Can you predict the functional fitness of a component based on dimensional accuracy?

A commenter has raised an important aspect of dimensional metrology in this thread. The point is a very important and fundamental one connecting dimensional measurement and functioning of a manufactured component. The core question that we should ask when we do a dimensional measurement is this – how does this measurement help me in ensuring that the component will function properly?

Let us rephrase the question a little – can a dimensional measurement guarantee proper functionality? Well, the short answer is No. As a manufacturer of a dimensional measurement equipment, I would like to escape responsibility!! The nuanced answer is a long-winded one. Have you seen a situation where all dimensions of an actual manufactured component are well within the tolerance of the given design drawing, but the component does not function properly? The situation may sound familiar to many – QC rejects the whole batch and blames Manufacturing Team, which in turn blames supplier or the Design Team, who say they did exactly as told by customer and the drawings were approved by them. In the end, customer is upset because things don’t work, and no one is happy!!

The real issue is the extension of geometric dimensioning and tolerancing analysis from being a necessary condition to a sufficiency criterion during evaluation a manufactured component. In many situations this may be true, but in some cases, it leads to wrong conclusions and heartburn (and money-burn). To understand why, allow me to use a simple analogy in everyday life. Consider you are on a holiday on the banks of a river. Water is flowing constantly, and you can see fishes swimming around. You take out your shiny new camera phone and take a picture. From this picture, can you estimate the flow rate in the river? Our situation is similar. Let me explain why.

Coordinate-based measuring systems fundamentally pick points on the edge/surface of the object of measurement, and construct ideal geometries (like straight lines, circles, etc), thereby generating a geometric model of the component. The system proceeds to measure this model, NOT the component!  But in reality, a perfect line or circle is as achievable as a frictionless surface in physics! Hence, measuring systems give the nearest ideal geometry to what is actually there in the component. This is computed as a “best-fit” for the given set of points (the algorithms for calculating this may vary from machine to machine). If you ask the system to generate a circle, it will always give you a circle, although your component may be oval in shape. Hence, the actual measurement numbers that are output from your measuring system may NOT indicate what is actually happening in the component. While the best-fit answer may show that the component is accurate, the component may fail ( for e.g., if you are looking at a connector in a flow piping system, you may see a leak). The remedy to this kind of a problem is to assess the geometry more thoroughly and hence newer GD&T techniques and standards have been developed (this kind of situation is likely the mother of “Profile of Shape” concept in the ASME Y14.5-2009 GD&T standard).

The lesson to take from this discussion is that we should not blindly accept a component simply because it matches ALL dimensions within specified tolerances, and/or reject all components because some of them may not. You need to take care of which dimensions are critical for function, and have a clear understanding and methodology in place to assess the fitness of a component for functionality.

Awaiting your comments and response !

Imtex 2018.

Imtex 2018 was excellent and we had a great response. It was nice to see many of our friends and customers, as well as welcome new people interested in the products.

We thank you for your visit and it was a pleasure to host you at the booth! See you next at the Mach Auto Expo in Ludhiana later this month!!

What is Metrology?

Measurements are an important aspect of our everyday life. We use measurements whenever we design, create, build or buy anything.

 What are all the things we measure?

We measure properties of things in order to describe or assess their suitability for their intended purpose.

So, here are some of the things we measure in daily life –

·         Physical dimensions – lengths, radii, area, volume etc.

·         Weight/mass of materials

·         Brightness

·         Temperature

·         Time

·         Energy

There is a scientific commonality to all measurements that are usually independent of the parameter being measured. This common science of measurement is what is called Metrology. The ability to measure correctly, easily and affordably is many times a fundamental criterion, based on which, people need to make critical business decisions.

My blog posts will focus on many aspects of dimensional metrology for mechanical engineers, spanning various verticals like Automotive, Aerospace, Injection Moulding, Medical/Pharma Device/parts manufacturing etc.

This is an attempt not only to share information and knowledge, but also to elicit readers to share their knowledge and experience, so that we can do better measurements and understand the intricacies of Metrology.

Happy New Year!

We wish you a very happy new year 2018! Welcome to the new, remodelled home of Rapid-I on the web. Hope you like it. There is a simple form to give feedback. You can request a demo or more information quickly. We are waiting to hear from you. If you are an existing customer, we have simple form to request support. This will reach all members of our dedicated Application Engineering team, and someone will contact you very quickly.

We have great stuff lined up for the website and in our product portfolio this year. Do try to visit our booth at IMTEX 2018 in Hall 3A Booth H106 and see the latest developments and products live.

We are starting a new Learning Resources section on our website, discussing fundamental concepts in dimensional metrology and application notes on Rapid-I.

Welcome to the new Rapid-I website!!

Hello! Welcome to the internet home of Rapid-I, India’s undisputed leader in Vision Measuring Systems. We have lots of new exciting stuff lined up to be posted on this site. We hope you like the new look and feel of the website. Please feel free to give your feedback by writing in the comments to this post.

Looking forward to closely interact with you, our customer, and hoping to hear from you soon!