MINIMIZING TOOL BREAKAGE COST

It's possible to minimize unexpected tool failure by adhering to best practices, error proofing, and other automation strategies

When a tool breaks during a machining operation, the part being processed is often destroyed, and sometimes the machine is damaged. Aerospace parts are often complex shapes, manufactured from exotic materials that require prolonged machining cycle times. Therefore, a scrapped part is a significant loss in raw materials and value-added machining.

Because single-piece lot sizes are not uncommon in the aerospace industry, the loss of a single part is a real hit to production yield. An aircraft part failure can have catastrophic results, consequently compliance controls and risk mitigation makes reworking damaged parts more complicated than in other industries. The loss of a part or a machine due to tool breakage can have a significant impact on profitability and customer satisfaction.

Many of the specialized machine tools used in the industry perform mission-critical machining. Due to the cost and the long lead times for these machines, they are most likely bottleneck assets, and a crash can have a significant impact on production capacityThere are many reasons for tool breakage during machining, and there is not one solution that can ensure 100% detection or protection. Purpose-built tool-breakage recovery cycles can also save parts and lost production. Given the cost of the machines, material, and value-added work-in-progress that are characteristic of the aerospace tdindustry, several levels of preventive and detection strategies are justified to protect the company's investment.

The value of the parts and types of materials machined in the aerospace industry demands that the highest quality tooling be used for most applications. But even the best tools will fail if the processing parameters in the part program are wrong for the particular tooling or application, or if the operator makes a mistake during setup or adjustment.

Aerospace parts are machined from forgings, castings, bars, and sheet stock, and from materials with generally poor machinability. Variations in material composition, surface conditions, and depths and widths of cut make it very difficult to specify optimum cutting parameters throughout the part program, and for every part produced.

Engine parts are manufactured from heat-resistant superalloys (HRSA), such as Inconel, Hastelloy, and Waspaloy. Titanium is also used for many aircraft parts. The machinability of these alloys is generally poor because of the very nature of the material structure that is required for the application. Cast or forged components typically have a rough, uneven surface.

High cutting forces and high temperatures are generated when these tough materials are processed. Carbide in the structures of HRSA materials is abrasive, and a tendency for work-surface hardening can cause tool notching. Other tool failure modes such as cratering, thermal cracking, chipping, edge buildup, and deformation can occur, as well as a machine crash, if the feeds, speeds, and depths of cut are not specified correctly for the application.

So the very nature of aerospace part machining is likely to cause uneven tool wear and high stresses, which are prescriptions for premature tool failure. These problems can be avoided, however, by optimizing process parameters.

Even if the process parameters are perfect, tool-setup tasks and tool-wear offset adjustments are error-prone. Measurement, calculation, and data entry mistakes are common causes for tool breakage and machine damage.

Given the high machinery and work-in-process values typical in aerospace manufacturing, it makes sense to implement several levels of safeguards to protect these investments. Some potential solutions are well documented, such as sonic or vibration monitoring, and the use of inspection and tool-setting probes to error-proof the tool setup and adjustment processes. Data collection and Failure Mode and Effects Analysis (FMEA) techniques can provide valuable insight into the root causes of tooling failures and related machine crashes. This analysis can help select the most effective strategies for a particular business operation.