Machining Techniques
Machining Techniques I)
EFFECTS of CIRCULAR TOOL PATHS on FEEDRATES A) The programmed feedrate for circular tool paths on almost all systems is applied along a path through the center of cutter along the direction of travel. If the cutter is removing a full cutter width of material, this is the appropriate feedrate. Unfortunately, this is usually not the normal condition. Cutters are usually removing only a partial cutter width of material. Under these conditions. the feedrate should be factored to more closely represent the actual chip load where the cutter contacts the arc. B) A condition that will clearly demonstrate this phenomenon is when machining the inside and outside of a cylindrical tube
1) If equal feedrates are applied to both the internal and external cut. a noticeable difference can be observed in horsepower requirements. Circular Path Feedrates
02-2
Machining Techniques On a low horsepower machine. The internal cut will either stall or nearly stall the machine. The external cut will barely register on the meter. (a) For this external cut the appropriate factored feedrate would be:.
fFEED is Factored Feedrate nFEED is Normal Feedrate CutArc is Cutter Path Arc PartRad is Part Radius fFEED
= = =
nFeed • CutArc / PartRad 20 • 2.5 / 1.75 28.6 IPM
(b) for this internal cut the appropriate factor feedrate would be:
fFEED is Factored Feedrate nFEED is Normal Feedrate CutArc is Cutter Path Arc BoreRad is Bore Radius fFEED = = =
nFeed • CutArc / BoreRad 20 • 0.75 / 1.5 10 IPM
2) Very few programmers expend the effort to accurately factor all circular cuts. However. the better programmers are aware of the phenomenon and make a reasonable effort to factor their feedrates for the more obvious conditions. 3) This is the kind of laborious effort that needs to be automated at a system level.
Circular Path Feedrates
02-3
Machining Techniques
Chapter 3
Chip Thinning Factors
03-1
Machining Techniques I)
CHIP THINNING FACTORS A) Chip loads as computed are accurate along a line parallel to direction of motion that passes through the centerline of cutter. For roughing cuts or deep facing cuts this is the appropriate feed. However, when performing radial cuts, the chip thickness diminishes as the width of radial cut is reduced (see chart on radial chip loads. Figure 3.1). This chip thinning effect is significant for light cuts or spring finish passes. B) The feedrate effects of removing a thin (0.020 to 0.030 thick) shelf of material with end of cutter in conjunction with finish spring passes is insignificant and can be basically ignored. Feedrates should be adjusted to comply with radial chip load chart values. These adjustments will have a significant reducing effect on cycle times without any detrimental affect on cutter wear, part tolerance or cosmetic appearance. C) If a cutter is making a regular facing cut, in conjunction with a peripheral cut, the chip thinning phenomenon must be disregarded. In these cases. the normal feedrate calculations should be used. D) The chip thinning principle can also have an effect on facing cuts, especially when a large fillet radius is being used (see chart in Figure 3.2 for applications). E) The table below lets you determine the radial chip thickness for a given cutter diameter and feed per tooth. Find the factor that corresponds to the given width of cut. The feed per tooth diameter multiplied by this factor gives the actual radial chip thickness (see sketch). F)
Example: 2.0” cutter diameter: 0.130 width of cut; 0.003 feed per tooth. Where the vertical line for 0.130 width of cut crosses the horizontal line for 2.000" cutter diameter. the factor is 0.50. This factor times 0.003 feed gives 0.0015 for maximum radial chip thickness.
Chip Thinning Factors
03-2
EFFECTS of CIRCULAR TOOL PATHS on FEEDRATES A) The programmed feedrate for circular tool paths on almost all systems is applied along a path through the center of cutter along the direction of travel. If the cutter is removing a full cutter width of material, this is the appropriate feedrate. Unfortunately, this is usually not the normal condition. Cutters are usually removing only a partial cutter width of material. Under these conditions. the feedrate should be factored to more closely represent the actual chip load where the cutter contacts the arc. B) A condition that will clearly demonstrate this phenomenon is when machining the inside and outside of a cylindrical tube
1) If equal feedrates are applied to both the internal and external cut. a noticeable difference can be observed in horsepower requirements. Circular Path Feedrates
02-2
Machining Techniques On a low horsepower machine. The internal cut will either stall or nearly stall the machine. The external cut will barely register on the meter. (a) For this external cut the appropriate factored feedrate would be:.
fFEED is Factored Feedrate nFEED is Normal Feedrate CutArc is Cutter Path Arc PartRad is Part Radius fFEED
= = =
nFeed • CutArc / PartRad 20 • 2.5 / 1.75 28.6 IPM
(b) for this internal cut the appropriate factor feedrate would be:
fFEED is Factored Feedrate nFEED is Normal Feedrate CutArc is Cutter Path Arc BoreRad is Bore Radius fFEED = = =
nFeed • CutArc / BoreRad 20 • 0.75 / 1.5 10 IPM
2) Very few programmers expend the effort to accurately factor all circular cuts. However. the better programmers are aware of the phenomenon and make a reasonable effort to factor their feedrates for the more obvious conditions. 3) This is the kind of laborious effort that needs to be automated at a system level.
Circular Path Feedrates
02-3
Machining Techniques
Chapter 3
Chip Thinning Factors
03-1
Machining Techniques I)
CHIP THINNING FACTORS A) Chip loads as computed are accurate along a line parallel to direction of motion that passes through the centerline of cutter. For roughing cuts or deep facing cuts this is the appropriate feed. However, when performing radial cuts, the chip thickness diminishes as the width of radial cut is reduced (see chart on radial chip loads. Figure 3.1). This chip thinning effect is significant for light cuts or spring finish passes. B) The feedrate effects of removing a thin (0.020 to 0.030 thick) shelf of material with end of cutter in conjunction with finish spring passes is insignificant and can be basically ignored. Feedrates should be adjusted to comply with radial chip load chart values. These adjustments will have a significant reducing effect on cycle times without any detrimental affect on cutter wear, part tolerance or cosmetic appearance. C) If a cutter is making a regular facing cut, in conjunction with a peripheral cut, the chip thinning phenomenon must be disregarded. In these cases. the normal feedrate calculations should be used. D) The chip thinning principle can also have an effect on facing cuts, especially when a large fillet radius is being used (see chart in Figure 3.2 for applications). E) The table below lets you determine the radial chip thickness for a given cutter diameter and feed per tooth. Find the factor that corresponds to the given width of cut. The feed per tooth diameter multiplied by this factor gives the actual radial chip thickness (see sketch). F)
Example: 2.0” cutter diameter: 0.130 width of cut; 0.003 feed per tooth. Where the vertical line for 0.130 width of cut crosses the horizontal line for 2.000" cutter diameter. the factor is 0.50. This factor times 0.003 feed gives 0.0015 for maximum radial chip thickness.
Chip Thinning Factors
03-2
