Serie de ensayos V3

Koskela  et  al.  (2012)  provide  a  brief  history  of  the  concept  of  waste  in  production,   and  emphasise  the  importance  to  understand  it  within  the  context  of  production.   The   authors   mention   that   although   it   is   a   foundational   notion   for   the   Toyota   Production  System  and  in  general  the  concept  of  lean,  it  is  not  recognised  well  in   the   theory   of   economics,   operations   management,   construction   management   or   management  in  general.  The  authors  found  through  their  research  that  the  up  to   the  end  of  the  18th  _{century  there  was  little  if  any  recognition  of  waste,  and  it  only}   emerged   in   the   19th   _{century   and   flourished   during   the   emergence   of   scientific}   management.   However   it   declined   starting   from   the   second   quarter   of   the   20th   century,   and   re-­‐emerged   in   the   last   quarter   of   the   20th   _{century   with   the   Toyota}   Production  Management  System.    

Liker  (2004)  mention  that,  the  elimination  of  waste  is  at  the  heart  of  the  Toyota   Production   System,   and   this   along   with   the   concept   of   continuous   flow   and   improvement,   were   how   Taiichi   Ohno   made   Toyota   a   very   efficient   car   manufacturer.  Ohno,  who  strived  to  drive  out  waste  from  the  end-­‐to-­‐end  process   rather  than  optimising  individual  functions,  considered  following  7  as  main  wastes   within  the  production  system  (Liker  2004):  

• Overproduction:   Any   items   produced,   which   are   not   ordered   by   the   customer,   are   considered   overproduction.   Overproduction   causes   excess  

stock,   and   inventory,   and   may   lead   to   other   waste   such   as   unnecessary   transport  or  rework.  In  construction,  any  work  that  is  carried  out  “outside   the   schedule”,   i.e.   was   not   planned   in   advance,   can   be   considered   overproduction.  

• Waiting  (time  on  hand):  Production  workers  having  to  wait  to  carry  out  the   next  planned  activity  is  considered  waiting  time  or  waste.  Also,  time  spent   in   watching   automated   equipment   (such   as   concrete   mixers)   is   also   considered   waste.   Reasons   for   waiting   time   could   be   lack   of   inventory,   equipment  downtime,  resource  unavailability  etc.    

• Unnecessary   transport   or   conveyance:   Any   movement   of   workers   associated  with  transporting  material  or  equipment,  “in  process”  work,  or   finished   parts   etc.   long   distance   is   considered   waste.   In   construction,   this   could   mean   transport   of   precast   elements,   or   concrete,   movement   of   workers.  The  reason  for  this  could  be  lack  of  attention  given  to  site  design,   bottlenecks  on  worker  movement  routes,  etc.  

• Overprocessing   or   incorrect   processing:   Any   unnecessary   steps   or   action   taken  to  carry  out  work  can  be  considered  overprocessing.  Also,  producing   work   that   is   of   higher   quality   then   required/ordered   is   also   considered   overprocessing.    

• Excess  inventory:  One  of  the  most  important  waste  considered  by  Ohno  is   excess   inventory.   Finished   parts   which   are   produced   out   of   turn   (unplanned)  and  waiting  to  be  processed  further  are  also  considered  excess   inventory.   Excess   inventory   causes   problems   such   as   bottlenecks   in   processing,  reduced  safety,  defects,  etc.  

• Unnecessary   movements:   Unnecessary   motion,   including   having   to   search   for   information,   looking   for   resources,   etc.   is   considered   unnecessary   movement.    

• Defects:   Work   that   is   completed   but   is   defective   or   requires   rework   is   considered  defects.  

All   the   above   wastes   exist   in   construction,   however,   Koskela   (2004)   introduces   another  category  of  waste  in  construction  called  “making  do”,  which  is  discussed   below.  

4.1.2.1  Making  do    

When  one  puts  this  new  point  in  front  of  the  existing  construction  practices,  many   shortcomings   arising   from   the   sole   “T”   implementation   start   becoming   obvious.   Crucially,  this  leads  to  a  new  category  of  waste  called  “Making  Do”  (Koskela,  2004).     Making-­‐do  as  a  waste  refers  to  a  situation  where  a  task  is  started  without  all  its   standard  inputs,  or  the  execution  of  the  task  is  continued  although  the  availability   of   at   least   one   standard   input   has   ceased.   The   term   input   refers   not   only   to   materials,   but   to   all   other   inputs   such   as   machinery,   tools,   personnel,   external   conditions,   instructions   etc.   Especially   in   production   situations   where   there   are   several   uncertain   inflows   to   the   task   (such   as   construction),   making   do   is   a   common  phenomenon,  and  requires  explicit  attention  (Koskela,  2004).  

Conceptually,   making-­‐do   is   opposite   of   buffering.   In   buffering,   materials   are   waiting   to   be   processed,   whereas   in   making-­‐do   the   waiting   time   of   one   of   the   material  or  input  is  actually  negative,  i.e.  processing  starts  before  the  material  has   arrived.   Here,   it   is   important   to   understand   that   buffering   (high   inventory)   and   making-­‐do   are   both   wastes   and   as   such   are   utilised   to   accommodate   for   the   variability  in  production.  Making-­‐do  is  applied  especially  in  circumstances  where   there  is  a  demand  to  speed  up  production  to  meet  deadlines.    

As   such   making   do   comprises   of   and   leads   to   several   other   wastes   such   as   overproduction,   movement,   defects,   etc.   However,   in   construction   “making-­‐do”   manifests   itself   into   a   significant   phenomenon   due   to   the   peculiarities   of   the   construction  industry  (Koskela,  2004).  

Transformation  View  is  the  main  reason  for  Making-­‐Do:  As  discussed  previously  in   Chapter  2,  the  CPM  method  of  production  planning  and  control  is  solely  based  on   the  “T”  view  of  production.  In  CPM,  a  plan  consists  mainly  of  a  Gantt  chart  and  an   activity   diagram.   In   the   CPM   method,   each   task   starts   when   the   master   schedule   indicates  and  when  the  preceding  activity  has  completed.  However,  it  fails  to  take   into   account   the   current   situation   on   site   and   also   the   other   flows   (or   prerequisites)  to  a  task.  However,  as  main  focus  of  production  is  on  the  realisation   of  tasks,  little  attention  has  been  paid  to  who,  when,  where,  what  and  how  of  the   flow   activities   (i.e.   making   the   inputs   available   to   workers).   To   deal   with   this  

situation   on   ground,   the   workers   on   site   tend   to   find   “work   around”   when   the   necessary  prerequisites  are  not  available,  resulting  in  “making  do”.