With a host of new controls and functionality entering the market recently, Machinery picks his way through the G-codes to make sense of it all
Do production engineers really need to be intimate with the finer points of CNC functionality? Well, no one chooses a new car without knowing a little about each of the engine specification options available, so, with this in mind, buying a new machine tool without any knowledge of the capabilities offered by the CNC is simply not advisable.
CNC preference can bear significant influence on the purchasing decision and, with many machine tool manufacturers offering several CNC options on new models, production engineers would do well to stay in touch with the latest developments.
For example, one of the newest CNCs on the market is the Sinumerik 828D from Siemens (0161 446 5731), which features (as standard) Siemens' ShopMill and ShopTurn interactive, graphic-assist operator interface. It also features bright and clear colour display, full keyboard, short-stroke keys and a video-like interface for increased shop-wide productivity.
Image: One of the newest CNCs on the market is the Sinumerik 828D from Siemens
"The new Sinumerik 828D CNC provides job shop owners and managers with distinct business advantages including ISO code programming, shopfloor communications, interactive animated elements, automatic measuring cycles and production-status text messaging," says Tony Bennison, business development manager at Siemens IA&DT,Fanuc (01895 634182) has also been busy on the development front, working hard to introduce specific machining functionality designed to help manufacturers achieve competitive gain.
For instance, new features for the CNC Series 0i -D include nano-interpolation, a function that satisfies demanding finish requirements at high feed rates and speeds. Dual Check Safety is another new feature, which uses the CNC's multiple processors to cross-check data to monitor the machine's safety critical parts. This enables compliance of the machine with international safety standards, without the need for additional safety units.
Other enhanced features of the 0i-D include: maximum total controlled axes increased to eight (milling model) and 11 (turning model); Al Contour Control II (milling model) uses a high speed processor that allows high speed machining of complex free-form parts that are programmed in continuous small block segments; nano smoothing (milling model) smoothes surfaces by converting small block segment programs into smooth NURB surfaces in real time; jerk control (milling model) for smooth acceleration; enhanced tool management (milling and turning models); and retraction capability for rigid tapping (turning model) to aid cycle time reduction.
Of course, there are plenty of machine tool builders developing their own proprietary CNCs, on the premise that machine and control are inseparable technology companions. Haas (01603 760539), for example, has designed into its control a facility called 'Maximum Rounding', which allows the user to define the machining accuracy of rounded corners within a selected tolerance. The default value is 1.27 mm, but it can be set to zero, in which case the machine will treat all corners as if an exact stop is required.
Elsewhere, Volumetric Error Compensation (VEC) methodology developed by MAG (0121 306 5600) is said to reduce the time required to determine whole volume error compensations (see also here for a full article about volumetric error compensation
). Multi-axis VEC was conceived to improve machining accuracies for large machine tools used to produce large, monolithic and complex-shaped parts. Multi-axis VEC treats collectively all of a machine's degrees of freedom that affect tool point positioning. Conventional approaches to volumetric compensation are generally limited to three linear axes and the associated total of 21 potential motion error sources. However, a typical 5-axis machine with linear and rotary axes can have 43 potential error sources.
MAG's multi-axis VEC system compensates for all of these, and even more, in machines with unique or more complex multi-axis configurations. It uses a laser placed in the workpiece position that directs a beam to an active target mounted in the machine tool's spindle. These interact to maintain a metrology beam lock during the volumetric calibration 'event'. To perform a VEC event, an NC program positions the active target to a cloud of some 200 points, representing a series of statistically random multi-axis positions within the work envelope.
The same NC program is run three times, first with the active target at a long tool length, then twice again at a short tool length. The 200 commanded and measured positions from the first two runs are combined mathematically to establish each tool axis vector orientation, while the third run gives a measure for repeatability. Automated software processes all position/point data as simultaneous polynomial equations to determine volumetric compensation, based on the kinematic error model of the machine. Compiling technology then integrates the compensations into real-time CNC path-control algorithms. Sometimes the requirement for a new CNC is driven by a retrofit project, as was the case recently when Stockport-based sub-contract toolmaker Nelson Tool wanted to restore a SIP 740 jig borer to its former glory by retrofitting a TNC 320 CNC system from Heidenhain (01444 247711).
"With several Heidenhain 320- and 530-controlled machines on site, we are well acquainted with the user-friendliness, flexibility and capabilities of Heidenhain CNCs," says Nelson director Keith Machin. "So when we discussed the project with machine tool rebuild company Electron Engineering Services (01422 327523), we had no hesitation in accepting Electron's recommendation that a TNC 320 would be the best solution."
DESIGNED FOR MILLING & BORING
Specifically designed for milling, drilling and boring machines, the Heidenhain TNC 320 features workshop-oriented/conversational programming via a TFT 15" monitor that presents a clear overview of all relevant information, such as program blocks, comments and error messages. Additional information is provided through graphic support during program entry, test run and machining.
Electron's activities on the SIP jig borer also included: the retrofit of new analogue drives and motors; the fitting of new axis measurement feedback systems (Heidenhain slimline LS487 linear scales and encoders); a new electrical panel with new interface equipment; and operator/programmer training.
But let's not overlook the potential for digital readout technology to fulfil machine tool positioning operations. New models available on the market include the DP700 from Newall Measurement Systems (0116 264 2730). An intuitive DRO housed in an elegant aluminium body, the DP700 works in combination with Newall's robust Spherosyn and Microsyn linear encoders.
Image: Newall Measurement's DP700 DRO
On the subject of encoders, Electronica (0116 279 6891) is about to launch its GS212 encoder, designed specifically for high end CNC tasks and metrology applications, such as optical stages and shadowgraph machines. Resolution is 0.1 micron, with accuracy quoted as ±3 micron per metre. "It's a slim encoder that is easily interchangeable with all of the main market-leading scales," says the company's technical director, Dr Mark Hudman. "It is equally suitable for OEM and retrofit markets."
First published in Machinery, August 2010