Techno-economic product designing

Technoeconomic

product designing K GROTLOH and E ROTHLIN SulzerBrothers, Winterthur, Switzerland Sulzer has been working for several years now on an overall concept for the integrated techno-economic designing and fabrication of technical products 7. The overriding concept for product designing is dealt with here. Taking an example from practice, individual working steps in the procedural technique are shown, as well as selected methods and working media for solving sub-tasks. Keywords: systematic design, methodology, engineering

The concept presented is based on more recent advances in systematic designing 2'3. The procedural plan (Table 1) is subdivided into the four stages of product designing; planning, conception, draft design and implementation. A selection of suitable methods and working media is apportioned between the design stages in a separate allocation plan (Table 2). The results achieved are critically assessed in individual working steps irrespective of whether a new development or an improvement, an adaptation, an entire product, a subassembly or design zone is involved. Steps already performed may have to be gone over again, or subsequent steps may be skipped. Similarly, methods and working media are selected and deployed according to the task involved in each particular case.

PLANNING Defining the development objective Owing to the increasing costs of fossil fuels, higher efficiencies in the energy conversion of thermal power plants are desired. As a result, the steam data (temperature and pressure) usual today at the boiler outlet are being raised significantly. In view of these requirements, it is necessary to examine how far the present proven design for high pressure turbine bypass valves is still acceptable. Stronger dimensioning brings disadvantages under cyclic thermal loading, and moreover production costs increase. The following task e m e r g e d from this basic " situation: the existing startup pressure and temperature reducing valve is to be adapted to the higher operating data by a new conception. The Federal German TRD calculation rules currently in force are to be met in full. At the same time, the designer is to be informed as to the anticipated production costs.

CONCEPTION Clarifying the task, working out the list of requirements

This paper was first publishedin the SulzerTechnicalReviewNo 3 (October 1982)

vol 4 no 3 july 1983

The development assignment provides a rough outline of the task involved. However, exact definition of the requirements and boundary conditions is required to enable the design department to work efficiently. A so-called reference type is laid down for effective working, since the assignment relates to a type series. The new design data (eg pressure, temperature, flow) is fixed for this reference type. The data necessary for the design is gathered together from talks with various people, especially with the project team. Also to be taken into account are the necessary calculation rules and experience (eg materials). A list of requirements for the new valve takes shape by assembling this information, subdivided into fixed requirements, minimum requirements and wishes (Table 3). The weight attached to minimum requirements and wishes is graded by a priority quantification method. Minimum requirements and wishes are graded separately (Table 4). The relative priorities resulting are transferred to Table 3.

0142-694X/83/030177-06 $03.00 ~) 1983 Butterworth & Co (Publishers) Ltd

177

Table 1. Procedural plan for product designing

Planning

I

Defining the objective <

I

(Trend studies, market analysis, research results, customer enquiries, previous developments, patent situation, environmentalism)

I

Fixing the development assignment

Conception

I

Defining the task

I

Working out list of requirements

I

Table 2. Allocation plan for product designing Designing stages Planning Conception

Methods and working media Draft

Implemenration Trend studies, market analysis List of requirements Abstraction and function methods Idea finding methods Morphological box Techno-economic assessment procedure Value analysis technique Relative costs Design guidelines Design families, similar types Standard and repetition parts Standards Quality handbook

Decision

I

Abstraction, subdividing the overall function into part functions '{

I

Searching for solution principles and elements to fulfil the subfunctions I (Orientational calculations and/or tests) I Combining solution principles to fulfil the overall function I (Selecting suitable combinations of principles) I Elaborating concept variants for the principle combinations

I

When everyone involved agrees on the requirements, the decision to proceed with the development work can be taken by the technical management.

Abstraction, subdividing the overall function into subfunctions

(Large-scale sketches or schematic diagrams)

I

Techno-economic assessment of concept variants I (Selecting the solution concept) I Decision

Draft design

I

Production of true-to-scale draft design • I Techno-economic assessment of draft design I (Elimination of weaknesses) I Improved draft design

I

(Selection of designing zones) I Optimization of designing zones I Finalization of the draft design

I

Decision

Implementation

I

Design of components • I Product documentation I (Drawings, parts lists, instructions) I Prototype production and testing, eg for series production Verification of costs

I

Decision

(Production go-ahead)

178

Experience teaches that there are often many answers to a given problem, often also differing widely. A major step forward is achieved by formulating the task in more abstract form. The objectives of the abstraction are identifying the essentials of the problem and widening the solution spectrum to provide suitable bases for the search after answers that follows. First the function of the entire system is circumscribed with the help of the 'black box' (Figure 1). The principle of this method lies in abstracting the processes within the system and examining only the interfaces between system and environment. The variables involved (energies, materials and signals) are divided into inputs and outputs. The laws governing the input variables (steam, injection water, opening and closing force, spindle position) and the output variables (steam, losses, cross-sectional alteration, actual positioning signal) and hence the behaviour of the system are described by its function (controlling admission pressure and outlet temperature). The input and output variables are defined in their concrete properties by quantitative and/or qualitative data. In addition, it is often effective to state the actual conditions and describe the environment. In a second stage, the overall system is divided into subsystems. This is best done by imagining the entire product broken down into elements or zones, making sure that 'function units' result from this subdi¥ision. After this, the function can be formulated for each element and the relation of the function presented in a structure. In this case the 'hierarchic function division' (Figure 2) is an excellent tool for abstract presentation of the design objective. It ensures that the superordinated problems are necessarily solved before the subordinate ones. DESIGN STUDIES

Table 3.

Requirements list for a starting and reducing valve

Number Nature 1

F

Requirements

Qualification

Design pressure - high pressure side - low pressure side

2

F

Ph Ph

F F

5

F

6

F

Th T~

Cage throttling surface Spindle opened by zip high pressure/low pressure Water injection - connection - nozzle area Flow cross section

7 8

F F

Material (housing, cover, cage) Fulfilment of stipulation TRD 303 by housing

9

F

10

F

11

F

12

F

13 21 22

F M M

Sudden temperature changes must not cause sliding surfaces to stick Minimum clearance to avoid spindle guide damage from vibration No abrupt wall thickness changes on account of high thermal cycles Geometry of seat sealing surface and tigtening force as reference type (single-seat valve, conical seat, sealing width, hardfaced seat) Control characteristic linear over 10-80 per cent Flow cross section Connection dimensions - inlet - outlet Acceptable production costs Minimum wall thickness possible for housing according to TRS 303 (shape-dependent) Simple fitting/stripping of internals Low noise level Easy replaceability of wear parts (injection part, cage, spindle, seat) Parts exposed to pressure not wear-sustaining Actuator mounting dimensions (lantern) unchanged Stuffing box cooling Existing standard parts used No special tools for fitting and dismantling Other calculation rules satisfied

23 24

M M

31 32 33

W W W

34 35 36 37 38 39

W W W W W W

bar bar

Design temperature - high pressure side - low pressure side

3 4

Importance

¢C °C cm 2

¢~

mm cm 2

max

cm 2

min

cm 2 lOCrMo910 ~,~ oB = 2.105 s=l

cm 2

¢ ¢

**

mm mm Sfr. ~
* ** * **** **** ** *** *** **** *** * ** .

* * * * Decisively important * * * Very important * * Important * Less important F Fixed requirement M Minimum requirement W Wish

Searching

for

solution

principles

to

fulfil

the

subfunctions

The d i s c u s s i o n of t h e f u n c t i o n structure e s t a b l i s h e d s h o w s that this is e q u a l l y v a l i d for t h e e x i s t i n g v a l v e t y p e as for the n e w o b j e c t i v e . O n l y a f e w p r o p e r t i e s related to the f u n c t i o n need c h a n g i n g f o r t h e n e w a s s i g n m e n t . In principle, t h e r e f o r e , t h e e x i s t i n g technical c o n c e p t i o n m a y be taken over. An essential s u b t a r g e t of the a s s i g n m e n t is cost reduction. A cost a n a l y s i s carried o u t p o i n t s u n m i s t a k a b l y to the h o u s i n g , b u t a s i g n i f i c a n t r e d u c t i o n is p o s s i b l e o n l y if the g e o m e t r y of t h e h o u s i n g is altered. U n d e r the g i v e n c o n d i t i o n s , t h e m e t h o d of s y s t e m a t i c v a r i a t i o n 4 offers itself as a s u i t a b l e aid in the search for an a n s w e r . T h e basic idea of this m e t h o d is to break up an e x i s t i n g c o n c e p t into its essential features. The

vol 4 no 3 july 1983

p r o p e r t i e s of t h e s e f e a t u r e s are then v a r i e d s y s t e m a t i c a l l y to o b t a i n the s a m e effect. Of t h e k n o w n v a r i a t i o n possibilities, f o r m v a r i a t i o n s u g g e s t s itself in this case. T a b l e 5 s h o w s a n u m b e r of possible form variations. T h e h o u s i n g f o r m d e p e n d s d i r e c t l y on the c a l c u l a t i o n rules. H o w e v e r , a c c o r d i n g to these rules, the closed s p h e r e is t h e ideal g e o m e t r y . For these reasons, ' v a r i a t i o n of t h e p o s i t i o n ' of t h e effective surfaces or f u n c t i o n e l e m e n t s on t h e basis of t h e spherical f o r m is i n d i c a t e d as a s u i t a b l e aid f o r ' a r r i v i n g at a s o l u t i o n , The f o l l o w i n g f e a t u r e s can also be d e t e r m i n e d as i n f l u e n c i n g t h e costs of t h e h o u s i n g : • • • •

position position position position

of of of of

the the the the

c o n n e c t i o n s (inlet/outlet) actuator water injection seat area

179

Table 4. Establishing t h e relative priorities of t h e m i n i m u m ments and wishes

require-

Overall function admission pressure and outlet temperature

Minimum requirements Code

Designation

Grading

Points rating

A B C D E

Flow cross section Inlet connection Outlet connection Acceptable production costs Minimum wall thickness possible

A B C D

2 1 3 4

Subfu~ction A C D E C D E D E E

E

medium

I AIh J flow I sec

--]

5

Points

Criteria

Stage

4-5 3 2 1

Decisively important Very important Important Less important

**** *** ** *

I clo', I fo Figure 2. Hierarchic function subdivision for starting and reducing valve

Table 5.

Possible form variations

Wishes

Code

Designation

Grading

Simple assembly and disassembly Noise level Exchange of wearing parts Wearing parts not exposed to pressure Actuator mounting dimensions Stuffing box cooling Use of standard tools Special tools Other calculation rules

Points rating

A B C D A F A H A4 B C D B B B B 7 C D C F C H C 6 D E F G H I

D F F H I

D D D D G H E F F I

9 2 7 2 5 3

Points

Criteria

Stage

8-9 6-7 4-5 2-3

Decisively important Very important Important Less important

**** *** ** *

Material conversion

Overall function controlling admission L pressureand outlet Steam: Tz,pz temperature Losses: noise (turbulence)

Steam : Th pl Spray water

Positioning energy conversion

1

Form variation on the component

1.1 1.2 1.3 1.4

Variation of shape (change of form) Variation of dimensions (dimensional change) Variation of number Variation of position of effective surfaces or form elements (change of position) Variation of outer characteristics Variation of inner characteristics

1.5 1.6 2

Form variation on the component assembly

2.1 2.2

Design with one or more parts Modified joining - variation of disconnectability - variation of indirectness - variation of closure - variation of joining mechanism Variation of relative position of components (position change)

2.3

Variation features Z formH ~ " Connections

Drive

Ii

D

Closing force: octuot0r with stroke Opening force : steam pressureAp Signal conversion

Alterction of flow cross section Losses: friction

Spindle positionset points

Actual position

I

Possible solutions

~

/1'

®

Angled

Straight through Y form

(~

~

/

@

"~

High pressure Low pressure side side / "

High pres/sure side J Injection

Sealing surface

J:,o® io®

Low pressure side Axial

Radial

High pressure Low pressure

signals for control

Conditions:material IOCrMoglO,calculation rules, design data, temperature shock

Figure I.

Black box for starting and reducing valve

The possible solutions with the separate variation features may be presented in overview form with the 'morphological box'. The variation features are entered as parameters in the first column of Figure 3. Possible solutions for the second and fourth features can be stated without much trouble. For the first feature, on the other hand, sensible and practical approaches must be examined and entered.

180

Figure 3.

Morphologic box with variation features

Combining solution principles to fulfil the overall function Overall solutions are reached by combining solution principles for the different part functions, or, in the case of our example, the different variation features. If one were to ascertain all combinations, the result w o u l d be 4 × 2 × 4 × 2 = 64 lines (entire solution field). The multiplicity of

DESIGN STUDIES

Table 6. box

Reasons for eliminating possible solutions in the morphologic

1 Requirement 4 F not met (spindle opened Ap high/low pressure) 2 requirement 5 F not met (connections for injection) greater flow through seat, available spray water pressure 3 Design problematical from strength aspect for high pressure valve 4 Possible solution/no new solution 5 Difficult technical feasibility 6 Technically like angle version, but more expensive

Problem field presentation Connections

(2 d ;

-a

Actuator Actuator High pressure 1 Low pressure High pressure 1 Low pressure 14 12 ’ II

I3

1

better overview. Then, in a further quantification step, another four combinations are struck off, stating the reasons (Table 61, leaving four still for further examination.

Elaborating concept variants, selecting the solution concept The four remaining combinations are elaborated into concept variants. Large-scale sketches are produced for further assessment of the variants. Drawing upon technical and economic criteria, the solution concept is arrived at in the next assessment step. In the particular instance, the variant 12 in Figure 4 is judged to be the most promising and adopted as the solution concept.

DRAFT DESIGN Producing a true-to-scale draft design Draft designs are produced to scale on the basis of the solution concept selected. Figure 5 shows the finalized draft for this solution concept (variant 2). Essential features of the new design are:

Figure 4.

Problem field presentation

solutions in the ‘morphological box’ must now be reduced in steps. The solution principles that can be dismissed are deleted stating adequate reasons (Table 6). These are mainly the approaches which do not satisfy the requirements according to the list, and those which are incompatible with others. This process of elimination leaves 2 x 2 x 2 x 1 = 8 lines (narrowed solution field). The remaining eight combinations are set out symbolically in a special form of the ‘morphological box’, the so-called problem field presentation (Figure 41, in order to obtain a

a

Ll

axial entry radial exit (as before) actuator at outlet (low pressure) side, hence simplified spindle guiding axial water injection, but with radial feed separate stuffing box cooling is eliminated actuator needs dismantling to change wearing parts bonnet on outlet side and stuffing box packings fixed with stud bolts.

Techno-economic assessment Before releasing the finalized draft design for the implementation stage, a techno-economic assessment is made to ascertain whether the objective has, in fact, been reached. Moreover, by working out relevant assessment

b

Figure 5. Design variants

vol4 no 3 july 1983

181

Table 7.

Technical assessment criteria

1 2 3 4 5 6 7

10

Technical assessment of the variants

Wall thickness Outlet connection dimensions Replacement of wearing parts Noise level Stuffing box cooling Pressure parts non-wearing Flow cross section

Sum of point ratings Technical quantification x

Quantification points Variant I Variant II Ideal 2 3 4 3 2 3 3 20" 0.71

4 4 3 3 3 4 4 25 0.89

08

4 4 4 4 4 4 4 28 1.00

/s,

/

I 0.8

I0

/ 06

/

/

._u

o4

/

Ld

criteria and applying them, cogent arguments for future customer talks are obtained as a rule. Concealed weaknesses in the solution may be brought to light for the designer. The following variants are to be taken into account for the assessment:

s°

/

0.2

/ /

j 0.2

i 0.4

I O.6

Technical quantification, x

• •

variant I (new solution, old form) variant II (new solution, angle type)

There are seven assessment criteria (Table 7) to establish the technical quantification x. Here it was found that there are no actual weaknesses for the new design (variant II). The solution variant I has reached its limits with regard to operating data. Though the TRD rules are fulfilled, the wall thickness reaches the maximum laid down by temperature cycle calculations. The production costs HK are decisive for the economic quantification y. The target figure according to the list of requirements was given to the designer as reference. In order to ascertain the economic quantification Yi in accordance with VDI guideline 22253, the ideal production costs work out as: HKi = O.8HKzuj

where HKzul = target figure according to list of requirements. Hence: Yul = HKi/HKul

On the strength of the calculated costs HKI and HK,, the economic quantifications Yl = 0.59 and Yll = 0.79 result for the two variants. Entering the technical and economic quantifications xand yin the sdiagram (Figure 6) reveals a higher

182

Figure 6. Quantification (s) diagram

value sH (x, = 0.89; YH= 0.79) for the new design. The minimum requirement concerning production costs is likewise met according to the list of requirements.

Implementation After the satisfactory assessment, the draft design is released for designing the components and preparing the production documentation (workshop drawings, parts lists, testing and inspection rules). Optimal design of the components to facilitate production is of prime importance at this stage.

REFERENCES 1

Arn, E 'Application of systems engineering in design, manufacturing and work study' Sulzer Tech. Rev. Vol 52 No 4 (1970) pp 251-258

2

Richtlinie VDI 2222: Konstruktions-methodik, Konzipieren technischer Produkte Blatt 1 (May 1977)

3

Richtlinie VDI 2225: Technisch-wirtschaftliches Konstruieren. Anleitung und Beispiele Blatt 1 (April 1977)

4

Pf'n~fner,M and Staubli, H Systematische Variation-eine Methode zur L6sungssuche Schweizerische Technische Zeitschrift No 37/38 (16 September 1976) pp 877-883

DESIGN STUDIES