Hood design-Week 2

                                                                            HOOD DESIGN

AIM: The main objective of this project is to learn the essential tools, commands, and surface modelling of Hood designing using Siemens NX Cad. This project is to develop a design idea for hood BIW that satisfies the manufacturing requirements, functional requirements, and EURO NCAP standards.

INTRODUCTION:

• The car’s hood consists of an inner and an outer panel. The inner panel provides strength, while the outer panel is just a metal cover. The underside of the hood is often covered with a sound-absorbing material.
• Hood is typically made of steel or aluminium, although aftermarket manufacturers may manufacture hoods out of fibreglass, carbon fibre, or dry carbon.
• The hood or bonnet is the hinged cover over the engine of motor vehicles that allows access to the engine compartment for maintenance and repair. A concealed latch on passenger cars may hold down a hood.
• Some high-performance cars have ‘hood scoops’ that channel outside air directly to the air filter, which gives improved performance and efficiency.
• It is a hinged thin sheet which covers and protects the main parts of the car like an engine. Its main function is to direct access to the engine, battery and other crucial parts of the cars for repair and maintenance and to protect these parts from direct sunlight and dust. It also gives good looks and helps to design a car aerodynamically stable.
• The hood release is a small lever, which is usually mounted under the dash. It is connected to the hood latch by a cable. The hood latch has a safety feature, which requires a second latch to be released before the hood will open. This is to prevent accidental opening while driving.
• The main objective of this project is to learn the essential tools, commands, and surface modelling of Hood designing using Siemens NX Cad. This project is to develop a design idea for hood BIW that satisfies the manufacturing requirements, functional requirements, and EURO NCAP standards.

DATA:

• Hood Thickness Information 

  • Outer Panel Thickness = 0.75mm
  • Inner Panel Thickness = 0.75mm
  • Reinforcement Thickness = 1.5mm

Design constraints to be followed: - 

• Passenger safety
• Pedestrian safety
• Manufacturing feasibility
• Joining techniques of the inner and outer panel.
• Position the striker along the Trajectory of the centre of the hinge axis.

Passenger safety:

Head Clearance criteria:

• Head clearance is decided upon the zone or country. So the same car if it is made for a different country will have a different opening angle depending on the country or region.
• The distance C and D shown in the image is represented as a graph in the upper right corner of the image. Choosing the right head zone position will decide on the angle of the hood opening.
• Product engineers will also get input from the marketing team for deciding the head zone.
• When a car crashes on a pedestrian, the whole human body wraps around the front shape of the car and the head impacts the bonnet or the windscreen. The distance at which the head impacts the car from the ground is called the Wrap Around Distance (WAD).
• To be specific the Wrap Around Distance is a measurement of the distance from the ground to the head impact zone over the outer surface of the car. The wrap-around distance is measured longitudinally in the centre of the vehicle from the ground.

The severity of the injury caused by the frontal crash depends on the type and shape of the vehicle, speed of the vehicle and the movement of the pedestrian relative to the vehicle. In addition to these parameters, the wrap-around distance plays a major role in the safety measures of a pedestrian. During the crash analysis, based on the Wrap Around Distance(WAD), two test areas will be created namely the Child head impact zone and the Adult head impact zone. The child head impact zone is between 1000 to 1700 mm WAD and the adult head impact zone ranges between 1700 to 2100 mm WAD. 

Pedestrian safety:

• Euro NCAP the European car assessment program is a European car safety performance assessment program based in Leuven and founded in 1997.
• They published safety reports on new cars and awarded star ratings based on the performance of the vehicle in a variety of crash tests including front side and pole impacts and impacts with pedestrians. The top rating is 5 star
• So here in Hood, we separate the whole area of the hood into several small parts/regions during frontal crashes. Hood is the major portion a person is gonna come in contact with. So Euro NCAP specified some guidelines under which we distribute hood region into several parts and try to get more green regions.
•  Here below I have pasted an image to get an overview.

• This region is distributed about the height of children and adults who come in contact from the front while an accident. So, here the main motto is to achieve more green region and for that we provide splits in embosses so that during head impact the consequences of collision come less effective. So here I have given splits accordingly to improve head impact zone effectiveness in providing less damage to the person who hit it.

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Views:

 

Design:

1. Inner panel
2. Outer panel
3. Emboss
4. Hemming
5. Corner relief
6. latch
7. Reinforcement 

Inner panel:

 

• The inner panel of the hood is not visible to the customer, but this is the engineering feature of the outer panel. The hood panel is required to have a high initial reaction force against the impact exerted on the hood to enhance the energy absorption capacity. The hood is further required to minimize a reduction of a reaction force by deformation in a collision. A hood inner panel according includes an inner panel main body forming part of a hood of a vehicle, a front bead provided on the inner panel main body and extending along a vehicle width direction, and a rear bead provided on the inner panel main body, located on a rear side of the front bead and extending along the vehicle width direction. The front bead includes a centre portion in the vehicle width direction that is curved toward the front of the vehicle and located in front of each end portion in the vehicle width direction, and the rear bead includes a centre portion in the vehicle width direction that is curved toward the back of the vehicle and located behind each end the portion in the vehicle width.

Outer panel:

 

• A car hood panel is one of the most important components of the BIW (body in white), it is considered the closure sheet-metal component. The outer panel has the aesthetic look to it but on its own is very weak and not capable of handling force during impact. Most automobile hood outer panels are made of traditional steel plates, and their quality does not meet the needs of lightweight development. For this reason, it is necessary to obtain lightweight effects through the application of automotive aluminium sheets. The most widely used
• d car aluminium alloys in the market are deformed aluminium alloys of 6111, 6016, and 5182. The production process of the outer panel of the hood mainly includes blanking, deep drawing, trimming, turnup, and side turn up. Among them, deep drawing is a key process to ensure the quality of parts.

Emboss:

 

• The design of embosses is done by the force distribution of frontal impact. It is designed so that the reduction of force starts when it is directed till the corner, i.e., up to the hinges, and loses the maximum amount (of force) till the end.

Hemming:

 

• The Heming process involves joining the outer and inner panels of the hood by bending their corner curvature areas to 180 degrees. There is also some corner relief given to the sheet to get stationed so that the rollers that do the Heming of sheets can roll appropriately in the required area. Hemming is a sheet metal operation widely used in the automobile sector because the welding or joining process can not be done on styling parts as it may affect the car's aesthetics.

Hinge:

• A hinge is a machine element that connects two bodies allowing angular movement about a fixed axis of rotation, all the while preventing translations and rotations on the remaining two axes. A hinge can be considered as a journal bearing with only one degree of freedom where a shaft is rotating in a hole. Hinges only allow one rotation, either yawing (the most common), pitching, or rolling. Hinges are jointed and flexible device that is attached to any swinging part. Hinges are mechanical bearings that are used to connect two swinging objects or points and give them the freedom to move relative to each other. Hinges have limited movement, allowing the joint to move only at one angle and restricting the other movements of swinging parts.

Latch:

• Latches are mechanical components that allow the temporary joining of parts that are moving relative to each other. They are actuated to release the coupling and allow the two parts to separate. Latches are mostly seen on doors and enclosure openings. They are also used in devices such as seat belts, clamps, straps, and objects with retractable parts. Different designs feature various methods of actuation, holding style, and mounting. The hood latch is extremely simple. When the hood is closed, the latch slides over what is called a catch, and a spring covers the latch to keep it snug. When we pull the knob inside the car to open the hood, the hood latch cable opens the latch, allowing it to bypass the catch and open.

Mastic sealant:

 

• The mastic points are regions where mastic interferes with the outer panel to the inner board. We can't use spot welding because this gives less elegantly fulfilling results. Accordingly, mastic is used to join the panel as it doesn't modify the actual metal.

Reinforcement:  

• The Zone near the turn and Latch has more chances of disillusionment in the hood panel. Consequently, to avoid any failure to rotate and latch region upheld with extra materials whose thickness is regularly directed by the vehicle. The reinforcements give additional fortitude inner panel of the centres where various parts, for instance, the lock and rotate, will be put. The reinforcement ensures that the turns and the snare have better assistance to avoid frustration.

Latch Trajectory:

 

• The latch trajectory shows the striker's way when the hood is opened and shut on a vehicle. The range of the round Trajectory is controlled by the set standard dependent on the typical stature of an individual. The range is estimated from the pivot hub up to the Latch. It is the Trajectory on which the movement of the hood (opening and closing are dependent). This circular Trajectory has a radius equal to the length from the centre point of the centre axis of the Hinge to the striker point on Latch. The striker point is also tangent to the Trajectory.

Corner relief:

 

• Reliefs are provided at the front and side portion of the panel for smooth rolling operation .so that no tearing of the sheet happens when the roller passes through a specific portion.

Deep drawing:

  

• In this corporation, a sheet is pulled into the ideal shape using a punch and pass-on gadget. The sheet is outlined in the condition the pass on by driving the punch down on it. To avoid the sheet wrinkling itself, the sides of the sheet are held someplace close to folios. In the automotive industry, deep drawing is usually carried out using rigid tools.

Tools:

• Offset surface- The offset surface gadget copies the picked surface at a provided distance and guidance.
• Emboss- The embossing contraption makes a punched surface of the picked shut contour. The punch is produced using a chosen surface containing the contour surface. Sketch. a draft can be obliged to the punch from either the end cap or the base surface.
• Trim sheet- The trim sheet gadget parts the target surface along the intersection curve of the target surface and the gadget surface. The piece of the cover on either side of the intersection can be either discarded or retained according to to need.
• Through curves- This contraption creates a surface between two various surface sections where the shape can change in section.
• Law Extensions- Creates an extended surface subject to an open-chain contour or a shut contour on the picked target surface. A draft can be obliged by the extension.
• Face blend- Creates a curved blend or fillet along two picked surfaces in gave direction vector. The blend curve can be changed regarding reach, width, and continuity.
• Extend sheet- Creates an extension of the picked sheet up to a given distance.
  Offset in the face- Creates an offset in the front or edge on the target face up to a provided distance.
• Bridge curve- Create a roundabout portion between two intersecting and non-intersecting curves. The beginning and endpoint of the roundabout changed by providing distance.
• Projected curve- Creates a projection of a curved profile onto a goal surface. The surface can be linear and curved. The direction can be changed by a reasonable vector.
• Sew- combines sheet bodies by sewing common edges together or combines solid bodies using sewing faces. Any opening between the surfaces can be closed.
• Mirror Geometry- Mirror a geometry along a face.
• The curve on the surface- Creates a surface spline feature directly on the face.
• Thicken- creates a strong body using thicken.
• Extracted body- Creates a body of picked geometry that can be changed by editing the parent feature and rebuilding the extracted feature.

Assembly:

 

Conclusion:

• All the parts of the hood are designed based on the required conditions and given dimensions with the completion of hood design manufacturability. consider the safety of occupants and designed under the EuroNCAP safety regulation.