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Hydro-forming of gas torches  

Automatic  hydro-forming plant joins the fins on
torch cooling injectors and replaces time-consuming brazed joint.

 

A well-known German manufacturer of gas torches was looking for an automated and flexible design for the assembly of torch cooling injectors. In this case, the responsible parties were particularly concerned about the joints between the fins and the water supplying copper pipe. The labour-intensive and time-consuming brazing process used until then was to be replaced by a new, future-proof technology that could primarily provide the process reliability to ensure consistent quality of the joints, therefore also increasing the torch efficiency.

 

The process selection was quickly made in favour of hydro-forming technology. The object now was to find a manufacturer who could meet the requirements of the specification document, and who was also able to provide the necessary know-how and engineering capabilities for such a complex plant. Dunkes from Kircheim/Teck was able to meet these specifications. Hydraulic presses have been part of the product line of this Swabian machinery builder from the very beginning, and they were also among the first who expended considerable resources on hydro-forming technology. The flexibility characteristic for this mid-sized operation – with respect to production and also by addressing customer needs – convinced the torch manufacturer to retain the press builder for the planning and fabrication of a complete plant to manufacture heat exchangers with the assistance of hydro-forming technology. 

 

The plant produces gas torches for thermal output ratings of 10, 20 and 25 kW. The three sizes merely differ in their length and the number of cavities. The components for each torch, such as the torch plate, mixing cavity, distributor, fins, and side support brackets are prepared for assembly by manually positioning these into a fixture. The parts are collectively joined to the U-shaped copper pipe. The manually assembled components are then forwarded to the hydro-forming plant for further processing.

 

The centrepiece of the plant is a 4-column press with servo-controlled ram travel and a closing force of 630 kN. The press bed supports the lower portion of the forming tool. A two-shelled compression element is mounted on the left side, the diameter of which is automatically adjusted to the diameter of the respective copper pipe. The two hydraulic cylinders that seal the pipe are located on the same side in a coaxial orientation to the half-shells. A hydraulically actuated carriage, which carries the forming tool for the copper pipe that is also configured as a half-shell, is installed on the right side of the base plate The other half of the forming tool is mounted to the ram with a tool plate as a mirror image; the compression element with moulding jaws and two half-shells is on the left, the carriage with the forming tool for the upper side is on the right.

 

The tool palette with the torch component travels automatically to the press centre. As soon as this location – precisely defined by dead stop bolts and centering pins – has been reached, the lower right moulding jaw is brought into the position that matches the copper pipe. A compression plate then travels against the lower dead stop and ensures the exact location of the pipe in the moulding jaws. The ram stroke now closes the tool from above and continues to apply pressure. The two closing cylinders are deployed at the same time and sealed the two pipe ends, while applying a pressure of 1000 bar to the copper pipe. The not enclosed copper pipe in the torch expands, and presses against the bores in the fins. This forming process creates an application-appropriate, positive connection that ensures a precisely defined joint with the copper pipe on two locations for each fin.

 

In order to evacuate the compression medium, a water-oil mixture, from the pipe, the workpiece pallet travels into a swivel mechanism after the forming process. This rotates the workpiece pallet and the torch by approximately 90° and maintains this orientation until the next part exits the press. A blower supports and accelerates the discharge of the compression medium, which is collected in a stainless steel pan and returned to the press via a filtration facility.

 

The customer's expectation in connection with the plant installation have been met in full. The level of automation and flexibility were significantly increased. For one torch type, the cycle time was reduced from previously 60 seconds to 30 seconds. Eliminating 40 brazing locations not only resulted in a significant time saving, but also resulted in completely overhauled quality standards due to the process reliability and the reproducible accuracy of the forming operation at the joints. The Dunkes specialists were able to ideally tackle the initially feared problem of " adapting an automated process to the various torch shapes". Controlled dead stops in various configurations, horizontal pushers and various clearance pre-centering operations ensure that the various dimensions and tolerances do not inhibit the automated process.

Hydro-forming plant with additional axis, PC control and high-pressure unit
Hydro-forming connects the fins with the water supplying copper pipe on a gas torch. The connection between the sheetmetal support
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