Roof Design

ROOF:

A roof is a solid structure covering the top side of a vehicle. This component lies between the Back door and the front windshield of a car. It covers the passengers protecting them from sun, wind, rain, etc.

* There are multiple components in a roof:

1) Front Roof Rail

2) Rear Roof Rail

3) Center Bow roof

4) Bow roof

* Types of roof are as follows:

1) Solid roof top - This is the traditional type of roof top found in most of the cars. It is a solid structure made out of steel or aluminum or a combination of both.

2) Convertible roof top - It a rooftop made out of fabric material and with a push of a button can be retracted and stored in the trunk of the car. It is lightweight and hence offer better efficiency. This rooftop gives an option to the driver to enjoy open-air driving.

3) Retractable roof top - This rooftop is similar to the convertible roof but this roof is made out of solid lightweight materials such as aluminum instead of fabric. Similarly, with a push of a button this can be retracted and stored in the trunk of the car. This rooftop gives an option to the driver to enjoy open-air driving.

4) Sunroof - This is a type of solid rooftop consisting of a transparent section which can be fixed or can be slid manually or with a push of a button.

There are 3 types of sunroof.

a) Pop-up sunroof - The least expensive of all the sunroofs, the Pop-up Sunroof is usually a manually operated tilting panel that does not fully retract. In some models, the pop-up roof is entirely detachable.

b) Sliding sunroof - This type of sunroof can be slid manually. It is usually made up of polycarbonate material.

c) Electric / Electronic sunroof - This is similar to sliding sunroof but it can be operated with the push of a button.

Now, we will create the Front Roof Rail, Rear Roof Rail and Center and Bow roof Rail 1 & 2.

Front Roof Rail:

Rear Roof Rail:

Center Bow Roof:

Center Bow Roof with Mastic Points:

Bow Roof 1 and 2:

Bow Roof 1 & 2 with Mastic Points:

Thicken Body:

Outer Roof Rail:

Front Roof Rail:

Rear Roof Rail:

Central Bow Roof:

Bow Roof 1:

Bow Roof 2:

Final Output:

Draft analysis:

Roof Outer Panel:

Front Roof Rail:

Rear Roof Rail:

Center bow Roof:

Bow Roof 1:

Bow Roof 2:

Roof design calculations:

Heat distortion temperature is the temperature at which the metal softens and deforms under a specific load.

This study is done to check the ability of the roof to withstand high temperature with respect to the positioning of the reinforcements which contribute to increased strength.

Why Heat Distortion Criteria?

• The use of high-tensile steel sheets on car bodies has increased, and the weight of bodies has decreased, for enhance fuel economy.
• by fabricating pieces from thinner sheets. The surface areas of outer panels such as a roof panel and door outers are large, so the effects of weight reduction are also large and thereby the needs for thinner panels are high.
• Some studies have noted issues with the outside quality where, when thinner outer panels are employed, the surfaces of shells bend owing to thermal strain during the painting and drying processes in addition to issues with the stamping performance (hence, referred to as thermal distortion).
• The washing, electrodeposition, sealing, and finish coating steps are all included in the painting of a vehicle's body. An automobile body is submerged in an electrocoating solution during the electrodeposition process to create an electrodeposited film.
• The body is then put through the drying process, where hot air from a furnace is used to dry the electrocoating solution. If thermal distortion is discovered, it requires a significant amount of labour -hours for reworking and checks for numerous parts and across multiple manufacturing processes.
• Thermal distortion is frequently evaluated by the exterior check conducted for completed vehicles with various parts installed.

Countries where the summer is high, there are chances of heat distortion due to sun heat. When the radiation of sun falls on the form of your car, then due to that heat, thermal expansion occurs and due to some thermal expansion, possibility of hanging the roof of the car is more in that area and the roof of your car becomes weak in that area.

By this calculation we verify these things whether your roof will be able to withstand in that condition or not?

If so that the area is not able to tolerate this condition then we have to give better support on that area to make your roof stronger.

Step 1: We have to select a plane on which we will do all the sketches and that plane should be parallel from your roof outer surface.

Step 2: After coming to the sketch, create 0-Y which will be the centre line of your roof, from that line you have to create an offset of 300mm which will be your 3-Y, Then 3-Y has to be offset 100mm- 100 mm respectively into up and down direction.

Step 3: Project the curves of the components and find intersection points and once intersection points are created then create a line at the middle of the two points and offset the line at a distance of 100mm on each side and mark intersection points in the four region highlighted in the below image and project the points on the roof surface

Step 4: Take the arc command and draw the arc with three-point option by specification start point, end point and mid-point. This operation you have to continue with all the horizontal and vertical points you petted. To display the radius of the created arc (Rx-Ry), the local radius command is used.

Calculations: (Judgement Condition: OK< 2.7)

W = [1.73 x 10^(-3) x L] + [1.85 x 10^(-8) x (R^2)/t] + [1.10x10^(-3) x l] - 2.68

where,

L = Roof Length in X-Direction[mm](Roof dimension in 0-Y)

R = Roof curvature

R = 2(Rx*Ry)/(Rx+Ry)

Rx = X curvature

Ry = Y curvature

t = Roof plate thickness [mm]

l = Bow Roof Span [mm]

From the above table it can be concluded that all values of 'W' is less than 2.7,which implies the position of roof rails are as per standard.

SNOW LOAD PREDICTION

• Snow Load Criteria study is done to check the withstand ability when the snow loads over the roof during winter in snow fall regions. This study will also analyse the roof that whether the permanent deformation occurs after removing the snow load. That it may bend but needs to be bounce back to its original position.
• roof design must pass through these calculations to ensure that it has sufficient stiffness to withstand the load due to accumulation of snow over the roof.

Step 1: Select the Plane parallel to the roof surface and create a center line and two line parallel to the middle line at an offset value of 100mm each

Step 2: Project the curves of the Front roof rail, center and bow roof 1 & 2 and the rear roof rail and create intersection points

Step 3: Create midpoint with the help of the intersection points created and then create a line with the help of the midpoint and create offset of the line on each side at a value of 100mm

Step 4: Now, project the points on the roof surface and use the Arc/Circle command and create arcs using the projected points and once the arc is created by using the "Local radius" command in the "Analysis" tab measure the local radius

Step 5: Project the Horizontal middle axis and project the outer curve of the roof outer panel and create intersection points

Step 6: Create intersection curve of the center and bow roof 1 & 2 and perform section inertia analysis

Calculations:

Qr = [Iy x t2] / [α x s x [(Rx + Ry)/2]2 x 10-8]

Note: The Qr value given over here is correct. There was a typo error in the formula given in the video.

Where,

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

t = Roof plate thickness [mm]

Ly = Distance between the front and rear roof Rails on the Vehicle along with 0Y[mm]

Length of Roof panel with the center point between Roof rail Front /Rear as the front and rear reference point.

Lx = Distance between the Left and Right end of the roof on the Roof BOW [mm]

The width of the roof panel is exposed on the surface.

Y = Distance front Front Roof Rail to Roof BOW[mm]

s = Distance for which Roof BOW bears divided load [mm]

s = L1/2 + L2/2

Iy = Geometrical moment of inertia of Roof BOW (Y cross-section )[mm4]

Rx = Lateral direction curvature radius of roof panel Y cross-section on Roof BOW [mm]

Roof panel curvature Radius of the Length Lx in Front view

Ry = Longitudinal Direction curvature radius of the Roof panel X cross-section on Roof BOW [mm]

Roof panel X curvature radius of length s in Side view

Judgment condition

Qr ≥ 3.1

From above calculations the value of 'Q' obtained is always greater than 3.1

Note: I have attached individual files if unable to open the zip file