Preserving resources by minimizing their environmental impact, improving energy efficiency, reducing waste, and adopting new environmental friendly technology will be the trends in the future for robot manufacturers. On the other hand, robots take part in producing environmental friendly products.
Reis, Germany - IFR-Partner
Practical success: Measurable energy saving in die casting automation
On Automatica 2012 the special introduction of VDMA 'Blue Competence' has met excellent feedback and praise from the specialist audience. Among the participating companies, Reis Robotics belongs to those which not only engage in permanent innovation projects, but have also already demonstrated sustainable success in practical use. Reis has established that it is possible to save plenty of energy even in the very energy-intensive die casting industry without any negative impact on the products - rather the contrary. The following article - with the specific example of Pierburg - demonstrates what is presently possible.
Increase of efficiency is possible in very many areas of automation technology. This begins with the robot and its power consumption through to the control systems in the robot which may contribute as energy managers, controlling the various systems involved in the process so they will not consume more energy than really necessary for the process. High process know-how on the part of the automation specialists is a precondition for this, because Blue Competence also is a question of consulting. Reis Robotics, as a turnkey supplier of total systems, is able to offer solutions optimizing the complete process and integrating all connected systems - not only robots - in a central control arrangement. Experience shows that it is not the robots which are the biggest energy consumers, but the entire peripheral equipment.
Potential savings in the foundry are not evident at first sight; in fact metal is molten and then in the die casting procedure is injected into a die with high pressure. How can you save anything here? Reis Robotics has made measurements and examinations about that for many years and the results are often very surprising: In many foundries which are not yet optimized, more than 40 percent of the energy consumption takes place in standby operation without the production process itself! And the robot is one of the lowest consumers in this.
Many systems - in many cases inadvertently - are not switched off in standby operation between the production cycles but keep on consuming current. Analyzing a conventional 800 ton standard casting cell, the trim press alone in standby operation consumed about five times as much current as all other peripheral units! This way annual energy costs in the five-figure range may soon arise without having anything produced at all. If you consider that the effective production time makes merely 60 percent of the total duty cycle, the saving potential becomes evident.
Dr. Michael Wenzel, general manager of Reis Group Holding: "We, too, were surprised how much energy is unnecessarily consumed in some systems. And this is just where the competence of Reis becomes effective, because the final question is how to optimize the energy consumption for an entire process or system. But this step also is only efficient and economic if optimization itself does not cause new high costs."
Pierburg in Nettetal, Germany used numerous die casting processes for many years in an almost unchanged manner. In view of rising energy costs and against the background of a planned move (2014) the plan arose to optimize the automated processes regarding cycle time and use of energy. Without keeping to the normal procedure all of the operations were put to the test. For example, on the basis of several decades of experience the idea was developed to split punching and trimming into two steps so that after the rough cut the fine cut will run free from faults. Air cooling of the castings also turned out to have improved in the project since during further processing no blast agent will stick to angular, still moist contours.
The goal was development of a flexible standard cell for a multitude of products saving energy wherever it is not needed - at least temporarily. In the project with Reis Robotics a sample cell was created which has been operative since mid-2012 and which distinguishes itself by considerable improvement in energy efficiency.
Detailed energy consumption analyses were made by Reis before using the cell. The resulting findings were utilized in the project with regard to energy saving.
Prerequisite for optimal energy saving was a superimposed control level being able to map the most diversified products and to vary the cycles for all connected system components and peripheral units accordingly. Based on impulses from Pierburg in the course of the project the idea was generated to develop a so-called head control with freely programmable production sequences together. Depending on product, paused system parts thus can enter a sleep mode operation. For instance to switch off those drives which are not needed at the moment already saves a lot of energy. The suction hood over the casting machine, the press drives, the robots, and the cooling fans are switched off at the push of a button on the central operating unit or automatically by the central controller. Besides this, there are weekend and pause buttons to centrally switch off all media, drives, and lights which were likely to be forgotten before. Due to this innovation in automation technology, Pierburg is realizing energy savings of up to 30 percent!
First, energy is used for the melting process and casting itself, then further energy is required for cooling the parts before further processing. Reis Robotics established that considerable savings potential can be leveraged by an intelligent control. In quench tanks Reis more and more often uses thermostatic cooling water controls and automatic switch-off of the cooling water circulation in order not to waste this energy unnecessarily. Furthermore, a certain casting residual heat is absolutely desirable for fast drying of the parts.
For cooling of castings with air Reis Robotics recommends the use of speed-controlled fans and an automatic switch-off at all deposit places in the cooling shelf where there is no casting. In the cooling shelf from Pierburg there is space for ten castings. Sensors in the shelf recognize when a part is inserted and only then switch on the relevant fan for a defined time. Temperature sensors are also possible and have already been considered in the control.
At Pierburg the robot picks the parts from the shelf after cooling and feeds them to the next work step. Now follows insertion into the two Reis trim presses. Activated by the head control, their drives stand still until a work step is waiting again. A conveyor system transports the scraps into a bucket; from there the scraps are fed to melting-down. This system part, too, will be switched off centrally as soon as no transport is necessary.
Robots in an automated die casting cell comparatively contribute little for energy consumption. Reis Robotics still made some optimization for saving energy. Generally, the control ROBOTstarV is in a position to switch off the drives of the robot if these are not used. As soon as the control gets the signal for the next work step from the connected peripheral equipment, same will be activated again immediately - comparable to a screen saver.
Even more is possible as Reis Robotics proves again and again. Energy efficient drive motors and innovative servo controllers allow further energy savings. Modified drive motors reduce heating and at the same time lower the expenditure for control cabinet cooling. Modified servo-converters of the drive components use the brake energy of a robot axis by buffering it in an intermediate circuit for subsequent acceleration of another axis. Furthermore, the intelligent control ROBOTstar allows to accelerate drives only as fast as required - not as possible - in order to meet the required process speeds. These optimizations in total save a considerable share of energy as the following diagram explains graphically:
Comparison of the movement speeds with/without energy optimizer and comparison of the required energy
Trim presses from Reis have a so-called load-sensing. This function allows even faster pro-duction if the full performance is not required, and saves energy. Pumps no longer feed against overpressure valves with full capacity and thus generate less heat loss.
Reis also included the motors of these pumps in its considerations. New highly energy effi-cient motors in Reis presses save the additional procurement costs very quickly. The break-even for a 15 kW electric motor is already reached with a service life of approx. 1000 hours - very short in industrial routine. A 22 kW motor reaches this effect after only 600 hours of operation!
The central control of Reis Robotics can optimize the provision of compressed air because same is a very energy intensive and thus an expensive medium. Each saving here has an immediate measurable effect on the operating costs.
According to experience from Reis Robotics, for some crucible furnace the temperature may be slightly reduced without impairing the safety or quality of the casting process. An example explains that more than 50 percent of energy can be saved in aluminum casting if the tem-perature is lowered by only 40°C. If the crucible is also furnished with a flap cover during the time when nothing is taken out, which is relatively cheap and can be easily retrofitted, even more cash can be saved again.
Minor lowering of the molten metal temperature and a covering for the crucible furnace can help saving a lot of energy.
Pierburg is convinced of the savings possibilities and of the production flexibility Reis Robot-ics enables with the new 'head-controlled" casting cell. Therefore the responsible persons intensively use the time until moving of the foundry for vast tests and setting work. After all, it is planned to multiply the flexible casting cell at the new site. Two to three further cells will be installed at the old site even before 2014. The foundry management at Pierburg sees an enormous advantage of the controls also in the fact that today troubleshooting can be made in the program even via remote access from Reis directly from their Frankfurt area headquarters - and thus without any travel charges. Thus, the systems for the new site will be not only considerably more economical, but will already be completely installed for an on-time start in the year 2014.
Author: Stephan H. Gursky