small scale resistance welding for medical and...

WJM TechnologiesExcellence In Material Joining

Small-Scale Resistance Welding for Medical and Industrial

ApplicationsGirish P. Kelkar, Ph.D.

(author of “The Weld Nugget”)

WJM Technologieshttp://www.welding-consultant.com/

WJM Technologiesexcellence in material joining

Difference Between Small and Large Scale

Small-Scale – size, power, equipment Materials Types of Bonds Weld Configurations Process Control


Small-Scale Physical Size: < 0.010” diameter, <0.005” thick Current: <5 kA Force: <30 lbs Time: <100 msec Often need microscope for welding

Smallest Weld 0.0008” (20 micron) thermocouple cross-wire weld 20 amps, 0.5 lbs, and 1.5 msec


Small-Scale Power supply is often a single unit

that includes controller and transformer and built-in weld monitors

HF: High Frequency (1-25 kHz) DC: Direct Current CD: Capacitor Discharge AC: Alternating Current


Materials Conductive alloys: Cu, Au, Pt, Ag Structural alloys: Steel, SS, Ni, Ti Refractory alloys: Mo, W, Ta

Welding of dissimilar material combinations Molybdenum to Aluminum Tungsten to Iron Copper to Stainless Steel


Types of Bonds Fusion weld is not common in small-scale

resistance welding: Fusion welds (10%) Solid-State Welds (60%) Solder (10%) Braze (20%)

Include in-situ braze: one of the parts itself acts like a braze alloy


Braze (foil)

BAg-1 braze foil Copper plated SS wire to SS shell

Tube

Wire

Braze


Braze (in-situ)

Steel foils sandwiching a Mo wire


Solid-State Bond

Commutator welds common in motor industry


Solid-State Bond

Fusing stranded wire before welding

ShoesElectrodes


Weld Configuration

Parallel gap weld and step welds are common since access for opposed welding is not often

available


Weld Configuration Single Weld designs are common

Each weld has to be good since supporting welds are often not possible

Need good process control and monitoring


Process Control Voltage, Current, and Power Pulsed Welding Resistance Conditioning Combo Mode


Voltage Control

Inconsistent Overlap Weld will draw current based on amount of overlap Reduced overlap or less number of coils will result in

reduced current


Power Control

Power control generates fixed amount of heat Works well for parts with multiple orientations

Consolidated Wire Bundle

High RLow I and High V

Low RHigh I and Low V


Pulsation

Pulsation allows the user to increase the proportion of heat generated at the interfaces

Time

Contact Resistance

Bulk Resistance

Res

ista

nce

Weld Energy

Time

Contact Resistance

Bulk Resistance

Res

ista

nce

Weld Impulses


Pulsation

Welding of Nickel Wire in single and multiple (4) pulses Single impulse exhibits excessive material squeezed out Multiple impulse weld produced considerably less material squeeze out

Single Pulse Multiple (4) Pulse


Resistance Conditioning

Variable first pulse (time) to control resistance Second pulse to provide weld energy Good for parts with inconsistent cross section or

variable oxide thickness

Voltage or Power ModeCurrent Cut-Off

First Pulse Second Pulse


Combo Mode

Initial part in voltage mode (to avoid blowouts) Second part in current or power mode for welding

Voltage or Power Mode

Current Mode


Summary Small-Scale welding applications are unique in

terms of size, application, type of bond, and process control needs

Key is to understand bond formation and design process accordingly

Process control is important for robust welding and consistent quality

small scale resistance welding for medical and...

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