CnC Gear Tooth Edge Deburring and Chamfering

Introduction

Deburring and chamfering of gears are not considered as glamorous gear production tasks [2, 3, 4, 5]. This might explain why there is so little gear literature on the subject. However, no “optimized” gear design will survive if the lubricant is contaminated by steel particles released by an un-deburred / un-chamfered component and therefore, deburring and chamfering are essential in gear production. Fig. 1 shows the Toe end of Coniflex[1] teeth after face milling: clearly some form of “clean-up” is required.

Fig. 1: Tooth Toe end after Face Milling

In the following, the term “chamfering” is used to describe the movements while “deburring” is considered as a chamfering operation where only a very small amount of material is removed.

Many manufacturers offer either integrated or discrete solutions for gear tooth chamfering, for example [6, 7, 8, 9], but these usually require dedicated equipment.

On multi-axis CnC machines, chamfering can be performed using different tools such as Ball Mill, End Mill, Chamfer tools or disks. Ball Mills will leave an undesired double edge caused by their spherical tip form. Alternatively, End Mill tools can easily be used to chamfer the tip of the teeth, but can be more limited at Toe or Heel when the helix or spiral angle is large. Disks also can be used to chamfer tooth tips; at Toe and Heel, they are cumbersome and when the tooth profile curvature is large, such as when the tooth number is low, it is difficult to ensure a constant chamfer. Chamfer Tools, i.e. End Mill tools with a conical end, are well adapted to chamfer the tooth tips, Toe and Heel edges, depending on the shaft angle. They are available off-the-shelf in various dimensions and cone angles, and are comparably inexpensive.

A General Approach to CnC Chamfering

This paper summarizes a general approach using End Mill tools for chamfering in a 5Axis CnC machine.  The approach is based on the HyGEARS [1] software and can be used with Face, Spur, Helical, Straight and Spiral bevel gears. Results show that End Mill and Chamfer tools provide excellent flexibility, involve only minimal cycle time and generally allow for consistent chamfering of both tooth flanks.

Because of space limitations, the EM is the only tool presented in this paper. A more in-depth look will be given at the 4th International Conference on Gear Production, held at the Technical University of Munich, Sept 15 to 17th 2021.

In the following paragraphs, standard “off-the-shelf” tools are used and the operations are performed on a 5Axis (or 4+1Axis for some gear types) CnC machine. The figures below are based on “AC” type CnC machines, i.e. Vertical Milling Centers. All methods also apply to “BC” type machines, i.e. Horizontal Turning Centers.

Off-the-shelf tools

Generally speaking, the considered off-the-shelf tools include:

  • End-Mill tools; these are available in a wide range of diameters from many manufacturers, and are relatively inexpensive; they are usually thrown away once worn;

Fig. 2: End Mill tool

  • Chamfer tools; these are more specialized, but are easily found at low prices in different sizes; tip cone angles of 60˚ and 90˚ are common;

Fig. 3: Chamfer tool

End Mill Chamfering

Because of its shape the End Mill (EM) appears to be more limited for some gear geometries and tooth areas. However, given its typically low price and wide availability, it can also be a tool of choice.

Toe and Heel chamfering

EM tools can be used to access the tooth Toe, Heel and Tip edges of most cylindrical gears, and most bevel gears for both small and large pitch cone angles.

When chamfering the Toe or Heel tooth edges, the EM tool must be angled relative to the tooth edge (left, Fig. 4) in order to create a beveled chamfer which then depends on the so-called “Pivot Angle”.

Fig. 4: Typical End Mill installation for Toe / Heel chamfering

Fig. 5: “AC” type CnC machine limits for Toe / Heel chamfering – small pitch cone angle bevel gear

Depending on the pitch cone angle, the CnC machine’s turn-table tilt capability may be exceeded, as is the case for the straight bevel pinion (left, Fig. 5) when chamfering tooth Toe: reducing the Pivot Angle brings the turn table angle to an acceptable value for most AC type machines.

For helical and spiral bevel gears, the Toe and Heel tooth ends present different angles on each tooth flank. Therefore, when chamfering the Toe and Heel tooth ends, it is good practice to adjust the chamfering depth of the obtuse angle to produce the same chamfer length as on the acute angle, or vice-versa.

Tip chamfering

Tip chamfering can be addressed in 2 ways: using either the tip of the EM tool or the side cutting edges of the tool.

Fig. 6: Tip chamfering of a small pitch cone angle bevel gear – EM tool side is used

When the EM’s cutting edges are used, large work piece rotation angles are to be expected when switching tooth flanks (left and center, Fig. 6) and therefore the operation should be split such that all the tips on one tooth flank are done, followed by all the tips on the opposite tooth, thus improving cycle time.

Tip chamfering can also be performed using the EM tool’s tip which, in most cases, is a better approach since the turn table tilt is less and there are no risks of tool interference. However, the tool diameter becomes a limiting factor to avoid damaging the opposite tooth flank.

When chamfering the Tip edges, the EM tool axis must be perpendicular to the axial direction of the tip and angled by the Pivot Angle to provide the desired chamfer (Fig. 7).

Fig. 7: Typical End Mill installation for Tip chamfering

Fig. 8: Before and after chamfering with EM – Straight bevel pinion

In the above, Toe and Heel tooth edge chamfering are performed with neither rotation of the work piece - apart from indexing - nor change in turn table tilt which improves the predictability of the movements. Thus 4Axis CnC machines can be used for Face, spur and helical gears and 4+1Axis CnC machines for straight bevel gears, even for tooth Tip chamfering. By contrast, Tip chamfering of spiral bevel gear teeth usually requires a continuous reorientation of the tool axis in reference to the work piece axis and, therefore, a true 5Axis CnC machine is required.

Fig. 8 shows the Tip edges of a Straight bevel pinion before and after chamfering using an EM. The resulting chamfers are consistent along all tooth edges.

Summary

This paper shows that gear tooth edge chamfering and deburring can be performed on multi-axis CnC machines, for small to medium batch sizes, using off the shelf tools such as End Mills and Chamfer Tools. While most gear machine manufacturers already offer several possibilities, either integrated to their gear cutting machines or in separate embodiments, these solutions are intended for mass production.

For small to medium volumes, and for a varying production in terms of gear types and sizes, such machines often are not economically viable since special tools are also required.

The approach presented in this paper opens the door to chamfering on 5, 4+1 and 4 Axis CnC machines that offer flexibility in the gear types that can be targeted on the same machine. End Mill and Chamfer tools were considered here, but the methods apply equally well to Ball Mill and Conical Side Milling Tools, i.e. CoSIMT.

In all cases, it is possible to chamfer either, or both, the Toe and Heel edges, and the Tip edges. In most instances, adjusting chamfer parameters allows chamfering every part of the tooth using a combination of End Mill and Chamfer tools.

While deburring and chamfering is an unloved task, it is fundamental in gear finishing and by far not a trivial task since the targeted geometries are complex and varied.

The methods presented in this paper are all integrated into the HyGEARS software, whose post-processor generates the part programs for any CnC machine and controller on the market. Therefore, an unused, or lightly used, 4, 4+1 or 5 Axis CnC machine could be put to good use chamfering parts.

Authors

Claude Gosselin, Ph.D., P.Eng., Involute Simulation Softwares Inc., Québec, Canada
B. Leitz, B.Ing., Neugart GmbH, Germany

www.HyGEARS.com
www.neugart.de

References


[1] Coniflex is a registered Trademark of The Gleason Works, Rochester, NY, USA

  1. www.HyGEARS.com
  2. Horst Bruce, A Basic Guide to Deburring and Chamfering Gears, Gear Technology, July August 1995
  3. McGuinn Jack, Chamfering/Deburring Still a Player – Now More than Ever, Gear Technology, September October 2018
  4. Klein Gottfried, The Evolution of Gear Chamfering, September October 2018
  5. Ribbeck Karl-Martin, Deburring – The Underestimated Task, September October 2018
  6. www.Liebherr.com, Deburring and Chamfering Machine LD 180 / 280 C
  7. www.redinmachine.com
  8. Weiler Abrasives, Gear Deburring with Brushes, www.WeilerAbrasives.com
  9. www.cwst.com/shot-peening-overview/glass-bead-peening