CN110978455A

CN110978455A - Double-screw type material extrusion device for 3D printing

Info

Publication number: CN110978455A
Application number: CN201911158971.8A
Authority: CN
Inventors: 陈祺睿
Original assignee: Individual
Current assignee: Individual
Priority date: 2019-11-22
Filing date: 2019-11-22
Publication date: 2020-04-10

Abstract

The embodiment of the invention discloses a double-screw type material extrusion device for 3D printing, and relates to the technical field of additive manufacturing. The driving screw and the driven screw are arranged in the melting shell and are meshed with each other, the two screws are connected through a synchronous transmission mechanism, and a thrust transmission mechanism is arranged between adjacent thrust bearings on the driving screw and the driven screw. The innovative extrusion mode that has used the twin-screw structure has improved holistic integrated level, makes the twin-screw structure extruder realize lightweight, large-traffic, high accuracy, makes it can be applied to the 3D printer, has improved control accuracy and real-time, satisfies the large-scale FDM3D printing technology of efficient and needs. The thrust is transmitted by the thrust transmission mechanism, so that the thrust of the screw is respectively and uniformly loaded on each thrust bearing, the thrust is dispersed, the total thrust is improved by several times, the extrusion device can bear huge reverse thrust generated by the high-pressure large-flow screw, and the high integration of the double-screw extruder is realized.

Description

Double-screw type material extrusion device for 3D printing

Technical Field

The embodiment of the invention relates to the technical field of additive manufacturing, in particular to a double-screw material extrusion device for 3D printing.

Background

Technical background of the manufacturing industry of large products: all products serve human life and production, the size of adults is generally one meter to two meters, the size of the products below one meter can be defined as small size, one meter to two meters are medium size, and the size of more than two meters is defined as large size by human scale.

In basic principle, the current industrial manufacturing method of the real object only has three process modes, namely material reduction manufacturing, equal material manufacturing and material addition manufacturing.

Reducing material manufacturing: in the age of stone products, the desired part is obtained by knocking a stone with another stone and subtracting the redundant part, and the finished product is formed by cutting a whole material with a cutter of a modern machine tool to obtain a part of the material. The material reduction manufacturing needs to prepare a piece of material larger than the finished product firstly, and then remove ten to ninety percent of the material, when the size of the finished product is small, the shape is simple, the absolute quantity of the removed and wasted material is not too large, when the size of the finished product is large, and when the size of the finished product is complex, the waste is very large, labor and time are wasted, the interference of the cutter is serious when the material is removed, and the cutter has inaccessible parts due to the obstruction of the three-dimensional structure of the finished product. The complexity is limited. But because the processing is carried out at the normal temperature of the solidified material of the substance, no substance phase change exists before and after the processing, and a more accurate finished product can be obtained. The disadvantages are as follows: waste of material, moderate efficiency, tool interference, and is particularly severe in large scale and complex structures. The advantages are that: the deformation at normal temperature is small, the stress is small, and the accuracy is high.

And (3) material preparation: from pottery to bronze era, fluid or liquid is injected into a mould, and a finished product with the volume equal to that of a mould cavity is obtained after cooling or sintering, and the finished product belongs to the class-material manufacturing from modern various injection molding and casting processes. The total volume of the mould is more than six times of that of the product, when the product enters a medium-large size, the volume weight cost of the mould is increased sharply, and meanwhile, the mould interference exists even though the material is not removed in the equal-material manufacturing process, and the part which can not be separated and demoulded is blocked by the three-dimensional structure of the finished product. Therefore, if a complex finished product is to be produced, the product is designed to be split into a plurality of unnecessary parts which are respectively machined and then assembled. And the manufacturing of the materials requires that the mold is prepared firstly, the early investment is high, but the high batch production efficiency can be obtained. But also saves raw materials. The disadvantages are as follows: the method has the advantages of high input threshold, long process period, large temperature change, phase change, large stress, large deformation, low overall precision and serious large-scale and complicated structure. The advantages are that: the mass production efficiency is high.

Additive manufacturing: electroplating, surfacing and spraying belong to additive manufacturing, but are generally not suitable for manufacturing of whole parts, and are generally used for repairing or other auxiliary processes, and an overall additive manufacturing process, such as 3D printing, is only recently performed, and a finished product is built by adding materials layer by layer. The core principle of 3D printing, which is one of the main technologies of additive manufacturing, is dimension reduction, the printing process is performed on a 2-dimensional surface, the 3-dimensional spatial interference problem does not exist, a complex 3-dimensional model is decomposed into a plurality of 2-dimensional sheet-like layers by special software, and the layers have thicknesses, but are thinner in the thickness direction relative to the whole body and can be approximately considered as 2-dimensional. The most important advantage is that the mould is directly formed by stacking layer by layer from nothing to nothing without the initial investment cost of the mould and preparing a blank larger than a finished product. And is insensitive to the complex structure of the product, since three dimensions have been reduced to two dimensions. However, as described above, the reduced material and the equal material are both surfaces of the whole material, and the 3D printing is a surface which is cut into the inside of the material and can be printed, and is far larger than the original surface area, so that the efficiency of the 3D printing is much lower than that of the former two methods at the same moving speed. The disadvantages are as follows: the efficiency is very low. Large temperature variation, stress and deformation. This is particularly true in the case of large products. The advantages are that: the complexity limit is very small, the internal and external integrated processing is realized, the material is saved, the early investment is very small, and the process period is short.

The prior art background that the 3D printing process is large-scale: with the economic development and the technical progress, particularly the development of the computer technology information technology in recent times, products are more and more complex, the variety is more and more, the batch of single products is less and less, the defects of material reduction and equal material manufacturing are more and more obvious, and particularly in the field of complex and light-weight products. 3D printing in this case has a principal advantage for complex products. Meanwhile, blanks larger than finished products are not required to be prepared, and materials are saved. And a mold is not required to be prepared in advance, so that the fixed investment is saved. The advantages emerge gradually, while the inefficient defects do not differ too much in absolute terms in efficiency at small sizes due to the smaller cardinality.

However, any 3D printing process is a comprehensive system of multiple technologies, and after the molding size is increased, the complementary technology cannot be matched with the molding size, and the size above meter level and the size at decimeter level are 10 times in size, but the cubic meter is 1000 times of the cubic decimeter by calculating the effective molding volume, so that the volume of the material to be processed by the printing equipment in the same time theoretically needs to be improved by nearly thousand times, and if reasonable efficiency is to be kept, the improvement is obviously not possible by a simple amplification structure.

Therefore, most of the existing 3D printing technology doors are only suitable for small products, namely, the size level from decimeter to meter, and even if the size of the 3D printing technology doors is barely reached, the printing is realized by adopting thin walls, low-density filling and other modes of sacrificing mechanical properties, the actual effective printing volume is very small, the environmental space size of human life is matched with the size of human body 1-2 meters, such as houses, furniture, automobiles, ships and the like, the internal space is a multiple relation of the human body size, and if the size of the 3D printing technology doors cannot reach the size of the meter used in daily life, the product size designed according to the height of people cannot enter the high-value mainstream market.

The following will briefly describe the reason principle that the currently mainstream SLA/DLP, SLS and FDM3D printing processes can not produce large-size products efficiently.

1. SLA/DLP is a 3D printing technique using a light-curing (hardening) resin as a raw material, and is different from DLP in the way of using light. SLA uses UV light beam to scan photocuring resin and obtains the shape of printing the layer, can regard as the process of point to line, line to face shaping gradually, and DLP uses the projection principle of similar projecting apparatus, throw the required light of a printing layer and solidify the resin, compare SLA technique and has skipped the process of point to line, line to face, DLP is more faster than SLA on the individual layer shaping speed, DLP has also got rid of the required high-precision optics deflection mirror system of SLA, therefore DLP's cost is lower, at present mass market mostly adopts DLP's technology to do photocuring 3D and prints.

The DLP technology is difficult to realize large-scale, because the projection resolution adopted by the DLP technology is limited (usually 1920 x 1080), the projection resolution is about 0.1mm when the DLP technology is used in a decimetric scale, after the DLP technology is large-scale, the volume is enlarged by 1000 times, the area of a single layer is enlarged by 100 times, in order to keep the size of the single pixel to be 0.1mm, the total pixel quantity of the DLP is also enlarged by 100 times, namely the resolution is required to reach 19200 x 10800, otherwise, the edge of a forming layer is provided with sawteeth (similar to sawteeth after picture enlargement), and the prior art cannot achieve the extremely high resolution. Even if high precision is not required, efficiency is difficult to improve in the case of large size, a photo-curing resin material used in the photo-curing technology must be cured by reaction of light, the thickness of each layer cannot be too thick in order to ensure sufficient curing of the resin material, otherwise the layer thickness is relatively too thin during molding of a large size object due to a drop in attenuation efficiency of light because of a sharp increase in scattering error of light, resulting in a large total number of layers and a sharp decrease in overall molding efficiency. The light-cured material has high production cost, dark reaction (curing under the condition of no light), is not durable (easy to decompose), has toxicity and insufficient mechanical property after being formed, has limited variety and cost performance due to the fact that the material must have photosensitivity and is difficult to select high-performance engineering resin which is mature and cheap in the market, the price is calculated according to grams, large-scale products have large material consumption and sensitive price, and the weight of objects commonly used by people is 10kg-50kg (such as sofas, chairs, tables and the like), so the light-cured material is not suitable for large-scale production in technical principle, economy and practicability.

2. The SLS process (selective laser sintering), which is a process for mainly manufacturing metal products, uses a high-energy laser beam to scan and process the material powder into extremely fine material powder, so that the material powder heated instantly is melted and bonded, the forming process is similar to SLA, and is a process of gradually forming point-to-line and line-to-surface, and the whole forming process is linear, so that the forming volume is increased, and the forming speed of a single piece is reduced by 3 times. Most of metal or thermoplastic resin can be used in an SLS process after being made into powder, the raw material needs additional powder processing cost which is several times of the raw material cost after being powdered, the powder of the material can cause the surface of an SLS formed product to form powder particles, air is arranged in the powder, the gas escapes during laser welding, the volume is shrunk, the stress is large, and the stress cracking is easy to occur when the size is large. The SLS process allows the material powder to fill the entire molding space, with the unsintered material being the support, so the SLS process can be used without printing a support structure separately, with little waste of powder material.

However, SLS processes require heating of the material powder to a temperature slightly below the melting temperature of the material when printing the product, thereby reducing the required output power of the laser and reducing the internal stresses that result from gradual cooling due to non-monolithic fabrication. After enlargement, the volume is enlarged 1000 times, and the volume is about 12m after enlargement³(2m 3m 2m), it takes tens of tons to fill the whole molding space with the plastic material powder, and even tens of tons to one hundred tons if the metal powder is used, it is necessary to heat the material and keep the temperature to 100 degrees or more. In order to solve the problem of material powder generation after large-scale production, the original mechanical structure design and process of the SLS process become very complicated, the total cost of materials is very high, and the energy consumption is also very large.

The SLS process uses the laser power and is closely related to the forming speed, the maximum power of the SLS process is generally between 0.4kw and 1kw, according to the principle of geometric amplification, the product volume is amplified by 1000 times, theoretically, the maximum power of the SLS process is also amplified by 1000 times correspondingly, otherwise, the SLS process is equivalent to using a tiny light spot to carve a picture which is increased by thousand times, the efficiency is unacceptably low, or the maximum power of a matched laser needs 400kw to 1000kw, according to the current laser technology, the common power is below 6kw, and 400kw can only be realized in the military field, so that the SLS process is difficult to realize at present.

The SLS printing layer height also has a large limitation because the principle is to sinter or melt the powder to form a solid state by using the high temperature generated by the focused laser focal spot, and the heat conduction is spontaneously diffused to the surrounding powder, if a deeper sintering thickness (layer height) is required, the heat diffusion can cause uncontrollable sintered line edges. Therefore, the size of the apparatus is not economically large in technical principle, and is not suitable for practical use.

3. The FDM process (fused deposition modeling), also called fuse deposition, the existing small FDM process mainly uses the thermoplastic plastic wire with the diameter of 1mm-3mm as the printing material, the printing head melts the wire to coat and form the shape of each layer, the technology required by the FDM process is the simplest of all 3D printing process types, except the moving structure, only the wire feeding mechanism and the heating head (printing head) are needed, the FDM process compares the SLS process and the DLP process, the FDM process does not use the expensive material and the expensive technology, the modeling principle is simpler, theoretically, only the printing line with ten times thicker thickness is used, the volume increment can be obtained under the condition that the original moving speed is not changed, the surface precision is sacrificed, but in the large material increase manufacturing field, the precision is not the main problem, on the one hand, the product with large size such as furniture, the requirements for the overall size precision of houses, lamps, decoration ornaments and the like are not high, large products on the two aspects need surface paint coating and other processes, the surface finish is determined by the coating process, the efficiency is the main problem when the size reaches the magnitude of several meters, FDM improves the line width and the layer height by improving the material flow, the forming volume efficiency can be greatly improved, and the FDM process has the possibility of large-scale production.

The small FDM process is a forming mode based on wires, a printing nozzle is coated and formed back and forth, the whole forming process is linear and is a process of gradually forming a body from a point to a line, from the line to a surface and from the surface, the volume is increased in three directions of length, width and height, the diameter of a printing line determines the increment of two directions, the movement speed determines the increment of a third direction, the increments of the three directions all need the equal proportion increment of material flow, and theoretically, the increment is 3 times of the average side length increment of a product, so that the extrusion efficiency of the printing line is greatly improved when the FDM is large.

In this case, the use of the filamentous material is impossible, the typical side length of the forming volume of the existing FDM printer using the filamentous material is about 0.1-1 meter, the typical side length of 1-10 meters is required for large-scale 3D printing and is basically 10 times, the conversion volume is 1000, the diameter of the wire needs to be amplified by 10 times and reaches 10mm-30mm, the wire is not a wire but a rod, the extrusion speed of the material is also amplified by 10 times, and as the diameter of the wire of the material becomes large, the wire becomes difficult to bend, the allowed bending diameter becomes very large, the wire is difficult to bend into a coil, the production is not easy, and additional processing cost is required. And the thermal conductivity of the material is limited, when the diameter of the wire is increased, the area of the outer surface of the wire is increased by a square, the volume is increased by a cube, the melting heating mode of a small machine only heats the outer surface of the wire, the melting efficiency of the wire is seriously reduced, and the heating principle of a printing head of the small machine is not applicable any more. The small-size conventional FDM printer uses crowded material gear and silk material surface meshing roll to produce and extrudes thrust, and after silk material line footpath became thick 10 times, the silk material sectional area enlargies and is close to 100 times, and extrusion speed need improve 10 times simultaneously, and the extrusion resistance of silk material becomes very big, and the intensity of silk material epidermis is difficult to bear the thrust of crowded material gear, leads to the epidermis to burst, and crowded material gear skids the idle running. The feeding mechanism of the small-sized machine and the melting structure of the printing head are not suitable after being enlarged.

In comprehensive analysis, the conventional small FDM process has certain practical value in small products, and the principle of the process can realize large-scale production, but the conventional melt extrusion mechanism can not meet the requirement of large-scale production.

The limitation of large-scale existing 3D printing process is as follows: the FDM technology realizes large-scale operation at a few of domestic and foreign companies to a certain extent, a gantry motion structure (similar to a gantry machining center) is generally adopted, a movable head type (printing head motion) motion structure is adopted, and a movable table type structure commonly used by the gantry machining center is adopted, so that a printing platform and a printing object are moved by the movable table structure, the motion inertia is far larger than the movable head type, and repeated acceleration and deceleration motion in 3D printing is not facilitated. The material melting and extruding mechanism is arranged on a lower probe shaft (Z axis), a single-screw extruder similar to an injection molding machine is generally used as the material melting and extruding mechanism, and granular raw materials are used as raw materials. In order to achieve a certain material extrusion flow rate, the material melting and extruding device arranged at the tail end of a moving structure has large volume and weight, so that the rigidity of a mechanical moving structure for installing and bearing the melting and extruding device must be designed to be strong enough, the inertia of the whole moving structure is large, products to be printed are complex and have local details, a printing head needs more short-distance reciprocating motion, a printing mechanism must be accelerated and decelerated repeatedly, and the moving structure has high motion inertia due to the weight of an extruder and the mechanism, so that the average acceleration is low, the average motion speed is low, the energy consumption is high, the printing quality is reduced, and the mechanical abrasion is accelerated. On the contrary, the weight of the extrusion device is reduced, the whole motion structure is lightened, the lighter melting extruder causes the material extrusion efficiency to be low, the extrusion flow is insufficient, and the flow and the weight are contradictory in structural design. Although the framework realizes the large-scale FDM process size, the movement speed and the discharge flow rate cannot be simultaneously improved, and the overall printing efficiency is still not high.

In the prior art devices capable of extruding 10kg of material per hour, which have a self weight of about 100 and 200 kg, i.e. a flow to weight ratio of less than 1, of about 0.1 to 0.05, the average movement speed can only reach 4000 mm/min, and thus the printing efficiency is low. Therefore, various performances of the melt extrusion device basically determine the system performance of the whole 3D printer, and directly influence the comprehensive forming efficiency of large FMD3D printing.

Large FDM printers typically use a single screw extruder in the plastics industry, and a brief analysis of the use of existing screw extruders in large FDM3D printing follows.

The single-screw extruder is simple in structure and easy to install and use, the high-performance double-screw extruder is complex in structure and large in size, printing speed can be increased only by light weight requirements of large-scale 3D printing, and therefore the single-screw extruder is difficult to be used for large-scale 3D printing, and the single-screw extruder is widely adopted and researched in the large-scale FDM3D printing industry at present. No case or literature has been found for large 3D printers using twin screw extruders.

The existing conical counter-rotating twin-screw extruder is very large in structure, except for necessary structures such as twin screws, machine barrels and heating sleeves, a thrust bearing device, a transmission system, a twin-screw synchronous mechanism, a driving and speed reducing mechanism, a base and the like have large volume and weight, and the existing conical counter-rotating twin-screw extruder is very not beneficial to high-mobility operation in a 3D printing process.

In addition, in the process of large-scale 3D printing, the movement and flow control are uniformly controlled by a master control system, the flow of the printing head must strictly correspond to the movement track and speed of the printing head according to the command of the master control, when the printing head moves at a variable speed, the change rate of the flow is strictly synchronous according to the command of the master control and the change rate of the movement speed, and the response speed of the printing flow which is instantaneously changed along with the master control command has a high requirement, otherwise, the line width and the line height of the printing line are out of control (larger or smaller), and the deviation is generated with the set value of the program command in the master control system. Moreover, for a printing scene which moves at a constant speed but continuously changes the line width and the line height, even a printing scene which moves at a variable speed and changes the line width and the line height, the requirements on the accuracy of flow control and real-time response are higher. In summary, even if the deviation is weak, according to the principle of 3D printing, the final accumulated error will be increased, which will cause a great influence on the appearance of the printed product, and even cause printing failure. Accurate flow control must therefore be achieved in large FDM3D printing processes. The existing conical counter-rotating double-screw extruder has a long transmission chain and is difficult to realize accurate transmission.

In summary, the existing conical counter-rotating twin-screw extruder has the important defects of too large volume and weight, too long transmission chain and the like, and certainly, the existing conical counter-rotating twin-screw extruder cannot be independently used for a 3D printing system because the hot melt material, besides the driving force of the extruder, also has the pressure generated by thermal expansion which is not controlled by the extruder, and also needs to be opened and closed at the tail end and controlled in a throttling way, and needs to be improved aiming at the characteristics of the 3D printing process. In order to realize an efficient large-scale FDM printing process, the following requirements must be satisfied simultaneously: the device has the advantages of small volume and weight, high-pressure and high-flow extrusion, high-precision tail end flow control, real-time flow change following instructions and good material plasticizing and exhausting effects.

Obviously, the existing extrusion equipment in the plastic industry or the existing extrusion mechanism in the 3D printing industry cannot manufacture large products.

Disclosure of Invention

Therefore, the embodiment of the invention provides a double-screw type material extrusion device for 3D printing, which is used for solving the problem of additive manufacturing of large-scale products, can simultaneously meet the requirements of small volume, light weight, high-pressure large-flow extrusion and high-precision flow control, and meets the requirements of a high-speed large-flow large-size FDM printing process.

In order to achieve the above object, the embodiments of the present invention provide the following technical solutions:

according to the first aspect of the embodiment of the invention, the double-screw type material extrusion device for 3D printing comprises a melting shell, a synchronous box shell, a driving screw, a driven screw and a melting heater, wherein the driving screw and the driven screw are arranged in the melting shell and are meshed with each other, the driving screw and the driven screw extend into the synchronous box shell and are connected through a synchronous transmission mechanism, the driving screw is connected with a melting extrusion power source through a speed reducer, the melting heater is arranged on the outer side of the melting shell, a printing nozzle and a raw material inlet are respectively arranged at two ends of the melting shell, a bearing sleeved at the end part of the driving screw and the driven screw is arranged in the synchronous box shell, the bearing comprises a thrust bearing and a radial bearing, a plurality of thrust bearings are mutually overlapped along the axial direction of the driving screw and the driven screw, a thrust transmission mechanism is arranged between adjacent thrust bearings, and a thrust transmission mechanism is also arranged between adjacent thrust bearings on the driven screw rod.

Furthermore, the driving screw and the driven screw are both conical screws.

Further, the synchronous transmission mechanism enables the driving screw rod and the driven screw rod to rotate in different directions.

Furthermore, the synchronous transmission mechanism comprises a driving gear and a driven gear which are meshed with each other, the driving gear is fixed on a screw shaft of the driving screw, and the driven gear is fixed on a screw shaft of the driven screw.

Furthermore, the thrust transmission mechanism comprises a thrust transmission inner diameter top ring and a thrust transmission outer diameter top ring, the thrust transmission inner diameter top ring is arranged between the thrust shaft rings of the two adjacent thrust bearings, and the thrust transmission outer diameter top ring is arranged between the thrust race rings of the two adjacent thrust bearings.

Further, the synchronous box shell is fixed at the upper end of the melting shell, and the printing nozzle is arranged at the lower end of the melting shell.

Furthermore, the melt extrusion power source is a servo motor.

The embodiment of the invention has the following advantages:

the embodiment of the invention innovatively adopts an extrusion mode of a double-screw structure, improves a synchronous structure and a thrust supporting structure of the double screws, integrates the double screws, improves the integral integration level, realizes light weight, large flow and high precision of the double-screw structure extruder, can be applied to a 3D printer, improves the control precision and real-time property, and meets the requirement of a high-efficiency large FDM3D printing process. The thrust is transmitted by the thrust transmission mechanism, so that the thrust of the screw is respectively and uniformly loaded on each thrust bearing, the thrust is dispersed, the total thrust is improved by several times, the extrusion device can bear huge reverse thrust generated by the high-pressure large-flow screw, the high integration of the double-screw extruder is realized, and the application to the field of 3D printing becomes possible.

The embodiment of the invention takes the servo drive as an accurate drive mode, further improves the integration level, reduces the weight and improves the maneuverability.

Further detailed effects and principle explanations are explained in the examples section.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are merely exemplary, and that other embodiments can be derived from the drawings provided by those of ordinary skill in the art without inventive effort.

The structures, ratios, sizes, and the like shown in the present specification are only used for matching with the contents disclosed in the specification, so that those skilled in the art can understand and read the present invention, and do not limit the conditions for implementing the present invention, so that the present invention has no technical significance, and any structural modifications, changes in the ratio relationship, or adjustments of the sizes, without affecting the functions and purposes of the present invention, should still fall within the scope of the present invention.

Fig. 1 is a schematic view of a twin-screw type material extrusion apparatus for 3D printing according to embodiment 1 of the present invention;

FIG. 2 is an enlarged view of a portion A of FIG. 1;

FIG. 3 is a schematic diagram of practical application of embodiment 1 of the present invention;

FIG. 4 is a schematic diagram of practical application of embodiment 2 of the present invention;

FIG. 5 is a partial enlarged view of the portion B in FIG. 4;

in the figure: 1-servo motor 2-speed reducer 3-synchronous box shell 4-driving gear 5-driven gear 6-radial bearing 7-thrust bearing 8-driving screw 9-driven screw 10-melting shell 11-raw material inlet 12-melting heater 13-printing nozzle 14-thrust transmission inner diameter top ring 15-thrust transmission outer diameter top ring 16-raw material bin 17-industrial robot 18-frame machine tool 19-feeding pipe.

Detailed Description

The present invention is described in terms of particular embodiments, other advantages and features of the invention will become apparent to those skilled in the art from the following disclosure, and it is to be understood that the described embodiments are merely exemplary of the invention and that it is not intended to limit the invention to the particular embodiments disclosed. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention. In the present specification, the terms "upper", "lower", "left", "right", "middle", and the like are used for the sake of clarity only, and are not intended to limit the scope of the present invention, and changes or modifications of the relative relationship thereof are also regarded as the scope of the present invention without substantial changes in the technical contents.

Example 1

Referring to fig. 1-2, the double-screw type material extrusion device for 3D printing comprises a melting shell 10, a synchronous box shell 3, a driving screw 8, a driven screw 9 and a melting heater 12, wherein the driving screw 8 and the driven screw 9 are arranged in the melting shell 10 and are engaged with each other, the driving screw 8 and the driven screw 9 extend into the synchronous box shell 3 and are connected through a synchronous transmission mechanism, the driving screw 8 is connected with a melting extrusion power source through a reducer 2, the melting heater 12 is arranged at the outer side of the melting shell 10, a printing nozzle 13 and a raw material inlet 11 are respectively arranged at two ends of the melting shell 10, bearings sleeved at the ends of the driving screw 8 and the driven screw 9 are arranged in the synchronous box shell 3, the bearings comprise a thrust bearing 7 and a radial bearing 6, a plurality of thrust bearings 7 are mutually overlapped along the axial direction of the driving screw 8 and the driven screw 9, and a thrust transmission mechanism is arranged between the adjacent thrust bearings 7 on the, a thrust transmission mechanism is also arranged between the adjacent thrust bearings 7 on the driven screw rod 9.

The driving screw 8 and the driven screw 9 are both conical screws, and the synchronous transmission mechanism enables the driving screw 8 and the driven screw 9 to rotate in different directions. The screw rod is the meshing type of spiral arris, and the screw rod is the incorgruous rotation, also can be the syntropy rotation type, and for 3D printing technology, toper incorgruous rotation twin-screw structure is optimum screw rod structure, screw rod and screw rod overcoat precision fit, and the clearance is less. In the embodiment of the present invention, a plurality of melting heaters 12 are installed outside the melting shell 10, and the plurality of melting heaters 12 cooperate with a temperature control system to maintain the temperatures required by stable regions in different regions of the extrusion device.

The synchronous transmission mechanism comprises a driving gear 4 and a driven gear 5 which are meshed with each other, the driving gear 4 is fixed on a screw shaft of a driving screw 8, the driven gear 5 is fixed on a screw shaft of a driven screw 9, and the synchronous transmission mechanism is directly connected without an additional transmission structure. The gears are directly arranged on the screw shafts, and the gears on the two screw shafts are meshed, so that the double screws can keep rotating in different directions (opposite directions). Each screw is provided with a set of bearing group for bearing axial thrust and fixing the screw in radial direction. In order to facilitate assembly and maintenance, the housing 3 of the synchronization box is divided into two parts by taking a plane formed by the axes of the two screws as a parting plane. Lubricating grease can be injected into the box body to provide lubrication for the bearing and the gear.

The thrust transmission mechanism comprises a thrust transmission inner diameter top ring 14 and a thrust transmission outer diameter top ring 15, the thrust transmission inner diameter top ring 14 is arranged between the thrust shaft rings of the two adjacent thrust bearings 7, and the thrust transmission outer diameter top ring 15 is arranged between the thrust race rings of the two adjacent thrust bearings 7. The thrust is transmitted by the top ring, so that the thrust of the screw is respectively and uniformly loaded on each thrust bearing 7, the thrust is dispersed, the total thrust is improved by several times, the extrusion device can bear huge reverse thrust generated by a high-pressure large-flow screw, the high integration of the double-screw extruder is realized, and the application to the field of 3D printing becomes possible. Thrust is upwards transmitted to the inner ring of the radial bearing 6 and then transmitted to the moving coil of the first thrust bearing 7 by the step of the conical screw, then transmitted to all the moving coils of the thrust bearings 7 by the inner top coil 14 of the thrust transmission, the moving coil of each thrust bearing 7 transmits thrust to the race of each thrust bearing 7 by the bearing balls, the race of each thrust bearing 7 transmits thrust to the race of the next thrust bearing 7 by the outer top coil 15 of the thrust transmission, and finally the thrust is transmitted to the last thrust bearing race and transmitted to the bearing step of the synchronizing box shell 3.

The sync box housing 3 is fixed to the upper end of the melting housing 10, and the printing nozzle 13 is provided at the lower end of the melting housing 10. The printing nozzles 13 with different calibers can be installed according to the requirements of different printing conditions.

The power source for melt extrusion is a servo motor 1. The servo motor 1 can precisely adjust the torque, the rotating speed and the position, and the speed reducer 2 is a high-precision planetary speed reducer 2. The embodiment is taken as a preferable scheme, and other driving modes which can meet the requirements can be adopted.

Referring to fig. 3, the 3D printing apparatus in the present embodiment is applied to an industrial robot 17, a raw material bin 16 is disposed on one side of the industrial robot 17, the raw material bin 16 is connected to a feeding port 6 of a material melt extrusion mechanism 1 through a feeding pipe 19, the material melt extrusion mechanism 1 is fixed on a robot arm of the industrial robot 17, and two printing heads 2 are fixed on two sides of the material melt extrusion mechanism 1. The device is generally suitable for 3D printing application of medium-high speed and medium-small flow, can be integrated on a load arm of the industrial robot 17 by using a light extruding device, and is suitable for 3D printing products with medium and small sizes.

Example 2

Referring to fig. 4 to 5, the 3D printing apparatus of the embodiment of the present invention is installed on a traveling rack type machine tool 18, is suitable for 3D printing applications with high speed, large flow and high motion stability, can use a structure of an external large extruder, and is suitable for large-sized or ultra-large-sized 3D printed products. The material melting and extruding mechanism 1 is fixed on a machine tool base, one side of a row frame type machine tool 31 is provided with a raw material bin 16 for supplying materials to the material melting and extruding mechanism 1, a melting material conveying pipe is arranged along the machine frame, and the printing head 2 is arranged on a row frame which can move horizontally and vertically.

The embodiment of the invention has the following advantages:

1. light structure integration (improve maneuverability and indirectly improve printing efficiency)

The structure of a large-scale melt extruder in the traditional industry is optimized, the double-screw extruder can be applied to a large-scale 3D printer, the driving structure of the melt extruder is specifically improved, the complex structure of a screw, a synchronizing mechanism, a reduction gearbox and multistage connection of the traditional extruder is simplified, and the improvement is a simple direct-drive mode. In the embodiment of the invention, no redundant transmission shaft body is arranged between the screw and the speed reducer 2. The thrust support bearing group, the thrust transmission mechanism, the radial bearing 6 and the like are directly arranged on the screw shaft, so that the whole driving structure is more compact, the volume is smaller, the weight is lighter and the service life is long.

2. High extrusion flow (benefit to improve printing efficiency)

Compared with a single screw, the double-screw extruder has larger double-screw flow, and simultaneously, as an optimal scheme of a double-screw structure, the double-screw extruding mechanisms rotating in different directions can form a closed cavity, so that the double-screw extruder has a forced conveying characteristic, the leakage flow is greatly reduced, the extruding pressure is greatly improved, and the large-flow extrusion is facilitated. Meanwhile, the multi-layer uniform-load thrust bearing set 7 is integrated, support is provided for huge reverse thrust generated by high-flow extrusion, and conditions are created for further increasing thrust to obtain higher extrusion flow, so that the extrusion flow of the whole double-screw melt extrusion device is comprehensively improved.

3. Precision real-time current-variable control (benefit for improving printing quality)

The double-screw synchronous structure and the thrust supporting structure are improved to be integrated, the integration level of the driving structure is improved, the speed reducer 2 and the screw shaft are in a direct-drive mode, the transmission rigidity is greatly improved compared with that of an original multi-shaft transmission structure, the transmission synchronism is high, the transmission precision is high, and the screw shaft of the extruding device is made to be a numerical control shaft, so that compared with a traditional single-screw extruding device, the extruding device provided by the embodiment of the invention is higher in flow control precision. The contra-rotating twin-screw extruder is a preferred twin-screw scheme, and has forced conveying characteristics similar to screw pumps, so that the flow control of the contra-rotating twin-screw extruder is more accurate, and the flow can be changed in real time according to program instructions.

4. Improving plasticizing performance and gaseous impurity removal capability (improving mechanical properties)

In the application of the 3D printing process, the extrusion plasticizing effect of the melting extrusion device on the material directly determines the mechanical property of the final printed product. The main factors influencing the plasticizing effect of the material are two, namely the plasticizing degree and the impurity removal degree (moisture, air, low molecular weight vaporized impurities and the like).

If the plasticizing degree of the material is insufficient during extrusion, the material is unevenly distributed and has loose multiple layers, and finally, the mechanical property of a printed product is poor. If the impurity removal degree is not sufficient when the material is extruded, especially when moisture and air are not completely removed, the molten material containing gas and moisture enters a normal temperature and normal pressure state (after being extruded from the printing nozzle 13), the pressure is suddenly reduced, the moisture in the material can be vaporized, so that the printing line expands, and after water vapor is discharged, the printing line shrinks, so that the printing line width and the line height are uncontrollable, and the printing line has more air holes, so that the printing effect is seriously reduced.

Compared with a single-screw structure commonly used in the industry, the double-screw extruding structure has good mixing, stirring, plasticizing and impurity discharging effects, a printing line is compact and uniform in plasticizing, and the printing effect is good.

Due to the mixing and stirring characteristics of the double-screw extruding structure, various auxiliary agents such as a toughening agent, a plasticizer, a filling agent, glass fibers, carbon fibers and the like can be added into a main material, so that the main material is modified and enhanced or other properties are added, the counter-rotating double-screw extruder has the forced extruding characteristic, powdery raw materials can be used, and the double-screw extruding structure has the advantage of material selection diversity compared with a single-screw extruding structure.

Although the invention has been described in detail above with reference to a general description and specific examples, it will be apparent to one skilled in the art that modifications or improvements may be made thereto based on the invention. Accordingly, such modifications and improvements are intended to be within the scope of the invention as claimed.

Claims

1. The utility model provides a 3D prints and uses double screw type material extrusion device which characterized in that: the double-screw type material extrusion device for 3D printing comprises a melting shell (10), a synchronous box shell (3), a driving screw (8), a driven screw (9) and a melting heater (12), wherein the driving screw (8) and the driven screw (9) are arranged in the melting shell (10) and are meshed with each other, the driving screw (8) and the driven screw (9) extend into the synchronous box shell (3) and are connected through a synchronous transmission mechanism, the driving screw (8) is connected with a melting extrusion power source through a speed reducer (2), the melting heater (12) is arranged on the outer side of the melting shell (10), two ends of the melting shell (10) are respectively provided with a printing nozzle (13) and a raw material inlet (11), a bearing arranged at the end parts of the driving screw (8) and the driven screw (9) in the synchronous box shell (3) in a sleeved mode, the bearing comprises a thrust bearing (7) and a radial bearing (6), the thrust bearings (7) are mutually overlapped along the axial directions of the driving screw (8) and the driven screw (9), a thrust transfer mechanism is arranged between the adjacent thrust bearings (7) on the driving screw (8), and a thrust transfer mechanism is also arranged between the adjacent thrust bearings (7) on the driven screw (9).

2. A twin-screw type material extrusion apparatus for 3D printing according to claim 1, wherein: the driving screw (8) and the driven screw (9) are both conical screws.

3. A twin-screw type material extrusion apparatus for 3D printing according to claim 1, wherein: the synchronous transmission mechanism enables the driving screw rod (8) and the driven screw rod (9) to rotate in different directions.

4. The double-screw type material extrusion apparatus for 3D printing according to claim 1 or 3, wherein: the synchronous transmission mechanism comprises a driving gear (4) and a driven gear (5) which are meshed with each other, the driving gear (4) is fixed on a screw shaft of a driving screw (8), and the driven gear (5) is fixed on a screw shaft of a driven screw (9).

5. A twin-screw type material extrusion apparatus for 3D printing according to claim 1, wherein: the thrust transmission mechanism comprises a thrust transmission inner diameter top ring (14) and a thrust transmission outer diameter top ring (15), the thrust transmission inner diameter top ring (14) is arranged between thrust shaft rings of two adjacent thrust bearings (7), and the thrust transmission outer diameter top ring (15) is arranged between thrust race rings of two adjacent thrust bearings (7).

6. A twin-screw type material extrusion apparatus for 3D printing according to claim 1, wherein: the synchronous box shell (3) is fixed at the upper end of the melting shell (10), and the printing nozzle (13) is arranged at the lower end of the melting shell (10).

7. A twin-screw type material extrusion apparatus for 3D printing according to claim 1, wherein: the melt extrusion power source is a servo motor (1).