DE2333136A1 - METHOD AND DEVICE FOR MANUFACTURING A SINTER METAL PRODUCT - Google Patents

Description

June 28, 1973 IG / bü S-2-98 78 M

Sumitomo Electric Industries, Ltd .:

No.15, Kitahama 5-chome Higashi-ku, Osaka - Japan -

Kabushiki Kaisha 0? Okai Hika Denki Seisakusho:

No.1, Azakamisuiri, Oaza-shimootai, Nishibiwajima-cho.

Mishikasugai-gun, Aichi - Japan -

Method and device for producing a sintered metal product

The present invention relates to a method and an apparatus for producing a sintered metal product by extrusion using a lubricant, in particular a high density sintered metal product for use as a machine part. For example, more sintered iron, sintered steel or sintered non-ferrous metals are embossed as sintered metals.

Since sintered metals have poorer mechanical properties than cast and forged materials, their use is on Limited machine parts that have complex shapes, but do not require high strength. In the past Years ago, sintered metal parts were made of high density and strength simply made by mechanically compressing the gaps or pores that exist in sintered alloys or by using improved sintering techniques to reduce pores.

Sintered metal machine parts usually have a complicated one Shape, sometimes requiring machining to achieve the final shape. A limit to manufacturability is also given by the fact that a part with

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a thin portion becomes non-uniform in density. To eliminate this limit it would be advantageous if sintered metals could be formed by means of a ¹ Iießpressverfahrene J, as is possible with cast and wrought materials. However, sintered metals contain a myriad of pores, so that the application of a conventional extrusion process to such metals leads to the formation of cracks in the interior and on the surface of the extruded product, whereby the product is almost worthless. Typical methods currently in use for forming a brittle material are, for example, a hydrostatic working method for aluminum alloys, magnesium, etc., or a method in which a counter pressure is generated at an operating temperature of about 1100 C or a ram.

Working temperature of about 11 00 C or higher by means of a

In a common hydrostatic working method, oil is used as the pressure medium and lubricant. Meanwhile that Oil penetrates under high pressure into a myriad of pores in the sintering preform ingot, can become in the extruded The product is easily cracked both inside and on its surface. Besides, there won't be any uniformly high density obtained.

The invention is based on the object of creating a method and an apparatus that can be carried out in an economical manner allow a sintered metal product to be made uniformly of high density and strength with good dimensional accuracy.

The method according to the invention is characterized by applying a lubricant coating to the surface of a sintered metal bar (-blanks) of low to medium density, the ingots at a working temperature of room temperature up to Maintain 750 ° C and extrude it while exerting counter pressure on the bar.

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The present invention also seeks to provide a method of effectively applying a lubricant coating to the surface of the ingot can be applied.

The device according to the invention for producing a sintered metal product by extrusion has a mold for receiving a sintered metal ingot (blank) lower to medium density, the surface of which is covered with a lubricant coating, as well as a stamp for applying an extrusion pressure on the ingot in the mold and is characterized by a second punch for applying a counter pressure, which is smaller than the pressing pressure, opposite to the deformation direction on the part of the billet which is caused by the pressing pressure has been deformed.

The invention is explained in more detail below with reference to the accompanying drawings. Show it

FIG. 1 shows a schematic view of a first embodiment of a device according to the invention with a counter-pressure device;

Fig. 2 is a schematic view of a second embodiment a device according to the invention with a counter pressure device;

Figure 3a shows the shape of an ingot for use in the first embodiment the device according to the invention;

FIG. 3b a vertical section of one of the bars of FIG. 3a produced product;

Fig.4a shows the shape of a bar for use in the second Embodiment of the device according to the invention;

FIG. 4b shows a vertical section of one of the bars of FIG. 4a produced product;

i? ig.4c a side view of the product of FIG. 4b;

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Figure 4d is a top view of the product of Figure 4-b;

5 is a diagram showing the density distribution in a product made of a sintered iron alloy using the method according to the invention;

6 is a diagram showing the formation of defects in the sintered material as a function of the counter pressure and the working temperature, where a) the formation external imperfections and b) indicates the formation of internal imperfections;

Fig. 7-1 to Ψ microscope photographs at points 1, 2, 3 and small product a produced without counter pressure, which has the shape from Fig. 3b to v / eist; and

Fig. 8- 1 to 3 microscope images at points 1, 2 and 3 of one with the first embodiment of the device according to the invention produced product a.

The essential feature of the present invention is that the sintered preform is subjected to a counter pressure that is at least $ 20 of the extrusion pressure. It is used for Forming parts or components of complex shapes that cannot be easily produced using conventional sintering techniques are, a special counter pressure device is used and extruded at a room temperature of up to 750 ° C. Before extrusion the sintered preform must be subjected to a lubricating treatment. Will apply a liquid lubricant directly Applied to the preform, the liquid penetrates into the interior of the preform, so that it is no longer possible to indent the pores is. So it becomes difficult to increase the density of the final product. Moreover, if the lubricating liquid hits the walls of the Contaminated pores, the strength of the product cannot be increased even if its density increases. These Disadvantages are eliminated with the lubricating treatment according to the invention described below.

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The porous sintered metal bar is put into a rotating drum with a powdery solid lubricating material such as a metal soap (e.g. zinc fearat), MoS ₂ or graphite, as well as with elastic grains made of rubber or plastic, which do not damage the sintered material, and whirled around with these additives The result of this whirling around is that the solid lubricating material forms a uniform and intd / men coating only on the surface of the sintered material without this surface being damaged.

The amount of powdery solid lubricant is sufficient if it can uniformly cover the surfaces of the sintered material and the elastomer grains. Usually, it is enough to add the lubricant in an amount of not more than 40% by volume of the sintered material and the elastomer grains, otherwise the adhesion becomes uneven. On the other hand, amounts below $ 2 are not sufficient. Advantageously, the sintered preform is ^{heated to about 10O 0} O, since this not only results in improved adhesion of the metal soap, but also opens up the possibility of tightly adhering an inorganic lubricant such as graphite.

The amount of elastic grains is at least equal in volume the sintered material. Hardly any surface damage occurs within the stated quantity ranges and is in the substantially uniform adhesion is achieved. If the amount of elastomer grains selected is lower, the sintered material occurs scratches occur due to impact, these scratches not "disappearing" even after an embossing treatment.

The swirling is advantageously carried out in a conventional rotary drum used for deburring. A mess a period of 3 minutes is usually sufficient and a longer period of confusion does not bring any advantages.

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Another option is the lubricant coating on the surface To apply the sintered metal is a solution in an organic solvent or a suspension a solid lubricant such as metal soap (zinc stea ■ rat), MoSp, graphite or glass, in water on the over the sidepoint of the organic solvent or water heated sintered material to be sprayed on. On the surface of the sintered material Then only the solvent or water evaporates instantaneously, while the solid lubricant only evaporates on the surface of the sintered material remains adhering without liquid penetrating into the pores.

If the spraying is carried out continuously over longer periods of time, the temperature of the material drops as a result of the evaporation of the solvent and the surface of the material becomes damp. In such a situation, the liquid would inadvertently be in penetrate the pores, so that the spray process should therefore be stopped and the material should be heated again a coating of the desired thickness can be obtained during the process.

The temperature to which the material is heated should be above the evaporation point of the solvent. However, temperatures that are too high should be avoided, as otherwise the solvent will evaporate before the jet of solution hits the sintered material. With water as a solvent, the heating temperature is expediently between I50 and 250 C, while in methylene chloride as a solvent, a suitable heating temperature to 60 ⁰ C, 4-0.

When extruding the above ingot in the usual way, its free, not in contact with tools, is subject to it Surface tensile stresses that lead to an enlargement of the pores and to surface cracks. On the surface that with When the tools are in contact, a myriad of cracks appear in the workpiece. Accordingly, from the beginning of the flow

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opposite to the extrusion direction, a counterpressure is exerted on the ingot due to its extrusion-free surface to apply · This application of a counter pressure prevents the enlargement of the pores and the formation of cracks both on the surface as well as inside the sintering bar.

The back pressure device used in the present invention is intended to eliminate the above disadvantages. To apply of the counter pressure on the sintering preform ingot, it uses a solid pressure medium. The device can simply be attached to a mechanical one Single-stroke press. Examples of such a device are shown in FIGS.

Fig. 1 shows a device for forward extrusion (direct current extrusion) of the material. The left half of the figure shows the device before the working stroke, while the right Half of the figure shows the state of the device after the working stroke. According to Fig. 1, the device comprises a stamp 1, a tool 2, an ejector (lower punch) 3, an ejector pin 4-, a fitting plate 5, an ejector pin guide plate 6, an oil hole 9, a relief valve 10, an upper press ram 11 and a press table 12. 8 denotes the workpiece. A space 7 "that of the fitting plate 5" of the ejector pin guide plate 6, the ejector 3 and the ejector pin 4- is kept airtight by means of O-rings. That through the oil hole 9 in the fitting plate 5 brought pressure oil (25 kg / sqmm) causes the ejector to move upwards and downward movement of the ejector pin. When the working stroke begins, the workpiece is rapidly extruded, around the ejector to depress. An oil pressure is generated in the space 7. The pressure can be controlled by the relief valve 10 will. The total working pressure at this point in time is kg / qmm.

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Pig. 2 shows an apparatus for reverse extrusion (countercurrent extrusion) of the material. In Hg. 2, a stamp for applying a counterpressure, 14 denotes a Punch holder, 15 a fitting plate for transmitting a counter pressure and 16, an upper die fitting plate. The punch 13 can slide vertically along an upper punch 1. A room 7, that of the punch holder 14, the fitting plate 5 »of the fitting plate 16 and the upper punch 1 is kept airtight by means of O-rings. From an oil or air hole 9 in the upper punch fitting plate 16 brought compressed air or brought up Pressure oil (5 kg / qcm) moves the stamp 13 downwards. The outer diameter of the fitting plate 15 is determined so that a pressure of 20 kg / qmm is generated on the face of the stamp. When the ram comes down and the working stroke begins, the extruded workpiece pushes the punch 13 upwards, whereby as in the device of Fig. 1 in the space 7 a pressure is generated. This pressure can be caused by the Relief valve 10 can be controlled. The total working pressure at this point in time is 100 kg / qmm.

Among the various advantages that the process according to the invention brings are:

1. There can be machine parts or components uniformly higher Density can be generated

2. The formation of harmful cracks inside and on the surface of the extruded product is avoided.

3 · The exposed surface during extrusion can be removed by applying a counter pressure on this surface can be smoothed. The dimensional accuracy can be increased significantly as a result.

^. Saving of machine post-processing, which means more considerable Reject is avoided.

5 «The process is economical as there are no expensive double-stroke presses required are.

6. Parts of more complex shape can be made by sintering processes

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getting produced.

7. The extrusion process improves the mechanical properties of the sintered metal product improved.

example 1

Each of the four starting powders of Pe, Pe-O, 2 C, Fe-O, 4 C and Fe-3Ni-0.3Mo-0.5 C were mixed with 0.8 $ zinc stearate in a mixer. The mixture was mm into an ingot having a size of 25 χ 17 "5 and a density of 6.8 gr./cnr formed, for one hour at 55O ⁰ C dewaxed and then for 30 minutes in a !! ,, - atmosphere in sintered in a continuous ^{sintering furnace at 1250 o C.}

A lubricant coating was applied to the resulting ingot by swirling zinc stearate (if the ingot was to be treated at room temperature) or by spraying a graphite suspension onto the heated ingot (if the ingot was to be treated at elevated temperatures). The ingot was subsequently heated for about 20 minutes in an atmosphere containing a hydrogen gas furnace, and kept at a room temperature to 75O ⁰ C. From here it was brought into a mold. In a molding press with a counter pressure device, it was finally given the desired shape.

The ingot was heated to room temperature up to 750 C and by the conventional method without the application of back pressure brought into the form b of Fig. 3, then were taken on the extrusion side of the product, such as the microscope photographs in Fig. 7 show fir-shaped (tooth-shaped) shear cracks.

In contrast, according to the invention, it was contrary to the extrusion direction a counter pressure applied, then the enlargement and destruction of the pores could be prevented, like the microscope images in Fig. 8 show. The product had an equal

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shaped high density according to the density distribution in Fig. 5 · 6 shows furthermore, that the properties of the sintered material, thanks to the application of the back pressure at a heating temperature of 4-5O ⁰ C both in the interior of which were good as well as on its surface .very. This shows the superiority of the method according to the invention.

Example 2

Copper powders obtained by electrolysis were compressed to a density of 7.9 g / cm * to form an ingot (20/5 χ 15) and then sintered ^{for one hour in an atmosphere at 79O 0 C.} A coating of zinc stearate was applied to the surface of the billet using the vortex technique described above, after which the billet was extruded at room temperature with the apparatus of FIG.

When the billet was extruded by the conventional method, tensile stresses were applied to the surface and inside of the extruded product and to the free surface not in contact with the tools. Since a myriad of pores within the sintered alloy existed _f stepped enlargement of the pores and the formation of surface cracks and the stationary with the tool in contact surfaces of the product on when the Fließpreßgeschwindigkeit not uniform v under the influence of deformation stresses / ar.

On the other hand, when extruding a counter pressure was applied (20 $ of the extrusion pressure) according to the method according to the invention, the formation of surface cracks, the enlargement the pores and the occurrence of internal cracks are avoided. A good quality product was obtained. The superiority of the method according to the invention is therefore beyond doubt.

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Claims (1)

Patent claims: 1. Method of making a sintered metal product by extrusion using a lubricant, characterized by the application of a lubricant coating on the surface of a sintered metal ingot (blank) of low to medium density, the ingot on a Maintain working temperature from room temperature up to 750 ° C and extrude it while simultaneously exerting counter pressure on the ingot. 2. The method according to claim 1, characterized in that that the application of the lubricant coating by swirling the bar in a mixture of one powdery solid lubricant with elastic grains that do not damage the sintered metal. 3. Method according to claim 2, characterized in that the solid lubricant is metal soap, MoS ₂ , glass or graphite. ^ -. Method according to claim 3? characterized, that the metal soap is zinc stearate. «Method according to claim 1, characterized in that that the application of the lubricant coating by spraying a mixture of a liquid solvent and a solid lubricant is applied to the ingot heated above the evaporation temperature of the solvent, whereby the solvent evaporates and the solid lubricant remains as a coating. 409834/0673 6. Apparatus for producing a sintered metal product by extrusion, with a molding tool for receiving a sintered metal ingot (blank) of low to medium size Density, the surface of which is covered with a lubricant coating, and with a punch for acting one Extrusion pressure on the billet in the mold, characterized by a second punch (3 * 13) to apply a counter pressure that is smaller than the pressing pressure, opposite to the direction of deformation on the Part of the ingot (8) which has been deformed by the pressing pressure is. 409834/0673 Blank page