Mechanical Fastening

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Definition and Classification of Mechanical Fastening

Methods

19 pages, 20 figures

Basic Level

Objectives:

− to introduce the principal types of mechanical fastening methods, i.e. screw joints,

folding, riveting and clinching by definitions and classification

− to illustrate the great variety of types of mechanical fastening methods and systems

available for joining aluminium parts

Prerequisites:

− eneral mechanical engineering bac!ground



4101 Definition and Classification of Mechanical

Fastening Methods

Table of Contents

"efinition and #lassification of $echanical %astening....................................................1

%astening $ethods............................................................................................................2

410101 !ntroductor" #e$ar%s

&endency of "evelopments in the 'oining &echnology.............................................(

'oining )ystems for &hin*walled +luminium #omponents......................................(

+ims of the $echanical %astening rocesses...........................................................-

#lassification of $echanical %astenings sed in the %abrication &echnology........-

/lementary and #ombined 'oints..............................................................................

41010& 'cre( )oints

#onstruction &ypes for )crew 'oints.........................................................................

e3uirements for )crew 'oints..................................................................................

&ypes of )crew 'oints for &hin )heets......................................................................4

5or!ing rinciple of %low*"rilling )crews..............................................................6

)crew 'oints for +luminium rofiles........................................................................9

41010* Folds10

)teps in the %olding rocess for )traight*/dged )heets.........................................105idths of 7verlaps in %olded 'oints.......................................................................10

410104 #ivet )oints11

'oining by iveting..................................................................................................11

ivet &ypes for the 8ndirect iveting of +luminium...............................................12

#ommercially +vailable ivet %orms and their %ields of +pplication...................1(

5or!ing rinciple of a Blind op: ivet...............................................................1(

#hoice of %astening /lements for $echanical %astening $ethods........................1-

41010+ Clinching1+

)chematic 8llustration of #linching 'oints, with or without Local 8ncision............1

+n +luminium #ar "oor +ggregate #arrier with #linch 'oints.............................1

41010, 'u$$ar"1-

#omparison of the &echnological #haracteristics of %astening $ethods...............14

41010- .iterature/#eferences1-

41010 .ist of Figures1

&+L+& -101 2



'oining is in many cases an important and often critical process step in the

manufacturing of aluminium components from shaped sheet and;or profiles.

$echanical fabricating processes fulfil the ever increasing demands on the joining

3uality and reproducibility during manufacturing as well as 3uality assurance. &hese

have low investment costs, are easy to use and can be easily adapted for automatic

processes.

410101 !ntroductor" #e$ar%s

• &endency of developments in the joining technology

• 'oining systems for thin*walled aluminium components

• +ims of the mechanical fastening processes

• #lassification of mechanical fastenings used in the fabrication technology

• /lementary and combined joints

Tendenc" of Develo$ents in the )oining Technolog"

"ue to technological and economical pressures, a large number of fabricating companies

have to reconsider their concepts regarding joining technologies used for joining in

aluminium constructions.

&he aim of new and newest developments in fastening techni3ues is to introduce

methods for fastening new materials, and to improve both reliability as well as economy

of the process Figure 41010101:.

&+L+& -101 (



Joining Systems for Thin-Walled Aluminium Components 4101.01.02

Training in Aluminium Application Technologies

alu

eometry of JointsA! "o#al $oints%! &'er "arge Areas

Suita(le forC! )nrelated *aterials+! ,on-*etalli# *aterials

Sour#e! Singh

Spot Weldingnert asWelding Adhesi'e "aserWelding

+eta#ha(le

Conditionally+eta#ha(le

)ndeta#ha(le

Classi#al ,e/

AC+ %C+

AC+ AC+%C

%C% AC A%

#re/ingS Clamping

3i'eting hingClin#olding

Joints of "ight Constru#tions

Main Aims of Improvements and NewDevelopments in the Joining Technology

To Improve the Economics and Degree of Automation

To Improve the Reliaility of the Joining !rocess

To Ma"e Joining Technologies Availale for new

Materials and #ields of Application

$ource% &ahre

Training in Aluminium Application Technologiesalu Tendency of Developments in the Joining Technology '()(*)(*)(

)oining '"ste$s for Thin2(alled 3lu$iniu$ Co$onents

+ccording to the development trends, two main methods can be used for joining

aluminium< the =classical= proven, standard: and =new= less !nown and seldom used:

methods.

Besides this rather imprecise definition, a further classification is possible, based on the

geometry of the process and on the possibility of joining different materials and, for that

matter, non*metallic materials with each other see Figure 4101010&:.

3i$s of the Mechanical Fastening Processes

&+L+& -101 -



$echanical fastening methods are gaining in popularity, both in the assembly as well as

for mass production, in fabricating processes where a =predictable= fastening technology

is absolutely essential.

/specially when joining aluminium, mechanical fastening methods can meet the

increasing demands on joint 3uality and reproducibility during production and at the

same time allow the production 3uality to be tested using non*destructive methods

Figure 4101010*:. &ypical for all mechanical fastening methods is that the joints can be made with none or hardly any heating.

Classification of Mechanical Fastenings sed in the Fabrication Technolog"

"epending on the joining principle used, a large number of joint designs are possible. +s

one can see from the systematic of the joining principles, the method of producing the

individual joints forms the basis for the classification, with each process having its

advantages and disadvantages see Figure 41010104:.

Mechanical #astening of Aluminium

Joining $heets and+ or !rofiles y #orming

Material ,ocally to !roduce a #orce or #orm

,oc"ing Joining Element

Joining without the Application of -eat.

Therey $aving Energy and !rotecting the

Environment

Joining Materials and /ominations there of

which are Normally Difficult to #asten Together

#aricating Reproducile Joining Elements -aving a

Defined Joining 0uality

$ource% &udde alu Aims of the Mechanical #astening !rocess '()(*)(*)1


&+L+& -101



8f an aluminium construction has to compete with a steel construction, then it is

important to consider the aspects of manufacturing technology, joining techni3ues and

economy. "ue to the lower modulus of elasticity, an aluminium component will have alower rigidity than the corresponding steel component of the same dimensions.

$echanical fastening methods can, however, be used to overcome this shortcoming, at

least partly.

Because of their good combinations of properties, the following joining methods have

proven to be especially suitable< screwing, clinching, bordering, folding and riveting.

5le$entar" and Co$bined )oints

$echanical fastening methods will not be considered here on the basis of the older

viewpoints. &hey are defined here as joining technologies in which the parts are jointusing a force or form loc!ing method li!e in clinching or riveting. &hese e>clude joints

in which there is an inter:loc!ing of materials as in welding and adhesive joining.

&he 3uasi form loc!ing joint is obtained by a plastic deformation process. )uch joints

incorporate the advantages of both form loc!ing transmitting large forces: and the force

loc!ing reducing play: type of joints Figure 4101010+:.

&+L+& -101



41010& 'cre( )oints

• #onstruction types for screw joints

• e3uirements for screw joints

• &ypes of screw joints for thin sheets

• 5or!ing principle of flow*drilling screws

• )crew joints for aluminium profiles

Construction T"es for 'cre( )oints

)crew joints belong to the group of detachable joints. &hese can be designed as pierced,

through or blind*hole joints Figure 41010&01:. 8f appropriate measures are ta!en

against corrosion, screw joints are suitable for shaped sheet components and ;or

aluminium sections and profiles.

&he joining elements should be made of corrosion resistant stainless steel steel group

+2;+-:. )ince aluminium alloys have relatively lower compressive strengths, the

contact surfaces must be protected by using washers under the screw and the nut.

#equire$ents for 'cre( )oints

)crew joints consist of multiple elements each of which has to fulfil various

re3uirements at the same time.

8n order to design durable, safe and cheap screw joints which fulfil the re3uirements for

different applications, systematically arranged information and other helps must be

available.

+pplication parameters for screw joints can be set up by systematically listing the main

re3uirements for design, calculation and corrosion protection Figure 41010&0&:.

&+L+& -101 4



alu


3e5uirements for S#re/ Joints 4101.02.02

Determining the Main #actors which Influence the Design./alculation and /orrosion !rotection of $crew Joints

(* 2eneral Information aout the /onstruction. #astenings and !arts to e #astened

3* Assemling !rocess

(. Mechanical and /hemical $tressing

-. !hysical Influencing #actors

. ,ife E4pectancy 5 $afety 5Reliaility

. Additional Re6uirements

4. !revious Design and 7sale E4perience

6. Economy

$ource% $ieling

T"es of 'cre( )oints for Thin 'heets

8n addition to the screw*and*nut fastening methods, thin sheets can be joint together

using a number of threaded fasteners, the most popular being sheet metal screws of the

self*loc!ing, self*tapping types Figure 41010&0*:.

5ith the help of screw*and*nut fasteners, it is possible to create large clamping forces.

)heet metal screws, on the other hand, are used to eliminate the drilling operation for the

final assembly, whereby the screw cuts out its own hole.

&+L+& -101 6



6or%ing Princile of Flo(2Drilling 'cre(s

+ drawbac! of most sheet metal screw joint is the very limited load bearing length of thescrew. 8mprovements can be made by forming cylindrical collars during the shaping

process.

8n the flow*drilling process, a carbide tipped tapered and unthreaded punch rotating at

high speed is forced down to pierce through the metal, deforming it plastically and

creating a collared hole. + thread can then be tapped in this hole Figure 41010&04:.

&+L+& -101 9



'cre( )oints for 3lu$iniu$ Profiles

)tainless steel sheet metal screws are most often used for joining light metal alloys.

refabricated profiles are being increasingly used for aluminium constructions. &he

profiles have longitudinal and transverse screw channels or grooves: to ta!e up the

stainless steel sheet metal screws Figure 41010&0+:.

41010* Folds

&+L+& -101 10



• )teps in the folding process for straight*edged sheets

• 5idths of overlaps in folded joints

'tes in the Folding Process for 'traight25dged 'heets

Bordering and folding techni3ues in a number of variations are traditionally used for joining aluminium effectively.

%orm loc!ed joints are created using the following steps< folding manually or

automatically, interloc!ing, pressing together and loc!ing by displacing the sheet edges

Figure 41010*01:.

8f this fastening method is carried out properly, the protective o>ide film is not damaged

so that the surface remains protected.

6idths of Overlas in Folded )oints

"epending on the application, various folding forms can be made, the width of the fold

being of special importance for individual parts in handicraft. 5hereas narrow folds

have low strength and tightness, too large overlaps amount to a waste of material

Figure 41010*0&7

&+L+& -101 11



5ith optimal fold thic!nesses, the ma>imum strength attainable then depends mainly on

the fold type as well as 3uality and thic!ness of the material.

410104 #ivet )oints

• 'oining by riveting

• ivet types for the indirect riveting of aluminium

• #ommercially available rivet forms and their fields of application

• 5or!ing principle of a blind pop: rivet• #hoice of fastening elements for mechanical fastening methods

)oining b" #iveting

%or a long period of time, riveting was considered to be outdated and uneconomical.

ecently, however, riveting is being rediscovered as a rational technology of high

3uality especially for special*purpose applications in the aerospace industry.

+luminium can be joined using the indirect and direct riveting methods Figure

41010401:.

8n the indirect riveting process the parts to be joined are clamped together with rivets

using an au>iliary joining element. 8n direct riveting, one of the parts to be joint is itself

designed to act as the au>iliary component so that a separate one is not necessary.

&+L+& -101 12



#ivet T"es for the !ndirect #iveting of 3lu$iniu$

#urrently, four different types of indirect rivets are used for producing undetachable

permanent: joints< solid rivets, blind #hobert or pop: rivets, huc! bolts screw rivets:

and punch rivets, whereby the rivet groups are classified primarily according to their

operational reliability Figure 4101040&:.

&+L+& -101 1(



)olid rivets are one*piece joining elements in which the rivet shaft is plastically formed

into the closing head. )uch rivets can only be used for components which are accessible

from both sides.

?uc! bolts screw rivets: are used for highly stressed rivet joints. )ince screw rivets are

made of high strength materials which cannot be formed easily during assembly, a

closing collet self*loc!ing nut: is fi>ed on to the rivet.

Blind #hobert, pop: rivets, including the multi*functional types, consist of one or moreelements and re3uire only one accessible side for mounting.

unch rivets are designed to be self*piercing, ma!ing it unnecessary to form holes

previously in the parts to be fastened.

Co$$erciall" 3vailable #ivet For$s and their Fields of 3lication

ivets are classified according to the shape of the rivet head formed during the riveting.

%or sheet metal and light constructions which do not need rivets of greater than 6 mm

diameter, closing heads with the same form as the rivet heads can be used. +luminium

rivets having a diameter of up to 6 mm can be fairly easily cold wor!ed Figure

4101040*:.

/ountersun" Rivet

#or

Thic"

Materials

-alfround Rivet

2enerally

7sed Rivet

-ead #orm

Mushroom Rivet

#or $mooth

$urface

Riveting on the

-ead $ide

#lat Rivet

#or ,ight $heet$tructures

Tue Rivet

#or /ases in

8hich 9nly ,ow Impact #orming#orce May e

7sed

9val5-eaded

/ountersun" Rivet

#or /ases in 8hich The!rotruding -ead

$hould e $mall

&+L+& -101 1-




alu

$ource% Alusingen /ompany Documents

/ommercially Availale Rivet #orms and

Their #ields of Application

6or%ing Princile of a 8lind 9Po7 #ivet

'ust li!e many other innovative rivet developments, the blind rivet was developed in the

aircraft industry. enerally, blind rivets consist of a hollow shaft and a pull*stem

mandrel: which serves as a tool for forming the closing head.

&he rivet is mounted by pulling the stem out with a special tool, whereby the stem head

is drawn into the protruding rivet material to form the closing head Figure 41010404:.

5hen the pulling force e>ceeds a certain level, the stem brea!s at a predetermined

position notched or brea!*stem:. &he brea!ing point can be chosen to lie either in the

shaft or at the rivet head.

Choice of Fastening 5le$ents for Mechanical Fastening Methods

$echanical fasteners using au>iliary fastening elements should be chosen so that both

fastener and the components to be joint are compatible as far as corrosion and recycling

aspects are concerned. 8t follows that the parts which come in contact with each other

must have similar electrochemical potentials and the material combination used must be

tolerant with respect to recycling Figure 4101040+:.

&+L+& -101 1

'()(*)'*)1



/hoice of Material for Joining Elements for the

Mechanical #astening of Aluminium /onstructions

&ecause of reaso ns of corrosion. parts which come into contact

with each other should have similar electrochemical potentials*

&ecause of reasons of recycling. the materials of the parts

involved should e compatile*

alu /hoice of #astening Elements for Mechanical '()(*)'*):

Training in Aluminium Application Technologies #astening Methods

%astening elements made of copper or brass are not suitable for joining aluminium parts.

8n an environment where the joints are subjected to weathering or chemical attac!, the parts must be isolated from the fastening elements, both for aluminium parts of different

alloys as well as for composite constructions.

41010+ Clinching

• )chematic illustration of clinching joints, with or without local incision

• +n aluminium car door aggregate carrier with clinch joints

'che$atic !llustration of Clinching )oints (ith or (ithout .ocal !ncision

+lthough clinching is now widely accepted and used as a =new= process for fastening

aluminium shaped sheet components and profile components as undetachable

permanent: joints, the rules and guidelines governing this type of fastening method

have still to be defined.

#linching covers processes for direct joining in which the material undergoes a local

plastic deformation with or without local incision Figure 41010+01:.

&he term clinching covers various processes !nown more popularly by their trade

names.

&+L+& -101 1



3n 3lu$iniu$ Car Door 3ggregate Carrier (ith Clinch )oints

&he technology for fastening methods based on clinching and the =newer= riveting

processes is being developed continuously, so that an ever increasing use of these

joining methods can be safely e>pected in the years to come.

resently, the most well !nown e>ample for a mass produced component using the

clinching fastening method is the door aggregate carrier for the +"8 60;90 in which

two aluminium sheet forms are clinched together Figure 41010+0&:.

&+L+& -101 14



&+L+& -101 16



Joining

Te#hnology

Chara#teristi#

Clin#hing 3i'etingAdhesi'e Joining

Spot Welding

Te#hnology

$ro#ess parameters

- time

- temperature

- pressure

'ery

#ompli#ated

short to long

relati'ely lo/

lo/ to high

#ompli#ated

'ery short

'ery high

relati'ely high

limited

'ery short

'ery lo/

relati'ely high

limited

short to long

'ery lo/

relati'ely high

Comparison of the Technological Characteristicsof Fastening Methods

Sour#e! %udde

alu


Comparison of the Te#hnologi#al Chara#teristi#s

of astening *ethods

4101.06.01

41010, 'u$$ar"

7 #omparison of the technological characteristics of fastening methods

Co$arison of the Technological Characteristics of Fastening Methods

iveting and clinching are typical e>amples for mechanical fastening methods.

&he above mentioned fastening methods are most promising since, compared to the

=conventional= fastening methods, these are easier to use, have shorter pressing times

and the parts to be joint are subjected to a lower heat stress Figure 41010,01:.

41010- .iterature/#eferences

&+L+& -101 19



1. 8ahre # @erbindungstechni! fAr dAnne Bauteile. &echnica ( 196: 10, 1*

2. 'ingh ' %Agen von +luminiumwer!stoffen im +utomobilbau. 8ngenieur5er!stoffe

2 1991: (, -*-6

(. 8udde . ntersuchungen ur Combination 3uasi*formschlAssiger und

stoffschlAssiger @erbindungsverfahren. "issertation ni*?*aderborn, 1969

-. ;; %ertigungsverfahren %AgenD /inordnung, nterteilung, Begriffe. "8E 69(,

&eil 0.

. <lein 8 %Agetechnologien des $aschinenbaus. "er Constru!teur 196: 11, *1-

. #oth < )ystemati! fester @erbindungen als rundlage fAr ihre sinnvolle

+nwendung und 5eiterentwic!lung. @"8*Berichte Er. (0, 4*19

4. 8eit= 6 enerelle estaltungsempfehlungen fAr )chraubenverbindungen. @"8*F

12 196(: , 24*2(

6. 'ieling P "rehschlagbetGtigte /insatwer!euge. @erbindungstechni! 1944: 4;6,

1(*2-

9. 'teeg >8 ationalisierungspotential "Annblechverschraubung. @"8*Berichte Er.

66(, 21*2(9

10. 8auer CO 5ege u sicheren und wirtschaftlichen )chraubenverbindungen. @"8F

12- 1962: 16, 4*4

11. .iebig >P Eieten und "urchsetfAgen. Blech ohre rofile (9 1992: (, 220*221

12. >offer < )ystemoptimierte @erbindungen im %lugeugbau. @"8*Berichte (0,

(1-(

41010 .ist of Figures

Figure ;o Figure Title 9Overhead7

-101.01.01 &endency of "evelopments in the 'oining &echnology

-101.01.02 'oining )ystems for &hin*5alled +luminium #omponents

-101.01.0( +ims of the $echanical %astening rocess

-101.01.0- #lassification of $echanical %astenings sed in the %abrication &echnology

-101.01.0 /lementary and #ombined 'oints

-101.0&.01 #onstruction &ypes for )crew 'oints

-101.02.02 e3uirements for )crew 'oints

-101.02.0( &ypes of )crew 'oints for &hin )heets

-101.02.0- 5or!ing rinciple of %low*"rilling )crews

&+L+& -101 20



-101.02.0 )crew 'oints for +luminium rofiles

-101.0*.01 )teps in the %olding rocess for )traight*/dged )heets

-101.0(.02 5idths of 7verlaps in %olded 'oints

-101.04.01 'oining by iveting

-101.0-.02 ivet &ypes for the 8ndirect iveting of +luminium

-101.0-.0( #ommercially +vailable ivet %orms and their %ields of +pplication

-101.0-.0- 5or!ing rinciple of a Blind op: ivet

-101.0-.0 #hoice of %astening /lements for $echanical %astening $ethods

-101.0+.01 )chematic 8llustration of #linching 'oints, with or without Local 8ncision

-101.0.02 +n +luminium #ar "oor +ggregate #arrier with #linch 'oints

-101.0,.01 #omparison of the &echnological #haracteristics of %astening $ethods

Mechanical Fastening

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