Guiding fiber-optic cables reliably

Reliable 3D energy-chain for a mobile laser hardening system

The centerpiece of this mobile hardening system is a high-performance diode-laser that must be guided reliably by a robot. Assembly-friendly energy supply systems are proving themselves by protecting the sensitive fiber-optic cable of the laser on the one hand, and, on the other, by providing the required mobility of the robot hand on the object to be hardened.

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Picture of multi-dimensionally moving energy supply systems

"A fiber-optic cable for our hardening systems can cost up to EUR 20,000", declares PhD.-Eng. Eckehard Hensel, Managing Director of ALOtec GmbH, located in Kesselsdorf near Dresden. "To prevent it from breaking, which interrupts processes that can result in quality defects on the component to be hardened, the cable must be reliably and effectively protected." This is accomplished with energy supply systems made by igus® GmbH, Cologne. The triflex® R product range, which provides movement in all directions, is used in this case. triflex® R is now available in its third generation. The chain was specifically developed for demanding 6 axes robot applications. It is able to address any requirements profile in rough industrial environments, ranging from large welding robots to small palletizing robots.

Advantages of laser beam hardening

ALOtec GmbH was founded in 1998 as an offshoot from the Dresden-based Fraunhofer Institute for Materials and Radiation Technology (IWS). Since then, the focus has been on the production of laser hardening systems to customer specifications. They are proving themselves in the machinery building, tooling and mold-making industries. Reference systems are located in Germany and Europe, as well as the US and India. "We also offer laser hardening as a service on our own laser hardening systems", the Managing Director explains. The company has established itself in the market with a total of twelve employees.

Laser hardening, or laser beam hardening has been in use by industry for approximately ten years. Among others, this boundary layer process also uses directly radiating and fiber-coupled high-performance diode lasers (HPDL). These operate in a relative short-wave spectrum. This results in notably more efficient energy absorption in the material when compared to other laser beam sources.

The laser hardening process involves a highly targeted, or partial, application of thermal energy into the component. The amount of thermal energy is significantly lower than with other processes. The benefit is that the component exhibits non-significant warping. This consequently limits, or even eliminates post-machining on the hardened component. In addition to high energy-efficiency, other benefits of laser hardening include short processing cycles, which makes the hardened components readily available for subsequent processing steps. Other features include the significant environmental compatibility and cleanliness. Coolant media, such as oil or water, are unnecessary. The only condition is the direct, unrestricted access of the laser beam to the component surface.

Picture of a laser unit in the working position

A real-world example

Basically, any surface made from steel castings, construction, alloyed and tool steels, but also various cast iron grades, such as cast iron with flake or spheroidal graphite can be hardened. For instance, the grooves on the outrunner of an electrical motor, which also functions as the traction wheel on an elevator, were hardened on location on a mobile hardening system as service. Grooves are machined into the traction wheel into which the elevator cable is clamped and retained. To prevent the grooves from wearing too quickly, the groove flanks are once again hardened on both sides.

The service life of an elevator must extend for several decades", Eckehard Hensel points out. "Of course, this also applies to the traction wheel. Its wear-characteristics are considerably improved by laser hardening."

Eckehard Hensel

Reliable processes

The radiation source of the high-performance diode laser is guided by a 6-axes robot with correspondingly high degrees of freedom. "The fiber-coupled diode laser operates with a fiber-optic cable. This means that a corresponding cable must be brought to the robot hand, the sixth axis", the Managing Director explains. "For these and other cables, such as compressed air or signal cables, we need durable cable guidance systems that last." “

One feature in this case is that the fiber-optic cable is located separately in its own guide. "Cable damage must be prevented during insertion, and it must be installed and removed with relative ease. The cable must also never be bent", Eckehard Hensel elaborates on the requirements profile. All cables are positioned in a triflex® series TRE.70 energy supply system, a 3D chain that is particularly easily to fill from the outside. The dual chamber principle of the TRE series facilitates the option to route sensitive cables in a separate chamber with a maximum of protection. The circumferential bending radius stop and the defined torsion stop prevent the load limits of expensive cables from being exceeded – this principle increases the service life and operating reliability of the application. Cables can of course be exchanged at a later point without difficulty. "If a fiber-optic cable needs to be exchanged, it can be quickly removed and replaced by only one person. Since our systems are also located abroad, it is incumbent on us to keep the service-call effort to a minimum. In addition, the production process at the system operator should not be interrupted for an unnecessarily long time!“

An additional design feature is that the energy supply system series can be shortened and extended very easily. "This gives me the ability to quickly respond to the local installation conditions when setting up a customer's system, by adjusting the length link by link", the Managing Director elaborates. Before the decision was made in favor of these energy supply systems, a host of other systems from other suppliers were tested. However, these were unable to prove themselves under real-world conditions. "This energy supply system cannot be out-performed with respect to assembly-friendliness." “

Picture of a trifelx®, which is easy to fill from the outside

The system manufacturer inserts fiberglass rods into bores prepared by the factory to ensure the required stiffness of the overall system. This limits the bending radius to the required 350 mm. "The topics of acceleration or tensile forces are not of concern to us; we are more interested in the system's mobility, reliability and assembly-friendliness", Eckehard Hensel stresses once again. "But we also have high requirements for temperature-resistance." “

The laser of the hardening system is generally rated at 10 2 to 6 kW. But depending on the system, the rating can also be much higher, e.g. the thermal radiation is greater because of the partial reflection of the laser beam on the component surface. And if concave shaped components are added, heat is focused as through a lens. In a worst case scenario, the power density of this focal point can burn through the fiber-optic cable. The system manufacturer is using a weld-protection sheath that protects from reflecting radiation and therefore safeguards the functionality of the optical cable. "The distance of the component from the radiation source is only a few centimeters. And when push comes to shove and only three or four plastic chain links need to be exchanged, this is much more compelling for the customer than an expensive total replacement", the General Manager explains.

Finding the solution step by step

These energy supply systems have been in use in all hardening systems since 2006. We developed today's solution step by step", igus®' technical sales consultant, Matthias Gebauer, states in retrospect. "In addition, other intermediate sizes have been introduced over the years, so that today, the corresponding chain cross-sections and chain-lengths are available for the various requirements from the factory. These only need to be adjusted to the individual situation. “Originally, the enclosed triflex® TRC.100 was the energy supply system of choice. But this created problems for the quick replacement of cables. "This is why we ultimately decided to go with the open energy supply system", Eckehard Hensel elaborates. Corresponding sample shipments have moved the decision forward. "The samples, the personal support, the immediate availability of all components have made a convincing case for us. In addition, all change requirements were responded to promptly. Today, we are able to provide high system reliability." “Of course, selecting the smaller multi-dimensionally moving energy supply systems also has had an impact of the overall system concept. Eckehard Hensel summarizes in conclusion: "The systems are basically very compact in their design. Among other factors, this is made possible by the energy supply systems. The hardening systems must operate impeccably over time. Their engineering is mature. And we are able to prove this. In spite of the high mechanical loads, we have not experienced a single failure of a fiber-optic cable world-wide!"