RU207453U1 - Extruder with ultrasonic forming head - Google Patents

Abstract

The utility model relates to devices for processing plastics and can be used in the manufacture of thermoplastic filaments for 3D printers that implement FDM technology. The extruder contains an ultrasonic forming head, a material unit with a connecting head mounted on it with a heating element, a pressure sensor and a temperature sensor placed on it, a worm for supplying a polymer material located in the material unit. The extruder also contains an electronic system for regulating and maintaining the temperature of the heating element. The ultrasonic forming head is installed on the connecting head and has replaceable sleeves with a channel that forms the product leaving the extruder. The shaping head is a waveguide in the form of two cones mated with large diameters, fixed to the connecting head by means of a threaded connection. A cylindrical cavity is made in the waveguide to accommodate a connecting head with a heating element. The replaceable sleeve is a disk die and is fixed between the end surface of the connecting head and the rear end surface of the waveguide. On the surface of the rear cone, cylindrical active pads are installed with a step of 120 °. Ultrasonic piezoceramic transducers are connected to the active pads with the help of pins so that their axes intersect in the center of the channel of the replaceable sleeve, the length of which does not exceed the diameter. The utility model makes it possible to improve the quality of polymer filaments formed from additive manufacturing waste generated during the removal of supports and cleaning the surface of products, bringing it closer to the characteristics of the new material. 2 wp cl, 4 dwg

Description

The utility model relates to devices for plastics processing and can be used in the manufacture of thermoplastic filaments for 3D printers that implement FDM technology, including in the manufacture of filaments by recycling additive manufacturing waste.

The technology of forming products of complex shape by layer-by-layer fusion of a thermoplastic filament in accordance with a computer solid-state model (FDM) is widely used in the manufacture of prototypes, models, visual aids, as well as parts of the main production that are not subjected to significant thermal and mechanical stress. Filaments made of additive thermoplastics are produced by specialized firms and are characterized by high stability of diameter and physical and mechanical properties, which ensures uniform melting in the extruder and feeding to the build platform. However, these materials are expensive. In the case of manufacturing complex parts with overhanging structures, the 3D printer generates so-called supports, which are removed after the completion of the process and must be disposed of. With a significant complexity of the structure being formed, the volume of material to be disposed of can be significant.

Many models of FDM 3D printers have a single-plate print head, which means they use the same material for the supports and the main structure. Taking into account the foregoing, this leads to additional costs for "proprietary" material and requires the implementation of measures for waste disposal.

It is possible to solve these problems by processing the waste generated during the removal of the supports into a thread by extrusion of the latter. However, it is not economically feasible to transport waste to manufacturers of threads for additive technologies. In this case, it is more efficient to process waste directly at the workplace, where additive equipment is used, using small-sized (bench-top) extruders, for example, a screw type. At the same time, it is obvious that the quality of the yarn formed from the waste can be inferior to the characteristics of the yarns produced by specialized enterprises, which makes it urgent to develop technical solutions for small-sized extruders that significantly improve the quality of the yarns obtained after secondary processing.

Various technical solutions of extruders for processing polymeric materials are known, including those using the introduction of ultrasonic vibrations into the forming zone, which make it possible to increase the rheological properties, the fluidity of the material through the die, and the uniformity of the density of the product structure.

From literature [Kobzev D.Ye. Solid-phase plunger extrusion of polymer nanocomposites using ultrasound / D.E. Kobzev, G.S. Baronin, V.L. Poluektov // Perspective materials. 2011. No. 11. S. 449-454] a method of solid-phase plunger extrusion using ultrasonic action is known, where ultrasonic vibrations are transmitted from the emitters directly to the metal of the high-pressure cell and through it act on the polymer blank.

The disadvantage of the method of plunger extrusion is the impossibility of forming extended products of the type of filaments, which is determined by the scheme of polymer processing by pressing. An ultrasonic device that implements this method also cannot be used to improve the quality of the formed filaments due to significant losses of acoustic energy due to the significant added mass of the forming tooling and its leakage onto the press frame. A decrease in the amplitude of ultrasonic vibrations is inevitable, since the tooling is clamped in the press connector and does not have the ability to perform vibrational movements.

The known method of two-stage processing of polymeric materials by solid-phase extrusion and ultrasonic exposure (patent RU No. 2574267, IPC В29С 43/00, published 02/10/2016, bull. No. 4). The processing process is divided into two stages, implemented in one device. At the exit from the main forming die of the cell, the product passes through an additional processing device that is not rigidly connected to the cell and vibrates with an ultrasonic frequency in a direction parallel to the axis of the forming tool. The device that implements the method contains an additional processing unit, not rigidly connected to the cell forming the product, vibrating with an ultrasonic frequency in a direction parallel to the axis of the forming tool (profiling die).

The described ultrasonic device is also a plunger, which excludes the possibility of forming extended products such as threads for additive technologies.

Known extrusion head for the manufacture of polymer two-layer pipes using ultrasonic vibrations (patent RU No. 2433913, IPC В29С 47/00, published on 20.11.2011). The extrusion head contains a body and a mandrel holder with a cylindrical section placed in it, between the ribs of which holes for the passage of the melt are made, mandrels mounted with the formation of a forming slot and channels for supplying the outer and inner layers of melts, located obliquely relative to each other and communicated with the forming slot and magnetostrictive emitter. At the same time, two magnetostrictive emitters are mounted in the junction zone of polymer melt layers on an inclined surface of the forming head; for smooth entry of the inner polymer melt layer into the forming head, a hemispherical element with grooves is provided, fixed at the end of the mandrel, the mandrel is made conical. The die belongs to a plastics processing device and can be used to make forming dies for the production of double-layer pipes and hollow products by extrusion.

The extrusion head has the following disadvantages. Since the head, in accordance with the technical purpose, contains a mandrel that forms the cavity of the pipe, it cannot be used in the production of small-diameter filaments intended for additive FDM technologies.

From the scientific and technical literature [Panov A.A. Influence of superposition of ultrasound on the main parameters of extrusion of polymer melt / A.A. Panov, G.E. Zaikov, T.A. Anasova et al. // Plastics, No. 4, 2013. S. 59-63] known experimental setup with a forming unit, which is the closest technical solution to the claimed utility model.

The device contains the material unit of the extruder, which houses the screw for feeding the polymer material. A connecting head with a heating element, a pressure sensor (manometer) and a temperature sensor is installed on the material element. A forming head with two magnetostrictive transducers and a replaceable sleeve with a channel forming a bar product emerging from the extruder is installed on the connecting head. By replacing the bushing, the channel length is changed (120, 160 and 180 mm). The diameter of the hole and, accordingly, of the formed polymer rod is 4 mm. The electronic system provides regulation and maintenance of the temperature of the heating element from 195 to 205 ° C.

The device is taken as a prototype.

The disadvantages of the device are as follows.

1. The device does not allow forming the standard diameter of polymer threads for the FDM technology - 1.75 mm, since the channel diameter is 4 mm, only its length changes.

2. The presence of a long channel increases the hydraulic resistance due to friction when the molten polymer moves along it, the channel length is commensurate with the wavelength of bending ultrasonic vibrations created in the replaceable sleeve (from 1/2 to 3/2 of the wavelength at an assumed vibration frequency of 18.5-23 , 5 kHz), which creates significant changes in the amplitude and intensity of ultrasound along the length of the channel from 0 to the maximum, which does not provide a uniform effect on the material.

3. The location of the forming head remote from the heating element in combination with heat removal through the surface of the replaceable sleeve leads to a decrease in the temperature of the polymer at the exit from the channel, a decrease in its fluidity and possible ruptures in the structure.

4. The use of magnetostrictive emitters assumes the presence of a water cooling system with a system of seals, nipple connectors and pipelines. Magnetostrictive emitters have significant dimensions and mass, the acoustic energy generated by them is excessive when applied to products of small cross-section such as filaments for additive technologies, which can lead to material discontinuities.

5. The power control of the emitters due to the magnetization system is not flexible enough, which does not allow smoothly adjusting the acoustic parameters of the process in accordance with the properties of the processed material and complicates the use in multi-product production.

6. The use of two emitters located in the same plane creates a plane wave of oscillations and does not provide a uniform distribution of the ultrasound intensity over the cross-section of the tooling and, accordingly, the product.

The technical problem of the proposed utility model is to increase the uniformity of ultrasound parameters in the area of filament formation, improve the controllability of the ultrasound intensity, reduce the mass and size characteristics of the forming head and reduce the resistance to the movement of the polymer material through the die opening, which meets the standard requirements for the diameter of polymer filaments.

The technical result of the proposed utility model is to improve the quality of polymer filaments formed from additive manufacturing waste generated by removing supports and cleaning the surface of products, close to the characteristics of the new material.

The technical result is achieved by introducing ultrasonic vibrations uniform in intensity along its cross section into the thread formation zone at the outlet of the spinneret and by reducing the resistance to the flow of the molten polymer by using three piezoceramic electromechanical transducers placed with a pitch of 120 ° and using replaceable washers with a hole length not exceeding its diameter.

The technical essence of the proposed utility model is as follows.

In an extruder with an ultrasonic forming head mounted on the connecting head and having replaceable sleeves with a channel forming an article leaving the extruder containing the material assembly of the extruder, with a connecting head mounted on it with a heating element, a pressure sensor and a temperature sensor located on it. material unit, a worm for feeding a polymer material, and also containing an electronic system for adjusting and maintaining the temperature of the heating element, the forming head is a waveguide in the form of two cones mated with large diameters, fixed to the connecting head by means of a threaded connection, and a cylindrical cavity is made in the waveguide to accommodate the connecting head with a heating element, the replaceable sleeve is a disk die and is fixed between the end surface of the connecting head and the rear end surface of the waveguide, on the surface of the rear cone, cylindrical active pads are installed with a pitch of 120 °, to which ultrasonic piezoceramic emitters are attached by means of pins so that their axes intersect in the center of the channel of the replaceable sleeve, the length of which does not exceed the diameter. The length of the generatrix of the front conical surface of the waveguide is 0.5λ, and the diameter through which the axes of three piezoceramic emitters pass at the location of the active pads is (3 / 2λ) / π, where λ is the wavelength of ultrasonic vibrations in the waveguide material at a given resonant frequency ... The connecting head is made of bronze, the waveguide and active pads are made of duralumin, and the active pads are connected to the waveguide by welding.

An example of the implementation of the utility model is shown in Fig. 1. In FIG. 2 shows the design of the forming head of the utility model.

FIG. 1 denoted: 1 - forming head, 2 - piezoceramic electromechanical transducer, 3 - temperature sensor, 4 - material hopper feeder, 5 - drive of rotation of the worm feeding material into the melting and extrusion zone, 6 - electronic unit of temperature sensor, 7 - ultrasonic generator, 8 - power supply unit of the heating element and the worm drive motor, 9 - base, 10 - material assembly of the extruder - worm body, 11 - heating element.

FIG. 2 indicates: 12 - conical common waveguide, 13 - active pad, 14 - piezoceramic ultrasonic emitter, 15 - tie rod, 16 - insulating fluoroplastic sleeve, 17 - electrodes, 18 - connecting head, 19 - replaceable disk die.

The extruder shown in FIG. 1, consists of a material assembly of an extruder, which is a sleeve connected to a hopper feeder for loading waste of polymeric material and feeding them into the inner cavity. A rotating screw (screw) is located inside the sleeve, which in turn delivers polymer waste from the feed zone to the melt zone in the connection head and provides the pressure required for extrusion. The connection head is made of bronze to improve the heat capacity of this area of the extruder. The inlet end of the connecting head is screwed onto the material unit of the extruder. At the outlet end of the connecting head, a forming head is fixed by means of a threaded connection, which consists of electromechanical piezoceramic transducers and a replaceable disk die. When fixing the forming head on the connecting head, the spinneret is installed between the end surface of the latter and the end surface of the conical waveguide in its cylindrical cavity, which ensures reliable transmission of ultrasonic vibrations to the thread forming zone. The use of a disk-type die ensures a constant amplitude of ultrasonic vibrations on the surface of the hole and, accordingly, in the formed material. The general waveguide of the electromechanical transducer is made of alloy D16T, which has a minimum acoustic resistance, and has the form of two cones conjugated with large diameters. Active plates of electromechanical transducers are welded to the surface of the rear cone so that their axes converge in the center of the disc die hole. This ensures the focusing of ultrasonic vibrations in the middle section of the spun thread. The length of the generatrix of the outer cone and the length of the active pads are 120 mm each, which ensures the resonance of the oscillating system at a frequency of 22 kHz. The large diameter of the waveguide is chosen equal to 114.7 mm. With this value of the length of the arcs between the axes of attachment of the active pads are also 120 mm, which corresponds to half the wavelength of ultrasonic vibrations at a given frequency and ensures stable operation of the transducer.

A ring heater with a specific power of 4 W / cm is installed on the bronze connecting head; this heater can provide temperatures up to 450 ° C. To maintain and regulate the temperature, the OWEN TRM - 500 thermostat is used, which allows to regulate the temperature by proportionally integral differentiating. A thermocouple is located in the connection head housing to control the temperature.

A DC electric motor with a stepless speed control and a gearbox is fixed on the same base with the extruder, and transmits the torque to the worm through a toothed belt drive.

The proposed extruder is used as follows.

To start work, adjust the required oscillation amplitude of the die, for which the generator is turned on, and the end of the die is touched by the dial-type indicator foot with a graduation of 1 μm (you can use inductive microdisplacement sensors of type 214 and analogs with a measurement accuracy of 0.5 μm. Rotating the regulator changes the resonance state The value of the amplitude, recorded by the indicator, is set equal to 2-3 microns. Then the generator is turned off and the power supply unit of the heater is turned on to warm up the melt zone to a temperature (40-60) ° C higher than the melting temperature of the polymer being processed. Warming up is carried out for 5-15 minutes, depending on the ambient temperature and material.Then, the polymer waste is loaded into the feeder hopper.After that, the electric motor of the worm drive is turned on and the rotation frequency (20-30) rpm is set to transport the polymer waste to the melt zone . After filling the melt zone, turn off the drive and carry out melting. no polymer, which occurs after 3-8 minutes, depending on the thermophysical properties and volume of the material. After that, the worm drive and the ultrasonic generator are turned on, extrusion is performed.

The effectiveness of the use of ultrasonic extrusion of filaments from polymeric materials for additive equipment using the proposed utility model is confirmed by the following experimental results presented in Fig. 3 and FIG. 4.

FIG. 3 presents screenshots of the dialog box of a laboratory computer setup for studying the strength of polymer and composite materials. FIG. 3 denotes: a - kinetics of the growth of the destructive load upon breaking of a filament made of ABS thermoplastic formed by the action of ultrasound on the die; b - kinetics of the growth of the destructive load at the break of a filament made of ABS thermoplastic, formed without ultrasound.

FIG. 4 presents photomicrographs of the filament surface formed without ultrasound on the die (a, b) and with ultrasound (c, d). FIG. 4 denotes: x40 magnification (a, c), x120 magnification (b, d).

The tensile strength of the formed filaments was investigated using strain gauge force sensors and Lab View software (IP "Mayorov", Orel) using special equipment on a laboratory computer setup. One end of the thread sample was fixed in the bracket holder mounted on the strain gauge body, the other end on the lever of the loading mechanism. A torque was applied to the lever, which was recorded by the sensor and displayed in the setup dialog box. The diameter of the thread sample was preliminarily measured with a micrometer with an accuracy of 0.01 mm. Tested 5 samples. The fracture stress at break was calculated according to the known relationship, as the ratio of the breaking load to the cross-sectional area of the thread.

The hardness of samples formed with and without ultrasound by Shore-D was studied using a Novotest TSh-Ts digital hardness tester.

The surface morphology of the filament samples was investigated using a Bresser LCD 50x-2000x digital microscope at a magnification of x40 and x120.

In the experiments, we used wastes of the most common additive polymer of the ABS brand.

The rotational speed of the worm drive was set equal from 20 to 25 rpm. The melt zone temperature was chosen equal to 250 ° C in accordance with the melting point of this polymer.

It was found that the extrusion speed with the ultrasonic vibrations of the forming head turned off was 75-90 cm / min. When ultrasonic vibrations are applied to the die, the yarn exit speed increases to 120 cm / min. In this case, the highest speed is achieved at a frequency of ultrasonic vibrations of 22.1 kHz. Experiments were carried out with both granular material and waste, the effect of ultrasound in both cases was the same.

The average value of the breaking stress, calculated from the test results, is 239.1 MPa for yarns made with ultrasonic action, and 145.6 MPa for yarns made without ultrasound. Standard ABS filaments have shown ultimate tensile stresses of 250-255 MPa. Thus, the extrusion of filaments from waste ABS plastic with the action of ultrasound on an extruder manufactured in accordance with the proposed utility model provides an increase in the tensile strength of filaments by 64% compared to filaments formed without ultrasound. At the same time, the decrease in strength compared to standard threads is no more than 5%, which allows the use of recycled ABS plastic in additive processes not only for the formation of supports, but also for the manufacture of basic parts.

Exposure to ultrasound also has a positive effect on the hardness of the threads. The hardness of a thread with a diameter of 1.5 mm, made with ultrasonic action, is on average 55 Shore-D units. The hardness of a thread made without ultrasonic treatment is 32 units on average. Thus, the increase is 71.8%.

The stability of the thread diameter was determined by measuring the thickness of the thread with a 0-25 mm micrometer. On 10 meters of filament made with ultrasound, the deviation of the diameter from the nominal value did not exceed 0.09 mm, which is acceptable for three-dimensional printing. In extrusion without ultrasound, the deviation was 0.11 mm. In this case, in the longitudinal section, the thread had a wavy shape, there were practically no sufficiently extended sections of the same diameter.

FIG. 4, it can be seen that the filament made with ultrasonic action on the die has a much more uniform surface morphology with minimal cavities and microwaves, which is due to a decrease in friction at the time of extrusion of the filament through the die, performing ultrasonic vibrations. It is also determined by acoustic flows in a plastic material and its mixing due to wave processes.

In the 3D printing process, this surface morphology and greater hardness and strength will help the filament pass through the print head hole better, prevent filaments from breaking and sticking, which will increase the stability of the process.

This solves the technical problem of creating the proposed utility model: increasing the uniformity of ultrasound parameters in the area of filament formation, improving the controllability of the ultrasound intensity, reducing the mass and size characteristics of the forming head and reducing the resistance to the movement of the polymer material through the die hole, which improves the quality of polymer filaments formed from additive waste. production formed during the removal of supports and cleaning the surface of products, close to the characteristics of the new material.

Claims (3)

1. An extruder with an ultrasonic forming head mounted on the connecting head and having replaceable sleeves with a channel forming an article leaving the extruder, containing a material assembly of an extruder with a connecting head mounted on it with a heating element, a pressure sensor and a temperature sensor placed on it, located in material unit, a worm for feeding a polymer material, as well as containing an electronic system for regulating and maintaining the temperature of the heating element, characterized in that the forming head is a waveguide in the form of two cones conjugated with large diameters, fixed on the connecting head by means of a threaded connection, and a cylindrical cavity for accommodating the connecting head with a heating element, the replaceable sleeve is a disk die and is fixed between the end surface of the connecting head and the rear end surface of the waves gadfly, cylindrical active pads are installed on the surface of the rear cone with a pitch of 120 °, to which ultrasonic piezoceramic emitters are attached using pins so that their axes intersect in the center of the channel of the replaceable sleeve, the length of which does not exceed the diameter. 2. Extruder according to claim 1, characterized in that the length of the generatrix of the front conical surface of the waveguide is equal to 0.5λ, and the diameter through which the axes of the three piezoceramic emitters pass at the installation site of the active pads is equal to (3 / 2λ) / π, where λ is the wavelength of ultrasonic vibrations in the material of the waveguide at a given resonant frequency. 3. Extruder according to PP. 1 and 2, characterized in that the connecting head is made of bronze, the waveguide and active pads are made of duralumin, and the active pads are connected to the waveguide by welding.

Images