JPH049639A - Method for finding out friction coefficient at the time of die molding of powder - Google Patents

Abstract

PURPOSE:To find out a friction coefficient mu(= F/P) by measuring force P vertical to the wall face of a movable die which is received from powder in the die and frictional force F in the wall face in a pressing direction by a cell fixed to the die. CONSTITUTION:At first, press stress (f) is applied from the rear face of the movable die 2 to contact faces 7, 7' and 8, 8' between the die 2 and a die body 1. In said state, the face pressure P is set up to '0'. When operation conditions are controlled so that the friction coefficient found out by said procedure and a stress-strain relational curve found out by a known method are always constant, molded product having the same density distribution can be obtained. When temperature distribution for sintering is controlled to a constant state, products having the same shape and size can be obtained. In said procedure, the friction coefficient and stree-strain relation can easily be related to various process dominant factors such as the material characteristic values of powder and die conditions.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for determining the coefficient of friction during molding of powder.

[Prior Art] In the field of manufacturing products by molding metal powders or ceramic powders using molds and sintering them, there are strict requirements for the shape and dimensional accuracy of the products. In order to meet such demands,
Alternatively, in order to improve the production yield, it is important to reduce various disturbance factors in each T-culm during the production, molding, and sintering of powder raw materials. For this purpose, it is necessary to constantly control important process controlling factors at each step and maintain them at a constant level.

The shape and dimensions of the sintered product are determined by the density distribution of the compact and the temperature distribution during sintering.

There are many factors that affect the density distribution of a compact.

For example, particle size distribution of raw material powder, lubricant, mold material,
This includes pressing methods, etc. Conventionally, we investigated the relationship between changes in these factors and the shape and dimensional accuracy of sintered products, and empirically investigated the relationship between these factors! They had found suitable operating conditions. However, the influence of these various factors is complex, and it has been quite difficult to quantify the degree of influence. By the way, from another perspective, the density distribution of a compact is mechanically determined by the stress-strain behavior of the powder in the die and the frictional behavior of the die wall (for example, "Plasticity and Processing" Vol. 27, No. 308, (
1986-10), p+, 125-ll31, and “
1989 Spring Lecture on Plastic Working J (1989-5)
, p. 195-198). Therefore, in order to make it easier to understand the effects of the various factors mentioned above on the shape and dimensions during sintering, we first increase the effects of the various factors on the stress-strain relationship and friction coefficient, and then improve the stress-strain relationship and friction coefficient. It is appropriate to consider the influence on the shape and dimensions during sintering.

[Problems to be Solved by the Invention] In order to use the method described above, it is necessary to determine the stress-strain relationship and the coefficient of friction. Regarding the stress-strain relationship, CI P (Co1d l5ostatic Pr
It can be determined from the relationship between load and density during compression with a uniaxial mold under conditions of good lubrication and negligible friction. This method is known (see the literature cited above).

The method for determining the coefficient of friction during mold molding is not necessarily known. Although there are examples where the coefficient of friction has been determined in the past, there is no guarantee that it is the same as the coefficient of friction during mold forming (r
The International Journal
of Powder MetallurgyJ
vol, 23. No.23. p83-93, and r
Journal of Powder & Bulk
5olid Technology V J , 11 (+9
87) 2; 15). For example, this r Journal
al of Powder & Bulk 5olid
In "Technology", the coefficient of friction is determined by sandwiching powder between two plates and sliding the plates in opposite directions while applying pressure, but the deformation mode is significantly different from mold forming.

The inventors of the present invention have studied various methods for measuring the coefficient of friction and have found that the following method is optimal.

[Means for Solving the Problems] The method for determining the coefficient of friction according to the present invention is based on a method for determining a friction coefficient according to the present invention, in which, in a powder axle compression mold, one or more portions of the die wall portion constituting the inner surface of the die are separated from the die body. The separated die wall (movable die) receives a force P perpendicular to the wall surface from the powder inside the die and a frictional force F within the wall surface in the pressing direction, which is measured by a load cell attached to the movable die. , the friction coefficient μ between the powder and the wall surface is determined from the relationship μ=F/′P.

The principle will be explained with reference to FIG. 1, FIG. 5, and FIG. 2. FIG. 1 shows a cross-sectional view of a rectangular axle mold press, and FIG. 2 shows a vertical cross-sectional view. 1 is the die body, 2 is a part of the die, but the body 1
It is separated from the die and is called a movable die. The reason why the movable die is separated from the die body is to measure the surface pressure P and frictional force F applied to the portion 2' of the inner surface of the die that is in contact with the powder. If the value of Niwara is known, the friction coefficient μ
can be determined from the relationship μ=F/P. The press work method will be explained below. First, a prestress f is applied from the back of the movable die. This force is applied to the contact surfaces 7.7' and 8.8' of the movable die and the die body. In this state, the surface pressure P is set to 0. Since f is the force applied to absorb backlash and to prevent the powder from initially entering the contact surface 7.7'8.8' between the movable die and the die body, it does not need to be a very large force.

If the operating conditions are controlled so that the friction coefficient determined by the above procedure and the stress-strain relationship curve determined by the known method are always the same, a molded body with the same density distribution can be obtained. If the temperature distribution during sintering is controlled to be constant, products with the same shape and dimensions can be obtained. The advantage of this method is
The reason is that it is easy to relate the coefficient of friction and stress-strain relationship to various process-controlling factors such as powder material properties and mold conditions.

In the above explanation of the principle, a mold with a rectangular inner surface was used as an example, but it is clear that similar measurements can be made with circular or polygonal shapes.

[Example] FIGS. 3 and 4 show an example of the apparatus. Among the four sides constituting the square inner surface of the die (20 mm opening), the die wall portions corresponding to two opposing sides are movable dies. Figure N3 is a longitudinal sectional view, and Figure 4 is a BB sectional view shown in Figure 3.

1 is a die body, 2 is a movable die, 3 is an upper punch, 4 is a lower punch, 5-1.5-2.5-4.5-5 is a load cell for measuring the plane rxP perpendicular to the inner wall of the die, 5-
3.5-6 is a load cell for determining the frictional force F on the inner surface of the die.1, 6-1.6-2 is a load cell.
69 is a VJ-cell for measuring the load Pu+Po of the j-bunch and lower bunch; 69 is a hole screw for applying prestress to the movable die; 10
is a ball screw that brings the friction of the sliding surface between the movable die and the die body close to O.

FIG. 5 shows an example of measuring the load when 20g of a mixture of alumina powder and graphite in an amount of 5% by weight was put into a chair and compressed. The horizontal axis is time t, and the vertical axis is load P. A is when the upper punch is lowered, b is when it is stopped, and C and d are when it is folded. P, , is the upper bunch load, p=p, +p2
is the normal force and P3 is the frictional force.

FIG. 6 shows the relationship between the friction coefficient μ-P3/(pi+p', ) and the aspect ratio X/D of a mixture of alumina powder and graphite powder. The graphite I of material A, abrasive B, and trade C is each 0.5.50% by weight. 30g, 20g, etc. in the figure indicate the amount of powder to be thrown into the die. μ is the average friction coefficient 4a. X is the distance from the die bottom to the upper punch surface, and D is the die inner diameter.

FIG. 7 shows a similar example in the case of soft ferrite powder. The friction coefficient μ-P6/(P4+p,) was also approximately the same value. As mentioned above, the value of the friction coefficient obtained with L〆 shows a reasonable change depending on the amount of lubricant (graphite), and is also a reasonable value compared to the conventional empirical value for bulk materials. It is.

[Brief explanation of drawings]

FIG. 1 shows a cross-sectional view of a rectangular uniaxial mold press, and FIG. 2 shows a vertical cross-sectional view. FIG. 3 and FIG. 4 show an example of the apparatus used in the example. FIG. 5 shows an example of measuring the load when 20 g of a material prepared by mixing 5% by weight of graphite with alumina powder is placed inside a die and compressed. FIG. 6 shows the relationship between the friction coefficient μ and aspect ratio of a mixture of alumina powder and graphite powder. FIG. 7 shows a similar measurement example of the coefficient of friction in the case of soft ferrite powder. 1... Dice body, 2... 6J moving tie, 3...
・Kita Punch, 4... Tobandi, 5-1゜5-2.5-
4.5-5 Load cell for measuring the surface 1 P perpendicular to the inner wall of the die, 5-3.5-6 Load cell for measuring the frictional force F on the inner surface of the die, 6-1 .6
-2-...Load P IJ of upper punch and upper punch respectively
Load cell for measuring , P I, 7.7'
, S, 8'... surface that vertically contacts the movable die and the die body, 9-m1 ball screw for applying prestress to the moving die, 10... sliding surface between the movable die and the die body ball screw to bring the friction close to 0

Claims (1)

[Claims] 1. A mold for uniaxial compression of powder has a structure in which one or more parts of the die wall constituting the inner surface of the die are separated from the die main body, and the separated die wall part (
The force P perpendicular to the wall surface that the movable die) receives from the powder in the die and the frictional force F in the wall surface in the pressing direction are measured with a load cell attached to the movable die, and the friction coefficient μ between the powder and the wall surface is calculated as μ= A method for determining the coefficient of friction during mold molding of powder, characterized by determining it from the relationship of F/P.