Five-axis machines bring world-class performance to Weston EU's blade machining

Citation

(2001), "Five-axis machines bring world-class performance to Weston EU's blade machining", Aircraft Engineering and Aerospace Technology, Vol. 73 No. 5. https://doi.org/10.1108/aeat.2001.12773eab.003

Five-axis machines bring world-class performance to Weston EU's blade machining

Five-axis machines bring world-class performance to Weston EU's blade machiningKeywords: Traub Heckert, Blades, Machining

Following the installation of ten Hermle C800U machining centres capable of five-axis simultaneous cutting (see Plate 2), precision engineer Weston EU Limited has seen up to eight operations consolidated into just one set-up and lead time reduced from up to six weeks to a matter of days – or even a few hours in an emergency.

We understand that such has been the success of the installation that the initial investment in three machines has quickly grown to ten. They are now arranged as separate six and four machine cells for producing aero engine components.

Plate 2 Ten Hermle C800U five-axis machining centres produce aero engine components at Weston EU

The ten machines were installed by Traub Heckert UK of Brackley at the Foulridge, near Colne in Lancashire factory of Weston EU, which is a well-established high precision machining based operation. The Weston business is still family-owned and was founded in 1948. It has grown progressively to become a key supplier to the aerospace industry for engine and airframe components and the electronics, computer and general precision engineering sector.

Weston's success owes much to its flexibility and adaptability, including willingness to develop novel approaches to solve particular manufacturing problems. For some time kaizen principles have been at the core of its manufacturing strategy, with the objective of minimising component costs by continuously improving methods, and it is very keen to form project partnerships with its customers. With a proven investment strategy the company has also committed to provide the appropriate level of high technology equipment such as the Hermle installations to guarantee consistency of production, quality and delivery.

Weston EU's business improvement manager Keith Bolton explains: "We have been producing this product family of components for some time. Initially, methods concentrated on turning and involved multiple stages of sequential operations as the volumes could not sustain a dedicated cell approach. However, we were aware of the potential to grow the contract further as quantities increased and sought to develop a more cost-effective machining process".

The company set out to devise a method that could satisfy customer requirements across the entire component family based on single operation machining. In order to maximise quality while minimising lead time and cost, five-axis machining seemed the most appropriate and cost-effective route. "Five-axis machining could provide the flexibility to position the component in almost any desired attitude, eliminated the need for multiple machine set-ups and made it far easier to maintain high levels of process capability," says Keith Bolton.

He continued: "After extensive evaluation of potential machining systems we identified the Hermle C800U as the ideal machine combining a trunnion-type table layout with excellent access, making loading and unloading easy. The machine also provided an ideal combination of spindle speed, torque and power from the 15kW driven".

He describes further attractions being its compact size and especially the single lift format with easy-to-satisfy foundation requirements. "We are firmly wedded to Kaizen lean manufacturing principles and have a regular need to re-site machines to optimise process flow. If the Hermle C800U worked from a 13 amp supply, we could re-site and re-start work on it within an hour," he quips.

The C800U is a modified gantry design of vertical machining centre with a fixed table and all three axes of movement generated by moving the spindle. This eliminates spindle overhang, typical of a C-frame machining centre and divorces the relative motions from any influence of component weight.

The mineral cast bed has three guideways which, in effect, halves the span and all guideway axes and drive components are mounted outside and above the machining area. The C800U also incorporates a two-axis trunnion table and has a working volume of 800mm x 600mm x 500mm.

An important aspect of the cell configuration at Weston is said to be its flexibility to machine any component on any of the machines. In practice, the 30-tool disc magazine of the C800U can hold enough tooling for any two jobs, while modular fixturing using common locations allows relatively easy set-up changes between components.

Flexibility is thought to be further enhanced through use of linked shopfloor gauging systems based on coordinate measuring machines (CMM). By using the Hermle machines in concert with the CMMs and high repeatability fixturing, the component's true position and orientation can be probed prior to loading onto the machining centre. Any program offsets are then loaded electronically to the Heidenhain TNC 430 control, resulting in virtually zero set-up time for individual components.

Steve Heap, the team leader of the six-machine Hermle cell, outlines how the cell works: "Within the cell we're responsible for our own quality so machining and measurement are parallel activities. This allows us to work without interruption and with very flexible manning. Depending on the component cycle time, up to four machines can be operated by one man but, as a general rule, the cell involves five people".

Hermle machines operate round the clock over a five-day week. While they are all DNC linked for program download, the machine setter/operators still have a limited scope to alter process parameters. However, work patterns are generally governed by standard operating procedures. SPC analysis of key features is carried out, based on the frequency of batches and all components are subjected to a 100 per cent check of around 30 dimensions with offset adjustment based on analysis of trends.

A Cpk of 1.3, which is effectively zero defects, is maintained on the blade production cell. This level of consistency is helped by the direct measuring scales on the Hermle machines, giving a resolution of 0.0001mm and positional accuracy of 0.008mm.

Machine performance is also monitored using a manual system which registers availability, performance, quality and overall equipment effectiveness. Reliability is aided by Weston's total preventative maintenance regime which includes a start-of-shift clean and checking schedule. In practice, the Hermle machines are stated to have performed in line with Weston's expectations of a "quality" machine, while maintenance back-up from Traub-Heckert is rated as excellent.

Further details are available from Traub Heckert UK Ltd. Tel: +44 (0) 1280 705482; Web site: www.traub-uk.com