Basically it is a point point presentation of the work which I have done / observed during my internship at RNAIPL.
When I started making this PPT, I was in great confusion about how a internship PPT looks like. I think it would help many of you. Please let me know if there is any mistake in this PPT , so that I could make a note of it and would not repeat that mistake further.
thank you
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Internship at RNAIPL
1. INDUSTRIAL INTERNSHIP REVIEW
(MEE 399)
ON
AUTOMOBILE MANUFACTURING
Internship at Renault Nissan Automotive India Private Limited
(RNAIPL)
By : MAHENDRA SINGH SISODIA (11BME1051)
MARCH 2014
2. Objectives of internship
• To work cooperatively in the company for 28 days
internship as required by the VIT University Chennai
Campus.
• To get acquaintance with the functional and
operational activities of the company
• To study about how various manufacturing concepts,
tools and techniques that we studied are theoretically
and practically applied in an industry.
3. About Renault-Nissan
• The first dedicated Alliance between Nissans and Renaults. Renault–Nissan
Alliance is a strategic Franco-Japanese partnership between automobile
manufacturers Renault, based in Paris, France, and Nissan, based in Yokohama,
Japan, which together sell more than one in 10 cars worldwide since 1999. It is
a modern and highly efficient plant producing top quality cars. But there’s more
which also produces zero emission cars. It’s now officially one of India’s safest
and most environmentally-friendly factories, too. That’s according to the
Confederation of Indian Industry (CII), which has given the plant its top award
for excellence in Environmental Health and Safety.
• In February 2008, the Renault-Nissan Alliance signed a MOU with
Government of Tamil Nadu to set up a manufacturing plant at Oragadam, near
Chennai with a minimum investment of Rs. 4500 Crore over a period of seven
years. On March 17, 2010, the Renault-Nissan alliance plant was inaugurated
in a record time of 21 months since its groundbreaking ceremony in June 2008.
The Plant has an initial capacity of 2, 00,000 units per year and planned to
reach 4, 00,000 units per year in full capacity.
5. Vehicles Manufactured at RNAIPL
• Renault
• Renault Fluence Renault Koleos
• Renault Pulse
• Renault Duster Renault Scala
• Nissan
• Nissan X-Trail Nissan Teana
• Nissan 370Z
• Nissan Micra Nissan Sunny
12. WTP (Water Treatment Plant)
• It treats the raw and rain water. Rainwater are collected through surface
ponds.
• The First main step of WTP is pre-treatment of water before entering RO
(Reverse Osmosis )system.
• In WTP Actiflo method is adopted to remove the suspended solids.Actiflo
method is a physico chemical treatment plant. This method has
advantage of efficient removal of heavy metal from water.
• Then the water is send to Press Sand Filter( PSF) and then to Activated
Carbon Filter (ACF).
• Then the water is send to MGF (Multi Grade Filter) , then to anti scalant
dechlorination. The water is then is then send to micron cartride filter (5
micron).
• And after first RO, it is feed to the 2nd R0 where every particle are removes
and water for UV filtration is sent in UV Filtration is used to avoid micro
organism growth. Its capacity is 10 micro /secs made free from everything
and feed to pain shop for painting.
13. WWTP (Waste Water Treatment Plant)
• The WWTP gets water from paint shop, water used for hand wash and
remaining water from central kitchen is collected at GA &GB tank.
• Then waste water in the tank is uniformly mixed by supplying air. The
waste water then moves to the DAF (Dissolved Air flotation) for oil
separation. Then lime and alum is added as PH booster.
• Then the polyelectrolyte is added for coagulation. It is kept for 5 hours as
the retention time. This water is feed to clarriflocculator (combination of
flocculator and the clarifier), this is done to remove heavy metals like zinc,
phosphates. Sludge water is moved to the sludge deposit bed where where
sludge is removed , then filteration takes place and water is again fed to the
collection tank. Then the ferric chloride is added for PH neutralization.
• It is feed to biological tank / aeration tank, here microbial activity takes
place. This is done to reduce COD(Chemical Oxygen Demand), BOD (Bio
chemical Oxygen demand).COD is reduced to less than 250 and BOD is
reduced to less than 20
14. • The water is then send to MDR (membrane separation) where suspended
particle is removed. To reduce smell we use carbon filter. Then the water is
send to MGF (Multi Grade Filter) , then to anti scalant dechlorination. The
water is then is then send to micron cartride filter .
• At last water is send to RO plant.The WWTP treated water is used in
cooling tower and car washing before painting and for toilet flushes. The
sluges are collected to bags and given to govt for disposal.
Clarriflocculator
15. BMS (Building Management System)
A Building Management System (BMS) is a computer-based control system installed in
buildings that controls and monitors the building’s mechanical and electrical
equipments. It consists of hardware's and software's.
All the information about utilities (driers, compressors etc.) like operating status,
present conditions (pressure, temperature, and flow rate) is transmitted through sensors
to BMS. In BMS five displays are using that display the operating status of the all
utilities. One main display is used for main control. For safety automatic alarm system
is there. If any problem occurs in any utility system then alarm rings and displays show
the place where problem occurs.
It also display’s about the problem. It is very fast and time saving system because
through these system we can easily know the location of problem, so it’s easy for any
specific person to go there and solve the problem so it helps in avoiding the checking
of all utilities.
17. PROCESS TEAM
INPUT
PROJECT ENGINEERING
TEAM
VALIDATE & CHECK
DESIGN OF SYSTEMS
VALIDATE & CHECK &
PREPARE BOQ
PURCHASE TEAM
TENDER FLOATING TO
CONTRACTORS
TECHNICAL ALIGNMENT
MEETING
NO YES
YES
YES
NO
TECHNICAL ALIGNMENT
MEETING
FINAL BOQ
(Technically aligned BOQ)
RNPO
TENDER FLOATING
RESEND QUOTATION
NEGOTIATION BY RNPO
SUPPLIER FINALISATION
PROJECT STRUCTURE AT RNAIPL (PHASE – I)
18. KICK OF MEETING
START OF PROJECT
DRAWING APPROVAL
DESIGN APPROVAL
PROGRESS REVIEW MEET
SCHEDULE MONITORING
SCHEDULE
MODE OF WORKING
WORK METHOD
RULES & REGULATIONS
PROJECT
COMPLETION
QC
&
PREPARING SNAG
LIST
SAFETY AUDIT
(PRIMARY &
SECONDARY)
PREPARE REPORT
CLOSING OF SNAG
LIST
HAND OVER TO
MAINTANENCE
PROJECT STRUCTURE AT RNAIPL (PHASE – II)
19. COIL
STAMPING SHOP
BODY SHOP
TRIM AND
CHASIS SHOP
CAR
Manufacturing process of a car goes
under these process. This process is
also known as
VEHICLE CHAIN
20. Stamping Shop
In stamping shop body parts of the car are
manufactured using steel sheet alloy. Following
sequence is followed in the stamping shop.
1. Blanking
2. Pressing and Piercing
3. Quality checking
22. Blanking Process
1. Coil-Car: Coils of steel sheet is pick up by crane and transferred to coil-car that
transfer the coil to uncoiler.
2. Uncoiler and advance correction machine: It sets the inner diameter of coil to
the center of the line by holding device that remove rolling habit of the tip of the
coil.
3. Washing: The device that removes the foreign material that has adhered to the
coil which is done by oil with the help of roller.
4. Leveler: used for levelling the blank by correcting the shape of the steel sheet and
makes it smooth. It works on the principle of less than 1 mm tollerence .
5. Looping: In this process steel plate is stretched into the pit and all the bends are
removed.
6. Feeder: Device that adjusts the coil material to press cycle and set the cutting
length and sends it to piler.
7. Press: It press the steel sheet and cut the steel into required dimension. Press can
be rotated at required angle to cut the steel plate at any angle.
8. Piler: The device that piles the cut material with accuracy. From here cut material
are transferred to pressing line. There are Two Piler zone here.
23. Pressing and piercing Line
Here are three pressing lines.
Pressing
Lines
Line-3
(5400 ton)
L-Line
(2400 ton)
XL-Line (5400
ton)
For pressing of larger
parts
For pressing of larger
parts
For pressing of small
parts
24. Pressing and piercing Line
Cont.
Each line have 4 presses.
PB: By this press,shape is given to steel plate by
using specific die according to drawing.
PC: By this press side or extra material is removed.
PD: By this press Piercing is done.
PE: By this press specific holes is made.
XL LINE AND
LINE-3
PB
PC
PD
PE
2400 ton
1000 ton
1000 ton
1000 ton
L-LINE
PB1200 ton
PC400 ton
PD400 ton
PE400 ton
26. BODY SHOP
• Place where the main manufacturing of car body takes place. The car body
design manufacturing is done by skilled engineer who have their work
divided.
• The parts which have been designed in the stamping shops come here for
assembling. engine compartments and mounting points, chassis, hood, front
cabin, rare cabin etc are made in the stamping shop while others are supplied
by vendors like JBM, Unipress, Technico. Unipress is the major supplier.
• Most of the parts are welded using spot welding while MAG welding is done
for filling.
• Most of the welding is done manually but welding of few parts are done using
Robots.
27. • Body shop consist of two main line, six sub lines and 290 sub stations.
• The main base of the car is not manufactured or designed , rather the sill
plate is supplied by the supplier in three pieces which are welded to the
part they have designed.
• In the first sub line the engine compartment, the front cabin and the rear
cabin are assembled using spot welding which is manually done.
• In the second sub line nearby parts of engine, doors, hoods are assembled
using welding and nuts.
• In main assembly line side doors, back doors, hood is assembled using
automatic nut runner machine. Finally quality checking is done of car body.
• Each car is given with the serial number which corresponds to the paint
colour.
• The body is sent to the metal line, where the aesthetics, finish doors, any
bumps or the dent or spots are check, If found the body is sent to the
sideways where it is sent or tested for the faults. Finally the car from the
body shop is sent to paint shop.
28.
29.
30. Paint shop
• The car body after the body shop is move to
this shop for painting. Car body is moved on
hanger.
• In paint shop there are two lines i.e. Line: 1
and Line: 2. both lines does the same work.
31. Pre treatment line
1. Pre-Degreaser-Washing using chemicals and safely removal of
oils, greases, fats and carbon deposited on the car body.
2. Degreaser-2 .- Final washing with chemicals of car’s body.
3. Pre-Raw water Rinse. -Here, car body is washed using raw water of specific
ph.
4. Raw water Rinse - Again washed with raw water of specific ph.
5. Conditioner- It is used to make the car body surface rough. Because at rough
surfaces coating more adheres.
6. Phosphate treatment zone- car body is coated with phosphate for providing
metal cleanliness and corrosion protection to the surface of the car body.
7. Pre-DI (Deionized) water Rinse zone- DI water bath is given to car body. For
DI Water rinse Fresh de-ionized water is used that is cleaner than drinking
water. If any contamination remains on the surface before the ED coating, it
will cause the application issue and raise the potential for product failure.
8. DI water Rinse (D/P). -Final DI water bath is given to car body.
32. Electro Deposit Line (ED-Line)
It has 3 stages.
1. ED-Bath-At this stage car body is covered with ED Paint. ED
(Electro-deposition) paint (cationic) is used as a primer for car
bodies. It imparts rust resistance and chipping resistance to the
car body.
2. UF-(Ultra Filtrate)-1-The paint bath can be contaminated
with pre-treatment chemicals like e.g. phosphates, chlorides,
and chromates. So, a part of ultra-filtrate has to be leaded out
to avoid contamination of the paint bath with these chemicals.
This process also removes excess paint.
3. Fresh water and Tilting stage-After UF stage car body is
washed with fresh water. After washing the car body is tilted
to remove all the water and waste paint from the car body.
Then car is tilted back to its initial position.
Here ED Line ends.
Cont.
33. ED-OVEN
Sealant is applied at every exterior edge of the car. Sealant is used
to resist the leakage through the car body. Then car body passes
through the Sealer Oven for drying the sealant. Temperature of the
varies 150 to 200 degrees.
Sealer-Zone
Then car body passes through the ED Sanding Zone. Here, extra
paint is removed to make ED paint layer uniform. This process is
completely manual. First workers check the ED paint layer and then
remove extra paint using Sanding paper.
ED sanding zone
Car body passes through the ED Oven for drying the ED paint.
First, air is heated and passed through oven chamber then car body
passes through the chamber. Thus ED paint is dried by hot air. The
temperature at the oven varies from 170 C to 200 C. Again after the
oven the thickness of the paint is checked manually.
35. Body arranging zone contd.
Cont.
When car body enters at storage are then barcode of car body is scanned, a
paper having code is given at the ED sanding shop , the scanned data is sent to
the CCR (central control room) panel.
Then the end of ED sanding involves 3 lines. In First and second line the body
are arranged according to FIFO(First In First Out) technique, in which the car
body of same color are arranged first for time management. If any car body of
different color comes in that line then it will be shifted to side line till it groups
with another bodies of same color. It is fully automated process according to the
color car bodies are arranged automatically in their respective line.
If after the ED Sanding stage body paint is not uniform or if some other faults
are found in ED paint then car body is transferred to repair line. From here body
is sent to repair zone for repairing.
36. Dust Off zone
Dust from the body is removed before painting. So that dust
doesn’t contaminate the paint. Feathers of Emu bird are used for
dust removal. The reason behind using EMU bird feathers is that
the feathers has long life.
• ACC (Anti corrosion Coating) (only for foreign country vehicle)
• Primer coat (Sprayed by robots) (35 micron thickness)
• Primer Paint (Manually for more accuracy)
• Primer flash off zone (Drying of primer paint)
• Base Zone (For main paint, first sprayed by robots ,then
manually) (70 micron thickness)
• Base flash off zone (Drying of base paint)
• Clear Zone (For clearing car surface for shining, First by
robots then manually for more shining purpose.)
TOPCOAT Zone
In this zone car is painted through following zone.
Car body is transferred to Trim & Chassis shop
37. The main purpose of this shop is to mold the parts. The parts include the bumper, mirror
cover and finisher. The waste plastic material is again used in order to avoid wastage. The
waste material which is used for the first time is called virgin material and the waste
material which is used for more than one time is called reused material.
The process starts from the plastic i.e. polypropene (PPE) which is supplied by the supplier
is stored. The pure polypropene and the grinded body part that has produced by grinding
the defected parts is sent to the drying chamber where the moisture is removed.
The PPE are then passed to the blending machine which uses vaccum to transfer the PPE.
The two purpose of blending machine are that it act as a carrier between the dryer and
extrusion machine just like an intermediate and it also mixes the pure and impure
The PPE are then moved to the intrusion machine. There are three intrusion machine in
the plastic shop two are mechanically operated while one is electrically operated. In the
extrusion machine the necessary operation take place like plasticizing the PPE and mold
into the shape take place. The temperature for plasticizing is 200 C.
Plastic shop
38. The heating takes time till the temperature reaches the melting point of PPE ,thus it will
be time consuming hence production will be effected. So the heating is done before the
die is loaded to the extrusion chamber. Cooling is done using water as coolant. The
coolant control system is placed near the extrusion machine for quick accesses.
• Electrical molding machine is preferable because it requires less maintenance and
works with good accuracy. In both types of machines hydraulic forces are applied.
• The time for extruding the one part is 28 seconds approximately. The time require for
changing the mold is 8 minute 20 seconds approximately which is a programmed
technique for changing the die. . For changing the mold for different units QMC
(Quick Mold Change) System is used. It is completely automated and controlled by
PLC.
The parts has been produced are collected by the robot which places them on to the
conveyor. At the end of manually the defects are checked and then the parts are then
send to the plastic paint shop.
39. Bumper Paint Shop
In this mainly the plastic body like bumper, finisher and mirror cover are
painted as well as finishing ,mostly in the same way as main body. Here,
punching and drilling operation are done for generating holes in bumpers
In this zone bumper is painted through following zone.
• Heating Zone (Low speed conveyor) (bumper is heated. For heating fire is
applied by the two robots. Fire flame length is 250 mm)
• Dust off zone (air is applied to bumper surface for clean the dust.)
• Primer coat (Sprayed by robots)
• Primer Paint (Manually for more accuracy)
• Primer flash off zone (Drying of primer paint)
• Base Zone (For main paint, first sprayed by robots ,then manually)
• Base flash off zone (Drying of base paint)
• Clear Zone (For clearing car surface for shining, First by robots then
manually for more shining purpose.)
• Backing Zone 1 & 2- (High Speed Conveyor) Both backing zones are
maintained at 120 degree Celsius temperature. By passing hot air in
banking chamber paint is dried. Then bumper is shifted from high speed
conveyor to low speed conveyor
40. Bumper Paint Shop
Cont.• Quality checking-Here, quality inspection is done. If any fault found in
bumper then it is sent for repair. If no fault is found then bumper is
unloaded from low speed conveyor and sent to vehicle chain.
After final painting process piercing robot is used to
generate holes in bumper
Robots generate small holes in bumper by drilling operation. Holes are used for
placing small sensors in bumper.
Rare punching machine: It is used to generate big holes in bumper. These
holes are used for placing little big sensors, lights and other components.
Front punching machine: It is used for generate big holes in rare bumper and
Front punching machine is used for generate big holes in front bumper
41. Trim and Chassis shop
• Here all the components of car are assembled. In this
department the body from the paint shop is brought
into the trim and chassis department.
• Initially the body is under the PBS( paint body storage).
The body from the paint body is stored. The body is
brought under the conveyor which is under the CCR
(central control room).
• SCM (Supply chain Management) area contains all the
parts which are supplied by CCR (Central Control
Room).
• The green signals are passed whether the parts are
been supplied for the body are for Micra, Duster or any
other and thus help is avoiding mishandling.
42. There are two main lines Line-1 and Line-2. Both lines are same.
• At each line total 31 stations are there.
• At each station 3-4 parts are assembled in car body.
• There are six sub lines in each main line:
Primary line
Trim Line
Chassis Trim line
Engine assembly
Pre final
Tester Line
Cont.
43. Cont.
Primary line- Car body comes from paint shop. Doors are separated.
Trim Line- Interior components are assembled manually. Ex. Seat
belt, floor cover ,Front and rear glass ,CMM (Speedometer,
Tachometer etc.). CCR controls the assembly.
Chassis and Engine Assembly line – Exterior parts are assembled.
Ex. engine, suspension system, exhaust system, fuel tank, exhaust
heat observer, brake system Chassis and Trim line- All assembled
components are checked. front and rear wheels.
Pre-final line- pre final line brake oil, fuel and coolant are filled
using combo filling machine. (The brake oil depend on the countries
climatic conditions and thus chosen accordingly.)
Final Line- Doors are assembled.
Tester Line- wheel alignment, Speed, braking system, Leakage are
tested.
Test Drive and Sale
47. Power Train Line
Three Lines are here
• JXX gear box assembly line
• Engine Line:1
• Engine Line:2
48. Cont.
Gear box assembly Line
Process
1. Gear box Scanning
2. Assembly of gears.
3. Gear shifter (for 1st and 2nd gear) attached to
secondary shaft
4. Primary shaft, secondary shaft with gear shifter
and differential are assembled in clutch housing
5. Gear shifters for 3rd, 4th and reverse gear are
assembled with both shafts.
6. Differential housing is assembled with clutch
housing
7. By using mechanical housing tire side of the gear
box is closed
8. In gear box a magnet is placed
49. Cont.
Gear box assembly Line
Process
9. Primary shaft thickness measurement
10. Sealant Deposition
11. Then mechanical and clutch gear boxes are fixed and closed
using nut
12. Gear Box leakage testing by pressurized air.
13. Final Testing of gear box by assemble it with engine.
14. First gear box is scanned.
15. All tests are control by a PC.
16. maximum speed at different gears, Noise level (Manually)
Speed at different torques, power required at different slops at
different speed are tested. It is a one time process.
17. unloaded at gearbox area.
18. Testing of machine by blue and red gear box.
19. All blocks for gear box are imported from Renault France
50. Cont.
Engine Shop Line
• At line-1 K9K (Diesel) engine is
manufactured.
• At line-2 XH (petrol) engine is
manufactured Gear Box leakage
testing by pressurized air.
51. Cont.
Process
1. Cylinder block scanning.
2. Oil jet is fixed in cylinder by Oil jet press (2 Hydraulic and 4
Pneumatic)
3. Marking of engine code on cylinder block.
4. Oil level indicator assembly.
5. metal pieces are assembled in cylinder block support the crank
shaft. These metal pieces work as a bearing.
6. Then D dimension machine measure the height between bottom
dead center and top dead center for selecting the proper piston.
7. then crankshaft, piston, connecting rod are assembled in
cylinder block
8. oil filter, oil pump and oil pan is fixed
9. In H dimension machine piston is inspected that the piston is
perfect or not for the corresponding bore.
52. Cont.
Process
10. cylinder head is fixed on the cylinder block using nut bolt.
11. Then Cam shaft is fixed. Then fuel injector and high pressure fuel pump is
fixed.
12. Timing Pulley and Timing belt is fixed.
13. Timing belt and gear transfer the power or motion from crank shaft to other
engine accessories like cam shaft, high pressure fuel pump. Fuel pump, cam
shaft and other accessories are synchronized with crank shaft.
14. Flywheel, vacuum pump ,Fuel pipe line, EGI harness cable, Intake manifold,
exhaust manifold , Then EGR (exhaust gas recycle) unit stabilizer, exhaust
air intake ,exhaust air filter, Clutch kit (clutch plate and disk), friction plate
are assembled.
15. Engine Testing
16. Then quality of engine is checked and visual inspection of engine is done. If
any fault is found then engine is sent for repair. Then finally engine is sent to
the SCM (supply chain management).
53. Casting Shop
In casting shop cylinder head and cylinder blocks are manufactured by
casting process.
In this shop two casting machines are here.
1 HPDC (High Pressure Die casting): Cylinder blocks
are manufactured by High Pressure Die Casting
because they are heavy in weight.
2 LPDC (Low Pressure Die Casting): Cylinder heads
are manufactured by Low Pressure Die Casting
Process.
HDPC process is same as LDPC. Only difference is
that pressure and die moving velocity is higher in
HDPC i.e. 60-70 Mpa and 308 m/s.
54. • The furnace capacity was 1.5 ton means 1.5 tones is melted per hour. The material of
ingot which is fed is (ACD 12 Al alloy Rectangular rods).
• The ingot is melted in moving furnace which is LPG operated (1 bar) then it is moved to
holding furnace (maintains temp 70 C) while air is fed using blower.
• Then the molten metal is moved to degassing unit where poisonous gases are removed by
forcing nitrogen through carbide rod. Then the molten metal is moved to LPDC machine
which moves it to electric heaters for re melting and while LPG heaters maintains
temperature.
• Then the core will be placed in the die and the molten metal will be poured into the die.
Near each die casting machine there is shell core machine which prepare the sand core
thus eliminating the need of die to be destroyed if the new model comes.
• The castings are then air cooled at temperature 100 to 150 degree Celsius. The other
coolant like water is not used because others will drastically reduce the temperature
which will be harmful for the castings while air reduces the temperature gradually.
• Then the casting goes to the knockout machines where 90 – 95% of the sand will be
removed which removed and by vibration. After that it goes for finishing operation where
runner and riser are removed.
• Then it goes for heat treatment process at 495 C which also helps in removing remaining
sand. Then it is quenched using water at 60 C. After that it again goes for hardening
process at 200 C and after that it is air cooled. After that Quality checking for cracks,
Visual inspection ,Air leakage checking
LPDC (Low Pressure Die Casting)
55. Overall this internship was very useful in providing enormous experience
about how a engineering is applied in industries. I have gained new
knowledge, skills and met many new people. I got insight into professional
practice. I learned the different facets of working. I have experienced how
every second is important for a manufacturing company and they work in
minimizing it. I have learnt that work management, is an important factor for
the progress of projects. Regarding the engineering related subject I have
learnt about the stamping shop, body shop , casting shop and welding. This
company gives very much importance to safety of workers and quality of
product. Every worker in the company was aware of what their life means.
Energy conservation is very important aspect of this company. From energy
audit to waste water treatment plant , it shows the importance of reducing the
consumption of it. At last this internship has given me new insights and
motivation to pursue a career in automotive field.
Conclusion
Notas del editor
chemical oxygen demand (COD) test is commonly used to indirectly measure the amount of organic compounds in water. Most applications of COD determine the amount of organic pollutants found in surface water (e.g. lakes and rivers) or wastewater, making COD a useful measure of water quality. It is expressed in milligrams per liter (mg/L) also referred to as ppm (parts per million), which indicates the mass of oxygen consumed per liter of solution.The basis for the COD test is that nearly all organic compounds can be fully oxidized to carbon dioxide with a strong oxidizing agentunder acidic conditions.B.O.D is the amount of dissolved oxygen needed by aerobic biological organisms in a body of water to break down organic material present in a given water sample at certain temperature over a specific time perioBOD is similar in function to chemical oxygen demand (COD), in that both measure the amount of organic compounds in water. However, COD is less specific, since it measures everything that can be chemically oxidized, rather than just levels of biologically active organic matter.
Here the reason was that foreign car generally moves with high speed thus there is a possibility that the paint may undergo oxidation and corrosion may occur on car body.