Demystifying Designing for ‘X’

Annette Carty-Mole B.Eng (Hons) Design Engineer, ProTek Medical

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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’.

INTRODUCTION TO DESIGNING FOR ‘X’

DESIGNING FOR ’X’

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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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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.

Figure 2 – Typical Product Reliability Curve

Start-of-Life Failure

End-of-Life Failure

DESIGNING FOR ’X’

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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.

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:

• 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.

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.

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.

FILLETED CORNERS

RIBSUNIFORM WALL

THICKNESS

TWO SHOTSURFACE

2 SHOT SOFT GRIP HANDLE

DRAFTSAPPLIEDWHERE

POSSIBLE

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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.

Figure 5 – Generic Medical Device Handle: Plastics Flow Analysis

DESIGNING FOR ’X’

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Figure 6 - Serial Product Design

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. 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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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]

DESIGNING FOR ’X’

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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. SUMMARYDesigning 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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4. REFERENCES

[1] Mazur, G. (1993), “Quality Function Deployment for a Medical Device”, Proceedings from the Sixth Annual IEEE Computer-Based Medical Systems Symposium[2] 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[3] Taylor, A. (2005), “ Design for Reliability Concepts, Causes and Identification”, White Paper Design1st Inc.[4] FitzGerald, A., “Design for Maintainability”, Journal of the Reliability Information Analysis Centre, Vol. 8 No. 4[5] Corbett, J. Dooner, M., Meleba, J., Pym, C. (1991) Design for Manufacture, Strategies, Principles and Techniques ,Addison-Wesley Publishers, Wokingham UK.[6] Sobek, D., Ward, A., Liker, J., (1999), “Toyota’s Principles of Set-Base Concurrent Engineering”, Sloan Management Review [0019-848X], Vol. 40 Iss. 2[7] 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[8] 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.)

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