The productivity of closed-die forging lines and ring-rolling plants strongly depends on the right handling equipment. This equipment ensures fast and efficient loading and unloading of workpieces to the forming machines. The different surrounding circumstances require customized solutions that perfectly match the situation.

The challenge is to fulfill contrary requirements such as long tongs for large presses and/or high maneuverability of a compact mobile machine. Dango & Dienenthal offers a great range of handling manipulators to serve various tasks. Due to new handling challenges, the range of special machines is continually extended.

Selecting a manipulator for the handling of heavy forgings should be done wisely. Answer a few questions that will help you choose the best solution to increase the productivity of your plant.

• Which and how much area must be covered by the handling device?
• Which equipment and positions must be reached by the handling machine?
• Are there other vehicles or cranes moving in this specific area?
• How much accuracy is required?
• What are the batch sizes of the production?
• How many unique parts have to be handled?
• What cycle times should be achieved, and what is the bottleneck that dictates the rhythm?
• What is the weight, size and shape of the workpieces?

Mobile Transport Manipulators

A mobile transport manipulator is a good choice if the area is big and the handling machine serves a lot of equipment, such as furnaces and presses. This machine can maneuver freely within the whole production area and is fast enough to cover long distances in short times. Most of these manipulators are driven by a diesel engine, which also allows traveling between several bays.

If the working area of the manipulator is only expected to be in one bay and serve only one production line, an energy supply by drag cable to feed an electrical hydraulic pump is an elegant way to forget about refueling the manipulator.

A forklift with attached tongs may be a cheap short-term solution, but will it improve your production sustainably? A big disadvantage is that the view to the workpiece is constantly blocked by the lifting mast in front of the operator. This makes it nearly impossible to handle the workpieces quickly and precisely. In addition, a forklift is not originally built to work in a forge shop, and it will not last very long.

However, mobile transport manipulators specially designed for the task deliver great performance and durability. The ±90-degree steering ability of the driven rear wheels allow them to turn around on the spot. The rigid lever system gives the tongs the degrees of freedom necessary for the handling of forgings in closed-die forges and ring-rolling plants, namely parallel lifting, vertical tilting and side-shifting.

The operator’s cabin is placed on the left side on the standard machines, which gives the operator a good view to the tip of the tongs, no matter in which position. But sometimes special circumstances require special solutions, such as shown in Figure 1, in which there actually are centered operator cabins.

Most of the time, the manipulator has to fit into given surroundings and not the other way around. The working area is often quite narrow especially in ring-rolling plants. But on the other hand, deep furnaces are used to provide sufficient heating capacity for the billets. In this case, we can provide lever systems with the additional ability to extend the tongs for loading and unloading of furnaces and ring-rolling machines and to retract the tongs for maneuvering in narrow areas (Figure 2).

Heavy-Load Robots (Stationary and Rail-Bound)

Sometimes we are asked to provide a range of heavy-load robots with payloads between 500 kg and 15,000 kg (1,100-33,000 pounds). To handle loads this size, we have designed robots to meet the large handling requirements of the metal-forming industry.

The sole consideration of handling a payload might suggest that these robots are comparable to standard industrial models. The enormous reach of up to 10.5 m (34.5 feet) from the rotational axis to the center of the gripper and the high load capacity in the entire work envelope, however, requires our heavy-load robots to have an application range beyond those of standard industrial robots. The high load moment is achieved through a special lever system and powerful drives. A complex control system and integrated encoders ensure a high level of positioning accuracy.

These machines pay off when the automatic handling of large batches is required. The handling sequence is always consistent and fast. Nevertheless, these automated manipulators can also be switched to manual control mode if small batches or single pieces must be handled. Although the system allows for the convenient reprogramming to a different sequence, the reprogramming for a one-off production cycle would be too time-consuming, and it might be easier to control the material handling system manually. 

The heavy-load robots with capacities larger than 1,500 kg are driven electro-hydraulically, because in this range the hydraulic cylinders and motors provide the best combination of force and speed. Below this capacity, the machines have an electro-mechanical drive system, which brings some remarkable advantages. These include no inflammable oil, less maintenance and higher efficiency.

A stationary heavy-load robot can cover a large cylindrical working envelope that allows for reaching several surrounding units located within this area. In contrast, if the production line extends across a linear area and the aggregates are located along a line, it is possible to use a rail-bound heavy-load robot and thereby increase the working envelope dramatically (Figure 3). Automatic and manual control are options in both instances.

Overhead Manipulators

A mobile transport manipulator can freely maneuver around your whole production facility but is not (yet) able to work fully automatically. The rail-bound heavy-load robot can be used fully automatically, but it is restricted to its rail track.

An overhead manipulator covers the gap between these two situations. It is crane-based and can reach each position within its cartesian coordinate system. Using an overhead manipulator keeps your shop floor clear and uncluttered with no energy supplies or floor-mounted rails (Figure 4). The lifting mast with the attached tongs, fixed on the bottom side of the crane trolley, is comparatively slim. It requires relatively less maneuvering space at ground level.

Tongs are the Manipulator/Workpiece Interface

Up to now we have only covered the basic style of forging manipulators. But what makes nearly each machine unique are the tongs, which are the interface between the workpiece and the transport machine. To describe all the possibilities would go beyond the scope of this article because the tongs are always adapted to the shape and dimensions of the workpieces (Figure 5).

What is common for most of the tongs in the closed-die and ring-rolling sectors is a rotation around the horizontal axis for reversing the workpiece. The tongs can also be equipped with an additional flipping axis in the jaws for erecting horizontally oriented billets.

Handling Rings

Sometimes the intense analysis of special handling tasks bears unique solutions. One example is a dedicated machine for the unloading of ring-rolling machines. Rings with diameters up to 4,000 mm (13 feet) can be handled very carefully and without unnecessary deformation. This is achieved by special gripping arms that fit into the cutouts of the support table of the ring-rolling machine (Figure 6). The rings are gripped from underneath and not clamped or squeezed by force. Gripping from inside and outside increases the range of workpieces dimensions that can be handled.

Which solution is the right one?

There is more than one solution for most applications. You must evaluate the possibilities together with an experienced project engineer. It is very important not to be misled by the cheapest solution with the least effort but rather to think in the long term. Keep things as simple as possible but as complex as necessary.