Solid Machining Making the move to
Solid Based Machining
Steve Sivitter, CEO
Pathtrace Systems, Inc.


Introduction

There has been a steady growth in the use of solid based Computer Aided Manufacturing (CAM) systems over the past few years. But what is solid based machining and why are many manufacturing companies, both large and small, making the move to solids? 

The manufacturing industry has changed significantly over the last 20 years through developments in computer technology. Component design has moved from the drawing board onto computer and has evolved from the creation of 2D wireframe geometry to solid model design. On the shop floor manual milling machines and
lathes have given way to CNC machining centres and CNC mill/turn lathes, requiring complex, CAM driven, CNC part programs.

During this time CAM software developers have had to keep up with the changing needs of these new CNC machine tool types, while at the same time realising, and leveraging, the benefits that each improvement in CAD provides to the CAM user, both in quality and in efficiency.

In the past, the use of solid modelling for the design of component parts and the creation of assemblies to represent a complete model of a product was only for the large corporations, such as those in the aerospace and automotive sectors. Today however, solid modelling is available and affordable to everyone.

The same holds true for solid based machining. There are many affordable and easy-to-use packages available which should be considered as essential in order for a manufacturing company to stay competitive.

Staying competitive

So what is solid based machining, how does it help to make a manufacturing business more competitive and what is required for its successful implementation?

In a nutshell, the key benefit of effective solid based machining is speed of NC programming. The ability to directly load the solid model and extract feature information from it, with an associative link back to the original model to monitor for design changes streamlines the production process. Modified parts can be reloaded with toolpaths automatically updated in line with changes, significantly reducing time-to-manufacture.

Manufacturing companies are being put under continued pressure to reduce costs and time to market. One solution to this is for the production engineering process to take place concurrently with design. This not only reduces the development lead time of parts into production, but also helps to foster a design for manufacture environment in which parts are designed with the manufacturing process taken into consideration. This provides for a reduced manufacturing part cost while maintaining the level of quality required by the design intent.

The main obstacle to concurrent working has been the production engineers inability to easily update CNC part programmes in line with the inevitable design changes that take place in a dynamic concurrent environment, without significant impact on the critical lead time.

CAD/CAM integration provides the link required to improve co-operation and collaboration between these two areas of the manufacturing cycle. The direct loading of solid models into CAM and the associative link back to the original design is the main element that facilitates this collaboration and cooperation between design and manufacture. The benefit of this is, of course, a reduction in design-to-manufacture time.

Information about features within the solid model can be used within CAM systems, incorporating knowledge and feature based functionality to provide a reduction in programming time. Knowledge of proven manufacturing methodology relative to feature types can be stored for use on subsequent parts. Identification of similar features on new parts can see the re-use of this knowledge to automatically provide best practice proven toolpaths.

The implementation of a solid machining CAM system can seem daunting a move into the unknown, requiring capital outlay, training of personnel and an inevitable amount of disruption during the transition period.

But we must also remember it isnt practical to transfer all of your wireframe and surface CAD models into solids. Consequently, any solid based CAM solution must be able to handle your legacy data. This capability will allow you to gently transition between your current CAM methodology and solids.

All these issues are real, as with implementing any new process, but should be put in perspective measured against the benefits that will ultimately be achieved.

Making the move to solids

By looking at what is required for a fully integrated solid based machining system and identifying what is required from each of them, this process can be made easier.

The three main elements are:

A solid CAD modelling system.
The ability to import the data contained within the model into the CAM system with no need for translation.
A CAM system that uses the inherent intelligence and functionality within the solid model.

With effective training of staff, all of this will result in a successful implementation and optimum results with the new software.

Define a solid model

The rapid advance in CAD design technology may have created confusion over the difference between the main three model types: wireframe, surfaces and solids. To help understand the difference between them and why solid models provide advantages to the manufacturing process above that of either wireframe or surface models, let us look at the information that can be extracted from each of these for use within manufacturing:

Wireframe parts are constructed in either 2D or 3D, through a combination of curves and lines. The shape that is created has no intelligence or features; it has neither surfaces nor volume.

Surface parts are a collection of trimmed surfaces that envelope a volume. These parts give a true visual representation within CAD of the part that is required. The part is however, just a collection of surfaces; features such as pockets, bosses and holes although visually present, contain no intelligence.

Solid models are built from features typically holes, pockets, slots, bosses, and contain all the geometric information about size and shape. A good solid based CAM solution will immediately recognize the feature and its parameters upon loading the model.

Utilising the intelligence

When a solid model is created, it is important that none of the data representing the design intent is lost through the transferral process to CAM, and that subsequent changes to the design model will be automatically identified.

Translation of the data using a format such as IGES changes the solid with all the feature knowledge that this possesses, into a surface part with no intelligence at all. Worse still, the surfaces that have been created may well have errors created by the translation process, producing gaps at intersecting surfaces. The manual creation of a part into a translated format has also broken the link between the design model and CAM. Any changes made to the design model will not be recognised by CAM.

It is obvious then, that in order to ensure no errors occur, there should be no data translation. The alternative and most successful method is to use a CAM system that has a CAD modelling kernel embedded within it. This not only removes the need for translation, but also the data used within CAM is associatively linked back to the native CAD model. The ability of the CAM software to link directly to the design model and track changes enables the CAM system to recognise changes to the solid model throughout its life cycle.

An alternative solution is to use a CAM system based inside your CAD system. This obviously removes any issues with data translation. Unfortunately it has a few disadvantages:

It is usually unable to handle legacy data
You need a license for the CAD system in your manufacturing environment.
The user interface is based around a designers requirements.
Due to the user interface the CAM system is normally limited in its capability.

In summary, a good stand-alone solid machining CAM system with a CAD modelling kernel will be the best solution. It should be able to load parts, assemblies of parts, thread information and in the future feature tolerances.

Intelligent CAM

Once the part is loaded into the CAM system, it can be interrogated to identify the features, pockets and holes for example, which are to be machined.

Toolpaths can then be produced in a conventional way, selecting the cutting tool, toolpath type and boundary of the feature to be machined. Alternatively, knowledge or rules based manufacturing processes can be applied in a one button click process. This process extracts information about features, reducing or removing the need for the manual input of parameters during the toolpath generation process. Knowledge of best practice is stored within templates, therefore automatic identification of this type of feature will trigger the use of this knowledge template and the toolpath will automatically be generated.

For example, a hole feature that is tapped and counter bored will be identified within solid based CAM not just as a collection of shapes, but as a hole feature including attributes relating to the thread such as pitch and core drill size. This information will be used to produce toolpaths to spot drill, tap drill, tap and counter bore as required. Not only is this programming process extremely quick, but owing to the associativity of the toolpaths to the design model, if these holes features were to change, the toolpaths would automatically be updated in line with the changes.

Dispelling the myths

The amount of information that can be attached to a solid model, such as material type, geometric tolerances and surface finish of features is constantly improving. With each new piece of information included within the CAD model, solid based CAM is developing tools and techniques to use this new information. The resulting benefits can be seen in a reduction in process development lead time and improved quality through the use of proven capable repeatable processes.

This process of information definition within CAD and information retrieval within CAM is continually developing and improving. Utilising the intelligence/knowledge held within the solid model, CAM systems will continue to make programming of components as efficient as possible.

There are, however, a number of limitations and myths about what can be achieved with CAD/CAM. These should be addressed in order to help understand the reality of where we are today and to help set realistic expectations regarding solid based machining.

Lets take a look at the following statements Ive heard regarding CAM systems:

The part will automatically program itself. New toolpaths will automatically be created if new features are added to the design. All toolpaths will automatically modify in line with design changes.

These statements are close to what is currently possible, but in general a level of manual intervention is still required in the programming of all parts. Decisions on machine selection, fixturing, material size and the order in which operations are to be performed are all parts of the production engineering process that require skilled manual intervention. A new feature added to a part may automatically have a toolpath created for it. However the addition of this feature should not be taken in isolation. Its impact on the manufacturing process may be significant, causing a change in fixturing, tooling or order of operations.

For this reason it is the intelligence within the system that should dictate what level of updating will take place. It is this level of intelligence which is constantly being improved upon in order to deliver better and better solutions to the challenge of automatic updating of part modifications. For example, if a pocket profile moves, it is reasonable for the toolpath to update. If the profile changes with the addition of an arc it will update correctly if the arc is bigger than the tool. If the arc is smaller than the tool, the toolpath will update but a new tool will have to be selected.

Conclusion

So, with all the benefits of solids based machining, why isnt everyone using it? Even some of the companies who already use solid based CAD havent made the move. Not only they, but also companies whose customers model in CAD, seem reluctant to make the transition.

The introduction of any new technology is always of concern to a business. The level of disruption during implementation can in some cases deter the implementation from taking place. This should not be the case with the introduction of solid based machining.

If a company already has a need to produce CNC programmes then the speed at which these can be produced using solid based CAD/CAM will very quickly compensate for any short term loss in productivity during the transition process. The primary consideration for the selection of a solid machining CAM system should be based upon the level of associativity with the solid CAD models that require programming. Other considerations should be the commitment of the CAM provider to further develop knowledge based tools and associativity with the CAD solution.

While developments in CAD and CAM have evolved together over time, the relationship between the providers of these two complementing technologies has remained on the whole independent. The providers of CAM solutions generally prefer a CAD neutral partnership environment that enables manufacturing companies to select the best match of CAD and CAM solution to fit their specific needs. This allows for many different scenarios of application. For example, designs being manufactured in-house by a specific CAD solution or supplied to sub-contracting companies by multiple customers using different CAD solutions.

Solid based CAM systems are producing good results today with respect to the speed at which parts are programmed. With the recent introduction of best practice based techniques to ensuring high quality and reliable repeatability, together with an associative link to the original design model the opportunities for automation increase.

Can anyone afford not to make the move?

-ends-

For more information contact:
Pat Gralinska
Ambo Technologies
1866 471 2626
pat@ambotech.com

About Pathtrace

Pathtrace Engineering Systems is a division of Pathtrace plc. Pathtrace Systems Inc. is a wholly owned subsidiary. Offices are also established in China and Japan, complementing a worldwide network of resellers.

Pathtrace Engineering Systems is the developer of EdgeCAM an extremely powerful, but easy to use software solution devoted to automating the process of NC programming for metal cutting machine tools. For information about Pathtrace and EdgeCAM visit our website http://www.edgecam.com/. EdgeCAM is Windows 2000
Professional and XP compliant and has over 28,000 users worldwide.