Manufacturing Process for a Rear Differential Housing - Report Example

Manufacturing Process for a Rear Differential Housing

A rear differential housing basically looks like the diagrams shown below

The piece is made from 7075 Aluminium and the manufacture process is an engineering process that requires a lot of precision and care in order to avoid any accidents.

A conventional differential fixed as required should look something like this

With reference to manufacturing of differential housings by Ford’s engineers, the ends of steel tubing that is drawn are flared out and then riveted together to produce differential housing made of malleable cast iron material. This is a method that ensured that manufacturing of cars hastened with time.

Production of a rear differential housing

The rear differential housing consists of two longitudinal sections that are welded to each other. Each of the sections is produced by reshaping a billet into a forging blanks’ general configuration. The billet must be rough for a good stick. The blank, through a series of steps, is forged into a flat member. The member is the forged into the shape of a housing after which all the excess material that are left are removed.

Parts of a differential housing. It is an exploded view of the whole axle housing asssembly

A differential housing requires the use of a differential shaft to hand over power to axle shafts. This entails that it should provide torque to both axles irrespective of the speed. Due to such extensive requirements in a super car that requires a lot of torque, all the parts of the differential are shown above and include a case, pinion, spider and ring gears and a differential carrier. This paper will entail details for manufacture of a rear differential case. The differential case is thus the part that holds the ring and spider gears as well as the inner axle ends. The part is mounted for rotation inside the carrier where bearings help in fitting the outer ends of the case and the carrier.

The two halves of the rear differential housing are welded along a longitudinal axis that is centrally located. This joint extends all the way round the housing. Depending on the stress required as per the function of the housing, the thicknesses round the axis may vary. In order to get the required material distribution as per the stress requirements, the billet mentioned previously is rolled and stretched until the proper distribution is gotten. The billet is then moved to dies that are used for forging where hammering successively using narrow tools. This process is extended using wider hammering tools in order to achieve the desired steps. These latter tools assist in widening the product and later roll it into the shape of a hosing.

Extrusion of mild steel bars and moulding of iron components

Extrusion involves passing a material (steel billets in this case) through a die so as to create objects with a cross sectional profile that is fixed. The tool used for this process closely resembles the same machine used for injection moulding. In this process granules are placed in a hopper where they are moved by a motor that turns screw threads through a heater. The granules, which are thermoplastic, become molten at this stage (Technology and Design, 2011). When these granules (in the molten state) are passed through a die, the extrusion is formed. The newly formed extrusion is then cooled, and forms as per the shape of the die. This process of extruding steel as explained is better known as hot extrusion (ThyssenKrupp Steel Services Division, 2016). The main advantage of hot extrusion is that complex shapes can be formed with all materials even those that offer substantial difficulties during formation. It is also possible to form many small sized forms at very economic levels. Hot extrusion also has the advantage of forming materials that require different thicknesses with a profile cross section, and can withstand very specific demands in terms of temperature and pressure (ThyssenKrupp Steel Services Division, 2016). This advantage makes this method perfect for formation of a rear differential housing as it almost has the same specific requirements. Cold extrusion is a feasible method but not best applicable for such formations as required in rear differential housings as it does not do well in hollow formations (Miles and Dower, 1974).

In moulding of cast iron components, the major methods used, especially in manufacture of vehicle components are permanent mould casting or gravity die-casting. In this method, castings can be produced at very high rates. Before the process starts, the moulds are coated with a surface coating. The mould is then filled with molten metal at an extreme pressure. This method produces very good mechanical and surface finishes. The molten metal in this process is either poured directly or through tilting the mould vertically. Considering that the mould is made in two halves, it is then suitable for moulding the rear differential housings discussed in this paper. In the static capacity, moulds are set vertically and the molten metal poured thus having a vertical parting line. In a tilting position, the mould is placed vertically after closing and the material poured, and later vertically tilted to allow parting. Main advantage is the high production capacity, whilst main disadvantage is that the metal form made is usually parted halfway thus if no such requirement was needed, it cannot be used. The method is also uneconomical for low productions due to high costs of tools.

Stresses and strains

These occur during metal formation as dislocations travel atom layers. Such dislocations may lead to inward curvatures that lead to ring dislocations that may travel to initial positions. In managing such problems, engineers may conduct tension, compression or even torsion tests. True stress and true strain tests may be conducted through drawing the requisite curves. With the curves, such as the true strain and true stress curve, done at the right conditions in terms of temperature, strain rate, accuracy of the instruments that are used to measure and the accuracy of elongation instruments, engineers can comfortably establish the correct configuration as per the set standards (Zhongchun Chen et al., 1999).

Manufacturing techniques

The advances in technology usually result in significantly improvement in the productivity of quality of finished component in relation to surface finish and accuracy. Wire erosion is a manufacturing process in which the desired shape of an item is obtained using the electrical discharges (Singh, 2014). The process is essentially accurate and efficient method of cutting hard metals that are cumbersome to work on by using traditional methods.  Usually, the material to be used is removed from the work-piece through a series of discharges that occur rapidly between the given electrodes. The electrodes are often separated by a dielectric liquid and with provisions for an electric voltage. Suffice to mention is the fact that one of the electrode is known as the tool –electrode. The other electrode is referred to as the work-piece-electrode (Singh, 2014). The two electrodes should not be in contact for an efficient process. When the voltage between the tool –electrode and the work-piece electrode is increased, the intensity of the electric field becomes greater as compared to the strength of the dielectric. This results into breaking and hence allowing current to flow between the two electrodes. This method of manufacturing has many benefits which include the following according to Singh (2014):

• It enables complex shapes that are difficult to manufacture using traditional methods to be much easier.
• It can be used to manage the very hard material to close tolerance.
• Produces excellent surface finishes with no traces of blurring
• Using the technology, it is very easy to make fine holes.

Waterjet cutting is as a form of micro erosion (Summers, 1995). It works by forcing a large volume of water through a small orifice in the nozzle. The constant supply of large volume of water traveling through a reduced cross sectional area triggers the particles to quickly accelerate. Suffice to mention is that the accelerated stream leaving the nozzle has an impact on the material to be cut. The high pressure generated by the accelerating water particles contacts a small area of the work- piece hence the work piece starts to develop small cracks as a result of the impact of stream. The waterjet usually washes away the material that comes out of the surface of the work piece. Ideally, the crack resulting from the waterjet impact is now exposed to the waterjet. Consequently, the high pressure and impact of particles in the following stream cause the small crack to occur until the material is cut through (Summers, 1995). Some of the tools and equipment used in this process include high pressure pumps, an injector that helps in drawing abrasive into the cutting stream, a mixing chamber and pressure intensifiers among others. Due to the uniqueness of waterjet cutting is a unique technique that is used in very applications. This process is usually more economical and useful as compared to the standard machine processes. Waterjet cutting is applied mostly to cut material with lower strength such as wood, plastics and food substances (Summers, 1995). The cost implication for the waterjet process is considerably low.