Fully-automatic gravity mold cleaning technique with robots for the automotive industry
Dipl.-Ing. Martin Rückert
Reis GmbH & Co. KG Maschinenfabrik Obernburg
Complete cleaning system consisting of beam space with robots, sand preparation and computer system
In recent years automated processes have arrived in application fields which were reserved for manual work so far. In foundries the mold coating applied before the casting process has to be removed regularly. For the worker this is a time-consuming job with heavy work-load and a lot of dirt. The time expenditure for cleaning a complete gravity-die for chassis components is approx. 30-50 minutes, depending on the complexity and size of the gravity mold.
For gravity mold cleaning different processes are used. The most common cleaning process is cleaning using the shot blast system. Among others, cleaning methods with chemical products, water or dry ice are used.
In the light alloy center of the Volkswagen plant Braunschweig both the dry ice blasting and the cleaning with shot blasting are used for gravity mold cleaning. The requirement for an automated system was to clean form geometries with both simple and difficult access. For this reason the decision was made in favor of the classical cleaning method with shot blasting. After comparison of different system concepts Reis Robotics was chosen as automation partner for implementation of the system. An intense cooperation with the operators of the light alloy center followed. After a planning and commissioning phase of only 6 months the system was handed over for production.
VW-light alloy center – innovative foundry for chassis parts
In Volkswagen AG Braunschweig works around 6.500 people are employed. 250 people hereof belong to the light alloy center which was opened in the year 2002. Here those chassis parts are produced which are assembled in the same plant as lightweight front and rear axes.
The product range comprises auxiliary frames, swivel bearings and knuckles from light metal. These components can be produced both in gravity die-casting and in CPC back pressure procedure.
It takes approx. 24 hours for a component to pass through the process from foundry via several quality controls up to completion. As the components are critical /safety components every process step and production parameter is monitored so that all components leave the factory in the same quality.
The daily melting capacity is 192 tons of aluminum which will be cast into the 40 existing gravity molds. They form the components and have to be cleaned carefully again and again.
Optimum cleaning using automated robot blast system
Before pouring the liquid aluminum into the gravity molds, same are provided with a mold coating, a separating agent on water basis. The mold coating has to be removed from the gravity mold again. This is done once a day in the automatic cleaning system from Reis. If the mold coating is not completely removed before new application casting defects may result.
Components of the automatic robot blast system
The blast system consists of a blast room where the cleaning process itself takes place, and a robot work envelope. Robot and blast room are separated by a highly flexible robot protection cover. This prevents damage or increased wear caused by blast agent to robot.
The operating components and the automatic blast medium conditioning are installed on an operator platform outside the cabin.
The gravity molds are supplied by means of a fork lift through an automatic lifting door at the system. The gravity molds are always provided with upper or lower mold on a rack. An upper and lower mold each are deposited on robot rotary table. The racks were designed as universal racks to allow cleaning of all existing gravity molds.
The cleaning process itself is effected through a high-capacity pressure blast nozzle, positioning of the nozzle via the movement of the robot. This procedure is supported by positioning movements of the robot rotary table. After the cleaning process the component is blast through an integrated air nozzle to prevent blast agent being carried off through the gravity mold to outside.
Rice ProVis user interface on Windows, the customizable user interface can be selected the different operations
New software tools for the man-machine interface
Programming of industrial robots today is mainly done with the portable teach pendant directly at the robot by teach-in procedure. In order to make programming more intuitive, the robot manufacturer Reis has integrated a graphical user interface into the robot control ROBOTstarV, which is based on Augmented Reality Technology.
Augmented Reality means "extended reality" and represents a new way of man/machine interaction. Information from the robot control, i.e. positions, paths, program data, will be faded into a real camera picture depending on the context and at the same time represented on the PC monitor.
The functionality of Augmented Reality is integrated into the operating surface based on graphics, ProVis-AR (Programming and Visualization in Augmented Reality) and may be used directly with a PC connected to the control. Since operation functions on freeware internet technologies, an installation of special software to the PC is not required. After calling the homepage for the robot the user interface will be loaded from the control to the PC and will be available there.
Use of the new software tools
This new software functionality is successfully used in the delivered blast system. The robot control has direct access to a high resolution camera installed in the system. The operator sees a picture on his monitor and can judge the intensity of the gravity mold cleaning process.
With a PC-mouse the worker selects the areas to be cleaned. The robot control selects the stored blast program then and fades in the stored path positions on the monitor.
After selection the selected area is sand-blasted. After the blast process has been finished a new image of the blasted gravity mold will be generated and displayed. At the same time the most important operating elements are indicated on the screen for the system is now waiting for decisions:
- Gravity mold in order
- Reblasting required with identical parameters
- Reblasting required with modification of the blast intensity of position shift
A great advantage of this application is the gain in time and the gentle treatment of the gravity mold. Unsoiled areas won't be blasted, needless material wear is avoided.
Further advantages of a user interface in Augmented-Reality technology are the simple and intuitive handling and identification of complex three-dimensional formations (robot and complicated workpieces). The intuitive handling with program data, positions and parameters gives certainty to the user and thus allows a simple and safe way to work with the robot. All information necessary for the user's work will be presented to him without having to pore over program lists and manuals. The user may choose just one or both the textual representation or the visual program representation of his user program at the same time. Both representations complement one another.
In the light alloy center of VW Braunschweig efforts are made to only use state-of-the-art technology regarding efficiency, technical demand and ergonomics.
Due to the intense partnership cooperation between Reis and the operators of the light alloy center a system with following features was designed:
- Flexibility: The complete gravity mold variety of the plant can be processed and have the flexibility to be used for future parts families
- Fully-automatic sequence of the cleaning work. The worker only takes over loading and unloading, as well as control work.
- Humanization of workplace: The strenuous cleaning process with noise and dirt emissions was replaced by an automatic encapsulated one
- Much less wear of molds compared to manual blasting. Due to the steady and automatic cleaning with fine dosage the gravity molds are treated more carefully than with a manual cleaning process.
“With this system Reis has implemented all demands that are compatible with our high standards to work safety and health protection as well as operating ergonomics”, confirms the manager of the VW light alloy center in Braunschweig.
The cleaning system developed by Reis can, depending on the customer’s request, also be equipped with alternative cleaning methods such as dry ice cleaning.