Aim : To Design outer panel, inner panel and necessary reinforcements

Theory :

                The hood or bonnet is the hinged cover over the engine of motor vehicles. Hoods can open to allow access to the engine compartment, or trunk on rear-engine and some mid-engine vehicles) for maintenance and repair.

Styles and materials

On front-engine cars, the hood may be hinged at either the front or the rear edge, or in earlier models (e.g. the Ford Model T) it may be split into two sections, one each side, each hinged along the centre line. A further variant combines the bonnet and wheelarches into one section and allows the entire front bodywork to tilt forwards around a pivot near the front of the vehicle (e.g. that of the Triumph Herald).

Hoods are typically made out of the same material as the rest of the body work. This may include steel, aluminum, fiberglass or carbon fiber. However, some aftermarket companies produce replacements for steel hoods in fiberglass or carbon fiber to make the vehicle lighter.

Release/ safety and security mechanisms

The hood release system is common on most vehicles and usually consists of an interior hood latch handle, hood release cable and hood latch assembly. The hood latch handle is usually located below the steering wheel, beside the driver's seat or set into the door frame. On race cars or cars with aftermarket hoods (that do not use the factory latch system) the hood may be held down by hood pins. Some aftermarket hoods that have a latch system are still equipped with hood pins to hold the hood buttoned down if the latch fails.

Features

A hood may contain a hood ornament, hood scoop, power bulge, and/or wiper jets.

Pedestrian safety

In Japan and Europe, regulations have come into effect that place a limit on the severity of pedestrian head injury when struck by a motor vehicle.^[2] This is leading to more advanced hood designs, as evidenced by multicone hood inner panel designs as found on the Mazda RX-8 and other vehicles. Other changes are being made to use the hood as an active structure and push its surface several centimeters away from the hard motor components during a pedestrian crash. This may be achieved by mechanical (spring force) or pyrotechnic devices.

Some hoods may need a power bulge to fit over the engine and air filters, or enhance the aesthetic appearance of the hood

A flipfront hood

A rear-hinged clamshell hood on a Saab 9-5

Parts of a Hood

• Hood outer panel
• Hood inner panel
• Latch and Striker
• Hinge engine compartment
• Hinge hood part

 

 

 

Hood outer panel

                        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 pannel cannot join by any welding process like spot welding or rivet, which spoil the outer look of a car

 

Hood inner panel

                                                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.

 

Latch and Striker

                                A latch or catch (called sneck in Northern England and Scotland) is a type of mechanical fastener that joins two (or more) objects or surfaces while allowing for their regular separation. A latch typically engages another piece of hardware on the other mounting surface. Depending upon the type and design of the latch, this engaged bit of hardware may be known as a keeper or strike.

A latch is not the same as the locking mechanism of a door or window, although often they are found together in the same product.

Latches range in complexity from flexible one-piece flat springs of metal or plastic, such as are used to keep blow molded plastic power tool cases closed, to multi-point cammed latches used to keep large doors closed.

Hinge Reinforcement

            Devices for preventing movement between relatively-movable hinge parts for maintaining the hinge in two or more positions, e.g. intermediate or fully open the maintaining means acting perpendicularly to the pivot axis with a coil spring perpendicular to the pivot axis specially adapted for vehicles

The present invention concerns a hinged door check, for vehicle doors in particular, consisting of two hinged parts  which are connected swivelling around an axis of rotation  by a hinge pin  and which have a holding device integrated between them defining different relative rotational positions. The holding device consists first of at least one catch element  kinematically connected with the first hinged part  and spring-loaded in a working direction perpendicular to the axis of rotation, and secondly of a track  kinematically connected with the second hinged part , essentially shaped like the sector of a circle and arranged coaxial to the axis of rotation  with respect to its radius of curvature, having at least one latching point cooperating with the catch element . The hinge pin  is connected detachable from the first hinged part  by fasteners , so that the hinged parts  are separable when unloosening the fasteners while keeping the connection between the hinge pin  and the second hinged part  and the holding device  assigned to the latter.

Mastic Data

            The challenges of automotive metal bonding described previously are still present. One difference between the two applications is bondline thickness. A hem flange maintains a very thin bondline, around 013 mm (0.005 in), while an anti-flutter bondline thickness is generally around 20 mm (0.75 – 0.8 in). The shape of the applied adhesive is also very different. Instead of a bead, the adhesive is applied in the shape of a gumdrop or chocolate drop. It is strategically spaced across the inside surface of the outer panel, aligning with the shape of the inner panel. The placement also provides support for the outer panel to pass compression tests (developed to survive someone sitting on the hood without causing a dent). After application of both adhesives, the inner panel is placed and the perimeter of the outer panel folded over to form the hem flange.

Emboss

                Stamping (also known as pressing) is the process of placing flat sheet metal in either blank or coil form into a stamping press where a tool and die surface forms the metal into a net shape. Stamping includes a variety of sheet-metal forming manufacturing processes, such as punching using a machine press or stamping press, blanking, embossing, bending, flanging, and coining. This could be a single stage operation where every stroke of the press produces the desired form on the sheet metal part, or could occur through a series of stages. The process is usually carried out on sheet metal, but can also be used on other materials, such as polystyrene. Progressive dies are commonly fed from a coil of steel, coil reel for unwinding of coil to a straightener to level the coil and then into a feeder which advances the material into the press and die at a predetermined feed length. Depending on part complexity, the number of stations in the die can be determined.

                        Manufacturing process

(a) Cutting and Shearing- Here the sheets are cut by using various tools. Blanking, piercing, perforation, notching etc. are various types of shearing operations.

(b) Bending Operation- The sheet metals are straining around a straight axis.

(c) Forming- Flanging and tube forming are forming operations to give shape to the sheets.

(d) Drawing Operations- Cupping, drawing, deep drawing are all drawing operations in which sheet metals are given cup or shell type shapes.

(e) Reducing Operations- Necking type of operations.

(f) Squeezing- For example coining operation is done in closed dies applying large force.

Bending:

 

It is a forming operation performed on a press to bend a sheet metal or a strip through required angle.

Salient features of bending are:

(a) It requires a press and tooling to do the bending operation.

(b) The sheet metal strip is permanently deformed to the required shape.

(c) When the sheet metal is pressed for bending in the die the outer portion is stretched while inner sides (towards the punch) are compressed.

(d) The radius of the corner should not be small i.e., the angle at the bent should not be too sharp—otherwise material can crack at the bend.

(e) After removal of the bent component from the press there is usually spring back up to about 4 degrees depending on the material hardness. Hard material have greater tendency to spring back while softer materials have less tendency to recover shape.

Blanking:

(a) Blanking is an operation of cutting an object of given shape from sheet metal strip. It may or may not be necessary to perform further operations on the blank. Piece detached from the metal strip is called blank. Examples are discs, washers.

(b) Blanking operations are extensively used in sheet metal working to make components like washers, discs etc. If needed other operations may be combined with the blanking operation. Blanking is usually the first operation in sheet metal.

(c) A blanking operation to make disc from a steel strip would require-

(i) A press

(ii) A punch and die with clearance at the lower side so that the disc can fall down freely.

(iii) The material for blanking operation is usually hard.

Piercing:

It is a distinct process of making a hole in sheet metals.

It is characterized by:

(a) The punch is sharp and pointed tool which is able to penetrate or pierce through the sheet metal.

(b) There is no scrap from the hole.

(c) The hole has rough flanges around the hole.

Notching:

Notching is removing small quantity of material from the edges of a sheet metal part. Notching may be done to avoid overlapping of material after bending at the seams. Proper notching would give the sheet metal joints a better fit.

Deep Drawing

Deep drawing is one of the most widely used processes in sheet metal forming. Apart from its use in many other sectors, it is applied in the automotive industry for the manufacturing of car body parts.

 

Process definition:

The deep drawing process is a forming process which occurs under a combination of tensile and compressive conditions. A flat sheet metal blank is formed into a hollow body open on one side or a hollow body is formed into a hollow body with a smaller cross-section.

Deep drawing processes are divided into three types:

Deep drawing with tools

Deep drawing with active means

Deep drawing with active energy

In the automotive industry, deep drawing is usually carried out using rigid tools.

Illustration of the deep drawing process

The figure illustrates the deep drawing process. The rigid tools consist of a punch, die and binder. In deep drawing, the plate holder closes after the metal sheet blank has been inserted.

Next the sheet is clamped between the die and the binder. This process slows down the flow of the sheet while it is being drawn and thereby prevents wrinkles from forming under the binder. The punch stretches the sheet over the die radius and forms it in the die. The amount of punch force necessary for forming is thereby continually increased up to the lower dead center of the punch.

Whereas in pure deep drawing there is no reduction of sheet metal thickness, forming is achieved in stretch forming purely as a result of a decrease in sheet metal thickness. Stretch forming is extensively used for the forming of only slightly curved parts with low depth of draw (e.g. roofs, doors).

When drawing complex car body parts in practice, there is usually a combination of stretch and deep drawing involved. It is necessary that the sheet metal is stretched as well as possible without reaching the material’s limits (e.g. splits, wrinkles).

There are approximately 300 to 400 sheet metal parts which fit together to form the body of a car. In order to manufacture high quality sheet metal parts optimally for their particular use, specialized software simulates the complete deep drawing process.

Hemming

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.

In car part production, hemming is used in assembly as a secondary operation after deep drawing, trimming and flanging operations to join two sheet metal parts (outer and inner) together. Typical parts for this type of assembly are hoods, doors, trunk lids and fenders.

The accuracy of the hemming operation is very important since it affects the appearance of the surface and surface quality. Material deformations, which occur during the hemming process, can lead to dimensional variations and other defects in parts. Typical hemming defects are splits or wrinkles in the flange, material overlaps in the corner areas or material roll-in. This is why it is important to use simulation tools in order to, on the one hand, better understand the hemming process and, on the other hand, significantly reduce the number of “trial and error” loops during tryout und production.

There are various types of hemming operations:

Conventional die hemming

Roll hemming

In conventional die hemming, the flange is folded over the entire length with a hemming tool.

In roll hemming, the hemming roller is guided by an industrial robot to form the flange.

Conventional die hemming

Conventional die hemming is suitable for mass production. In die hemming, the flange is folded over the entire length with a hemming tool. Normally the actual hemming is a result of a forming operation in which the flange is formed with a hemming tool after the drawing and trimming operations have been completed. The formed flange is then hemmed in several process steps. These steps include, for example, the pre-hemming and final hemming depending on the respective opening angle of the flange. Production plants for conventional die hemming are very expensive, but the cycle times are very low.

Roll hemming

Roll hemming is carried out incrementally with a hemming roller. An industrial robot guides the hemming roller and forms the flange. Roll hemming operation can also be divided into several pre-hemming and final hemming process steps. Roll hemming is very flexible to use and tool costs are significantly lower as compared to those of conventional die hemming. However, the cycle times are much higher since the hemming is realized using a hemming roller which follows a defined path.

 

Features Used in NX Cad

Offset Surface:

 Offset surface command is used to offset a surface or face. Selecting a surface to offset will generate an IntelliShape offset surface that is defined by the originating surface. This IntelliShape will update if the originating surface is modified

Offset in face:

Use the Offset Face command to offset one or more faces along the face normals. You can offset faces either by positive or negative distances, provided the topology of the body does not change.

Trim sheet:

Use the Trimmed Sheet command to trim sheet bodies to intersecting faces and datums, and projected curves and edges.

Through curves:

 through curves command use to create a body through multiple sections where the shape changes to pass through each section. Sections are curves, points, solid edges, solid faces.

Law Extension:

Use the Law Extension command to extend an existing surface or sheet based on the laws for distance and the angle of the extension. Law Extension creates flanges or extensions when a particular direction is important or when it is necessary to reference the existing face

Trim and extend:

This option lets you extend and trim one or more surfaces using a set of tool objects composed of edges or surfaces. 1 Two intersecting solid bodies. 2 Selected body on the right is the object to trim (the target).

Face Blend

 Face Blend is enhanced to provide a dedicated type for blending along intersection edges of bodies combined with a Boolean feature. Face Blend is primarily used to blend between faces of separate bodies. It can also be used to blend between faces of a single body.

Edge blend

Edge blend command use to round sharp edges between faces. The radius can be constant or variable.

 

Emboss

 Emboss is mainly used on surfaces, you can use an intersecting solid as Michael shows, you can also use a curve or sketch profile. create your sheet feature. select emboss, and select your face and sketch. Attached is an example of an embossed sheet.

Sketch:

 Creates a sketch in the current application. Use the direct sketch tools to add curves, dimensions, constraints, etc.

Datum plane:

 Creates a datum plane used to construct other features.

WAVE Geometry Linker:

Copies geometry from other parts in the assembly into the work part.

Extend sheet:

Extend a sheet body by distance or to the intersection with anotherbody.

Mirror geometry:

 Copies geometries and mirror them across a plane.

Sew:

 sew command use to combine sheet bodies by sewing common edges together, or combines solid bodies by sewing common faces. The selected sheet bodies must not have any gaps larger than the specified tolerance

Thicken:

Use the Thicken command to offset one or more connected faces or sheets into a solid body. Thickening occurs by offsetting the selected faces along their face normals, and then creating sidewalls. The Thicken command is similar to the Offset Face command.

Curve on surface:

Creates a surface spline features directly on face.

Extract body:

Use the Extract Body command to create an associative body by extracting faces from another body.

Front view:

Side view:

Top view:

Bottom view:

Conclusion:

            The Hood design successfully completed with help of NX Cad.

https://drive.google.com/file/d/1SIMtc34b3XtygmkLE0PL8fDtw6UeS6ZW/view?usp=sharing