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CAD/CAM Programs Get Parts On, Off Machine Faster, More Efficiently

Ed Sinkora
By Ed Sinkora Contributing Editor, SME Media

Software advances focus on toolpath improvements, reducing job setup time, integrating with digital tool libraries and improving machine simulation, verification and analysis tools

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High-speed roughing methods, such as NX CAM’s Adaptive Milling, can reduce machining time by up to 60% while extending tool life. Photo courtesy Siemens PLM Software

Ask almost any CAD/CAM vendor what they’re focused on and they’ll tell you it’s the same today as it was five years ago, and it’ll be the same in five years: Get the part onto the machine as fast as possible and get it off the machine as fast as possible. Here’s the current state of play in those two main areas.

There have been various changes to CAD/CAM software in recent years to increase efficiency and reduce job setup time. But “there’s no silver bullet,” as Vyncent Paradise, director of product development for NX CAM, Siemens PLM Software (Plano, TX), put it. He referred to automation as the most important aid, to include the use of predefined templates plus increased use of product and manufacturing information (PMI) within CAD files.

“We’re always trying to add more information to the CAD modeling process that can be used downstream in CAM, like tolerances and finish requirements,” Paradise explained. “And if you can read the smart digital model, you can use it to automatically choose machining methods based on the required tolerance.”

Alan Levine, managing director of Open Mind Technologies USA (Needham, MA), echoed the value of automating CAM programming through the use of macros that store a shop’s best practices. “Let’s say you like to drill your deep holes a certain way, with different pecking steps and feeds. We make it easy to save these processes as macros so the programmer doesn’t have to continually go through these steps,” he said. Open Mind’s software also helps users categorize the macros, making them easy to find and apply. Also, a Programming Assistant module automates certain setup tasks that differ from shop to shop but are generally standardized within a given shop, like where to set the zero point.

The hyperCAD-S module in Open Mind’s hyperMILL software speeds CAD-oriented tasks for NC programmers by making it easy to select points, curves, faces, solids or polygon meshes. Levine said elements can be quickly added, deleted, modified, shown or hidden, and all functions are tailored to the tasks of NC programmers. Beyond that, the module includes the positioning of fixtures, providing the ability to adjust to match whatever side of the part the user is making. For example, elements such as clamping jaws can be moved linearly or radially to the optimal position.

Along the same lines, Mark Gadsden, manager of product marketing for PowerMill and FeatureCAM at Autodesk (San Rafael, CA), noted that operators using FeatureCAM do not have to program a machine stage by stage; instead, they program it using everyday shop terms, such as ‘turn,’ ‘bore,’ ‘bolt’ and so on. It has sufficient intelligence to recognize needs and requirements from such terms and will automatically adopt the right speed and torque strengths without having to be instructed, line by line.”

Gadsden also pointed to FeatureCAM’s Directed Automated Feature Recognition (DAFR) capability that “automatically recognizes holes, bosses, sides and pockets in a single workflow, which enables faster programming. While standard AFR slices the model in the active Z axis and produces complete features as it makes its way down the model, DAFR allows users to select the features they want even before recognition begins. It minimizes programming time and helps to reduce cycle time. In a break with convention, DAFR can also be used in turning projects. It gives users the option to choose index angles. This helps to reduce the number of Z-axis moves required and so speeds up cutting.”

Daniel Remenak, product manager for 3D Systems (Rock Hill, SC), also spoke to programming aids that go beyond milling: “GibbsCAM’s MTM product provides a complete machining solution for multitask machines, allowing you to program milling, turning and other operations across multiple spindles to access all sides of a part, and assisting with synchronization and automatic part transfer operations, which can enable single-setup, lights-out machining. Similarly, GibbsCAM’s Tombstone Management System offers automated part layout of one or multiple jobs on tombstone fixtures, allowing the machine to be utilized full-time while the next tombstone is being set up outside the machine.”

Ben Mund, senior market analyst at CNC Software (Tolland, CT), developer of Mastercam software, noted that most shops receive part files from a variety of customers in a variety of formats. “So a big part of our focus has been on creating CAD tools for machinists designed to prep a part and get it on a machine faster. Things like hole filling, fixture creation and repairing surfaces or solids often come in corrupted or incomplete.” Mund added that machinists often deal with situations that the designer may not have considered when modeling the part, another impetus to giving the machinist specialized CAD capabilities.

Simulating or Ignoring

Three-dimensional machining simulation has been a huge programming aid and keeps getting better. Take the simulation of the complete machine tool, including robotic loading and even the logo on the sliding door. It may not be necessary from a machining standpoint, but as Mund observed:

“The operator’s going to run a tool through a chunk of metal. Anything you can do to boost their confidence in the accuracy is good. And it’s a great way of instilling confidence in verification as a whole.” He added that for complex multitasking machines, simulating every detail becomes important because otherwise it’s difficult for the programmer to foresee and avoid collisions.

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Modern CAM, such as Mastercam shown here, uses a full cut and constantly adjust the toolpath to maintain consistent material removal.
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A conventional milling path (above) follows the intended profile with a predetermined offset and may repeat multiple times with step downs in Z.

Remenak agreed that CAM vendors are expanding the breadth of what’s simulated, “as programmers demand accurate simulation for new types of machining, such as interpolation turning, thread whirling and polygon turning, broaching, or even additive metal deposition processes.”

Siemen’s Paradise made the interesting observation that “CAM systems have long known a lot more about the toolpath than we made available to the programmers. But we’ve started displaying much more toolpath information in the last few years.” Examples include showing the tool angle, the thickness of the material left, and indicating if there’s a problem, taking the programmer right to that point.

“It all sounds very obvious but it’s quite new,” he noted. “These things can be quite important for a programmer who’s trying to understand what’s going on or trying to get an outstanding finish.” And while automatic collision detection has been a common attribute in CAM packages, they didn’t always make it easy for the programmer to find out where and why. Paradise said that’s changing. “We are giving users more accurate info about what’s going on to help them create better machining operations.”

Mund of CNC Software added that color coding of motion helps. “At a glance you can see speeds and feeds, or the type of motion, or the type of tool that’s used.” He echoed Paradise’s view that modern CAM offers both broad toolpath analysis tools for verification and what the program yields, plus analysis tools that let the programmer “get in and pick apart one piece of motion and see the numbers powering it. It’s less common that people need that, but when they do it’s important that they have it.”

Conversely, sometimes it’s best to not show things exactly as they are. Mund said the transition from CAD to CAM can be aided by giving the machinist the ability to temporarily suppress a feature, like a radius on a part corner, to make machining easier.

According to Paradise, there are also times in when it helps to reduce the detail of the CAD model while still telling the CAM program to machine features in that area. “I save modeling time. I save file size. And I automate my CAM. All in the same process.” This last example reminds us that, like Autodesk, Siemens PLM offers a complete CAD/CAM package with NX.

Finally, Paradise argued that not all CAM simulation is equally accurate and seamless. “We drive our simulation inside NX CAM using the final G-code that will go to the machine tool. The postprocessing is built right into the system. So immediately upon programming a path the system will generate G-code and we use that G-code to drive the simulation.”

Paradise said most CAD/CAM packages use a third-party product for machining simulation. “You have to export G-code from your postprocessor and import it into a different system. And you have to replicate your machine model, workholding and cutting tools in that system as well. Then you run your G-code driven simulation there. And if there’s a design modification or an issue you have to go back to your CAM system, make a change, and go through the cycle again. We’re unique in doing all that inside NX CAM on the fly.”

Parts Off

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Constant, consistent tool engagement is a key goal in modern CAM, shown here with Mastercam’s Dynamic Motion.

The ability to automatically program the optimum feed rate based on a volumetric analysis of the material just ahead of the cutter is perhaps the hottest topic in the drive to slash cycle times. Every CAM provider offers the capability, with different names and variations in the operations and axis configurations. In Mastercam it’s called Dynamic Motion because, as Mund explained, the software “is constantly changing the tool’s engagement so that the chip load remains constant.”

An easy example is going fast on a straight section and slowing down around a corner, whereas the old way to program the cut would be to set a feed rate the tool could survive in the corner and apply the same rate for the entire periphery.

The goal is also to stay engaged with the workpiece as much as physically possible, distinguishing the technique from both conventional roughing and trochoidal machining, which cuts a section of the part and then loops around to cut another small section. When viewed from above Dynamic Motion’s toolpaths can look chaotic by comparison, while the chips are consistent in size and shape. It’s also better for the cutter, because disengagement and re-engagement contributes to tool wear.

Mund added that another ideal is to use as much of the tool’s cutting surface as possible, taking deep axial cuts, “albeit a little shallower radially than you would in conventional machining. It seems counterintuitive but it’s much faster to take a deeper axial cut with a shallower radial engagement versus stepping down with a series of deep radial cuts.”

Mund acknowledged that most CAD/CAM packages have a similar technique and said it has “become the standard way of both complex rough-ing and 2D finishing over the last few years. It’s as close as we’ve come to creating a universally beneficial toolpath type. We’ve seen shops with older machines and non-premier tooling cut machining time 50 to 60%.”

Open Mind’s approach was to license the basic VoluMill kit from Celeritive Technologies Inc. (Moorpark, CA) and add their own methods for things like slicing to get multiple depths, sectioning and collision check. Given the customization, they chose a distinct name for the product: Maxx Machining roughing.

Levine said the most unique aspect of the implementation is extending it to five-axis machining. “If you have a shaped component like a tire mold or an aircraft engine casing, we can present it [with] five-axis roughing paths. If you use traditional CAM on a curved surface like a tire mold, you do lots of Z cuts and end up with lots of stairsteps on that surface. When we apply high-performance roughing in five-axis we morph to the shape, leaving a constant amount of material for the finish path. The entire process moves better and you can save a lot of intermediate cleanup cuts.”

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Visual toolpath analysis in NX CAM and other modern CAM software reveals information about machining, such as swiveling axis angle.

Mund said Mastercam recently added Dynamic Motion to five-axis roughing and turning, and Gadsden said PowerMill’s new “automatic tool-axis tilting … provides a single solution that helps generate smooth and safe five-axis motion for all model shapes and toolpath types, making it as easy to create five-axis programs as it is with three-axis code.”

GibbsCAM also uses VoluMill and Remenak credits it with dramatic improvements in cut time and tool life. He added that “recent advances have applied the lessons learned in these high-efficiency milling algorithms to turning, and the result is a new generation of turning toolpaths such as VoluTurn, available in GibbsCAM 12. These new turning toolpaths offer high rates of material removal while reducing machine and tool stresses to improve cut quality and cutter life.”

Cutting Non-Cutting Time

Naturally modern CAM also minimizes non-cutting time by reducing both lift-off heights and lift-off distances. “Lift-off height sounds like a tiny thing but it can make a big difference on a large part,” observed Paradise. He’s also keen on the importance of smoothing the travel of both cutting and non-cutting paths.

“The easy way to deal with non-cutting motion is to tell the machine to stop, lift-off, and move rapidly to a spot above the next machining area, stop again, move down, and engage. That’s fine for a few moves, but if it’s a part you’ll be machining over time, this could be thousands of such moves in exactly the same positions on the mechanics, and that damages the machine. It’s also slower. Calculating the appropriate curve and building in acceleration and deceleration at each end is the best way to go. For example, a large customer recently saved 10% in cycle time on hundreds of their machines just by smoothing the non-cutting paths.”

Smoothing non-cutting time doesn’t require a sophisticated control or an expensive machine. It’s an easy way to increase the productivity of even an economical machine. And because it also reduces wear on the machine, it increases machine longevity.

Other Exciting Advances

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Typical Z-level roughing can leave stair-steps against shallow surfaces (left) while hyperMILL MAXX Machining roughing with five-axis shape offset leaves a uniform stock for finishing operations (right).

Additional improvements include the new 3D-optimized roughing cycle in Open Mind’s hyperMILL, which has been enhanced for applications with high-feed cutters (which take shallow cuts with high stepovers). The stepover distance can be calculated from the scallop height measured against the high-feed cutter geometry and a special toolpath movement removes rest material from corners when there is a large stepover.

Levine said the secret is precisely modeling the geometry of the bottom of the cutter, whereas “other software approximates a high-feed cutter as a bullnose cutter with a corner radius. The bottom of a high-feed cutter actually has a large effective radius and we model it as such.”

One benefit is being able to machine closer to walls because the software knows where the cutter’s geometry leaves room, while simulations that approximate the cutter with a flat bottom see contact where there is none. Levine added that modeling the cutter also enabled better calculations for the distance between adjacent cuts to control surface quality.

Another Open Mind feature that’s not limited to high-feed cutters is “intelligent cut division.” If, for example, a section of a workpiece required the removal of 4.1″ (104 mm) of material and the programmer specified a 1.0″ (25.4 mm) stepover, the last cut would be very thin (and could be even thinner than this example). Aside from being inefficient, machining such slivers can be very detrimental in some materials, said Levine. “So we offer this option to override the prescribed stepovers, recalculating based on the total number of steps so that every cut is taking equivalent material.”

Finally, many companies are enabling the use of “circle segment end mills” and other new conical barrel tool designs. (See “New Tool Designs Power Faster-Than-Ever Cutting,” ME Tooling & Workholding issue, Spring 2018). As Levine explained, such tools feature an effective radius as large as 1,500 mm, making stepover distances of 6 and 8 mm a reality for a superior surface finish with cycle time reductions exceeding 90%. “You don’t have to switch cutters to finish adjacent areas such as rounded interior corners, and hard-to-reach areas can be machined in an efficient, secure manner,” he said.

Gadsen said they partnered with a customer three years ago to optimize five-axis machining of very complex blisks using barrel tools and were able to reduce milling cycle times from 200 hours to 35. “That’s a savings of 83%, and we also reduced tooling costs by 72%.”

Another improvement area is 3D printing. Autodesk’s Gadsden highlighted the growing availability of machines that combine subtractive and additive processes. “These hybrid machines look set to transform how we manufacture parts, but they present a programming challenge for CAM software because additive processes are not just subtractive ones in reverse. With this in mind, Autodesk has added specialized tools to PowerMill to program, control and simulate high-rate, additive manufacturing processes.”

 

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