3D printing, particularly FDM 3D printing, involves a lot of heat. Heated print head, heated build chamber, heated build platform – it’s all necessary to melt plastic filament and ensure that it stays soft enough to adhere to the build plate and to each subsequent layer before hardening. But Thermwood Corporation, which introduced the Large Scale Additive Manufacturing (LSAM) hybrid 3D printer and CNC machine last year, is taking a different approach.
Thermwood’s new “Universal” print head design for LSAM machines is the only heat source involved in the printing process. Rather than printing a small bead in a heated environment, Thermwood’s print head prints a large bead at such a high output rate that the deposited material needs to actually be cooled rather than heated to achieve the correct temperature for layer-to-layer adhesion. Thermwood describes it as an “exercise in controlled cooling.”
How it works is that the Universal print head prints each layer at a rate that allows it to cool to the proper temperature for adhesion before the next layer is applied. If the layer is too hot, print speed is reduced to allow it to cool before the next layer of material is deposited. If the layer becomes too cool, print speed is increased. A built-in thermographic imaging system displays a real time image on the CNC control screen, allowing the operator to maintain the ideal temperature throughout the 3D printing process.
The LSAM Universal Print Head can achieve temperatures of up to 450ºC, and uses a Siemens temperature control module integrated within the print gantry CNC control. Each print head can be equipped with one of three interchangeable “melt cores,” which consists of a feed housing, extruder and polymer melt pump. Each melt core has a different maximum print rate, which determines the longest bead that can be printed during the cooling time between layers.
Cooling time varies depending on material, amount of fan cooling and part shape. The faster the print rate, the more material can be laid down during the cooling period, which means that faster print heads create larger parts without necessarily printing them any faster. Even a standard 40mm melt core prints so fast that it often needs to be slowed between layers to allow them time to cool, which means that multiple parts can be printed in the same time it takes to build one part.
The LSAM 3D printer is equipped with a 40mm melt core, which includes a patented 40mm high speed extrusion screw with a corresponding melt pump and print head. This melt core is capable of 3D printing 150 pounds of material per hour, and can create parts with a print layer lap length of up to 175 feet while printing a bead that is .200 inches thick and .830 inches wide. If longer bead layer lengths are required, a 60mm melt core can process 50% more material, and a 70mm melt core can 3D print over 500 pounds of material per hour. The higher output melt cores do, however, have a minimum operating speed so may not be suitable for smaller parts.
In operational tests, the 40mm melt core was able to print 20% carbon fiber reinforced ABS as well as 40% and 50% carbon fiber reinforced PPS. This was using the 10′ x 10′ LSAM machine; the Universal print head will also be installed on a 10′ x 20′ demonstration machine, which is currently under construction. Discuss in the Thermwood forum at 3DPB.com.
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