In the 21st century, mankind has entered an era of rapid development of the knowledge economy. Traditional manufacturing techniques and modes of production are undergoing a qualitative leap, and advanced manufacturing technologies are gradually being applied in the manufacturing industry, driving the development of the industry.
In recent years, the advanced manufacturing technologies that have gradually been applied include rapid prototyping, virtual manufacturing technology, flexible manufacturing units and flexible manufacturing systems, etc.
1. Rapid Prototyping
With the diversification of demand and the shortening of product life cycles, resulting in the reduction of the batch size of parts and products and the shortening of delivery times, to adapt to this change in the market, a new and advanced concept of part prototyping technology was developed overseas in the late 1980s based on the full development of CAD/CAM, data processing, CNC, and laser sensing technology- rapid prototyping, also known as “layer manufacturing” technology.
Rapid prototyping (also known as rapid forming) is, along with virtual manufacturing technology, referred to as the two pillars of the future manufacturing industry.
(1) Basic Principle of Rapid Prototyping
Rapid prototyping is a system technology that integrates CAD technology, numerical control technology, laser processing technology and material technology to achieve the integration of part design and three-dimensional entity prototype manufacturing.
It uses the principle of software discretization and material stacking to achieve the forming of parts. The rapid prototyping manufacturing principle is shown in Figure 1-9.
The specific process is as follows:
1. Use CAD software to design the three-dimensional surface or solid model of the part, or if there is already a part, obtain the three-dimensional contour data from the part sample scan.
2. According to the process requirements, divide the generated CAD model into sections along a certain coordinate direction (such as Z direction) with a certain thickness. The thickness of each layer can be 0.05-0.5mm, generally around 0.1mm to ensure that the prototype is smooth enough and fast enough.
3. Process the layer information according to the process requirements, select the processing parameters, and the system will automatically generate the tool movement trajectory and NC processing code.
4. Simulate the processing process to confirm the correctness of the NC code.
5. Use the NC device to accurately control the movement of the laser beam or other tools, and process the appropriate cross-sectional shape on the current working layer (two-dimensional) by scanning the contour.
6. Lay a new layer of forming material and process it again until the entire part is processed.
It can be seen that the rapid prototyping process is a work process from three-dimensional to two-dimensional (software discretization) and then from two-dimensional to three-dimensional (material stacking).
Rapid prototyping can not only be used for rapid generation of parts in original design, but also for rapid replication of physical objects (including enlargement, reduction, modification).
(2) Main Process Methods of Rapid Prototype Technology
Stereolithography Light-cured Forming Method (LSL Method)
LSL method is a rapid forming method characterized by using various resins as forming materials and helium-cadmium lasers as energy sources, and using resin heating for solidification.
Physical Layer-by-layer Manufacturing Method (LOM Method)
LOM method uses sheet materials (such as film, plastic film or composite materials) as materials, uses CO2 lasers as energy sources, uses laser beams to cut the edge of the sheet to form the outline of a certain layer, and uses heating and pressure methods to bond each layer. The method has a wide range of materials and low cost.
Selective Laser Sintering Method (SLS Method)
SLS method uses various powders (such as metal, ceramics, wax powder and plastic) as materials, uses roller laying, uses CO2 high-power lasers to heat the powder until it is sintered into a block, and can process metal parts that can be used directly.
Fused Deposition Modeling Method (FDM Method)
FDM method uses wax wire as raw material, uses electrical heating to melt the wax wire into wax liquid, and sprays the wax liquid to a designated position to fix it, and processes parts layer by layer. The method has low pollution and materials can be recycled.
(3) Characteristics of Rapid Prototype Technology
The characteristics of rapid prototype technology are as follows:
• Suitable for processing complex, irregular parts.
• Reduce the requirements for skilled workers.
• There is little or no waste, it is an environmentally friendly manufacturing technology.
• Successfully solves the problem of “visible but untouchable” three-dimensional modeling in CAD.
• The system is flexible and can generate different shaped parts by simply modifying the CAD model.
• Technology integration, design and manufacturing integration.
• Wide range of material adaptability.
• No special fixtures and molds are required, shortening the trial time of new products.
Therefore, rapid prototype technology is mainly suitable for new product development, rapid single and small batch parts manufacturing, complex shaped parts manufacturing, mold design and manufacturing, and processing of difficult-to-process material parts.
2. Virtual Manufacturing Technology
Virtual manufacturing technology is based on computer-supported simulation technology and virtual reality technology, and models the entire generation and operation activities of the enterprise. It “virtually” designs products on the computer.
This technology can realize the entire enterprise functions, including processing and manufacturing, plan making, generation scheduling, operation management, cost and financial management, quality management, and even marketing, and then physically operate the enterprise based on the optimal operating parameters obtained.
Virtual manufacturing includes simulation of the design process and simulation of the processing process. In essence, virtual manufacturing is an extension of general simulation technology and is the highest stage of simulation technology.
The key to virtual manufacturing is the modeling technology of the system, which maps the real physical system into a virtual physical system under the computer environment, and builds a virtual information system with real information system. The virtual manufacturing system does not consume energy and other resources (except for computer power consumption), the processes are virtual processes, and the products are visible virtual products or digital products.
The system architecture of the virtual manufacturing system is shown in Figure 1-10.
The architecture of virtual manufacturing system is shown in Figure 1-10.
As shown in Figures 1-10, through the use of system modeling tools, the physical and informational systems of the real world are first mapped to virtual physical and informational systems within a computer environment.
Then, simulation machines and virtual reality systems are utilized to simulate the design process and results, as well as the process of fabrication and the operation status of the enterprise. The final product is a high-quality digital product that meets user requirements and the best parameters for the operation of the enterprise.
The best parameters are used to adjust the operation process of the enterprise to ensure that it is always in the best operating state, and finally produces high-quality physical products for market release.
3. Flexible Manufacturing System (FMS)
In China’s relevant standards, FMS (Flexible Manufacturing System) is defined as: a flexible manufacturing system is an automated manufacturing system composed of CNC processing equipment, logistics storage and transportation facilities, and computer control systems.
It includes multiple flexible manufacturing units that can quickly adjust according to the completion of the manufacturing task or changes in the production environment and is suitable for multi-variety, medium and small batch production.
Foreign experts have provided a more intuitive definition of FMS: a flexible manufacturing system is a manufacturing system composed of at least two machine tools, a logistics storage and transportation system (with automation from loading to unloading), and a computer control system.
It can manufacture any of the various parts by simply changing the software.
FMS is generally composed of processing systems, logistics systems, information flow systems, and auxiliary systems.
(1) Processing system
The function of the processing system is to automatically process various workpieces in any order and to automatically change the tools and cutting tools. It is mainly composed of CNC machine tools and machining centers.
(2) Logistics system
Logistics is a general term for the flow of materials in FMS. The materials flowing in FMS mainly include workpieces, tools, fixtures, chips, and cutting fluid.
The logistics system is a system that implements the automatic recognition, storage, allocation, transportation, exchange, and management of these materials from the import of FMS to the export.
It includes automatic transport vehicles, three-dimensional warehouses, and central tool libraries, mainly for the storage and transportation of tools and workpieces.
(3) Information flow system
The information flow system is a system that controls, coordinates, schedules, monitors, and manages the processing process and material flow process of FMS. It is composed of computers, industrial control machines, programmable controllers, communication networks, databases, and corresponding control and management software, and is the neural center and lifeblood of FMS and the link between the various subsystems.
(4) Auxiliary system
The auxiliary system includes cleaning workstations, inspection workstations, chip removal equipment, and deburring equipment, among others.
These workstations and equipment coordinate with the processing system and logistics system under the control of the FMS controller to achieve the functions of FMS.
FMS is suitable for parts with moderate complexity in shape, precision, and batch. Because all equipment in FMS is controlled by a computer, changing the workpiece only requires changing the control program, making the system very flexible, especially suitable for the dynamic market demand.
4. Flexible Manufacturing Cell (Fmc)
A flexible manufacturing cell can be considered a small-scale FMS and typically includes one or two machining centers, combined with a tray library, an automatic tray exchange device, and a small tool library, capable of handling parts with moderate complexity.
Because FMC has a lower level of complexity, smaller scale, lower investment, and reliable operation compared to FMS, and is also easy to connect and expand the functionality of FMS, FMC is a developing direction for FMS and a promising form of automation.