Parallel machining technology in large prototype r

2022-05-20
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Parallel machining technology in large prototype rapid manufacturing

Abstract: it is considered that layered solid manufacturing process (LOM) is the most efficient one of several mature rapid prototyping processes, which is most suitable for manufacturing large prototype. The idea of partition parallel machining based on LOM Process is proposed, that is, the machining plane is divided into machining areas, the data of the machined parts are divided, and the control system drives multiple scanners to process in parallel. The key technologies are analyzed. The forming efficiency of LOM Process can be greatly improved by using partitioned parallel machining technology

key words: rapid prototyping; Large prototype; Partition parallel processing; After nearly 10 years of development, the application field of advanced manufacturing technology

rapid prototyping technology is expanding. At the same time, industrial production also puts forward new requirements for rapid prototyping technology. How to obtain large-scale prototypes is an urgent need in many industrial fields, such as automobile manufacturing. However, the current rapid prototyping system can only manufacture small and medium-sized prototypes, and the prototype size is generally less than 1 m × 1 m × 1 m。 In order to meet this requirement, it is necessary to adopt new design ideas and develop a rapid manufacturing system that can manufacture large-scale prototypes

rapid prototyping adopts the process principle of discrete stacking, and the thin layers of 0.1 mm ~ 0.2 mm are stacked into prototypes with a certain size. Therefore, how to improve the processing efficiency has always been an important topic of rapid prototyping technology, and it is also the main obstacle to the large-scale of rapid prototyping technology. Therefore, what kind of rapid prototyping process and design idea to adopt have become the primary problem in the design of large-scale prototype manufacturing system

1 processing efficiency of typical rapid prototyping process the price rise of copper foil can be smoothly transmitted to copper clad laminate manufacturers. Compared with

rapid prototyping process adopts the process principle of discrete stacking. According to the fact that it can accurately obtain various data of the measured object, its minimum forming unit is different, it can be divided into different forming methods: some are composed of points to form lines, then lines to form surfaces, and finally surfaces are stacked into bodies, and its minimum forming unit is points; Some are formed by lines and then by surfaces. The smallest forming unit is lines; Some directly form a layer, which is stacked into three-dimensional entities, and the minimum forming unit is the surface. Obviously, the larger the minimum forming unit, the higher the forming efficiency. See Table 1 for the comparison of several typical forming methods

the estimation of processing efficiency of several typical processes (SLS, SLA, MEM, FDM) is shown in Table 2

note: 1) the dimension of the first floor of SLS and SLA is 100 mm × 100 mm × 0.1mm; The dimension of LOM and FDM first floor is 200 mm × 200 mm × 0.1mm。

the comparison of forming methods of the above typical processes and the estimation of forming time show that the layered solid manufacturing process (LOM) takes the surface as the minimum forming unit, has the highest forming efficiency and is most suitable for manufacturing large-scale prototypes

2 zonal parallel processing technology

among various rapid prototyping processes, layered solid manufacturing process has the highest processing efficiency, but there are still two problems in the existing LOM Process: ① forming a 1 m × 1 m × The prototype of 1 m takes 16 days, and the efficiency is still too low; ② The actual large prototype size required is larger, such as 1 m × 2 m × 1 m, so new design ideas are needed to further improve the processing efficiency

in LOM Process, the time required for processing a layer consists of two parts: one part is the scanning processing time (contour processing + grid filling + frame processing, accounting for about 80%); One part is the processing preparation time (paper feeding + hot pressing + worktable adjustment). Based on this, this paper puts forward the idea of partition parallel machining design, that is, the machining plane is divided into machining areas and processed by multiple scanners in parallel, which will greatly improve the machining efficiency of rapid prototyping (see Figure 1)

Fig. 1 Diagram of parallel processing in zones

the processing time estimation of dividing a rectangular processing area into two processing areas is shown in Table 3. If parallel processing technology is adopted, the processing efficiency can be improved by about 40%

analysis of key technologies of zonal parallel machining

using parallel machining technology, we must first solve two problems: ① how to segment the geometric data of a part; ② How two sets of scanning devices work in parallel

3.1 segmentation of part geometric data

the general processing process of rapid prototyping technology data is shown in Figure 2a, which is divided into five stages

Figure 2 data processing process in rapid prototyping technology

(1) in the CAD modeling stage, various CAD modeling software provide the function of entity segmentation, but form a new boundary of two entities at the boundary of segmentation. In this way, the scanning will be repeated twice at the boundary, which should not be processed

(2) the surface triangle of CAD solid model is discretized to generate STL file, which cannot be segmented

(3) generate cli files by layering STL files. Due to the need of filling in the next step, the contour line must be a closed polysemy line. In order to close the contour line, two unnecessary line segments need to be added at the division, and two scanning lines will also be added at the places where the boundary should not be processed

(4) fill the CLI file to get the filled cli file. The filled cli file can be divided, because there is no requirement that the contour line must be closed at this time, and the original appearance can be maintained at the boundary. Therefore, the division of part geometric data is suitable for the filled cli file

(5) convert the filled cli file into NC code file, which can not be divided, and it is also difficult to divide the data in the process of NC code generation

On the other hand, it can maintain the original appearance of any waste data after segmentation. The data processing process of partitioned parallel processing technology is shown in Figure 2B. The above analysis can be summarized as shown in Table 4

Table 4 feasibility analysis of part segmentation in data processing process of rapid prototyping technology

whether the data form can be segmented

whether the original appearance can be maintained at the boundary after segmentation

whether the CAD solid model can

STL file no no

whether the CLI file can

whether the CLI file can

NC code file no

3.2 the parallel work of multiple sets of scanning devices Row processing technology is another key problem. To solve this problem, a distributed control system can be used (see Figure 3). Two sets of controllers are used to control two sets of scanning devices respectively. The controller has enough memory and separate CPU, which can repair NC code files independently. In this way, during scanning processing, the industrial computer transmits one layer of processing code to each controller at a time, each controller works in the background, and two sets of scanning devices process in parallel

Figure 3 block diagram of distributed control system of double scanning device

4 one-time simultaneous processing of small batch prototypes

the large-scale prototype manufacturing system using partitioned parallel processing technology can not only manufacture large-scale prototypes, but also use the layout technology of parts to process multiple smaller parts at the same time. On the one hand, it can maximize the utilization of raw materials, on the other hand, it can improve the manufacturing efficiency of rapid prototyping system. The data processing process is shown in Figure 4. Firstly, several STL files with CAD modeling and surface discretization are reasonably arranged and merged into one STL file; The filled cli file is obtained by filling the file in layers. The CLI file is divided and processed in parallel

Fig. 4 simultaneous processing of small batch parts

5 Conclusion

(1) large prototype is a new important requirement in many application fields of rapid prototyping technology. Developing a rapid prototype manufacturing system that can manufacture large prototype has a good market prospect

(2) the main difficulty in developing large prototype rapid manufacturing system is how to improve the processing efficiency of the manufacturing system. The effective way to greatly improve the processing efficiency is to adopt layered solid manufacturing process (LOM) and partitioned parallel processing technology

(3) the two key technologies of partitioned parallel machining technology, that is, the segmentation of part geometric data and the parallel work of multiple sets of scanning devices, are feasible

(4) using parallel processing technology can not only manufacture large prototypes, but also process multiple parts at the same time, which can not only improve the utilization of raw materials, but also improve the processing efficiency

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