Intelligent Use Of Non-Productive Time

Intelligent Use Of Non-Productive Time
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Robots can free up additional capacity for machine tools and increase productivity. By Andreas Schuhbauer, Market Segment Manager for Machine Tools, KUKA Roboter

According to an industry study from 2013, German machine tool operators see their greatest challenges in ever-shorter delivery times and the increasing complexity of the components to be machined. At the same time, quality requirements are rising and prices are falling. The measures that companies are taking to meet these challenges include investment in machining centres, in milling machines and lathes as well as in automation. The focus is shifting increasingly onto robot-based automation – for good reason.

In the past, machine tool and mechanical engineering companies assumed that the automation of machine tools was only suitable for mass production. Manufacturers with batch sizes of 100 or with components that have long throughput times in excess of 90 seconds have only rarely been taken into account. However, the new challenges are gradually leading to a rethink. Outsourcing to countries with a lower wage level is increasingly reaching its limits in terms of the need for short supply chains, the hiring of specialist personnel and quality control. The degree of automation in the industry, when compared to other sectors, is currently at a lowly 1.5 percent – but the pressure to automate is building.

Higher Robot Performance At A Lower Price

Automation using robots can be the right answer here. Robots work with a very high degree of precision – even with complex and heavy components, the reject rate is practically zero. They can work around the clock, and their performance is just as good after 24 hours as in the first minutes. In heavily automated production shifts, they improve the capacity utilisation of the machines and reduce the unit labour costs. Beyond this, unlike wages, the costs for robots have decreased continuously – while their performance has increased at the same time.

Versatile Helpers For Handling, Machining And Assembly

Already today, robots load machine tools quickly and precisely with blanks and then remove the machined parts. During the operating time of the machine tool, the robot can use non-productive time effectively and carry out tasks such as drilling, brushing and deburring. This reduces the spindle runtime per part. On components requiring intensive machining, the robot can also carry out roughing, leaving the machine to take care of the smoothing alone.

Where productivity is concerned, every second counts. About 20 percent of all machine tools can be operated more efficiently in conjunction with robots. It is true that a robot cell can double the investment costs for a machine tool. However, the payback period is often only two years – even with an extensive range of parts.

Robots Are Helping To Build Kuka Robots In Augsburg

At Kuka Roboter in Augsburg, six robot-based solutions are in use. In the case of long machining times, the robot can be gainfully employed between the loading cycles. For example, a robot of the KR QUANTEC series is deployed in the machining area (where parts of the in-line wrists for Kuka robots of the same series are manufactured) to make use of the non-productive times of an automated machine tool. It not only loads the ‘DMC80 U duo Block’ machining centre from Deckel Maho with blanks and unloads the machined parts from the machine, but also machines the sixth side of the workpiece and then deburrs it.

All the machining steps that are required in production of the workpiece are carried out entirely in the new cell. The automation system is designed in such a way that it can be simply adapted to changing production procedures. The result: Kuka is now producing about 4,500 more parts per year than before the automation.

The use of robots in two further machining centres at Augsburg has resulted in an average increase in productivity of more than 15 percent. Since 2013, DMG MORI machine tools have been manufacturing 14 components from castings and sawn sections that are then installed in the adjacent robot assembly shop. A KR 150 R2700 extra robot loads and unloads the machine tools. Once a layer of the pallet has been completely filled with machined components, the robot picks up the suction gripper and takes a cardboard slipsheet from another pallet. It then sets it down on the completed layer of finished parts. Once the carriages on the supply conveyors are empty, the robot places them on the return conveyor.

The robot-based solution allows the company to machine a large number of different components and to flexibly adapt the batch sizes to the quantities required. This automation solution is characterised by its high degree of flexibility in the smallest of spaces. Thanks to the buffering of the components, a maximum unmanned runtime of eight hours is made possible. Kuka has managed to reduce the costs per part while also increasing the operating hours – without the need for additional resources.

In the Burkhardt & Weber machining centre at Kuka in Augsburg, the machine is loaded and unloaded by a KR 500 robot that also processes the workpieces, measuring up to 1.5 m in length, during otherwise non-productive time. The result: productivity has increased by 10 percent. Compared with a conventional solution, the company has since been able to machine 300 more components each year. The greater productivity is attributable to the fact that system operation is 70 percent unmanned and additionally that night shifts run in fully automated mode. Whereas, in the past, each system required one dedicated operator per shift, automation enables staggered working practices.

The operator no longer has to carry out the time-consuming loading of the workpieces directly into the fixture, but places them on the simply-designed locations of the material feeder to the robot. The material feeders are designed as two-axis positioners and are implemented in the robot controller as axes seven and eight. The two material feeders can each carry eight parts. This is enough to keep the system running in unmanned operation for eight hours. Prior to automation, it took up to 15 minutes to clamp a workpiece. The robot now only requires two minutes. The precise alignment of the workpiece, which was physically strenuous for the operator, is dispensed with by the robotic loading, which also eliminates the risk of damaging the expensive clamping equipment during loading and unloading with the crane. Beyond this, downstream tasks, such as deburring the machined workpieces, no longer have to be performed since this task is also carried out by the robot. The company expects a payback period of no more than 2.6 years. If non-productive times can be more effectively utilised – for example, by drilling holes on the link arm and rotating column – this period might be even shorter.

Simple Operation Guaranteed

Six-axis robots are suitable for machining and handling tasks directly at the CNC machine. In order to keep training requirements to a minimum, machine tool manufacturers must pay attention to the ease of operating the robots. The central user interface of the company’s robot on the SINUMERIK-CNC opens up the possibility of seamlessly integrating robots into machine concepts and production processes using the KR C4 controller, for instance. This minimises the training requirement for employees since the operator control panel of the machine tool makes it possible to display, operate and program the company’s robots in the same system that the user is familiar with from using the machine tool.

Conclusion

The examples make it clear: there is potential for productivity increases in every manufacturing step. The use of modern robots allows the potential of machine tools to be tapped through a wide variety of automated processes – such as marking and measuring workpieces, as well as quality control in the machine during the manufacturing process. Performance can be fully maximised especially if the robot is linked to multiple machines.

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