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How Transducer Technology Revolutionizes Geometric Tolerancing (GD&T)

Hole positioning and dimensioning with geometrical tolerance. High resolution. Focus on pen tip.Consistency is key for precision parts manufacturers. Clients need to trust that every part they purchase will be fully up to specifications. This means detailed process control on assembly lines, ensuring complete fidelity on the journey from design to final product. However, on a fast-moving production line, this is far easier said than done. That’s why automation solutions such as transducer technology offer incredible benefits to modern manufacturers. Keep reading to learn more about GD&T, its place in today’s factory, and how automated metrology is transforming what’s possible for in-line inspection.

What is Geometric Dimensioning and Tolerancing (GD&T)?

Created in the 50s, GD&T acts as a standard for defining and communicating engineering tolerances. More specifically, it’s a system by which designers can communicate constraints and tolerances with respect to an absolute position. This is extremely important because in reality, manufacturing can never be exact. As a result, engineers build acceptable levels of error (tolerances) into their designs, which is described using the symbols and notes of GD&T.

GD&T in Integrated Manufacturing and Assembly

Obviously, all the careful tolerancing in the world means nothing without factory inspection. If the first half of GD&T comes in the drafting phase, the second half is the testing. Here, it’s determined if the manufactured parts fall within spec. Traditionally, testing was conducted off-line, with trained technicians taking detailed measurements on a CMM machine.

This is a perfectly functional method, but it also comes with some major drawbacks. First, manual inspection is slow and prone to human error. Even a master technician can only work so fast, and even then mistakes are possible. Off-line metrology also means there can be no real-time data tracking.

Second, when working manually it is very difficult to measure complex pieces, especially ones with detailed curvatures. This is where the benefit of automated metrology systems come into play. Transducer technology such as contact probes provide extremely precise feedback at many data points, function on diverse surfaces, and are adaptable to different kinds of tolerancing measurement.

How Does an LVDT Probe Work?

 The CNC bore machine boring the intake and exhaust valve port at cylinder head .The engine part overhaul process by CNC machine.

A Linear Variable Differential Transformer (LVDT) is an electromechanical transducer, meaning it converts linear motion into an electrical signal. Current devices are sensitive enough to register changes on the scale of millionths of an inch. The construction of an LVDT consists of two parts: The coil assembly, and the core.

The coil assembly is made up of several windings—a primary winding in the middle, and two secondary windings on the sides—housed by several protective layers of metal and epoxy. The core is a separate tubular armature which moves freely within the coil assembly, only contacting the component directly.

Measurements are taken by exciting the primary winding with an AC current, which develops a magnetic flux, coupling the primary and secondary windings . When the probe is centered on the primary winding (known as the null position), the differential voltage out between the two secondary windings is approximately zero. However, when the probe moves closer to either side, the differential voltage changes, signifying a specific degree of motion.

This zero-contact measurement system results in a friction-free measurement system with fast dynamic response and essentially infinite resolution. As a result, LVDTs are ideal for high-volume precision part testing, which requires rapid, repeatable action with ruggedized equipment.

Examples of Geometric Tolerance with Contact Transducers

Custom Bore Gauges

Some components such as engine blocks require dozens of unique bores with exacting precision. Transducer technology allows the process to be reliably automated while delivering thousands of data points to track production. Automated systems also allow seamless changeovers, reducing downtime without sacrificing precision and accuracy.

Positional Inspection

Also known as dimensional or size tolerancing, this type of inspection regulates the measurements in a given direction. This includes the ideal component size, as well as the acceptable upper and lower deviations which make up the tolerance band. When components for assemblies with many moving parts such as gearboxes are machined, the ability to ensure high volumes of parts fall within spec is vital to a successful process.

Form Inspection

Coordinate measuring machine taking detailed data of block cylinder gauge with probe

Form or geometric tolerancing regulates relational and shape aspects of a component. These factors include parallelism, tilting, curvature, and run-out, among others. Even with comprehensive dimensional inspection, there is still room for significant deviations, which could harm component strength or function. Form inspection works in tandem with dimensional tolerancing to ensure not only that a component has proper scale, but that the relation between individual scale measurement also remains consistent.

Automate with Us!

Want to learn more about transforming your GD&T process with automated metrology? Download our brochures! To discover the detailed +Vantage integration process and the vast array of automation services we offer, visit our website. To discuss how our systems can benefit your custom process, contact us to speak with an engineering design consultant today!


    Brandon White

  • DATE

    September 30, 2021

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