This invention is concerned with a connecting rod and a process for making such a connecting rod.

The process of making components from sintered metal powder is well-known and is used for parts which would require considerable machining if made by conventional means. The process involves introducing metal powder into a die having the shape of the required part, applying pressure to consolidate the powder and cause it to flow into all parts of the die, removing the consolidated powder from the die (the pressure has caused it to adhere together sufficiently to allow this), and introducing the consolidated powder into a furnace in which the powder is caused to sinter together as a result of the heat applied thereto. Various powders can be used depending on the properties required of the component which can if necessary be machined to give it its final shape, e.g. by cutting threaded holes. The part may also be pressed again and heat treated prior to machining.

One component which has been considered as a candidate for manufacture by the above-mentioned process is the well-known connecting rod used in the automotive industry which has a big end and a small end. However, because of the necessity for high strength at the small end it was found necessary to provide additional powder at the small end which, although the sintered connecting rod weighed no more than one made by conventional means, caused the connecting rod to be out of balance in that the weight of the small end was out of proportion. This rendered the connecting rod unacceptable. This problem

could be solved by using a powder giving higher strength which would allow the small end to be designed in the correct proportion but the use of such powder increases the cost unacceptably. Another problem with the use of higher strength material is that it is more difficult to machine, e.g. for cutting bolt holes in the big end.

It is an object of the present invention to provide a process for making a connecting rod having a big end and a small end in which the above-mentioned balance problem is avoided without incurring unacceptable expense.

The invention provides a process of making a connecting rod which defines a small end and at least part of a big end comprising introducing metal powder into a die cavity having the shape of the required connecting rod, applying pressure to the powder in the die cavity thereby consolidating the powder in the shape of the cavity, removing the consolidated powder from the cavity, and heating the consolidated powder in a furnace thereby causing the powder to become sintered, characterised in that a first powder is introduced into the portion of the cavity having the shape of the small end and a second powder is introduced into the portion of the cavity having the shape of at least part of the big end, the first powder having greater strength than the second powder.

In a process according to the last preceding paragraph, a connecting rod is produced which has additional strength in the material at the small end so that the rod can be designed to have the correct balance point but the more expensive stronger material is used at the small end only reducing the additional expense.

Furthermore, more readily machinable material is located at the big end where machining of bolt holes may be required.

Preferably, the first and the second powders are introduced into the cavity simultaneously, e.g. from a shoe which is divided into two portions each with its own powder supply. Simultaneous introduction of powders militates against a powder spreading beyond its intended portion of the cavity.

The first powder may suitably be an at least partially pre-alloyed powder containing Nickel, Molybdenum, Copper or Carbon or a combination of these elements.

Where the connecting rod defines only a part of the big end, the process may also comprise making a cap to complete the big end. The cap is suitably made from the second powder.

The invention also provides a connecting rod which is formed from powder which has been sintered, characterised in that the connecting rod comprises a small end portion sintered from a first powder, and a big end portion sintered from a second powder, the first powder having greater strength than the second powder. Preferably, the first powder contains Nickel or Molybdenum in greater proportion than the second powder.

There now follows a detailed description to be read with reference to the accompanying drawings of a process and two connecting rods in accordance with the invention.

In the drawings:

Figure 1 is a plan view of a first connecting rod;

Figure 2 is a plan view of a second connecting rod; and

Figure 3 is a diagrammatic view of apparatus for carrying out a process for making the connecting rods of Figures 1 or 2.

The first connecting rod 10 shown in Figure 1 comprises a small end portion 12 including a hole 13 to receive a shaft and a shank portion 15 having an elongated central hole 17 therein. The small end portion 12 is adapted to be pushed on to a shaft (not shown). The connecting rod 10 also comprises a big end portion 14 having a hole 19 surrounded by a metal band 21 which is adapted to be cut or split and provided with threaded bolt holes so that it can be clamped around a shaft received in the hole 19.

The small end portion 12 is sintered from a first powder which is a partially pre-alloyed powder containing Iron and proportions of Nickel, Molybdenum, Copper and Carbon as required for the desired strength.

The big end portion 14 is sintered from a second powder which is similar to the first powder but contains lower proportions of Nickel, Molybdenum, Copper and Carbon giving lower strength, easier machining and lower cost.

The line 16 in Figure 1 indicates the approximate location of the boundary between the first and the second powders although in this region there is some intermingling of the powders.

In variations of the connecting rod 10, the composition of the first and second powders may be selected from a wide range of possibilities. Not only partially pre-alloyed and fully pre-alloyed powders may be used but also elemental mixtures in appropriate circumstances. The proportions of Nickel, Molybdenum, Copper and Carbon may also vary and indeed, in appropriate circumstances, one or more of these elements may be absent or may be replaced by other constituents. The first powder should, however, be selected so as to give, after compacting, sintering, possible repressing and heat treatment, a density of at least 6.9 gms per cu.cm. and a tensile strength of at least 600 Newtons per sq.mm. The second powder should give, after the same treatment, a density of at least 6.8 gms per cu.cm. and a tensile strength of at least 400 Newtons per sq.cm.

The second connecting rod 10a shown in Figure 2 has a small end portion 12a which is similar to the small end portion 12 of the rod 10 but its big end portion 14a differs in that only a part of the big end is defined. Instead of a hole 19, the portion 14a has a recess 19a which is adapted to be closed by a cap (not shown) when a shaft is received in the slot 19a. The rod 10a is sintered from the first powder (the portion 12a up to the line 16a) and the second powder (the portion 14a). The cap may be sintered from the second powder or may be made by other methods.

Figure 3 shows diagrammatically apparatus used in the process of making the first connecting rod 10 or the second connecting rod 10a. The apparatus comprises a lower punch 20 which incorporates ejecting means (not shown), a die 22 having a die cavity 24 having the shape of the connecting rod 10 or 10a, a vertically movable

upper punch 26 which can be raised into the position shown in which it is clear of the die 22 and lowered into a position on top of the die 22 so that it applies pressure to powder in the cavity 24.

The apparatus also comprises a shoe 28 which is movable horizontally between the position shown in which it is on top of the die 22 and beneath the upper punch 26 and an out-of-the-way position (not shown) clear of the die 22 and the upper punch 26. The shoe 28 is effectively a box closed at the top and open at the bottom and divided into two chambers 32 and 34 by vertical walls 33. Two flexible pipes 35 and 36 lead into the chambers 32 and 34 and are connected to sources of powder (not shown) operaole to dispense powder into the cavity 24 via the chambers 32 and 34.

In the process, while the upper platen 26 is in its raised position, the shoe 28 is moved from its out-of-the-way position to the position over the die 22 (shown in Figure 2). This movement (which is in a direction towards the viewer of Figure 3) causes the shoe 28 to push a previously ejected connecting rod, which was on top of the die 22 after ejection from the cavity 24 by the ejection means, to be pushed clear of the cavity 24. The connecting rod can then be carried to a furnace for sintering.

When the shoe 28 arrives in position over the die 22, the first powder is supplied via the pipe 36 to the chamber 32 and the second powder is simultaneously supplied via the pipe 35 to the chamber 33. Thus, the metal powder is introduced into the cavity 24 by falling through the open bottoms of the chambers 32 and 34. A

central vertical wall 34 is located above the line 16 or 16a.

After the die cavity 24 has been filled with powder, the shoe 28 is moved to its out-of-the-way position and the punch 26 is lowered to apply pressure to the powder to cause it to consolidate in the shape of the cavity 24. The punch 26 is then raised and the consolidated powder is ejected from the cavity 24 by operation of the ejection means. The consolidated powder is pushed away from the cavity 24 in the next operation of the apparatus and transported to the furnace where it is heated and thereby the powder is caused to become sintered. The connecting rod may be re-pressed and heat treated.