Hood design-Week 2

Out of these requirements, Pedestrian safety & Occupant safety are the most important factors. Euro NCAP is a voluntary vehicle safety rating system that will provide European consumers with information regarding the safety of passenger vehicles. The more stars, the better safety it will be provided to the customer. Thus, a design engineer must need to follow these requirements to provide better safety to the customers.

 

 

NCAP stands for New Car Assessment Program. To give a brief background, in 1978 USA became the first country to come up with a program to provide car crashworthiness information to consumers, which eventually expanded to crash testing and reporting the results. The US-NCAP model formed the basis for similar programs in other regions, and today there is the Australasian NCAP, Euro NCAP, Japan NCAP, ASEAN NCAP, China NCAP, Korean NCAP, and Latin NCAP. Global NCAP, an independent charity registered in the UK, was formed in 2011 to enhance cooperation between the various NCAPs and primarily promote vehicle crash-testing and reporting in emerging markets. ‘Safer Cars For India’ and ‘Safer Cars For Africa’ are its key initiatives at the moment.  

 

 

every NCAP has its own protocol to crash-test and score cars, and so the results are not interchangeable. Euro NCAP, for instance, conducts full-frontal, front offset, side-impact, and side pole tests. Global NCAP ratings, on the other hand, are based on front offset crash tests alone. A front offset crash test is designed to simulate a head-on collision between two cars. In the Global NCAP test, the car is driven at 64kph and with 40 percent overlap into a deformable barrier which is the equivalent of a crash between two cars of the same weight, both moving at 50kph.

 

 

WAD (Wrap-Around Distance) is the geometrically traced distance from the contact point with the Ground Reference Plane, vertically below the front face of the bumper, to any point on the vehicle front structure.

During most pedestrian-vehicle crashes the car front impacts the pedestrian and the whole body wraps around the front shape of the car. This influences the head impact on the vehicle. Meanwhile, the windscreen is a major impact point and tested in NCAP conditions. The severity of injuries is influenced by car impact speed; type of vehicle; stiffness and shape of the vehicle; nature of the front (such as the bumper height, bonnet height, and length, windscreen frame); age and body height of the pedestrian; and standing position of the pedestrian relative to the vehicle front. The so-called Wrap Around Distance WAD is one of the important measurements for the assessment of the protection of pedestrians and of bicyclists as well because the kinematic of bicyclists is similar to that of pedestrians.

 

During crash analysis, based on the wrap-around distance, two test areas will be created namely the Child Head Impact Zone and the Adult Head Impact Zone.

 

Test Area:

Impactor: 

 

 

 

Safety is the most important criteria in automobile designs which concentrate on both pedestrian and occupant safety. 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 accidents is due to the head injury resulting from the hard impact of the head against the stiffer hood or the ground. This leads to the necessity of a new inner hood panel that is less stiff and pedestrian-friendly. The head impact analysis on the present hood of the car was done to study the response of the adult head form at two different locations. Structural and modal analysis for the same present hood assembly was done to observe the local and global stiffness. In order to reduce the head injury of the pedestrian the local stiffness over the area of the head, the impact has to be reduced thus the new design of the hood inner panel was focused on that and the structural and model analysis was done for the new design. The design with lesser local stiffness and similar global stiffness compared to the existing hood was finalized.

 

 

Head Impact:

 

car-pedestrian accidents account for a considerable number of automobile accidents in industrialized countries. Head injury continues to be more concerned with Automobile impacts. Because the head is the most seriously injured part in many collisions including in pedestrian automobile collisions. To reduce the severity of such injuries international safety committee has proposed subsystem tests in which head foam impactors are impacted upon the car hood.

 

Pedestrian Safety:

 

According to the requirements of the Australian New Car Assessment Program (ANCAP) for pedestrian protection, it needs to define zones of car hood for analysis, as shown in Figure 4. It can be noted that when the collision projection point locates between (Wrap Around Distance) WAD 1000 and WAD 1500, the head type will use the children's head type. The adult head type will be used while the collision projection point locates between WAD 1700 and WAD 2100. In the collision projection point located at WAD 1000 when the children's head type will be used.

 

 

 

 

Noise, Vibration, and Harshness (NVH) is the study and modification of the noise and vibration characteristics of vehicles, particularly cars and trucks. To improve NVH, mastic sealants were provided on the inner panel to attach with the outer panel. Here mastic points on the inner panel play a major role to avoid Noise and Vibration in the cabin. NVH is measured by the instruments, namely microphones, accelerometers and force gauges, or load cells. Component and subassembly NVH tests are most commonly performed using a vibration Shanker while entire vehicles are usually on the test track or road stimulator testbeds.

 

 

Noise, vibration, and harshness are caused by the car's mechanical and electrical systems, as well as the car's interaction with road surfaces and its passage through the air. The main sources of NVH in a car are its engine, drivetrain, and tires, as well as the sound of airflow along its body. Tires are a huge source of noise, due to vibrations created by their rotation, which then travel along with suspension mounts and into the cabin. Low-profile tires, found on sportier cars, tend to transmit more vibration through the suspension because the tighter, stiffer rubber can't absorb as much. Wide tires are more susceptible due to a larger contact patch, but the soft, wide tread patterns of off-road tires are the worst offenders. Airflow over the car's body causes quite a bit of noise, especially at higher speeds and in large cars with the aerodynamic properties of a shipping container. Any interruptions the air faces in its journey across the car - such as aerials, roof racks, and door mirrors-are rewarded with howling, whipping, or buzzing noises in the cabin.

 

 

Canceling out NVH comes down to three basic principles-reducing it at the source, isolating it from the car's main structure, and absorbing as much as possible before it enters the cabin. The first - if not the easiest way to reduce NVH is to curb the number and volume of the sounds, vibrations, and shocks produced in the first place. The second and perhaps equally complex way to reduce NVH is to isolate the car's main structure from the source. chassis and steering column from road surfaces, removing vibration and shocks. To further isolate the sources of noise, engine, suspension, and exhaust components are mounted on rubber and polyurethane bushes rather than solid metal; the softer compounds work against the transmission of vibrations. The last resort in the war against NVH is also the most conventional: absorbing as much as possible. Mechanically speaking, this tends to refer to steering dampers, which absorb the worst of the shocks introduced by poor road surfaces.

 

•  Blanking and Piercing
•  Deep Drawing
•  Embossing
•  Hemming

BLANKING AND PIERCING:

In Blanking, Piercing, and sharing processes a punch and die are used to modify webs. The tooling and process are between the two are the same, only the terminology is different. In blanking the punched-out piece is used and called blank whereas in piercing the punched-out piece is scrap. The process for parts manufactured simultaneously with both techniques is often termed pierce and blank, an alternative to piercing is punching

Purpose:

• Reduce bodyweight.
• Improve the strength of the body.
• Improve Mileage of car.
• Distribute impact force.

DEEP DRAWING:

Deep drawing of sheet metal is used to form objects with dept. it is plastic deformation in which a flat sheet metal or plate is formed into a recessed three-dimension part with a depth several times the thickness of the metal. The process of deep drain begins with a flat sheet metal held on the upper surface of the die. It is used in manufacturing inner panels. The material used is aluminum as it can absorb twice the crash energy of mild steel. Lighter dent-free and make body panels thicker while still lowering weight.

Purpose:

Operation in which thickness of the shell wall is reduced and its surface smooth. When the material gets compress between punch and die, which reduces the thickness and increases the height of the cup.

EMBOSSING:

Sheet metal embossing s is a stamping process for producing raised or sunken designs or relief in sheet metal. This process can be made by means of matched male and female roller dies or bypassing sheet or a strip of metal between rolls of the desired pattern. . It s-is done by pressing a sheet of paper into the female die, that has a design attached to it. This is usually done with a male counterpart underneath the paper so that the two and design are transferred to the paper.

Purpose: Embossing enables you to highlights important elements of your printed products, such as letters (Company name) and designs ( corporate logo), to make sure they stand out. Embossing can also be combined with foil stamping to help create the effect of 3D images on printed paper that really shines.

HEMMING:

Hemming is a sheet metal forming process in which sheets are joined by bending them to 180degree. Automotive body panels and automotive parts such as decks-lids, trunk-lids, doors, hoods, and tailgates are formed by the hemming process, in this process usually, a sheet is bent with the help of the inner and outer sheet.

    

Designing of the Hood using NX software

Input Data

1. Outer hood panel thickness=0.75 mm

2. Inner hood panel thickness=0.75 mm

3. Reinforcement thickness=1.5 mm

Master sketch

HOOD OUTER PANNEL

Outer panel is nothing but a outer skin of inner panel. Otherwise called as a cover of inner panel. It is the part. which gives luxurious look to the hood or bonnet. Outer pannel and inner panel cannot join by any welding process like spot welding or rivet, which spoil the outer look of a car.

Design of Outer Panel:

The given Class A surface has been used to create the outer panel. It is then trimmed into half using the XY plane.

The outer surface is offset to a distance of 0.5mm and the sharp edge is filleted to a radius of 30mm and the main panel is split with the offset created. Then the outer edge is swept using Law extension and the offset is created for the Sweept model at a distance of 20mm.

An offset is created with the main panel at a distance if 3.25mm and the inner surface if the panel is trimmed with the offset.Then considering all the top panel,offset panel and the Law extension an edge blend using the three surfaces is created. This is the hem that is required to create in the panel. Inorder to give reliefs in the front and right of the panel draw splines using G1 continuity on the front and back side of the hem.

After trim the surface using the created lines. Mirror the obtained panel using Mirror geometry and Sew the surface.

HOOD INNER PANNEL

This study introduces a new method for decreasing the hood stiffness, by making a hole on the inner hood panel. To determine the most effective hole position on the inner hood panel, the method of modal stiffness was employed, in an attempt to reduce the HIC from a collision between a vehicle and a head-form impactor. FRF (frequency response function) results for the reference vehicle model on head-form impact simulation were obtained. In addition, modal analysis of the entire vehicle model was simultaneously carried out. Subsequently. using the results of these two analyses, dominant frequencies (41.7 Hz and 83.3 Hz) were obtained, which related to deformation of the inner hood panel. Then, adequate hole positions at each modal frequency were selected, and the inner hood panel was improved, by making a hole at these positions. Finally, through head-form impact simulations on the improved vehicle model with the hole, it was demonstrated that the new method applied in this study is acceptable and useful. In the case of the improved vehicle model with a 40 mm diameter hole on the inner hood panel, this showed a significant reduction in the HIC of approximately 12.2%, compared to the original vehicle model.

 

Designing of model:

The inner panel is designd using the given Class A Surface. Trim the Surface using the XY plane.

Offset the Surface to 2mm,4mm and 25mm and create offset to the boundaries at distance of 20mm on first offset 22mm and 35mm on second offset,50mm on the third offset respectively.Trim the sheet as per the offset and discard the material from the sheet as required. Then use through surface and join the three sheets as required and then use edge blend to give fillet to the edges of the surfaces. Allow pace for latch and Hinges and then create a profile to create an emboss on the surface.On this emboss create separate profiles and emboss them also to a distance of 7mm.

Create individual profiles on these profiles and also emboss them. In these emboss create profiles allowing places of the mastric points such that the mastric points are given at these places and then trim these profiles from the obtained emboss sheet.These profiles are mainly added for weight reduction of the hood and also for reducing the head impact.

In the left over pace at the bottom left corner create a plane at an angle of the orientation of the panel and then then a profile is drawn on the plane for adjusting the hinge on the panel and it is embossed from the plane to get a straight emboss. Then the panel is mirrored using mirror geometry and it is then sewed together to get a single panel.

 

Latch trajectory

While assembling the latch with the hood panel it is strictly recommended that the position of latch striker should be placed such that the latch striker exactly fit into the lock hole in the engine compartment. Keeping this in mind, the latch striker is placed on the inner hood panel using latch trajectory path. This path is created using the the hinge axis taken as reference to draw a big trajectory path.

  

MASTICS

The main purpose of the outer panel is for aesthetic looks. Thus we cannot use bolts or welding. this has to be done with the help of hemming and mastic sealants. Mastic sealants are elastic compounds that behaves like the rubber. It is placed between the outer and inner panels. Initially it is in paste form t-but after the hot furnace bath, it will get hardened thus joining the outer panel and inner panel, Mastic sealants has the tendency to increase the strength of the panel and has the tendency to increase the strength of the panel and has the influence of 80mm diameter. Usually in designing these are created in inner panel using sketches and projecting them on panel. Later trimming of the sheet and blending it.

 

  

Draft analysis

In Siemen NX is one of the tool used to study the deep drawing feasibility easily through checking draft angle in the various faces.The Designer should Define a tooling direction in-order to check the draft angles For my design (inner panel), I have done draft analysis by defining a tool direction which is perpendicular to the plane created using the corner points of the model.

From the above picture , we can notice that there are some negative drafts.

So to overcome this I have increased the draft angle of the the embose. in the picture below we can notice that the negative draft is cleared.

COMMANEDS USED:

• EXTRACT GEOMETRY:

creates associative copies of bodies faces, curves, points and datums and associative mirrored copies of bodies, within the same part

• TRIM SHEET:

Trims off a portion of a sheet body.

• OFFSET SURFACE:

creates a body by offsetting a set of faces.

• OFFSET CURVE IN FACES:

offsets curves along the faces on which they lie.

• THROUGH CURVES:

Creates a body through multiple sections where the shape changes to passthrough each section.

• LAW EXTENSION:

Creates a law controlled extension from a base sheet, dynamically of based on laws for distance and angle.

• FACE BLEND:

Adds tangent blend faces between selected sets of faces. The blend shape can be circular, conic or law controlled.

• TRIM AND EXTEND:

Trim or extends a set of edges or faces to the intersection with another set of edges or faces.

• EDGE BLEND:

Rounds sharp edges between faces. The radius can be constant or viable,

• PROJECT CURVE:

Projects curves, edges or points onto faces or planes.

• EMBOSS:

Modifies a body with faces made by projecting a section along a vector with options for end cap location and shape.

• MIRROR GEOMETRY:

Copies geometries and mirrors them across a plane.

• EXTEND SHEET:

Extends a sheet body by distance or to the intersection with another body.

• SEW:

Combines sheet bodies by sewing common edges together or combines solidies by sewing common faces.

• THICKEN:

Creates a solid body by adding thickness to a set of faces. WAVE GEOMETRY LINKER: Copies geometry for other parts in the assembly into the work part.

• DRAFT ANALYSIS:

Draft analysis is carried out to see that the panel can be drawn or not. It also helps to find the negative draft present in the component which can cause difficulty in manufacturability. FORCE 

Final assembled images

 

                     

                    

CONCLUSION

The complete assembly of the hood outer and hood inner panel was designed as per requirement. The latch and the hinges were also placed at appropriate position by following a latch trajectory strategy.