Requirements on Machining Allowance for Castings
GB/T 11350-1989 outlines the requirements for the machining allowance for castings. This standard is applicable to casting mechanics, such as the lathe, milling, drilling and grinding machines. Specifically, it applies to the requirements of machining allowance for the following types of castings: ferrous metals and non-ferrous metals castings.
For ferrous and non-ferrous casting mechanics, an average allowance of 0.3mm-0.7mm is required. For an assembly of multiple parts, an allowance of 0.5mm-1mm is recommended. For shapes and sizes of work pieces that are below 20mm, an allowance of 0.2mm-0.5mm is recommended. Machining allowance should also be considered for tolerances on the work piece dimensions. The allowance addresses the potential of any change in geometry or size of the part after mechanical finishing.
The conditions of the machining allowance should be taken into consideration, such as whether it is feasible to turn, mill and drill on the part with the allowance, as well as any other conditions necessary for machining. Machining allowance measurements should also be made for holes, threads, grooves, and other parts of the work piece that require processing.
In order to keep the machining allowance level, a specific scale or graph should be established. The graph or scale should be used to judge whether or not the process requirements are being met.
Furthermore, the ease of machining can also be determined by analyzing or discussing the surface roughness, depth of cut, and chip forming of the machining allowance with regard to the parts that are being machined.
In the end, the requirements of this standard should all be regarded when implementing the machining allowance for fabrication. Once met, the requirements are constantly reviewed and improved to ensure that there is no inconsistency in the machining allowance of different castings.
In conclusion, in order to efficiently achieve the part tolerances that are requisitioned with low cost, the GB/T 11350-1989 standard should be followed for the machining allowance for castings. Not only does this standard guarantee that the machining allowance is up to standard and maintain consistency in the machining allowance of different parts, but the standard also guarantees a smooth machining process.
