According To The Result Of Test, the Main Elements Of Destroying Drill Is Investigated.
Keywords: of Turn Destroying of of Micro-hole Drill uses twist drill of high-speed steel straight power to get cut small hole (1mm is the following) when, breaking off is the main form that broach destroys. Breaking off as a result of broach happen suddenly, forecast hard beforehand, and the broach head that broke off often gets stuck in half-baked Kong Zhong, take out very hard, caused a lot of troubles to production, also make automation is gotten cut small hole to come true hard. Getting in cutting a course, broach is turned round, bend and reduce the assorted effect that waits for 3 kinds of load, break off to broach fracture surface undertakes study with circumstance getting power, can make clear broach breaks off reason and each load the effect that in broach the place in breaking off has, take necessary step thereby, prevent broach to break off suddenly. For example, the main load that applied getting cuts the appearance that measure power to break off to creating bit undertakes online detect, increase fair numerical value when this load when, issue alarm signal, make broach go back, cut quality to drop with avoiding to broach breaks off and be gotten. 1.
Observation of broach fracture surface and analysis fold absolutely mouth to undertake to tiny bit microscopical enlarge observes discovery, majority fracture surface happens in broach helix chamfer mid arrive between root ministry, be apart from cutting blade further. Look to helix chamfer direction, fracture surface is sectional outside the included angle of normal and broach axes is about between 50 ° of 40 ° ～ . Graph 1 for 0.
The twist drill of high-speed steel straight power of 34mm is being gotten when cutting alloy steel of 18Cr2Ni4WA low carbon snap picture of absolutely mouth SEM. Graph 1 auger cut basis of fracture surface of broach of low carbon alloy steel stretch and mechanical reach metallic stuff strength academic, be not round sectional lever when freedom is turned round, shearing stress of pointed part part is equal to on cross section 0, groove place shearing stress is the greatest (namely critical point) , lever cross section is in for the greatest shearing stress namely sectional; What be in at shearing stress is the greatest o'clock is the biggest stress place is sectional for danger sectional, this are sectional be in with the greatest shearing stress sectional the included angle between is 45 ° . Accordingly, when broach suffers torque effect, the greatest shearing stress happens on the cross section of ministry of helix bottom land, the biggest what stress is in is sectional it is 45 ° with the included angle between broach cross section. Because fracture surface of actual measurement broach is sectional,suffer the dangerous and sectional direction when reversing load action to agree basically with broach, can conclude, turning round load is the mainest reason that broach breaks off greatly too. 2.
Broach suffers respectively twist, the validity that the curved, fracture surface actual measurement when controlling load function and analysis analyse for above of test and verify, to 0.
The twist drill of high-speed steel straight power of 34mm parts according to ideal turn round, bend, till broach is destroyed,reduce to load of 3 kinds of means, destroy its fracture surface and auger cut destroy fracture surface to undertake comparative. Broach suffers pure when curving load action, the biggest stress happens on cross section, broach fracture surface should agree with direction of broach cross section, this and be identical of experimental result photograph (see a picture 2) . Graph 2 broach suffer pure curve load to fold press press of absolutely mouth broach to shrink when load action, will produce shear failure, fracture surface should be the greatest shearing stress the place is sectional, it and broach cross section show included angle of about 45 ° . With sufferring those who turn round load action to differ is fracture surface azimuth it is random, have nothing to do with the position of helix chamfer, in the random that shows 45 ° included angle with cross section the position all can happen, in this a series of inclined sectional on shearing stress is worth equal. Actual measurement compresses fracture surface sectional become 45 ° included angle with cross section (see a picture 3) , agree with afore-mentioned analysises. Graph 3 broach press press shrinks load folds absolutely mouth to pursue 4 suffer for broach pure when reversing load action destroy fracture surface, with the graph a shown bit is getting the fracture surface azimuth that in cutting a course, breaks off to agree basically. Turn round the characteristic that destroys fracture surface to one is highlighted, when looking to broach helix chamfer namely, fracture surface is sectional become 45 ° included angle with cross section, what this also is in at shearing stress is the greatest o'clock just about is the biggest the azimuth with stress sectional place. Graph 4 broach suffer pure turn round load to fold absolutely mouth 3.
Tiny bit breaks off case study is imperceptible the dispersive sex of broach service life is very big, still with 0.
The high-speed steel twist drill of 34mm is gotten cut alloy steel of 18Cr2Ni4WA low carbon to be exemple, when hole depth is 2mm, broach life is about between 10 ～ 80mm. Use microscopical magnifier undertakes observing discovering to broach cutting blade, before the broach with partial taller life breaks off ever since knife face has more apparent grind blunt trace, and partial broach still does not have the situation that worries blunt trace apparently to fall to break off in cutting blade, have drawback or because broach data is inside,having fraction bit additionally is cutting blade blade grind angle error bigger, its service life still not as good as 10mm. Visible, get a few random elements in cutting a course to be affected to broach service life very big. Getting each load in cutting a course to be in the carrying capacity of broach normally, and should get cut torque abrupt wave motion, when exceeding its carrying capacity, broach can break off. Tiny bit gets core ply opposite bigger, of the ply that get core and broach diameter it is than making an appointment with 0.
3 ～ 0.
4 (the broach of common diameter is in 0.
2 the following) , make helix chamfer more shallow, ability of look bits, platoon bits is inferior, together with liquid has exterior pulling force, cutting fluid enters small hole very hard inside, cause extremely easily cut bits to jam, make get cut torque to increase suddenly and make broach breaks off. Visible, cut bits to jam, cutting blade wears away bring about auger cutting torque to make defect with broach greatly too is the main reason that imperceptible twist drill breaks off. Accordingly, before will tiny bit is used at getting to cut treatment, answer to grind angle to undertake detecting to cutting blade blade first, eliminate deviation lives old bit; Applied getting cuts the appearance that measure power to undertake getting cutting force online when detecting, should cut torque in order to get to regard as detect, control index. CNC Milling