Hood design-Week 2

A detailed report about the Hood Design which includes a detailed explanation about hood and its components, Latch Trajectory, Mastic Data, Emboss Definitions, Manufacturing process like Deep-Drawing and Hemming, and all the parameters followed in the design?

1.DEFINE HOOD :- THE HOOD IS AN OPENING BODY PANEL THAT COVERS THE ENGINE IN FRONT ENGINE VEHICLE.THE HOOD IS ALSO CONSIDERED AS ANOTHER TYPE OF DOOR IN A VEHICLE AS IT CONSIST OF AN OUTER PANEL AND INNER PANEL.THE INNER PANEL PROVIDES STRENGTH WHILE OUTER PANEL FUNCTIONS AS THE METAL COVER.

IMPORTANCE OF HOOD:

• SAVE AND SAFETY OF PURPOSES INSIDE THE CAR.
• COVER ALL ENGINE PARTS AND RADIATORS.
• REDUCE THE AIR EFFECT DUE TO DESIGN AERODYNAMIC SHAPE.
• PROVIDE ACCESS TO THE ENGINE FOR REPAIR AND MAINTINENCE.

HOOD OUTER PANEL:

• OUTER PANEL IS THE AESTHATIC ELEMENT OF A CAR.IT IS THE STYLING TEAM WHO PROVIDES THE SKIN FOR THE OUTER PANEL.
• IN DESIGN PERSPECTIVE THE SHAPE,POSITION AND ISZE OF THE HOOD SHOULD MEET SOME SPECIFIC CONDITIONS LIKE PEDESTRIN SAFETY,HOOD FOR THE LOCK STRIKER.EHILE DESIGING THE HOOD WE SHOUD GIVE MORE IMPORTANCE TO PEDESTRAIN SAFETY.

HOOD INNER PANEL:

• INNER PANEL IS THE PART THAT GIVES STRENGTH AND RIGIDITY TO THE OUTER PANEL THE MASTER SECTION REPRESENTS THE INITIAL EMBOSS SHAPE AND SIZE.THEN WE PROVIDE THE EMBOSS FOR THE LATCH AND HINGE ELEMENTS AFTER FIXING THE LOCATION.

HINGE:

• THE HOOD HINGE IS A PIVOT AND BRACKET MECHANISIM THAT MAKES IT POSSIBLE FOR YOU TO OPEN AND CLOSE YOUR HOOD.EACH CAR TYPICALLY HAS A PAIR OF HOOD HINGES INSTALLED IN THE FRONT OF THE VEHICLE.

• 

HOOD STAY:

• THERE ARE TWO TYPES OF HOOD STAYS.

1. SUPPORT ROD:

• THE SUPPORT ROD FUNCTION IS TO HOLD THE HOOD IN A OPEN POSITION.
• IT SHOULD OPERATE MANUALLY TO LIFT THE HOOD UNTIL THE SUPPORT UNTIL THE SUPPORT ROD LOCKS.
• SUPPORT ROD LENGTH IS DECIDED BASED ON THE OPENING ANGLE OF THE HOOD.
• IN THE SUPPORT ROD MAXIMUM BEND OF 35MM IS GIVEN IN ORDER TO STRENGTHEN THE SUPPORT ROD TO BEAR ALL THE LOAD OF THE HOOD.
• SUPPORT RODS CAN EITHER MOUNTED ON THE HOOD OR ON THE BODY OF THE CAR.
• THE ANOTHER IMPORTANT THING WHILE DESIGNING HOOD IS,THE ROD SHOULD BE MOUNTED ON THE OPPOSTE SIDE OF THE BATTERY BECAUSE,THIS ROD SHOULD NOT PRODUCE ANY INTERFACE WHILE INSTALLING THE BATTERY.

2.GAS STAY:

• GAS STAY HELPS INEAISLY LIFTING THE HEAVY HOOD AND HOLDING THE HOOD IN THE PEN POSITION.THERE IS NO HUMAN EFFORT NEEDED FOR GAS STAY.
• GAS STAY IS A MINI A MINI VERSION OF THE BICYCLE PUMP IN WHICH THE COMPRESSED NITROGEN IS STOREDD IN THE PUMP WITH OIL AND TIGHTLY SEALED SO THAT THE GAS CAN'T ESCAPE.

LATCH AND STRIKER:

• A CATCH THAT HOLDS THE HOOD OF A CAR SHUT IS KNOWS AS LATCH.
• LATCH AND STRIKER MECHANISM IS PROVIDED TO LOCK THE HOOD, IN ORDER TO PREVENT ACCIDENTAL OPENING OF THE HOOD DURING DRIVING.
• THE LATCH IS PRESENT ON THE ENGINE COMPARTMENT WHILE THE STRIKER IS ATTACHED TO INNER PART OF HOOD.

IMPORTANT CRITERIA:

• WHEN EVER,OPEN THE HOOD THERE SHOULD BE A CLEARANCE BETWEEN THE TIP POINT OF THE HOOD AND TO THE STRIKER.
• STRIKER IS GOING TO ATTACH THE HOOD FOR LOCKING PURPOSE.
• TO UNLOCK THE HOOD WE HAVE THE SECONDARY LATCH.
• THE SECONDARY LATCH IS THE ONE WHICH IS AVAILABE AT OUTSIDE THE CAR.
• THE HOOD IS OPENED AT PRIMARY MOTION,THAT PRIMARY SITUATION IS ACTUATED FROM THE LEVER INSIDE THE CAR.
• AFTER THE PRIMARY MOTION,WE WILL HAVE THE SPACE TO ACCESS THE SECONDARY LEVER WHICH IS INSIDE THE HOOD TO OPEN THE HOOD COMPLETELY.
• THE PARTICULAR GAP OF PRIMARY LATCH IS 10-15MM WILL BE SAME AT ALL REGIONS.

RE-INFORCEMENTS:

• REINFORCEMENTS ARE THE ONES WHICH ARE ADDITIONALLY GIVEN TO COMPENSATE THE LOSE.WHICH HAPPENS THAT AREA LOCALLY. OR
• INTENTIONALLY GIVEN TO IMPROVE THE STRENGTH LOCALLY.
• HERE,WE PROVIDE THE ADDITIONAL MATERIAL BECAUSE WE LOSE THE STRENGTH AT LATCH,STRIKER,HINGE REINFORCEMENTS.
• ADVANTAGE IS AN AUTOMATICK PART
• HOLDS HEAVY WEIGHT FOR LONG LENGTH HOODS.
• THE MAIN DIS-ADVANTAGE IS MUCH COSTLIER AS COMPARED TO SUPPORT ROD.

STIFFNER PAD:

• WHICH DOESN'T HAVE ANY PREDEFINED SHAPE.
• STIFFNER PAD IS GIVEN A TYPE OF SPONGE(I:E ATTACHED TO THE HOOD OUTER PANEL)DURING MOTION HOOD WILL BE VIBRATE TO AVOID VIBRATIONS[NVH]
• N-NOISE
• V-VIBRATIONS
• H-HARDNESS
• HERE HOOD INNER PANEL,OUTER PANEL SAME AT THICKNESS BUT REINFORECEMNTS ARE VARY IN THICKNESS DEPENDING ON STRATEGY,BUDGET,REQUIREMEN.

MASTIC DATA:

• THE OTHER IMPORTANT CRITERIA WE USED BETWEEN THE HOOD OUTER PANEL AND INNER PANEL ARE MATSTIC SEALENTS.THIS ALSO IS NVH TOPIC.
• EVERY MASTIC SEALE HAVE THE TENDENCY OF IMPROVING THE STRENGTH LOCALLY AT AROUND 80MM DIAMETER.
• TO IMPROVE NVH WE ADD MASTIC POINTS,MASTIC SEALENTS.WHICH IS AGAIN RUBBER PART WHICH IS A KIND OF HARD RUBBER.
• MASTICS ARE JOINED HOOD OUTER PANEL & INNER PANEL.
• IF WE JOIN INNER AND OUTER PANEL WITH SPOTWELDING,RIVETS THR AESTHATIC SURFACR WON'T HAPPEN IT SEEMS LIKE VERY BAD SURFACE.THATS THE REASON MASTIC,HEMMING,GLOWING ARE INTRODUCED.

EMBOSSING:

• EMBOSS ARE CREATED FOR ,IF COLLOSION HAPPENS TO DIVERT IMPACT FORCE OUTWARD,CUTOUTS FOR WEIGHT REDUCTION.
• WE HAVE TO CREATE EMBOSS IN V OR Y DIRECTION .
• IF WE CREATE V OR Y DIRECTION THE IMPACT FORCE WILL GOES OUTWARD.
• SHEET METAL EMBOSSING IS A STAMPING PROCESS FOR PRODUCING RAISED OR SUNKEN DESIGNS.

DEEP DRAWING ,HEMMING AND BLANKING ARE THE COMMON SHEETMETAL OPERATIONS THAT ARE USED IN MANUFACTURING HOODS IN AUTOMOTIVE INDUSTRIES.

HEMMING:-

• HEMMING IS A SHEET METAL FORMING PROCESS IN WHICH SHEETS ARE JOINED BY BENDING 180 DEGREE .AUTOMOTIVE BODY PANELS,PARTS SUCH AS DOORS,HOODS AND TAILGATES ARE FORMED BY THE HEMMING PROCESS.
• IN THIS PROCESS USALLY A SHEET IS BENT WITH THE HELP OF INNER AND OUTER SHEETS.HEMMING IS FORMED IN WHICH THE EDGE OF THE SHEET IS FOLDED OVER ANOTHER MATING AND ROOLERS WILL ROLL THROUGHOUT THE SHEET TO ACHIEVE A TIGHT FIT.CALLED ROLLED HEMMING.

DEEP DRAWING:

• DEEP DRAWING IS A SHEETMETAL FORMING PROCESSIN IN WHICH A SHEET METAL BLANK IS RADIALLY DRAWN INTO A FORMING DIE BY THE MECHANICAL ACTION OF A PUNCH .IT IS THUS A SHAPE TRANSFORMATION PROCESS WITH MATERIAL RETENTION.
• DEEP DRAWING OF SHEET METAL IS PERFORMED WITH A PUNCH AND DIE.
• AS THE LOAD APPLIED THROUGH THE PUNCH,THE SHEET METAL IS FORCED TO FLOW RADIALLY AND SINK INTO THE DIE CAVITY TO FORM A SHAPE.THE PROCESS IS BEST SUITABLE FOR COMPLEX SHAPE PROBLEMS.

DESIGN CONSIDERATIONS AND STANDARDS OF HOOD:

1.Hood head zone criteria

2.EURO N-CAP Rating

3.Wrap around distance

4.NVH (noise,vibration,harshness).

The first important criteria for designing the hood is the opening angle of the hood

• This criterion is considered as a average height of the humans in the region. For example, the average height of a human being in India is 5.8 feet whereas in European countries the average height of a human being is 6 feet. Hence the opening angle of the hood greatly depends on the height of the human which can be controlled by the support rod or gas stay.
• The opening angle is considered important criteria because when the opening angle is less there is a chance of head injury to the human.
• By varying the length of the support rod the opening angle can be varied.
• If the same car is made for different country will have different opening angle depending on the country or region.
• The distance C and D shown in the image is represented as graph in the upper right corner of the image. Choosing the right head zone position will decide upon the angle of the hood opening.

Euro NCAP Rating:

• The European New Car Assessment Programme (Euro NCAP) is a European voluntary car safety performance assessment programme based in leuven(Belgium) formed in 1996.They publish safety reports on new cars, and awards 'star ratings' based on the performance of the vehicles in a variety of crash tests, including front, side and pole impacts, and impacts with pedestrians.
• The first result were release in feb-1997.
• Euro NCAP ratings take into account three factors of protection — for adults, children and pedestrians — plus the level of safety technology on-board a car.
• It serves as a truly independent testbed for new cars on the market. It’s not a legal requirement for cars to have a Euro NCAP test. Such is the status of the ratings though, it can and has had an effect on sales.

Euro NCAP Ratings Calculated by :

• Several tests are undertaken to determine a score in each category.

TESTS CARRIED OUT FOR EURO NCAP ASSESSMENT :

• Pedestrain Impact Zone :

WRAP AROUND DISTANCE:

When a car crashes the pedestrian , the whole human body wraps around the front shape of the car and head impacts either on the bonnet or on the wind screen . The distance at which the head impacts the car from the ground is called wrap around distance

The severity of the injury caused by the frontal crash analysis depends on the

• Shape of the vehicle
• Speed of the vehicle
• Movement of the pedestrian relative to the vehicle

During the crash analysis test based on the wrap around distance two test areas are created , namely

• Child head impact zone
• Adult impact zone
• Wrap around distance for child head impact zone is 1000-1500 mm
• Wrap around distance for adult head impact zone is 1500-2100 mm
• This study helps the designer to design the outer surface panel in a softer and to remove the material from the inner panel at specific portions at child head impact area and adult head impact area so that even though the car hits ,the pedestrian may not get effected worse and causes the minimum damage .

NVH ( Noise , Vibration and Harshness ) :

• Noise, vibration, and harshness (NVH), also known as noise and vibration (N&V), is the study and modification of the noise and vibration characteristics of vehicles, particularly in cars and trucks.
• Interior NVH deals with noise and vibration experienced by the occupants of the cabin, while exterior NVH is largely concerned with the noise radiated by the vehicle, and includes drive-by noise testing.
• Hood also causes the NVH in the car body , this can reduced by using the stiffener pad.
• These pad is introduced between the hood inner panel and outer panel to increase the strength locally . During the motion of the car the hood will wobble and causes the noise . To avoid these vibration and reduce NVH stiffener pad is introduced.
• These are the considerations and safety standards to design a Hood.

Master section: