Text/Meite Polymer zhongming
According to latest data, US uses FDM 3D to print N95 masks, and it takes 45 hours to make 4 masks. In my opinion, FDM 3D printing technology has low precision, poor surface quality and slow printing speed, it seems that it can only make some gadgets such as toys that are useless. To think so is to underestimate its value. As everyone knows, FDM technology with lowest price and highest popularity has been widely used in aerospace, clothing, automobile, industrial and other high-tech industries, and has completely replaced metal in some aspects. So, how to understand 3D printing?1. What is 3D printing?
3D printing is a rapid prototyping technology that can create different shapes and unique structures. Fused Deposition Modeling (FDM) 3D printing equipment is low cost and easy to operate, and is widely used in various fields. 3D printing technology first appeared in 1980s, was launched to meet needs of highly specialized modeling and rapid prototyping (RP) and has found wide application in various fields. Metals, ceramics, and polymers can be used to make custom parts using mold-free additive manufacturing in traditional casting processes. While traditional manufacturing is limited by technological limitations associated with industrial mass production, AM inherently allows for faster design and customization of industrial facilities to meet individual and application specific needs. AM allows production of 3D structures with a high degree of shape complexity, as shown in Figure 1.
Figure 1. Schematic diagram of basic principle of 3D printing2. Types of 3D printing and printing principle of conventional FDM lamination.
AM includes three types: SLA light curing molding, SLS laser sintering molding, and FDM laminating molding. The most commonly used is FDM lamination casting. The FDM mechanical system mainly consists of five parts: nozzle, wire feeder, movement mechanism, heating studio and workbench (as shown in Figure 2). The materials used in welding process are divided into two parts: one part is molding material, and other is auxiliary material.
Fig. 2. Block diagram of FDM formation and system simulation diagram
The low melting point filamentous material is melted into a liquid through extrusion head of heater, so that filament of molten thermoplastic material is extruded through nozzle and extrusion head moves precisely along contour of each section of part. , semi-flow extrusion The thermoplastic material is deposited and solidified as a precise thin layer of real parts covering built parts, and quickly solidifies within 1/10s. The scanning die cross-section is applied layer by layer until last layer, so that solid model or part is built layer by layer from bottom to top.
When FDM is formed, each layer accumulates on previous layer, and previous layer plays a role in positioning and supporting current layer. As height increases, area and shape of layer profile will change. With a strong change in shape, profile of top layer cannot provide sufficient positioning and support for current layer, which requires design of some auxiliary structures - “supports” to ensure smooth implementation of molding process. Supports can be made of same material, and at present, dual nozzles for independent heating are commonly used, one is used to spray model materials for making parts, and other is used to spray auxiliary materials as supports. are different from each other, and supports are quite easy to remove after manufacturing. . The wire feed mechanism feeds raw material to nozzle, and wire feed must be stable and reliable. The wire feed mechanism and nozzle use two-stroke combined method to ensure stable and reliable wire feeding and avoid wire breakage or wire buildup.3. Disadvantages of FDM Rapid Prototyping Process
(1) There are obvious streaks on surface of prototype. (2) The strength in direction perpendicular to section is low. (3) It is necessary to design and manufacture supporting structure. (4) The molding speed is relatively slow, which is not suitable for making large parts. (5) Raw materials are expensive. (6) The nozzle is prone to clogging and inconvenient to maintain.Fourth, advantages of FDM rapid prototyping process
(1) Low cost. Fused deposition modeling technology replaces laser with a liquefier, and equipment cost is low; in addition, raw material utilization efficiency is high and there is no poisonous gas or chemical pollution, which greatly reduces molding cost. (2) The use of water-soluble auxiliary materials makes it easy to remove stent structure and allows you to quickly create complex internal cavities, hollow parts and disposable assemblies. (3) The raw material is supplied as a wire spool, which is easy to handle and can be replaced quickly. (4) Various materials can be used, such as ABS engineering plastic, polycarbonate, PPS, and medical grade ABS in various colors. (5) During molding process, there is no chemical change in raw material, and deformation of workpiece during warping is negligible. (6) Prototype parts cast in wax can be directly used for investment casting. (7) The FDM system is non-toxic and does not produce odor, dust, noise or other pollution. No need to spend money on creating and maintaining a dedicated site suitable for an office design environment. (8) The material has excellent strength and toughness, and can be assembled for functional testing.Five, scope of FDM
- FDM for Aviation
Pictured above is a custom made piece provided to Airbus by Spanish airline Indaero for attaching expandable frame to inside of a helicopter wing. The part is traditionally made of aluminum alloy, weighs 12 kg and requires two operators to fix it and mark holes; Indaero has redesigned it with 3D technology while using FDM printers combined with engineering plastic to weigh just 12kg. kg.3 kg, not only can stand on their own, but also fully match curvature of wing, while price of new parts is cheaper. That's who said that FDM can only play with toys, isn't that also heaven? ! The components above are just one of them, and it's not only one that can take to skies. 2. FDM for cars Since 2014, Volkswagen Autoeuropa plant in Portugal has been using 3D printers to produce mold components for assembly lines. Volkswagen has already announced that in 2016 plant saved $160,000 a year by using desktop FDM 3D printers, cutting traditional production costs by more than 90 percent and tool development time by 95 percent. In 2016, plant 3D printed about 1,000 FDM parts for car production, and in 2017 it will save $200,000, and price of several FDM models is much less than this amount. 3. FDM is also used in other industries. In aviation industry, it is necessary to use a three-dimensional measuring machine to measure accuracy of parts, and a three-dimensional measuring machine requires use of special fixtures to fix parts. In past, such a special fixture had to be outsourced from steel. Today, FDM printers are used to make low-cost fixtures from engineering plastic. The production cycle is shorter and cost is lower. You can print as many as you need, reducing burden on inventory.