Method of machining screw

Patent metadata

Field	Value
Publication number	US-10173257-B2
Application number	US-201615501368-A
Country	US
Kind code	B2
Filing date	Jan 28, 2016
Priority date	Jan 28, 2016
Publication date	Jan 8, 2019
Grant date	Jan 8, 2019

Abstract

A method of machining a screw is provided that is capable of preventing formation of a protruding section at a thread tip section. A thread is formed by cutting on a cylindrical body, and a surface of the thread is plastically deformed by rolling. Because of the cutting, a width between-side surfaces of a thread tip section is in a narrowed state as compared to a normal width. This width is narrowed toward a tip of the thread while a thread body section has a width expanded as compared to a normal width. Consequently, the side surfaces are formed to bulge by an excess thickness portion as compared to normal side surfaces. The rolling plastically deforms both side surfaces to cause the excess thickness portion to plastically flow toward the side surfaces.

First claim

The invention claimed is:

1. A method of machining a screw including forming a thread on a work material by cutting and subsequently plastically deforming a surface of the thread by rolling,
wherein because of the cutting, a width between both side surfaces of a tip section of the thread is in a narrowed state as compared to a width between both normal side surfaces of the thread tip section and is gradually narrowed toward a tip of the thread while a body section closer to a base end as compared to the tip section of the thread has a width between both side surfaces of the thread body section expanded as compared to a width between both normal side surfaces of the thread body section so that each of the side surfaces of the thread body section is formed to bulge by an excess thickness portion as compared to the normal side surfaces of the thread body section, and
wherein the rolling plastically deforms the both side surfaces of the thread body section to cause the excess thickness portion to plastically flow on the both side surfaces of the thread tip section such that the width of the tip section increases to normal and the thickness of the thread body section decreases to normal.

2. The method of machining a screw according to claim 1 , wherein the cutting forms the thread tip section into a shape tapered toward a tip thereof.

3. The method of machining a screw according to claim 1 , wherein the cutting forms an underfill space between each of the side surfaces of the thread tip section and each of the normal side surfaces of the thread tip section and an excess thickness portion between each of the side surfaces of the thread body section and each of the normal side surfaces of the thread body section such that the underfill space and the excess thickness portion have volumes close to each other.

4. The method of machining a screw according to claim 1 ,
wherein the work material is a cylindrical body,
wherein the cutting is performed by using a cutting tap on an inner circumferential surface of the cylindrical body to form a female screw on the cylindrical body inner circumferential surface, and
wherein the rolling is performed by using a rolling tap on body side surfaces of a thread of the female screw.

5. The method of machining a screw according to claim 1 ,
wherein the work material is a shaft body,
wherein the cutting is performed by using a threading die on an outer circumferential surface of the shaft body to form a male screw on the shaft body outer circumferential surface, and
wherein the rolling is performed by using a rolling die on body side surfaces of a thread of the male screw.

6. The method of machining a screw according to claim 1 ,
wherein a multiple start screw is formed by the cutting on the work material, and
wherein the rolling is performed on threads of the multiple start screw.

7. The method of machining a screw according to claim 1 , wherein the rolling is followed by a heat treatment to increase surface hardness of a thread as compared to a state before the heat treatment.

Assignees

• Nittan Valva

Inventors

• Kameda Michihiro
• Inoue Masaaki

Classifications

• C21D9/0093 Primary

  for screws; for bolts · CPC title

• B23G1/02 Primary

  on an external or internal cylindrical or conical surface, e.g. on recesses (B23G1/16, B23G1/22, B23G1/32, B23G1/36 take precedence) · CPC title

• B23G5/06

  Taps (chucks therefor B23B31/00) · CPC title

• B21H3/10

  twist-drills; screw-taps · CPC title

• B21H3/08 Primary

  internal screw-threads · CPC title