Getting The Most From A CNC Swiss-Type

The capabilities of today's multi-axis CNC Swiss-type lathes can be astounding, according to Amphenol Inc. (Danbury, Connecticut). Amphenol manufactures interconnect products. About a year and a half ago, when the company was looking to cut cycle times and increase precision by eliminating costly secondary operations, it decided to invest in complex CNC Swiss machines from Marubeni Citizen-Cincom (Allendale, New Jersey). It didn't take long for Amphenol to realize how important an efficient programming scheme was in the pursuit of achieving the potential productivity enhancements its new Swiss machines offered.

Based on a recommendation from its machine dealer, Amphenol automated its CNC programming through the use of a CAD/CAM system called PartMaker SwissCAM from PartMaker Software/IMCS Inc. (Fort Washington, Pennsylvania). The software is a visual CAM system developed specifically around the needs of multi-axis and Swiss-type lathes.

It operates from graphic representations of various faces of the part. Lenny Bennett, CNC production supervisor at Amphenol, decided to begin using the software after the new Citizens had been on the floor for over a year. According to Mr. Bennett, the company was able reduce setup time by more than 50 percent within the first 30 days of using the system by creating programs that were correct the first time and required little or no operator intervention or editing once sent to the machine.

"The setup of these machines is really quite easy once you have a good program," Mr. Bennett says. "With SwissCAM we're making programs now that run the first time."

The complexity in programming CNC Swiss machines is two-fold. Swiss parts often have a number of turned and milled features. As a result, the programmer must handle a variety of different coordinate systems on a single part. A multi-axis CNC Swiss machine is more than merely a lathe and a mill. These machines actually have upwards of nine different types of milling capabilities with unique characteristics.

Further complicating matters is the issue of synchronization. In the case of Amphenol's Citizen M, a single part actually requires three CNC programs to be written simultaneously to control the motion of the machine's 13 axes. These three programs are linked together through codes referred to as either "sync" or "wait" codes or "queuing" commands. These codes act as stop signs for the simultaneously executed programs functioning to coordinate the motion of the multiple axes. The use of these synchronization codes allows the programmer to run various operations together or independently, depending on what the application requires.

With SwissCAM software, Mr. Bennett is able to try different synchronization strategies and see the impact on cycle time at his desktop. Using "what if" scenarios that can be simulated means he knows the cycle time for the part is already optimized before he sends the program to the machine, and he does not need to worry about the operator having to make corrections or improvements.

Historically, CAD/CAM has been the domain of the milling world, and as a result only recently has it truly addressed the needs of the programmers of CNC Swiss. In Amphenol's case, SwissCAM allows manufacturing personnel to program a part "off-line" on a desktop PC, while the machine is busy cutting other parts. Programming a part off-line with a CAD/CAM system from an engineering drawing has a number of benefits.

First and foremost, CAD/CAM systems make programming faster because cutter movements and tool paths are created via a visual interface. The user enters machining parameters and lets the software perform the trigonometric calculations and output the requisite NC programs for a particular machine tool.

In the case of SwissCAM, the software breaks down a part into a series of faces. Each face can be planar or rotational in nature and have different machining functions assigned to it. These machining functions are graphically represented, making it easy for the programmer to choose the face that corresponds to the type of feature to be machined.

Since Amphenol acquired its Swiss turning equipment, Mr. Bennett has seen the economic slowdown erode lot sizes, though not the number of actual jobs. He estimates lot sizes have dropped from an average of 2,500 a year ago to 200 to 600 pieces today.

Programming with a CAD/CAM system also provides a better organization of the manufacturing process leading to more consistent results across jobs and machines. This can be achieved through the use of knowledge-based machining (KBM), a hallmark of SwissCAM's programming approach. KBM stores the unique knowledge of the most experienced machinists in the shop regarding such issues as tooling, feeds and speeds and repetitive processes being executed from part to part. Capturing this information allows it to be reapplied automatically to future parts. Not only does this speed up programming, it allows less experienced personnel to benefit from the expertise of the most knowledgeable machinists in the shop. Incorporating the accumulated process experience from one job to the next yields consistency and allows for better process control, according to Mr. Bennett.

"If you want consistency from job to job you need control over the process. This is something only a programming system can give you," he says.

Programming CNC Swiss machines off-line with a CAM system can provide cost savings because of better utilization of capital equipment.

In addition, the right CAM system will not only speed programming but will also allow programmers to optimize programs at their desktop PC. Often, when programming manually, programmers have spent so much time just writing the program, they do not devote proper time to optimizing it—making sure the capabilities of the machine tool are correctly utilized. In the case of a CNC Swiss-type lathe, this can entail making sure operations on both spindles are as closely "balanced" as possible, meaning machine cycle times running on either the main or subspindle are as close to equal as possible. The software allows the user to view an optimized time study on screen.

CAM systems also provide the programmer a platform for verifying the manufacturing processes every step along the way. When Amphenol manufacturing engineers program a part, they can see exactly how the part will be machined before committing resources. This means programmers can see if the guide bushing is providing adequate support for the length of cut being taken and actually watch the part cut on screen in 3D to guard against crashes on the shop floor.