*Corresponding author. Antony Lowe Department of Mech-anical Engineering, University of She$eld, Mappin Street, Shef-"eld, S1 3JD, UK. Tel.: 0-114-2227767; fax: 0-114-2753671.
E-mail address:a.j.lowe@she$eld.ac.uk (A. Lowe)
QFD in new production technology evaluation
Antony Lowe
!
,
*
, Keith Ridgway
!
, Helen Atkinson
"
!Department of Mechanical Engineering, University of Shezeld, Mappin Street Shezeld S1 3JD, UK
"Department of Materials Engineering, University of Shezeld, Mappin Street, Shezeld S1 3JD, UK Received 21 September 1998; accepted 12 October 1999
Abstract
The large number of new technologies being developed means it is vital for organisations to make appropriate selections that will translate limited capital resources into maximum competitive advantage. However, a thorough
economic evaluation of a technology requires considerable time and e!ort. This paper presents a tool developed from the
techniques of quality function deployment. This tool allows a rapid evaluation of the feasibility of using the thixoforming process to manufacture products. The paper describes the semi-solid metal processing technology of thixoforming, the
relevant quality function deployment techniques and the approach used to develop the tool. ( 2000 Elsevier Science
B.V. All rights reserved.
Keywords: Quality function deployment; Technology; Selection; Evaluation; Thixoforming
1. Introduction
Computer Aided Design, Computer Aided Manufacture, Computer Integrated Manufacture, rapid prototyping, high-speed machining, hot iso-static pressing and thixoforming are just a small selection of the many innovative technologies being promoted around the world. All of these technolo-gies have the potential to provide manufacturing organisations with a competitive advantage over their competitors. The major di$culty though is in selecting and investing in the most suitable techno-logy. Not only does an organisation have to make
this selection accurately but also rapidly if it is not to lose the opportunity to an ambitious competitor. Investment in many of these technologies in-volves a degree of risk, especially for those with few or no existing commercial applications. In these cases the lack of available process expertise means that investment in research and testing will be necessary to develop a stable and reliable process. For such a developed commercial application the bene"ts which have been attributed to the techno-logy by its proponents may not appear as antici-pated. There is therefore a need to ensure that this investment and development e!ort is not wasted on inappropriate technologies.
Investment appraisal techniques have been re-"ned over a number of decades to provide a reason-able "nancial measure of the value of making an investment in capital equipment. Techniques used include Payback Period, Net Present Value and
Materials at the University of She$eld have been involved in the development of one such innovative manufacturing technology. The technology for the
semi-solid processing of metals, also called
thixoforming, has been available for some years. Although commercialised in Japan, the US and Europe it has yet to be commercialised in the UK despite the many bene"ts promised. A three year
study on the`Exploitation of Semi-Solid
Process-inga was embarked upon to provide stimulus for
this adoption. One of the key components of this work was a software package for potential users of
the technology. This software`ThixoCostawas to
provide facilities for carrying out a `Cost}Bene"t
Analysisaof the technology using a business
pro-cess perspective, for the application circumstances of any user company. During the development of this software it became obvious that before the managers of a company were able to commit the resources necessary for gathering the cost data for
such an analysis, they wanted an`expertaopinion
on whether their particular products were likely to be suitable.
Part of the aim of the project became to analyse the experience held within the Thixoforming Research Group and incorporate it, in a structured way, into a decision making tool within the software, to o!er users such an opinion.
Initially, the application of a neural net was con-sidered. This could accept as inputs, measures of relevant attributes that characterise a product. The net could be trained with the details of existing commercial thixoformed products and those of products currently recognised as unsuitable. The
upon semi-solid metal alloys was "rst recognised
by Spencer et al. [2] while studying the unusual properties of vigorously stirred tin-lead slurries in the early 1970s. The microstructure of the stirred alloy comprises rounded particles of solid sur-rounded with liquid of a lower melting point, rather than the normal angular and interlocking dendrites (Fig. 1). This microstructure gives the material its thixotropic properties, i.e. when
sheared the material #ows but when allowed to
stand it thickens.
Thixoforming is one member of the family of semi-solid forming processes and possesses charac-teristics of both casting and forging. The solid feed stock for thixoforming must be pre-treated, so that on heating into the semi-solid state the microstruc-ture is spheroidal rather than dendritic.
A general thixoforming process cell incorporates four operations (Fig. 2):
1. A bar of thixoformable raw material is cut into appropriate slug lengths.
2. The slugs are heated in a controlled manner, using either an induction coil or a mu%e furnace
into a uniform`mushyastate.
3. The heated slug is transferred to the shot sleeve of a suitably modi"ed die casting machine. Ini-tially, the heated billet of material behaves like a solid, holding its shape unsupported and able to withstand the low stresses of handling. When the semi-solid material is subjected to shear
stresses during injection into a die, it #ows in
a smooth laminar manner and accurately "lls
Fig. 1. Dendritic (left) and spheroidal (right) microstructures.
Fig. 2. The thixoforming process. 4. The component feeding and gating systems are
then removed using a clipping press or band saw.
Since the alloy #ows under very low stresses
(around 0.1 MPa) the mechanical stresses acting on
the die during"lling are small. This property allows
softer die materials, such as graphite, easily machi-nable stainless steels and disposable one-shot non-metallic dies as utilised in the work carried out by McLelland et al. [3] to be used. This permits the economic application of thixoforming to the small production volumes required by rapid prototyping and mass customised production.
Kirkwood [4] describes the attributes of thixoforming as follows:
f An energy e$cient process which is easily
auto-mated and controlled to achieve consistency.
f Production rates that are similar to pressure die
casting or better.
f Smooth"lling of the die with no air entrapment
and low shrinkage porosity giving parts of high
integrity and allowing application to high strength heat treatable alloys.
f Lower processing temperatures reduce the
ther-mal shock of the die, promoting die life and allowing the processing of high melting point alloys (such as tool steels and stellites) that are di$cult to form by other means.
f Fine, uniform microstructures giving enhanced
Fig. 3. A generic QFD house of quality [10]. conditions, the degree of integration into the
exist-ing production process and the demands of an organisation's business environment.
Chiarmetta [5] and Kenney et al. [6] document a number of drawbacks which currently limit the commercial viability of thixoforming:
f The high cost of raw material and the low
num-ber of its suppliers.
f Considerable research e!ort and expense is
re-quired to implement a viable manufacturing pro-cess due to the limited available propro-cess knowledge.
f Die development costs are higher than for
conven-tional forming technologies because of the lack of available process experience and design rules.
f The personnel employed to operate and
main-tain thixoforming plant require a higher level of training than equivalent traditional operators and command higher wages.
The number and type of bene"ts and drawbacks attributed to thixoforming are typical of many new manufacturing technologies. For an organisation
to make an accurate assessment of the "nancial
attractiveness of an investment the potential impact of all these must be considered. This would necessitate a considerable data gathering exercise and the requirement for a detailed understanding of the technology. The proposed QFD-based tool
provides a "rst step to prevent the majority
of inappropriate assessments and can also speed
the eventual"nancial analysis by highlighting the
most important bene"ts and drawbacks to be evaluated.
3. Quality function deployment and the prioritisation matrix
3.1. Quality function deployment
Quality function deployment (QFD) is a set of powerful product development tools and proced-ures originated in Japan to take the concepts of quality control from manufacturing and transfer them to the new product development process.
Akao [7] "rst began to develop the concepts of
QFD in the mid-1960s and this led to the "rst recognised implementation of the approach in 1972 at the Mitsubishi Heavy Industries Kobe Shipyard [8].
The house of quality (HOQ) matrix is the central construct of QFD and is its most recognised form. It is described by Hauser and Clausing [9]:
The house of quality is a kind of conceptual map that provides the means for interfunctional plann-ing and communications.
There are nearly as many forms of the HOQ as there have been applications and it is this adapta-bility to the needs of a particular project or user group which is one of its strengths.
Fig. 4. Prioritisation matrix with weighted rows and cells.
components:
1. Customer requirements (Whats) 2. Technical requirements (Hows) 3. Planning matrix
4. Interrelationship matrix 5. Technical correlation matrix
6. Priorities, benchmarks and targets for technical descriptors
The HOQ matrix translates the needs expressed by a customer into the design targets of a proposed new product. This is e!ected by entering weightings into the central Interrelationship Matrix which represent the scale of the perceived relationship between each customer and technical requirement. These weightings are combined with measures of the relative importance of each customer require-ment to calculate a priority for each of the technical requirements in terms of satisfying customers. The remainder of the HOQ contains competitive benchmarking and market analysis information which is also relevant to the setting of the target design values.
A simpli"ed form of the HOQ matrix was utilised in this work. The Technical Correlations and Planning matrices were removed and only the prioritised requirements row included at the base. The resulting matrix format is referred to as a prior-itisation matrix.
3.2. The prioritisation matrix
In a prioritisation matrix, as in the HOQ, the interrelationships expressed in individual cells are assigned a value. Numbers or symbols are com-monly used in QFD to represent the strength of such an interrelationship.
Weightings are also used to illustrate the relative importance of items within the list of customer
requirements. An overall value for the`importance
of the strengthaof a particular interrelationship can
then be numerically calculated. This involves multi-plying the weighting in each matrix cell by the relative importance of the row item with which it is associated (see Fig. 4). These values can then sum-med down a column to give a measure of the
`importance of the strengthsa of the overall
rela-tionships between a particular column item and the entire list of row items (see Fig. 4).
In this manner the matrix allows the items of one list to be ranked based upon their relationships with the items of another list.
4. Building the technology evaluation tool
This basic matrix tool was developed in order to focus upon the interrelationships between a prod-uct's characteristics (customer attributes in the HOQ) and the characteristics of the thixoforming process (engineering characteristics in the HOQ). The weightings of these interrelationships were combined in a manner similar to that used in a pri-oritisation matrix to illustrate the relative import-ance of the characteristics of thixoforming. The sum of these values was used to give a product a score for its overall suitability for thixoforming
(see Fig. 5). The "nal tool was referred to as
a multi-attribute matrix analysis.
Fig. 5. Proposed multi-attribute matrix analysis technology evaluation tool.
The latter three thixoforming process character-istics (raw material, process development & skills/ wages) are considered to currently be the major drawbacks of the technology. The weightings ap-plied to these characteristics were therefore sub-tracted rather than added in the calculation of the overall product suitability score.
To standardise the characterisation of a product under consideration, each of the eight product
characteristics were allocated three settings.
For example Critical/Important/Unimportant,
High/Small/No, Complex/Medium/Simple and
Long/Medium/Short depending upon the nature of the characteristic. Before the matrix relationships could be discussed, it was important to be clear about the de"nition of each characteristic and each of its settings (see Table 1).
The next stage was to establish the values for each of the interrelationships that could be dis-played within the matrix. These were selected from a four-point scale:
5 Strong relationship between the product and thixoforming characteristics
the basis for the weighting values to be allocated to
each cell. Once again these"gures were subject to
several discussions and reviewed to ensure all pos-sible perspectives were included. Table 2 illustrates the transition from a combination of character-istics, to the relevant issues and so into cell weight-ings.
The completed weighting evaluations were then developed into a tool within the ThixoCost soft-ware package (illustrated in Fig. 6). This was writ-ten in Visual Basic 4.0 and allows a user to rapidly characterise their product using a scrolling menu for each of the product characteristics. As each characteristic setting is chosen the interrelationship values are automatically entered into the cells of the matrix. A second set of scrolling menus provides the user with a facility to enter the relative import-ance of each product characteristic. These allow entries on a scale of 1}5.
To ensure comparable scoring between users (i.e. avoid the situation where a user rates all character-istics with the highest or lowest level of importance) a system for the allocation of importance scores is recommended, as detailed in Table 3 (an applica-tion of this importance scoring system is shown in Fig. 6). The system does not have to be strictly adhered to but the use of the full range of import-ance scores is necessary if the calculated product suitability score is to be analysed correctly by the software.
Once the user has selected a setting and import-ance weighting for each product characteristic, the
software calculates a`priorityafor each
De"nitions of product characteristic levels
Product characteristic Setting 1 Setting 2 Setting 3
Weight Critical: Minimising the weight of the
com-ponent is a critical issue
Important: The weight of the component is important but not critical
Unimportant: The weight of the component is not important
Strength Critical: The strength of the component is a
critical issue
Important: The strength of the component is important but not critical
Unimportant: The strength of the component is not an important issue
Geometry Complex: The geometry of the component is
highly complex. e.g. fuel rail
Medium: The geometry of a component is of medium complexity
Simple: The geometry of the component is basic. e.g. a chisel
Tolerances Critical: The meeting of demanding material
property and dimensional tolerances is a critical issue
Important: Material property and dimensional tolerances are important but not critical
Unimportant: Meeting dimensional and material property tolerances is not important
Price premium High: The market will allow a premium price
to be charged for a thixoformed product
Medium: The market will allow a small premium price to be charged for a thixoformed product
No: The market will allow no premium to be charged for a thixoformed product
Lead Time Long: The lead time between receiving an
order and despatching a product is not important and is greater than 3 months
Medium: The lead time between receiving an order and despatching a product is between 3 months and 1 month
Short: The lead time between receiving an order and despatching a product is critical and is less than 1 month
Flexibility High: A customised product is produced
in small batches, unique to each customer
Medium: A medium sized range of standard products is produced
Low: A single standard product is produced in large batches Finishing operations High: In the current process there are
more than 3 machining/"nishing/reinforcing operations which could be removed through thixoforming
Medium: There are 1 or 2 machining/"nishing/ reinforcing operations in the current process which could be removed through thixoforming
Table 3
Recommended relative importance scoring Relative
importance score
Application of score
5 The single most important characteristic 4 The next two most important characteristics 3 The two characteristics of medium importance 2 The next two less important characteristics 1 The single least important characteristic
Table 4
Interpretation of product evaluation scores Product evaluation score Software interpretation
Greater than 100 The product under consideration is suitable for the application of thixoforming technology and a detailed cost bene"t analysis should now be undertaken.
Between 100 and 80 The score allocated to this product by the multi-attribute matrix analysis shows it to be a borderline case. You may wish to repeat this evaluation paying close attention to the characteristic settings and importance weightings chosen before deciding whether to pursue a further cost bene"t analysis.
Less than 80 The product under consideration is presently unsuited to the application of thixoforming. prioritisation matrix. The magnitude of these
col-umn totals illustrate those bene"ts and drawbacks which are of the greatest and least impact in the considered potential implementation of the
techno-logy. This information is useful in concentrating any "nancial studies on appraising the use of the techno-logy as well as focusing the development necessary in implementing the process (in the Fuel Rail example shown in Fig. 6, the near net shape capabil-ity of thixoforming is highlighted as the most impor-tant bene"t by its highest characteristic score. Process development is also highlighted as being the most serious drawback by its lowest score).
The overall product suitability score (referred to
as the`Evaluation Scoreain Fig. 6) is the sum of
these`prioritiesa, with the three drawback column
Table 5
The multi-attribute matrix analysis applied to existing thixoformed products
Existing thixoformed product Multi-attribute matrix analysis evaluation score
Fuel rail (Weber}Italy) 117
Steering link (Buhler}Switzerland) 105 Automobile wheel (Alumax}US) 109 Suspension subassembly (Stampal}Italy) 125
Fig. 6. The multi-attribute matrix analysis screen from ThixoCost. thixoformed products, potential products and
those product types deemed unsuitable to the process as identi"ed and characterised by the Thixoforming Group.
5. Validation of the evaluation tool
In order to verify the validity of the recommen-dations made by the technology evaluation tool
a series of tests were carried out. A set of 20 prod-ucts were selected that were not used in the devel-opment of the suitability score interpretation model. These products included commercially pro-duced thixoformed products and also products under consideration for application of the process. The software output was then compared with the opinions of the Thixoforming Group.
Table 5 illustrates example values produced by the tool for existing thixoformed products.
6. Further applications
The validity of the evaluation tool was proven for the range of products with which it was tested. In addition to successfully di!erentiating between those products that are suitable and unsuitable for the process, it e!ectively highlighted the most im-portant process characteristics for consideration in
any further analysis and in the"nal development of
7. Conclusions
The multi-attribute matrix analysis tool has been developed from the techniques of QFD and applied to the evaluation of potential products for an inno-vative metal forming process.
This technology evaluation tool does not substi-tute for a comprehensive economic analysis. The level of subjectivity necessary in allocating charac-teristic settings, importance weightings and interre-lationship scores, if such a tool is to be applied generically, means speci"c accuracy cannot be achieved in each case. Instead the value of such a tool is in the focusing of a subsequent economic analysis or removing the need for it altogether.
From this work, it would seem that a similar approach could be as e!ectively applied to the analysis of other new innovative technology ap-plications. High-speed machining for example has both bene"ts (e.g. rapid production cycle, thinner webs, etc.) and drawbacks (e.g. high cost of machin-es, lubricants and tooling) which the tool could evaluate against relevant product characteristics (e.g. geometry, material, machinability, etc.).
Metallurgical Transactions 3 (1972) 1925}1932.
[3] A.R.A. McLelland, P.R.G. Anderson, H.V. Atkinson, D.H. Kirkwood, The application of ceramic moulds to semi-solid metal forming, Proceedings of the Fourth Inter-national Conference on Semi-Solid Processing of Alloys and Composites, The University of She$eld, 1996, pp. 274}277.
[4] D.H. Kirkwood, Semisolid metal processing, International Materials Reviews 39 (5) (1994) 173}189.
[5] G. Chiarmetta, Thixoforming of automobile components, Proceedings of the Fourth International Conference on Semi-Solid Processing of Alloys and Composites, The University of She$eld, June 1996, pp. 204-207.
[6] M.P. Kenney, J.A. Courtois, R.D. Evans, G.M. Farrior, C.P. Kyonka, A.A. Koch, K.P. Young, Semisolid metal casting and forging, Metals Handbook, 9th Edition, ASM International, Metals Park, OH, 1988, p. 333.
[7] M. Kogure, Y. Akao, Quality function deployment and CWQC in Japan, Quality Progress 16 (10) (1993) 25}29. [8] N. Singh, Systems approach to computer-integrated
design and manufacturing, Wiley, Chichester, UK, 1996, p. 133.
[9] J.R. Hauser, D. Clausing, The house of quality, Harvard Business Review (1988) 63.
![Fig. 3. A generic QFD house of quality [10].](https://thumb-ap.123doks.com/thumbv2/123dok/3115822.1378508/4.544.271.478.47.238/fig-generic-qfd-house-quality.webp)
