Almost every assembly process can be carried out in several ways.The option that a manufacturer or integrator chooses for the best results is usually one that matches a proven technology to a specific application.
Brazing is one such process.Brazing is a metal joining process in which two or more metal parts are joined by melting filler metal and flowing it into the joint.The filler metal has a lower melting point than the adjacent metal parts.
The heat for brazing can be provided by torches, furnaces or induction coils.During induction brazing, an induction coil creates a magnetic field that heats the substrate to melt the filler metal.Induction brazing is proving to be the best choice for a growing number of assembly applications.
“Induction brazing is much safer than torch brazing, faster than furnace brazing, and more repeatable than both,” said Steve Anderson, manager of field and test science at Fusion Inc., an 88-year-old integrator in Willoughby, Ohio Said, specializes in a variety of assembly methods, including brazing.”Plus, induction brazing is easier. Compared to the other two methods, all you really need is standard electricity.”
A few years ago, Fusion developed a fully automatic six-station machine for assembling 10 carbide burrs for metalworking and toolmaking.The burrs are made by attaching cylindrical and conical tungsten carbide blanks to a steel shank.The production rate is 250 parts per hour, and the separate parts tray can hold 144 blanks and tool holders.
“A four-axis SCARA robot takes a handle from the tray, presents it to the solder paste dispenser, and loads it into the gripper nest,” explains Anderson.“The robot then takes a piece of blank from the tray and places it on the end of the shank to which it is glued. Induction brazing is performed using an electrical coil that wraps vertically around the two parts and brings the silver filler metal to a liquidus temperature of 1,305 F. After the burr component is aligned and cooled, it is ejected through a discharge chute and collected for further processing.”
The use of induction brazing for assembly is increasing, mainly because it creates a strong connection between two metal parts and because it is very effective in joining dissimilar materials.Environmental concerns, improved technology, and non-traditional applications are also forcing manufacturing engineers to take a closer look at induction brazing.
Induction brazing has been around since the 1950s, although the concept of induction heating (using electromagnetism) was discovered more than a century before by British scientist Michael Faraday.Hand torches were the first heat source for brazing, followed by furnaces in the 1920s.During World War II, furnace-based methods were frequently used to manufacture large quantities of metal parts with minimal labor and expense.
Consumer demand for air conditioning in the 1960s and 1970s created new applications for induction brazing.In fact, the mass brazing of aluminum in the late 1970s resulted in many of the components found in today’s automotive air conditioning systems.
“Unlike torch brazing, induction brazing is non-contact and minimizes the risk of overheating,” notes Rick Bausch, sales manager for Ambrell Corp., inTEST.temperature.”
According to Greg Holland, sales and operations manager at eldec LLC, a standard induction brazing system consists of three components.These are the power supply, the working head with the induction coil and the cooler or cooling system.
The power supply is connected to the work head and the coils are custom designed to fit around the joint.Inductors can be made from solid rods, flexible cables, machined billets, or 3D printed from powdered copper alloys.Usually, however, it is made of hollow copper tubing, through which water flows for several reasons.One is to keep the coil cool by counteracting the heat reflected by the parts during the brazing process.The flowing water also prevents heat build-up in the coils due to the frequent presence of alternating current and the resulting inefficient heat transfer.
“Sometimes a flux concentrator is placed on the coil to strengthen the magnetic field at one or more points in the junction,” explains Holland.”Such concentrators can be of the laminate type, consisting of thin electrical steels tightly stacked together, or ferromagnetic tubes containing powdered ferromagnetic material and dielectric bonds compressed under high pressure. Use either The benefit of the concentrator is that it reduces cycle time by bringing more energy into specific areas of the joint faster, while keeping other areas cooler.”
Before positioning metal parts for induction brazing, the operator needs to properly set the frequency and power levels of the system.The frequency can range from 5 to 500 kHz, the higher the frequency, the faster the surface heats up.
Power supplies are often capable of producing hundreds of kilowatts of electricity.However, brazing a palm-sized part in 10 to 15 seconds requires only 1 to 5 kilowatts.By comparison, large parts can require 50 to 100 kilowatts of power and take up to 5 minutes to braze.
“As a general rule, smaller components use less power, but require higher frequencies, such as 100 to 300 kilohertz,” Bausch said.”In contrast, larger components require more power and lower frequencies, typically below 100 kilohertz.”
Regardless of their size, metal parts need to be positioned correctly before being fastened.Care should be taken to maintain a tight gap between the base metals to allow for proper capillary action by the flowing filler metal.Butt, lap and butt lap joints are the best way to ensure this clearance.
Traditional or self-fixing are acceptable.Standard fixtures should be made of less conductive materials such as stainless steel or ceramic, and touch the components as little as possible.
By designing parts with interlocking seams, swaging, depressions or knurls, self-fixation can be achieved without the need for mechanical support.
The joints are then cleaned with an emery pad or solvent to remove contaminants such as oil, grease, rust, scale and grime.This step further enhances the capillary action of the molten filler metal pulling itself through the adjacent surfaces of the joint.
After the parts are properly seated and cleaned, the operator applies a joint compound (usually a paste) to the joint.The compound is a mixture of filler metal, flux (to prevent oxidation) and a binder that holds the metal and flux together before melting.
Filler metals and fluxes used in brazing are formulated to withstand higher temperatures than those used in soldering.Filler metals used for brazing melt at temperatures of at least 842 F and are stronger when cooled.They include aluminum-silicon, copper, copper-silver, brass, bronze, gold-silver, silver, and nickel alloys.
The operator then positions the induction coil, which comes in a variety of designs.Helical coils are circular or oval in shape and completely surround the part, while fork (or pincer) coils are located on each side of the joint and channel coils hook onto the part.Other coils include Inner Diameter (ID), ID/Outer Diameter (OD), Pancake, Open, and Multi-Position.
Uniform heat is essential for high-quality brazed connections.To do this, the operator needs to ensure that the vertical distance between each induction coil loop is small and that the coupling distance (gap width from coil OD to ID) remains uniform.
Next, the operator turns on the power to begin the process of heating the joint.This involves rapidly transferring intermediate or high frequency alternating current from a power source to an inductor to create an alternating magnetic field around it.
The magnetic field induces a current on the surface of the joint, which generates heat to melt the filler metal, allowing it to flow and wet the surface of the metal part, creating a strong bond.Using multi-position coils, this process can be performed on multiple parts simultaneously.
Final cleaning and inspection of each brazed component is recommended.Washing parts with water heated to at least 120 F will remove flux residues and any scale formed during brazing.The part should be immersed in water after the filler metal has solidified but the assembly is still hot.
Depending on the part, minimal inspection can be followed by nondestructive and destructive testing.NDT methods include visual and radiographic inspection, as well as leak and proof testing.Common destructive testing methods are metallographic, peel, tensile, shear, fatigue, transfer, and torsion testing.
“Induction brazing does require a larger up-front capital investment than the torch method, but it’s worth it because you get the extra efficiency and control,” Holland said.”With induction, when you need heat, you just press. When you don’t, you press.”
Eldec manufactures a wide range of power sources for induction brazing, such as the ECO LINE MF intermediate frequency line, which is available in various configurations to best suit each application.These power supplies are available in power ratings ranging from 5 to 150 kW and frequencies from 8 to 40 Hz.All models can be equipped with a power boost feature that allows the operator to increase the 100% continuous duty rating by an additional 50% within 3 minutes.Other key features include pyrometer temperature control, temperature recorder and insulated gate bipolar transistor power switch.These consumables require little maintenance, operate quietly, have a small footprint, and are easily integrated with workcell controllers.
Manufacturers in several industries are increasingly using induction brazing to assemble parts.Bausch points to automotive, aerospace, medical equipment and mining equipment manufacturers as the largest users of Ambrell induction brazing equipment.
“The number of induction brazed aluminium components in the automotive industry continues to increase due to weight reduction initiatives,” Bausch points out.“In the aerospace sector, nickel and other types of wear pads are often brazed to jet blades. Both industries also induction braze various steel pipe fittings.”
All six of Ambrell’s EasyHeat systems have a frequency range of 150 to 400 kHz and are ideal for induction brazing of small parts of various geometries.The compacts (0112 and 0224) offer power control within 25 watts resolution; the models in the LI series (3542, 5060, 7590, 8310) offer control within 50 watts resolution.
Both series have a removable work head up to 10 feet from the power source.The system’s front panel controls are programmable, allowing the end user to define up to four different heating profiles, each with up to five time and power steps.Remote power control is available for contact or analog input, or optional serial data port.
“Our main customers for induction brazing are manufacturers of parts that contain some carbon, or large mass parts that contain a high percentage of iron,” explains Rich Cukelj, Fusion Business Development Manager.”Some of these companies serve the automotive and aerospace industries, while others make guns, cutting tool assemblies, plumbing taps and drains, or power distribution blocks and fuses.”
Fusion sells custom rotary systems that can induction braze 100 to 1,000 parts per hour.According to Cukelj, higher yields are possible for a single type of part or for a specific series of parts.These parts range in size from 2 to 14 square inches.
“Each system contains an indexer from Stelron Components Inc. with 8, 10 or 12 workstations,” explains Cukelj.”Some workstations are used for brazing, while others are used for inspection, using vision cameras or laser measurement equipment, or performing pull tests to ensure high-quality brazed joints.”
Manufacturers use eldec’s standard ECO LINE power supplies for a variety of induction brazing applications, such as shrink-fitting rotors and shafts, or joining motor housings, Holland said.More recently, a 100 kW model of this generator was used in a large parts application that involved brazing copper circuit rings to copper tap connections for hydroelectric dam generators.
Eldec also manufactures portable MiniMICO power supplies that can be easily moved around the factory with a frequency range of 10 to 25 kHz.Two years ago, a manufacturer of automotive heat exchanger tubes used MiniMICO to induction braze return elbows to each tube.One person did all the brazing, and it took less than 30 seconds to assemble each tube.
Jim is a senior editor at ASSEMBLY with over 30 years of editorial experience.Before joining ASSEMBLY, Camillo was PM Engineer, editor of the Association for Equipment Engineering Journal and Milling Journal.Jim has a degree in English from DePaul University.
Submit a Request for Proposal (RFP) to a vendor of your choice and click a button detailing your needs
Browse our buyer’s guide to find suppliers of all types of assembly technology, machines and systems, service providers and trade organisations.
Lean Six Sigma has been driving continuous improvement efforts for decades, but its shortcomings have become apparent.Data collection is labor-intensive and can only capture small samples.Data can now be captured over long periods of time and in multiple locations at a fraction of the cost of older manual methods.
Robots are cheaper and easier to use than ever.This technology is readily available even for small and medium manufacturers.Listen to this exclusive panel discussion featuring executives from four of America’s top robotics suppliers: ATI Industrial Automation, Epson Robots, FANUC America, and Universal Robots.