Process Input method - Product and human conversion in manufacturing line

There are 2 major types of change over in a manufacturing line which we need to consider in this article:  model change over  and human change over.

Model change over 

No manufacturing process will continue to produce a single part until the product life cycle ends.  In fact with consumer growing appetite for variety,  most of the organization is trying to compete using variety either in the product aesthetics or feature with different pricing to suit different market segment.  A good example would be in the early 21st century,   laptop computer were only offered in black colour (equivalent to Ford model T automobile in early 20th century).  Later on Apple started to sell laptop and desktop computer in different colour which had been a delighter to the PC consumer market at that time. 

Variety in consumer market would mean that manufacturing facility must be able to convert a manufacturing line to produce different part and still achieve consistent good product.  This is done through development of standard method for model conversion for manual to fully automated line.
Recommended procedure for seamless manual line conversion to manufacture other models would be  :-

  • Determine the common  parts use for production which do not need to purge and identify those common parts clearly
  • Ensure all materials, hardware items such as jigs and fixture for next model is kitted properly off line
  • Where possible,  prepare just enough to complete the quantity required by customer for that batch  to prevent purging of the extra parts in the production floor
  • During conversion ensure all materials which is not needed are purge from the line
  • Developed a line conversion checklist for operator to do verification to ensure standardization throughout the manufacturing.  This will help to reduce variation. 

It had always being challenge to convert a highly automated line with heavy machinery.  A  good equipment conversion method should follow the principle of a lean methodology,  single minute exchange of dies (SMED) developed by Toyota engineer Shigeo Shingo. In the early days the biggest pain point for Toyota was long conversion time (> 1 day) needed to change tooling die in heavy stamping equipment to produce different automobile body parts.  Equipment will be down for days just to prepare another model die for change and time was also wasted to fit die precisely to the stamping equipment.  Conversion method had to carry out with accuracy and precision to prevent defect from being produce.  If you follow my previous article,  we already know equipment or automated process could produce consistently bad part if not setup properly.

After a series of experiment,  Shingo and team manage to reduce the change over time from days to less than 10 minutes, thus SMED was originated.  The strategy in SMED is to divide changeover activities to 2 categories and then minimize machine shut down and have as many preparation done off line as possible. The 2 categories of conversion activity are :-

  • Internal -  activities which need to stop equipment operation and done in the equipment
  • External -  activities which can be done off line and equipment can run as normal. As we would like to minimize equipment downtime therefore  it is ideal to have as many external activities conversion process.

SMED is achieved through

  1. Determine which conversion activities are internal and external
  2. Where possible convert internal to external conversion
  3. Regulate external off line activities
  4. Standardize machine parts where possible
  5. Use auto alignment mechanism to fit conversion machine part
  6. Design easy to install and uninstall fasteners or clamps
  7. Do internal and external activities in parallel

Concept of SMED

Human change over

Besides model conversion,  we would also need to address human change over,  operator shift change.  Once again standardize method must be developed to manage the variation cause by operator shift change.  An acceptable practice for operator shift change method would be

  1. Communication -  create a communication channel for shift handover to communicate items which need attention eg. quality issue
  2. Establish beginning of the shift checklist which include 5S  check on the work station such as cleaning, Verify all tools needed for production are available and in good condition
  3. Confirm all the setting of tools and equipment are correct
  4. Production supervisor  must ensure operator perform all above and work other team to rectify item which is not in accordance to the documented procedure. 

Very often,  change over method is overlooked by manufacturers as it always form a weakest link in production.   Change over in the form of parts and human should follow  a structural approach with standardize methods to govern the whole process. 

If  there is no standardization a changeover method  in a manufacturing it could lead disastrous quality issue such as shipped mix/wrong  part to customer.  Change over process especially equipment should encompass 1st part verification process.

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