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Afbeelding: 71. 9 factors for the right IM machine - ENG

How Rompa chooses the right injection moulding machine for your plastic product

4 March 2020

To produce a plastic product, you need an injection moulding machine. These are like cars; they come in all shapes and sizes. Rompa uses a number of renowned brands of injection moulding machines, including Arburg, Engel, Demag and Haitian. We make sure to choose the right injection moulding machine for your product. Below, we explain 9 of the factors that affect this decision.

1. The required clamping force

To shape a plastic product, we inject liquid plastic into a mould at high speed. This high speed creates pressure from inside the mould. In other words: both halves of the mould are pushed apart. This allows the plastic to escape over the partition and results in a product with a fleece or burr. To avoid this, the mould needs to be held shut by something called the clamping force (in kN). The required clamping force depends on the projected surface area of the product and the mould’s internal pressure. The clamping force of Rompa’s machines varies from 250 kN up to 12.000 kN. This range allows us to manufacture products from 0.5 grams up to five kilograms.

New Engel injection moulding machine
New Engel injection moulding machine

2. The shot volume

The shot volume is the amount of material needed for a single production cycle. The shot volume must be 15-80% of the maximum melting capacity (this is different for some types of thermally unstable plastics). This rule exists to safeguard the quality of the molten material and the reproducibility of the process.

3. Dimensions of the mould

The dimensions of a mould are of the utmost importance when choosing the right injection moulding machine and should be checked at all times. In addition to the mould’s length and width, its height is also a major factor. The machine and the mould must be able to open to more than twice the height of the product in order to remove the product from the mould. This opening is known as the “daylight opening.” Furthermore, there has to be room for the optional use of a robot in the production process. Lastly, when choosing the right injection moulding machine, it is important to decide whether the machine needs to have tie bars. This affects the size of the usable part of the floor plate.

One of our machine operators

4. Required injection pressure

In order to achieve the necessary injection pressure, Rompa’s machines are equipped with different screw-cylinder combinations. If necessary, the screw-cylinder combination is adjusted to provide the desired speed and pressure during the injection phase.

5. Available capacity

A product is assigned to a machine depending on the required capacity. Products in high demand, which require a lot of capacity on an annual basis, are given their own dedicated machine at Rompa.


6. Cycle time

The cycle time also factors into the choice of machine. Products with a short cycle time require extremely fast injection moulding machines, the so-called sprinters. These are specialist machines that are more expensive to purchase and maintain.

7. Robotic handling

The plastic product can already retain its shape, but it has not cooled down entirely yet when it is ejected from the mould. This means it can get damaged during the ejection. In that case, we transport the plastic product from the mould to the conveyor belt with a robotic arm. This means there must be room for the robot near the injection moulding machine.

8. Core pullers

A mould can feature multiple hydraulic or pneumatic sliders. Each motion requires a separate core puller. The number of motions an injection moulding machine can control depends on the number of core pullers. The machine must have enough core pullers to control all sliders.