Resistance Microwelding Techniques in Braze Set-Up Operations
Resistance Microwelding Best Practices in Braze Set-Up Operations Jay A. Kapur Vice President - Aimtek, Inc. [email protected] IBSC 2018 Aimtek Background 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 IBSC 2018 Ball Tack Welding Poke Tack Welding Honeycomb Tack Welding IBSC 2018 Joules First Law: P = IR(t) P = Power (Energy per unit time) I = Current (welding current) R = Resistance (ohms) t = time (milliseconds) IBSC 2018
Selected Properties of Common Materials Metal Thermal Conductivity (W/ mK) 20C Melting Point (C) Electrical Resistivity (x 10 m) 20Cm) 20C Copper 223
1084 1.724 Aluminum 118 660 2.65 Zinc 67 419
5.92 Iron 42 1482 9.71 17-26 1455 69 Inconel
8-9 1350 129 Hastelloy 5-6 1355 118 Stainless Steel Values from various industry sources
IBSC 2018 Power Supplies and Processes Capacitor Discharge Inverter Ball Tacking Poke Tacking IBSC 2018
Ball Tacking Poke Tacking Honeycomb Tacking Integration with Sensors Automation Types of Current Waveforms Single phase AC Capacitor Discharge 3 phase DC MFDC (Inverter) Illustration from Soudax Equipements IBSC 2018
Ball Tack Welding Purpose: To properly position details prior to brazing IBSC 2018 Ball Tack Welding Typical Equipment: Capacitor discharge or Inverter power supply Vacuum welding pen and pump
Tacking balls any metallic material Grounding fixture IBSC 2018 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. Courtesy of Amada Miyachi Co. IBSC 2018 Ball Tack Welding Common Applications Tubes and Manifolds IBSC 2018 Ball Tack Welding Common Applications Vanes IBSC 2018
Ball Tack Welding Common Applications Photos from Soudax Equipements LPT Nozzle Assembly Sleeve and Air Duct IBSC 2018 Ball Tack Welding Best Practices 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 IBSC 2018 Ball Tack Welding Best Practices Electrode selection Grounding IBSC 2018 Ball Tack SEM After Brazing IBSC 2018
Poke Tack Welding Purpose: To attach foil preforms or tack thin segments IBSC 2018 Typical Equipment: Capacitor discharge or Inverter power supply Welding hand tools or head Electrodes Grounding fixture IBSC 2018 Poke Tack Welding Common Applications Presintered Braze Preforms (PSP)
Foil Preforms IBSC 2018 Poke Tack Welding Best Practices Mo or W insert 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 IBSC 2018 Honeycomb Tack Welding Purpose: To properly position honeycomb segment prior to brazing IBSC 2018 Typical Equipment: Inverter power supply Pneumatic welding head
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 IBSC 2018 Preparation (cont) Preloaded honeycomb can be inconsistent IBSC 2018
Preparation (cont) Identify cell size Parameter development Electrode and fixture design IBSC 2018 Honeycomb Tack Welding Best Practices Parameter Development
Ag/Cu IBSC 2018 Poor Electrode Design Excessive Burning Excessive Force - deformation IBSC 2018 Complete bonding Additional Best Practices: It is necessary to make sufficient spot welds (across the full width of the honeycomb and in ring seals along the honeycomb edges) to ensure that the honeycomb remains in intimate contact with the backing support throughout the entire brazing cycle. It usually is necessary to test the proper degree of overlapping needed, based on the spot weld electrode used.
For consistent resistance welded honeycomb structures, proper electrode amperage and force settings, once developed, should be in written procedures, controlled and monitored. This can help prevent arcing, flashing, sparks, and burns holes in the honeycomb and possible crushing of the honeycomb at the weld interface. IBSC 2018 Processes Can Be Automated! Collaborative Robot Turnkey Cell IBSC 2018 Please visit our website for more information and videos: www.aimtek.com
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