GD & T - Power of Feature Control Frames using SolidWorks

Feature Control Frame forms the heart of the Geometric Dimensioning and Tolerancing ( GD & T ) practice for engineers involved in creating, manufacturing and inspecting designs. In fact it is the greatest invention of engineering expressions in symbolic language that it is finding unilateral acceptance by the engineering community as a whole.

For the un-initiated, let us considere a hole dimensioned as follows:
Read from left to right, the Feature Control Frame states that "Position of the Axis of a pattern of 8 holes when produced within stated size limits, can be off-centre within a diametral tolerance zone of 0.50 when produced at Maximum Material Condition, when the part is located on Datum A as Primary, Datum Feature of Size B when produced at Maximum Material Condition as Secondary and Datum C as Tertiary references."

Feature Control Frames have a characteristic symbol in the first cell, a tolerance value with a zone descriptor and material modifier (if any) as the second cell followed by cells having Datum references ranging from 1 to 3 depending on the design specification that the tolerance definition is intended to convey. Number of datums depend and possible material modifiers (on datum features of sizes) depends on the intention and feature that is controlled.

Many a times, design intent and design specifications are wrongly used interchangeably while producing drawings. GD & T Drawing is intended to convey design specifications in an unambiguous manner and not the design intent. Sounds strange? Read again !

GD & T symbols, when used with care and purpose, have been proven to reduce costs and greatly improve quality while ensuring part interchangeability and protecting the parts' intended fit, form and functions.

SolidWorks helps designers achieve a great level of definition control with GD & T using DimXpert. Even Imported geometries can have the complete Dimensional schematic completed in no time with accurate representation of the design specifications.

Feature Control Frame Definition using DimXpert

User specified Datums with selected order of precedence alongside features of sizes can be defined for various levels of control based on size, form, orientation and location. Features defined using feature control frame are ascertained for completeness of definition. Features shown as green are complete in dimensional definition. If the feature selected is a part of a pattern of features, say a hole pattern, then a common reference frame with necessary number of features are provided automatically.

Using SolidWorks, this is possible even in the case of imported geometries as shown. This approach enhances accuracy and adequacy, when dimensioning a part with a huge history of features requiring dimensioning.

When a circular feature of size, such as Datum B shown in the Figure, is selected as a datum for another feature, the feature dimensioning is automatically defined in all aspects with appropriate Feature control frame (in this case Perpendicularity) in context to the datum feature used (in this case Datum A) in precedence. This approach, not only saves time, but also ensures dimensional completeness thereby preventing ambiguity in manufacturing and inspection downstream during part manufacture.

Hole depth is also indicated in the Feature Control Frame while defining size limits. Tolerances specified as based on default values specified by the user that can be modified based on cost and practical manufacturing considerations (including machine Cp and Cpk).

When multiple features refer to the same Datum, this is automatically recognized by SolidWorks and common Datum sequence is followed in all relevant Feature Control Frames, signifying a single setting during manufacture and inspection.

In summary, DimXpert inside SolidWorks reduces effort required to develop GD & T drawings while improving accuracy of representation and completeness in definition. This eliminates ambiguity, resulting in overall cost and time savings.

Overcoming Market Challenges - A Design Approach

Recessionary trends in markets always force customers to re-think before spending and postpone high-value investment decisions. In these days of wild economic oscillations, every company involved in manufacturing and marketing of products is faced with the following scenarios:

1. Reduced Orders for Products
2. Shrinking profit margin
3. Competitive pricing from predatory products

Add to these challenges, the burdening effects of increased input raw material costs, extended product development time and costly re-work due to failures, we have a problem of monstrous proportions that affects the company bottom-line and survivability.

In order to stay competitive, increase market-share and provide more value for less money, product development companies need to do three things:

1. Innovate
2. Improvise
3. Implement

It is well known that 80%-85% of a product cost is driven/ decided by Design. Input raw-material, number and sequence manufacturing operations, product testing, product/ design re-work, field failure correction, enhancing product performance, improving efficiency all have their main input from Design. No time is better time than NOW to revisit our Designs and see how we can address Critical Business Issues.

Cost Reduction Exercise should be done in a conscious and time-bound manner to have any effect. Simple steps, when followed with due diligence, can turn around companies towards higher growth path and profitability. History is replete with testimonies to this cause. 'Jelly-bean' type rounded shape of Ford Taurus increased sales and profitability for Ford Motor Company in the mid-eighties on account of the three 'I's mentioned above.

Step I: Set Goals

Goal setting is an important process that determines the success rate of the exercise. Such goals should have clear alignment with Critical Business Issues facing the company. For example, let us say, a Company ABC that has had a successful run with one of their mainstream products is facing competition from an overseas Company in terms of price. The Goal could be:

Increase Overall Profit margin by 5% while addressing the following:

1. Reduce finished product cost by 10%
2. Integrate new features that lowers overall cost of ownership to end-consumer by 10%
3. Implement within 1 month

Goal Setting in terms of tangible benefits within specified time-line helps in more ways than one: Events Force Action

Step II: Design Action Plan

Design Team, identified to achieve stated goals, then needs to work on a definitive Action Plan with an accepted mission statement: 'Failure is not an Option'

Steps involved in the Action Plan could have following indicators:

• Reduce Number of Parts going into an Assembly (by integration, elimination or augmenting product functions)
• Reduce Manufacturing Operations required to produce a part (by simplifying geometry)
• Reducing number of serviceable parts (thereby reducing service parts inventory)
• Revisit Bill of Materials to standardize on parts (replace parts with Standard Catalog parts where permitted)
• Reduce fasteners and/ or standard parts to minimum required quantities
• Minimize product configurations to achieve modular variants
• Evaluate Power-to-Weight Ratio for optimal utilization
• Check tolerances of parts going into assemblies and perform tolerance stack-up calculations to reduce/ eliminate rejections at part/ assembly levels
• Validate Designs for Fit, Form and Functional aspects with emphasis on least cost
• Ask Questions such as: Why, Why-not, How, When and What for every design feature that adds to overall cost

Step III: Perform Fit, Form and Functional Validation

Revisiting every design to have a better understanding, in terms of cost is bound to be a profitable exercise. However, for proven products, the inertia to change or the fear of 'tinkering' with a working design over-powers the incentive to adopt new technologies and processes that result in a final product having the least cost and best functionality in its range. This 'fear' or 'reluctance' can be avoided or confronted ( based on the company's approach) by Validating every aspect of Design in terms of their Fit, Form and Function. This provides a basis for the engineering evolution of the product and helps revisit equations in a changed economic scenario.

Step IV: Implement

By adhering to the action plan that helps reach goals within stipulated time frame, cost reduction end benefits are assured. The will to implement after overcoming the fear of change has to be a pre-requisite to the conduct of this exercise. By re-visiting the goals and seeing how close or how far the benefits are, it helps set clear targets for further re-assessments that help build a competitive product.

None of the above would help succeed without the Team taking the ownership for the success or the not-so-successful exercise of competitive product development.

In bleak market scenarios, this exercise provides more benefits even to other areas of an Enterprise:

1. Redefining Value and Enhancing Customer Satisfaction
2. Confidence in Product Performance and Augmented USP
3. Pride of Ownership for a Superior Product

All the above go a long way in instilling a higher level of resolve to face competition, enhance value and reduce the overall cost of ownership for Customers and Prospects alike.

Notwithstanding other exercises, Design Re-validation is a Necessity that protects the bottom line while ensuring higher profitability for Product Development companies.

Integrated Design Validation for Fit, Form and Function Using SolidWorks - Part II

Part I highlighted the Fit and Form aspects of Design Validation using SolidWorks. Additional Form Validation tools are highlighted in this part.

Form validation starts from the first step, namely, concept design. Form is validated all the time. Every dimension involves form validation. Shape optimization directly interacts with form and validates for optimal weight, cost or any variable that the designer uses to arrive at a design solution.

Draft Analysis, inside SolidWorks, helps designer to analyze designs for form requirements that are mandatory from manufacturing considerations. DraftXpert provides a range of tools for form validation inside SolidWorks.

Draft Analysis Settings and Results for Plastic Part

Curvature continuity and tangency on surfaces can be checked by using Zebra Stripes Visual Display availabel inside SolidWorks.

Zebra Stripes on Plastic Part

Undercut Detection on parts, be they plastic or die-cast, is required tofind trapped areas in a model that cannot be ejected from the mold. These areas require a side core. When the main core and cavity are separated, the side core slides in a direction perpendicular to the motion of the main core and cavity, enabling the part to be ejected. SolidWorks enables designers to perform Undercut Detection analysis to ensure manufacturability issues are addressed.

Undercut Detection in a plastic part

Similarly Curvature Analysis of parts is an important part of the design process that can be accomplished using SolidWorks with interactive measurement of curvature by traversing the mouse over the surface being analyzed.

Curvate Analysis on a Plastic Part Surface

Similarly, at Sketch level, insight into curvature variations on curves can be shown to understand form variation and control using Curvature Comb in SolidWorks.

Curvature Comb Display on Sketch Curves

Manufacturability has a direct influence on feature form. It is possible to analyze turning, milling and hole drilling operations using DFMXpress inside SolidWorks. Hole Depth-to-Diameter ratio, Minimum percentage of hole area inside a part, Milling Tool Depth-to-Diameter ratio, minimum corner radius and percentage bore relief on turned parts, minimum linear and angular tolerance zones are some of the rule-based checks that can be performed on parts designed using SolidWorks for Manufacturing feasibility.

DFMXpress Machining Feature Recognition on Pump Housing

DFMXpress Analysis of Machining Features in Pump Housing

Numerous features inside SolidWorks help Designers perform Design Validation of Form on a continuous basis. This helps avoid re-work and getting designs done right the first time.

More the next article....

Integrated Design Validation for Fit, Form and Function Using SolidWorks - Part I

Competitive scenarios are compelling companies take a re-look at the Designs of their Products to incorporate higher levels of functionalities and efficiencies while addressing cost and profitability pressures. It is important to delineate Design parameters in terms of and Fit, Form and Function (F-Cubed) and validate the same to achieve stated objectives.

To recall the definitions of F-cubed, Fit addresses the interchangeability of parts in assemblies and enables assessment of the dynamic interactions of tolerances placed on features of sizes and their influences on inter-part relationships that would define functional behaviour. Form defines shape, dimensions, mass and other attributes that essentially address the design space in the context of the assembly as unique characteristics of the part being designed. Function explicitly defines the intended performance during the operational life of the part.

Design Validation of Fit, Form and Function is important to achieve stated objectives. SolidWorks offers rich set of tools to Validate designs as they evolve giving the Design Engineers a choice of alternatives to make qualified decisions. SolidWorks tools that enable the user can be classified as follows:

1. Fit: Tolerance Analysis (Tolanalyst)
2. Form: Geometry Analysis ( Sketch Xpert, DFMXpress, Draft Analysis, Curvature Analysis)
3. Function: Kinematic Analysis, Finite Element Analysis and Computational Fluid Dynamics

Fit:

Tolerance study inside SolidWorks for Real-world designs can be performed using TolAnalyst.

Using four simple steps, Stack-up Analysis can be performed on assemblies with ease.


1. Using DimXpert, dimension and tolerance part features either using manual or automatic mode.


2. Define Assembly Sequence for parts in order to assess dimensional chains that influence the outcome.


3. Establish Assembly Constraints to understand how each parts relates to the assembly.

4. Perform Analysis to Evaluate and review the minimum and maximum worst case tolerance stacks.

Form:


Design Validation for Form helps to arrive at a basis for the dimensions provided on the design, clarify critical dimensions that influence performance and ensure unambiguous understanding of part shape that would meet functional requirements.

Sketch level understanding of concept feasibility is easily achieved in SolidWorks.


Examples shown here of different mechanisms involving lower and higher order pair help understand the functionality of SolidWorks in achieving higher levels of confidence during the design process.

The sketches can be used in layout stage to exploit Top-Down approach in the detailed engineering design of individual parts either by an individual or as a part of a team for higher collaborative efficiency.

More in the Next article ....

CAD Obsolescence - Wither Pro/Engineer?

A nondescript Russian Genius created a monster in the mid '80s - shaking the Design World with a new Paradigm called Bi-Directional Parametricity. At a time when the CAD market was ruled by the likes of IBM and EDS, along came Samuel P. Geisberg - a mathematician - from Leningrad to the Great American Promised Land - to re-write the script and re-cast the deck with all Aces up his sleeve. Rest is history. Parametric Technology Corporation, known for its Pro/Engineer came, divided and conquered, much to the chagrin of prevailing well-established CAD Software houses.

Due credit should be given to PTC for creating a new market for a new technology - driven by the passion to perform or perish. Be it Technology - Created, derived or acquired, Sales, Marketing or sheer Grit, PTC had it all. It was a great American Dream of an Enterprise that started to conquer the mind and hearts of Engineers of all hues. Sure enough, there came a time when if you were not using Pro/Engineer you were perceived as a loser or a Not-Destined-to-Succeed type.

When Success gets to the head, it starts a downslide that only self-analysis can stop. PTC was no exception. The same innovation, that helped PTC scale great heights, proved to be its nemesis. With few innovations coming in, slower adoption of, by-now-ubiquitous, Microsoft Operating System coupled with easy-to-use functional modellers (read SolidWorks) breathing down the neck, PTC had already started to show signs of cracking.

Grapevine has it that, when PTC was downsizing to stay profitable, after the acquisition of Computer Vision, a Management representative was sent to CV's not-well-known Minnesota office to close it down. Flustered by an extremely warm reception accorded to him, he reviewed the work done and was taken aback by a new product that was under development. His initiative prevented the Division closure and, surreally, PTC's own. The product ? None other than Windchill.

A re-vamped user interface (relatively easy to use toolset - much to the chagrin of the Pro/Engineer loyalists), costly re-training efforts, stability issues, loss of focus, lack of innovation and loss of marketshare, lead PTC on a downward spiral, much to the frustration of its User community and fiercely passionate loyalists who would wage a World War III in its favour.

No company that does not listen to its Customers can survive. Not an unfamiliar adage? Still PTC chose to ignore them and with them their wads of Dollars that PTC just could not get. Is it a surprise that PTC was able to add only a fraction of new users Year-on-Year while contemporary CAD software corporations continued to grow with users at many orders of magnitude? Losing new orders, a shrinking client base due to attrition by vibrant new CAD products, and increased frustration amongst its own user community (who looked, with disdain, at PTC's stock getting flogged ) is perilous, however cash-rich a company may be.

Spending hard-earned dollars on acquisitions of Abortext (just because one of its large clients wanted a synergy between Pro/E and Abortext publishing), MathCAD, NC Graphics and, now, CoCreate, while losing focus on Mainstream product that took PTC to its dizzying heights added to the ills. Nevertheless, PTC was intent on playing its own requiem.

Now, PTC is up for sale, by its looking-to-cash-on-the-last-stop operatives. A relevant message for all CAD companies is apparently written on the wall.

Innovation, Improvisation, Hearing customers and Raising the Technology Bar are the Pre-requisites for any CAD Technology Company to survive and conquer. It is not the dollars in the bank that matters in the long run. It is the place in the broad hearts of the CAD users, aspiring to create new designs, that cements a permanent position. Money will come in with popularity and acceptance.

Alas PTC is scripting its own Swan's song for Pro/Engineer.... So long comrade ....

Direct Editing of Imported Geometries using SolidWorks 2008 - Choices for the User

SolidWorks has been a peacefully co-existent, co-operative, neighbour for almost all contemporary 3D CAD platforms. Its ease-of-use combined with the ability to import, edit, update and possibly re-hash complete designs, has made it more popular among the design community. How effective is SolidWorks in terms of direct editing of imported history-free geometries while preserving history data in edit-mode? This article sets out to explore the new features in SolidWorks 2008, that enables an Engineer to work with non-native geometry providing rich functional tools to help get the job done.


As shown, 3D CAD model of a plastic telephone part, in Parasolid Format, was taken as an example to explore the functionalities available in SolidWorks 2008 to perform Direct Editing functions on non-SolidWorks geometries. The Parasolid Geometry came in fine without any errors.



By just picking on the filleted surface (as shown), Instant3D functionality immediately recognized the multiple-radii fillets and made the feature dimensions available to the user for parametric modification. Multiple selection of features, such as fillets, were possible for instant editing, saving on time and effort.



Chamfers, even on thin-walled sections, were recognized for parametric modification and update, as shown. Again, this was possible for multiple-selections. In addition to Instant3D, FeatureWorks (available in SolidWorks Office Professional) could be used to completely de-feature the imported 3D CAD model, either interactively or using the Automatic option.


Adding or editing existing draft always poses a challenge in Imported geometries. SolidWorks provides DraftXpert as well as Draft recognition tools in FeatureWorks to make parametrically editable draft features, that would have otherwise taken more time to manipulate without history-based associativity.


As shown in the figure, adding adequate draft and incorporating fillets on features of CAD parts can be challenging and sometimes impossible. Inside SolidWorks, if draft has been incorporated in the imported geometry, it can be modified by using FeatureWorks, avoiding surface manipulation that can sometimes be time consuming. Alternately, new draft can be added to existing drafted surfaces resulting in updated geometries for re-use.


Interestingly, if a fillet is added at the root of the feature, before the draft, regeneration of the model can result in regeneration errors due to feature-precedence problems. This could result in loss of productive time, effort and increase frustration for the user, especially if there are too many of them.



Figure shows fillet being added before a draft and subsequent regeneration error.

FeatureXpert helps resolve such problems with ease, in addition to providing users with multiple options to either eliminate or overcome the problem. In this case, FeatureXpert has helped re-order the draft and fillet features on the history-tree thereby eliminating such time-consuming errors, upfront.

There are bound to be situations wherein imported geometries have bad surface definitions necessitating only a brute-force surgical correction to help overcome problems. SolidWorks provides editing of model surfaces in terms of deleting, deleting and patching and deleting and filling thereby providing the user with multiple options and choices for use, per the situational demands.

Re-construction of surfaces and replacing existing ones with the new ones are possible. This functional advantage results in time and cost savings while augmenting design for manufacture practices. SolidWorks ability to handle large and complex feature data sets provides a good platform for inter-operability with other 3D CAD systems.

Some of the problems of feature-based editing and modification, in the past, has been the time taken to regenerate the model and time / effort required to fix regeneration errors during the process of re-design incorporating SolidWorks Intelligent Feature Technlogy ( SWIFT ) to dynamically re-order features and giving customers a choice of alternatives to overcome/ avoid regeneration errors, SolidWorks has established a new paradigm in Intelligent editing of imported 3D non-native geometries without compromising on proven parametric history-based technology that has made 3D popular as it is today, with bi-directional associativity.

New SolidWorks Videos

Exciting SolidWorks Videos have been added to EGS India Website for the benefit of the Design Engineering Community.

Following Videos highlight latest trends in Design Technologies using SolidWorks.

1. Mechanism Design Functions in SolidWorks
2. SolidWorks Intelligent Feature Technology ( SWIFT ) - Benefits in Design
3. New Features in SolidWorks 2008
4. Large Assembly Management using SolidWorks 2008
5. SolidWorks 2D Drawing Creation - Capturing Design Intent

Contact EGS India - SolidWorks Reseller in Chennai, Coimbatore INDIA for your Design Requirements.

Synchronous Technology from Siemens - History-Free modelling - Myth or Reality?

Of late the CAD Market has been active with discussions on the 'new' technology marketed by Siemens as Synchronous Technology - a new paradigm in Mechanical CAD. Some CAD gurus term it revolutionary, path-breaking and a panacea for the ills of Parametric Technology ( not PTC !), while other seasoned users and I-have-seen-this-often CAD specialists want to be cautious and adopt a wait-and-watch approach.

One of the common thread underlying the discussions on Pro's and Con's has been that Parametric approach has been beset with two issues , namely errors during regeneration and time taken to edit a design having a long history-tree. Hence history-free modelling approach seems to offer a solution to these issues. Instead of taking extreme stand with respect to either History-based or History-free approach, a middle path trying to capitalize on the benefits of both approaches seems to be emerging. This is definitely a positive trend for the 3D CAD Industry and the user as well.

From the perspective of a Design Engineer using 3D CAD, following points remain in focus for any tool to retain its popularity and acceptance:

1. Ease of Use
2. Bi-directional Parametricity with easy-to-generate-drawings having driving dimensions
3. Tolerance Analysis for stack-up calculations
4. Knowledge Management for re-use of design procedures
5. Design Drawing Automation
6. Error-free 2D Drawing for downstream usage in Manufacturing, Inspection, Assembly, Service among other functions.
7. Dimensional Management for Fit, Form and Function

Most of these requirements would need parametricity, constraints, relations between Features of Sizes that goes well with Parametric History-based approach.

One of the points that needs to be addressed critically, is Freedom to Edit Designs developed on any CAD system. Let us look at a scenario wherein an organization develops a design and transfers the same to another manfuacturing facility for prototype development. If the Design data can be changed inadvertantly without leaving a trace of the change (read history-free) it sounds scary with obviously undesirable implications! Freedom can result in abuse !!

Every technology has its advantages and dis-advantages.

Development of 2D Drawings that enables parametric updates and changes to dimensions need to have higher focus. This gets complicated with History-free approach on account of the bi-directional facility enjoyed by the Engineering community.

Simply said, History-based technology provides a facility to Undo, Modify and Redo a design concept at any stage in design process. History-free approach necessitates correctional approach that may involve re-work. Things done in a fraction of a second may require more steps with History-free approach. Parametric dimensions on a drawing would necessarily have to be re-visited by the Designer when a model undergoes a change in History-free approach while it would not be so with History-based approach.

I guess a consensus would emerge with more players such as SolidWorks (that already has Instant3D and SWIFT to address direct editing and regeneration/re-ordering issues) working on ways to address this requirement without sacrificing on the benefits currently enjoyed by the Design community.

Convergence of methods is sure to be in focus for time to come. At the end of the day, Users would be the winners !!

EGSIndia: Engineering Design Newsletter - June 2008 Edition Released

EGS India has launched the June 2008 Edition of its Newsletter for the benefit of the Engineering Design community.

Interesting articles on Time Management for Projects, Finite Element Thought for the Day, Geometric Dimensioning & Tolerancing ( GD & T ) - Usage of GD & T Symbols, Kinematic Analysis of Ingenuous Mechanism Designs using CosmosMotion are provided in this recent edition of EGSIndia Newsletter.

Thought provoking article in the 'Did You Know' column and Benefits of a recent Design Seminar conducted by EGSIndia - Reseller of SolidWorks, Cosmos, PDMWorks in Chennai, Coimbatore, India are highlighted.

Please visit following web pages for more information:

http://www.egsindia.com/index.php

http://www.egsindia.com/June-08/NS-June-08-newsletter.html

http://www.egsindia.com/gdandt.html

Geometric Dimensioning and Tolerancing Course Offered by EGS India

EGS India has been offering a Comprehensive Practical course on Geometric Dimensioning and Tolerancing per ASME Y 14.5 (2000) standards for Organizations in India.

In addition to teaching the basics of GD&T for participants, EGS India has been providing hands-on training with practical problem solving to customers having wide-ranging applications from Consumer products, Defence, Automotive, Machine Tool to Power and Process applications.

Contact EGS India at info@egs.co.in for more details on GD&T courses for Corporate Requirements.