New era in die mould with Mitsubishi Electric CNC

April 29, 2015 5:36 pm

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In India high-end technologies, precision engineering and metalworking industries will continue to grow. Fully developed nano-machining technology ensures the highest level of precision and resulting in the need of high performance and automated production facilities will continue to increase.
Mitsubishi Electric CNC products are engineered with cutting edge solutions and technologies to meet the requirement of the precision industries.
Here we discussed on the best surface finishing of the die mould machines. The technology of “SSS” (Super Smooth Surface) control provides an optimal speed control function for machining die mould with smooth surface.Conventional problemAs for the mould machining of three-dimensional shape, the smoothness of the machined surface (surface accuracy) is important. In recent years, even at the case of more than 5m/min feed speeds, the request of high surface accuracy in several μm or less has increased especially. In this case, the quality of instruction shape described in the machining program is often regarded as a problem.
Generally, in CAM to create a machining program, the motion curve of the tool relative to the workpiece is calculated by approximating the minute line segments. Therefore small error is more or less included in the data of minute line segment. For example, as shown in Fig.1, there are many cases like the minute error of the zig-zag shape or the shape of a level difference is contained within the limits of the permissible error (tolerance) on CAM processing, to form the process originally.
In NC, it’s essential to have the process of determining the rate at which moves according to the shape in order to maintain the trajectory accuracy. If some errors are included in the instruction shape, it is difficult to calculate the accurate determination of the appropriate speed movement. Especially in scan line machining, there are some cases that the fluctuation occurred in the trajectory of movement of the machine and scratch streaky occurred in the machined surface when the magnitude of the error contained in the instruction form by path difference.
In order to cope with such problems, is developed Fairing Function to correct shape in the NC Conventional, so as to reduce the error and it has been used in (Fig.2 (a)). However, at first glance zig-zag shape or a minute level difference which seems to contain an error, it is difficult for NC to distinguish whether it is a thing with the sense which should be processed essentially. Especially the program die-mould machining consists tens of thousands of blocks of minute line segments, as for at least several positions, the part which cannot restore the exact shape correctly and where sufficient accuracy is not acquired in many cases.
Since shape correction was performed as shown in Fig. 2 (b), it is shifted to the contrary original form, and there was also an example for which accuracy gets worse (A to D part in a figure).  SSS ControlHere, we discuss of different way from such shape correction in which potential risks are hidden. In the process of determining the movement speed depending on the shape, the process is not affected by the error contained in the directive shape and it can generate the stable and optimal pattern of speed, it is possible to obtain a smooth cutting result even if the pattern and magnitude of the error included in the instruction by the path shape are different. The “SSS Control” was developed so as to realise the speed control method in this way. The following original processing modes are adopted in SSS control.• The global shape judgment based on prediction of instruction form determines the optimal feeding speed• Efficient acceleration and deceleration without waste even in shape• Processing a uniform that does not depend on the speed and shape instruction.
As a result, the following effects can be obtained in the SSS control.
A stabilised and high-quality processing is realised• Irrespective of the speed and shape command to achieve high quality processing in a stable.• There is no streaks on the processing surface even in the command shape that changes consecutively
Reduction of processing time• Conventional ratio 5:30 per cent of time reduction (comparison with the same accuracy)• Especially the effect is remarkable when feed rate is higher.
Easy parameter setting• Parameter adjustment for correction of shape is not required• Easy adjustment such as efficiency-oriented and accuracy-oriented.Sample of processing resultsThree samples processing of SSS Control are: Dome-shape worked sample (Fig 3): This is the sample shape consisting of the upper half and plane part of hemisphere. This is processed by the scan line processing of the left-right direction (round trip). The tool used in this processing is Ball end mill of diameter 4 mm, feed speed is 2m/min and shaft rotation speed is 12,000 min-1.
By the SSS control, beautiful and shiny processing surface which does not include fringes caused by vibration and streaks are realised in both the part of hemisphere and plane portion. Furthermore, also at the boundary portion both hemisphere and plane portion, excellent accuracy is obtained without any streaks.
Corrugated plate type processing sample (Fig 4): This is the sample shape which contains the convex portion, concave portion and the sharp edge portion. Scan line processing was implemented from the lower left side to upper right direction (one way) in the figure. The tool used in this processing was Ball end mill of diameter 4 mm, feed speed is 1 to 8m/min and shaft rotation speed is 20,000 min-1. Even in the part where the command speed is increased up to 8m/min, it is appropriately controlled at a required speed in order to maintain the accuracy. Therefore, the command speed is even location of 8m/min, a sharp edge (concave portion, convex portion) and a smooth curved surface without streaks is obtained. In addition to sample, the characteristic type of plastic, there is the point where the shape is continuously changes little by little, without shape changes discontinuously along the way, natural processing shape was obtained.                                      Noh mask-type processing sample (Fig 5): This is the example of sample which contains various part of shape such as the concave portion, the convex portion, edge portion, plane portion and so on. This was processed by the scan line processing from lower left to the upper right direction (round trip). The Tool used in this processing was Ball end mill of diameter 6mm, feed speed is 2m/min and shaft rotation speed was 20,000 min-1. Even in such complex shapes, by SSS control can be realised the beautiful working surface with shiny overall is obtained. n
Authored by__Sandip Chakraborty, Manager-Planning, CNC- Factory Automation & Industrial Division, Mitsubishi Electric India