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Laser heat treating – a short course

Blue River Digital

Maybe you’ve heard a little about laser heat treating and you think it might be all smoke and mirrors. Or, maybe you’re surprised a laser could be used for something other than cutting metal, and you’d like to know how it might benefit your operation. Either way, the technology is tried and tested in multiple applications in nearly every industry in America.

Here’s how it works.

Laser heat treating is much the same as any other thermal hardening process, except that it uses the highly controllable energy of a CO2 laser. Regardless of the energy source, the object is to raise the temperature of the piece to the point where its internal structure begins to crystallize (the transformation temperature), then allow the piece to cool rapidly.

In conventional case-hardening, the cooling (quenching) is hastened by chilling the piece with oil, water, or forced air. When treated by laser, the workpiece can usually be self-quenched, or cooled in ambient air.

Used at full intensity, the laser is able to cut through a metal piece. Reduce the energy somewhat, and the beam melts the surface, making it possible to weld–or to create a tough clad coating. Reduce the beam energy further, or shorten its duration, and the surface is only heated; if brought to the transformation temperature, then cooled, the surface becomes harder than before.

A laser beam causes very rapid heat input into a small area of the work-piece. There is rapid transformation, then an extremely high cooling rate, as the heat is conducted into the workpiece by its own mass. The real advantage of this type of heat treating lies in the uniformity of the method and the precise control of the depth of the hardened area.

The depth of hardening is determined by a number of factors. The slower the treatment speed, the deeper the hardening effects. Power density and treatment speed determine the actual heat input into the workpiece surface.

BMR Group has over two decades of experience in laser heat treating. We know what works and what doesn’t.  Because we offer multiple hardening technologies to fit applications across most industries, you can be sure we’ll help you select the best technology for your components and your operating environment.

BMR Group has more expertise and experience with laser materials processing than any other company in the business. Need proof? Look at these articles.
The Art & Science of Laser Heat Treating
Job Shop Laser Heat Treating
Toughening Up Capstan Surfaces

If you have components that require case hardening and you’re tired of problems of distortion and failure, call BMR Group at 260-635-2195 and discover how easy it can be to gain the advantages of laser heat treating.

Laser cladding fundamentals

Blue River Digital
Using a laser to deposit a rugged clad surface on wear-prone components can be relatively inexpensive and can yield highly effective results.

Cladding is the association of layers of metals of different natures by molecular interpenetration of the surfaces in contact. Limited diffusion of the surface material is a characteristic of clad products and differentiates them from products metalized in other manners, such as normal electroplating. Large scale cladding processes include pouring molten cladding metal onto a basic metal followed by rolling or simple hot-rolling of the cladding metal to ensure efficient welding to the basic metal. Smaller-scale cladding methods include superimposing the cladding material (nickel, chromium, etc.) by a thermal process to ensure welding. In these methods the cladding metal is applied to the basic metal by heat treatment at the appropriate temperature.

Cladding is a highly flexible technique for developing a tough corrosion and erosion resistant surface to metal surfaces. Laser cladding is simply a finely-tuned technology for heating the cladding and substrate materials to the proper temperature. It involves depositing a hard material, usually in the form of powder, onto a surface to enhance the wear and corrosion resistance of the substrate material. The process is actually fairly simple: A laser beam melts a very thin layer of the work piece, some cladding alloy is added to the melt pool, and this surface freezes to the work piece with a metallurgical bond. The resulting thin surface has all the desirable properties of a wear coating without significant changes to the substrate material. The result is a highly effective and economic hardened surface that can extend the life of the component.

Laser cladding offers one of the most cost effective ways of developing a wear- or corrosion-resistant surface layer to components in repair and life-extending maintenance. It is used to build up worn surfaces, repairing components, and to produce low volume parts.

BMR Group has more expertise and experience with laser materials processing than any other company in the industry.  If you want to know anything about how this technology can help your operational up time and pad your bottom line, call one of our technical specialists at 260-635-2195 or email info@bmrgroup.net.

Laser heat treating fundamentals

Blue River Digital
Laser heat treating can provide an exceptionally hard surface on certain types of steel that helps resist wear…and the risk of distortion is virtually zero!

In surface heat treating of steel, the surface of a piece of steel is hardened by heating it to a suitable temperature at which it begins to change its internal structure, and then causing it to cool rapidly. This process is referred to as transformation hardening, because the surface of the metal is transformed to another state. In laser heat treating the concentrated light energy emitted by the laser is converted into heat energy when absorbed by the metal, causing the transformation.

The transformation involved when steel is hardened is actually a change in the arrangement of the atoms in the metal. Technical people involved in heat treating sometimes referred to this as a change in the “crystallographic lattice network” of the metal. That may give you a good word picture of what actually happens. This change occurs at critical transformation temperatures both when the metal is being heated and as it is cooled. The transformation temperature is the temperature above, or below which solid state transformation takes place.

The exact temperature depends on the alloy composition of the steel being treated The changes, and the structures they produce in the metal, all take place while the metal is in the solid state. That is. the metal is not actually melted, because transformation occurs before the surface reaches the melting temperature. After the metal surface is heated, it has to cool at the critical cooling rate, which is the rate at which the heated material is cooled from the transformation temperature to a lower temperature .

In conventional heat treating, high cooling rates are achieved after the heating process by chilling, or quenching the work piece with oil, water or forced air. In most laser heat treating applications the material is allowed to “self-quench ” or cool? in ambient air. That is possible with laser heat creating because the area heated at any one instant is so small.

The transformed area of the steel is called martensite, and it is the iron-carbon structure that is produced upon a very rapid cooling to the martensite transformation temperature. Martensite is the structure that produces the high hardness in ferrous materials The greater the degree of martensite formation, the higher the hardness. Typical heat treatments for most industrial applications result in hardness of 56 – 62 points of the Rockwell C scale.

Normally, 0.4 per cent carbon content is the minimum that can be successfully hardened to this range by any heat treating method, and laser heat treating is no exception to this rule The big advantage the laser provides is uniformity and precise control of the depth of hardened area.

BMR Group has more expertise and experience with laser materials processing than any other company in the industry.  If you want to know anything about how this technology can help your operational up time and pad your bottom line, call one of our technical specialists at 260-635-2195 or email info@bmrgroup.net.

C02 Laser Design

Blue River Digital

The CO2 laser, once an industry work-horse, has been eclipsed by newer laser designs that are more narrowly focused toward specific uses. However, because of its unique design and function, the CO2 laser is still an irreplaceable tool for many industrial applications that cannot be matched by other technologies.  Optical systems can focus the light energy into small spot sizes useful in metal cutting, welding, cladding, and heat-treating applications. Here’s why it works so well in so many heat treating, welding, and other hard-surfacing applications.

Essential components

The CO2 laser is comprised of two basic parts. The first part includes the components that generate the laser energy, and the second part is the beam delivery system that translates the laser energy into a light beam that can be used. The energy-generating part of a CO2 laser consists of a lasing medium, an optical resonator to contain the lasing medium, and an excitation source for the lasing medium.

A lasing medium is the original source of the energy for the laser. The lasing medium in a CO2 laser is a mixture of carbon dioxide, helium, and nitrogen gas.

In an axial-flow type of CO2 laser, the gas is contained in a long double walled glass tube. This glass tube is the optical resonator and has reflecting mirrors mounted at each of its ends. High electrical voltage is the excitation source applied to the gas in the resonator to excite the CO2 molecules to a higher energy level.

Making light

As the gas mixture is electrically charged, the excited molecules try to find a more stable energy level. In the process, they emit energy in the form of photons. This is similar to a controlled chain reaction, as each emitted photon stimulates the emission of more photons from other excited molecules. Every photon emitted by the excited CO2 molecules has exactly the same wavelength.

As the energy beam develops from the excited photons, the mirrors at the ends of the optical resonator catch the photons traveling parallel to the axis of the resonator and reflect them back down the resonator. This process further amplifies the energy content of the beam by stimulating the emission of even more photons. The optical resonator makes all the energy flow in one direction, since all reflected photons are traveling in a direction parallel to the resonator’s axis.

The energy within the laser is of no value until it can be directed out of the unit and onto a work surface. An output coupler is used to get the energy out of the optical resonator so it can be used for some work application. To form the output coupler for a CO2 laser, one of the mirrors on the end of the resonator tube is made only partially reflective.

This partially reflective mirror allows about 50 percent of the laser beam to exit the optical resonator, and that portion is used for the laser’s intended application. The remaining 50 percent of the beam continues to stimulate photon emission in the excited CO2 molecules inside the resonator. The output coupler focuses the exiting beam to produce high energy densities in a small area.

Making heat

The laser beam is simply an energy source until it contacts the surface of a work piece. To make the light beam useful, lasers have optical systems that use reflectors and lenses to direct the beam from the optical coupler to the work piece.

Because a CO2 laser beam retains most of its power over long distances, the optical systems can direct the beam to a workstation located quite a large distance from the laser. The beam can even be split and shared among more than one workstation, as it is in BMR Group’s facility in Wolf Lake, Indiana.

BMR Group has used CO2 laser technology for two decades, helping customers conquer or alleviate wear problems caused by everyday operation in difficult production environments. If you’d like to learn how this same technology might help you improve your productivity and your bottom line, call BMR Group at 260-635-2195 or drop us an email explaining what you want to accomplish.

How a laser can improve bearing life

Blue River Digital

The CO2 laser offers a way to case-harden bearing surfaces to extend their life without distorting the part.  And that means more production from your operations.

Costly shutdowns and maintenance programs are frequently the norm for heavily loaded bearings and other PT components subject to wear. In the quest for longer wear life of these components, companies are searching for more effective case hardening techniques.

One of the most promising tools for case hardening bearing surfaces is the multi-use laser. Though lasers have many uses, few manufacturers are aware of their case-hardening abilities. This is despite the fact that CO2 lasers have been used to harden metal surfaces for at least 20 years.

Why a laser?

The laser can heat treat different types and shapes of bearing elements. The most commonly treated elements are shafts that mate with bearings, especially heavily loaded bearings.  Heat treating these shafts reduces the likelihood of galling when the bearing is pressed onto the shaft.  Also, for bearings that require frequent replacement because they operate in hostile environments, it reduces the risk of bearing seizure, which would otherwise damage the shaft.

Normally, rollers, balls, and other small bearing components are not good candidates for laser heat treating.  But the surfaces on which the bearings run can be hardened in many applications.

The type of material being treated affects the hardness and like other technologies, laser hardening works best if the bearing metal being treated has a minimum of 0.4% carbon content. In most steels containing 0.4% to 0.7% carbon, the laser achieves a case hardness of 58 to 62 Rockwell C for a depth typically ranging from 0.010 to 0.080 in. Deeper cases are generally not advisable with laser hardening because of the risk of melting the surface.

Shaft and bearing applications

In a typical application, lasers heat treating is effective on bearing areas and tapered seating , areas on arbor shafts used in coiler and recoiler mandrels. These bearing areas, which support the inner races of rolling element bearings, are highly susceptible to wear because of heavy shaft loading.

The tapered areas provide seats for nonrotating elements that support heavy compression loads. Frequently, these areas can’t be treated by other methods because of possible shaft distortion.

Aside from the reduced risk of distorting a component during heat treating, and the ability to precisely treat a specific wear location, prolonged service life and better performance are two primary benefits of laser heat treating bearing seat areas. Manufacturers turn to laser heat treating of their shafts and bearing surfaces because the technology reduces the chance of line shutdowns caused by wear problems, and the related maintenance requirements.

If you have components that require case hardening and you’re tired of problems of distortion and failure, call BMR Group at 260-635-2195 or send an email and discover how easy it can be to gain the advantages of laser heat treating.

The basics of case-hardening

Blue River Digital

In surface heat-treating, or case hardening, the surface of a piece of steel is heated to a suitable temperature at which it begins to change its internal structure, and then it is cooled very rapidly. The heating and rapid cooling process causes a permanent transformation in the steel, and it becomes harder. This process is known as transformation hardening, because the molecular structure of the metal surface is transformed to another state.

The transformation involved when steel is hardened is actually a change in the arrangement of the atoms or a change in the crystallographic lattice network of the metal. This change occurs at critical transformation temperatures both when the metal is being heated and as it is cooling.

The transformation temperature is the temperature above or below which solid-state transformation takes place. The exact temperature depends on the alloy composition of the steel being treated. The changes and the structures they produce in the metal all take place while the metal is in the solid state. In other words, the transformation occurs before the surface material reaches its melting temperature.

If a piece of steel is heated to its transformation temperature and allowed to cool slowly in ambient air, it passes through several states or arrangements in its microstructure. One of these arrangements is called martensite, a microstructure required to form high hardness in ferrous metals. The greater the degree of martensite formation, the higher the hardness.

To obtain the desired martensite formation, the heated steel must cool at the critical cooling rate, which is the rate at which the heated material is cooled from the transformation temperature to the desired lower temperature. With most heat-treating methods, critical cooling rates are achieved after the heating process by quenching.

In quenching, the surface is sprayed or immersed in water or oil to make it cool very rapidly. Quenching causes the heat-treated area of the steel to bypass other possible states and go directly to martensite.

The most commonly used scale for determining the hardness of steel is the Rockwell C (RHC) scale. The requirements for typical industrial hardening applications are 56 to 62 points Rockwell C.

Although many types and compositions of steel are used, machinable steels usually need a minimum of 0.4% carbon content before they can be successfully hardened to this range by any heat treating method. The carbon content of the metal being treated is the most important factor in determining the maximum attainable surface hardness of a steel, and the higher the carbon content, the greater the potential hardness.

The depth of the hardened case depends on how far below the surface the martensite can form in sufficient quantities. The chemical composition or alloy content of the steel determines the depth to which the maximum hardness can be achieved on a given piece of steel.

The most widely used case hardening technologies are flame hardening, induction hardening, laser hardening.

BMR Group has used CO2 laser technology for two decades, helping customers conquer or alleviate wear problems caused by everyday operation in difficult production environments. If you’d like to learn how this same technology might help you improve your productivity and your bottom line, call BMR Group at 260-635-2195 or drop us an email explaining what you want to accomplish.

Heat treating with CO2 lasers

Blue River Digital

Few manufacturers are aware of laser heat-treating technology and how it can be used. Market awareness of laser heat-treating is familiar to almost every laser shop involved in processing materials. Designers and manufacturers just don’t know what the laser can do. But the fact remains, no other heat-treating process can control depth and hardness within a few percent like the laser can.

In spite of its status as a largely unknown technology, the laser is an established and recognized method for heat-treating the surface of carbon-based steels. It is used for small components such as guide rails, bearing seats, and wire drawing capstans, as well as for very large components such as coiling mandrels, steel rolls, and mold machine shafts. In fact, laser heat-treating is used in almost every industry that processes or uses carbon-based steel in its products. It is highly attractive because the laser heat-treating process produces a finer grain structure than other conventional heat-treating methods, thus providing better wear and fatigue characteristics.

Unfortunately, there are few options are available to manufacturers who want to exploit this technology. There may be fewer than two dozen job shops in the US that have the types of lasers needed to do heat-treating and have enough knowledge of the process to provide laser heat-treating services.

Alternative designs

Laser design and construction over the past 20 years have resulted in lasers of varying construction, power, and size. The Nd:YAG laser and the CO2 gas laser have become the most popular types for working with steel.

Most YAG lasers generally operate at power levels of less than 2 kilowatts and are suitable for cutting, drilling, and seam welding. CO2 lasers can be made to generate up to 25 kilowatts, with those from 3 to 5 kilowatts being used most often for surface heat-treating and other materials processing applications.

The CO2 laser tends to be used more widely for these applications because they can deliver a beam ½-inch square with an energy density of 2 kilowatts per square centimeter or more. Beyond that, CO2 lasers are less expensive in terms of dollars per kilowatt delivered.

The big payoff

Laser heat-treating does not require those post-treatment operations, so the costs associated with laser heat-treating can look higher than other options. Laser equipment cost is a drawback, and optic systems are expensive to procure, maintain, and operate, and they require special expertise. However, many manufacturers turn to materials processing job shops to handle a significant portion of their heat-treating needs without investing in equipment themselves.

If you have components that require case hardening and you’re tired of problems of distortion and failure, call BMR Group at 260-635-2195 or send an email to discover how easy it can be to gain the advantages of laser heat treating.

 

Welcome to the BMR Group of companies

If your parts break, wear out, or just don’t get the job done, you can count on the companies of BMR Group to deliver the repair services you need to keep you up and operating.

  • Timely service

  • Reliable information exchange

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  • Conformance to your requirements

What you need…BMR Group delivers!

We specialize in thermal-sprayed coatings, laser heat treating and cladding, and welded overlays and other technologies that help you combat the effects of component wear in your daily operations.

We serve industry in northeast Indiana, the greater Chicago area, and southern West Virginia, so when you need to keep your operation running on time, we can get you the help you need, when you need it.