AUTOMATION IN CASTING FINISHING

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.

Finishing cells for large series

With this kind of plant the design of the overall configuration is tailored to one type of product, the most important feature being the functionality of the cell with its different operations, taking the cycle time into account. The means used are designed with little flexibility, even though there is no exclusive concentration on one single product type.

This type of plant also allows for a variety of different combinations. There may, for instance, be the following architectures:

• inspection line with component identification and palletising,
• coarse deburring, de-coring, sawing and fine deburring,
• pre-sawing and de-coring,
• trimming and component inspection,
• trimming and shot-blasting as well as
• component identification, trimming and additional finishing by sawing or milling.

The list of possibilities is a very long one and generally tailored to the customer’s process requirements.

Figure 5: Flexible machining cell for aluminium intake manifolds, their main configuration consisting of:
1 “Arcade” trim press with twin shuttle (1),
2 industrial robots (2),
2 sawing and milling stations (3),
4 air/air leak test stations (4),
3 discharge belts of the test stations from the cell and a turntable for visual inspection of the finished parts (5), and
1 discharge belt for returns (6).

Combination of trimming and shot-blasting
This plant shows how the products of the individual companies within the group can be integrated into the end customer’s systems easily and without any additional expenditure. The co-operation of the different product groups provides the advantage that the necessary tests can be carried out in the final configuration and after one-time assembly. Any possibly interfaces, fine tuning and process determinations are integrated into the plant.

Trimming cell for die-cast aluminium engine blocks with integrated shot-blasting machine and removal of abrasives

The plant consists of

• a twin chain conveyor system for engine block feeding (1)
• a linear manipulator (2)
• an industrial robot (3)
• two shuttle trim presses with swing frame (4)
• an shot-blasting machine (here an SPH 3 spinner hanger shot-blasting machine with three chambers) (5)
• an engine-block turning station for the removal of the abrasives, and discharge roller track (6).

Figure 6 shows a view on the trim presses and the linear manipulator. The feeding conveyor is located between the two trim presses, shortening the travel of the linear manipulator within the working range of the robot. Due to the auxiliary cranes and the shuttle the trim tools can be changed within a few minutes and production can be continued. The combination of rapid fasteners for the hydraulic and electric fittings also greatly facilitates a change of tools.

Figure 7 again shows the configuration of the auxiliary cranes. The industrial robot – in this example a foundry robot, type ABB 6600 – feeds a DISA SPH 3 shot-blaster where surface treatment takes place following trimming. After unloading of the shot-blasting the industrial robot places the engine blocks onto the turning station to remove the remaining abrasives.

Twin chain conveyor. From the superposed cooling line the engine blocks are conveyed to the twin chain conveyor together with their gating system. Both possible types of casting are transported at the same time. At the conveyor outlet the blocks are separated and realigned. A recognition system chooses the trim press to be selected for the individual type of component.

Linear manipulator. The linear manipulator is used to allocate the engine blocks to their respective trim press. Electrically driven by servo motors these manipulators have a high speed and accuracy of position necessary to place the components onto the pick-ups of the trim dies. The use of the manipulator releases the industrial robot, which enables the latter to remove the abrasives. Component pick-up by the manipulator is guaranteed by pneumatic grippers. The assembly and connections facilitate a change of parts for a changeover to another series. The gripper itself is designed to a large extent in such a way that it can already handle a large number of different types of parts.

Industrial robot. The industrial robot used is equipped with the same gripper system as the linear manipulator. The robot unloads the trim presses and loads/unloads the shot-blasting machine. The master control station allocates the different runs of the robot. Thus it is the master control that defines the priorities and sends them to the robot. This technology makes the robot interface definite, and it only communicates with one single control. This relief from a multitude of tasks enables the robot to empty the engine blocks from abrasives prior to re-loading.

Figure 6: Inlet conveyor, robot

Figure 7: Shot-blasting machine (DISA, Type SPH3)

Shuttle trim press. The shuttle trim presses used (Figure 8) are equipped with a C-frame. The shape of these machines in connection with the hydraulically driven shuttle has the advantage that the trim dies can be loaded and unloaded from above, without any access problems. The 300 kN presses used here are equipped with a swing-frame system that carries out a 180-degree movement after unloading, removing the burrs that might still remain on the tool dies.

In combination with the swing frame that is air cleaned while tilted, the shuttles provide a degree of cleanliness that guarantees the uptime of the equipment. This technology rules out the possibility that remaining burrs can easily be pressed into the component pick-up, as it happens in many other cases. Moreover, the shuttle greatly facilitates and speeds up the replacement of the trim die. The combination of automatic rapid fasteners for the hydraulic and electric systems makes tool change a matter of just a few minutes.

The tool fastenings can be disconnected without any additional devices; the shuttle moves the entire tool from the cylinder area, where it is removed by crane. Normal replacement time is approximately ten minutes. The tools are designed for one coarse and fine deburring operation in one single cut. Thus the gating systems are removed directly; the further course of the operation includes fine trimming. The maintenance platform and the hydraulic unit that is attached to the machine provide ready access to the main elements of the plant.

Shot-blasting machines. A variety of shot-blasting machines are used depending on the production task and on the material to be machined. Charging modules or robots are used to automate the peripheral functions and increase performance. Multiple-chamber shot-blasting plants facilitate shot-blasting during loading. Thus, the effective shot-blasting time can be prolonged as and when required to achieve a better surface finish. In connection with programmable sequences (turning, swinging, holding), critical areas can be subjected specifically to the blast of abrasives. Fully automatic machines are equipped with component recognition systems through which the blasting parameters are controlled (blasting time, sequence of movements of the components within the blast stream, number of blasting wheels, discharging time). After shot-blasting the residual abrasives are evacuated from the components.

Low personnel expenses and the high output of finished parts make these plants a finishing concept that considerably reduces the costs for casting finishing per component and furthers production at the classic foundry bases. The concepts described here do not yet include grinding machines or the combined plants for decoring, coarse trimming, fine trimming and saws of the DISA Group that will be the subject of another article.