Designing and Modeling the hood of a car
Designing and Modeling the hood of a car
Objective
To model the hood of a car with using Catia V5 with necessary embosses, mastic points to fulfil the pedestrian safety requirements
Introduction
Car hood is also called as bonnet or engine cover. It a critical component to design and model because it has to be strong and hard enough for frontal crash requirements, and at the same time it should absorb the impact force from pedestrians (as it should not cause any severe injury to pedestrians) to deliver a good pedestrian safety requirements.
The car hood consists of the following parts
- Outer panel
- Inner panel
- Hinge
- Latch and Striker
The hood modeling involves 2 stages
- Modeling of the individual parts
- Assembling of the parts
Designing
Figure 1: master sketch
A master sketch is used which provides us the dimensions of the parts that are designed. The master sketch which is used for modeling is shown in the figure. The maximum gap between inner and the outer panel is 25mm.
Modeling of parts
Parts like outer panel, inner panel, locker & latch are modelled in surface work bench (Generative Shape Design) then the model is thickened. Hinge is modelled in solid work bench (Part design). Support rod is not modelled here in this project
Outer panel
Figure 2: outer panel
Outer panel is the Class A surface where aesthetics is mainly concentrated because only these surfaces are visible in the car.
Figure 3: Hemming
The outer panel is hemmed with the inner panel. Spot welding can also be done but it affects the aesthetics of the car.
Figure 4: Relief at corners
Relief is provided at the corners to ease the process of joining the outer panel and the inner panel by rolling
Commands used: offset, split, boundary, project, tri-tangent fillet, parallel curve, symmetry, join, thicken etc.
Inner panel
Figure 5: Inner panel
Inner panel provides the necessary strength to the outer panel, so that the car hood is strong enough to meet all the safety requirements, therefore aesthetics is not an issue as it is placed in the blind region of the car. The inner panel is provided with embosses which helps in reducing the weight and improves the strength.
Figure 6: Embosses
Embosses are added to the inner panel to improve the stiffness and strength. Embosses are done via deep drawing operation therefore a minimum draft angle of 4 degree must be provided to perform the deep drawing operation smoothly.
Figure 7: Impact force dissipated and distributed towards hinge
The embosses are designed in such a way the if any impact is made, the impact force is directed toward the hinge as hinge is a reinforcement part it has necessary strength to withstand the force
Suppose the inner panel itself want to withstand the impace force then the thickness of the inner panel is to be increased which will increase the weight of the car which reduces the pay load capacity.
Therefore if the forces are not dissipated and directed towards the hinge it would directly affect the passengers insde the car.
Figure 8: mastic sealants
Mastic sealants are placed between the outer panel and the inner panel in the form of a paste . It is made of hard rubber of 5mm thickness and are used to reduce the noise, vibration and harshness. It improves the strength locally around 80mm diameter.
Figure 9: Pedestrian safety criteria
Mastic sealants and embosses helps to meet the pedestrian safety standards. The adult and child impact zone are taken into consideration, anthe deformation zone considered with respect to the engine compartment and the outer panel thereby determining the interference.
This generated deformation are considered critical and needs to be relocated or tuned to fill. Relocating or tuning leads to reduce the force exerted on pedestrians espcially in head during collision
Generally, inner and outer panel are made of 0.65 mm – 0.75 mm thick. Reinforcements are given a thickness of 1.5mm. Adding more reinforcements improves the strength but it also increases the cost.
Some of the commands used in generative shape design are offset, split, extrude, sweep, project, trim, shape fillet, edge fillet, boundary, parallel curve, symmetry, join, thicken etc.
Hinge
Figure 10: Hinge to be merged with inner panel and engine compartment respectively
Hinge is to enable the open and close motion of the hood. It is reinforcement part to which also increases the strength of the hood. It has two parts one part mounted to the engine compartment and other one is mounted to the inner panel
Hinge is modelled in part design work bench some of the commands used are Pad, pocket, split, draft, edge fillet etc.
Latch and striker
Figure 11: Latch and striker
Latch and striker is the used for locking the hood with the engine compartment. It is placed with respect to the trajectory obtained perpendicular to the hinge axis. Latch and striker is a reinforcement part.
Support rod
Support rod is used as a structure to provide support to the hood whenever it is opened. Gas stay is also used but it is used mainly in premium cars or when the hood is heavier due to its size. Grommets are provided for placing the support rod when it is not used. This is to reduce the noise and vibration. Bends are added to the support rod not more than 35mm as it is a standard. Bends are provided to the rod to improve the strength, bends more that 35mm will reduce its stiffness.
Support rod is always placed opposite to the battery for example, if the battery is placed in left hand side then the support rod is place in right hand side and vice versa.
Assembly
The modelled parts are imported one after the other and the constraints like fix, offset, coincidence, symmetry (with mirroring the part) are used to assemble the parts where it is to be placed.
Inner panel is the first part that is imported and is fixed as all the primary parts are to fixed
Figure 12: inner panel
Hinge is then imported and the respective surfaces of the hinge and the inner panel are selected and the offset distance is set as zero.
Figure 13: inner panel and hinge assembly
Figure 14: hinge mirrored about middle plane
Then the hinge parts are mirrored about the plane that is in the middle.
Figure 15: Outer panel with inner panel
Outer panel is imported and the planes of the outer panel and the inner panel are selected and they are made to coincide with offset distance as zero.
Figure 16: latch with inner panel
Latch and striker is then imported respective surfaces of the latch & striker and the inner panel are selected and the offset distance is set as zero.
Thus all the parts are modelled and assembled to form the complete front hood of a car
Learnings from the project
In this project “Designing the hood of the car“, I was able to explore a lot of information and gain knowledge about process of designing the hood of a car in automobile industry. When we design a part or a product for hobby or fun project we don’t follow any procedure or criteria and we don’t consider the real time restrictions, rules and regulations that exist.
But in this project, the hood is designed according to the procedure and criteria that is followed in automobile industry. A master section is taken into consideration and is kept as a source for structuring the hood, the master section consists of maximum and minimum dimensions within which the hood is designed
During the hood design, I was able to able to know the purpose of embosses, mastic sealants, reinforcements, latch and striker, placement of support rod or gas stay.
The hood is a critical part it should be designed in such a way that it has to be strong enough to sustain a crash and it should be pedestrian friendly. The hood should consist child impact zone and adult impact zone so that it does not cause any injury to the pedestrian by absorbing the impact force during an accident.
CATIA V5 was used for designing the hood, I was able to explore commands like offset surface, extrude surface, project, split surface, trim surface, sweep surface, shape fillet, edge fillet, tri-tangent fillet, symmetry, join, thicken etc.
Working in this project “Designing the hood of the car“, was a fantastic experience. I had the opportunity to learn the way of creating sketches in a better way and to explore features especially in surface modelling, so that the model could be developed a better way, in less time and effort.