Despite the productivity benefits HSM (High Speed Machining) can offer, many manufacturers may be missing out because they are not using the correct CAM software. Katherine Crichton reports.
THERE IS no doubt that high speed machining (HSM) has revolutionised machining practices, offering manufacturers a viable alternative to EDM (electrical discharge machining) and other conventional processes.
However, despite investing tens of thousands of dollars into the technology and advances in machine tools and tooling, many manufacturers are failing to experience the true potential of HSM because they are not using the proper software.
This is a trend that Dennis Colusso, marketing director of Product Lifecycle Management Australasia (PLMA), says is surprisingly common, with software and the overall CAM package almost always left out of the HSM equation.
“When a company considers the purchase of a new machine, often they carefully investigate the machinery and cutting tools but are not getting the results they had anticipated because they cannot program the machines in a way that is suitable for HSM.
“Unfortunately, most of the information used to purchase this equipment is based on the machine specification alone. The cutting methods and other features of the CAM package do not get the same investigation because there are no set specs.”
Colusso says it’s very important to get a CAM package that can support HSM, but admits this can be difficult as there are very few software packages traditionally used in the CAM market that has this capability.
“The more complex the shape and the harder the material, the more important the approach to machining, requiring sophisticated cutting control.
“The methods that we consider in conventional machining are not adequate enough to cope with the higher speeds and feeds involved in HSM.
“Important machining aspects such as cutter deflection and breakage as well as surface finish and overall cost-effective cutting time also needs to be taken into account.
“If the software is not intelligent enough to cope with these additional demands, this leads to problems such as tool breakages, which always result in reduced productivity, the opposite of what HSM is meant to achieve,” Colusso told Manufacturers’ Monthly.
Tool breakages often result from exceeding a tool’s permissible loading conditions and Colusso explains that it is the peaks in the loading that is the number one cause of tool failure.
“Milling tool paths, for example, produce varying rates of material removal. In a typical high speed roughing path with depth of cut and stepover each equal to 10% of the tool diameter, the tool could see as much as 10 times its intended level of material removal when it first enters a channel, and as much as five times that level when it enters an interior corner.”
Colusso says a shop’s typical response to this kind of situation is to change the feed rate, depth of cut or stepover.
“Though reducing any of these values might bring the peak loading conditions back down below the threshold, this response will also reduce the metal removal rate of the tool path overall, greatly reducing productivity,” he said.
“The software needs to have the inherent features required for HSM, so these means constant metal removal and tool loading, requiring features such as trapizodal milling motions, auto feed correction and tool path optimisation, etc, along with machining strategies suitable for HSM.”
“In order for the software to perform these functions, it needs to be three dimensional, it needs to understand the model of not only what being made but also the material model – what is being removed.
“A 3D solid model deals with volumes so the software can know and start to predict what sort of loading will be put on the tool so it will slow down in corners and speed up again when it’s out of it,” he said.
Choosing the right package
As well as offering manufacturers the ability to eliminate processes such as polishing and to machine in hardened materials, according to Robert Simunic, business development manager with Camplex, the most important benefit a dedicated HSM package can offer; is confidence.
“Confidence that when their programmer loads a job onto the machine, the part will come off the machine to the correct size, with the right surface finish.
“A HSM style toolpath will run smoothly, minimising wear on the machine as well as costly maintenance bills,” he said.
Simunic advises that some of the functions a HSM specific package should include features such as roughing strategies designed to suit the machine tool.
“Some HSM machines prefer shallow cuts at a high feed rate, with the new developments in cutting technology allowing operators to use more traditional full depth cuts to achieve high metal removal rates. This needs to be supported by toolpathing methods (rounded cornering, smoothing of cutting passes, equalised stepovers, etc) which support smooth machine tool movement.
“Another function of the package should include a variety of finishing toolpathing methods to allow the programmer to achieve exactly the style of finish they need. This allows for minimal hand finishing and a more accurate job.
“Easy editing of toolpaths is also important to allow for smooth approach and departure movements (lead-in and lead-out moves). This minimises the impact on the machine tool, and removes vibrations carried into the tool through sudden changes in direction,” Simuc said.
He stresses verification to ensure a job is machined correctly the first time, and support of the product from people within the industry as also vital to the whole success of the process.
“The manufacturer really needs to be aware implementing a HSM software is a process. That process needs to be managed with training, or re-training of programmers, and supported with complementary tools. This may include using balanced tool holders and tooling, more rigid work holding devices, or even a controller upgrade,” Simunic told Manufacturers’ Monthly.
While software is obviously an inherent component in the HSM process, both Colusso and Simunic stress that successful HSM is a combination of a number of factors, including the machine tool, spindle and cutting tool.
“What is needed includes good quality machine tool suited for the required task, a spindle which has minimal run-out, CNC control capable of processing HSM style toolpaths, which are often much larger than conventional toolpaths, correctly chosen and applied cutting tools, rigid work holding, correct machining method selected by programmer and above all operator training in all of the items listed above.”
Colusso added that manufacturers should also get the CAD/CAM supplier to show them the cutter paths they are using and check they have the inherent features required for HSM – constant metal removal and tool loading.
Both men say HSM will continue to evolve, with cutting tools, machine tools and software getting faster and more intelligent.
“Machine tools will have even higher spindle speeds and with the consistent improvement in cutting tools and machining algorithms, the cutting motions will get further optimised, providing productivity benefits to better enable Australian companies to be successful on the global manufacturing stage,” Colusso said.