http://www.protek.ie/ Annette Carty-Mole B.Eng (Hons) Design Engineer, ProTek Medical When a company is given the task of designing a new product or redesigning an existing product, it is important to keep in mind the three main goals of cost, quality and speed. These goals can be further split into more quantitative criteria which are relevant throughout the product’s life cycle. Designing for manufacture and assembly are typical examples of two criteria which will have a large impact on the cost, quality and speed at which the product is developed. The methodology of design that meets an all-encompassing range of criteria is known as designing for ‘X’.

1. Demystifying Designing for ‘X’
Annette Carty-Mole B.Eng (Hons)
Design Engineer, ProTek Medical

2. INTRODUCTION TO
DESIGNING FOR ‘X’
When a company is given the task of designing a
new product or redesigning an existing product, it
is important to keep in mind the three main goals
of cost, quality and speed. These goals can be
further split into more quantitative criteria which
are relevant throughout the product’s life cycle.
Designing for manufacture and assembly are typical
examples of two criteria which will have a large
impact on the cost, quality and speed at which the
product is developed. The methodology of design
that meets an all-encompassing range of criteria is
known as designing for ‘X’.
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3. DESIGNING FOR ’X’
1.
DESIGNING FOR ‘X’
For a product to be successful it must meet the customer’s
needs whilst still being profitable to the company. It must
therefore satisfy the product requirements, but still be
produced within the shortest timeframe possible and as
cost effectively as possible.
The strategy of designing for ‘X’ involves designing all aspects of the
product’s life cycle. There are numerous criteria to be met when designing
a product, including the following:
1.
Voice of the customer.
2.
Human factor engineering.
3.
Reliability.
4.
Maintainability.
5.
Environment.
6.
Design for Manufacture.
7.
Design for Assembly.
1. Voice of the customer
For a product to be successful it must meet a customers need, therefore it
is essential that the customer is consulted in the initial stages of product
development to gather information for the design requirements.
A generic medical delivery device is shown in Figure 1. Before designing this
device, sales and marketing will meet its end users to collate their opinions
and requirements for it. This information will often be qualitative and must
be translated from the customer’s language into quantitative, measurable
product targets [1]. A surgeon, for example, may request that a catheter
is designed to easily navigate anatomy. This can be quantified in terms of
the catheter materials minimum required flexibility. A Quality Function
Deployment matrix may be used to determine these quantitative targets.
Figure 1 – Generic Medical Delivery Device
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4. 2. Human factor engineering [2]
Human Factor Engineering consists of three elements: the user, the user device’s
interface and the device environment.
A medical device must be designed with the end user in mind. Different users, such
as surgeons, nurses and patients, will have differing knowledge of the device. They
may have different physical strengths and sizes and they may be using the device in
stressful conditions. These must be accounted for during the design of the device. The
device’s interface, such as its sliders and releases, must be simple to use and intuitive.
Users will presume that the product is operated in the same way as other similar
devices.
Factors of the device’s environment must be considered. For example, the level of
lighting, noise and the amount of space around the device will all effect its ease
of operation. Consideration should also be given to the interoperability with other
medical devices.
3. Reliability [3]
If a medical device fails it can have a detrimental effect on the patient’s safety, on
revenue, and on the company’s reputation. Therefore it is important that a device is
designed for reliability, keeping its required service life in mind. Different products will
have different reliability requirements, for example: disposable needles have a short
service life over which they must be reliable. Products with longer service lives can
have their reliability increased with Preventative Maintenance.
The typical device reliability curve is shown in Figure 2 and it is clear that the highest
chance of failure is at the start and end of a product’s life. The start-of-life failures can
often be avoided if high quality assembly procedures are followed and the product
has been adequately designed for the stresses it will encounter. The end of life failures
are attributable to fatigue. If the device is correctly designed for its target service life,
then these failures will not occur.
Start-of-Life
Failure
End-of-Life
Failure
Figure 2 – Typical Product Reliability Curve
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5. DESIGNING FOR ’X’
4. Maintainability [4]
•
A product designed with maintainability in mind will be
able to provide cost and time savings to the manufacturer.
Designing maintainability and serviceability into a product
will also reduce the chance of a device failing. Design
considerations include:
•
1.
Self-diagnostics for quick identification
of the problem/reminders for servicing.
2.
Easy access to parts for replacement.
3.
Modular design so that parts can be quickly
and easily replaced.
4.
Fail-safe design of part orientation for
re-assembly.
5.
Design for standard fasteners and tools.
5. Environment
All manufacturers must meet environmental regulations
for their products. These regulations apply at all stages
of the product life cycle, including manufacturing. For
example these regulations govern the manufacturing
processes used, materials used, waste disposal, the
amount of packaging produced and final product
disposal. Such design allows the company to benefit
from cost savings, either through energy efficiency or
through reduced environmental levies and penalties.
•
•
A uniform wall thickness is used and where possible
this is the minimum amount recommended for
the material. This reduces the cooling time which
reduces the cycle time of the part.
Corners are rounded to improve plastic flow and
reduce stress.
Drafts are applied to aid removal from the mould.
Ribs are used to provide structural support.
FILLETED
CORNERS
RIBS
UNIFORM WALL
THICKNESS
DRAFTS
APPLIED
WHERE
POSSIBLE
TWO SHOT
SURFACE
Figure 3 – Generic Medical Device Handle: Design
for Manufacture
This part has soft grip areas on the handle which are
manufactured using 2-shot injection moulding. The
finished handle with the grip is shown in Figure 4.
6. Design for Manufacture
There are certain guidelines for design which aid
in ease of manufacturability. Different guidelines
and rules apply depending on how the part will be
manufactured. For example machined parts, injection
moulding, sheet metal stamping, die cast etc. all have
different design requirements.
Best practice is being followed for the injection
moulding of this device’s handle section, as shown
in Figure 3 and in the following methods:
2 SHOT SOFT
GRIP HANDLE
Figure 4 - Generic Medical Device Handle: Design
for Manufacture
As well as designing individual parts for manufacture, it
is also important to design the factory flow of the entire
product. This includes designing modular components,
calculating and coordinating cycle times, using family
moulds etc.
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6. Figure 5 – Generic Medical Device Handle: Plastics Flow Analysis
As part of the design for manufacture of this
component, a plastics flow analysis can be performed
to ensure that it can be optimally manufactured by
injection moulding. The results of a typical plastics flow
analysis are shown in Figure 5.
7. Design for Assembly
Reductions in time and cost can be achieved if the
product is designed with best assembly practices in
mind. Standard guidelines for best assembly practices
are as follows [5]:
1. MINIMISE: parts and fixings, variations in design,
assembly movements and assembly directions.
2. USE: lead-in chamfers, automatic alignment, easy
access for locating surfaces, symmetrical parts or
exaggerated asymmetry, easy to handle parts.
3. AVOID: visual obstructions, simultaneous fitting
operations, parts which will tangle or nest,
adjustments which affect prior adjustments.
2. IMPLEMENTING
DESIGNING FOR ‘X’
It can be challenging to incorporate all of the design
criteria equally into one product, especially when
different design criteria are controlled by different
departments.
Serial design [6]
Traditionally each department is responsible for
different aspects of a product’s design. As a product
develops, so does its requirements, as each department
adjusts the design to suit their own criteria (as shown in
Figure 6).
This is known as serial design. There is little
communication between departments except to hand
the product over to the next stage. The manufactured
product may be very different from the customer’s
original requirements.
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7. DESIGNING FOR ’X’
Point based design [6]
Point based design, as shown in Figure 7, is another
type of design structure. This method requires one
department to liaise with the others, coordinating all
design for ‘X’ activities. Every change requires a design
review involving all departments. The design review
may create more changes which again require updates
and another design review. This design structure
assumes that after enough iterations of the design, an
agreement between the departments will be reached.
Concurrent engineering [6]
When it comes to designing for ‘X’ product
development, this method is preferred in the industry.
The different departments progress the design of
multiple products simultaneously through stage gates
[7]. Figure 8 illustrates this process. This model can be
adapted for different timelines, for example gates 1-2
can be combined and gates 3-4 can be combined to
create a 2-stage gate process. Although Figure 8 is
shown as a linear process, activities within the stages
may circle, overlap or happen in parallel.
Figure 6 - Serial Product Design
Where possible, each department quantifies a range of
acceptable limits for a specific criterion, within which the
design may fall. This allows for several different designs to
be progressed in parallel until the testing and validation
phase, at which the final design may be selected. No
individual department is responsible for a particular stage
and so it allows for all of the design for ‘X’ criteria to be
met.
Figure 7 – Point Based Design
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8. Figure 8 – Concurrent Engineering with Stage Gates [7]
DFSS as part of concurrent engineering
Design for six sigma (DFSS) is a methodology employed from the beginning
of product development though to product manufacture and can be
applied to concurrent engineering. Traditional six sigma methodology
focuses on improving existing manufacturing processes to ensure the
products reach a quality standard of 3.4 defects per million. DFSS shifts the
quality focus to the entire product development process as shown in Figure
9.
Figure 9 – Design for Six Sigma Methodology vs.Traditional Six
Sigma Methodology [8]
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9. DESIGNING FOR ’X’
With DFSS, the emphasis is on design optimisation rather than process improvement. Traditional six sigma
implements strict processes which measure, analyse and remove variation in production. This stringent approach
to production results in a very high quality product. However, traditional six sigma methodology needs to be
adapted if it is to be applied to the early development stages of a product in concurrent engineering. Design for six
sigma is this adapted methodology, as shown in Figure 10. DFSS promotes creativity which can potentially lead to
more successful product generation, as it follows the stage-gate product design process.
Figure 10 - Design for Six Sigma Vs Traditional Six Sigma Methodology [8]
3. SUMMARY
Designing for ‘X’ ensures that all design criteria for a product are gathered, analysed and met where possible. Some
of these criteria will have a positive effect on the product’s quality, some on the cost to produce the product and
some on the speed at which the product is produced. This will result in a product that is easier and quicker to
manufacture whilst also being of higher quality.
Designing for ‘X’ can become complicated if multiple design departments are involved in product development.
In practice, different departments will be responsible for different design criteria. By communicating ranges of
acceptable limits for design criteria between the departments, several product concepts can be progressed
through the stage-gates of product development. This concurrent engineering approach minimises ‘back-tracking’,
as all departments are simultaneously involved in development decisions. A company which successfully applies
this methodology will achieve a development process capable of producing high quality, low cost products in a
highly efficient manner.
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10. 4. REFERENCES
[1]
[2]
[3]
[4]
[5]
[6]
[7]
[8]
Mazur, G. (1993), “Quality Function Deployment for a Medical Device”, Proceedings from the Sixth Annual IEEE Computer-Based
Medical Systems Symposium
U.S. Department of Health and Human Services Food and Drug Administration Center for Devices and Radiological Health (2000),
“Medical Device Use-Safety: Incorporating Human Factors Engineering into Risk Management”, Guidance for Industry and FDA
Premarket and Design Control Reviewers
Taylor, A. (2005), “ Design for Reliability Concepts, Causes and Identification”, White Paper Design1st Inc.
FitzGerald, A., “Design for Maintainability”, Journal of the Reliability Information Analysis Centre, Vol. 8 No. 4
Corbett, J. Dooner, M., Meleba, J., Pym, C. (1991) Design for Manufacture, Strategies, Principles and Techniques ,Addison-Wesley
Publishers, Wokingham UK.
Sobek, D., Ward, A., Liker, J., (1999), “Toyota’s Principles of Set-Base Concurrent Engineering”, Sloan Management Review [0019-848X],
Vol. 40 Iss. 2
Cooper, Dr R. (2008), “Perspective: The Stage-Gate Idea-to-Launch Process - Update, What’s New and NexGen Systems”, Journal of
Product Innovation Management, Vol. 25 No. 3
Kiemele, Dr M. (2003), “Using the Design for Six Sigma (DFSS) Approach to Design, Test and Evaluate to Reduce Program Risk”, NDIA
Test and Evaluation Summit (Victoria B.C.)
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11. DESIGNING FOR X
DESIGNING FOR ’X’
Demystifying Designing for ‘X’
For more information on how ProTek can help you, please contact:
ProTek Medical Ltd. Finisklin Business Park, Sligo, Ireland
Tel.: +353 (0)71 9171808 Fax: +353 (0)71 9171810 Email: info@protek.ie