■ What Matters in Volume Production Is Not Peak Performance
In prototyping, attention tends to go to peak performance:
the temperature went down the most,
it could be made the thinnest,
it could be made with the highest precision.
But in volume production,
the average,
variation,
and worst-case values
are important.
For example,
an average temperature of 70°C.
Very good.
But some units reach 85°C.
If the specification upper limit is 80°C, they are defects.
In other words, in volume production, staying within specification even under worst-case conditions matters more than peak performance.
■ Success with One Unit and Process Capability Are Different
One unit can be processed at ±0.05 mm.
This is technical capability.
But in volume production,
even after making 10,000 units,
even when material lots change,
even when equipment wears slightly,
the same accuracy is needed.
In other words, what really matters is not “can ±0.05 mm be achieved,” but
“can ±0.05 mm be maintained as a process.”
■ Volume Production Is the Work of Managing Variation
Materials have tolerances.
Equipment has tolerances.
Processing has tolerances.
Measurement has errors.
These cannot be reduced completely to zero.
That is why in volume production, rather than eliminating variation,
it is important to create processes that stay within product specifications even with variation.
■ Absorbing Material Lot Differences
Even with the same material part number,
thickness,
hardness,
adhesive strength,
peel force,
and surface condition
may change little by little.
The material lot used during prototyping was easy to handle.
The volume production lot is slightly harder.
Then processing results may change.
In other words, it is necessary to create processing conditions that work even when material lots change.
■ Giving Processing Conditions Margin
It only succeeds at a pressure of 100 N.
Defective at 99 N or 101 N.
This process is weak in volume production.
On the other hand, if
it succeeds stably between 80 and 120 N,
it is easy to mass-produce.
In other words, what is needed is not a single optimal condition, but a range of conditions that works stably.
■ Creating a "Process Window" Rather Than the Best Conditions
Rather than choosing only
the conditions with the best thermal performance
or the fastest processing speed,
look for the range in which quality can be maintained even if conditions change somewhat.
For example, a state where
it is stable within
speed 8–12 m/min,
pressure 90–110 N,
and temperature 20–30°C.
This becomes a process strong in volume production.
■ Tolerances Stack Up Rather Than Standing Alone
For example,
TIM thickness ±0.05 mm,
application position ±0.2 mm,
mating part height ±0.1 mm,
and cooling plate flatness ±0.1 mm.
Each is within specification.
But if they overlap in the bad direction, insufficient contact may occur.
In other words, even if each part is within specification, the finished product can be out of specification.
■ Consider the Worst-Case Conditions
Combining averages works without problems.
But in volume production,
the thickest TIM,
the largest gap,
and the lowest pressing force
may occur at the same time.
Does it perform even with that combination?
This must be checked.
In other words, the perspective must shift from average design to worst-case design.
■ Design Margin Exists for Volume Production
The specification upper limit is 100°C.
The prototype result is 99°C.
By the numbers alone, it passes.
But in volume production, there are
material differences,
environmental differences,
and equipment differences.
It may easily exceed 100°C.
That is why margin is needed in volume production.
Design margin is not overdesign, but a buffer to absorb variation.
■ Controlling Dimensions Alone Does Not Stabilize Thermal Performance
The TIM outer shape.
Dimensions pass.
However,
thickness,
compression state,
air bubbles,
and application position
differ.
Then thermal performance changes.
In other words, for thermal management components, drawing dimensions alone are not sufficient.
It is necessary to identify and control the process conditions that affect product function.
■ Identifying Critical Characteristics
Not all dimensions need to be strictly controlled.
For example,
the TIM’s position relative to the heat source,
the insulation edge position,
and total thickness
are important.
On the other hand,
some dimensions related to appearance may not be so important.
In other words, in stabilizing volume production, it is important to determine which characteristics govern function.
■ Also Identify Critical Process Conditions
Pressure,
speed,
tension,
temperature,
peel angle,
and die condition
do not all need to be controlled with the same importance.
Which conditions strongly affect
dimensions,
application,
air bubbles,
and thermal performance?
This is confirmed.
In other words, what is needed is not increasing control items, but correctly choosing the important ones.
■ Dies Change Little by Little
Die-cutting dies wear with use.
The blade edge condition changes.
Burrs increase.
The cut surface changes.
Dimensions may also change little by little.
In other words, processing conditions
cannot be decided with the day-one die alone.
It is necessary to look at whether quality can be maintained throughout the entire die life.
■ Replacing Dies After Defects Appear Is Too Late
Defects occur.
The die is replaced.
By then, many defective units may already have been made.
So
shot count,
burrs,
dimensional trends,
and blade edge condition
are monitored.
When a certain state is reached, preventive maintenance is performed.
In other words, equipment maintenance is part of quality assurance.
■ Preventive Maintenance and Volume Production Stability Are Connected
Rather than fixing equipment after it breaks,
signs are found before it breaks.
Rollers.
Blades.
Guides.
Suction heads.
Each has replacement criteria.
This prepares the process before defects occur.
In other words, in stabilizing volume production, manufacturing and maintenance are not considered separately.
■ Equipment Temperature Can Also Change Quality
First thing in the morning.
The equipment is cold.
Several hours later.
The equipment temperature rises.
Then the state of
dies,
rollers,
and material tension
may change.
In other words, in volume production, it is necessary to look at the difference between
startup
and stable operation.
■ Warm-Up Conditions Also Become Process Conditions
Production starts right after the equipment is started.
Only the first 100 units have different dimensions.
This can happen.
In that case,
warming up for a certain time,
test punching,
and starting volume production after confirmation
are done.
In other words, standardizing even the production start conditions leads to stable volume production.
■ Temperature and Humidity Also Change Material Condition
Films,
adhesives,
and foams
can be affected by temperature and humidity.
In summer,
winter,
and the rainy season,
material elongation,
adhesive strength,
peelability,
and static electricity
change.
In other words, process conditions include not only equipment settings, but the factory environment as well.
■ Absorbing Seasonal Variation in the Process
If defects increase only in summer,
or peeling defects occur only in winter,
the season and material behavior may be related.
This is addressed with
temperature and humidity control,
material storage,
and processing condition correction.
In other words, “the same settings mean the same process” is not necessarily true.
■ Material Storage Is Also Part of the Volume Production Process
Materials are stored appropriately.
Some materials have specified
temperature,
humidity,
storage period,
and time after opening.
Quality begins even before loading into the processing machine.
In other words, it is necessary to think of the material warehouse as part of the manufacturing process.
■ FIFO Alone Is Sometimes Not Enough
First in, first out.
Important.
However, some materials require managing even
how many hours since being taken out of the refrigerator
and how many days since opening.
In other words, material management sometimes looks at a combination of
lot,
time,
and environment.
■ Raising Processing Speed Changes Conditions
Prototype speed.
Low speed.
Volume production.
High speed.
Then
material tension,
adhesive behavior,
heat,
and static electricity
change.
In other words, even with “the same equipment and the same material,” a change in speed can make it a different process.
■ Balancing Takt Improvement and Quality
Speed is raised to increase productivity.
Defects increase.
It is set back.
Rather than this,
confirm
how far quality can be maintained.
In other words, in volume production, aiming for the highest stable productivity rather than the highest speed is more important.
■ Summary of Part 1: Stabilizing Volume Production Starts with "a Range of Conditions with Margin," Not "the Best Conditions"
Prototype success is merely the starting point for volume production.
What is asked in volume production is
the average,
variation,
and worst-case values.
Material lots.
Stacking of tolerances.
Die wear.
Equipment temperature.
Seasonal temperature and humidity.
Material storage conditions.
Processing speed.
Such variations cannot be completely eliminated.
That is exactly why what is needed is
having a process window rather than a single optimal condition,
making it work even under worst-case conditions rather than with average design,
identifying critical characteristics and critical process conditions that govern function,
and catching signs of change before defects appear.
In other words, what we looked at in Part 1 is “where variation comes from” and “how to design processes that can absorb it.”
In Part 2, we consider the systems for continuing to reproduce that process even when people, equipment and sites change.
Column Supervisor: Koji Kakumoto (President, OTIS Co., Ltd.)
After studying abroad and working in planning and development at a trading company, he joined OTIS Co., Ltd. in 2011. While primarily working in the Corporate Planning Department, he has also served concurrently in manufacturing and technical divisions, and since 2018 has served as President, working to drive business growth and strengthen the organization.
This article is a general technical explanation intended for educational purposes and does not refer to any specific company, product, or technology.
