Hood design-Week 2

OBJECTIVE:

Project is about design a Hood or Bonnet BIW that satisfies the manufacturing requirements and functional equipment of Hood or Bonnet using NX-CAD.

INTRODUCTION:

Hood may be hinged at either front or rear edges in earlier models. it maybe split into two sections one each side, each hinged along the centreline. A further variant combines the bonnet and wheel arches into one section and allows the entire front body and wheel arches into one section and allows the entire front body work to tilt forward around a pivot near the front of the vehicle.

Hood is made aerodynamic in shape to reduce air effect and used to decorate the front portion of the car and to add a luxurious look of cars. Hood generally used to cover car engines, radiators and any other components, therefore the hood must be designed in such a way that all the maintenance on the engine. In addition to that f it come across any accidents from the front portion most of the time the hood system gets damaged first and absorbs most of the impact energy resulting from the crash.

PURPOSE:

• Provide access to the engine maintenance.
• Covers all engine, radiator and other components.
• Safety passengers.
• Reduce air effect due to its aerodynamic shape design.
• Reduces engine noise which helps for quieter drive.

Figure : Hood or Bonnet of car

COMPONENTS OF HOOD:

• Hood Outer Panel
• Hood Inner Panel
• Latch and Stricker Reinforcement
• Hinge Reinforcement
• Stiffener Pad

MATERIAL REQUIREMENTS:

Hood are typically made out of the same material as the rest of the body work. Its includes steel and aluminium. However some market comapines produce replacement of steel hood with fibre glass or carbon fibre to make vehicle lighter.

MANUFACTURING REQUIREMENTS:

1. Deep drawing process is used for manufacturing of the inner panel.
2. Material requirement – Steel, Aluminium, Fibers.
3. No negative draft.
4. No Sharp Corners
5. Provide appropriate corner relief on the area of curvature.
6. Thickness of the Outer Panel -0.75mm.
7. Thickness of the Inner Panel = 0.75mm.
8. Reinforcement thickness = 1.5mm

DESIGN ASPECTS:

1. Pedestrian safety
2. Vehicle Quality
3. Occupant Safety
4. Styling
5. Manufacturing

A. PEDESTRIAN SAFETY:

Pedestrian safety from front collision is also to be considered. The European New Car Assessment (Euro NCAP) is a European car safety performance assessment program which has developed test specification and t=rating systems for vehicles such tests include a series of tests using impactors designed to mimic a collision at a speed of 40Kmph. They describe a situation in which pedestrian is situated laterally and a car first hits one of his legs. Tests are conducted on the leg, upper leg and most importantly head, as head trauma is most commonly responsible for casualties.

B. VEHICLE QUALITY:

Torsional stiffness, Flutter resistance, dent resistance (Palm print)., dent resistance (Hail/Stone chip), Corrosion resistance, low mass-ease of opening, low mass- vehicle COG, Noise attenuation.

C.OCCUPANT SAFETY:

Collapse-Front-impact, system integrity- impact, retention-impact.

D. STYLING:

Tight Hem Flanges, Painted surface quality, stretch flanges, shape in low strained areas.

E. MANUFACTURING:

Paint drain features, Outer panel dent resistance, clean sheared edges, surface quality post forming, Galling resistance-inner panel ,Manufacturing occupant- Safety quality.

MATERIAL REQUIREMENTS:

Hoods are typically made out of the same material as the rest of the body work, this includes steel and aluminium. However, some market companies produce replacements for steel hoods with fibre glass or carbon fibre to make vehicle lighter.

SHEETMETAL OPERATIONS:

1. Blanking and Piercing
2. Deep Drawing
3. Embossing
4. Hemming

a. 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 same, only the terminology is different. In blanking the punched out piece is used and called blank where as 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 of piercing is punching

Purpose:

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

b. DEEP DRAWING:

• Deep drawing od sheet metal is used to form object 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 panel.
• Material used is aluminium 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 material gets compress between punch and die, which reduce the thickness and increase the height of the cup.

c. 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 by passing sheet or a strip of meta between rolls of the desired pattern.
• It s=is done by pressing a sheet of paper into female die, that has a design attached into it. This is usually done with a male counter part underneath the paper so that the two and design is transferred to the paper.

Purpose:

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

Figure : Embossing

d. HEMMING:

• Hemming is a sheet metal forming process in which sheets are joined by bending it 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 inner and outer sheet.

Figure : Hemming

Purpose:

• To fasten two sheet parts by folding the edges of sheet back on itself.

Types of Hemmings:

1. Open Hemming
2. Teared drop Hemming.
3. Closed Hemming
4. Rolled Hemming

WAY OF APPROACH:

Top -v Down Approach – top down assembly design, one or more features of a part are defined by something in an assembly such as layout sketch or the geometry of another part. The design intent comes from the top ( the assembly) and moves down(into parts)., hence the phrase ”Top-down”.

DESIGNING COMPONENTS:

Designing of Inner Panel:

Master Section : The master section is created based on the requirements received from the marketability team and the manufacturing requirements.

Master Sketch:

• Extract the body from the given dump solidly body and start creating inner panel using that extracted one.
• Create a part fie in assembly named after “ Inner Panel”. Trim the half portion of it as we are going to mirror it at the end.
• Create a offset surfaces as per sketch from linked body.
• Use offset curve on face to create curves in faces using edges and trim off the unwanted portion.
• Use Through Curves command by selecting appropriate surface which usually creates a body through multiple sections where the shapes changes through each section.
• Create one more surface using offset surface and connect it with previous surface using law extension. Trim off the over extend portion using trim and extend.
• Blend the faces of the of the sheets using face blend by giving appropriate dimensions.
• Now create a Sketch by selecting a plane Parallel to the panel surface and project the curves on the panel using Projected Curve.
• Create a Emboss to modify the body with faces made by projecting a section along a vector by selecting embossed face as end face and projected curve as curve. Use edge blend to blend them.
• Create more embosses as per requirement by projecting drawn sketches on panel.
• Use trim sheet to create voids or holes on sheet as per requirement.
• Hinge Emboss : Use wave Geometry linker to extract the hinge face and use it as reference to create sketch for its positioning.
• Latch Emboss : This emboss is created once the trajectory of hood opening and closing finalized.
• Thicken the part at the end to make it solid body.

• MASTIC DATA DESIGN:

• 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.

Figure : Mastic Data Design

• LATCH AND HINGE REINFORCEMENT:

• To further more reduce the impact to the occupants inside the car, additional latch and hinge reinforcements are provided to the hood. When latch and striker are place, there is a drop in strength at that position thus reinforcements are provided to compensate that loss. Alos stiffener pads are placed to reduce NVH(Noise Vibration Hardness). Hinge and latch reinforcements thickness are kept at 1.2mm but it may vary.

Figure : Latch and Striket Reinforcement

Figure : Hinge Reinforcement

• HINGE AND STRIKET POSITIONING:

• For proper opening and closing of hood, the striker should be perpendicular to the trajectory of the hood. For this, the hinge is assembled at its position.
• Once it is placed, the hinge axis is drawn by connecting sketch points created on hinge edges.
• Create a datum plane using midpoint of hinge axis.
• Now sketch a circle into such a way that helps in positioning latch.
• Now position the latch using above drawn circle which has to be perpendicular to the hood trajectory.
• Once positioned create a Emboss on inner panel by extracting the face of the latch.

Figure : Hinge Position Design

• DESIGNING OF OUTER PANEL:

Hemming:

• Use offset curve on face to create curve alone the faces by selecting above offset surface.
• Extend the sheet by selecting the above offseted curve.
• Create one more surface at an offset of calculating thickness and gap between flanges on opposite direction to above surface.
• Offset the above created law extension as per requirement using offset face.
• Now trim the extra surfaces which are not required.
• Use face blend and select the top, rear and middle face to create hemming.

Figure : Outer Panel

Relief Data:

• Relief is provided onto the part or component in order to remove any stresses developed in a particular area i.e. sharp corners that take place during hemming process are carried out. Thus corners are rounded or chamfered.
• Create a sketch and project it on panel using project curve trim the extra portion using trim sheet by selecting projected sketch as boundary.

Figure : Relief Data

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 DISTRIBUTION:

In the below images show the force distribution on the inner panel. the arrow show the force distribution of the inner panel.

Figure : Force distribution on Inner Panel

HOOD AND HINGE ASSEMBLY:

Final Output assembly model of the Hood Or Bannet of car shows below.

Figure : Assembly of Hood or Bonnet of car

CONCULSION:

In this challenge Hood or Bonnet is designed successfully in a top-down approach and a creating the Inner panel using given Master Sketch and assemble the Latch and striker and hinge assemble with reinforcement. Which satisfies the industry manufacturing requirements.