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Taking control of productivity on the factory floor

20 August 2018

Brexit is creating uncertainty, and the manufacturing of mechanical parts industry in the UK needs to redouble its efforts in striving for productivity. Following several years of optimisation in workshops, however, one might be left wondering where further productivity gains can be found.

If we were to examine the process for the manufacturing of mechanical parts, the main achievable gains would be in the machining process itself, the handling that occurs between the successive steps in the process and subsequent control.

Historically, instinct was to invest in ultra-rapid machine tools as the added value comes from machining the part. Machine manufacturers certainly realised this, and for years have been competing to gain shorter and shorter machining times by designing machines that are ever faster and more versatile.

Whereas productivity can be improved by saving time between the manufacturing sequences, ‘control’ is rarely considered. It is still too often considered as an operation whose added value is barely justifiable in terms of investment, but one that is essential nonetheless. 

In all likelihood, the explanation can be found in the widening gap between improving the productivity of machine tools and that of control equipment. In fact, the performance of machine tools such as machining speeds, the number of axes, tool changes and digital controls has steadily progressed, while external measuring equipment (of a multidimensional or comparator type) and three-dimensional measuring machines remain more or less limited to the same dynamic performance.

The consequences of this are clear: where only a few seconds are required to manufacture a mechanical part, a few minutes or even hours are required before the outcome of the control process can be obtained.

Production bottlenecks

Control therefore naturally becomes a bottleneck; owning the fastest machine tool in the world is of no benefit if it needs to be stopped too frequently while awaiting control results. 

Parallels could be drawn here with the economic model of ‘low cost’ airline companies. They are not looking to buy faster aircraft but rather to minimise the plane’s unproductive time on the ground by optimising boarding time, disembarkation and even pre-cleaning of the aeroplane during the flight.

The strategy underpinning mechanical workshops should follow the same logic: the more machining my machine tool does, the more profitable it is, and the more added value I can create for my customers.

Optimisation for controlling and setting-up machine tools is based on two essential factors: the fastest availability of measurement results; and the quickest and most accurate interpretation for machining adjustment.

A new generation

Two types of control equipment exist for measuring dimensional and geometrical values: dimensional gauging systems and coordinate measuring machines (CMM).

A third option is also now available combining benefits that allow one to get nearer to optimal control.  ‘High-speed control centres’ such as ‘Scanflash’ from ESPI use 3D comparison principles to control the full range of dimensional and geometrical measurements for a particular part, in a single, high-speed and ultra-high-precision operation, with the device lying at the foot of the machine tool. Measurements can now be made on the shop floor, and with their unprecedented speed (10 times faster than CMMs), the results are available to the machine-tool operator instantly.

The era of digital piloting

Measurement results availability is only one part of the whole process. In fact, results are usually given in such a way that the operator cannot simply affect tool offset updates in the computer control (i.e the CNC). This ‘translation’ operation requires time and experience. Because machining is becoming more and more complex and reduced to a single operation, controlling the dimensional drift of a geometrical feature machined with multiple tools is similarly becoming longer and more complex.

ESPI’s Tool’sDriver software is able to calculate tools offsets updates from measurement results and provide the updated tools offsets values to the targeted CNC. This helps operators in their decision making and reduces set-up time and setting-up scraps during changeovers. This new controlling optimisation is called Dynamic Process Control (DPC), and its true value is in the responsive machine-tools updates it provides.

Initial feedback from DPC users seems to indicate remarkable performance for medium and large series productions. Change-over can be achieved four-times faster than ‘traditional’ approaches, the accuracy of the end-product is more consistent for longer, and wastage is reduced to a minimum.

Another benefit in being able to quickly and efficiently make changes ‘on the line’ is that the manufacturer can be more flexible in the product and volumes they choose to make. To achieve the greatest economic benefits, manufacturers are not obliged to produce large batches of product; smaller batches can now be economically viable, enabling them to be more fleet-of-foot in their operations, reducing stock levels and therefore supporting improved cashflow.

Further savings are realised in direct and indirect costs through reduced operator times, fewer control operations, fewer square meters of occupied space, and finally, more robustness across the machining processes with support provided to regulators.

 



 
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