Quality Audit of BOXNHL Wagon Production at SPJ

Quality Audit of BOXNHL Wagon Production at SPJ.

A CASE STUDY

G. Chowdhury

Prof.(EM)/IRIMEE

INTRODUCTION

• QA done on request of CME/ECR

• Only welding aspects were covered

• Average production of 25 Wagons/pm

• So far, SPJ have produced 200 odd nos.

• Another 250 of combination joint at CS

• Next 150 of only SS joint at CS

• Then total ‘HAT’ section from trade

General Information

• BOXNHL stands for BOXN Higher Load

• Tare Wt.: 20.6 MT

• Pay Load: 71 MT, Axle Load:22.9 MT

• Length over Head Stock: 10034mm, Width:3250mm, Height:3301mm, Vol:61m3

• Rake 58 wagons, 636m

• Coated with PU paint

General Information

• whole under-frame and superstructure is made of ferritic stainless steel of IRSM-44, except the end portions of centre sill which are made of mild steel of IS: 2062.

• Three types of welding are involved;joining SS to SS M2 Class

SS to MS D ClassMS to MS C2 Class

General Information

• WPS No. WD-WPS-BOXNHL-08.

• Calls for welders as per IS: 7310 Pt-I

• Recommended welding practice: MIG/MAG or MMAW

• Welding ferritic SS needs special expertiseHighly sensitive to heat inputMoreover, Cr loss is a serious issue

Welding Equipments

• 12 numbers of MIG welding machinesOnly one is functionalProcuring a few new machines

• MMAW machines are in good condition. All having multiple hand made joints in

cables, one just after machineAdvised to use lugs if unavoidable

• Plasma Arc used for cutting of SS

Welding Consumables

• Meticulously using different types of electrodes as specified in WPS

• Both 3.15 mm dia. and 4 mm dia.

• Storage conditions also very good

• Special care for absorption from floor

• SS wire brush & chisel for SS welding

• Consumable wire lying unused. Advised to send to workshops using MIG/MAG

Edge preparation & Fitment

• Quality of edge preparation is not good

• Grinding wheel is being used producing a “Double V” sort of edge with

irregular contourEdge angle & neck not being maintainedTaking a long time without quality output


• Alternatively, slant cutting by Plasma arcAvoids grinding & produce a better edgeLight dressing by grinding stone (not Wheel)

to remove oxide layer & form neckOne such piece made & shown to CWMWith some fine tuning and practice it is

possible to produce good quality edge with much less effort and time


• In some places, edge preparation is being done in situ, i.e. after tack welding or partial welding of two pieces together

• The practice should be discontinuedAll edges should be prepared before tacking

the pieces together


• The quality of fitment is quite poor

• Large gaps between two pieces to be joined, both in Butt and Fillet weld, even in centre sill joining (HRF to CRF)Unduly large amount of metal deposition Higher heat input affecting mechanical

properties of SSIncreased production cost & aesthetics


• In exigency, SS strips can be used as back plate to cover up gap in butt weldThe plate can be removed later during sealing

run from the opposite side

• The present practice of using copper plate for backing should be discontinuedIt may lead to copper entrapment & lack of

fusion due to chilling effect

Preheating of Electrodes

Preheating is highly important as it reduces hydrogen content of weld, responsible for delayed cracking

•Electrode preheating ovens installed in many areas

None of them are working except one in Centre Sill Joining area

In most of the places electrodes are being used w/o preheating


• In that lone oven also, the temperature indicator not showing proper temperatureWhen checked by a non-contact type

pyrometer, the inside temperature was showing only 139°C as against 266°C shown by the digital indicator

As recommended preheating is at 250°C/ 350°C, basic objective of preheating is getting defeated


• The ovens must be calibrated periodically

• A non-contact type pyrometer can be kept in the shop for cross checking

• For preheating temperature and time, the recommendation given on the packets by the manufacturer must be religiously followed


• Welders taking out a bunch of electrodeRemaining electrodes are becoming cold and

reabsorbing moisture

• Procure flask type portable ovensPlugged in at the actual workMaintain temperature around 1100CIndividual electrode can be taken out from the

portable oven and consumed

Welding Team

• Basic qualification on lower side

• The WPS calls for welders certified as per IS: 7310 Pt-I, but unfortunately none possesses such certificate.

• Out of 75 odd welders, only 39 trained in DLW and 10 more being sent now

• 26 welders have been sent to RCF also.

Welding Team

• DLW also not certifying as per IS:7310 Pt-IOwn system of gradingAll welders secured grade ’B’, i.e. good

• Some supervisors also need upgradation of knowledge, particularly in SS weldingThe lack of knowledge possibly leads to

adoption of non-standard or short cut method of working

Welding Team

• At least a percentage of welder be trained and formally certified as per IS: 7310 Pt-I from some reputed training institutes like ESAB, ADVANI etc.

• Skill may be further supplemented by training in SS welding at RCF

• Specially employed for welding of structural members of underframe.

Actual Welding & Workmanship

• Following proper polarity

• In many places, much higher welding current than recommended Electrodes are becoming red hotTotally unacceptable practiceAffects the mechanical properties of ferritic

SS very adversely in HAZAlso affects quality of weldment


• Calibrated Tong Tester to cross check the actual welding current and OCV

• Some welders are not following ‘Back Tracing’ or ‘Whip Back’ technique

• In many places, porosity, undercut etc. are found in the centre sill, even though the job has been completed and released for next stage of working


• In assembly area manipulator not usedPoor quality of horizontal/vertical welding

• Welding after painting, not healthy

• General workmanship needs improvementLarge gaps and misfits are observedPacking of metal chip was observedIn plain lap joints of two sheets in door area, 3-4 mm

gap was observed


• Poor dimensional adherence of trade items aggravating the problem of misfit

• Welding stopped for some time due to water logging from rain

• In body sections, rain water accumulations over the sheets due to leakage from roof

• Cleaning prior to welding was improperWelders have been advised to remove all dirt, metal

dust etc. before welding

General Guidance

• Locking of cracks before repair grinding

• Adjusting OCV rather than current

• Use of thermal chalks for cross checking inter-pass temperature

• Size of tack welds 30-50 mm with one electrode length spacing (350 mm)

• Stray arc marks

• Storage of IRSM-44 grade SS sheets

Discussion with Welding Team

• A discussion with all supervisors & CWM

• Major issues like high welding current, preheating, crack repair etc. explained

• Fitment of electrical lugs

• Edge preparation by slant cutting

• Procurement of Tong tester & pyrometer

• Training of welders & supervisors

Trouble Shooting

A particular lot of SS Z section has given a lot of problem in joining

– All the pieces have been rejected after multiple attempt of repairing

Advised given:– welding with preheated electrodes– Checking Chemistry, particularly carbon

content

Recommendations

• Attention in major area of concernPreheatingHigh Welding currentEdge preparation & fitmentTraining

• Formation of weld inspection team

• Edge preparation from Trade

• Internal review- follow up recommendations

Quality Audit of BOXNHL Wagon Production at SPJ

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