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Boxtrees Precision Engineering is using Renishaw probe systems on a Mazak Integrex in a fully integrated intelligent system that has achieved reduced unit costs and set-up times.

The company has employed a Renishaw OMP400 high-accuracy touch probe and NC4 non-contact laser tool setting system on a Mazak Integrex 200-IV ST to reduce non-productive setting.

Improvements have also been seen in component accuracy and the consistency of cycle times, with a direct effect on production scheduling.

In addition, the majority of post-machining inspection has been eliminated.

Boxtrees make all the machined parts for a range of educational machine tools supplied by sister company Boxford, along with other sub-contract work.

The Mazak Integrex, originally fitted with the Renishaw systems when supplied, has been installed at Boxtrees for 11 months, one of three CNC machine tools in active use in a large machine shop now containing increasingly inactive manual machines.

In that time, Steve Randerson, production manager at Boxtrees, has created machining programs for more than 200 different components, which can be machined in many different materials, usually mild steel, cast iron or aluminium.

Each of these programs relies on Renishaw part setting and tool breakage detection macro routines to control the process, making the most of the flexibility offered by the Mazak multi-axis mill-turn machine.

Randerson said: ‘Everyone talks about reducing the time taken to cut the part.

‘I’m more interested in minimising tool wear to keep tooling costs down, so we don’t cut as fast as we used to, and now get 20 per cent more tool life.

‘I’m also keen to identify that occasional scrap part and make sure it doesn’t make its way through to final assembly.

‘If an out-of-tolerance part is assembled into a Boxford machine it can mean a four-hour strip-down to change it.

‘So the programs use the optimum speeds and feeds for long tool life, cut out any wasteful machine movement, and employ logic that allows the machine to make ‘intelligent’ decisions according to the feedback from the probe systems,’ he added.

The Mazak Integrex is used for twin-spindle billet work during the day when the operator is present, with many different shapes and sizes of billets, while overnight it runs unmanned, with material supplied by a bar feed.

In both cases, final part inspection is performed by the touch probe on the machine, with measured values recorded in a text file.

This is fed back to the production scheduling system as a permanent record of the critical dimensions of the component and whether any feature was out of tolerance – in other words, a scrap part.

The OMP400 is an ultra-compact probe, ideally suited to multi-axis machines thanks to Rengage technology, which delivers good 3D measurement performance.

The dimensions of each individual raw billet vary considerably, often over- or under-size.

The first operation after it is loaded will always be to check the billet length using the OMP400 touch probe, which is loaded into the machine spindle from the tool changer, like a cutting tool, when needed.

In some cases the billet can be over-size by up to 8mm – the program changes the number of cuts used on the first face accordingly.

If it is under-size, the billet is rejected before the machine wastes time attempting to cut it.

Features on the billet may be measured by the touch probe during the machining cycle – for example, checking a bore before adding a keyway.

Critical features on every finished part are inspected to decide whether the part is within tolerance; in some cases extra datum features are added to the design to enable easy measurement of the critical features.

During the day, the production scheduling system, on a networked PC in the planning office, is ‘loaded up’ with machining jobs to run overnight according to orders received, often on that day.

These will all be of one material, typically mild steel, cast iron or aluminium, but the quantity of parts can be set to any value.

The schedule automatically adds the relevant machining program, drawing it in from a database, and then adjusts it according to the quantity required.

Any mixture of jobs can be added in any order, all of these cut from standard bar stock.

The Mazak Matrix controller is based on a PC, which is connected to the Boxford group network, and receives the NC machining files across the network.

The machine is left to run at the end of the day, with the touch probe and tool setting probe systems trusted to be the eyes and ears of the operation.

If a finished part is out-of-tolerance, the logic in the program does not employ the parts catcher to remove the finished part when it is parted off; instead it falls into the swarf bin, so there is no chance of bad parts going to assembly.

At this point the machine is programmed to make another of the same part, so that enough parts are ready in the morning.

Good parts are collected on a parts conveyor, with part dimensions recorded and reported back to the SPC system.

The Integrex is fitted with a Renishaw NC4 non-contact laser system, which can set the tools for length and diameter initially, but can also be used for a rapid breakage check, looking for a significant change in length.

Small, delicate tools are checked after every use, while the less vulnerable tools might not be checked at all, but it can also depend on which material is being cut.

The same tool can be used for six different materials, so on aluminium it might not be checked, but on cast iron it is checked periodically.

If a tool breakage is detected the machine does not stop, as Randerson does not want to lose production time or be missing one part – an identical ‘sister’ tool will be loaded instead and machining continues.

Components have been redesigned to enable and improve machining on the Integrex.

A high-capacity 120-tool changer system was purchased with the machine, but even this would not accommodate all the tools that were needed previously, especially when provision has to be made for sister tooling.

Randerson gave the designers a far shorter list of tools that could be used to machine all the jobs in all the different materials – a number of changes were made to accommodate this.

Not only that, but they also took a more sensible view on tolerances and surface finishes, with blanket tolerances on surfaces thrown out and each feature closely examined to see what was actually necessary for function and appearance.

Boxtrees also have a Mazak VTC300, a CNC machine tool with a long fixed bed that can be divided in half with a solid screen (although occasionally the screen is removed for very large jobs), all three axes of movement being in the machine head.

The operator can be safely loading a job on one half of the bed, while the machine is cutting on the other, but the machine used to spend a lot of time idle while it was being set.

A spindle-mounted Renishaw touch probe was fitted, which is now used to set the job accurately, eliminating the need to make or purchase elaborate fixtures, but also removing the need for manual part setting.

The VTC has the capacity to hold 48 tools, using a tool recognition system based on a chip on the tool shank, but was not supplied with a tool setting system, leaving the potential to make mistakes loading the wrong tool data.

Renishaw retrofitted a NC4 laser system to control the tool-setting procedure, and by employing logic routines in the machine program the machine cannot go wrong anymore.

Renishaw

A world leader in engineering technologies, Renishaw’s core skills in measurement and precision machining serve sectors as diverse as dimensional metrology, spectroscopy, machine calibration, motion control, dentistry and surgical robotics.

A world leader in engineering technologies, Renishaw’s core skills in measurement and precision machining serve sectors as diverse as dimensional metrology, spectroscopy, machine calibration, motion control, dentistry and surgical robotics.

Sensors for co-ordinate measuring machines (CMMs) are an industry standard, from basic touch-trigger probes through to automated stylus and probe changers, motorised indexing probe heads, and revolutionary five-axis measurement systems.

Machine probes for CNC machine tools allow automated tool setting, workpiece set-up, in-cycle gauging and part inspection. Products include laser tool setters, contact tool setters, tool breakage detectors, touch probes and high accuracy inspection probes.

For motion control, Renishaw supplies laser encoders, optical linear encoders, optical angle encoders, optical rotary encoders, magnetic rotary encoders, magnetic chip encoders and magnetic linear encoders.

To analyse the static and dynamic performance of position-critical motion systems, Renishaw’s laser interferometer and environmental compensation system offers a linear measurement accuracy of 0.5 ppm, readings of up to 50 kHz and a linear measurement speed of up to 4 m/s, with a linear resolution of 1nm.

Renishaw’s Raman spectroscopy products exploit the Raman effect to identify and characterise the chemistry and structure of materials. A diverse range of analytical applications include pharmaceutical, forensic science, nanotechnology, biomedical and semiconductors.

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