• Evaluation of CAM package

To Evaluate cam package one has to have be very clear understanding of his CNC machine. Here CNC machine addressed by normal CAM packages are

(a) CNC Milling and Machining Centers
(b) CNC Lathe and Turning Centers
(c) CNC Turret punch pressers
(d) CNC Wire EDM Machines

Important thing to understand is how many axes my machine has and how many can be moved simultaneously. This depends upon base mechanical and electrical structure of Machine. This will also govern type of operations can be performed on the machine.

(1) One axis cutting and 2 axis positioning will be for locating drill positions.
(2) 2 axis cutting and 1 axis position
(3) Normal profiling or contouring operations pocketing (being irregular area removal). In this case objective is to plunge in Z-axis. And then cut in XY axis.
(4) 3-axis cutting: Here interpolation of Ron point to point and continuos simultaneous XY movement exists. This is required in typical mould making industry.
(5) 2 to 3 axis cutting and 4th axis indexing typical jobs like gearbox crankcase required operation to be performed on various angled faces. Normally horizontal machining centers are preferred for the operations.
(6) Simultaneous linear (2 axis) and rotary (1 axis). To generate drum cams such movement is required. In this case rotary axis should rotate continuously.
(7) Simultaneous linear 2 to 3 axis and rotary (2 axis). This machine refereed as 5 axis machining which required for cutting turbine blades, impellers and such complex shapes. As such 5 axis machine has varieties like Table-Head, Table - Table and Head- Head rotations.
(8) Turning centers are for revolving parts like round bottle and designated as XZ axis milling captive. As such some turning machine have 2 axis milling capacity either for drilling peripheral holes or for slotting operations, this normally referred as 'C' axis.
(9) Wire EDM machine normally has 2 axis (X, Y) straight cuts, or with uniform taper angle (Q) with or without iso radii. Advanced 4 axis machine support different profiles at top and bottom.
(10) CNC Turret Punch Presses are for sheet metal up to 4-mm thickness. It support special cycles for punching and nibbling. As such the functioning is similar to 2 axis milling m/c.
(11) There can be CNC spark, CNC grinding machines are available, they are low in volume and it supports special purpose cycles.

Normally when we refer CAM package people assumed that it would be of multi-purposes and take care of their all machines as seen above understanding of CNC m/c is first step.

After understanding our application one can look for following factors:

(a) Whether required cam suits his requirement e.g For Mass Production, the software should support subroutines. It should generate program from wire frame (No need to have surface and solids for this). On other hand mould dies application should buy software which has various types of toolpaths and 5-axis may required very high end sophisticated software.
(b) Whether CAM package is self sufficient to create requisite geometry for machining. At the same time how good the software to translate geometry from other package.
(c) Whether it generates 100% codes required for my controller. The terminology used for this is post processor, which depends upon type of CNC m/c controller and typical procedure followed in that particular industry. Software should be flexible to accommodate changes required for this. This saves time on directly editing on Control Panel.
(d) Data transfer : Software should take care of downloading NC code generated by an computer
(e) Reverse Post: Many industries have legacy data, developed NC codes manually for years together and after that purchased CAM software. Here main objective would be to convert existing NC codes to cutter location file of software, which will show tool movements and also can be used to convert the NC programs to other controller language.

Surface modeling Vs Solid modeling

Confused ! What is there in a surface or solid, as long as my application is fulfilled ? In software, a lot of Buzz words and jargons are used, ultimately a software is just a mathematical tool, which helps us in doing our activities at efficient way. How powerful the tool is determines the increase in efficiency resulting in accurate (quality) and timely result.

Surface normally is referred as an extension of area-surface in 3 dimensional space. It is fitment of cover, which is spread on a skeleton of 2D and 3D curves.

Surfaces are classified in two ways:

(a) Application specific, Depending upon Input information of oriented curves is available, surfaces can be coons, loft, swept mesh of curves, revolutionary etc. This terminology also can be changed from computer software to software.
(b) Mathematical representation: Between given curves surfaces can be fitted by various mathematical equations, there are linear, parabolic, cubic equations. Higher the order of the equation are accurate its representation. Here care has to be taken to select optimum order equation in the sense it is always better to fit line (liner equation) between 2 points instead of putting spline (higher order equation)

Solids normally are referred to as a geometrical model, which has bounded volume. Say cube of size 10 mm consists volume of 1000 mm3. Also cube contains 6 surfaces with 12 edges. Initially when solid modeling concept has launched it used to only refer primitives (easy to defined objects like cylinder, cube, sphere, cone etc.) Presently even complex shapes (surfaces) having common edges making closed boundary is also referred as a solid. Hence now a days boundary between surface and solid is very faint, people represent surface is solid with zero thickness hence doesn't have volume (third dimension for volume)

Solids normally represented by two mathematical ways:

(a) Constructive solid geometry (CSG): Entire volumetric information is stored.
(b) Boundary representation (B-rep): Here information of only boundaries bounding individual faces (surfaces) is stored.
(c) From application point of view solids are used when information of mass properties like volume, weight, center of gravity, moment of inertia is required. Hence solids are mainly used in product design, analysis and assembly application

Here is a simpler way to explain the difference. If you draw a circle, and extrude the surface area, the end result will be a solid cylinder, with properties such as mass, Moment of Inertia, volume etc.. This is an example of solid modeling. Now instead, if you just extrude the circumference of the circle, the result will be a hollow cylinder, without any wall thickness. This is an example of surface modeling.

In case of machining (NC code generation) one is only interested in area that can be machined from particular coordinate system, hence surface information is enough. Since machining requires say outside entry direction, some times surfaces are to be extended. In this case if we use solids, common edge condition is violated and it is better to use surfaces for modeling. Hence, most of the CAM software are predominantly surface modelers. However, considering the need of the hour, some of the High end CAM packages too, now allow solid modeling features.

With latest technology surfaces can be considered as a subset of solids. Surfaces can be considered as building blocks for solids at the same time solid can be used to extract surfaces.

In case of applications where models have to be created and used in assemblies and mechanisms or have to be analyzed for stress- strain and other properties, solid modeling is mainly used.

Surface modelers normally have more functionality for extremely complex surfacing features, allowing NURBS Geometry etc.. Comparatively, solid modeling allows lesser flexibility due to the structure in which it works.

There are a number of Solid modeling and surface modeling software available today. Many of them allow only one type of modeling, i.e either only surface or only solids. However, some high end software support hybrid modeling, thus allowing you to work with solids and surfaces in the same model.

Still confused ! A little advise- Use software from maximum utilization (Implementation) point of view. A hybrid modeler will allow you to work with a variety of applications.

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