Wednesday

Transforming a 2D Drawing to 3D CAD Data

With rapid change in technology, especially in the area of Computer Aided Design, customers are demanding quick and accurate 3D models for their easy visualization and quick project completion time. Further there is a rapid transformation from 2D CAD to 3D CAD solutions. This article provides an overview and basic technique available to convert the existing 2D CAD drawings into 3D CAD models without much loss in time and data using 3D Computer Aided Design software’s like Autodesk Inventor. This technique not only allows users to convert CAD 2D drawings, but also allows conversion process with more accuracy. Further the various concepts involved in converting the 2D CAD drawings into 3D CAD Models leading to easy conversion of STL format, which can be later used for physical prototyping is a also discussed

Introduction

3D is a real object or true depiction of real image. Though we may be viewing 3D image on plane paper or computer monitor (both flat 2D), our brain compares 3D image with its own archive of 3D real objects as seen by our eyes in past and hence even not so good 3D image provide more information to our brain than plain 2D drawing. Even for a layman, identification of high rise sky scrapper is just easy if you show him a 3D model but extremely difficult if you show him Plan, Elevation and Sectional Drawings of same building. For engineer, both are good enough, because he is trained to understand 2D. Well! In simple terms, understanding 3D is part of natural process, where as you need to get trained to understand 2D

Design engineers generally focus on one main issue; they include either designing or drafting or in some applications both. The primary difference between 2D and 3D technology is apparent in the amount of time designers spend on these tasks when they use the respective tools. Unlike 2D drafting tools, 3D modeling technology provides life like representation of a design, from structural composition and the way parts fit and move together, to the performance impact of characteristics such as size, thickness, and weight. When design engineers can see the sum of the parts in 3D, they can see issues and opportunities without ever having to spend time creating documentation. Further any CAD user would definitely affirm that a simple 2D drawing doesn’t attract much attention, but the third dimension tends to impress people Rather than starting a new product concept with meticulous 2D technical drawings of elements that might not function as planned, this technology quickly shows whether a design idea is viable or not based on existing data. This difference amounts to business advantage for companies that otherwise might have to retrace all manufacturing processes in search of an answer or build physical prototypes of products that don’t function as desired.

2D to 3D Conversion Technology

With the emergence of 3D modeling tools, which occurred two decades ago, it is estimated that roughly 75% of the current CAD user base still primarily employs 2D drafting. Although with rapid change, the pace of migration from 2D drafting to 3D modeling to have accelerated, unyielding time-to market constraints offer no opportunity for manufacturers to allow users to adapt to new paradigms and convert legacy drawings into new formats without being productive at the same time. Yet some manufacturers are not only accomplishing this feat, but excelling in top-line and bottom-line measures.

All 3D CAD tools available in the market today can easily generate a 2D drafting view from a 3D CAD model and this further proves to be genuine true. Further this technology is used in every day project activity by a designer, which in turn can be directly used by a machine operator to manufacture the component using any sophisticated CNC machine. However the concept of converting a 2D drawing into a 3D native CAD model is quite challenging and the process of conversion looks quite complicated. However this process is now simplified using popular 3D modeling tools like Autodesk Inventor, Solid Edge which is a 3D CAD solution provider. Further one needs to understand that, the concept of 2D to 3D technology is to simplify the process of creating 3D part models from existing 2D CAD drawing.

Further this technology helps design and manufacturing engineers to improve productivity to a greater extent. Typically, reconstructing a 2D geometry into 3D model involves the use of basic Extrude feature and this is easily accomplished if the projected views are aligned on orthogonal planes. Apart from features mentioned above, other features like hole, chamfer, and fillet are ideally created by Boolean operations which involves cut and intersect options. The algorithm that works in achieving this technology is generally based on Boolean operation. To understand this technology, the 2D to 3D conversion is carried out from AutoCAD 2008 to Autodesk Inventor 2008 developed by”AutoDesk®”.

Benefits of 3D in an organization

With many companies migrating from 2D CAD to 3D solid modeling for mechanical design, Solid modeling shortens design cycles, streamlines manufacturing processes, and accelerates product introductions by improving the flow of product design information and communication throughout an organization, as well as among its suppliers and customers. For any business, this means faster time-to-market and higher quality products translate into increased revenue, while reduced design costs provide larger profit margins.

Some of the benefits of 3D are listed below

Faster product design (roughly around 45% faster on average)
Automatic flattening of sheet metal parts (with bend allowance)
More effective communication with suppliers/customers
Visualize more ‘what-if’ scenarios during the design process
The ability to create renderings and animations for design proposals or reviews
More effective internal design reviews
Generation of virtual prototypes allows non-CAD people to participate in the process
Easily incorporate late design changes
Test and validate designs to reduce costs from quality problems, errors, ECO’s
Reduce the need and cost of physical prototypes
Automatic Bills of Materials
Better employee morale
Increase customer confidence and loyalty
Data management to organize and manage your design data
Helps to standardize on detailing and drafting practices
Easily manufacture your designs with industry leading partner products
Automate your design process and increase speed and accuracy of output and response to customers
Allow non-technical personnel such as sales department (and even customers) to quote, specify and configure product whilst maintaining your design & engineering integrity

3D CAD and Product Development Process

Nowadays the product development team must look way beyond questions of drawing productivity when deciding on the right CAD tools to specify. 2D CAD technology has delivered all the drawing productivity improvements that are likely to get and those benefits have long ago been absorbed. 3D CAD, on the other hand, is a completely different technology, capable of delivering far more wide-ranging benefits across the whole of the engineering and collaborative engineering process. Whereas 2D CAD shortens time scales to some extent, 3D CAD goes much further, directly supporting the whole product development cycle, speeding up every activity and increasing the quality of design by
removing many sources of inaccuracy and error, the accurate 3D solid geometric model, together with all the non-geometric engineering information attached to it, becomes a complete ‘digital product model’ for purposes of design review, holding all the information required to analyze, procure and make it, in a form immediately usable by all engineering processes. When allied to product data management and the Internet, 3D solid modeling provides an entire foundation for product information flow across the collaborative engineering network. A 2D drawing is an indirect and incomplete representation of an engineering product or system, subject to interpretation and error. Taking off data in correct form for downstream analysis, simulation and manufacturing processes requires additional effort and is subject to mistakes. Sending drawings electronically to partners, customers and suppliers is fine, but the potential for errors and misinterpretation remain. By contrast, 3D solid modeling produces a complete and accurate geometric model of the product, analogous to a physical model. Any required geometric and physical information can be derived from it for purposes of engineering analysis, simulation and manufacture, using linked specialist applications that have become an integral part of the concurrent engineering process. Given this high degree of integration it becomes feasible to iterate through several cycles of design, analysis and manufacturing simulation at an early stage in design in order to encourage innovation while achieving the best possible product within the time available. Product and engineering data management, similarly integrated, ensures that the engineering product is fully and accurately documented by the time the design is complete

Basic 2D to 3D Conversion Methodology

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Typically any 3D modeling tool that involves the conversion of 2D to 3D should work in line with the above flow chart in order to create accurate and quick 3D models from existing 2D drawings. The same process is also used by Autodesk Inventor 2008, in generating 3D CAD models. However during transfer of data from 2D to 3D sufficient care should be taken to ensure smooth transition process. This includes exporting only the desired geometry (lines and polylines) and retaining the layers, dimension styles, all axis lines that exist in the 2D data. Further the properties like line type, line weight are also vetoed.

Further with reference to the figure 2 if all the views are oriented in a glass box, i.e. in their respective position, then the process of extrusion and Boolean operation becomes easier. This is the basic concept of 2D to 3D conversion.

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Interoperability Issues

From recent developments, in area of CAD, interoperability is the key issue which integrates various CAD CAM CAE tools. Further, this technology helps seamless transition of CAD data either from 2D to 3D or from 3D CAD tools to CAE tools. The geometric kernels, used in these tools are seamless, since they work on the same coding using popular programming tools like C++, C# and VB.

Stages in conversion from 2D to 3D

Converting 2D files to 3D solid models can be expensive and tedious for large manufacturers with tens of thousands of product drawings. But a programming mathematics combines the series of thin slices on a logical path to form a 3D object. Every 3D object used in AutoCAD or Inventor got its base as 2D shape. Box got rectangle as base shape and Cylinder got circle as a base shape. When dealing with 2D model, the third dimension is silent (zero value), as soon as third dimension assumes some value other than zero is given to accommodate the changes in 2D to 3D, model is now termed as 3D model. How ever, the fundamental concept is to arrange the 2D geometry onto a”glass box” making it easy to convert the design into 3D

The key concept apart from use of tools like Extrude and the work flow that involves in conversion from 2D to 3D is listed below in 4 steps leading to effective conversion technique. Further a simple case study is taken to understand the conversion process.

1. Establishing the base geometry (front View)
2. Identification of projected geometry (Side and Top View)
3. Alignment of various geometric views
4. Extrude (Boolean operation)

1. Establishing the Base Geometry (front View)

A 2D drafting tool like AutoCAD having file extensions as *.dwg provides seamless data transition into any 3D CAD system. Hence a drawing as shown in figure 3 is generated in AutoCAD 2008. Further this data is imported into Autodesk Inventor 2008 using Insert AutoCAD file option. During this translation process, using filter technology option built in, Autodesk Inventor, data like dimensions, various line type parameters, layers are filtered before they are actually imported into the 2D to 3D module. This process leads to effective and accurate conversion from 2D to 3D. Once the views that are drawn using AutoCAD are imported into inventor, the base view is aligned along the XY plane. However, this process can be extended to conversion of a manual drawing into CAD drawing using the technique of raster to vector conversion. The base view generally refers to the front view in any orthographic projection.

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2. Identify Projected View geometry

With a seamless data transition from a 2D CAD package to a 3D parametric CAD tool, it is essential to have a significant technique to enable quick and accurate orientation of data from various views. This process can generally be established by orienting various views into a box, which provides all three planes like XY – YZ – ZX, since a 3D model can be viewed from 6 different orientations. To better understand this, consider a cube, which includes all the 4 views followed by top and bottom view. Based on the view type, the corresponding views can be selected to better associate with the front view as shown in figure 05.

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3. Alignment of various geometric views

Once a the basic views are identified, that are necessary for creation of a 3D Model, the orientation and alignment issues are very important before the 3D model can be extruded. These alignments are generally carried out using basic translation technique which basically includes only move command to appropriate plane, since other technique cannot provide an accurate 3D model. However it is clear that when translation process is carried out, the entire view is made use to position accordingly. Figure 6 provides the three view alignment before this could be converted into a 3D model.

4. Extrude (Boolean operation)

The models, after appropriate orientation, need to be extruded for creating the 3D model. The conversion is generally made easy by selecting one view at a time. Once the basic view is extruded, it is essential that all other views needs to be created using a combination of Extrude and Boolean operation, by accomplishing this process the final 3D Part model would be ready without any errors. However the user must ensure proper use of the sketch, since, once the sketch has been utilized for extrusion or Boolean, that sketch cannot be used again. The process of cut and intersect is mainly used for arriving at the final model. To better understand this technique refer figure 7.

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Conversion from CAD to RP files

Any 3D modeling tool, has the capability of converting a 3D CAD model into an STL file. This conversion is again using the triangulated format technique; generally know as the STL format. These formats help users to directly interface with any Rapid Prototyping machine to quickly create a 3D Model. This technique calls for quick concept to market scenario since, the process of physical prototyping is taken care in a short time. Further any changes can always be done within considerable time, leading to better sustainability in the market. The concept of rapid prototyping reduces the manufacturing mistakes. Some manufacturing companies require a physical prototype due to ergonomics in mind. No matter how good the model looks on the screen, one can’t tell how it will behave once he or she handles the model.

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Conclusion:

Most 3D modeling systems offers features that help manage the accuracy and completeness of 2D to 3D conversion. However, the stages of conversion seem to be a major concerns, if the extrude and Boolean operation is not used properly. Further, Manufacturers plan to add 3D modeling to 2D drafting instead of replacing it. This is the main reason which calls for such conversion technique. However if these technologies can accommodate, conversion of 2D assembly drawing into a ready to use 3D assembly models, then the technology growth would be at its peak and most companies would go into 3D technology, and the cost factor would drastically drop down. This will encourage even mid-sized companies to wrap up 2D to 3D technology and this trend would continue to grow among all verticals.