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....