PCM (Patternless Casting Manufacturing) is developed by the laser rapid forming center of Tsinghua University. The rapid prototyping technology is applied to the traditional resin sand casting process. First, the casting CAD model is obtained from the part CAD model. The STL profile of the casting CAD model is layered to obtain the profile information, and then the level information is used to generate control information.
Part 1: About PCM
Patternless Casting Manufacturing(PCM) process is a new rapid forming process combined with the traditional resin bonded sand process. The basic principle is: the principle of discrete / stacked forming of RP technology is adopted, and the contour scanning and spray solidification process are adopted to realize the rapid and direct forming of the casting without appearance. The basic principle is shown in the following figure:
First, the casting CAD model is obtained from the part CAD model. The STL profile of the casting CAD model is layered to obtain the profile information, and then the level information is used to generate control information.
Other, the first nozzle in each layer show good original sand spraying binder accurately controlled by computer, second nozzles along the same path or by spraying a catalyst, a double nozzle composite injection technology according to the contour information at the same time spraying binder and catalyst.
The adhesive reaction takes place and a layer of solidified sand is formed. Where the binder and catalyst are combined, the primary sand is solidified together, while the other raw sand remains a granular dry sand.
When the layer is cured, the next layer is bonded. After all the layers are glued together, a space entity is obtained. The original sand in the binder does not spray the place, or dry sand, relatively easy to remove.
By removing the intermediate uncured sand, a mold with a certain wall thickness can be obtained and applied to the casting of the metal after being coated or impregnated with the paint on the inner surface of the sand mold.
Part 2: Features of PCM Process
With the traditional mold manufacturing technology, PCM technology has incomparable advantage, it not only makes the casting process is highly automated and sensitive, reduce labor intensity, but also break through the many obstacles to the traditional process in technology, the constraints of design and manufacture is greatly reduced. Specific performance in the following areas:
1.Molding time is short
The use of traditional methods of casting mold must be processed appearance, whether ordinary processing or numerical control processing, appearance of the manufacturing cycle is longer. For large and medium castings, the casting cycle is usually calculated in months. Due to the automatic processing of computer, the information processing of PCM process usually takes only a few hours to tens of hours. Therefore, from the manufacturing time point of view, the process has the advantages of traditional modeling methods can not be compared.
2.Low Manufacturing Costs
PCM process has a high degree of automation, its equipment one-time investment is larger, other production conditions, such as raw sand, resin and other raw materials preparation process, and the traditional self hardening resin sand molding process is the same. However, because it does not need to look like the shape, for some large and complex castings, the cost of the mold is higher, so its revenue is obvious.
As the traditional mold needs to die, it is generally required to separate it along the largest section of the casting (parting surface), that is to adopt the parting design. This often limits the casting design freedom, casting some surface and cavity complex have to use multiple sub surface modeling, assembly process, the box greatly increased the difficulty of molding, casting to produce the "flying side", resulting in increasing the amount of processing machine.
The PCM process adopts the principle of discrete / stacked forming and has no die forming process, so the design of parting faces is not the main obstacle. Parting surface design can even according to need not set in the largest section of castings, but in non critical parts of the casting for some castings, can use the method of manufacturing integration, forming the upper and lower type at the same time. The most obvious advantage of integrated modeling is that it reduces the design constraints and the amount of machining, and makes the dimensional accuracy of castings easier to control.
4.Simultaneous Forming of Core and Core
The traditional process for the mould cavity is taken into account, some internal structure is designed as a core, and the core are made separately, and then the two together, the assembly process requires correct positioning, must also consider the stability of the core. The mold, core and core of the PCM process are stacked at the same time without assembly, and the position accuracy is easier to guarantee.
5.Easy to manufacture a mold with free surface
In the traditional process, it is difficult to guarantee the accuracy of the appearance by using ordinary machining methods. The programming of NC machining is complicated, and the problem of tool interference is also involved. Therefore, the traditional process is not suitable for the manufacture of castings with free surface or curve. And the PCM process based on the discrete / stacked forming principle does not have the geometric constraint of forming, so it can easily realize the modeling of arbitrary complex shapes.
6.Modelling material is cheap and easy to obtain
The molding material used in PCM process is a common casting sand. It has low price and wide range of sources. The binder and catalyst are also very common chemical materials, and the cost is not high. Therefore, for many domestic and foreign resin sand foundry manufacturers, the process is not only cheap, but also easy to promote, and therefore has a strong appeal.
To sum up, the upper hand PCM process in technology is quite obvious, no mould, fast, flexible, correct manufacturing cavity, complex surface castings, especially suitable for single and small batch production, the complex shapes of large and medium-sized castings production and new products. However, it also has some disadvantages, mainly because of large investment in equipment and unsuitable for mass production. Best suited for small, batch or single production with high flexibility.
Part 3: PCM process equipment
Equipment is the material basis and basic condition for process research and implementation. PCM equipment is a complicated mechanical electronic product which is highly integrated by mechanical, electronic, material and computer software and hardware technology.
Mechanical and electronic products are closely related to the field of electronic technology and mechanical engineering. They are a kind of products developed on the basis of mechanical and electronic technology.
The general thought of machinery and electronics products refers to the main body function, information processing and control functions, the introduction of the electronic technology and mechanical devices and electronic equipment and software combine to constitute the system.
According to the technological process, the PCM technology can be divided into four sequential basic sub processes:
Information processing, modeling process, post process and pouring process.
Among them, the information processing process is to prepare the corresponding control program (NC code) file for the modeling process;
The modeling process uses the NC code generated by the information processing process to drive the molding equipment and complete the NC machining of the mold;
The post treatment process aims to improve the casting surface quality and the casting process performance and to create conditions for the casting process;
The casting process is to complete the postprocessing to mold casting workshop, the gating system and the internal cavity of the liquid metal injection mold into high-temperature melting, solidification forming ultimate qualified castings with certain surface quality, accuracy and complexity.