Modern industry is unimaginable without plastics. Modern industrial-grade polymers are easy to produce and process. They are very robust, resistant to corrosion and, above all, very light compared to metals. This is why they are so popular among industrial designers. Due to this popularity, plastic prototyping techniques have become very popular in recent decades. Let's see what they can offer us today.
Plastic Prototyping Today
For a long time, plastic production was the domain of mass production. You needed an injection mold and a machine tool that injected plastic into the mold. The entire system was very expensive and any kind of change in the design of such a system is very expensive. This is why metal has been the number one prototyping material for a long time, especially since the rapid development of digital systems and therefore computer-aided numerical controls. However, this changed with the advent of rapid prototyping processes.
The development of rapid plastic prototyping
The first of these techniques was vacuum silicone casting, in which hard tools were replaced by soft tools. Silicone molds are much cheaper and easier to make.
The next changes came with innovative additive manufacturing processes, which do not require raw parts or tools. Furthermore, they offer unprecedented design freedom.
Eventually, CNC machining processes made plastic injection molding possible quickly. Interchangeable aluminum molds, which are easier to manufacture compared to tool steel, can reduce tool delivery time by up to 60%. Additionally, changing the cavity of an aluminum mold is much easier than with heat-treated steel.
The Benefits of Implementing Plastic Rapid Prototyping
Where plastic prototypes can help
Plastic prototype parts are used for more than just kitchenware and appliances. They have many other possible uses. For example, many medical products are made from plastic because some polymers adhere well to human tissue and are very light. Transparent plastic parts are often used in vehicle lighting. They are less fragile than glass. Many plastics provide good insulation or thermal insulation. Therefore, if the product has heated or high voltage surfaces, plastic handles and casings ensure user safety. Due to their good friction properties, some polymers are used to make cheap and efficient bearings.
The 4 most important options for rapid plastic prototyping
With rapid advancements in the manufacturing industry, molding, 3D printing, injection molding, and CNC machining are becoming increasingly popular. These technologies, based on CAD-based rapid 3D prototyping tools, are often used for plastic parts.
1. Casting techniques for producing plastic prototypes
Silicone molding is a great process for producing small-volume plastic prototypes because it requires a master model (a sample) to create the molds. Typically you hang the master model over an empty tank. Then you add some technological elements (usually also made of plastic) to the model, such as the channel where the plastic is poured, ventilation, etc. After that, you pour liquid silicone into the tank, wait for it to solidify and harden sometimes in the oven. You divide the mold in half and it is ready to make up to 25 plastic parts. No capital investment is required.
2. How to use 3D printing for plastic prototyping
Additive manufacturing or 3D printing as it is often called is a comparatively innovative process for producing various parts. What defines 3D printing is the change in mass. The blank is usually larger than the final piece. However, with AM it is completely different. The blank is a fine powder or thread. It is applied layer by layer to the printer base plate and sintered or cured to copy the current cross-section of the part. AM has come a long way since its invention in the 1980s. The precision, surface finish, material selection and lead time of additive manufacturing have remained the same.
Selective laser sintering (SLS)
Selective laser sintering is the first process among the many additive manufacturing techniques used for rapid plastic prototyping. It is the most universal type of additive process that can be used for virtually any type of material. Of course, this also includes plastics. They do not require high laser power to be sintered, and the main advantage of spraying powder onto the base plate is that it acts, to some extent, as a support structure for pendant elements.
Fused Deposition Modeling (FDM)
FDM is the cheapest and simplest additive process for producing plastic prototypes. Many hobbyists build FDM 3D printers at home. FDM uses raw material in the form of a plastic thread, which is liquefied and placed on the plate in the shape of the current cross-section of the part. The protruding structures are supported using a different material – a more fragile type of plastic that can be easily removed. Overall, FDM is the cheapest process that produces the worst surface finish and quality and requires the most post-processing when aesthetics are important.
Stereolithography (SLA)
SLA is considered the father of all 3D printing processes. It is also the process with the best part quality. The surface finish is almost perfect and the accuracy is limited only by the diameter of the UV/laser light. The process is often used to create master models for castings and later prototypes when aesthetics are a concern. However, SLA is the most expensive process because the liquid polymer is very expensive and a significant amount of it has to be poured into the tank. Another problem with SLA is the support structures. They can only be made from the model material and must be removed mechanically. This can cause stains on the surface that need to be reworked.
Multijet printing (MJP)
Multijet printing is a popular choice for plastic prototypes because it offers many of the advantages of FDM and lacks some of the disadvantages of the SLA process. The purpose of the MJP is to melt the raw plastic into droplets and eject them from the printer nozzle in the desired contour. The advantage of MJP is that the quality of the parts is similar to SLA, but you don't have to fill an entire tank with liquid polymer and think about what to do with the rest. MJP is also the only multicolored process among those mentioned.
Post-processing of 3D printed prototypes
Despite successes in the field of additive manufacturing, plastic parts often require post-processing. The most common methods are machining, polishing and chemical processes. The first technique is relatively simple. You install the manufactured part on a machine tool and machine it with a milling machine. Polishing is also a well-known process. A special paste and polishing device are used to obtain the perfect surface finish. Chemical processes include acetone processing and coating. The first method uses acetone gas to melt the surface of the piece and make it smoother. The process is very efficient, but is only suitable for a limited number of polymers. The coating is more universal. They basically cover the piece with paint or another element to improve the surface quality.
3. How to create a plastic prototype using rapid injection molding
Rapid plastic injection molding is a variant of traditional injection molding technology. The main difference is in the details. For example, quick forms have more connections. The mold cavity is connected to the base. Therefore, if you need to change the design, simply remove the cavity and change it without changing other elements. This reduces accuracy but increases flexibility. Furthermore, aluminum alloys are used instead of hardened steel, which is suitable for millions of iterations. Although they are less durable, their manufacturability is up to five times better. All modifications make it possible to use plastic injection molding even for prototypes. However, it is advisable to use it for the highest quality work, as the procedure is still quite expensive.
4. When using CNC machining to produce plastic parts
When it comes to machined plastic and metal components, many plastic prototype manufacturers use CNC machining for testing the form, fit and function of plastic parts due to its advantages in the area of prototyping. With the improvement in production-grade material selection that machining brings, we at Wayken use CNC prototyping to produce prototype plastic and metal parts. This allows your design team to accurately simulate the final appearance and function of the product, while also reflecting the validity of the assembly work and allowing sufficient time and space to modify and optimize the design.
The Future of Plastic Rapid Prototyping Technology
Most experts assume that additive manufacturing will take an even larger share of the prototyping market in the future. Finally, it is perfect for this purpose as additional developments are made to improve printing speed and part quality. Porosity is also a current problem. There is a lot of research to be done to address the shortcomings of 3D printing, and it is likely that AM will be the perfect choice for plastic prototyping in the next decade unless another innovative process is invented. If you would like more information, you can find our plastic processing options.
