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Resistance Microwelding Best Practices in Braze Set-Up Operations
Jay A. Kapur
Vice President - Aimtek, Inc.
IBSC 2018
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Aimtek Background
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• Founded in 1973 in Worcester, MA USA• Independently (Family) Owned and Operated• Value-Added Manufacturer and Global Supplier of Brazing
Alloys, Welding Alloys, and Thermal Spray Products • North American Distributor for Soudax Equipements (France)• Global Distribution and Representation Network• Primary Industries Served: Aerospace, Industrial Gas
Turbine, Automotive, Defense, Semiconductor• 2-time Region I Small Business of the Year• 3-time Pratt & Whitney Small Business Supplier of the Year• AS9100/ISO9001 Registered Quality System• UTC Supplier Gold since 2010• All Major Aerospace OEM Qualifications
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•Ball Tack Welding• Poke Tack Welding•Honeycomb Tack Welding
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Joule’s First Law: P = I²R(t)P = Power (Energy per unit time)
I = Current (welding current)R = Resistance (ohms)t = time (milliseconds)
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Selected Properties of Common Materials
Metal Thermal Conductivity (W/mK) 20°C
Melting Point(°C)
Electrical Resistivity(x 10⁻⁸ Ωm) 20°C
Copper 223 1084 1.724
Aluminum 118 660 2.65
Zinc 67 419 5.92
Iron 42 1482 9.71
Stainless Steel 17-26 1455 69
Inconel 8-9 1350 129
Hastelloy 5-6 1355 118
Values from various industry sources
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Power Supplies and Processes
Capacitor Discharge Inverter
• Ball Tacking• Poke Tacking
• Ball Tacking• Poke Tacking• Honeycomb Tacking• Integration with Sensors• Automation
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Types of Current Waveforms
Illustration from Soudax Equipements
Capacitor Discharge
MFDC (Inverter)
3 phase DC
Single phase AC
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Ball Tack Welding
Purpose: To properly position details prior to brazing
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Ball Tack Welding
Typical Equipment:
• Capacitor discharge or Inverter power supply
• Vacuum welding pen and pump
• Tacking balls – any metallic material
• Grounding fixture
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Courtesy of Amada Miyachi Co.
Solid State Bond - In a Solid State Bond (also called thermo-compression Bond), dissimilar materials with
dissimilar grain structure, e.g. molybdenum to tungsten, are joined using a very short heating time, high weld energy, and high force. There is little melting and minimum grain growth, but a definite bond and grain interface. Thus the materials actually bond while still in the “solid state.” The bonded materials typically exhibit excellent shear and tensile strength, but poor peel strength.
Fusion Bond - In a Fusion Bond, either similar or dissimilar materials with similar grain structures are heated to
the melting point (liquid state) of both. The subsequent cooling and combination of the materials forms a “nugget” alloy of the two materials with larger grain growth. Typically, high weld energies at either short or long weld times, depending on physical characteristics, are used to produce fusion bonds. The bonded materials usually exhibit excellent tensile, peel and shear strengths.
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Ball Tack Welding Common Applications
Tubes and Manifolds
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Vanes
Ball Tack Welding Common Applications
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LPT Nozzle Assembly Sleeve and Air Duct
Photos from Soudax Equipements
Ball Tack Welding Common Applications
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• Ball material compatible with base materials (304L, 410, 625, X, CP-Ti)• Minimum ball size that will hold parts (0.5 to 2.0mm diameter)• Return current (ground) fixture close to welding position• Good contact on mating surfaces• Short to Medium discharge time
Ball Tack Welding Best Practices
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Ball Tack Welding Best Practices
Electrode selectionGrounding
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Ball Tack SEM After Brazing
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Poke Tack Welding
Purpose: To attach foil preforms or tack thin segments
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Typical Equipment:
• Capacitor discharge or Inverter power supply
• Welding hand tools or head
• Electrodes
• Grounding fixture
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Poke Tack Welding Common Applications
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Presintered Braze Preforms (PSP)
Foil Preforms
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Poke Tack Welding Best Practices
• Electrode configuration compatible with part geometry• Identify electrical resistivity• Minimum current to secure part• Return current (ground) fixture close to welding position• Good contact on mating surfaces• Short discharge time
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Mo or W insert
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Honeycomb Tack Welding
Purpose: To properly position honeycomb segment prior to brazing
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Typical Equipment:
• Inverter power supply
• Pneumatic welding head
• Copper electrode
• Grounding fixture
Photos from Soudax Equipements
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Preparation:
• Verify honeycomb geometry
• Transfer tape (BFM) is properly placed and pressed onto the honeycomb
• Honeycomb contact surface scraped to reveal the bottom edges for subsequent resistance welding
Photos from Dan Kay
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Preparation (con’t)
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Preloaded honeycomb can be inconsistent
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Preparation (con’t)
• Identify cell size
• Parameter development
• Electrode and fixture design
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Honeycomb Tack WeldingBest Practices – Parameter Development
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P/N Height Width Cell Size Electrode Size Docking Squeezing Force Ramp Flat Forging
1 8 32 1.6 25 x 32 100ms 200ms 50% 3ms 35% @ 3ms 100ms
2 6 25 0.8 25 x 25 100ms 200ms 40% 4ms 40% @ 3ms 100ms
3 6 25 0.8 24 x 24 100ms 200ms 40% 4ms 40% @ 3ms 100ms
4 4 25 1.6 25 x 25 100ms 200ms 35% 4ms 25% @ 4ms 100ms
5 7 31 1.6 25 x 31 100ms 200ms 40% 3ms 35% @ 3ms 100ms
6 8.5 46 0.8 25 x 46 100ms 200ms 50% 4ms 50% @ 3ms 100ms
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Honeycomb Tack WeldingBest Practices – Electrode Design
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Copper Braid Conductive Silicone Ag/Cu
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Poor Electrode Design
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Excessive Burning Excessive Force - deformation
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Additional Best Practices:It is necessary to make sufficient spot welds (across the full width of the honeycomband in ring seals along the honeycomb edges) to ensure that the honeycomb remainsin intimate contact with the backing support throughout the entire brazing cycle. Itusually is necessary to test the proper degree of overlapping needed, based on thespot weld electrode used.
For consistent resistance welded honeycomb structures, proper electrode amperageand force settings, once developed, should be in written procedures, controlled andmonitored. This can help prevent arcing, flashing, sparks, and burns holes in thehoneycomb and possible crushing of the honeycomb at the weld interface.
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Complete bonding
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Processes Can Be Automated!
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Collaborative Robot Turnkey Cell
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Please visit our website for more information and videos:
www.aimtek.com
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