02 April 2007
Casting Plant & Technology 1/2007
By launching the DISA MAC shot blast machine, the DISA Group has expanded its range of shotblast systems especially designed and engineered for the surface treatment of light alloy castings. This article serves to highlight the variety of applications of the new machine concept and describes some of the other systems developed by the DISA Group for the blast cleaning of cast metal components.
Figure 1: DISA MAC shotblast machine working in combination with a robot
Responding to the pressing need for better fuel economy, greater safety and more recycling possibilities, the automotive industry is steadily increasing its share of light metal components. The average European car now contains more than 100 kg, with a steep rise to be seen at the luxury end of the market. Light alloy castings are mainly used for components, such as cylinder heads and blocks, gear boxes, and wheels. As automobile designers increasingly favour aluminium or magnesium alloys, the use of these metals throughout the automotive industry is expected to double within the next ten years.
Regardless of their type and shape, cast components for the automotive industry require meticulous cleaning of surfaces and internal passages before undergoing final machining. It is at this stage that the advantages of shotblasting are obvious.
It is not surprising that a number of shotblast equipment manufacturers have developed and launched machines of an entirely new concept to meet the requirements of the foundry industry with regard to aluminium and magnesium castings. The DISA Group has been a forerunner in catering for the needs of foundries specialised in the production of complex aluminium and magnesium components. As a supplier of foundry machinery and surface finishing equipment in general, the DISA Group, time and again, has set the pace by developing, manufacturing and successfully installing comprehensive foundry systems and surface treatment equipment.
Today, the DISA Group’s vast experience in the foundry field manifests itself in the strength of its Shotblast Division with centres of competence and a network of manufacturing and sales facilities on three continents. All are dedicated to developing new engineering and process control concepts and new machinery. They also make test runs, commissioned by customers. In Europe, the machines are manufactured and assembled in the state-of-the-art production facilities at Pribram, in the Czech Republic.
Shotblasting and deburring of light metal components
The DISA Group manufactures a comprehensive range of shotblast machines particularly suited for the surface treatment of aluminium components. Among these are the recently launched DISA MAC manipulator-type shotblast machines and further industry-proven systems: Spinner-hanger shotblast machines, overhead monorail shotblast systems, wire-mesh shotblast machines, manipulator-type shotblast machines for the treatment of complex components produced in large series have all met with wide approval. All machine variants are known for their efficiency in producing the desired desanding, deburring and finishing results, and are recognised for their high capacity and throughput speeds.
Figure 2: DISA MAC can be operated in single or tandem mode
DISA MAC shotblast systems have been specifically designed for the surface treatment of high-tech aluminium and magnesium alloy castings. Depending on the particular layout of the shotblast system used and the complexity and cleaning requirements of the components to be processed, up to 200 casting with a maximum pieceweight of 15 kg can be cleaned. DISA MAC shotblast systems operate in conjunction with a multi-axle industrial robot equipped with a double gripper that serves to receive and deliver the castings and to remove the shot. Depending on the desired output and configuration, robot and shotblast machine will operate in single or tandem mode. Hence, one robot works for one or two shotblast systems with individual, synchronised operations. In other words, while shotblasting takes place in one cabin, other operations, such as shot removal, component pickup or component delivery will run in parallel.
Figure 3: One robot in use for one or two shotblast systems with individual, synchronised operations (click to enlarge)
Overlapping operations
The heart of the DISA MAC system is the shotblast cabin designed to accommodate two or three blast wheels and a C-shaped manipulator-type holding device that serves to receive the components. The C-shaped manipulator- type holding device is equipped with one movable and one stationary clamping arm and self-adjusting springs. This ensures that the workpieces are firmly held in place even during a power failure. Once in the grip of the manipulator, the workpieces simultaneously rotate around two axes in front of the blast wheels. The movements and speeds – slow and fast rotating, swinging, stop and start – can be programmed individually by servomotors to obtain a maximum repetitive movement accuracy for optimal finishing results. The uninterrupted motion of the workpieces ensures continuous shot removal from recesses and internal passages thus preventing shot build-up that might weaken the impact of the blasting stream. The blasting stream and the different movements of the work-pieces are individually programmable.
Sequence of operations
The industrial robot is fitted with a swivel head and a double gripping device for two workpieces. As the cycle begins, a workpiece is seized, and the robot moves into the shotblast machine. The empty gripper serves to pick up the cleaned workpiece from the holding fixture of the manipulator in the shotblast machine, thus allowing the vacant manipulator to be loaded with the uncleaned workpiece. The doors on the loading side of the shoblast machine close as soon as the robot arm has retracted, and the finishing cycle begins. In the manipulator the component rotates around its longitudinal and transverse axes in front of the blast wheels for thorough cleaning of all surfaces and internal passages. Critical surfaces are exposed to the blast stream for targeted and more intensive cleaning. The exact and repeatable movements are controlled by servomotors and encoders.
This selective exposure of the workpieces to the blasting stream ensures optimal surface impingement and full utilization of the blasting energy. The uninterrupted movement of the manipulator causes the shot to be continuously removed from the internal passages of the workpieces. Complete shot evacuation can be effected inside or outside the machine. For this purpose, the gripper attachment of the robot is equipped with a vibration device. Replacement of the gripper tools of the robot is simple and timesaving. The new machine concept with dual functions – robot equipped with gripper for loading/unloading and manipulator made of high wear-resistant material – shields the gripper attachment and the robot head from the impact of the blast stream, thereby preventing wear and dynamic load.
Figure 4: Targeted blasting of critical surfaces, cavities and internal areas
DISA MAC shotblast systems are tailored to the specific requirements for the surface treatment of aluminium and magnesium castings, bearing in mind the latent risk of spark ignition and fire hazards due to metallic dust build-up. To keep the dust evacuation distances to an absolute minimum, the separation system is situated underneath the shotblast cabin to prevent metallic dust from building up. In combination with a wet filter, the shotblast systems are configured to be explosion-proof in compliance with prevailing European and international protection and safety guidelines.
The DISA Group’s range of shotblast systems also includes wire-mesh shotblast machines designed for deformation- free cleaning of flat or thin-walled components, and overhead monorail shotblast machines, notably the socalled spinner-hanger machine for the treatment of smaller-sized light metal castings. All of these systems are available in different sizes and have been widely accepted by the foundry industry. In conjunction with a robot, these machines can easily be integrated into continuous production lines. Spinner Hanger Machines include two or three compartments, each fitted with a rotary hook. The systems can be complemented with an auxiliary airblast station for the final cleaning of internal areas and for surfaces with difficult accessibility to the blast stream.
Manipulator-type shotblast systems
The range of manipulator-type shotblast systems is designed for the surface treatment of large and heavy iron or aluminium metal castings, such as cylinder blocks, cylinder heads, transmission boxes, crankshafts etc., up to 700 kg manipulator load, and manufactured in large series for the automotive industry. These machines are available in three basic versions of modular design to accommodate different output and space requirements. The machines are equipped with one to eight manipulators. They can be combined with air-blast stations and are often integrated in automatic fettling and trimming lines.
In all these systems the manipulators, which are fitted with movable gripper tongs or rotating support shafts, hold the components and move them through the blasting zone. The gripper tools automatically adjust to the shape of the castings and are capable of handling simultaneously individual components or several components of different heights. A loading device or an industrial robot serves to deliver the castings to the manipulator where they are clamped and firmly held in position as they are rotated while passing through the shotblast zones, one by one.
The manipulators are laid out to perform uni-axial movements. They also permit targeted and component-specific cleaning.
All manipulator-type shotblast systems feature a high degree of flexibility and are used in over a hundred different applications, primarily in the automotive industry.
Figure 5: Manipulator shotblast machine