The choice with fixed position principle and standard at 6 o'clock fixed position (add)

If pursue,3-33 place shows the give a demonstration that is tine base fixed position. Pursue among them A is short sell He Daping face to locate, old plane was restricted, , 3 freedom are spent, short sell limitation, 2 freedom are spent, had not had fixed position; Graph B is long sell He Xiaoping face to locate, long sell limitation, , , 4 freedom are spent, facet restricted a freedom to spend, because this also has not had fixed position; Graph C is long sell He Daping face to locate, long annul limitation, , , 4 freedom are spent, big planar limitation, , 3 freedom are spent, among them, for two place of fixed position component is restricted, had produced fixed position so. Because cross the influence of fixed position, may produce workpiece to cannot be loaded, workpiece or clamping apparatus are out of shape wait for consequence, destroy the correct fixed position of workpiece. When because this should have appeared,locating, should take the undesirable effect that significant step is eliminated or has reduced fixed position. The undesirable effect that eliminate or has reduced fixed position is like below two kinds of measure commonly: 1. If graph 3-34 place is shown,change tabulator structure, use spherical gasket, eliminate, two each repeat limitation by what spend, had avoided the undesirable effect of fixed position. 2. If the positional precision that raises the job and clamping apparatus to concern the surface pursues in 3-33d, E, if can improve skill,the aperture inside workpiece and the verticality that carry the front are mixed raise fixed position to sell as planar as fixed position verticality, also can have reduced the undesirable effect of fixed position. 3, after the number of degrees of freedom that locates fiducial choice should machine a requirement to decide workpiece should be restricted according to workpiece, the limitation that some direction freedom spends often can have a few fixed position fiducial and optional choose, put forward how to select the issue with standard fixed position correctly right now. Fixed position is standard have thick fiducial with the cent with fiducial essence. In machining initiative working procedure. The surface that can have machined with the have not on semifinished product only serves as fixed position fiducial, criterion this surface is called thick fiducial. Use the surface that already had machined to serve as fixed position fiducial, call essence of life fiducial. (one) thick fiducial choice selection is wide fiducial when. Basically consider two issues: It is to assure to machine face and do not machine the requirement of mutual position precision between the face; 2 it is reasonable the mental allowance that distributes each treatment scale. The reference when specific choice is following principle: 1. To having treatment surface and the part that do not machine the surface at the same time, machine the positional precision between the surface and treatment surface for guarantee against, should choose not to machine the surface to regard as thick fiducial. If pursue,3 -35a place is shown. If there is many not to machine the surface on the spare parts, criterion with among them the surface with higher demand of precision of as mutual as treatment surface position serves as thick fiducial. Be like graph 3-35b, this spare parts has 3 not to machine the surface, if ask the surface the 4 walls that comprise 2 times with the surface are large even, should choose not to machine the surface 2 as thick fiducial will machine step aperture. 2. The workpiece of surface of more to having treatment, the selection is wide fiducial when, should consider reasonable allocation to machine exterior mental allowance each. Reasonable allocation mental allowance is to point to the following at 2 o'clock: (1) should make sure each are main the surface has enough mental allowance. To satisfy this requirement, should choose the surface with semifinished product the smallest surplus to regard as thick fiducial, be like the axis of a flight of stairs that graph 3 -35c shows, outside should choosing φ 55mm, round face serves as thick fiducial. (2) the certain and important surface that goes up to workpiece (wait like slideway and important opening) , to make its surface mental allowance even as far as possible, should choose important surface to regard as thick fiducial. If pursue,the face of lathe bed slideway that 3-36 place shows is important surface, requirement wearability is good, and the mechanical property that has cardinal principle to agree inside whole slideway face. Accordingly, when machining slideway, should choose slideway surface to regard rough standard treatment as lathe bed underside (graph 3 -36a) , it is plane of standard treatment slideway with underside next (graph 3-36b) . 3. Thick fiducial should avoid to repeat use. On same size direction, thick fiducial can use only normally, lest produce bigger fixed position error. If pursue,the small axis that 3-37 place shows is machined, if repeat,use B face to machine A face, C face, criterion the axes of A face and C face will produce bigger coaxial to spend an error. 4. Choose thick fiducial plane should level off, did not irrigate the blemish such as rising head or flash, so that fixed position is reliable. (2) the alternative energy with fiducial essence chooses fiducially to answer from make sure the spare parts machines precision to set out, at the same time consideration outfit places structure of convenient, clamping apparatus simple. Choice essence of life is fiducial and average should consider following principles: 1. "Fiducial coincide " principle 　 faces his to design fiducial relative position precision to ask to obtain treatment easily to express, the design that should choose to machine the surface is standard locate for its fiducial. This one principle calls fiducial coincide principle. If the design of treatment surface is standard as fiducial as fixed position not coincide, can increase fixed position error, the account that its produce and computational method are issueing section discussion. 2. "Fiducial and unified " principle 　 when with some team spirit when workpiece standard fixed position can machine other surface conveniently quite, should use this group of energy in most working procedure as far as possible standard fixed position, this is " fiducial and unified " principle. For example axis kind working procedure of spare parts great majority locates with central Kong Wei fiducial; The tine base of gear and tooth form treatment use the aperture inside gear and end panel to be fixed position more fiducial. Use " fiducial and unified " the cost that the principle can reduce tool design to make, improve productivity, can avoid the error that causes because of fiducial changeover. 3. "It is oneself fiducial " principle 　 rectifies surplus of requirement of treatment working procedure when work precision work or light as far as possible small and even when, should choose to machine exterior itself to serve as fixed position fiducial, this is " it is oneself fiducial " principle. For example when face of slideway of grinding lathe bed, serve as fixed position with face of lathe bed slideway fiducial. If pursue,3-38 place is shown. Right now bed foot plane just has the effect of plane of a bearing, it is not is fixed position datum plane. In addition, with aperture of float reamer bore with a reamer, pull the aperture, circle outside be being ground with inadvertently grinder to wait with broach, all be it is fiducial example oneself. 4. "Each other is fiducial " principle 　 to obtain even mental allowance or taller positional precision, can use each other to be fiducial the principle that machines repeatedly. When machining accurate gear for example, first fixed position of less than opening machines tooth form face, need to undertake roll flute after tooth flank temper by dipping in water is hard. Because tooth flank temper by dipping in water is hard the layer is thinner, requirement grinding surplus is so small and even. Right now usable tooth flank is fixed position fiducial grind inside aperture, again less than aperture is fixed position face of fiducial roll flute, the grinding surplus that assures tooth flank thereby is even, and get more easily assuring again with the mutual position precision of tooth flank. 5. Fiducial choice should assure essence of life workpiece locates accurate, clamp reliable, operation is convenient. Be like graph 3-39b, when machining C face, if use " fiducial coincide " principle, choose B face to serve as fixed position fiducial, if graph 3-40 place is shown,workpiece holds clip. Such not only workpiece outfit places inconvenience, clamping apparatus structure is more complex also; But if use what what graph 3 -39a shows,locate with A face, although place recognizance form,clip of simple, outfit goes to the lavatory, but fiducial not coincide, fixed position error is bigger. Should point out, afore-mentioned wide choice are fiducial choose a principle, often cannot satisfy entirely, the circumstance of mutual contradiction often can appear when applying actually, this asks to consider integratedly, distinguish primary and secondary, emphasize resolve main contradiction. (3) when auxiliary and standard application work locates, to assure to machine positional precision of the surface, mostly first choice is designed fiducial or assemble fiducial as main fixed position fiducial, these are fiducial and general the main surface that goes up for the spare parts. But some spare partses are in treatment, go to the lavatory to hold clip or come true easily fiducial and unified, factitious ground creates a kind of fixed position fiducial. The craft protruding stage that goes up like semifinished product and axis kind the central aperture when the spare parts is machined. These surfaces are not the working surface on the spare parts, the fixed position that just need to satisfy craft and designs technically on workpiece is standard call auxiliary and fiducial. The less important surface on in addition certain part (blame cooperate the surface) , because the appropriate on craft makes fixed position fiducial and when raising its to so that locate,machine precision and exterior quality, use. This kind of surface also is called auxiliary and fiducial. For example, of guide screw outside round face, from whorl deputy drive looks, the less important surface that its dispute cooperates, but in the treatment in guide screw whorl, round face often serves as fixed position outside fiducial, its circularity and cylinder spend the treatment precision that affects whorl directly, want the round treatment precision outside rising so, reduce its surface surface roughness to be worth. CNC Milling