REPLACEMENT OF MIG(CO2) WELDING IN BIW FABRICATION OF 709 AND II09 LPTProject byVishwarath Taduru,GET-CVBU(PUNE).Under the guidance ofMr. Ishwar Babar (Senior Manager-Production),E-BLOCK.

PROLOGUE

Strive for perfection and you will reach excellence

Seek the best, ask for it, work for it zealously and you will get it.

My experiences in TATA motors-E-BlockWhat I liked and desired:The brand name enabling loyalty- It is engraving, exercising and energizingb. Close co-ordination between various functional departmentsc. Co-operative people d. Availability of resourcese. Core subject project-Manufacturingf. Freedom to move around absorbing knowledge.

As technology advances there is more stress on replacing conventional welding processes with more economical, aesthetically superior and environment friendly technologies. Taking this into consideration Tata Motors has provided me the opportunity to undertake a project for replacing of CO2 welding with spot welding or other alternate processes. The area of operation is cab-cowl line(E-6) where cabs and cowls of MCV vehicles like 707 LPT are fabricated. I am ably guided in my work by Shri. Ishwar Babar (Sr.Manager) who provided me with many valuable inputs during the course of the work.The objective of the project is to ensure that the BIW has the least application of CO2 welding. The fabrication process done in-house and components obtained from outside should be free from the CO2 welding.

INTRODUCTION

ROADMAP TO IMPLEMENTATIONWeld data acquisition esp. of CO2 weldFamiliarization with processesObservations and suggestionsValidation from ERCFeasibility studychangeyesImplementationPrototypeImplementationAlternativesnoAdvanced Developmentsstudy

Details of CO2 welding in the fabrication process for single cabLEGEND

F-Feasible

NF-Not feasible

R-Reduce

In-house improvements1) MANUFACTURE STAGE

2) DESIGN IMPROVEMENTS

ALTERNATE WELDING PROCESSESFigure 1- Trends for welding processes in BIW assembly across the world

WELD BONDING

Adhesive application is followed by spot welding to position and fixture the parts together accurately before the heat-curing adhesives harden to full strength during the paint process.

Advantages:1)The adhesive enables an evenly stressed, fully sealed joint to be formed

2) The number of spots are reduced and the potential for localized high stresses is minimized through the action of the adhesive, which is the primary load carrier.

3) Adhesive bonding is a well-known complement to help resolve problems with cracks around spot welds occurring as a result of fatigue loads. BUTWeld bonding requires special preparation of surfaces before the process is applied. The joint characteristics also depend on the room conditions which affect the curing properties of the joint by as much as 50%.

CLINCH WELDINGClinching, also known as press-joining, is a joining technique for sheet metal in which plates undergo plastic deformation.

When clinching, the connection is established using simple tools: a punch, a die and possibly a stripper.

Clinching provides advantages such as low consumption of power and also joining dissimilar metals. But it also suffers from following draw backs:

a) Special equipment(dimensions)b) Initial capital expenditure is high (about 20% more than spot welding equipment)c) High pressing force

The strength of clinch joint is comparable with spot welded joints. Active research is going on in this area.Small equipment can be hand held or suspended. Pedestal stand alone machines may be used, or complex robotic cells can be assembled, sometimes with multiple working heads.Failure limit (N)

DETAILS OF EACH PROCESSWELD DATADESIGN REQUIREMENTSUGGESTIONFEASIBILITY ANALYSISACTION TAKENIMPLEMENTATION

FRONT GUSSET CO2 WELDThe current front gusset weld is done at the bottom as well as on the front flange of sub-structure.

It may not be feasible to replace weld run of (a) with spot welding at present as it requires the design of top down rotating fixture and spot weld machine of appropriate reach.

Spotting may be done between the front edge and substructure as shown in (a)(a)(b) The welding done at the bottom face of (b) is not feasible to replace with spotting as the face of substructure is curved.

The weld run between C-channel(1) and gusset bracket(2) is done on the gusset assembly.

An alternate C-channel post which has a rear face with tug (dimple) is as shown in (b).

This face may be used to spot this bracket with gusset. The tug provides additional strength to the member.(a)(b) This will lead to elimination of CO2 welding at this juncture which is further reinforced in cab full welding.

The alternate arrangement is as shown in Fig . (c)12

FRONT GRILL WELDING Four tacks of 40 mm are done on front grill and sub-structure. At present 20mm tack weld is done between front grill and substructure at the middle for support. It is not feasible to eliminate this process or replace it with spotting at this stage as there is no approach for the spot welding gun.

IDEA The procedure of tack welding may be eliminated by providing for High Pressure auto clamps which may be used directly at Stn-4 and do spotting between step panel inner and front grill (OR) between fire wall and front panel

TACK WELD OF FIRE WALL WITH SIDE WALLAt present 210 mm of CO2 welding is done between the side wall and sub-structure on LH and RH side. It is not feasible to replace this with spot welding but the extent of welding as per drawing is 15mm+60mm on both inner and outer side. This may be reduced.

Clearly defined process flow is to be mentioned in place of availability based process plans.

In the modified cab design only 2 tacks of 20 mm each are done for the outer flange and one tack on the inside.

ROOF PANEL TACK The welding between roof panel and side wall takes place at four places of 60 mm length. It is feasible to replace this with spot welding and it requires fixtures like aperture gauge fixture at the initial stations to hold these components in place and do only spotting. We may also opt to go for keyways and slots between the roof panel and the side wall. Thus we may fix the component in place and go for only spotting. As the welding is done only for tacking and is negligible modification is not done at this stage for the sample cab.

IDEATo eliminate tacking it is feasible to provide for alternate joining arrangements like key and slot between the side door and roof panel. After insertion into the slot of roof panel the operator turns the key to lock it in position.

One consideration is whether the key will have sufficient strength to withstand the weight of the entire structure when lifted by hoist-tackle.

To ensure the success it is advisable to have a conveyor belt type of system which may not be a feasible idea.

FRONT PANEL TACKThe front panel is mounted on the sub-structure and 15 mm of tacking is done at three placesTo avoid tack welding at this stage it is necessary to use grip clamps that hold the front panel and only spotting is done at the subsequent station.

The aperture gauge is used it also does the same function.

As the weld length is negligible it may not be feasible to incur expenditure for bringing in very minor changes

REAR WALL AND REINFORCEMENTThe rear wall is tack welded with the side wall at four places of 60 mm length. The tack between roof reinforcement and rear wall is of 20 mm length.It is feasible to replace the roof bow tack with spot welding if we use hand grip fixture to hold the components together.

Then there is approach for the spot gun from inside the rear wall window and top. It requires use of specially designed spotting machine.

The rear wall tack to side wall is of 60 mm length (LH/RH).It can be avoided in if we use keys and slots to hold the components together and send directly for spotting at subsequent stations.REAR WALL TACK WELDING TO SIDE WALLThis process is left untouched as the weld length is very small.

DASH BOARD WELDINGThe dash board tack of 40 mm is done at Stn-3 followed by full welding at conveyor line of length 150 mm. Three runs are made for the entire assembly.It is not possible to replace this with spot or other processes as the metal CS area is high.

It may be feasible to have a bolted dash board as for HCV in tilt body format.

For dash board bolting the factors to be kept in mind are: i) Time consideration-effect on productivity ii) Strength and durability-limitation on ruggedness.iii) Alternate design of dashboard featuring nut

Figure showing bolting as is done for HCVFig .NUT welded onto dashboardFigure showing nut and weld run for cab For the trial cab the approach of bolting and then performing two weld runs was implemented.

UNDERBODY WELDThe under body weld length is of 360 mm. The current practice is to tack weld at 6 places with 30-35 mm length on both sides.

The CO2 weld length may be decreased by increasing the no. of spots between the side panel inner and sub-structure at Stn-1.

Fig-Spotting may be increased.Underbody CO2 weld

The underbody CO2 weld according to drawing is 6 tacks of 20 mm length. This sums up to 240 mm of CO2 weld length compared to 360 mm followed currently. One way to reduce this excessive welding is to provide checking gauges with slot of 20 mm so that the workman gets the perception of what should be approximate weld size. The operator was clearly explained what the weld length should be before performing the operation and the outcome was reduced weld length to required standards.Fig-Drawing portion of underbody weldFigure showing less amount of welding20

FRONT PANEL TACKThe front panel tack of 30 mm on conveyor belt may be avoided

b)a) Figures showing the front panels of the cabs with and without the unnecessary CO2 tack weld.

SIDE WALL WELDING TO FIREWALL.As per design requirement 100 mm of CO2 tack welding is sufficient on the conveyor belt. This contrasts with approximately 170 mm of CO2 welding done presently on both LH/RH side.

The correct weld positions and dimensions were marked on the cab before performing welding operation resulting in reduction of weld length.20

SUBSTRUCTURE FULL WELD

The substructure to the fire wall full CO2 weld is currently 420 mm comprising 14 tacks of 30 mm length.

It is feasible to reduce this much CO2 welding by increasing number of spots between sub-structure and fire wall in Stn-1 by allowing access to the spot welding machine.

The substructure full weld may be decreased if reinforcement plate is used.

It is found that the same design criteria for 709 vehicle is extended to the higher load bearing vehicles like 1109 and 1112.Thus it is sought to reduce the amount of substructure weld.

Figure showing the welding done for the substructure with fire wall for a) side flap and b) central floor.

In the proto cab the weld run was marked as 4*35*150 for the side flaps and 2*40*180 for the central floor assy. of substructure. This resulted in saving of approximately 120 mm( 420-300) of CO2 weld run.15035a)b)4050

SUBSTRUCTURE REINFORCEMENTAt present 220 mm of CO2 weld is done for welding one reinforcement plate between substructure and fire wall. It may be feasible to reduce this welding if the substructure and fire wall assembly is properly sealed with reinforcement plates of lesser dimensions.

This is not feasible because the corners are sharp and the plate will be of complex surface.

Fig-Reinforcement may be placed here.

As can be seen, to avoid more welding than necessary we incorporate special features in the reinforcement plate like holes for plug welding rectangular notches at the edges so that the welding is done to the accurate dimensions and not exceeds the limit specified

Figure showing a) reinforcement plate preparation for weld at given places and b) the plate welded and arrow marks showing zigzag design for more strength.

For the cab under prototype stage the weld run was given as under 5*25*100 for bottom side and 6*25*100(80) for the top portion. This sums up to 250mm of welding for entire plate. It is feasible to eliminate the weld run pointed with red color and end tacks for reduction of weld length.a)b)

An alternate design where the reinforcement plate is itself spot welded to the substructure before the full CO2 weld for heavy duty vehicles may be thought of.This idea is not feasible to be implemented in plant because there is no approach for spot gun in Stn-1.

Though it may be done at the vendors end it is not recommended to go ahead because the fire wall assembly at Stn-2 may get affected in the present setup.

BACK WALL REINFORCEMENTAt present 80 mm of CO2 weld is done to place the back wall reinforcement in place. The back reinforcement is meant to be plug-welded through holes of 6mm diameter.

After tacking the operator enlarges the weld size to around 10mm in diameter. This may be avoided.

It is also observed that a run is also made on the edge of the reinforcement due to mismatching of plates. a)b)

SUPPORT WELDINGFront gusset welding full welding is done to ensure longer period durability. The weld runs are done in as many as 5 places leading to overall length of 184mm on both LH/RH sides.

The welding shown at the front portion of the C-channel and front grill may be avoided if we provide for flange and then spot welding can be done between it and the top portion of front grill.

FRONT MTG BRACKET AND FRONTGRILL As per current setup around 54 mm of CO2 welding is done between the MTG bracket and front grill It may be feasible to have a bolted butt joint plate in between the two components which adds to the overall strength and also decrease in weld length (b).

Snap head Blind rivets may also be used for joining along with a reinforcement tack of CO2 welding at corners.

It is not feasible to implement idea at present because there is no approach for the spot gun to reach this. (a)(b)

As per drawing the weld between front grill member and mtg-bracket is to be done on the top and bottom edges. The current practice is to do so on the inclined edge. This may lead to decrease in strength of the joint.

Reinforcement of fire wall to side panel can be minimized in conveyor belt.The present weld length is 40 mm in four places.The replacement can be done by increasing the number of spots done in Stn-4.

a) b) c)

Figures showing a) design criteria b) present practice and c) smaller weld for proto cabOUTER WALL REINFORCEMENT As per drawing the outer wall reinforcement is 20 mm weld at four places which is 80 mm compared to 160 mm done presently.40204020

Front grill to side wall

The front grill to the side wall weld run is currently 70 mm on each side.

This may be reduced to a considerable extent by increasing number of spots between front grill and side wall in Stn-4 which are irregularly placed because the of welding done already for side wall assy. (frame, post etc) .

As per design requirement there is no provision of weld to be done here.a) Welding on front grillb) Without welding

The weld run on inside of the side panel to outer step board may be reduced.If the number of spots are increased then the structure would sustain the load.

Step panelOuter front grillThis weld contains no reference in the drawing hence it may be feasible to reduce or eliminate this.SIDE PANEL REINFORCEMENT

For the cab under preposition this weld run is completely eliminated resulting in saving of 60*2=120mm of CO2 weld per cab.

a) beforea) beforeb) after

VENDOR IMPROVEMENTSAt Autoline Industries Ltd.- ChakanFOR-SUBSTRUCTURE

ASSEMBLY BRACKETThe assembly bracket top(2 no.s) are presently welded by using CO2 weld runs of 40*2=80mm for each component summing up to total 160 mm on LH/RH side.

There is approach for the spot gun on both sides.

Thus it is feasible to replace this process by spot welding if fixture is used.

The thickness of the bracket is a consideration to incorporate the spot weld design.

To weld the front insert 3+3 CO2 weld runs of 40 mm along with 8 no. of plug hole welding is done on the component.

There is approach for the spot welded gun on both sides where the CO2 weld is done

Thus with the use of proper fixture to hold the bracket it is possible to eliminate this weld.

MUDFLAP MTG.60mm of CO2 welding is done to weld the mudflap mtg onto the long member and reinforcement side.As per the present design it is difficult for the spot gun to reach the box-type structure on one end.

Spotting may be possible if the under part of the bkt end is properly fixed in position using appropriate fixture.

CROSSMEMBERThe present welding length is 120mm on both the members. It is not possible to replace this process with spot welding.

REAR MOUNTING BRACKETThe present weld length between cross member and Bkt cannot be avoided. But the weld between the cover plate and mounting bracket may be avoided as shown in the figure

SUB-ASSY LONG MEMBER TO MOUNTING BKTThe present practice is of doing welding of 4 CO2 weld runs of 20mm each summing up to 160 mm on both sides. This exceeds the design requirement of 2 tacks of 20 mm each.Figure showing excess weld run being made

In the modified setup the changes were made and this resulted in a decrease of 90 mm for both sides (LH/RH).

LONG MEMBER REINFORCEMENTAs per requirement 4 CO2 weld runs of 25 mm each are to be done for welding floor with sub-structure. This may be reduced to considerable extent by improving quality of spotting. This is done at four sides of the long members. This revision in drawing was carried out recently owing to the mismatch between the floor and the long member assy. Thus if the components are checked at source it may be feasible to eliminate this welding completely.

CLUTCH PEDAL STOPPER BKT.The present welding of Bkt is done in the assembly line of floor panel with sub-structure. If this component can be spot welded with floor in the initial stages CO2 welding may be eliminated.

REAR CORNER PANELThe assy. Substructure is CO2 welded with rear corner panel with four tacks of 25 mm each. It is feasible to replace this with spot welding if we provide scissor-like fixture but access of spot gun may be difficult owing to the rear panel.

Rear wall improvementsThe weld runs of total length between the ASSY.BKT.-HINGE BODY SIDE TOP and rear wall comprising of length 45mm may be avoided. It is not mentioned in the drawing.

In the proposed design this is eliminated and only spotting is done.

The center panel is welded to the rear wall at 10 places of total length 200 mm. This is not mentioned in the drawing.

This is modified in the subsequent process.

But a problem of black spots was found to be occurring especially at the bottom portion.

A possible reason for this is the mismatching of the skin components-the operator has to press them together. Thus there is possibility of air gaps.

Another problem was the spill over while spotting especially at the edges. This is caused due to the big length of arms of spot gun. This may be overcome by increasing length of flange which is in-fact sufficient now.

Tack welding of M-10 NUT can be avoided.In BOM for this component M-5 nut is mentioned but the manager says that the projection welding equipment is not capable for welding M-10 nut.

The major concerns highlighted in minutes of meeting were:a) supply of copper plates to avoid deep burrsb) drawing modificationsc) improved spot guns for welding coated material

Improvements in Autoline.The CO2 welding may be replaced by spotting in a number of ways. The gun has to be re-oriented to do spotting.

The appropriate flange may be provided to incorporate spotting.

With improved process parameters it is possible to spot weld even thick metal components to thin ones.

One side of connecting bracket may be spot welded using gun which has reach.

At AnasuyaInstead of doing CO2 welding through holes on door inner panel it may be possible to provide outer flange and do spotting.The component may be spot welded.