WITTMANN Begins Mission to Minimise Removal Times
The finished parts removal sequence, more specifically the mould-open time in the injection moulding process, contributes substantially to the total cycle time. WITTMANN is looking to minimise this removal time through the use of its robots that feature several functions such as SmartRemoval, Push and iVac.
The production process for making injection moulded plastic parts consists of innumerable phases, which all have an effect on the total cycle time. One of these is the finished parts removal sequence, where the minimisation of mould-open time contributes substantially to shortening the cycle time.
Modern robot systems offer the advantages of highly efficient motors and weight-optimised axes. Here, WITTMANN uses a well-balanced material mix of thin steel sheets combined with aluminium. The choice of materials in each case depends on the specific application and the stroke length of the removal robots. The available model range covers highly rigid combinations for load capacities of up to 150 kg, as well as weight-optimised solutions for acceleration rates of up to 80 m/s².
However, even the best design makes no difference unless the response times of the appliances are able to keep up with it. This is why WITTMANN has been operating with a 4 ms cycle time for several years, which is a vital factor in the command processing time of the robot’s teach-program and thus constitutes an essential component of every WITTMANN robot application. All WITTMANN robots, including the compact models of the PRIMUS series right up to the large WX appliances, operate on the basis of this cycle time, regardless of the robot’s actual control system version.
Another significant aspect is the efficient conversion of command input and control signals into appropriate travel movements. This is where the patented SmartRemoval function from WITTMANN, installed in all robots as standard, shows its advantages. The main feature of SmartRemoval is its anticipatory inward movement of the robot axis – in top-entry models generally the vertical axis and the horizontal axis in horizontal appliances.
The analysis of the injection moulding machine’s cycle permits the initiation of the anticipatory axial movement before the platen is completely opened. No special interface is required to carry out this analysis since EUROMAP E12 (in older machine models) or EUROMAP E67 already provides the necessary signals for calculation. SmartRemoval makes it possible for the robot to reach its maximum speed in the mould area at a very early stage. By almost complete elimination of the acceleration phase after the moving mould platen has reached its end position, in combination with phased vacuum monitoring of the finished parts, mould-open times are reduced by 10% – 30%.
For complex parts which offer no facility for a stable hold in the ejector’s end position and thus complicate the task of programming a safe transfer to the removal gripper, the WITTMANN robot control system provides a special feature known as the ‘push’ function. Another common form of this function found on the market for this type of requirement is releasing the brake on the robot’s demoulding axis. However, this can have an extremely adverse effect, since in such cases the ejector presses the part directly into the gripper and consequently onto the demoulding axis. As a result, deformations and other defects may occur on the finished parts, and in the long run, also damage the mechanism of the removal device.
By contrast, the ‘push’ function from WITTMANN enables a gentle, torque-monitored transfer of the parts. Here, the actual presence of a finished part is continually monitored by what is known as the iVac function, the freely programmable vacuum monitoring system from WITTMANN. iVac offers the advantage of having the moulded part picked up with only a fraction of the necessary vacuum pressure, together with a simultaneous start of the removal sequence. During the robot’s outward movement, the vacuum pressure rises to the maximum level. As soon as the set reference pressure for the moulded part has been reached, the release signal for closing the mould is given. This release can already take place several tenths of a second before the robot leaves the mould area. In this way, signal delays in the interface between the robot and the injection moulding machine are compensated, thus minimising the mould-open time.
With the standard functions of the WITTMANN robot control system as described above, injection moulders receive not only a sophisticated system for optimising applications but also continuous monitoring of manufacturing processes.
Wittmann Battenfeld
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