How do you replicate plastic parts?

How plastic parts are manufactured

The process of obtaining a plastic part by injection follows an order of operations that is repeated for each part. This order, known as injection cycle, can be divided into the following stages

The cycle begins with the closing of the mold, preparing it to receive the injection of the molten material. In this phase, the clamping nut is applied, which is the one made by the machine to keep the mold closed during injection. It depends on the projected surface of the part and the actual pressure (specific pressure) in the mold cavity.

Once the mold is closed and the clamping force is applied, the mold filling (injection) phase begins. The screw of the injection unit injects the molten material into the mold at a high pressure; while injecting, the screw advances without rotation. The duration of this stage can be from tenths of a second to several seconds, depending on the quantity of material to be injected and the characteristics of the process.

Copy plastic part

Figure 2 shows the front section of the spindle and barrel after the compensation phase. Here the cushion value is 0.15 inches. It is important to note that this is not an adjustment, but a result of the molding process. There should always be a cushion present in front of the spindle.

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We can illustrate this concept (Figure 3) by a theoretical assembly of two chambers joined by a connector. In the upper chamber there is a piston and in the lower chamber there is a pressure gauge. In scenario 1 there is fluid in chamber 1 and a force exerted on the fluid will be transferred through the connector to the fluid in the lower chamber. This can be confirmed by the pressure increase shown by the pressure gauge. However, if the upper chamber is empty, as shown in scenario 2, any force applied on the piston will not exert any pressure on the fluid in the lower chamber, and the pressure gauge will always indicate zero pressure. Therefore, it is clear that there must be some amount of fluid in the upper chamber in order to see any pressure in the lower chamber.

How to inject plastic at home

With scientific molding, two stages are used to form a part: the first stage, brings most of the plastic into the part, typically 90% to 99% by volume. And the second stage fills the part and replicates the texture and shape of the steel cavity. The second stage generally moves relatively little plastic into the cavity but is critical to surface finish, cosmetics and part dimensions. Molders work with two parameters for setting the second stage, pressure and time.

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Controlling the change from the first to the second stage is perhaps the most critical element of a molding process. It can be the secret to the success or failure of your process in producing high quality parts and is often the reason processors cannot replicate parts from one machine to another. For most applications, the changeover should be as short as possible, which means a quick change from the pressure at the end of the first stage to the pressure needed for filling and maintaining the second stage. It is necessary to know how the machine controller handles this changeover to set it correctly.

How to make recycled plastic parts

In-mold casting processes refer to those in which a part is replicated using a die to produce an identical production run on a medium scale. The material of the part and die varies according to the intent of the final product. Casting processes are common when replicating hollow parts or parts made of ceramic materials, elastomers, resins with very specific characteristics or other materials that normally do not meet the molding requirements needed to be produced in other prototyping technologies.

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In Tecnoimpre 3D we take advantage of our capacity and knowledge in various rapid prototyping technologies to achieve combinations that allow us to produce plastic, ceramic or even metallic molds, with these molds we are able to replicate parts cast in resins, silicones and ceramic materials.

The mold casting processes achieve lower production costs when large quantities of parts are required, allowing samples, short productions of final products or even prototypes for consumer studies at very low cost.