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Plastic Metal - Injection molding machines

High quality, reliability, and technology have always characterized Plastic Metal injection molding machines and marked the company’s growth over the years.
Gefran’s products are based on the same philosophy and help achieve constantly higher quality. Gefran provides high-quality, reliable, and easy-to-use products that simplify the operation of injection molding machines.

High quality, reliability, and technology have always characterized Plastic Metal injection molding machines and marked the company’s growth over the years.

The machines have an extremely robust structure and are built with high-quality parts whose technical specifications exceed the industrial standards normally applied to plastic processing machines. 

Gefran’s products are based on the same philosophy and help achieve constantly higher quality. Gefran provides high-quality, reliable, and easy-to-use products that simplify the operation of injection molding machines.

The customer

Founded in 1954, Plastic Metal Spa is a leading manufacturer of injection molding machines for thermoplastics.On the Italian market, it is a reference point for high-quality, strictly Made in Italy injection molding machines, providing flexible solutions that meet its customers’ production requirements.

Plastic Metal Spa manufactures injection molding machines with double toggle clamping system and clamping force from 35 to 3200 tons. Plastic Metal has a 15,000 m2 factory and about 100 employees.

Through its sales and customer service network, it is present in almost every Italian region as well as in other European countries, in the United States, South America, and the Middle East.

The process

The injection molding process has a high number of physical parameters that must be conditioned in order to obtain an excellent price/performance ratio, and can create very complex products with extremely precise details.

Plastic is heated to the melting point and then injected under pressure into a closed mold to fill the entire cavity. The plastic is then cooled so that it solidifies, after which the mold is opened and the product is extracted.

The problem

The main physical parameters involved in the injection process are position, pressure, and temperature. The customer has to precisely monitor these parameters in order to ensure a reliable process and, therefore, a high-quality final product.

A linear transducer is used to measure four movements: position of the injection unit and of the screw, mold opening/closing, and extraction.
The majority of the movements, such as clamping, metering, and injection pressure, are hydraulic. Therefore, oil pressure has to be controlled to improve machine performance and guarantee precisely molded products.

The final parameter to be considered is temperature in the barrel (part of the injection unit, heated externally by electrical resistances, in which the plastic is plasticized), in the nozzle, and in the hot runners (system of heated ducts that convey the melt to the mold cavities). The temperature influences the viscosity of the thermoplastic material and therefore filling of the mold.

The production lines of Plastic Metal demanded elevated dynamics, precision, and rapid work sequences therefore the factory needed a product that offered high-performance control of brushless motors and that should be able to handle and coordinate the main mechanical organs (loading, extraction, injection, and molding).

Plastic Metal  needed also an automation product with a software full of options so that the design could be configured and adapted to numerous product lines without having to utilize the development software.

The solution

 

Sensors

For Plastic Metal, Gefran is the perfect partner: a specialist with years of experience in IMM and in the design and manufacture of transducers to measure main physical parameters as position, pressure and temperature.  

To ensure precise control of injection screw movements, Plastic Metal chose the PK rodless (cursor-type) rectilinear displacement transducer. Its compact, rodless design offers versions with very long strokes.

To control the movement of the injection unit and of mold opening/closing, Plastic Metal installed an LT series displacement transducer, offering proven technology, easy installation, robustness, reliability, and high resolution (0.01 mm even in extreme conditions).

Plastic Metal chose a TPSA extensimetric transducer to control hydraulic pressure.

With guaranteed robustness and high accuracy (±0.1% FS), the TPSA is one of Gefran’s most suitable products for this type of application, which requires measurement in a very harsh environment with dust, strong vibrations and high temperatures.

To map temperatures in key zones, Plastic Metal installs TC1 thermocouples, specifically designed for the plastics processing industry.  

 

Motion control

The main mechanical organs for handling and coordination (loading, extraction, injection, and molding) are managed by the AXV300 modular servodrive, which offers high-performance control of brushless motors on production lines that demand elevated dynamics, precision, and rapid work sequences.

Powering each multiaxis system with a common DC bus optimizes energy costs and management: balanced by the common bus, excess energy is dissipated in dynamic braking on a single resistance or with clean power technology via regenerative power supplies.

Motor control axes are synchronized by a single, powerful CPU able to close loops in 250µs.

The processing speeds of speed and current loops are 1250µs and 62.5µs, respectively: excellent performance that guarantees fast machine cycles, repeatability, precise movements, and accurate control of pressure and temperature.

 

Automation

Gefran’s automation provides a completely customized HMI: the 12” TFT full color touch screen has a keyboard designed and produced based on Plastic Metal’s drawing.

The ad hoc application software is full of options so that the design can be configured and adapted to numerous product lines without having to utilize the development software.

Energy efficiency receives special attention: depending on the model, the technology employed saves from 30 to 60% of the energy required to mold thermoplastic material.

In addition to safeguarding the environment, the SW solution adopted with combined control of motor speed/pressure simultaneously limits overheating of oil and load leaks typical of traditional hydraulic systems, thereby lengthening system life and guaranteeing long-term reliability.