Computer-aided manufacturing (CAM) is the use of computer software to control machine tools and related machinery in the manufacturing of workpieces.
Traditionally, CAM has been considered as a numerical control (NC) programming tool, wherein two-dimensional (2-D) or three-dimensional (3-D) models of components generated in CAD software are used to generate G-code to drive computer numerically controlled (CNC) machine tools. The marriage of CAM software and control systems is critical to the successful implementation of any CNC machine.

An application for machining 'sheet' goods (metal plates, plastic sheets, thin woods, leather, glass etc.) should handle materials and sheets, it should be able to handle intricate Cutting Layouts, automatically place them on the sheet making optimal use of the raw material, permit manual intervention by the user regarding the best placement of the cutting layouts, generate the required code for inside and outside contours, pockets and drilling cycles, make any printouts needed by the operator and lastly but not least, make everything fast and keep records of the jobs done to be able to repeat them at any time in the future.

Photo: Plate Configuration

A reliable CAM software should allow the nesting of parts and have features for copying, duplicating, rotating to angles of any degrees and mirroring parts to cut wastage to the minimum. It should also allow for parts to be aligned perfectly along the machine axes by automatically aligning the drawing to the actual part.

Photo: Part Import

CAM is a software program that must be judged as a whole: all of its functions are, more or less, equally important. It could, for example, take very good hand of autonesting of the parts in the plate, but we could never have to wait through this process for 20 minutes! Or, still worse, it is not permissible, having generated the G-Code on the fly, for us to find out, when the actual cutting job is well on the way, that cut quality is unacceptable! There is only one way to address CAM choice: We want it all, and we want it fast!

Photo: G-Code Generation

All modern CAMs take hand of manual or automatic placement (Auto-Nesting) of the parts to be cut. Generally they do the job, provided we do not have to wait too long for their automations to be implemented. Nevertheless, this is usually done at the expense of raw material and, sometimes, of the final product quality. The software that will do our job best is the one that also takes into consideration cost and cut quality factors. To reduce scrap to the minimum and improve the product quality our CAM, as far as Part placement is concerned, should also feature:

• Manual rotation of the placed Part in optional rotation steps (degrees)
• Part transfer and mirroring along optional axes
• Automatic nesting with built-in option for setting the rotation angle of a Part while the software is testing for its optimal placing
• Option for setting minimum Part to Part distance
• Setting minimum Part to Lead-In and Lead-Out distance
• Auto or Manual Search step
• Option to allow for Top Placement to save on raw materials

During the Auto-nesting process the imported parts are automatically arranged so that optimal use of the material is made; it is only logical that part placement starts from the top of the plate. This Top Placement is embodied into any software by default, and it is a good first step to most auto placement arrangements. Most of them, but not all! Sometimes the shape/size of the parts imported makes imperative that the Top Placement command be by-passed if we are to achieve optimal nesting results (and, aometimes, shorter Routing). This is why advanced programs are equipped with some “let-yourself-free-of-Top-Placement-command” button or check-box.

To explain the situation better, we have included the photo to the right; please click on it to enlarge. It shows two alternative auto-nesting layouts of a job, one with Top Placement activated (obviously with inferior results) and another one without Top Placement.

Depending on the type of the material, the thickness of the plate or even the cutting layout, we should sometimes be able to switch to "Random" to avoid overheating of the material and warping of the plate or the final products.

Photo: Checking the "Random" checkbox before setting the final Route

Sometimes we are obliged to change the Kerf just before having the final G-Code generated. If this correction cannot be materialised at this point, we should go many steps backwards wasting our time. Some restrictions, though, are imposed here: the manually configured Kerf cannot be wider than half the distance between two adjacent parts, and this is only logical, otherwise the cutting process would cut away part of the material of the actual profiles.

Photo: Option to Change Kerf before pressing the "Build CNC Code" button

After the generation and saving of the final CNC code by pressing some kind of “Build CNC Code” button there should be an option which, when activated, show on our screen the actual itinerary of the machine cutting head, in other words the actual cutting route. What we should get is the actual cutting job magnified, plate and parts in it, together with the programmed route. (Please enlarge photo) We could now zoom in and check the correctness of the code generated. Because layout details could easily be confused if shown together with the Routing path, the latter should get invisible, but not deleted; by deactivating this option routing should be restored, reactivating it the actual cut would be visible again.

Photo: Getting the actual cutting route

When the worksheet is thin, and the parts to be cut are large and with long sides, they risk bending and warping if left on their own; that is why we leave at intervals uncut tabs, so that they remain connected to the plate. Therefore, it is a useful feature if our programme could arrange for such gaps(tabs).

Photo: Add to Job Form, adding Gaps (Tabs), among others (Nos 12-13)

This option is useful when we have to cut very small objects. Due to their size, if we cut around the whole length of their perimetre, they detach from the plate and get lost among the scrap. An uncut tab keeps them attached to the mother-plate.

Photo: Add Tab (Cutting Gap) to a small object perimetre

This option manages to keep cut velocity constant when we deal with cutting layouts with angles, resulting in a high quality cut. The way to achieve this is to add an outer circle to our cutting path, as shown in the drawing to the right.

We must make clear, though, that Loops are not to be added to all corners. There are conditions to be followed every time, which should be taken into account by your CAM program.

Because it is here that the user can determine whether the machine will function as an engraver or a cutter (in the case your CAM drives a laser machine), whether Open Drawings can be imported and cut or even whether it is possible to Import Parts with sides which are not supposed to be cut; this happens in the cases we want to have common cuts, that is processing the edges of two adjoining parts with the same cut, with the purpose of saving material, cutting gas and time.

Photo: PLT Layer Creation in CorelDraw X3