Komage success story:
Komage strikes out in new directions with cross presses
As part geometries become increasingly complex, the demands on powder presses and press tools are increasing which means constant development among press manufacturers. So now hydraulic or even mechanical-hydraulic presses with up to 8 or more pressing axes in a uniaxial pressing direction are standard for the manufacture of complex molded part geometries. It is also easy to produce holes and cut-outs in the pressing direction using core rods and punch shapes.
In uniaxial pressing, compaction of the molding compound takes place only in the vertical direction by means of the punch movements (in the ejection principle) or by means of the top punch movement and a relative movement between the die and the bottom punch (withdrawal principle). In the process, decreases in density (press-neutral zone) occur towards the center of the pressed part due to friction effects between molding compound and die wall. These then lead, depending on the height of the part and the material compressed, to dimensional changes due to shrinkage processes during sintering in the lower density zones.
The incorporation of holes or recesses extending transversely to the pressing direction is more difficult. They may be any shape from very shallow to extending through the complete cross-section.
At the Ceramitec 2012 trade fair in Munich, Komage was the first press manufacturer to exhibit a system in which a cylinder with 5 pressing axes in the axial direction was manufactured with a transverse passage extending through the whole cross-section (Fig. 1). This transverse passage was introduced by means of two laterally mounted core rods which were designed as a hydraulically controlled axis. From a technical point of view, this way of manufacturing transverse passages does not make any particularly high demands on the press system. Here, it should merely be noted that the position of the transverse core rods must always be in the region of the press-neutral zone, otherwise forces from the pressing punches will act on the transverse core rods and may deform or damage them. Since the press-neutral zone is often placed at half the height of the part in parts which are higher in the direction of pressing, the transverse passage must necessarily also be shifted to this point.
In products with a hole positioned off center, this means that the press-neutral zone must also be transferred there. This can easily be achieved by programming the punch positions and speeds of the vertical pressing punches.
Demands arising from tungsten carbide tool production for undercut geometries can no longer be satisfied with the simple systems described above as several undercuts are usually necessary around the periphery of the pressed part. The systems currently available on the market allow the integration of no more than 6 cross pressing axes in their adapter systems. As the mechanical and control engineering effort (one system per cross pressing axis) of these systems is very high, high acquisition costs and a higher level of service are inevitable.
Komage, in collaboration with well-known manufacturers of tungsten carbide parts, developed a system which operates all the cross punches with only one drive unit in order to implement a competitively priced and flexible cross pressing device. This meant that the control engineering and mechanical effort could be minimized. This solution also enables fast setup of the press tool It is also possible to retrofit this system easily in existing presses. It has been patent-protected.
The construction of this cross pressing device is intended to enable the number of cross pressing punches required to be adjusted to the product to be manufactured by simple installation and removal of the cross pressing axes (Figure 2). Thus it is possible to integrate an even or also an odd number (6 or more) of cross pressing punches in the base unit. In order to obtain the highest possible rigidity of the system, all punch holders of the cross pressing punches are supported on a conical ring.
This ring, which produces the press movement and generates the force of the cross pressing punches is moved by 3 controlled hydraulic cylinders arranged in a vertical direction (Figure 3). The pressing position of the cross pressing punches is therefore freely programmable from the ring position which is approached by the hydraulic cylinders. It is also possible to program the cross pressing punches to a certain force and thus to enable dense compression in the crosswise direction. The conical ring which is mounted in a hardened cylinder enables backlash-free movement of the cross pressing punch holders. These in turn are individually adjustable in the horizontal pressing direction and also make it possible to adjust remachined cross pressing punches.
The actual pressing punches are inserted in the cross pressing punch holders together with the press die via backlash-free T slots. The cross pressing punches are installed in the cross die openings outside the cross pressing device. After complete tool assembly, the lateral pressing device is covered with a die plate on which the filling system is then constructed.
The complete pressing process is then split up into the following process steps:
The die is filled using the filling system by traveling across the press die. The actual filling movement then takes place due to the movement of the bottom punch or the die moving upwards in relation to the fixed bottom punch. Filling of the die in the case of a continuous transverse core rod may be performed in several steps. In this case, with the core rod retracted, only the powder column which is needed under the rod is filled. Then the powder column is lowered until the transverse core rod can be moved in without touching the powder. The next step is filling of the remaining filling space. In the case of round core rods, they can also be inserted before the filling process and a higher filling column is filled so that it can be raised a little before the pressing process is initiated. Unlike the transverse core rod, care must be taken during lateral pressing to ensure that the cross pressing punches do not project into the die. This is necessary to ensure that as far as possible no deadwater areas (lack of powder) occur under these tool parts. Care must also be taken to ensure that these tool parts do not stand too far back in the die, and that molding compound cannot build up uncontrolled in front of them which can result in varying densities in the product during pressing.
In the first step, pressing is carried out in the vertical direction by the top and bottom punch or top punch and die, until a certain density is reached. After this, depending on the paths to be traveled by the individual punch axes, coupled weighted compaction can take place in the vertical and horizontal direction. With certain part geometries it is also possible to move the lateral pressing axes into the pressing position and to complete the pressing process by subsequently re-pressing in the vertical direction.
Before the pressed part can be removed from the die, the pressure is relieved in the vertical and then in the horizontal direction. Once the cross pressing punches have been retracted into their starting position, the pressed part is demolded by being ejected by the bottom punch, or by withdrawing the die. This may then take place with or without applied loads of the top punch during the demolding process.
The newly developed transverse press system from Komage has been subjected to intensive tests in the tungsten carbide sector. It is also planned to use it in the iron powder sector with multi-punch vertical pressing axes.
This new innovative system was developed in cooperation with industrial users and is therefore adapted to the needs and requirements of cutting edge production processes.
As a result, manufacturers of complex molded parts will meet the future requirements of the market in respect of quality, productivity and flexibility by using presses with a lateral pressing unit from Komage.