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"Even today, most schools don't offer engineering students GDA&T training unless specifically requested," says Thompson, general manager of the CAD business at Boston-based PTC Inc. That's a shame. Because of what I learned back then, I couldn't bring myself to do design work without thinking about the manufacturing process." What was once little more than a confusing set of symbols on a 2D drawing has since become a critical component of model-based definition (MBD), a building block of the digital thread. Because of the latter, job shops and OEMs alike are seeing one of the most significant strategy shifts in decades - the move to digital manufacturing. Here, team members enjoy cross-functional integration between design, manufacturing and the supply chain while gaining closed-loop feedback and robust data management across a products entire lifecycle. "GD&T and its subsequent role in model-based definition has been around for quite some time," notes Hiren Kumbhojkar, senior director of Go-to-Market Strategy for Hexagon's Nexus, part of the company's Manufacturing Intelligence division, North Kingstown, R.I. "For instance, I began working in the CAD space during the late nineties and was already hearing about MBD, a concept that was initially led by aerospace companies," he says, "but then, because of its significant value, started to trickle down into other industries." [...]the 3D CAD modelis quickly becoming the authority, greatly reducing the dependence on paper drawings. "Because GD&T is inherently geometry-based, this trend is actually increasing its importance," Olson says.
How manufacturers are weaving the digital thread, cutting costs and ensuring product form, fit and function as they go
When Brian Thompson first entered the engineering field in the early'90s, he received training in geometric dimensioning and tolerancing (GD&T) from a tool and die maker at the company where he worked. It was a rare opportunity.
"Even today, most schools don't offer engineering students GDA&T training unless specifically requested," says Thompson, general manager of the CAD business at Boston-based PTC Inc. That's a shame. Because of what I learned back then, I couldn't bring myself to do design work without thinking about the manufacturing process."
This disconnect between technical education and practical manufacturing requirements persists even as GD&T has evolved. What was once little more than a confusing set of symbols on a 2D drawing has since become a critical component of model-based definition (MBD), a building block of the digital thread. Because of the latter, job shops and OEMs alike are seeing one of the most significant strategy shifts in decades - the move to digital manufacturing.
For the non-engineers among us, PTC describes MBD as "an approach to creating 3D models so that they effectively contain all the data needed to define a product." This means there's far less reliance on 2D drawings because engineers embed product information directly into 3D CAD, creating "a single, reliable source of truth for the whole extended team that prevents errors and saves everybody time."
Unfortunately, many companies are not yet prepared to leverage MBD, let alone its big brother, model-based enterprise (MBE), which as its name indicates, is an enterprisewide deployment of model-based definition. Here, team members enjoy cross-functional integration between design, manufacturing and the supply chain while gaining closed-loop feedback and robust data management across a products entire lifecycle. Meet the digital thread.
And yet, far too much of the industry prefers instead to stick with the paper drawings they've relied on for decades, failing to embrace the potential benefits before them. Chief among these is an improved understanding.
"Engineers come out of school and they might know how to use 3D solid modeling tools, but far too many don't actually understand mechanical design and how part tolerances relate to form, fit and function," Thompson says. 'But when a design engineer learns GD&T and sees it applied in 3D, it all begins to make sense."
Drawings to Digital
GDA&T has existed as a design specification since 1982, when the American Society of Mechanical Engineers first published Y14.5M Dimensioning and Tolerancing. As its name suggests, this document was intended to establish uniform practices for defining maximum allowable variations -tolerances for size, location, orientation and form-in part geometry via a standardized symbolic language. It soon became the standard by which designers communicated their dimensional requirements.
"GD&T and its subsequent role in model-based definition has been around for quite some time," notes Hiren Kumbhojkar, senior director of Go-to-Market Strategy for Hexagon's Nexus, part of the company's Manufacturing Intelligence division, North Kingstown, R.I. "For instance, I began working in the CAD space during the late nineties and was already hearing about MBD, a concept that was initially led by aerospace companies," he says, "but then, because of its significant value, started to trickle down into other industries."
Despite its longevity, Kumbhojkar notes, GD&T understanding and implementation continues to challenge manufacturers. Respondents to arecent survey on Hexagon's website answered about 60% of GD&T questions incorrectly, demonstrating a persistent knowledge gap across the industry. At least some of this disconnect stems from GD&T's shift from paper-based, 2D drawings to a digital, three-dimensional model-based environment.
"Where we see the gap, which is still pretty prevalent across the market, is the inability to connect the dots," Kumbhojkar says. When there's a lack of information or design intent communicated to the downstream teams, whether they're from manufacturing or quality or wherever, it can create a lot of problems. The question then becomes, how do you ensure that they're looking at the right data? Much of this starts with GD&T."
Moving Beyond Paper
David Olson, director of sales and marketing at Verisurf Software Inc, a metrology software developer in Anaheim, Сай, seconds this. "GD&T was first implemented in 2D by all major CAD vendors, butithad limited value," he says. "That's where the struggle was. It was designed to reduce ambiguity but created a whole new vocabulary and language, and that in itself is an ambiguity. Fortunately, all of that goes away when manufacturers transition to solid models."
Many manufacturers still rely heavily on 2D drawings, and while Verisurf promotes MBD, Olson says the software "also includes digital workflows where design authority is provided via paper or annotated PDF drawings, enabling the verification of parts against those drawings and the associated GD&T. This allows shops to automate the inspection process for repeatable process control, whether they are provided 2D drawings or intelligent 3D models."
Despite having entered the workforce in the Reagan era, when the only solid models were those constructed of wood and plastic, GD&T's superpower blossoms in the 3D world. Here's where the digital model becomes the authority, Olson says, because it allows designers to embed product manufacturing information (PMI) such as material specifications, assembly instructions and more (including GD&T) directly into 3D models. This makes it the bridge between GD&T and MBD; think of PMI as a container for all of the information needed to manufacture a part.
"MBD refers to 3D models with embedded PMI and, by extension, GD&T, Olson explains. "Not only does it eliminate the need for paper drawings, it encompasses the entire digital thread - from product design through to manufacturing, inspection and beyond. Simply put, it allows the CAD model to serve as a single source of truth for all downstream processes."
When engineers create drawings with GD&T callouts, they're essentially translating 3D design intentinto 2D representations, Which users must then reinterpret. The process, Olson notes, introduces opportunities for errors and inconsistencies. As a result, the 3D CAD modelis quickly becoming the authority, greatly reducing the dependence on paper drawings.
"Because GD&T is inherently geometry-based, this trend is actually increasing its importance," Olson says. "It almost requires CAD models to make it work effectively."
Big Benefits
As more manufacturers recognize the inefficiencies of the traditional approach, the transition toward all-digital environments is accelerating. That's because the advantages of model-based definition and GD&T extend throughout the manufacturing workflow, from design and production planning to inspection and quality control.
As Thompson noted, GD&T-at least when applied to a three-dimensional part representation - provides clearer communication of design intent. By associating tolerances directly with 3D geometry, he points out, engineers can better visualize a component's functional requirements, how it will fit together with mating components and what controls are needed to accomplish this.
Many software systems today support and extend this visualization, providing immediate feedback on whether tolerances and dimensions are properly specified according to industry standards.
"Back in the day," Thompson says, "the engineer might send a drawing to the floor, only to see the person actually making the part come back a few hours later shaking his head, a red-lined print in his hand: Hey buddy, you missed three dimensions, this bolt hole pattern doesn't have a positional tolerance and what the heck is this thing over here?" Thompson laughs.
"With our solution- Sigmetrixs GD&T Advisor integrated with Creo - that's no longer possible," he continues. "The design engineer knows when her job is done because everything turns green once it's been properly constrained."
Hexagon offers similar functionality. As Kumbhojkar explains, production engineers will appreciate the fact that model-based GD&T provides the critical information needed for more effective process planning.
"When used with our Nexus platform, digitally defined tolerances help determine appropriate manufacturing methods, machine selection and tooling requirements," he says. "Verifying manufacturability is one of the key functions that planners would like to do first. By accessing a model with complete GD&T information, users can simulate different machining strategies and make better decisions about how to produce parts efficiently, all while ensuring they can meet the design intent."
Avoiding the QC Queue
Finally, there's quality control. "Where GD&T and PMI really come into play is for the automation of partinspection programs," says Greg Holdsworth, product manager for Autonomous Metrology Solutions at Hexagon's Nexus. "The software interrogates the GD&T, validates that the PMI is correct-which is very important-and generates all of the programming needed for measurement."
Holdsworth goes on to note an unpleasant fact, of which most manufacturers are already keenly aware: For every 10 or 20 machine tools, there's probably one coordinate measuring machine (СММ) -and finding a CMM expert to program is often more difficult than hiring qualified CNC programmers and setup people.
Making matters worse: Even the most skilled quality control technician might need several hours or more to program a complex part, during which they're unable to tackle other metrology tasks.
"Even if it takes the software two hours, you can go away and apply yourself to more value-added tasks while it's busy," Holdsworth says. "But just as importantly, it brings standardization to the measurement process. Because Nexus automates everything,iteliminates all of the program variation. It doesn't matter who clicks the buttons in the software - the end result is identical."
Olson applauds this last capability, suggesting inspection automation is perhaps the most transformative impact of model-based GD&T. "Verisurf has a feature called MBD to Plan," he says. "It's basically a one-click feature that analyzes the part, extracts all the GD&T and PMI data, and builds an inspection plan automatically.
"But we also have shops using it for reverse engineering of parts, assembly guidance and to support fixture design and tool building," he continues. "These are all metrology applications."
Tying the Digital Thread
Two of the standards needed to implement such technical wizardry are STEP AP 242 (ISO 10303-242) and QIF (Quality Information Framework). According to the organization that helped develop the first of these, www.ap242.org, today's highly competitive global marketplace "has forced manufacturers to reduce expenses and become as responsive as possible to changing market requirements. Successful design and manufacturing enterprises and their supply chain partners must invest in the latest model-based development and product lifecycle management solutions in order to remain competitive."
It's a lengthy standard, one filled with all manner of rules and guidelines pertaining to mechatronics, sustainability, data quality and the exchange of material data for increased compliance with environmental regulations. In a nutshell, AP 242 serves as a neutral file format that preserves the intelligence of model-based definitions across different CAD systems. In other words, it supports all of the capabilities discussed so far.
Where it comes up a bit short is in the quality control room. Enter QIF, which extends beyond STEP AP 242 to embrace the entire inspection process, providing a standardized way to define measurement requirements, resources, rules, results and the statistical analyses thus garnered. QIF provides the ability to take the actual measurements of part features and log them against that part, even down to the exact serial number, Olson explains.
"Serial number one is measured and saved back to the software; serial number two is measured and saved back to the software," Olson explains. "On and on until you have enough data to perform statistical process control on critical part features and see which way eachis trending."
Friendlier Formats
Despite № clear benefits, however, many manufacturers struggle to implement model-based GD&T effectively. Challenges ranging from technical limitations to organizational resistance to workforce training issues.
Thompson cites the former as one such roadblock. "When you export to an independent standard format like STEP AP 242, you might lose the engineering definitions used to create the CAD model - parametric values, for instance, and similar functionality that only exists in the native format. So if a feature is not governed directly by GD&T, you can lose the intelligence behind it."
Its not surprising, then, that Thompson is a big fan of the Creo file format espoused by his employer. 'Many companies vertically integrated in manufacturing, using Creo for design and Windchill for enterprise PLM," he explains, "find that they don't need to use the independent standard formats for internal collaboration."
Even so, this doesntimply Thompson isnta STEP AP 242 supporter. PTC is a member of the consortium that helped guide the standard forward, Thompson says, as are its competitors, all of whom support interoperability with numerous neutral CAD formats.
"The industry's adoption of these standards is critical for realizing the full potential of model-based enterprises," he notes. "Everyone recognizes this and agrees to abide by certain fundamental criteria for communicating this kind of information across the enterprise."
Its important to point out the elephant in the room: The digital twin, which as Verisurf's Olson explains, takes MBD and MBE to the next logical step. "A digital twin not only contains all of the information required to make a part, but (also) potentially everything associated with its manufacturing lifecycle."
This includes what materials and components are needed, its weight, dimensions and tolerances, all of the processes used to produce itand who was responsible for each. And, assuming the QIF format was used, Olson adds, digital twins allow traceability to know which parts were measured on a machine, at what time and what were the results. "Everything but the ability to hold the physical part in your hand is right there," he says.
Resistance is Futile
Whether talking about the digital twin, MBD, MBE, QIF and, to a certain extent, even GD&T, all have met with the resistance to change so prevalentin the manufacturing community Despite this, everyone should prepare for the inevitable.
"A number of major equipment manufacturers are testing the waters, but two factors are slowing adoption," Olson says. "The first is they're afraid of the cost it's going to take to implement it, compounded by the fact that they don't want to scare suppliers away. At the same time, their suppliers might say, We don't have the software, technology or knowledge to , ? m support what you're asking for.
This resistance creates a chicken-andegg problem: OEMs hesitate to require model-based deliverables because suppliers aren't ready, while suppliers wait to invest in new capabilities until OEMs require them.
Olson's advice to suppliers? "Маке the commitment to say, Tm going to implement a model-based inspection program so that I can share the resulting data to downstream software applications, like an SPC application or a PLM program. Now I'm at leastin the game."
Compounding matters even further is the point made at the beginning of this article - education remains a roadblock. In fact, a detailed understanding of GD&T can be a skill unto itself.
"In today's world, as things are transitioning to 3D, the struggle is mostly about the fact that people dont understand GD&T," confides Hexagon's Holdsworth. "So now they're also being asked to both apply it and learn it at the same time. This knowledge gap can be difficult for companies to overcome, especially smaller organizations with limited resources.
"Despite this, GD&T isn't particularly complex or difficult to master." he continues. "Manufacturers just need to take the time and invest the money needed to send people on the relevant training. After that, its a matter of ongoing exposure."
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