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Emmaco UK has installed the Argotech PA-2 acoustic tool-monitoring system at MSP, a turned-parts subcontractor.

MSP was experiencing a problem when machining components from Hastelloy bar on a CNC sliding-headstock lathe.

The material’s toughness was causing unpredictable and early failure of drills and taps, which was slowing production and proving expensive.

Fitted with an acoustic sensor, the Argotech PA-2 automatically checks the sound frequencies produced during a critical drilling operation, stopping the machine instantly in the event of tool wear or failure.

The PA-2 has a second channel that is used by MSP to monitor the power being drawn by the main spindle of the lathe during machining operations, ensuring that it remains within preset limits.

The subcontractor was having particular difficulty producing a 2.5mm-diameter blind hole with an M3 x 0.5mm x 6H thread to a minimum depth of 4.2mm in two component variants, after the customer altered the material specification from 316Ti stainless steel to Hastelloy C-276.

The weak link was the drilling operation.

Each high-speed steel drill from OSG produces typically 250- 300 holes in Hastelloy before it fails.

However, its breakage is unpredictable and early failure is frequent.

The drill is relatively inexpensive at GBP5, but a broken bit in the hole, or a hole that is absent or not drilled to depth, will destroy an GBP80 Vardex solid-carbide thread-milling cutter as it tries to enter.

Fast and responsive tool monitoring was needed to avoid the problem and the Argotech PA-2 is to provide that.

It is mounted on the front of the Star lathe and wired into its CNC system, with connections also to the sensors within the machine.

The acoustic sensor is clamped to the sliding-head lathe’s tool platen, which carries the endworking drill.

It is this close mechanical link between tool and monitor on a sliding-head lathe that allows sound to be detected with such precision.

This sensor was found to be the most sensitive and accurate at recognising that the small-diameter drill was no longer cutting at any point during the pecking cycle, signifying that the tool was broken.

It also allows drill replacement before breakage, provided that the tool wears predictably rather than failing suddenly.

The spindle power sensor is used to monitor tooling not associated with the tool platen.

Leroy Lippett, engineering manager at MSP, said: ‘Setting up acoustic monitoring is straightforward.

‘We ran a peck drilling cycle on a component using a new tool and recorded an ideal acoustic profile on the screen of the PA-2.

‘We then drew boundary boxes at strategic points along the trace where it is essential for the drill to be present.

‘These are on the second peck to make sure that the drill did not break during entry, on the last peck to verify that the hole is completely machined and on retraction to warn if the drill breaks on the way out.

‘If there is no alarm, it is certain that the hole has been drilled to the required depth and is clear of obstruction, so it is safe for the thread-milling cutter to enter.

‘When the drill does eventually break, the lower threshold of one of the boundary boxes detects the absence of sound and the lathe is stopped instantly.

‘Alternatively, the same boundary box detects when the noise from the drilling operation increases beyond the upper threshold and similarly stops the machine to avert tool breakage and allow its early replacement.’ During a full year of operating this system, MSP has not lost a single thread mill prematurely.

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