Case Study
 

Knowledge-Based CAD/CAM: Separating the Hype from True Machining Intelligence


More and more CAM software developers are moving in the direction of knowledge-based machining. In today’s hard-driving push to make parts faster and cheaper, these CAM systems offer push-button automation while retaining control over the machining process.

With machining intelligence built right into the program, CAM systems that incorporate knowledge-based machining increase efficiency by requiring less time to program parts and producing more consistent NC code. The latest CNC machines are already automated, so programming should be too. In addition, knowledge-based machining should provide expanded capabilities to help manufacturers utilize more cost-effective methods at the production level so that parts are cut as fast as possible with the most efficient use of tools.

If your company is considering an upgrade to knowledge-based machining (KBM), following are discussion points to help in your evaluation of your own CAD/CAM system and others on the market.

Knowledge-Based is Changing the Limits of CAM

Knowledge-based machining can be incorporated into CAD/CAM systems at various levels. By comparing operations-based and process-based CAM systems to the automation capabilities offered by feature-based machining, you can see the full range of capabilities afforded by KBM.

  • Operations-based CAM systems require the user to go through multiple steps to machine each part. The user must select which type of operation to use and then select the machining boundary, the type of toolpath to use and then manually select tools, feeds and speeds, and multiple machining options such as stepover distance and the incremental step in Z. These multiple steps must be repeated one at a time for every operation on a part, making it a time-consuming process that is prone to error. These systems offer little to no KBM.
 
  • Process-based CAM systems attempt to reduce these steps by grouping operations in standard processes. KBM is used here as the program remembers the processes used and repeats them for future operations. However, this method only works when a shop uses the same processes over and over for the same types of parts. When a process is applied to different types of parts or parts made of different materials, the CNC programmer must still verify that the correct operations were used and that the correct tools, stepovers, and speeds and feeds were selected because a static machining process does not automatically adapt to every part.
 
  • Feature-based CAM systems use a set of interrelated machinable features to describe a complete part. The beauty of features is that they not only describe shape, they are also made up of one or more associative operations that describe the preferred method for cutting that shape at the NC machine. A predefined set of machining rules and user preferences are applied to a part. KBM in these systems streamlines the manufacturing process by building the highest level of machining intelligence right into the CAM system. Machinable features contain information and rules describing how and where material removal should occur, cutting depths, whether to use climb cutting, whether to spot drill or center drill, and preferred machining strategies for roughing and finishing. The CAM system evaluates the part geometry and part material, then automatically selects the most appropriate tools and operations, recommends machining strategies, calculates feeds and speeds, then automatically generates the NC code.
 

Capturing Best Practices

A major component of KBM is the ability of users to define their own set of machining preferences. Look for KBM that comes equipped with a set of predefined machining rules programmed into the CAM system and allows you to enhance these rules with your own customizations. This set of rules—based on workpiece material, feature parameters, and user preferences—are used to create operations automatically.

View preprogrammed rules as guidelines and recommendations from the CAM vendor, not laws set in stone. By providing a set of standard machining rules already in place, it’s easier for you to customize the software to reflect the machining preferences of your shop.

Setting up your own machining preferences and rules in the CAM system not only reduces the time it takes to generate programs, it also streamlines production because the approach to machining every part is predictable and consistent. Machine operators can rely on the fact that each job will be machined in a predictable manner regardless of who did the programming.

Feature-Based Technology Gives You More Power with KBM

Feature-based technology allows CAM programs to utilize the greatest amount of capabilities with knowledge-based machining. First of all, features define shape. They define the machinable faces of the part, the size and shape of pockets, slots, bosses, and grooves, the location and types of holes, and so on. Features also describe more detailed information such as whether those shapes have chamfered or rounded edges.

Updating a feature, which is as simple as changing one or more individual parameters, automatically updates all associated operations. Features give you the ability to think about and view the entire part at a higher level. When knowledge-based machining is combined with feature-based machining, CNC programming becomes virtually automatic.

Building Intelligence into a CAM System

Knowledge-based machining, combined with feature-based machining, provides a high level of automation that is flexible to design changes and a wide range of parts. When the physical properties of a part model are defined by a set of features, the CAM system uses its intelligence to analyze individual features and their relationship to one another.

With a good CAM system, automation is not just occurring within individual features. Automation of machining processes is also occurring between all of the features that make up a part, resulting in toolpath optimization. As you create features, the CAM system constructs a process plan for you. Operations are ordered based on a system analysis to reduce tool changes, rapid distance, and the number of tools used.

Knowledge-based and feature-based machining has many advantages:

  • Dramatically shorter part programming time
  • Part revisions do not require reprogramming
  • NC code is consistent and predictable regardless of the CNC programmer
  • Tools are optimized and tool changes reduced
  • Toolpath is automatically optimized for faster machining
 

One of the leaders in knowledge-based machining and a pioneer in the use of feature-based machining is FeatureCAM, by Engineering Geometry Systems. Intelligence is built into every level of FeatureCAM. By taking a look at the steps in programming a part with FeatureCAM, we can easily see the difference between true intelligent KBM and other methods.

Easy as 1, 2, 3

With FeatureCAM, the process of programming a part is reduced to three simple steps:

  1. Draw or import a part
  2. Identify features
  3. Simulate operations

You are Done!

FeatureCAM automatically performs the following:

  • Determines all rough and finish operations for the entire part
  • Selects the appropriate number of tools and tool sizes
  • Calculates feeds and speeds
  • Determines stepover and Z increments
  • Generates leads, plunging, and ramping moves
  • Generates toolpath
  • Creates NC code
 

All automation is produced per user specifications and preferences.

Compare this with the steps required by process-based or operations-based CAM systems:

Operations-Based CAM

Process-Based CAM
  1. Import or draw part.
  2. Select a Rough operation.
  3. Select rough boundary
  4. Select type of toolpath
  5. Select roughing tool
  6. Select feeds and speeds
  7. Select stepover and Z steps
  8. Select a Finish operation
  9. Select finish boundary
  10. Select type of toolpath
  11. Select a finishing tool
  12. Select stepover and Z steps
  13. Select feeds and speeds
  14. Click Simulation
  15. Create NC code
  1. Import or draw part.
  2. Identify features
  3. Select machining processes
  4. Click Simulation
  5. Create NC code

Are You Done? No.

You must analyze and verify:

  • Does the Process have the correct operations?
  • Does the Process use the correct size tools?
  • Are the correct feeds and speeds used?
  • Does the Process have the correct stepover and Z increments?

When evaluating a CAM system, look for software that adapts to the needs of users, offering a range of control from total push-button automation to full control over the machining process. Powerful and effective knowledge-based technology allows you – the user – to determine the amount of automation that is used.

Artificial Intelligence?

Although a number of CAM systems have implemented or are implementing KBM, the level of automation and input required from customers varies. A CAM system may require a high level of front-end effort by users to embed their machining practices and rules. Some may require computer programming skills and the setup of custom databases and perhaps spreadsheets before automation occurs. Since most manufacturers don’t have people with those skills in-house, they must hire outside consultants to set up automated machining processes at considerable cost.

When machining intelligence is already built into a CAM system, there is no need to develop your own automation processes. The structure, process rules, and databases already exist in the software, so the only thing you have to do is customize the automation to fit the needs of your own shop.

Knowledge-based machining should include:

  • Predefined machining rules that are adaptable to a user’s own machining preferences
  • A database of standard tools
  • A database of preprogrammed speeds and feeds
  • A database of standard materials
 

Truly intelligent CAM systems have:

  • NO requirement for users to create databases of standard machining data
  • NO library of static machining processes since operations are dynamically created
  • NO hand coding required before the NC program is sent to the machine
 

Taking KBM to the Next Level

An important factor of KBM is retaining the design knowledge and information already inherent in a CAD model and utilizing the power of that information. By forming partnerships, CAD and CAM developers work together to provide the highest level of integration between their products. Tighter CAD integration makes problems caused by data transfer a thing of the past.

Translation protocols like IGES and STEP merely transfer the part geometry, losing the features and intelligence already defined in a solid model. When design and NC programming are integrated, the design intelligence contained in a solid model is not “lost in translation.” For example, several native CAD file formats can be opened directly in FeatureCAM. These include SolidEdge, SolidWorks, SolidWorks Assemblies, AutoDesk Inventor, Pro/E, CATIA Version 4, and CATIA Version 5.

Automatic Feature Recognition

One revolutionary concept is the ability to machine a part directly from a CAD model. To this end, look for a CAM system with the ability to examine an imported CAD model and identify its features automatically. More importantly, look for a system that automatically identifies features correctly. Once these features are recognized, the CAM system can automatically create matching machinable features that contain the process for machining the entire part so that the CAM system can automatically generate the NC code.

When those machinable features are associative with the solid model, it is only a matter of importing the same CAD model after changes are made in order to automatically update the CAM features and generate new toolpath. There should be no need to reprogram the part when changes are made to the design. Design changes are inevitable, so a good CAM system should make it as easy as possible to accommodate those changes.

FeatureCAM’s AFR uses the design knowledge and information inherent in the CAD model to create fully associative machinable features and toolpath. Once a solid model is imported into FeatureCAM, you simply click the AFR button to recognize the CAD features and automatically create all the 2D machinable features in the part and generate the NC code.

Since the machinable features are fully associative with the original solid model, importing the revised model prompts FeatureCAM to compare the original model with the revised one. A list of every feature displays along with whether that feature is new, unchanged, modified, or deleted. FeatureCAM is smart enough to leave the unchanged features alone. When features are revised, changes are made only to the specific machining parameters that are different from the original solid, such as the depth of a hole or pocket.

User-Defined Features

Feature-based CAM systems provide a standard set of machinable features using common shop terms such as slot, groove, pocket, hole, side, or face. To further improve automation and machining productivity, companies need to look for a CAM system that lets them develop their own sets of custom features along with specialized machining processes.

For example, many companies have one or more elaborate or unusual holes they frequently drill. Not only can a company reap the benefits of adding these custom holes to the library of standard features for easier selection, they can also associate custom drilling cycles with these features. Every aspect of an elaborate hole configuration can be combined into a single easy-to-use feature.

A user-defined feature (UDF) can define virtually any 3D shape along with associative machining parameters to suit a company’s own design and programming needs. UDFs result in faster, more consistent programming because programmers only need to manage a single feature for a complex shape and the same machining parameters are encoded into each UDF they create.

CAM Tomorrow

CAM software will continue to add to the depth and breadth of the machining intelligence inherent in the software until the CNC programming process becomes completely automatic. This is especially true for advanced multi-function machine tools that require a more flexible combination of machining operations. CAM software will continue to automate more and more of the redundant work in manufacturing that can be handled faster and more accurately by computers, while retaining the control that machinists need.

Ann Mazakas is president of Intelligent Creations, a technical information provider for the manufacturing industry.

For more information on FeatureCAM, please call 888-393-6455 or visit www.featurecam.com.