Design of backdoor
AIM:
To design the back door inner panel with the styling surface as input with all the necessary engineering features that strengthens it using software NX CAD.
BACK DOOR:
The back door is a BIW(Body In White) rear part of the car which protect the passenger from rear crash. It also used to shape a compartment for the boot space. The rear windshield, brake lamps, license plate, car logo ,wiper are mounted on the back door.
The back door is designed in a way that it should fully utilize the injury-avoidance for the passengers in the car. There are certain regulations that a back door should displace a certain length during the application of load . The back door designing and production must meet those requirements.
Depending on the model of the car the back door is used for example in Suzuki swift it can be used only for cargo loading often called as trunk lid yet in the case of Mahindra bolero,it is used for passenger entry or exit.
DESIGNING OF BACK DOOR:
ASSEMBLY: The assembly of back door in NX consists of outer panel ,inner panel,hinges,gas stays, wiper motor,latch and their respective reinforcements.The following figure clearly depicts the assembly of back door.
FEATURES IN BACK DOOR PART: The following features used in the designing are frequent one.These are used repetitively.
Emboss: The emboss is used to extrude a part in back door which is bounded by sketch . It adds strength to the part.Embossing is typically used to indent the metal with a design .
Trim sheet: This features removes a certain part guided by boundary objects.Holes, cut-outs can be achieved by the trim sheet feature.
Offset curve in face: The curve is drawn on the surface of the part at some offset distance from the original curve .
Through curve mesh: The role of this feature is use to fill the surface that is missing or removed using primary and guided curves.Overlapping,non-intersecting faces can be repaired using this feature.
Bridge curve: The curve that connects two edges.The bridge curve is used to act like guide curve for the through curve mesh.
Curve on surface: It is similar to offset curve in face but instead of offseting ,we generate curve by drawing points on the surface.Corner edges can be removed using this.
Edge blend: The blend is used to smoothen the sharp edges as it affects the produceability of the parts.
TOOLING AXIS:
When a part is manufactured using any process like deep drawing or stamping etc., it must follow a direction to done the work.That direction is called as tooling direction.The curve is usually normal to the surface. Depending on the part geometry we use one or more tooling direction.
BACK DOOR OUTER PANEL:
The back door outer panel is comprised of two portion the upper one and the lower .The upper is used for mounting the windshield ,wiper blade,car logo .The lower will usually carry license plate.In the following image the part in strong brown is upper and the rest is lower.
BACK DOOR INNER PANEL:
The inner panel of back door is the habitat for all the engineering features.The inner panel is called as engineer's surface.The reinforcements for the hinge,gas stay,latch and striker,wiper motor are placed in the inner panel.The embosses are placed in the inner panel for improving the strength.
In the following figure,
1 - The surface is extruded upwards near the outer panel having the distance between outer and inner panel as 4-5 mm for the mastic sealant placement.
2 - It is depression in that area throughout the inner panel for the mountin rubber sealant that fills that gap when closing the door leaving no gap.
3 - The dots represent the spot welding which connects the outer and inner panel.
LATCH TRAJECTORY:
A path tracing the opening and closing of the back door leads to the mounting of latch and striker in precise position,for that hinge axis is taken and a perpendicular line is drawn with the hinge axis as centre draw a circle that touches the approximate position of the striker.The striker axis must be perpendicular to the trajectory circle in order to get that hinge position is adjusted till the striker gets the required position.
REINFORCEMENTS:
When an additional part is attached to the parent part ,the area will have an negative impact on the parent part strength.To compensate that we have to introduce these reinforcements.Here we have four reinforcements which are named as hinge reinforcement,gas stay reinforcement,latch reinforcement,wiper motor reinforcement.
DRAFT ANALYSIS:
To check whether a part is produceable or not we have to make an analyse on the product before sending the drawing to the production unit.Draft analysis play a vital role in that .With a tooling axis the part is checked for necessary draft angle that is recommended in engineering standard.For sheet metal the draft angle is about 7 deg.for solid it is about 3 deg.
** Calculation of section modulus, examining geometry , check mate are other analysing tools which used to improve the part**
PRODUCTION OF BACK DOOR:
The production process of back door is done by,
i)DEEP DRAWINNG:
Deep drawing is used in the shaping of sheet metal .Deep drawing of sheet metal is performed with a punch and die.
The punch is the desired shape of the base of the part. The die cavity matches the punch and is a little wider to allow for its passage, as well as clearance. The schematic diagram represents the deep drawing,
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The emboss formation is a sheet metal operation achieved by deep drawing where the male and female die is used for the required shape
Tearing is the defect that arise in deep drawing which may arise due to excessive force applied, thinning of sheet metal.
ii)STAMPING:
Stamping, also referred to as pressing, is a low-cost high-speed manufacturing process that can produce a high volume of identical metal components. The stamping operation may consists of one or more series specific operations like punching,blanking,coining etc.,
HEMMING:
Hemming is a edge bending operatioin performed on sheet metal,a type of flange .This process helps in joining of outer panel with the inner panel.There are various types of hem like open hem,close hem.
JOINING OF SHEET METAL:
The joining process in back door can be achieved by,
i)Laser brazing:
Laser brazing is the joining of two metals by melting the filler material between the two parts unlike melting the base material in rest of the welding methods.This joining method gives a attractive look which is not achieved in others.
ii)Spot welding:
The spot welding process involves, joining of two metal pieces together one above the other.Current is passed into the metal pieces by copper electrode welding guns,as the current passes the metal acts as resistor and get fused together due to heating. A car can contain about 5000 spot weld spots.
CONCLUSION:
The back door/Tailgate is designed with all necessary reinforcements and embosses successfully. The back door is analysed for manufacturability using draft analysis.
References:
1.Deep Drawing Of Sheet Metal (thelibraryofmanufacturing.com)
2.Why Automotive Spot Welding Is More Popular Than Ever | Intran
3.ALO3 Adaptive Laser Brazing Optic | Product Overview - YouTube