The connecting rod for a typical passenger car engine - Essay Example

The fracture split surfaces have large surface area at the ends, as compared to the conventional machined surfaces. Hence, the load carrying capacity is also increased. In addition, the number of operations is reduced while using this fracture split method. The sequence of operations will be like this: Grinding of the joining faces of the cap and connecting rod. Bolt holes operation to be carried separately using different fixtures for the rod and the cap. To achieve a positive grip the serration on the rod and cap faces should be either broached or surface ground with perfect precision.

Bolt hole drilling should be done, using Specific rotary dial index or linear transfer machines, to ensure that the correct center distance is maintained between the bolt hole of the rod and the cap. Bolt size and straightening is very important, as that will determine the quantum of undue stress on the bolt area, after the assembly of the connecting rod. The use of computerized design like CAD is helpful and the CNC machine tools should be utilized for optimum machining performance. As the bolt hole finishing is very important and critical, the tools and jigs should be such that the two holes are placed parallel to each other and at the same distance.

Tolerance in the bushes should be kept at low, to the maximum of 10 microns. For this purpose, the reamers are required with front and rear guides. To avoid any misalignment caused by the spindle, the reamer is held in a floating holder. For longer life, the bushes are made of tungsten carbide, which also ensures maintenance of closer tolerances in the long run. The distance between piston pin and crank bores should be controlled with zero tolerance, more so for gasoline engines. CNC slides for Boring heads and cartridge type fixtures help in the maching of different connecting rods on the same machine tool.

To give the proper twist and bend to the connecting rod for the final assembly, use of “corrective fixtures” is recommended.