The hottest laser rapid prototyping technology and

2022-07-25
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Laser rapid prototyping technology and its application in product design

I. The importance of model in product design

engineering design is a kind of thinking activity and "a rigorous pre conception of the creativity of technical products" [1]

the design process is a process in which the designed object changes from uncertainty to certainty with the designer's thinking activities

on the one hand, this process means opportunities for technological innovation. The technical content, technical performance, manufacturing cost and marketing income of a product largely depend on the design

on the other hand, this process means a kind of risk: the risk of detours, the risk of going wrong, and even the risk of failure. The higher the complexity of the product, the greater the risk. Designers can not ignore this risk in the design process, and often give up innovation in order to avoid the risk. How can we make full use of the opportunity of innovation, improve the design quality, reduce the design cost, minimize the risk and improve the first-time success rate of product development? In addition, the fierce market competition also requires that the design and development work be completed in the shortest period and the response speed to the market demand be improved. Therefore, it is necessary to study the characteristics and laws of engineering design, which is the thinking activity itself, so the design methodology was born

according to the point of view of design methodology, the thinking activity of engineering design has both internal and external characteristics. The so-called "internal" means that thinking is carried out in the designer's brain, and everyone has different ideas and thinking methods, which are invisible to outsiders; The so-called "externality" means that the designer's thinking process and thinking results should be recorded and expressed in a certain form, and communicate with others (other designers, manufacturers and users). Although this kind of thinking process and thinking results can be expressed in the form of language, they are more expressed through models in Engineering design. Schematic diagrams and sketches are models, drawings and calculations are models, cardboard models, wood models and clay models are models, calculation models, CAD models and finite element models in the computer are models, and the manufactured prototype is also a model. Therefore, the "model" here is generalized, which includes all the contents expressed in sketch, drawing, model and prototyping in English words. At different stages of the transformation of the designed object from uncertainty to certainty with the engineering design process, these models play different but important roles that can not be ignored. Especially with the improvement of the complexity of the designed object and the implementation of concurrent engineering aimed at improving the design efficiency, shortening the design cycle and improving the first-time success rate, the requirements for models in the early stage of the design process become more and more urgent

3D CAD model can effectively meet this demand. With three-dimensional CAD model, we can analyze the structure and performance, simulate the assembly, render the appearance modeling, and even operate and use in the virtual reality environment. Virtual design and virtual manufacturing have injected new research contents into design methodology

however, the emergence of virtual models in computers does not and cannot completely replace other models, especially those with three-dimensional solid forms. For example:

in product modeling design, we should not only examine the shape and color effect of the product, but also its hand feeling

in the design of aviation and spacecraft, the "wind tunnel" test of aerodynamics has not been abandoned due to the adoption of 3D CAD. Similarly, the "collision" test of structural safety cannot be omitted in the development of any new vehicle model in the automotive industry

although there is a very detailed military map, the "sand table" is still indispensable in the command of large-scale campaigns

all this is because:

1 After all, the computer model can not provide all the information of the product (such as feel)

2. Computer models can only simulate the environmental conditions we know

3. The solid model in 3D space is more "realistic" and "touchable" than the model on 2D screen.

4 The computer model itself needs to be validated

therefore, while vigorously studying and applying virtual design and virtual manufacturing based on 3D CAD, we should actively study and adopt rapid prototyping technology, which is also generated and developed on the basis of 3D CAD

II. Principle and characteristics of laser rapid prototyping technology she said that

someone once told a sculpture master (Michelangelo/Rodin?) After consulting the secret of sculpture, the master replied, "leave what you need and get rid of what you don't want", which disappointed the inquirer. In fact, what the master said is the true meaning of sculpture technology - material division. Most of the traditional industrial forming technologies also follow this method, such as turning, milling, drilling, grinding, planing; Others are formed with moulds, such as casting and stamping. However, laser rapid prototyping (LRF) is based on a new forming principle - layered processing and superposition forming. For those who have studied advanced mathematics, this principle is no stranger. In the application of definite integral, it has been mentioned that the volume calculation of a rotating body whose generatrix is a known curve and the volume calculation of a three-dimensional body whose parallel section is known. Both of them take the section with a thickness of △ Xi, approximately regard it as a flat cylinder or a curved cylinder, and then add it:

when ‖ △ x ‖ → o, the volume of a rotating body or a three-dimensional body whose parallel section is known will be obtained respectively

the landform is composed of complex curved surfaces. However, as long as we map the contour lines of different heights, we can cut curved edge planes of different sizes and shapes on the flat plate (of course, the height difference between the plate thickness and the two adjacent contour lines should conform to the scale of the topographic map), and then stack them. As long as the contour lines are dense enough, we can make a realistic terrain model

at present, there are many kinds of laser rapid prototyping machines developed according to this layered processing and superposition forming principle. Here, the main ones are selected for a brief introduction:

1. Selective solidification of liquid photosensitive polymer (sla:streolithographyparatus stereolithography equipment)

, In 1986, another U.S. patent proposed the rapid prototyping scheme of using laser to irradiate liquid photosensitive resin to make three-dimensional entities. Based on this, 3dsystems company of the United States produced the first bio based polyurethane rigid foam energy-saving thermal insulation material series sla-250 with laser rapid prototyping and its various quality indexes reaching the level of petrochemical products in 1988

the configuration material used in this laser rapid prototyping machine is a liquid photosensitive polymer, which will undergo polymerization and curing reaction under the irradiation of ultraviolet light, and change from liquid to solid

its advantage is that it can directly obtain resin parts similar to plastics, and the surface roughness is small

its disadvantages are:

(1) the chemical and physical changes in the forming process make it difficult to guarantee the dimensional accuracy, and creep will occur

(2) the whole section must be scanned and cured. The forming time is long, and further curing treatment is required after forming

(3) since the part not irradiated by the laser beam is still liquid, the support shall be designed in advance for the overhang part, and then removed after curing

(4) after curing, the photosensitive resin is brittle, easy to fracture, poor processability, the working temperature cannot exceed 100 ℃, it will absorb moisture and expand, the corrosion resistance is not strong, and the price is expensive (/kg)

(5) the service life of the laser tube producing UV laser is about 2000 hours

2. Selective cutting of thin materials (lom:laminatedbjeetanufacturing layered object manufacturing)

the configuration material used in laser rapid prototyping is paper coated with hot melt adhesive in advance, and its forming process is similar to the process of making terrain model described above

its advantages are:

(1) high dimensional accuracy

(2) only the contour line needs to be cut, and the manufacturing efficiency is high

(3) no design support is required

(4) the sample made has the hardness similar to that of wood products, which can be used in the environment below 200 ℃ after a little treatment, and can be subject to certain cutting processing

(5) the service life of the CO2 laser used is up to 20000 hours

(6) the configuration material is cheap (8 /kg)

its disadvantages are:

(1) plastic parts cannot be directly made

(2) the surface roughness is high, and there are obvious step lines on the workpiece surface, which should be polished after forming

(3) it is easy to absorb moisture and expand, and the surface shall be moisture-proof treated as soon as possible after forming

(4) the workpiece lacks elasticity

3. FDM (fusedepositionmodeling)

the configuration material used by this rapid prototyping machine is filiform thermoplastic material, and its working principle is similar to the production of logo cake. The filiform material is sent to the nozzle by the wire supply mechanism, heated to the molten state in the nozzle, coated on the workbench according to the cross-sectional shape, and quickly cooled and solidified. After one layer is completed, the nozzle rises one layer high, Then apply the next layer

its advantages are:

(1) it can directly make ABS plastic

(2) high dimensional accuracy

(3) high material utilization

its disadvantages are:

(1) the surface roughness is high and needs post-treatment

(2) long forming time

(3) expensive materials (/kg)

(4) support shall be set at the cantilever structure, but the new FDM rapid prototyping machine is equipped with two nozzles, one spraying forming material and the other spraying supporting material, and the supporting material can be removed by water solution, which reduces the post-treatment time

4. SLS: selectedaserintering (selective laser sintering)

the working principle of this rapid prototyping machine is similar to SLA, but the forming material used is not a liquid photosensitive resin, but a mixture of powdered polymer materials, metals or ceramics and adhesives. The diameter of the powder is μ M. when forming, a layer of powder material is first laid on the workbench and heated to a temperature slightly lower than the melting temperature, Then the laser beam is scanned according to the cross-section shape, and some of the scanned materials are melted and bonded to form. The non scanned powder materials are still powder particles as the support of the workpiece. After the forming of one layer is completed, the workbench drops one layer high, and then the next layer is paved and sintered: [hj]

its advantages are:

(1) plastic, ceramic or metal parts can be directly obtained, with good machinability

(2) no design support is required

its disadvantages are:

(1) the structure of the formed part is loose and porous, and the surface roughness is high

(2) low forming efficiency

(3) the obtained plastic, ceramic or metal parts are far inferior to those of similar materials obtained by traditional forming methods, which need post-treatment such as copper infiltration, but it is difficult to ensure the dimensional accuracy of the parts in the post-treatment

through the introduction of the above four rapid prototyping machines, we can see that the laser rapid prototyping technology is the integration of a variety of advanced manufacturing technologies

because different rapid prototyping machines have different characteristics, they should be properly selected according to different use requirements. In the selection, the size of the formed parts, the accuracy requirements of the formed parts, the purpose of the formed parts, the shape of the formed parts, and

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