DE102011110804A1 - Three dimensional printing head, useful for melting and depositing layers of wire-shaped materials, comprises feed channel consisting of array of highly heat-conductive materials e.g. aluminum and low heat-conductive materials e.g. PTFE - Google Patents

Abstract

The three dimensional printing head comprises a feed channel, which consists of an array of highly heat-conductive materials such as aluminum, copper, steel or graphite and low heat-conductive materials such as PTFE or polyetheretherketone, where the fed printing material has contact surfaces with the inside of these materials. An independent claim is included for a feed channel.

Description

Three-dimensional printing wires (filament) according to the FDM method are pushed via a feed channel (wire feed) into a melting chamber in which they melt and exit through an opening (nozzle). The leaked amount forms the object to be printed in layers.

The manufacturers of such printheads try by structural measures to minimize the heat transfer that emanates from the melting chamber. For this purpose, materials with a low thermal conductivity coefficient are used at the connection points of the melting chamber and the feed channel.

The plastics used for this purpose PTFE or PEEK also have a low coefficient of friction, which is why the filament slides well in the feed channel. This has hitherto been regarded as an advantage since a filament, which undergoes only slight friction, can be conveyed with high accuracy (delivery volume / time) and exerts only slight resistance on the actual delivery unit.

In practice, however, shows that temperature-sensitive materials (filaments), just those that soften even below, for example, 50-70 ° C, not first melt in the melting chamber, but already absorb so much heat within the filament feed that they soften and because of the pressure when pushing in the filament into the feed channel are compressed and thereby bulge before they are inserted into the actual melting chamber.

The bulging means that the filament is pressed against the wall of the channel and experiences there a greatly increased friction (heated to molten filament against the wall) up to the "near-gluing" with this wall.

From this moment on, no exact conveyance of the filament is possible anymore.

The pressure required for the feed increases rapidly, a blockage has occurred. The conveyor unit continues to encourage and destroys the wire as it rubs off of this material.

Remedy only the removal of the filament, followed by the complete cooling of the extruder head with feed channel and re-loading with ungestauchtem, material to room temperature.

Conclusion:

However, it proves to be disadvantageous in the above-described previous construction to use materials with low thermal conductivity, since they nevertheless conduct the heat, albeit poorly, to where it is disadvantageous. The feed channel is badly coolable in the sequence, he stores rather even the heat.

By this type of filament feeder, the filaments in zone 2, in which they are supposed to slide only slightly, almost heated up.

This process is also promoted with low feed of the filament (long residence time).

It is proposed here to solve these problems
to produce the longest part (zones 2 + 3) of the feed channel from a material which conducts heat well and to leave only a small part for thermal separation from poorly conducting material. This redesigned zone can now be cooled quickly.

The filament therefore still has room temperature until shortly before entering the melting chamber. Premature softening followed by blockage is successfully avoided.

Even if the coefficients of friction of aluminum or copper are higher than previously used PTFE, then this does not adversely affect, since the increased effort by friction losses to push the filament into the melting chamber is negligible (meaning friction at room temperature).

The temperature profiles shown along the extension of the filament in the feed channel and the following melting chamber show the difference in temperature reduction achieved in the critical region 2 of the feed channel.

In 2 takes place only in the short zone 2a a sudden increase in temperature, in 1 however, over the entire zone 2.

The imaginary route A-C describes the extent of a feed channel, with the distances C-B and A-B should be the same length and halve them into two imaginary parts.

The more important half of the feed channel lies along route A-C.

Their walls should consist of more than 60% of their extent of good heat conducting material, optimally even more than 85%.

If the half B-C to a lesser extent or not at all made of good heat-conducting material, so that is irrelevant for the temperature profile.

In 3 along the route BC a thermal barrier Tb3 is drawn from a poorly heat-conducting material. This does not disturb the expression of a temperature profile similar to Fig. 2a, since this half is not acted upon by heat of the melting chamber. Description / Legend Fig. 1 PRIOR ART: 3D print head with feed channel Tb1 made of poorly heat-conducting material, which is cooled by the cooler C1 pushed over it Fig. 2 3D printhead with two-part feed channel, which consists of the thermal barrier Tb2 of poor thermal conductivity material, as well as the cooler C2 of good heat conducting material. Fig. 3 Alternative to the arrangement in Fig. 2, the feed channel is 3-piece: it consists of Tb3; C3; Tb4. The cooler C3 is limited by the heat barrier Tb4 on the melt chamber side. On its other side, the filament is passed through Tb3, a piece of feed channel from a poor heat conductor. The cooling section C3 is optionally designed to be heatable in order to heat the filament in the event of blockage for the purpose of removal. C3 can be forcibly cooled via AIR, but can also be connected to a water circuit. Zone 1 Suggested temperature profile within the melting chamber. The filament has target temperature = melting temperature. Zone 2 The material of the feed channel Tb1 has absorbed so much heat from direct contact with the melting chamber that the filament in the zone 2 is already heating up strongly. It is an object of the invention to lower the filament temperature in this area. Zone 3 Range of the lowest temperature of the filament. A End point of the feed channel. The filament is pushed into the melting chamber. B Center of an imaginary route AC. C Input of the feed channel. The filament is fed here to the print head. T The distance AT marks the extent of a thermal barrier between the melting chamber and the parts of the feed channel which conduct heat well. F Filament, print material to be melted K The dashed line indicates the dimensions of the print head. S molten filament H Heating unit for heating the melting chamber H2 Heating unit for heating C3 O object to be printed Tb1 Feed channel according to the prior art throughout as a thermal barrier from poorly formed the heat-conducting material. Tb2 Thermal barrier of the feed channel, executed in its extension 2a particularly short. Tb3 Thermal barrier along the top half of the feed channel FU delivery unit

Claims (5)

3D print head for melting and layering of wire-shaped materials and associated wire, characterized in that it has at least one feed channel, which consists of an array of highly heat-conductive materials, such as preferably aluminum, copper, steel or graphite and low heat-conductive materials such preferably PTFE, PEEK, wherein the supplied printing material (filament) has common contact surfaces with the inside of these materials. Feed duct according to claim 1, characterized in that it extends along the feed duct bisecting line AB over an extension of more than 60%, optimally over 85% from high thermal conductivity material and to less than 40%, optimally down to less than 15% from poor thermally conductive material. Feed duct according to claims 1-2, characterized in that it extends optimally along the distance AC over an extent of more than 80% to over 90% of highly heat-conducting material and to less than 20%, optimally to less than 10% from poorly heat-conducting Material is defined, wherein higher thermal conductivity is defined here starting at values> 10 W / m · K, preferably rather values greater than 100 W / m · K, lower thermal conductivity at values <9 W / m · K, preferably values of less than 0 , 5 W / m · K. Feed duct according to claims 1-3, characterized in that this a) is cooled by means of air or water, b) is designed to be heated and c) has a temperature sensor. Feeding duct according to Claims 1-4, characterized in that it has an extent of less than 10 mm, preferably between 1-5 mm, of poorly heat-conducting material along the distance A-C.

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