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AIM: To design the automotive hood component which includes the outer panel, inner panel, hinge as well as latch assembly with the necessary reinforcements following the master section with the design guidelines and parameters. ABSTRACT: A car hood is the metal part that covers the engine of an automobile. The term car…
Lishon Abraham
updated on 10 May 2021
AIM:
To design the automotive hood component which includes the outer panel, inner panel, hinge as well as latch assembly with the necessary reinforcements following the master section with the design guidelines and parameters.
ABSTRACT:
A car hood is the metal part that covers the engine of an automobile. The term car hood is a North American term, used primarily in America and Canada. Hood comes from the Old English word hod which means a hood, a soft covering for the head. Hood is one of the other major closure systems in a vehicle and is fundamentally a reinforced skin with many design quality and safety regulations. Hood may come with several subcomponents, but the two most important ones are the outer and inner panels. A car hood, also referred to as a bonnet in some other countries, is the hinged cover that rests over the engine of a front-engine vehicle. Its purpose is to provide access to the engine for repair and maintenance.
The inner panel serves as a structure for the vehicle to dissipate and channel shock waves at the event of a crash while the outer panel serves more as an aesthetic for the automobile’s overall presentation and to channel airflow over the vehicle. Hence, both require critical precision as well as a dedicated strategy right from the design conceptualization to the production step.
A concealed latch is typically used to hold down the hood. On vehicles with an aftermarket hood and on race cars, hood pins may be used to hold down the car hood. Hoods sometimes also contain a hood scoop, wiper jets, power bulge, and/or hood ornament. Car hoods are typically constructed from steel and sometimes from aluminum. Aftermarket car hoods may be constructed from various other materials, including carbon fiber, fiberglass, or dry carbon etc.
All parts of a Hood assembly is shown below:
Hood can fix by two methods
The below figure shown are the Support Rod and Gas Stay used for fixing the hood with the car.
DESIGN CONSIDERATIONS FOR CAR HOOD:
Head clearance zone is the clearance such that when the hood is in fully open condition it does not hurt the head of the person that is standing next to the hood. This is controlled by the opening angle of the hood. The opening angle of the hood is decided for the region the car is manufactured. Some region may have people with average height of 5.5 ft and another region may have people with average height of 6 ft. So deciding the right opening angle for the hood is an important criteria.
The opening angle of hood will give A, C, B And D with respect to the ground is given in the above figure. Those A, B, C & D are decided in the head zone. Opening angle varies from region to region depending on average human weight. Depending on the standards we are deciding the angle. So from the angle data, Support rod or Gas stay is designed.
NVH plays an important role in car design. The noise and vibration produced by the car should be minimized.
Adding latches and stiffener pad: Latches are added where and all the weight is added. On the inner panel we have Hinges and striker, which are attached to the inner panel so due to this attachment the strength of the inner panel is going weak. In order to strengthen the inner panel Latches will play a very important role. Stiffener pad is the sponge-like material place b/w Inner and outer panel to reduce vibrations.
Mastic Seals: Mastic Seals place b/w Inner and outer panel to reduce Noise, vibration, and harshness. Every Mastic will have an effect of 80mm Dia locally. shown in the fig 3.1. Inner and outer panel gap is 2 to 5mm
Safety is the most important criteria in automobile designs which concentrates on both pedestrian and occupant safety. The pedestrians are the most vulnerable road users and are at high risk of traffic accidents. The major reason for the fatality of the pedestrian in traffic accident is due to the head injury resulting from the hard impact of the head against the stiffer hood or the ground. In order to reduce the head injury of the pedestrian the local stiffness over the area of head impact has to be reduced thus the new design of hood inner panel was focused on that and the structural and modal analysis was done for the new design. The design with lesser local stiffness and similar global stiffness compared to the existing hood was finalized. ]
Inorder to make Hood for different pedestrial rating, following methods are used:
Inlaid Hood:The line which is drawn 45 deg. from ground to Side Reference of carand which is meeting point on fender is called Inlaid Hood.
Wrap Around Hood: The line which is drawn 45 deg. from ground to front surface of the Hood and which is the meeting point on the outer panel is called Inlaid Hood.
Emboss are provided in the inner panel of the hood assembly. This helps in weight reduction of the hood and also to dissipate the force during collision. Force dissipated during collision is shown in the below figure with the designed inner panel.
Hemming is a sheet metal forming process in which sheets are joined by bending it usually to 180°. Automotive body panels and automotive parts such as deck-lids, trunk-lids, doors, hoods and tailgates are formed by hemming process.Hemming is a forming operation in which the edges of the sheet are folded or folded over another part in order to achieve a tight fit. Normally hemming operations are used to connect parts together, to improve the appearance of a part and to reinforce part edges.
DESIGN PROCEDURE:
1. Import the file: The given input file has to be made in an assembly named Hood_assembly under which all parts can be created. First create an assembly tab, and using the Add or Create new options available in the assembly tab. Only the inner panel folder tab has to be created, while all other components are given as input.
2. Start with the design of inner panel from the given class A styling surface of outer panel of the hood. Make hood_inner_panel as the Work part and start with the operation in the Part navigator.
3. Split the surface into half w.r.t YZ plane using the Trim body tool in the Surface panel.
4. Next step is to Offset the outer panel(working surface) 2mm downwards as per the mastersecion. Using the Offset cuve in face, create a curve 20mm from the boundary of the surface and using the Trim Sheet tool available, trim the portion as required.
5. Also from the working surface, create an offset of 4mm downwards and with a curve 22mm from the boundary has to be created. Trim it in the opposite direction of that done earlier.
6. We have got two surface between which a surface has to be created, the same can be devoloped using the Through curve option in the Surface toolbar.
7. After the outer profile is created, now the features like Emboss has to be created using the Emboss tool in the surface panel.
8. Inorder to create the Emboss, a closed profile sketch is needed which has to be drawn by giving gaps for latch and hinge placement.
9. After creating the sketch, project the curve into the face and select the emboss tool and note that it has to be created in the outer panel side.
10. Also another sketch has to be drawn to remove the material in the inner panel to reduce the strength and emboss with two layers have to made in the bondary areas to increase the structural stability and the boundary has to be designed in such a way that the mastic sealant has to be used to seal the inner and outer panel so that some projection has to be made for the attachment.
11. All faces and corners has to given with face blend and edge blend respectivily which also helps to sew parts together.
12. Next will be the hinge assembly constraint in the inner panel. First move the hinge component close to the inner panel and in the correct position. Now create a datum plane which is parallel to the inner panel surface so that hinge emboss surface will be flat and the hinge will be constrained properly with the Parallel constraint in the Asembly toolbar.
13. With the created datum plane create an Emboss and using the Distance constraint tool with an offset distance of 0mm.
14. As one side of hinge assembly is finished, the other one in the opposite side is mirrored using Mirror Assembly tool in the Assembly panel.
15. Next is the Latch and striker assembly which has to be made with respect to the hinge assembly.
16. For that, create a midpoint line in between the hinge assembly so that the created point act as centre point and draw a cicle with the radius through the striker so that the opening and closing of the hood depends on the path of circle.
17. Draw a tangent line from the circle and draw another line parallel to the striker locally. Make this two lines overlapp using the touch align constraint tool, so that the striker is in the exact position.
18. Now to create the latch emboss, use the wave geometry linker to exract a surface from the striker and with the extracted surface , create an Emboss by changing the End cap geometry to Plane of section with the required dimension.
19. After the Latch and Hinge is assembled , use the mirrror geometry to mirror the part so that complete inner panel is created.
20. Now Sew or join both the parts and inorder to cross check or examine use Examine geomtery tool, which will notify any errors or gaps in the model.
21. Thicken the part for an offset distance of 0.75mm.
22. Similarly next is the creation of Hem in the outer panel. Make the Hood_Outer_panel as the Work part and start with the tool operations.
23. First offset the outer panel downwards to the required dimension inorder to create the bottom face of the Hem.
24. Using the face blend with three face helps to create the Hem in the outer panel.
25. Note that the hemming created with the clearence is same as that of the required given dimensions and also the gap for the mastic seal is between 2and 5mm.
26. Also in the hem, proper relief has to be given in the front and rear section.
27. Thicken the outer panel with the same offset distance of 0.75mm.
28. The last step in this operation is to check the draft for inner panel by creating a Datum CSYS plane and using the draft analysis tool, and make the limit angle to a minimum of 5 degrees and simulate it. If the whole component turns green, the nthe part has positive draft.
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