Secure logging system protects propeller data

In all, seven Eurotherm DAQs are used throughout Dowty's propeller fabrication process at Gloucester, all of which are permanently connected to the company's central server via an Ethernet databus.

Dowty Propellers, a part of Smiths Aerospace, is the world's leading manufacturer of composite bladed aircraft propeller systems.

The company operates a sophisticated and highly skilled propeller fabrication operation at its Gloucester factory, which involves many complex stages, including carbon fibre cloth lay-up, heat treatment and resin moulding processes.

All of these need to be accurately monitored, with key parameters being automatically logged for regulatory purposes.

The data from each part of the process are centrally archived in a secure, tamperproof form to ensure that records are maintained to the high standards of integrity necessary.

Dowty has installed a number of Eurotherm data acquisition and recording products throughout the facility to do this, all of which are connected permanently via an internal Ethernet datalink to a central server and database.

The environmentally controlled facility at Gloucester has a number of unique processes and includes specialised areas for composite lay-up, vacuum and injection moulding processes, bonding, robotic spraying, and NDT.

The multistage fabrication process ensures that propellers are built to consistently high standards, reflecting the high reliability generally required for aircraft components, and the exceptional stress placed on propeller systems when airborne.

All Dowty composite blades, of whatever size or shape, use the same fundamental well-proven design concept and assembly processes.

The basic propeller structure always consists of two "mirror image" carbon fibre spars and a central polyurethane foam core which are enclosed by a resin impregnated glass/carbon shell forming the aerofoil profile.

The process begins with advanced computer aided design routines, which define the shape, size and construction details of each type of propeller in both 2 and 3D forms.

This computerised process produces detailed cutting patterns, allowing carbon fibre cloth to be automatically cut on a computer controlled cutting table to form the complex layered shapes required for each spar.

The layers are then laid up by hand using shaped carbon formers, prior to a heat treatment process which bonds the layers in each spar together strongly enough to be handled.

This first heat treatment process is monitored and logged using a Eurotherm 5100V six-channel DAQ (data acquisition unit).

The 5100V is a compact graphic recorder which also acts as a 100mm process viewer.

Based on 32bit RISC processor technology, it provides a seamless interface between the plant floor and the IT environment.

It can take up to 12 universal inputs, and offers high visibility bargraph, digital and chart displays which show both current and historical values.

The instrument has a clear, quarter-VGA TFT colour touch screen interface, and offers Ethernet communications for remote data logging as a standard feature.

When this first spar heat treatment process is complete, the two spars are brought together within a single heated mould, for the injection under heat and pressure of a polyurethane foam core.

Temperature control for this three stage process (mould preheat, foam injection and curing) has to be accurate to within +2.5C.

The complete moulding process is monitored using a 24-channel DAQ (Eurotherm Model 5180V), which simultaneously measures several jacket temperatures on each of the four moulding stations.

The 5180V is a highly accurate multichannel graphic recorder for applications which require more than 12 inputs, or need exceptional screen visibility.

This instrument can take up to 24 inputs, all of which can be shown simultaneously on the standard 12in SVGA TFT colour display.

This gives similar visibility to 250mm paper chart recorders, making it a logical replacement for older equipment.

The touch screen provides a clear and unambiguous operator interface, and as with the 5100V, Ethernet communications is provided as standard.

The injection process involves the use of a large precision-formed heated mould containing the blade assembly held vertically.

Resin is forced into the mould under pressure, progressing through a three stage (mould preheat, resin injection, resin cure).

Temperatures need to be controlled to within +2.0C throughout the cycle, and again, two separate 12-channel 5100V DAQs are used to monitor mould temperatures and transfer pressures over the four separate resin injection stations.

When each blade is removed from its mould, it is post cured at high temperature, and temperature variations over time within the curing chamber are recorded using an additional six-channel 5100V DAQ.

The internal structure of the blade is now virtually complete, and after curing and deflashing each unit is subjected to a gruelling NDT programme.

The in house testing facility at Gloucester examines each blade comprehensively using dimensional, ultrasonic, X-ray and other techniques, rejecting any which show internal faults such as air bubbles, micro cracks etc.

In all, seven Eurotherm DAQs are used throughout Dowty's propeller fabrication process at Gloucester, all of which are permanently connected to the company's central server via an Ethernet databus.

All process and batch data are uploaded hourly, including parameters such as temperature, pressure, time and probe identification, operator login details, and part/batch numbers.

All logged data are totally secure and tamperproof, allowing Dowty to meet the most demanding standards of the world's aviation authorities.

While local operator login is mandatory, screen entry of data is inherently secure on all 5000 Series DAQs as there is no operator interaction required (apart from the original configuration which is normally already validated).

The data files logged by the instruments are in a compressed, binary format using a proprietary data compression algorithm unique to Eurotherm.

Records are also check-summed throughout to ensure that data have not been corrupted or modified, and that any data which have been corrupted is virtually unusable.

The entire process monitoring system, including historical data, can be viewed from a supervisory workstation, located in the management centre.

This runs a standard version of Eurotherm's Review software, as well as a unique batch system, which enables any production batch details to be accessed.

Supervisors thus have access to detailed information such a curing temperatures and times, and are able to view and print process records in chart form.

Rich Morgan, Advanced Manufacturing Engineer at Gloucester, chose the Eurotherm data acquisition solution for a number of reasons.

He comments: "Because of aviation industry regulations we have always had to keep accurate and detailed records of each stage of the propeller manufacturing process.

This meant, in the days of chart recorders, keeping huge files of paper records indefinitely, most of which were never needed again.

In addition, running out of paper, paper jams or inking problems usually meant we had to carry out that part of the fabrication process again".

"The move to electronic records has removed that disadvantage completely, making the entire data logging process much easier, with data held more securely and more easily accessible on our central server system.

Having once made the decision to 'go electronic', the Eurotherm solution was an obvious choice because of hardware and software versatility, touch screen functionality, Ethernet communications and high standards of on-site support.

To date we have been very pleased indeed with our choice".

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