Choice approach

CNC programming can be carried out online from the office or on the shop floor, and operators favour one or the other. Martin Oakham discusses their merits.

There are two distinct schools of thought when programming CNC machine tools. For many, the online approach operated by a dedicated office-based team is seen as the best way to increase productivity, while many others see programming carried out on the shop floor as the best solution.

Online requires a central hub of dedicated programmers to write numerical control (NC) code, which can be posted and sent to any machine tool on the shop floor via a standard network. Alternatively, a CAM system might be used.

Shop floor programming is preferred by others, chiefly because the majority of expertise is with the operators who have built up a great understanding of the machines they operate and know how to get the best from them.

Nearly all of today’s shop floor CNC programming uses some form of conversational, or interactive, software to aid program development. Many find this method offers many more benefits than manual or CAM system online programming.

While manual NC code is useful for simple jobs, it can be tedious and error prone. CAM systems remove some of this tediousness, but when compared to conversational programming, they lack efficiency.

One of the pioneers of conversational programming solutions for CNC is Japan’s Mazak, whose European headquarters and manufacturing base is in Worcester.

The company’s Mazatrol T-1 CNC was designed in 1981 to increase productivity and manufacturing competitiveness. This was the world’s first conversational CNC for turning centres and was seen as a great breakthrough in machine tool history.

This control system offers conversational programming based on the format of questions and answers designed to eliminate the need for traditional punched tapes, tape-punching machines and tape readers at the machine tool, as well as the specialists required to produce them.

The system was designed to allow the operator to modify programs quickly with a few keystrokes at the machine as dimensional changes. Prior to conversational programming, even minor changes necessitated creating an entirely new tape.

By 1994, the fourth-generation Mazatrol T-Plus and M-Plus were sufficiently powerful to integrate conversational programming with EIA/ISO in the same control, and by 1998, the Mazatrol fused CNC control with current 64-bit PC technology. This allowed program and production information to be accessed directly, and managed with Windows-based operations.

The latest sixth-generation Mazatrol Matrix offers significant advantages in productivity and safety and is now standard equipment on Mazak’s new Integrex IV series, Integrex e-series, Variaxis II series, Nexus series, Vortex 5-axis machining centres and Cybertech Turn machines.

According to Japanese CNC machine tool manufacturer Mori Seiki, conversational programming has lost none of its attraction over the years. The company’s experience has shown that users prefer to use this option, especially where cycles such as drilling patterns or milled keyways are desired. The company offers both shop floor systems and networked PC-based conversational programming solutions.

Its programming systems are applications allowing users to create machining programs easily on their PC. thanks to the easy operation — requiring users to follow instructions on the screen to enter information about a product’s shape — programming time can be dramatically reduced.

Functions, data and operability are fully compatible with the conversational system of the Mori Seiki Advanced Programming Production System (MAPPS) II/III operating systems. Using Mori-servers enables data input/output between machine and PC through a LAN cable, so the user can edit and exchange data quickly. Data for cutting conditions which are changed on MAPPS can be transferred to a PC and re-edited there.

Mori Seiki’s conversational controls include the Mori-APM automatic programming system for machining centres; the Mori-APL automatic system for lathes; and the Mori-APNT automatic system for Integrated Mill Turn Centres (NT-Series).

Although the company unveiled its MAPPS conversational interface around 10 years ago, MAPPS I, II and III all share the same operating principle of having standardised user interface, while being independent of the controller manufacturer. This means an operator will immediately know where to find menus, regardless of the system it is running on.

MAPPS I employed the OS/2 operating system and gave the operator the option to work in DIN and ISO formats. This graphic user interface offered considerably improved conversational functionality suitable for lathes, milling machines and multi-axis turning/ milling centres. The NC data could be exchanged between PCs and machines via Mori Seiki’s network tools ‘Mori Server’ and ‘Mori DSN’.

MAPPS II and MAPPS III work on the same principle, but have improved 3D graphics running on Windows 2000, XP and Vista. The workpiece can also be displayed, rotated and turned in 3D form to visually test the functions of the NC program.

When working with 5-axis turning centres in particular — where the motions of the axes become so abstract that they cannot be understood by the machine operator — the MAPPS 3D collision display is a valuable aid. Because with chucks and jaws, tools and possibly several parallel acting turrets, there are plenty of parts liable to cause collisions.

Conversational programming requires a great deal of information from the operator. The cutting speed and depth are contained in the tool definition from which the program calculates the necessary number of cuts. However, it can be a disadvantage that although all of these values function, they may not necessarily be optimal.

This does not play a role where small batch sizes are concerned. Whether the part requires five or six minutes to cut is unimportant, but it does matter a great deal in mass production.

Here the paths must be optimised to achieve a cost-effective result. So those who produce an NC program conversationally will at least need to fine-tune it, write the retraction points smaller or optimise the feed rates, which requires a sound knowledge of DIN/ISO programming.