(Steve Krar, Consultant – Kelmar Associates)
manufacturing is a concept of stockless production that was developed to assist
manufacturers who were looking for ways to improve productivity, reduce costs,
reduce scrap and rework, overcome the shortage of machines, reduce inventory
and work-in process (WIP), and utilize manufacturing space efficiently, Fig.
10-5-1. The JIT process is aimed at organizing manufacturing processes so that
the best quality parts, manufactured or purchased, are supplied to the shop
floor only when they are needed – not too soon and not too late.
JIT strategies eliminate waste
through inventory reduction, shorter lead times, product and process design,
education, and other related programs. (Kelmar Associates)
originated with the Toyota automobile company; its initial concept was to
supply or produce parts only when they were required for the manufacturing or
assembly process. Through careful planning, it was found that there was much
waste that could be eliminated, plant space better utilized, and overall
productivity improved. Its success led to a revolution in production planning
and inventory control.
CONVENTIONAL vs. JIT MANUFACTURING
a conventional batch-oriented manufacturing operation, parts are bought or
produced in mass quantities to take advantage of quantity discounts and machine
setups. This strategy seems to be efficient since parts are pushed through a
system due to the economics of manufacturing and purchasing. A push system
feeds on itself by forcing parts to be produced faster, only to have to wait
longer before they are used in the manufacturing process. Parts are generally
wanted early because of the unreliability of the parts being available at the
time they are required. This leads to large inventories and over reliance on
informal manufacturing and inventory control systems. JIT is a pull system in
which parts are manufactured only when they are needed, sometimes resulting in
machines and workers being idle at times. Parts are bought or produced, then
pulled to the next workstation based on when they are required.
parts are produced until an authorization, commonly called Kanban (Japanese
word for authorization), is issued from the next workstation. Once this
happens, the workstation is open and parts can be sent to this station to be
processed. If the workstation is not ready to receive parts because others are
still waiting to be processed, the parts wait at the present locations until
they receive authorization. If delay happens often, the process in the specific
workstation must be changed to eliminate as much of the delay as possible.
DEFINITION OF JIT
can be defined as the philosophy of business excellence that can be reached
through eliminating waste wherever it occurs. Considering only the
manufacturing portion of a business, waste can be defined as anything that does
not add value to a product. The definition is a little unclear when defining
value and product.
easy and widely used way to explain value is to define it in traditional
accounting terms. Value is the actual work done on a product in fabrication,
machining, sub- and final assembly that increases the value of a product. Any
work or activity that increases the cost of a product without increasing its
worth is waste. A product may be any item that is produced during a
problem with this definition is that attention is usually focused on the shop and
ignores that JIT principles must also apply to the office. Inventory and set-up
time reduction programs, total quality control programs to eliminate the need
for inspection, scrap and rework, and equipment layout to reduce travel
distance are all shop oriented.
JIT can be seen as a manufacturing revolution that can make a
company competitive, free up working capital, improve product quality, while
reducing leadtime and manufacturing costs.
is no better way to showcase a JIT program than to attack some of the highly
visible areas of waste on a factory floor. Office applications are not quite as
visible, but have an important effect on the success of a JIT program.
Companies have always known that waste exists on both the factory floor and in
office applications and that eliminating any or all waste would make their
operation more efficient and profitable. Taking an overview of JIT itself, it
is nothing more than common sense. The key is to identify value-added processes
in every area of manufacturing, regardless of traditional accounting
definitions that tend to lump certain activities into overhead that do not add
value to a product. JIT is not a replacement for shop-floor control, a zero
inventory program, a set-up or lead-time reduction program, or a zero-defect
these examples apply JIT principles to problem areas, they are not JIT
programs. JIT is not a type of program, it is:
goal and philosophy that is aimed at achieving business excellence
business-wide strategy whose goal is to eliminate areas and causes of
waste through inventory reduction, lead-time reduction, quality assurance,
education, product and process design, system design, vendor
qualification, and other related programs.
is anything that does not add value, as real worth by the customer, to a
product. Worth includes functionality, performance, product quality, design,
reliability, availability, aesthetics, warranty, and service.
product is a manufactured item produced by a shop or industry. The information
required to manufacture that product is produced by an office. Information is
an important raw material without which a product cannot be designed, built,
tested, marketed, and sold.