The French Have The Process

The French are noted for manufacturing high tech products. They must export to survive because their domestic market is not large enough to consume their entire production of the aircraft, automobiles, and other products they produce.

Columns From: 9/1/1999 Modern Machine Shop,

The French are noted for manufacturing high tech products. They must export to survive because their domestic market is not large enough to consume their entire production of the aircraft, automobiles, and other products they produce. One facility that I visited was indicative of how some French manufacturers are dealing with world competition.

For example, Snecma designs, develops, manufactures and markets jet engines for both commercial aircraft (75 percent of total business) and military aircraft (25 percent). With experience that dates back to 1907, Snecma today is a world leader in the high tech sector.

Inaugurated in 1987, Snecma's plant at Le Creust is dedicated to machining turbine disks, which are vital to jet engines. It employs 170 people (mainly technicians) and has 11,000 square meters of offices and technical rooms. Le Creusot turns out 290 turbine disks of 12 different types each month.

Turbine disks, the main components in turbofans, are subjected to considerable stresses, including extremely high rpm rate, temperatures exceeding 600° C, and centrifugal force of more than 2,200 lbs exerted by each blade the disks support. Dimensions and tolerance limits must be met accurately despite the difficulties of machining the highly resistant superalloy used for these disks. Automation, based on a systems approach, meets all the reliability and precision requirements necessary for manufacturing these parts.

The plant is based around a flexible machining cell comprising 16 CNC machines set out on both sides of a high central aisle—12 vertical boring and turning mills on the left-hand side and four milling machines on the right. A main computer handles all the programs providing complete process automation. Wire guided trolleys move noiselessly between the palletizing stations.

From part loading to machining tool selection and utilization to built-in dimension check, the computer system controls all the tasks performed by machines. Only technical incidents or failures interrupt work and necessitate human intervention. Together with the flexible machining cell, the plant contains quality control cells plus production cells for broaching (with five machines, including one of the largest in Europe), manual and robotic deburring, brushing, shot peening, sandblasting and balancing.

Automation is backed up by built-in process checks. These checks guarantee that specific quality requirements are met at each stage of production. The "health" of material both inside and out is systematically checked using chemical tests and ultrasonic and dye penetrant inspections. Dimension and geometric checks are made through systems integrated in machining stations and three-dimensional measurement machines. A final conformity check is made against the technical definition before the disk is sent to the warehouse for shipping.

Before 1987, it took six months to machine a turbine disk. Today, the plant can turn one out in six weeks. Now the objective is to reduce this to less than a month. Time has been saved both through rationalizing the manufacturing process, particularly by reducing the distance parts travel between operations, and by developing the flexible machining cell. The adaptability of the machining cell is the result of considerable progress in the methods used in the plant. All the boring, turning, milling and broaching machines can switch operations for each new part without any specific preparation or modification to their programming. Not only does this flexibility shorten the manufacturing cycle, but it also means that production can be stepped up to meet specific needs.

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