We had been thinking to make an all-purpose extruder for all materials but failed because the properties of plastics are very different from each other. As ABS is the primary material Tiertime had been focusing on for many years, our extruder was optimized toward ABS and similar styrene base materials such ASA, PC-ABS, HIPS and etc. However as people start to experiment and print whatever plastics that can be extruded to filament, the extruder design cannot provide good reliability to all of them. Therefore, we classified 3 major types of extrusion behaviors of plastic and derived 2 more extruders base on our ABS optimized design. Here are some insights why these 3 extruders will work better.
- Extrusion mechanism
The extrusion mechanism for ABS and PLA are the same, The filament is feed through a fixed width gap between the extrusion gear and bearing. This mechanism is well tested and very reliable and provide good result provided that the filament diameter and hardness are well controlled. For TPU extruder the extrusion mechanism is spring loaded and the extrusion gear is groved. As TPU or other soft is flexible and will change filament diameter under pressure, these design can effectivly prevent slippage and apply maximum extrusion force.
- Heater Module and filament path
Heater module for all 3 extruders are made similarly but with some key small adjustment. All 3 extruders use 24V 80W heater tube and Pt100 temperature sensor. They all use silver coated wire with PTFE tube protective tube to ensure maximum reliability.
Where the difference lays is the actually the filament path. The ABS heater module use a bare stainless steel tube while PLA and TPU use a PTFE lining inside the stainless steel tube. This is because PLA and TPU has large friction with steel but can be effective lubricated with PTFE. For TPU extruder the extrusion path is also fully constrained so that the soft filament will not be squeezed out from the path while applying a large extrusion force.
However PTFE is material that can only work consistently at about 280, so if you print ABS or other high temperature materials, the PTFE will degrade overtime and impaire reliability of the printing. So ABS extruder, which has a full metal hotend, is choice for prolonged high temperature operations and should be considered to use when printing materials such as PA, PC, PP and etc
Extruder cooling is also a very important factor for print quality and print reliability. For material that has large shrinkage ratio such as ABS, minute or even no cooling is needed. If too much cooling is applied the print will warp or distort and result in print failure. However for materials with small shrinkage ratio and lower melting temperature eg. PLA, an adequate amount of cooling to the nozzle will effectively improve print quality. Also the temperature gradient between the hotend and coldend also critical for materials with lower melting temperature. As temperature climb up to cold end, the filament could soften before going into the nozzle and cause clogging.
Base on the property of these 3 typical materials, ABS extruder has the least amount of cooling and usually need to close the wind door for better results. PLA requires the largest amount of cooling to nozzle and extra cooling is applied to its heat sink and extruder motor to prevent premature softening of the filament. TPU extruder has a cooling amount designed to be less than PLA but more than ABS.
As Tiertime now provide a number of nozzle options, use the suitable nozzle to an extruder may also improve print quality. The all-purpose 0.4mm nozzle base on our experience is a little too small for flexible filaments and so we made the default nozzle of TPU extruder to be 0.5mm, this give better flow of the material and better print quality and reliability. For PLA and ABS user could choose from 0.2mm, 0.4mm, 0.6mm nozzles. 0.4mm nozzle has the widest working range, it gives good quality prints from 0.1mm layer to 0.3mm layers, so could be considered as a all-purpose nozzle. The 0.2mm nozzle is for fine, high resolution prints, it work best for layer thickness from 0.1mm to 0.05mm. 0.6mm nozzle ，in contrast is for printing thick layers start from 0.3mm or above. It provides the best flow of filament and allows the fastest print speed, good for drafting. Some users also believe thick layers will increase overall print strength, therefore use 0.6mm nozzle for structure parts.
0.4mm and 0.6mm nozzle also have hardened steel types as options, so it will retain its precision even when printing abrasive materials such as carbon fiber or glass fiber filled materials.