Ethan Clarke
Plastic shrinkage is a phenomenon where the volume or dimensions of plastic decrease during the injection moulding process as it cools and solidifies. ABS (acrylonitrile butadiene styrene) is a durable and versatile plastic commonly used for 3D printing. It has a shrinkage rate of 0.4% to 0.9%, which is higher than some other plastics. This means that ABS warps easily as it cools and contracts. To reduce ABS plastic shrinkage, it is important to consider factors such as material selection, mould design, and injection moulding process parameters. One of the most effective ways to reduce ABS shrinkage is by adding extra perimeters, which strengthen edges and corners. Other methods include using a heated chamber to control the cooling process, printing slowly, increasing the number of perimeters for rigidity, and using large layer heights to speed up crystallisation.
| Characteristics | Values |
|---|---|
| ABS shrinkage rate | 0.4% to 0.9% overall |
| Warping prevention | Use a raft or brim to improve bed adhesion |
| Layer adhesion | Reduce print speed |
| Cooling | Use a heated chamber to reduce cooling and crystallization |
| Print speed | Print very slowly, 15-25 mm/s |
| Perimeters | Increase the number of perimeters to 8-10 solid shells for rigidity |
| Layer heights | Use large layer heights like 0.28 mm to speed crystallization |
| Molding temperature | Consistent molding temperature reduces shrinkage |
| Injection pressure | Increased injection pressure decreases shrinkage |
| Melt temperature | Higher melt temperature reduces shrinkage |
| Mold temperature | Higher mold temperature increases shrinkage |
| Pressure | Prolonged pressure maintains shrinkage reduction |
| Cooling time | Longer cooling time within the mold decreases shrinkage |
| Injection speed | High injection speeds slightly increase shrinkage |
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What You'll Learn
Use a raft or brim to improve bed adhesion
When printing with ABS, bed adhesion and warping can be improved by using a raft or brim. A raft is a 3D-printed base that sits underneath the part, acting as a platform that anchors the part to the build platform. Rafts are particularly useful when the build surface is warped or damaged, as they can provide a level base for your print. However, they consume a lot of material and can be challenging if your print requires a smooth, precise base. Most slicer software programs have raft integrations built-in, so you don't have to design them yourself.
On the other hand, a brim is a 3D-printed border that attaches to and extends from the edges of the 3D-printed part, increasing the surface area of the print's base and encouraging better first-layer adhesion. Unlike a raft, a brim does not go underneath the 3D printed part's first layer. Brims are effective for securing a part to the build platform, especially for parts with a small base or footprint that might become unstable during the printing process. You can set a ""Brim Distance"" in your software, and setting that to around 0.10 mm can make the brim easier to break away when it's no longer needed.
Both rafts and brims are helpful tools to improve bed adhesion, but they are suited to different situations depending on the object's geometry and contact area with the build plate. For example, if you are using a higher-temperature filament like ABS, which has a greater ratio of shrinkage and warping, a brim can promote better layer adhesion and reduce warping. If you are working with a new or good-quality print surface, a brim will usually be sufficient to improve bed adhesion, and you may not need to use a raft.
In addition to rafts and brims, there are other techniques to improve bed adhesion and reduce warping when printing with ABS. One technique is to increase the number of perimeters to 8-10 solid shells for rigidity. Another technique is to use a heated chamber to control the cooling process and reduce warping. Finally, reducing the print speed can also improve layer adhesion and slower cooling, with 60 mm/s being ideal for ABS.
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Reduce print speed for better layer adhesion
ABS (acrylonitrile butadiene styrene) is a durable and versatile plastic commonly used for 3D printing. It has a shrinkage rate of 0.4-0.9%, which is higher than that of PLA. One way to reduce ABS shrinkage is to add extra perimeters, strengthening edges and corners.
Reducing print speed is another effective method to improve layer adhesion and reduce ABS shrinkage. When printing at high speeds, the layers may not have sufficient time to bond well, resulting in weak adhesion and potential layer separation. By decreasing the print speed, you allow more time for each layer to adhere properly to the next, creating a stronger and more cohesive final product.
Each filament type has unique properties that require specific strategies to optimise layer adhesion. ABS, for instance, requires a higher extruder temperature of around 220-250°C, and a heated bed at approximately 100°C to ensure the first layers stick well. For ABS, a print speed of 50mm/s is considered good, while 30mm/s is a common slower speed.
It is important to note that there is a limit to slowing down the print speed. If the speed is too slow, issues such as overheating, warping, and stringing may occur. Therefore, finding the optimal speed for your specific filament and model is crucial.
By reducing the print speed and implementing other strategies such as temperature control and adding perimeters, you can effectively minimise ABS shrinkage and improve layer adhesion, resulting in stronger and higher-quality 3D prints.
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Add extra perimeters to strengthen edges and corners
ABS (acrylonitrile butadiene styrene) is a durable and versatile plastic commonly used for 3D printing. It is especially popular for functional parts that require good impact resistance. ABS has a shrinkage rate of between 0.4% and 0.9%, which is slightly higher than that of PLA. During the cooling and contraction process, ABS warps easily.
To reduce ABS shrinkage and strengthen edges and corners, adding extra perimeters is one of the most effective methods. This technique is particularly useful when printing parts with holes for screws, as it provides extra compressive strength in those regions. By increasing the number of perimeters, you can create solid shells that enhance rigidity and overall strength.
To implement this method, you can adjust your printing settings to specify a higher number of perimeters for specific sections of your model. For example, you might want to set 8 to 10 perimeters for the edges and corners that require reinforcement. This can be achieved by using software tools that allow you to modify the perimeter settings for different areas of your model.
Additionally, consider using a heated chamber to control the cooling process and further reduce shrinkage. Printing slowly, at a speed of 15-25 mm/s, will also promote even cooling and help mitigate ABS shrinkage.
By following these instructions and adding extra perimeters, you can effectively strengthen the edges and corners of your ABS-printed parts while minimising the impact of shrinkage.
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Control temperature, pressure, and holding time
The shrinkage rate of plastic is the percentage difference in the dimensions of a plastic part at moulding temperature and after it has been cooled to room temperature. The shrinkage rate is influenced by the type of plastic, crystallinity, molecular weight, and modifications. For instance, the shrinkage rate of PP resin can be reduced by increasing the injection pressure and melt temperature while keeping the moulding temperature unchanged.
The design of the mould's cooling system also affects the cooling efficiency of the plastic, thereby influencing the shrinkage rate. A well-designed cooling system can reduce the overall shrinkage rate by speeding up the cooling and solidification process.
In the injection moulding process, it is crucial to adjust the moulding parameters according to the plastic's properties and the mould design. This involves controlling the temperature, pressure, and holding time.
Firstly, controlling the temperature is essential as excessively high injection temperatures can reduce the viscosity of the plastic melt, accelerating the cooling and solidification process, which increases the shrinkage rate. Therefore, maintaining the appropriate temperature for the specific plastic being used is crucial to reducing shrinkage.
Secondly, pressure plays a significant role in the shrinkage rate. Excessive injection pressure can increase shrinkage. To reduce shrinkage, it is recommended to increase the pressure while keeping the moulding temperature unchanged.
Lastly, the length of the holding time impacts the cooling and solidification of the plastic, affecting the shrinkage rate. A longer holding time can reduce the shrinkage rate, but it is important to note that the shrinkage rate is not affected after the gate is closed.
By carefully controlling these factors, it is possible to minimise ABS plastic shrinkage and achieve the desired dimensions and quality in the final product.
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Understand the impact of material type, composition, and moisture absorption
Understanding the impact of material type, composition, and moisture absorption is crucial when addressing ABS plastic shrinkage.
Material type plays a significant role in shrinkage rates. For instance, ABS (acrylonitrile butadiene styrene) has a higher shrinkage rate than PLA, averaging 0.4-0.9% overall. The type of resin used also influences shrinkage, with some resins exhibiting greater shrinkage than others. Crystalline plastics, such as nylon, generally exhibit greater shrinkage than amorphous plastics like PETG.
The composition of the material is another critical factor. Thicker walls lead to longer cooling times and greater shrinkage. Features like reinforcements and engravings resist shrinkage, resulting in lower shrinkage rates. The addition of fillers to plastics can significantly reduce shrinkage. For instance, the inclusion of plastic aggregates in cementitious materials can enhance durability and reduce sensitivity to shrinkage cracking.
Moisture absorption also influences shrinkage. Drying shrinkage occurs when the external humidity is lower than the internal moisture content, leading to evaporation and a reduction in volume. The amount of water present, the rate of evaporation, and the presence of internal or external restraint can all impact the degree of drying shrinkage.
By comprehending these factors, you can make informed decisions about material selection and design optimization to minimize ABS plastic shrinkage and achieve the desired outcomes.
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Frequently asked questions
Plastic shrinkage refers to the percentage decrease in dimensions from the initial, uncooled size of a plastic product to the final, cooled room-temperature size. It is caused by the rearrangement and tightening of molecular chains as the plastic cools and solidifies.
The shrinkage rate of plastics is influenced by various factors, including material type, composition, moisture absorption, mould temperature, thickness, molding processes, and environmental conditions. Additionally, thicker walls lead to longer cooling times and higher shrinkage rates.
To reduce ABS plastic shrinkage, you can try the following:
- Use a raft or brim to improve bed adhesion and prevent warping.
- Reduce print speed for better layer adhesion and slower cooling.
- Scale models up to 100.4-100.9% in your slicer to match the desired final dimensions.
- Add extra perimeters to strengthen edges and corners.
