selecting cnc controls

The selection of the numerical control (NC or CNC) system

for a machine tool has become a major consideration for the

manufacturing manager in recent years. The advanced features,

increased flexibility, maintenance reduction, and cost oftoday’s

CNC systems can make a major impact on the productivity and

price of the machine tool.

The days of selecting a metalcutting machine that can provide

the best capacity to machine the average part assigned to the

machine have changed, Most machines are not dedicated to

only a few distinct parts for long periods of time. The machine

and CNC system must be considered for long-range plans as

well as the short run. Since machines can be called on to

machine different types of parts, the CNC system should not be

the limiting factor in the machine’s performance. Just as

machine tools have limitations in the size of part they’ can

handle, the spindle speed it can operate at, the power available

at the tool, etc., CNC systems have their limitations as well. A

CNC system has limitations in the speed of execution of

computer instructions; the size of memory (feet or meters of

part program tape it can store); the maximum dimension and

feed rates; the sophistication of software programs for utilization

of DNC; special contouring heads; probes; etc.

Today’s manufacturing manager now has the challenge of

selecting a machine and a control that will be the best package

as this new tool will be a key element in the company’s profits.

The top priority is still given to the best machine for the assigned

parts; but once that is decided, the selection of the best CNC

system needs to be wrestled with. Some experts believe that if

the machine tool builder also manufactures the CNC system,

there is a high probability this package will be the most

compatible and will provide the best value to the purchaser. In

recent years, many machine tool builders have recognized this

possibility and have supplied their machines with their own

designed and manufactured control or at least have standardized

on a limited number of CNC systems purchased from specific

control builders.

The trend with newer CNC systems is to make most of the

software features (such as editing, which primarily requires only

additional memory). The list of optional features contains

essentially hardware items such as larger part program

memories. When a feature is critical in the operation of the

equipment, the purchaser should analyze the feature for

essential qualities, The fact that a CNC system has tool length

compensation is no guarantee it has the capability desired. For

example, tool length compensation has a number of variables.

The number of offsets can vary from 10 to 100 or more. The

range of the offset values can vary from tO.000” to *99.9999”

on machines which are programmed in U.S. customary units.

Historically, tool offset lengths have been loaded into the

control system by the operator. Alternately, tool length offsets

in some newer CNC systems can be loaded via the CNC tape,

via the machine automatically, or via an automatic gaging

center. Any one of these qualities may have a profound effect on

the ability to use the machine and tooling effectively. Most

software options can be added at a later date and at a minimal

additional price, whereas hardware options may cost signifi-cantly

more to add at a later date.

The selection of a CNC system breaks down into four major

categories of consideration: machine design interface, software

features, hardware features, and control design specifications.

A spread sheet on all the CNC system specifications should be

made and compared as a basis for selection,

Resource : http://cncmachinetools.blogfa.com