Hood design-Week 2
TOPIC : HOOD DESIGN
To design the car hood and understand the mechanism behind the design of hood, then development& its safety features as per the design consideration.
The following task is performed:
- Design Outer Panel with the Hem
- Develop the Inner Panel
- Develop all the Necessary Reinforcements
- Mirror and position the Hinge & Striker
- Provide Mastic Data
- Provide the required Emboss definition
- Develop a detailed Report for the Mastic position and Embosses you have placed.
Design Considerations in Hood
While designing a hood several design parameters are to consider such as the opening angle of the hood, Support system for the hood, Pedestrian safety rules, etc.
Hood head zone for striker locking: While designing the hood this parameter should be taken into consideration because when we open the hood to get access to the engine compartment to perform any operation while the hood is in open condition the minimum height of the hood should be such that it does not collide or hit to head of the person who is operating. So, the height of hood in open conditions should be more than the average height of humans in that region thereby no human gets hurt.
Following data should be used for deciding Hood head zone
Hood Stay:
This is the support system for the hood as when we open hood we need it to rest to keep it in open position & this can be done by placing it over something or by providing support to it. While designing this one should keep in mind that the support system should be self-sustainable to take the load of the hood even if any external force is been applied on it due to wind or any other reason & it should facilitate easy opening and closing of hood.
Support Rod: It is a rod that accommodates itself easily inside the engine compartment and support the hood when we open it by attaching the rod in the hook provided inside the hood. Initial bends are been provided to the support rod to provide stiffness.
This can be done by using two ways
1. Support Rod
2. Gas stay
Gas Stay: This type of apparatus is used in most heavy vehicles where the weight of the hood is more and it is difficult for a human being to open it conveniently. So, basically, a gas stay system uses gas-filled telescopic cylinders which only require an initial force to set it in motion.
Hood assembly components:
Now let's have a brief discussion about how a hood assembly is done what are the main components involved in it. So, we know that any assembly consists of two or more parts joined together to form a complete product.
Hood also embodies several parts they are as follow:
1) Hood outer panel or skin of the hood
2) Hood inner panel
3) Hinge assembly
4) Striker
1) Hood outer panel:
This part of the hood acts as a covering or casing for all the other parts of hood which are enclosed inside this part. The outer surface of this part is provided with a good surface finish, painted with corrosion-resistant paint to prevent the inner parts from corrosion and also to give an aesthetic look to the car from the outside. This part forms the shape of our hood and it is given different styling and shapes to enhance the look & performance of the vehicle to reduce the forces exerted by air when the vehicle is in motion.
Fig. 3.0 Hood outer panel
2) Inner panel:
This part is enclosed in the outer panel it forms an integral part of the hood and provides rigidity to the hood, it is the part on which hinges, striker are to be fixed to make our hood fully functional it also consists of embossed sections for proper force distribution and mastic sealant points are also located on this part with reinforcement for hinge & striker. To reduce the weight of our hood some material is removed from the hood inner panel as shown below.
Fig. 3.1 Hood Inner panel
3) Hinge assembly:
It is an important part of our hood because by use of this part only we are able to open and closed our hood whenever required with ease. This part should be strong enough to take the load of the hood and also the forces which act upon the hood in case of crash. So, this part should be designed with utmost care that it should not fail during its operation.
Fig. 3.2 Hinge assembly and its placement on hood inner panel
4) Striker:
This part is used for providing locking to the hood it consists of a latch-type mechanism and it is located on the inner panel of the hood to decide the position of our striker, the trajectory method is used with the help of this method we can easily locate our striker. This part holds our hood in closed condition unless it is being open by pulling the latch lever to open our hood.
Fig.3.3 Striker
Now to start with our hood design some standard or master data is to be followed for deciding the dimensions of our hood such as thickness of inner and outer panel, heming data, etc.
Hood input data:
- Thickness of outer panel: 0.75mm
- Thickness of inner panel: 0.75mm
- Reinforcement thickness: 1.5mm
This thickness is to be followed throughout the hood design
Master section:
This data is used for the design of our hood inner panel it gives all the information about the standard dimensions to be followed for the inner panel also information about radius values, maximum height of the hood inner panel from the top.
Manufacturing processes for production of hood inner & outer panel:
Hood inner & outer panels can be manufactured by performing forming operations on a thin metal sheet.
Deep Drawing:
Deep drawing is a sheet forming process in which a sheet metal blank is radially drawn into a forming die by the mechanical action of a punch. It is thus a shape transformation process with material retention. The process is considered "deep" drawing when the depth of the drawn part exceeds its diameter. This is achieved by redrawing the part through a series of dies. The flange region (sheet metal in the die shoulder area) experiences radial drawing stress and tangential compressive stress due to the material retention property. These compressive stresses result in flange wrinkles (wrinkles of the first order). Wrinkles can be prevented by using a blank holder, the function of which is to facilitate controlled material flow into the die radius.
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 that 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.
Heming:
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 and production.
There are two types of heming process use:
a) Conventional die Heming
b) Roll Heming
a) Conventional die heming:
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. Production plants for conventional die hemming are very expensive, but the cycle times are very low
b) Roll Heming:
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 that follows a defined path.
PURPOSE OF HOOD DESIGN
- Safety of the passenger.
- Covers all engine, radiator, and other necessary components.
- Reduce air effect due to its aerodynamic shape design.
- Reduce engine noise which helps for a quieter drive.
- Provide access to engine maintenance.
- Absorbs most of the impact forces when a frontal crash occurs.
CONCLUSIONS
It was to ensure that the new design of hood performs satisfactorily under a variety of loading conditions and thus can function satisfactorily during its normal operation. With this objective in mind, the design had been subjected to a variety of loading conditions which involved impact loads, static loading, and vibration. During the analysis, it has been observed that the design is capable of sustaining all the loading conditions with satisfactory performance. The deformations were well
within limits for the load cases as were the stresses. Thus, with this design verification procedure, it can be concluded that the proposed design of the bonnet meets the various safety and quality parameters setforth by the various testing
and standards organisations.