International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.

-2017
http://iraj.in
REDUCTION OF DEFECTS THROUGH QUALITY ASSURANCE
NETWORK IN AUTOMOBILE INDUSTRY
1
MOHAMMED NOUFIL, 2MOHAMMED ISMAIL
1 2
student, M.Tech II year (Production), Associate Prof
Dept.Industrial & Production EngineeringThe National Institute of EngineeringMysore, India
E-mail:1noufil1@gmail.com

Abstract - The Quality Assurance Network presented in this paper is followed by Japanese automotive companies to trap the
defects within the shop itself, as automotive company has enormous number of operations, we just consider weld shop as a
case study as it is one of the most crucial part of manufacturing automotive. Spot welding is most widely used operation in
weld shop, hence welding defect control is given prior importance.

Keywords - Heijunka, Andon

I. INTRODUCTION missing some spots might be OK, but for quality

assurance it should be made sure that no spot is
Quality of a product can be defined as degree or missed, hence all spots are divided into 5 types
extent to which it meets the requirements, by meeting
or exceeding the customer expectations. Most of the 1. Pimple spot : press panels itself are designed so as to assist
times Quality Assurance is confused with Quality weld operator where exactly to make spot welds, with the help
of simple pimple like projections, mainly on the inner parts
control. Usually Quality control is the process of that we generally don’t see
inspection of already manufactured product, for its 2. Guided spot: here the jigs are designed with guides that assist
specifications & functions whereas Quality weld gun to make spots at exact points, hence the name guided
spots
Assurance is concerned with manufacturing defect
3. Panel spot: just like pimples, here the points where welds
free product & even if a defective product is should be done are pressed more than adjacent part that also
manufactured it doesn’t outflow. Therefore quality adds to looks, easy assembly etc.
Assurance is more than Quality control, with Quality 4. Back bar spot: areas very difficult are provided with back bars,
control as a part of it. Quality Assurance Network is usually made of copper & incorporated in jigs that will assist
welds spots to be done at exact places.
Japanese method of creating network that traps 5. Memory spot: the operator needs to memorize the exact
manufacturing defects effectively to ensure 100% location where he has to make spots, which induces errors, so
defect free product. It is mainly done whenever there operator can make markings on the jigs or repeatedly refer to
the drawings to reduce defects, but even though it has highest
is Introduction of new car model, newer version of
probability of misplacing of spots or missing of spots.
existing cars, or any change in any of the operations /
processes. The purpose of QA network is to assure It is primary requirement of any automotive industry
100% defect free vehicles. One of the most important to check each & every spot, as every spot has its
part of QA is to maintain documentations of the defined importance, location etc., it is necessary to
network created. As we are restricting our QA have spot confirmation method.
network to weld shop, little explanation of weld shop The range of defects that can occur in each kind of
is done in the next section spots are
II. WELD SHOP

It is the area where metal skeleton of an automotive is

created. It consists of numerous jigs with conveyers
& dollies to supply parts & semi-finished products.
The line may be dedicated to a single model or it can
have 2 or more models being produced on the same
line which is termed as Heijunka (levelled
production) in Japanese. Apart from welding metallic
parts, operations like sealer application, parts
fastening is also done. Spot welding is widely
accepted because of its large number of advantages,
& arc welding is done where spot welding doesn’t
prove to be effective. Figure 1- Range of defects that occur in each kid of spot

Types of spots: A single car these days is known to Spot confirmation methods
have around 3500 spot welds, so one can think Spot quality will be confirmed by 5 ways:

Reduction of defects through Quality Assurance Network in Automobile Industry

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 International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.-2017
http://iraj.in
 Magic check: with the help of magic marker, it is perform the function of joining & filling gaps to
a kind of visual check & assurance is marked by maintain air tight contact.
magic marker
 Visual check: only visual check is dine as it Three types of sealers are usually used
could be the outer part that needs very good
surface finish 1. Hemming sealer – used to join outer & inner
 Chisel check: to check the strength, as the spots panels of Hood, Front door, Back door, Rear
will not be made in corners, the sides of the weld door etc.
are opened without touching weld & after 2. Mastic sealer & sealer tapes – used to create
checking they are closed by hammer damping effect for vibrations & also seal parts.
 Destruction check: usually the tests like impact It is used in Hood, Roof, Front door, Rear door,
which assures that the welds can resist particular Back door, Side member etc.
limit of loads, but the specimen used for 3. Pad pillar – used as a backup for metal parts.
checking will be useless These are like solid plastic parts that inflate on
 Cut check: to check the strength of every spot entering into oven. It is used in under body &
individually, this type of checking is done. It is Back door.
performed thrice in a year or at particular
intervals on each & every weld spot made on Technology to improve spot welding
vehicle so as to ensure there is no deviation or Spot welding uses copper electrodes & metals to be
deterioration in energy of components. A good welded will be having lesser electrical conductivity
product randomly chosen & checked. It’s like than copper, but wear out of copper electrodes is
wasting 1 body to assure strength in thousands of unavoidable & on an average for every 4 hours, the
bodies. electrodes need to be changed. Which adds to the
Apart from joining parts, weld shop also involves manufacturing cost & the Nugget quality deteriorates
sealer application process that aims to prevent water as electrode gets used up, hence better results have
leakages, reduce vibrations & so on. These are used been recorded by using Aluminum strip between
to seal the components, so that a sub assembly Copper electrode & Work metals. A schematic
behaves like a single integrated part. Sealers usually comparison is shown below

Figure 2 – Comparing spot welding before & after application of Aluminum strip

Reduction of defects through Quality Assurance Network in Automobile Industry

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 International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.-2017
http://iraj.in
From the figure it is clear that allowing aluminum  Sub assembly accuracy management: a jig
strip not only increases Nugget quality but also will have many parts, so there is an
reduces Copper electrode wear out. The heat effected interdependency on movements & holding
zone has also been reduced. which should be regularly monitored
 Retainer & bracket accuracy: retainer &
III. DEFECTS ENCOUNTERED IN brackets are very small parts so it should be
WELDSHOP limitedly loaded & accurately attached.

Usually 5 kinds of defects are encountered in weld Welding defects are subdivided into:
shop.  Spot welding: it uses copper electrodes,
1. Wrong & Missing parts carrying high current joins the metal parts
2. Surface defects. that are kept in between them due to lesser
3. Fitting defects electrical conductivity of metal part, in other
4. Welding process defects words due to resistance metal gets melt in
5. Water leak defects. local area & are joined.
 Arc welding: It uses a non-consumable
Wrong & Missing parts type defects can be electrode to create arc between electrode &
subdivided into: metal parts to be joined, heat from the arc
 Welding of Nuts: usually with threads in inside melts the metal & thus the parts are joined.
face to facilitate temporary fastening of parts  Brazing:
 Small parts welding: like brackets, angles that  Laser welding: uses heat from the laser
plays the part of supporting, fastening etc. source to melt & join the parts
 Stud bolt welding: usually threaded bolts are  Projection welding:
welded that can be fastened to the parts with  Stud welding:
welded nuts for servicing purpose
 Tightening of parts: screws, nuts, bolts etc. on Water leak defects are subdivided into:
the parts that should not be welded because of  Datum pin set: datum pins are used to locate
design restrictions parts accurately on the jigs but if they are
out of standards, they might increase hole
Surface defects can be subdivided into: diameter & unwanted indentations with
 Hemming: it is a process of joining 2 large parts micro holes that might result in water leak.
with the aid of a gumming material in between  Main body accuracy: in main assembly line
them, & by applying high pressure for a limited larger parts are joined where a little offset in
amount of time. Defect in pressing machine or small parts or holes will not interfere with
hemming sealer sticking to the surface are the 2 work because of intense pressure used for
major kind of surface defects that take birth here. joining parts, but in the later stages it will
 Part transfer: Parts are transferred with the help result in water leak spots
of Dollies, Conveyers, Pneumatic suckers etc.  Welding: excessive welding current can melt
parts hitting each other, and parts contacting extra metal & even some metal might get
foreign materials during transfer are the kinds of evaporated, that will result in mini holes
defects that come into picture here. finally contributing for water leak
 Welding: Welding spatter & Burrs are the  Bolt tightening : some bolts will have
contributing ones for surface defects here. conical shape near head to create airtight fit,
 Magic mark: Magic marker not disappearing, impact wrenches having pre calculated
non-standardized magic marker usage & torque will be ideal, but when torque is less,
excessive usage will result in remnants of it will result in bolt head & part surface gap,
impressions even after painting. with a micro gap between bolt thread & part
inner thread that will result in water leak.
Fitting defects are subdivided into:  Weld strength check: It is done with the help
 Fitting jig accuracy: Lack of calibration can of specified chisels & Hammers, especially
cause improper matching or offsetting of for spot welds. Area near weld is opened &
parts weld continuity is checked, & then
 Jig set: Maintenance of jig for any welding/ hammered back to original shape. When
Machining dust, smooth edges etc. are more than specified parts are opened, it will
included result in decrease in weld strength & small
 Tightening: bolt fastening with the help of holes enough to account for water leakage.
power wrenches, the wrenches need to be Every spot will have a specially designed
providing stable torque & should maintain chisel hammer set & only those must be
alignment used.

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 International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.-2017
http://iraj.in
 Sealer sticking: Sealer sticking on holes & bolts fastening. These parts missing can be easily
edges will block correct vision that will detected by the inability to do a process, & even if the
result in offsetting of parts & gaps for water parts are misplaced, it can be easily detected.
leakage.
 Panel gap: it will be mainly due to improper Stage 3: Within group, Interdependency, Visual,
welds, or lesser number of welds, lesser Functional, QC gates.
torque used in fastening, but when these
parts are assembled with other parts the Stage 4: Within shop: Interdependent, Fitting,
panel gap will multiply & at a particular Functional, QC gates.
stage sub-assemblies will not assemble or a
need will be aroused for forces assembly, Stage 5: Outflow.
that will create number of mini holes to If the defect is not detected anywhere, it outflows to
assist water leakage. the customer, that results in the degradation of
company brand.
A. 5 stage defect detection system
A five stage defect detection system is designed IV. QUALITY ASSURANCE NETWORK
which can assure zero defect outflow are
QA network is done in four stages.
Stage1: In process, with the aid of pokayokes,
Templates, Karakuris, Magic checks & QC gates.
Pokayokes are fool proof devices that use electronic
sensors to detect part presence or process completion
such as fastening or welding. Mostly proximity
sensors are used here & when a part or process is
missed, it doesn’t clamp off or blocks further
operations, thus are very difficult to fool these
devices. Regular maintenance is required as its
functionality might fade away with time & the main
purpose might not be served.Templates are the
supporting structures on jigs or fixtures that helps for
easy installing & removing of parts, absence of any
part can be known by part of template exposed as Figure 3- QA network web
after installing all parts mostly templates will be
covered. It is dependent on human visibility & Green lines – Process
presence of mind so probability of mistakes is more Blue lines – Process group
than pokayokes. Karakuris are Mechanical kind of Yellow lines – Process shop
sensors\pokayokes that resist part installation if all Red lines – Customer
parts are not kept, as they have some spring loaded
protrusions & locating pins with mechanical linkages, First stage of it is to evaluate the process management
so it is more dependable, but it needs regular sheet under which every jig is evaluated for kinds of
maintenance like oiling & calibration etc. it cannot be defect that can take birth in it.
done for too big parts as it need very stable & First being analysing the kind of defects than can rise
sophisticated parts for that purpose.Magic checks are in every single process & Machines. Collecting the
visual checks that uses magic marker for information in process management sheets. It is one
confirmation. Magic marker has a unique property of of the most important step as it acts as template for
giving bright display when marked & has ability to next processes. Every kind of defect has a pre
disappear after two or more hours of application, thus designed check sheet for effective analysing of
it doesn’t interfere in the finishing process, but it also problem.Second step being evaluating the check
needs good human visibility & presence of mind.QC sheets very carefully. Every check sheet has 2 major
gates are installed after every major operation, & the sub divisions.
inspector does sampling inspection, with some
irregular intervals, & also shorter intervals to obstruct 1. Occurrence prevention.
defect outflow from a particular region. 2. Outflow prevention
Occurrence prevention is further divided into
Stage 2: Successive processes, with the help of Facilities (Tools), Materials (Parts), Method, Person.
Templates, Karakuris, Interdependency, Visual It checks Tool maintenance, working in tool section.
checks & QC gates. In Parts section the parts of the product is check for
Interdependency refers to the parts that are inserted or shape, finishing, foreign substance, etc. In Method
processed at previous section but has significant section the work order, Ergonomics of workplace, &
effect on further processes like hole punching, nuts & checking is monitored. In Person section it is checked
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 International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.-2017
http://iraj.in
that standard way of operation is followed. & in case It is a pre-designed rule that the check sheet giving
of defect formation there is certain predefined most negative evaluation is taken first for evaluation
procedure to correct it. Outflow prevention is & attempt is made to bring both occurrence &
Subdivided into Concluding in own process, in own outflow to a ranking. Usually repair check sheets are
group & finally in shop. Own process means defect is considered to be of less importance because it is
corrected in the same machine (Jig) itself as is it difficult to have repair area for each jig. Small repair
detected, as it requires lesser time & no sophisticated areas have been allotted after every weld department.
tools requirement. Group level conclusion means the After the weld shop there is a dedicated offline repair
defect is detected after it flows to the further area to correct all major kind of defects. Keeping
processes by the aid of inspection & interdependent cycle time in mind it is always tried to keep
processes. Then it is repaired online or offline occurrence prevention system at best possible level.
depending on the kind of defect. There is a special Third step in QA network after check sheets are
offline repair area dedicated to all kind of repairs. If a evaluated is filing & keeping these created documents
kind of defect is un repairable then the product is sent for further reference. The status of each jig is
for recycling. Concluded within shop means the represented in large sheets in the production &
product defect is caught at quality gates or at final meeting areas so as to create awareness of the present
inspection, where the defects are removed & quality situation. Colour coding is done for easy
confirmed once again to finally release out for understanding & attraction. A rank is provided with
market. Both Occurrence & Outflow check sheets are green colour. B with blue colour. C with yellow
filled with entries A, B, C or D. colour & D with red colour. It is a usual practice to
keep the chart in green & blue colour as far as
In Occurrence Prevention, possible. Each jig is represented with a chart
A: There is pokayokes & there is no chance of defect
occurrence, Table 1 – QA network representation of single Jig
B: There is no pokayokes but the standardized work
followed is enough for defects not to occur,
C: There is a probability of defect occurrence when
there is mere deviation from standardized processes
&
D: Even after everything runs smoothly there is a BLUE colored area is for headings. M, F, S, W & L
chance of defect occurrence & the uncertainty is very represents 5 kinds of defects. O & F represents
high. Occurrence & Outflow prevention. R represents
result. YELLOW area is to be filled with A, B, C or
In outflow prevention, D. GREEN area is to be filled with 4 symbols
A: If a defect is occurred, it is found & corrected in
⓪, 0, ꓯ or X. the result finding algorithm is as
same process itself, otherwise the process will be
follows
shown incomplete. B: If a defect is occurred, it is Table 2 – Quality rating indicator
tackled in next successive process & there is no
chance of defect outflow out of the section.
C: The defect is busted & cleared in the group mainly
in the Quality gate.
D: The defect occurred is corrected in shop when
there is final inspection X: the defect is not caught
anywhere in the shop & the defect is out flowed ⓪, 0, ꓯ & X are provided with GREEN, BLUE,
undetermined. Usually X is not applicable anywhere. YELLOW & RED colour respectively.
In defect outflow prevention systems, either all
spot\part checking can be done, or sampling Fourth stage of it is to take the counter measures to
inspection can be adopted depending on the number improve the condition of the jigs. After the counter
of spots\parts to be checked & importance of that measures are taken, that particular jig is evaluated
particular part. When a particular area is suspected to once again so as to ensure its improvement & assure
produce more defects, then it is advised for all any negative effect on any other operation.
quantity check until a significant stability is reached.
QA network is used whenever a defect occurs & to Counter measures need not be anything very
get quick & correct sight of what is the most probable Innovative, but something simple changes will be
reason for the occurrence of this defect. There are 2 enough to improve the condition, & many operations
columns for evaluation in each check sheet will have D rating because of non-compliance of
• Before countermeasures standard operations, manipulating of machines & so
• After countermeasures on. Hence machines with pokayokes installed will
have a control panel designed with some complexity

Reduction of defects through Quality Assurance Network in Automobile Industry

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 International Journal of Mechanical And Production Engineering, ISSN: 2320-2092, Volume- 5, Issue-7, Jul.-2017
http://iraj.in
so that only specific persons can change its settings, CONCLUSION
turning it ON & OF etc.
QA network helps to find the origin of a specific kind
V. SAFETY & MAINTANANCE of defect within a region in no time, provided it is
done with maximum accuracy. It needs to be updated
As weld shop uses high electricity & large parts every time certain changes are made, & is very
movement with conveyers etc., safety should be difficult to maintain the network if some information
maintained with zero tolerance. High pressurised is missed, as manipulating the information will be
hemming machines & conveyers are equipped with worse than no information.
light curtains, where there will be a light source & a QA network has been proved an effective tool to
receiver, & whenever something obstructs it, the decrease DPV (Defects per vehicle), improve DOK
operation in process is stopped until full way for light (Direct O.K) & keep PDS (Pre Delivery Schedule)
curtain is not cleared. nearest to zero.
In spot welding, spot dents & burrs are regularly
occurring defects, so they can be controlled by
regularly changing electrode tips & continuous
monitoring current supply & un interrupted cooling
water supply. So there is a separate department
allotted for tip board management, & current & water
supply. Similarly JIG TPM group are concerned with
maintaining of all jig related activities, jig transfer in
case of layout change, updating jigs whenever there is
change in design of car, & facilitating smooth
operation of jigs thereby reducing cycle time &
reduction of non-value added time. After every sub
Figure 6 – DPV before & after QA application
group there are repair jig & after complete weld shop
there is separate repair area, whose maintenance & all
Blue – Before QA applied
other activities are done by repair team.
Red – After QA applied
Material supply management is done with the help of
Andon system, where every jig group is provided
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Figure5 - Andon for better material supply management



Reduction of defects through Quality Assurance Network in Automobile Industry