Introduction to Metal Rapid Prototyping Process

Mold manufacturing technology A new precision and high processing and forming method In modern processing and manufacturing, mold parts are generally formed in three ways, namely, removing forming, adding/stacking forming, and net/forced forming. The technology of RP_rapidprototyping, which appeared in the late 1980s, belongs to the addition/accumulation molding in object forming. Rapid prototyping technology is a very important kind of modern advanced manufacturing technology. It can quickly respond to market demand in the manufacturing of molds, and is the most significant innovation in the field of manufacturing technology in the past 20 years. Based on the principle of discrete manufacturing, a new rapid prototyping method for directly manufacturing metal molds is proposed from the combination of removal molding and addition/stacking molding in mold/part molding.

Introduction to Metal Rapid Prototyping Technology In the current rapid prototyping technology, metal mold and product rapid manufacturing technology can be divided into two categories: direct metal rapid manufacturing technology and indirect metal rapid manufacturing technology. Direct metal part/mold rapid manufacturing technology. The rapid manufacturing technology of direct metal parts/dies mainly refers to the direct use of metal materials from existing rapid prototyping processes and the development of new processes suitable for direct metal forming. At present, it has been successfully applied in sheet metal overlay manufacturing, powder sintering and stacking forming, metal wire melting and stacking, metal droplet deposition forming and vapor deposition forming.

Superimposed metal sheet manufacturing is to directly use metal sheet as the material, and bond the metal sheet to form metal parts through laser cutting, arc welding or adhesive. The main disadvantage of this method is that the classification of rapid manufacturing of metal products and moulds or the performance of moulds is low, and it is difficult to meet the technical requirements of actual needs.

At present, this technology is mainly in the basic aspects of testing. Metal powder stacking is formed by laser sintering or bonding metal powder with adhesives. Typical examples are powder laser sintering (SLS) and three-dimensional printing (3DP) processes. At present, there are commercial equipment based on SLS process, but it can only use extremely limited forming materials, which is difficult to form large prototypes, and laser sintering equipment is expensive, which is difficult to reduce manufacturing costs. The molten deposition of metal wire is a metal material that can be formed by FDM process developed by Stratasy Company in the United States. The metal powder is mixed with the binder, and then extruded into a wire with sufficient bending strength for FDM equipment forming. This method can produce stainless steel, tungsten and tungsten carbide parts. Metal droplet deposition forming is the direct forming of metal parts/dies by means of metal droplet deposition/spraying. This molding method has high efficiency and can manufacture large prototypes. However, because metal droplets are used as the basic manufacturing unit, manufacturing flexibility is limited. Vapor deposition molding is proposed by Connecticut University in the United States. It is a molding technology based on the decomposition and precipitation of active gas. It uses the heat or light energy of high energy laser to decompose an active gas, deposit a thin layer of material, and manufacture layer by layer. By changing the composition and temperature of the active gas and the energy of the laser beam, parts of different materials can be deposited, However, the manufacturing speed is relatively slow. Indirect metal products and mold rapid manufacturing process.

At present, the rapid manufacturing processes of indirect metal products and molds can be classified into four categories, namely, precision casting, electroforming, powder metallurgy and droplet spray deposition. The combination of rapid prototyping technology and casting technology is the most direct, lowest cost and best performance rapid prototyping process. The disadvantage of this method is that the dimensional accuracy and surface quality of the forming die are low, the manufacturing cycle is long, and it is difficult to realize the rapid manufacturing of functionally graded materials products and dies. Electroforming. The Queensland University of Technology in Australia has developed the electroforming mold making technology based on the SL process. First, the SL prototype is manufactured, the silica gel mold is reproduced, the nickel metal shell is electroformed, the metal frame is placed, and the aluminum powder reinforced epoxy resin backing shell forms the mold, which can form 0.50.8mm aluminum plates. The advantages are high precision, while the disadvantages are slow forming speed and low mold life. Powder metallurgy forming is a rapid sintering manufacturing process introduced by 3DSystems of the United States and 3DBeltoolDrexel University. These methods need to reproduce the silica gel mold to obtain the green blank of the mold, remove the binder through sintering to obtain the mold blank with internal loose structure (30% porosity), and finally increase the density and mechanical strength of the material through copper infiltration, and ensure the precision of the mold through machining, Its disadvantage is that it needs high temperature sintering and the process is complex. Metal deposition forming includes spray molding method, direct spray stainless steel powder deposition molding method, and rapid manufacturing method based on arc spraying deposition. The current metal direct rapid prototyping method has the disadvantages of low precision and poor material performance, especially the difficulty of molten metal deposition determines that it is difficult to quickly commercialize. However, metal indirect rapid manufacturing technology is difficult to produce high precision and good surface quality molds due to the need for process conversion, long cycle and precision loss. However, there is a huge market for rapid manufacturing of metal parts/molds, and the products are required to have a rapid response to the market. For these reasons, rapid prototyping technology is still developing. A direct metal rapid prototyping method based on ultrasonic welding is proposed, which can directly realize solid molding without using any adhesive, overcome the disadvantages of phase change, thermal expansion, shrinkage and other defects of molding materials, and can directly manufacture large workpieces and molds. It is a new precision, efficient and low-cost rapid prototyping method.

Rapid prototyping mechanism based on ultrasonic welding Ultrasonic welding principle Ultrasonic welding is a special welding method that uses the mechanical vibration energy of ultrasonic frequency (>16kHz) to connect the same or different metals, semiconductors, plastics and cermets. In metal ultrasonic welding, neither current nor high temperature heat source is transmitted to the workpiece, but elastic vibration energy is transformed into friction work, deformation energy and subsequent limited temperature rise between workpieces under static pressure. Metallurgical bonding between joints is realized without melting of base metal, so it is a solid state welding. The working principle of ultrasonic welding is shown in.

The frequency conversion ultrasonic generator converts the power frequency current into the oscillating current of ultrasonic frequency (1516kHz). The vibration direction contraction effect of the sound pole in the vibration direction of the amplifier converts electromagnetic energy into elastic mechanical vibration energy. The amplifier is used to amplify the amplitude and is coupled to the workpiece through a coupling rod and an upper acoustic pole. Here, the natural frequencies of the transducer, amplifier, coupling rod and upper acoustic pole will be designed as the same frequency. When the oscillating current frequency of the variable frequency ultrasonic generator is consistent with the natural frequency of the transducer, amplifier, coupling rod and upper acoustic pole, the system will generate resonance, thus outputting elastic vibration energy to the workpiece under static pressure F. The thin workpieces are bonded together. The advantage of ultrasonic welding sheet is that it can be used for welding a variety of metal, non-metal and various combination materials. It is a low-cost processing method, without using some consumables, such as expensive solder, solder oil or hard soldering. The energy consumption is small. Compared with resistance spot welding, the power consumption is only about 5% of resistance spot welding. Its weldment deformation is small, generally not more than 3% 5%, and the requirements for the cleanliness of the workpiece surface are not high. The welding is fast, and the general welding time is within 0.5s. It belongs to low temperature operation, and the temperature of ultrasonic welding spot will not diffuse, which will not cause high temperature of weldment. In view of these advantages, ultrasonic welding is used as the Z-direction (vertical direction) sheet connection method in this forming method.

Rapid prototyping mechanism This rapid prototyping method uses thin sheet metal or strip with a thickness of 0.11.5mm. The surface of the material does not need to be coated with any adhesive. During processing, it is carried out layer by layer. First, ultrasonic welding is used. The combination between layers realizes solid connection. After each layer is welded, according to the data information of CAD graphics in the computer, the tool is driven to perform plane processing, and then new layers are stacked for processing, Until the completion of the mold or parts manufacturing, thereby realizing a new precision, efficient and low-cost processing and forming technology. The device diagram of the rapid manufacturing method is based on the schematic diagram of the rapid manufacturing method system of the mold or product of ultrasonic welding. The specific processing method is as follows: each layer is first welded by ultrasonic welding, and then the cutter plane cutting is completed. After that, the worktable drives the formed workpiece down and separates it from the strip sheet (strip); The feeding mechanism rotates the receiving shaft and the feeding shaft to drive the material belt to move, so that the new layer moves to the processing area; The worktable rises to the processing plane; Use the hot pressing roller to hot press the new layer and the parts on the workbench to preheat the workpiece; The number of layers of the workpiece is increased by one layer, and the height is increased by one material thickness; Then weld the new layer on the new layer and cut the profile of the new layer according to the data information. This is repeated until all sections of the part are welded and cut to obtain a solid die or part manufactured in layers. Flow chart of its rapid manufacturing process.