History of CAD
Designers have long used computers for their calculations. Initial developments were carried out in the 1960s within the aircraft and automotive industries in the area of 3D surface construction and NC programming, most of it independent of one another and often not publicly published until much later. Some of the mathematical description work on curves was developed in the early 1940s by Robert Issac Newton from pawtucket, Rhode Island. Robert A. Heinlein in his 1957 novel The Door into Summer suggested the possibility of a robotic Drafting Dan. However, probably the most important work on polynomial curves and sculptured surface was done by Pierre Bezier (Renault), Paul de Casteljau (Citroen), Steven Anson Coons (MIT, Ford), James Ferguson (Boeing), Carl de Boor (GM), Birkhoff (GM) and Garibedian (GM) in the 1960s and W. Gordon (GM) and R. Riesenfeld in the 1970s.
It is argued that a turning point was the development of the SKETCHPAD system at MIT in 1963 by Ivan Sutherland (who later created a graphics technology company with Dr. David Evans). The distinctive feature of SKETCHPAD was that it allowed the designer to interact with his computer graphically: the design can be fed into the computer by drawing on a CRT monitor with a light pen. Effectively, it was a prototype of graphical user interface, an indispensable feature of modern CAD.
First commercial applications of CAD were in large companies in the automotive and aerospace industries, as well as in electronics. Only large corporations could afford the computers capable of performing the calculations. Notable company projects were at GM (Dr. Patrick J.Hanratty) with DAC-1 (Design Augmented by Computer) 1964; Lockheed projects; Bell GRAPHIC 1 and at Renault (Bezier) – UNISURF 1971 car body design and tooling.
One of the most influential events in the development of CAD was the founding of MCS (Manufacturing and Consulting Services Inc.) in 1971 by Dr. P. J. Hanratty[6], who wrote the system ADAM (Automated Drafting And Machining) but more importantly supplied code to companies such as McDonnell Douglas (Unigraphics), Computervision (CADDS), Calma, Gerber, Autotrol and Control Data.
As computers became more affordable, the application areas have gradually expanded. The development of CAD software for personal desk-top computers was the impetus for almost universal application in all areas of construction.
Other key points in the 1960s and 1970s would be the foundation of CAD systems United Computing, Intergraph, IBM, Intergraph IGDS in 1974 (which led to Bentley Systems MicroStation in 1984)
CAD implementations have evolved dramatically since then. Initially, with 3D in the 1970s, it was typically limited to producing drawings similar to hand-drafted drawings. Advances in programming and computer hardware, notably solid modeling in the 1980s, have allowed more versatile applications of computers in design activities.
Key products for 1981 were the solid modelling packages -Romulus (ShapeData) and Uni-Solid (Unigraphics) based on PADL-2 and the release of the surface modeler CATIA (Dassault Systemes). Autodesk was founded 1982 by John Walker, which led to the 2D system AutoCAD. The next milestone was the release of Pro/ENGINEER in 1988, which heralded greater usage of feature-based modeling methods and parametric linking of the parameters of features. Also of importance to the development of CAD was the development of the B-rep solid modeling kernels (engines for manipulating geometrically and topologically consistent 3D objects) Parasolid (ShapeData) and ACIS (Spatial Technology Inc.) at the end of the 1980s and beginning of the 1990s, both inspired by the work of Ian Braid. This led to the release of mid-range packages such as SolidWorks in 1995, Solid Edge (Intergraph) in 1996, IronCAD in 1998, and Autodesk Inventor in 1999. Today CAD is one of the main tools used in designing products and architects.
Saturday, March 29, 2008
The CAM Question: How Much Does Your Shop Need?
During the past ten years, few aspects of manufacturing have progressed as rapidly as PC-based CAD/CAM technology. As with most innovations, the market presses for improvements, and eager hardware and software developers strive to meet the demands. But as PC-based CAD/CAM software grows more sophisticated, it becomes difficult for a shop to decide exactly what they require. As amazing as some of this software is, how much CAD/CAM capability does a shop really need?
To start with, the prospective buyer must determine the needs and desires of the company or department that he or she is working for. Get out into the shop! Take a look at your NC and CNC equipment. List the types of machines you are using, their abilities and the current work being produced on them.
It’s also important to consider what type of work you plan to do in the future. Many shops prefer a system that lets them purchase the capabilities they need now, and also offers additional functions they can add as their needs change. This lets them build on their initial software investment and avoids the need to learn a new system later.
Despite the complexity of many systems on the market, a shop may only need specific CAM functions. For the purposes of this article, we have broken these functions into four general levels of complexity. The following is a quick rundown of these levels and how they relate to different types of work.
1. The Basics
A talented programmer can stand at a control and program a part with basic shapes and angles. However, this becomes much more difficult and time-consuming for a part containing complex curves, odd angles or shapes requiring multiple passes.
Simple 2D or 3D shapes can be machined in planar fashion with most CAD/CAM packages. Shops that do primarily 2 or 2 1/2-axis work need a few basic machining functions and probably not much else:
Contouring – programs the cutter to stay at a constant Z-depth while following a series of lines or curves.
Drilling – instructs the machine to drill holes in the stock at different locations, depths and cycles. This type of function typically includes other plunge operations such as boring, counterboring, tapping and reaming.
Pocketing – removes material from the inside of a boundary to create a cavity in the stock. Good 2D pocketing avoids islands within the pocket, and does not force the cutter into an area that is too small for it. Pocketing can be done in several different ways:
Zigzag pocketing moves the cutter back and forth across the cavity with the same step-over for each pass.
Spiral pocketing starts at the inside or outside of a pocket and spirals out or in until the stock is removed.
One-way pocketing creates a series of parallel passes in the same direction, allowing all cutting to be climb or conventional instead of a combination of the two.
Morph pocketing creates a spiral toolpath that gradually changes from an internal to external shape, keeping a constant load on the cutter.
Facing cleans material off the top of an area that may lie between depths, such as the top of an island.
Pocket re-machining identifies areas left uncut from a previous operation and cleans out those areas with a smaller cutter.
Toolpath Associativity – This maximizes the above processes by linking toolpath and geometry. If either the toolpath or geometry are changed, a new, updated toolpath can immediately be generated. This means that a part only has to be programmed once, with any changes made to the model or machining process updated with a single mouse click. For example, a programmer may want to change drill size and hole location on a series of operations. Rather than reprogram the entire set of operations, he simply selects a new tool, moves the geometry and clicks a button. The result is a new, accurate toolpath reflecting those changes.
Many shops find these 2 and 2 1/2-axis CAM capabilities are well suited for a large number of their applications. More complex work can be done with these functions, but with increasing difficulty. In addition, shops often come across parts that are not extremely complex, but are difficult or impossible to program using 2 1/2-axis functions. An example is a spherical-bottom pocket. Since the bottom of the pocket does not lie exclusively in the X-Y plane, toolpath functions with greater control over the Z axis are needed.
2. The Next Step – Adding a Third Dimension
Most complicated parts with complex curvature can be defined using surfaces. A surface is a geometric entity that mathematically defines the curvature at any given point. Surfaces are applied to 3D geometry like a skin, and are trimmed or filleted together to fully define the curvature of the part.
Surfaced geometry requires toolpaths that are flexible enough to follow sculpted shapes. One method of achieving this is through single-surface machining. This level of machining is suited to parts that can be defined with a few sculpted surfaces that are tangent to one another. Each surface can be programmed separately and the toolpaths can be combined into a single NC program.
Once projects become more complex and contain surfaces that are not tangent, machining with single-surface functions becomes somewhat difficult.
3. Multi-Surface Machining
Multi-surface roughing and finishing are suited for applications such as complex prototyping or mold making. These functions allow a single toolpath to be generated across multiple surfaces of any type. All selected surfaces are considered when calculating the toolpath, thus delivering a consistent finish and avoiding gouging.
A good CAD/CAM system offers several options for roughing and finishing a multi-surface part. This allows the NC programmer to choose the most efficient machining strategy for a specific project.
Parallel machining – This is basic multi-surface machining. The tool moves back and forth across the model. Flexible parallel machining allows you to cut in zigzag or one-way motion.
Constant Z machining – This function cleans all the material from a given depth before moving on to the next depth. The result is less tool wear and a more consistent finish on some surfaces.
Scallop machining – Scallop machining keeps a consistent tool step-over in 3D space. This provides a more uniform scallop height around the entire model and therefore reduces the amount of handwork required to finish a part.
Flow-line machining – Flow-line machining uses the natural shape of a set of surfaces to determine tool movements, resulting in a more efficient toolpath.
Radial machining – This type of toolpath radiates out from a center point like spokes on a wheel. It is ideal for spherical parts.
Containment boundaries – Definable containment boundaries allow the programmer to define a specific area to be cut, even if it contains only parts of surrounding surfaces. This is useful when a specific area of a multi-surface part needs a different machining strategy than the rest of the part.
After a finish pass is run, there is often material left in small or hard-to-reach areas. A good CAD/CAM system provides automatic options to remove that extra material.
Multi-Surface Leftover Machining – This function identifies areas that are left uncut by a previous multi-surface operation, and programs a smaller tool to clean out those areas.
Pencil Tracing – Pencil tracing walks a small cutter along surface intersections to achieve the best possible finish in hard-to-reach areas.
Shallow / Steep Machining – This function identifies and machines steep and shallow areas that have scallops left from a previous cut
These 3-axis functions provide most of what a complex mold, prototype or production shop needs. There are, however, additional machining options available.
4. Machines That Do More
Some operations not only require software that is capable of generating the toolpaths, but machine tools that provide the appropriate capabilities.
4-axis machining – This adds a fourth dimension of simultaneous movement, and requires a machine with a rotary table or tilting machine head.
5-axis machining – This adds a fifth dimension of simultaneous movement, and requires a machine with one or more rotary tables and/or a tilting machine head. Good CAM software automates 4- and 5-axis requirements such as calculation of leads/lags and surface normal vectors.
High-Speed Machining – Machines that support high-speed cutting need CAM that delivers features such as tangential entry/exit arcs, smooth tool direction changes and plunge roughing.
Additional Tools to Consider
There are several NC programming features which are important in all 2-, 3-, 4-, and 5-axis applications. These include:
Post processors – In most systems, the post processor translates the toolpath information into NC code for the machine. Therefore, good post processors are essential in any level of machining software. CAM vendors typically have a library of these to run with most machines. Many CAM systems include user-customizable post processors, allowing programmers and machinists to make adjustments themselves or with a quick phone call to their vendor’s tech support.
Toolpath Verification – Solid model toolpath verification runs your toolpath on-screen on a piece of “virtual stock.” The result is a solid model of the finished part that can be inspected from all angles to ensure the toolpath produces the desired results. This helps eliminate dry runs and test cutting.
Data Translators – If a shop plans to receive files from other CAD systems, good translators are vital. If a shop can accurately accept a wide variety of data formats, such as IGES (Initial Graphics Exchange Specification), they do not have to spend time recreating geometry that is already available. Many vendors provide these translators with their software; others charge extra.
CAD Capabilities – Regardless of the type of work shops do, most find it necessary to have CAD as well as CAM capabilities. Even if a shop receives all its work electronically as CAD files, the programmer often needs to edit the geometry to make it machinable. Many shops prefer a package that includes both CAD and CAM. Using a tightly integrated CAD/CAM system eliminates the need to translate files between separate CAD and CAM packages. Since an integrated CAD/CAM system uses a common database for the CAD and CAM information, complete data compatibility is maintained at all times. In addition, this type of CAD/CAM system shares a common interface, avoiding the problem of training programmers on two separate systems.
Know Your Needs – for Today as well as Tomorrow
When selecting the level of CAM capability you need, keep in mind your machines’ capabilities, the type of work you produce now, and the type of work you plan to produce in the future. Many shops prefer a system that lets them add capabilities as their needs change. This allows them to purchase only what they require and lets them plan for the future by providing an upgrade path to more complex functions.
Choosing a system that grows with your business also helps reduce your learning curve. If your CAD/CAM package provides a growth path, you won’t have to learn new software when you want to expand your capabilities.
Many CAM developers provide a family of software for milling, turning, wire EDM and other types of machining. If you decide to expand the category of machining you do, this lets you get a system with a familiar interface, further reducing training time.
Choosing a good CAD/CAM system with the correct functions helps you improve the quality, productivity and profitability of your shop.
During the past ten years, few aspects of manufacturing have progressed as rapidly as PC-based CAD/CAM technology. As with most innovations, the market presses for improvements, and eager hardware and software developers strive to meet the demands. But as PC-based CAD/CAM software grows more sophisticated, it becomes difficult for a shop to decide exactly what they require. As amazing as some of this software is, how much CAD/CAM capability does a shop really need?
To start with, the prospective buyer must determine the needs and desires of the company or department that he or she is working for. Get out into the shop! Take a look at your NC and CNC equipment. List the types of machines you are using, their abilities and the current work being produced on them.
It’s also important to consider what type of work you plan to do in the future. Many shops prefer a system that lets them purchase the capabilities they need now, and also offers additional functions they can add as their needs change. This lets them build on their initial software investment and avoids the need to learn a new system later.
Despite the complexity of many systems on the market, a shop may only need specific CAM functions. For the purposes of this article, we have broken these functions into four general levels of complexity. The following is a quick rundown of these levels and how they relate to different types of work.
1. The Basics
A talented programmer can stand at a control and program a part with basic shapes and angles. However, this becomes much more difficult and time-consuming for a part containing complex curves, odd angles or shapes requiring multiple passes.Simple 2D or 3D shapes can be machined in planar fashion with most CAD/CAM packages. Shops that do primarily 2 or 2 1/2-axis work need a few basic machining functions and probably not much else:
Contouring – programs the cutter to stay at a constant Z-depth while following a series of lines or curves.
Drilling – instructs the machine to drill holes in the stock at different locations, depths and cycles. This type of function typically includes other plunge operations such as boring, counterboring, tapping and reaming.
Pocketing – removes material from the inside of a boundary to create a cavity in the stock. Good 2D pocketing avoids islands within the pocket, and does not force the cutter into an area that is too small for it. Pocketing can be done in several different ways:
Zigzag pocketing moves the cutter back and forth across the cavity with the same step-over for each pass.
Spiral pocketing starts at the inside or outside of a pocket and spirals out or in until the stock is removed.
One-way pocketing creates a series of parallel passes in the same direction, allowing all cutting to be climb or conventional instead of a combination of the two.
Morph pocketing creates a spiral toolpath that gradually changes from an internal to external shape, keeping a constant load on the cutter.
Facing cleans material off the top of an area that may lie between depths, such as the top of an island.
Pocket re-machining identifies areas left uncut from a previous operation and cleans out those areas with a smaller cutter.
Toolpath Associativity – This maximizes the above processes by linking toolpath and geometry. If either the toolpath or geometry are changed, a new, updated toolpath can immediately be generated. This means that a part only has to be programmed once, with any changes made to the model or machining process updated with a single mouse click. For example, a programmer may want to change drill size and hole location on a series of operations. Rather than reprogram the entire set of operations, he simply selects a new tool, moves the geometry and clicks a button. The result is a new, accurate toolpath reflecting those changes.
Many shops find these 2 and 2 1/2-axis CAM capabilities are well suited for a large number of their applications. More complex work can be done with these functions, but with increasing difficulty. In addition, shops often come across parts that are not extremely complex, but are difficult or impossible to program using 2 1/2-axis functions. An example is a spherical-bottom pocket. Since the bottom of the pocket does not lie exclusively in the X-Y plane, toolpath functions with greater control over the Z axis are needed.
2. The Next Step – Adding a Third Dimension
Most complicated parts with complex curvature can be defined using surfaces. A surface is a geometric entity that mathematically defines the curvature at any given point. Surfaces are applied to 3D geometry like a skin, and are trimmed or filleted together to fully define the curvature of the part.
Surfaced geometry requires toolpaths that are flexible enough to follow sculpted shapes. One method of achieving this is through single-surface machining. This level of machining is suited to parts that can be defined with a few sculpted surfaces that are tangent to one another. Each surface can be programmed separately and the toolpaths can be combined into a single NC program.
Once projects become more complex and contain surfaces that are not tangent, machining with single-surface functions becomes somewhat difficult.
3. Multi-Surface Machining
Multi-surface roughing and finishing are suited for applications such as complex prototyping or mold making. These functions allow a single toolpath to be generated across multiple surfaces of any type. All selected surfaces are considered when calculating the toolpath, thus delivering a consistent finish and avoiding gouging.
A good CAD/CAM system offers several options for roughing and finishing a multi-surface part. This allows the NC programmer to choose the most efficient machining strategy for a specific project.
Parallel machining – This is basic multi-surface machining. The tool moves back and forth across the model. Flexible parallel machining allows you to cut in zigzag or one-way motion.
Constant Z machining – This function cleans all the material from a given depth before moving on to the next depth. The result is less tool wear and a more consistent finish on some surfaces.
Scallop machining – Scallop machining keeps a consistent tool step-over in 3D space. This provides a more uniform scallop height around the entire model and therefore reduces the amount of handwork required to finish a part.
Flow-line machining – Flow-line machining uses the natural shape of a set of surfaces to determine tool movements, resulting in a more efficient toolpath.
Radial machining – This type of toolpath radiates out from a center point like spokes on a wheel. It is ideal for spherical parts.
Containment boundaries – Definable containment boundaries allow the programmer to define a specific area to be cut, even if it contains only parts of surrounding surfaces. This is useful when a specific area of a multi-surface part needs a different machining strategy than the rest of the part.
After a finish pass is run, there is often material left in small or hard-to-reach areas. A good CAD/CAM system provides automatic options to remove that extra material.
Multi-Surface Leftover Machining – This function identifies areas that are left uncut by a previous multi-surface operation, and programs a smaller tool to clean out those areas.
Pencil Tracing – Pencil tracing walks a small cutter along surface intersections to achieve the best possible finish in hard-to-reach areas.
Shallow / Steep Machining – This function identifies and machines steep and shallow areas that have scallops left from a previous cut
These 3-axis functions provide most of what a complex mold, prototype or production shop needs. There are, however, additional machining options available.
4. Machines That Do More
Some operations not only require software that is capable of generating the toolpaths, but machine tools that provide the appropriate capabilities.4-axis machining – This adds a fourth dimension of simultaneous movement, and requires a machine with a rotary table or tilting machine head.
5-axis machining – This adds a fifth dimension of simultaneous movement, and requires a machine with one or more rotary tables and/or a tilting machine head. Good CAM software automates 4- and 5-axis requirements such as calculation of leads/lags and surface normal vectors.
High-Speed Machining – Machines that support high-speed cutting need CAM that delivers features such as tangential entry/exit arcs, smooth tool direction changes and plunge roughing.
Additional Tools to Consider
There are several NC programming features which are important in all 2-, 3-, 4-, and 5-axis applications. These include:
Post processors – In most systems, the post processor translates the toolpath information into NC code for the machine. Therefore, good post processors are essential in any level of machining software. CAM vendors typically have a library of these to run with most machines. Many CAM systems include user-customizable post processors, allowing programmers and machinists to make adjustments themselves or with a quick phone call to their vendor’s tech support.
Toolpath Verification – Solid model toolpath verification runs your toolpath on-screen on a piece of “virtual stock.” The result is a solid model of the finished part that can be inspected from all angles to ensure the toolpath produces the desired results. This helps eliminate dry runs and test cutting.
Data Translators – If a shop plans to receive files from other CAD systems, good translators are vital. If a shop can accurately accept a wide variety of data formats, such as IGES (Initial Graphics Exchange Specification), they do not have to spend time recreating geometry that is already available. Many vendors provide these translators with their software; others charge extra.
CAD Capabilities – Regardless of the type of work shops do, most find it necessary to have CAD as well as CAM capabilities. Even if a shop receives all its work electronically as CAD files, the programmer often needs to edit the geometry to make it machinable. Many shops prefer a package that includes both CAD and CAM. Using a tightly integrated CAD/CAM system eliminates the need to translate files between separate CAD and CAM packages. Since an integrated CAD/CAM system uses a common database for the CAD and CAM information, complete data compatibility is maintained at all times. In addition, this type of CAD/CAM system shares a common interface, avoiding the problem of training programmers on two separate systems.
Know Your Needs – for Today as well as Tomorrow
When selecting the level of CAM capability you need, keep in mind your machines’ capabilities, the type of work you produce now, and the type of work you plan to produce in the future. Many shops prefer a system that lets them add capabilities as their needs change. This allows them to purchase only what they require and lets them plan for the future by providing an upgrade path to more complex functions.
Choosing a system that grows with your business also helps reduce your learning curve. If your CAD/CAM package provides a growth path, you won’t have to learn new software when you want to expand your capabilities.
Many CAM developers provide a family of software for milling, turning, wire EDM and other types of machining. If you decide to expand the category of machining you do, this lets you get a system with a familiar interface, further reducing training time.
Choosing a good CAD/CAM system with the correct functions helps you improve the quality, productivity and profitability of your shop.
Saturday, March 22, 2008
wHat??
Computer-aided design(CAD)refers to the use of computer tools to assist engineers, architects and other design professionals in their design activities. It is the main geometry authoring tool within the Product Lifestyle Manufacturing (PLM) process and involves both software and sometimes special-purpose hardware. Current packages range from 2D vector based drafting systems to 3D parametric surface and solid design modellers. CAD is sometimes translated as "computer-assisted drafting", "computer-aided drafting", or a similar phrase. Related acronyms are CADD, which stands for "computer-aided design and drafting"; CAID, for Computer-aided Industrial Design; and CAAD, for "computer-aided architectural design". All these terms are essentially synonymous, but there are some subtle differences in meaning.
Basically CAD is not just a drafting tool, its a very accurate and robust design tool too. Due to the complexity of computations in design methodology, the power of computers is leveraged to compute solutions to complex problems like stress analysis, shear analysis, thermal analysis and fluid flow analysis. The CAD offers very simple, easy to use, less time consuming and clean methods to study and evaluate the design process and arrive at a close-to-perfect design.
Computer-aided Manufacturing(CAM) refers to the use of computersystems for the control of robotics and tools during the product manufacture. Integrating CAM with CAD systems provides quicker and more efficient manufacturing processes. This method is applied in different areas. In CNC manufacturing the CAM system is used to simplify the machining and designing process. In most cases the CAM system will work with a CAD design mad
e in a 3D environment. The CNC programmer will just specify the machining operations and the CAM system will create the CNC program. This compatibility of CAD/CAM systems eliminates the need for redefining the work piece configuration to the CAM system. In other words: CAM software usually comes with a machine such as a lathe or chisel. The entire system tends to be extremely expensive. (A lathe and computer system with software will cost in excess of $1 million).Cad/Cam systems offer the advantages of increased programming accuracy, geometric conformance to design parameters, ability to make minor and often major changes to part configuration and programming metrics within the same system. CAD/CAM systems utilize either "wireframe" or "solids" for the part feature generation necessary for post-processing intermediate code files derived from cutter toolpaths into usable "nc" code readable by numerical control machines. Wireframe geometry can be either in two or three dimesional planes, while solids are in 3d. CAD/CAM is used widely across the world at schools and companies who design, innovate and manufacture new products
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