JPH039108A - Manufacturing method for screw parts - Google Patents

Abstract

PURPOSE:To ensure stabilized strength of a screw by forming a wire rod obtained by carburizing of a low carbon steel wire rod or a steel material obtained by carburizing of a low carbon steel material into the shape of a screw, and thereafter performing surface-hardening only on the top of thread by refine-hardening. CONSTITUTION:A low carbon steel material or a low carbon steel wire rod is carburized, and the formed into the shape of a screw by a cold (or warm) pressing-molding machine and a thread rolling machine. After that, only the top of thread is surface-hardened by refine-hardening. As a result, a carburized layer with high hardeness is formed on the top of thread, and the root of thread becomes a structure of least caburized layer. Thus, the desired stabilized strength can be obtained so as to prevent the generation of delay-breakage.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing threaded parts such as self-tapping screws in which only the threaded portions are surface hardened.

(Prior Art and Problems to be Solved by the Invention) Tapping screws and forming screws are used in many assembled products such as automobiles and home appliances. These screws are fastened to parts made of various materials, such as iron plates, brass plates, aluminum, zinc die-casting, and resin, by forming female threads. In this way, with self-tapping screws, the surface of the male thread part needs to be hard in order to form a female thread in the mating material at the male thread part, but since a large axial force is sometimes generated when tightening the screw, the thread part If the entire part is made hard, delayed failure will occur.

For this reason, these threaded parts are generally subjected to surface hardening treatment by carburizing and quenching to make the surface hard and the inside soft (FIG. 6). When observing the fractured surface of a threaded component that has suffered delayed fracture, it was found that cracks occur from the thread troughs, which propagate to the inside and cause the thread to break, which has become a major problem.

In addition, recently, many screw parts have been used in which flat washers are incorporated into tapping screws and forming screws. The conventional method for these is to incorporate a washer before thread rolling, process the thread rolling process, and then simultaneously carburize and harden the thread and washer. The flat washer is made of low carbon steel, but if it is carburized and quenched, it may crack when fastened, so before it is assembled into the screw, a copper patch is applied to prevent carburization, and after the carburization and quenching is completed, the copper is removed by acid treatment. There is. This method not only increases the cost of applying copper plating and the cost of removing copper plating, but also increases the manufacturing period. Furthermore, there are many issues such as the risk of pollution caused by acid treatment. The present invention was invented with the aim of solving these problems.

(Means for Solving the Problems) In order to achieve this object, the first invention involves processing the shape of threaded parts using a carburized low-carbon steel wire or a carburized low-carbon steel. line.

The second invention is a method for manufacturing screw parts in which only the thread threads are surface hardened by temper quenching. This is a manufacturing method for threaded parts in which thread rolling is performed, followed by temper quenching to surface harden only the threads. Further, in the third invention, only carburizing is performed on a blank formed using low carbon steel material before thread rolling processing, a washer or a part is assembled therein, thread rolling processing is performed, and then temper quenching is performed. This is a method for manufacturing screw parts in which only the threads are surface hardened. Furthermore, the fourth invention provides a blank that is surface-hardened by carburizing and quenching and is not yet subjected to thread rolling processing, is once made to have a low hardness by annealing, and then subjected to thread rolling processing,
This is the method for manufacturing a threaded component according to the second or third invention, in which the thread is then subjected to temper quenching to surface harden only the threads.

(Function) If you make a blank using a wire rod whose surface has been carburized, or if you process a blank from a low carbon steel wire rod and only carburize it, then perform thread rolling, the carburized portion of the thread root will be removed. Since the thread rolling structure moves to the thread ridge, the carburized part at the thread root disappears, or even if it remains, it is very small, and the high carbon due to carburization in the thread crest is present on both sides of the thread. Accumulates near the surface. When temper quenching is performed after this, a high hardness part exists on the surface of the thread due to quenching, and the thread root part has low carbon, low hardness, and creates an ideal threaded part with toughness. be able to.

In addition, for screws with built-in washers, the blank is only carburized before the washer is installed, the washer is installed and the thread is rolled, and then temper quenching is performed, so that the thread ridges become carburized and quenched, and the thread valleys become carburized. The washer and washer can be used to create low-carbon, tough, and low-hardness threaded parts.

(Example) Embodiments of the present invention will be described below based on the drawings.

First, as shown in Fig. 1, in the first embodiment, a low carbon steel material or a low carbon steel wire rod is carburized, the steel material is cut, and a threaded part is shaped using a heading forming machine and a thread rolling machine. This is a method of manufacturing screw parts in which only the threads are surface hardened by subjecting them to temper quenching.

Next, in the second embodiment, as shown in Fig. 2, a low carbon steel material is cut, a blank before thread rolling is formed using a heading forming machine, only carburizing treatment is performed, and the blank is thread rolled. This is a method for producing threaded parts in which only the threads are surface hardened by performing T-forming, followed by temper quenching.

In addition, in the third embodiment, as shown in Fig. 3, a low carbon steel material is cut, a blank before thread rolling is formed using a heading forming processing machine, only carburizing treatment is applied to the blank, and a washer or a part is formed on the blank. This is a method of manufacturing threaded parts in which only the threads are surface hardened by assembling the parts, subjecting them to thread rolling, and then subjecting them to temper quenching.

Furthermore, as shown in FIG. 4, in the fourth embodiment, a low carbon steel material or a low carbon steel wire is cut, a blank before thread rolling is formed using a heading machine, and this blank is surface hardened by carburizing and quenching. This blank is then annealed to lower its hardness, and this blank is then subjected to thread rolling, followed by temper quenching to produce a threaded part in which only the threads are surface hardened. This method can be applied to both normal threaded parts (those that do not incorporate washers and the like) and threaded parts that incorporate washers and the like.

In these manufacturing methods, a blank is made using a wire rod whose surface has been carburized, or a blank is processed from a low carbon steel wire rod and only carburized, followed by thread rolling. Because the carburized part moves to the thread thread part and becomes a rolled thread structure, the carburized part at the thread root disappears, or even if the carburized part remains, it is a very small amount, and the thread part has a high carbon content due to carburization. is accumulated near the surface of the screw image. When temper quenching is performed after this, as shown in Figures 5 and 7, there is a high hardness part on the surface of the thread due to quenching, and the valley part of the thread is made of low carbon and low hardness. It is possible to create ideal threaded parts that are both tough and durable.

In addition, for screws with built-in washers, the blank is only carburized before the washer is installed, the washer is installed and the thread is progressed, and then thermal quenching is performed, so that the thread part becomes carburized and quenched, and the thread root and Washers can be used to create low-carbon, tough, and low-hardness threaded parts.

(Effects of the Invention) As is clear from the embodiments described above, the manufacturing methods of claims 1 and 2 are characterized in that a blank is made using a wire rod whose surface is carburized, or a blank is made from a low carbon steel wire rod. This is a method in which only carburization is performed after processing, then thread rolling is performed, and then temper quenching is applied.A carburized layer with high hardness is formed at the thread crest, and the thread root has a structure with very little carburized layer. Therefore, screws with the desired stable strength can be manufactured without causing delayed fracture.

The manufacturing method according to claim 3 is a method in which only carburizing is performed on a blank before thread rolling processing, parts such as washers are assembled therein, thread rolling is carried out, and temper quenching is then performed. Since the parts are not carburized and quenched, and a highly hard carburized layer is formed only on the threaded portion, screwed parts with the desired stable strength can be produced without changing the material properties of the washer.

In the manufacturing method of claim 4, the blank before thread rolling is once made to have a low hardness by annealing, parts such as washers are assembled thereto for thread rolling, or the blank is subjected to direct thread rolling processing, and then adjusted. This is a pre-quenching method, and by including an annealing process depending on the material of the screw material, it is possible to obtain effects such as facilitating thread rolling and extremely extending the life of the tool.

[Brief explanation of drawings]

Figure 1 is a manufacturing process diagram showing the first embodiment, Figure 2 is the manufacturing process diagram showing the second embodiment.
Fig. 3 is a manufacturing process diagram showing the third embodiment, Fig. 4 is a manufacturing process diagram showing the fourth embodiment, and Fig. 5 is a threaded part location in this embodiment. Carburization distribution map of the surface,
FIG. 6 is a carburization distribution diagram of the threaded portion of a conventional self-tapping screw, and FIG. 7 is a microscopic photograph showing the metallographic structure of the threaded portion of the present example.

Claims (1)

[Claims] 1) A threaded part is shaped using a carburized low-carbon steel wire rod or a carburized low-carbon steel wire, and then only the threads are surface hardened by temper quenching. Features: Manufacturing method for screw parts. 2) A screw characterized by carburizing a blank formed from low carbon steel before thread rolling, subjecting it to thread rolling, and then subjecting it to temper quenching to surface harden only the thread threads. How the parts are manufactured. 3) Only carburizing is performed on a blank made of low carbon steel before thread rolling, then a washer or part is assembled into this and thread rolling is performed, and then temper quenching is performed to surface harden only the threads. A method for manufacturing a screw part, characterized by: 4) A blank that has been surface hardened by carburizing and quenching before thread rolling is once lowered in hardness by annealing, then thread rolling is performed, and then temper quenching is performed to surface harden only the threads. The method for manufacturing a threaded component according to claim 2 or 3, characterized in that: