The principle of LOM:
Foil laminated solid production is based on the contour line of each section of the three-dimensional CAD model, under the control of the computer, issued the command to control the laser cutting system, so that the cutting head moves in the X and Y directions. The feeding mechanism sends the foil coated with hot sol on the ground (such as coated paper, coated ceramic foil, metal foil, and plastic foil) to the worktable section by section. The laser cutting system cuts the paper on the table along the contour line with the carbon dioxide laser beam along the contour line according to the cross-sectional contour extracted by the computer, and cuts the non-contour area of the paper into small pieces. Then, the layers of paper are compressed and bonded together by the hot pressing mechanism. The lifting table can support the workpiece being formed, and after each layer is formed, the paper thickness is reduced to feed, bond and cut a new layer of paper. *Form a three-dimensional prototype part surrounded by many small scrap blocks. Then take it out, remove the excess scraps, and finally get a three-dimensional product.
Due to the fact that the layered entity manufacturing is more suitable for paper materials in production, the cost is low. Moreover, the manufactured wooden prototype has external insensitivity and some special qualities, so this technology is used in product conceptual design visualization, modeling design evaluation, assembly inspection, and investment casting core. Sand casting wood molds, rapid mold making master molds and direct mold making are widely used!
Advantages and disadvantages of LOM:
The advantages are:
A. The forming speed is fast. As long as the laser beam is cut along the contour of the object without scanning the entire cross-section, the forming speed is fast. Therefore, it is often used to process large parts with simple internal structure and low manufacturing cost.
B. No need to design and build supporting structure.
C. The prototype has high precision and small warpage.
D. The prototype can withstand temperatures up to 200 degrees Celsius, and has higher hardness and better mechanical properties.
E, can be cut and processed.
F. Waste materials are easily peeled from the main body and do not require post-curing treatment.
The disadvantages are:
A. There is laser loss, and a special laboratory needs to be built, the maintenance cost is too expensive;
B. There are few types of raw materials that can be applied. Although several raw materials can be selected, paper is currently commonly used, and others are still under development;
C. The printed model must be immediately subjected to moisture-proof treatment. Paper parts are easy to absorb moisture and deform, so they must be coated with resin and moisture-proof paint after molding.
D. It is difficult to construct fine-shaped, multi-curved parts with this technology, which is better than simple-structured parts.
E. At the time of production, the temperature in the processing room is too high, which may easily cause a fire and require special personnel to guard it.
LOM molding material: LOM material generally consists of two parts: sheet material and hot melt.
A. Sheet material: According to the performance requirements of the model to be constructed, determine the use of different sheet materials. The sheet material is divided into: paper sheet, metal sheet, ceramic sheet, plastic film and conforming material sheet, among which paper sheet has the most applications. In addition, the constructed model has the following performance requirements on the substrate sheet material:
A, moisture resistance. b. Good invasiveness. c. Tensile strength. d. The shrinkage rate is small. e. Good peeling performance.
B. Hot sol: The hot melt adhesive used for LOM paper base is divided into: ethylene-vinyl acetate copolymer hot melt adhesive, polyester hot melt adhesive, nylon hot melt adhesive or other mixtures according to the matrix resin. At present, EVA hot melt adhesives are widely used. Hot melt adhesives mainly have the following properties:
A, good hot-melt cold-setting performance (curing at room temperature);
B. Its physical and chemical properties are stable under repeated “melting-solidification” conditions;
C. In the molten state, it has better coating and uniformity to the sheet material;
D. Adequate bond strength;
E. Good waste separation performance.
Manufacturing process of LOM prototype molding:
The LOM molding manufacturing process is divided into three main steps: pre-processing, layered superimposing molding, and post-processing:
Step A is the pre-processing, that is, the graphics processing stage. If you want to manufacture a product, you need to use 3D modeling software (such as: PRO/E, UG, SOLIDWORKS) to manufacture the 3D model of the product, and then convert the produced 3D model to STL format, and import the model in Jiang STL format into slicing software Carry out slicing in the middle, which completes the first process of product manufacturing.
B. The second part is base production. Due to the frequent take-off and landing of the workbench, when manufacturing the model, the stack of the LOM prototype must be firmly connected to the workbench, then this requires the manufacture of the substrate, the usual method is to set up a 3-5 layer stack As a substrate, but sometimes in order to make the substrate stronger, then the table can be heated before making the substrate.
Part C, the third part is prototype production: After the substrate is completed, the rapid prototyping machine can automatically complete the prototype production according to the preset process parameters. However, the selection of process parameters is closely related to the precision, speed and quality of model selection. Among these important parameters are laser cutting speed, heating roller heat, laser energy, broken mesh size, etc.
D. Post-processing: Post-processing includes residual material removal and post-processing.
Removal of excess material means that after the model is printed, the staff removes the excess material around the model to show the model!
Post-processing means that after the residual material is removed, in order to improve the surface quality of the prototype, it is necessary to post-process the prototype. Post-processing includes waterproof and moisture-proof. Only after post-processing, the manufactured prototype will meet the requirements of rapid prototype surface quality, dimensional stability, precision and strength! In addition, the surface coating in the post-treatment is to improve the strength, heat resistance, moisture resistance, extended service life, smooth surface of the prototype, and better for assembly and functional inspection.
Four reasons for errors in layered physical prototypes:
Errors caused by A, CAD model STL file output;
B. Error caused by input setting of STL file of slicing software;
C. Equipment accuracy error: inconsistent constraints, improper molding power control, shredded mesh size, unstable process parameters;
D. Errors caused by environmental factors after molding: deformation caused by heat, deformation caused by moisture.
Measures to improve the accuracy of prototyping:
A. When performing STL conversion, it can be determined according to the different complexity of the part shape. Under the condition of ensuring the complete and smooth molding shape, try to avoid too high accuracy. Different CAD softwares have different accuracy ranges. The range selected by eg:pro/E is 0.01-0.05㎜, and the range used by UGⅡ is 0.02-0.08㎜.