Difference between revisions of "Manufacturing Technologies for Contact Parts"

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Besides the selection of the most suitable contact materials the design and type
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Besides the selection of the most suitable contact materials, the design and type of attachment is critical for the reliability and electrical life of contact components for electromechanical switching devices. The most important factors here are the material-saving use of precious metals and the most economical manufacturing method for contact parts..
of attachment is critical for the reliability and electrical life of contact
 
components for electromechanical switching devices. The materials saving use
 
of high cost precious metals and the most economic manufacturing method for
 
contact parts are most important factors.
 
  
There are two basic manufacturing solutions available: One can start with single
+
There are two basic manufacturing solutions available: One can start with single contact parts, such as contact rivets or tips, which then are attached mechanically or by brazing or welding resp. to carrier parts. In the second case, a base material coated or clad with the precious contact metal - for special applications also clad with another non-precious material – in the form of strips or profiles is manufactured as a semi-finished pre-material from which the contact components are then stamped and formed. Besides mechanical cladding other processes such as electroplating and deposition from the gas phase are utilized.
contact parts such as contact rivets or tips which then are attached
+
Which of the following manufacturing processes is finally chosen, depends on the final application of the contact components in their respective switching devices or electromechanical components. Other considerations, such as the required number of electrical operations, the most economical use of precious metals and the anticipated volumes of parts are also important for the process selection.
mechanically or by brazing or welding resp. to carrier parts. In the second case
 
a base material coated or clad with the precious contact metal - for special
 
applications also clad with another non-precious material – in the form of strips
 
or profiles is manufactured as a semi-finished pre-material from which the
 
contact components are then stamped and formed. Besides mechanical
 
cladding other processes such as electroplating and deposition from the gas
 
phase are utilized.
 
Which of the following manufacturing processes is finally chosen depends on
 
the final application of the contact components in their respective switching
 
devices or electromechanical components. Other considerations such as the
 
required number of electrical operations, the most economical use of precious
 
metals and the anticipated volumes of parts are also important for the process
 
selection.
 
  
===3.1 Manufacturing of Single Contact Parts===
+
==Manufacturing of Single Contact Parts==
The group of single contacts includes contact rivets, contact tips, and formed
+
The group of single contacts includes contact rivets, contact tips and formed parts such as weld buttons. Contact spheres (or balls) are today rarely used because of economical considerations. <br>
parts such as weld buttons. Contact spheres (or balls) are today rarely used
+
Main Articel: [[Manufacturing of Single Contact Parts| Manufacturing of Single Contact Parts]]
because of economical considerations.
 
  
===3.1.1 Contact Rivets===
+
==Manufacturing of Semi-Finished Materials==
 +
Semi-finished contact pre-materials can be manufactured from solid precious metals, precious metal alloys or precious metal containing composite materials. <br>
 +
Main Articel: [[Manufacturing of Semi-Finished Materials | Manufacturing of Semi-Finished Materials]]
  
===3.1.1.1 Solid Contact Rivets===
+
==Attachment of Single Contact Parts==
 +
The following segments give an overview of the usually applied attachment technologies for contact parts to carrier components. They include mechanical, as well as brazing and welding methods used for electrical contact assemblies.
  
Solid contact rivets are the oldest utilized contact parts. Their manufacturing
+
Main Articel: [[Attachment of Single Contact Parts | Attachment of Single Contact Parts]]
requires a ductile contact material and is done without scrap on fully automated
 
special cold heading machines. A wire slug is cut off and the rivet head is
 
formed by pressing and hammering. This way contact rivets with various head
 
configurations such as flat, domed, spherical, or pointed can be manufactured
 
depending on the final application and switch or relay design.
 
  
*Typical Contact Shapes of Solid Contact Rivets
+
== Evaluation of Braze or Weld Joints==
Bild
+
The switching properties of brazed and welded contact assemblies is strongly dependent on the quality of the joint between the contact and the carrier. The required high quality is evaluated through optical methods, continuous control of relevant process parameters and by sampling of finished products.
*Contact Materials
 
Bild
 
*Dimensional Ranges
 
Bild
 
The respective parameters cannot be chosen independently of each other.
 
They mainly depend on the ductility of the required contact material. Before a
 
final decision on the dimensions we recommend to consult with the contact
 
manufacturer.
 
  
*Qualitätsmerkmale und Toleranzen
+
Main Articel: [[Evaluation of Braze or Weld Joints| Evaluation of Braze or Weld Joints]]
Bild
 
  
===3.1.1.2 Composite Contact Rivets===
+
==Stamped Contact Parts==
Clad rivets for which only a part of the head (composite or bimetal rivets) or also
+
Stamped electrical contact parts typically consist of a base carrier material to which a contact material is attached by various methods (<xr id="fig:Plated and contact containing pre-stamped strips and stamped parts"/><!--(Fig. 3.17)-->).
the shank end (tri-metal rivets) are composed of contact material – with the
+
They serve as the important functional components in many switching and electromechanical devices for a broad range of electrical and electronic
balance of the body mostly being copper – have replaced for many applications
+
applications. On the one hand, they perform the mostly loss-free electrical current transfer and the closing and opening of electrical circuits, while on the other hand, the contact carriers are important mechanical design components, selected to meet the requirements on electrical, thermal, mechanical and magnetic properties.
solid rivet versions because of economical considerations. The cost savings
 
depend on the contact material and its required volume for a specific
 
application. These composite rivets are also produced scrap-less from wire
 
material on special machinery with two process variations utilized.
 
  
During ''cold bonding'' and heading the bond between the contact material and
+
The increasing miniaturization of electromechanical components requires ever smaller stamped parts with low dimensional tolerances. Such precision
the copper is achieved without external heat energy by high plastic deformation
+
stamped parts are needed in the automotive technology for highly reliable switching and connector performance. In the information and data processing
at the face surfaces of the two wire segments ''(Fig. 3.1)''. The bonding pressure
+
technology, they transfer signals and control impulses with high reliability and serve as the interface between electronic and electrical components.
must be high enough to move the lattice components of the two metals within a
+
<figure id="fig:Plated and contact containing pre-stamped strips and stamped parts">
few atom radii so that the adhesion forces between atoms become effective.
+
[[File:Plated and contact containing pre-stamped strips and stamped parts.jpg|left|thumb|Figure 1: Plated and contact containing pre-stamped strips and stamped parts for different applications]]
Therefore the head to shank diameter ratio of 2:1 must be closely met for a
+
</figure>
strong bond between the two metals.
+
<br style="clear:both;"/>
 +
Main Articel: [[Stamped Contact Parts| Stamped Contact Parts]]
  
Fig. 3.1: Cold bonding of bimetall rivets (schematic)
+
==References==
 
 
During ''hot bonding'' the required heat energy is applied by a short term electrical
 
current pulse ''(Fig. 3.2)''. In the case of Ag and Cu a molten eutectic alloy of
 
silver and copper is formed in the constriction area between the two wire ends.
 
When using metal oxide containing contact materials the non-soluble oxide
 
particles tend to coagulate and the bonding strength between the component
 
materials is greatly reduced. Therefore the cold bonding technology is preferred
 
for these contact materials. The during cold bonding required high surface
 
deformation ratio can be reduced for the hot bonding process which allows the
 
head to shank diameter ratio to be reduced below 2:1.
 
 
 
For composite rivets with AgPd alloys as well as alloys on the basis of Au, Pd,
 
and Pt the above methods cannot be used because of the very different work
 
hardening of these materials compared to the base material copper. The
 
starting material for such composite rivets is clad strip material from which the
 
contact rivets are formed in multiple steps of press-forming and stamping.
 
Similar processes are used for larger contact rivets with head diameters > 8 mm
 
and Ag-based contact materials.
 
 
 
Fig 3.2. Hot bonding of bimetal rivets (schematic)
 
 
 
*Typical contact shapes for composite rivets
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Base materials
 
bild
 
 
 
*Dimensional ranges
 
bild
 
These parameters cannot be chosen independently of each other. They depend
 
mainly on the mechanical properties of the contact material. Before specifying
 
the final dimensions we recommend to consult with the contact manufacturer.
 
 
 
*Quality criteria and tolerances
 
bild
 
 
 
*Typical contact shapes of tri-metal rivets
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Base materials
 
bild
 
 
 
*Dimensional ranges
 
bild
 
 
 
*Standard values for rivet dimension
 
bild
 
 
 
===3.1.1.3 Braze Alloy Clad Contact Rivets===
 
For special cases, especially high surrounding temperatures with high thermal
 
and mechanical stresses during switching operations, a full metallurgical bond
 
between the contact rivet and the contact carrier may be required to prevent a
 
loosening of the connection and early failures of the device. To accomplish this
 
superior bond a thin layer of brazing alloy is added to the underside of the head
 
and the rivet shank. During assembly a thermal treatment is added after the
 
mechanical staking.
 
 
 
===3.1.1.4 Contact Rivets with Brazed Contact Material Layers===
 
For certain applications contact rivets with non-ductile or brittle materials such
 
as tungsten, silver–tungsten, or silver–graphite are required. Rivets with these
 
contact materials can only be fabricated by brazing. Small round tips are brazed
 
to pre-fabricated copper or steel bases using special brazing alloys in a
 
reducing atmosphere.
 
 
 
===3.1.2 Contact Tips===
 
Flat or formed contact tips, welded or brazed to contact carriers, are frequently
 
used in switching devices for higher power technology. Depending on the
 
contact material and specified shapes these tips are produced by various
 
manufacturing processes. The most frequently used ones are:
 
 
 
*Stamping from strips and profiles
 
*Cutting from extruded rods
 
*Pressing, Sintering, and Infiltrating
 
*Pressing, Sintering, and Re-Pressing
 
*Pressing and Sintering
 
 
 
For stamping sufficiently ductile semi-finished materials are needed. These are
 
mainly silver, silver–alloys, silver–nickel, silver–metal oxide, and silver–graphite
 
(with graphite particle orientation parallel to the switching surface). silver–metal
 
oxides and silver–graphite need an additional well brazable or weldable silver
 
layer on the underside which can be bonded to the bulk of the contact material
 
by various processes. To further facilitate the final attachment process strips and
 
profiles are often coated on the brazing underside with an additional thin layer of
 
brazing alloy such as L-Ag 15P (CP 102 or BCuP-5).
 
For Ag/C with the graphite orientation perpendicular to the switching surface the
 
brazable underside is produced by cutting tips from extruded rods and burning
 
out graphite in a defined thickness.
 
 
 
The press-sinter-infiltrate process (PSI) is used mainly for Ag/W and Cu/W
 
material tips with tungsten contents of > 50 wt%. A silver or copper surplus on
 
the underside of the tip later facilitates the brazing or welding during final
 
assembly.
 
 
 
The press–sinter–re-press method (PSR) allows the economic manufacturing of
 
shaped contact parts with silver or copper contents > 70 wt%. This process also
 
alloys parts pressed in two layers, with the upper being the contact material and
 
the bottom side consisting of pure Ag or Cu to support easy attachment.
 
 
 
Press–sinter processes are limited to smaller Ag/W contact tips with a Ag
 
content of approximately 65 wt%.
 
 
 
*Contact materials
 
bild
 
 
 
*Typical contact shapes of tips and formed contact parts
 
bild
 
 
 
*Dimensional ranges
 
bild
 
Because of the wide variety of shapes of contact tips and formed contact parts
 
the user and manufacturer usually develop special parts specific agreements
 
on quality and tolerances.
 
 
 
===3.1.3 Weld Buttons===
 
 
 
For contacts used at higher temperatures, such as for example in controls for
 
stove tops, the use of contact rivets or the direct welding of silver based contact
 
materials on steel or thermo-bimetal carriers is usually not feasible. For such
 
applications weld buttons are suitable contact components.
 
 
 
Weld buttons are round or rectangular tips manufactured from clad contact bimetal
 
or in some cases tri-metal semi-finished materials. The surface layer is
 
produced from the specified contact material, the bottom weldable layer from a
 
material with higher electrical resistivity such as steel, nickel, or for example a
 
copper-nickel alloy. For precious metal savings a third high conductive layer of
 
copper may be inserted between the contact material and weld backing. To
 
improve the welding process the underside often has an embossed pattern with
 
one or more weld projections.
 
 
 
The manufacturing of weld buttons from bi– or tri–metal strip requires a ductile
 
contact material. Weld buttons with tungsten contact layers are therefore
 
produced by brazing of tungsten discs to a weldable pre-formed base.
 
 
 
*Typical contact forms of weld buttons
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Carrier materials
 
bild
 
 
 
*Dimensional Ranges
 
bild
 
 
 
Equipment for the Production of Wires, Rivets and Miniature - Profiles
 
bild
 
 
 
*Quality criteria of standard weld buttons
 
bilder
 
 
 
===3.2 Manufacturing of Semi-Finished Materials===
 
Semi-finished contact pre-materials can be manufactured from solid precious
 
metals, precious metal alloys, or precious metal containing composite materials.
 
They are made in wire, strip, and profile form by known processing technologies
 
such as extrusion and subsequent annealing and drawing or roll-forming. They
 
are supplied following the manufacturer's internal standards usually related to
 
DIN EN specifications for copper based materials. The most important materials
 
are two – or multiple material layered semi-finished materials with the contact
 
material bonded in its solid phase to non-precious carriers by cladding, brazing,
 
or welding. The contact material can also be deposited on the carrier from the
 
liquid or vapor phase.
 
 
 
===3.2.1 Clad Semi-Finished Pre-Materials (Contact-Bimetals)===
 
Clad materials consist of two or more layers of different materials, the contact
 
material and the carrier, which are firmly bonded to each other. Depending on
 
the electrical requirements the contact material is mainly an alloy of gold,
 
palladium, or silver based while the carrier material are mainly copper alloys. To
 
bond these materials various technologies are utilized, the two most important
 
ones being described in more detail below.
 
 
 
During ''hot cladding'', the classic process, the materials to be clad are
 
assembled into a cladding package in block or plate form, heated to about
 
800°C and clad (or “welded”) together under high pressure ''(Fig. 3.3)''. At the
 
interface between the two materials a non-separable bond is formed by either
 
diffusion of the reaction partners or in liquid phase by forming a AgCu eutectic
 
alloy when an additional brazing alloy foil is placed between the two materials.
 
Further processing is done by rolling with required annealing steps between
 
subsequent thickness reductions. The disadvantage of this process is the
 
usually limited short length of final material strips.
 
 
 
Fig. 3.3: Hot cladding of pre-materials (schematic)
 
 
 
In the ''Cold Roll-Cladding'' process the bond between the contact and carrier
 
material is achieved by cold deformation of > 50% in one rolling pass ''(Fig. 3.4)''.
 
The high plastic deformation causes cold welding in the boundary layer between
 
the two materials. To increase the quality and strength of the bond a subsequent
 
diffusion annealing is performed in most cases. This process is most suitable for
 
clad semi-finished strips with thin contact material layers (> 2 μm) and large strip
 
length (> 100 m).
 
 
 
Fig. 3.4: Cold roll-cladding of semi-finished strips (schematic)
 
 
 
*Typical configurations of clad contact strips
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Carrier materials
 
bild?
 
 
 
*Dimensions
 
bild
 
When specifying the contact material layer thickness it is recommended to use the
 
minimum required thickness.
 
 
 
*Quality criteria and tolerances
 
Strength properties and dimensional tolerances of clad contact bi-metals are
 
derived from the standards DIN EN 1652 and DIN EN 1654 for Cu alloys. When
 
specifying the width of the contact material layer it is recommended to use the
 
minimum required value. All dimensions should be specified originating from one
 
strip edge.
 
 
 
===3.2.2 Brazed Semi-Finished Contact Materials (Toplay–Profiles)===
 
The toplay process starts with a flat or profile – shaped contact material strip
 
which is fed together with the wider non-precious carrier material and in most
 
cases an intermediate thin foil of brazing alloy into a induction brazing machine
 
''(Fig. 3.5)''. An evenly distributed and reliable braze joint can be achieved this way
 
between contact and carrier materials. The combined material strip is rather soft
 
after the brazing process and re-hardened during a subsequent profile rolling
 
step. In this way different shapes and configurations can easily be achieved.
 
 
 
Fig. 3.5: Toplay brazing with an inductive heating inline equipment (schematic)
 
 
 
*Typical configurations of toplay contact profiles
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Carrier materials
 
bild
 
 
 
*Quality criteria, dimensions and tolerances
 
bild
 
 
 
Strength properties and dimensional tolerances of toplay profiles are derived
 
from the standards DIN EN 1652 and DIN EN 1654 for Cu alloys.
 
 
 
===3.2.3 Seam–Welded Contact Strip Materials (FDR–Profiles)===
 
Seam–welding is the process by which the contact material in the form of a solid
 
wire, narrow clad strip, or profile is attached to the carrier strip by overlapping or
 
continuous weld pulses between rolling electrodes ''(Fig. 3.6)''. The weld joint is
 
created by simultaneous effects of heat and pressure. Except for the very small
 
actual weld joint area the original hardness of the carrier strip is maintained
 
because of the limited short time of the heat supply. Therefore also spring-hard
 
base materials can be used without loss of their mechanical strength. The use of
 
clad contact pre-materials and profiles allows to minimize the use of the costly
 
precious metal component tailored to the need for optimum reliability over the
 
expected electrical life of the contact components.
 
 
 
*Typical configurations of seam–welded contact strips
 
and stamped parts
 
bild
 
Fig. 3.6: Seam-welding process (schematic)
 
 
 
*Contact materials
 
bild
 
 
 
*Carrier materials
 
bild
 
 
 
*Dimensions
 
bild
 
 
 
*Quality criteria and tolerances
 
Strength properties and dimensional tolerances of toplay profiles are derived from the
 
standards DIN EN 1652 and DIN EN 1654 for Cu alloys..
 
 
 
===3.2.4 Contact Profiles (Contact Weld Tapes)===
 
Contact profiles span a broad range of dimensions. Width and thickness are typically
 
between 0.8 – 8.0 mm and 0.2 – 3.0 mm resp. Special configurations, often defined
 
as miniature-profiles or even micro–profiles can have a
 
width < 2.0 mm.
 
 
 
Miniature–profiles are mostly composed of a contact-bimetal material with the contact
 
material being a precious metal alloy or composite material clad, welded or coated by
 
electroplating or vacuum-deposition (sputtered) onto a weldable base material. Since
 
these profiles are attached to carrier strip materials usually by segment– or seam–
 
welding to the base materials, materials with good welding properties such as nickel,
 
copper-nickel, copper-tin, as well as copper-nickel-zinc alloys are used. The bottom
 
surface of the profiles usually has formed weld rails or similar patterns to ensure a
 
solid continuous metallurgical weld joint between the profile and the contact carrier.
 
 
 
Contact profiles in larger sizes are often used for switching devices in the low voltage
 
technology. For these the contact layer mostly consists of arc erosion resistant
 
materials such as silver–nickel, silver–metal oxides or the weld resistant silver–
 
graphite. The brazable or weldable underside of the metal oxide or silver–graphite
 
materials is usually pure silver with also quite often a thin layer of a phosphorous
 
containing brazing alloy applied to aid the welding process.
 
 
 
*Typical configurations of multi-layer contact profiles
 
bild
 
 
 
*Contact materials
 
bild
 
 
 
*Carrier materials
 
bild
 
 
 
*Brazing alloy
 
bild
 
 
 
*Quality criteria
 
Beause of the variety of configurations of contact profiles usually the quality
 
issues are separately agreed upon between the manufacturer and the user.
 
 
 
*Dimensions and tolerances
 
bild
 
The thickness of the Au top-layer, which is sputtered for example, is between 0.2
 
and 5 μm, depending on the requirements. Tolerance of thickness is about + 10%.
 
 
 
===3.3 Attachment of Single Contact Parts===
 
The following segments give an overview of the usually applied attachment
 
technologies for contact parts to carrier components. They include mechanical
 
as well as brazing and welding methods used for electrical contact assemblies.
 
 
 
===3.3.1 Mechanical Attachment Processes===
 
Rivet staking and the insertion and forming of wire segments into pre-stamped
 
carrier parts or strips with punched holes are the most commonly used methods
 
for the mechanical attachment of contact materials.
 
 
 
Riveting (or staking) for smaller volumes of assemblies is mostly done on
 
mechanical, pneumatic or magnetically operated presses. For larger volumes
 
the staking process is integrated into a progressive die for fully automated
 
assembly. Rivets are fed in the correct orientation through special feeding
 
tracks into the staking station of the tool. To ensure a mechanically secure
 
attachment the rivet shank must be dimensioned correctly. As a general rule the
 
shank length of the rivet should be about 1/3 longer than the thickness of the
 
carrier material.
 
For switch-over contacts part of the rivet shank is formed into the secondary
 
rivet head. To minimize deformation of the contact blade carriers, especially thin
 
ones, this head forming is often performed by orbital riveting.
 
 
 
The insertion and forming of wire segments can be easily integrated into stamp
 
and bending multi-slide tooling ''(Fig. 3.7)''. Compared to the use of composite
 
rivets this process uses more precious contact material but for silver based
 
contact materials these costs or often offset by higher and more efficient
 
manufacturing speeds. For the more brittle Ag/SnO<sub>2</sub> materials however close
 
attention must be paid to the danger of crack formation.
 
 
 
Fig. 3.7: Direct press-insertion of wire segments
 
 
 
===3.3.2 Brazing Processes===
 
Brazing is a thermal process for the metallurgical bonding of metallic materials in
 
which a third metal component (brazing alloy or solder) is added. In addition a
 
flux or processing in a protective atmosphere is applied to eliminate oxidation of
 
the non-precious carrier. The melting range of the brazing alloy starts at the
 
beginning of the melting (solidus temperature) all the way to complete liquid
 
phase (liquidus temperature). This range always is below the melting points of
 
the two materials to be joined. During the brazing process with solubility of the
 
materials in each other diffusion processes are thermally activated by which
 
elements of the base material diffuse into the brazing alloy and elements of the
 
braze alloy diffuse into brazing alloy. This increases the bond strength and
 
therefore the mechanical stability of the brazed joint.
 
 
 
For attachment of contact parts to carrier base materials only brazing alloys (as
 
opposed to solders) are used. The reason is the higher softening temperature
 
and melting point as well as higher mechanical strength and electrical
 
conductivity of these alloys. The brazing alloys and fluxes used for electrical
 
contact attachment are listed in Chapter 4 in more detail. Following the most
 
frequently used brazing methods are described.
 
References to the bond quality are given according to the test methods
 
described in Chapter 3.4.
 
 
 
===3.3.2.1 Flame (or Torch) Brazing===
 
The simplest way to produce braze joints is the use of a gas torch fueled by a
 
burning gas and air or oxygen containing gas mixes. For higher production
 
volumes partial automation is applied. The parts to be assembled are
 
transported after adding the suitable amounts of brazing alloy and flux through a
 
series of fixed gas burners on a turntable or belt driven brazing machine.
 
To limit the amount of flux or gas inclusions it is recommended to slightly move
 
the contact tips forth and back (also known as puddeling) as soon as the
 
brazing alloy is liquefied. The bonded area achieved in torch brazing is typically
 
65 – 90% of the contact foot print depending on the size and geometry of the
 
contact tip.
 
 
 
===3.3.2.2 Furnace Brazing===
 
Furnace brazing is usually defined as brazing in a protective atmosphere or in
 
vacuum. Both processes do not require the use of fluxes.
 
 
 
The protective atmosphere brazing is conducted in batch operation in either
 
muffle or pot furnaces or as a continuous process in belt furnaces using a
 
reducing atmosphere of pure hydrogen (H<sub>2</sub>) or dissociated ammonia (H<sub>2</sub>,N<sub>2</sub>).
 
 
 
A vacuum is a very efficient protective environment for brazing but using vacuum
 
furnaces is more complicated and rather inefficient. Therefore this process is
 
only used for materials and assemblies that are sensitive to oxygen, nitrogen, or
 
hydrogen impurities. Not suitable for vacuum brazing are materials which
 
contain components with a high vapor pressure.
 
 
 
Parts with oxygen containing copper supports should not be brazed in reducing
 
atmosphere because of their susceptibility to hydrogen embrittlement. Similarly
 
contact tips containing silver–metal oxide should not be exposed to protective
 
atmospheres because a reduction of the metal oxide even in a thin contact
 
surface layer changes the contact properties of these materials.
 
 
 
===3.3.2.3 Resistance Brazing===
 
In this process the resistive heating under electric currents is the source of
 
thermal energy. For contact applications two methods are used for resistance
 
brazing
 
''(Fig. 3.8)''.
 
 
 
During Direct Resistance Brazing the electric current flows straight through the
 
joint area composed of the contact tip, brazing alloy, flux, and the contact
 
carrier. These components are secured between the electrodes of a resistance
 
brazing machine and heated by an electrical current until the brazing alloy
 
liquefies.
 
 
 
In Indirect Resistance Brazing the current flows only through one of the
 
components to be joined (usually the non-precious contact carrier). This
 
process allows to move the contact tip (“puddeling”) when the brazing alloy is in
 
its liquid stage and this way remove residue bubbles from the heated and boiling
 
flux and increase the percentage of the bonded area.
 
Two different kinds of electrodes are used for resistance brazing:
 
 
 
*Electrodes from poorly conducting carbon containing materials (graphite)
 
The heat is created in the electrodes and thermally conducted into the
 
joint area
 
 
 
*Electrodes from higher conductive and thermally stable metallic materials
 
The heat is created by the higher resistance in the joint area which,
 
through selected designs, creates a constriction area for the electrical
 
current in addition to the resistance of the components to be joined.
 
 
 
Graphite electrodes are mainly used for indirect resistance brazing and for joint
 
2 2 area > 100 mm . For contacts tips with a bottom area < 100 mm which are
 
already coated with a phosphorous containing brazing alloy the heating time can
 
be reduced to a degree that the softening of the contact carrier occurs only very
 
closely to the joint area. For this “short-time brazing” specially designed metal
 
electrodes with compositions selected for the specific assembly component
 
pairings are used.
 
 
 
The bond quality for normal resistance brazing with the application of flux ranges
 
from 70 to 90% of contact size, for short-time welding these values can be
 
exceeded significantly.
 
 
 
Fig. 3.8: Resistance brazing (schematic)
 
 
 
===3.3.2.4 Induction Brazing===
 
During induction brazing the heat energy is produced by an induction coil fed by
 
a medium or high frequency generator. This creates an electromagnetic alternating
 
field in the braze joint components which in turn generated eddy currents
 
in the work piece. Because of the skin–effect these currents and their resulting
 
heat are created mainly on the surface of the assembly components. The
 
distance of the inductor must be chosen in a way that the working temperature
 
is generated almost simultaneously in the full joint area. For different contact
 
shapes the geometry of the induction coil can be optimized to obtain short
 
working cycles. One of the advantages of this method is the short heating time
 
which limits the softening of the material components to be joined.
 
Typical bond qualities of > 80% can be reached with this method also for larger
 
contact assemblies. The widely varying working times needed for the different
 
brazing methods are given in Table 3.1.
 
 
 
Table 3.1: Brazing Times for Different Brazing Methods
 
 
 
*Examples of brazed contact assemblies
 
bild
 
 
 
*Contact materials
 
als bild?
 
Ag, Ag-Alloys., Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO),
 
Ag/SnO (SISTADOX), Ag/ZnO (DODURIT ZnO) and Ag/C (GRAPHOR D) with 2
 
brazable backing, refractory materials on W -, WC- and Mo-basis
 
 
 
*Brazing alloys
 
L-Ag 15P, L-Ag 55Sn et.al. als Bild?
 
 
 
*Carrier materials
 
Cu, Cu-Alloys. et al. als Bild?
 
 
 
*Dimensions
 
Brazing area > 10 mm²
 
 
 
*Quality criteria
 
The testing of the braze joint quality is specified in agreements between the
 
manufacturer and the user.
 
 
 
===3.3.3 Welding Processes===
 
Welding of contact assemblies has both technological and economic
 
importance. Because of the short heating times during welding the carrier
 
materials retain their hardness except for a very small heat affected area. Of the
 
methods described below, resistance welding is the most widely utilized
 
process.
 
 
 
Because of miniaturization of electromechanical components laser welding has
 
gained some application more recently. Friction welding is mainly used for
 
bonding (see Chapter 9). Other welding methods such as ball (spheres) welding
 
and ultrasonic welding are today used in only limited volume and therefore not
 
covered in detail here.
 
Special methods such as electron beam welding and cast-on attachment of
 
contact materials to carrier components are mainly used for contact assemblies
 
for medium and high voltage switchgear.
 
 
 
===3.3.3.1 Resistance Welding===
 
Resistance welding is the process of electrically joining work pieces by creating
 
the required welding energy through current flow directly through the
 
components without additional intermediate materials. For contact applications
 
the most frequently used method is that of projection welding. Differently
 
shaped weld projections are used on one of the two components to be joined
 
(usually the contact). They reduce the area in which the two touch creating a
 
high electrical resistance and high current density which heats the constriction
 
area to the melting point of the projections. Simultaneously exerted pressure
 
from the electrodes further spreads out the liquefied metal over the weld joints
 
area. The welding current and electrode force are controlling parameters for the
 
resulting weld joint quality. The electrodes themselves are carefully designed
 
and selected for material composition to best suit the weld requirements.
 
 
 
The waveform of the weld current has a significant influence on the weld quality.
 
Besides 50 or 60 Hz AC current with phase angle control, also DC (6-phase
 
from 3-phase rectified AC) and medium frequency (MF) weld generators are
 
used for contact welding. In the latter the regular AC supply voltage is first
 
rectified and then supplied back through a controlled DC/AC inverter as pulsed
 
DC fed to a weld transformer. Medium frequency welding equipment usually
 
works at frequencies between 1kHz to 10kHz. The critical parameters of
 
current, voltage, and weld energy are electronically monitored and allow through
 
closed loop controls to monitor and adjust the weld quality continuously. The
 
very short welding times needed with these MF welding machines result in very
 
limited thermal stresses on the base material and also allow the reliable joining
 
of otherwise difficult material combinations.
 
 
 
===3.3.3.1.1 Vertical Wire Welding===
 
During vertical wire welding the contact material is vertically fed in wire form
 
through a clamp which at the same time acts as one of the weld electrodes
 
''(Fig. 3.9)''. With one or more weld pulses the roof shaped wire end – from the
 
previous cut-off operation – is welded to the base material strip while exerting
 
pressure by the clamp-electrode. Under optimum weld conditions the welded
 
area can reach up to 120% of the original cross-sectional area of the contact
 
wire. After welding the wire is cut off by wedge shaped knives forming again a
 
roof shaped weld projection. The welded wire segment is subsequently formed
 
into the desired contact shape by stamping or orbital forming. This welding
 
process can easily be integrated into automated production lines. The contact
 
material must however be directly weldable, meaning that it cannot contain
 
graphite or metal oxides.
 
 
 
Fig. 3.9: Vertical wire welding (schematic)
 
 
 
===3.3.3.1.2 Horizontal Wire or Profile Welding===
 
During horizontal welding the wire or profile contact material is fed at a shallow
 
angle to the carrier strip material ''(Fig. 3.10)''. The cut-off from the wire or profile
 
is performed either directly by the electrode or in a separate cutting station. This
 
horizontal feeding is suitable for welding single or multiple layer weld profiles.
 
The profile construction allows to custom tailor the contact layer shape and
 
thickness to the electrical load and required number of electrical switching
 
operations. By choosing a two-layer contact configuration multiple switching
 
duty ranges can be satisfied. The following triple-layer profile is a good example
 
for such a development: The top 5.0 μm AuAg8 layer is suitable to switch dry
 
circuit electronic signals, the second or middle layer of 100 μm Ag/Ni 90/10 is
 
used to switch relative high electrical loads and the bottom layer consists of an
 
easily weldable alloy such as CuNi44 or CuNi9Sn2. The configuration of the
 
bottom weld projections, i.e. size, shape, and number of welding nibs or weld
 
rails are critically important for the final weld quality.
 
 
 
Because of high production speeds (approx. 700 welds per min) and the
 
possibility to closely match the amount of precious contact material to the
 
required need for specific switching applications, this joining process has
 
gained great economical importance.
 
 
 
Fig. 3.10: Horizontal profile cut-off welding (schematic)
 
 
 
===3.3.3.1.3 Tip Welding===
 
Contact tips or formed contact parts produced by processes as described in
 
chapter 3.1.2 are mainly attached by tip welding to their respective contact
 
supports. In this process smaller contact parts such as Ag/C or Ag/W tips with
 
good weldable backings are welded directly to the carrier parts. To improve the
 
welding process and quality the bottom side of these tips may have serrations
 
(Ag/C) or shaped projections (Ag/W). These welding aids can also be formed on
 
the carrier parts. Larger contact tips usually have an additional brazing alloy
 
layer bonded to the bottom weld surface.
 
 
 
Tip welding is also used for the attachment of weld buttons (see chapter 3.1.3).
 
The welding is performed mostly semi or fully automated with the buttons
 
oriented a specific way and fed into a welding station by suitably designed
 
feeding mechanisms.
 
 
 
===3.3.3.2 Percussion Welding===
 
This process of high current arc discharge welding required the contact material
 
and carrier to have two flat surfaces with one having a protruding nib. This nib
 
acts as the igniter point for the high current arc ''(Fig. 3.11)''. The electric arc
 
produces a molten layer of metallic material in the interface zone of the contact
 
tip and carrier. Immediately afterwards the two components are pushed together
 
with substantial impact and speed causing the liquid metal to form a strong joint
 
across the whole interface area.
 
Because of the very short duration of the whole melt and bonding process the
 
two components, contact tip and carrier, retain their mechanical hardness and
 
strength almost completely except for the immediate thin joint area. The
 
unavoidable weld splatter around the periphery of the joint must be
 
mechanically removed in a secondary operation.
 
The percussion welding process is mainly applied in the production of rod
 
assemblies for high voltage switchgear.
 
 
 
Fig. 3.11: Percussion welding (schematic)
 
 
 
===3.3.3.3 Laser Welding===
 
This contact attachment process is also one of the liquid phase welding
 
methods. Solid phase lasers are predominantly used for welding and brazing.
 
The exact guiding and focusing of the laser beam from the source to the joint
 
location is most important to ensure the most efficient energy absorption in the
 
joint where the light energy is converted to heat. Advantages of the method are
 
the touch-less energy transport which avoids any possible contamination of
 
contact surfaces, the very well defined weld effected zone, the exact
 
positioning of the weld spot and the precise control of weld energy.
 
 
 
Laser welding is mostly applied for rather small contact parts to thin carrier
 
materials. To avoid any defects in the contact portion, the welding is usually
 
performed through the carrier material. Using a higher power laser and beam
 
splitting allows high production speeds with weld joints created at multiple
 
spots at the same time.
 
 
 
===3.3.3.4 Special Welding and Attachment Processes===
 
In high voltage switchgear the contact parts are exposed to high mechanical
 
and thermal stresses. This requires mechanically strong and 100%
 
metallurgically bonded joints between the contacts and their carrier supports
 
which cannot be achieved by the traditional attachment methods. The two
 
processes of electron beam welding and the cast-on with copper can however
 
used to solve this problem.
 
 
 
===3.3.3.4.1 Electron Beam Welding===
 
The electron beam welding is a joining process which has shown its suitability
 
for high voltage contact assemblies. A sharply focused electron beam has
 
sufficient energy to penetrate the mostly thicker parts and generate a locally
 
defined molten area so that the carrier component is only softened in a narrow
 
zone (1 – 4 mm). This allows the attachment of Cu/W contacts to hard
 
and thermally stable copper alloys as for example CuCrZr for spring hard
 
contact tulips ''(Fig. 3.12)''.
 
 
 
Fig. 3.12:
 
Examples of contact tulips with Cu/W
 
contacts electron beam welded
 
to CuCrZr carriers.
 
 
 
===3.3.3.4.2 Cast-On of Copper===
 
The cast-on of liquid copper to pre-fabricated W/Cu contact parts is performed
 
in special casting molds. This results in a seamless joint between the W/Cu and
 
the copper carrier. The hardness of the copper is then increased by a
 
secondary forming or deep-drawing operation.
 
 
 
*Examples of Wire Welding
 
bild
 
 
 
===Vertical Wire Welding===
 
 
 
*Contact materials
 
Ag, Ag-Alloys, Au- and Pd-Alloys, Ag/Ni (SINIDUR) als bild?
 
 
 
*Carrier materials
 
Cu, Cu-Alloys, Cu clad Steel, et.al. als bild?
 
 
 
*Dimensions
 
bild
 
Functional quality criteria such as bonded area percentage or shear force are
 
usually agreed upon between the supplier and user and defined in delivery
 
specifications.
 
 
 
===Horizontal Wire Welding===
 
 
 
*Contact materials
 
Au-Alloys, Pd-Alloys, Ag-Alloys, Ag/Ni (SINIDUR), Ag/CdO (DODURIT CdO),
 
Ag/SnO (SISTADOX), Ag/ZnO (DODURIT ZnO), and Ag/C (GRAPHOR D)
 
 
 
*Carrier materials
 
(weldable backing of multi-layer profiles)
 
Ni, CuNi, CuNiFe, CuNiZn, CuSn, CuNiSn, and others.
 
 
 
*Braze alloy layer
 
L-Ag 15P (CP 102 or BCUP-5)
 
 
 
*Dimensions
 
bild
 
 
 
*Quality criteria
 
Functional quality criteria such as bonded area percentage or shear force are
 
usually agreed upon between the supplier and user and defined in delivery
 
specifications.
 
 
 
===Percussion Welding===
 
 
 
*Contact materials
 
W/Cu, W/Ag, others
 
 
 
*Carrier materials
 
Cu, Cu-Alloys, others
 
 
 
*Dimensions
 
Weld surface area (flat) 6.0 to 25 mm diameter
 
Rectangular areas with up to 25 mm diagonals
 
 
 
*Quality criteria
 
Test methods for bond quality are agreed upon between supplier and user
 
 
 
Fig. 3.13: Examples for percussion welded contact parts
 
 
 
 
 
===3.4 Evaluation of Braze or Weld Joints===
 
The switching properties of brazed and welded contact assemblies is strongly
 
dependent on the quality of the joint between the contact and the carrier. The
 
required high quality is evaluated through optical methods, continuous control
 
of relevant process parameters and by sampling of finished products.
 
 
 
===3.4.1 Brazed Joints===
 
Despite optimized brazing parameters non-wetted defect areas in the braze
 
joint cannot be avoided completely. These wetting defects can mostly be traced
 
to voids caused by flux inclusions in the braze joint area. Depending on the
 
shape and size of the joint areas, the portion of the fully wetted joint is between
 
65% and 90%. In its final use in switching devices a joint area of 80% is
 
considered good or excellent if the individual void size does not exceed 5% of
 
the joint area. Frequently wetted joint areas >90% with voids <3% can be
 
obtained.
 
 
 
Evaluation of the quality of the joint can be performed either by destructive or
 
non-destructive methods.
 
 
 
===3.4.1.1 Destructive Testing===
 
Destructive tests can be performed on a sampling basis in rather simple ways:
 
 
 
*De-brazing
 
The contact tip is being removed by slow heating and simultaneous application
 
of force perpendicular to the contact surface area. Visual inspection of the
 
separated components reveals the non-wetted defect areas as discoloration
 
from either flux remnants or oxidation of the carrier material.
 
 
 
*Milling Sample
 
The contact tip is milled off in layers to a depth that makes the joint area visible
 
for optical evaluation.
 
 
 
*Saw-Cutting
 
A crossing pattern is cut with a fine saw into the contact tip. Areas that are not
 
bonded fall off in pieces.
 
 
 
*Metallographic Micro-section
 
In a metallographic micro-section perpendicular to the contact surface wetting
 
defects can also be made visible ''(Fig. 3.14)'' which however are only indicative
 
of the brazing temperature and brazing time.
 
 
 
Fig. 3.14:
 
Braze joint with voids.
 
Ag/CdO tip on Cu carrier.
 
 
 
*Shear test
 
The contact tip is sheared off from the carrier with the required shear force being
 
a measure for the bond quality. This method is especially suitable for hard and
 
brittle contact tip materials such as for example tungsten.
 
 
 
===3.4.1.2 Non-Destructive Test Methods===
 
Typically the non-destructive testing of braze joints requires more elaborate test
 
equipment. Besides this such test methods have limitations regarding the
 
shape of the contact tips and/or carriers. The prevalent methods are ultrasound
 
testing and X-ray analysis.
 
 
 
*Ultrasonic testing
 
 
 
This method is based on the disruption of the propagation of sound waves in
 
different media. High resolution modern test systems with graphic print-out
 
capabilities and analytical software are capable to detect even small (<0.5 mm
 
diameter) voids in the braze joint. The portion of the wetted areas is calculated
 
as a percentage of the whole joint area. Fig. 3.15 shows an example of different
 
braze qualities for a Ag/SnO<sub>2</sub> contact tip brazed to a copper carrier and
 
illustrates the position and size of void areas as well as the final joint quality.
 
 
 
Fig. 3.15: Ultrasound print-out of braze joints between Ag/SnO 88/12 tips and Cu carrier with 2
 
different degree of wetting (dark areas = voids)
 
 
 
*X-Ray testing
 
 
 
X-ray testing is an additional method for evaluating brazed joints. Using finefocus
 
X-ray beams it is possible to achieve a sufficient picture resolution. There
 
are however limitations about the thickness of the contact tip compared to the
 
size of the void area. This expensive test method is rarely used for contact
 
assemblies.
 
 
 
===3.4.2 Welded Joints===
 
Since welded contact assemblies are usually produced in rather high quantities
 
the quality of the weld joints is monitored closely. This is especially true because
 
of the high mechanical and thermal stresses quite often exerted on the joint
 
areas during switching operations. The quality of the joints is dependent on the
 
process control during welding and on the materials used to manufacture the
 
welded assemblies.
 
 
 
Despite the ability to closely monitor the relevant welding parameters such as
 
weld current, voltage and energy, simultaneous testing during and after
 
manufacturing are necessary.
 
 
 
A simple and easy to perform quality test is based on the shear force.
 
Evaluations of welding assemblies in electrical performance tests have shown
 
however that the shear force is only a valid measure if combined with the size of
 
2 the welded area. As rule of thumb the shear force should be > 100 N/mm with
 
the welded area > 60% of the original wire or profile cross-sectional area. For
 
critical applications in power engineering, for example for high currents and/or
 
high switching frequency, a higher percentage of the joint area is necessary.
 
 
 
During series production every weld is usually probed in a testing station
 
integrated in the manufacturing line with a defined shear force – mostly 20% of
 
the maximum achievable force. In this way defective welds and missing
 
contacts can be found and sorted out. The monitoring of the actual shear force
 
and size is performed during production runs based on a sampling plan.
 
 
 
Fig. 3.16: Ultrasonic picture of a weld
 
joint, Ag/C tip on Cu carrier
 
(ABB-STOTZ-KONTAKT)
 
 
 
Besides destructive testing for shear force and weld area the non-destructive
 
ultrasound testing of the joint quality is also utilized for welded contact
 
assemblies ''(Fig. 3.16)''.
 
 
 
===3.4.3 Selection of Attachment Methods===
 
In the preceding sections a multitude of possibilities for the attachment of
 
contact materials to their carriers was described. A correlation of these
 
methods to the switching current of electromechanical devices is illustrated in
 
Table 3.2. it shows that for the same switching load multiple attachment
 
methods can be applied. Which method to chose depends on a variety of
 
parameters such as contact material, material combination of contact and
 
carrier, shape of the contact, required number of switching operations and last
 
but not least the required volume of parts to be manufactured.
 
 
 
Based on the end application the following can be stated as general rules:
 
Electroplated contact surfaces are limited to switching without or under
 
extremely low electrical loads. In the lower and medium load range contact
 
rivets and welded contacts are used. For high switching loads brazing,
 
especially resistance and induction methods, are utilized. For extremely high
 
loads, for example in high voltage switchgear, percussion welding, electron
 
beam welding, and copper cast-on processes are preferred.
 
 
 
Table 3.2: Correlation between Contact Joining Methods and Switching Currents
 
 
 
 
 
===3.5 Stamped Contact Parts===
 
Stamped electrical contact parts typically consist of a base carrier material to
 
which a contact material is attached by various methods ''(Fig. 3.17)''. They serve
 
as the important functional components in many switching and
 
electromechanical devices for a broad range of electrical and electronic
 
applications. On the one hand they perform the mostly loss-free electrical
 
current transfer and the closing and opening of electrical circuits. In addition the
 
contact carriers are important mechanical design components selected to meet
 
the requirements on electrical, thermal, mechanical and magnetic properties.
 
 
 
The increasing miniaturization of electromechanical components requires ever
 
smaller stamped parts with low dimensional tolerances. Such precision
 
stamped parts are needed in the automotive technology for highly reliable
 
switching and connector performance. In the information and data processing
 
technology they transfer signals and control impulses with high reliability and
 
serve as the interface between electronic and electrical components.
 
 
 
Fig. 3.17:
 
Plated and contact
 
containing pre-stamped strips and
 
stamped parts for different
 
applications
 
 
 
===3.5.1 Types of Stamped Parts===
 
Stamped parts are produced as single pieces, in pre-stamped strip and comb
 
configurations. Depending on the requirements and application the contact and
 
base material as well as the coating and attachment technology is carefully
 
selected.
 
 
 
*Coated stamped parts
 
Stamped parts can be selectively or completely coated with precious metal
 
containing materials based on gold, palladium, and silver as well as
 
non-precious materials such as tin, nickel and copper ''(Fig. 3.17)''. For stamped
 
parts in high volumes like those used as electrical components in automobiles
 
the carrier material is mostly coated in a reel-to-reel process starting with either
 
solid or pre-stamped strips (see also chapter 7.1.1.3). Frequently the prestamped
 
strip will be used directly in further automated assembly of the finished
 
functional component. As an alternative finished stamped parts can be
 
electroplated using barrel and rack plating methods.
 
 
 
Very thin coating layers with tight tolerances are deposited by electroplating. For
 
many applications the high mechanical wear resistance is advantageous. Since
 
even very thin layers are mostly pore-free, these coatings also act as an
 
effective corrosion inhibitor. The type of coatings, the sequence of multiple
 
layers, and the coating thickness, for example for connectors, are chosen
 
according to the requirements for the end application.
 
 
 
*Clad stamped parts
 
 
 
For many applications thicker precious metal surfaces or AlSi layers are
 
necessary. These cannot be deposited by electroplating. Besides meltmetallurgically
 
produced materials on the basis of gold, palladium and silver,
 
also powder-metallurgical materials are required frequently. The metallurgical
 
bond between these contact materials and the mostly copper based substrates
 
is achieved through various mechanical cladding methods (see also chapter
 
3.2.1). In this way also aluminum clad strips are manufactured in which the
 
aluminum layer serves as the bondable surface in the interface between
 
electromechanical connections and electronic circuits. These clad semifinished
 
materials can be further fabricated into pre-stamped strips, in comb
 
form, or single stamped parts ''(Fig. 3.18)''.
 
 
 
Fig. 3.18:
 
Examples of clad stamped parts
 
 
 
*Welded stamped parts
 
 
 
Welded stamped parts can be fabricated by various methods (see also Chapter
 
3.3.3). Single contact pieces can be attached to pre-stamped or finished
 
stamped strips as weld buttons and wire or profile segments by electrical
 
resistance welding. Contact parts can also be stamped from seam-welded
 
semi-finished strip. Fitting the end application contact materials based on gold,
 
palladium and silver. Depending on the contact material and the design of the
 
finished contact component the contact bottom surface may be consist of a
 
weldable backing material.
 
 
 
*Brazed stamped parts
 
 
 
Brazed stamped contact assemblies are manufactured by two joining methods
 
(see also chapter 3.3.2). The contact material is either attached by resistance
 
or induction brazing to base metal carriers as prefabricated contact tip or they
 
are stamped from brazed semi-finished toplay strip. It is typical for brazed
 
contact parts that the contact material consists of silver based contact material
 
and a good conducting copper base material with larger cross-sectional area
 
for the usually higher current carrying capacity.
 
 
 
*Stamped contact parts with rivets
 
 
 
Riveted stamped contact parts are manufactured with the use of contact rivets
 
which are transferred over suitable feed mechanisms correctly oriented into
 
holes punched into the carrier ''(Fig. 3.19)''. Frequently also wire or wire segments
 
resp. are used which are subsequently coined and formed into the desired
 
contact shape (see also chapter 3.3.1). Both attachment methods have their
 
distinct advantages. Using composite or tri-metal rivets allows limiting the use
 
of precious metal custom tailored to the volume needed for specific switching
 
requirements. For wire staking the precious metal usage is usually higher but
 
the staking can be performed at significantly higher production rates
 
and the additional rivet making step is eliminated.
 
 
 
Fig. 3.19:
 
Examples of riveted stamped parts
 
 
 
*Pre-mounted component stamped parts
 
 
 
Components stamped parts consist of a minimum of two carrier parts which
 
differ in their material composition and geometrical form and the contact
 
material
 
''(Fig. 3.21)''. The assembly of these components as single pieces or stamping
 
progressions is performed in a stamping die by riveting or coining. To increase
 
the current carrying capacity at the joining area an additional welding step can
 
be added. Depending on the requirements the different properties of the two
 
carrier components can be combined. As an example: the high electrical
 
conductivity of a contact carrier blade is joined with the thermal or mechanical
 
spring properties of a second material to form a functional component. For this
 
process both carrier base materials can also be coated with additional
 
layers of other functional materials.
 
 
 
Fig. 3.20:
 
Examples of pre-mounted stamped
 
component parts
 
 
 
Stamped parts which are insert molded into or combined with plastic parts are
 
used in electromechanical components (see Chapter 10).
 
 
 
===3.5.2 Stamping Tools===
 
For the design of stamping tools the latest CAD software systems are used.
 
Modern stamping tools usually employ a modular design with integrated
 
dimensional and functional controls ''(Fig. 3.21)''. Depending on the requirements
 
on the parts and the volumes they are built with steel or carbide (-steel) inserts
 
which are coated with a wear resistant material such as for example TiN for
 
longer life.
 
 
 
A special stamping process is precision stamping for contact parts made from
 
thin strip materials with thicknesses in the range of 0.05 – 2.5 mm. With high
 
capacity stamping technology up to 1400 strokes/min can be reached for high
 
volume parts. During the actual stamping operation frequently other processes
 
such as thread-forming, welding of contact segments and insertion and forming
 
of contacts from wire segments are integrated. Depending on the production
 
volumes these operations can also be performed in multiples.
 
 
 
The quality of the tools used for stamping, like progressive dies and stamp-forming
 
tools is important for the final precision and consistency of the parts. During high
 
speed stamping the tools are exposed to extreme mechanical stresses which must
 
be compensated for to ensure the highest precision over long production runs. With
 
such high quality progressive dies parts of high precision with a cutting width of less
 
than the material thickness and with strict quality requirements for the cutting surfaces
 
can be manufactured.
 
To ensure the highest demands on the surface quality of precision contact parts quite
 
often vanishing oils are used as tool lubricants. Cleaning and degreasing operations
 
can also be integrated into the stamping process. Additionally most stamping lines
 
are also equipped with test stations for a 100% dimensional and surface quality
 
control.
 
During the design of stamping tools for electrical contacts minimizing of process
 
scrap and the possibility to separate the precious metal containing scrap must be
 
considered.
 
 
 
Fig. 3.21:
 
Progressive die for stamped contact parts
 
 
 
 
 
===References===
 
  
 
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
 
Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen.
Line 1,080: Line 56:
 
Jinduo, F; Guisheng, W.; Fushu, L.; Hongbing, Z.; Wenland, L.: Study on
 
Jinduo, F; Guisheng, W.; Fushu, L.; Hongbing, Z.; Wenland, L.: Study on
 
Reliability of AuAg10/AgNi10/CuNi30 Micro Contacts,
 
Reliability of AuAg10/AgNi10/CuNi30 Micro Contacts,
th Proc. 24 Int. Conf.on Electr. Contacts, Saint Malo, France 2008, 206-209
+
th Proc. 24<sup>th</sup> Int. Conf.on Electr. Contacts, Saint Malo, France 2008, 206-209
  
 
Dorn, L.: Grundlagen der Löttechnik. in: Hartlöten Grundlagen und
 
Dorn, L.: Grundlagen der Löttechnik. in: Hartlöten Grundlagen und
Line 1,103: Line 79:
 
Bolmerg, E.: Aufschweißtechnik von Kontakten in Hinblick auf ihre Anwendung.
 
Bolmerg, E.: Aufschweißtechnik von Kontakten in Hinblick auf ihre Anwendung.
 
VDE-Fachbericht 51 (1997) 103-109
 
VDE-Fachbericht 51 (1997) 103-109
 +
 +
[[de:Technologien_für_die_Herstellung_von_Kontaktteilen]]

Latest revision as of 09:18, 12 January 2023

Besides the selection of the most suitable contact materials, the design and type of attachment is critical for the reliability and electrical life of contact components for electromechanical switching devices. The most important factors here are the material-saving use of precious metals and the most economical manufacturing method for contact parts..

There are two basic manufacturing solutions available: One can start with single contact parts, such as contact rivets or tips, which then are attached mechanically or by brazing or welding resp. to carrier parts. In the second case, a base material coated or clad with the precious contact metal - for special applications also clad with another non-precious material – in the form of strips or profiles is manufactured as a semi-finished pre-material from which the contact components are then stamped and formed. Besides mechanical cladding other processes such as electroplating and deposition from the gas phase are utilized. Which of the following manufacturing processes is finally chosen, depends on the final application of the contact components in their respective switching devices or electromechanical components. Other considerations, such as the required number of electrical operations, the most economical use of precious metals and the anticipated volumes of parts are also important for the process selection.

Manufacturing of Single Contact Parts

The group of single contacts includes contact rivets, contact tips and formed parts such as weld buttons. Contact spheres (or balls) are today rarely used because of economical considerations.
Main Articel: Manufacturing of Single Contact Parts

Manufacturing of Semi-Finished Materials

Semi-finished contact pre-materials can be manufactured from solid precious metals, precious metal alloys or precious metal containing composite materials.
Main Articel: Manufacturing of Semi-Finished Materials

Attachment of Single Contact Parts

The following segments give an overview of the usually applied attachment technologies for contact parts to carrier components. They include mechanical, as well as brazing and welding methods used for electrical contact assemblies.

Main Articel: Attachment of Single Contact Parts

Evaluation of Braze or Weld Joints

The switching properties of brazed and welded contact assemblies is strongly dependent on the quality of the joint between the contact and the carrier. The required high quality is evaluated through optical methods, continuous control of relevant process parameters and by sampling of finished products.

Main Articel: Evaluation of Braze or Weld Joints

Stamped Contact Parts

Stamped electrical contact parts typically consist of a base carrier material to which a contact material is attached by various methods (Figure 1). They serve as the important functional components in many switching and electromechanical devices for a broad range of electrical and electronic applications. On the one hand, they perform the mostly loss-free electrical current transfer and the closing and opening of electrical circuits, while on the other hand, the contact carriers are important mechanical design components, selected to meet the requirements on electrical, thermal, mechanical and magnetic properties.

The increasing miniaturization of electromechanical components requires ever smaller stamped parts with low dimensional tolerances. Such precision stamped parts are needed in the automotive technology for highly reliable switching and connector performance. In the information and data processing technology, they transfer signals and control impulses with high reliability and serve as the interface between electronic and electrical components.

Figure 1: Plated and contact containing pre-stamped strips and stamped parts for different applications


Main Articel: Stamped Contact Parts

References

Vinaricky, E. (Hrsg.): Elektrische Kontakte, Werkstoffe und Anwendungen. Springer-Verlag, Heidelberg, Berlin 2002

Witter, G., J.; Horn, G.: Contact Design and Attachment in: Electrical Contacts. Hrg.: Slade, P., G., Marcel Dekker, Inc.,New York, Basel, 1999

Mürrle, U: Löten und Schweißen elektrischer Kontakte. In: Werkstoffe für elektrische Kontakte und ihre Anwendungen: Hrg.: Schröder K.-H. u. a.; Expert-Verlag, Band 366, (1997), 146 - 175

Eisentraut, H.: Verbundwerkstoffe aus der Walze. Kaltwalzplattieren von Mehrschichtverbundhalbzeugen, Metall 48 (1994) 95-99

Weik, G.: Kontaktprofile ganzheitliche Lösungen für elektrische Kontaktsysteme, Metall 61 (2007) H. 6, 399 403

Jinduo, F; Guisheng, W.; Fushu, L.; Hongbing, Z.; Wenland, L.: Study on Reliability of AuAg10/AgNi10/CuNi30 Micro Contacts, th Proc. 24th Int. Conf.on Electr. Contacts, Saint Malo, France 2008, 206-209

Dorn, L.: Grundlagen der Löttechnik. in: Hartlöten Grundlagen und Anwendungen. Hrsg.: Dorn, L. u.a., Expert-Verlag, Band 146 (1985) 15-40

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