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1、Formation and Control of Drlling Burrs Abstract：In this paper, a new forming model of the feed-direction burr for process is presented. The feed-direction burr formation is experimented and studied. The related theories are analyzed, and the influential factors of the feed-direction burrs are pointe
2、d out. Furthermore, certain number of new measures to prevent and decrease the burr in drilling process is advanced.Key words: feed-direction burr, drilling, debarring technology, precision machiningThe cutting burrs are often formed on the side, corner, edge and ends of a workpiece in the precision
3、 machining, FMS and the automatic metal cutting processes. It seriously affects the accuracy of measure and shape of the workpiece.，using life of the workpiece is greatly shortened and machining productivity is reduced and so on. In recent years, engineers and scholars of machinery engineering in so
4、me countries began to study the forming principle of cutting burrs and debarring technology. And a certain number of new positive results are achieved. It promoted the development of mechanical technology greatly.There are two kinds of the cutting burr produced in drilling operation based on the bur
5、r classification system of the cutting motion and cutting edge of tool, they are (in feed-direction) entrance burr (I-F) and feed-direction burr (O-F). The feed-direction burr is comparatively large in size and deburring work is of difficulty. It often becomes an obstacle of the following machining
6、operation. But so far academic papers of forming principle and deburring technology of the feed-direction burr in drilling process are not many. In the paper the type of forming mechanism and main influencing factors of the burr are experimented and studied, and related theories are analyzed. The th
7、eoretical and predictive bases are made in order to decrease and control feed-direction burr in drilling.1 A Forming Model of the Feed-Direction Burr in DrillingIn the drilling process, if the material of the workpiece to be cut is even, plain twist drill is not partial, the geometry parameters of t
8、he relative point on the major cutting edge of drill is all the same and accuracy of the workpiece to be located is with great precision, a forming model of the feed-direction burr is shown in Fig. 1. From Fig. 1, the diameter of the drill is (mm), drilling feed is f (mm) and drill included angle is
9、 2. The end material of the workpiece to be out in feed-direction is crushed out of shape by the function of the axial thrust farce .Supposing warp amount of a certain point contacted with tool major cutting edge on the workpiece is ,then:Fig. 1 The forming model of the feed-direction burr in drilli
10、nga) When = 0, drilling process continues;b) In the range of 0 , feed-direction burr is formed because the part material of the workpiece end is pressed and pushed under the action of .The main factors affecting burr formation in drilling include the workpiece material, the shape of the workpiece en
11、d, cutting parameters and cutting geometry of the drill, etc. In order to obtain a clear understanding of the forming process of burr in drilling, the experimental study and theoretical analysis are carried out as follows.2 Experiment Condition and Measure MeansIn the experiment, the drilling machin
12、e used is up right drilling machine Z5140. The universal twist drill made in H. S. S. is selected, drill diameter is 20 mm, and emulsions are used as cutting fluids. Workpiece material: H68, and HT15-33 plate, the thickness of the plate is 15 - 20 mm. And H68 is selected as standard material for the
13、 test. The mechanical property of the workpiece material and drilling condition for experiment is shown in Tab. 1and Tab.2. The surface of the workpiece end is roughly ground before the test.The burr height H in the test is measured by dial gauge (accuracy of the measurement is 0.01 mm) and burr roo
14、t thickness B is treasured by tool microscope (accuracy of the measurement is 0.01 mm). The farms of the feed-direction burr in drilling are classified on the basis of the experimental observation.Tab. 1 Mechanical property of the workpiece materialsTab. 2 drilling conditions3 Experiment Results and
15、 Discussions3.1 forms and character of the feed-direction burrFrom observation in the test, feed-direction burr in drilling can be classified into types, and burrs (See Fig.2). They have some special properties as follows:Type burr: the end of workpiece is hollow and its called cutting fracture. Bur
16、r height H and root thickness B are very small(H0, B0) in normal casesInfluence of typeburr to accuracy and property of workpiece is not much, but, it easily destroys forming accuracy of the fix case, assembly and travelling for machining etcTypeburr: the burr height is Hd/2 and burr root thickness
17、is B0When the requirement of cutting accuracy of the workpieee is higher, type burr must be debarred, and the work time of the deburring is comparatively short. Type burr: type burr in size is very large in the burrs produced for drilling, that is Hd/2，B is very bigThe workpiece with type burr produ
18、ced has to be deburred and the work time of the debarring is much. In most cases, it becomes one of the important factors to reduce machining productivity and increase cutting cost of the workpiece.Fig. 2 Forms of the feed-direction burr in drilling3.2 Effect of the cutting speed vAfter cutting spee
19、d v is changed, feed-direction burr produced is shown in Fig.3 .Fig.3 shows that the burr height H and root thickness B，are reduced with the increase of cutting speed v , this is because that the temperature of the drilling area is increased and the material to be cut is softened with the increase o
20、f the cutting speed. Then drilling force is reduced, the burr size is shorten.Fig.3 Effect of the cutting speed v on burr3.3 Effect of the feed fFig.4 is result experimented after feed f is changed. Form Fig.4，it is known that burr size increase with of the increase of the feed f. This is because th
21、at axial thrust force becomes large, the warp amount of the material to be cut on the workpiece end will be large with the increase of the feed.3.4 Effect of the drill included angle 2After drill included angle 2 is changed, feed-direction burr produced is shown in Fig.5 in order to know the effect
22、of dull-included angle. From Fig.5, it is known that burr size increases fast with change of the drill-included angle. This is because that underformed chip is increased and width of the uncut chip is reduced，and M are reduced and axial thrust force is increased along with the increase of drill incl
23、uded angle 2.Fig.4 Effect of the feed on burr Fig.5 Effect of the drill included angle3.5 Effect of the helix angle Fig.6 is a result tested after helix angle is changed. Burr size reduces with the increase of the helix angle. This is because that the larger the working orthogonal rake angle of the
24、drill is, the larger the helix angle is, and the chip will flow easily. and M will reduce with the increase of the helix angle .Fig.6 Effect of helix angle of the drill3.6 Effect of the worhpiece materialsIn the standard drilling condition, the size of the feed-direction burr for h r workpiece mater
25、ials H68, and HT15-33 is shown in Fig.7. It shows that the size of the burr is changed with the difference of the material to be cut. Type burr is formed in drilling HT15-33 and type burr is formed in cutting , andH68. This is because of the difference of the mechanical property of the workpieece ma
26、terial (They are tensile strength and specific elongation).That is, the larger the burr sizes are, the bigger the specific elongation of the material is and so on.Fig .7 Effect of workpiece material4 The Measures to Restrain and Decrease Burrs4.1 Overlap of the workpieceIn the drilling process, the
27、support strength of the material on the exit of the drill is one of the important factors to effect burr size. The overlap method of the workpiece is selected in order to increase strength of the end of the workpiece (in Fig.8). The change of burr size after overlap of the workpiece is shown in Tab.
28、3. We can see that the burr size formed in cutting workpiece (1) and (2) is much smaller than that in cutting workpiece (1). 4.2 Selection of the drilling parametersIn the light of specific drilling condition and requirement, the high cutting speed v (see Fig.3) and the small feed f (see Fig.4) are
29、first selected on the possible condition, therefore and burr size are reduced, the cutting productivity is increased and the cutting quality is guaranteed.Tab.3 Experiment of overlap method of the workpiece4.3 Adjustment of the drill geometryFrom Fig.5 and Fig.6, it is known that the burr size is re
30、duced with the increase of the helix angle or reduce of the drill include 2.So that the geometry of the drill can be selected in the possible condition to effectively reduce and control the size of the shape of the feed-direction burr in process.4.4 Drill type improvementThe drill type improvement i
31、s shown in Fig.9, the test results are shown in Tab.4 using improved drill type. Form Tab.4, we can know that the burr root thickness B is reduced by 25%-33% after using drill (a)or (b), but the burr height H is almost not changed .This is because that the cutting heat is given out fast, the wear am
32、ount of the drill reduces on the connection area of the drill major cutting edge and minor cutting edge, the length of the cutting edge increases, the specific cutting force for drill is improved. The angle of the range of the drill major cutting edge and minor cutting edge increases, the support st
33、rength of the workpiece is relatively raised. 4.5 Strengthening method of the end material of the workpieceThe end material of the of the workpiece can be treated with strengthening method in order to reduce and control the burr in drilling (to increase fragility of the material using hammer or spra
34、ying ball made in steel) or to reduce specific elongation of the material on the end material of the workpiece by painting chemical matters and so on.Fig.8 Overlap method of the workpieceFig.9 Drill type improvementTab.4 Experiment result of drill type improvementConclusions1) In the drilling proces
35、s, there are three types of the feed-direction burrs: type,and burrs .2) The main factors to affect burr formation in drilling are workpiece material, drill geometry, drilling parameters and the end of the workpiece, etc.3) We can take up the overlap method of the workpiece, selection method of drilling parameters, adjustment method of the drill geometry, method of the drill type improvement and strengthening method of the end material of workpiece to reduce and restrain feed-direction in drilling process.
