The MJ thread is a metric aerospace thread. Its basic tooth type is different from the basic tooth type of the metric ordinary thread. The outer thread bottom has a larger radius of the bottom of the tooth, and the bottom of the tooth is a continuous smooth curve. The radius of the arc of the place shall not be less than 0.1 50 11 P, and its accuracy is higher than that of the ordinary thread. Because the precision requirement is relatively high, the processing is also more difficult. This threaded hole is used in the Cummins natural gas engine block and the main housing of the EFI engine block.
This article describes how to improve the life of 14 M J12 bolt hole tapping taps on the main housing of Cummins EFI engine cylinder block.
Since January 2008, MJ threaded holes have a slight drop and surface roughness value, and the thread after processing has failed to pass the rule. The tool wear is accelerated, and the average tooling of 15 to 30 pieces requires a tool change. In view of the on-site situation, the following two improvements are proposed from the design of the tap.
(1) Option 1 For the tap that has been worn out, re-grind and then apply a surface coating.
In the present case, consider controlling the diameter of the threaded bottom hole to the upper limit to reduce the amount of wear of the tap and improve the life of the tap. In the case where the stock of taps is allowed, the re-grinding taps are currently used as little as possible. Because the life of the taps is inconsistent after re-grinding, it is easy to see the unsatisfactory thread of individual threaded holes in mass production, and also increase the inspection and repair work. the amount. If you have to use a regrind tap, re-grind and then apply a surface coating to increase the diameter of the tap to ensure that the tap diameter is acceptable.
At present, the small diameter of the tap, or the Japanese OSG recently processed the first thread that failed the thread, and commissioned the Dongfeng company to measure the surface of the used tap after re-grinding. The Japanese O SG tap can be directly processed. The surface coating is coated with a medium diameter of 6 μm to test whether it is processed and the life of the tap is collected.
(2) Scheme 2 The method of increasing the diameter of the new tap by 0.01mm was used to verify the test of Dongfeng Company Measuring Instrument Factory, Japan OSG, Wuxi New Age and Zhuzhou Diamond Carbide Tap.
1 Dongfeng company measuring instrument factory tap
The tool material belongs to ordinary high-speed steel. The new tool can be processed by 30 pieces at a time. The surface roughness of the machined thread hole can meet the requirements, and the pass-through inspection can be guaranteed. The old tap surface coating after grinding has a life expectancy of about 30 pieces and a high surface roughness value. The main reason may be that the edge of the tap will become dull after the surface coating of the tap, resulting in a sharp edge at the time of cutting, resulting in a relatively high surface roughness value.
The diameter of the tap was increased by 0. 01mm and 0.0 2mm on the basis of the original, and 10 pieces were produced for testing. First test the tap with a diameter of 0.01mm (K 23 D 2 - 1 28 C ) (test holes No. 6 003, 600 5, 600 7, 6009, 6011, 60 13 and 6015), the first inspection except 6007 holes In addition to the 2 buckles, the rest are qualified, so far more than 220 pieces have been processed (only about 25 pieces can be processed before the tap diameter is increased), and the processing can be continued from the point of view of the wear of the tap.
Later, the tap with a diameter of 0.02 mm was tested (K 23D 2 - 128D ) (test holes No. 6003, 6005, 6007, 6009, 601 1, 601 3 and 6015), and the first piece was checked except for 6007 holes. The regulations are about 4 buckles, the rest are qualified, and the final life is more than 300.
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