Geometric Product Specifications: Standards enable digital continuity and raise efficiency
In a globalized economy you won’t succeed with drawings that note dimensions in a local language
What could be wrong with the usual ways to note dimensions in my company? Why should I invest in training my teams to use and understand ISO GPS and the US-pedant, ASME GD&T?
Train your teams to use and understand ISO GPS because this standard allows you to document design intent in an unambiguous, clear and repeatable way. And these qualities pay off in many ways.
Let me give you an example. Some weeks ago, I, was called in by a company that was seeking for a new outsourcing supplier to reduce time and cost of components production. They contacted a well-known supplier on another continent and were surprised to find that there were assembly and functionality issues with the supplied parts, although parts inspection sheets were well within specifications.
A quick check of the drawings revealed that the supplier did a good job, all geometric specifications were met, and the reason the parts were not good was that the drawings did not depict the functional requirements, and were some partial ambiguous sort of local ISO GPS accent.
It is easy to see why the management decided to change something about this. Today, you need to be quick to adapt sourcing, but in a global market, you don't know who's going to end up manufacturing or measuring your parts. Failing to meet standards in geometric product specifications means that you are at risk of losing time and quality.
Improving collaboration with suppliers and customers is certainly a plus for my competitive position. What about the product creation process inside my company? How does the switch to ISO GPS raise efficiency?
ISO GPS allows you to document design intent in an unambiguous, clear and repeatable way. And these qualities pay off in many ways.
Going through your departments there are some obvious gains. Let’s look at design. Using ISO GPS makes design reuse more productive. Also, design review gets easier and volume variations are more practical. In contrast, when we use plus-minus tolerancing, we're ignoring the direction, we are ignoring the form, we are ignoring the variation in orientation.
The shop-floor team can easily focus on what is important and find the quickest and cheapest way to yield a good part. From my experience, in many cases manufacturers produce parts that are heavily, heavily over-engineered. It happens that a work piece is manufactured to thousandth of a millimeter, even though the functionality would not call for this accuracy. Only because the design intent is not clear and manufacturers fabricate the part to the process capability (since the functional specification is absent). Whereas with ISO GPS, you may reduce manufacturing time, you reduce cycles and can be much more competitive in quotes.
To name just one of many aspects for your quality department, their collaboration with design and production improves. As geometric specifications are clear and unambiguous, you put a stop to discussions like "you did not measure this correctly...", "this is not how it should be measured" and “this is not what needs to be measured". Functional geometric limits in the 3D-Model allow engineers to choose the best measurement approach.
Let's look at the bigger picture of digital transformation initiatives that decision makers want to introduce in their company. e.g. finding ways to implement the digital twin and Industry 4.0 models. How does the use of a standard for Geometric Product Specifications help in this endeavor?
The 3D model describes the ideal geometry very well and repeatable, but it does not provide any information about the functional variation limits of the geometry.
With ISO GPS we can document the functional limit for the geometry variation digitally and this enhanced model can be reused through the whole lifecycle of the product.
The CNC programmer, for example, does not have to reintroduce the geometric limits as the CNC software can read and use the digital information from the 3D model. Likewise for inspection software - it can read the digital information about ISO GPS limits for the geometry and interpret the measurement.
Once again, we save time. We don't have to enter data that already exists, and we reduce the risk of typing errors and misinterpretations. Overall, we increase the level of digital consistency in the product creation process by using the same data set over and over again.
If I decide to go ahead with ISO GPS and Digital Twin, how can I motivate Design, Quality Management and Production to embrace this initiative?
First of all, people oppose change that they fear. So as a manager, you will need to show the benefit or value for the people, so they will want to move ahead and open this new chapter.
- For designers – reduced effort and time spent on tolerancing
- For manufacturers – 3D annotated model is readable by software, allowing the programmer to focus on the process rather than retyping information that is already on the annotated ISO GPS model.
- For Metrologiests – CMM software also reads 3D PMI (Product Manufacturing Information), saving on programing and reporting effort.
Taking advantage of ISO GPS (or ASME GD&T) allows designers to focus on their primary responsibility, which is the parts shall function. Cost, manufacturability are important constraints, but not sufficient. We cannot go for low cost parts that do not assemble or function. Manufacturing and Metrology are constraints that need to be addressed, but they are not the GOAL!
Introducing ISO GPS has something to offer here. The engineer can focus on the defined functional requirements and then consider manufacturing and measuring as constraints. A clear definition of design intent can help doing design reviews. Also, accepting or not accepting change requests gets much easier because functional specifications are documented.
Everybody involved in the production process will gain from the fact that with ISO GPS you reduce ambiguity and the possibility of disagreement. Collaboration is much more productive when the specifications are clear-cut and backed up by a standard.
To round it up for the management perspective: ISO GPS or GD&T offer a perfect opportunity to reduce cycles time and costs while improving quality at the same time. You make an important step forward on your way to digital continuity in the product creation process and that is a core requirement for the digital twin!
Gili Omri, TES-RND owner, ISO-GPS /GD&T Trainer & Consultant, is a seasoned R&D engineer with vast mechanical product development experience in Aerospace, Defence, Automotive, Medical devices and consumer products. Mr. Omri is a Participating member and technical expert of ISO\TC 213, currently leading a task force aimed at improving ISO GPS system usability, as well as a certified senior ASME Y14.5. Dimensional management mentor, trainer & consultant, tolerance variation and accumulation expert.
WHAT DO THE STANDARDS ISO GPS AND GD&T STAND FOR?
ISO GPS or GD&T (Geometric Dimensioning and Tolerancing) is an international, concise and precise symbolic language developed for the express purpose of documenting design intent, to detail the functional requirements of a manufactured assembly part and to ensure the compatibility and interchangeability of those parts. GD&T is the tool for precisely and clearly defining functional specifications for size, form, orientation. GD&T provides the links between theoretical 3D models, CAD (Computer Aided Design), CAM (Computer Aided Manufacturing) and CAI (Computer Aided Inspection) and the real world and location of the elements of a manufactured part.
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