The physical phenomenon in metallic cutting and basic rule (6)
- source:NODIE CNC Machining
Knife face wears away before when metal of cutting plasticity, if cutting rate is higher, feed is bigger, cut bits the indentation that place of advanced knife face can grind a depression shape of a crescent moon gradually, as cutting continuity, crescent moon depression deepness increases ceaselessly, when approaching point, can make point dies suddenly. Before the size of knife face wear extent, with crescent moon depression width KB and deepness KT express. Graph 2-30 place is shown. 2. Knife face wears away after the knife after is mixed as a result of point faces workpiece to transfer exterior extruding and attrition, in cutting blade and its lower part hind a width is formed gradually on knife face not divide evenly, bestrew depth of differ channel mark wear away arris face. If pursue,2-30 place is shown. Part of point of a knife (C area) intensity is low medicinal powder heat is differred again, wear away more serious, its value is VC; Advocate the appearance that cutting blade approachs work is in (N area) , as a result of semifinished product crustaceous or the reason such as treatment sclerosis, also grind a bigger deep channel, its maximum is VN; Intermediate place (B area) wear away evener, average width expresses with VB, maximum expresses with VB Max. 3.
Before, hind knife face wears away at the same time is become when cutting plasticity metal, be like cutting ply moderate, before often happening, hind knife face wears away at the same time. Face of the knife after having as a result of of all kinds cutting tool wears away, and hind knife face wears away to be measured easily again, use normally so can wear away on behalf of cutting tool quite the size that the VB of function and VB Max will come to to represent cutting tool wear extent. (2) of reason of cutting tool tatty causes cause of cutting tool tatty very complex, it is get below high temperature and high pressure mechanical, thermochemistry action and happen, particular branch is the following kinds of reasons: Hard particle wears away taller than hardness of cutting tool material hard particle is contained in workpiece material, softer to cutting tool in cutting process matrix can engrave a mark of a channel and cause mechanical wear. When low speed cutting, hard particle wears away is cutting tool tatty main reason. Felt wears away the felt dot between workpiece or the surface that cut bits and cutting tool surface, because move relatively, the particle of cutting tool one party is taken away and cause wear away. Felt wears away to be concerned with cutting temperature, also concern with the affinity between workpiece material and cutting tool material. 3.
Diffuse wear away to fall in high temperature, there is the atom that kisses the element with action in workpiece material and cutting tool material, diffuse to go in the other side each other, make the chemical composition of cutting tool material produces change, the cutting function that weakened cutting tool and cause wear away. 4. Change wear away cutting tool material lifts because of cutting temperature, achieve change temperature, and the change that produces metallographic organization, make cutting tool hardness is reduced and cause wear away. If high-speed steel cutting tool is achieved when cutting temperature,change when temperature, happen to change wear away, and lost cutting property. Cutting tool wears away to still have other reason: Oxidation wears away, hot - chemistry wears away, report - chemistry wears away etc. The place on put together is narrated, cutting temperature heals tall, cutting tool wears away more fast, because this cutting temperature is cutting tool tatty main reason. (3) blame is normal wear away in cutting process, cutting tool is divided grind a loss to go outside cutting ability normally, still blade of be turned, collapse, broken or factitious attaint waits, make cutting tool loses cutting ability, these belonging to blame is normal wear away. In application, should carry correct option cutting tool material, choose the measure such as the operation method with cutting condition, reasonable regulation reasonably, avoid to be not normal tatty to happen. Provide durability to reach its of main influencing factor 1, cutting tool wears away limit cutting tool wears away limit is to point to the maximum that stipulates a permissible wear is measured, also say to grind blunt standard. Cutting tool wears away limit sets commonly go up in face of the knife after cutting tool, express with the average VB of wear extent. Express what 2-8 is hard alloy and high-speed steel lathe tool to wear away limit. 2, cutting tool durability durability of cutting tool is the cutting tool that shows a Xin Ren is ground, from begin cutting to come achieve wear away the cutting time that limit place passes, will express with T. Cutting tool life is a new cutting tool from use discard as useless the cutting time till. Cutting tool durability besides be shown with cutting schedule, also can use the amount that processes same part or cutting distance length to wait sometimes will express. Always affect factor of cutting tool tatty apparently, also affect cutting tool durability no less. Tatty of influence cutting tool is main the element is cutting temperature, and cutting rate is the oldest to cutting temperature influence, because this cutting speed is right the impact of cutting tool durability is the biggest. When the relation cutting of cutting speed and cutting tool durability, after workpiece material, cutting tool material and angle of cutting tool geometry are affirmatory, cutting speed V C is the mainest factor that affects cutting tool durability. What graph 2 -31a shows is high-speed steel or cutting of hard alloy cutting tool the circumstance of the cutting time of common structure steel and wear extent. V C heals tall, cutting temperature heals tall, wear away accelerate, cutting tool durability heals small. If graph 2-31b place is shown,be the logarithm curve of T of cutting tool durability and cutting speed V C. Can get V C by experimental method- - the concern of T is as follows: of V CT M=C namely V C==C/T M (2-9) the T in type -- -- cutting tool durability (C of of Min) -- -- coefficient, dosage of its numerical value and workpiece material, cutting tool material, cutting about; M -- -- index, state V C is right the influence degree of T, see watch 2-9. M value heals small, demonstrative V C heals to the influence of T big. M 0 of cutting tool of pottery and porcelain of cutting tool of hard alloy of cutting tool of high-speed steel of material of cutting tool of M of index of durability of watch 2-9 cutting tool.
2-3 of exemple of 4 uses cutting of YT15 of hard alloy cutting tool 45 steel, when Vc=100m/min, t1=160min of cutting tool durability; If other condition is changeless, raise cutting rate Vc= 300m/min, try beg right now cutting tool durability T2.
Solution: The numeric and usable following method of T 2 begs of Vc1/vc2=(T2/T1) M of reason of of Tm2 (2-10) of · of Tm1=vc2 of · of Vc1 of giving to take M =0 by watch 2-9.
25, criterion 100/300=(T2/160) 0.
T2=1 of of 25 .
975min raises 2 times when Vc it is thus clear that, and cutting tool durability dropped 80 times. From now on exemple what can see the cutting speed effect to cutting tool durability is big. can maintain the reasonable durability of cutting tool productivity highest or the durability of cost lowest, call reasonable durability. Namely reasonable durability has highest productivity durability and lowermost cost durability (economic durability) . Cutting tool durability restricts cutting speed, cause the change that changes a knife to reach the number that grind a knife, affect productivity and cost thereby. If durability is decided exorbitantly, although can decrease,change a knife to reach the number that grind a knife, but sure meeting lowers cutting rate, those who affect productivity rise; If durability is chosen too lowly, although can raise cutting rate, but increase necessarily change knife and the time that rub a knife, raise cost. Because this rises,productivity is mixed reducing cost often is contradiction sometimes. In using, from specific production only the condition sets out, choose appropriate durability, ability makes highest productivity and lowermost cost are achieved unified. At present great majority uses lowermost cost durability, namely economic durability. Its numerical value is commonly: On general purpose machine tool, durability of hard alloy lathe tool is 60 ～ 90min roughly; Broach durability is 80 ～ 120min roughly; Durability of milling cutter of hard alloy end panel is 90 ～ 180min roughly; Durability of gear cutting tool is 200 ～ 300min roughly. Cutting tool heals complex, cutting tool durability should be decided a few higher, blade is ground and adjust fee in order to decrease. But the innovation as cutting tool and manufacturing technology and development, example exactly the number accuses a machine tool to be used extensively but dislocation cutting tool, because its change knife time and cutting tool cost to be reduced greatly, can take inferior durability, in order to raise cutting rate, achieve improve productivity, do not raise cost again. But the durability of dislocation lathe tool is desirable for 15 ～ 20min. To the cutting tool on machining center or transfer matic, can use the method of cutting tool of the preliminary adjustments outside machine, shorten the time that change a knife, take inferior cutting tool durability, achieve the goal that improves productivity. CNC Milling