Click on the advert above to visit the company web site

Product category: Form/co-ordinate, optical and vision instrumentation
News Release from: Renishaw | Subject: QC10 ballbar
Edited by the Engineeringtalk Editorial Team on 26 July 2005

Ballbar sets standard in machine tool
verification

Renishaw's QC10 ballbar has become a vital tool in changing how users worldwide think about machine tool performance verification.

Determining a machine tool's capabilities before machining, and subsequent post-process part inspection, can greatly reduce the potential for scrap, machine downtime and as a result, lower manufacturing costs Bad machining may result from bad tooling, worn spindles or workpiece clamping, but the major causes of defects can usually be attributed to positioning errors in the machine tool itself

In the past this may have been achieved by machining test (or "master") parts and then inspecting them.

However, the process was time consuming and gave limited confidence when machining parts with geometries different to the master part Over the last 15 years the use of a specialised diagnostic tool, Renishaw's telescopic ballbar, has gained widespread recognition as the best and most practical method for quickly checking machine positioning performance.

A ballbar test works by measuring minute variations in circle radius as a machine tool is driven round a pre-programmed test circle.

By comparing the actual measurements to the programmed value, special software can calculate an overall "indicator" for positioning accuracy.

Typically, the test takes less than 5 minutes to run, depending on the test radius and machine feedrate.

The "circularity" or "circular deviation" value and the telescoping ballbar test itself are recognised in ASME B5.54 and ISO230 standards as a test for the positioning performance of machine tools.

Such a compact and portable tool can take the guesswork out of determining a machine tool's capabilities, allowing users to quickly establish a performance level before the machine cuts parts.

The software used with the Renishaw QC10 ballbar goes much further than the basic "circularity" or "circular deviation" reports, and can detect every motion-affecting error that exists in the axes under test.

These errors include backlash, reversal spikes, lateral play, cyclic error, servo mismatch, scaling errors and geometry errors such as squareness and straightness, presenting this data in easy to follow reports.

These can either be viewed on a PC's screen or printed out as part of the QA documentation for the machine.

Tests can generally be run in the range of 50mm radius to over 1m by using different ballbar extensions which cater for different machine types (including machining centres and many lathes).

Different ballbar lengths can also be used to increase sensitivity to particular errors.

For example, a longer ballbar may be used to increase sensitivity to geometry errors such as squareness, and a very small radius may be used to highlight dynamic errors such as servo mismatch.

The Renishaw QC10 ballbar is used by machine tool manufacturers, end users, service and maintenance companies and resellers for preproduction tests, predictive maintenance programmes, new machine prove-out, machine grading and comparison, and machine "check after wreck".

Early error detection with the ballbar permits optimum efficiency in scheduling maintenance and repairs.

Besides isolating errors, the ballbar also allows process optimisation.

For example, users can determine what feedrate delivers the best accuracy for a specific cutting procedure, such as contouring, through dynamic checking of the machine tool as it is driven at different feedrates.

In short, the QC10 ballbar has evolved into far more than just a tool for QA system "compliance".

For several years ballbar analysis software has been available which incorporates auto diagnosis.

This "expert system" type software diagnoses a machine's errors, producing a comprehensive diagnostic report that enumerates familiar play, geometry and dynamic errors, ranking them in order of contribution to the overall positioning error.

This feature significantly increases the appeal of a ballbar because it can be used firstly to calibrate, and then suggest fixes for a machine.

The product appeals to quality, maintenance and production departments alike.

Two further developments have greatly increased the attractiveness of machine testing with a ballbar.

The first of these was the introduction of Windows compatible software which provided easy-to-use on-screen graphics and: the ability to set up machine folders and custom tests (a key to repeatable and comparable testing); live displays of data during the capture process; improved analysis screens; and a comprehensive online manual that can be accessed directly from analysis pages using "hotlinks".

More recent developments such as Renishaw's HPS software have further extended the power of ballbar testing.

The HPS history review function allows variations in the performance of each machine over time to be displayed graphically, indicating performance trends (allowing the prediction of maintenance requirements in advance, minimising unscheduled downtime and avoiding unnecessary maintenance).

Effectively a complete ballbar "medical record" for a machine can now be created.

The software also makes it possible to set up standard tests, including supervisor-selected acceptance limits for all test parameters, allowing the operator to make testing a very simple (yet standardised) routine.

Testing is no longer the preserve of skilled technicians.

If the test results exceed any preset acceptance limit, the operator will get an immediate on-screen warning.

The part program generator can automatically generate the NC machine code required to suit the selected test setup, a boon for those working on a variety of controllers or for less specialised staff.

Finally, a simulator gives operators a "what-if" tool, taking the test results and allowing the machine and test parameters to be altered, and the effect of these to be immediately displayed, allowing the most cost and time effective remedies to be quickly arrived a, without any trial and error on the machine.

Over recent years, pressures on the "average" machine shop have changed drastically.

The requirement for lower costs are higher than ever, caused by the economic climate and increasingly open markets.

There has been a rapid development in the use of widely recognised quality system standards such as ISO9000, as well as a growth in the use of specific machine performance standards.

The use of more advanced CAD/CAM systems has eliminated errors introduced during manual part programming and increased expectations that even complex, expensive components can be cut "right first time".

As a result of these pressures, many businesses have had to cut down on maintenance and/or contract work out.

The pressures also mean that the need to minimise scrap and the reworking of components has never been greater.

The availability of sufficient and adequately skilled staff is another growing problem.

Tools such as the Renishaw QC10 ballbar provide an answer to all these problems and the key to this lies in its ease of use and the power of its analysis capabilities.

A ballbar allows for repair and maintenance to be carried out only when required, minimising direct costs and losses due to downtime.

With such a simple test, it is also easy to see if the repair works carried out have resolved the initial problem, or created new ones.

Machine users who outsource these services can either carry out the checks themselves, or stipulate that a "before and after" test report is supplied to verify such work.

Where QA programmes are in place, a ballbar is an ideal interim check between major (laser) calibrations, and when there is any doubt about the dimensional accuracy of finished parts (eg after machine crashes).

So simple is the test, that many users specify a ballbar test before beginning any new batch of components.

Like any metrology tool, the Renishaw QC10 ballbar should be calibrated regularly and traceable to international standards.

With the widening implementation of "Six Sigma" programmes, there is a need to define and measure process capability factors.

A ballbar offers a practical solution to this need.

From the viewpoint of machine tool repair and maintenance service providers, a ballbar has become a vital tool in an increasingly competitive market.

By speeding up testing, improving analysis and providing independent verification of results, ballbar testing saves time and money, whilst improving the quality of service to the customer.

With multilingual software available, the appeal of Renishaw's QC10 ballbar is spreading even further afield, and has become a vital tool in changing how users worldwide think about machine tool performance verification. Request a free brochure from Renishaw ...

• Renishaw: contact details and other news
• Email this article to a colleague
• Register for the free Engineeringtalk email newsletter
• Engineeringtalk Home Page

Search the Pro-Talk network of sites

Put your news on Engineeringtalk  |   Advertise  |   Get the free Engineeringtalk newsletter  |   Engineeringtalk Home
About Engineeringtalk  |   Copyright © 2000-2008 Pro-Talk Ltd, UK