1 Introduction <br> <br> indexable broaching tool has high efficiency, good processing quality, long tool life, tool change and blade adjustment and easy, is the first choice for advanced automotive crankshaft roughing cutter. The broaches used in China's automobile industry have long relied on imports. Due to the high price, the processing cost of the crankshaft has been greatly increased. In order to realize the localization of indexable broaching knives, many domestic enterprises have developed broaching knives in succession in recent years. However, due to the complex structure of the indexable broaching knives, high technical content, difficult manufacturing, processing conditions and processing The precision is strict (need to be processed on high-precision five-axis CNC machine tools), and most of them are manually programmed by the operator, which results in long tool manufacturing cycle, difficult machining accuracy and high scrap rate.
Our company used SUN graphics workstation and I-deas software of SDRC Company of USA to combine the Ingersoll MAX-I indexable tool design theory imported from Germany, and successfully solved the indexable car broach by CAD/CAM technology. The design and manufacturing problems ensure the product quality and processing efficiency of the domestic indexable broach.
2 broaching tool design <br> <br> complete vehicle by a plurality of sectors broach broaching knife block assembled to the drum. Let's take a fan-shaped broaching block as an example to introduce the CAD/CAM method of the broach.
For the crankshaft machining, the cutting allowance is large (about 4~5mm), the shaft diameter and the sidewall width tolerance are strict (roughing +0.1mm, finishing +0.04mm), and the cutting efficiency and surface roughness are high. The structural design points of the knife are as follows:
Adopting the German Ingersoll MAX-I type vertical milling cutter structure. The blades of the broach are arranged in a tangential direction, and the blades are fastened with a single screw and clamped by a cutting force. The cutter structure of the tool structure is easy and quick to transfer, and the tool accessories are small, which can increase the chip space and the number of effective cutting teeth. Compared with the flat-blade structure, the vertical blade structure can increase the area of ​​the blade to withstand the cutting force, that is, increase the cutting blade's ability to withstand the cutting load, thereby achieving high-efficiency cutting of large feed and large depth of cut.
The front end of the fan-shaped broach block has a replaceable module structure. The cutting edge and the impact load of the blade at the front end of the broach are the largest, so the blade and the body at this place are most likely to be blunt, chipped and damaged. The replaceable module structure at the front end of the broaching tool enables quick replacement when the blade or the body is damaged, thereby shortening the tool change cycle and effectively protecting other blades and the body from large loads. The structure can prolong the service life of the tool, save production cost, and ensure good machining accuracy.
The blades are arranged in a tooth lift. Arrangement of the blades according to the amount of tooth lift enables layered cutting of the crankshaft, thereby effectively reducing the cutting resistance, reducing the bending phenomenon during cranking, and improving the machining quality and cutting efficiency.
The circumferential direction of the blades is arranged with unequal pitches, and a set of blades of the same size are staggered by a phase angle, thereby reducing cutting vibration and increasing cutting stability.
Use reasonable geometric angles and high dimensional accuracy requirements.
Broaching tool 3 <br> <br> crankshaft CAD processing step of FIG user-supplied, drawn cart layered broach cutting line graph shown in FIG. 1, and accordingly determines the distance of each layer (i.e., the amount of tooth liters And the radial dimension and axial width dimension of each layer. The first five sets of blades are used for roughing, with larger tooth lifts; the last five blades are used to ensure crankshaft machining accuracy, and smaller tooth lifts are used.
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According to the blade lap diagram and the diameter of the broach and the size of the fan, the effective number of teeth of the broach is determined, and the circumferential distribution is carried out in the sector block, and then a set of cutting teeth at the front end of the broach is fastened. Change the module.
The amount of misalignment of each blade is calculated to form a drop value. The calculation formula isC - the difference
D——the diameter of the circle where the blade is locatedSince the diameters of each set of blades are different, it is necessary to separately calculate the misalignment values ​​of each set of cutting teeth, and then transfer each set of blades to the required position on the fan blade face and arrange the unequal pitch.
Two identical sets of blades of the same diameter are rotated by a phase angle.Each blade is rotated about its end face edge to create a side blade back angle a.
The chip space is determined based on the position of the blade. Since the number of teeth on the broaching block is large and the chip space is relatively small, the chip space should be increased as much as possible in the design of the chip squeezing groove, and it should be opened at an angle to the direction of the chip discharging.Determine the mounting structure, dimensions and dimensional accuracy of the broach. The structure of the broach according to the above CAD steps is shown in Fig. 2.
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