The improvement of broach reachs his to choose: The improvement of high-speed steel twist drill and choose

In This Article, the Author Introduces Some Methods For Improvement And The Correct Use Of High-speed Steel Twist Drill In Different Situations.

In machining, aperture machines the 1/3 that occupies its sum of processes about, among them bore is occupied about 25% . Bore diameter limits is ф 0.

1~ ф 100mm, can achieve economical accuracy to be IT13~IT11. Bore is half enclosed cutting, accordingly, platoon bits, quantity of heat is passed medicinal powder, cutting fluid is pouring more difficult. The cutting tool that bore uses, especially the aperture that the diameter is less than ф 35mm, produce at present on still the high-speed steel with the standard (HSS) twist drill is given priority to. Because twist drill has stiffness to differ (because have two wide deep helix chamfer) , oriented sex is poor (two very narrow first flank and hole wall contact are only oriented) enter with axial send muscularity (main the existence because of horizontal blade) characteristic, and the bit that worries via manual blade, two advocate cutting blade hard accurate semmetry, consequently easy generation broach is brought when bore slant, bore diameter expands, difference of hole wall quality, with broach service life lower problem. For this, the blade look that needs pair of bit and structure try to improve, and practice already also proved, do the result so very good. The improvement of high-speed steel twist drill the improvement of high-speed steel twist drill has two kinds of methods: It is when be being designed and making bit, change its structure and material; 2 it is to the standard twist drill undertakes repairing grinding, choose reasonable cutting angle. Of Chinese original creation group get even if use to standard twist drill reasonable long grind a kind when change and become to be gotten newly model. The improvement of twist drill material makes the material of twist drill, use commonly general-purpose high-speed steel W6Mo5Cr4V2. If choose W2Mo9Cr4VCo8(M42) of high-powered high-speed steel, W6Mo5Cr4V2Al (501) with pulverous metallurgy high-speed steel (PMHSS) , its service life can raise 1~2 times. In addition, finishing also is one of important ways that improve broach life, if can use steam,nitrogen of processing, oxygen is changed, soft nitrogen is changed, sulfur nitrogen in all ooze and coating. Via using the high-speed steel twist drill after coating of TiN, TiAlN, its service life can raise 1~3 times, the cutting performance that does not have coating broach still is compared after and weigh be being ground advantageous. The improvement of twist drill structure can get the ply that get core by the standard (0.

125D~0.

15D) Mm increases (0.

35D~0.

40D) Mm (the D in type is broach diameter, the unit is Mm) or shorten appropriately the length of broach, in order to raise the intensity of broach and tigidity; Increase a paragraph of small auxiliary and oriented share (graph 1a) , of oriented ministry outside circumferential go up not to leave first flank and direct wear is cylindrical (its parameter is: D/D=1/4~1/2, / D=1/3~1, the D in type is the diameter of oriented ministry, d is broach diameter, the length that is oriented ministry) , use it and the Kong Mo clearance fit that get, certain and oriented effect has already when bore, can raise broach radial tigidity again, increase the certain disappear display vigour since damp to use; Increase helix angle to arrive 35~40, get the torsion when cutting and axial power in order to reduce; Use bit of 4 first flank (graph 1b) , in order to raise broach tigidity, the centering when improving bore is oriented quality; Cancel to get core rake (graph 1c) , use parabola a kind of new chamfer that hold bit is sectional appearance (graph 1d) , at the same time groove wide than (edge law discharges bits chamfer width and blade to carry width on the back to what measure than) the 1~1 that gets by the standard.

2 increase 1.

5~4, make broach has already thicker get core, have the larger space that hold bit again; Use inside fluid of cooling supply cutting (1a seeing a picture) , wait in order to improve cooling result. A few kinds of afore-mentioned methods can be used alone, also can combine use. The Kong Zuan, worm form twist drill that shows 3 times with the graph uses the oil that uses extensively on numerical control machine tool what the graph shows 2 times alone namely, use afore-mentioned methods with combination, the applied give typical examples that broach structure improves. The characteristic of twist drill of Nextpage worm form is: Use thick get core (without the rake that get core) , sectional appearance is blade channel parabola or approximate parabola, 35~40 big helix angle, the big vertex angle of 130, increased the tigidity of broach and look bits space already, increased platoon bits capacity again. Use at the same time repair the blade that grind a horizontal stroke crisscross, in order to reduce resistance of cutting of horizontal blade point. Approximate parabola cut form parameter: D= of the ply that get core (0.

22D0.

2) Mm, blade bandwidth B= (0.

1D0.

2) Mm, r=0 of circular arc radius.

5D (D is broach diameter, d=3.

2~38mm) . This kind of broach can get a hole depth and aperture last time in common device than amounting to the deep aperture of 20. Of twist drill long grind with group get the existence on structure of standard twist drill and geometrical parameter to wear a lot of defect, be like: Advocate cutting blade change of the character before going up is big, place of close external diameter can be amounted to 30, and close center part is - 30, and the horn before be being lost on horizontal blade is amounted to - 50~-60, reason cutting condition is poor; The horn after be not being had on first flank, attrition wears away big; Advocate cutting knife is long, cut bits wide, platoon bits not free, cutting fluid hard infuse arrives cutting area. For this, personnel of the operation in production often is ground through repairing will try to improve. Be like but: Long worry a double vertex angle, bit that grind cent groove and grind piece inside the means such as blade of sunken circular arc will change advocate cutting blade appearance, in order to increase cutting blade length, reduce the cutting negative charge on length of unit cutting blade, rise to improve broach centering, reach cent bits and the purpose that break bits; Will shorten through repairing the blade that grind a horizontal stroke its length, avoid horizontal blade to be in cutting of the horn before losing; The bit with older diameter still can be ground in first flank front piece deputy hind horn, wait with decreasing to chafe and wear away. Group get even if apply a variety of forms integratedly to repair the series that grind a method to change and becomes to get model, comfortable at processing different data. The graph is shown 4 times for basic model group get geometrical figure. Group auger basically did tripartite face to repair grind, form 7 cutting blade: It is in twist drill outside predestined relationship place is ground outside giving the vertex angle of 125 to form two straight blade AB, the middle grinds those who give two semmetry inside BC of blade of sunken circular arc, plunging knife two side form two new tops to nod, as sharp as center of horizontal blade office drop forms 3 needles to nod, have centering effect, central needle nods tall H=0 of sharper than both sides drop.

03D (D is broach diameter, the unit is Mm) ; 2 it is to repair the blade that grind a horizontal stroke, wear of will horizontal blade two inside straight blade CD mixes narrow horizontal blade B, make its length is the 1/5~1/7 that grows formerly, increased the role before horizontal blade is in, reduced horizontal blade adverse effect; 3 it is the diameter is more than ф 15mm broach, on the blade outside a side reopen divides bits chamfer, make the wider cent that cut bits is become narrow, facilitating platoon bits. Accordingly, group characteristic of the form that plunge knife is: 3 needles in the van of 7 blade acute, chamfer of crescent moon arc separates a side, the blade outside a side opens bits slot, horizontal blade is ground low narrow pointed. Group because have reasonable cutting point of view,get, cutting is so light, when cutting group the axial power that get can reduce 35%~50% , torsion drops 10%~30% , broach service life can raise 2~4 times. Because broach centering sex is good, bore precision is tall, the surface is rough the value is lesser also. The improvement that twist drill blade grinds a method face of the knife after the edge undertakes the blade of twist drill is ground. When blade is ground, should assure advocate the horn after cutting blade to go up is worth " inside big outside small " , the horn after getting core to be in nearly namely wants big, the horn after the circle outside leaning is in wants small. Still should make horizontal blade point gets appropriate bevel at the same time, before cost of the character after horn is mixed. Twist drill is ground with manual blade commonly, more reasonable method is to use mechanical blade to grind. At present commonly used mechanical blade grinds a law to taper seat blade grinds law and helicoid blade to grind a way, be about to of broach hind the one part of taper seat of knife face wear or helicoid. But in last few years, because be on machine tool of modular machine tool, numerical control and automatic product line,use bit in great quantities, because this is right the stability demand that broach blade worries quality is very high, and because grind the broach horizontal stroke that go out,planar blade grinds a way the part before blade point is lost is small, axial force is small, blade grinds used machine tool motion is simple, adjust convenient, easy implementation automation and the blade that assure broach grind quality, reason application day is wide. Alleged and planar blade grinds a way, it is face of the knife after pointing to two of twist drill is comprised by plane, of two plane intersect the line forms horizontal blade. The graph shows the geometrical figure that is 3 planar broach 5 times. The characteristic of 3 planar broach is blade 3 plane have on valve: Hind knife face 1 form the first plane, and the 2nd plane 2 with the 3rd plane 3 be located in respectively all round blade valve with the part that get core hind back. 3 planar broach are ground in blade when, the horn after the law on 3 plane is like next relations normally: . If, make double planar bit namely. Be like, it is the bit that common and planar blade worries. On 3 planar broach, as a result of the 2nd with the 3rd planar law to section plane inside hind horn is independent pilot, obtain parameter of the most reasonable horizontal blade geometry likely consequently, improve the cutting condition of horizontal blade, assure taller bore precision. Use correctly of twist drill (1) dosage of right choice cutting, very important to improving the service life of broach. Twist drill bore, as knife of aperture of two retrorse cars at the same time cutting, reason getting cuts deepness to be decided by bore diameter D (=D/2, the unit is Mm) , need not choose. Because the feed of broach accepts broach intensity and rigid restriction, it is F=(0 commonly.

01-0.

02)D, the unit is Mm/r; Classics is reasonable repair the broach after grinding desirable F=0.

03Dmm/r; The diameter is less than broach of 5mm of ф 3~ ф , feed of commonly used hand. Cutting speed: Cut steel =15~30m/min, cut cast =20~35m/min. Bore diameter is less than ф 35mm normally, if exceed this to be worth appropriate to divide second auger cut, should get for the first time (0.

5~0.

7) times aperture, the 2nd again reaming. (2) when bore, must supply enough cutting fluid, when cutting steel, can use extremely press emulsion, usable light diesel fuel or kerosene are cooling when machining cast. (3) the axes that gives opening to make get can the coincide of line of centre of turning circle with workpiece, workpiece turn had better be used when bore, broach makes axial feed motion only. To prevent and reduce the deflection of broach, can adopt on craft machine first piece wait for bore end panel, make its and broach perpendicular, or setting getting is covered undertake directing. Carry out a proof, use getting an oriented result is better. CNC Milling