Plastic Injection Moulding

Do you need a partner that produces your plastic components consistently, part after part, without you having to chase suppliers? FPM has been handling contract plastic injection moulding for over 40 years, at its site in Lodrino, in the province of Brescia.

Our advantage is simple: we build the mould ourselves and then mould the part, right through to finishing. A single point of contact from your idea to the component ready for assembly, with quality verified by ISO 9001:2015 certification.

Moulding is the set of techniques that give shape to a plastic material using a mould. The principle is always the same: the polymer is brought to a fluid or plastic state with heat, forced into the mould cavity, allowed to solidify, and the part is ejected with the required geometry.

Materials fall into two broad families. Thermoplastics (such as PP, ABS, polyamide, polycarbonate) soften with heat and turn solid again on cooling: this cycle can be repeated, so they can be reprocessed and recycled, and this is the family we work with in injection moulding. Thermosets cross-link irreversibly during forming and, once solidified, do not become fluid again.

There is a second distinction that weighs heavily on the result, and that almost no one explains: the molecular structure. Amorphous polymers (ABS, PC, PS, PMMA) have disordered chains, shrink little, generally below 0.8%, and stay dimensionally stable. Semi-crystalline polymers (PP, PE, PA, POM, PBT) have ordered regions that compact as they cool: they shrink more, even over 2%, and tend to warp if cooling is not uniform. Knowing which family your material belongs to lets us predict shrinkage, tolerances and warping risk right from the mould design stage.

There is no single moulding technique: the choice depends on volumes, part geometry and material. We work with injection moulding, the go-to solution for precision technical components in series. We know the other techniques and will explain them to you, because when we quote we tell you honestly whether injection really is the right route for your part or whether another process would suit you better.

The heart of moulding is the injection press, made up of two units: the injection unit, which melts and pushes the material, and the clamping unit, which holds the mould closed against the thrust of the melt. The clamping force, expressed in tonnes, is the parameter that decides which press your part needs: it must exceed the thrust the material exerts on the mould walls, that is the cavity pressure multiplied by the projected area of the part. This is why a large, thin part can require more tonnage than a small, thick one.

Presses differ in how they move these units:

• Hydraulic. They use hydraulic pumps and actuators. They are robust and handle high pressures and large parts well, but consume more and need more maintenance.
• Electric. All movements are driven by electric motors. They are precise, repeatable and energy-efficient, at a higher initial cost.
• Hybrid. They combine electric motors for injection with hydraulic actuators for clamping: a compromise between efficiency and high clamping force.

When we quote we choose the tonnage and press type best suited to your part and volumes.

We work with a wide range of thermoplastic polymers, from the most common ones to high-performance engineering polymers, including glass-fibre filled grades for the most demanding applications. We choose the material with you based on the component’s mechanical, aesthetic, thermal and chemical performance.

Every polymer has its own processing window and its own cooling behaviour. Three things matter most: the temperature the melt has to reach, the shrinkage with which it contracts as it solidifies, on which the mould dimensions depend, and the hygroscopicity, that is how much moisture it absorbs. Hygroscopic materials such as polyamide, polycarbonate, ABS, PBT and PET must be dried before moulding, otherwise the water in the granules causes bubbles, streaks and drops in strength on the finished part.

Good moulding shows in the parts that don’t come back. Most defects arise from a mismatch between part geometry, mould and press parameters. Working the mould in-house too gives us an edge: when a defect originates from the tooling, we act directly, without going through third parties. Here are the most common defects, where they come from and how we prevent them.

• Sink marks. Surface depressions where the part is thicker, for example above a rib. They arise from non-uniform wall thickness, holding pressure or time that is too low, or uneven cooling. They are prevented by evening out wall thickness at the design stage, coring out heavy sections and tuning the holding phase properly.
• Weld lines. They form where two material fronts meet again, for example around a hole, and do not weld well. They depend on gate position and on a temperature that is too low. They are reduced by moving the gate, adding vents and raising temperatures.
• Flash. Excess material along the mould parting line. It comes from excessive pressure, insufficient clamping force or a worn mould. It is solved with the right parameters, a press of adequate tonnage and mould maintenance.
• Flow lines. Streaks left by the flowing material. They depend on injection speed and non-uniform temperatures. They are corrected by adjusting speed and temperature control and reviewing the gate position.
• Warping. The part comes out twisted or bowed. The most frequent cause is uneven cooling combined with the differential shrinkage of semi-crystalline materials. It is prevented with balanced cooling and a geometry that shrinks evenly.
• Short shots. The cavity does not fill completely. It arises from insufficient shot size or pressure, clogged vents or material that is too cold. It is solved by increasing shot size and pressure and improving the vents.
• Burn marks. Dark spots caused by trapped air which, as it is compressed, burns the material, the so-called diesel effect. They are eliminated by improving the vents and reducing injection speed at the critical point.

The full troubleshooting, parameter by parameter, is covered in depth on the injection moulding page. We know these defects because we deal with them every day, and we close out most of them already at the mould stage, before they become a production problem.

This is where we make the difference compared with those who only mould. At FPM you find every stage under one roof:

1. Construction of the mould to measure, with in-house co-design and design.
2. Moulding of the components on a contract basis.
3. Finishing, pad printing and assembly to deliver the part ready for assembly.

This means shorter lead times, fewer suppliers to coordinate and a single person responsible for the result, from the first drawing to volume supply. If a defect that originates from the mould emerges during testing, we fix it on the tooling ourselves.

Entrusting a contract production run to us means giving us your project and getting the finished parts back, without having to invest in a mould, presses and staff. The path is straightforward.

Good moulding shows in the parts that don’t come back. We check the components’ dimensions and keep the press parameters under control on every batch, so that production stays consistent from the first to the last part. ISO 9001:2015 certification frames all of this within traceable procedures, so you always know how your batch was produced.

When the component requires it, we carry out more thorough dimensional checks and agree the incoming inspections with you. The goal is a single one: that the parts arrive compliant and that you don’t have to redo the checks at your end.