Evaluating a CADCAM and Nesting system for composite material cutting
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 such as a composite knife cutter 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 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 system in use, this can be done interactively, automatically or in some combination of both. This information differs from machine to machine.
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:
- What rotations a component will be constrained to, if any (usually because the material has a grain)
- Whether common line cutting should be used between parts on the nest or a ‘skeleton’ between parts will be left. There are a number of considerations dictating this, such as the price of material, thickness and its resulting integrity etc
- Clustering components together, ’broken orders’ – for one reason or another, you may identify a need to group certain parts together as much as possible – 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 profiling settings as you continue to apply them, 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. A simulation will show exactly what will happen when the nest is run on the machine. 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 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 labeling devices, conveyor systems etc. When you purchase your CAM system from an 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 – it 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 have several CAM systems supporting various machine tools and you want to remove the 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 – 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 select depends very much on your company’s operation, machines in use and the quantities/mix of parts being produced. Materials you are processing and their prices also figure strongly in this evaluation.
There are numerous CAM systems available, offering various levels of functionality, but few offer a range of levels from the fairly simple and inexpensive to full ‘hands-off‘ 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 machine today with limited programming needs, but in a year the situation may change and you suddenly realize that you need to program other machines, and that you need higher CAM functionality and automation to be able to cope. At that time you may also decide that, as your material usage increases, 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 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 parts will reside on a number of different CAM systems…
Questions to analyze:
- How many machines do we need to program? Will one or two 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 licenses also require more personnel to operate them. It is a false economy to save money 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 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, i.e. 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?
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 them. What you are prepared to pay (specifically relating 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 mount up and can often easily be quantified, making what might seem like a steep investment much more palatable.
The process of evaluating a system
The key to an effective evaluation process is being able to demonstrate quantifiable savings in three key areas:
- Staff time, covering programming, reporting and anything else related to the CAM process
- Machine cycle time (also referred to as runtime)
- Material utilisation
All of the above have quantifiable costs. Before you even consider evaluating CAM systems you need to understand what those costs currently are. Man-hours are generally simple enough to cost, as are your machine run times and costs, although it is always a worthwhile exercise to follow a few jobs through all processes and note all costs associated with them. Material efficiency is not much more difficult to calculate if you look at it in terms of waste rather than output. Obviously, the lower the waste, the better off your company is and there are potentially huge savings to be made with the right software. Once you have a clear understanding of all the above, you are ready to move onto the next stage – the benchmark comparison.
Calculating your return on investment
By now you should have a clearer idea of what you need, so it’s time to start investigating the market. Recommendations are important, especially if they come from users that have the same machines as you. Once you have selected your vendors you need to arrange for a benchmark comparison. Provide each vendor with a series of parts in the form of DXF or IGES files, along with tooling and nesting parameters and ask them to perform the following:
- Demonstrate the process of interactively and (if applicable) automatically tooling the parts
- Demonstrate the process of interactively and (if applicable) automatically nesting the parts
- Demonstrate how easy it is to move parts or nests between machines (useful in the event of a machine breakdown)
- Provide the final nests and reports so that you can compare the efficiency against your own nests
- Demonstrate how information can be extracted from the system for reporting purposes so you can compare it with current methods of creating similar reports. See if additional beneficial information can be retrieved that may be unavailable using your current methods.
It is important to check and recheck the figures that you are provided with – do not take them on face value as it has been known for figures or nests to be doctored to make them appear more favourable. Check to ensure that no parts are overlapping on the nest or that they have not been rescaled slightly in order to fit a particularly complex nest. Check gaps between components and components and material edges. Due to each machine generally being uniquely configured it probably will not be possible for them to provide you with resulting CNC programs to check machine run time.
In addition to the savings that you can tally up there may be other benefits which might not be so easy to spot but that will help in providing a quicker return nonetheless. For example, more efficient nesting and the ability to produce complex dynamic nests quickly might allow you to standardise on fewer material sizes. Not only would this make stockholding simpler it can have a knock-on effect on your purchasing power. Once you have your set of figures it is then a simple process of adding them up and comparing old versus new. Take the difference and divide it by 52 (or your company’s number of working weeks). You now know to the week when your CAM system will have paid for itself!
Various CAM software approaches:
Some CAM systems will simply take component geometries, nest them and then apply tooling or cutting at the nest level. This saves the vendor significant development overheads, but there is a very significant drawback for users in employing this technique. Such systems cannot retain any information regarding machining of individual parts - any machining information added or modified on a particular component only exists on that particular nest and if you need to nest that same component in the future again, that machining information will have to be added/modified manually again. It is impossible to use such systems for reliable automation except for simple machining technologies where interactive modifications to the way a part is cut are never required.
Other CAM systems will store part machining information in a special component file together with component geometry, but this file may be required for each machine the user may want the part made on, and even for each different angular position of the component on a nest. This still complicates matters, as any revision of geometry or tooling may force modifications of many similar files, which is obviously time consuming and error prone. However, as the machining information is stored together with component geometry, there is no need for re-entering any of it when a component needs to be nested again.
The most capable CAM systems will utilize a combination of both methods to achieve the most flexible and efficient machine programming, while storing geometry and machining information in a single component file. In such systems, once programmed (either manually or automatically) a component file will store any important machining information for any angular position that a particular component is desired to be nested at (ie. 0, 90, 180, 270 degrees) and for any number of machines a user may be operating, ready for nesting at any time, at any angle, on any machine, without any human intervention. Depending on the machine tool selected, to finalize a nest, additional machining or modifications (ie. common line cuts, repositions etc.) may be added to the nest by the system automatically.
This means that if a particular machine breaks down, all unfinished component orders can be redirected to another machine and new nests created in seconds, whether manually or automatically. It also means that parts can be nested and produced ‘Just-in-Time’ on any machine at any time, based on the current machine loading, ideally keeping all the machines busy all the time.
Points to remember:
- Automation without high reliability is worse than no automation at all
- Lesser automation means more human resources are needed and the scope for mistakes is larger
- A well implemented reliable, highly automated and efficient CAM system will save any size company considerable amounts of money in material utilization, reduction in human resources, machine utilization and other areas
In evaluating a CAM system you should also ask:
- Is this product reliable, as there is no true automation without reliability? In general, the more support personnel vendor has, the less reliable and/or understandable their software will be. So if a salesman tells you that they have large support department to answer your calls, ask yourself why they are expecting your calls in the first place.
- Will it offer good support for all machine tools we have now and may acquire in the future? Is the software scalable so we can upgrade to support more machines, higher functionality or full automation in the future? Does this higher functionality and automation already exist and can it be demonstrated?
Other issues to consider:
- Installation - How much time, consultation and effort will be required to install and implement the CAM system, how much and for how long will it disturb your day-to-day operations? This varies dramatically between different products and vendors.
- Training - How much training is required before the CNC department is sufficiently proficient?
- Software Updates - how difficult is software update implementation? Is it as simple as inserting a CD into the drive and waiting a little while, or will it require support from the CAM vendor
- Update compatibility - will new updates be fully compatible with existing work files, technology databases and settings regardless from which to which version you are updating?
Reliable answers to many of these questions can only be obtained from existing users. So ask for references and talk to them. It may save you a lot of grief in the future.
Software rarely has the same perceived value associated with it as hardware – you cannot touch it, for example, so it is very easy to overlook the positive and negative effects that the right or wrong product can have on your business. Whether it’s your MRP system that’s gone down or your CAM system is causing problems it all boils down to the same thing – time and money. Over time visionary companies will all opt for reliable completely automated solutions to increase throughput and minimise overheads and waste. While the initial cost of automation has a perceived price and technological barrier a review of existing practices versus future savings can quickly identify this as false. Selecting the right CAM system to be a reliable and efficient unmanned interface between the order and the output is the key to this success.
About the Author/Company:
Martin Bailey is the Marketing Manager for JETCAM International, and is also the author of several marketing and technology sector books. JETCAM Expert is used in over 7000 locations worldwide and supports virtually all punching and cutting/profiling CNC machines in the sheet metal, aerospace/automotive and other industries.
For more information visit www.jetcam.com.