FLEX is a special type of filament. Products made of this material can be bent and twisted, but they do not lose their shape. The plastic can be installed in a conventional 3D printer. It is only necessary to set the right printing parameters and not to forget about safety. In some cases, it may be necessary to slightly modify the printing device.
What is Flex plastic?
Flex plastic is a resilient material of a light shade. It withstands high loads in terms of torsion and stretching, if you compare it, for example, with PLA or ABS. Its characteristics are similar to those of hard silicone. The application area of Flex is very wide: from toys and souvenirs to prototypes of car parts and medical prostheses.
Interesting! New Balance created sneakers with a Flex sole in 2016.
The main characteristics of the filament are:
- Durability and flexibility at the same time;
- the material is resistant to aggressive media: acids and alkalis (at room temperature);
- density: 1.18-1.25 g/cm³;
- melting temperature of the plastic: 200-225 ° C;
- maximum heating point: up to +125 °C (some brands hold up to +140 °C);
- operating temperature: -40 to +100 °C;
- filament glass transition temperature: -10 to -50 °C;
- tensile elasticity 63.7 mPa.
Ready-made Flex products are easy to process: cutting, welding, dyeing, sterilization.
Information! The first copies of Flex were produced in 1959. The thermoplastic polyurethane was invented by Lubrizol Engineered Polymer. The company experimented with alternating copolymers: isocyanate and polyol. As a result the company managed to reach the optimal strength and elasticity indices. The finished material was named TPU. In 3D-printing it was renamed to Flex.
The material is valued for a number of advantages:
- Excellent tensile performance under twisting, compression or stretching;
- the filament is resistant to high and low temperatures;
- a wide range of post-processing;
- low price;
- Plastic can be recycled.
But there are some disadvantages:
- Difficult printing process;
- incompatible with Bowden extruders;
- the material is hygroscopic;
- not suitable for storing food.
It is also worth considering the safety precautions that must be observed when working with Flex.
Precautions for flex printing
Before you start work you need to prepare thoroughly:
Open the vents or windows so that the room is well ventilated.
Be sure to wear gloves and a respirator when printing. You may wear a jacket with long sleeves so there are no exposed skin areas.
It is better to print Flex on a 3D printer with an enclosed chamber that has a forced exhaust. Vapors should be diverted through a separate ventilation duct.
If the material comes into contact with the skin, immediately cool the area with cold water. After that first aid should be given, as in a thermal burn. If the person feels worse, consult a doctor.
Important: The material should not be disposed of in household ovens. It must not be incinerated or melted. Polymer emits a caustic toxic gas. You can be poisoned by it.
How to print: step by step instructions
This material has a number of features that must be taken into account when printing. Moreover, even the plastic must be stored in a special way. Let’s look at all the steps of working with Flex, from storage methods to post-processing.
Filament storage
The coil of plastic is stored in an airtight box that should be emptied of all air. Ideally, if it can create a vacuum. The material easily absorbs moisture, so you need to put moisture absorbers in the container. For example, silicone balls. It is better to dry the entire coil in the drying chamber beforehand.
Information! A Wanhao Boxman-2 camera can be used for drying. This is an inexpensive device, which can also be used to prepare other materials for printing. For example, some brands of nylon.
Printer settings
The preparatory step includes calibrating the print platform, as well as following the printing conditions:
- Do not try to nudge the plastic from the top. It will just bend inside the extruder.
- Set the print speed to the slowest setting possible. Exact recommendations are listed below.
- Keep the distance between the thermal barrier and the feeder as small as possible. Otherwise, the filament will bend and tangle.
If the material clogs the extruder time after time, try setting the forced cooling of the top of the hot-end. The main task of the 3D maker is to make the optimum temperature for the filament exactly at the bottom of the hot-end, but not higher.
Platform temperature
Another important point is to set the temperature of the working platform, as well as preparing the surface for printing. It is recommended to preheat the table to 45-60 °C. The surface of the platform can be covered with masking tape or kapton. Another option is to install a polyesterimide (PEI) based sheet.
Information! Also a special varnish is used to improve the adhesion properties. It is applied to the surface before printing.
Printing speed and parameters
The next important step is the setting of the printer parameters:
- printing speed: from 10 to 20 mm/s (or the minimum);
- filament feed coefficient: 1.03;
- Thickness of printed layer: 20% less than nozzle diameter;
- Extruder temperature: 235-240 °C.
The exact settings can be found on the material label. Or you can try to set the parameters by trial and error. Here we give general recommendations that work in most cases.
Cooling
Blowing the top of the hot-end will be necessary if the filament is coming out in chunks. Simply install a small computer fan. Even a small aluminum radiator glued on thermal paste or thermal gasket will save the day. It is also worth including a blower on the model itself.
Finishing the Part
How to process your model? After finishing printing leave the model in the drying oven for 2-3 hours. The drying temperature is 200 °C. The figure should lie face up. The finished product will have a smooth glossy surface. Maybe the top layers will melt a little. This is not critical and is almost imperceptible.
Methods of post-processing:
- Mechanical machining. Supports are fairly easy to cut with a stationery knife. But sanding the workpiece is problematic. It must be fixed in one position or held by hand. It is best to do machine processing with CNC machines.
- Gluing. Before gluing the two Flex workpieces, you need to treat both parts with alcohol. Solvents based on dimethyl sulfoxide, tetrahydrofuran, and dimethylformamide can be used as glue. Normal glue for rubber products will also work.
- Puttying. Dimensional models are often covered with a layer of putty. Filament holds the finishing material well. Most often putty is applied for subsequent painting.
- Painting. The finished model can be painted both on the surface of the product and on the putty layer. It is better to take a paint based on silicone, so the top layer will not crack if the figure will be bent or twisted.
When gluing two pieces of Flex it is worth working with gloves and a respirator so as not to get a slight chemical burn.
Flex printing mistakes and how to avoid them
The most common mistakes made by 3D-makers:
- Lack of cooling or thermal barrier in the printer device. You need to replace the hot-end or put a forced air blower.
- High print speed. Plastic jams are occurring. Turn down the plastic feed rate to a minimum.
- Thread jamming when the print head passes over empty areas. Enable the retraction feature, so that the extruder pulls up the filament as it moves over unprinted areas.
- Plugged nozzle or hot-end. Thoroughly clean the entire structure of previous plastic before you start.
- Improper filament storage. Be sure to use sealed boxes with water absorbers.
- Ignoring safety precautions. Thermal burns or poisoning by caustic gases as a consequence. Be sure to use gloves and a respirator.
Set accurate print settings as recommended by the manufacturer.
Flex is a very interesting and creative material. It can be used to make spring-loaded models. You can create different dampers and shock absorbers. But you have to keep in mind the storage conditions of the material as well as the correct print settings.
