Evaluating a Sheet Metal-Composite CAM System

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, latierrademisamores 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:

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.
What rotations a component will be constrained to, if any (usually because the material has a grain, such as brushed stainless or composite fabrics)
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
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.
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
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. 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.

We are now in a position to generate NC code, however programmers will often want to simulate the job prior to running it on the machine. On a capable CAM system, simulation will show exactly what will happen when the nest is run on the machine tool. A large amount of time and money can be saved by graphically simulating the machining process, and identifying any possible problems, such as a component being cut/punched/unloaded incorrectly, wrong machining sequences specified, etc. Simulation gives the CNC programmer a great deal of confidence, assuring that when the operator presses the Green Start button on the machine tool, he is not going to have any major disasters.

Once we are satisfied with the simulation, a CNC program for the machine can be generated. This is normally done by a special module in the CAM system, which takes the ‘generic’ machining data stored in the CAM system’s database for a particular nest and converts it to CNC program instructions a particular machine tool will ‘understand’. This is referred to as ‘post processing’ and the module is usually called ‘postprocessor’ (regardless whether it is an internal or external function to the CAM system). Just about every machine tool requires different instructions and to complicate the matter still further, each machine tool can offer a wide range of options such as complex loading/unloading systems, tapping attachments, labeling devices, etc. Additionally, there are so called ‘combination’ machines, which combine two or even three different machining technologies in one machine tool (ie. Punch/Laser or Punch/Right Angle Shear combinations, etc) and these can also have any or all special options, mentioned above. When you purchase your CAM system from and independent vendor, you will choose a postprocessor to match your machine. This is actually one of the most important aspects of a CAM system as without a well constructed postprocessor you will not get the best out of your machine. A postprocessor could be compared to a printer driver – taking your printed document and converting it to something that your printer can understand and produce. Ask the vendor for details of some of their existing customers that have the same machine tool so that you can find out their experiences. If the machine is new and no postprocessor exists, you will probably need to supply machine programming manual and other information to the CAM vendor in order to allow them to develop the required postprocessor for you.

When should an organization consider buying a new CAM system?

When a first machine tool is purchased – that beautiful piece of machinery just installed in your facility becomes an expensive ‘paper weight’ if you cannot feed it fast enough with reliable CNC programs! Most machine tool manufacturers offer some sort of CNC programming system with their machines. These may come from independent software vendors or may be developed by the machine manufacturer. The ones developed by machine manufacturers usually support only their own machine tools, so keep in mind that if you acquire such CAM system and you decide to buy another machine tool from another manufacturer in the future, your CAM system will not be compatible with it and you will need another one to program the new machine. In any case, it is always a good idea to compare offerings from other independent CAM system vendors when purchasing a machine tool.
When you are buying another machine tool and you have an existing CAM system or systems which cannot support it. In such cases it would be prudent to contemplate the replacement of the existing CAM system(s) with a single one which can support both of your machines and is also ‘future proof’ as much as possible.
If you organization has a collection of various CAM systems supporting a collection of various machine tools and you or somebody else in your organization finally decided to stop the unmanageable mess and waste of resources such situation creates and consolidate all the programming into one single CAM system.
If you want to improve production yield and minimize material wastage
If you desire to fully automate component ordering, nesting, CNC program generation and improve machine efficiency and loading
If you desire any combination of the above
‘Small, medium or large?’ The price point of software that you evaluate will be determined by the functionality and automation it offers. As with everything else, you get what you pay for. It is a fact that although CAM systems have impact on numerous areas of the business, many companies make the mistake of tasking the selection of CAM software to the CNC programming department alone. Ideally it should have sponsorship and final expenditure sign-off at board level, members of which should understand potential impact of it on the whole operation.
Which CAM system you should select depends very much on your company’s operation, machine tools in use and the quantities and mix of parts being produced. Materials you are processing and their prices also figure strongly in this evaluation.

There are numerous CAM systems available worldwide, offering various levels of functionality, but only few offer a range of levels from the fairly simple and inexpensive to full ‘no-hands’ automation. If you decide that your organization currently has no need for high functionality and automation and selects a lower level CAM system, make sure that it will grow with you. You may have only one simple machine tool today with limited programming needs, but in a year or two the situation may change and you suddenly realize that you need to program another machine or two that you just acquired, and that you need higher CAM functionality and automation to be able to cope with the potentially dramatically increased workload. At that time you may also decide that, as your material usage is increasing, you want the most effective automatic nesting to cash in on potential material savings. Because of this, you want to make sure now that the CAM system you select can be easily upgraded to high levels of functionality and automation and that it can effectively support any machine tool you may purchase in the future.

Take into account that should you be forced to change to a CAM system from different vendor sometimes in the future, your current component and nesting files and your technology databases will be most likely incompatible with the new CAM system and you will have to start all over again. Also, should you end up having (or perhaps already have) two or more programming systems supporting different machine tools, you will not only significantly increase your CNC programming overheads, but also limit the flexibility of your production department, as quick changes of jobs between machines become difficult and keeping track of revisions/modifications to components become a nightmare, since numerous copies of same components will reside on a number of different CAM systems… Questions to analyze:

How many machine tools do we need to program? Will one or two seats (licenses) of a particular CAM software be sufficient to program machine(s) we have or do we need more than that? The answer to this question will very much depend on the level of automation and functionality you select for your new CAM system, but remember that more seats (licenses) also require more personnel to operate them. It is a false economy to save x amount of cash not buying advanced automation where available, if you then spend two, three times as much on personnel salaries within the first 12 months!
Should we replace existing CAM systems programming other machines within our facility to consolidate programming of all machine tools into one system?
Does the vendor have postprocessors for all of our machines and if not, are they capable to develop the ones they do not have?
How easy is it to get information in and out of the system (such as CAD files, reporting etc)?
If we need more than one seat (license) of the software, do we need them to all run concurrently? (Some vendors offer ‘floating licenses’ which allow a set number of users to work with the system simultaneously)
What type of parts are we nesting? Do we need automatic nesting, and if so do we need rectangular or free form? How important is nesting efficiency? Are we cutting now or in the future expensive materials, ie. composites?
How much automation do we require? Can the CAM system we are evaluating be integrated with our MRP system? Can our MRP system supply the CAM system with component orders automatically? Can the CAM system receive such automatic ordering and report back to MRP current status? Would we like the CAM system to run and execute component orders and program machines unattended?
Like many industries the CAM business has a vast array of acronyms and terms to describe functionality. Whilst there will be features that you know you definitely will need, do not get too bogged down in creating a features list. Concentrate on the end goal – accurate and efficient CNC programs to drive your machines, with the minimum amount of effort required to generate it. What you are prepared to pay (specifically in regards to automation) will essentially dictate the level of effort that will be required. Low cost systems might generate accurate NC code but it may not be optimised to run quickly on the machine, may waste material through inefficient nests and may be cumbersome to use. Automation may come at a price, but the savings quickly m

Leave a Reply

Your email address will not be published. Required fields are marked *