Precision Welding of Leadwires and Resistor Elements, Wireforms and Glass Tube Cutting for Lighting and Electronics

+1 724.253.3161
info@cit-hadley.com

facebook
blog
youtube

ROHS Compliant Precision Welding of Leadwires
and Resistor Elements, Wireforms and Glass Tube Cutting for Lighting and Electronics

Outline

 

Contact CIT

Component InterTechnologies
2426 Perry Highway
Hadley, PA USA 16130

Tel: 724-253-3161
Fax: 724-253-3853
Email:

 

Products & Services

 

CIT Innovations

 

Company Profile

how can we help?

Resistance and Percussive Arc Welding
- page 3

1.4 Dumet To CCFE (Copper Clad Iron)

There are four types of dumet:  OXIDIZED, BORATED DUMET, PLATED
DUMET AND BARE DUMET. 

Oxidized dumet consists of copper clad nickel iron that is passed through a heating process which causes copper oxide to form on the copper clad surface.  This dumet is normally used in applications employing some form of controlled atmosphere in the sealing process. 

The borated dumet also utilizes copper clad nickel iron that is oxidized.  However, after oxidation the dumet is heat treated with a borax solution to form a surface of sodium tetraborate that facilitates glass sealing in flame-type processes,

CCFE (copper clad iron steel wire) comes in various sizes and a range of 20% to 88% conductivity.  The conductivity of pure copper is considered 100%.

Diode Assembly

To manufacture a welded dumet to CCFE assembly, as shown in Figure 6, it is necessary first to cut the dumet slug to the proper length.  This cut, made properly, requires that both ends of the cut slug be free of burrs and that a smear of copper be carried across approximately 75% of the surface opposite the weld as shown in Figure 8A, and that the sealing surface of the dumet be free of any scratches or marks that could affect the glass-to-metal seal.   The CCFE wire is then cut to length, forming a chisel-type point as shown in Figure 8B.  This chisel point is cut at various angles, typically <30%, to provide a relatively high resistance point at the weld junction.

Copper Smear

The dumet slug and CCFE wire are brought together under pressure and the welding current is applied through a set of clamp-type jaws on the CCFE wire and through an electrode that contacts the dumet slug on the side opposite the weld, as shown in Fig 1.  When current passes through the work pieces, the relatively high resistance of the CCFE/Dumet interface causes the junction to heat rapidly as the welding pressure forces the two work pieces together, welding the two metals.  The actual weld process on DO 41 and DO 35 welds takes from 3 to 8 milliseconds, depending on material, conductivity, and wire size.

1.5 Pressed and Sintered Tantalum to Tantalum Wire

Tantalum to tantalum welds are used to manufacture tantalum capacitor anodes.  The actual welding process is the same as that used in welding dumet to CCFE.  However, since the slugs are pressed from powdered tantalum, they must be fed into the welder by using a vibratory bowl and feeder track.  The resistance welding process is well suited for this type of weld, because tantalum, when heated, is highly reactive to oxygen and other gases and can actually be ignited by an electrical arc. 

Resistance welding produces no arc which could cause the rapid oxidation of the powdered tantalum metal slug.  It also minimizes the effects of both oxygen and nitrogen that could cause the formation of oxides and nitrides in the weld junction and the area surrounding the weld.  Handling, straightening, and cutting of tantalum requires care to avoid the adherence of lubricating oils that would degrade the finished capacitor. 

Tantalum is extremely abrasive.  It requires that cutting be done with tungsten carbide tools and that the dies in a rotary straightener be made either of ceramic or nylon to prevent premature wear.  Because tantalum is so abrasive, the tantalum dust that accumulates on welding machines must be removed by daily cleaning to prevent excessive wear of moving parts.

Next: Resistance and Percussive Arc Welding - page 4