What are the best practices for using GD&T to ensure manufacturability?

Purpose of using GD&T is mainly for achieving precision and additional geometric details and it's control, especially for the Automotive industry, Pharmaceutical machinery and other industries where high precision is needed.

Well, in as much as GD&T is concerned, this aspect is very important in the Engineering circles. For instance, Bearings type NU, N, NJ for Cylindrical Rollers bearings, especially NU type which is mostly used in controlling end-float in many devices are all made and manufactured to the same standards and specifications despite the locations and manufacturers. Because of GD&T, if an enhanced Deep Groove Ball Bearing 6313EM/C3 with clearance C3 has been manufactured here in Africa, it would be to the same standards and dimensions with the bearing of same number that can be manufactured in Sweden. As a result, the supply has even engulfed the demand in the market.

Comunicating right GD&T actually saves time and cost, those who say adding GD&T increases the cost of the part simply dont understand the GD&T.

?? Best Pracrices to use GD&T: ?? Datum selection must be driven by function, accessibility & stability of feature. ?? For irregular geometries, use datum targets ?? Dimensions, Geometric controls, modifiers & tolerances must be driven by function of mating parts. Like, assy or min clearance ?? To save mfg cost, begin with general tolerances & if function demands, only then tighten up the tolerances. ?? Where possible study mfg variations & leverage it to define tolerance ?? Use M / L modifiers in FCF wherever tighter control is not needed (take advantage of Bonus tol) ?? When you have choice, use cost effective Geometeic control for that application. ?? Conduct tol stack analysis to optimize dimensions & tol for function.

GD&T allows the repeatability, quality control and reliability of manufacturing processes of each part or for whole assembly It also helps to prepare for the next manufacturing processes along the line. Lastly, it will ensure the functional fit to other parts down the processes or final assembly This is very important specifically for machining with tight tolerance and fittings

For the first category, geometric characteristics, it is important for the designer to know how each characteristic works in regards to form, location and orientation, including particular/exceptional cases depending on the used modifiers. For the modifiers, I find it relevant to consult the relevant norms since these provide a thorough explanation and examples. So when considering pattern definition, material condition, offset zones, specific trajectories for the control or other modifiers, I recommend to consult the respective norms.

The annotations provided in GD&T such as the welding length and thickness should be appropriately mentioned . Also the designer should ensure that all the characteristics of the design such as materials are properly mentioned as these drawings are referred by a huge chain of people. Through the perspective of CAE , GD&T helps the engineer to understand the weld area, material and the tolerances of critical components like bushes and bearings.

Here are some tips for avoiding over-tolerancing and under-tolerancing: 1. Use the simplest and most appropriate GD&T symbols that convey your design intent and meet the functional requirements. Don't use more complex GD&T symbols than necessary. 2. Consider the manufacturing process and equipment capability when choosing tolerances. Make sure that the tolerances you specify can be achieved with the available manufacturing processes and equipment. 3. Use a tolerance chart to help you choose appropriate tolerances. Tolerance charts provide guidance on typical tolerances for different types of features and manufacturing processes.

GD&T symbols are divided into two categories: geometric characteristics and modifiers. Geometric characteristics describe the type of variation that is allowed for a feature, such as flatness, parallelism, position, or profile, while modifiers add additional information, such as tolerance zone shape, material condition, or datum reference. When choosing the right GD&T symbols, you should take into account the feature's function and how it interacts with other features or mating parts, the manufacturing process and equipment capability, the inspection method and instrument accuracy, and the cost and time implications of applying the symbols. It's important to use the simplest and most appropriate GD&T symbols that convey your design intent.

Standards are widely accepted common languages to specify engineering requirements. However, when you are sourcing parts globally from multiple sources, care need to be taken to clarify all the parties involved the drawing convention followed, if it's ASME or ISO...

Geometric Dimensioning and Tolerance is a tool used in engineering drawings. It focuses on the geometry (shape), dimension (size), and Tolerance (allowance). This helps the design engineer communicate effectively with the manufacturer on how the part is made.

Nowadays the software tools have improved the accuracy, efficiency and eliminate any minor human errors that may arise. Also, help in documenting and easy visualizing the tolerance stack-ups and adding confidence.

Although there is a great variety of software for geometrical control and on every new release there is new and improved functions, an essential aspect to consider is which the software allow work the raw data. Since a GD&T evaluation only evaluates how well the part meets the design, having local information from the points measured on the part (either by scanning or probe hit) will allow finding additional information, such as part deformation trend, minimum and maximum material condition (to make adjustments in the process) and even evaluate if GD&T results are consistent with the raw measurement data to evaluate whether geometric control is being applied correctly.

GD&T defines critical dimensions and tolerances that are essential for product quality (CTQ) and, by extension, for successful manufacturing processes (CTP). When performing DFMEA, GD&T considerations can highlight potential failure modes related to these critical dimensions and tolerances, helping engineers and designers proactively address quality and reliability concerns. Collaboration among stakeholders, including designers, engineers, and manufacturing experts, is vital to achieving these goals. This approach ensures that designs are not only functional but also manufacturable and aligned with quality standards.

Dimensions and tolerances in technical drawings will normally go through multiple review processes. In manufacturing plant, new drawings will be made by a design engineer, and will be reviewed by the chief design engineer to be validated for making sample parts. During this stage, it is essential for the design team to perform Design for Manufacturing (DFM). DFM discussions should ideally involve at least design engineers, process engineers, tooling engineers, and quality engineers. Main aspects such as material selection, tolerances and fittings of the mating parts, and ease of assembly should be thoroughly discussed. In my experience, if such collaborations are done properly, we can ensure the manufacturability of any new parts.

GD&T application should be achievable by an OEMs existing and proven system established. It should not bring in special process or deviation from existing set up. Cost vs benefits should be assessed before introducing complex GD&T. Understanding ground reality of supplier or QC capability is much needed, before applying GD&T

Yes, as true with almost everything we do, collaboration is key. Circular communication over one-way communication can achieve efficiency. Not spending too much on unnecessary accuracy Vs not reducing quality.

Beyond applying geometric control that ensures quality and functionality in the design of a part, it is important to consider that the definition of GD&T elements must also be consistent with the manufacturing process, since it is common that for the evaluation of certain characteristics the construction of theoretical geometries is required (which can be interpreted as imaginary geometric elements), which sometimes, according to the capabilities and environment of processes and machinery, are not traceable due to their intangible property, making the adjustment process for the characteristics of the part have no relationship between the measurement system and the manufacturing system, creating information gaps.

It should be obvious from the GD&T on a drawing what the intended function of a part is. One area where this is extremely important is the positional control of mounting features to ensure the proper mating of parts. If a group of features are to be used simultaneously when a part is mated, they should be controlled as a pattern in the GD&T callouts such that this intended functionality is clear. Another related area where GD&T is very useful is in the control of features used to precisely align parts to each other in an assembly - for example the positional control of alignment holes and slots in a pinned assembly.

Our experience with aging facilities, limited design documentation and maintenance records, the incorporation of Geometric Dimensioning and Tolerancing (GD&T) in inspection, maintenance and diagnostics engineering becomes even more critical. GD&T provides a structured framework for specifying and assessing component geometries, allowing for precise re-measurements and tolerance definitions. This is invaluable in the absence of detailed records, as it helps ensure that replacements or repairs are accurately re-engineered to fit within the existing constraints. By improving measurement accuracy and standardizing interpretations, GD&T facilitates safer and more cost-effective maintenance, extending the life and reliability of aging facilities.

1. Recording learnings and best practices for future use. 2. Identifying similar parts and Developing tools and templates or simple spreadsheets for stack-up calculations etc for improving efficiency. 3. Capturing manufacturing capabilities within the ecosystem we are working and aligning the expectations on tolerances in the design for cost optimization. This can help in reducing dependency on few suppliers that may achieve tighter tolerance and charge a lot.

It is important to ensure the used GD&T can be controlled on the physical part. Unfortunately, I have seen too many uses of GD&T that cannot be measured.

GD&T is only as good as the vendors who will make and inspect parts. It's a great idea to coordinate with machine shops and metrology departments to ensure GD&T callouts are able to be interpreted by their staff and can be inspected with available equipment. It may be better to use a simpler GD&T callout (and design around any reductions in tolerances) if it means the machine shop will actually understand the drawing and be able to inspect the parts.