Alexei Volkov
Injection molding is a process in which molten plastic is injected into a molding cavity, cooled, and shaped. The two main types of molds are the moving mold and the fixed mold. The leftover plastic from molding can be melted and reused, but this can be challenging and expensive. Some people have attempted to melt leftover plastic and use it for crafting, but the results are mixed. Additionally, the type of plastic used and the melting temperature must be carefully considered to avoid deterioration.
| Characteristics | Values |
|---|---|
| Rotational Molding | A powder or liquid resin is placed into a metal mold and rotated in an oven until the resin coats the inside of the mold. |
| Injection Molding | Used for making high-volume custom plastic parts. |
| Blow Molding | A method of making hollow, thin-walled, custom plastic parts. |
| Compression Molding | Heated plastic material is placed into a heated mold and pressed into a specific shape. |
| Extrusion Molding | Similar to injection molding but produces a long continuous shape. |
| Leftover Plastic | Can be melted and molded into new products, or sent to a company offering credits for every kilo of PLA waste. |
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What You'll Learn
Recycling leftover plastic from 3D printing
The leftover plastic from 3D printing can be recycled and reused. However, there are some challenges to recycling 3D-printed plastic, and not all types of plastic can be recycled using current methods.
Types of 3D Printing Plastic
3D printing plastic materials can be split into three main types: thermoplastics, thermoset plastics, and elastomers. Thermoplastics are used by nearly all Fused Deposition Modeling (FDM) 3D printers because they become pliable and workable when heated past their melting temperature. Thermoplastics can be recycled as, in theory, the polymers can be re-melted. However, different thermoplastics have different recycling difficulties, and not all recycling facilities are equipped to recycle all types of thermoplastics.
Thermoset plastics, such as polyurethane or silicone, are moulded and then cured. They are often used in vat polymerization 3D printing processes like Stereolithography (SLA). Thermoset plastics cannot be recycled using current methods because they are cured, which makes them perfect for high temperatures but impossible to recycle.
Elastomers can be natural, like rubber, or synthetic, like thermoplastic elastomer (TPE). Thermoplastic rubbers are a type of copolymer made with rubber and plastic and are not widely used in 3D printing and cannot be recycled.
Despite the challenges, there are two main ways to recycle 3D-printed parts. The first is to turn the plastic back into material that can be reused for 3D printing. The second is to use the recycled plastic to make objects used in other manufacturing processes, such as injection moulding.
Some companies offer recycling programs where users can send in their leftover plastic from 3D printing to be recycled and, in return, receive credits to buy recycled filament. There are also companies that offer to recycle failed prints from students and turn them into filament for the next student.
There are also methods of recycling leftover 3D-printed plastic at home. Some people have melted leftover PLA scraps and treated them like modelling clay to create new objects such as coasters, bowls, and art. Others have discussed melting leftover plastic and pouring it into a mould to create new objects, but the ideal temperature for doing this without deteriorating the plastic is unclear.
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Melting and moulding leftover plastic
Leftover plastic from 3D printing, such as PLA scraps, can be melted and moulded into new shapes. One approach is to melt the plastic in an oven and then pour it into a mould. Alternatively, plastic shreds can be placed into a mould and melted. However, it is important to note that the maximum temperature must be determined to prevent the plastic from deteriorating and becoming too viscous.
When working with plastic bags, it is recommended to shred them first to achieve a finer texture. The shredded plastic can then be melted in a pot or double boiler with oil, such as canola oil, to prevent overheating. This method can also be applied to HDPE plastic bottles. Resin Identification Codes #2 and #4 are suitable for this process, while PETE/PET or #1 may also work.
After melting the plastic, it can be shaped into the desired form. For example, a salsa container can be used as a mould for a wheel, with a wine bottle creating a hole in the middle. The plastic should be allowed to cool, and the final product can be carved, machined, turned, or drilled for a more precise shape.
It is worth mentioning that moulding leftover plastic is a complex process, and there are limited resources available on the topic. Additionally, the recycling of plastic from failed 3D prints can be challenging due to the lack of acceptance by municipal recycling systems. However, some companies offer incentives, such as credits for PLA waste, encouraging the recycling of plastic materials.
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Types of plastic moulding
Plastic moulding is the process of manufacturing by shaping liquid or pliable material using a rigid frame called a mould or matrix. When moulding plastics, a powder or liquid polymer such as polyethylene or polypropylene is placed into a hollow mould so that the polymer can take its shape.
There are six main types of plastic moulding:
- Thermoforming: This involves heating a large sheet of plastic until it is soft and flexible, then stretching it over a single-sided custom mould. Vacuum pressure or compressed air presses the thermoplastic tightly against the mould, creating the desired shape.
- Injection moulding: This involves melting a thermoplastic to a liquid and then injecting it into a double-sided mould using a highly pressurised injector. This is commonly used for making very high volumes of custom plastic parts.
- Extrusion moulding: This is used to manufacture long, straight pieces such as tubing, hoses, or pipes. It involves forcing liquid plastic into a die to form a shape. The shape of the die can be customised and can be round, T-shaped, L-shaped, or square.
- Compression moulding: This is often used with thermoset plastics whose chemical structure changes when melted and cooled, resulting in a hard, rigid final product. Plastic resin is heated to a soft, almost "putty" state and then placed into a heated mould. It is then pressed into shape by the mould and allowed to cool.
- Blow moulding: This is similar to injection moulding as the plastic is heated to a liquid state and injected into a mould. However, once the plastic is in the mould, air is injected into it, inflating it so that it presses against the walls of the mould. This is ideal for producing thin, hollow-walled pieces such as water bottles.
- Rotational moulding: This involves pouring melted plastic into a mould, which is then rotated at high speed. This coats the plastic evenly along the walls of the heated metal mould, leaving the interior hollow. This method is primarily used for large, hollow-walled containers, storage bins, and kayaks.
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Plastic moulding applications
Plastic moulding is a process of manufacturing plastic parts by shaping liquid or pliable plastic material using a rigid frame known as a mould or tool. There are several types of plastic moulding, each with its own unique techniques and applications. Here are some common types of plastic moulding and their applications:
Injection Moulding
Injection moulding is one of the most popular and widely used plastic moulding techniques. It involves using a ram or screw-type plunger to force molten plastic or rubber material into a mould cavity. The plastic solidifies and takes the shape of the mould. Injection moulding is commonly used to process thermoplastic and thermosetting polymers, with the former being more prevalent due to its ease of recycling, versatility, and ability to soften and flow when heated. Injection moulding is ideal for producing large quantities of plastic parts such as bottle caps, storage containers, toys, car parts, and surgical components. It offers design flexibility and is often used for insert moulding, creating plastic parts with protruding metal screws.
Rotational Moulding
Also known as rotomoulding, rotational moulding involves placing liquid plastic or resin inside a mould, which is then rotated at high speeds. This technique creates hollow parts with evenly thick walls, such as car parts, bins, storage tanks, and kayaks. Rotational moulding allows for customisations like adding bends and signage to the products by placing them into the mould.
Extrusion Moulding
Extrusion moulding involves pressing hot melted plastic through a shaped hole or die to create lengthy shaped plastic parts. This method is used for producing high volumes of consistently shaped parts, such as straws or PVC pipes. It is a low-cost process due to its simple equipment and high productivity.
Compression Moulding
Compression moulding is a technique where liquid plastic is poured into a heated mould and then compressed to form the desired shape. This method is similar to rotational moulding in that it uses compression to shape the plastic. Compression moulding is used for creating big and hollow parts, such as car parts, bins, cones, and storage tanks.
Blow Moulding
Blow moulding is a type of plastic moulding where custom plastic parts are produced with hollow and thin walls. This method is ideal when uniform wall thickness is required in the final product.
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Cost of plastic moulding
The cost of plastic moulding varies depending on several factors, including the size, complexity, material, and anticipated quantity of the mould. The cost of producing plastic injection moulds ranges from $500 for a simple design to over $30,000 for a complex one. The cheapest option is a small desktop injection moulding machine, perfect for in-house projects, which can cost anywhere from $1,500 to $7,000. On the other hand, large industrial moulding machines operated by service providers and large manufacturers can cost anywhere from $50,000 to $100,000 or more.
The type of plastic resin used also affects the cost, with prices ranging from $2 to $20 per pound. Aluminium moulds are typically cheaper than steel, but steel moulds are more durable and can lower the per-piece price. The number of parts produced also influences the overall cost, as higher production numbers can lower the final per-piece cost.
To reduce costs, it is recommended to minimise unnecessary product features, eliminate cosmetic finishes, and re-evaluate the part size. Obtaining an accurate quote for plastic moulding costs can be complex, and it is important to consider all variables to determine the overall injection mould cost.
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Frequently asked questions
Leftover plastic from molding is the excess plastic material that remains after a product has been molded into its desired shape.
Common types of plastic molding include rotational molding, injection molding, compression molding, and extrusion molding. Each process has its unique advantages and applications, catering to different volume, precision, and shape requirements.
Leftover plastic from molding can be reused or recycled. Reusing involves placing the excess material back into the mold, while recycling may involve melting and reshaping the plastic or sending it to a company that offers credits for PLA waste, which can be used to purchase recycled filament.
