Powder metallurgy molding is a process in which metal powder or mixture is placed in a female mold cavity, and pressure is applied to the powder through die punching to form a compact with a certain shape, size, porosity and strength. Below I have compiled some papers on powder metallurgy parts forming technology. Welcome to read! Part 1 of the paper on powder metallurgy parts forming technology

A brief description of the powder metallurgy forming method

Abstract: Powder metallurgy forming is the process of converting metal into A process in which powder or mixture is placed in a female mold cavity, and pressure is applied to the powder through die punching to form a compact with a certain shape, size, porosity and strength. Whether the molding method is reasonable or not directly determines whether the product can be produced smoothly and whether it has the ability to produce in batches and reduce costs. In addition, the molding effect will affect the subsequent processes of the product and the final quality of the product. This article explains several common methods of powder metallurgy molding, as well as the corresponding principles of different methods and the density distribution of the pressed blanks. It also provides a theoretical basis for how to choose the most appropriate method for molding and pressing different types of products.

Keywords: One-way suppression Two-way suppression

CLC classification number: TP217.4 Document identification code: A Article number: 1672-3791(2015)02(b)-0000 -00

　1. Introduction

Powder metallurgy uses metal powder (or a mixture of metal powder and non-metal powder) as raw materials to manufacture metal materials and composite materials through shaping and sintering. And the process of various types of products1. With the development of powder metallurgy technology, the performance requirements of powder metallurgy products are also constantly improving, resulting in a variety of different molding methods. At present, there are two traditional pressing and molding methods: one-way pressing and two-way pressing. The two-way pressing is divided into female mold floating type pressing and female mold pulling down type pressing.

2. Molding method

2.1 One-way pressing

The working principle of one-way pressing: the positions of the female mold cavity and the lower die punch are fixed, and the upper die Driven by the cam of the press, the punch enters the female mold cavity downwards and pressurizes the powder in the female mold cavity, so that the powder is pressed into a blank with a certain density and strength. 2, 3

A cycle of one-way pressing has the following steps.

A Powder filling: Powder is fed manually or with a mechanical powder feeder, and is filled into the female mold cavity using powder gravity.

B One-way pressing: After the powder is filled, the positions of the female mold cavity and the lower die punch are fixed, and the upper die punch is driven by the press cam downwards into the female mold cavity, so that the powder is pressed into into a blank with a certain density and strength.

C Pressure holding: In order to effectively transmit the pressure and ensure uniform density distribution of the blank, the upper die punch should be kept stationary at the 180-degree forming and pressing position for a period of time to ensure that there is enough air in the blank. Time escapes. 4.

D demoulding: After the pressure holding is completed, the upper die punch is driven upward and out of the female mold cavity by the reset of the press cam, and the lower die punch is pushed up by the force of the lower cylinder of the press. Exit the vaginal model cavity.

E Reset: The upper die punch retreats to the highest point, the powder feeder pushes out the pressed blank, and the lower die punch returns to a fixed position. At the same time, the powder is filled in the female mold cavity under the action of gravity.

2.2 Two-way pressing

Two-way pressing is generally divided into female mold floating pressing and female mold pull-down pressing.

　2.2.1 Female mold floating pressing

Working principle of female mold floating pressing: The female mold is supported by a spring and is in a floating state. The lower die is fixed and the upper die is punched. Driven by the cam, it enters the female mold cavity downwards and exerts downward pressure on the powder. When starting to pressurize, since the friction force between the powder and the female model cavity wall is less than the spring support force, only the upper die punch moves downward. As the pressure increases, the friction force between the powder and the female model cavity wall is greater than the spring support force. The female mold cavity moves downward together with the upper die punch, and moves relative to the lower die punch, thereby achieving a two-way pressing effect. 2, 3.

A cycle of female mold floating pressing has the following steps.

A Loading: Load the powder evenly into the female mold cavity manually or by an automatic powder feeder.

B Upper punch and lower press: After the powder filling is completed, the female mold is supported by the spring, and the lower punch position is fixed. Driven by the press cam, the upper punch enters the female mold cavity downwards and aligns the female mold. The powder in the mold cavity exerts downward pressure.

C Female mold floating: As the pressure exerted by the upper die punch continues to increase, the friction between the powder and the wall of the female model cavity also continues to increase. When this friction force is greater than the spring support force of the female model cavity At this time, the female mold cavity and the upper die punch move downward together until the blank is formed

D pressure holding: In order to effectively transmit the pressure and ensure uniform density distribution of the blank, the upper die punch and the female mold cavity Move downward to the molding position of the blank and hold it still for a period of time to allow enough time for the air in the blank to escape. 4.

E Demolding: After the pressure holding is completed, the upper die punch is driven upward by the reset of the press cam to separate from the female mold cavity, and the female mold is moved downward by the downward pulling force of the pressing cylinder of the press until the blank is The piece protrudes from the female mold cavity.

F reset: the upper mold punches back to the highest point, the powder feeder pushes out the blank that has come out of the female mold cavity, and then the female mold is returned to the powder filling position by spring support, and at the same time the powder is filled under the action of gravity in the female model cavity.

2.2.2 The female mold is pulled down for pressing

The lower punch is fixed in a fixed position, and the upper punch is driven by the cam, downwards into the female model and into the cavity While the powder exerts downward pressure, the negative mold cavity also moves downward together with the upper die punch due to the downward pulling force of the pressurizing cylinder, and moves upward relative to the lower die punch. This achieves two-way suppression of upper and lower punches 2 and 3.

One cycle of the female mold pull-down pressing process has the following steps.

A Loading: Load the powder evenly into the female mold cavity manually or by an automatic powder feeder.

B Two-way pressing: After the powder filling is completed, the upper punch, driven by the cam, enters the negative mold cavity downwards and exerts downward pressure on the powder in the cavity. At the same time, the female mold is also pressed down by the press. Under the action of the downward pulling force of the cylinder, they move downward together, causing the lower die punch to move upward relative to the female die.

C Pressure holding: In order to effectively transmit the pressure and ensure uniform density distribution of the blank, the relative position of the upper and lower punches and the female mold cavity remains unchanged for a period of time, so that the blank The air in the piece has enough time to escape. 4.

D Demolding: After the pressure holding is completed, the upper die punch is driven upward by the reset of the press cam to separate from the female mold cavity, and the female mold is moved downward by the downward pulling force of the pressing cylinder of the press until the blank is The piece protrudes from the female mold cavity.

E reset: The upper mold punches back to the highest point, the powder feeder pushes out the blank that has come out of the female mold cavity, and then the female mold removes the downward cylinder pressure and returns to the powder filling position. At the same time, the powder is in the It is filled into the female model cavity under the action of gravity.

3 The relationship between pressing methods and blank density and their applications

3.1 The relationship between one-way pressing blanks and density

Density analysis of one-way pressing: from It can be seen from the pressing principle that the pressure of one-way pressing is transmitted downward from the upper die punching direction. From a transverse analysis, the density of the upper layer of the blank that is in contact with the upper die punch gradually increases from the center to the edge, and the edge part of the top has the highest density. This is because the pressing process will produce a lateral reaction force on the powder on the wall of the female mold cavity, so The rim is higher than the heart. From a longitudinal analysis, the density gradually decreases from top to bottom. At this time, due to the pressure in the process of compacting the powder, the slip and deformation of the powder will generate an upward reaction force. As the transmitted pressure continues to decrease, it is more difficult for the powder to slip and deform, ultimately resulting in a low density of the bottom blank5. It can be seen that the density distribution of the single-pressed blank gradually decreases from the edge to the center and from top to bottom.

3.2 Relationship between bidirectional pressing blanks and density

Density analysis of bidirectional pressing: From the principle of bidirectional pressing, it can be seen that the pressure of bidirectional pressing is transmitted from both ends to the center. At both ends of the blank that are in contact with the die punch, transverse analysis shows that the density also gradually increases from the center to the edge. The theory is consistent with unidirectional pressing. From the longitudinal analysis, since the pressure is transmitted from both ends to the center, the powder at both ends of the blank can fully undergo slip deformation and the density is high. However, as the pressure transmission decreases, the density powder in the center cannot fully slide and deform, and the density is low. It can be seen that the density distribution of the bidirectionally pressed blank gradually decreases from the edge to the center, but the blank is pressed by pressure from both ends, which reduces the height-to-diameter ratio of the blank and reduces the difference in pressure reduction along the height, making the density distribution more uniform. 5.

4 Conclusion

With the continuous development of social science and technology, powder metallurgy has also undergone earth-shaking changes, and various forming and pressing methods continue to appear. But no matter what kind of pressing method (friction mandrel pressing, lower die punch floating pressing, combined punching pressing, reversing pressing, etc.), the theoretical basis can be found from the principles of the above three pressing methods. Therefore, mastering the principles and application principles of the above three methods can lay a solid foundation for powder metallurgy mold design.

1 Huang Peiyun. Principles of Powder Metallurgy. [M]. Beijing. Metallurgical Industry Press. 1997 (Reprinted in January 2006). 1

2 Powder Metallurgy Teaching and Research Section, Central South Institute of Mining and Metallurgy, Powder Metallurgy Basics, Metallurgical Industry Press, 1974

3 Huang Peiyun. Powder pressing problems. (Central South Institute of Mining and Metallurgy). 1980

4 Huang Peiyun. Principles of powder metallurgy. [M]. Beijing . Metallurgical Industry Press. 1997 (Reprinted in January 2006). 213

5 Huang Peiyun. Principles of Powder Metallurgy. [M]. Beijing. Metallurgical Industry Press. 1997 (Reprinted in January 2006). 204

< p>About the author: Ruan Zhiguang (1985-)? Male, Han, from Foshan, Guangdong, bachelor's degree, graduated from Hefei University of Technology, mainly engaged in research and development of powder metallurgy.

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