{"id":7132,"date":"2015-05-02T11:00:51","date_gmt":"2015-05-02T15:00:51","guid":{"rendered":"https:\/\/blogs.solidworks.com\/tech\/?p=7132"},"modified":"2023-09-20T17:41:51","modified_gmt":"2023-09-20T21:41:51","slug":"5-steps-to-gdt-enabled-drawings-for-higher-product-quality-and-lower-cost","status":"publish","type":"post","link":"https:\/\/blogs.solidworks.com\/tech\/2015\/05\/5-steps-to-gdt-enabled-drawings-for-higher-product-quality-and-lower-cost.html","title":{"rendered":"5 Steps to GD&T Enabled Drawings for Higher Product Quality and Lower Cost"},"content":{"rendered":"

First Time Right is becoming mandatory for the manufacturing industry to save costs and increase profitability.\u00a0 Add to it the requirement that ideas need to be translated to product and brought to market faster, the situation looks untenable. There is increasing pressure on design to address all these challenges.<\/p>\n

Every department in a manufacturing organization has to deal with drawings either directly or indirectly.\u00a0 They get influenced by the drawing, its correctness, completeness and alignment with the quality objectives of the company.\u00a0 If there are errors on the drawings, assumptions made due to the incompleteness of the drawing representation, then the organization bleeds in terms of re-work, rejections, recalls and delays that cost money.<\/p>\n

Why is GD&T Important?<\/strong><\/p>\n

ASME Y14.5 – 2009 Version of Geometric Dimensioning & Tolerancing (GD&T) Standard on Engineering Drawing and Related Documentation Practices states in its Foreword, thus, ‘This revision contains paragraphs that give a stronger admonition<\/strong> than in the past that the fully defined drawing should be dimensioned using GD&T<\/strong> with limit dimensioning reserved primarily for the size dimensions for features of size<\/em>.’<\/p>\n

This statement comes as a result of deliberations on the poor quality, assumptions in part definition that go with incomplete and intrinsically deficient approach using Plus\/Minus Tolerancing.\u00a0 It is incumbent upon Engineering Industries to adopt the GD&T practices that have been proven to deliver in terms of costs, quality, reliability and safety.<\/p>\n

Let us look at the example of a Pressure Relief Valve shown in Figure below:<\/p>\n

 <\/p>\n

\"Pressure<\/a>
Pressure Relief Valve Section View<\/div><\/div><\/div><\/div>\n

 <\/p>\n

If we look at the Plunger that is housing the spring and located inside the housing (Body), the sequence of assembly is evident.<\/p>\n

This process of identifying the assembly process and sequence enables the selection and prioritization of the Datums.\u00a0 This step of identifying the Datums is critical to avoid downstream Quality issues.<\/p>\n

 <\/p>\n

\"Plunger\"<\/a>
Plunger used in Pressure Relief Valve<\/div><\/div><\/div><\/div>\n

Conventional Plus\/Minus Tolerance based drawing would be similar to the following:<\/p>\n

\"Conventional<\/a>
Conventional Dimensioning and Tolerancing Schema for Relief Valve Plunger<\/figcaption><\/figure>\n

 <\/p>\n

This drawing creates more confusion regarding the setup for Manufacturing and Inspection since it does not clarify how the designer intended to control.<\/p>\n

 <\/p>\n

Simple Steps towards a Correct & Complete G D & T Drawing<\/strong><\/p>\n

Step 1:<\/strong> Define Part features that would serve as origin with specific directions for measurement<\/p>\n

This step relates to Datums.\u00a0 Datums need to be selected based on the following criteria:<\/p>\n

1.\u00a0 Representative of Mating Features<\/p>\n

2.\u00a0 Reflect Functional Assembly<\/p>\n

3.\u00a0 Stable<\/p>\n

4.\u00a0 Repeatable<\/p>\n

5.\u00a0 Accessible<\/p>\n

All of the above criteria are equally important. The choice and order of Datums Selection need to be in alignment with the Quality objectives we intend to protect.\u00a0 In other words, Design For Assembly (DFA), that influences Datum Selection and Precedence (order), needs to be in alignment with Design For Quality (DFQ) objectives.<\/p>\n

In this case, the datums would be as shown in the picture below.<\/p>\n

 <\/p>\n

\"Plunger<\/a>
Functional Datum Selection<\/figcaption><\/figure>\n

 <\/p>\n

Step 2: <\/strong>Specify Nominal (Basic) Dimensions for Location and\/or Orientation of Features from Datums<\/p>\n

In our example, since the Cylindrical and Conical features are located concentric to Datum A, they are at Zero Basic Dimension and hence not shown.<\/p>\n

Step 3: <\/strong>Specify Tolerance Zone Boundaries for Part Features in terms of shape and size along with specific rules for compliance<\/p>\n

 <\/p>\n

\"G<\/a>
Plunger G D and T Drawing<\/figcaption><\/figure>\n

 <\/p>\n

This step requires knowledge of process capability existing (with the organization or suppliers).\u00a0 Additionally the dimensioning schema should have the least number of dimensions between the datum reference and features that form a part of the measurable Design for Quality Objective.\u00a0 This is essential to identify the correct Critical To Quality (CTQ) or Key Characteristics for the part that would help in inspection and reporting.\u00a0 In comparison to the Plus\/ Minus Tolerancing Schema, the GD&T approach ensures clarity in setup during manufacture & inspection, alignment with Quality objectives while keeping cost as a driver for change.<\/p>\n

Step 4: <\/strong>Allow Dynamic Interaction of Tolerance Zones between Features in a Part, and across parts, simulating Assembly possibilities for Maximizing Tolerances<\/p>\n

This step differentiates G D & T from Plus \/ Minus Tolerances in enforcing a methodology that would help reduce cost while meeting Quality objectives.\u00a0 Drawing is incomplete without this step.\u00a0 Even companies that incorporate GD&T, fall short of this requirement, sometimes leading to an erroneous conclusion,that GD&T is expensive and its impact on quality is not significant.<\/p>\n

 <\/p>\n

\"Tolerance<\/a>
Impact of Part Tolerances on Assemblies – Visualizing Tolerance interactions<\/figcaption><\/figure>\n

 <\/p>\n

Step 5:<\/strong> Cost of Precision Vs Cost of Poor Quality Analysis for Optimal Tolerances<\/p>\n

By choosing alternate Process Capability, providing costs incurred to maintain specified tolerances and performing a risk assessment based on Risk Priority Number (RPN) of Design Failure Modes & Effects Analysis (DFMEA), a designer can arrive at optimal tolerances and provide KC’s (Key Characteristics) on drawings.\u00a0 This step ensures that management is provided with alternatives in terms of costs, choice of suppliers and investment in machinery and manufacturing lines to achieve desired levels of quality in an objective manner.<\/p>\n

 <\/p>\n

Benefits of incorporating G D & T<\/strong><\/p>\n

While there are many benefits implementing GD&T, some of them stand out as compelling reasons to change, as under.<\/p>\n

    \n
  1. Elimination of errors, re-work, rejections and scrap<\/li>\n
  2. Fail safe approach to tolerancing<\/li>\n
  3. Easy to identify deviating processes that affect Quality and restore them for maximizing yield<\/li>\n
  4. Improved Product Reliability<\/li>\n<\/ol>\n

     <\/p>\n

     <\/p>\n","protected":false},"excerpt":{"rendered":"

    First Time Right is becoming mandatory for the manufacturing industry to save costs and increase profitability.\u00a0 Add to it the requirement that ideas need to be translated to product and brought to market faster, the situation looks untenable. There is<\/p>\n... Continued<\/a>","protected":false},"author":238,"featured_media":7155,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[11,16,21],"tags":[788],"class_list":["post-7132","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-design","category-lets-go-design","category-solidworks","tag-design-for-quality"],"acf":[],"_links":{"self":[{"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/posts\/7132","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/users\/238"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/comments?post=7132"}],"version-history":[{"count":20,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/posts\/7132\/revisions"}],"predecessor-version":[{"id":7177,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/posts\/7132\/revisions\/7177"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/media\/7155"}],"wp:attachment":[{"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/media?parent=7132"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/categories?post=7132"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.solidworks.com\/tech\/wp-json\/wp\/v2\/tags?post=7132"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}