EP0862508A1

EP0862508A1 - Method for producing a sintered part

Info

Publication number: EP0862508A1
Application number: EP97944843A
Authority: EP
Inventors: Volker Arnhold; Eberhard Ernst; Wieland Kynast
Original assignee: GKN Sinter Metals GmbH and Co KG; Sintermetallwerk Krebsoege GmbH
Current assignee: GKN Sinter Metals GmbH
Priority date: 1996-09-09
Filing date: 1997-09-06
Publication date: 1998-09-09
Also published as: DE19636524A1; WO1998009752A1

Abstract

The invention concerns a method for producing a sintered metal part, specially a connecting rod or a filter. Said method is used to form a green compact from a sinterable powder containing binders in a basic forming process having at least one step and by applying pressure and/or heat. Said green compact represents a basic form of a part. It is then given the desired form for sintering in at least one further forming process and afterwards sintered.

Description

Description Process for the production of a sintered component

description

Components manufactured using powder metallurgy are produced by pressing a green compact from a sinterable powder composition and then sintering. The finished sintered component can then be calibrated, forged and / or subjected to a mechanical aftertreatment in order to obtain the desired component shape and property.

A special pressing process is hot pressing, in which the powdery base material is compacted at elevated temperature to form a green body that has the final shape desired for sintering. From EP-A2-0 555 578 it is known to mix a sinterable metal powder with a lubricant. The use of this lubricant reduces the wear on the walls of the mold during the hot pressing of green compacts when compacting or also when the green compact is ejected. Furthermore, the use of this lubricant requires a reduced force to push the green body out of the mold. In addition, an improved density and increased strength properties of the green body are achieved.

The pressed green body receives the required strength in the subsequent sintering process under protective gas, depending on the time and temperature, without a major change in shape taking place. To be an elaborate and expensive mechanical

To keep processing as low as possible after sintering, the green compact is pressed as close to the final contour as possible.

The methods prove to be disadvantageous if sintered components are quickly and inexpensively used as samples,

Prototype or to be produced in small series. To create a pattern of a sintered component that after sintering has the same properties as a later series part, a press tool must be produced that produces a green compact in the desired final shape. If the sintered component is subject to increased strength requirements, a corresponding forging tool must also be built. The samples produced can then be functionally checked under operating conditions. Any redesign of the component that results after testing the same component under operating conditions requires that a new press tool and, if necessary, forging tool, adapted to the redesign, have to be built before the samples produced with it can be checked again. A redesign and a matching press tool and possibly forging tool may also be necessary due to changed customer specifications. The need to examine samples with the properties that would also have components of a series production results in a very time-consuming, cost-intensive and material-intensive manufacturing process.

Another way of producing samples of sintered components is to produce a sintered component with simple geometry and standardized pressing tools. Alternatively, a press tool can be built that comes very close to the desired later shape of the sintered component. Both options include the fact that the sintered component has to be subsequently mechanically processed in order to obtain the desired final shape of the pattern. Both of these process options are also time, cost and material intensive. However, it has proven particularly disadvantageous in these two process variants that the components do not have the same properties as the tool-falling components due to the necessary mechanical processing, ie components whose external geometry is no longer significantly changed after sintering. In particular, the subsequent mechanical processing induces high residual stresses in the sintered component and influences the surface, so that it is only possible to a limited extent to test the component properties determined on test benches on transferring serial components, making it difficult to decide whether such patterns can be used in system solutions.

The known methods also prove disadvantageous for the series production of sintered components, since sintered components, which may also have been forged and / or aftertreated, have increased strength properties and consequently subsequent mechanical processing is made more difficult. This leads to longer machining times and higher tool wear. In particular when machining high-strength sintered and possibly additionally forged connecting rods, the mechanical processing of the individual component parts still to be machined after the sintering process, such as flange surfaces, connecting rod screw bores, connecting rod eyes and the like, has proven to be complex due to the difficult machinability of the sintered connecting rod.

It has also proven to be disadvantageous in the production of sintered filters that during machining of the filters, the pores required for the function of the filter are at least partially closed by the processing, so that there is a poorer flowability and thus a poorer filter effect.

From the two publications by Rutz, H.G., Cimino, T.M. Luk, S.H., "A Novel Machining Method for High Performance Ferrous P / M Materials", SAE Publication No. 960379, SÄE International, Warrendale, PA and by Cimino, T.M. , Luk, S.H., "Machinability Evaluation of Selected High Green

Strength P / M Materials ", Advances in Powder Metallurgy & Particulate Materials - 1995, Vol. 2, Part 8, pp 129-148, Metal Powder Industries Federation, Princeton, NJ. It is only known for the experimental determination of process parameters to produce a rod-shaped test specimen for drilling green compacts from a powder metallurgy material, on which the machining conditions are then examined, the geometry of the test specimen itself. ie its external shape was not changed or edited in all investigations.

The object of the invention is to avoid the disadvantages set out above and to simplify the process for producing sintered components, this relating both to samples and small series and to series parts.

This object is achieved according to the invention by a method for producing a sintered component, in particular a connecting rod or a filter, by means of which, in an at least one-stage basic molding process from sinterable powder containing binder, a green body is formed under pressure and / or heat, which is a basic component shape and which is given the shape desired for sintering treatment in at least one further shaping process and which is then sintered.

The method according to the invention has the advantage that the basic component shape of the green compact can have a simple geometry which can be produced by simple pressing tools which are inexpensive to produce. A basic component shape of the green compact can be described, for example, by a cuboid, a spatially curved shape or any combination thereof. The green body, which has a simple geometry, is brought to the desired shape in a further shaping process following the basic shaping process and then subjected to the sintering treatment. The method according to the invention is suitable for all binder-containing sinter powder compositions, but in particular for corresponding metal sinter powder. For example, ANCORDENSE ™ materials from HOEGANAES can be used, which enable green compacts to be manufactured with a high green density and green strength.

The use of such green compacts is particularly interesting in the production of small series, samples or Prototypes. As a result of the further shaping process which follows the basic shaping process brought about by means of a simple basic shaping tool, the green compact can be given its intended final shape even in the green state and a shaping which is complex in terms of production technology and thus expensive can be avoided or reduced in the sintered state. The essential further shaping operations can already be carried out in the green state by the method according to the invention. Depending on the circumstances, the shaping processes can be carried out by mechanical cutting or non-cutting processing or other influences. Processing after sintering can practically be omitted, so that the patterns therefore do not have any processing-related residual stress. The component properties subsequently determined on test benches, such as surface quality, density, residual stresses, dimensions, hardness, warpage and strength, can therefore also be transferred to series components that are manufactured as tool-falling parts. This enables an early decision to be made as to whether the sample produced fulfills the specifications made for the series component or whether a new one

Pattern must be produced as a variant and must be examined again for its component properties. This makes it possible to shorten the time-consuming and costly production of samples compared to the known production methods and thus to implement rapid prototyping for sintered components as well. In particular, there is the possibility of producing several variants of a sample for tests under operating conditions at short notice. In the method according to the invention, it is possible to produce samples in a few days, in contrast to a production time of a few months using the known methods, and this shortening can also be supported by a CAD-CAM link. When the final shape of the component has been designed after the tests, the final basic mold for the production of the green body can also be manufactured as a tool-falling part in series production.

A particular advantage of the invention is that Dimensional behavior of the final component can be determined exactly. The dimensional behavior characterizes the dimensional deviation of a sintered component compared to a green body, this dimensional deviation being caused by the distortion during the sintering process. While this dimensional behavior has so far only been able to be determined relatively inaccurately by means of test specimens which did not have the final shape of the component, the method according to the invention enables the dimensional behavior to be determined precisely for a given component shape. If the dimensional behavior is determined on the basis of the final shape of the green compact, then exact specifications for maintaining the dimensions in the pressing tool can be derived and this can then be produced. In this way, costly and time-consuming reworking of the pressing tool is avoided or reduced to a minimum, and a possibly necessary new production of the pressing tool is eliminated.

In a particularly advantageous embodiment of the invention, the basic component shape generated by the basic molding process approximately corresponds to the final shape of the component, i. that is, the basic component shape is close to the final contour. Such a form of the green body is particularly suitable for parts which are already produced in series in this form, since after sintering no or only slight shaping processes are necessary to achieve the desired, final shape of the component. A shape of the green body that cannot be realized or can be realized only with great difficulty by pressing technology can, however, be realized by shaping processes carried out before the sintering.

In an advantageous embodiment of the invention, the green compact is given the green compact sufficient green density and green strength for the subsequent further molding process.

In a further preferred embodiment of the invention, the basic molding process is an original molding process, in particular a pressing process, an injection molding process, an extrusion process and / or a hot pressing process.

In a further advantageous embodiment of the invention, the green body is given a relative density of 40% -95% of the theoretical density by the basic shaping process (regardless of the alloy composition).

In a particularly advantageous embodiment of the invention, the green body is given the shape desired for the sintering process in the further shaping process using a mechanical processing method. Machining methods that are preferably used are drilling, turning, milling, thread cutting, broaching, shaping and grinding. It is known from EP-A-0 330 830 to provide a preform with a scribe and crack course notch also by mechanical processing. While EP-A-0 330 830 teaches to produce a very small scribe and crack course notch with low feed and low cutting pressure in order not to destroy the green compact, which is sensitive to pressure and vibrations, the method according to the invention also enables the green compact to be machined high cutting speeds, high cutting pressure, large cutting volume and high cutting performance. Overall, it is much more cost-effective to carry out as many shaping steps as possible on the easily machinable green compact than to carry out these on the sintered component, which is much more difficult to machine, after sintering.

In a preferred embodiment of the invention, the component is forged after sintering. In particular, if increased strength requirements are placed on the sintered components, the component can be forged directly from the sintering heat, or it is heated again after the sintering and then forged. This considerably reduces the effort for a complex pressing tool. There is only a less expensive forging tool to create. If there are high accuracy requirements for the component, it can still be calibrated after sintering. There is also the possibility of mechanically processing or post-treating the component even after sintering, for example by hardening and / or galvanizing.

In a particularly advantageous embodiment of the invention, in the case of a sintered metallic connecting rod, the individual component shapes, in particular the flange surfaces, screw bores, threads, the large and small connecting rod eyes, the retaining grooves for the bearing shells, the scribe notch and / or the oil bores are produced by at least one further shaping process and / or post-processed. For the series production of connecting rods, it makes sense, for example, to press the basic component shape of the connecting rod close to the final contour, so that no or only a few shaping processes are necessary to match the outer contour of the connecting rod

To produce connecting rods according to the final shape of the connecting rod. Since, in particular, the oil bores for the connecting rod eyes and the bores and threads for the connecting rod bolts cannot be produced and / or are difficult to produce when pressing the green body for reasons of press technology, it is advantageous if they subsequently become relatively easy in comparison to the sintered connecting rods machining green body to avoid processing the sintered connecting rod. Then only the above-mentioned necessary individual component shapes are introduced and / or reworked into the basic component shape of the connecting rod, so that the connecting rod can then be sintered.

In a further advantageous embodiment of the invention, the sintered metallic connecting rod can be forged after sintering, for example in order to improve the strength properties of the connecting rod.

In a particularly advantageous embodiment of the invention, a sintered filter can be produced by the method according to the invention, the individual component shapes of which, for example the bore or grooves of the filter, are produced and / or reworked by at least one further shaping process. the. Filters that have been produced by the known method have hitherto been difficult to process after sintering. For example, by inserting and / or reworking the filter bore in the filter, the surface of the component molds was changed by the mechanical processing so that the pores between the metal powder parts clog by drilling, turning, milling, grinding or the like, and thus the function of the Filters was no longer guaranteed. By creating an individual component shape, such as a filter bore, the pores no longer clog when using the method according to the invention and the function of the filter is retained.

The invention is explained in more detail with reference to schematic drawings of exemplary embodiments. Show it:

1 is a plan view of a lever,

2 is a plan view of a connecting rod in its basic component shape,

3 is a plan view of a finished connecting rod,

4 shows a section along the line IV-IV through a finished connecting rod,

Fig. 5 is a vertical section through a sintered filter.

In Fig. 1, a lever 1 is shown in a top view. Three samples I - III are to be produced from lever 1, which are varied and optimized in their geometry and, after sintering on test benches under operating conditions, are to be examined with regard to their component properties. Due to the fact that the mechanical processing was carried out before sintering, the components produced in this way after sintering have approximately the same geometrically conditioned components Machining affects component properties like tool-falling components and can therefore be compared better with them. The bores 3, 4 and 5, since they are predetermined by the kinematics of the application for the He to be developed, can already be created with the basic mold intended for the production of the basic component shape I.

In order to produce the different patterns I - III, a green compact is first pressed into a basic component shape I by hot pressing a sinterable metal powder provided with a binder. After cooling, this green compact has an editable green density and green strength. The angular basic component shape I of the lever 1 can be realized through the use of simple, inexpensive to produce basic molding tools.

In the case of the pattern I, the outer geometry of the basic component shape I is maintained in accordance with the line drawn through and, if necessary, after finishing the bores 3, 4 and 5, the pattern I is sintered so that it can then be examined for its component properties.

In the case of pattern II, on a green compact with an outer geometry of the basic component shape I, the outer shape is changed in accordance with the dashed line by a further shaping process, for example by milling, in order to be able to examine the changed shape with regard to the structural strength. Subsequently, the green body processed in this way is sintered and examined under operating conditions for its component properties, which have changed in comparison to pattern I.

In a last optimization step, for example, pattern III is then produced from a blank with basic component shape I based on the previous investigations, which pattern is given an external geometry corresponding to the crossed line, for example by milling. After the mechanical processing, the sample III is sintered and finally tested. The measurement results determined by the test then show whether further changes need to be made to the shape or whether series production can be started on the basis of this pattern using the method according to the invention.

In order to explain the method, only the machining of the edge contour of the green compact as a further shaping process was described above. A change in the thickness of the basic component shape can be carried out entirely or only in partial areas or can also be contoured, for example by incorporating, in particular milling, indentations, in accordance with the requirements also on the green compact. This is indicated in FIG. 1 by a depression 2.

2 shows, as a further exemplary embodiment, a connecting rod which is to be manufactured in series and which is to be developed using the method according to the invention. In a basic molding process, a green compact is pressed into a basic component shape 6 from a sinterable metal powder, which is provided with a binder, by hot pressing. After hot pressing, the cooled green compact has a machinable green density and strength.

3 and 4 show the finished connecting rod 7. In the green body, the collar surfaces 8 are pre-ground and the screw holes 9 for the connecting rod screws 10 are drilled. Threads 11 are cut into the screw holes 9. The large connecting rod eye 12 is then rotated and ground and the retaining grooves 13 for the bearing shells on the large connecting rod eye 12 are milled. The small connecting rod eye 14 is also pre-turned and ground and the oil hole 15 is made in the small connecting rod eye 14. The oil bore 16 is drilled in the large connecting rod eye 12.

Thereafter, the connecting rod 7 can be separated along the crack course notch 17 pressed in during hot pressing or later mechanically inserted and then sintered. As a variant of this method, a crack course notch 17 can be pressed in during hot pressing or can be introduced into the machinable green compact. The green body is then sintered and the connecting rod 7 is separated along the crack course notch 17.

5 shows a vertical section through a sintered filter 20. To produce the sintered filter 20, a green compact can be produced in a basic component shape, for example cylindrical, using the method according to the invention. The filter bore 21 is introduced into this green compact. In particular for the series production of sintered filters 20, it makes sense to press the green compact close to the final contour. For example, when the green body is pressed, the filter bore 21 can already be provided, which is brought to its final dimension after the pressing by a further shaping process, for example drilling, turning, milling or grinding. A processing of sintered filters in the green state has the advantage that the pores between the metal powder particles are not clogged by the mechanical processing and thus the function of the filter, namely a good through-flow availability, remains guaranteed.

The basic molding process can vary depending on the circumstances of the

Basic component shape and / or the sintered powder composition used are preferably formed by a pressing process, an injection molding process or an extrusion process.

Are increased strength requirements for the sintered

Provided components, the component can be forged directly from the sintering heat, or it is heated again after sintering and then forged. This considerably reduces the effort for a complex press tool. There is only one less expensive forging tool to manufacture.

If there are high accuracy requirements for the component, it can still be calibrated after sintering. Furthermore, it is also possible to mechanically process or post-treat the component even after sintering, for example by hardening and / or galvanizing.

Claims

claims

1. A method for producing a sintered metallic component, in particular a connecting rod or a filter, by means of which, in an at least one-stage basic molding process from binder-containing sinterable powder, a green body is formed under pressure and / or heat, which is a basic component shape and which is formed in at least one further Forming process is given the shape desired for the sintering treatment and is then sintered.

2. A method for manufacturing according to claim 1, characterized in that the component basic shape generated by the basic molding process corresponds approximately to the final shape of the component, d. H. is designed close to the final contour.

3. The method according to claim 1 or 2, characterized in that the green compact is given a green density and green strength sufficient for the subsequent further molding process by the basic molding process.

4. The method according to any one of claims 1 to 3, characterized in that it is a pressing process in the basic molding process.

5. The method according to any one of claims 1 to 3, characterized in that it is an injection molding process in the basic molding process.

6. The method according to any one of claims 1 to 3, characterized in that the basic molding process is an extrusion process.

7. The method according to any one of claims 1 to 6, characterized in that the pressing process is hot pressing.

8. The method according to any one of claims 1 to 7, characterized in that the basic molding process gives the green compact a relative green density of at least 40% to 95% of the theoretical density.

9. The method according to any one of claims 1 to 8, characterized in that the green body is given the shape desired for the sintering process in the further molding process with a mechanical processing method.

10. The method according to any one of claims 1 to 9, characterized in that the component is forged after sintering.

11. A method for producing a sintered metallic connecting rod according to one of claims 1 to 10, characterized in that the individual component shapes, in particular collar surfaces, screw holes, threads, the large and small connecting rod eyes, retaining grooves for the bearing shells, scribing notches and / or oil holes, by at least a further shaping process is generated and / or reworked.

12. A method for producing a sintered filter according to one of claims 1 to 9, characterized in that the individual component molds, in particular the filter bore, are produced and / or reworked by at least one further shaping process.