Kutz M. Handbook of materials selection

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1036 PLASTIC PARTS PROCESSING II

Rubin, I. I., Injection Molding: Theory and Practice, Wiley, New York, 1972.

Tadmor, Z., and C. G. Gogos, Principles of Polymer Processing, Wiley, New York, 1979.

Tadmor, Z., and I. Klein, Principles of Plasticating Extrusion, Van Nostrand Reinhold, New York,

1970.

Journals

Injection Molding, Abby Communications, Inc., 10 Fairmount Avenue, Chatham, NJ 07928.

International Polymer Processing, The Journal of the Polymer Processing Society, Carl Hanser GmbH

& Co., Kolbergerstrasse 22, D-81679 Munich, Germany.

Modern Plastics, A Chemical Week Associates Publication, 110 William Street, New York, NY

10038; the mid-November issue is the Modern Plastics World Encyclopedia.

Plastics Engineering, Society of Plastics Engineers, Inc., 14 Fairﬁeld Drive, Brookﬁeld, CT 06804-

0403.

Plastics Technology, Bill Communications, Inc., 355 Park Avenue South, New York, NY 10010-1789.

Polymer Engineering and Science, Society of Plastics Engineers, Inc., 14 Fairﬁeld Drive, Brookﬁeld,

CT 06804-0403.

1037

CHAPTER 34

COMPOSITES FABRICATION

PROCESSES

Michael G. Bader

School of Mechanical and Materials Engineering

University of Surrey

Guildford, Surrey, UK

1 INTRODUCTION 1038

1.1 Nature of Composites 1038

1.2 Role of Fiber Architecture on

Mechanical Properties 1039

2 BASIC PRINCIPLES FOR

PROCESSING 1045

2.1 Aims and Objectives 1045

2.2 Common Features of

Composite Processing Routes 1046

2.3 Design of Reinforcements to

Enhance Permeability 1053

2.4 Tooling 1054

2.5 Rate of Build 1056

2.6 Economic Implications of

Choice of Feedstock 1057

3 CONTACT MOLDING 1058

3.1 Principles 1058

3.2 Key Factors and Variations 1059

3.3 Laminate Design for Contact

Molding 1061

3.4 Some Variations on Basic

Contact Molding Process 1062

3.5 Productivity and Economics 1064

4 PRESS MOLDING 1065

4.1 Basic Process 1065

4.2 Reinforcements and Resins for

Press Molding 1065

4.3 Ambient Cure Press Molding 1066

4.4 Elevated Temperature Cure

Press Molding 1066

5 AUTOCLAVE PROCESSING OF

PREPREG 1067

5.1 Autoclave 1067

5.2 Prepreg 1068

5.3 Tooling 1068

5.4 Cutting the Prepreg 1069

5.5 Hand Lay-up 1069

5.6 Automated Lay-up 1071

5.7 Cure Monitoring Sensors 1072

5.8 Tool Preparation for Curing 1072

5.9 Autoclave Operation 1073

5.10 Performance, Productivity, and

Economics 1076

6 OTHER PROCESSING OPTIONS

FOR PREPREG 1076

7 RESIN FILM INFILTRATION 1077

7.1 Basic Principles 1077

7.2 RFI with Autoclave Cure 1077

7.3 RFI with Press or Oven Cure 1078

7.4 Other RFI Options 1078

8 RESIN TRANSFER MOLDING 1078

8.1 Basic Principles 1078

8.2 Basic Process Details 1080

8.3 Low-Pressure, Ambient Cure

RTM 1083

8.4 High-Pressure RTM 1084

8.5 Manufacture of Preforms for

RTM 1084

9 FILAMENT WINDING AND

TOW PLACEMENT 1085

9.1 General Concepts 1085

9.2 Filament Winding 1086

9.3 Tow Placement 1090

10 PULTRUSION 1090

10.1 Principle 1090

10.2 Reinforcement Options for

Pultrusion 1092

10.3 Process Variations 1093

10.4 Summary 1094

11 CONTINUOUS LAMINATION 1095

12 SHEET AND BULK MOLDING

COMPOUNDS 1095

12.1 General Principles 1095

HandbookofMaterialsSelection.EditedbyMyerKutz

1038 COMPOSITES FABRICATION PROCESSES

12.2 Sheet Molding Compounds 1095

12.3 Molding SMC 1096

12.4 Bulk Molding Compound 1099

13 GLASS MAT

THERMOPLASTICS 1099

13.1 Principles 1099

13.2 Reinforcements and Matrices 1100

13.3 Processing 1100

14 HIGH-PERFORMANCE

THERMOPLASTIC MATRIX

COMPOSITES 1101

14.1 General 1101

14.2 Feedstock 1101

14.3 Processing Principles 1102

14.4 Autoclave and Press

Processing 1102

14.5 Diaphragm Forming 1103

14.6 Economic and Performance

Implications 1103

15 COMMINGLED

THERMOPLASTIC MATRIX

COMPOSITES 1103

15.1 Principle 1103

15.2 Co-woven Fabrics 1104

15.3 Commingled Tow Materials 1105

15.4 Fiber–Powder Combinations 1106

16 SRIM OF MONOMER

PRECURSOR

THERMOPLASTICS 1106

17 INJECTION-MOLDED

SHORT-FIBER-REINFORCED

THERMOPLASTICS 1107

17.1 General 1107

17.2 Principal Systems 1107

17.3 Compounding 1107

17.4 Injection Molding 1108

BIBLIOGRAPHY 1110

1 INTRODUCTION

1.1 Nature of Composites

Composite materials (see Chapter 12) are composed of a continuous phase, or

matrix, with a discontinuous reinforcement phase dispersed within the matrix.

The matrix may be polymeric, metallic, or ceramic and the reinforcement may,

likewise, be polymeric, metallic, or ceramic. The discussion in this chapter will,

however, be limited to polymeric matrices and the reinforcements will be glass,

carbon (graphite), or the high modulus textile ﬁbers based on poly-aramids and

polyoleﬁns. The reinforcing phase normally consists of ﬁbers, although some

particulate reinforcement is used. There is a subtle distinction between partic-

ulate composites in which the particles reinforce and ﬁlled plastics where the

particles are added for reasons other than stiffness and strength enhancement.

The ﬁbers are typically of the order of 10

␮

m in diameter (about half that of a

human hair), but some are less than 5

␮

m and others up to 150

␮

m. The ﬁbers

may be continuous (i.e., dimensions that could stretch right across a workpiece,

up to several meters), long discontinuous [which are deﬁned here as having an

aspect ratio (length/diameter) greater than 10,000 (length of a few centimeters)],

and short discontinuous, which have an aspect ratio less than 1000 down to 2

(lengths of a few millimeters or less). The ﬁbers may be arranged within the

matrix in various ways, which are described as uniaxial or longitudinal (i.e., all

ﬁbers aligned in one direction), biaxial in plane, multiaxial in plane, random in

plane, and three-dimensional arrays which may be organized (e.g., orthogonal)

or random. The properties of the ﬁbers and their disposition in the matrix control

the mechanical properties of the composite and also profoundly inﬂuence the

ways in which they may be processed.

1 INTRODUCTION 1039

Table 1 Comparative Properties of Reinforcement Fibers and Typical Metal Alloys

Material

(GPa)

␴

(GPa)

␳

(kg/m

) E

␴

E-glass ﬁber

(typical)

70 3.5 2540 1.1 54

Aramid ﬁber

(Kevlar 49)

127 2.6 1470 3.4 69

Polyethylene ﬁber

(Spectra 1000)

100 3.0 970 4.0 121

High-strength carbon

ﬁber (T300)

230 3.6 1800 5.0 78

Intermediate modulus

carbon ﬁber

(T800)

300 5.8 1800 6.5 126

Mild steel

(typical)

200 0.2 7800 1.0 1.0

Alloy steel

(typical)

200 1.0 7800 1.0 5.0

Aluminum alloy

(7000 series)

72 0.8 2700 1.0 12

E, Young’s modulus;

␴

, maximum tensile strength;

␳

, density; E

, normalized speciﬁc stiffness;

␴

normalized speciﬁc strength.

1.2 Role of Fiber Architecture on Mechanical Properties

Fiber Properties

The ﬁbers used in composites have been developed to have very high strength,

very high stiffness, or both relative to the polymeric matrix. They mostly also

have low density compared with metals and speciﬁc mechanical properties ex-

ceeding those of most metallic alloys. A comparison of some properties of the

principal ﬁbers used as reinforcements with those of typical engineering alloys

is given in Table 1. The speciﬁc stiffness (E/

␳

) and speciﬁc strengths (

␴

␳

)have

been normalized to those of mild steel. These show that the ﬁbers have a stiffness

advantage over metals of up to 6.5 times and strength advantage of over 100

times in some cases. It should be noted that the properties of a composite will

generally be less than half that of the ﬁber depending on the proportion of ﬁber

and ﬁber architecture. This still results in some composites showing a signiﬁcant

advantage over metals.

Fiber Architecture

There are two related aspects of ﬁber architecture; the ﬁber volume fraction, V

and the ﬁber orientation. A perfectly collimated uniaxial array of ﬁbers may be

packed to a V

of 0.9, i.e., 90% of the volume is ﬁlled by ﬁbers. However, the

practical maximum is closer to 0.7. Such an array would result in a composite

with stiffness in the ﬁber direction of approximately 70% of that of the ﬁbers.

The transverse properties would be much lower and closer to those of the matrix.

On the other hand if the ﬁbers were arranged in a random but planar array, the

maximum achievable V

would be less than 0.3; and, since the ﬁbers are at

random, the stiffness would be uniform in all directions, but only about 10% of

1040 COMPOSITES FABRICATION PROCESSES

Single filament:

Fiber

Untwisted fiber bundle:

Tow or Strand

Twisted tow = Yarn

Several tows combined:

Fiber Roving

Fig. 1 Schematic illustration of single ﬁlaments, tows, and strands and rovings. Note that the

term ‘‘yarn’’ strictly refers to twisted tows but is often used interchangeably.

that of the ﬁber. The mechanical properties are completely dominated by these

two considerations and, thus, control of ﬁber architecture is a vital consideration

when selecting a processing route.

Fibers for reinforcement are available either as continuous tows or rovings

consisting of parallel, untwisted arrays of 100 to more than 50,000 ﬁlaments, or

in various sheet or web forms suitable for making laminates. The most common

sheet formats are random mats, woven or knitted fabrics, braids and nonwoven,

stitch-bonded fabrics. These are discussed brieﬂy in the next section.

Commercial Reinforcement Formats

Tows are bundles of ﬁbers containing from about 100 to more than 10,000 ﬁbers.

These bundles are generally untwisted. Twisted forms are designated yarns, al-

though these terms are often confused. Rovings are formed by combining a

number of tows to form a larger bundle, as shown in Fig. 1. These continuous

bundles are supplied in spools or ‘‘cheeses,’’ often containing up to 100 kg of

ﬁber. The size of the bundle is usually designated by the mass of a standard

length. The international standard is the tex, which is the mass in grams per

kilometer of yarn. An alternative, still used in the United States, is the denier,

where 1 tex

⫽ 9 deniers. Rovings used for reinforcement typically have linear

masses ranging from 50 to 5000 tex.

Random mats may be manufactured in two ways. The ﬁrst is formed by

chopping rovings into short lengths, typically 10–75 mm, and letting these fall

freely onto a moving belt. The resulting random planar array of short bundles

is consolidated by application of a binder and passing between rolls. The resul-

tant roll of mat is termed chopped strand mat or CSM. Areal weights of CSM

are generally in the range of 100–2500 g/m

. The second method is to form a

mat by placing random swirls of continuous roving onto a moving belt and then

consolidating in a similar manner to that of CSM. The product is known as

continuous random mat, CRM, or swirl mat. It is produced in similar areal

weights as CSM.

1 INTRODUCTION 1041

Chopped strand mat - CSM

Randomly oriented bundles

of fibers - 25 - 75 mm long

Continuous random mat - CRM

Random swirls of continuous

fiber tows

Fig. 2 Illustration of the structure of chopped strand mat (CSM) and

continuous random mat (CRM), also termed swirl mat.

These two products are very widely used in the industry. They allow a max-

imum V

of about 0.3 to be achieved with a random planar ﬁber orientation

distribution. They are cheap and easy to process. Their molding qualities depend

on the areal weight of the mat and the type of binder employed. The structures

of CSM and CRM are shown schematically in Fig. 2.

Woven fabrics are manufactured using standard textile weaving technology

from ﬁber rovings and to some extent yarns. Standard fabrics are biaxial, i.e.,

they have weft (ﬁll) and warp rovings set at right angles. Plain weaves, twills,

and satin fabrics are commonly used at areal weights between 200 and 5000

g/m

. Special fabrics include planar triaxial formats, three sets of rovings at

120

⬚ to each other, and three-dimensional forms. Two important aspects of wo-

ven materials are the degree of crimp and drapeability. Crimp is the degree to

which the rovings deviate from a linear path as they pass over and under each

other. Crimp is undesirable as it reduces the reinforcement efﬁciency. Satin

weaves have less crimp than plain weaves, as shown in Figs. 3a and 3b. The

other aspect is drape, which is the degree to which the fabric is able to conform

to contours on the mold. Lightweight cloths and satin weaves generally show

better drape than plain weaves. Any binder incorporated into the reinforcement

will also inﬂuence drape. Braid may also be considered as a woven form of

reinforcement. Braid is typically tubular and is formed by counter rotating braid-

ing wheels that carry the roving packages. Braids are usually manufactured with

weaves designed for speciﬁc products. They are particularly suited to hollow

tubular forms and many variations in structure are possible. Knitted fabrics are

also manufactured for reinforcement, these may be either ﬂat or tubular as knit-

ted. The general feature is a high degree of crimp and low ﬁber fraction. How-

ever, it is possible to ﬁll the knitted form with heavy unidirectional rovings

aligned in one or more directions (cf. noncrimp fabrics below), so that the knitted

structure holds together the main reinforcement.

Noncrimp fabrics, as the name implies, have been developed to eliminate the

problem of crimp. Unidirectional arrays of rovings are bonded together by stitch-

ing using a light thread, usually polyester, sometimes aramid. Several layers may

1042 COMPOSITES FABRICATION PROCESSES

Warp

Weft [Fill]

PLAIN BALANCED WEAVE

(a)

Warp

Weft [Fill]

FIVE-HARNESS SATIN WEAVE

Weft face shown

(b)

Fig. 3 (a) Structure of a balanced plain woven cloth. The warp and ﬁll tows cross in an alter-

nating over and under sequence. (b) A 5-harness satin weave. The ﬁll tows pass under one,

then over four warp tows in a repeated sequence. This results in less crimp and

better drape characteristics than a plain weave.

be bonded together with the ﬁbers aligned differently in each layer. Thus, one

layer of noncrimp fabric is equivalent to up to four, sometimes more, uniaxial

plies. Typical orientations are 0

⬚,90⬚;0⬚, Ⳳ45⬚,90⬚; and 0⬚, Ⳳ45⬚. Areal weights

range from about 400 to 3000 g/m

. The rovings in each layer can be very

closely packed so that the fabric results in composites with higher V

than can

be achieved with woven material. It is also possible to incorporate layers of mat,

woven, or core-forming material between the plies. A further possibility is that

the construction of the fabric can be modiﬁed by a carefully designed set of

open channels within the layers to increase the permeability allowing faster

molding than with equivalent reinforcements.

Precompounded Reinforcements with Thermosetting Matrices

The reinforcements discussed above are dry, i.e., they contain no resin, apart

from small amounts of binder. The resin matrix has then to be inﬁltrated into

the reinforcement later in the processing cycle. An alternative is to use a pre-

compounded reinforcement, which contains all the resin necessary for further

processing. The advantages are that the inﬁltration is effected in a highly con-

trolled manner that guarantees the correct resin fraction and uniform distribution.

The disadvantages are increased cost, restricted shelf life, and more limited proc-

essing possibilities. In the ﬁrst place only certain thermosetting resin are suitable.

They need to be in soft but not liquid or too sticky state. They need to be fully

formulated, i.e., already contain any necessary curing agents, initiators, or ac-

celerators. This means that the resin must be inherently unstable and will start

to cure as soon as the compound is manufactured. The rate of cure is temperature

dependent, and the resins used are usually formulated to cure at 100–200

⬚Cin

10–60 min. This then allows them to be stored at much lower temperatures

between manufacture and ﬁnal processing without unacceptable advance of the

cure. Most commercial systems have a shelf life at room temperature (20

⬚C) of

1 INTRODUCTION 1043

at least one month. However, many require them to be stored at subzero tem-

peratures, typically

⫺15⬚C, when they have a storage life of up to one year. This

complicates the logistics of processing and inevitably adds to the costs.

Compounded reinforcements are available as impregnated tows or rovings, as

preimpregnated warp sheet, or prepreg, preimpregnated woven fabrics and mats,

and preimpregnated random ﬁber compounds such as sheet molding compound

(SMC) and bulk molding compound (BMC). The processing principles are com-

mon. The material contains all the ﬁber and resin (possibly an excess) for man-

ufacture of the component. After assembly by laying tows or laminating sheet

forms, the material is subjected to heat and pressure. First the resin softens,

allowing consolidation, elimination of trapped gases, and any resin excess, then

the resin cures to form the solid part. In some cases, e.g., prepreg, which is

comprised of continuous ﬁbers, no lateral ﬂow of the ﬁbers can occur. So the

plies have to be precisely tailored to the shape of the part. In other processes,

e.g., SMC, there is considerable ﬂow of both resin and ﬁber so that complex

shapes including stiffening ribs and other features may be formed from blanks

of simple shapes. Prepreg consists of a uniaxial array of continuous ﬁbers pro-

duced as a continuous roll up to about 2 m in width. The resin is applied to the

web of ﬁber and the compounded material then consolidated between two rolls

of protective ﬁlm. One is usually a silicone-coated paper and the other a poly-

oleﬁn ﬁlm. The ﬁnished standard prepreg has an areal density of 100–200 g/

and when cured is designed to have a thickness of 0.125 mm per ply. Thus

8 plies are required to form a laminate 1 mm thick. While this would be in-

convenient for the manufacture of thick structures, it does allow very precise

tailoring of the laminate properties by varying the lay-up sequence. A quasi-

isotropic laminate may be formed by the 8-ply sequence [0

⬚, Ⳳ45⬚,90⬚]

, the

subscript ‘‘s’’ indicating symmetric. Alternative sequences, usually symmetric,

give a different balance of longitudinal, transverse and in-plane shear properties.

Prepreg is also manufactured in thinner formats and also using ﬁne woven fabrics

of plain or satin weave which typically laminate to 0.25 mm/ply.

There has recently been much interest in developing prepreg-like materials

more suitable for manufacturing thick laminates. These are based on combina-

tions of woven and noncrimp fabrics and mats, impregnated with suitable ther-

mosetting resins, usually vinyl-ester or epoxies. Areal densities exceeding 6000

g/m

have been produced. The same problems of handling and shelf life apply

but, outside the aerospace industry, subzero storage is seldom acceptable and

shelf lives exceeding 3 months are demanded. This limits the range of resin

systems but satisfactory systems are now available. A concern with all precom-

pounded materials is the degree of tack or stickiness. Too little tack means that

lamina do not stay in place as the laminate is laid up. Too much tack renders

the material difﬁcult to handle as it sticks to everything it contacts. Aerospace

prepregs are manufactured to a precisely controlled tack, but even this tends to

lessen as the material approaches the end of its shelf life. A technique recently

introduced for heavier reinforcements is to make a multiple layer material but

to conﬁne the resin impregnation to the central layers, shown in Fig. 4. Such a

material handles like a dry reinforcement, although it tends to be much less

springy; when subjected to heat and pressure, the resin content softens to a low

viscosity and ﬂows uniformly throughout the reinforcement. Developments such

1044 COMPOSITES FABRICATION PROCESSES

Ply of reinforcement fabric

Coated on one side with pasty resin

Second ply applied to form a sandwich

Partially consolidated so that resin infiltrates part-way

through the two layers of reinforcement

Fig. 4 Sequence of manufacture of a partially impregnated fabric reinforcement.

A layer of pasty resin is sandwiched between two layers of fabric or mat. This produces

a dry material with good handling characteristics and is particularly suitable

for heavier grades of reinforcement.

as this illustrate how the industry is using imaginative techniques to improve

productivity while maintaining quality.

Sheet molding compound (SMC) and bulk molding compound (BMC) are

well-established precompounded materials, which are widely used in the auto-

motive and general engineering industries. SMC is manufactured by impregnat-

ing a continuous thick mat of chopped glass rovings, typically 50–75 mm long,

with a suitable resin, usually an unsaturated polyester or vinyl-ester containing

a large proportion of particulate ﬁllers, such as chalk. The resin is specially

formulated so that it hardens to a thick paste on maturation after the compound-

ing operation. This takes about 72 h. The product is a continuous sheet of resin-

impregnated chopped rovings, typically about 5 mm thick and up to 2 m wide.

It has a dry but pliable consistency with no tack. It may be cut using shears or

a blanking tool. The cut pieces are compressed between hot matched tools. At

ﬁrst the resin softens allowing the charge to ﬂow to ﬁll the mold; then the resin

cures. The part is ejected hot. The whole process takes from 5 to 20 min, ac-

cording to the size and complexity of the molding. This material and process is

particularly compatible with the production environment in the automobile and

other mass production industries. BMC is of similar formulation but typically

uses shorter ﬁber bundles, 10–25 mm, and is formed into a rope,

⬃50 mm

diameter. This is used as feedstock for either compression or injection molding.

Once again the parts are ejected hot and the molding cycle can be as short as 1

min. Both materials consist of ﬂow-oriented quasi-random arrays of ﬁber bundles

and the ﬁllers in the cured resin matrix.

Thermoplastic Matrices

These present a totally different set of processing considerations. Thermoplastics

are processed by a melt–freeze cycle and no chemical curing reactions are in-

volved. The materials are always solids at ambient temperature, and common

2 BASIC PRINCIPLES FOR PROCESSING 1045

systems melt at temperatures ranging from 150 to 400⬚C. The main processing

problem with thermoplastics is that their viscosity in the molten state is orders

of magnitude higher than that of the common thermoset systems prior to curing.

There are a few thermoplastics, e.g., polyamides 6, 11, and 12, that can be

processed by in situ polymerization of monomer precursors and are exceptions

to this generalization. Preimpregnated tow and sheet materials comparable with

prepreg and SMC can be prepared, but they are rigid and boardlike below their

melting point. They are processed by preheating and then pressing or stamping

between cold tools. In general thermoplastic-based systems are limited to some-

what lower V

than comparable thermoset composites. An alternative strategy is

to prepare commingled products by combining reinforcement ﬁbers with ther-

moplastic ﬁbers by spinning or weaving together. An extended discussion of

these products will be found in Section 15.

Mechanical Properties of Laminates and Moldings

As indicated earlier, the mechanical properties of a composite are controlled by

the proportion of ﬁber, V

, and the overall ﬁber architecture or ﬁber orientation

distribution. Fully uniaxial laminates have the highest stiffness and strength in

the ﬁber direction but are relatively weak in the transverse direction and in shear.

They are seldom used because they can split parallel and between the ﬁbers.

Most practical laminates therefore contain a proportion of their ﬁbers in different

directions. A balanced woven fabric has about 50% of its ﬁber in each of two

directions mutually at right angles. A quasi-isotropic laminate has 25% of its

ﬁbers in each of the four directions 0

⬚,90⬚, and Ⳳ45⬚. In each of these cases

the laminate will be less anisotropic than the uniaxial but the actual stiffness

and strength will be lower. A lower ﬁber fraction will reduce the stiffness and

strength in all of these directions. A random in-plane distribution, such as results

with the use of CSM, gives uniform properties in all in-plane directions but at

a level of less than a third that of a uniaxial array. This must be factored by the

fact that the V

will be no more than 0.3 compared with a possible 0.7 for the

uniaxial. It is useful to calculate an orientation constant, C

, for each type of

reinforcement; this is 1 for uniaxial, 0.5 for the balanced biaxial fabric, and 0.3

for random in-plane. This may then be multiplied by the actual V

to give a

reinforcement efﬁciency factor,

␩

. Table 2 indicates the reinforcement potential

for a number of common forms of reinforcement calculated for an E-glass/epoxy

resin system. E

max

is the Young’s modulus in the stiffest direction and G

max

the in-plane shear modulus, both in units of GPa. Note that the maximum achiev-

able V

decreases as the format becomes more random and also that the inclusion

of the

Ⳳ45 orientation enhances the shear modulus. As V

decreases, the values

for E and G converge toward those of the resin. The symbols RTM and RFI are

for resin transfer molding and resin ﬁlm infusion, respectively.

2 BASIC PRINCIPLES FOR PROCESSING

2.1 Aims and Objectives

The aim in selecting a processing route is to manufacture the part to meet all

the speciﬁed objectives at the required production rate and at the lowest possible

cost. Selection of a processing route certainly includes selection of appropriate