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You can have the fastest engine strapped to the leanest, lightest chassis, but replace proper tyres with wheels from a shopping trolley and you’ll end up going nowhere fast. The same analogy applies to the relationship between a CNC machine tool and the software that programs it. More specifically, the requirements placed on the software will dramatically change based upon the machine technology in use – now and in the future. So what should you be looking for in a CAM system and how can it improve the efficiency of your machine, your work force and your material utilization?

 

CAM systems are used to take electronic part drawings (CAD files), process and ‘nest’ them onto sheets or rolls of material and convert the resulting nesting layouts to a series of coordinates and machining instructions, known as CNC programs so that the part can be accurately and effectively machined on a specific machine tool. The resulting code is sent electronically to the machine tool, ready for machining. These CNC programs are very specific to each particular CNC machine technology and machine  controller.

There are several stages to creating a CNC program, starting with the definition (drawing) of component geometry if CAD facilities in CAM system are being used, or with importing and ‘healing’ of component geometry which was created in an external CAD or unfolding software. Once the correct component geometry is available within the CAM system, tooling and/or profiling/cutting information needs to be added. Depending on the CAM system in use, this can be done interactively, automatically or in some combination of both. This information differs from machine to machine and across machine tool technologies in use.

Once all of the machining information has been applied to components the next task is to ‘nest’ them – squeezing as many components on the sheet or a roll of given size as possible. A nest might consist of the same parts or a mixture of different parts, and can be classified as either rectangular or ‘free form’ (true shape). Rectangular nesting, as the name suggests nests each component as if it were a rectangle, which will result in a significant waste of material if you are cutting many irregular shapes. With rectangular nesting parts may be nested at different angles, but are usually nested at 0 and 90 degrees. Free form nesting offers the best material yield by being able to nest parts at any angle and also taking advantage of any scrap material within larger components, such as cut-outs, etc. Depending on the level of automation within a particular CAM system, the placements of parts will either be a manual or automatic process (or could be a combination of the two). Manual nesting for dissimilar components is often performed by dragging and dropping parts on the nest, also known as bump nesting. Unless the operator is very skilled, this process can result in significant material waste, and in any case is invariably a very slow process. Because of this, many companies currently produce so called ‘static’ nests, which were created manually and are regularly re-used. The problem with this is that all of the parts will be produced each time a particular nest is run on the machine, regardless of whether they are all needed or not. ‘Dynamic automatic nesting’ on the other hand allows for unique nests to be created as and when required, providing a ‘Just In Time’ approach whilst retaining high material efficiency. This of course is especially important when processing expensive materials.

A reasonable CAM system should, among others, allow you to also consider:

  1. How parts will be unloaded – depending on machine technology and part size, parts may be unloaded through a part chute (‘trap door‘), cut off by a right angle shear attachment, micro-tagged to keep them in place whilst on the machine and manually removing them afterwards, picked by a robot arm or a special unloader, etc.
  2. What rotations a component will be constrained to, if any (usually because the material has a grain, such as brushed stainless or composite fabrics)
  3. Heat avoidance – when cutting thicker materials, heat can build up when cutting more intricate areas. In these instances the user or the system must be able to specify cutting path which will prevent excessive heat build up by cutting elsewhere on the sheet until such area has sufficiently cooled
  4. Whether common line cutting should be used between parts on the nest or a sheet ‘skeleton’ between parts will be left. There is a number of considerations dictating this, such as the price of material, sheet thickness and its resulting integrity, machine technology in use (moving or stationary sheet), etc.
  5. Clustering components together, ’broken orders’ – for one reason or another, you may identify a need to group certain parts together on a single sheet as much as possible and a good auto nesting facility will allow you to do this easily
  6. Nesting flexibility – many free form nesting modules will run their single nesting algorithm once, producing not so spectacular results, whereas others will run through various nesting algorithms and can be set to run for a desired period of time from few seconds to say overnight, to deliver the best possible material yield

Some systems will intelligently ‘learn’ your preferred tool placement settings as you continue to apply tooling, quickly becoming self-sufficient.

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At this point we now have our nest with all of the cutting information applied; however there is another important consideration that has a significant impact on the cutting time – the sequence in which these instructions are processed. Sequencing can either be an interactive or automatic process and there can be a vast difference in the sequencing efficiency between various CAM systems.

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