Farnborough based TISICS is one of only two companies in the world to manufacture silicon carbide continuous core monofilaments – primarily for use as fibre reinforcement in titanium composite parts. Titanium components containing monofilament reinforcement offer functional attributes on a par with that of a similarly temperature-resistant steel component, but typically at half the weight, and with greater strength and corrosion resistance. The material is of immense interest to the aerospace sector, considering the falling price of titanium, as well as other sectors whose applications require a combination of strength and low weight.
Following a recent plant relocation, the company decided that in order to make best possible use of the new manufacturing space available, it needed to migrate from its existing manual recipe creation and control process to one that included contemporary automation and control systems. At the same time it also needed to address the major safety issues that arise due to the chemistry of the coating process.
Meeting the challenge
The process involves chemical vapour deposition (CVD). Not only does CVD involve very high temperatures (typically around 1,300oC) and very high voltages, it also uses Dichloromethylsilane, which can be extremely hazardous if not contained appropriately.
As well as the obvious safety implications, the process is also extremely sensitive to parameter variations. Prior to adopting an automation infrastructure, TISICS relied on a distributed manual process to control the coating operations. Both the voltage and the chemicals were controlled separately, with the vaporisers using direct potentiometer inputs from the heater; there was no electronic control. According to TISICS process development manager, Renny Moss, it was a very basic manual process that was also very unforgiving. ”The main issue was that we did not know if we had faced a problem with the deposition process until the fibre had emerged and could be tested."
In most cases, specific customer applications require certain types of fibres; the more variables that are introduced, the more complex the process becomes to control. Using the manual process it was also extremely time-consuming to develop and test new recipes – a procedure that was often measured in years prior to the plant being automated.
TISICS opted for a SCADA based process control system, choosing Rockwell Automation's Integrated Architecture, employing an Allen-Bradley ControlLogix process automation controller (PAC) running RSLogix 5000 with a FactoryTalk View SE top end. For monitoring and control, the ControlLogix PAC passes all process data up to an FTView SE server. Operators thus have a clear on-screen graphical representation of the process using an HMI system developed by one of Rockwell Automation’s system integrator partners. Mr Moss elaborates:
"The Rockwell Automation hardware feeds all the necessary information to us on one screen and as it will not allow any process variability outside acceptable levels, it offers us a much greater level of safety functionality. Another extremely useful facet of the installation is its expandability. It is our intention to bring more production into the factory and with the current hardware we know we can simply add production lines to the ControlLogix PAC without any major re-programming headaches.
"Most of the safety issues are on the gas side. The PAC controls the flow of reagents, measuring the amount of material moving through the system based on weight and the pressure parameters, never overfilling the bubbler, and helping to ensure all cleaning operations take place by giving operators clear and concise logic instructions.
“Materials handling used to be a major day-to-day operation here; we can now load materials, confident that the safety and control system have it contained, because we know it is being accurately monitored. It was never our intention to de-skill, we simply wanted to remove the safety worries from the operators."
As well as safety and functionality, TISICS is also able to develop new formulations and recipes in a fraction of the time it used to take. Mr Moss again:
"What used to take us years, we can now achieve in a matter of months. What is more, the amount of variables is now not an issue because of the level of control the PAC offers us. I freely admit that I look at the FTView SE SCADA system and the PAC as a black box. I don't need to know how it works, but I can be confident that everything is under control and that all of the operators have an easier-to-understand readout for everything.
"In the short term, the Rockwell Automation equipment has bought us far better control of our processes, while offering us the capability to expand in the medium term. It has also taken care of all the safety-critical aspects that we used to worry about."