Abstract
I believe that the integration of digital technology in designs is very necessary and cannot be avoided. This is because of its extensive effects on architecture and its general ambiguity. This paper, I believe, will make it possible for individuals and institutions to analyze and decide appropriately on the use of digital prefabrication, as a new technology in the design systems. Although many opinions have been presented with different position statements, the immediacy of proactive consideration on the digital systems is of utmost importance. In this paper, I have explored the relationship between CAD and CAM, computer and production.
Introduction
Digital Prefabrication is of greatest interest in architecture. The need for the translation of the geometric designs in CAD system into understandable production data calls for a proper digital system. This enables a higher rate of transformation into industrialization as the fabrication is properly controlled. As a result, simple, elegant and clean designs are achieved in more economical ways and prefabrication. After the computer aided designs are made, there is a subsequent manufacturing process called the CAM (Computer Aided Manufacturing). In CAM, computer software is used to control the machinery and the related machine tools in the process of manufacturing the work-pieces. CAM employs the use of a computer in the control of all the operations of a manufacturing process including management, planning, transportation and storage. A link between the computer aided designs and the CAM models necessitates digital prefabrication. In this work, I aimed at clarifying this need.
Today, there is a rising need for the exchange of data. The optimization of the digital data exchange from design to production, calls for digital prefabrication. One of the expectations of a designer is a high quality or a faultless (perfect) result in a digital system. The question is, “how can this high quality be achieved?” First, there is the need to understand and know how to select and combine the materials to be used in the prefabricated component systems. Thus, the component design and prefabrication should be viewed as both a selection process and a research and development process that results into customized closed-system components for specific applications. From the individual parts or the components, we move to a collection of parts that have a related functional performance; the concept of assemblies, which results into the elements. The system components are considered from an angle of parametric control of both the theoretical model and the methods of production (CNC). This extraordinary computational solution has not been friendly to the modular prefabrication industries. It only affects the speed and efficiency of production. In a case where a functional object is considered as a technical system, the need for innovation is created.
The parametric formworks support a fabrication process that is rapid and efficient. The process also allows for changes in the profile, forming the link between the digital systems, computational models, and the physical manipulation of the material form. The parametric systems give a unity mapping of data from the digital models to the physical framework. The development of the parametric systems in EFAB studios reveals that there are chances for the production of new “object intelligence.” The end result, as we have seen, is the birth of “digital prefabrication”.
Before digging deep into digital prefabrication, let us first consider some applications of prefabrication in the real life situation. To start with, let us look at the building industry where the use of both prefabricated concrete and steel has a series of advantages. Prefabrication of steel sections away from the site eliminates onsite welding and cutting and the most likely hazards. The construction of the framework for the moulds of concrete components can be difficult on site. Also, the delivery of wet concrete can be quite hectic. When prefabricated, the moulds can be reused. The concrete can also be mixed on the spot eliminating the need for transporting wet concrete to the construction site. In the apartment blocks construction, prefabrication techniques are applied. Housing developments that have repeated housing units also employ prefabrication techniques. Factory buildings, office blocks and warehouses also apply the technique. In the construction of avalanche galleries and bridges, prefabrication is very vital, as weather conditions may not favor complete onsite construction. When the elements are prefabricated, the bridge designer and contractor get a series of advantages including safety, reduction of the construction time and cost, and environmental advantages. The tower constructions also in most cases employ the prefabrication technology. The mobile phone towers and the modern lattice towers consists of prefabricated elements assembled together. The assembly of spacecrafts and aircrafts widely employ the prefabrication technology.
The main aim of digital prefabrication is to construct a 4-D model with all the dimensional information, both qualitative and quantitative, that is necessary for the design, analysis, fabrication, and the actual construction. The time factor also matters a lot. Therefore, the time-based information for the assembling must also be inclusive. This results into a single compact data source with all the necessary information for the design and production. This single data source makes it possible for the designers or architects to be the master builders or coordinators of information in various fields of design.
Overview of the CAD/CAM and the Digital Prefabrication
CAD/CAM softwares have been seen to posses numerous inadequacies that necessitate intensive high level involvement of skilled CNC machinists. CAM outputs a code for the least capable machine, and the machine tool control added to the standard G-code set. This increases flexibility. Cases where the CNC machine is manually edited before the program runs smoothly have been experienced, probably due to inappropriately set up CAD software or specific tools in CAM. A skilled machinist or a thoughtful engineer could overcome these issues for prototyping or small product runs because the G-code is a very simple language. Different sets of problems have been encountered in high precision/production shops where the machinist must hand-code program and run CAM software.
The integration of the CAD with components of CAM and CAE in the PLM (product lifecycle management) environment needs an effective CAD data exchange. The CAD operator is therefore forced to export the data in the common data formats like IGES and STL which are almost universally supported by a variety of softwares. This is what has led to the success of digital prefabrication. The IGES (Initial Graphics Exchange Specification) is a data format which allows the digital exchange of information among CAD systems. With the IGES, product data models can be exchanged in various forms including wireframes and circuit diagrams. The IGES Import for AutoCAD creates the ability for the importation of geometric data from IGES files. The IGES files contain graphical data in a format that is universally accepted by most CAD and CAM systems.
The STL (Stereolithography) file format is a Rapid Prototyping industry's standard data transmission format that is used with stereolithography software. Its key role is to generate the information needed for the production of 3D models that are used in the stereolithography machines. In general terms, a STL file gives a triangular representation of an object in 3D. The object surface is divided into logical series of triangles and each triangle is defined uniquely by its normal and the three points that represents the vertices of the triangle. The file completely lists the coordinates (XYZ) of the vertices and the normal. For a proper STL file, the adjacent triangles have two common vertices. Also, the orientation of the triangles must be in harmony. In case of a problem, the original CAD model can always be modified. Problems normally exist due to translation issues. In several CAD systems, the user is able to define the number of triangles representing the model. Creation of too many triangles can lead to a STL file size that is not manageable. Creation of too few triangles makes it difficult for curved areas to be properly defined. The aim, therefore, is to achieve a proper balance between the unmanageable file size and well defined model that has smooth curved geometries. In the absence of STL conversion software, a designer can use other softwares like Bastech. This software accepts surfaced IGS, parasolid, Pro-Engineer, dxf, step, and Unigraphics part files. If the translation is not clean, additional CAD clean up may be necessary. From the CAM software, a simple text-file of G-code is given as the output. This output is transferred to a machine tool via a DNC (Direct Numerical Control) program. The CAM packages do not reason like a machinist. They cannot optimize the tool paths to the extent of mass production. A user selects the tool type, the machining process, and the path, while an engineer has the working knowledge of the G-code programming, optimization and wear issues over time.
Importance of STL files in CAD/CAM Systems
Several Computer aided design systems can easily output the Stereolithography file format due to its easy and quick implementation. Triangulated models are required by several Computer aided manufacturing systems as the core basis of the calculations. Due to the fact that an output of an STL file is readily available from a given CAD system, it’s usually used as a very quick and easy method for the importation of necessary triangulated geometry into a given CAM system. It is also used in data exchange between the computational environments like Mathematica and the CAD/CAM systems. Although this file is not the most efficient method for data transfer in terms of memory and computation, there is very little motivation to change, if any, once it works. Because of the impossibility of the STL file format to go wrong, most of the integrated CAD/CAM systems prefer it for the geometric data transfer.
Other file formats that can encode triangles also exists e.g. the DXF and the VRML. The major problem with these formats is that it is possible to add foreign materials other than the triangles resulting into the production of ambiguous and unusable products.
The development of a digital file is not just about CAD modeling; it combines the whole processes of development activities, including business planning, as stipulated in the Product Lifecycle Management. The file optimizes decision making as it provides a unit source of information about the product in a form that makes sense to every user; a technique of digital prefabrication. The use of the digital file makes it possible for the implementation of designs which are requirements-driven as in digital prefabrication. In a requirements-driven design, the product requirements directly influence the file development decisions. In such a design, the customer or the client provides all the necessary information, including the features of the product which must be incorporated in the file; before the file is used in the actual design process.
The preparation of the digital file for a requirement-driven design starts with the customer’s request, in form of a quote or a proposal. Most of the customers’ proposals (bids) contain the specifications, the general terms and conditions, the site layout in a CAD file, etc. A decision is then made on whether or not to follow up the request for quotation (RFQ). A standard template or a routing slip is then assigned to the relevant authority for a feasibility study. The response for the RFQ is then prepared. The feasibility analysis can then be viewed as a new task. The necessary information that supports the request is automatically routed to the authority, reducing the time wastages. This is the greatest factor that supports digital prefabrication. The completion of the feasibility study is quick and the process moves to the next step. The managed development platform keeps the digital file development process in pace by making sure that all the necessary data reaches the next level. Most CAD systems have uncontrolled approach, encouraging designers to rush into details at an early stage, connecting geometry, adding constraints and encouraging multiple variables and dimensions with little or no regard for the model application. The use of digital file systems in digital prefabrication completely eliminates the above CAD system weaknesses.
With the use of digital design softwares like the NX, the digital file can be used to make a design that can be captured in the visual editor. This allows the engineer or the architect to add different dimensional information, which also allows for the “what if analysis”. With the principal parameters entered, changes can be propagated to the whole assembly in a controlled manner. Visual feedback before and after can also be provided by the digital prefabrication softwares. This makes it easy for the architect to determine the consequence of any changes. The digital file systems in the prefabrication process allow for the saving and searching of the components and modules based on their role and functional requirements. If the customer’s request incorporates specifications created in a different system like an AutoCAD drawing, there is a provision for the access of this data in spite of its source, without the need for the translation of data which may be costly and risky. Digital prefabrication techniques give the customer an advantage of incorporating data in different systems, and the access of the data without the use of a translation software. Once the feasibility states are complete, the architect approves the file. After realizing that the file results into a feasible product design, and starting with platform engineering, a detailed design follows.
The greatest advantage of digital prefabrication production is the ability to set up a managed parts library which ensures that the design components meet the company and program requirements. Once a component parts dictionary is created, there is an easy and quick identification and location of the components, eliminating redundant component design and accelerating the design cycle time. The inventory costs are reduced by minimization of part proliferation. This lowers inventory levels and eliminates obsolete and excess inventory.
Other areas that are possible with the digital prefabrication systems, which I’ll just mention, are: creation of visual assemblies, simulating and validating the design, and the design documentation.
CAD Development
The CAD systems provide users/architects with perfect input tools that help in reformation of the whole design process. It also helps in drafting, documentation, and the entire manufacturing process. The development of CAD softwares and the creation of multi-CAD development environments have created a very conducive atmosphere for the emergence of "digital prefabrication”
As architects search for a way of implementing an environment that can support these different systems, the general requirements of data exchange start to become a central theme of the discussion. This has resulted in the co-existence of several different CAD systems in today’s design world, and has been necessitated by the consolidation of the mechanical CAD market. Digital prefabrication has been arrived at as the platform that supports the implementation of these different systems, and enables data exchange, as the need dictates.
Digital prefabrication has been necessitated by various business processes existing in a multi-CAD environment. These processes include Interoperability, Collaboration, Coexistence, Migration, and Achieving. The use of the CAD system and Data Management is actually based on these processes.
The first process is the Interoperability which calls for the sharing of design data between different builders. Here, a design is made using one of the CAD softwares e.g. AutoCAD. The design data is then made in a manner that it can be shared between two or more users or builders. Here, there is no modification of the design data. The key issue in interoperability is the ability to share same data of a given design, amongst several builders, which is the driving force towards digital systems.
Collaboration and co-existence also call for the sharing of the design data. In collaboration, the design is made using any of the available CAD systems and any user has the advantage of modifying the data. The modification can be done by the use of any CAD system and is controlled by PDM (Product Data Management) or PLM (Product Lifecycle Management) systems. We talk about co-existence when two or more CAD systems are used by the builders at the same time. In such a case, data needs to be shared by users on an ad hoc basis as per the requirements. This case goes beyond the design data and stretches well into the analysis of the design data. In interoperability, there is no modification of the design data; in collaboration, the design data can be modified by any builder; while in co-existence, there is both the modification and the analysis of the design data. With digital systems, the achievement of this process is quite evident.
If a customer wishes to replace one CAD system with another, a period of coexistence must be passed before the replacement becomes completely successful. In the period of the coexistence, also called the trial period, two different CAD systems are operated simultaneously. The requirement here is a system that can handle all the data of the two design systems at the same time without any alteration. This is the process of migration and Digital systems provide the ultimate solution. An example is when a designer wishes to migrate from, let’s say, AutoCAD 09 to AutoCAD 10, a trial period must first exist. During this period, the designer runs the two systems at the same time so as to get acquainted with the new system.
Clients or customers have different requirements in regard to data security. Some clients require that the design data be preserved for a longer duration, probably decades, for future generation’s reference while others need it just for a short time. For the compliance with these requirements, a neutral representation of the design that factors in all the clients’ needs should be created. This is what achieving is all about and it directly necessitates digital prefabrication.
PDM is within PLM and its main responsibility is to create, manage and publish the product data. It employs the use of software or a program or a tool that controls the data related to a given product. For the data to be tracked there must be technical specification of the product as given by the client to the manufacturer. The specification must include the types of the materials required for the production of the goods. By using PDM, the manufacturer can track various costs associated with the creation of the product. The centre of focus in a PDM is the management and the tracking of all the information related to a given product. The information can be stored in one or more files and includes the engineering data like CAD models, the drawings and their corresponding documents. PDM is the central source of knowledge for the product history and the processes, and encourages the exchange of data among the users of the product. PDM is capable of giving the following: access control, component or material classification, product structure, process management, engineering changes, and collaboration.
PDM has greatly helped in the development of the digital prefabrication technology. In the product Lifecycle Management, there is an integration of data, people, processes and business systems. The rising demand for various design products has intensified the integration of PLM into the digital prefabrication architecture. PLM has been the chief source of product information that is used by several CAM systems.
For Interoperability, Collaboration, Coexistence, Migration, and Archiving, there are specific requirements for each, based on data translation. This is to aid in the reduction of misunderstanding and misinformation on the side of the user community or builders. These requirements are summarized here-below
- Interoperability requires very accurate geometry with unambiguous product structure. Key annotation must also be included.
- Collaboration calls for a complete Feature information, the agreed mapping between system users, and the understanding of the technology behind all the systems involved.
- Coexistence, in most cases, has similar requirements to that of Interoperability. However, some applications may dictate that the exchange of data becomes feature-based. With such a requirement, the builder has to analyze the data, based on the future projections as necessitated by the application.
- Migration call for a clear understanding of the items to be translated and how the translation will affect future business. Also, the understanding of the limitations of available technologies is another important requirement. Once the limitations of a given CAD software are clear, it is very possible for the builder to explore the new CAD software and make a perfect comparison between the two during the trial period. This eliminates the rush into a CAD system that may possess similar limitations.
- Archiving necessitates the ability to see in to the future. After the future forecast, one decides the healthiest format to preserve the complex design data.
On the CAD development, let us first accept the fact that nothing is the same. By definition, there are no any repetitive elements, implying that non-standard architecture always exists. The CAD, however, by use of such processes as Interoperability, Collaboration, and Coexistence, tries to link several elements. This link paradoxically leads to an increase in the number of details contained by a given design system. For this non-standard architecture, the appropriate approach is through mass customization. This is the need for designing a parametric detail and producing it with unique parameters supplied by the designer. A parametric detail encompasses different natures. The parametric detailing is an architectural process that concentrates many design problems into one unifying solution. The parametric details are the core of any building process that takes the architect’s data and produces it directly. This is the file to factory process that is necessitated by the above mention business processes. However, concentrating many design problems into one unifying solution comes with numerous consequences. First, unifying details must be created. The parametric details must serve a wide range of solutions. Secondly, the parametric details must be given some underlying control-structure. The end result is the evolution of Digital prefabrication.
Technical foundation
The design geometry comes in two basic representations in today’s market depending on the business practices. They are the B-rep (Boundary Representation), and the Future Based.
All of the available CAD systems are considered Future Based modelers. In spite of some CAD systems like Parasolid and ACIS having their roots on commercial kernels, most of the largest systems in terms of the market share contribute a good percentage of proprietary entities and construction methods to the kernels. For the future based designs, the vendors add special features and options to features that are intended to improve the sale of the product. For every user, the added features may be quite significant; however, the exchange of data between different systems becomes very complicated and in most cases not realistic. An attempt to achieve this calls for the “digital prefabrication”.
B-rep is a method of representing shapes using the limits. It is used in almost all Computer Aided Designs and in solid modeling. This method connects the elements of shape i.e. faces, edges and vertices, and subgroup these elements into logical units, also called geometric features. These features form the basis of several developments, as they allow for high level geometric reasoning about the shape. The high-level geometric reasoning about the shape is necessary for comparison, manufacturing, and process planning. This is what digital prefabrication is based on.
The Boundary Representation form of data exchange has been in use for well over 20 years and still is not perfect. However, successful transfer rates deviation of 5% has been realized. In this transfer, the geometry from a solid in one system is translated to another solid in the other system. The physical properties of these solids remain similar. For the accomplishment of this transfer, translators are required. The currently available translators are the commercially based point to point translators and the standard based translators (IGES, STEP). As driven by the multi-CAD requirements, the commercially based solutions have a higher degree of success in an enterprise data exchange setting.
A summary of the two fundamental representations based on quality, performance, content and accuracy is tabled below.
This table gives different characteristics of the two fundamental representations of the design geometry, based on the product features. The limitations presented in this table calls for a more direct and faultless method of representation of data. The emergence of digital prefabrication is linked to this, as it tries to bring solutions to the above tabled problems.
Real life experience
Several companies have come to the realization that, with the increasing number of customers and suppliers, the development of digital systems is one of the basic requirements.
A general belief is that the solution to the available problems is the feature based data exchange. However, the expectation of the market is not fully met by this level of information exchange.
Future Projection on Digital Prefabrication
In the CAD market, the consolidation of the key players led to the exploitation of the current major tools by various entities that depended on the tiered suppliers. These tools are projected to remain in use for a couple of years even without proactive marketing by the vendors.
With the rapid change in the electronic and communication industry, the data exchange will be more critical. With the digital communication and the digital prefabrication, data exchange will be faster and with high demand throughout the entire supply chain. With the use of PDM systems in the control of the automatic generation, data exchange is projected to be more accurate. The alternate representations of the designs are also expected to service the supplier chain. They are expected to have various levels of intelligence, as they are certified for special and specific tasks. Some are projected to be of visualization only, others for design and manufacturing, and some for inspection. In most cases, single representation would be desirable. However, this would be impractical due to the proliferation of systems which add value to the design geometry.
Proper data management is another requirement that will take digital prefabrication to a whole new level. It will make it possible for the multi-CAD data exchange to gain more popularity as a result of the ability of these systems to enable background creation of additional representation of master parts. Today, several companies recognize the importance of digital prefabrication. They understand the communication geometry and the main explanations between systems and at the same time maintain the design ownership.
For this technology, changes can only be made in the original authoring system. The back office system is another enabler of this technology. The back office system can automatically process the translations based on data management directions.
The digital prefabrication is projected to be in use for several years. Its use may result in a drag on the business or a differentiator in the processes. Whichever way, the designer must take his/her time to understand the actual requirements of data exchange. At the same time, the architect must understand the capabilities of the technology in use. I don’t wish to be left behind.
Reference
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