The high speed milling of structural member of thin wall whole
- source:AMANCIO CNC Machining
35kg, the structural member of whole of much muscle thin wall that belongs to a model, semifinished product material is plank of cuboid of antirust aluminous LF21(GB1173-86) , belong to aluminium alloy of a kind of plasticity, quality is made an appointment with 12.
25kg, machine through milling by " draw out empty " , material excision rate is 80.
8% , its material hardness is 45HB, tensile strength 180MPa, percentage elongation 12% . Metallic excision amount is large, finished product wall is thin, stiffness is low, the chief problem that the need in treatment solves is control and reduce be out of shape. Use technique of milling of average rate numerical control, handling time is as long as 50h, need intermediate heat treatment to be out of shape in order to remove treatment stress, control, accordingly, still need hard to improve treatment in treatment efficiency, shorten time and reduce cost. According to foreign data report, remarkable to tensile strength the aluminium alloy under steely material, can use high speed cutting to help sb to fulfill his wishes a task of thick, finish machining; Set out from process market Central Plains, use machining center of cutting of a high speed merely namely. Experiment condition experiment uses machining center of milling of high speed of linkage of German Hermle C1200U 5 axes, if pursue,2 are shown. Its main job parameter is: ～ of N=20 of main shaft rotate speed 24, 000r/min, power of the biggest output is 23kW, torque is 79Nm; Edge X, y, the journey of Z axis is respectively 1, 200, 800, 500mm, 30m/min of speed of the biggest linear feed, 4m/ S-2 of the biggest acceleration, fixed position precision 0.
01mm; A axis swings limits - 15 ° of 97 ° ～ , c axis is workbench, 360 ° are rotational; 800mm of workbench face diameter, carrying capacity 1t. CNC(computerized numerical control) the system is German Heidenhain ITNC 530, computation treats the rate that a numerical control dictates, from on the 4ms of generation system is reduced 0.
5 Ms, machine tool stock 30 knives knife library, and laser type cutting tool is online testing system, with contact workpiece online detect, data is infra-red and wireless transmission device. Before the experiment is machined, the system of software of CAD/CAM of UG NX edition that uses installation to go up in workstation of high-powered personal computer above all finishs test specimen three-dimensional model, draft high speed milling to machine craft like later development introduction next, reuse UG NX generates process designing of knife course file, numerical control and postposition processing. Receives CNC Machining order conveys through the network after system of numerical control of machine tool CNC, move to complement with necessary modification through trying, just use at experiment treatment. Treatment of control of technology of high speed milling is out of shape the influence machines metabolic element a lot of, trend of the constituent construction that includes semifinished product, fiber and internal stress distributing, all sorts of active force in treatment, heat and the test specimen physics that cause and chemical change. Should be controlled and reduce treatment to be out of shape, need reasonable preparation or select semifinished product, logical choice outfit places means, to semifinished product or semi-manufactured goods heat treatment, adopt reasonable arrangement working procedure and go cutter track line, reasonable to choose cutting tool and cutting dosage parameter, reasonable refrigeration is lubricant, will drop cutting force and cutting temperature. Article experiment considers not to involve the preparation of semifinished product or option, and discuss other technology in order to omit working procedure of intermediate heat treatment is emphasized below for one of targets optimize measure. The means that hold clip 3 it is even wave guide over all dimension 791mm × 156.
8mm × 32mm, those who grow wide area and ply dimension is particularly bigger than calculating. Be compared through the analysis and experiment, the 4 action place that from semifinished product with pressing plate two side craft knows groove is its impaction on machine tool workbench (like the graph 2 show) , can prevent test specimen effectively to be out of shape, and when convenient province, do not need to make special fixture. Force of cutting of material of aluminium alloy of high speed milling is small, reduce clamping force to be helpful for preventing to install clip to be out of shape appropriately. Of if test specimen is long wide area and ply dimension very lower than very big, stiffness, need adds the likelihood to a large number of clamp are nodded and make special fixture. The method holding clip of test specimen often can become one of craft keys. Working procedure is arranged and take cutter track line 3 handsome antrum mixes even two sides of wave guide positive and negative long chamfer, mid still appear two groups of I-shaped open slot, if pursue,2 are shown. So, when arranging working procedure, need abides by the principle of the treatment that separate a side and departure of thick finish machining. Among them, machine in order to separate a side again preferential, machine opposite rework front namely, repeat outfit clip merely; The process of complete thick precision work of test specimen one side is completed in holding clip. Its purpose depends on decreasing repeat outfit clip to search namely test specimen frequency, improve precision and efficiency. Graph 3 circular arc or tilt ground radial is cut, cut a test specimen to avoid to be in a local and successive development excises Bao Bi test specimen at a draught a large number of material, and cause stress to distributing sharp change and even treatment are out of shape, thick finish machining is abided by statified the principle of cutting; After milling cutter cuts person test specimen to achieve some deepness, in attribute same kind and of space each model inside antrum or long chamfer ordinal take a knife. Among them, arrangement takes cutter track line as far as possible give attention to two or morethings arrives maintain overall geometry semmetry and Bao Bi two side are symmetrical. In cutting tool cut means and dosage of course taking a knife, cutting parameter respect, thick finish machining has many change. High speed cutting moves relatively rate is high, let milling cutter circular arc or tilt ground radial cuts test specimen (like the graph 3 show) , or feed of axial helix ground (show) 4 times like the graph, be helpful for maintaining cutting course smooth, improve treatment precision and exterior quality, prolong cutting tool life. This second experiment rough machining antrum, head when knife axial cuts semifinished product substance, used with on planar included angle is less than 5 ° tilt feed means. Finish machining is cut deep small, helix or tilt feed and it is more difficult to be cut nevertheless, make milling cutter direct drop along axial so. The knife of finish machining orbit forms final outline surface, want to avoid knife of the advance and retreat on outline of clingy and outer form. In addition, the area that finish machining needs to excise rough machining to remain (also call odd material mill to cut) , the diametical D of cutting tool is smaller. Treatment of cutting tool experiment basically uses world-famous tool manufacturer comfortable the cutting tool of integral hard alloy that waits for a variety of workpiece material at aluminium alloy of cutting steel, cast-iron, plasticity, there is TiCN coat outside. Their precision is tall, dynamic balancing is good, life is long, be out of shape to control, raised treatment precision and exterior quality to produce favorable result, because the bottom of test specimen and wall are thin, flat bottom is used to establish milling cutter in treatment, the active force that be down arises in order to avoid when belt round horn establishs milling cutter cutting, cause warpage of test specimen bottom. Cutting dosage and treatment of average rate milling are same, rough machining of high speed milling still is given priority to with raising material excision to lead, general its axial cuts deep Ap, radial to cut deep Ae and every tine feed Fz is bigger; And finish machining is given priority to with reaching treatment precision and exterior mass, cutting speed Vc is taller. Graph feed of 4 axial helix and statified surround the knife passes test of test of temperature of survey and cutting force, cutting, when confirming data of aluminium alloy of plasticity of high speed milling, ought to choose milling linear velocity Vc ＞ 1, 583m/min, perhaps choose Vc ＞ at least 804m/min, so that make cutting force and cutting temperature rise to drop significantly as Vc, reduce treatment to be out of shape at the same time, improve treatment quality and efficiency. Diameter of milling cutter of be confined to, cutting tool is dangerous extend and environmental temperature restrict a condition, rotate speed of the main shaft in the experiment did not reach highest value, actual Vc Max ≈ 1, 13lm/min. Test test makes clear further, reduce axial to cut deep, proper increase radial to cut deep especially feed, be helpful for reducing cutting force and cutting temperature and control treatment to be out of shape. Accordingly, the Ap ≤ 1mm of each working procedure in experiment treatment, and come by rough machining finish machining is ordinal and degressive. In principle, ae=0.
75D, mill antrum is mixed when groovy head knife cuts entity, ae=D, and extend a time limit accepting slot is made, take a knife the 2nd times normally Ae ＜ 0.
75D. When mill antrum, d is bigger intensity is higher, fz=0.
107 ～ 0.
200mm, the Fz=0 of cant of figuration mill housing.
094mm, and when mill chamfer, d small intensity is low. The course experiments, choose Fz=0.
048 ～ 0.
072mm. Among them, when D=3mm, fz=0.
048 ～ 0.
056mm, can avoid milling cutter to break off. Above comparatives below every tine feed and operating mode of average rate milling. But N of this rotate speed of second experiment main shaft is as high as 15, 600r/min. Calculate type Vf=fzZn/1 according to feed speedometer, 000=fzZvc/pD(Z is) of mill tooth number, can calculate Vf=3 ～ 6m/min, greatly prep above is common speed milling. Small axial is cut deep, big feed speed, it is another when high speed cutting machines main feature, also be at the same time implementation reduces treatment to be out of shape, a when improve treatment quality and efficiency basic premise. Milling means and cooling and lubricant semifinished product are done not have coarse and hard cortical. Test test makes clear, force of cutting of suitable mill means is reduced apparently, and theoretical analysis and document point out, it is helpful for forming cut bits, maintain cutting course smooth and improve treatment surface quality. Treatment plasticity aluminium alloy uses refrigeration of fluid of efficient emulsification cutting to lubricate, be helpful for dropping cutting force and cutting temperature, can prevent to cut bits felt irresolvable on milling cutter of integral hard alloy and make cutting tool discards as useless. Improve treatment efficiency as above, a lot of control machine metabolic technology measure, include first consideration to divide treatment, thick finish machining is apart, big feed speed, can improve efficiency at the same time, shorten handling time. Besides, arrangement working procedure should notice to reduce the number that change a knife as far as possible. This second experiment incorporates clear part for a working procedure, those who put each treatment is final, save time and do not affect treatment quality. Milling of certain high speed machines cutter track line, need to notice to avoid to change knife direction and feed rate suddenly above all; Use what the graph shows 4 times is statified surround knife, when can avoiding traditional reciprocating type to walk along knife inverting stop urgently choppy cause impact, what transverse shift is apart from generation small paragraph one need to receive knife mark every time after also taking a knife without closed circuit, accordingly, treatment efficiency and quality are high, cutting tool life is long. 2 tests result optimizes measure through adopting above technology, the experiment is machined 3 omited even wave guide working procedure of the heat treatment intermediate, thick finish machining is cost in all 14.
13h, optimize target time 16h under what book. With 3 coordinate measuring instrument and exterior surface roughness appearance detects, finished product speech is main appearance and qualification of positional dimension precision. Make with the front fiducial, rough surface spends the opposite that measures for 0.
16mm, exterior surface roughness Ra ≤ 1.
6µm, achieved blueprint requirement. This experiment considers to make clear, technology of milling of applied high speed machines structural member of thin wall whole, be controlled effectively and reduce treatment to be out of shape, and improve efficiency substantially, shorten time. Crucial technology segment, depend on semifinished product, workpiece holds clip, working procedure arrangement, take cutter track line, cutting tool and cutting dosage parameter, milling means and refrigeration are lubricant. Among them alleged high speed, it is the cutting rate with high machine tool and main shaft rotate speed of course above all, but it still needs to have rate of high axial feed motion and acceleration, and the computation with expensive system of CNC numerical control treats rate, the computer with expensive system of CAD/CAM soft hardware assists modelling and process designing speed. CNC Milling CNC Machining