Abstract This document and the accompanying files describe the process of modelling a bell housing jig using the 3D software Catia V5. The manufacturing process by which the bell housing would be created has been described. A set of manufacturing drawings conforming to BS8888:2008, which can be used to manufacture the items, has been shown. Part A Bell Housing Model Please see attached Catia files. Part B Manufacturing Process The assembly model has been made of component parts and a jig is constructed from such constitutes for the purpose of creating apertures. An outline of the creation of such a bell housing and the drilling process is briefly described. The cast iron bell housing is (as its name implies) manufactured from the casting process. This is a solidification process whereby the iron is heated to its melting point (about 1300 o C, but dependent on specific chemical constituents) and this is then poured into a mould and allowed to solidify. The casting process is an ancient process, approximately 6000 years old. [1] In its advances these modifications have been made to the process: - The mould can be made from many different types of material, depending on material and quantities produced. These include sand casting, low cost wax process, and evaporative pattern and plaster mould process. The major differences are the type of material used to create the mould, and subsequent complications and their solutions described below. Sand casting involves using a pattern (a physical and topologically accurate representation of the bell housing) and using moistened sand & aggregate solution similar to clay to make a mould of the pattern. It is usually done by compressing the sand onto the mould in a contained area. This mould pattern is larger than the original to allow for a reduction in area as the iron solidifies. The molten iron is poured into the mould, either as an open process or more commonly as a closed process. By closing the system this incurs complications. For example, the air that is present in the mould. An exit hole is usually allowed in the mould for the retraction of the air that was present. The addition of extra holes internal to the cast is used to compensate for the reduction during solidification. Inserts can be added to the inside of W. Shipway ID1029062 1
the mould to allow for more complex internal geometry of the iron cast. This cast is then allowed to cool, at a specific rate and specific time depending on the process and material constitutes, and then removed. This is either done by creating a tapered mould and lifting the solid cast out, or breaking the comparatively low stiffness of sand (a brittle material) compared to the iron cast (a less brittle material). This is the fundamental aspect of using sand, the fact that it has a high resistance to temperature, thus an insulator and ceramic material, but is not of comparable toughness (i.e. fracture resistance). To ensure better production when breaking the mould, the sand can be re-used, and the pattern can create multiple moulds, ergo increasing productivity. Specific to the cover, the jig facilitates the need for mounting holes and in essence holds the cast in place whilst it is drilled to a high degree of accuracy, which is usually automated. The jig is mounted to the part to be drilled and tightened to ensure any vibrations from the drilling machine will not a) misalign the apertures and b) not damage the drill bit (note bit has a specific meaning, not for want of a better word). To further align the drill as it makes its vertical pass there are liner bushes (item 4) that act to protect the jig. Thus it is imperative that the liner bushes are made of a hardened material. Although, it is equally important that the bushes are not as hard as the drill bit, to ensure that the bit does not lose its edge, which is more costly than the bushes. Therefore the bushes will need to be replaced in production runs as they will wear to an unsuitable thickness, thereby potentially allowing the jig to get damaged. The location hole is created to ensure the drilled parts are aligned. The cast will then be heat treated to give it better material properties to serve its purpose, and/or finished to a certain degree by removing any burrs, increasing surface smoothness, or putting surface coatings on the material. Cast iron is ferrous (by definitions) and these finishing processes are an attempt to prevent corrosion. [1] Ravi, B. (2004), Metal Casting - Overview, IIT Bombay. W. Shipway ID1029062 2
Part C Catia Modelling Process A description of each modelling process has been explained, using the given specification in Fig. 1. Figure 1. Given specification of product Bell housing jig. Note: All measurements used and shown mm. Although the stated measurements are in cm on the given specification it is assumed this is incorrect. The M16 nut and shaft define the dimensions (mm) for items 3 and 5, and for the assembly construction to fit all other items must be of the same type. For example the M16 nut would slip through the c-washer due to the size difference. W. Shipway ID1029062 3
1. Jig Body Figure 2. The jig body sketch. To create the jig body a). A sketch is created as fig. 2, and then the revolve tool was used. Note in Fig. 2 the highlighted lines are unconstrained due to the lack of data given in the specification (i.e. height of jig body not specified). Figure 3. Drill hole created. W. Shipway ID1029062 4
b). Then a sketch of a hole was created on the top plane of the revolved part, as Fig. 3. The diameter was taken from the specification of item 1 and offset item 2 (so the holes line up). Then the pocket tool was used to create a hole. c). The circular pattern tool was used to repeat the drill holes, as per fig. 4. The advantage of this is for part redesigning where more holes are needed, the parameters can be changed (angle, amount of holes (instances)) instead of manually creating each hole. Figure 4. Circular pattern is exploited. d). The location hole is made by use of the pocket tool again, specifying a depth of 14mm. Figure 5. Fillet radii, a (left) and b (right) e). At 3 points a fillet is created of 2mm radius by selecting these edges and holding ctrl, then using the fillet tool. The 3mm radius is then created the same way. The part tree shows the items stated 1 to 5 of the jig body. W. Shipway ID1029062 5
Figure 6. Part tree associated with the jig body. In a more complex model each sub tree can be renamed for clarity. 2. Jig Plate Figure 7. Jig plate initial sketch a). For example purposes this part was completely modelled in one sketch, by using the mirror tool for the 4 drill holes (dia. 16mm). However in industry this would be constrained to the drill holes of item 1 and so would be modelled by the same process (circular pattern tool). b). A fillet radii of 2mm was created around the outer edges. W. Shipway ID1029062 6
3. M16 Nut The hexagon tool was used to construct the nut sketch and extruded. See Fig. 9. Dimensions were obtained for a standard M16 nut from BS 3692:2001, with an example shown in Fig. 8. Figure 8. Typical data found in BS 3692:2001 ISO metric precision hexagon bolts, screws and nuts specification. Figure 9. Sketch of nut W. Shipway ID1029062 7
b). A hole (pocket) was created and the thread tool was used to create an M16 tap, specifying the diameter, pitch and depth as defined in BS3692:2001 c). A groove sketch was created of 30 o to cut off the burr when manufacturing. Although BS3692 specifies the angle on both the top and bottom surfaces only the top surface was cut as shown in the spec. given. The point filter tool was used to ensure the new sketch picked up the existing extrusion. Figure 10. The surface cut of the M16 nut. 4. Liner Bush a). The Liner Bush was created by sketching a hollow cylinder and extruding, then using an edge fillet radius of 2.5mm internally and 0.8mm externally. 5. Stud a). The stud was created by extruding the inner shaft and then creating an offset plane 30mm up the shaft. This was used to create the larger stud diameter, as per Fig. 11. W. Shipway ID1029062 8
Figure 10. The stud outer diameter extruded by use of an offset plane. The chamfer tool was used and then the thread tool used to the required depth as specified in fig 11. Figure 11. The thread depth varies from each end of the shaft. 6. C Washer The washer was created in one sketch, using the trim tool. Then a chamfer was added. W. Shipway ID1029062 9
Figure 12. The c-washer sketch. 7. Pin This was extruded as a shaft and then either end was rounded by creating a shaft revolute sketch as per Fig. 13 as the normal edge fillet could not be used because the radius is too large. This was then mirrored about the horizontal axis. The curvature (rounding ) can easily be adjusted from the constraints on either side and the opposite side will mimic it, ensuring uniformity. Figure 13. The rounding of the pin, by drawing one profile, mirror and then revolving. W. Shipway ID1029062 10
8. Component The simplified bell housing was created by the shaft tool of sketch as per Fig. 14. Figure 14. Housing shaft (rotation) sketch and fillet tool The edge fillet tool was used as per Fig. 14 and then the pin location hole was pocketed. 9. New Housing The new housing was completed as item 1-component, except for these additions: The mirror tool was used for the 10 holes as Fig. 15. The lugs were constructed by creating 2 circles with diameter as the original extrusion, then creating one lug. Axis lines were defined at 120 o, and then the mirror tool was used on these axis lines. The trim tool was then used where the lugs overlapped the original 2 circles to ensure a closed drawing. It was ten extruded into the W. Shipway ID1029062 11
original model by 2.5mm. It is noted in Fig. 16 the original lug on the right where all the other lugs take their symmetry constraint. Figure 15. Additional holes in the bell housing Figure 16. The lugs of the housing W. Shipway ID1029062 12
Part D Manufacturing Drawings A set of manufacturing drawings is given in this document which are capable of communicating information which can be used to create physical parts accurately. All drawings are confirmed to BS8888:2008, and in third angle projection. Appendices For display purposes the colours have been changed (Tools>options >display>visualisation) W. Shipway ID1029062 13