INTRODUCTION
Geometric Dimensioning & Tolerancing (GD&T) methods were originally developed during the 1940s and officially published in 1966 by the American National Standards Institute. Today the American Society of Mechanical Engineers (ASME) undertakes the responsibility of developing a standard for GD&T. Society’s current revision of the standard is known as ASME Y14.5-2009. The standard was originally developed to deal with confusion that had been occurring as companies struggled with using traditional plus and minus tolerance methods to define part geometry and effectively communicate the limits of that geometry to manufacturers.
Within the definition of GD&T, the term “geometric” refers to various forms, such as a plane, cylinder, cone, square, or hexagon. In theory these forms are perfect, however, since it is impossible to manufacture perfect forms, it is necessary to specify the amount of variation allowed from perfect forms. GD&T was developed specifically to accomplish this task.
This technical paper provides a detailed look at how GD&T is currently utilized throughout Alexandria Industries and the steps Alexandria Industries is taking with regards to GD&T, to continue to be a global, premier supplier of engineered products.
CONTINUOUS IMPROVEMENTS
Today’s undergraduate education system supports teaching the fundamental knowledge of GD&T, but withholds advanced topics from the coursework. With this lack of advanced training, students are left with an incomplete set of skills that are becoming a necessity to have throughout the manufacturing industry. Alexandria Industries recognized the need for advanced skills and as a result has sought out GD&T experts to train employees to an advanced level, a much higher level than what a technical or university course by itself is capable of providing.
Alexandria Industries supports training programs throughout all of its facilities to continuously improve employee skill level and capability. The Customized Training Center at Alexandria Technical and Community College (ATCC) has been a key resource for introductory concepts and applications of GD&T; Alexandria Industries has relied upon this resource for several years to teach fundamental knowledge and prepare employees for further advanced training in this area.
To bring a high level of GD&T knowledge into Alexandria Industries, management has committed to multi-year training programs to assure that its manufacturing employees have the advanced skill set they need to thoroughly interpret and apply GD&T standards. Alexandria Industries turned to Dr. Greg Hetland of the International Institute of Geometric Dimensioning & Tolerancing (IIGDT) for course instruction in several key areas that are critical for a complete understanding of GD&T. Up to three courses have been made available to Alexandria Industries employees depending upon the individual’s skill level; the courses cover fundamental and advanced applications of GD&T, as well as tolerance optimization.
SMART INVESTMENTS
Having a high level of knowledge alone is not sufficient enough for a company to become properly prepared to handle all applications of GD&T; companies must also invest in keeping their metrology equipment current. Part quality is a direct result of the equipment used to measure and verify that a part is held within specifications; having equipment capable of checking a GD&T callout is necessary in order to make this claim. Alexandria Industries invested in its first coordinate measuring machine (CMM) back in 1994, owning a CMM capable of checking simple and complex geometry is undeniably critical for accurate GD&T analysis. Not only is the CMM itself essential, but also is having an assortment of probes with scanning capabilities, allowing Alexandria Industries to state with confidence that the part is held within the tolerance specified on the drawing.
Alexandria Industries has selected SmartProfile® as the software of choice for analyzing tolerances of form, profile, orientation, and location. SmartProfile® imports and overlays point cloud data, made available from the scanning head probe on the CMM, into the 3D model and compares the measured data against the nominal CAD model to determine whether or not the part is within tolerance. Alexandria Industries will also use this software as a communication tool for discussing and suggesting alternative solutions for applying GD&T callouts to customer drawings; SmartProfile® simplifies the decision making process by providing a real-time view of how part tolerances are impacted as GD&T callouts are manipulated.
BENEFITS & STRATEGIC PLANS
Staying committed to GD&T is a part of Alexandria Industries strategic plans moving forward, Alexandria Industries has already made investments to bring its equipment and employees up to date with its latest CMM technology and continuous improvement training programs. Taking a proactive approach with using and applying GD&T is expected to bring an assortment of benefits to Alexandria Industries The benefits include increasing the capability to manufacture more to the original design intent of the part, lowering initial design and manufacturing costs, increasing part quality, and improving communication to customers, all of which will become apparent due to the increased capabilities at Alexandria Industries.
Alexandria Industries is dedicated to keeping design and manufacturing costs to a minimum, as this is essential for any manufacturing company to remain competitive. Alexandria Industries customers are increasingly using more and more GD&T on their prints; communication between Alexandria Industries and the mechanical designers can occasionally become a time consuming process when standards are incorrectly applied to the drawings. To determine allowable tolerance ranges for part features, one must know what the part application is and the tolerance range of the mating part(s). By collaborating with customers to achieve design intent, applying correct GD&T to the print will become less time consuming as more information about the functionality of the part is made available, resulting in quicker project start-up times. Utilizing a software program, such as SmartProfile®, will present a much clearer understanding of the implications that tolerance adjustments will have on a part feature and it’s mating parts.
Just as important as educating your current workforce, so too is continuing the education as changes are implemented. As new technologies are developed, new employees are brought on-board, industry standards change, and customer requirements evolve, training will continue to be an ongoing process within Alexandria Industries, Alexandria Industries is committed to staying involved with ATCC and IIGDT to fulfill these plans. At ATCC, coursework is being suggested by A.I. to include machining projects that require the student to interpret GD&T callouts when verifying that their parts are made to print, allowing the students the opportunity to take a hands-on approach mixed with a classroom environment.
An expert team has been formed at Alexandria Industries to serve as a knowledge base for applications of GD&T, the team consists of employees within AI that have participated in all training courses offered to them and are in positions directly related to understanding applications of the standards. Several members of the team are actively pursing Geometric Dimensioning and Tolerancing Professional (GDTP) certification, offered through the ASME. During the biweekly meetings the team addresses concerns with new customer prints and generates solutions for such prints based on manufacturability of the part and applicable GD&T callouts. Another part of the team’s responsibility is to evaluate the metrology equipment that Alexandria Industries is currently using and determine whether or not investing in new equipment is necessary.
Alexandria Industries has taken a strategic approach with GD&T and the ASME Y14.5-2009 standard by making investments now to make these benefits available to its customers. Benefits such as these allow Alexandria Industries to continue to be the manufacturer of choice for providing custom aluminum extrusions, castings, heat sinks, and injection molded products. Emails can be sent to GDandT@AlexandriaIndustries.com to discuss your GD&T applications with Alexandria Industries.