4 AXIS PROGRAMMING

For Agie Wire EDM Machines

Straight talk about programming Agie wire EDM machines. Advanced conics and 3D, do you know the difference? If you donít you should. If you will have applications which will require 4 axis programming capability then this document will provide a brief education on the subject. Most CAM (computer aided machining) systems offer 4 axis programming as an option which you will pay extra for. Before you spend those precious dollars be sure that the system you purchase will provide you with the best solution for your needs.

4 AXIS PROGRAMMING

What exactly is 4 axis programming? 4 axis or independent UV programming is a method whereby two distinctly different shapes or contours are developed on two different planes. This will result in a ruled surface being created in the workpiece. Mold making and extrusion dies are the most common examples of this type of programming.

ADVANCED CONICS

The term advanced conics applies to a specific type of 4 axis program for an Agie CNC 123 control. This program type is unique to an Agie. The most common use of an advanced conic program would be on a contour where some segments are tapered and others are not. This would result in an upper shape that would be distinctly different than the bottom shape but is not drastically changed. When programming an advanced conic program the .GEO file can contain circular interpolation (G02 & G03) moves, which are not allowed in the more traditional 4 axis program. The following rules must be adhered to if advanced conics programming is to be used:

The contour must start on a linear segment.

The contour can not have consecutive arc segments.

The lower and upper contours must have the same number of segments.

Segments from the lower and upper shapes must be matched in type (line to line, arc to arc).

All arcs must be either perfect cones or cylinders. The definition or a perfect cone is that the center point for the lower and upper arcs must be the same X & Y coordinates. A cylinder means that the lower and upper arcs are the same radius value.

The contour must end on a linear segment.

If any of these rules is violated then the part must be programmed as a 3D program (arcs are broken into small linear segments).

There are two different methods of programming an advanced conics program. The first method is the most cumbersome and involves developing two separate shapes. In most cases of advanced conics there is only one contour defined on the print. Certain areas of this contour have taper while other areas do not. If a second shape is required by the CAM system then the programmer must manually calculate how the second shape will differ and construct it using parallel lines. The second method is easier because the programmer will only develop one shape and the system will allow tapers to be applied to certain areas and automatically develop the second shape.

3D PROGRAMMING

This type of programming is the more traditional type of 4 axis programming. All arcs are broken into small linear segments. The most common method and the preferred method of auto segmenting are to break the arcs using a cord height tolerance. By using a tolerance different size radii are broken with different line lengths depending on the requirements of the tolerance. When programming a 3D style program there are several rules to be considered. They are as follows:

The Agie wire offsets are not allowed. The reason for this is that for the Agie offsets to properly function all intersections must be tangent. When the arcs are broken into linear segments, these segments will not be tangent. This rule means that programmed wire path for each cut must be offset by the programming system.

The entry move (lead in) can have the wire tilt in the direction of travel but not to the right or left. This means that the beginning of the lower and upper contour must both fall directly on a line, which if drawn from the wire thread location would pass through all three points.

There must be movement on both shapes for each segment of the program.

The exit move (lead out) has the same requirements as the entry move.

There are several methods of controlling the relationship between the two contours. The first method would be for the two contours to have the same number of segments. Although this method is the simplest it is rarely the case and if a programmer is forced to create contours with equal numbers of segments it can be a very time consuming process. The second method is for the CAM system to compare the two contours and then segment them automatically to have equal numbers of segments. This method will work reasonably well if the two shapes are symmetrical. A square to a circle would be an example of this type of situation. The third method which is the most complex, also allows for the most control of the relationship between the contours. This method involves choosing reference points on both the lower and upper contours. The system then compares each section between the reference points and automatically segments the contours into equal numbers of segments for each section. This is the preferred method when dealing with distinctly different shapes such as extrusion dies. In many cases this technique is a trial and error method. It is important that any system which allows the use of reference points to also allow for easy editing of these points without selecting all of them again, since the number of these points can be significant on a complex part.

U & V vs. Q & R

The Agie CNC 123 control is unique in the fact that it uses Q & R values when programming the upper shape during 4 axis programming. All other controls use U & V to program the upper shape which are some sort of incremental offset (depending on the control) of the X & Y coordinates which represent the lower shape. The Agie use Q which is the angle of tilt perpendicular to the direction of travel and R which is the angel of tilt parallel to the direction of travel. Whether this is better or worse can be argued, but it is a fact, and any system that programs an Agie must calculate these values.

The AgieVision

The AgieVision uses a completely different method of 4 axis programming. This method involves split line programming, which means that each line in the program is split into two parts. The first part defines the lower contour segment while the second part defines the upper contour segment. This method allows arcs to be programmed on either or both contours. The wire offset is fully functional using this technique. This method is much more sophisticated than the CNC 123ís method. However it puts additional demands on the CAM system. If the two contours do not have the same number of segments then the split line programming will not work. The CAM system must be capable of automatically creating equal numbers of segments on the two contours. This is achieved using the same basic techniques as in 3D programming.

SUMMARY

The programming of 4 axis workpieces is perhaps one of the most difficult tasks a CAM system can be asked to perform. The unique requirements of the Agie control may make this task unobtainable for many software packages. If you intend to create 4 axis programs for your Agie then you need to confirm that the software that you purchase is up to the task. It is to your advantage that any package you consider offer both advanced conics and 3D capability. If you are doubtful of a systems ability to program your parts, ask that a program be generated for your machine and then have that program tested on an Agie machine. A pretty picture on a computer screen is not the same as a properly machined workpiece.

If you have made the decision to purchase one of the best machine tools, you do not want its capabilities limited by a second rate CAM system.

About the Author

Randy Mell is the President of CAM-1 and has been involved in NC/CNC programming since 1976. His experience includes working as the Sr. CNC Applications Engineer for KGK International for 5 years and Sales Manager for Camtek USA for 3 years. He has extensive experience in the programming of wire EDM machines and has been instrumental in the development of several CAD/CAM software packages specializing in wire EDM.

You may contact Randy directly at the following e-mail link rmell@CAM-1.com with any further questions you may have.