The CNC is the heartbeat of any machine tool. Understanding its capability is paramount to achieving genuine competitive gain. Steed Webzell reports
It is true that many production engineers take CNC units for granted, either because they believe that mastering the basics is good enough for the majority of machining operations, or simply because they don't have sufficient time to get more familiar with the control. Both scenarios lead to a common outcome: missed opportunity. CNC developers are introducing new functionality almost continuously in an attempt to entice new users and gain important market share.
Take Heidenhain (01444 247711), for example. Many will recognise its proven TNC controls as a common sight in industry, particularly on 5-axis machining centres. To meet the ever increasing accuracy requirements of 5-axis machining, Heidenhain has introduced KinematicsOpt and KinematicsComp functions. With a touch probe in the spindle, KinematicsOpt automatically measures the machine's rotary axes. The results will be the same, regardless of whether the axis is a rotary table, a tilting table or a swivel head. From the measured values, the TNC calculates the static tilting accuracy. The software minimises the spatial error arising from the tilting movements and, at the end of the measurement process, saves the machine geometry automatically in the respective machine constants of the kinematics table.
With KinematicsComp, the control is capable of compensating the geometric position and component error of the machine tool axes. Only the position of the tool centre point is corrected, while the tool orientation to the workpiece remains unaffected, so preventing undesired movements during simultaneous multi-axis machining.
Fanuc (01895 634182) has also focused on introducing new CNC functionality for 5-axis machining. For instance, with regard to '3+2'axis machining, the new tilted working plane (TWP) function offers easy and rapid programming set-up. When defining the TWP, an input guidance screen provides visuals to support the operator, while requesting the required data in a dialogue. Input data can be in any of six different formats: Euler angles; the roll, pitch and yaw command; three points; two vectors; projection angles; or the programmed tool direction.
In addition to the current auxiliary CNC functions, Fanuc has also recently launched further benefits for 5-axis machines – including enhancements to '3D interference check'. The 3D interference check is a function integrated into the CNC kernel, which, Fanuc says, when configured by the machine tool builder, helps to prevent machine collisions with almost 100 per cent reliability. It safeguards collision-risk areas by defining them as geometric elements to determine whether any moving part of the machine may collide with fixed elements.
With the overlap between CNC and CAM a grey area, and with the increasing desire to buy manufacturing technology from a single source, visitors to the Mori Seiki (0844 800 7647) showroom can now buy a new machine tool, complete with the company's recently launched MAPPS IV CNC featuring embedded Esprit CAM as standard.
"It's a strategy that allows users of complex machines the advantage of buying a total package from one supplier and making the decision process simpler," says the company's vice president of sales, Steve Finn.
The main features of MAPPS IV include: an improved user-intuitive hardware and interface with vertical soft keys and PC-type keyboard; an internal/external camera option; file display and memo function, so that tool data, drawing data and set-up procedures can be viewed on the MAPPS screen; and a screen list function to enable operators to jump to their frequently-used screens. The integration of Esprit into MAPPS IV is timely, in light of the trend to transplant 3D programming from the CAM room back to the shopfloor. Thus, CADCAM and production departments don't have to engage in a lengthy exchange to decide on a program. In addition, machinists can see the process through from start to end, creating the toolpath, establishing their own machining strategies, observing how well the machining technique is working and making adjustments, as needed. They can also better implement last-minute engineering changes.
One company that can provide testament to this approach is P&C Precision of Leighton Buzzard, which uses a raft of Haas (01603 760539) machining centres to produce components on a sub-contract basis. In similar vein to Mori Seiki, Haas uses a proprietary control.
"Because of short lead times, we are often faced with programming online at the machine," says P&C production director Steve Holliday. "The Haas control provides us with a massive boost when up against tight deadlines – the system saves a tremendous amount of time. Our other machines feature an industry standard control, which is great in its own right, but the Haas control beats it hands down."
The Haas CNC has a number of innovative features, such as word-processor editing, one-button features, multi-function jog handle and 'Visual Quick Code' programming. Yamazaki Mazak (01905 755755) also has a proprietary CNC and its latest incarnation is known as Mazatrol Smart, which is designed purely with 2-axis turning and 3-axis milling in mind. By eliminating functions that would be expected on its multi-tasking machines, Mazak has created a control that is both easy to use and provides a more cost- effective solution to those customers who do not require these additional functions. The operator interface remains as a Windows-based system with a QWERTY keyboard and, as well as the Mazatrol conversational programming, has EIA/ISO functionality as standard.
Image: Mazak Quick Turn Smart features the new Mazatrol Smart CNC
Go one step farther and we enter the territory of digital readouts (DROs) and linear encoders, which remain popular for jobbing shop users of manual mills, lathes and grinders. And yet the pace of DRO/encoder development is no less frenetic. A case in point sees Electronica Mechatronic Systems (0116 279 6891) launch a new range of enclosed magnetic linear encoders, designed to combine the ease of mounting of optical encoders with the robustness of magnetic measuring systems. Compatible with almost all brands of digital readout (DRO), the MG232 range of linear encoders features non-contact operation, so there are no bearing or springs, to ensure high levels of reliability.
Image: Electronica's enclosed magnetic linear encoder
Available with an IP67 rating, this means the new high speed linear encoders offer high robustness and are capable of running in the harshest of shop floor working environments without suffering oil, dust or coolant ingress. In fact, they can even run fully submerged!
Impressive operating speeds mean the units are suitable for high speed mill, lathe or grinding machine operations, either as OEM first fit or retrofit applications. The MG232 is capable of achieving traverse speeds of 2 m/s at 0.001 mm resolution, or up to 10 m/s at 0.005 mm resolution. Although MG232 encoders can be paired with virtually all major brands of DRO, for those seeking a single source of supply Electronica can recommend the use of its recently introduced EL400 high specification, low cost DRO, which is suitable for mill, lathe and EDM applications in 2, 3 and 4-axis versions.
Perhaps the most recent DRO to enter the market is the DP700 from Newall Measurement Systems (0116 264 2730). Initially 2-axis and 3-axis versions will be introduced, with a single-axis unit available at a later date.
The design principle of the DP700 was to create a DRO that featured the essential functions for all machining applications, while providing operators with an intuitive and 'answer-the-question' type of interface. Operators can select the functions they would like to use or disable, so they can make use of the most advanced or basic features.
Spare parts galore
XYZ Machine Tools (01823 674200) has announced that it now holds more than £77,000 worth of Siemens spares at any one time. This parts-holding service is in support of its CNC machine tool range of lathes, turning centres and machining centres, equipped as standard with Siemens 810D and 840D Shopturn and Shopmill conversational control systems.
Image: Spares galore
First published in Machinery, Feb 2010