Technology >>異質材料汽車零組件接合技術與應用Bonding
AutomotiveComponents
Made ofHeterogeneousMaterials Technology & Application

Hardware & Fastener Components - no.56/2022

In automotive production, there are readily visible
components like those for mounting car seats. There arealso many components using mechanical fasteners (screws,bolts, etc.) in invisible areas to fasten carpets, interior/exterior
decorations as well as metal plates (welding or riveting).
It is easy to assemble with fasteners, but they add weight tothe vehicle. Component bonding comes with many optionsand variations. Below I will briefly explain the methods
for bonding va rious automotive components made ofheterogeneous materials.

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Automotive Components Bonding
Technology & Application

The whole fastening process with self-piercing rivets
doesn’t require heating. This method can be used toconnect the same or different materials on body in white,such as steel-to-steel or aluminum-to-steel bonding. Selfpiercing riveting is a room temperature bonding method
for connecting two or more metal plates. The custom-maderivet pierces through the top plate without going throughthe bottom plate, and spans out its hollow structure to forma secure riveting spot. Figure 1 shows the self-piercing
riveting of thin plates. Through external force, the rivet pierce
through the first-layer and middle-layer materials and flows
and extends within the bottom material, thereby forming
an interlocking and permanent plastic-deformed riveting
process. The bonding creates a flat surface on one side and a
protruding cylindrical shape on the other.

(1) Self-piercing Riveting
Aluminum alloy has a wider use in the automotive industry, increasing the use of aluminum bonding with aluminumor steel. Spot welding is not the best choice in most cases,
because aluminum is highly oxidizable. The high temperaturein spot welding is more likely to form a thin coat of oxidized
aluminum that gets in the way of metal bonding. Self-piercing
riveting is the alternative option which we can consider to use
on connecting aluminum alloy as well as other different materials.
Self-piercing riveting can connect aluminum, steel,plastic, carbon fiber reinforced composites and variousmaterials. The whole process doesn’t require pre-drilling.

Source: Manufacturing Science, July 2022

Fig. 1. Self-piercing Riveting with Thin PlatesTechnology >>Self-piercing riveting relative to other bonding methods havethe following features:(1) It can connect two or more layers of plates of different materials, widths and strengths. It is the best method to connect different lightweight materials.
(2) It doesn’t deform from heat and can be used to connect coatedor electroplated plates without undermining the coating.
(3) Compared to conventional riveting, it is highly efficient, requires less equipment investment, consumes less energy andtherefore the cost is lower.

Flow drill screw is a room temperature forming methodthat utilizes high-speed spinning to heat up and deform plates,
tap and then deform the plates, as shown in Figure 3. Its advantage is being applicable to single-sided bonding to makebonding thin plates and small holes possible. It is mostly usedon riveting components on car body plates (such as structuralparts with little bonding space) that doesn’t work well. It canbe used to connect automotive components. The restriction on
flow drill screws is that the bonding spot needs higher rigidity.
The screw is detachable and can potentially loosen off and leadto insufficient strength when the car body is in service for a longterm. Figure 4 shows flow drill screws in use with Ford F-150.

(4) It is safe and environmentally friendly, and doesn’t generate
heat, fume, spark, dust and scrap.
(5) Stable riveting quality; high repeatability; allowing for visualcheck of riveting spot quality.
(6) Able to couple with bonding.
Self-piercing riveting is actually used on Audi’s TT and A8models. Fig. 2 shows self-piercing riveting on the TT model. Thismethod is gradually spreading among European carmakers. It isgaining attention in North America where local carmakers havemore opportunities to use aluminum alloy and other lightweightmaterials that can’t be connected with conventional spot welding.
There was less than 1% of aluminum alloy composition in car body
before 2015. Spot welding remains to be the most common bonding
method for body in white. However, lightweighting is gaining moreand more attention and self-piercing riveting can connect aluminum alloy, steel plates, plastic, carbon fiber reinforced composites
and various material combinations. The whole process does requirepre-drilling. Lightweight manufacturing is worthy of attention.
Source: lightweighting world, May 2022

Hardware & Fastener Components - no.56/2022

Fig. 3. Flow Drill Screw

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Source: invetr.com(2022/05)

Fig. 2. Self-piercing Riveting on the Audi TT Model(2) Flow Drill Screw
Thread forming tapping screws evolves directly from self-tapping screws. The use of thread forming tapping screws requires
pre-drilling and then driving the screws into the holes to create
female threads via a strong force. The material originally on thefemale threads will be squeezed to the male threads. This is themechanism of thread forming tapping screws and it can only be
used on thin and deformable materials. Later comes the inventionof thread cutting tapping screw with one or more slots at the tip of
the screw. The screw utilizes its tip and threads when it drives into
the pre-drilled hole and creates female threads in a way similar toa thread tap. It can be used to connect thick plates, and harder orfragile materials that are not easy to form.

Source: www.assemblymag.com (May 2022)

Fig.4. Flow Drill Screws in & Use with Ford F-150(3) Friction Stir Welding
Friction stir can be divided into two types of manufacturing
processes. T he f i rst one is f r iction sti r weldi ng wh ich
concentrates on metal bonding, and the second one is friction stirprocessing focusing on grain refining materials or adding finegrains. Metal alloys or metal-based composite materials usuallyare either very hot or contain high energy to heat up the weldedarea to the melting point. Next is to add or not add filler metals
and the molten substances spread to both sides of the spot thathas to be fastened. The two sides will connect into one after themolten area cools down and solidifies.

Technology >>Friction stir is a new manufacturing method and a new welding method
developed by The Welding Institute in UK. Unlike conventional welding,friction stir welding is a solid state bonding that brings flawless high quality
bonding and creates better mechanical properties compared to average fusion
welding. Therefore, friction stir is used on aluminum alloys such as 7075 and2024 that would have been hard to connect using conventional welding. In
recent years, friction stir has been widely applied to the bonding of other lightmetals and their alloys. Friction stir utilizes mechanical spinning and friction
to generate heat. The stirring head is made of a hard material. It reaches in two
workpieces that has to be bonded and spins hard to create friction. When thematerial softens (the plastic transforms), the head moves slowly and continues
spinning. Lastly, the head is taken out and the bonding is complete. Figure 5
illustrates friction stir.
Friction stir best suits the bonding, surface modification, precipitation
hardening type material bonding, and dissimilar materials bondingof average or superplasticity light alloys and their composites. It also
suites low-melting alloys such as aluminum alloy, magnesium alloy andtheir automotive components or composites. Figure 6 shows an example
of friction stir applied to the bonding of car body plates made of different
materials.

Source: lightweighting world, May 2022

Hardware & Fastener Components - no.56/2022

Fig. 5. Friction Stir094

Source: bioage.typepad.com, May 2022

Fig. 6. Friction Stir Applied to the Bonding of Car Body Plates
Made of Different Materials(4) Cold Metal Transfer
There has been tremendous progress in the automotive industry in recentyears. More and more technologies are applied in automotive manufacturing.
Fusion welding is indispensable in automotive manufacturing. Car bodyplates are thin. They have a high standard forthe quality of appearance and they weld fast.
Therefore, the conventional metal inert-gas
welding and metal active-gas welding have
limited applications in the automotive industry.
The new cold metal transfer technology canproperly solve the difficulty in welding theautomotive t h i n plates. T he na me wh ich
contains the word “Cold” derives from the factthat the heat input is much less than gas metalarc welding. Cold metal transfer is a type of arc
welding mainly used with thin plates, steel andaluminum-mixing welding, and other tasks thataren’t easy to solve with metal inert-gas welding
and gas metal arc welding.
CMT (Cold Metal Transfer) monitors theglobule state of welding wire to accurately feed
the welding wire. When the globule short-circuits the molten pool, the short circuit signal
is sent to the digital processor and the welding
machine stops outputting electric currents, while
the welding wire feeder withdraws the wire to
separate it from the globule and let the globuletransfer by itself. This is when the welding machine enters the “cold” state. After the globule
separates with the welding wire, the signal issent again to the digital processor and the feeder
continues to feed. The welding machine re-outputs the electric currents and the machine entersthe “hot” state. The CMT wire feeding systemcomprises two feeding mechanisms that work intandem to intermittently feed the wire in the process. The subsequent wire feeding system feeds
the wire to the pool at a fixed speed, and thepreceding wire feeding system feeds the wire at
a fixed rate according to the instructions by thedigital processor. The digital processor collects
signals and accurately analyzes the movement of
the globule to achieve accurate wire feeding andelectric current output control. The cyclic “hot- cold - hot - cold” states of the globule in theCMT globule transfer process clearly reduces
spattering and the input of welding heat.
Cold metal transfer is a brand-new typeof metal inert-gas welding and metal activegas welding. Compared with conventional
cou nt er p a r t s , cold met a l t r a n sfer ha s
extremely low heat input and can weld plates
as thin as 0.3 mm. It can also bond highstrength steel plates with aluminum alloys.
It has been applied to bonding Tesla’s EV
thin plates. This bonding technology can gain
accurate control, and has a fixed short-circuit
transfer cycle that is not subject to randomparameters. Cold metal transfer has literally
zero electric currents and can effectively reduce
splattering to give fine welding quality. Figure 7
illustrates cold metal transfer. Its mechanism isto weld one side of the aluminum alloy material(such as 6061 series) and bond with the steel
material on the other side. The base material
doesn’t melt and there is little deformation.

Technology >>Source: Manufacturing Science, July 2022

Fig. 7. Cold Metal TransferHardware & Fastener Components - no.56/2022

Opportunities for
Taiwanese Automotive
Component Companies

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T he use of heterogeneous a ndcomp osit e mat er ia ls is i nc r e a si ng
every year in response to automotive
lightweighting. Taiwanese companies
are good at low volume, diverse, flexible
and high quality manufacturing, so they
are suited to increase application ofbonding heterogeneous materials suchas aluminum alloy with steel materials(plates), composites (ca rbon fiber)with metal, setting a different price forlightweight automotive components tolift product value-adds. Topics on savingenergy and reducing carbon emission
are gaining public awareness. The useof non-ferrous metals, plastic/rubbermaterials, composite materials andlightweight alloys is increasing every
year. It is better for Taiwanese companies
to develop advanced manufacturing(e.g., laser welding instead of glue
bonding car light covers and light seats)
to reduce material consumption andimprove component strength. Taiwanesecompanies mostly start with automotive
components when they tap into theleadi ng automa kers’ supply chai n.
They should target vehicle functions,or modularized bonded components
to avoid over- desig n i ng mater ia ls,
simplify material application, enhance
properties that make for component
sharing, effectively reduce the numberof components used and of cost, andimprove profits.
Article by James Hsiao
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