In cutting process " plunge into a knife " theoretical analysis of the phenomenon and its precautionary measures

  • Time:
  • Click:16
  • source:EAGLEBURGER CNC Machining
Because 1 foreword suffers the effect of systematic stiffness and cutting damp, in metallic cutting generation of the meeting in machining a process misses firm appearance. Break firm phenomenon to call trends to be not stabilized by what negative damp causes, break firm phenomenon to call a static state to be not stabilized by what negative stiffness causes. The author is measured with high yield quality is being promoted in machining process, reduce cost to use up for the target, the because cutting tool is out of shape,creates static state in machining a process to metallic cutting broke firm phenomenon to undertake analytic study, announced in metallic cutting process " the phenomenon that plunge into a knife " substaintial, generation prevents in putting forward to producing practice " the phenomenon that plunge into a knife " significant step. Graph when 12 cutting " plunge into a knife " the process cuts treatment to be with dig exemple (if the graph is shown 1 times) of the generation in analytic treatment process " the phenomenon that plunge into a knife " . When dig cuts treatment, workpiece with speed V from left decide right motion, ply of workpiece surface layer is cut by cutting tool for a metal of S0, cutting force is P0. Below the action of P0 cutting tool produces flexibility to be out of shape, position of the edge in the graph by not the O site when cutting changed O dot. Right now the flexibility of cutting tool restores force Fs and balance of photograph of cutting force P0. But this kind of balance is temporary, not stable. In cutting process any accidental, tiny interference can break this kind of balance. For example the some horniness point that edge cuts workpiece material to go up, cutting force P0 obtains an increment DP immediately. Below the action of DP edge moves to be in to O" dot by O again. Right now point is out of shape because of cutting tool moved backward Dx, and dropped Ds. Ds makes cutting ply produces the instantaneous increment of a same amount, and the accretion that the addition of cutting ply causes cutting strength once more again, make cutting tool point farther next moving, point of a knife plunges into workpiece greatly. The result of such loop can make point of a knife makes with generation because of the cutting power that increases quickly collapse blade. We call this kind of phenomenon that metallic cutting appears in treatment process " plunge into a knife " . Graph 2 graphs 33 " the phenomenon that plunge into a knife " the cutting system that theoretical analysis graph shows 1 times is a feedback system that has displacement apparently, this system but by block diagram 2 express. Graph 2 in the block diagram above is cutting tool system, its input a quantity is action the change of the cutting force on cutting tool measures DP, and sendout is edge produces the horizontal displacement after be out of shape to measure Dx from this; The block diagram below expresses the control orgnaization of cutting force, inputting a quantity is Dx, because the change of force of the cutting after horizontal displacement measures DP,sendout is edge, DP feedbacks again action provides a system at the knife. If the plan a shown cutting system arranges hour hand to turn,cross 90 ° , can regard cutting tool as approximately one cantilever bridge (its diagram sees graph 3) . The outfit clip that sets cutting tool is completely rigid, by material the stiffness of mechanical and knowable cutting tool is the L in type of K= DP = L3 Dx 3EI(1) -- of cutting tool dangerous extend length EI -- the equivalent stiffness K that the stiffness defying a turn of cutting tool material produces by displacement feedback place can beg by the following method piece: Request a plan above all 1 in Dx(of perpendicular and as stretchy as its quantity also is the Dx of horizontal displacement quantity of edge the increment of cutting ply) the relation between. Of oversight cutting tool self-prossessed, because arbor is one cantilever bridge, the action that carry a department has one to center load DP, criterion the deflection F that its carry a department and corner Q are F= DPL3 3EI(2) Q= DPL2 2EI to be in respectively graph 3 in, the distance between the neuter range that sets the crucial point to arbor is Z, and A of end points of hypothesis median plane moves on plumb line only, select A site by A namely, have Dx ≈ =f AA(3) by the graph 3 medium geometry concern knowable Ds=qZ, era enters type (2) , type (3) can get Ds= 3Z Dx 2L(4) in addition, cutting force! With the function between cutting ply $ relation P(s0+ds) exhibits power series P(s0+ds)=P(s0+ DP(s0) Ds+ around S0... the increment of force of Ds criterion cutting is DP=P(s0+ds)+P(s0)=ksds+ ... (the Ks=dP(s0)/ds in 5) type, because P(s0+ds) is of Ds,add function, reason is due Ks>0. type (4) generation enters type (5) skips high-ranking minim, DP=ks 3Z Dx 2L gets equivalent stiffness coefficient is K= DP =ks= 3Z Dx 2L(6) from this criterion total stiffness of the system is type of K-k= L3 -ks 3Z 3EI 2L(7) in, - Ks · 3Z/2L is the equivalent negative stiffness that causes as a result of displacement feedback. Apparent, generation " the phenomenon that plunge into a knife " the condition is (L3 -ks 3Z)<0 3EI 2L(8)4 " plunge into a knife " precautionary measures by afore-mentioned analysises knowable, if type (in 8) - the equivalent negative stiffness that Ks · 3Z/2L(causes by displacement feedback namely) turn into stiffness, can prevent generation " plunge into a knife " phenomenon. In producing practice, appear through changing arbor appearance to prevent normally " plunge into a knife " phenomenon. Graph 4 graphs when 5 dig cut treatment, planing tool of bend of instead of planing tool of will straight head (if pursue,show) 4 times. Bend right when arbor when be out of shape, cutting blade retreats those who leave work to already machined the surface at the same time, can avoid " plunge into a knife " . When turning is machined, the lever of machete of circular arc form that will rigid straight arbor changes to have flexibility (if pursue,show) 5 times. When the lathe tool that uses this kind of structure is machined, its cutting point basically turns along one circular arc below the action in cutting force, retreat thereby because of,can prevent " plunge into a knife " and phenomenon of generation collapse blade. The lathe tool of this kind of stretch structure is multi-purpose machine at the grooving of workpiece, appear very practical when cutting off treatment especially. CNC Milling CNC Machining