surface is smooth. Roughness is typically considered to be the high frequency, short wavelength component of a measured surface. Roughness plays an important role in determining how a real object will interact with its environment. Rough surfaces usually wear more quickly and have higher friction coeffici coefficients ents than smooth smooth surfaces surfaces.. Althoug Although h roughne roughness ss is usually usually undesir undesirable able,, it is difficu difficult lt and expens expensive ive to control control in manufact manufacturin uring. g. Decreas Decreasing ing the roughne roughness ss of a surface will usually increase exponentially its manufacturing costs. In some cases, the physical geometry of the measuring instrument may have a large effect on the data. This is especially true when measuring very smooth surfaces.
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4. SPEC SPECIM IMEN EN & EQU EQUIP IPME MENT NT a)
Specimen – piston cylinder
b) A computer computerized ized Surfa Surface ce Roughne Roughness ss Machine Machine c)
Digital planimeter
5. PRO PROCEDU CEDURE RES S Machining Processes 1.
A cut off wavelength of 0.8mm by 8 sections were selected on the machine. The machine were set to a vertical magnification magnification to auto and horizontal magnification magnification too 100.
2. The compon component ent is placed placed on the auto leveling leveling table table at a suitabl suitable e position position such that that when hen pick pick up head head is low lowered ered,, its its sty stylus lus cont contac acts ts the the surf surfac ace e of the the specimen.
Figure 2: Computerized Surface Roughness machine
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5.
The machine was set; the measurement is ready to be recorded.
6.
The roughness profile graph for the specimen was obtained.
Manual Processes
CLA Line
CLA Line
L
L
Figure 3: Roughness Profile
1.
Three peaks on the profile graph were selected.
2.
Two vertical lines were drawn for the three peaks. 4
3. A center centerline line (CLA) (CLA) line line was was drawn drawn.. 4. The The area areas s abov above e and below elow the the CLA line line was meas measur ured ed usin using g a digit igital al plan planim imet eter er.. Three hree meas measur urem emen ents ts were ere take taken n and and the the aver averag age e of the the measurements was calculated. 5. The value value of CLA was calculat calculated. ed. 6.
The computerized result for CLA was compared with the manual result.
6. RESUL RESULTS TS & DA DATA ANA ANALYS LYSIS IS i.
ii.
The value of R a from computerized result is 3.48 µm. For manual manual calculat calculation, ion, we must calculat calculate e the the CLA CLA and and the the perce percentag ntage e error. error. CLA
= ΣA / ( L x Mv ) where: ∑A = sum of the area above and below the centerline L = sample length 5
Mv = vertical magnification
Percenta Percentage ge of error error =
iii. iii.
x 100% 100%
The The val value ue of L = 10 10 cm cm and and Mv = 21 2100. 00.
Area above the line(m 2)
Area below the line(m 2)
Sum of area above and below the line(m 2)
A1
0.00025
0.00064
0.00089
A2
0.00022
0.00060
0.00082
A3
0.00022
0.00062
0.00084
ΣA
= (0 (0.000 00089+ 89+0.00 .00082+ 082+0. 0.0 0008 0084) / 3 = 8.5 x 10 -4 m2
CLA
= ΣA / ( L x Mv ) = (8.5 x 10-4 )/ (10 x 10 -2 x 2100 ) = (8.5 x 10 -4 )/ 210 = 4.048 µm
Percenta Percentage ge of error error =
=
x 100% 100%
x 100%
= 16.32%
7. DISC DISCUS USSI SION ONS S
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From the result, the roughness value that we get using Center Line Average (CLA) method is 4.048 µm and the percentage of error is 16.32%. The percentage of error that we get is acceptable since the value is still below 20%. If the value of percentage of error is above 20%, the error is considered large. There are some errors that occur during the experiment which caused the percentage of error value equal to 16.32% which is the inconsistent of hand movement. When the hand movement is not consistent, the result will be affected. The inconsistent of the hand movement cannot be controlled controlled since it is normal for each people. In our opinion, we believe that the value of Ra is depends on the peak value and how often the peak is occur. If the peak occurs in many time and high, it will affect the value of area and directly affect the value of roughness that we get from manual calculation. Since the value of R a is get from the computer, we know that it will give the most accurate value compare to the manual result. The manual result will give us more error since it can be affected by environment factor. One of the causes of incorrect measurement is the selection of the wrong cutoff wavelength. Selecting the incorrect cutoff length could make the values appear larger or smaller than the desired values. The cutoff wavelength must be at the centre wave or close to the center of wave. The tracing speed of the person who is conducting this experiment is also not the same. In this experiment, we use three different people to measure the profile of the surface roughness. So, the speed between the three of us is not the same. It may differ according to the method of our group members. If the trace speed is too high, it will effect the measurement data because it will cause the data recorded is not exactly as the exact value. It also will cause the distortion to occur when the tracing speed is too high. Other than that, one of our group member was used the left hand to measure the profile of surface roughness. It will affect the result because the instrument is more suitable for people who use the right hand to handle this instrument. When handling this instrument, suddenly we stop the measuring process and will proceed the process to complete the measurement. So, when we proceed the process, some mistakes will 7
occur during the proceeding the process. The instrument may not stay in contact with the surface continuously. So, when this happen it will cause the error to occur. The environment condition also will influence the reading of the result. During the measurement process, if the table or papers are move during measurement, the error will occur. The digital planimeter is the sensitive instrument, so it must be carefully handle to avoid the error from occur. Finally, the error may occur if the surface to put the graph paper has dirt. If there any dirt appeared, the accuracy of measurement for area above and below centerline will decrease. This is because of the sensitivity of the digital planimeter. There are several precautions that should be taken and considered to ensure accurate data and result is obtained. Firstly, students should ensure that the profile graph paper is clean from any dirt and positioned correctly and neatly on the table. Other than that, students should handle the digital planimeter planimeter carefully and not to touch the screw at the back of the planimeter. This is because it will affect our reading. To obtain obtain accurat accurate e results, results, students students should should consider consider taking taking three three measurem measurements ents and calculating the average. Also, students should make sure that the person who is in charge of measuring the graph area has steady hands and of the same person to get accurate and consistent results.
8. CONC CONCLU LUSI SIO ON From this experiment, we found that the value of the roughness of the specimen by using CLA method is greater than the Roughness Average (Ra) method. The error is acceptable since the percentage of error is less than 20%. To overcome this error, we should do the experiment carefully by considered the precaution in this experiment. Other than that, in order to get the result that is close to the Ra method, we must take at least three times reading. The more reading that we take, the more accurate value we will achieved. Besides, we also must know the error that might occur in this experiment experiment to prevent the mistake occur in the next time. 8
As a conclusion, the objective of this experiment is successfully achieved since we had got the value of roughness by using CLA method or Ra method. We also have succe succeed eded ed to deter determin mine e the the erro errorr and and the meth method od to over overcom come e the error error in this this experiment. 9. RECO RECOMM MMEN ENDA DATI TION ON Students should take measurements using the digital planimeter at least three times and calculate its average. This is to ensure accurate data and result is obtained. It is also recommended that the students should pick the suitable place on the table to put the roughness profile graph so that the person who is going to use the digital planimeter is comfort comfortable able when when measurin measuring. g. Student Students s should should handle handle the equipme equipment nt with with care care especially the digital planimeter as it is a very sensitive equipment. The screw below the digital planimeter should not be disturbed to ensure exact and accurate measurements were taken. It is recommended that the same student who measures the area of the grap graph h usin using g the the digi digita tall plan planim imet eter er shou should ld also also calc calcul ulat ate e the the area area of the the grap graph h themselves.
Nowadays, the quality of product is very important in manufacturing area since many companies are competing with each other. Usually, the product which has rough surf surfac ace e is unde undesi sira rabl ble. e. This This prob proble lem m is diff diffic icul ultt and and expe expens nsiv ive e to cont contro roll in manufacturing. So, we must have a machine that can measure the roughness of the product. The Computerized Roughness measuring machine are recommended because it can reduce the problem error and faster than manual method. This machine is also more accurate than manual method. We suggest that each company has this kind of machine so they can determine their product surface roughness and improve of it from time to time. 10.REFERENCES 9
a) http://claymore.engin http://claymore.engineer.gvs eer.gvsu.edu/~jac u.edu/~jackh/eod/m kh/eod/manufact/ anufact/manufact manufact-84.html -84.html b) http://www.mfg.mtu http://www.mfg.mtu.edu/cy .edu/cyberman berman /quality/sfinish/ter /quality/sfinish/terminology minology.html .html
ASSIGNMENT: Roundness Objective 1. To calibra calibrate te a Dial Gaug Gauge e using using Calibrat Calibration ion Tester Tester 2. To find find the error error on on each each reading reading of of the dial dial Gauge Gauge 3.
To obtain the accuracy of the gauge 10
Introduction Roundness can in general is defined as ‘trueness of form’ of a circular part. Some of the common causes of out of roundness are clamping distortion, rotational imperfec imperfection tions s in the process process of manufac manufacture ture,, vibratio vibration, n, heat, heat, strain strain induced induced during during machini machining, ng, strain strain release released d after after machinin machining g and residual residual surface texture texture left by the process. A study of roundness and its measurement is essential in order to specify the required roundness. The roundness of parts like spindles, bearings is very important since the proper functioning of these parts is crucial for generating a round part. To get an effective functional of parts, it is essential that the parts should conform to their geometry, roundness in this case as close as possible Apparatus Calibration Test Piece (of roundness 11.2m), centering tool, stylus arm 63.5mm, roundness chart paper. Procedure 1.
The calibration test piece is placed on the turn table. The stylus arm is adjusted until it gets near the test piece. The pen shift knob is set to the centre position. The magnification is set to x100.
2. The The stylus stylus arm is adjus adjuste ted d until until it touch touches es the test test piece piece right right positio position. n. The needle is ensured to be at the centre. 3.
The turn table is switched on after we switched on the power supply. The test piece is adjusted using centering meter with in range.
4.
Step 1-4 is repeated by changing the magnification to x200, x500, x1000 and x500 x5000. 0. The The need needle le is chec checke ked d if it is with within in rang range e in the the cent center erin ing g mete meter r every everytim time e we chang changed ed the magn magnifi ifica catio tion. n. The The test test piece piece is adjus adjuste ted d using using centering tool.
5.
The The roun roundne dness ss polar polar grap graph h is inser inserted ted into into polar polar grap graph h reco recorde rderr after after the the magnification reached x5000 and ensured that it is in correct position.
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6.
The chuck clamping knob is turned clock wise until the graph is rotating. The record button is pressed once. The recording pen is ensured that it is plotting the profile of the test piece on the graph paper.
7.
The chuck clamping knob is turned anti clock wise direct. The graph paper is taken out from the recorder.
8.
The result is analyzed analyzed using Transparent Transparent Template. If the value of result is equal to or close to the value given by the test piece, calibration is completed and the machine can be use for measurement.
Findings Peak, P value: 1.4 µm Valley, V value: 1.6 µm P + V = 3 µm Conclusion From From our obse observ rvati ation, on, we know know that that all round round objec objectt is not not exact exactly ly in round round shape. It can be in cylinder or oval shape. To observe whether the object is exactly round or not, we can see by using roundness measuring machine. For example, a piston is actually in cylindrical shape although we see it roughly in round a shape.
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