Drill tolerances and standard dimensions

DRILL TOLERANCES AND STANDARD DIMENSIONS FULL
DRILL TOLERANCES AND STANDARD DIMENSIONS SERIES

It often happens that closer tolerances and lower variability in the machining of the individual components will lead to fewer problems in assembly, final product testing, field service, and customer acceptance. This is not to suggest that looser tolerances are always good. However, if the designer specifies a tolerance of РІВС’.025 mm, then an additional reaming operation is needed to satisfy this tighter requirement. For example, if the product designer specifies a tolerance of РІВС’.10 mm on a hole diameter of 6.0 mm, this tolerance could be achieved by a drilling operation.

DRILL TOLERANCES AND STANDARD DIMENSIONS FULL

Environmental benefits and quality improvements will also result from full implementation of this technology.Tighter tolerances usually mean higher costs. Economic benefit is estimated to be nearly $800 million per year. The fully implemented potential benefit of thread forming fasteners in as-cast holes of aluminum and magnesium is estimated to be 6 trillion Btu per year for North America. There does not appear to be any significant increase in clamp load variation due to the application of thread forming fasteners in as-cast holes of aluminum or magnesium over the effective life of a die casting mold. It was concluded that this work showed that clamp load variation with thread forming fasteners is consistent with industry expectations for standard steel bolts and nuts at +/- 30%. The robustness range (.05mm larger and smaller holes than the expected wear pattern of a die casting die at full life cycle) results also fell within the industry expectations for standard threaded fasteners. The results for the thread forming fasteners in magnesium cast holes were all well within industry expectations of +/- 30% for all three conditions. However, when compared to the actual Battelle results (+/- 40%) for a standard bolt and nut the tread forming fasteners performed slightly better. The results for the dry and lubed extreme conditions were only slightly higher than industry expectations at +/- 35.6%. The results for the thread forming fasteners in aluminum cast holes were well within industry expectations of +/- 30% for out of the box and robustness range testing. Results from previous work performed on the same test cell for a Battelle project using standard M8 bolts into standard M8 nuts were included as a comparator for a standard bolt and nut application. Again all clamp loads were recorded and analyzed similarly to the Taptites in aluminum cast nuts. In a like fashion, a second set of experiments were run with cast magnesium nuts and ALtracs thread forming fasteners, (a widely used thread forming fastener suitable for magnesium applications). The clamp load corresponding to the target input of 18.5 Nm was recorded for each fastener. The clamp load data was used to determine the range of clamp loads to be expected. Taptite thread forming fasteners, (a widely used thread forming fastener suitable for aluminum applications), were driven into the various cored, as-cast nuts at a constant input torque and resulting clamp loads were recorded continuously.

DRILL TOLERANCES AND STANDARD DIMENSIONS SERIES

First, a series of cast aluminum nuts were made reflecting the range of shape and size variations to be expected over the life cycle of a die casting die. The cast bosses were cut into nuts that could be used in the Ford Fastener Laboratory test-cell to measure clamp load when a thread forming fastener was driven into a cast nut. This established range of variation was captured in a set of 12 cast bosses by designing core pins at the size and draft angles identified in the sited previous work. The range of variation that can be expected in as-cast hole size and shape over the full life cycle of a high pressure die casting die was established in previous work completed by Pacific Northwest National Laboratory, (PNNL). There is little data available to understand the magnitude of this concern or to form the basis of potential solutions if the range of clamp load variation is very high (> +/- 30%). The torque used for thread forming may not be consistent due to variations in casting material, hole size and shape due to tooling wear and process variation (thermal and mechanical). The clamp load consistency concern is founded in the fact that a moreР’В Р’В» portion of the input torque used to create clamp load is also used to create threads. * No known data to understand the effect on consistency of clamp load as casting dies wear. input torque in either aluminum or magnesium castings. The primary issues at the source of engineers reluctance to implementing thread forming fasteners in lightweight castings are: * Little proof of consistency of clamp load vs. The ultimate objective of this work was to eliminate approximately 30% of the machining performed in typical automotive engine and transmission plants by using thread forming fasteners in as-cast holes of aluminum and magnesium cast components.

Drill tolerances and standard dimensions