Indexable turning broach for machining crankshaft

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indexable turning broach for machining crankshaft has the advantages of high machining efficiency, good machining quality, long tool life, convenient tool change and adjustment, and is the preferred advanced tool for rough machining of automotive crankshaft at present. The broach used in China's automobile industry has long relied on imports, which has greatly increased the processing cost of crankshaft due to its high price. In order to realize the localization of indexable turning broach, many domestic enterprises have successively developed turning broach products in recent years. However, due to the complex structure of indexable turning broach, high technical content and great manufacturing difficulty, it has strict requirements on processing conditions and processing accuracy (it needs to be processed on a high-precision five coordinate digital control machine tool), and most of them adopt manual programming processing by operators, resulting in long tool manufacturing cycle and difficult guarantee of processing accuracy, The scrap rate is high

using sun graphics workstation and I-DEAS software of SDRC company in the United States, combined with Ingersoll max-i indexable tool design theory imported from Germany, our company has successfully solved the design and manufacturing problems of indexable turning broach by using cad/cam technology, and better ensured the product quality and processing efficiency of domestic indexable turning broach

2 structure design of turning broach

the complete turning broach is assembled by multiple fan-shaped turning broach blocks on the drum. Taking a sector turning broach block as an example, the cad/cam method of turning broach is introduced

in view of the large machining allowance (about 4 ~ 5mm) of the crankshaft, the strict requirements on the tolerance of the shaft diameter and side wall width (rough machining +0.1mm, finish machining +0.04mm), and the higher requirements on the cutting efficiency and surface roughness, the key points of the structural design of the turning broach are as follows:

the structure of max-i end mill of Ingersoll, Germany is adopted. The blades of the turning broach are arranged in a tangential direction. The blades are fastened with a single screw and clamped by cutting force. The tool structure has the advantages of convenient and rapid blade rotation, less tool accessories, and can increase the chip holding 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 bear the cutting force, that is, the ability of the cutting edge to bear the cutting load, so as to achieve high-efficiency cutting with large feed and large cutting depth

the front end of the sector turning broach block adopts a replaceable module structure. The cutting force and impact load borne by the blade at the front end of the turning broach are the largest, so the blade and tool body are most likely to be blunt, broken and damaged. The replaceable module structure is adopted at the front end of the turning broach, which can realize rapid replacement in case of blade or blade body damage, so as to shorten the tool replacement cycle and effectively protect other blades and blade bodies from large load impact. This structure can prolong the service life of the tool, save the production cost, and ensure good machining accuracy. However, if we have repaired it

the blades are arranged according to the tooth lift. The arrangement of the blades according to the tooth lift can realize the layered cutting of the crankshaft, so as to effectively reduce the cutting resistance, reduce the bending phenomenon of the crankshaft during machining, and improve the machining quality and cutting efficiency

the blades in the circumferential direction are arranged with unequal tooth pitch, and a group of blades with the same size are staggered by a phase angle, which can reduce the cutting vibration and increase the cutting stability

adopt reasonable geometric angle and high dimensional accuracy requirements

3 turning broach CAD steps

according to the crankshaft machining drawing provided by the user, the turning broach layering as shown in Figure 1 can be drawn, so it can match the cutting line diagram with the different materials tested, and based on this, the spacing of each layer (i.e. tooth lift) and the radial dimension and axial width dimension of each layer can be determined. The first five sets of blades are used for rough machining, with large tooth lift; The last five blades are used to ensure the machining accuracy of the crankshaft, and smaller tooth lift is selected

Figure 1 layered cutting line diagram of turning broach

carry out line segmentation based on the layered cutting line diagram of turning broach, and draw the arrangement and overlap diagram of cemented carbide inserts (see Figure 1)

determine the effective number of cutting teeth of the turning broach according to the blade overlapping diagram and the diameter and sector size of the turning broach, and conduct circumferential distribution within the sector block interval, and then change a group of cutting teeth at the front end of the turning broach into a quick change module

calculate the misalignment of each blade to form a drop value. The calculation formula is

x=0.5{wb+c[d2/(WB2 +c2) -1]} where: WB - blade width on the axial section

c - drop value

d - diameter of the circle where the blade is located

since the diameter and size of each group of blades are different, the dislocation value of each group of cutting teeth must be calculated separately, and then each group of blades must be transferred to the required position on the sector surface of the turning broach block and arranged with unequal tooth spacing

rotate and stagger two blades of the same group with the same diameter by one phase angle

rotate each blade around its end face side edge to produce a side edge back angle A

determine the chip holding space according to the blade position. Since the number of teeth on the turning broach block is large and the chip holding space is relatively small, the chip holding space should be increased as much as possible when designing the chip holding groove and make it open an angle towards the direction of smooth chip removal

determine the installation structure, dimension and dimensional accuracy of turning broach. The structure of turning broach designed according to the above CAD steps is shown in Figure 2

Figure 3 programming flow chart of indexable turning broach

4 turning broach cam steps

leading the sustainable development blueprint

using I-DEAS according to the determined structural scheme and design sketch

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