ISO GPS: opportunity instead of a useless monster

In some companies – from individual employees to entire departments – ISO Geometrical Product Specification (GPS) is seen as an obstacle or sometimes even as a cumbersome, useless monster. Unfortunately, this view fails to recognize many of the opportunities that GPS offers. For plastic components in particular, GPS can significantly reduce the costs of drawing creation and quality assurance.

“I am forced to use GPS anyway!”

Using GPS is not compulsory. Only a few standards are. But, if you want to be on the safe side as well as remain informed about future developments and deliver comprehensible quality, you should try GPS. Classic dimensioning exhibits some massive deficiencies, especially in the areas of measurement technology and validation. Therefore, if you stay with classic dimensioning, you are not working with state-of-the-art technology and are incorporating liability risks. In the event of a dispute, you will always be at a disadvantage with classic dimensioning because everything that is not clearly specified leaves room for interpretation. However, in some cases, the classic methods can still work. Therefore, it is important to understand all the implications instead of blindly relying on one system.

“Yes, but it also worked before!”

Correct! However, using a classic plastic component drawing as an example, we notice that it seems overloaded, even though some dimensions are still missing, and some parts are oversized.

Frequently asked questions…

• Were the general tolerances truly validated, or did they simply say: “That is good enough!”?
• Could you really specify the function and was this provable using a specification tool?
• Does the measurement report use Gaussian deviations instead of a precise specification evaluation?
• Why do I have to tell the machinist exactly how to manufacture the component – shouldn’t it just work?
• Why do I get different measurement results for the same component depending on which employee does the incoming goods inspection or which measurement laboratory checks it?

Such uncertainties can be avoided with a sensible GPS.

Where do I see the problems with implementing GPS?

• Culture: Change is an essential attribute of a healthy company. Yet, realistically, there is often a lack of willingness to break away from the existing system and eagerly embrace the new. Fear of the unknown creates significant resistance to GPS. In companies that are new to GPS, it is often perceived as “hieroglyphs” or “overloaded geometrical tolerances”. In fact, GPS is an explicit set of geometrical requirements that must be met for smooth and simple functioning of the component. A clear personal desire for change and solid support from management are necessary.
• Lack of knowledge: If I can’t immediately understand a drawing, does that mean the component definition is bad or inefficient?
  Building up the knowledge base about GPS should be planned carefully. It involves identifying the shortcomings of both systems, offering and evaluating solutions for them, and deciding where and when GPS makes sense. Uncertainties need to be clarified. A short compulsory training course, exclusively for engineers and without the necessary practical application or room for information exchange, is not a sustainable solution.
  The changeover process should not be limited to the design department. Also production, suppliers, the quality department, and even management must understand the new language or, at least, recognize its usefulness.
  Therefore, low-threshold access to this knowledge base is essential. The use of targeted training and the support of subject matter experts are vital to ensure that the understanding of GPS is strengthened and used correctly throughout the engineering process.
• Fear of costs: Manufacturing partners frequently say that geometrical tolerance means a higher cost. However, in practice, it turns out that the size of the tolerance – and thus the required precision – has a much greater influence on the costs than the method of determination (whether dimensional or geometrical). In addition, during technical drawing creation, the initial costs are often seen as a problem. An early functional analysis allows an optimized specification to be defined, and this usually leads to cost savings, especially in the case of complex parts with a low functional geometry (e.g., plastic parts). This is a classic investment where the advantages outweigh the disadvantages. Of course, training has a cost, but it should be considered an investment, not a necessary evil.

Where does this path lead?

STEP242 paves the way for continuous data processing. By using “model-based definition” (MBD), engineers can define geometrical requirements and other data for the function of a component. Simulation and tolerance calculations can then use this information directly without the need for further preprocessing. The data set can also be automatically converted into a machine program by the CAM software without laborious post-processing based on drawings or other parameters. After production, the measuring machine program is created based on the MBD data set, and quality assurance efficiently compares the model with the measurement results to make sure that there is a clear match. This reduces the possible sources of error from the measurement process and the measurement technician’s interpretation.

Conclusion

With GPS, we primarily define “every geometrical condition that is necessary for the function of a component” which we can clearly and understandably measure.

GPS has long ago left its childhood behind and is becoming a mature standards system.

GPS is a toolbox that we can use. Every tool requires a certain amount of learning, but sometimes it is better not to solve everything with the well-known hammer…

Support from konplan

In the past, we have also supported other customers successfully regarding the use of ISO GPS. Working together with the design and development teams of the customer and using measurement technology, the existing drawings were analyzed based on assembly functions and manufacturing experience to bring them up to a GPS-compliant standard. Now, the manufacturing documents provide a much better overview and are easier to interpret because unnecessary mass and views have been reduced. Furthermore, the representation of the function was improved by directly defining the orientation for measurements according to the installation situation. This resulted in the number of incorrectly rejected components being reduced which means cost savings by reducing lost mass as well as measurement effort.
In the spirit of our slogan “developing together”, we at konplan would be happy to support you in analyzing your component drawings to make them, and especially your employees, fit for the future. We flexibly adapt to your needs and ensure frictionless implementation. Your added value is our motivation. _________________________________________________________________________

Author:

Marc Hofstetter, Mechanical Engineer

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