Servo-motorised electric powder compacting presses equipped with electrical drives for pressing forces up to 150 kN have gained significantly in use in the PM industry since their first introduction by Dorst Technologies of Kochel-am-See, Germany, at Ceramitec 2009 in Munich. Their success lies in their ability to achieve the highest dimensional precision at the maximum stroke rate of the press when producing relatively small parts such as hard metal cutting tool inserts and structural PM parts. Additional advantages are their green qualities such as minimum energy consumption, low noise (typically less than 65 dB), and the absence of environmentally critical fluids such as hydraulic oil.
Dorst has, however, seen demand for even greater precision in the height tolerances of small green compacts to lower than ±0.05 mm, and this has led to the development of a new powder press which was on working display at the World PM2016 Exhibition in Hamburg, Germay (Fig.1). Lutz Lackner of Dorst stated in a presentation that the new presses are available with a pressing force of 60 kN and 120 kN and are designated EP6/12 – Flashspeed. They are said to offer four closed-loop controlled movements for upper punch, die, core rod and powder filler with each of these capable of positioning the axes within ±0.001 mm (1 µm).
Lackner reported that this level of accuracy results from the optimum stiffness and rigidity of the closed frame which comprises four columns carrying the linear guiding for the upper punch and the die. This axial rigidity minimises the unavoidable elongation of the press during powder compacting leading to better accuracy, said Lackner. The highly dynamic electric servomotors allow stroke rates of more than 200 spm with each stroke able to maintain the positioning accuracy of the axes to the level described above. The compact design of the new press requires a footprint of only 2 m2 , stated Lackner, with a height of only 2.2 m and an operating height of 1.35 m.
One of the features of the new electrical EP6/12 presses is that the filling hopper is arranged above the press centre. This is said to ensure a steep angle of the powder hose and therefore gives a reliable flow of powder into the tool cavity. It also allows mounting two lateral filling hoses, one on each side of the filling shoe, ensuring optimum powder flow into the tool cavity, even at half the filling time. By further minimising the height of the filling shoe, it is possible to reduce travel of the upper punch, thereby giving an additional boost to the production rate.
The EP12 press on working display in Hamburg also featured the new Dorst Speedfill system which is said to further boost production rate in powder compacting (Fig. 2). Lackner stated that in a normal die filling cycle the filling shoe usually moves forward and backward over the die cavity. The retraction of the filler is not needed for the purpose of the die filling, but is necessary to provide the space for the upper punch movement. In order to save time within the compaction cycle, Dorst successfully managed to reduce the filler travel significantly, by only moving in one direction for die filling and then compacting the powder. Thus the compaction cycle is now as follows: filler forward – upper punch down / compaction – filler backward – upper punch down / compaction – and so on. Lackner said that this oscillating movement reduces filling cycle time by almost half, and thus increases the stroke rate. The EP12 press on display was programmed and monitored using the Dorst Visualisation System/DORST Control System (DVS/DCS®) which has proven successful for many years on closed-loop controlled presses.
From results of production tests on the new EP6/12 presses Lackner reported that cemented carbide pins normally produced in multi-cavity tools on a mechanical powder press at 26 spm achieved a rate of 85,000 pieces/hour. The production rate on an EP12–Flashspeed press was significantly higher at 45 spm achieving an output rate of 149,000 pieces/hour. In another example small structural PM parts weighing just 2.212 g each and which needed to be produced to height tolerance of ±0.03 mm using double cavity tooling, could be compacted in an EP12-Flashspeed press at a production rate of 85 spm thus manufacturing around 10,000 pieces/hour. The new Speedfill system with two hoses arranged on opposite sides of the filling shoe contributed greatly to the constant and uniform powder fill of the double cavity tool.