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Plastic injection moulding

For 75 years now, Rosti has proudly and successfully contract manufactured millions of useful products that touch people’s everyday life – ranging from the first cup of coffee to keeping our food and drinks stay fresh longer. Rosti produces products that help detect illnesses in time to find a cure, make our homes personalised and smart, and produce customer solutions that are reducing the CO2 emissions globally. Each and every one of the products is made with technical precision plastic injection moulding – and continuous improvement and innovation throughout time.


Precision plastic injection moulding simply explained

Simply described, plastic injection moulding is a process of melting plastic pellets and injecting it into a mould or cavity to form a shape. Once the shape is formed, the material is cooled, ejected from the machine and – voilà – a finished, functional, esthetically pleasing injection moulded product or part is ready!

Most products in our world today – items you see on your desk, in your home and at work (vacuum cleaners, espresso machines, speakers, health aids, electric tools, smart home devices, electric transport, cashless payment system, and virtual reality goggles) – are precision plastic injection moulded, and almost 90 % on everything produced in an automotive product is injection moulded.


The four main advantages of injection moulding

Rosti’s technical capability in precision plastic injection moulding, can, from one single process, and in one shot, create a product or part that is repeatable, accurate, cost effective, has a desired function, and correct surface finish.

Repeatability – the same shape can be produced in the millions

Accuracy – the manufactured product or part is not only repeatable, but can also be produced to a tight tolerance consistently

Functionality – it is possible to design a number of features into the injection moulded part including complex shapes that cannot be practically achieved by other materials or processes

Surface finish – with different injection mould processes coupled with specific tooling, a wide spectrum of surface finishes can be achieved, from high gloss to textured surfaces to simulated natural fibers

Cost and weight efficiency – When producing volume parts, the main cost is the tooling. Once invested, the actual production parts can be a fraction of the cost to produce versus other options. The weight of the part itself compared to traditional metal parts can also offer cost savings from functionality to lower logistic costs.


Rosti locations worldwide

Rosti is strategically located with facilities in China, Germany, Malaysia, Poland, Romania, Sweden, Turkey, and the UK. 


Technological advances in injection moulding

Liquid Silicon Rubber (LSR)

The impetus to invest in the industry’s technical megatrend – LSR – was driven by a customer who needed a clearly differentiated product. The right LSR solution was developed with great care, as the product was to touch sensitive parts of the skin.

Due to various physical characteristics, including excellent compression set and elastic properties, wide temperature resistance (from -110 to +300°C) and high clarity, which enables bright colouring, LSR is a rapidly growing material in many markets. Furthermore, LSR is a highly inert material with several medical approvals. All told, this makes LSR highly suitable for both single-use and reusable applications.

Multi-shot moulding

Multi-shot moulding is a process in which different materials or colours are delivered into a cavity to produce a part in a single step. When using two materials it is known as 2k, using three materials is 3k, and so on. Multi-shot moulding reduces the need for additional tools and production steps, and results in an optimised, cost-effective manufacturing process. When a soft seal is required on a harder plastic – e.g. a toothbrush with a soft grip and hard body – multi-shot moulding is a very suitable technology.

Multi-shot moulding toothbrush


Overmoulding, or insert moulding, is a process in which a component is inserted into the cavity of a tool and then moulded onto the component. This is often used in applications requiring metal contacts or studs when forming part of a plastic housing in many technical products. Due to the significant advantage of removing the additional assembly step and thereby reducing costs and improving the repeatability of the product, the overmoulding process is increasingly required by Rosti’s customers for electronic circuit production.

As the technology in electronic circuits improves, the option of manufacturing a product in different shapes, enabled by the flexible electronic circuit structure, allows designers far more flexibility in the design of products.

Decoration options in injection moulding (IML and IMD)

Different applications are available to add labelling or decoration to a part. In general, requirements differ from industry to industry.

In-mould labelling (IML) is often used in the food industry for products such as yoghurt pots, where the shelf life of a product is often measured in weeks or months rather than years. In this process, a pre-printed thin walled foil is added into a mould tool prior to the injection cycle. The foil attaches to the tool due to electrostatic charge or with a vacuum system, and forms part of the product after the injection process.

In-mould decoration (IMD) follows the same process but utilises a thicker foil and is therefore used in applications that require a product life measured in years. It is a more expensive process than IML, but offers a robust long-life label or decoration. The process is used, for example, in the labelling and branding on power tools.

Compared with painting a product, which involves an additional process, in-mould labelling and in-mould decoration both offer a cost-effective, repeatable process.

Digital printing

Rosti also offers digital printing. This is the real-time process of printing labels or decoration onto parts after they are produced in a moulding machine. The main advantage of the digital printing process is high-speed printing with a quick changeover of the printing design. For example, high-volume parts (often from a high cavity tool) can be printed in batches to suit different markets.


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Rosti moulding facts & figures

  • More than 400 injection moulding machines
  • Clamping force from 25T to 1500T
  • Hydraulic, hybrid and full electrical
  • Supported by robots or tailor made automation cells
  • Fast cycling from 2.5 seconds
  • Part weight from 0.3 g to kilos
  • High cavitations up to 72 cavities
  • Precision moulding down to 0.24 mm
  • Tolerances down to +/- 0.03 mm
  • Stack moulds with up to 64 cavities
  • Tools as small as 27 kg to more than 12T
  • More than 4000 customer tools and automations
  • BPA free zones