Roof Design

                                               DESIGN THE ROOF ASSEMBLY OF THE CAR WITH REINFORCEMENTS  ( BOW ROOF RAIL, CENTRE ROOF RAIL, FRONT AND THE REAR ROOF RAILINGS

AIM: In this project we design the roof assembly of the car with the provided input roof  surface thereby creating the supportive railings including the centre roof rail, Bow roof rails, Front & the rear rooif railings by making the aid of the master sections provided for the railings and following the proper design rules and the constrains and the design is done in the siemens nx cad software

Objective : The main objective ofthe project is to design the roof assembly accomplished bycreating  the mandatory railings at the desired location with proper  design parameters ,so that the roof can be able to  pass out the darft analysis of the componemt so that it can be manufacturable and claer the  Heat distortion test ,  snowed load condition and crash loading conditions 

Roof of the car:

An automobile roof or car top is the portion of an automobile that sits above the passenger compartment, protecting the vehicle occupants from sun, wind, rain, and other external elements.

There are at least three types of roofs commonly installed on cars, namely sunroofs, moonroofs, and also panoramic roofs. Sunroofs are often even called moonroofs. The three are actually different in terms of use and benefits

In the past roof was introduced as cover for passenger compartment but later on, it also used as a luggage carrier, sunroof and in recent past years with the introduction of the solar panelled electric vehicle got a major boost in the automotive industry.

Roof has the following functions:

• protects from external damage
• prevents passenger and vehicle from accidents
• luggage carrier
• design of the roof also affects in giving aerodynamic shape to vehicle
• sunroof
• solar panelled roof in EV

Since the roof has numerous functions so the roof has to be stronger enough to withstand the damage experienced by it. 

Sunroof

Sunroofs can be opened and closed using an electronic system. Sunroofs cars allow light, fresh air, or even both to enter the car cabin. It’s easier to imagine sunroof as a window on the car roof.

Commonly, sunroofs carry two types of panels made from the same solid metal used for the car ceiling exterior and can be pulled by hand to open the glass panel. Above it is colored glass which can be tilted backward to allow air from outside to enter the cabin.

.

Moonroof

The working systems between moonroofs and sunroofs are also slightly different. Sunroofs will open outwards when activated, while moonroofs will open backward into the car roof. Up until now, there is no standards to differentiate between sunroofs and moonroofs. For information, in the 80s, the sunroofs were only coated with metal and did not have a glass.

Panoramic roof

 

In the last couple of years, the different kind of roofs, namely panoramic roofs is embedded in luxurious cars. Recently, the panoramic roofs have become increasingly popular in premium SUVs.

This type of car roof is generally similar to the moonroofs, which has a large glass panel stretching across the roof, right above the first to the second rows. The panoramic roofs can open wider compared to the moonroofs in general. Panoramic roofs also have coating blinds to keep the cabin cool when the glass layer is closed, but the view in the sky is still visible.

Objectives of the project:

The main objective of this project is to come up with a new design for CAR ROOF from styling surfaces that satisfies,

1. The design requirements for the roof and its components.
2. Functional requirements.
3. Roll over test regulations & requirements.
4. Bow Roof position justification.
5. Snow load condition predition 
6. Joining techniques like spot welding and providing the mastics.

Design the roof of the car:

The main function of the car carry lot of functions and able to withstand the damage during the collision or any activity so inorder to increadse the strength and the stiffness to the roof we provide the additional supports called as the rails and in this project we include the following

1. Front roof rail
2. Bow roof rail 01
3. Centre roof rail with Bow roof rail inbuilt
4. Bow roof rail 02
5. Rear roof rail

The design of these rails are creted based on themaster section provided and the design rules and the parameters need to satisfy the safety criteria of the roof which includes the crash test , side load test , Bow roof rail predition and teh location along side with the snow load predition, after all passing these tests we can able to conclude that the design and the position of the rails are accurate amd these can ba able to increase the strength and the stiffness to the roof component.

Inputs :

The input surface provided from the Alias engineer is the class A surface of the roof which enables us to create the entire assembly

So lets strat creating the new assebly with the name as the roof assembly and use th wave geometry linker tpo extreact the surface of the roof to work on the outer panel of the roof 

The commands we use for the assembly are the following

• Wave geometry linker
• Bridge curve
• Offset curve in face
• Project curve
• Intersection curve

Surface commands

• Trim sheet
• Untrim
• Studio surface
• Law extension
• Through curves
• Edge blend
• Sew
• Offset surface
• Emboss
• Extend sheet.
• dart
• Section inertia analysis

Now start designing the outer panel of the roof :

For the outer panel to work on we need the wave geometry linker to extract the surface of the class A input surface provided Aand uncheck the asssociatve so that the relation should be break 

so, these holes might create the problem in the further proceedings so, use the untrim option to detach teh holes from the surface.

The master section thus provided for deigning the front end and the rear end of the ropof are mentioned in the master sections of the Front roof rail  and the rear roof rail

So just extend the surface to avalue of 6 to 8 mm and law extend the sheet to a value mentioned in the master section

 

 

Law extend the sheet along the side part to create the side flanges for the roof 

 

Now we can able to create the bride curves for filling the intersection or the cross over part inbetween the front and teh side flange

For this we use the studio surface to create the intersection surface

Now apply the proper edge blends on the sharp corners to avoid the stress concentration factor

Coming to teh rear part of teh roof outer panel

use the law extension feature to craet the rear end flange 

 

Now the falnge is create as per the master section if any valus is not mentioned accurately in the master section we need to assume a proper value as the reference nad proceed with tyhe design creation

Now sew the law extended sheets to make as a single flange

Apply the proper edge blands as mentione din the master sction to avoid the sharp edges ad the corners

So, now mirror the geometry along teh plane to for the entire outer panel

Now, sew the two componets together and check is there any gaps in the sew If , the gaps are present then the thicjken option will not work 

Now thicken the panel to avalue of the 0.75 mm downward folowing teh master section

Perform the draft analysis with a minimum darft angle of 7 deg and seklect the vector axis as the desired tooling location

 

And the side slanted surfaces are claered along teh side tooling axis 

Front roof rail design :

The master section for designing teh front roof rail provided is 

Use teh same feature wave geometry linke to extract teh surface in the outer panel to accomodate in the front roof rail for designing

Offset teh surface to a value of 32 mm below 

Nad use teh law extension sheet feature to create the flanges of teh front roof rail with the dimensions mentioned

Use teh offset curve in face feature to trim the offsetted sheet as per the mentioned dimensions 

Use the sew option to make the falnges as the single component.

Use the edge bland option to apply the corner fillets to avoid the sharp edges . Before applying teh fillets we need to provide the extra strength and the stiffness to the front and the rear roof of teh acr as these atr teh attachments with teh other parts of teh car . Such as the front roof with teh wind shield glass And teh rear roof rail with the back door assembly of the car. So, to maintain the extra strength we need to create teh darts on the slanted faces an=d the embosses on the flat surfaces these can be able to improve the strength of the front and the rear roof rail to withstnd the imapct loads 

Condition for applying teh dart:

The two surfcaes where the dart need to be placed has to be sewed properly the input values are the 

1. Angle of the dart
2. Width of the dart
3. radius of the dart
4. Distance / the % of the location of the dart

Provide as many darts as required and nned to maintain a proper clearance among the two darts and apply tehn blends for the corners of the dart

 

Apply the blends an all the sharp corners including the dart corners too to avoid the deposition of the stress concentration which leads to teh failure if the component

Now create teh embosses on teh falt surfcaes

Requirements for the embosses :

1. Fully constrained CLosed curve 
2. Face for projection
3. Plane for applying the draft
4. Draft angle 

The sketch always need to be constrained properly 

Then project the curve on to the face of the front roof with teh help of the project curve option

Now use the emboss option in the surface toolbar and provide the required inputs 

We must need to ensure thet a minimum of 5 to 10mm gaps need to be provided for the surfaces nearer to the emboss 

  

This has to mained for all the embosses provided on the surface

 Now mirror teh geometry with respect to the mid plane and sew the two parts properly without any gaps 

Now thicken the component to value of 0.75 mm outward

Now change the color of the front roof rail with ctrl +J so , that we can easily distinguish in between the rails 

Now perfom the draft analysis for the front roof rail with an angle of 7 deg for the sheet metal components 

Input are the 

1. SElect the body faces and select the front roof rail component
2. Provide the angle 
3. Specify the tooling axis direction or else provide the vector direction as the tooling axis direction 

The color variants in the draft analysis includes the 

So it clearly shows that the component draft angle is 7 or grater than 7 so it can be manufacurable or if else it pops up other colors we need to work on the surfcae or report to the class A surface team if there might be any curvature defects in the input surface provided 

 

Design of the rear roof rail :

the master section for the rear roof design is teh one which we use for the rear end design of the roof outer

Now create a datum plane for creating the intersection curve for generating the flanges of the rear roof rail 

  

Now create the offset curves on the linked surfces obtained from the roof into the rear roof rail with the help of the wave geometry feature

 

Now offset the surface to a values of  4.5mm , 6.5 mm as mentioned in teh master section and perform the trim option to create teh falnges using the offset curves as teh guides for trimming the sheet

Use teh studio surface or the througth curves to form the intermediate surface between the two flanges

sAme as the darts and teh embosses which we create for providing the additional strength to the frint roof rail follow it for the rear roof rail too

Sewed the falnges all together to form a single roof rail surface

Now create teh darts and teh emboss required 

apply the edge blends on teh sharp coners 

Now mirror the geometry along the mid plane and thicken the component outward to a value of 0.75 mm

Now perform the draft analysis with an angle of 7 deg

Almost all the surfaces are clearing the draft angle oof 7 deg 

Design of the Bow roof 01:

Obtain the surfcae of the roof in teh Bow roof design using the wave geometry linker 

Then create the Datum plane and intersection surve of teh surfcae wiith the datum palne to create teh offset curve in face for generating the flanges of the roof rail with the master sectiopn provided

As we can see that lot of dimensions are missing so we need to work on the dimensions so that all the dimensions provided should be incorporated and satisfied the length criteria of 65 -75 mm

Procedure:

• Create a datum plane at areference distance of 600  mm

• use the intersection curve option to create the intersection line on the surface and use the intersection line on teh surface 

• create the offset curve in face option to create the curves on the surfaces which are used to create theb flanges out of it by trimming the offsetted sheets which are offsetted at a distances of 6.5mm, 11.5mm , 8.5 mm 

    

• Now use the studio surfcae feature or the through curve option to form, the intermediate surface between the two flanges

• Now apply the edge blends on the corners as mentioned values in  the master section

    

Once the Bow roof rail struucture is completed check whether it has a length in between the 65- 75 mm

So the length is staisfactory we can continue further

• Now offset the side flange to a distance of 6.5mm downward such that in away when these are thickened there might have a gap of 5 mm in between the two components that is the outer roof panel and the bow roof so that the mastics acn be introduced for proper joining of the two components 
• use the datum planes and trim the offsetted side flange to the required length and use the ridge curve option to create the guide curves in between the bow roof and the trimmed side flange 
• Create the surface in betweem them using the studio surface feature by using the two guide curves for the proper surface formation

• Sew the surafces all together to get the singe surface out of it

 

• Now sketch the comb pattern on the bow roof rail so , that the stress concentration is uniformly distributed rather than of depositing o the single points which leads to the failure of the components in withstanding the high impact loads

• Now extend the sheet to an minimum value and trim it with the midpalne so, that the gaps in between the surfaces can be eliminated

• Now mirror geometry the surface of the Bow roof rail along the mid plane 

 

• Now sew the two surfcaes .

• Thicken the surfaces to avalue of 0.75 mm outside

• Calculate the section inertia modulus for the flange section

• Now perform the draft analysis to a minimum draft angle of 7 deg

Through the top toling axis 

Through the side tooling axis

The side falnges are claered the draft in the side tooling axis 

Design of the Bow roof 02:

the design of the bow roof 02 gollows teh samne mastersection as well as the same steps which are followed in the creation of the Bow roof 01

So just follow the steps mentioned above for the creation of the Bow roof 02 

Apply the edge fillet at teh corners of the bow roof rail to avoid the stress concentration factor

calculate the inertia section modulus for the solid

Perform the draft analysis to an angle of 7 deg

The length of the Bow roof rail 02 is

 

DEsign of the centre roof rail with the Bow the Bow roof rail included  :

The master section provided for the design is 

So, the length of the flanges acn be taken as the reference such that after formation of the roof rail the length should lies in the range of 80-90 mm

So as it was a centre roof rail create the datum plane at teh centre of the curve to create teh intersection curve 

    

Now using the intersection curve create the offset curve on face with suitable dimension for thr creation of flanges such that the length of the rail satisfies

Then create the flanges with the help of the offset curve on faces by trimming the offsetted faces which are offsetted at adistance of 7.25mm, 15mm, 12mm

measure the distance between the falnges as it satisfies the length condition

.

Now use the studio surface to create the intermediate surface between the flat surfaces. Now sew the surfaces together and apply the edge blend of appropriate value 

 

Now offset the side flange and form the intermediate surface between the centre roof rail and the side flange using the bride curve and the studio surface features

 

Now sew the surfaces together and mirror geometry the surfcae and sew the mirrored surfcaes  amnd create teh emboss for providing the external strength and stiffness

Now thicken the surfcae to  a value of 0.75 mm upward 

Now calculate the section inertia analysis for the centre roof rail

Now perform the draft analysis 

.

Now use the same operations to create the bow roof rail in the centre roof rail and perform the draft analysis 

The length of the bow rail in teh centre roof rail is 

Perform the draft analysis

 

Now checking the gaps for the mastics locations which are used to attach the rails with the roof outer panel

Now measure teh distance of 5 mm claerance for the mastics for each roof rail by using teh clip section view

Front roof rail 

Bow roof rail 01

Centre roof rail

Bow roof rail 02

Rear roof rail 

once all the design process is completed Then save all the parts as a single assembly file and proceed for the calculations

ROOF CRUSH TEST :

Roof crush test is the design given by the IIHS ( insurance institute of highway safety ) . After analyzing the many accidents IIHS has then fixed some regulations , that how to perform the  crush test .

IIHS gives the rating based up on this test . For this they consider two points while giving the rating

• How fast the car can reforms to its original shape after the roll over and
• How deep is the protrusion after the roll over

 

Bow–Roof Prediction Formula

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]

Judgment Condition

OK< 2.7

Project the 5 points of the grid on to the roof oute panle and calculate the Rx And the R y values

 

Now all the valuesare obtained and calculate teh bow predition in the excel sheet and the obtained values 

We need to calculate for the following

1. Front roof rail & the Bow roof rail 01
2. Bow roof rail 01 & the centre roof rail 
3. Centre roof rail & the Bow roof rail 02
4. Bow roof rail 02 & teh Rear roof rail

For all the Bow predition calculation we get the values less than 2.7 so our position of the rails are correct and we can proceed for the snow load calculation

Bow roof prediction formula	Rx	Ry	t	l	L	R	W	Judgement condition
Front roof &n Bow roof 01	2801.79	5719.512	0.75	467.01	2034.6	3761.132	1.702507	Ok
Bow roof 01& centre roof  Rail	6209.83	4969.22	0.75	401.7	2034.6	5520.686	2.033518	Ok
Centre roof rail and bow roof 02	9795.65	4135.08	0.75	443.396	2034.6	5815.316	2.161768	Ok
Bow roof 02& Rear roof rail	13937.46	3380.63	0.75	512.06	2304.6	5441.408	2.600577	Ok
	All dimensions measured above table are in mm

 

 

Snow load calculation:.

SNOW LOAD CRITERIA :

This test is done to know how is the roof behaving when there is a snow over . normally  due to the snow weight the dent will happen. But the  roof  should be designed in such a way that when the snow is removal the roof should go it its original position . This is the basic requirements for snow load criteria .

 

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

Where

α = My x Lx2 x 10-12 , My = Y(Ly-Y)

Judgement condition = Qr ≥ 3.1

                250 ≤ s ≤ 380

 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 reference point of the front and the rear.

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

        Width of the roof panel 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]

 

 Calculate the Qr values by finding all the values relted for the formula 

 

snow load condition
	Rx	Ry	L1	L2	Ly	S	Y	My	Lx	α	t	Iy	Qr	judgement
Front roof &n Bow roof 01	2833.25	4379.28	546.94	413.58	1959.54	480.26	546.94	772607.4	1181.656	1.078801	0.75	265.817	2.219077	NG
Bow roof 01& centre roof  Rail	6397.45	3779.94	413.58	431.335	1959.54	422.4575	960.53	959579.1	1133.783	1.233504	0.75	792.244	3.302516	OK
Centre roof rail and bow roof 02	10589.6	4235.5	431.33	567.67	1959.54	499.5	1391.86	790131.1	1109.495	0.972635	0.75	266.918	0.562445	NG
Bow roof 02& Rear roof rail	15873.21	4091.67			1959.54

so, the Qr values are not satisfied in the case of the Front roof & bow roof 01 , and in the case of Centre roof rail and the bow roof 02 

So the snow load condition is not good so , we need to provide additional strength on teh roof outer panel to incorporate the snow load calcaltion failure so , that the roof can be able to hold the snow load condition 

For this we create the embosses on the roof outer panel covering the area under the failure of the snow load condition 

 create the datum plane for the sketch

Now crete the sketch for the embosses

project teh sketch on teh roof using the project curve feature

Now crete the embosses and apply the edge blends on the corners properly as it was the aesthetic surface and is visible to the customers so, create the embosses in the more aesthetic surface without any improper surface

crete the required embosses on the roof 

perform the draft analysis on the roof with embosses supports 

 

manufacturing techniques :

The manufacturing process of the roof follows the following steps 

1. Formability analysis 

Formability is the efficiency of a given sheet metal to undergo a plastic deformation without fracturing and damaging or without any kind of failure. However, the deformation efficiency of plastic of metallic sheet parts is limited to a certain extent at which the part could experience wrinkling, fracture or tearing. The general parameter which indicates the formability of the sheet metal part is the crack or fracture strain determined by uniaxial tensile testing. Additionally, formability depends not only on the properties and parameter of the material but also depends on the process factors in practical forming operation. This paper paid special attention to the forming process factors in the manufacturing of sheet metal domain, such as wrinkling, rupture, and springback. These factors usually occurred in the manufacturing process due to the sheet metal property.

2. Spring back defects

In the automotive industry springback is one of the major factor influencing the quality of stamping sheet metal parts. In most dynamic metal forming operations, the nonlinear deformation process tends to generate a large amount of elastic strain energy in the blank sheet. This elastic energy that stored in the blank sheet will release while pressure is removed. This release of energy is the driving force of springback, generally causes the blank to deform towards its original geometry. Hence, the final part shape in a sheet metal forming process depends on not only the contours of the dies, but also the amount of elastic energy stored in the part while being plastically deformed.

Springback is the hotspot focused in the field of sheet metal forming and stamping. It causes the inaccuracy of the part shape so that prediction and compensation of springback is significant to obtain the final desired shape. The part final shape depends on the springback amount formed. If the springback amount exceeds the tolerance allowed, the part size precision become reduced and failed to satisfy the requirement of assembly. In order to compensate the size deviation caused by the springback, it is needed to use the latest automobile sheet metal forming technology rather than traditional try and error die process.

 

The Design of Blank Shape and the Direction of Drawing

Most automobile panel shapes are complex and difficult to get through to start the initial blank geometry shape. In addition, the geometric expansion factor does not consider plastic deformation. Practically, variations in material properties, thickness distribution, blank dimensions, environmental conditions and springback properties make the reproducibility and predictability of a blank sheet metal forming process quite difficult.

The selected part is relatively simple design using Dynaform to estimate the stock load and to get directly through the geometric shape of the initial blank sheet metal. The simplified rectangular blank sheet metal shape model shown in Figure 1 has the maximum die size 30 cm, the smallest cell size 0.5 mm, and the offset rate 0.05 mm mesh parameters.

In actual production, sheet metal (blank shape) is placed on the blank holder and the blank holder is the part that holds the sheet metal while the punch force is applied. Punch is a curved and relatively large degree of bending force placed under the blank holder, bounded by gravity. If the simulation set the blank sheet metal without calculating the shape deformation then it will certainly bring some errors. However, it must first set on top of the mold and calculated after the shape deformation due to gravity. In Dynaform, a module used to calculate the gravity load called the gravity loading. The model shown in Figure 2 is the calculated result of rough, coarse and a re-refined mesh of the blank sheet metal.

The result shown in Figure 3 is the blank sheet metal after the gravity loadbounded by gravity to bend.

The analysis of the forming of the auto roof panel should first determine the direction of drawing. Automobile roof panel is the part of the car body, according to its installation position and the consistent order the part should be placed at the roof of the car. In most cases when placing the car body parts automobile companies use the press fit in the convenient direction in order to avoid inconsistent placement of the body parts. Even when designing, choosing the appropriate direction of the drawing will determine the smooth implementation of the

direction of stamping process. See Figure 4.

5.2. Blank Sheet and Mold Parameters

After taking stock of the grid model of gravity loading and further refinement take the grid size 10 mm, the billet steel plate thickness is 0.7 mm and the calculation automatically by the program areas of intense deformation re-division of the minimum mesh size 2 mm. The sheet metal parameters are defined as follows, the sheet metal thickness 0.7 mm, Poisson’s ratio (V) 0.3, elastic modulus (E) 207 GPa, tensile strength (TS) 3 MPa, yield strength (σ) 174 MPa,, mass density (ρ) 7.83 × 109 kg/mm³, strain hardening coefficient (K) 518 MPa, thickness anisotropy coefficient 1.91, 1.65 and 2.2 and the hardening coefficient (n) 0.242 Pa.

In the molding process stamping simulation of the blank sheet usually set in three phases, such as simulation of the blank holder (closed stage), forming simulation stage and unloading springback simulation stage. In the closing stage, the blank holder must be added before the forming simulation stage, but no blank holder force should be applied, and the drawing type is single action. Moreover, the upper and lower blank holder gap is set to (t) as a blank thickness together and speed is 5000 mm/s. See Figure 5 and Figure 6.

5.3. Addendum

Addendum is a key element in the part of the stamping process design. Stamping direction is determined by the direction of drawing to meet the requirements of the implementation process. However, the vast majority of auto body panel which requires stamping are determined by the shape, contour or depth of addendum designed draw bead. Advanced stamping process design is an important indicator whether the addendum parts directly affects the drawing process while the deformation parameters rough conditions applied. The size of deformation, the deformation distribution, surface quality, cracking, wrinkling and other problems are the indicator of design failures. Addendum should be designed to comply with the car body panel complementarily with the whole surface part, in a simplified structure and attractive enough. See Figure 7 and Figure 8.