Mass production is a way of thinking that starts with the principle of economies of scale. The focus on mass production is individual efficiency – efficient use of individual machines and individual operators. To make the overall system in Figure 1 more efficient mass production thinking attacks the efficiency of value-added activities. For example, one might reduce the cycle time needed cut the titanium foil. Figure 1 shows that the total benefit of reducing the cycle time of value-added activities amounts to a small portion of overall lead time, because value-added time is a small portion of total lead-time.

Lean thinking focuses on value-added flow and the efficiency of the overall system. A part sitting in a pile of inventory is waste and the goal is to keep product flowing and add value as much as possible. The focus is on the overall system and synchronizing operations so they are aligned and producing at a steady pace. Lean manufacturing is a manufacturing philosophy that shortens the time between the customer order and the product build/shipment by eliminating sources of waste (Appendix 1). Waste is anything that does not contribute to transforming a part to your customer’s needs.

The results of the lean approach are illustrated in Figure 2 below. Lean manufacturing will take some waste out of the value-added activity shrinking it down as in the mass production approach, but more importantly, it reduces the pure non-valued added activities, which has the large impact on lead-time. When our lean manufacturing process is in action, we should ask: what does the customer want from this process? This then defines market value and can be used to measure the lean outcomes [6]. Then it is worth asking what transformation steps are needed to turn materials entering the process into what the customer wants.

Based on this we can observe a process and separate the value-added steps from the non-value added steps. As an example, this is demonstrated for a generic manual assembly operation on fan blade in turbine engine in Figure 3 taken from RR internal report [10]. There are many individual steps, but generally only a small number add value to the product. In this case only those steps highlighted in red add value. The point is to minimize the time spent on non-value added operations, for example, by positioning the material as close as possible to the point of assembly.

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The TPS in Figure 4 goals to illustrate the roots of concept -quality, cost, and delivery through shortening the production flow by eliminating waste. Traditional mass production focused primarily on cost reductions through individual efficiency gains within individual operations. It is learned from other studies [7] that in fact by focusing on quality – “doing it right the first time” – we could simultaneously reduce cost and improve quality. The focus of TPS is on total system costs by taking a value stream perspective. The two main pillars of TPS are Just-In-Time and Built-in Quality, which are mutually reinforcing.

Creating a JIT flow may result to increased quality. Without the inventory buffers of mass production, JIT systems will fail if there are frequent quality problems that interrupt the flow. At the centre of lean manufacturing are people who must bring the system to life by continually improving it. The TPS was translated to a lean turbine engine model shown in Figure 5. It includes all the elements of TPS, but shown within an assembly line with the engine as the centrepiece. The main model elements were based on the Rolls Royce business processes described elsewhere [8] and will be explained below.

The ideal for JIT is a one-piece flow. This means identifying families of parts that go through the same set of processes and dedicating a production line to that product family. All products assigned to the cell will go through those operations one piece at a time. Figure 6 gives an example of batch processing versus one-piece flow. In the batch processing case some rectangular titanium shapes for a fan blade are cut to create a hollow mainframe of the blade, along with some stiffeners, if any. This is done in large batches which are moved as large batches to be cut into more specific curved shapes.

These parts must be sorted before they are cut into the actual shapes needed. This batch cutting leads to a large pile of inventory which must be moved to another buffer and then sorted through to be sub-assembled, and finally the subassemblies are moved and sorted through to get the parts needed to construct the actual blade. Notice how much non-value added work there is on this process all of the moving and storing and sorting is pure waste. The alternative ideal from a lean manufacturing point of view is a pure one-piece flow that is shown in the bottom of Figure 6.

In this case you would cut just the material you need, pass it on do the final cutting, pass it on, do the subassembly, pass it on, and build up the blade. While it may not be feasible to make one and move one, the smaller the batch size the better from a lean manufacturing point of view, within feasible limits. The lean manufacturing is even speed-up by new innovations introduced in the process. Hollow fan blades (Fig. 7) currently enclose a strong, stiff metallic structure to maintain the cross-sectional profile of the blade when subjected to the large forces in flight.

Introducing nanotechnology-based process the stiffeners in the blade core are replaced by synthetic foam with nanoscale fillers to stiffen hollow fan on large civil aircraft engines. In the cavity-fill fan concept [11], the light-weigh core replaces this metal structure simultaneously acting as both strengtheners and vibrations reducing elements. The next generation blades are composed of a titanium root and composite internal/external manifolds with nanomaterials reinforcement.


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