Machining Centers

University of Nevada Las Vegas	MEG426/626 Manufacturing Processes
Department of Mechanical Engineering	Fall Semester 2000

　　

Brazing, Solding, and Adhesive Bonding

Brazing: is a joining process in which a filler metal is melted and distributed by capillary action between the faying surfaces of the metal parts being joined.

No melting of the base metals occurs in brazing. Only the filler melts.

Temperature: T_m > T > 840⁰F (450⁰C)

Where T_m is the melting temperature of the base material.

Advantages:

1). Any metals can be joined;

2). High production rate;

3). Can be applied to join thin-walled parts that cannot be welded.

4). Less heat and power required than in fusion welding, therefore, less heat affected defects.

Disadvantages:

1). Less joint strength than welded joints;

2). Joint is the weak point to cause part failure;

3). Different color from base metals.

Clearance: optimum clearance range between 0.001 and 0.010 in. (0.025 and 0.25 mm).

Brazing Methods:

1). Torch Brazing: a torch is used to direct a flame against the work in the vicinity of the joint. After the workpart joint areas have been heated to a suitable temperature, filler wire is added to the joint.

2). Furnace Brazing: uses a furnace to supply heat for brazing and is best suited to medium and high production.

3). Induction Brazing: utilizes heat from electrical resistance to a high-frequency current induced in the work. The parts are preloaded with filler metal and placed in a high-frequency AC field, the parts do not directly contact the induction coil.

4). Resistance Brazing: heat to melt the filler metal is obtained by resistance to the flow of electrical current through the parts.. The parts are directly connected to the electrical circuit.

5). Dip Brazing: Assembled parts are immersed in the baths contained in the heating pot. Solidification occurs when the parts are removed from the bath.

6). Infrared Brazing: uses heat from a high-intensity infrared lamp.

Brazing Materials:

Braze metal family	Materials commonly joined	Brazing Temperature (^oF)
Aluminum-silicon	Aluminum alloys	1050-1150
Copper and copper alloys	Various ferrous metals as well as copper and nickel alloys and stainless steel	1700-2100
Copper-phosphorus	Copper and copper alloys	1300-1700
Silver alloys	Ferrous and nonferrous metals, except aluminum and magnesium	1150-1800
Gold-based precious metals	Iron, nickel, and cobalt alloys	1650-2000
Magnesium	Magnesium alloys	1100-1150
Nickel alloys	Stainless steel, nickel, and cobalt alloys	1700-2200

Soldering: is a joining process in which a filler metal with melting point (liquidus) not exceeding 840⁰F (450⁰C) is melted and distributed by capillary action between the faying surfaces of the metal parts being jointed.

Filler metal: solder.

Clearance: 0.003 to 0.005 in. (0.076 to 0.127 mm).

in. (0.025 mm) for the surfaces are tinned.

Solder Metals: most solders are alloys of lead and tin with the addition of a very small amount of antimony, usually less than 5%.

Three most commonly used alloys contain 60, 50, and 40% tin and all melt below 465⁰F (240⁰C).

Tin has better fluidity, and higher strength, but is more expensive. For joints where little strength is required, solders containing only 10-20% tin are used.

Lead and lead compounds can be quite toxic. Can not be used in drinking-water lines and foods related industry.

Solding Methods:

Hand Solding: is performed manually using a hot soldering iron.

Wave Solding: is a mechanized technique that allows multiple leadwires to be soldered to a printed circuit board (PCB).

Adhesive Bonding: is a joining process in which a filler material is used to hold two (or more) closely spaced parts together by surface attachment.

Adhesive: the filler material.

Adherents: the parts being joined.

Joint strength in adhesive bonding is determined by the strength of the adhesive itself. And the strength of attachment between adhesive and each adherent.

Created by Dr. Wang