Gears need to be chamfered and deburred with a controlled, high quality process so as to avoid breakage as excessive carburising along the tooth edges can often cause breakage when the gear is running. It also helps to avoid damaging gears and bearings as, if burrs are not removed, they may chip off during the running cycle and cause damage to the other gears and bearings. Additionally, it aids in avoiding poor tool life in the finishing processes and helps in removal of very sharp burrs, which reduces the risk of tool handling injuries.
Chamfering specified on gears is of the following types - in only one or in both flanks, with a constant size along the profile, with or without chamfer in root diameter. Sometimes, a further rolling operation is required as well.
Chamfering with plastic deformation tools
Advanced chamfering tools use compression (as against cutting) for creating chamfers on the edge. The pressure and deformation of the material may modify the structure of the steel. The chamfering tool is like taper gear, with a width of roughly 10–15 mm, and normally is very well finished, with a surface like a mirror in order to prevent a quick wear.
The key benefits of chamfering with such tools are stronger gear tooth due to better material flow and accurate chamfer angles. The angles of the chamfers are definite by the tool drawing, but the size depends on the rolling time and the pressure of tool against the gear. If the contact time between the tool and piece increases, the chamfer becomes bigger.
The pressure, which defines the deformation force, is generated with a pneumatic cylinder. This method guarantees an ‘elastic force’ that prevents some breakages. Self-centered tools guarantee symmetrical chamfers on both sides of the work piece, even in the instance of slight displacements between adjacent teeth (for example, in a cluster gear). This results in symmetrical and constant chamfer in all teeth.
Gears require a rolling operation after chamfering due to the plastic deformation caused by this operation and to eliminate the ‘burs’ or swellings that form on the material. Whilst burs on the gear face may be removed by deburring tool, those on the lead remain. These burs, usually in the range of 0.05–0.07 mm, cause problems in subsequent grinding phases and actually put the grinding wheel at risk. At this point, a rolling operation on the gears becomes necessary.
The Samputensili method of chamfering-rolling uses a common chamfering/rolling tool and a deburring tool to complete the chamfer-roll-deburr simultaneously.
Before hardening, chamfering and rolling cause structural deformations so that they render the structure more compact. Chamfering causes a build-up of excess material along the profile. Rolling is necessary in order to smooth over this material and it causes the material to become more compact. After the heat treatment, the following is observed:
Cracks do not form in the rolled area
The structure is normal and corresponds to all the structural characteristics of the material
Cracks do not form in the area of material build-up
Tool configuration options
Chamfering/deburring tools can be organised in various configurations for different types of gears, geared shafts and sprockets. For example, cluster gears can be processed in a single operation with multiple chamfer/deburr tools.
Typical tool life
Tool life can be affected by the type of steel, work piece burrs or a particular customer’s requirements. Typical tool life observed in production is as follows:
Deburring tools: 10,000 pieces for each sharpening, maximum 5 sharpenings (6 usages for each tool) and 60,000 workpieces for each deburring tool
Standard chamfering tools: 50,000 pieces for each sharpening (approximately 1.5 milion teeth), maximum 2 sharpenings (3 usages for each tool) and 150,000 workpieces for each chamfering tool
Chamfering/rolling tools: 35,000 workpieces (approximately 1 million teeth) and no sharpening
Gear chamfering/deburring machines require being sufficiently rigid with accurate alignments to e sure best results. Machine configurations based on the chamfering/deburring process are typically either on the horizontal axis (for both shaft type gears and loose gears) or vertical axis (for loose gears). While the horizontal axis configuration is the most versatile, the vertical axis configuration is also popular due to its compactness.
Gear chamfering/deburring is a key process technology in automotive powertrain for achieving smooth gear transmissions. The capability to produce strong accurate chamfers is essential. In addition, for gears that are later finished, a rolling operation can be integrated with chamfering/deburring. Multiple configuration options in tooling enable a solution for a wide variety of automotive gears.☐