MACHINING ELIMINATION THROUGH APPLICATION OF THREAD FORMING FASTENERS IN NET SHAPED CAST HOLES

Cleaver, Ryan J. ; Cleaver, Todd H. ; Talbott, Richard

UNITED STATES COUNCIL FOR AUTOMOTIVE RESEARCH LLC, Southfield, MI

关键词: Casting;    Life Cycle;    Thread Forming Fasteners;    Economics;    Machining;   

DOI  :  10.2172/1039333
RP-ID  :  DOE/EE0003482-1
RP-ID  :  EE0003482
RP-ID  :  1039333

美国|英语

来源: UNT Digital Library

【 摘 要 】

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. 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. input torque in either aluminum or magnesium castings. * No known data to understand the effect on consistency of clamp load as casting dies wear. The clamp load consistency concern is founded in the fact that a portion of the input torque used to create clamp load is also used to create threads. 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). 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 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). 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 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. There were two sets of experiments run. 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. 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. The clamp load data was used to determine the range of clamp loads to be expected. The bolts were driven to failure. The clamp load corresponding to the target input of 18.5 Nm was recorded for each fastener. 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). Again all clamp loads were recorded and analyzed similarly to the Taptites in aluminum cast nuts. 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. 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. The results for the dry and lubed extreme conditions were only slightly higher than industry expectations at +/- 35.6%. 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 thread forming fasteners in magnesium cast holes were all well within industry expectations of +/- 30% for all three conditions. 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. These results were very encouraging. 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%. 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. 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. Economic benefit is estimated to be nearly $800 million per year. Environmental benefits and quality improvements will also result from full implementation of this technology.