The Joint Strike Fighter, JSF, next generation tactical strike aircraft is a stealth, multi-role aircraft. Based on a single, common design with three variants, including a Short Take Off & Vertical Landing (STOVL) option, the end users will be the US Marine Corp, Navy and Airforce together with partner nations forces, such as the UK, and Canada.
In 2001, the US Department of Defense selected the Lockheed Martin X-35 concept plane, which has now become the F-35 Lightning II Joint Strike Fighter. With an estimated programme requirement of 3,500 aircraft, the US government funded budget will be in the region of $298bn spread over 30 to 40 years.
Aerospace manufacturer Rolls-Royce will contribute to the programme by manufacturing several key components, including highly complex Blisks.
For conventional take off, there are two engine derivatives available. The F-135 engine is a purely Pratt & Whitney engine in which Rolls-Royce have no stake. The F-136 engine is a joint collaboration between General Electric and Rolls-Royce, with Rolls-Royce responsible for the manufacture and supply of several key modules, one of which is the full fan system at the front end of the power plant. The fan system consists of three large diameter Blisks, which will initially be manufactured in existing Rolls-Royce plants in the UK.
For those customers who wish to have STOVL capability, the Rolls-Royce Liftsystem is the only option. The Liftsystem comprises of four key components, one of which is the shaft driven liftfan. The liftfan contains a further two large diameter Blisks. The Liftsystem can produce a thrust of in excess of 40,000lbs. Compare this to the Harrier, which in combat mode in conventional flight only produces about 30,000 lbs of thrust.
What does this mean in terms of a Blisk New Product Introduction (NPI) programme within the company? The first thing Rolls-Royce did was to establish a Blisk pre-production facility, dedicated to manufacturing a range of new Blisks. Introducing many new manufacturing technologies, many of which had never before been applied on Blisks, the purpose of the pre-production facility is to finalise the manufacturing development and to seal the method of manufacture on each of the Blisk components and, then, to gradually increase the facility’s output to its full capacity.
Dean Whiteside is responsible for measurement processes in Rolls-Royce’s UK Blisk manufacturing plants. Currently, Dean is probably the lead protagonist within the organisation for the need to develop 5 axis scanning technology within the measurement process for more complex geometry, such as aerofoils and free form shapes.
One of the first challenges he faced was the establishment of the measurement cells at Hucknall, a Blisk pre-production facility, which had received a capital investment of approaching £1.3m in measurement systems alone. “At the start of the programme, we had to demonstrate our capability, in a small demonstration area, to produce one Blisk every three months. Now, we’ve migrated to pre-production and are required to demonstrate that we can produce at a rate of one Blisk per week. When we migrate from pre- production and go to full factory production, (in a facility yet to be built) the rate has to increase to one Blisk per 8-hour shift at peak volume. So in the space of 11 years up to 2017, we will go from producing a Blisk every three months to one Blisk every eight hours. Clearly, we have a major challenge ahead of us in ramping up to these numbers.”
This NPI programme is unprecedented within Rolls-Royce. Explains Dean Whiteside, “We are introducing up to six new products, whilst simultaneously introducing new manufacturing processes to produce these parts. We have very demanding customers in the Liftsystem and F-136 projects who are understandably pushing manufacturing to make sure they meet their critical milestones.”
Blisk manufacture involves extremely complex processes. The majority of these processes are novel and, as a result, there has been a significant demand on the measurement processes to support and establish the capability of these processes. Measurement plays a critical role in this plant, not only in product conformance at the end of the line but also to assist in manufacturing development. “Right from the outset, it was clear to me that measurement, within a concurrent engineering environment, would play a key role in ensuring the successful delivery of JSF Blisks. To meet these tight schedules we had to utilise the capabilities of off-line programming of coordinate measuring machines (CMMs).
For off-line programming, we required functionality which would allow us to produce a very large number of CMM part programs over a very short period of time for the six variants of Blisk.”
Adding to the challenge was the absence of a physical part to program around on the CMM. “To meet the tight customer milestones, we had to minimise the time the parts spent on the CMMs. We couldn’t wait for the parts to arrive at the CMM and then begin writing the CMM program. This would add a significant lead-time onto the manufacture of the first off Blisks, which was completely unacceptable.
When the actual part arrives at the CMM, I allowed a day per CMM program to test and prove out the off-line written part program on the actual part. For this to work, we required the off-line programming software to be capable of producing and simulating 90-95% of the required functionality with minimal time required for subsequent editing. However, we soon found that in reality the level of capability required fell some way short. For various reasons, the off-line programming systems were only capable of delivering 40-50% of the required functionality. (These comments are not aimed at saying a particular CMM software does not deliver what we require. We’ve come to the conclusion within Rolls-Royce that there is no one single offline solution that provides all our requirements in terms of CMM programming capability).”
The primary reason for this is that the Blisk component is one of the most complex parts that Rolls-Royce manufactures featuring a combination of prismatic and freeform geometry. The more complex functionality required to measure Blisks was not supported by the off-line systems. Also, several items of ancillary equipment that are key to the measurement process, such as rotary tables, were not integrated, at that point, within the virtual CMM environment. A true measurement process couldn’t be fully simulated prior to the part actually arriving at the CMM. This meant the measurement team still had to write a large proportion of the CMM programs on the physical part when it arrived at the CMM.
Product Life Cycle Management
Adding to the challenge, the measurement process has to operate within the context of a Product Life Cycle Management (PLM) rollout being piloted by JSF Blisk manufacturing within Rolls-Royce. PLM works if all the data relationships are truly integrated. For example, in the Blisk programme, Design Engineering, based in Bristol are the authority for geometry of the product. They interface directly with the component owners, who themselves are the individuals responsible for the product within the manufacturing environment. The component owners can interface directly, (exchange geometry in terms of master models, stage models etc.) with the various machining process owners via UGS TeamCentre within the manufacturing environment. The process owners are the individuals responsible for the various manufacturing processes used to manufacture Blisks. The ability to interface between Design Engineering, Component Owners and Process Owners provides full geometry associativity. If there are any design changes driven by Design Engineering an automatic cascade of these changes and the relevant associativity is applied to the manufacturing processes via the TeamCentre environment.
PLM does support concurrent engineering. But where does measurement fit in? “It doesn’t currently,” says Dean Whiteside. “ (As far as we are aware), there is no PLM solution that truly integrates the measurement process within the PLM environment as it does with CAM. The measurement process was isolated from the PLM/TeamCentre environment. It was and still is a stand alone process with no direct interfacing with the PLM system. This can cause major problems, particularly for the measurement process if geometry changes are not communicated to the whole integrated project team. Rolls-Royce uses UniGraphics Siemens PLM and we are in the very early stages of starting to understand how to migrate the measurement process into UGS PLM. But progress is slow and there is still a very long way to go!
Today, measurement is an integral element of our manufacturing systems. We need to ensure that latest measurement capabilities are built into future PLM developments. Equally, we need to recognise that since original implementation, technologies have advanced. Alternative forms of sensor probing devices need to be investigated such as on-machine, and 5-axis CMM scanning, that potentially offer a more cost effective and integrated solution. These developments clearly need to be captured in the PLM environment.”