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3D printing

Lesson 2:

Other manufacturing techniques.

In the previous lesson, we saw that 3D printing is an example manufacturing technique, that is, a method to manufacture objects. However, there are many other manufacturing techniques that have been in use long before 3D printing started, and are still in use today.

Below are some of the most commonly used techniques:

  • Injection moulding: consists in introducing a molten material (usually a metal or a plastic) into a mould with the shape of the object that is going to be manufactured. It is used to make plastic containers, boxes, chairs… as well as little metal parts. A mould is just a set two parts that form a cavity in between. Once the material is introduced, it is cooled, and then the mould is opened to extract the object. In the case of plastics, the molten plastic is usually injected into the mold by means of a leadscrew (large screw), as seen in the gif:
  • Blow moulding: it is the technique used to make most plastic bottles and other types of containers. It consists in blowing compressed air inside a plastic piece in such a way that it expands and takes the shape of the mold that surrounds it, leaving its inside hollow:
  • Extrusion moulding: this technique is quite similar to injection moulding. The only difference is that in this case a mould does not exist. The plastic is forced to pass through a part called die, with the desired shape. This technique is used to manufacture continuous objects such as pipes or hoses. You can see an explanation of the process in the following video that describes the three manufacturing techniques that have been explained so far:
  • Rolling: it is a widely used manufacturing technique to produce, for example, metal plates. It consists of dropping molten metal between rollers that progressively reduce its thickness (Video)
  • Bending: it is a technique that consists of bending a sheet (usually metal) to give it a certain shape. Metal shelves or tables are frequently manufactured using this technique.
  • Deep drawing: It is the technique used to make the large amount of cans that are consumed daily around the world. It consists of deforming a metal sheet using a piece called a punch, as can be seen in the following video.

Advantages of 3D printing

Once we have seen that there are other ways to manufacture objects apart from 3D printing, it is worth wondering what makes us decide between one technique or another. This decision is very important when manufacturing any product, since choosing the most appropriate technique will make the final product have better or worse quality and the manufacturing costs will higher or lower.

The key to decide the best manufacturing method for a given product is the number of copies that are going to be made. Think, for example, of the difference between making water bottles and making a dental prosthesis.

In the case of water bottles, when a company is going to commercialize them, it has to make the design of the bottle which will be repeated thousands or millions of times. In that case, the company should choose one of the more traditional manufacturing methods that we have seen in the previous section (blow moulding for example). In this case, it is said that manufacturing should be highly automated.

The reason is that these methods allow you to make exact copies of the product at a very high speed. The disadvantage is that it is necessary to buy large machines that are very expensive and that, in this case, can only be used to make plastic bottles. In addition, the installation and start-up of the manufacturing facility is time consuming. The good part is that once the necessary investment has been made and the equipment is installed, the manufacturing cost of each bottle is ridiculous.

The example of dental prostheses is radically different. When a dentist is going to manufacture one for a specific patient, he must make sure that it perfectly adapts to the measurements of his mouth. This means that each of the products it manufactures will have slight differences what makes it impossible to use a machine that makes copies automatically. In this case, it is said that manufacturing should have a high degree of customization. It is just in these cases when the use of 3D printers is very interesting.

The following lists summarize the advantages and disadvantages of 3D printing as a manufacturing method.

  • It is quite versatile, what allows to create completely customized objects.
  • The process of design and manufacture is quite fast.
  • It does not require large investments in machinery.
  • Allows the use of different materials with the same printer.
  • If you want to make a great number of copies of the same product, there are much faster and cheaper alternatives.

What materials can be 3D printed?

Nowadays, after decades of research, it is possible to print with almost any material that you can think of. However, depending on the material you want to use one or another printing technique must be chosen. We’ll talk about it in the next page.

Below are some of the most commonly used materials for 3D printing:

  • Plastics: Probably the first material that comes to your mind when talking about 3D printing is plastic. Out of all the types of plastics, thermoplastics are the most commonly used. This group of plastics gathers all those that can be melted and solidified several times, which is the reason why they are recyclable materials. These types of materials are the cheapest option of all the materials used for 3D printing and the differences between them are limited to small differences in strength and surface finish. Below are some of the most used.
  • Resins: they are actually another type of plastics, in this case not recyclable, since once they are formed they cannot be melted and solidified again (they degrade and lose their properties). Among its properties we find good flexibility and very smooth surfaces.
  • Metals: strangely enough , metals are also an option when it comes to 3D printing and in fact they have been used with this technology for many years. As will be explained on the next page, there is a specific technique that allows any metal to be printed from very small particles that are fused to form the object.
  • Other materials: in the last years, new materials have begun to be printed. And, though they are not as widely used as plastics and metals, they also have quite interesting applications… For example, wax 3D printing allows to manufacture moulds to create metallic parts (see lost-wax casting):
  • Composites: are mixtures of materials, usually plastic with another material, whose main purpose is to achieve a good aesthetic result while maintaining the advantages of printing plastics.
  • Materials for specific applications: as explained on the previous page, some of the applications of 3D printing that have been developed in the last years, and that are currently under development, require very specific materials.

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