Car Bonnet manufacturing

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CES InDepth >ProcessUniverse >Case Studies

Process Selection Case Study

Car Bonnet

As weightsaving assumes greater importance in automoile design! the replacement o" steel

parts with polymercomposite sustitutes ecomes increasingly attractive# $his case study

e%plores the competition etween steel and thermosetting composites "or manu"acturing a

onnet hood o" a passenger car Die&enach '()# $he weight o" the onnet depends on the

car model* a typical weight is aout + ,g# $he shape is a dishedsheet and the re-uirements

on tolerance and roughness are .#/ mm and / 0m! respectively# $he design re-uirements "or

the car onnet are listed in $ale (#

Clic, on the utton elow to open the case study in CES Selector1 with the Process data

module#

Selection o" manu"acturing processes

2evel 3 ProcessUniverse


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4igure (# A Car Bonnet

5aterial Class

steel or thermosettingcomposite

Process Class

primary! discrete

Shape Class

sheetdishednona%isymmetricshallow

5ass

+ ,g

Sur"ace 4inish 6oughness/

0m or etter

$olerance

.#/ mm

Batch Si7e


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/..!...

$ale (# Car onnet* design re-uirements

$he Selection

http://www.grantadesign.com/education/Inepth/htm!/indepth/processin"o/processcasestud#$%onnet.htm 1/5


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4igures /89 show the selection# 4igure / shows the :rst o" the selection stages* a ar chart o"

mass range against material class# ;4errous; and ;thermosets; and ;polymer matri% composites;

were selected "rom the material class menu! causing the chart to e divided into three

sections! one "or each class o" material# $he selection o% "or the onnet is placed at a mass

o" aout + ,g# 5any processes pass this stage#


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4igure /# A chart o" mass range against material class# $he o% isolates processes which can shape

oth "errous metals and thermosetting composites and can handle the desired mass range#

$he second selection stage is shown in 4igure 3! where ;primary shaping processes; is selected

"rom the process class menu "or the %a%is# Sur"ace roughness is plotted as the ya%is# $he

o%selection isolates processes which are capale o" achieving roughness levels o" / 0m or

etter#


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4igure 3# A chart o" roughness range against process class# $he chart identi:es primary processes

capale o" achieving roughness levels o" / 0m or etter#


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4igure =# A chart o" tolerance against shape class# Processes which can ma,e the desired shape are

plotted and the o% isolates processes which can produce tolerances o" .#/ mm or etter#

$he speci:cations "or the car onnet! so "ar! have caused many processes to "ail the selection

stages# nly two processes survived* one "or "errous metals and one "or thermosetting

composites# $hese arepressforming "or a metal onnet andSMC molding "or a composite

onnet# $he results are listed in $ale /#

$he choice etween these depends on the atch si7e# In 4igure 9! a atch si7e o" /..!... is

represented y the selection o%# Both press "orming and S5C molding are competitive "or the

desired atch si7e! according to our chart#


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http://www.grantadesign.com/education/Inepth/htm!/indepth/processin"o/processcasestud#$%onnet.htm &/5


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4igure 9# A chart o" economic atch si7e against process class

Press "orming

S5C molding

$ale /# Processes "or ma,ing the car onnet

Conclusions and Postscript

$wo processes out o" (3( are capale o" ma,ing the onnet# 5ost other processes "ailed

ecause they cannot handle the material or ma,e the shape# A atch si7e o" /..!... was

chosen! at which oth press "orming o" steel and S5C molding "or a composite onnet

emerged as the success"ul processes# 5ore detailed cost analysis is needed e"ore a :nal

selection is made# Commercially! press "orming is used "or ma,ing onnets out o" steel 8

which is the material commonly used "or production volumes o" /..!...#

6e"erences

Die&enach! ?#6# (@@/! ;$echnical Cost 5odelling;! Boothroyd and Dewhurst Design 4or

5anu"acture Assemly 4orum! ?une (@@/#


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