Thomas Gerst, Caudan, France
First published in Giesserei No 6, 2005 and Casting Plant and Technology No 2, 2005
In today’s foundries the modernization of casting finishing is of paramount concern due to the high degree of labour intensity and cost involved for manual fettling. For many years the DISA group has been working on the development of solutions in casting finishing. DISA SERF in Caudan/France, the competence centre for casting finishing, has considerable experience and has implemented a vast number of solutions for iron and aluminium foundries.
Casting finishing includes
- shot-blasting,
- grinding,
- trimming,
- milling, drilling and
- quality testing.
Developing a concept
The following factors must be taken into consideration when developing automated, compact systems for casting finishing:
Fettling time. Without automation a high headcount is necessary to meet the specifications with reduced cycle times, which increases the costs.
Material flow. The material flow in the foundry has to be adjusted to the requirements of the different production variants (e.g. iron or aluminium, large series or small series), which can result in bottlenecks during the various stages of casting finishing.
Finishing quality. The quality of finishing that may be expected nowadays requires a very high repeating accuracy, which can cause quality control problems when accuracy varies, e.g. in the case of manual fettling. Subsequent process steps, such as cutting/machining, may be greatly disturbed, which increases the costs for tooling and equipment.
Recovery of returns. To lead back a high amount of returns to the melting process, a next-to-noncutting removal is vital. In mechanical machining the amount of swarf produced can often be reduced more easily than in manual fettling.
Flexibility. Today’s fast changes in production planning and the short production times require quick changeover among the different products.
Modularity / Use of manufacturing surface. The modularity of the systems is important to allow for immediate adjustment to the modified process steps. Here, cell solutions can be very helpful. They have the advantage of providing a definite interface with the adjoining operations and a clear definition of the process within the cell. With these models the use of the manufacturing surfaces can also be improved considerably.
Degree of human labour. Labour input is to be kept as low as possible to reduce the costs and improve the working conditions. The staff’s self-esteem is raised as the workers are employed as plant operators and not as fettlers.
Figure 1: Robotic cell
Automation depth means the degree of interlinking and execution of the individual process steps in fully automatic operation. All machining steps are combined in groups and linked directly by various transport and handling methods. As the case arises, automation depth or interlinking of the process steps is defined by the special needs of the foundry and its structural environment. When the methods and techniques are chosen, both product diversity and the remaining manual steps must be integrated accurately. The necessary criteria include:
- size of serial production,
- complexity of the operations on the component,
- degree of utilisation of the individual elements of the production line,
- complexity of the functions and, consequently, risks caused by lack in operator competence,
- structural possibilities within the foundry,
- investment limits,
- integration of existing plant elements, and
- component identification.
When defining the needs these issues have to be taken into careful consideration; there must be particular focus on a technically and economically manageable interlinking of the production sequences. This is particularly the case with system parts that can be used for a diversified production, such as decoring machines, test equipment and trim presses.
Solution models for the layout of the various process needs
Individual cells
A cell solution in the form of individual cells means a high degree of specialisation as far as the execution of the working steps is concerned, but requires additional effort with regard to internal transport and the temporary storage of components. Production control and component tracking are impeded and called into question by transport movements.
When identification methods are used, transport increases the number of inspection points, which makes both hardware and software solutions more expensive.
However, the use of these cells allows for a rapid change of process steps within a constant environment. Standardisation concepts can easily be taken into consideration and facilitate the new design of a production line. Manufacturing steps can be added and also removed from the process, while the modification time is short and standardisation guarantees the re-usability of the removed cell. With this method complete solutions with a high degree of re-usability can be found. As output rises, the number of cells can be increased without having to change the design of the total plant. When a product is modified or the number of parts produced is reduced, a cell can be removed from the configuration and installed in a different area.
Figure 2: Robot with tools
The design of the cells with their integrated control and complete sound protection makes them manufacturing points that are easy to position. Simple transport, made possible by the favourable format, allows for a fast start-up. The outside dimensions are about 5100mm × 2480 mm × 3200 mm (including the operator platform) and thus meet the limiting values for truck transport. The booth design greatly facilitates transport including the integrated robot. The setup of the outer periphery only takes little time, so that the robot functions can be triggered off and checked within a short period of time. Production can then be started with programmes that have already been prepared in advance. The overall design of the cells provides the possibility of interlinking or operation as stand-alone units (Figure 1). Manual feeding is also possible, which creates a high degree of flexibility.
With this kind of cells the use of robots has proved to be a success. The robots may either be equipped with the tool or guide the tool. The choice of method depends on the working steps to be carried out and the shape of the components. The present example (Figure 2) shows a guided tool (circular saw). The machined component is accessible for the tool and can thus be clamped directly to the workpiece support. The robot carries out the working steps on the clamped component. The use of different types of tooling within one and the same size of cell makes a flexible production planning possible.
Feeding the cell
Loading and unloading of the cell takes place with the help of a turntable system (Figure 3). This system helps to overlap machining time by handling time, while the entire cycle time is cut down. The costs for component-specific tooling are low, because multiple workpiece carrier technology is dispensed with. For operation ease and convenience, the easy loading and unloading of the turntable by manual feeding means simple and fast access for automatic loading. The turntable is secured in position. Operator safety is guaranteed by variable safety equipment (safety fences and safety light curtain).
Figure 3: Turntable, loading and unloading station
Transport of returns
The volume of returns as a result of the machining steps is transported automatically from the cell (Figure 4), while swarf and directly re-useable returns are separated. The conveyor can either be installed to the right or to the left of the front face of the cell. In the case of interlinked cells the conveyor can be adjusted to the number of cells in order to concentrate the collecting points of the material. After the returns have been transported away from the operating area of the cell the material is separated. Separation is guaranteed by grids at the outlet, with the material being fed directly into containers.
The cells enable a wide variety of different working steps, while the cycle times achieved greatly depend on the components. The cutting time for axle suspensions, for instance, that require ten different cuts with a circular saw, is just 34 s. The movements of the turntable with a diameter of 2400 mm have a cycle of 2 s. The turntable is driven by a servo-motor control. A high degree of positioning flexibility and turning speed is achieved at the same time. The machining accuracy is within the standard values met by industrial robots.
Flexible complete cells
These cells are systems for the integration of several working steps with products of the same type. Pressure-die casting cells, in particular, often have an identical basic structure and enable the flexible production of almost all products within one and the same size class. With these systems flexibility can be achieved by means of handling with the help of robots or manipulators. Besides the staff issue, the pooling of several working steps generally has the following benefits:
- better use of existing possibilities,
- the configuration of the cell is cycle-time oriented,
- faster changeover to similar types of products,variable use of working steps,
- integration of test functions into finishing and easy component tracking,
- reduced manufacturing space, and
- less intermediate transport by direct machining in the manufacturing cells.
Figure 4: Returns conveyor
The choice of the working steps to be integrated is made depending on the customer’s internal requirements and is determined by the types of product.
Design possibilities
In these plants industrial robots and all kinds of manipulators are used as handling equipment. The choice depends on the kind of steps to be carried out and on the cycle time to be reached. The configuration must be geared to the various operation sequences, e.g. in the case of the flexible machining cell for intake manifolds made of aluminium (Figure 5).
Configuration principle of the machining cell
Arcade trim press. The trim press is loaded manually with de-cored castings. The press is ergonomically accessible for the operator due to the shuttle that brings the component pick-up within his reach away from the trimming position. During the loading process carried out by the operator the castings trimmed in the previous cycle are put down onto the second position of the shuttle. As soon as these two operations are finished, the shuttle is driven to the rear position, where the components are trimmed and also discharged by the robots.
Industrial robot. Each of the two robots picks up a casting and carries out the required sawing and milling operations. The configuration of the fences also facilitates the operation with one robot following an emergency strategy while maintenance work is carried out on the second robot.
Sawing and milling stations. The sawing and milling stations are integrated into a sound booth that also offers protection from flying swarf. Application and equipment of the tooling (saw blade and cutter) are chosen depending on the production and the components to be machined. The rotational speeds are controlled by frequency converters, the feed is determined by the robot movements. Each casting is subjected to its individual machining programme.
Air/air leak test stations. When the robot has finished all processing, the castings are placed into the air/air inspection unit. The test is carried out on two supports for each robot for a prolonged inspection time and higher accuracy of results. The robot can place the inspected components down at any time. As soon as a cycle is finished, the inspection head is driven to the second position, and the inspected component is unloaded.
Removal of the finished parts. Unloading takes place with the help of a component tracking system. The unloading conveyor is equipped for forward and backward movement. The inspection result determines the transport direction. Sound parts are led to a collecting belt and turntable for visual inspection; there they are packed by an operator. The defective parts are loaded directly into containers after the leak test.
Transport of returns. The returns are transported on a central belt conveyor that includes the two sawing / milling stations and the trim press. At the outlet swarf and returns are separated again, while transport is carried out in containers.
Product change. Every time a product change takes place only the trim dies, the robot grippers and the leak-test pickups have to be changed. These changes take place within a very short period of time, facilitated by the shuttle at the trim press and supported by an auxiliary crane or factory hall crane. The robot grippers and component pickups can also be replaced easily, which guarantees that production can be taken up again after a brief interruption. The cycle time of the plant is between 25 and 30 s, depending on the component.