Integration creates productivity advantages A major increase in the production volume in the same production time and a high level of quality - this is the result of the complete automation of the construction chemicals sector and the Kreis dissolver plant at the Hilti Industriegesellschaft für Befestigungstechnik mbH. In this way, compound dowels and fire protection compounds can be manufactured much more efficiently.

Hilti AG is well-known in the building industry. The range of products covers, amongst others, products for laser measuring technology, direct fitting and drilling and dowel technologies. In addition, there are the drilling and demolition machine sectors, installation technology, electrical mounting systems, construction chemicals and wood processing devices. However, as a leading company for construction and demolition technology, Hilti is also affected by the current economic situation and the competitive pressure in the building industry. Therefore, manufacturing processes must run as smoothly and efficiently as possible. Improvements in productivity are more important than ever, in order to be able to defend its leading position in the market.

The factory in Kaufering, Germany, with 500 employees, manufactures fire protection compounds and compounds for compound dowels. In 1999, plans for expansion, and with this, the procurement of a dissolver plant - a metering and mixing unit for the manufacture of various products and subproducts for compound dowels and fire protection compounds - resulted in more complex manufacturing processes at Hilti: additional components were added to the dissolver, new storage and metering silos and tanks were connected.
Until then, the control of the production plant, for example, the weighing, mixing and metering of the solid and liquid components had been implemented using small, individual solutions. The data, for example, the proportions of ingredients, manufacturing temperature or vacuum content, could not be automatically logged and archived during the production. Therefore, the isolated solutions in the mixing plant had to be integrated in the total production process via a process control system. Additionally, the new area of fire protection compounds - in which two different products are manufactured - was also integrated in the control system.
ProLeiT AG, Herzogenaurach, Germany, was entrusted with the implementation of the process control system for both areas. The software specialists were confronted with ambitious project goals: Within the framework of the replacement of the out-of-date control and communication system, Hilti wanted an integrated data and batch tracing, a fully automatic, recipe-controlled metering with remetering pulses, and a visualization of the process data, with the option of manual operation of each individual actuator. Intervention in partly and fully automatic processes should also be possible, as well as the checking and the adjustment of plant and metering parameters.

Individual recipe modifications possible

For the automation of the processes, the SIMATIC S7-400 controller has been implemented for both areas. In terms of PC facilities, the system is equipped with a data server for the storage, logging and archiving of process data and with two operator stations for the monitoring, visualization and operation of the plants. The ProLeiT Plant Batch iT system which is used, is adapted to the specific requirements of the batch-controlled processes. A configuration tool is used for the parameterization of the technological plant structure. Special parameters for the dissolver plant and individual basic functions can be specified here. In this way, a plant model is created which mirrors the technical conditions and is the basis for creating and carrying out manufacturing guidelines and control recipes. The server carries out the central communication and coordination functions on the plant level as a system service. An additional advantage is that control recipes can be generated batch-related and transferred to the controller which executed them.
For Hilti, an important part of the control was the capability for order and batch logs. Previously the weighed products were logged manually, the batch numbers from the production and order control system added. The Batch iT system now guarantees an automatic logging of all order and batch data so that an optimized back-tracing of the batch data with measured value recording is possible. In addition, the continual logging of batch numbers for raw materials and products allows uniform batch tracing from the supplier of the raw material through to the final product.
A further requirement was the capability to individually change the recipes, also during the production process. In this way, experience and knowledge which has been gained can be integrated and this results in more exact manufacturing guidelines. It is also important to be able to compensate for differences in the raw material batches of an item beforehand. The plant operator is shown an overview of all the batches currently running in the plant in a matrix. In the detail view of a batch, the operator can stop or abort running or pending processes, and change their setpoints and control parameters, at any time. To be able to compensate for different raw material batches of an item, master recipes with proportional tolerance limits for the individual components are created. However, the important proportion of the ingredients remains the dominant factor. It is retained constantly; the plant operator can only slightly vary the ingredient proportions of a product within specified limits. The structure of the overall recipe is not affected as the system detects and suppresses this by checking the user rights. This guarantees the basic composition of a product as well as the involvement of the plant operator for the raw material batch compensation and achieves a continuously uniform product quality.
The entire plant is visualized on the PC. This ensures an optimized production monitoring and fault analysis. The process pictures display, for example, the various states of the actuators, speed values, production temperatures, pressure, scale weights and filling levels as well as pending warnings and messages. For manual weighing, the plant operator has an integrated display of the on-site scales terminal which shows the components with setpoints and an exceeding of the permissible tolerance window. All automatic meterings are optimized via settable metering parameters (rough flow and fine flow control, remetering pulse duration, scale settling time) and therefore aligned to the setpoint.
Scale terminals of type IT9000 are used for the connection of the weighing cells. These distributed PROFIBUS nodes are linked to the Simatic S7-400 via PROFIBUS DP. The automatic metering with simultaneous mixing on the scales, is automatically coordinated, monitored and controlled by ProLeiT BatchiT. This synchronous execution of the two processes achieves a major time saving during production.

Message to the quality assurance

To constantly guarantee high product quality, Hilti uses an internal CAQ system. The production values and quality data of the manufacturing processes are sent as a text file from the new control system to the CAQ system. After every batch produced, there is a feedback of the actual values to the quality assurance system. This is performed in a very detailed way by recording the minimum and maximum values of each component, all setpoints and actual values and the batch numbers. This makes the fault analysis much easier. To further increase the plant availability, faults, for example, on the peripheral devices, network connections or within program sequences are signaled immediately and can therefore be corrected quickly. Error and fault messages can be detected very quickly at the operator station via the visualization of the complete plant. Also the capability of manual operation of each individual actuator and intervention in all processes has an immediate effect on the productivity. Today, the dissolver plant produces three times the amount of compound dowel components compared to the previous plant, in the same time. This has partially been achieved by the parallel weighing and mixing process, a basic function in the Batch iT system. In the future, all storage tanks, a second dissolver, all internal and external silos and an additional manufacturing area for compound dowels, will be integrated. With the integration of the ProLeiT Materials Management, a program for the management, coordination and checking of item and product inventories in their respective warehouse, time-intensive stock adjustments and inventories will also be able to be carried out more effectively in the future. The new projects in the Hilti production are already defined: In the future, five SIMATIC S7-400 with a total of 6 PCs will be in use.