Tool Calibration: Process, Importance, and Practices

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Tool Calibration: Process, Importance, and Practices

Tool calibration ensures precision in the production process and reliability and accuracy of measurement or operations within specified tolerance limits, consistency, and adherence to strict quality standards.

Usually, wear and tear, improper use, or overuse of equipment or machine tools are typical causes of tools degradation. The output of their measurement often drifts/deviates, making them unreliable and less accurate.

Tooling calibration is a principal requirement for organizations that seek to comply with industry standards such as ISO 9001. It also contributes to process performance or production quality since it helps to detect wear and tear early, mitigate tool degradation, and maintain the quality of products. Several other impacts of tool calibration include:

// Detect process deviations early;

// It ensures the optimization of production processes;

// Proper tool calibration is critical to First Article Inspection (FAI) and put them into mass production;

// Calibrating tools for manufacturing help reduce scrap costs.

Which Tools Should Be Calibrated in the Workshop?

Product manufacturers and engineers leverage various tools to create safe, accurate, quality products that meet specifications. Each of these tools has its respective function in manufacturing operations. They collectively help align the machine measurements with established calibration standards to achieve precision and desired tolerances in product manufacturing. Examples of standard tools that require calibration in the workshop.

Measure Tools

Measuring tools such as micrometers, height gauges, depth gauges, calipers, dial indicators, and micrometers require calibration to measure parts’ dimensions accurately.

CNC Machines

CNC machines, including CNC mills, routers, grinders, and lathes, must be calibrated often to ensure movement accuracy and cutting tool precision.

Testing Machines

Calibrating material testing machines like impact testers, tensile testing machines, and hardness testers regularly help ensure accurate and reliable results.

Welding Equipment

Welding equipment such as welding gauges, plasma cutters, TIG and MIG welders are often calibrated to deliver appropriate gas, current and voltage for uniform weld quality.

Laser Machines

Laser cutting and engraving machines must be calibrated regularly for proper laser focus and alignment.

Other Power and Hand Tools

Power tools like drills, sanders, saws, and grinders and hand tools like wrenches, pliers, screwdrivers, files, and hammers require regular calibration to prevent mechanical failure due to improper torque.

Tool Calibration Standards

Since tool calibration is important to various industries, manufacturers adhere to various calibration standards to ensure safety and prove the accuracy or quality of manufactured products. Here are the common tool calibration standards:

ISO 9001

This international calibration standard establishes the requirements of organizations’ quality management systems (QMS). It defines its conditions on calibration in clause 7.1.5 in a section titled Monitoring and Measuring resources – which should be regarded as the minimum guidelines for any tool calibration. The tooling calibration requirements for ISO 9001 standard are broad, including:

// Measuring instrument calibration must be performed at specified intervals against national or international traceable standards.

// Companies must ensure their measuring instruments are ideal for the measurement operations they are intended for.

// Organizations must maintain their tools and instruments to ensure their continued.

// These instruments must be protected against adjustments that would invalidate their calibration status or damage.

AS 9100

AS 9100 is an essential management system for the aerospace industry. It builds upon the requirements of the ISO 9001 standard. NQA states that the standard applies to companies that design, develop, or supply defence, aviation and space products and services. AS 9001 comprises aerospace specific recommendations for safety in parts development and production. Hence, the measuring equipment undergoes greater scrutiny levels than in other industries.

ISO 17025

This calibration standard is a specific standard detailing stipulations for the technical capability of calibration laboratories. Although ISO 17025 focuses more closely on the calibration lab’s management structure and processes, it shares several principles with ISO 9001. Besides, it requires the traceability of measurement and the application of measurement uncertainty.

Laboratory personnel’s training level, environmental factors, and utilized calibration equipment are typical procedures that an ISO 17025 audit covers. Hence, companies that choose a calibration service with ISO 17025 accreditation can be assured that their equipment will be calibrated with a high competence standard and higher accuracy.

ISO 13485

Medical device manufacturers or organizations providing medical-related services follow ISO 13485 calibration requirements. These comprise companies that develop, manufacture, distribute, install, or service medical equipment and devices. Unlike other industries, companies that handle medical devices must meet industry-prescribed regulations like the EU Medical Device Directive. Moreover, these organizations are better prepared to meet stringent standard requirements when they adopt ISO 13485 as their tool calibration strategy.

MIL-STD-45662

MIL-STD-45662 was one of the first standards specific to calibration and was drafted by the US Department of Defence. Although discontinued in 1995, MIL-STD-45662 remains a relevant standard to companies in the civilian and military sectors today because it formed the foundation for other standards, such as ISO 17025.

IATF 16949

IATF 16949 is a quality management system for the automotive industry. Like AS 9100, IATF 16949 is built on ISO 9001 calibration standards. However, it includes requirements that are specific to the automotive sector. As stated by NQA, the IATF 16949 standard stresses the development of a process-oriented quality management system that allows continual improvement, the prevention of defects, and the reduction of waste and variation in the supply chain.

The IATF represents a group of manufacturers and trade associations with the goal of improving automotive products’ quality globally. The calibration requirement of IATF 16949 applies to any company in the automotive supply chain.

Calibration Procedures for Various Purposes

Calibration is to every device and tool measuring any physical parameter. However, manufacturers reserve calibration procedures for processes requiring only the highest degrees of accuracy or where regulations necessitate since the process can be time-consuming and expensive.

Mechanical Device Calibration

Mechanical device calibration is similar to other calibration procedures. It involves calibrating dimensional physical quantities, including weight, force, and torque. It includes measurement devices, balances, torque tools, load cells, and scales.

A known value of a specific parameter is applied to the mechanical device under test, and then the output is compared with the known reference value. However, mechanical device calibration requires several tools since each parameter is produced by varying physical forces.

Electrical Device Calibration

Electrical device calibration is compatible with devices and instruments that calculate typical electrical quantity, including current, capacitance, voltage, resistance, and inductance. Oscilloscopes and scope meters, as well as digital and analog multimeters, are standard electrical devices that require calibration.

Engineers compare measurements of their output to those of precise devices of known performance to calibrate electrical devices. These devices produce measurement functions like current, resistance, and voltage. The traceable calibration tools will create an extensive range of the desired quantity, including voltage supply for meter testing, which might develop from fractions of a volt to hundreds.

Pressure Calibration

Analog and digital pressure sensors can be calibrated since analog sensors output a current/voltage signal based on the fluid pressure. In contrast, the digital (discrete) pressure sensors switch on or off at precise levels. Various pressure calibration tools are based on the fluid medium (gas or liquid).

In pressure calibration, a portable pump generates a known pressure. The tested pressure device is linked to a portable pump through appropriate connectors. The pressure of the portable pump is compared with the pressure of the device under test. Digital indicators, pressure gauges, transducers, and pressure transmitters are typical pressure devices that require calibrating.

Temperature Calibration

Temperature calibration involves verifying temperature sensors (RTDs, thermistors, thermocouples, etc.). It helps determine if any deviation in the temperature sensor output is within acceptable range. Here, the calibration process occurs by stimulating and comparing a known temperature value with the tested temperature device. Physical and electronic simulating are typical temperature calibrators.

Physical simulating tools comprise a carefully controlled heat source, like a hot bath, capable of generating the desired temperature. The tested temperature sensor is placed in the heat source (hot bath), and its output is compared to the heat source’s temperature.

Conversely, electronic simulating tools are handheld instruments that simulate the preferred temperature value as an electric signal, like 0 – 10 V or 4-20 mA. This calibration process might test the signal wires after the physical temperature changes to an industrial signal level.

Humidity Calibration

This calibration format is core to manufacturing industries like chemicals, pharmaceuticals, and food, even though humidity impacts any electrical process or system. Uncontrolled humidity and moisture can cause condensation and corrosion. The humidity generator inside the calibrator generates a gas steam of known humidity levels that is compared with the humidity sensors’ value.

A visual display on the humidity generator shows the amount of humidity generated. The calibration can either be marked as failed or passed depending on the humidity sensor’s visual display and signal output.

How Often is Tool Calibrating Required?

Although the frequency of tool calibration is sometimes based on equipment usage rate, there is no universal standard calibration schedule. Various factors, such as the type of tool, its usage rate, and working environment, determine the calibration frequency.

In addition, ISO 9001 does not identify calibration periods but requires a calibration register that indicates each tool, its frequency of calibration, and confirmation that a tool was calibrated on schedule. Below are criteria to consider when deciding tool calibration frequency.

Tool’s Measurement History Stability: With regular tool examination and results documentation, it would be easy to identify inconsistencies or significant deviations from the calibrated measurements.

Tool Calibration Frequency Recommendation: Some manufacturers often recommend calibrating the equipment or machine after a predefined number of use cycles. This recommendation serves as an ideal consideration for scheduling tool calibration.

The Importance of Measurement Taken: Tooling calibration is less critical if the tool is only used to measure reference dimensions that are not used to confirm the accuracy of products.

Risks and Potential Consequences: The accuracy of some dimensions is more paramount than that of others. Besides, the machine tool involved doesn’t require consistent calibrating if an inaccurate tolerance has no significant impact on the final product.

However, to ensure peak performance of your machine, experts recommend calibrating tools at least once every three to six months based on usage. It may be necessary to perform tool calibration more frequently in high-volume production situations.

Considerations and Practices for Tooling Calibration

Tooling calibration is fundamental to achieving optimal machine performance and ensuring measurement accuracy and reliability for top product quality. This process restores out-of-specification tools, machines, and instruments to their original performance accuracy. Here are helpful practices for tool calibration.

Implement Regular Tool Calibration

Committing to regular tool calibration helps achieve high-quality and reliable data. Besides consistent instruments, calibrating schedules offers cost-saving benefits, increased profit margin, and production of precise and top-quality objects.

Safety Precautions

In a manufacturing environment, implementing safety protocols before calibration procedures ensures proactive measures, from mechanical risks to electrical hazards that might occur during tooling calibration. Thus, manufacturers can prevent risks and ensure personnel well-being in the calibration process by adhering to stringent safety precautions and guidelines.

Ensure Measurement Traceability

When calibrating tools, measurement traceability is paramount. It involves accurately documenting the calibration process, including the standards employed and the derived outcomes. Ensuring measurement traceability in tool calibration provides confidence in the accuracy and reliability of the machine tools since it helps ensure that the measurements can be traced back to standards (national or international).

Environmental Conditions

The slightest temperature variations can cause machine tools to contract or expand in precision machining, impacting measurements. Different environmental conditions, such as humidity, vibration, and temperature, can affect the performance and calibration of tools. Therefore, experts advise maintaining a controlled environment to mitigate the influence of these environmental conditions when calibrating.

Check Tool for Wear and Tear

Implement regular tool inspection to identify contamination, damage, or wear that can hinder tool performance. Besides, you might need to calibrate CNC machine tools used in extremely harsh environments more frequently or replace them if necessary. Thus, when you regularly check your tool for wear and tear, you can easily maintain tool accuracy and achieve tight tolerances in machined products.

Conclusion

At IDEAL, we excel in providing top-quality custom machining services tailored to meet your project needs. Our advanced technology and skilled team ensure your specifications are met with exceptional accuracy and efficiency.

Contact IDEAL today to see how we can assist with your next project!