Hood design-Week 2
HOOD INTRODUCTION:-
Hood is also called as bonnet,it cover the engine compartment and also to give aesthetic look of a car,as it present of front side ,beside this the bonnet is also crusical and critical component and needs to br designed in a way to provides protection for passengers inside car during crash and to reduce the impact
A typical hood assembly consists of hood outer pannel,inner pannel,latch and striker,hinge ,hood stay.Hood stay is an apparatus for supporting engine hood of a vehicle in its opening postion .the purpose of openning the engine hood is for inspecting engine room,replensihing cooling water engine oil,changing parts and making repairs etc,,common types of hood stays are support rod and gas stay.whenever gas stay requires no manpower but high cost is required.this may includes steel and aluminium.Deep drawing,Hemming,Blanking and Piercing are the common sheet metal operations used in manufacturing hood
DESIGN PARAMETERS:-
hood thickness info
Outer pannel thickness= 0.75mm
inner pannel thickness=0.75mm
Reinforcement thickness=1.5mm
master section:-
components;-
=>Hood outer pannel
=>Hood outer pannel
=>Reinforcement
Hood outer pannel:-
outer pannel are the aesthetic elements of a car.It is the styling team who provides the skin for the outer pannel.the shape,size postion and size of the hood should be satisfy the saftey norms.so while designing the hood we should give more importance to pedestrian safety.the outer pannel is attached to the inner pannel by hemming.so it is neccesary to provide required hemming flange and reliefs for the hemming operations.we also provide mastic sealent between outer pannel and inner pannel to reduce vibrations
Hood inner pannel:-
Hood inner pannel is the part that gives strength and rigidity to the outer pannel.the master section represents the initial emboss shape and size.then we provide the emboss for the latch and hinge elemets after fixing the location
.
Reinforcement:-
Reinforcements provided according to the design requirements.mainly it is provided at the hinge and latch regions to improve the strength locally.usually thickness of reinforcements will be higher than the that of the inner pannels and value varies according to the cost and requirement.according to the design requirement here it is given 1.5mm thickness both hinge and latch reinforcements
Latch trajectory:-
latch trajectory is given by the circle drawn from the hinge axis point.hinge axis point is the center point of the hinge axis.first we can fix eighter latch or the hinge.if we have fix the hinge postion then we should plot the trajectory circle for latch.for proper matting condition the striker axis through the tip of the striker should be tangential to the latch trajectory.
Mastic sealent data:-
Hood commonly posses large surface area and hemming can only be provided through its boundary.we cannot use other joining techniques like welding,reviting etc because they leave marks on the outer panel which spoils its aesthetic apperance.so,mastic sealants are used to stick the inner surfaces of the inner panel and outer panel.mastic sealants are elastic compound that behaves like rubber.it is applied between inner and outer panels at specified spots.each spot of mastic sealants has its effect around a circular region of 80mm diameter.thus, the points are arranged in such a way that it covers the areas away from the hemming which are more vulnerable to vibrate.
A hood stay is an device which used to keep the hood in an open postion
SUPPORT ROD:-
Support rod is basically long cylinderical rod.it safely keep an engine hood in an open state even if extrnal forces are abruptly generated due to vibration and wind
GAS STAY:-
Gas stay/strut is an another kind of support rod that opens and hold the hood by gas expansion inside the strut.this can be acheievd by applying a slight extrnal force to the hood.
Noise Vibration and Harness(NVH):-
Noise vibration and harness(NVH),is the study and modification of the noise and vibration characterstics of vehicles,particularly cars and trucks.while noise and vibration can be readily measured,harshness is a subjective quality,and is a measured either via jury evalutions
Pedestrian saftey:-
In japan& europe,regulations have come into effect that place a limit on the severity of pedestrain head injury when struck by a motor vehicle.this is leading to more advanced hood designs,as evidenced by multicone hood inner pannel.other changes are being made to use the hood as a active structure and push its surface several centimetres away from the hard motor components during a pedistrain crash.
DEEP DRAWING:-
The molding process wher by means of pressure and tensile stress a sheet metal blank is changed into a curved body.Deep drawing is a form of metal forming ,where rigid tools such as punch,die and blank holder is used.the blank is placed between the die and the holder and then deformed by the punch pushing the sheet into die and the blank finally assumes the shape of the die.The metal plate is fixed between the die and the holder before processing begins,this prevents the formation of undersired deformations such as wrinkless.
Deep drwing changes metal sheets into curvd parts with smaller dia from already curved details
HEMMING:-
it is a forming process in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit.normally hemming process is used to connect parts together,to improve the apperance of part and to reinforce part edges
the accuracy of hemming operation is very important since it affect the appearence of the surface and surface quality.material deformations, which occur during the hemming proces,can lead to dimentional variations and other defects in parts.
in car production,hemming is used in assembly as a secondary operation after deep drawing trimming and flanging operation to join the two sheet metals parts they are outer pannel and inner pannel are assemble in hood
They are two types of hemming operations
1) conventional die hemming 2)Roll hemming
FINAL ASSEMBLY:-
