The present invention relates to an improved bushing and a process for manufacturing a bushing for use in mechanical guide systems, the improvement relating in particular to a joint between a sleeve and an outer shell of the bushing.

Mechanical guides or guide systems allow movement of a particular element in an assembly only in a certain direction, the aim being that the movement in that direction is as smooth as possible, without friction, and that the movement is very precise, that is to say, with the least possible deviation from that direction. Linear guide systems allow the movement of an element in an assembly in a linear direction. For example, linear guide systems are used in a variety of machines to provide the desired positioning accuracy and positioning repeatability, for example in tools for the forming metal or plastic products or semi-finished products.

The basic elements of a linear guide system are at least one bushing and at least one guide pillar, with the bushing being mounted on the guide pillar. Most commonly, a bushing moves along a guide pillar in a linear direction during operation, but the reverse is also possible, with the guide pillar moving along the bushing, or a combination of the two movements. Within the context of this text, the reference to one way of movement is also meant to refer to all the other ways of movement mentioned.

One example of the use of a linear guide system is in a sheet metal forming machine, a press, where the desired forming of the sheet metal material sandwiched between two faces is achieved by the interaction between a lower and upper faces of the tool, which are adequately shaped, while one face is being brought towards the other, for example, the upper face is being brought towards the first face. The term "forming of the material" within the context of the present invention refers to cutting, carving, embossing, deforming and other ways of changing the shape of the material which can be achieved by bringing the faces of the tool closer together when the material is sandwiched between the two faces. Usually, the lower tool face is fixed and the upper tool face is approached, but the reverse is also possible. Another example of the use of linear guide systems is when the lower and upper faces of the tool, when pressed together, form a mould into which material, such as various plastics in liquid form, can be injected to produce a product from that material. Once the material in the mould has solidified, the plates are disengaged and the product can be removed from the mould.

A first face of the tool is usually attached to a first support member of the machine, for example a fixed machine base such as a machine table, to which a first end of at least one guide pillar of at least one guide is attached. Typically, a linear guide system consists of several guides, namely a combination of one guide pillar and one bushing, usually two or four, to provide greater stability of the moving part or moving parts of the machine in the direction of movement. A second face is attached to another support member of the machine, for example an upper push plate, to which at least one bushing of at least one guide pillar is attached, the other end of each guide pillar being inserted into its associated bushing. If several guides are used in a linear guide system, the longitudinal axes of the guide pillars of these guides are parallel to each other.

In different machine configurations, linear movement between the first support member and the second support member can be achieved either by moving one member towards the other while the second member remains fixed, or by moving both support members towards or away from each other.

The movement of the first support member relative to the second support member in terms of power and amplitude is achieved by a drive placed between the first support member and the second support member, which can be controlled in a variety of known ways.

The precision of the positioning of the first face of the tool relative to the second face of the tool during operation is essential in the forming of the material and the formation of the mould, as inaccuracy may cause the products to be defective or not to be produced and may cause damage to the tool or to the first face or the second face of the tool.

Precise positioning and movement of the first tool face relative to the second tool face, in terms of minimising deviation from the desired linear direction of movement, is achieved with linear guide systems. On the other hand, it is desirable to have as little friction as possible between the bushing and the guide pillar, so that the movement in the desired direction is as unhindered as possible.

In order to minimise the friction between the guide pillar and the bushing, there are two known methods of guiding a bushing along a guide pillar: ball bearing guidance and sliding guidance.

The present invention relates to a bushing and a process for manufacturing a bushing for sliding guidance of a bushing along a guide pillar, the guide pillar being circular in cross-section and the bore in the bushing also circular in shape. The materials of which the guide pillar is made in the prior art are various, most commonly hardened steel; or other metals or alloys thereof, which are physically treated, for example by heat, to achieve the necessary properties, for example adequate load bearing capacity and hardness of the outer surface of a guide pillar.

Friction between the bushing and the guide pillar is undesirable because it increases wear and thus significantly reduces the life of the bushing and guide pillar and may also lead to damage to the bushing and guide pillar.

A bushing for sliding guidance is made of an outer shell and a sleeve in the outer shell. In prior art, the outer shell is made of various metals or alloys, most commonly heat-treated steel, which provides sufficient load-bearing capacity for the bushing. A bushing sleeve is made of a softer material to ensure good sliding (tribological) properties during operation of the guide in contact with the outer surface of the guide pillar. These softer materials are, in the prior art, various softer metals or alloys, for example various bronzes, optionally with graphite added. Sintered material may also be used for a bushing sleeve, which, due to its porosity, contains lubricating oil, which contributes to the good sliding properties of the sleeve and consequently extends the life of the bushing, increases the resistance of the bushing to loading forces and allows higher operating speeds.

The sleeve and the outer shell of the bushing must be fixed together to a so-called non-dismountable joint to prevent them from detaching from each other during operation or when being under load. In known prior art, a joint between the sleeve and the outer shell is achieved, for example, in the following ways:

1. Glued joint. The outer diameter of the sleeve is identical to the inner diameter of the outer shell. A glued joint bushing is made by coating the outer surface of the sleeve or the inner surface of the outer shell with glue, inserting the sleeve into the outer shell and allowing the glue to dry. A disadvantage of the manufacturing process is that the two diameters have to be matched to very tight tolerances and the surfaces to be glued have to be meticulously cleaned, which is demanding. The joint is quite strong, withstanding loads of up to several tonnes.

2. Press joint. Before insertion, the outer diameter of the sleeve is slightly larger than the inner diameter of the outer shell. This difference in diameter ensures that, after insertion, the force exerted by the outer surface of the sleeve on the inner surface of the outer shell is sufficiently high, and vice versa, so that the frictional force between the two surfaces ensures a non-dismountable joint. The insertion of the sleeve into the outer shell is carried out by pressing, i.e. pushing the sleeve into the outer shell with a high force. The second method of insertion, the so-called shrink fit, uses the difference between the temperature of the sleeve and the temperature of the outer shell, for example, to heat the outer shell, thus increasing its internal diameter and allowing the sleeve to be inserted into it. When the temperature of the outer shell returns to ambient temperature, the inner diameter decreases and the inner surface of the outer shell begins to press against the outer surface of the sleeve, providing a friction force. This joint withstands a load of up to several tonnes. A disadvantage of this joint is that after insertion large internal stresses remain in the outer shell material and in the sleeve material.

The above-mentioned disadvantages are solved by the bushing of the invention.

The invention will be described in more detail hereinbelow and in the embodiments and illustrated on the figures which show:

Figure 1 shows a housing of a stamping tool, showing a prior art linear guide system with four guides, each guide containing one guide pillar and one bushing;

Figure 2 shows a first embodiment of an assembled bushing according to the invention for use in guides for a stamping tool;

Figure 3 shows a first embodiment of the bushing according to the invention before assembly, when the sleeve is not yet inserted into the outer shell;

Figure 4 shows a first embodiment of the bushing according to the invention, when the sleeve is inserted into the shell, yet before the sleeve is expanded;

Figure 5 shows a second embodiment of an assembled bushing according to the invention for use in plastic injection moulding tool;

Figure 6 shows some embodiments of the shape of an embossing protrusion in cross-section.

Figure 1 shows some relevant parts of a machine or tool 1 , for example a stamping tool, as an example of the prior art use of linear guide systems 2. The linear guide system shown comprises four guides 3, and each of them comprises one guide pillar 12 and one bushing 4, wherein each guide pillar 12 is inserted into a corresponding bushing 4, and the bushings 4 slide along the guide pillars 12 during operation. A first support member 13 of the machine, to which all four guide pillars 12 are fixedly attached, is located below a second support member 14 of the machine, to which all four bushings 4 are fixedly attached. The first support member 13 of the machine is fixed during operation, while the second support member 14 of the machine moves linearly during operation, i.e. it approaches or moves away from the first support member 13. The movement of the second support member 14 is controlled and limited by the guide system 2. The drive which allows the controlled movement of the second support member 14 relative to the first support member 13 is not shown in the figure. Also not shown in the figure are the first tool face and the second tool face which form the material during the operation of the press. The front two guides 3 in Figure 1 are shown in cross-section for illustrative purposes.

The bushing 4 according to the invention is formed of an outer shell 6 and a sleeve 9, the sleeve 9 being made of a softer material than the outer shell 6. Preferably, the outer shell 6 is made of hardened steel and the sleeve 9 is made of sintered material or bronze. The sintered material provides the necessary softness or tribological properties for the sliding contact between the guide pillar 12 and the bushing 4 during operation of the linear sliding guide 3, and also provides the porosity of the sleeve 9 which, in combination with the lubricants in the porous material, allows lubrication of the sliding contact between the guide pillar 12 and the bushing 4 during operation of the guide 3.

At least one embossing protrusion 8 is positioned on an inner surface 7 of the outer shell 6 and has a height H in the radial cross-sectional direction. Preferably, there is a plurality of embossing protrusions 8. The embossing protrusion 8 may be point-like, segmental or extend in an elongate form over the surface of the inner surface 7 of the outer shell 6. Preferably, the embossing protrusion 8 extends along the entire circumference of the inner surface 7 drawn by the cross-section of the outer shell 6. The different directions of extension of the embossing protrusion 8 along the inner surface of the outer shell can be divided into two components: a circumferential component, i.e. a component in the direction of the circumference of the crosssection, and a longitudinal component, i.e. a component in the direction of the longitudinal direction of the outer shell. The elongated embossing protrusion 8 extends in a direction having a component of the circumferential direction. The embossing protrusions 8 on the inner surface 7 of the outer shell 6 may be produced in several ways, for example by turning.

The embossing protrusions 8 are made of a harder material than the material of the sleeve 9, preferably of the same material as the outer shell 6. The embossing protrusions 8 are preferably integrally formed into the inner surface 7 of the outer shell 6.

The outer surface 10 of the sleeve 9 in the fabricated bushing 4 according to the invention substantially, but preferably completely, fits the inner surface 7 of the outer shell 6, the embossing protrusions 8 being recessed into the outer surface 10 of the sleeve 9, i.e. forming recesses 11 in the outer surface 10 of the sleeve 9. The non- dismountable joint between the sleeve 9 and the outer shell 6 is predominantly based on a form-fit connection between the embossing protrusions 8 of the outer shell 6 and the recesses 11 of the sleeve 9.

The joint described in the bushing 4 according to the invention is generally capable of withstanding significantly higher loads than a glued or pressed joint from the prior art. A further advantage of the described joint is that, after fabrication, there are no or negligible internal stresses in the material of the sleeve 9 and the material of the outer shell 7.

In the bushing 4 according to the invention, the sleeve 9 may extend along the entire length of the outer shell 6 or, in some embodiments, for example in some plastic injection moulding tool guides, the sleeve 9 may extend along only a portion of the entire length of the outer shell 6.

The steps in the process of manufacturing the bushing 4 according to the invention are as follows:

A. The manufacture of the outer shell 6 having at least one embossing protrusion 8, preferably more than one embossing protrusion 8, and the manufacture of the sleeve 9, wherein the initial cross-sectional diameter d1 of the outer surface 10 of the sleeve 9 is substantially identical to or greater than the diameter D2 of the inner surface 7 of the outer shell 6, the latter diameter not taking into account the height H of the embossing protrusions 8.

B. Insertion of at least one sleeve 9 into the outer shell 6. There are several ways of inserting the sleeve 10 into the outer shell 6; preferably the sleeve 9 is pushed into the outer shell 6 by pressing. After insertion, the outer surface 10 of the sleeve 9 is in contact with the embossing protrusions 8 in the region of the embossing protrusions 8, but is not in contact with the inner surface 7 of the outer shell 6 in regions outside the region of the embossing protrusions 8. When inserted, the sleeve 9 is elastically deformed, since the actual diameter d1 ' of the cross-section of the outer surface 10 of the sleeve 9 must be reduced in order to allow it to be inserted into the outer shell 6 with the embossing protrusions 8 of height H.

In some embodiments, two sleeves 9 are inserted into the outer shell 6: a first sleeve 9 into the opening on one side of the outer shell 6 and a second sleeve 9 into a second opening on the other side of the outer shell 6. After the insertion of the two sleeves 9 into the outer shell 6, it is possible that the adjacent edges of the sleeves 9 in the outer shell 6 may be in contact, or that there may be a gap between them. In further embodiments, more than two sleeves 9 may be inserted into the outer shell 6, i.e. more than one sleeve 9 is inserted from one side of the outer shell 6.

In some embodiments, the first embossing protrusion 8 is geometrically and height-adjusted from the direction of insertion of the sleeve 9 to facilitate insertion of the sleeve 9 into the outer shell 6.

C. Expansion of the sleeve 9 by pressing on an inner surface 15 of the sleeve 9 to expand the actual outer diameter d1 ' of the sleeve 9 to the size of the diameter D2 of the inner surface 7 of the outer shell 6 over the entire length of the sleeve 9, whereby plastic deformation of the outer surface 10 of the sleeve 9 occurs at the points of contact between the outer surface 10 of the sleeve 9 and the embossing protrusions 8 because the embossing protrusions 8 emboss the recesses 11 into the outer surface 10 of the sleeve 9. This maximises the contact between the outer surface 10 of the sleeve 9 and the inner surface 7 of the outer shell 6, including the contact between the embossing protrusions 8 on the inner surface 7 of the outer shell 6 and the machined recesses 11 on the outer surface 10 of the sleeve 9. The latter contact forms the aforementioned form-fit connection, which provides a non- dismountable joint between the sleeve 9 and the outer shell 6 during the operation of the bushing 4 in the guide 3, when the bushing 4 is in sliding contact with the guide pillar 12.

In embodiments where two sleeves 9 are inserted into the outer shell 6, each on a different side of the outer shell 6, the expansion of the two sleeves 9 is preferably carried out simultaneously by applying pressure to the inner surface 15 of the two sleeves 9 as described in this step.

After step C above, a machining step of the inner surface 15 of the sleeve 9 or of the side edges of the sleeve is preferably added, for example by grinding, turning or milling, in order to achieve the desired properties of the inner surface 15 of the sleeve 9 and/or of the dimensions of the sleeve 9 in the bushing 4, for example the size and uniformity of the inner diameter of the sleeve 9 over the entire length of the sleeve 9. When finishing the inner surface 15 of the sleeve 9 when the latter is made of sintered material, care must be taken to ensure that the pores in the sintered material do not close, as this will cause the sintered material to lose its tribological or lubricating properties.

The height H of the embossing protrusions 8 depends on several parameters, for example on the dimensions of the outer shell 6 and the sleeve 9, including the wall thickness of the sleeve 9 in the bushing 4, the load exerted on the bushing 4, the material properties of the outer shell 6 and the sleeve 9. Given these parameters, a person skilled in the art will be able to determine the height H of the embossing protrusions 8 by considering the following conditions, for example: the greater the height H of the embossing protrusions 8, the more likely it is that the sleeve 9 will already be plastically deformed during insertion into the outer shell 6, which is not desirable. Also, too large a height H may cause the embossing protrusion 8 to damage the outer surface 10 of the sleeve 9 during insertion, for example, that a part of the material of the sleeve 9 is removed (scraped) during insertion, which is also undesirable. On the other hand, the lower the height H, the less effective the form-fit connection will be and the bushing 4 will withstand less load during operation, which is not desirable. The height H of the embossing protrusions 8 in relation to the thickness of the wall of the sleeve 9 must not be such that, after the sleeve 9 has been extended (step 3 above), the embossing protrusion 8 would emboss the recess 11 in the outer surface 10 of the sleeve 9 so deeply that this deformation would considerably thin the wall of the sleeve 9 and thereby impair the mechanical properties of the sleeve 9 and, consequently, of the bushing 4 during operation. Typically, the height H of the embossing protrusions 8 is between 0.2 mm and 0.5 mm.

The height H of the embossing protrusions 8 in the bushing 4, in which the outer shell 6 has a plurality of embossing protrusions 8, may be the same for all the embossing protrusions 8, but the heights H may be different from one another.

The potential difference between d1 and D2 depends on several parameters, for example on the dimensions of the outer shell 6 and the sleeve 9, including the wall thickness of the sleeve 9 in the bushing 4, the load exerted on the bushing 4, the material properties of the outer shell 6 and the sleeve 9. Given these parameters, a person skilled in the art will be able to determine whether d1 and D2 will be essentially identical or what the difference between d1 and D2 will be, taking into account, for example, the following conditions: It is not desirable for the sleeve 9 to be plastically deformed already during insertion into the outer shell 6. Once the sleeve 4 has been fabricated, it is not desirable for there to be significant internal stresses in the sleeve 9. It is desirable that, when the bushing 4 is fabricated, said form-fit connection is as tight as possible and that the outer surface 10 of the sleeve 9 as fully as possible fits the inner surface 7 of outer shell 6 over the entire surface, including the contact between the embossing protrusions 8 on the inner surface 7 of the outer shell 6 and the recesses 11 on the outer surface 10 of the sleeve 9. Typically, d1 is greater than D2, the difference being in the range of 0.01 to 0.05 mm.

In some embodiments, in particular in plastic tools, channels are provided on the sliding surfaces of the guide pillars 12 to allow lubrication of the sliding contact between the bushing 4 and the guide pillar 12 during operation, which is otherwise known in the prior art.

In some embodiments, in particular when the sleeve 9 in the bushing 4 is made of bronze, channels may be provided on the inner surface 15 of the sleeve 9 to allow lubrication of the sliding contact between the bushing 4 and the guide pillar 12 during operation, which is otherwise known in the prior art.

Figures 2 to 4 show a first embodiment of the bushing 4 according to the invention for use in guides 3 for a stamping tool intended, for example, for forming, punching sheet metal. In this embodiment, the sleeve 9 of the fabricated bushing 4 extends the full length of the outer shell 6, which is 93 mm. The guide pillar, which is not shown in Figures 2 to 4, is circular in cross-section and an opening 5 in the bushing 4 is also circular in cross-section. Typically, a linear guide system is used for this type of press, which has four guides 3. The outer shell 6 of the bushing 4 is made of hardened steel. On the inner surface 7 of the outer shell 6, seven embossing protrusions 8 are made which extend around the entire circumference of the inner surface 7 of the outer shell 6, which is drawn by the cross-section of the outer shell 6. These embossing protrusions 8 are made by turning. The distance between the embossing protrusions 8 is approximately 14 mm. The sleeve 9 is made of sintered material. The height H of the embossing protrusions 8 is 0.3 mm. In cross-section, the embossing protrusions 8 are in the form of a symmetrical trapezoid with the larger base of the trapezoid coinciding with the inner surface 7 of the outer shell 6. The embossing protrusions 8 are made of the same material as the outer shell 6 and are integrated into the outer shell 6. The initial cross-sectional diameter d1 of the outer surface 10 of the sleeve 9 is substantially identical to the diameter D2 of the cross-section of the inner surface 7 of the outer shell 6 and amounts to 35.5 mm, the latter diameter not taking into account the height H of the embossing protrusions 8. The diameter of the cross-sectional section of the inner surface 15 of the sleeve 9 is 30 mm.

Figure 2 shows the bushing 4 of the first embodiment already fabricated, i.e. after all three steps of the above described process for manufacturing the bushing 4. There is a virtually complete overlap between the outer surface 10 of the sleeve 9 and the inner surface 7 of the outer shell 6, including between the embossing protrusion 8 and the recess 11 . This overlap forms a form-fit connection between the outer shell 6 and the sleeve 9 of the bushing 4 which, by its shape, prevents the sleeve 9 from being forced out of the outer shell 6 during the operation of the bushing 4 when the guide pillar, not shown in Figure 2, moves along the opening 5 of the bushing 4. Detail A in Figure 2 shows the embossing protrusion 8 which is part of the inner surface 7 of the outer shell 6, in full contact with the recess 11 made in the outer surface 10 of the sleeve 9.

Figure 3 shows the outer shell 6 and the sleeve 9 in the first embodiment separately when the sleeve 9 is not yet inserted into the outer shell 6, i.e. after step one and before step two of the bushing 4 manufacturing process described above. Detail A in Figure 3 shows the cross-sectional diameter D2 of the inner surface 7 of the outer shell 6 and the initial cross-sectional diameter d1 of the outer surface 10 of the sleeve 9. The actual diameter d1 ' of the sleeve 9 is identical to the initial diameter d1 of the sleeve 9 before insertion. In this embodiment, the diameter D2 of the outer shell 6 and the initial diameter d1 of the sleeve 9 are identical.

Figure 4 shows the bushing 4 in the first embodiment during a manufacturing process, namely when the sleeve 9 is inserted into the outer shell 6 yet not expanded, i.e. after step two and before step three of the bushing 4 manufacturing process described above. The sleeve 6 is elastically compressed as a result of insertion into the outer shell 6. The recesses 11 have not yet been made because the sleeve 9 has not yet been expanded. The actual diameter d1 ' of the sleeve 9 at this stage of the manufacturing process is less than the initial diameter d1 of the sleeve 9 and the diameter D2 of the outer shell 6 by approximately two heights H of the embossing protrusions 8, as shown in detail A of Figure 4.

Figure 5 shows another embodiment of the bushing 4 for use in plastic injection moulding tool guides. Typically, a linear guide system is used for this type of tools, which has four guides. When the bushing 4 is fabricated, the sleeve 9 does not extend the full length of the outer shell 6. The pillar, which is not shown in Figure 5, is circular in cross-section and an opening 5 in the bushing 4 is also circular in crosssection. The outer shell 6 of the bushing is made of hardened steel and is 75 mm long. On the inner surface 7 of the outer shell 6, five embossing protrusions 8 are made which extend around the entire circumference of the inner surface 7 of the outer shell 6, which is drawn by the cross-section of the outer shell 6. These embossing protrusions 8 are made by turning. The distance between the embossing protrusions 8 is approximately 13 mm. The sleeve 9 is made of sintered material and is 75 mm long. The height H of the embossing protrusions 8 is 0.2 mm. In this embodiment, the embossing protrusions 8 are in the form of a symmetrical trapezoid in cross-section with the larger base of the trapezoid coinciding with the inner surface 7 of the outer shell 6. The embossing protrusions 8 are made of the same material as the outer shell 6 and are integrated into the outer shell 6. The initial cross-sectional diameter d1 of the outer surface 10 of the sleeve 9 is 34 mm and is identical to the diameter D2 of the inner surface 7 of the outer shell 6, the latter diameter not taking into account the height H of the embossing protrusions 8, this is shown in Detail A on Figure 5. Detail B in Figure 5 shows the part of the bushing 4 where part of the outer shell 6 fitted with the sleeve 9 and part of the outer shell 6 not in contact with the sleeve 6 come into contact. The cross-sectional diameter D3 of the inner surface 7 of the outer shell 6 in the part not in contact with the sleeve 9 is larger than the cross- sectional diameter of the inner surface of the sleeve 9 so that it is not in contact with the guide pillar 12 during operation, said pillar not shown in Figure 5. The diameter of the cross-sectional section of the inner surface 15 of the sleeve 9 is 30 mm. Figure 6 shows some embodiments of the embossing protrusions 8 in cross-section. Most of the cross-sections shown are convex in shape, with the exception of crosssection C. The embossing protrusions 8 may have sharp edges in cross-section, such as C, D, E, F, I, J and K, or rounded edges, such as A, B, G and H. The sides of the embossing protrusions 8 in cross-section may be straight, for example D, E, F, I and J, rounded, for example H, or a combination of straight and rounded, for example A, B, C, G and K. The embossing protrusions 8 shown are made of the same material as the outer shell 6 and are integrated therein, namely into the inner surface 7 of the outer shell 6.