Role of Pneumatic/ Hydraulics in BIW welding fixture design

Pneumatic system-

v  System operated with Air.

v  Open loop system

v  Generally used for low pressure

v  Generally delivers less force compared to hydraulic system

v  Cheaper compared to hydraulic for basic cost. But compressor running cost is more

Hydraulic system-

v  System operated with  fluid - oil.

v  Closed loop system

v  High pressure system

v  Generally used for heavy force delivery

v  Initial cost is high

v  More expensive

Pneumatic system  is mostly preferred over  hydraulic system  in BIW welding fixture.
All toggle clamp, pin cylinder, slides are operated via pneumatic.
Generally cylinder are designed to operate max pressure 12-13 bar. As it expensive and difficult to maintain 10-12 bar in shop floor it is preferred to do design pneumatic systems at 6 bar pressure

Types of Spot Welding Guns

IT- Integral Transformer
Non-IT- Transformer is separate from gun body.
MFDC- Medium Frequency DC Gun.
Depending upon the application IT and NON IT Guns are selected.

It has been observed that for under body welding application where floor width is more it is better to used Non IT gun.
In under body guns arm length is longer due to spot distance .Due to this weight increase and it is better to use NON IT gun. Transformer is mounted/hanged on top.

Many OEM not preferring MFDC guns nowadays. MFDC are costlier.

3-2-1 principle

Every part has 6 degree of freedom (3 linear + 3 rotary) which need to be arrested to ensure proper location of the part in space.The location principle used to to achieve this is called 3-2-1 principle.

1)       3 stands For - Minimum 3 Rests with clamps to establish a part plane thus restricting 1 up-down motion plus 2 Rotary motion

2)       2 stands For – Two locating pin in a round hole that restrict motion in the two directions in the established plane.

3)       1 stands For – A Round locating Pin in a slot that restricts the rotary motion in in the established plane about the round pin.

Basics Of BIW

We design BIW fixture which are frequently used for welding purpose in automobile industry.BIW is body or shell of a vehicle in stage before adding component.

Fixture is a device which is used to support,locate and hold the work piece(BIW component in case of spot welding) so that required maching can be performed.

Fixture is a special purpose devices which is used for increasing rate of production and simultaneously reduces the human effort required for producing these parts.

Its different types is given as follows

1.  Welding Fixture

2.  Machining Fixture

3.  Checking Fixture

       4.Hemming fixture 
5.Assembly fixture

Software used for BIW Spot and MIG Welding Fixture design

Various software used for BIW Fixture design.

Earlier CATIA v5 was used by most of car manufacturer for BIW fixture design except GM.
Now there is shift from CATIA v5 to UG by few OEM'S.
Daimler , FIAT shifted to UG.

            1. CATIA V5
            2. UG
            3. Fides
            4. Autocad
            5. SolidEdge (Very few)

What is BIW ?

BIW stands for Body In White which is assemble of sheet metal after welding and before painting.

Simply we can consider it as car sheet metal welded structure (body shell).

BIW consist welding of various sub-assemblies like Under body, Body side Left Hand Side/ Right Hand Side, Front End, Roof etc. which gets welded together by various metal joining process like resistance spot welding, Laser welding,MIG welding.

All the Interior Parts(Commonly used in Automotive) e.g. Dashboard, Trim (Door Trim, Pillar Trims, Roof liner, Seats are mounted on the BIW shell with the help of various brackets or nuts mounted on the BIW.

Exterior (Commonly used term in car industry) components e.g. Front Bumper, Rear Bumper, Fender LH/RH, Side Mirrors are mounted on the BIW shell with the help of various brackets or mounting systems.

 In car industry outer look defines the style. BIW sheet metal part shell defines overall car style.

Material of BIW : BIW is made of different steel grade such as DD,DP,HDP  and in some cases it is made of aluminium alloy such as audi A8.

Type Of Welding Fixtures Units

1) Rest Unit
2) Clamp Unit
3) Pin Unit
4) Combination Of Clamp and Rest Unit
5) Dump Unit

Design Input

1; System layout
2: Functional and Performance requirement
3:Car panel
4:Tool information sheet
5:Weld Study Information
6:PLP Point
7:Gun Study