6Theta has proven to be a powerful and successful process for obtaining robust designs that perform consistently at high quality. This presentation gives an introduction to what the process contains and provides simple case examples of how it is used.

1. November 2012
Design for 6θ
- an introduction to the process and methods

2. Situation in industry: Product recalls and quality issues. But…
Toyota Gas Pedal Offshore Windturbines BMW 2012-recall
Cause: Variation in design Cause: Overconstrained design Cause: Risk of battery cable cover
parameters causes pedal to ’lock’ creates parasitic forces that being mounted incorrectly. Details
Cost: $2 billion decreases lifetime of critical not released. 1.3 mio cars recalled
components from 20 to 2 years. Cost: Unknown
Cost: DKK 200 mio.
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3. …only the ‘tip of the iceberg’ reaches the market. Most quality issues are solved
during product development and production ramp-up. But because the issues are
discovered late in the development process, redesign is often costly and
challenging. Product complexity makes it difficult to find the root cause for the
issue. As a result, product launch is delayed and revenue is lost.
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4. So where do quality issues come from?
A quality issue is defined as any deviation of a product’s functional performance from its
nominal value - e.g. the force required to pull off the cap of a whiteboard marker.
The markers above no. 10000 and 10001 produced by the same production line with
identical specifications. But, they perform differently. The force required to take off the cap is
not the same. What causes this variation in performance and how can we reduce it?
• One strategy is to reduce the variation of the components – geometry, materials,
surfaces. This is called Six Sigma – a well-proven strategy alraedy adopted by industry.
• Another strategy is to reduce the sensitivity to variation. Valcon has successfully
developed 6θ - a coherent set of metrics and methods to reduce the sensitivity of a
design.
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5. How did Design for 6θ™ arise?
Design for 6θ™ combines research on quality engineering with years of experience on designing moving mechanics for
the automotive and medical industry. Combining the disciplines, and converting them to an operable and coherent
design procedure, a new product development paradigm has emerged.
Kinematics
Design of
Robust
Experiments
Design
(DOE)
Experienced effects:
• Transparency in projects
• Predictability/precision in time-to-market
Robot
design
6θ Precision
instrument
design • Lower sensitivity to variance
• Embedded quality – with fewer
specifications
Minimum
• ’Design Freedom’
constraint Statistics
design
Axiomatic
Design
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6. How does 6θ work?
6θ has two focus areas: Clarity and Robustness
The force required to activate a drug delivery device can vary from batch to batch and device to device. Design Clarity
removes this variation by identifying and redesigning ambiguous interfaces and overconstrained designs. Optimisation
using robust parameters further enhances the performance of the design.
n (Number of devices)
Desired performance
Force required
8N
Design for 6Theta™
Method 1: Clarity Method 2: Optimisation
Coupling Degree 6Theta
(Kinematics and Design (Sensitivity and
Clarity) Specifications)
6 Source: novonordisk.com

7. A brief introduction to Method 1:
Kinematics and Design Clarity
X
Kinematic design can be applied at an early stage
(system level / architecture). Using Kutzbach’s Y Z
Formula the mobility of a design can be GEAR-
BOX
C SHAFT
quantified.
j j Principal example of a windturbine-concept
B 6 n 1 Ui F id
i 1 i 1
A design which is overconstrained is sensitive to
variation. For example, a misalignment of the
gearbox and shaft in the example to the right, will
result in parasitic forces in the bearings, thereby The design is overconstrained by 5 degrees of freedom
decreasing their lifetime.
Introducing e.g. an Oldham coupling will provide
the sufficient degrees of freedom and the system
is now insensitive to any misalignments and
variation of the components. One possible coupling solution: The Oldham
Coupling introduces 5 degrees of freedom.
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8. A brief introduction to Method 1:
Kinematics and Design Clarity
The components of a design have intended interfaces,
constraints (SOC)
but poor design, e.g. too many constraining surfaces,
can lead to abrupt changes of functional surfaces.
System Over-
The intended and actual number of constraining
surfaces can be visualised in a cockpit, thereby
providing an overview of the current state of sensitivity
in the design.
constraints (POC)
Part Over-
Designs with ambiguous interfaces should be No. of interfaces (I)
addressed, because an unintended change of
interface results in performance variation.
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9. A brief introduction to Method 2:
Quantifying and improving robustness
With an unambiguous design, it
is now possible to derive the
transfer functions (the
correlation between design
parameters and functional
performance).
The transfer functions can be
derived by
• Analytical derivation
• Simulations
• Experiments (DoE)
The gradient of the transfer
function indicates the sensitivity
of the design and allows for
optimisation.
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10. Example of Method2:
Designing a press-fit
Which design is best?
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11. Example of Method2:
Designing a press-fit
The design parameters that contribute to the holding force of the press fit in the two designs are identified and the
Theta-value is calculated. Is is seen, that the force is particularly sensitive to the hole and shaft diameter. However, in
the second design, the Theta value is relatively higher, indicating that this is a better design.
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12. Example of Method2:
Designing a press-fit
A Monte Carlo-simulation confirms, that the second design has a higher yield rate.
98.13% 99.92%
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13. Effects: Selected cases
The table contains selected cases of 6θ applied in industry.
Project Issue Source Change & Effect
Industrial grinder Vibrations and noise Mechanism design was Overconstraints removed.
overconstrained, resulting in large Noise and vibrations
and varying internal forces. disappeared.
Large-scale scanner Noise on scanner Overconstrained and ambiguous Overconstraints removed.
images design led to varying torque on Noise removed from
motor images.
DVD Tray Motor unable to drive Overconstrained design leading to Overconstraints removed.
tray in & out. Bigger sensitivity of parallellity of bearing Old motor re-installed.
motor used, but new shafts Noise removed.
motor is noisy.
Medical device Milestone missed. Lack Ambiguous design. Redesign with focus on
of overview in tolerance ambiguity. Improved
analysis. Variation in tolerance overview.
functional performance.
Medical sampler Leakage between liquid Ambiguous design. Unintended Redesign of parts (minor
reservoir and flow (and hence uncontrolled) changes) enhancing
channel component elements influenced design clarity. Leakage
positioning of parts stopped.
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14. Valcon
Advanced methods:
6θ™ contains more methods and metrics to help identify and obtain quality
in design:
KPI TARGET NEXT ACTIONS STATUS LEGEND WEEK 32
Through interface analysis of all body Coverage 100% Primary target. Must be Subsystem XXX must be Main interface groups have Normalized couplling degree: number of
COUPLING
and part interfaces a coupling degree Normalized coupling completed (100%) in week included into the been solved. Detail improvement points per interface
DEGREE
for the product can be calculated as degree: 3 or below. 34 kinematic cockpit - modelling and cleanup still
follows: (System DEADLINE XXX to do
improvements*interfaces + part
improvement + number of
interfaces)/number of interfaces. This
4 Coupling
degree
provides a number describing how
many improvements per interfaces the
product currently has
TOLERANCE STRUCTURE MATERIALS
A measure of how many components Coverage 100% Materials is secondary. Find / create a standard Critical components have Percent of components with assigned
have had an approved material 100% materials Begin process after week material list - DEADLINE materials. Springs and material
assigned, living up to all requirements assigned 34 XXX visual components still to
do. Visual components
need input from designer
A measure of the distribution of safety Coverage 100% Process parallel with Areas which are There are interfaces which Green: safety factor > 1.4
factors against relevant failure criteria All safety factors results from coupling dependent on strength have not yet been solved . Yellow: 1.4>safety factor > 1
for all identified calculations higher or equal to 1,4 degree. and flexibility should be A short review estimates Red: Safety factor < 1
Begin process week 22 found - DEADLINE XXX that most of these
interfaces can be solved
with a small effort at level
1. Calculations below
safety factor 1 needs
redesign
A measure of the distribution of all Coverage 100% All weeks. Must be • X, Y, Z. Alignment The focus has been on the Green: acceptable tolerance specification
tolerances specified. Tolerances are No critical tolerance determined in week 44 at tolerance chain must be tolerances concerning the (IT grade higher or on par with
divided into categoryies by their IT specifications the latest solved, this will tell us precision of the alignment recommendation)
grade equivalent compared to the Minimum 85 % about the concept - of the gasket over the Yellow: Challenging tolerance
process necessary to produce the acceptable tolerances DEADLINE XXX solution pack. Remaining specification (IT grade between 0 and 1
component in question calculations are mostly lower than recommended)
• Sensor tolerance fittings . Red: Difficult tolerance specification (IT
chains (unsolved) Snap calculations should grade more than 1 lower than
• 2,5 N packing spring have priority recommended)
(unsolved)
• 1 N constant force
spring (unsolved)
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15. How to make your organisation design 6θ -solutions
Valcon has gained experience from many succesful product development projects working with the 6θ -methods and
metrics, and offers a variety of services to clients that are interested in improving their quality and predictability of their
product development process.
• Implementation of 6θ™ • Executing 6θ™-product • 6θ™-training of
in the organisation. development in a relevant personnel –
• Training of engineers, specific project. from engineers to top
project managers and • Ongoing management
directors. documentation and • Certification (green,
• Integration into improvement of 6θ™- yellow & black belts)
corporate NPD- level.
process
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16. 6θ™ in an academic context
6θ™ is also being applied in academia
• Valcon and DTU (Technical University of Denmark) are sponsoring a PhD Research
Project on robust design.
• DTU is developing a course on robust design scheduled to launch in the fall semester
2013. Valcon will contribute with knowledge and cases.
• Master Thesis Projects on robust design are currently underway.
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17. Contact
For further information, contact Valcon:
Janus Juul Rasmussen
Director of Valcon Design
Mail: jjr@valcon.dk
Telephone: (+45) 24 43 97 69
Martin Ebro
6θ™-specialist
Mail: mec@valcon.dk
Telephone: (+45) 24 43 97 86
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