Measuring with precision to meet bottle cap manufacturing industry regulations

The worldwide consumption of PET bottle caps is estimated at four billion pieces a day, but this lucrative industry has relentless rules and regulations. The Czech producer of base plates for multiple injection moulds, the Tirad company, has been a part of the supply chain, at the end where the most significant players like Coca Cola or Pepsi have figured for several years. To be such an integral part of this supply chain, Tirad has implemented measuring systems from Blum-Novotest.

While the tolerance of cavity positioning was formerly ±0.01mm/m, the Tirad company has carried out orders for customers that have a working tolerance of ±0.005 mm/m. “We had to adapt to the market with regard to precision and also to the size of frames that are made up to dimensions of 1500 x 2500mm. When you realize that our coordinate measuring machine determines the position and achieves an accuracy of 0.004mm/m, we are, in fact, approaching a tolerance band more akin to a laboratory than a production facility,“ said Stanislav Vesel, executive director of Tirad

At Tirad, considerable investments were directed especially towards the thermal and technological stability of the manufacturing process and towards the reduction of human errors. Manufacturing technology in air-conditioned space is actually subject to strict in-house regulations. A minor deviation, in form of a tool set-up to an incorrect length against the verified length, may cause vibration in the cut and this may exceed the micron tolerance.

The principal role in the choice of laser and touch probes was played by maximum accuracy and long-term process reliability in the machining area.  

Vesel said: “Following trials, we have five machines fitted with the Micro Compact NT laser and with the TC50 touch probe.“

The TC50 probe is designed for universal applications in machine tools, particularly in those with limited accuracy demands at high dynamic and measuring speeds of up to 3m/min. Robust symmetrical design, non-contact signal generation and higher measuring force are attributes that guarantee exceptional measurement repeatability independently of speed, stylus length or pollution of the measured surface.

Using the TC50 touch probe, Tirad automatically determines the zero point and monitors the flatness of the base plate in 7 points having a tolerance of 0.005mm. This is a demanding application that takes full advantage of the progressive measuring mechanism inside of the probe. In the course of measuring, a text file is generated that stores measured values and can be used for a possible reverse analysis.

Micro Compact NT

Each cutting tool is measured first by the Micro Compact NT laser system whereby measurements are taken using a focused laser beam of 0.03mm in diameter. This calibration takes place under identical conditions as machining. In this way, it is possible to get results approaching the absolute reality – unlike an external measuring device.

The measured length offset compensates inaccuracies resulting from tool change clamping errors or from temperature and dynamic changes in the spindle and the machine. The automatic data transfer into a tool offset table eliminates any human error and the tool data is retrospectively available in a text file. The combination of optics, micro-electronics, mechanics and software, guarantees excellent measurement repeatability and almost maintenance-free operation in the long term.

 

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