Selection of Materials and Processes

8/3/2019 Selection of Materials and Processes

http://slidepdf.com/reader/full/selection-of-materials-and-processes 1/14

Int J Adv M anuf Tech nol (1991) 6:98-1119 1991 Springer-Verlag Lo ndo n Limited

T h e InternationalJ o u r n a l o f

AdvancedManufacturingTechnology

R E S E A R C H P R O G R A M O N T H E

S E L E C T I O N O F M A T E R I A L S A N D

P R O C E S S E S F O R C O M P O N E N T P A R T S

G . B o o t h r o y d , P . D e w h u r s t a n d W . A . K n i g h tDepartmen t of Industr ia l and M anu factur ing Engineer ing, Un ivers i ty of Rhode

Is land, Rhode Is land, USA

I t is no w wide ly accep ted tha t the f ina l cos t o f a m anu fac tured prod uc t i s large lydeterm ined at the design stage. The research p ro gr am m e described in this pa peraddresses decisions that must be made early in the design procedure , namely

the select ion o f su i tab le processes and mater ia l s for the pro pos ed com po nen tparts o f the prod uct . General ly , designers w i l l tend to conceive parts in termsof the processes and mater ia l s wi th w hich they are fami l iar a nd may , as aconsequen ce, exclud e fr o m considerat ion process and process~material com bi-n a t i o n s t h a t m a y h a v e p ro v e d m o re e c o n o m i c .

A sati~factoo, m eth od for the system atic selection o f suitab le process~materialcom binat ions for par t man ufac ture is no t curren t ly ava ilab le . Such a me thod isb e i n g d e v e l o p e d a n d i m p l e m e n t e d i n a c o m p u t e r e n v i ro n m e n t f o r u se d u r i n g

the early s tages o f pr od uc t design.

Keywords: Design; Materials; Processes

1. Introduction

T h e w r i t er s h a v e b e e n w o r k i n g f o r o v e r a d e c a d e o n s u b j e ct s r e l a t e d to thedesign a n d m a n u f a c t u r e o f p r o d u c t s a n d t h e w a y s in w h i ch d e s ig n decisionsa f fe c t m a n u f a c t u r i n g c o st s. E a r l y w o r k , d i r e c t e d by G . B o o t h r o y d , w a s

s u p p o r t e d b y th e N S F a n d s u b j e c t s s t u d i e d s i n c e t h a t t i m e h a v e i n c l u d e d :

Accepted for pub lication: 25 February 1991



Research Program o n the Select ion of Mater ials and Processes for Com ponent Parts

Product structure analysis and product design for assembly (DFA) [1-8]

Selection of appropriate materials and processes for the manufacture ofindividual parts [9, 10]

Early cost estimating and component part design for ease of manufacture byvarious processes [11-18]

As the work proceeded and industrial input was provided, it became clearthat the subjects of greatest industrial concern were design for assembly andthe early consideration of material and process selection for part manufacture.Consequently, the subject of design for assembly was given the greatest priorityand this has resulted in the well known DFA procedures now used widely inindustry [19, 20].

Although excellent initial work was carried out on material and processselection by Wilson and his co-workers [10], the procedures they proposed

were never developed to the point where they could be applied in practice.We are now developing and testing a variety of approaches to this problem.Three complementary research programmes are underway.

99

2 . O b j e c t iv e s o f t h e R e s e a r c h

The basic objective of the work is to develop a systematic procedure whereby

various feasible material and process combinations for the manufacture of apart can be ranked in order of preference and according to various criteria. Itis believed that many opportunities for major manufacturing improvements arelost through limited selections of manufacturing processes and associatedmaterials in the early stages of product design. In a survey of designers'knowledge of manufacturing processes carried out in Britain [21], more thanhalf professed little or no knowledge of metal extrusion, two-thirds knew littleabout glass reinforced moulding and over three-quarters were uninformedabout plastic extrusion, technical blow moulding and sintering. For less commonprocesses such as hot isostatic pressing, outsert moulding and superplasticforming, the percentage of designers claiming some process knowledge was

only 6%, 7% and 8% respectively. The effect of this lack of processingknowledge is that designers will have a great tendency to conceive parts interms of the small number of process/material combinations with which theyare familiar. In this way the possibilities of using other processes which maybe much more cost effective will be missed.

In order to be of real design value, the information on which the selectionof material/process combinations and their ranking is to be based should bethat which is generally available at the early concept design stage of a newproduct. Such information might include, for example:

Product life volume

Permissible tooling expenditure levelsPossible part shape categories and complexity levels

Service requirements or environment

Appearance factors

Accuracy factors



100 G . B o o t h ro y d , P . D e w h u r s t a n d W . A . K n i g h t

3 . P r e l im i n a r y S e l e c t i o n o f P r o c e s s e s a n d

M a t e r i a l s

It appears that only one research programme has been carried out in the areaof combined material/process selection. This work by Wilson and co-workers,referred to in the introduction to this paper, resulted in the development of aFortran-based computer program given the acronym MAPS [10].

Unlike the procedure used in MAPS, it is proposed to organise the materialdatabases into classes related to the principal shape generating processes usedin discrete parts manufacture. Primary processes used for producing materialforms for other processes will not be included, since discrete parts manufacturestarts with materials that have already undergone primary processing. Thus,

separate material databases in the proposed work will include, for example,standard metal stockforms (wire, rod, etc.), sand and permanent mould castingalloys, die casting alloys, metal powders, thermoplastics granules, thermoplasticsheet and extruded stockforms, etc. For example, a part identified as havinga small constant cross-section and requiring high strength might be manufacturedby four-slide wire forming, with the wire material selected from the standardmetal stockform database.

In this section of the proposed work, the investigation of a primarymaterial/process selector is being undertaken using a commercially availablerelational database system. The selector has the acronym CAMPS, forcomputer-aided material and process selection. In the selector, inputs madeunder the headings of Part Shape, Size and Production Parameters are usedto search a comprehensive process database to identify processing possibilities.However, it is recognised that process selection completely independent ofmaterial performance requirements would not be satisfactory. For this reason,required performance parameters can also be specified by making selectionsunder the general categories of Mechanical Properties, Thermal Properties,Electrical Properties and Physical Properties. As many selections as required

can be made, and at each stage a list of candidate processes is presented tothe system user. Processes may be eliminated directly because of shape or sizeselections, or when performance selections eliminate all of the materials

associated with a particular process. Figure 1 shows the main menu of theprototype version of CAMPS and it can be seen that the database currentlycontains 31 processes. All of these processes are shown to be available sinceat this point no selections have been made. During an initial search phasewhen a rapid response to changes in input is essential, it would be inappropriateto search extensive material databases in order to identify precise metal alloys,polymer specifications, powder mixes, etc. This would lead to unacceptablyslow search procedures and would provide information largely irrelevant toearly process/material decision making. For example, listing all of thethermoplastic resins which would satisfy the specified performance requirementswould clearly be premature in early discussions of the relative merits of

alternative processes, their required tooling investments, the likely size andshape capabilities, etc. A more efficient procedure is being adopted, in theCAMPS system, where, for each process, a type of supermaterial specificationwhich comprises the best attainable properties of all of the materials in thecorresponding category is provided. The supermaterial specifications aremaintained automatically by the program. Thus, if a new alloy is added to the



Re sea ~h Program on the Selec tion of Mater ia ls and Processes ~ r C om pone nt Par ts

C A M PS M A I N M E N U - - 3 1 P r o c e s se s m e e t T O T A L c r i te r i a

[ A ] S H A P E

[ B ] S I Z E

[ C] P R O D U C T I O N P A R A M E T E R S

[ D] M E C H A N I C A L P R O P E R T I E S

[ E] T H E R M A L P R O P E R T I E S

[ F] E L E C T R I C A L P R O P E R T I E S

[ G] O T H E R P H Y S I C A L P R O P E R T I E S

[ HI O P E R A T I N G E N V I R O N M E N T

[ I] S P E C I F I C A T I O N S C O M P L E T E

[ J] Q U I T / R E S E T A L L C O N D I T I O N S

101

Fig. 1. M ain me nu of the CAM PS system.

d i e c as t in g m a t e r i a l d a t a b a s e , f o r e x a m p l e , i ts p r o p e r t i e s a r e c o m p a r e d w i t ht h e d i e c a s t i n g s u p e r m a t e r i a l s p e c i f i c a t i o n , w h i c h i s t h e n u p d a t e d a s n e c e s s a r y .

T h e a p p r o a c h t o p r e l i m i n a r y p r o c e s s s e l e c t i o n t h r o u g h s u p e r m a t e r i a ls p e c if i ca t io n is c o m p a t i b l e w i t h t h e t r a d e o f f an d c o m p r o m i s e d e c i s io n s w h i c ha r e p a r t o f e a r l y d e s i g n w o r k . A t y p i c a l s c e n a r i o m i g h t i n v o lv e t h e s p e c i fi c a t io n

o f p o s s ib l e s h a p e a t t r i b u t e s , s iz e a n d o n e o r m o r e p r o d u c t i o n a n d p e r f o r m a n c e

p a r a m e t e r s . T h i s t h e n r e s u l t s i n a n i n v i t a t i o n t o c h a n g e t h e i n p u t s p e c i f i c a t i o n s

o r a d d t o t h e s p e c i f i c a t i o n l i s t , o r t o i n v e s t i g a t e a p r o c e s s f u r t h e r f o r a c c e p t a b l ea s s o c i a t e d m a t e r i a l s .

I t h a s b e e n d e c i d e d i n t h e C A M P S s y s t e m t o c l a ss i fy a ll p o ss i b l e s e le c t i o n s

i n t o r a n g e s l a b e l l e d A - F . T h i s i s i n t e n d e d t o e n s u r e e a s e o f u s e i n t h e e a r l y

s t a g e s o f d e s i g n w h e n p r e c i s e n u m e r i c a l v a l u e s f o r m a n y o f t h e p a r a m e t e r sw o u l d n o t b e k n o w n . F o r e x a m p l e , f o r a s tr u c t u r a l p a r t , y i e l d s t r e n g t h w ill

c l e a rl y b e a n i m p o r t a n t r e q u i r e m e n t . H o w e v e r , t h e m i n i m u m a l l o w a b l e y i e lds t r e s s v a l u e w i l l d e p e n d o n t h e p a r t w a l l t h i c k n e s s , w h i c h w i l l i n t u r n d e p e n d

o n t h e p r o c e s s / m a t e r i a l c o m b i n a t i o n t o b e u s e d . F i g u r e 2 s h o w s t h e s e l e c t i o n

o f y i e ld s tr e s s a s [ C ] o r b e t t e r f o r a p a r t m e a s u r i n g 1 2 x 15 x 3 0 i n f o r w h i c h[ C ] o r b e t t e r ( e q u i v a l e n t t o 1 0 % o r g r e a t e r ) h a s a l r e a d y b e e n c h o s e n f o r

e l o n g a t i o n . A t t h is s ta g e o n l y f o u r p r o c e s s es r e m a i n a s c a n d i d a t e s f o r

m a n u f a c t u r e o f th e r e q u i r e d p a r t . I t is a n t i c i p a te d t h a t C A M P S w il l p r e s e n t ,o n d e m a n d , a d e t a i l e d d e s c r i p t i o n o f th e c a p a b i l it ie s a n d l i m i t at i o n s o f th e

c a n d i d a t e p r o c e s se s . T h e p r e s e n t p r o t o t y p e o f C A M P S w ill m e r e l y g iv e al i st i n g o f t h e p r o c e s s e s a s s h o w n i n F i g . 3 . T h i s s h o w s t h e d a t a b a s e a b b r e v i a t i o n s

w h i c h i n t h i s c a s e r e p r e s e n t b e n d i n g , f a b r i c a t i o n , m a c h i n i n g a n d s a n d c a s t i n g ,

r e s p e c t i v e l y . C h o o s i n g S a n d C a s t i n g p r o d u c e s t h e l i s t s h o w n i n F i g . 4 w h i c hi n d i c a t e s t h a t 1 4 m a t e r i a l s , c o m p a t i b l e w i t h s a n d c a s t i n g , w i ll s a t i sf y t h e

r e q u i r e d p e r f o r m a n c e r e q u i r e m e n t s . T h e n u m b e r s o p p o si te Y i e ld S t r e n g th a n dE l o n g a t i o n s h o w t h a t o f a t o t a l o f 7 5 c a s t i n g a l l o y s i n t h e d a t a b a s e , 4 3 s a t i s f y

t h e r e q u i r e d l e v el o f y i e l d s t r e n g t h a n d 2 8 sa t i sf y t h e s e l e c t e d m i n i m u me l o n g a t i o n . T h e r e a s o n f o r s h o w i n g th e s e s e p a r a t e m a t e r i a l c o u n t s is t o a ll o wt h e u s e r t o i d e n t i f y w h ic h r e q u i r e m e n t s s h o u l d b e r e l a x e d i f n o m a t e r ia l s s at is f ya l l o f t h e s e l e c t e d p e r f o r m a n c e v a l u e s .

T h e s y s t e m n e x t p r o v i d e s a l i s t o f t h e a v a i l a b l e m a t e r i a l s a s s h o w n i n F i g .

5 . T h i s s h o w s t h a t , f o r t h e p r e s e n t e x a m p l e , o n l y a s u b s e t o f c o p p e r , n i c k e l



1 0 2 G . B o o t h ro y d , P . D e w h u r s t a n d W . A . K n i g h t

C A M P S MA I N M E N U - -

- - M E C H A N I C A L P R O P E R T I E S

- - Y I E L D S T R E N G T H

4 P r o c e s s e s m e e t T O T A L c r i t e r i a

[A]

[ B ]

[ c]

[ D ]

[ E ]

[ F ?l [ G]

[ H I

- - A t h r u C

Y I E L D S T R E N G T H , 1 0 " 3 P S I

O V E R l O 0

5 0 TO I 0 0

2 5 T O 5 0

1 2 . 5 T O 5 0

6 . 3 T O 1 2 . 5

L E S S T H A N 6 , 3

P R E V I O U S M E N U

P R O P E R T Y D E S C R I P T I O N

E q u a l s C C t h r u F R E T U R N

Fig. 2. Selection o f yield strength

- - C A M P S M A T E R I A L A N D P R O C E S S S E L E C T O R

P O S S I B L E P R O C E S S E S

P R O C E S S C O D E - S E L E C T O N E

B E N D

F A B R

M A C H

S A N D

Fig. 3. Abbreviated process list .

a n d z i n c / a l u m i n i u m a l l o y s s a ti s f ie s t h e s e l e c t i o n c r i te r i a . I t c a n b e s e e n t h a t

t h is t a b le o f m a t e r i a l s a l s o h a s p r o v i s i o n f o r a c o s t r a n k i n g . T h i s i s o n e o f t h e

s u b j e c t s f o r f u r t h e r w o r k i n t h e p r o j e c t . I t i s a n t i c i p a t e d t h a t t h e u s e r w i ll b e

a s k e d t o a s s i g n w e i g h t i n g f a c t o r s t o t h e s e l e c t e d p r i m a r y p e r f o r m a n c e

p a r a m e t e r s o r t o d e n i e d p a r a m e t e r s . T h e s y s t e m w i l l t h e n p r o v i d e a r a n k i n gb a s e d o n m a t e r i a l c o s t p e r p e r f o r m a n c e v a l u e s . I t i s r e c o g n i s e d , o f c o u r s e ,

t h a t t h e c h o i c e o f t h e p r o c e s s t o b e u s e d is o f t e n t h e m o r e i m p o r t a n t c o s t

d e c i s io n . T h e d e v e l o p m e n t o f m e t h o d s f o r c o m p a r i n g a l t er n a t iv e p r o c e s s

s e l e c t i o n s i s a m a j o r p a r t o f t h e p r e s e n t w o r k a n d w i l l b e d i s c u s s e d i n t h e

f o l l o w i n g s e c t i o n s .



R e s e a r c h P r o g r a m o n th e S e le c tio n o f M a te r ia ls a n d P r o c e s s e s fo r C o m p o n e n t Par ts 10

P R O C E S S = S A N D

C O S T . . . . . . . . . . . . .

Y I E L D S T R E N G T H . . .

E L O N G A T I O N . . . . . . .

M O D O F E L A S T ' Y . . .

I M P A C T S T R E N G T H . .

E N D U R A N C E L I M I T . .

H A R D N E S S . . . . . . . . .

T H E R M A L C O N D ' Y . . .

7 5

G E C

4 3

G E C

2 8

C O E F O F E X P A NS I O N

S P E C I F I C H E A T . . . .

V O L E L E C T R E S I S T .

D I E L E C S T R E N G T H . .

D I E L E C C O N S T A N T . .

D I E L E C F A C T O R . . . .

A R C R E S I S T A N C E . . .

S P E C I F I C G R A V I T Y .

F L A M E R E S I S T A N C E .

T R A N S P A R E N C Y . . . . .

W A T E R A B S O R P T I O N .

T E M P M A X I M U M . . . ..

T E M P M I N I M U M . . . . .

R E S U L T S . . . . . . . . . .

C H A N G E O P E R A T O R .

E X I T . . . . . . . . . . . . .

1 4 M A T E R I A L S A V A I L A B L E

* I N D I C A T E S V A L U E M I S S I N G

F i g . 4 . R e d u c t i o n o f a v a i l a b l e m a t e r i a ls f o r s a n d c a s t i n g .

P O S S I B L E M A T E R I A L S F O R P R O P E R T I E S A N D P R O C E S S S E L E C T E D

* I N D I C A T E S M I S S I N G V A L U E S

M A T E R I A L C O S T

C 8 2 4 0 0 A S C 3

N I H A S T E L L O Y C A S C 3

C 8 2 2 0 0 A S C 3

C 8 2 6 0 0 A S C 3

C 8 1 5 0 0 A S C 3

C 8 2 5 0 0 A S C 3

N I A L L O Y G A S C 3

C 9 7 8 0 0 A S C 3

C 9 5 5 0 0 A S C 3

C 8 6 3 0 0 A S C 3

09/12/90I D : P i p e B r a c k e t

D E S I G N E R : R e p o r t

M A T E R I A L C O S T M A T E R I A L

C 8 2 8 0 0 A S C 3

C 9 6 4 0 0 A S C 3

C 9 5 5 0 0 H T 3

Z N Z A - 2 7 F H T 3

Fig. 5. List of ma terials me eting the criteria for sand casting,

C O S T

4. Exp er t Processing Seq uence Selector

T h e s e c o n d a s p e c t o f t h is w o r k d e a l s w i th p r o c e s s i n g s e q u e n c e s . M o s t

c o m p o n e n t p a r t s a r e n o t p r o d u c e d b y a s i n gl e p r o c e s s , b u t r e q u i r e a s e q u e n c e

o f d i f f e r e n t p r o c e s s e s t o a c h i e v e a ll o f t h e r e q u i r e d a t t r i b u t e s o f t h e f in a l p a r t .T h i s i s p a r t ic u l a r ly t h e c a s e w h e n f o r m i n g o r sh a p i n g p r o c e s s e s a r e u s e d a s

t h e i n i t i a l p r o c e s s a n d t h e n m a t e r i a l r e m o v a l a n d f i n i s h i n g p r o c e s s e s a r e u s e d

t o p r o d u c e s o m e o r a l l o f t h e f in a l p a rt fe a t u re s . C o m b i n a t i o n s o f m a n y o t h e r

p r o c e s s e s a r e o b v i o u s l y u s e d a n d t h i s i s n e c e s s a r y b e c a u s e a p p l i c a t i o n o f a

s i n g l e p r o c e s s c a n n o t i n g e n e r a l r e s u l t i n a l l o f t h e f in i s h e d p a r t a t t r ib u t e s .



tO4 G. Boothroyd, P. Dewhurst and W. A. Knight

A n a p p r o a c h t o t h e p r e l i m i n a r y s e l e c t i o n o f m a t e r i a l s a n d p r o c e s s e s h a s

b e e n d e s c r i b e d a b o v e . W h i l e t h i s a p p r o a c h m a y g e n e r a l l y r e s u l t i n s e l e c t i o n

o f a p p r o p r i a t e c o m b i n a t io n s o f m a t e ri a ls a n d p r i m a r y p r o c e s s e s , t h e r e m a y b e

c a s e s w h e r e m a t c h i n g o f th e m a t e r ia l a n d p r i m a r y p r o c e s s a l o n e t o t h e f in i sh e dp a r t a t t r ib u t e s , w i t h o u t c o n s i d e r i n g v i a b l e s e q u e n c e s o f o p e r a t i o n s , m a y l ea d

t o t h e o m i s s io n o f s o m e a p p r o p r i a t e c o m b i n a t i o n s o f p r i m a r y p r o c e s s e s a n d

m a t e r i a l s . A n e x p e r t p r o c e s s i n g s e q u e n c e g e n e r a t o r i s b e i n g i n v e s t i g a t e d t o

e n h a n c e t hi s a s p ec t o f m a t e r i a l a n d p r o c e s s s e l e c t io n . T h i s p r o c e d u r e u t il iz e s

C L I P S - - a n a v a i la b l e e x p e r t s y s te m s h e l l, w i th fl e x ib l e p a t t e r n m a t c h i n g

c h a r a c t e r i s t i c s .

O n c e t h e o v e r a l l f u n c t i o n o f a p a r t is d e t e r m i n e d , it is p o s s i b l e t o f o r m u l a t e

a lis t o f e s s e n ti a l g e o m e t r i c a l f e a t u r e s , m a t e r i a l p r o p e r t i e s a n d o t h e r a t t r i b u t e s

w h i c h a r e r e q u i r e d . T h i s r e p r e s e n t s a " s h o p p i n g l i s t " w h i c h m u s t b e f i l l e d b y

t h e m a t e r i a l s a n d p r o c e s s s e l e c t o r . I t s h o u l d b e n o t e d t h a t t h e l i s t m a y i n i t i a l l y

b e v e r y s p a r se a n d w ill g ro w a s d e f i n i ti o n o f t h e p a r t b e c o m e s m o r e p r e c is e .T h e a t t r i b u t e s o n t h e " s h o p p i n g l i s t" a r e r e l a t e d t o t h e f in a l f u n c t i o n o f t h e

p a r t a n d a re d e t e r m i n e d b y g e o m e t r i c a n d s e r v ic e c o n d i t i o n s . P r o d u c t i o n

q u a n t i t i e s a n d t o o l i n g c o s ts a r e n o t c o n s i d e r e d , a s t h e s e i n f l u en c e t h e r a n k i n g

o f a n y s e l e c t e d s e q u e n c e s , w h i c h w i ll b e c o n s i d e r e d s e p a r a t e l y . T h e r e a r e a

l ar g e n u m b e r o f d i f f e r e n t m a t e r i a ls a n d p r o c e s s e s u s e d f o r m a n u f a c t u r i n g a n d ,

a t f ir st s ig h t, t h e r e s e e m s t o b e a n i m m e n s e n u m b e r o f d i f f e r e n t c o m b i n a t i o n s

p o s s ib l e to b u il d u p p r o c e s s i n g s e q u e n c e s . H o w e v e r , t h e n u m b e r o f p o ss i b le

c o m b i n a t i o n s i s l i m i t e d b y th e f o l l o w i n g :

1. M a n y c o m b i n a t i o n s o f p r o c e s s a n d m a t e r ia l s a r e n o t p o s s ib l e .

2 . M a n y c o m b i n a t i o n s o f p r o c e s s ar e n o t p o s s i b le .

3 . P r o c e s s e s a r e d i v i d e d i n t o th e f o l l o w i n g c a t e g o r i e s :

P r i m a r y p r o c e s s e s

S e c o n d a r y / p r i m a r y p r o c e s s e s

T e r t i a r y p r o c e s se s

P r i m a r y p r o c e s s e s a l w a y s a p p e a r f i rs t in t h e s e q u e n c e o f o p e r a t i o n s a n d t h e

c a t e g o r y i n c l u d e s t h e m a i n s h a p e g e n e r a t i n g p r o c e s s e s s u c h a s c a s t i n g , f o r g i n g ,

i n j e c t i o n m o u l d i n g a n d s o o n . T h e s e c o n d a r y / p r i m a r y p r o c e s s e s c a n a p p e a r a t

t h e s t a r t o r l a te r in t h e s e q u e n c e a n d t h is c a t e g o r y i n c l u d e s t h e m a t e r i a l

r e m o v a l p r o c e s s e s a m o n g o t h e r s . T e r t i a r y p r o c e s s e s w i ll a l w a y s a p p e a r t o w a r d s

t h e e n d o f t h e p r o c e s s i n g s e q u e n c e a n d i n c lu d e f i ni s hi n g p r o c e s s e s s u c h a s

s u r f a c e t r e a t m e n t s , h e a t t r e a t m e n t , a n d s o o n . I t s h o u l d b e n o t e d t h a t m o s t

t e r t i a r y p r o c e s s e s m a y o n l y i n fl u e n c e o n e a t t r ib u t e o f th e p a r t .

T h e m e t h o d o l o g y b e i n g d e v e l o p e d u s e s t h e e s s e n t i a l f e a t u r e s a n d m a t e r i a l

p r o p e r t i e s o f t h e p a r t a s i n p u t t o g e n e r a t e a lis t o f v ia b l e s e q u e n c e s a n d

m a t e r i a l c o m b i n a t i o n s . A n e x p e r t s y s t e m s h e l l w i th t h e c a p a b i l it y f o r fl ex i b le

p a t t e r n m a t c h i n g m a t c h e s u s e r i n p u ts t o m a t e r i a ls a n d p r o c e s s e s . R u l e s o f t h e

f o r m

I F. . . .

( c o n d i t i o n 1 )

( c o n d i t i o n 2 )

( c o n d i t i o n 3 )

T H E N . . . . .

( a c t i o n 1 )



Research P rogram on t he Se lec t ion o f Ma te r ia l s and P rocesses fo r Com pone n t Par t s 10',

a r e u s e d t o s e l e c t p r i m a r y p r o c e s s e s , c o m p a t i b l e m a t e r i a l s , s e c o n d a r y p r o c e s s e s

a n d t e r t i a r y p r o c e s s e s t o f u lf il t h e f u n c t i o n o f t h e p a r t . T h e c o n d i t i o n s r e p r e s e n t

p r o c e s s o r m a t e r i a l c a p a b i l i t i e s o r r e s t r i c t i o n s a n d t h e a c t i o n i s t h e s e l e c t i o n

o f a c a n d i d a t e p r o c e s s o r m a t e r i a l, i n t h is fa s h i o n th e s y s t e m " r e a s o n s " t o w a r da s e q u e n c e o f m a n u f a c t u r i n g p r o c e s s e s an d a m a t e r ia l t o p r o d u c e t h e p a r t.

I n f o r m a t i o n a b o u t t h e p a r t p r o v i d e d b y t h e u s e r c o n si s ts o f t h e s iz e o f t h e

p a r t , t h e d o m i n a n t s h a p e o f t h e p a r t , a d e s c ri p t i o n o f t h e p a r t ' s c r o s s -s e c t io n ,

t h e t o l e r a n c e s a s s o c i a t e d w i t h t h e p a r t , t h e m a t e r i a l r e q u i r e m e n t s f o r th e p a r t

a n d a g e n e r a l d e s c r i p t i o n o f t h e f e a t u r e s w h i c h f u lf il a fu n c t i o n a l r e q u i r e m e n t .

T h e s i ze o f t h e p a r t i s d e s c r i b e d b y t h e p a r t e n v e l o p e . T h e s m a l le s t r e c t a n g u l a r

o r c y l in d r i c a l p r i sm t h a t e n t i r e l y e n c l o s e s th e p a r t i s t h e p a r t e n v e l o p e . T h e

d o m i n a n t s h a p e o f t h e p a r t is i d e n t if i e d b y t h e f u n d a m e n t a l p a r t e n v e l o p e .

T h e f u n d a m e n t a l p a r t e n v e l o p e is t h e r e c t a n g u l a r o r c y li n d r ic a l p r is m t h a t h a s

t h e m o s t s u r fa c e a r e a i n c o m m o n w i th t h e p a r t. T h e d i f f e r e n c e b e t w e e n t h e

p a r t e n v e l o p e a n d t h e f u n d a m e n t a l p a r t e n v e l o p e is t h a t f e a t u r e s , s p ec i fi c al ly

p r o j e c t i o n s , c a n lie o u t s id e o f t h e f u n d a m e n t a l e n v e l o p e w h e r e a s t h e e n t i r e

p a r t i s i n s i d e t h e p a r t e n v e l o p e .

C a n d i d a t e p r i m a r y p r o c e s s e s a r e c h o s e n o n t h e b a s is o f e n v e l o p e s iz e a n d

s h a p e , f u n d a m e n t a l e n v e l o p e s iz e an d s h a p e a n d f e a t u re s t h a t a re a n i n h e r e n t

e f f e c t o f t h e p r o c e s s . S u r f a c e f in i sh , p r o f il e t o l e r a n c e a n d t h e p r e s e n c e o f

f e a t u r e s t h a t c a n n o t b e f o r m e d b y th e p r i m a r y p r o c e s s w ill n o t e x c l u d e a

p r i m a r y p r o c e s s f r o m i n i ti a l c o n s i d e r a t i o n , s i n c e c o m p a t i b l e s e c o n d a r y p r o c e s s e s

m a y f u l f i l t h e s e a t t r i b u t e s .

A f t e r a c a n d i d a t e p r i m a r y p r o c e s s h a s b e e n c h o s e n , t h e s y s t e m s e a r c h e s a

m a t e r i a l d a t a b a s e f o r t h a t p r o c e s s t o s e le c t a n a p p r o p r i a t e m a t e r i a l. A s e p a r a t ed a t a b a s e f o r e a c h p r o c e s s is u s e d , b e c a u s e t h e w a y a m a t e r i a l is p r o c e s s e d o r

f o r m e d a f f e c t s i ts p r o p e r t i e s . A l s o , t h e m o d u l a r n a t u r e o f a s e p a r a t e d a t a b a s e

s t r u c t u r e m a k e s t h e s y s t e m e a s i e r t o d e v e l o p , u p d a t e a n d e x p a n d . M a t e r i a ls

a r e s e l e c t e d b y m a p p i n g t h e u s e r ' s in p u t o n t o t h e m a t e r i a l p r o p e r t i e s . M a t e r ia l

p r o p e r t i e s t h a t c a n b e a f f e c t e d b y t e r ti a r y m a n u f a c t u r i n g p r o c e s s e s w ill n o t b e

u s e d t o e x c l u d e m a t e r i a l s f r o m c o n s i d e r a t i o n , a t t h i s s t a g e . F o r e x a m p l e ,

c o r r o s i o n r e s i s t a n c e c o u l d b e a c h i e v e d b y p l a ti n g o n o t h e r w i s e u n a c c e p t a b l e

m a t e r i a l .

A f t e r a m a t e r i a l h a s b e e n s e l e c t e d , t h e s y s t e m e x a m i n e s t h e list o f g e o m e t r i c a l

f e a t u r e s t h a t t h e p r i m a r y p r o c e s s c o u l d n o t f o r m a n d s e l e c t s s e c o n d a r y

o p e r a t i o n s t o f o r m t h e s e f e a t u r e s . P r o c e s s e s a r e s e l e c t e d b y m a t c h i n g p r o c e s sc a p a b i l i t i e s t o g e o m e t r i c a l f e a t u r e s . T h e s y s t e m w i l l c o n s i d e r m a t e r i a l a s w e l l

a s g e o m e t r i c a l c o n s t r a i n t s . F o r i n s t a n c e , e l e c t r i c a l d i s c h a r g e m a c h i n i n g c a n

f o r m d e e p , a c c u r a t e h o l e s , b u t o n l y in c o n d u c t i v e m a t e r i a l s. F i n a l ly , th e s y s t e m

s e a r c h e s f o r t e r t i a r y p r o c e s s e s t o s a t i s f y a n y u n f u l f i l l e d m a t e r i a l r e q u i r e m e n t s .

I f t h e s y s t e m c a n n o t f i n d a s u i t a b le p r o c e s s o r m a t e r i a l t o f o r m r e q u i r e d

f e a t u r e s o r s a t i s f y m a t e r i a l r e q u i r e m e n t s t h e n t h e s y s t e m b a c k t r a c k s t o s o l v e

t h e i m p a s s e . B a c k t r a c k i n g s i m p l y m e a n s t h e s y s t e m w ill c h a n g e a p r i o r p r o c e s s

o r m a t e r i a l s e l e c t i o n th a t h a s c a u s e d t h e p r e s e n t i m p a s s e . F o r i n s t a n c e , i f a

s u i t a b l e m a t e r i a l c a n n o t b e f o u n d , t h e n t h e s y s t e m m u s t b a c k t r a c k a n d c h o o s e

a n o t h e r p r i m a r y p r o c e s s . S i m i l a rl y , if a t e r t i a r y p r o c e s s c a n n o t b e f o u n d t o

s a ti s fy a m a t e r i a l r e q u i r e m e n t , t h e n t h e s y s t e m m u s t b a c k t r a c k a n d c h o o s e a n

a l t e r n a t i v e m a t e r i a l .

A c h a r a c t e r i s t ic o f t h is a p p r o a c h t o m a t e r i a l a n d p r o c e s s s e l e c t io n i s t h a t a s

t h e l is t o f a t t r i b u t e s t o b e f u l f il le d g r o w s , t h e n u m b e r o f p o s s ib l e s e q u e n c e s

m a y a l s o i n c r e a s e . T h i s d i f f e r s f r o m t h e p r o c e d u r e f o r s e l e c t i n g p r i m a r y



106 G. Boothroyd, P. De wh urst an d W. A. Knight

process/material combinations in which the list of possible combinationsgenerally decreases as the specification of the part becomes more precise. Forexample, the addition of surface finish tolerance to the attribute list will

introduce secondary processes into sequences which could produce thisrequirement. For this reason it is important that consideration is given to theranking economically of the processing sequences generated, and this is theemphasis of another part of this overall investigation.

5 . C o s t -B a s e d P r o c e s s / M a t e r ia l R a n k i n g

The objective of this portion of the research program is the development of aprocess/material ranking method that will ultimately yield the lowest costcomponent part. There are many ways that any given part may be produced,each containing a series a manufacturing processes. For example, it may bepossible to produce a part by machining from solid stock, or by a near netshape process such as casting. There are many different casting processes thatmight be applicable, each with varying degrees of finishing required. Processessuch as sand casting may require extensive machining to meet tolerancerequirements, whereas die casting may, for some applications, require only theremoval of flash from the parting line. An approach to identifying suchsequences has been described. However, the difficulty lies in identifying thelow cost methods prior to the detailed design of the part, allowing the designerto exploit fully the most cost effective manufacturing processes.

The major task in this approach is to develop cost estimating algorithms fordifferent processing sequences using general input parameters such as batchsize, volume, material, tolerances and geometrical complexity. In each case,the processing sequence will be based upon the initial selection of principalshape generating processes, as discussed earlier, together with additionalrequirements defined by geometrical inputs, surface finish, tolerance require-ments and so on. Material specification will initially be by general class suchas aluminium, cast iron, copper, low carbon steel, magnesium, zinc, etc. The

different classes of materials will be specified according to their influence onprocessing cost. The estimated processing costs generated by the algorithmswill be used to compare and rank the viable processing sequences.

The proposed cost-based material/process selection methodology is perceivedto contain the following steps:

1. Establish the technically feasible manufacturing process sequences based onearly design specifications such as part size, possible shape classifications,material class and initial selection of the principal shape generating processes(as described above).

2. Perform cost analyses for each of the specified manufacturing process

sequences.3. Rank the processes relative to cost.

The results of considerable research at the University of Rhode Island aremaking this approach possible. Early cost estimating procedures for numerousprocesses are under development [11-18]. In the proposed research these



Research P rogram on t he Se lec t ion o f Ma te r ia l s and P rocesses f o r Componen t Par t s

d e t a i l e d p r o c e d u r e s w ill b e s i m p l if ie d t o d e v e l o p s u i ta b l e a l g o r i t h m s f o r t h ep u r p o s e o f p r o c e ss c o s t c o m p a r i s o n .

1 07

6 . C o s t o f M a c h i n e d P a r t s

A s a n e x a m p l e , w e s h a ll l o o k a t h o w e a r l y c o s t e s t i m a t e s c a n b e m a d e f o r a

p a r t i c u l a r p r o c e s s . F o l l o w i n g a d e t a i le d a n a ly s is o f c o s t e st i m a t i n g f o r m a c h i n e dp a r t s [ 1 1 , 1 2] it w a s c o n c l u d e d t h a t , in g e n e r a l , t h e t i m e t o r e m o v e a g i v e nv o l u m e o f m a t e r i a l in r o u g h m a c h i n i n g w a s d e t e r m i n e d m a i n l y b y t h e s p ec i fi c

c u t t i n g e n e r g y ( o r u n i t p o w e r ) o f th e m a t e r i a l a n d th e p o w e r a v a i la b l e f o r

m a c h i n i n g . F o r fi ni sh m a c h i n i n g a g iv e n s u rf a ce a r e a , t h e r e c o m m e n d e d s p e e d sa n d f e e d s f o r m i n i m u m m a c h i n i n g c o s t c o u l d b e u s e d . A l s o , it w a s f o u n dp o s s i b l e to m a k e a p p r o p r i a t e a l l o w a n c e s f o r t o o l r e p l a c e m e n t c o s ts .

F u r t h e r r e s e a r c h [2 2] s h o w e d t h a t a l a rg e a m o u n t o f s t at is t ic a l d a t a w e r ea v a il a b le o n t h e s h a p e s a n d s iz es o f m a c h i n e d c o m p o n e n t s a n d t h e a m o u n t o fm a c h i n i n g c a r r i e d o u t o n t h e m . S t a t i s t i c a l d a t a w e r e a l s o u n c o v e r e d o n t h es i z e s o f m a c h i n e t o o l s r e l a t i v e t o t h e s i z e s o f t h e w o r k p i e c e s m a c h i n e d .C o m b i n i n g t h e s e d a t a w i t h i n f o r m a t i o n g a t h e r e d o n m a c h i n e c o s t s a n d p o w e ra v a i l a b i l i t y i t w a s s h o w n t h a t e s t i m a t e s o f m a c h i n e d c o m p o n e n t c o s t s c o u l d b em a d e , b a s e d o n t h e m i n i m u m o f d e s i g n i n f o r m a t i o n [ 2 3, 2 4 ].

T h e i n f o r m a t i o n r e q u i r e d c a n b e d i v i d e d i n t o t h r e e a r e a s :

1. W o r k p i e c e an d p r o d u c t i o n d a ta

2 . F a c t o r s a f f e c t i n g n o n - p r o d u c t i v e c o s t s

3 . F a c t o r s a f f e c t i n g m a c h i n i n g t i m e s a n d c o s t s

T h e f irs t i te m u n d e r t h e h e a d i n g o f w o r k p i e c e a n d p r o d u c t i o n d a t a d e s c r ib e st h e s h a p e c a t e g o r y o f th e w o r k p i e c e . I t w a s f o u n d i n p r e v i o u s s t u d i e s [2 5] t h a t

c o m m o n w o r k p i e c e s c a n b e c l a s s i f i e d i n t o s e v e n b a s i c c a t e g o r i e s , a s i l l u s t r a t e di n F i g . 6 . O t h e r i t e m s u n d e r t h i s f i r s t h e a d i n g i n c l u d e : t h e m a t e r i a l ; t h e f o r mo f t h e m a t e r i a l ( s t a n d a r d s t o c k o r n e a r - n e t s h a p e ) ; d i m e n s i o n s o f t h e w o r k p i e c e ;c o s t p e r u n i t w e i g h t ; a v e r a g e m a c h i n e a n d o p e r a t o r r a t e ; b a t c h s i z e p e r s e t -

u p .K n o w l e d g e o f t h e w o r k p i e c e a n d p r o d u c t i o n d a t a n o t o n l y al lo w s th e c o st

o f t h e w o r k p i e c e t o b e e s t i m a t e d , b u t w i l l a l s o a l l o w p r e d i c t i o n s t o b e m a d eo f t h e p r o b a b l e m a g n i t u d e s o f th e r e m a i n i n g i t e m s n e c e s s a r y f o r e s t im a t e s o fn o n - p r o d u c t i v e c o s t s a n d m a c h i n i n g c o s t s .

F o r e x a m p l e , f o r t h e w o r k p i e c e s h o w n in F ig . 7 , th e t o t a l c o st o f t h e f in i s h edc o m p o n e n t w a s e s t i m a t e d t o b e $ 2 4 . 3 2 , a f i g u r e o b t a i n e d f r o m k n o w l e d g e o ft h e w o r k m a t e r i a l , i ts g e n e r a l s h a p e c a t e g o r y a n d s i z e , a n d i ts co s t p e r u n i t

v o l u m e . A c o s t e s t i m a t e f o r th i s c o m p o n e n t , b a s e d o n i ts a c t u al m a c h i n e df e a t u r e s a n d u s i n g t h e a p p r o x i m a t e e q u a t i o n s d e v e l o p e d i n t h e p r e s e n t w o r k ,g a v e a t o t a l c o s t o f $ 2 2 . 8 3 , w h i c h i s w i t h i n 6 % . A m o r e d e t a i l e d e s t i m a t e

o b t a i n e d u s i n g m o r e t r a d i t i o n a l c o s t e s t i m a t i n g m e t h o d s g a v e a t o t a l c o s t o f$ 2 2 . 9 5 .

C o m p a r i s o n o f t h e s e t h r e e e s t im a t e s , t o g e t h e r w i th c o m p a r i s o n s f o r se v e ra lo t h e r w o r k p i e c e s , a r e p r e s e n t e d i n F i g . 8 , w h e r e i t c a n b e s e e n t h a t t h e

a p p r o x i m a t e m e t h o d u s i n g a c t u a l d a t a g i v e s f i g u r e s s u r p r i s i n g l y c l o s e t o t h e





Research Program on the Select ion of Mater ials and Processes for Compon ent Parts 109

Fig. 8. Com parison of machining cost estimates.

accura te e s t ima te . A lso , the in i t i a l c rude es t ima te based on typ ica l workpieces

i s qu i t e accura te and probably suf f i c i en t for the purposes of ea r ly cos t

es t ima t ing , when va r ious mate r i a l and process combina t ions a rc be ing

c ons i de r e d , a nd be f o r e t he c ompone n t ha s be e n de s i gne d .

7. Application to CAD System s

Grea t in te res t i s p resent ly be ing shown in the cont inua l p red ic t ion of

ma nuf a c t u r i ng c os t s w h i l e c ompone n t s a r e be i ng de s i gne d on CA D s ys t e ms - -

pa r t i cu la r ly those sys tems us ing fea ture -based pa ramet r i c so l id mode l ske tch ing

p r oc e du r e s c u r r e n t l y be i ng de ve l o pe d by var i ous c ompa n i e s . I f one o f t hes e

sys tems was equipped wi th the cos t e s t ima t ing procedures be ing deve loped in

t he p r e s e n t r e s e a r c h p r og r a mme , t he de s i gne r w ou l d be p r e s e n t e d w i t h a nupda t e d ma nu f a c t u r i ng c os t a s e a c h f e a t u r e i s a dde d t o t he s ke tc h o f the

com po nen t . Idea l ly , the des igner wou ld s t a r t w ith a s e t o f feas ib le mate r i a l

a nd p r oc e s s s e que nc e c ombi na t i ons s e l e c t e d by t he me t hods de s c r i be d e a r l i e r

and obta in upda ted cos t s for each of these combina t ions as the des ign i sd e v e l o p e d .



110 G. Boothroyd, P. Dewhurst and W. A. Knight

I n t h e a b o v e d i s c u s s i o n , o n e p r o c e s s w a s s e l e c t e d f o r i l l u s t r a t i o n p u r p o s e s

a n d t h e b a s i c i n f o r m a t i o n n e e d e d t o p r o d u c e c o s t e s t i m a t e s f o r m a c h i n e d

c o m p o n e n t s w a s d e sc r ib e d . I n th e r e s e a r c h p r o g r a m m e a t t h e U n i v e r si ty o f

R h o d e I s l a n d , e a r l y c o s t e s t i m a t i n g m e t h o d s f o r s e v e r a l o t h e r p r o c e s s e s a r eu n d e r s t u d y ; n a m e l y , i n j e c t i o n m o u l d i n g , s h e e t m e t a l s t a m p i n g , d i e c a s t i n g

a n d p o w d e r m e t a l p r o c e s s in g . F o r e a c h o f th e s e p r o c e s s e s i t h a s b e e n p o s s i b le

t o d e fi n e t h e i m p o r t a n t p a r t c h a r a c t e r i s t ic s w h i c h l a rg e l y d e t e r m i n e t h e c o s t

o f t h e f in i sh e d c o m p o n e n t p a r t . I t w a s f o u n d t h a t t h e r e a r e m a n y c h a r a c t e r is t ic s

o r p a r a m e t e r s n o t n o r m a l l y a v a i l a b l e a t t h e m o d e l l i n g s t a g e o n a C A D s y s t e m

a n d t h a t c o n s i d e r a t i o n w o u l d h a v e t o b e g i v e n t o t h e i n p u t o f a d d i t i o n a l d a t a

d u r i n g m o d e l l in g i f c o n t i n u a l l y u p d a t e d m a n u f a c t u r i n g c o s t e s t im a t e s a r e t o

b e m a d e a v a i l a b l e t o t h e d e s i g n e r .

8 . C o n c l u s i o n s

T h i s p a p e r h a s d e s c r i b e d a m a j o r r e s e a r c h p r o j e c t c u r r e n t l y u n d e r w a y o n t h e

s e l e c t i o n o f m a t e r i a l s a n d p r o c e s s e s f o r c o m p o n e n t p a r t s . I t i s a n t i c i p a t e d t h a t

t h e r e s u l t s o f t h i s w o r k w o u l d b e a p p l i e d e a r l y i n t h e d e s i g n o f a n e w p r o d u c t

a n d w h e r e t h e f in a l s t r u c t u r e o f th e p r o d u c t a n d d e t a i l e d d e s i g n o f t h e p a r t s

h a d n o t y e t t a k e n p l a c e .

I n c o n s i d e r i n g a p a r t i c u l a r c o m p o n e n t p a r t , t h e d e s i g n e r w o u l d f i r s t o b t a i n ,

u s i n g a m i n i m u m o f i n f o r m a t i o n , a l i s t o f t e c h n i c a l l y f e a s i b l e m a t e r i a l a n d

p r o c e s s s e q u e n c e c o m b i n a t i o n s . T h e n , u s i n g a l g o r i th m s o f t h e k in d d e s c r i b e d

h e r e , t h e d e s i g n e r w o u l d o b t a i n a p p r o x i m a t e e s t i m a t e s o f m a n u f a c t u r i n g c o s t s

i n o r d e r t o r a n k t h e m a t e r i a l / p r o c e s s c o m b i n a t i o n s a n d , h o p e f u l l y , t o b e a b l e

t o m a k e a p p r o p r i a t e t r a d e - o f f s a s t h e p a r ts a r e s k e t c h e d o n a C A D s y s t e m .

T h e w o r k c o m p l e t e d t o d a t e h a s d e m o n s t r a t e d t h e fe a s ib i li ty o f t hi s a p p r o a c h

a n d h a s i n d i c a t e d t h a t q u i t e a c c u r a t e c o s t e s t i m a t e s a r e o b t a i n a b l e w i t h t h e

m i n i m u m o f i n f o r m a t i o n o n th e p r o p o s e d c o m p o n e n t p a r t.

A c k n o w l e d g e m e n t s

T h a n k s a r e d u e t o t h e f o l lo w i n g c o m p a n i e s w h o h a v e p r o v i d e d f u n d i n g in

s u p p o r t o f t h e p r o d u c t d e s i g n fo r m a n u f a c t u r e r e s e ar c h p r o g r a m a t U . R . I . :

A l l ie d S i gn a l C o r p . , F o r d M o t o r C o . , G e n e r a l M o t o r s C o r p . , G i l le t te C o . ,

D i g i ta l E q u i p m e n t C o r p . , L o c t i t e a n d N a v i s t a r.

T h i s w o r k i s f u n d e d b y t h e N a t i o n a l S c i e n c e F o u n d a t i o n .

R e f e r e n c e s

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Resea rch P rogram on the Se lec t ion o f Ma te r ia l s and P rocesses f o r Com pone n t Par t s 111

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I n d u s t ri a l a n d M a n u f a c t u r i n g E n g i n e e r i n g , U n i v e r s i ty o f R h o d e I s h m d , 1 9 87 .1 2. G , B o o t h r o y d , " ' G r i n d in g co s t e s t im a t i n g , " R e p o r t 1 6, D e p a r t m e n t o f I n d u st r ia l a n d

M a n u f a c t u r i n g E n g i n e e r i n g , U R I . 1 98 7.1 3. P . D e w h u r s t a n d D . A r c h e r , " C o s t E s t i m a t i n g f o r i n j e c ti o n m o l d e d c o m p o n e n t s " , R e p o r t 1 9,

D e p a r t m e n t o f I n d u s tr i a l a n d M a n u f a c t u r i n g E n g i n e e r i n g , U n i v e r s i ty o f R h o d e I s la n d , 1 98 7.

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Correspondence and offprint requests to: P r o f . G . B o o t h r o y d ~ D e p a r t m e n t o f I n d u s t r ia l

a n d M a n u f a c t u r i n g E n g i n e e r i n g , U n i v e r s i t y o f R h o d e I s la n d , K i n g s t o n , R I 0 2 8 81 , U S A .

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