CHAPTER 30

Brazing, Soldering, Adhesive-Bonding, and Mechanical-Fastening Processes

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Brazing

Figure 30.1 (a) Brazing and (b) braze welding operations.

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Typical Filler Metals for Brazing Various Metals and Alloys

TABLE 30.1

Base metal

Aluminum and its alloys Magnesium alloys Copper and its alloys Ferrous and nonferrous (except aluminum and magnesium) Iron-, nickel-, and cobalt-base alloys Stainless steels, nickel- and cobalt-base alloys

Filler metal

Aluminum-silicon Magnesium-aluminum Copper-phosphorus Silver and copper alloys, copper- phosphorus Gold Nickel-silver

Brazing temperature, (°C)

570–620 580–625 700–925 620–1150 900–1100 925–1200 Kalpakjian • Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 30-3

Furnace Brazing

Figure 30.2 An example of furnace brazing: (a) before, (b) after. Note that the filler metal is a shaped wire.

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Induction Brazing

Figure 30.3 Schematic illustration of a continuous induction-brazing setup, for increased productivity.

Source

: ASM International.

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Joint Designs Used in Brazing

Figure 30.4 Joint designs commonly used in brazing operations. The clearance between the two parts being brazed is an important factor in joint strength. If the clearance is too small, the molten braze metal will not fully penetrate the interface. If it is too large, there will be insufficient capillary action for the molten metal to fill the interface.

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Brazing Design

Figure 30.5 Examples of good and poor design for brazing. Kalpakjian • Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 30-7

(a)

Stenciling

Figure 30.6 (a) Screening or stenciling paste onto a printed circuit board: 1. Schematic illustration of the stenciling process; 2. A section of a typical stencil pattern. (continued) Kalpakjian • Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 30-8

(b)

Wave Soldering

(c) Figure 30.6 (continued) (b) Schematic illustration of the wave soldering process. (c) SEM image of wave-soldered joint on surface-mount device.

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Types of Solders and their Applications

TABLE 30.2

Tin-lead Tin-zinc Lead-silver Cadmium-silver Zinc-aluminum Tin-silver Tin-bismuth General purpose Aluminum Strength at higher than room temperature Strength at high temperatures Aluminum; corrosion resistance Electronics Electronics Kalpakjian • Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 30-10

Joint Designs Used in Soldering

Figure 30.7 Joint designs commonly used for soldering. Note that examples (e), (g), (i), and (j) are mechanically joined prior to being soldered, for improved strength.

Source

: American Welding Society.

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Typical Properties and Characteristics of Chemically Reactive Structural Adhesives

TABLE 30.3

Impact resistance Tension-shear strength, MPa (10 3 psi) Peel strength, N/m (lbf/in.) Substrates bonded Service temperature range, °C (°F) Heat cure or mixing required Solvent resistance Moisture resistance Gap limitation, mm (in.) Odor Toxicity Flammability

Epoxy

Poor 15.4 (2.2) < 525 (3) Most materials –55 to 120 (-70 to 250) Yes Excellent Excellent None Mild Moderate Low

Polyurethane

Excellent 15.4 (2.2) 14,000 (80) Most smooth, nonporous –160 to 80 (-250 to 175) Yes Good Fair None Mild Moderate Low

Modified acrylic

Good 25.9 (3.7) 5250 (30) Most smooth, nonporous 70 to 120 (-100 to 250) No Good Good 0.75 (0.03) Strong Moderate High

Source

: Advanced Materials & Processes, July 1990, ASM International.

Cyanoacrylate

Poor 18.9 (2.7) < 525 (3) Most nonporous metals or plastics –55 to 80 (-70 to 175) No Good Poor 0.25 (0.01) Moderate Low Low

Anaerobic

Fair 17.5 (2.5) 1750 (10) Metals, glass, thermosets –55 to 150 (-70 to 300) No Excellent Good 0.60 (0.025) Mild Low Low Kalpakjian • Schmid Manufacturing Engineering and Technology © 2001 Prentice-Hall Page 30-12

General Properties of Adhesives

TABLE 30.4

Type

Acrylic Anaearobic Epoxy Cyanoacrylate Hot melt Pressure sensitive

Comments

Thermoplastic; quick setting; tough bond at room temperature; two component; good solvent chemical and impact resistance; short work life; odorous; ventilation required Thermoset; easy to use; slow curing; bonds at room temperature; curing occurs in absence of air, will not cure where air contacts adherents; one component; not good on permeable surfaces Thermoset; one or two component; tough bond; strongest of engineering adhesives; high tensile and low peel strengths; resists moisture and high temperature; difficult to use Thermoplastic; quick setting; tough bond at room temperature; easy to use; colorless.

Thermoplastic; quick setting; rigid or flexible bonds; easy to apply; brittle at low temperatures; based on ethylene vinyl acetate, polyolefins, polyamides and polyesters Thermoplastic; variable strength bonds. Primer anchors adhesive to roll tape backing material, a release agent on the back of web permits unwinding. Made of polyacrylate esters and various natural and synthetic rubber

Applications

Fiberglass and steel sandwich bonds, tennis racquets, metal parts, plastics.

Close fitting machine parts such as shafts and pulleys, nuts and bolts, bushings and pins.

Metal, ceramic and rigid plastic parts.

“Crazy glue.” ™ Bonds most materials. Packaging, book binding, metal can joints.

Tapes, labels, stickers.

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General Properties of Adhesives (cont.)

TABLE 30.4 (continued)

Type

Phenolic

Comments

Thermoset; oven cured, strong bond; High tensile and low impact strength; brittle, easy to use; cures by solvent evaporation.

Silicone Formaldehyde: -urea -melamine -phenol -resorcinol Urethane Water-base -animal -vegetable -rubbers Thermoset; slow curing, flexible; bonds at room temperature; high impact and peel strength; rubber like Thermoset; strong with wood bonds; urea is inexpensive, available as powder or liquid and requires a catalyst; melamine is more expensive, cures with heat, bond is waterproof; resorcinol forms waterproof bond at room temperature. Types can be combined Thermoset; bonds at room temperature or oven cure; good gap filling qualities Inexpensive, nontoxic, nonflammable.

Applications

Acoustical padding, brake lining and clutch pads, abrasive grain bonding, honeycomb structures.

Gaskets, sealants.

Wood joints, plywood, bonding.

Fiberglass body parts, rubber, fabric.

Wood, paper, fabric, leather, dry seal envelopes.

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Adhesive Peeling Test

Figure 30.8 Characteristic behavior of (a) brittle and (b) tough adhesives in a peeling test. This test is similar to the peeling of adhesive tape from a solid surface.

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Joint Designs in Adhesive Bonding

Figure 30.9 Various joint designs in adhesive bonding. Note that good designs require large contact areas between the members to be joined.

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Configurations of Adhesively Bonded Joints

Figure 30.10 Various configurations for adhesively bonded joints: (a) single lap, (b) double lap, (c) scarf, (d) strap.

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Rivets

Figure 30.11 Examples of rivets: (a) solid, (b) tubular, (c) split (or bifurcated), (d) compression.

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Design Guidelines for Riveting

Figure 30.12 Design guidelines for riveting. (a) Exposed shank is too long; the result is buckling instead of upsetting. (b) Rivets should be placed sufficiently far from edges to avoid stress concentrations. (c) Joined sections should allow ample clearance for the riveting tools. (d) Section curvature should not interfere with the riveting process.

Source

: J. G. Bralla.

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Metal Stitching and a Double-Lock Seam

Figure 30.13 Various examples of metal stitching.

Figure 30.14 Stages in forming a double-lock seam.

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Figure 30.15 Two examples of mechanical joining by crimping.

Crimping

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Spring and Snap-In Fasteners

Figure 30.16 Examples of spring and snap-in fasteners used to facilitate assembly.

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