The working principle and processing flow of LOM rapid prototyping are briefly introduced, and the factors influencing the efficiency of rapid prototyping are summarized. The factors that affect the processing efficiency, such as the high workpiece, mismatch of laser intensity and processing speed, improper heating temperature and heating roller moving speed, improper setting of grid parameters, were analyzed and corresponding countermeasures to improve processing efficiency were put forward.
Since the LOM (Laminated Object Manuafctuirng) manufacturing rapid prototyping machine is mainly used for processing large-sized workpieces, the processing time may be as much as one hundred hours or more even though the equipment is largely In the process of automation, but in the process of processing, the need for staff to monitor continuously, from time to time to add the workpiece material, remove excess waste, eliminate some common failures, etc., for how to improve its work efficiency, research at home and abroad The author did not pay much attention. This article uses LOM as an example to analyze the factors affecting the efficiency of rapid prototyping, and proposes measures to improve the efficiency of various factors affecting the processing efficiency. It has certain guiding significance and practical value for related research and application.
How 1LOM rapid prototyping machine works
The LOM rapid prototyping machine processes the rapid prototyping parts in layers. In the production process, the parts with a certain spatial geometry are decomposed into thin layers that can be controlled by precision or post-processing, and processed in layers. Certain methods join and stack adjacent layers. The production of rapid prototyping parts is shown in Figure 1.
As can be seen from Fig. 1, the pretreatment determines the height direction in which the workpieces are layered and the number of layers that need to be manufactured in layers; the layered superposition molding is a manufacturing implementation that is used to carry out the layered manufacturing of the workpieces and the adjacent layers are Linking to form parts; Post-processing is the use of parts, and takes certain problems in the processing and problems that will occur in the use of the parts, and takes certain measures, such as removing parts not belonging to the parts and removing the use of processing. Some of the auxiliary structure, improve the surface quality of the workpiece and so on.
2 Factors that affect the efficiency of rapid prototyping
The factors that affect the efficiency of rapid prototyping are:
(1) The workpiece is too high;
(2) The heating temperature of the workpiece material is not proper, so that the lamination of the workpiece layer and the layer can not be effectively fit;
(3) The machining position of the workpiece on the workpiece surface is too far away from the coordinate origin of the cutting laser head;
(4) The laser intensity does not match the speed of its movement;
(5) Improper adjustment of paper feed speed;
(6) Improper setting of grid parameters;
(7) Improper adjustment of the speed of the table up and down when focusing;
(8) Improper adjustment of the heating temperature and the speed of the heating roller;
(9) The ease of post-processing.
3 Analysis of Causes of Low Efficiency of Rapid Prototyping Processing and Countermeasures
3.1 The workpiece is too high
3.1.1 Reasonably choose the height direction of the workpiece
When determining the height direction of rapid prototyping, it is mainly based on the strength and precision requirements of the workpiece. The height direction strength of the workpiece should be the lowest. It should be said that after the workpieces are layered, the precision and strength in the layers are high, and the layers are formed by cementation. The thickness of the adhesive layer and the integrated thickness formed by the adhesive film and the substrate are subjected to pressure by the heating roller. Impact.
3.1.2 Segmentation in the height direction, combined machining of different workpieces
If the size of the workpiece in the height direction is too large and the dimension in the direction perpendicular to the height is small, the workpiece may be divided, and the divided components may be combined to be layered in the same rapid prototyping file. In the segmented model, after the rapid prototyping part is finished in Gaya, the parts that belong to the same part are glued into one body with glue. Although this has a certain degree of influence on the machining accuracy, as long as the processing is done properly, the same quality will be obtained. High rapid prototyping parts.
This method is not only suitable for the case where the single piece is too high, but it can also be applied when there are many pieces. If there are many parts, the parts with similar heights can be combined to make the same production file and processed in layers. This can process several parts at a time. The rapid processing time of the rapid prototyping machine in the rapid prototyping machine can be expressed by formula (1) according to the working principle of the rapid prototyping machine:
Where T represents the total time for rapid prototyping; 
Indicates the auxiliary processing time, including the cleaning of the work table before processing, the selection and installation of the workpiece material specification, the cutting and seating of the workpiece floor, the cutting of the workpiece auxiliary layer, the adjustment of the process parameters, the related trial cutting, and the removal of waste roll paper during processing. Excessive waste on the cylinder, also includes the workpiece removed from the molding machine after the workpiece is processed, the grid removed, the bonding of the partitions, grinding, painting, etc.; 
Indicates the sum of the time required for the workbench to drop and add a layer of material to the workbench after the current layer of processing is completed. 
After adding a layer of material to the workbench, it will take time for the workbench to focus and heat up. 
The sum of the time required to slice the contour of the workpiece; 
The sum of the time required to slice the outside of the workpiece and the grid.
Fig. 2 and Fig. 3 are schematic diagrams of the processing of rapid prototyping parts. Fig. 2 shows one layer covering a thin material at a time, focusing and heating, and processing only one workpiece. Fig. 3 shows covering a thin material, focusing, and heating. Machining 8 layers belong to different parts of the same workpiece or cross sections of several different workpieces. In this way, because the multi-layer processing only uses the preparation table, workpiece material, test cutting, focusing, heating, and removal of workpieces from the workpiece table once, this time will be reduced to 1/8 of the original. The time for fast forwarding and rewinding has also been greatly reduced, which is not difficult to find in the comparison of Fig. 2 and Fig. 3 .
 If the same workpiece is processed in multiple layers at the same time, the above equation (1) can be simplified to the form of (2):
Obviously ## whether the same workpiece is divided into multiple blocks at a time or different workpieces are combined for processing, the production time of the workpiece is greatly reduced. If the worktable is large enough, the accuracy of the workpiece is not too high, and the strength of the workpiece can be satisfied, this method is obviously effective in improving the processing efficiency and shortening the working time.
If the work piece is small, it is better to use a molding machine with a small table top to allow a long time idle stroke of the cutting head and the heating roller if conditions permit.
Of course, the summary of the above legend or formula is not comprehensive enough. For a batch of models, which are large or small, small and large counter-collocations or nestings can be used for rapid prototyping, and models with similar dimensions can also be collected together. Processing can effectively improve processing efficiency while saving raw materials needed for processing.
3.2 The laser intensity does not match the cutting speed
The intensity of the laser in the processing is matched with the feed motion speed of the laser cutting head, that is, the intensity of the laser just makes the cutting motion cut through only one layer of the workpiece. If the laser intensity is too high at a certain speed, the layer that has been added will be cut off, which will affect the processing quality. In severe cases, machining will not be able to form the workpiece effectively. If the laser intensity is too low, the current layer will not be cut. After wearing, the scrap part cannot be effectively stripped after the processing is completed. This undoubtedly reduced the overall processing efficiency.
In this case, the cutting parameters are adjusted according to the equipment use instructions and operating procedures combined with the operator's cutting test at the site, and full consideration is given to the minimum turning radius of the work of the servo system of the equipment, the corresponding feed rate, and the characteristics of the parts of the workpiece itself. The process is continuously monitored and adjusted appropriately so that the laser intensity matches the moving speed of the cutting head to achieve the best cutting results and maximum cutting efficiency.
3.3 heating temperature and heating rod speed adjustment improper
Similar to the relationship between the laser intensity and the moving speed of the laser head, the temperature of the heating roller and the moving speed of the roller must be matched with each other. If the temperature is adjusted higher, the moving speed of the heating roller can be made a little larger; if the temperature is adjusted, If it is lower, the heating roller needs to be made smaller and the heating time is longer. This requires repeated debugging during actual processing, or consults the user manual and related material parameters, and uses the recommended values ​​in combination with on-site test cutting to perform debugging.
3.4 Grid parameters are not set properly
During the machining process, the outer contour of the workpiece is cut out of the grid so that scraps outside the contour of the workpiece can be more easily peeled off from the workpiece. For the parts outside the outer contour, the general problem is not great. For the part inside the inner contour, this is very important, because if the inner contour can not be marked on the grid, it will bring great difficulties to the post-processing to remove the excess part. When setting the mesh parameters of the rest material, it should be noted that the minimum hole to be stripped must also be at least a grid. As shown in Fig. 3, if the hole in the workpiece fails to mesh the mesh, because it is located inside the workpiece, if it is a straight hole, it can still be removed from the workpiece. If the hole is a spatial hole, it is difficult to Was removed. For some shell-like workpieces, the waste is surrounded by the outer shell, and it is difficult to remove the waste even if the grid is struck. In the layered manufacturing process, some wastes are removed, so that the formed grid-wrapped waste cannot be layered. Sticking to form a whole, but naturally become pieces, making it relatively easy to clear after processing, which can greatly reduce the difficulty and workload of post-processing.
In short, based on the improvement of LOM's rapid prototyping efficiency, it is necessary to comprehensively consider the ease and efficiency of the processing and post-processing work. It is also not appropriate for the workpieces that are not too high in the stratified height direction to be divided into too many blocks, otherwise it will increase. The difficulty of processing and affect the final accuracy of the workpiece. For workpieces of large or small sizes, it is important to consider that small parts must be removed from large parts without loss of size.
In addition, because the application of rapid prototyping technology is not very popular, only some research institutions and large-scale enterprises or specialized service organizations have this phase of equipment. Different rapid prototyping methods have their own processing laws and require that the process personnel and operators actually work. Constantly sum up experience in order to meet the needs of modern industrial development for the application of rapid prototyping technology.
4 Conclusion
Rapid prototyping, as one of the effective means for product development and research, is playing an increasingly important role in product development. However, due to fewer engineering personnel who are exposed to this type of equipment and processes, their research on process efficiency is relatively low. less. This article combines the author's experience in the management and operation of LOM rapid prototyping machines, analyzes the factors affecting the machining efficiency in LOM rapid prototyping, and proposes countermeasures to improve machining efficiency, and practical application of rapid prototyping technology. The development of related equipment has certain reference value.
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