What is calibration and why does it matter so much?

Let’s start this blog with the basics. The foundational question is “what is calibration”? After we’ve answered that, we can move on to considering calibration specifically in the context of machine tools. Then, we’ll look at a particular example of machine tool calibration, camera-based measurement. This will show us how the field of calibration is evolving.

In the simplest possible terms, calibration is the comparison of a measurement device against a traceable equivalent. As such, it involves comparing measurements taken from any system that’s under test (a machine tool is one among many examples) with a set of established reference values.

The results of this comparison can be used to correct (or “calibrate”) the device against the expected values, with any resulting adjustment (calibration) returning it to its desired original state. Because devices and their performance erode over time with use, wear and tear, or for other reasons, calibration is generally performed regularly and, in some cases, continually, to keep them operating effectively.

This definition is, of course, a general one but it adequately explains the procedure and outcome of any calibration process. Of course, when applied to a specific industry or set of devices such as machine tools, greater detail and definition emerge alongside the wider context. So, let’s look now directly at machine tool calibration.

Machine tool calibration

Machine tools are a central component in industrial manufacturing. In broad terms, the completion of almost any industrial manufacturing project will require the shaping of the raw materials from which the necessary constituent parts of whatever’s being built are made. These parts will be subsequently installed, assembled, or configured together to produce the finished article.

The making of the parts is done through processes such as cutting, grinding, milling, pressing, boring, drilling, and others so, of course, the devices involved, which need to be calibrated, will be grinding machines, milling machines, boring machines, etc.

A complex subject

As you can readily imagine, the result is – to differing degrees depending on the task – complex. Industrial manufacturing outputs tend to be large scale, multi-part, and intricate by nature (think of a jet engine or a Magnetic Resonance Imaging machine). This means, in terms of putting things together, that accuracy and tolerance are at a premium. And the pursuit of successful manufacturing outcomes has in recent times been further advanced by the evolution of technologies like Computer Numerical Control (CNC) and Computer Aided Design (CAD).

CNC and CAD as well as other enhancements in machine tooling, however, only improve manufacturing for a limited period because over time and with use as we noted earlier, even the best machine tool’s performance erodes. The challenge for manufacturers is thus to ensure accuracy and performance remain the same over time. If they don’t, the penalties (for instance, the need to re-work or scrap outputs) can be punitive. So, ensuring such an outcome isn’t the case is important and that is where machine tool calibration comes into the picture.

It’s worth saying here that there’s nothing abstract about this; to ensure consistency the International Organization for Standardization (ISO) and the American Society of Mechanical Engineers (ASME) have defined and standardised Machine Tool Calibration (MTC) measurements since the early 2000s.

Calibration use case: Camera Based Tool Measurement

Now that we have a basic understanding of the principles of calibration, let’s apply the definitions to practice and see how calibration in action works. There are many possible examples but in this one, we’ll consider a particularly progressive use case: camera-based tool measurement calibration for milling tools (it’s one of the machine tool examples we mentioned earlier).

Milling tools must operate reliably, deliver consistently accurate outcomes, and function with a high degree of quality and precision throughout their lifetimes, so calibration is not only vital but must also be a continuous function. The cutting implements in milling tools (which are the essential component for delivering the required output) can be deformed during production, suffer wear and tear – and more. As a result, the quality of the workpieces produced can deteriorate.

In this domain, perpetual tool analysis across multiple parameters is necessary, with real-time processing of collected information to deliver findings (and enable them to be acted on) quickly to keep the tool performing optimally.

Historically, a range of tools have been used to calibrate milling tools, identifying issues such as deformation, variation in cutter length, spindle runout, and more. But calibration is now moving into a new era with optical-based measurements.

Thanks to innovations by Conoptica, legacy approaches are increasingly giving way to camera-based measurement systems, which are installed or integrated within the milling machine itself and give users the data necessary to determine the accuracy of the milling tools more precisely and more quickly – data that can be shared with other processes.

Camera based systems can drive calibration across almost limitless parameters – radius, length, tool angles, cutter variation, deviations – and more. It would take a lot of lasers to deliver the same information, if they could be configured effectively at all.

Calibration improves outcomes

To extend and conclude this example, camera-based tool measurement (as with calibration generally) drives both process and operational gains. Calibration-related advantages include:

  • Improved predictive maintenance
  • The ability to measure and compare tool effectiveness
  • The ability to process corrections in situ, immediately
  • Full traceability for all measurements

Furthermore, camera-based measurement enables the tracking of deformation and changes in dimensions to manage, when necessary, tool replacement. When wear reaches defined levels, tools can be changed – maximizing return from tool investments. It also measures tool runout, machine saturation, and spindle position – allowing real-time adjustments to production, enhancing end-quality – ensuring that required tolerance values are adhered to. Auto-correction, meanwhile, ensures consistency.

The result of any calibration process is tools that perform accurately. Progressive solutions such as camera-based measurement deliver this to an unprecedented degree.

Summary: why it’s important

Milling tool calibration has historically been categorized as being within the domain of quality assurance, but perhaps not surprisingly that’s changing. It’s now increasingly viewed – because calibrated machines lead directly to an improvement in throughput (feed rates can be set higher when machines are known to be accurate) – in a production and performance context.

This makes sense particularly when you consider the advantages of the progressive, camera-based measurement systems described above. Correctly calibrated machines (ones that are “in tolerance”) produce parts with higher accuracy, which has the beneficial side effect of reducing downstream costs in areas like assembly, warranty, and in-field service.

Additionally, such calibration provides an early warning function when the positioning of a machine tool may need to be repaired. This can reduce interruptions of sometimes critical production runs for maintenance operations.

There you have the basics. The key takeaways are that:

  1. In the machine tools domain, calibration is a critical process.
  2. It impacts both costs and profits, so its benefits are measurable (and considerable).
  3. It cannot (realistically) be ignored without suffering negative consequences. If you don’t calibrate, your machine tools’ performance will be compromised sooner or later.
  4. How calibration works is evolving and, as both machines and tools become more complex, so does the process of calibration itself.
  5. Better, progressive, approaches to calibration that are now emerging deliver considerable return on investment – led by Conoptica.

About Conoptica

Conoptica is the market leader for measurement equipment in the wire & cable industry and has been providing high tech camera-based measurement solutions for the metal working industry since 1993. We make sure that the metal working industry has access to key quantitative data about their products and tools.