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LINEAR AND ROTATORY AXIS Thousand reasons per second to scan CNC machines

May 30, 2022

In the machining world, where seconds matter, using a touch-trigger probe in a cycle with hundreds of measured points requires a lot of time. Renishaw, vouch on their SPRINT technology for results in much shorter time. This article explains how SPRINT technology can give machinists the necessary confidence that a work piece has been machined within tolerance extremely quickly and accurately. - Venkatesh Kulkarni, Head Of Technical Services, Renishaw

Here is an important question: what is a 3D scanning probe? And further, why is it useful, and, in some applications, vital for the process? For an answer, one needs to go back in time. When the kinematic touch-trigger probe was invented by Renishaw’s founders nearly 50 years ago, no one knew the impact it would have on the manufacturing industry. As with all technology, probes have evolved. While touch-trigger probing meets the needs of users wanting to automate simple setup and precision inspection, scanning takes measurement to a whole new level by inspecting form, surface condition and detailed dimensions at an incredible speed.

In this context, the OSP60 probe can continuously measure up to 1000 points per second in XYZ simultaneously. So, depending on the resolution that you want, it can measure as fast as preferred – even at G0 speeds in some cases. SPRINT technology can give the machinist the necessary confidence that a work piece has been machined within tolerance extremely quickly and accurately. Like a coordinate measuring machine (CMM), it reads the encoder or linear scale values from the CNC and compensates for any potential errors. It can even scan rough surfaces like castings. Thanks to numerous innovations, it can achieve real-world repeatability better than ±1 μm.

Being able to check part geometry while a part is still fixed on the machine tool is priceless. Without on-machine scanning, the finished part is typically measured offline, and any problems would be identified after the machining process. If problems were detected, in most cases, by then the part would have been identified as scrap, and if not, it would need to be fixed on the machine for a second time. It is well-known how difficult it is to set up an already machined part. Another key advantage of SPRINT technology is the ability to check surface finish quality of a part. It can detect the waviness that has been either machined intentionally, or caused by tool wear, breakage, chattering, vibrations, and lack of coolant on the cutting tool or a combination of these.

SPRINT technology

Installation of the on-machine scanning system starts with mapping machine tool characteristics such as tool path errors and latency. An advanced calibration process, which takes only a few minutes, ensures reliable and accurate probe performance on the machine. This delivers ±1 μm repeatability on a capable machine.

SPRINT technology software

A variety of software packages is available with the OSP60 probe to make the best use of collected data. The more advanced of these software packages is connected to the CNC machine and the probe in real-time. The software receives the data collected by the probe and the positions sent by the encoders or linear scales from the machine. This combination provides accurate surface data points or a 3D model of the scanned surface. For the most advanced applications, this data can be used in adaptive machining of cast, welded, printed, or machined parts. After scanning the current form of the part, the software adapts the nominal tool path to the real shape of the part.

This automated process happens in seconds. A variety of software toolkits, designed through many years of real-world collaboration with numerous successful users, is available for a wide range of industry applications and controllers. What if adaptive machining is not required and a measuring probe is only necessary for feature verification such as bores and bosses? If you want to stay ahead of your competition that are already heavily engaged in using this technology, it is worth knowing that the OSP60 probe can be used in ‘macro mode’ for both touch-trigger and scanning operations. There are multiple shapes and processes available in easy-to-use macro packages for various types of CNC controllers.

These are programmed through G-code, so no CAD or CAM knowledge is required. The macro-based tools dramatically reduce probing cycle times. For instance, in the automotive industry, bore measurement and surface quality verification can be completed in just a few seconds. What other capabilities can be achieved by having a true 3D scanning probe on a machine tool? Machine health performance is a key factor in producing consistent, high-quality parts within desired tolerances. Renishaw AxiSet™ Check-Up software has long been combined with the industry-standard QC20-W ball bar test to check and optimise machine performance. These tools are used at planned intervals or in response to a problem, and sometimes need the expertise of an external machine service contractor.

SPRINT technology now offers a rapid and automated ‘pass or fail’ health check, in-cycle. This monitors any changes or deterioration in linear and rotary axis performance, such as rotary axis actual pivot points, and can be completed in a matter of seconds, before or during each machining process. This can even be done by machining a small cone on the workpiece itself and skimming it off after the machine health check process is completed. Effectively, the machine can be verified before machining each part. This can help eradicate scrap parts produced due to machine wear and tear, thermal expansion, and similar problems. While offline verification (typically via CMM) will always be required for a sample of parts, SPRINT technology brings full in-process control and verification to the shop floor.

Performance inside a machine tool

The OSP60 probe is extremely robust. Thanks to its patented spring system and thorough sealing, the probe is designed for harsh environments such as the inside of a machine tool where there are constant vibrations, hot chips, coolant, oil, and other debris. The probe is certified to IPX8 level which means it can be fully submerged in coolant. As a matter of fact, it is advised to use coolant while scanning with the OSP60 probe to reduce friction, stylus wear and ball pickup for maximum scanning accuracy.

Possibility of customisation

Although there are many toolkits and macros available out-of-the-box, SPRINT technology is also very customisable. Bespoke cycles, processes and toolkits can be modified for the user’s application to utilise the full potential and advantages of this cutting-edge technology. SPRINT technology is supported on a wide variety of CNC controllers. In essence, SPRINT technology offers a ‘one probe’ solution for touch-trigger, scanning, surface finish monitoring, adaptive cutting, and rapid machine health checking.

Some notable applications of SPRINT technology include:

  • Chamfering a cast or a welded part. Having an even chamfer all around a cast workpiece where the dimensions are not accurate can be very challenging. Some companies resort to chamfering manually which can result in damaging the part and scrapping the workpiece, which often is very expensive.

  • Scanning a welded section on a free form surface.

  • Scanning blades, bladed disks, impellers, and other complicated forms.

  • Scanning engine blocks and cylinder heads for surface quality and bore measurement.

  • Scanning the drive train of electric vehicles.

  • Scanning medical prosthetic parts to verify a match to the precision design tolerances specified.

  • Scanning valve blocks or ball valve components rapidly.

In a nutshell

SPRINT technology increases productivity, reduces cycle times, and helps eliminate scrap. Touch-trigger probes collect their points individually, so, although they can be optimised with fast measurement, they will never match the 1,000 points per second collected by scanning. That is why once a company starts using on-machine scanning, it revolutionises its experience of probing. It saves time and cost and effectively makes more money for the company. If a company wants to stay ahead of the competition in this rapidly changing world, implementing new methods and using the latest technologies is vital.

In the machining world, where seconds matter, using a touch-trigger probe in a cycle with hundreds of measured points requires a lot of time, while with SPRINT technology, this can be achieved in a much shorter time. Users have experienced total cycle time (machining and probing) reductions of 30% as a result of using the scanning probe. So, it is no longer the size of your production facility that matters but the intelligence of your production capabilities. Intelligent machining enabled by fast and accurate probing can result in huge rewards in terms of costs savings and making money.

Courtesy: Renishaw

Image Gallery

  • The OSP60 probe can continuously measure up to 1000 points per second in XYZ simultaneously

  • SPRINT technology now offers a rapid and automated ‘pass or fail’ health check, in-cycle. This monitors any changes or deterioration in linear and rotary axis performance.

  • Venkatesh Kulkarni

    Head Of Technical Services

    Renishaw

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