Thermoplastic Moulds

Do you have a plastic component to bring into production and are you looking for someone to build the right mould, not a cut-price quote? FPM has designed and built custom thermoplastic moulds for over 40 years, in Lodrino, in the province of Brescia, with ISO 9001:2015 certification.

We make moulds for presses up to 1200 tonnes, from small parts with metal inserts to complex thin-walled geometries, and we follow the project from feasibility through to the sampling of the first parts.

A thermoplastic is a polymer that softens when heated and turns solid again on cooling, and this cycle can be repeated many times without an irreversible chemical change. The reason lies in the molecular structure: the chains are linear or branched, not stably bonded to each other, so they slide over one another when heat arrives and lock again when the material cools. It is precisely this reversibility that makes thermoplastics suitable for injection moulding in series and makes them recyclable.

Thermoplastics are in turn divided into two groups that change how they behave in the mould. Amorphous polymers (ABS, PC, PS, PMMA) have disordered chains, shrink little and stay dimensionally stable. Semi-crystalline polymers (PP, PE, PA, POM, PBT) have ordered regions that compact as they cool: they shrink more and tend to warp if cooling is not uniform. Knowing which group your material belongs to helps to size the mould cavity correctly and to predict shrinkage and tolerances right from the design stage.

The question comes up often, because it decides which type of mould is needed. There is only one difference, but it changes everything: thermoplastics can be remelted, thermosets cannot.

A thermoplastic melts with heat and resolidifies on cooling, endlessly, with no permanent chemical reactions. This is why it is injection moulded, it is recyclable and it covers the vast majority of technical and cosmetic plastic components. A thermoset (phenolic, epoxy, melamine resins, some rubbers) cross-links irreversibly during forming: the chains bond to each other and the material, once solidified, no longer becomes fluid. It resists heat and continuous load better, but it cannot be remelted or recycled by remelting, and it is worked mainly by compression or transfer moulding.

We work with the entire range of thermoplastics, from common plastics to high-performance engineering polymers, including glass-fibre filled grades for the most demanding applications. Every polymer has its own processing temperature, its own shrinkage and its own cooling behaviour, and the dimensions to give the mould cavity depend on these. Choosing it well, already at the feasibility stage, avoids problems that would otherwise emerge only during sampling.

A thermoplastic mould is almost always built from steel, because it has to last over time and hold its dimensions for hundreds of thousands of shots. The steel is chosen according to its role: pre-hardened or quenched-and-tempered steels for the mould bases and plates, hardenable steels for the moulding surfaces subject to wear, stainless steels where corrosion resistance and a cosmetic finish are needed, for example with polymers that release aggressive gases or for visible parts.

Aluminium comes into play above all for prototype moulds and short runs: it is quicker to machine, costs less and cools rapidly, but it wears sooner and does not withstand high volumes. At the feasibility stage we tell you honestly which solution suits your numbers, without selling you a premium steel where a simpler choice will do.

Building a thermoplastic mould is not a single step but a path, and at FPM we manage it in-house stage by stage. Each stage has its own in-depth page, because it goes into technical details that deserve the space.

1. Feasibility study. We analyse the part drawing, material, undercuts and critical points, and define the number of cavities, the type of mould, costs and lead times.
2. Reverse engineering. When you start from a physical sample rather than a drawing, we survey it and rebuild the 3D CAD model from which to design the mould.
3. Prototyping. We make prototypes of the component to validate form, function and assembly before investing in the definitive mould.
4. Design and co-design. We design the mould in CAD, working with you on the mouldability of the part: wall thickness, draft, gate positions.
5. Injection simulation. We simulate the filling of the cavity to predict weld lines, sink marks and warping, and correct them before cutting the steel.
6. Sampling. We trial the mould on the press and produce the first parts, checking the dimensions and fine-tuning the parameters.
7. Mould construction. Machining, EDM, assembly and finishing of the moulding surfaces: the mould takes shape right through to delivery.

Having all these stages under one roof means shorter lead times, fewer suppliers to coordinate and a single point of contact responsible for the result, from the first drawing to a tested mould.

Many moulding problems are avoided at the design table, before the mould is even built. When you bring us a drawing we look at a few things that affect the result and the cost of the tooling:

• Uniform wall thickness. Walls of constant thickness reduce sink marks and warping; heavy sections should be cored out or ribbed.
• Draft angles. Vertical walls need a slight taper to come out of the mould without scoring or getting stuck.
• Undercuts. Undercut geometries require extra slides or ejectors, which raise the cost and complexity of the mould: better to know in advance.
• Gates. Where the material enters decides the filling, the position of the weld lines and the final appearance of the part.
• Radii and fillets. Sharp corners concentrate stresses and hinder flow; fillets improve filling and strength.

This design-for-moulding work, known as DFM, we do together with you during mould design and verify it with injection simulation.

When you entrust a mould to us you don’t just buy a tool: you get a mould maker that follows the part from feasibility to sampling, and that knows the mould because it has been making them for over 40 years.

• Fully in-house cycle, from feasibility to simulation through to construction and sampling, with no back-and-forth between suppliers.
• Presses up to 1200 tonnes for sampling, from small parts with metal inserts to complex geometries.
• Engineering polymers, technical grades included, from glass-filled polyamides to Ixef polyarylamide.
• ISO 9001:2015 quality and over 40 years of experience in plastic and die-casting moulds.
• In Lodrino, in the province of Brescia, at the heart of the Lombardy mould-making district.

If you also need the parts produced, we do that: you find contract plastic injection moulding in the same company, from the mould to the finished component.