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Fiber Laser Welding Cuts Costs And Improves Results

Fiber Laser Welding Cuts Costs And Improves Results

Lasers have been employed in a variety of welding applications for many years. And, as laser technology further develops and diversifies, its uses in welding continue to expand. This article by Coherent provides an overview of high power lasers in keyhole welding.

Most traditional (non-laser) welding techniques currently in use are variations of arc welding. In these methods, two pieces of metal are first brought into contact or close physical proximity. The edges of the pieces may have been shaped to facilitate their joining. A high voltage is established between an electrode and the contact region, creating an arc which melts the material (or, in some cases an additional filler material or the electrode itself). The melted material fills any gap between the workpieces, or overlays them, and then solidifies to join the parts.

The primary advantage of most arc welding methods is their relatively low cost, particularly in terms of the capital equipment expenditure. Furthermore, arc welding techniques are well understood and widely employed, and standards for producing and testing them are well established, so there’s not much of a learning curve in bringing these processes on line.

The major disadvantages of arc welding mostly derive from subjecting parts to high heat. This can result in microstructures in the melted material that yield poor strength in the weld joint, and a relatively large heat affected zone in the material adjacent to the weld. Additionally, the parameters of the arc are influenced by the local electric field, and can therefore not be set independently.

Laser Keyhole Welding

Most laser welding techniques can be classified into two basic categories, “keyhole” and “conduction mode” welding. Both of these welding modes are capable of being performed autogenously, that is, without filler metal, as well as with filler, if so desired.

Keyhole, or deep penetration welding, is commonly encountered when welding thicker materials at high laser powers. In keyhole welding, the laser is focused so as to achieve a very high power density at the work piece. At the focus of the laser beam, the metal actually vaporises, opening up a blind hole (the keyhole) within the molten metal pool. Vapour pressure holds back the surrounding molten metal and keeps this hole open during the process. The laser power is mainly absorbed at the vapour melt boundary and the keyhole walls. The focused laser beam and the keyhole continuously move along the welding path. At the front of the keyhole, new material is molten, and at the back, it resolidifies to become the welded joint.

The small size of the keyhole region results in a precise, narrow fusion zone, with a high aspect ratio (depth to width) as compared to arc welding methods. Furthermore, the highly localised application of heat means that bulk of the work piece acts as an effective heat sink so the weld region heats up and cools down rapidly. This minimises the size of the heat affected zone, and reduces grain growth. Thus, the laser can generally produce stronger joints than arc welding, which is one of its primary benefits.

Laser welding also offers greater flexibility than arc welding, since it is compatible with an extremely broad range of materials, including carbon steel, high strength steel, stainless steel, titanium, aluminium, and precious metals. It can also be used to join dissimilar materials, as differences in material melting temperatures and heat conduction are of minor importance in the process.

In addition, laser welding delivers significant cost advantages over traditional methods, when all the process steps are considered. In particular, the precise application of heat minimises distortion in the weld and overall part, thus eliminating the need for post processing in many cases. Plus, the ability to project the laser beam over relatively long distances with essentially no power loss makes it easy to integrate laser welding with other production processes, and lends itself well to integration with manufacturing robotics. Last, but not least, new product configurations with reduced flange sizes can be realized, which is critical for light weight vehicles in the automotive industry.

Fibre Lasers for Welding

Modern CO2 and fibre lasers easily deliver the beam parameters and power requirements for keyhole welding. Since almost all metals become increasingly absorptive at shorter wavelengths, process efficiency is enhanced at the shorter fibre laser wavelength of ~1 μm, as compared to CO2 laser wavelength of 10.6 μm.

Fibre lasers, in particular, match the requirements of keyhole welding extremely well. They typically offer output powers in the range of 500 W to 10 kW, and can readily achieve focused spot sizes in the necessary range between 40 μm and 800 μm, even at relatively large working distances. From a practical standpoint, the use of beam delivery fibre expands integration options and facilitates the use of the laser in the manufacturing environment. Finally, the high reliability, excellent uptime and favourable cost of ownership characteristics of fiber lasers make them an economically viable and attractive choice for production welding applications.

There are currently several manufacturers of high power fibre lasers for welding and other materials processing applications. Coherent | Rofin fibre lasers, for example, can deliver a combination of performance, reliability, ease of integration and cost characteristics that is optimum for welding and other materials processing applications. To understand how this is achieved, it’s useful to examine some of the design and construction details of these lasers.

The drawing shows the main elements of the fibre laser oscillator employed by Coherent | Rofin. The laser resonator is formed by a large mode area (LMA), Yb-doped, double clad optical fibre and fibre Bragg gratings for resonator mirrors. This is pumped from each end by a series of diode laser pump modules, whose outputs are fibre coupled into the gain fibre.

Coherent | Rofin fibre laser oscillator schematic, including 12 diode laser pump modules, and 6×1 fibre coupling modules which inject pump light into the gain fibre, and allow efficient extraction of the laser output.

Based on this design, one set of pumps and gain fibre can produce output powers of up to 3kW. The output from up to four of these single mode fibre laser units can then be combined into one multimode fibre to achieve powers of up to 10kW. Alternately, the “standard” cabinet supports splitting the output from a single fibre laser into four separate fibres through the use of the integrated fibre-to-fibre switches.

Thus, this modular construction approach allows Coherent | Rofin to offer several options in terms of output power, delivery fibre diameter, and beam parameter product. The benefit is the ability to readily adapt the laser beam characteristics to precisely match the exact requirements of a specific process.

Some users have experienced fibre laser damage or process inconsistencies caused by back reflections when processing highly reflective metals, such as copper and brass. Coherent | Rofin lasers utilise an optimised power generation and delivery technology, as well as sensors at different positions within the system, to protect laser components from such damage. These safeguards eliminate the problem of back reflections, and allow reliable welding of brass, aluminium and copper without any concern for damaging the laser.

Of course, the fibre laser is just one part of the entire welding system, which also includes a beam focusing welding head, as well as control electronics. In addition to fibre lasers, Coherent | Rofin also offers beam delivery components which mount into customers’ machines. These can be fixed optics or complete, integrated scanning solutions, which include control of all relevant laser parameters, to fully optimize the welding process. Moreover, these integrated solutions often feature fast and flexible beam scanning technology which allows rapid beam movement from one welding contour to the next. This increases the productivity of a laser processing system enormously.

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Harnessing Synergies – Combining Competencies

Harnessing Synergies – Combining Competencies

Paul Horn GmbH uses additive manufacturing to produce its own tools, particularly when making prototypes, special tools and tool holders.

Having recognised the advanced possibilities offered by additive manufacturing, Horn is now making these available to its customers and partners as well. To facilitate this step into the future, Horn is creating a new “Additive Manufacturing” production area. This department is closely linked to mechanical production and powder analysis as well as quality assurance.

Horn is using a process called SLM (selective laser melting), a powder bed process that also goes by the name of direct metal laser sintering. In this technique, the metal powder is applied to a lowerable platform in layers and then the relevant area is targeted and melted by the laser. This process is repeated until the required component height has been achieved. The only materials being used by Horn for the time being are aluminium (AlSi10Mg) and stainless steel (1.4404). However, other materials are currently being tested. The maximum build area is 300 x 300 x 300 mm (11.811 x 11.811 x 11.811″).

As Horn keeps all the production stages in-house, it is able to respond to customer requirements directly. The parts are produced in various designs according to customers’ wishes. Horn also helps customers to choose a structure that is compatible with the SLM method and to select appropriate powder-based parameters. Depending on what customers require, Horn can produce everything from unfinished and semi-finished products right through to the finished component. Further advantages are the ability to make use of the available machinery and appropriate measuring equipment.

Images 1 and 2: Components that can be produced using the additive manufacturing method.

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EuroBLECH 2018: Bystronic Displays “World Class Manufacturing” Innovations

EuroBLECH 2018: Bystronic Displays “World Class Manufacturing” Innovations

In time for EuroBLECH 2018, Bystronic is systematically driving forward the vision of “World Class Manufacturing”. This is based on a comprehensive range of new products and services with which Bystronic is gearing its users’ process landscape towards networked production. “We accompany our customers step by step on the path to the smart factory,” explained Bystronic CEO Alex Waser.

With “World Class Manufacturing”, Bystronic has described the matching supporting programme as one that features innovative solutions that go far beyond the conventional idea of a machine tool. It’s about fusing the individual processes relating to laser cutting and bending into a network of intelligent components, said Mr. Waser. Users can thus achieve a higher degree of flexibility and transparency in their production environment. Both are important prerequisites in order to manufacture products faster, more cost-effectively, and more intelligently than ever before.

In future, thanks to new software solutions, users will be able to create quotes more rapidly, plan their production processes in an efficient manner, and make the best possible use of their resources. Live monitoring systems represent an additional building block. They provide users with real-time information about the running processing steps from their production environment. All this will result in the optimisation of costs and processes. And this in turn, is the prerequisite for growth and sustainable competitive success.

With flexible system solutions, Bystronic is expanding the rules of the game in the field of sheet metal processing. Until now, there was always a trade-off between fast and versatile. In future, users will be able to produce small series or individual mass-produced products at conditions similar to a standardised high-volume series.  As commented by Mr. Waser, “With the new generation of our cutting and bending systems, users can adapt their processes much more easily and thus respond more quickly to their customers’ requirements.”

The integrated automation of production steps is another key success factor. To achieve this, Bystronic uses modular solutions for the material handling in the field of laser cutting. Automation systems that grow with the customers’ requirements and with increasing laser output. In the field of bending, the company is driving forward the development of flexible automation modules that enable fast transitions between automated and manual manufacturing.

Service remains another key issue for Bystronic. Within the networked production environment, network steps are interdependent. This makes process reliability and the preventive maintenance of all integrated systems more critical than ever before. New service solutions help users increase the efficiency and process quality of their production.

Learn more by visiting Bystronic at EuroBLECH 2018 from October 23 to 26, 2018 in Hanover, Germany. Hall 12, Booth B66.

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Automotive Manufacturing: Remote Laser Welding

Automotive Manufacturing: Remote Laser Welding

Automotive manufacturing, given its complexity and volumes, requires the use of efficient, high-volume processes which can guarantee productivity and quality. In practical terms, this can be translated in the need for effective performance-based welding solutions that deliver both speed and precision – the drivers behind the increasing use of lasers for cutting, welding and brazing. Alessio Cocchi – Comau Robotics Marketing Manager shares more on this.

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The High Five In Cutting

The High Five In Cutting

As time goes on, the advances of water jetting continues to happen especially in the case of accuracy and more industries are seeing its viability in the market for faster, more accurate cuts, Syed Shah explains.

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Hexagon: Leica T-Probe

Hexagon: Leica T-Probe

The Leica T-Probe from Hexagon is a measurement tool that is accurate to +/-35 µm and has a point rate output of 1,000 points per second and a tracking speed of >1 m/s.

The T-Probe has a feature which automatically re-establishes interrupted line of sight, allowing users to work freely without having to regularly stop and relocate the beam, resulting in less downtime.

The measurement tool comes in various styli lengths, and can gather data in hard-to-reach places without the need for direct line of sight. The laser tracker can be set in a specific position to measure within a spherical volume of up to 40 m using the T-Probe, which helps to ensure accuracy, maintain data integrity and save time.

The High Five In Cutting

The High Five In Cutting

As time goes on, the advances of water jetting continues to happen especially in the case of accuracy and more industries are seeing its viability in the market for faster, more accurate cuts. Syed Shah explains. 

Waterjet cutting has long been making inroads into every area of manufacturing and engineering. New materials often demand waterjet cutting – in fact it is pretty much the standard in many production lines now. With single and multiple head five-axis waterjet cutting available on a single machine, the technology is now one that is accessible, and it would literally be competitive disadvantage to not be in possession of it.

Waterjet is opening doors – forgings are being replaced with parts nested into sheet material effortlessly cut into the most complex of shapes. Castings are being scanned and flashing trimmed, eliminating multiple tedious steps and labour. Near net shape cutting of everything from complex blades to helical rack and pinion to accurate cutting of composites, laminates of high nickel alloys, glass and phenolics, plastics, ceramics, armour plating of most every make and composition are easy.

And this is no longer limited to flat, plane cutting. If you can imagine it, waterjet can probably be used to cut it. The principles of waterjet cutting are fairly simple. In a nutshell, water at pressure of 60,000 psi or more is channelled to a cutting head through sheathed, 0.25” diameter autofrataged stainless steel tubing that in short lengths is not flexible. Abrasive is fed to the cutting head where the water pressure, as it transitions from potential energy to kinetic energy, accelerates the abrasive grains to over 2,200 miles per hour in a nozzle that is 3” long.

Accuracy – Spot On

In years past, when multi-dimensional water-jetting was new, the understanding was that there would be a sacrifice in tolerances. This is no longer the case. With advances in engineering of the nozzles and orifices used, the width of the waterjet stream is now predictable to 0.0005”, allowing manufacturers to support demands for precision five-axis parts.

Key to creating an accurate five-axis mechanism is the ability to measure the results. As such, a 3D spatial laser tracker is employed to measure the actual mechanisms and correct for any ‘real world’ inaccuracies that crop up in the manufacturing processes or from material properties.

Standard laser interferometers are incapable of measuring all of the parts once they are assembled and operating in space. Once a final mechanism is measured, the data can be used to electronically compensate, on the fly, for any repeatable errors that occur, pushing the envelope on accuracy to new bounds.

High Pressure Water

Imagine your finger is the nozzle in a cutting head. Now wave it around and notice how flexible your wrist, elbow and shoulder are, not to mention the muscles as they twist and flex. So how do you get high pressure water bolted to a fixed position on the face of the Z carriage to the fixed position of the cutting head mounted on the other end of an ‘arm’ that twists, spirals and rotates?

Any additional forces generated in flexing the high-pressure tubing will typically cause variations in positional and repeatable tolerances. Coiling the high-pressure tubing to reduce these forces normally shows unacceptable results in laser tracking.

By directing the high-pressure tubing through the centre of rotary actuators, it is possible to virtually eliminate varying torsion, sheer and moment loads on the cutting head. The combination of swivels and routing the 0.25” high-pressure tubing means no coiling is necessary.

There is no wind up of the high-pressure tubing often associated with five-axis waterjet cutting and lengths of the high-pressure tubing are short. All high pressure tubing eventually fatigues and fails, releasing high-pressure water from hairline fractures. It is important to design a mechanism that fails in a safe manner and is easily repaired.

Getting Abrasive To The Cutting Head

The abrasive, which is typically garnet ranging from 150 to 50 mesh, is fed into the waterjet stream 3 to 4 inches above the tip of the nozzle.

There is a way to direct the abrasive through the middle of the actuator without any wind up of the 3/8” abrasive resistant hose. This reduces the length of the path the abrasive travels from the mini hopper to the cutting head. An ingenious swivel system allows the abrasive to be passed through the centre of the motor, collected and directed back into a flexible hose.

The result is seamless delivery of garnet to the cutting head no matter what the cutting head position or angle of attack. Bulky tubing and awkward mechanisms subject to pinching, clogs and blockages are reduced into a simple straight path from abrasive hopper to cutting head.

Covering All Angles

Any five-axis programming revolves around a common mandate that the part does not change position while cutting. Fixturing for a five-axis mill is often substantial to ensure the part does not move. In waterjet cutting, one has to presume materials will move through the redistribution of stresses as material is cut.

A spring assisted, self-locating crash sensor has a low voltage signal passed through the foot which when interrupted detects a crash. The height sensor is pneumatically controlled and can take periodic samples of the location of the material or continuously ride on the material. The analog feedback allows adjustments to be registered and responded to.

What is most impressive is the height and crash sensor can be deployed to work while the head is cutting at angles approaching 50 degrees off the vertical.

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