【正文】 切削速度是指切削刃通過工作面的速度。刀具必須由適當(dāng)?shù)牟牧献龀?；它必須有一定的?qiáng)度，粗糙度，硬度和抗疲勞度。舉例來說，內(nèi)線流程是很少產(chǎn)生任何方式以外的其他機(jī)械加工并且緊接著壓力操作后零件上的小洞可能被加工。如果在其他工序中大批量生產(chǎn)，很多低量零件會(huì)產(chǎn)生出低的但可接受的公差。高精度，表面精度。通過利用總成本高但沒有特殊模具的設(shè)備，加工是有可能的；從幾乎任何形式的原材料開始，只要外部尺寸足夠大，由任意材料設(shè)計(jì)形狀。是鑄造，鍛造和壓力工作，產(chǎn)生每一個(gè)特殊形狀，甚至一個(gè)零件，幾乎總有較高的模具成本。小批量，低成本。機(jī)械加工過程是一個(gè)產(chǎn)生形狀的過程，在這過程中，驅(qū)動(dòng)裝置使工件上的一些材料以切屑的形式被去除。而大直徑的工件有時(shí)裝在兩個(gè)中心，它們最好有由面板夾持在主軸承尾部來順利得到能量轉(zhuǎn)換；許多車床夾頭并不能足量的轉(zhuǎn)換能量，雖然可以作為特殊的能量轉(zhuǎn)換。由車床中心提供的調(diào)整將不能持續(xù)并且爪盤的壓力會(huì)損壞中心孔和車床中心，甚至是車床主軸。工件不允許被卡盤和車床中心夾在主軸承上。在車床上加工另一端，中心孔充當(dāng)精確定位面和承載工件重量和抵制切削力的支撐面。在兩個(gè)中心之間支撐工件可以得到非常精確的結(jié)果。工件接近為架的那端通常由尾架中心支撐，在靠近主軸承的那端由主軸承中心支撐或由爪盤夾緊。一般來說，較長的工件同時(shí)被一個(gè)或兩個(gè)車床中心支撐。精加工為工件獲得最后尺寸，形狀和表面精度。所有的加工工序包括車削，鏜孔可以被歸類為粗加工，精加工或半精加工。那些用單點(diǎn)刀具在外表面的操作稱為車削。切削深度是進(jìn)入的深度和溝槽的深度。它們都影響去除金屬的力，功率和速度。其他的量數(shù)是攻絲和刀具材料，冷卻劑和刀具的幾何形狀，去除金屬的速度和所需要的功率依賴于這些變量。一臺(tái)機(jī)床履行三大職能：。磨削過程形成了屑片，但磨粒的幾何形狀是不可控制的。拋光和打磨是磨削和去除磨料工序的變形。機(jī)床執(zhí)行五種基本的去除金屬的過程：車削，刨削，鉆孔，銑削。后者是廢棄物，是由塑性材料如鋼的長而不斷的帶狀物變化而來，從處理的角度來看，那是沒有用處的。可以產(chǎn)生橫向或縱向軸旋轉(zhuǎn)并且可以在任何三個(gè)坐標(biāo)方向上進(jìn)給。在銑削時(shí)一個(gè)帶有許多切削刃的旋轉(zhuǎn)刀具與工件接觸，工件相對(duì)刀具慢慢運(yùn)動(dòng)。使用雙刃槽鉆鉆深度是鉆孔直徑510倍的孔。成形面可以通過成型刀具加工產(chǎn)生。在刨削時(shí)對(duì)于較大的工件更容易將刀具固定并將工件置于刀具下面。如果刀具接觸點(diǎn)以改變半徑的方式運(yùn)動(dòng)，那么一個(gè)外輪廓像球的工件便產(chǎn)生了；或者如果工件足夠的短并且支撐是十分剛硬的，那么成型刀具相對(duì)于旋轉(zhuǎn)軸正常進(jìn)給的一個(gè)外表面便可產(chǎn)生，短錐形或圓柱形的表面也可形成。如果一個(gè)空心的管子以同樣的方式在內(nèi)表面加工，這種操作稱為鏜孔。大多數(shù)加工工序產(chǎn)生不同幾何形狀的零件。切屑是被廢棄的產(chǎn)品，與其它工件相比切屑較短，但對(duì)于未切削部分的厚度有一定的增加。它們?yōu)楣ぜ偷毒咛峁﹦傂灾尾⒖梢跃_控制它們的相對(duì)位置和相對(duì)速度。 operation, and it benefits the customer in the event of the need to replace worn parts. 基本加工工序和切削技術(shù)機(jī)床是從早期的埃及人的腳踏動(dòng)力車和約翰 to replace another of the same dimension and material specification, the parts are said to be interchangeable. A system of interchangeability usually lowers the production costs as there is no need for an expensive, 39。 in the literal sense. J It is obvious that the two parts would have to remain together, and m the event of one having to be replaced, the fitting would have to be done all over again. In these days, we expect to be able to purchase a replacement for a broken part, and for it to function correctly without the need for scraping and other fitting operations.When one part can be used 39。 workpiece size, method of clamping ,and cutting tool rigidity relative to the machine tool structure, instability can be set up in the tool which causes it to vibrate. Under some conditions this vibration will reach and maintain steady amplitude whilst under other conditions the vibration will built up and unless cutting is stopped considerable damage to both the cutting tool and workpiece may occur. This phenomenon is known as chatter and in axial turning is characterized by long pitch helical bands on the workpiece surface and short pitch undulations on the transient machined surface. (4)The effectiveness of removing swarf. In discontinuous chip production machining, such as milling or turning of brittle materials, it is expected that the chip (swarf) will leave the cutting zone either under gravity or with the assistance of a jet of cutting fluid and that they will not influence the cut surface in any way. However, when continuous chip production is evident, unless steps are taken to control the swarf it is likely that it will impinge on the cut surface and mark it. Inevitably, this marking besides looking. (5)The effective clearance angle on the cutting tool. For certain geometries of minor cutting edge relief and clearance angles it is possible to cut on the major cutting edge and burnish on the minor cutting edge. This can produce a good surface finish but, of course, it is strictly a bination of metal cutting and metal forming and is not to be remended as a practical cutting method. However, due to cutting tool wear, these conditions occasionally arise and lead to a marked change in the surface characteristics. Limits and Tolerances Machine parts are manufactured so they are interchangeable. In other words, each part of a machine or mechanism is made to a certain size and shape so will fit into any other machine or mechanism of the same type. To make the part interchangeable, each individual part must be made to a size that will fit the mating part in the correct way. It is not only impossible, but also impractical to make many parts to an exact size. This is because machines are not perfect, and the tools bee worn. A slight variation from the exact size is always allowed. The amount of this variation depends on the kind of part being manufactured. For examples part might be made 6 in. long with a variation allowed of (threethousandths) in. above and below this size. Therefore, the part could be to in. and still be the correct size. These are known as the limits. The difference between upper and lower limits is called the tolerance. A tolerance is the total permissible variation in the size of a part. The basic size is that size from which limits of size arc derived by the application of allowances and tolerances. Sometimes the limit is allowed in only one direction. This is known as unilateral tolerance.Unilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is shown in only one direction from the nominal size. Unilateral tolerancing allow the changing of tolerance on a hole or shaft without seriously affecting the fit.When the tolerance is in both directions from the basic size it is known as a bilateral tolerance (plus and minus). Bilateral tolerancing is a system of dimensioning where the tolerance (that is variation) is split and is shown on either side of the nominal size. Limit dimensioning is a system of dimensioning where only the maximum and minimum dimensions arc shown. Thus, the tolerance is the difference between these two dimensions. Surface Finishing and Dimensional Control Products that have been pleted to their proper shape and size frequently require some type of surface finishing to enable them to satisfactorily fulfill their function. In some cases, it is necessary to improve the physical properties of the surface material for resistance to penetration or abrasion. In many manufacturing processes, the product s