Koren Y. The Global Manufacturing Revolution: Product-Process-Business Integration and Reconfigurable Systems
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machines per system), and inspection equipment to measure the machined parts to
tolerances as precise as 10 mm. The powertrain plants are the most expensive plants
in the auto industry, more expensive than assembly plants by far. In parallel to the
manufacturing of the major powertrain components, first-tier suppliers make other
powertrain components, such as pistons. These parts are added to the engine block,
together with the electrical wiring, fuel lines, and belts, in the powertrain assembly
section of the engine production plant.
At the sam e time, other first-tier suppliers build the entire front instrument panel
(IP) sub-assembly, including air-conditioning and temperature control, audio system,
airbags, gauges, etc. The components in the IP are supplied to the first-tier supplier
by second-tier suppliers. Other first-tier suppl iers build the car seats, the exhaust
system, etc.
After painting, the vehicle shell enters the assembly shop. A typical assembly shop
has three sections: trimming, chassis asse mbly, and final assembly. The cars enter
trimming on moving platforms, each car on a separate platfo rm, which travel one after
another in a line. Trimming is a manually intensive assembly process; workers,
arranged in teams, stand on the slowly moving platform and assemble various parts in
the car interior, such as the IP and steering column, as well as the windshield, lamps,
bumpers, and exterior molding. Each team of workers is responsible for a limited set
of tasks that takes about 50 seconds. They are doing these tasks repetitively all day.
Figure 6.3 A flowchart of automobile production.
PRODUCTION OF COMPLEX PRODUCTS 151
Note that the (quite complex) IP, for example, is shipped from the first-tier supplier as
one sub-assembly and installed in the car at the line cycle speed of about 50 seconds
including all of its various connections.
Next, the chassis assembly is done. In chassis assembly, the bottom of the car is put
together. There are plants in which the whole chassis, including all of the powertrain
and exhaust system components, is pre-assembled and attached to the car at the line
cycle speed, again within 50 seconds. Finally, the car moves to the final assembly
section where the car seats and wheels are installed, and fluids are added. The engine
starts, and the car rolls off the assembly line on its own power, at an average rate of one
car per minute. Keep in mind that cars rolling out at a rate of one per minute must also
be sold at a rate of one per minute.
Our student, Craig Ashmore, described the manufacturing process of the IP.
“I was recently at an IP manufacturing plant and saw this process first hand. The IP being
built was a skin and foam panel. The skins were created about every 3–4 minutes. The skins
then went over to the next line where foam was put between the retainer and skin and then
sent to a water jet line. The water jet cut out all the extra skin material. The IP was then sent
to an area where AC vents were installed. Immediately the top panel was sent to a line where
it was mated to the cross-car beam and all the other items were added. The complete IP was
then loaded onto racks and loaded on a truck to be shipped that day to the plant. The IP is
then installed into a car the day it is received at the manufacturing plant. I was very
impressed at the efficiency that was used in the plant. The whole IP line was contained in an
area about 1000 square feet.”
6.2.2 Production of Appliances
The appliance industry is a growing global manufacturing sector. It includes the
production of washers and dryers, refrigera tors, freezers, dishwashers, ranges,
compactors, room air conditioners, and microwaves, together with portable appli-
ances such as stand mixers, hand mixers, and blenders. The 100 top global appliance
companies earned combined sale revenues of more than $900 billion U.S. in 2005.
1
Whirlpool Corporation, for example, accounts for over $14.3 billion of these sales,
and its brand names are marketed in more than 170 countries worldwide.
*
One of the most common appliances in the global market place is the refrigerator.
In 2007 there were 10 million refrigerators exported from the United States by
domestic home appliance manufacturers. The manufacturing of a refrigerator is
a multifaceted process and requires the expertise of many skilled workers as well as
manufacturing processes such as extrusion, thermoforming, stamping, welding, and
injection molding.
*
This section was written by Kate Presnell, Lukasz Skalski, and Katherine Warner, former students of the
global manufacturing class, who are Whirlpool’s employees; see also www.whirlpoolcorp.com.
152 TRADITIONAL MANUFACTURING SYSTEMS
Like most manufacturing processes, the refrigerator begins with raw materials;
most notably in the form of plastic pellets and coils of steel. A number of
preparation steps and sub-assemblies occur before the product enters the final
assembly line. The first of these sub-assemblies is the door and can be found on the
left side of Figure 6.4. The plastic pellets are extruded into a sheet, which is then
thermoformed. The thermoforming proce ss includes heating up the plastic liner
sheet, forming it over a mold, and cooling the product in a temperature-controlled
environment. The liner is then assembled to the metal doors. The doors are formed
by straightening the coils of steel into flat sheets, then cutting, stamping, and
welding them accordingly.
Between the plastic liner and the metal door, the appropriate internal ice and water
sub-system components are attached. These components typically consist of
conduits for the wiring harness and water inlet, as well as the reinforcing structure
for the exterior elements of the system added later in the assembly process.
Expanding adhes ive foam insulation is then sprayed into the vacant space between
Figure 6.4 A flowchart of refrigerator production.
PRODUCTION OF COMPLEX PRODUCTS 153
the inner and outer doors. This foam serves as the insulating agent as well as adds to
the structural stability of the door. This sub-assembly then proceeds down a conveyor
to where the external door features including dispenser electronics and housing,
handles, and water inlet hose are added.
The other major sub-assembly consists of the main refrigerator cabinet and its
components. The cabinet is formed much like that of the door described earlier, of an
inner liner and metal exterior. These two parts are assembled and foam insulation is
again injected into the vacant space between the two pieces and allowed to expand.
Once again, the foam serves to both insulate the cabinet and add structural rein-
forcement. The cabinet is then equipped with the cooling system that consists of
a condenser, compressor, evaporator, and necessary conduits. These conduits are then
charged with refrigerant.
The cabinet then travels to the main assembly line. Here, the remaining features are
installed: shelves, drawers, bins, etc. Once the inside of the refrigerator is assembled,
the doors are attached. There is then a quality check to ensure the refrigeration system
is sealed with no leaks. Some refrigerators may proceed to performance testing for an
additional quality check while the majority of finished goods are packaged and sent to
the distribution centers.
6.3 THE STATE OF ART AT THE END OF THE TWENTIETH CENTURY
Multi-stage manufacturing systems are made up of many machines or assembly
stations connected via a material transfer mechanism. The transfer mechanism may be
an overhead gantry system, a conveyor, or an autonomous-guided vehicle (AGV). The
machines may be dedicated to one fixed set of operations, flexible such as robots in an
assembly system, or programmable computerized numerically controlled (CNC)
machine tools. CNC controllers are very versatile and can be easily applied in milling,
turning, dri lling, grinding, shaping, laser processing, etc.
To be regarded as a true manufacturing “system,” the operation of at least the
critical elements of the line must be coordinated through a supervising central
command station where a computer controls and synchronizes the operations of
the machines. The two most common manufacturing system types that were available
at the end of the twentieth century were the dedicated manufacturing line (DML) and
flexible manufacturing system (FMS). Many manufacturing industries combine
a portfolio of dedi cated and FMSs to produce their products. This approach has
evolved because neither approach, on its own, is adequate to meet the ever-expanding
challenges of a global economy of rapidly changing demands and consumer tastes
while maintaining low prices.
6.3.1 Dedicated Manufacturing Lines
Dedicated lines (also referred to as “transfer lines”) are designed to produce just one
product, but at very high throughput. (The average output of a production machine or
154 TRADITIONAL MANUFACTURING SYSTEMS
system, measured in parts per time unit, is called throughput.) The DML is based on
a collection of relatively simple machines arranged sequentially in a line, where the
processed part moves in a synchronous manner from one machine (or station) to
the next. The high throughput of DML is cost-effective when very large quantities of
the product are needed.
An example of a dedicated machining line composed of 10 dedicated machining
stations is shown in Figure 6.5. This system was built to produce just one part. An
operator loads the raw parts and unloads the finished parts. The part moves along the
conveyor and stops at each station for processing. In some stations several tools work
on the part simultaneously. Two stations in the system of Figure 6.5 even have
machines that do machining operations on both sides of the part simultaneously. The
DML control is done by fixed automation (called hard automation) that in practice
cannot be changed. This production line has very high throughput of identical parts.
Once in place, DMLs operate reliably and are well suited to produce high volumes of
identical parts at great efficiency.
Each station or machine in a DML performs a single unchangeable operation on
every part passing through. Special multi-spindle tools that drill or tap a fixed pattern
of several holes at one stroke contribute to the high throughput of DMLs that produce
machined parts. The pattern of holes fits only certain part geometry, as shown in
Figure 6.6.
Figure 6.5 A dedicated machining line.
THE STATE OF ART AT THE END OF THE TWENTIETH CENTURY 155
DMLs have been a basic element of high-volume manufacturing for generat ions.
True to the mass production paradigm, since their output volume is high, the cost per
part is relatively low. Once fully in place, DMLs perform at a constant designed rate,
outputting identical high-quality parts at large quantities. However, with increasing
pressure from global competition, the demand for specific parts can vary widely.
Situations often occur where dedicated lines do not operate at full capacity, and when
that happens the cost per part is muc h higher.
For example, a dedicated line can produce an engine block every 30 seconds. As
long as the dedicated line operates at its planned capacity, it produces many parts at
very attractive costs. However, if engines are produced at a rate of 30 seconds each, it
stands to reason that they have to be assembled into corresponding numbers of
vehicles that will be sold at a rate of a car every 30 seconds. What happens when cars
cannot be sold at a rate of one every 30 seconds? Then the rate needed has been
reduced, say to one every three minutes. When that happens the dedicated line is
underutilized, and loses its economy of scale. The cost per product becomes higher. In
fact, because of increased market volatility and competitive pressures, DMLs are
increasingly underutilized. A report published in Italy in 1998
2
indicated that the
average utilization of the surveyed DMLs in a European auto manufacturer was only
53%! One common reason for this low average utilization is that in the introductory
stages of new products, or at the end of a product life cycle, fewer parts are required,
considerably lower than optimal volumes. But because of global competition, even
products in the mature phase do not always reach the production volumes forecast
when the line was designed.
At the other extreme, DMLs also fail when demand goes above the design capacity
(Figure 6.7). If a product’s popularity exceeds all market expectations, or when new
Figure 6.6 A multi-spindle head.
156
TRADITIONAL MANUFACTURING SYSTEMS
uses are found for existing products, the DML is powerless to respond, resulting in
a loss of sales.
If market demand for a product increases quickly, the fixed maximum capacity of
the DML d oes not allow the manufacturer to grab the opportunity to produce and sell
more products. This results in substantial losses in potential sales and actually entails
much larger economic losses than those from unused capacity.
In the quote below we cite Ronald Zarrella, a former President of General Motors
(GM), who described how a shortage of engine blocks (a component produced largely
on DMLs) caused a loss in sales of entire vehicles.
General Motors Corp.’s top executive said that a sharp rebound in market share
would not be possible if the industry sales continue at their torrid pace because GM
could not produce enough full-sized pickup trucks to meet demand. “GM simply
cannot make enough big V8 engines to build all the full-sized pickup trucks it
needs to meet the market share goal,” said Ronald Zarrella, the president of GM’s
North American Operations. But Zarrella said low gasoline prices, which help
sales of sport utility vehicles and pickup trucks, were still better than high gasoline
prices, which help sales GM’s low-profit cars, for which it has extra production
capacity. “If gasoline prices rose , he said, there’d been positive in terms of
market share and lots of negative in terms of profitability.” (The New York Times,
February 12, 1999).
The main drawback of DMLs in the globalization era is that these lines are not
designed to change, and therefore they cannot be converted to produce new products
easily. In the globalization era, the marketable lifespan of a product becomes shorter
and shorter with competing products being introduced faster and faster. This all makes
Figure 6.7 A DML system is an excellent choice when it is operating at its designed
throughput capacity, which cannot be easily changed. Losses can occur in unmet demand
when a product is popular, as well as in unused capacity as its popularity wanes.
THE STATE OF ART AT THE END OF THE TWENTIETH CENTURY 157
the building of DMLs uneconomical, and for this reason they are vanishing in many
manufacturing industries.
6.3.2 Flexible Manufact uring Systems
As we have said, DMLs cover the high-volume/low-variety work and stand-alone
computer numerically controlled (CNC) machines are for low- to medium-volume,
high-variety production on the other end of the spectrum. The middle ground (mid-
volume/mid-variety manufacturing) is taken by FMS and by reconfigurable
manufacturing systems. The FMS is defined as: An integrated group of processing
units, such as CNC machine tools, linked by an automated material handling
system, whose operation is controlled by a supervisory computer.
History of Flexible Manufacturing Systems: One of the first firms to develop an
integrated manufacturing system was Molins Company in the United Kingdom. In
1967 this company presented the “Molins System 24,” a flexible and integrated
system demonstrating a novel way to increase productivity. In this system several
machining stations were lin ked by an automated handling system for transferr ing
parts that were mounted on pallets.
Four years later, in 1971, Sundstrand (in Illinois, USA) developed the “Shuttle Car
System”, a rail-type pallet transfer system on which parts flow to and from the
machining stations, located along the rail track.
3
This system, however, was suitable
only for long and variable machining times.
At the Leipzig Spring Fair in 1972, Auerbach, a German machine tool builder,
presented their manufacturing system “M250/02 CNC”. It was quipped with two
three-axis machining centers, three two-arm changers, and one four-arm robot; this
system enabled a complete five-face machining of prismatic parts. A central computer
was used to control the machining centers, but the part handling was done manually
from an operator’s station.
In the mid-1970s FMS emerged for producing small batches of many different
parts. Cincinnati Milacron, a machine tool builder in Ohio, was an industry pioneer in
the development of FMSs.
4
Production cells linked with automated material handling
systems emerged in the 1980s (e.g., by Max M
€
uller and Fritz Werner). In the last
20 years of the twentieth century FMSs proliferated throughout the industrialized
world, although the trend in some industries has been to utilize smaller, less expensive
flexible manufacturing cells.
FMS is a major enabler of mass customization because it can produce a variety of
components or products within its stated capability. FMS also enables the redesign of
products to meet new market requirements without adding substantial investments in
the manufacturing system. Most of the experience gained with FMS installations has
been with machining systems.
5,6
The building blocks of FMSs are CNC machines (in machin ing systems), or robots
(in assembly systems and automatic welding lines). Both have sophisticated oper-
ational controllers integrated with a material handling system that transfers the parts
between machines and/or assembly stations. CNC mac hines in flexible machining
systems include machining centers, drilling machines, and laser cutters, and
158 TRADITIONAL MANUFACTURING SYSTEMS
sometimes automated inspection machines. Typical material handling systems are
conveyors, overhead gantries, and AGVs. The successful operation of a whole FMS is
based on coordinating the operation of its flexible pieces of equipment.
In order to perform various operations quickly, CNC machines are equipped with
rotating tool magazines and automatic tool changers (ATCs), as depicted in Figure 6.8.
The variety of tools in the magazine enables CNC machine tools to perform different
milling and drilling operations on the part on one machine. If the tool magazine of the
CNC machine is large enough to contain all the tools needed to produce several parts,
the CNC can even be programmed to produce a variety of parts.
In machining systems parts are located and clamped on fixtures, which allows
transferring the part for succeeding machining operations. The fixtures are built to
precisely fit the part geometry, and their clamps must be located such that they allow
for cutting tool accessibility. The fixtures with their parts are mounted on pallets,
which are transferred between machines through the whole system.
The data stream sent to the CNCs, and the robots that constitute the FMS, is
a sequence of tasks that they have to perform (e.g., drill, change tool, mill, weld, move
a part, etc.) in order to manufacture a particular part. This data stream is called a part
program. The machines and robots are designed to accurately follow the series of
numerically defined steps over and over. Producing a new part type requires loading
a new part program as well as having the right tools in the tool magazine and using the
proper fixtures to hold the new parts.
If the tool magazine of each CNC machine contains the tools needed to produce
several types of parts, the FMS can rapidly switch its production from one part type to
another. The operation of an FMS produces several types of parts, each type in a batch
of multiple identical parts. For example, if three parts A, B, and C have to be produced,
Figure 6.8 A machining center with a chain-type tool magazine and an automatic tool
changer.
THE STATE OF ART AT THE END OF THE TWENTIETH CENTURY 159
then a certain number (called the lot size, or batch) of parts A are produced first, then
a batch of part B, followed by a batch of part C, and then a batch of part A is produced
again.
The size of the tool magazine and the total number of operations needed on each
part are the two important factors in deciding the number of parts that a machine can
produce without replacing tools in the magazine. However, when the tool magazines
in a system are too small to contain all the tools needed to produce all types of parts, an
optimization algorithm that balances the workload per machine can be utilized to
allocate the operations (and their cutting tools) of a selected subset of the parts that
will be processed.
7
Adding sensors to the machines, and transmitting their data continuously to the
CNC controller, greatly enhanc es machine diagnostics. Typically, accelerometers and
vibration sensors are used, although other sensor types such as acoustic emission
monitoring and force/torque sensors are sometimes utilized. Cutting tools may be
changed out based on these sensor readings, the number of parts cut by the tool, or at
the end of each work shift.
6.3.3 Is a Pur e-parallel FMS Practical?
It is a common assumption that FMS should be able to produce (1) any part (within the
machine envelope), or (2) any mix of parts produced at any sequence (namely, non-
batch operation) . But only a purely parallel FMS can fulfill these requirements
effectively without losing time because of balancing processing-time issues between
stages. A purely parallel FMS, however, is not designed for multi-stage operations; it
is rather a group of CNC machines arranged in parallel, where each machine produces
the entire part (Figure 6.9).
This parallel configuration provides the highest flexibility and efficiency in
producing a variety of parts or products simultaneously. Parallel FMS may be found
in the aerospace and opto-mechanical industries, for example.
Figure 6.9 A parallel FMS.
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TRADITIONAL MANUFACTURING SYSTEMS