Choosing the Right Injection Molding Machine

Injection molding is one of the most widely used processes for producing large quantities of parts in series, particularly in the automotive and aerospace sectors or for producing medical products. This is a fast process, suitable for mass production, which is carried out using an injection molding machine, also known as an injection press. This machine consists of two main parts: the injection unit and the clamping unit.

The injection unit consists of a feed hopper, which receives the granulated or powdered material, and a heated screw, which has the function of plasticizing (making malleable), homogenizing, and injecting the material. The clamping unit, meanwhile, is responsible for keeping the mold closed during injection and for subsequent cooling.

This is the most common method of manufacturing plastic parts worldwide and is used in a wide variety of applications.

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  • What are the different types of injection molding machines?

    The type and characteristics of the machine have an influence on the result obtained (finished part). Injection molding machines can be classified according to the type of driving system they use, thus dividing them into hydraulic, electric, and hybrid models.

    Hydraulic injection molding machines

    These have a hydraulic pump connected to a constant-speed electric motor.

    – They are capable of producing large parts.
    – They have constant injection and extraction.
    – They are robust and therefore durable.
    – Spare parts for these machines are easy to find.

    – They consume a lot of energy.
    – They do not allow for high-precision molding.
    – There may be a risk of oil leakage.

    Electric injection molding machines

    The drive is carried out by servomotors with numerical control. They offer various functionalities.

    – They consume very little energy.
    – They offer high precision and reliability.
    – They are easy to operate.

    – They require a larger initial investment than hydraulic machines.
    – The parts must be replaced periodically, which means regular maintenance.

    Hybrid injection molding machines

    Hybrid machines are driven by a servomotor coupled to a hydraulic pump, also known as a servo pump. This system allows for continuous adjustments according to actual electricity needs, resulting in fewer emissions, less noise, and energy savings.

    They consume less energy than hydraulic injection molding machines since hydraulic pressure is not used constantly, mainly due to the electrical part.
    – They offer high precision.
    – They have a good clamping force.

    – They can present repeatability problems.
    – Both the electrical and hydraulic systems need to be serviced.

  • What criteria should be taken into account when choosing an injection molding machine?

    When buying an injection molding machine, there are several criteria that must be taken into account:

    Injection capacity/maximum injection volume:

    This is the maximum amount of material (usually thermoplastic) that the machine can inject into the mold each cycle. It is indicated in cm³ on European and Asian machines, and ounces of general-purpose polystyrene (GPPS) on North American machines.

    It is recommended to opt for a machine with an injection volume 30 to 40% higher than the parts require.

    Clamping force:

    Expressed in tons, it is the force needed to keep the mold closed during the injection phase. The force applied to the plates varies according to the pressure of the material in the cavity, to guarantee the quality of the parts. The clamping force can range from 5 tons to over 4,000 tons, depending on the model. To estimate the right clamping force for your machine, consider the area of the part and the viscosity of the plastic to be injected.

    The distance between the columns and the maximum opening between the plates must be greater than the maximum dimensions of the molds so that they can be positioned on the machine without any problems.

    Energy efficiency:

    Energy efficiency is an important criterion for choosing an industrial machine. In general, today’s injection molding machines, thanks to technological advances, can consume up to 50% less energy than those manufactured a decade ago.

    Electric and hybrid injection presses consume the least.

  • What are the costs of an injection molding machine?

    Large injection machines cost between 50,000 and 200,000 euros on average. Certain models can exceed this value.

    In addition to the price of the machine, there are other costs to take into account:

    Price of molds: The most basic plastic molds, such as 3D printed ones, cost around 100 euros. Aluminum molds cost between 2,000 and 5,000 euros. The price of steel molds can exceed 100,000 euros. Plastic injection molding machines make it possible to mass-produce plastic parts at an affordable price.

    Price of the raw material: These machines can inject various types of plastic (ABS, PP, PC, PE, etc.), which have different prices. For example, a kilo of plastic pellets usually costs around 5 euros.

    Installation, operating, and maintenance costs: Injection molding machines are also subject to strict installation requirements and require skilled labor to operate and maintain them. The cost of labor and regular maintenance must therefore be taken into account.

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