Hood design-Week 2

Hood Assembly Profile:

Introduction

        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. In design perspective hood should meet some specific conditions like pedestrian safety, hood head zone for the lock striker, force distribution when subjected to frontal collision (occupant safety), manufacturability etc.

          A typical hood assembly consist of hood outer panel, inner panel, latch and striker, hinge, hood stay. Hood stay is an apparatus for supporting the engine hood of a moto vehicle in its open position. The purpose of opening the engine hood is for inspecting engine room, replenishing cooling water and engine oil, changing parts and making repairs etc. Common types of hood stays are Support Rod and Gas Stay. Support rods are manually operated and they are cost effective and simple to design whereas gas stays require no man power but they are costly. Hood are typically made out of the same material as the rest of the bodywork. This may include steel and aluminium. Deep drawing, hemming, blanking and piercing are the common sheet metal operations that are used in manufacturing hoods in automotive industries.

Design parameters

Hood Thickness Information

Outer Panel Thickness = 0.75mm

Inner Panel Thickness = 0.75mm

Reinforcement Thickness = 1.5mm

Hood Design: -

                  Car hood/bonnet is a hinged cover that rests over the engine in a front-engine car. A latch is provided under the hood in order to prevent accidental opening during driving. Purpose of hood is to provide access to the engine and battery for repair and maintenance. It also protects these parts from direct sunlight and dust.

• Components

                    The car hood consists of following components,

  1) Hood Outer Panel

                           The outer panel works as a metal cover. It is responsible for aesthetics of the vehicle.

2) Hood Inner Panel

                         The inner panel provides strength and supports the outer panel. It is where hood balancer and hinges are attached.

3) Hinges

               Hinges allow the hood to rotate around a fixed axis for opening and closing movement. One part of the hinge is fixed with the engine compartment, while other part is connected to hood.

4) Latch and Striker

                          Latch and striker mechanism is provided to lock the hood, in order to prevent accidental opening of the hood during driving. The latch is present on the engine compartment while the striker is attached to inner part of hood.

• Latch Trajectory:

                    It is the path along which the hood rotates during opening and closing movement. The striker on the hood follows a particular path while opening or closing the hood, which is along circumference of a circle with centre at the hinge axis. This path is nothing but latch trajectory. It is a very important aspect in hood design, in order to decide hinge, latch and striker installation points.

• Mastic Sealant:

 

                      Mastic sealant helps to locally improve strength of the hood. It is generally a hard rubber part, which is introduced as a paste in between inner and outer panel of the hood, which will get hardened inside the furnace. Every mastic sealant point will have a tendency to improve the local strength in around 80 mm diameter. Considering this, the mastic points are positioned such that most of the hood region is covered.

• Design Methodology:

                     The procedure followed for designing the hood and its components is as follows,

• First the inner panel is designed from the given master section using the various commands and features. We create the embossing using the offset surface from the original master section. Similarly, we create the cuts on the emboss by sketching and using trim surface option.
• Then the outer panel is designed from the same master section. Here we are supposed to provide the hemming to outer panel. The parameters of hemming are taken as per given values.

• Now, on the inner panel, the embossing for hinge and striker are produced by considering their respective dimensions and assembly positions. First the emboss for hinge is created and then by fixing the hinge into its position, we draw an axis passing through both side hinge axes to form a common axis. And then we position the striker such that it will move along circumference of a circle whose centre is at midpoint of the common axis. Thus, position of striker is decided and we can create emboss for the same.
• Using the hinge emboss we created, we can create our hinge reinforcements by creating new parts in the assembly itself.

Data Provided

                    Outer Panel Thickness – 0.75mm

                    Inner Panel Thickness – 0.75mm

                    Reinforcement Thickness – 1.5mm

Important Features used in designing:

• Trim Body – It is used to trim one or more bodies using a face or plane. You can also specify the bodies to retain and the bodies to discard.
• Offset Surface – It allows you to offset one or more existing surfaces.
• Offset in Face – This command will allow you to offset particular edges or curves on selected faces.
• Trim Sheet – It is used to trim off a portion of a sheet body using curves, faces, edges or planes.
• Through Curves – It will allow you to create a body Through multiple sections, where it’s shape changes to pass through each section.
• Law Extension – This command extends a curve or edge to create a sheet body at desired angle length by changing the rules under angle law and length law.
• Trim and Extend – It helps you to trim and extend intersecting surfaces and make corner at their intersection.
• Face Blend – It creates fillets between faces.
• Edge Blend – It creates fillets on edges.
• Extend Sheet – It will allow you to extend an existing surface to required distance.
• Emboss – Emboss command creates an embossing by modifying a body with faces created by projecting a curve/section along a direction. You can modify the emboss using options like endcap location and draft angle.
• Projected Curve – It is used to project an existing curve/curve on a selected plane or surface by selecting a direction for projection.
• Mirror Geometry – As name suggests, it allows you to mirror geometries about selected plane or surface.
• Sew – It combines sheet bodies together by sewing their common edges. There shouldn’t be any gaps larger than specified tolerance.
• Thicken – It is used to convert a surface to solid body by providing thickness.
• Extrude – It helps you to create a feature from a sketch. You are also able to create thin feature using a sketch or curve under this command.
• Wave Geometry Linker – With this you can create, associative or linked copies of any entity of a part into other parts. It may be a surface, edge, curve, body, sketch etc. The changes made to the original entity will be reflected in the copy of that entity.
• Hemming –Hemming is a forming operation in which the edges of the sheet are folded over other part or simply folded in order to achieve a tight fit. 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.

Conclusion:

The design considerations for the Hood is taken are discussed and taken into consideration while designing the hood.The manufacturing feasibility of the hood is taken into consideration.Draft Analysis is performed to check if the faces are clearing for the required draft angle for manufacturing the emboss.