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Samenvatting - boek "lean production for competitive
advantage"
Production Planning & Quality Control (Rijksuniversiteit Groningen)
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Production Planning & Quality Control
Chapter 1
What differentiates winners from losers is that winners are better able to
consistently provide products and services that are competitive with regard to
quality (better), price (cheaper), time (faster), and response to change (agile).
See book page 2
In traditional firms, product ideas tend to move sequentially through functional
areas, whereas in lean firms they are honed in production development teams.
Lean production is management that focuses the organization on continuously
identifying and removing sources of waste so that processes are continuously
improved. Lean production is also called justintime(JIT).
TQM is management that focuses the organization on knowing the needs and
wants of customers, and on building capabilities to fulfill those needs and wants.
Lean organizations greatly increase the number of people involved in identifying
and eliminating obstructions. Besides, the primary process is reduction of
inventory.
Lean production is a way of continuously tinkering so the pipeline and the
material coming out of it are the best possible. Lean production continuously
seeks way to make the pipeline more adaptable to whatever materials or flow
rates are desired, to match the flow of materials as closely as possible to
customer demand, and to make the material coming out of the pipeline ever
more acceptable to the customer.
The first change in the auto industry came after WWI when Henry Ford and
Alfred Sloan advanced manufacturing from craft production to
mass
production. The second change came after WWII when Toyota Motor Company
pioneered lean production.
With the implementation of the interchangeable part in production of products,
the slow transformation that would replace hand labor and craftsmanship with
mechanization and visions of labor began. Interchangeable parts are made in
batches such that any one part would fall within design tolerances and fit into an
assembled product.
Frederick Taylor introduced the idea of improving operations by studying and
simplifying them. Always looking for the one best way to do something. One
consequence of this theory was to take most of the skills and thinking away from
factory workers and give them to legions of managers and specialists.
Ford introduced a
moving assembly line which brought the cars past stationary
workers, eliminated time wasted by workers walking and forced slower workers
to keep up with the pace of the line.
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The system of mass production today is largely a result of the combined
influence of Ford, Sloan and organized labor.
The system Toyota developed, called the Toyota Production System , is the
prototype for lean production and JustinTime manufacturing. Though
developed for automobile production, the principles of the system have since
been applied in all kind of industries.
● Reduced setup times: if a setup takes a long time, it would be necessary to
produce things in large batches to justify that setup time. Since setup
times were usually long, largebatch production became the norm in
manufacturing.
● Small lot production and OnePiece flow: producing things in large batches
results in larger inventories because it takes longer to use up the batch
and that results in higher holding costs. The classical way to determine
optimal batch size is based on the economic order quantity (EOQ)
formula: EOQ= √2DS/H , where D is demand, S is setup costs, and H is
holding costs. It became possible for Toyota to economically produce a
variety of things in small quantities. The smallest size demand is one unit,
and Toyota set the goal of being able to produce anything, one unit at a
time. This is called
onepiece flow.
● Employee involvement and empowerment: Ohno organized his workers by
forming teams, and gave them responsibility and training to do many
specialized tasks. They were allowed time to meet to discuss problems
and find ways to improve the process. The notion of workers asking why
five times to get to problem rootcauses was first introduced at Toyota.
● Quality at the source: Ohno reasoned that to eliminate product defects,
defects must be discovered and corrected as soon as possible, which
means going to the source of defects and stopping them there. If the
defect could not be readily fixed, any worker could halt the entire line by
pulling a cord:
Jidoka/line stop .
● Equipment maintenance: operators are assigned primary responsibility
for basic
preventive maintenance since they are in the best position to
detect early signs of malfunction.
● Pull production: to reduce wastes Ohno developed the pull production
method wherein the quantity of work performed at each stage of the
process is dictated solely by the demand for materials from the
immediate next stage. Ohno also developed a scheme called Kanban to
coordinate the flow of materials between stages so that just as a container
was used up, a full container from the previous stage would arrive to
replenish it (origin of JIT).
● Standard work: a concept wherein worker teams create the standards that
define the work they currently do. The standard work also serves as the
baseline from which to improve processes to better suit changes in
customer demand and the work environment.
● Supplier partnerships: Ohno saw the need for a different kind of
relationship wherein the manufacturer treats its suppliers as partners
and integral elements of the production system. Essentially, suppliers are
trained in ways to reduce setup times, inventories, defects, machine
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breakdowns, and in return they take responsibility for delivering the best
possible parts/services to the manufacturer in a timely manner.
The single greatest use of computers in manufacturing has been for material
requirements planning (MRP) systems that link together information about
parts and components that go into a finished products and generate schedules
and purchase orders for assembled and procured parts.
Computeraided design (CAD) enables designers to design a part or product,
and test its features and compatibility with other parts and products, all with a
computer.
Computeraided manufacturing (CAM) refers to software that translates
design requirements into instructions for controlling production machinery.
A flexible manufacturing system (FMS) aims to achieve highvariety output at
low cost.
The next step beyond FMS is computerintegrated manufacturing (CIM). It
links CAD/CAM.
Electronic data interchange (EDI) refers to computertocomputer exchange of
information, usually meaning between multiple companies.
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Chapter 13
Variation in scheduled batch sizes and batch intervals results from
management’s attempts to match production levels with demand. Demand levels
vary because of sales fluctuations, promotions and so on, and management
adjusts the sizes and intervals of production batches to compensate.
Variation in production schedules also stems from variability inherent in the
production process.
A common way for the upstream stages of the productiondistribution chain to
absorb this variation, is to carry buffer stocks of raw and inprocess material.
Buffer stocks provide some degree of certainty, and during periods of slack
demand they keep materials flowing and workcenters productive. This is one
tactic for
leveling production.
A drawback of this tactic is the consequence of high inventories. Another,
sometimes better way to minimize variation is simply to level the production
schedule by establishing a master production schedule (MPS) where every
product is produced on a regular basis and in a fixedsize batch.
With a uniform, level production schedule , the same quantity is made in each
production run for a product, and the production runs occur at regularly
scheduled intervals. Besides the time, cost and quality benefits of smaller WIP,
level schedules give supervisors and workers more time to focus on the work at
hand. (see figure page 354)
For production leveling to be practical, three requirements must be met:
1.
Stable product demand
2.
Shorten setups
3.
Match production with demand
Continuous, stable demand
To maintain a level production schedule in the presence of fluctuating demand,
some quantity of finished product must be held as buffer stock. This buffer stock
protects the entire productiondistribution process from product demand
variability, and allows upstream stages to operate on a somewhat level basis.
To keep the inventory small, the company must manage the demand so as to
minimize variation. One way to do that is to segregate customers into tiers:
· First tier: high volume, common processes (no special setups or operations).
· Second tier: substantial volume and much process commonality.
· Third tier: low volume, sporadic orders with little process commonality.
Short setup times
The time to change over a process from one product to another must be short.
Ceteris paribus , they also mandate larger batch sizes, which restrict the
allowable degree of production leveling.
Production= demand
The frequency and batch size of production runs in leveled production should
roughly correspond to the average actual demand for the product. This means
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