| In modern manufacturing industry, sheet metal forming technology has been always playing an important part. With the rapid development of society, new products update more and more quickly, people's desire for their products' individuation increases rapidly. This leads to sheet metal forming production become multi- varieties, small batch, and this character becomes more and more obvious. Traditional sheet metal forming method uses two dies; it has a broad serviceability, high production efficiency and is suitable for mass production. So for many years, this method dominates the sheet metal forming industry. But this method needs dies, it takes a long time to design and manufacture the dies, and the cost for the dies' material and manufacture is high, so, obviously, this method is out of date. Because of all of these disadvantages, many countries around the world do a lot of research in the field of sheet metal forming without of dies, and a lot of new ways appear. The research on sheet metal incremental forming with water jet is just one of these.Sheet Metal Incremental Forming is a new sheet metal forming method which was first advanced by a Japanese scholar S. It adopts the idea of "layered manufacture" which is used in rapid prototyping technology. Complex 3D shape is divided by a series of 2D planes, the tool head moves along the profile of the part on XY plane, so plastic processing takes place on these 2D planes, and this can achieve the goal of forming dielessly.Water jetting technology is applied in many fields from automotive and aerospace industry, mining, construction business and even in the fields such as medicine and food processing. It is mainly used as a cutting process, but considerableefforts are focused on surface treatment processes such as surface cleaning, de-coating, surface hardening, etc. This technology can also be combined with other machining processes like turning or grinding, where a WJ is directed on the cutting zone to increase the cooling effect.Sheet metal incremental forming system using metal tool head has a large friction between the tool and the part surface; this can generate a lot of heat in the process of forming. If the heat accumulates too much, it will burn the tool head and the part surface. So our system uses high pressure water jet instead of metal tool head to avoid friction, further more this will avoid burning of the part and the tool. Besides this, this system also has the advantages of low cost and no pollution.The research on Sheet metal incremental forming with water jet system involves high pressure, numerical control, control engineering and computer software technology, it is a Multi-disciplinary, multi- domains research filed. We studied the key technology and control method in the development of sheet metal incremental forming prototype, this included the following aspects:(1) Open Numerical Control SystemOpen NC System is based on an open platform. It has modular structures, and is allowed by customers to select and assemble based on their own needs. It is interoperable, portable, interchangeable, extendable and so on.We use PC+ Motion Control Unit type to design our NC system. The parallel double CPU control mode which is based on PC+ Motion Control Unit uses general PC as its platform and open motion control unit as its control core. The general PC is responsible of NC code compile, user interface management, external communications and so on, while the motion control unit fulfills motion control and logical control of the machine tool. This kind of frame supports secondary development and self expansion. Not only does it have the open character of PC, butalso has the open character of special NC modular.(2) Digital PID Control AlgorithmIn engineering practice, the most commonly used control algorithm is PID Algorithm, which is also called proportional, integral, differential control algorithm. This algorithm has a simple structure, good stability, reliable work, and convenient adjustment. In order to apply digital control more easily, we worked out incremental digital PID algorithm.The sheet metal incremental forming with water jet system needs to control thewater pressure precisely, and regulate the pressure steplessly. Just based on this algorithm, we use a SCM to control a digital overflow valve, then the system's pressure feedback to the SCM by a pressure sensor, and all these consist of a close loop control system. There is a step motor inside of the digital overflow valve. When the step motor rotates, the valve opens a certain amount. So the fact of controlling the digital overflow valve is controlling the step motor. So digital PID algorithm is just suitable for our system.When apply this algorithm to practice, we must determine the exact value of each parameter to make sure the system satisfy every control target. In light of the characteristics of this system, we discussed some means of setting parameters.(3)Hardware interface designThe main parts of the sheet metal incremental forming using water jet system prototype are motion control unit PMAC, industrial PC, SCM, step motor and so on. We must design the hardware interface based on the characters of each part and the character of the system.(4) The development of control softwareIn order to make the system work normally, and based on the desires of the system, we must develop a control software. The software needs to have the following functions, first, it can analysis the NC code which is generated by CAM software, and calculate the pressure needed for each layer based on the NC code. Second, the software must make sure the PMAC and PC can communicate with each other. Finally, the software must help to control the system's water pressure via PID algorithm. Using these theories, we developed the sheet metal incremental forming prototype using water jet, and also we developed the control software using Visual C++ 6.0.
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