Many professionals have come to understand that "more" isn't always better, particularly when "more features" are related to "more complexity", "less reliability", "more training" and, potentially, "less accuracy". Nevertheless, when some professionals enter into the machine tool market, they strive to purchase the most complex tool within their price range. The rationalisation is that "we may have a need for all those features at a later date". This is an understandable approach and, provided that the aforementioned problems have been taken into account, may also have some merit. However, in the case of CNC grinding tools, one, leading-edge manufacturer has found that the application of state-of-the-art technology can give end-users "more" without creating additional problems.

A modern CNC machine tool is coordinated by a multi-level control system. Each physical axis of movement is propelled by an a.c. or d.c. motor which is, in turn, controlled by a servo-drive system (typically composed of power electronics and digital processing technology). Each servo-drive is then controlled, at a higher level, by the CNC. Every physical axis of movement therefore adds considerably to the overall mechanical and electronic complexity of the machine. Consequently, a machine with 12 physical axes of movement can theoretically do considerably more than a machine with three physical axes but the reliability and accuracy of the more complex machine may be compromised as a result.

Some manufacturing applications, such as CNC tool and cutter grinding, don't necessarily require a complex machine with many physical axes of movement, provided that the control system is sufficiently intelligent to achieve the same result with less physical axes. The "doing more with less" concept was converted into reality by ANCA Pty. Ltd. in their state-of-the-art CNC's, which are collectively known as the System 32. The objective was to enhance the functionality of tool and cutter grinding machines without compromising accuracy or reliability. The result was referred to as a "soft axis" approach and was internationally patented by the company. Essentially, soft-axis control means that a tool and cutter grinder with only five physical axes can be programmed as though it has seven axes of movement - the remaining axes are created in intelligent software (hence the terminology). This gives end-users many of the benefits of a more complex machine but with far better reliability and accuracy.

Soft axes weren't just an experiment in intelligent control. In fact, since their development, they have been extensively applied in industry, around the world, on ANCA's tool and cutter grinding machines (FASTGRIND TG7 and MG7) and burr grinding machines (FASTGRIND BG7). One of their most significant advantages is in enabling the company's machines to perform "plane grinding" operations on work-pieces such as ball-nose end-mills, radiused end-mills and tapered ball-nose end-mills.

The benefits of plane grinding are well known and are significant, particularly in terms of producing high-precision tools which require ball-nose or corner-radius grinding. In plane grinding, the contact pressure of the work-piece is evenly distributed across the face of a grinding wheel, thereby preserving the wheel profile and maintaining the outer edge (or qualifying point) of the wheel to a high degree of accuracy. This is important because the outer edge of a grinding wheel is the reference point from which dimensions are calculated.

A disadvantage associated with the plane grinding of certain tools has been the need for a relatively complex machine with as many as seven or eight physical axes of movement. Some manufacturers have tried to resolve the problem by creating a more complex (and potentially less reliable) machine tool, while others have chosen to retain their five-axis machines and to apply an alternative grinding technique known as "point grinding".

In point grinding, the outer edge of the grinding wheel is used as the mechanism for achieving a particular radius on a work-piece. One of the problems, however, is that the pressure on the outer edge of the grinding wheel is such that the edge wears rapidly. Since the outer edge is also used as a reference, this means that the accuracy of the grinding diminishes with each work-piece, unless continuous offsets are made. Although the accuracy of point grinding can be improved by subsequent finish grinding, the process can still lead to a situation where the cutting edge of a work-piece becomes "hollow ground". A cutting tool edge which has been hollow ground by the point pressure of the grinding wheel can be weakened and therefore unacceptable to end-users.

Traditionally, manufacturers have had to trade-off machine complexity and accuracy for the benefits of plane grinding. However, ANCA's fusion of soft axis CNC technology with tool and cutter grinding technology meant that the company was able to tackle the problem of plane grinding from a different perspective. The application of soft axis technology enabled ANCA to design a machine which was capable of performing plane grinding operations, on ball-nosed and radiused tools, while still retaining the reliability and simplicity of a machine with five physical axes. From the end user's perspective, the result has been a machine which can produce cutting tools with a superior surface finish to those produced with a point or hollow grinding approach. The trade-off against a more complex machine architecture has been eliminated by intelligent software and a unified machine/controller design.

Plane grinding is only one of a number of benefits that can accrue from the application of soft axis technology to overall machine tool design. However, it is also a good example of the importance of ANCA's unified approach to machine tool design, where the mechanics and controls of a machine are designed to behave as a single entity, rather than a collection of modules. For end users, it also means that sometimes "more" can be "better".
 

Buckley Owens Machinery Corp. 6416 Fly Road | East Syracuse, New York 13057 Telephone 315.432.0708 Fax 315.432.0736 Email: info@buckleyowens.com