CA1215257A - Process and product for increasing speed and precision of gear manufacture - Google Patents

Abstract

Abstract of the Disclosure A gear cutting tool having roughing and finishing cutting blades is provided with a titanium nitride coating on only the roughing cutting blades of the tool

Description

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1 Background and Brief Description OI Invention It is known in the art of manufacturing gears to utilize cuttin~ to~ls which have two basic forms of cutting blades included on the tool for contacting a workpiece. A first type of cutting blade is designed to form a rough tooth slot in a work blank and is referred to as a "roughing" cutting blade or tool. The second type of cutting blade is designed to complete the specific geometry of the tooth form of the gear being manufactured, and this type of blade is referred to as a "finishing" cutting blade or tool. A typical tool which includes both forms of cutting blades and which is designed for manufacturing straight bevel gears is illustrated and discussed in Wildhaber, et al, U.S. Patent 2,620,709 dated December 9, 1952. This patent provides information about the type of cutting tools which are the subject of this specification.
~ n recent years, there has developed an interest in treating cutting tools in some way to extend the life of the tool and to permit higher cutting speeds and greater productivity. Various forms of coating treatments are now available and offer varying degrees of improvement in tool life, cutting speed, and/or quality of finish. However, it has no~ been learned that ~he use of coating materials sometimes changes the basic cutting characteristics of known cutting tools so ,'Y~

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as to introduce changes in the tooth geometry or finish of a given gear-cutting job. In the case of the cutting tools of the type described above in which roughing and finishing blades are included on a single cutter body, it has been necessary to provide considerable adjustment in machine settings in order to compensate or modifications in tooth geometry or fin~sh introduced by the use of coating materials on the cutting blades themselves. This requirement for machine adjustment reduces the desireability of using coating materials because many of the set-up procedures for given machines operating to produce specific forms of gears are well known and established in manufacturing plants and would be subjec-t to extensive monitoriny to compensate for changes introduced by coated cutting tools. Thus, a manufacturing operation would not only have to adjust machines according to whether coated or uncoated cutting tools were being used, but would also have to create a system for assuring that such adjustments are made at the appropriate times. This would result in aaditional lost time between production runs and could lead to possible scrap losses for work performed with incorrect settings. ~urthermore, it has been found, in certain instances, to be nearly impossible to fully adjust for the errors introduced by otherwise very acceptable coating materials in the specific Gleason machines which utilize the type of cutting tool disclosed herein.

The present invention involves a rather remarkable discovery that substantially all of the expected advantages of coating of tools (e.g., increased tool life, higher speed cutting, and improved quality of finish) can be obtained with presently known coating materials if the coating material is applied only to the roughing cutting blades of the tool and not to the finishing cutting blades of the tool. Thus, the roughing cutting blades which are removing substantial amounts of metal from a work blank are provided with the additional advantages obtained with the use of coating materials, while the finishing cutting blades, which remove very little material, are able to finish the gear teeth profiles to precise and known geometric profiles without a need for adjusting machines from their traditional settings for doing a particular job.
Thus, even though the discovery is a relatively simple concept, it is one which has significant impact on the ease with which production machines can be used ~or manufacturing various types of gears. Productivity can be increased without sacrificing quality of finish or precision of shape, and all of this can be done without a need for relearning specific machine settings for a specific job. In addition, the invention produces the quite unexpected result of providing for all of these benefits through a use of a lesser amount of expensive coating material since only the roughing blades of a given process need be coated in accordance with the discovery of this invention.

These and other features and advantages of the invention will be discussed below where reference will also be made to the accompanying drawing as briefly described below.

Brief Descri tion of Drawin P g The drawing shows an elevational view of a typical cutter head having roughing and finishing cutting blades incorporated in its structure.

5'~'7 Detailed Description of Invention Referring to the drawing, a typical cutting tool is illustrated. The tool includes a cutter body 10 upon which are secured a number of cutting blade segments 11 and 12. Each cutting blade segment is designed with a plurality of cutting blades extending outwardly therefrom so that an assembly of a number of such segments on a cutter body 10 produces a tool of the t~pe shown. Such tools are well known in the art ancl are mounted for rotation on well known machinery which provides for a rotation of the tool relative to a workpiece mounted on a spindle. In addition, relative transversing motion is provided between the tool ana the workpiece so that the rotating tool can advance along the length of a tooth slot being formed. In this way, a completed tooth slot can be formed with a single rotation of the tool.

Tools of this type are designed to include a number of roughing cutting blades 14 arranged in series about one portion of the cutter body 10 together with a number of finishing cutting bla~es 16 arranged in series about a different portion of the cutter body 10.
In the illustrated embodiment, forty-four roughing cutting blades 14 are carried on eleven blade segments 11, while twenty finishing cutting blades are carried on five blade segments 12. In addition, although not pertinent to the present invention, the tool may be provided with a chamfering device 18 positioned between the two series of cutting blades.

- 30 In accordance with the invention, it has been discovered that only the roughing cutting blades 14 need be coated with a material to increase their hardness for improving tool life and cutting speed. In S ~5 ~

fact, by not ~oating the finishing cutting blades with the same material, it has been discovered, quite unexpected]y, that the overall speed and precision of the process can be greatly improved. Thus, the finishing blades 16 are left in their sharpened condition without a need for additional treatment of the type provided for the roughing cutting blades which are illustrated.

As an example of a specific coating material that may be applied to the roughing blades, the following has been used successfully:

1~ Titanium Nitriae (TiN) was applied to a twenty-one inch (di~neter~ cutting tool manufactured from M2 steel. Coating was applied by a known physical vapor deposition process at ab~ut 1000 degrees F. Distortion was minimized (tool tolerance requirements were on the order of 0.0002 inches).

2. The coated tool was tested on a Gleason No. 725 REVACYCLE machine on a standard production job. The machine was operated so as to rough and finish each tooth slot in a single pass of the tool relative to the workpiece.

Although the invention has been described with reference to a specific form of cutting tool which can be greatly improved through the use of a coating on only its roughing blades, it is contemplated that the basic relationship between roughing ana finishing tools can be maintained in other processes and with other forms of equipment. For example, tools of the type illustrated are also manufactured with only roughing l5Z~ ~

blades on a single cutter body and with only finishing blades on a single cutter body. In accordance with the basic discovery of this invention, it would be possible to provide a coating on only the cutter body having the roughing blades for forming the roush tooth slots on a gear blank while omitting any use of coating on a separate cutter head ~7hich carries only finishing blades. These and other variations are intended $o be includea within the scope of this invention as more completely defined in the claims which follow.

Claims (7)

What is claimed is:

1. A process for improving the speed and precision of a cutting tool designed for manufacturing gears, said tool being of the type which includes roughing cutting blades and finishing cutting blades on a single cutter body so that gear tooth slots can be rough cut and finish cut in a single set-up of the tool relative to a work blank, said process comprising the coating of only the roughing cutting blades of said tool with a material which increases hardness of the roughing cutting blades.

2. The process of claim 1 wherein said coating material comprises titanium nitride.

3. A cutting process for increasing the speed with which gears can be manufactured comprising the steps of rough cutting tooth slots in a gear blank with cutting blades which have been coated with a material to increase hardness of their cutting surfaces, and finish cutting the rough cut tooth slots with cutting blades which have not been coated with said material.

4. The process of claim 3 wherein said cutting tools for rough cutting tooth slots are coated with titanium nitride.

5. In a tool of the type which includes a plurality of roughing cutting blades and a plurality of finishing cutting blades on the same cutter head body, the improvement comprising said roughing blades being provided with a coating for increasing hardness said finishing blades being not coated with said coating used on the roughing blades.

6. The improvement of claim 5 wherein said coating comprises titanium nitride.

7. The improvement of claim 5 wherein said cutting blades are formed on segments which can be removably secured to said cutter head body, and wherein the segments for said roughing blades are arranged in series about the periphery of one part of the cutter head body and the segments for said finishing blades are arranged in series about the periphery of another part of the cutter head body.