What are the benefits of implementing systematic GPS?
The savings and improvements reported by companies using systematic GPS include:
- 15-20% overall product cost savings.
- Reduced time to market
- Fewer design iterations needed to get the product right
- Less discussion of drawing interpretation
- Less trial and error to make the specification work
- Reduced production set-up time
- Higher outsourcing success rate
- Looser tolerances leading to lower cost
- Products that function because of the tolerancing rather than in spite of it.
- Better communication
- Designers focusing on innovation instead of explaining their drawings.
- Functional requirements recorded for the future.
A systematic tolerancing procedure
By employing a systematic tolerancing procedure, all your drawings will have a similar tolerancing dialect. Everybody touching your drawings will see the distinct similarities and start having an easier time interpreting and understanding your drawings. This starts with the consistent use of functional datum systems, continues with geometrical tolerancing that consistently references the functionally relevant datum system for each feature and ends with dimensional tolerancing only being used for features of size involved in fits.
When the tolerancing in all your drawings have the same structure, reading your drawings become like reading books that have the same storytelling template, e.g. introduction of the characters (which are the functional features), start the action (which are the functional datums), rising action (tolerancing ensuring the internal soundness of the datum system), climax (geometrical tolerancing of the functional features to the functional datum systems) and resolution (dimensional tolerancing of features of size, tolerancing of surface texture and edges). When all your drawings have the same structure, they will be easier to read and understand.
Fewer iterations
When you apply a systematic tolerancing procedure with formal reviews at significant milestones, e.g. to ensure that the right functional datum systems have been selected before further tolerancing is applied, you will need fewer iterations to complete the tolerancing and the overall time to complete the tolerancing will decline.
Less discussion of drawing interpretation
Systematic GPS tolerancing based on current standards will reduce the discussions about the proper interpretation of drawing indications, as the tolerances will be well-defined, as opposed to e.g. dimensional tolerances applied to something other than features of size.
Less trial and error to make specifications work
Dimensional tolerancing and hybrid tolerancing tend to require a trial and error approach, either because the dimensional tolerances do not exist in a coordinate system, as envisioned by the designer, or because unexpected form and geometry deviations show up in production. This process tend to repeat every time the production is moved to a new line or supplier.
Systematic GPS tolerancing creates tolerances that are locked together in carefully selected coordinate systems that are aligned to the functional datum systems. Because the tolerances are aligned in coordinate systems and because geometrical tolerances control the geometry of the entire surfaces, there tends to be a lot less surprises and unexpected deviations in what can pass the tolerances.
It may be that simplified inspection methods may have to be upgraded to catch the specific deviations generated by a production line, but the specification itself will be a lot more robust.
Reduced production set-up time
As discussed above, dimensional tolerancing and hybrid tolerancing are usually based on an unfounded expectation from the designer that tolerances exist in a coordinate system. The problem for manufacturing engineers is that with these types of drawings it is hard or impossible to tell which features have to be aligned with each other and which alignments do not matter. Therefore the manufacturing engineer is forced to guess and select fixturing features and processing steps based on assumptions about how the component is going to function. When the manufacturing engineer guesses wrong - and there is little to help him avoid that - the manufacturing processes and sequences have to be re-engineered.
With systematic GPS tolerancing it is clear to the trained reader what features are related to each other and which therefore have to be manufactured in the same step. It is also clear which feature define the coordinate systems in the component, so this can be taken into account when selecting fixturing features.
Higher outsourcing success rate
Because the drawings are easier to understand for a trained reader and because it is clearer which features are related to each other, systematic GPS drawings are much better at standing on their own without additional explanations or people on-site babysitting and filling in the information that is not embedded in the drawings. Therefore outsourcing stands a much higher chance of success, when it is based on systematic GPS drawings. This applies whether the outsourcing is to the next town over, another country or another continent. The more the drawing is unambiguous and can stand on its own, the better the chance of success.
Looser tolerances
It seems counterintuitive, but systematic GPS tolerancing often leads to larger tolerances. This is because when the tolerances are locked in a common coordinate system, looser tolerances can ensure functional components. Another reason is that when it is clear from the structure of the tolerancing which features have to be related to each other, it is unnecessary to use excessively tight dimensional tolerances to force features to be manufactured in the same process step.
Products that function because of the tolerancing
Dimensional tolerancing and hybrid tolerancing tend to require a lot of additional explanations and notes and locking down manufacturing processes to ensure that you continue to reliably produce functioning components. Systematic GPS tolerancing can express the functional requirements unambiguously, so you no longer have to rely on extraneous documentation or part approval processes to make your components work.
Better communication
Because systematic GPS tolerancing can express the functional requirements unambiguously, it makes for much clearer communications amongst designers, suppliers, production and inspection.
More time to design
One of the more profound changes that systematic GPS tolerancing brings is that because of the disciplined approach and the unambiguous expression of the functional requirements, designers tend to use a lot less time maintaining their old designs and participating in meetings and discussions to clarify the requirements. They also have to allocate much less time and effort to remember the functional requirements that did not quite make it into the drawing, but have to be inferred from the existing dimensional or hybrid tolerances.
This means that designers can use a much higher percentage of their time on designing new products.
Functional requirements recorded for the future
When the drawing truly become the repository for the functional requirements, it also becomes a corporate memory. It is no longer necessary to rely on access to the designer of the previous product generation to understand what the necessary requirements are or have the old drawing explained. Therefore designers can easily incorporate the know-how embedded in the previous generation of systematic GPS drawings, when designing the next generation product.
Henrik S. Nielsen
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