Multiaxis CNC Machine Machine simulation can go a long way into improving part quality and productivity. By Karlo Apro, product marketing, technical manager at CNC Software, Tolland, CT USA
Multiaxis CNC Machine equipment has the potential to improve accuracy and reduce machine cycles even for geometrically complex work. However, to take full advantage of this potential, the shop has to move outside of its comfort zone and use equipment aggressively. Because this increases the potential for catastrophic interferences and collisions, the user may back off and use the equipment conservatively, defeating its purpose.
This article will explain how machine simulation can help multiaxis users achieve superior results that are both safe and highly efficient and then move on to creative uses that provide unique competitive advantages.
Multiaxis CNC Machine simulation provides you with additional layers of visualisation so that you can zoom in and zoom out at will to observe everything that will happen during your machining process.
You can move the simulation along very quickly in program segments where you are certain that the part, tool, holder fixtures, and peripheral devices (eg: robots) are in no danger of colliding. When everything is happening in a confined space, you can slow the simulation down to observe these interrelated movements in slow motion or step through them in block fashion.
Eliminate On-Machine Programming & Proofing
There are still many five-axis CNC users who program parts at the machine and then single-step through the program to make the first piece or cut a test part using a foam workpiece.
Another old school trick is to replace the cutting tool with a pipe cleaner and run the program on a finished part. Then, an experienced programmer will spend hours or even days watching close calls with the pipe cleaner and altering the program to avoid them. This is a tremendous waste of spindle time and programming time.
One user we know of spent an average of 10 hours creating programs at the machine. Today, he uses Mastercam with five-axis machine simulation. He can create programs and simulate comparable first piece programs in an hour. This gives him nine additional hours for programming, frees up the machine for 10 additional hours of machining time, and allows a qualified operator to set up and attend more than one machine on the shop floor.
Improve Part Quality
Simultaneous five-axis motion allows you to reach areas that would be either impossible or very inefficient to reach with traditional methods. The drawback is that when you move the machine in the continuous five-axis mode, the rotary brakes must be off.
The Multiaxis CNC Machine is running in the ‘loose’ mode. To minimise the error unavoidably generated in this mode of operation, it is essential to position the workpiece in the machine’s sweet spot.
The sweet spot is a location near the centre of the machining envelope where the shortest possible tool can be employed to reach all of the areas that require machining with axis movements that are as close as possible to the centre of their range of travel.
You accomplish this by creating the tool paths and then simulating them at various locations until you arrive at the ‘happy place’ where tool movements are tightly choreographed (minimal air cutting), well-supported and all potential interferences have been detected and avoided.
When simulating five-axis tool paths, these are the rule of thumb that allows you to quickly achieve the most important quality and safety improvements:
- Minimise and control all motion.
- Consider every element of the cutting process.
- Keep the tool as short as possible.
- Design fixtures that allow minimum distance between the workpiece and the machine’s rotary centre point.
- Eliminate air cutting. (Special tools are available within the simulation software to facilitate this.)
- Avoid collisions at any cost.
Expand Multiaxis Capabilities
When newcomers think about multiaxis machining, their minds often jump to the manufacturing of complex geometries like blisks and impellers. These are, in fact, very complex examples of five-axis work and only a small percentage of five-axis users actually make parts like these. There is actually a long list of multiaxis CNC capabilities ranging from simple four-axis contouring to continuous five-axis machining of complex geometries.
Whenever possible, gain experience on the simpler multiaxis machining strategies using machine simulation as a learning and training tool. Once you become proficient in a relatively straightforward multiaxis machining application, move on to something a little more difficult.
If you are proficient in three-axis programming, it is fairly simple to move into single setup three + two programs using the multiaxis system to index the part to the correct coordinates for the next machine operation.
Indexing the part on a multiaxis machine (with the confidence the clearances have been checked via machine simulation) is vastly more productive than changing setups for multiple operations on a three-axis machine.
With this sequential approach to growing your five-axis expertise, your equipment will be paying for itself in very short order.
Get Creative & Achieve Competitive Advantages
Machine simulation will assure the safety of your manufacturing process. Then you can move beyond safety to achieve the big payoffs resulting from your enhanced manufacturing efficiency and creativity. Here are some examples.
- Try out the same job on multiple machines.
- Accurately estimate multiaxis machine time for complex parts.
- Grow unattended machining capabilities.
- Achieve higher machining density.
- Integrate machine simulation with iterative design processes.
- Experiment with advanced machining strategies away from the machine.
- Provide faster turns on short-run and prototype parts.
- Respond faster to new program and market opportunities.
- Present multiaxis machining capabilities to your customers.
Important Multiaxis Preliminaries
Before a shop can enjoy the many benefits of machine simulation and advanced CAM software for multiaxis machining, a number of steps must be taken. These steps will assure that the types of simulation chosen are most appropriate and that the results generated via the simulation process will be accurate and trustworthy.
1. Choose between CAM (intermediate code) and G-code simulation
There are two types of machine simulation:
CAM Simulation (such as Mastercam’s Machine Simulation) examines the intermediate code generated by the CAM software in combination with a CAD model of the machine and associated tooling to generate the various components of the machine motion.
G-code Simulation (eg: Vericut from CGTech) uses the actual G-code generated by the postprocessor and detailed machine models including kinematics to generate an ultra-high-resolution simulation of the manufacturing process.
CAM-based machine simulation does not cost a lot and it is easy to implement and use. It can be very effective most of the time. However, since it does not work from the G-code (which is the form of instructions the machine actually operates from) and does not incorporate machine kinematics, CAM simulation is not as accurate or as reliable as G-code simulation.
2. Build your virtual machine carefully
If you are going to use CAM simulation, then you will need to create a model of your machines within the CAM software. Although this may sound like a daunting prospect, creating the machine model is usually quite straightforward.
Mastercam makes it easier by providing a library of generic multiaxis CNC machines, which can be used as a template for developing the model from your specific machine. Modelling involves inputting specific dimensions taken directly from the machine or from the OEM’s literature. G-code simulation involves a much more extensive modelling process, which is typically done by the software provider.
3. Resolve post processor issues
The post-processor is an intermediate software that translates code generated by the CAM software into G and M code that is understood by a specific CNC machine. CAM software is shipped with generic post processors that must be tweaked to satisfy a myriad of machine-specific options.
The user can optimise his post processor so that his machine will behave as desired (and provide accurate simulations) by working through the documentation provided by the post-processor vendor and activating or deactivating various ‘switches’ in the post. Or it may be faster and more satisfying in the long run to hire an expert to install and clean up the posts.
4. Get training
For those making the transition from 3D to five-axis programming with little or no five-axis experience, just a little training can go a long way to establishing a far more productive mindset.
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