2024年1月12日发(作者：)

Fundamentals of Machine Tools

In many cases products from the primanry forming processes must undergo further

refinements in size and surface finish to meet their design specifications. To meet such

precise tolerances the removal of small amounts of material is needed. Usually machine

tools are used for such operation.

In the United States material removal is a big business-in excess of $36×10 per year,

including material, labor, overhead, and machine-tool shipments. Since 60 percent of

themechanical and industrial engineering and technology graduates have something

connected with the machining industry either through sale, design, or operation of

machine shops,or working in related industry, it is wise for an engineering studet to

devote some time in his curriculum to studying material removal and machine tools.

A machine tool provides the means for cutting tools to shape a workpiece to required

dimensions; the machine supports the tool and the workpiece in a controlled relationship

through the functioning of its basic member,which are as follows:

(1) Bed, Structure or Fram. This is the main member which provides a basis for, and a

connection between, the spindles and slides; the distortion and vibration under load

must be kept to a minimum.

(2) Slides and Slideways. The translation of a machine the slide) is

normally achieved by straight-line motion under the constraint of accurate guiding

surfaces(the slideway).

(3) Spindles and Bearings. Angular displacements take place an axis of rotation; the

position of this axis must be constant within extremely fine limits in machine tools, and

is ensured by the provision of precision spindles and bearings.

(4) Power Unit. The electric motor is the universally adopted power unit for machine

tools. By suitably positioning individual motors, belt and gear transmissions are reduced

to minimum.

(5) Transmission Linkage. Linkage is the general term used to denote the mechanical,

hydraulic, pneumatic or electric mechanisms which connect angular and linear

displacements in defined relationship.

There are two broad divisions of machining operations:

(1) Roughing, for which the mental removal rate, and consequently the cutting force,

is high, but the required dimensional accuracy relatively low.

(2) Finishing, for which the metal removal rate, and consequently the cutting force, is

low, but the required dimensional accuracy and surface finish relatively high.

It follows that static loads and dynamic loads, such as result from an unbalanced

grindingwheel, are more significant in finishing operations than in roughing operations.

The degree of precision achieved in any machining process will usually be influenced

by the magnitude of the deflections, which occur as a result of the force acting.

Machine tool frames are generally made in cast iron, although some may be steel

casting or mild-steel fabrications. Cast iron is chosen because of its cheapness, rigidity,

compressive strength and capacity for damping the vibrations set-up in machine

operations. To avoid massive resistance to bending and torsional stresses. Tow basic

types of ribbing are box and diagonal. The box formation is convenient to produce,

apertures in walls permitting the positioning and extraction of cores. Diagonal ribbing

provides greater torsional stiffness and yet permits swarf to fall between the sections; it

is frequently used for lathe beds.

The slides and slideways of a machine tool locate and guide members which move

relative to each other, usually changing the position of the tool relative to the workpiece.

The movement generally takes the from of translation in a straight line, but is sometime

angular rotation, e.g. tilting the wheel-head of a universal thread-grinding machine to an

angle corresponding with the helix angle of the work piece threat. The basic geometric

elements of slides are flat, vee, dovetail and cylinder. These elements may used

separately or combined in various ways according to the applications. Features of

slideways are as follows:

(1) Accuracy of Movement. Where a slide is to be displaced in a straight line, this

line must lie in two mutually perpendicular planes and there must be no slide

rotation. The general tolerance for straightness of machine tool slideways is

0~0.02 mm per 1000mm; on horizontal surfaces this tolerance may be disposed

so that a convex surface results, thus countering the effect of “sag” of the

slideways.

(2) Means of Adjustment. To facilitate assembly, maintain accuracy and eliminate

“play” between sliding members after wear has taken place, a strip is sometimes

inserted in the slides. This is called a gib-strip. Usually, the gib is retained by

socket-head screws passing through elongated slots; and is adjusted by

grub-screws secured by lock nuts.

(3) Lubrication. Slideways may be lubricated by either of the following systems:

(i) Intermittently, through grease or oil nipples, a method suitable where

movements are infrequent and speed low.

(ii) Continuously, e.g. by pumping through a metering valve and pipe-work to the

point of application; the film of oil introduce between surface by these means

must be extremely thin to avoid the slide “floating”. If sliding surfaces were

optically flat oil would be squeezed out, resulting in the surface sticking.

Hence in practice slide surface are either ground using the edge of a cup

wheel, or scraped. Both processes produce depressions which retain “pocket”

of oil, and complete separation of the parts may not occur at all points;

positive location of the slides is thus retained.

(4) Protection. To maintain slideways in good order, the following conditions must be

met:

(i) Ingress of foreign matter, e.g. swarf, must be prevented. Where this is no

possible, it is desirable to have a form of slideway, which does not retain

swarf, e.g. the inverted vee.

(ii) Lubricating oil must be retained. The adhesive property of oil for use on

vertical or inclined slide surface is important; oil are available which have

been specially developed for this purpose. The adhesiveness of oil also

prevents it being washed away by cutting fluids.

(iii) Accidental damage must be prevented by protective guards.

Lathes

A machine tool performs three major functions: (i) it rigidly supports the work piece

or its holder and the cutting tool; (ii) it provide relative motion between the work piece

and the cutting tool; (iii) it provides a range of feeds and speeds.

Machines used to remove metal in the form of chips are classified as follows:

Machines using basically the single-point cutting tools include: engine lathes, turret

lathes, tracing and duplicating lathes, single-spindle automatic lathes, multi-spindle

automatic lathes, shapers and planers, boring machines.

Machines using multipoint cutting tools include: drilling machines, milling machines,

broaching machines, sawing machine, gear-cutting machines.

Machines using random-point cutting tools (abrasive) include: cylindrical grinder,

centreless grinders, surface grinders.

Special metal removal methods include: chemical milling, electrical discharge

machining, ultrasonic machining.

The lathe removes material by rotating the work piece against a cutter to produce

external or internal cylindrical or conical surfaces. It is commonly used for the

production of surfaces by facing, in which the work piece is rotated while the cutting

tool is moved perpendicularly to the axis of rotation.

The engine lathe, shown in Fig.1, is the basic turning machine from which other

turning machines have been developed. The drive motor is located in the base and

drives the spindle through a combination of belts and gears. The spindle is a sturdy

hollow shaft, mounted between heavy-duty bearings, with the forward end used for

mounting a drive plate to impart positive motion to the work piece. The drive plate may

be fastened to the spindle by threads, by a cam lock mechanism, or by a threaded collar

and key.

The lathe bed is cast iron and provides accurately ground sliding surfaces (way) on

which the carriage rides. The lathe carriage is an H-shaped casting on which the cutting

tool is mounted in a tool holder. The apron hangs from the front of the carriage and

contains the driving gears that move the tool and carriage along or across the way to

provide the desired tool motion.

A compound rest, located above the carriage, provides for rotation of the tool holder

through any desired angle. A hand wheel and feed screw are provided on the compound

rest for linear motions of the tool. The cross feed is provided with another hand wheel

and feed screw for moving the compound rest perpendicular to the lathe way. A gear

train in the apron provides power feed for the carriage both along and across the way.

The feed box contains gears to impart motion to the carriage and control the rate at

which the tool moves relative to the work piece. Since the transmission in the feed box

is driven from the spindle gears, the feeds are directly related to the spindle speed. The

feed box gearing is also used in thread cutting and provides from 4 to 224 threads per in.

The connecting shaft between the feed box and the lathe apron are the feed rod and

the lead screw. Many lathe manufacturers combine these two rods in one, a practice that

reduces the cost of the machine at the expense of accuracy. The feed rod is used to

provide the accurate lead necessary for the thread cutting. The feed rod is driven

through a friction clutch that allows slippage in case the tool is overloaded. This safety

device is not provided in the lead screw, since thread cutting cannot tolerate slippage.

Since the full depth of the thread is seldom cut in one pass, a chasing dial is provided to

realign the tool for subsequent passes.

The lathe tailstock is fitted with an accurate spindle that has a tapered hole for

mounting drill, drill chucks, reamers, and lathe centers. The tailstock can be moved

along the lathe ways to accommodate various lengths of work pieces as well as to

advance a tool into contact with the work piece. The tailstock can be offset relative to

the lathe ways to cut tapers or conical surfaces.

The turret lathe is basically an engine lathe with certain additional features to provide

for semiautomatic operation and to reduce the opportunity for human error. The carriage

of the turret lathe is provided with T-slots for mounting a tool-holding device on both

sides of the lathe ways with tools properly set for cutting when rotated into position.

The carriage is also equipped with automatic stops that control the tool travel and

provide good reproduction of cuts. The tailstock of the turret lathe is of hexagonal

design, in which six tools can be mounted. Although a large amount of time is

consumed in setting up the tools and stops for operation, the turret lathe ,once set, can

continue to duplicate operations with a minimum of operator skill until the tools become

dulled and need replacing. Thus , the turret is economically feasible only for production

work, where the amount of time necessary to prepare the machine for operation is

justifiable in terms of the number of part to be made.

The multi-spindle automatic lathe is provided with four, five, six, or eight spindles,

with one workpiece mounted in each spindles. The spindles index around a central shaft,

with the main tool slide accessible to all spindles. Each spindle position is provided with

a side tool-slide operated independently. Since all of the slides are operated by cams, the

preparation of this machine may take several days, and a production run of at least 5000

parts is needed to justify its use. The principal advantage of this machine is that all tools

work simultaneously, and one operator can handle several machines. For relatively

simple parts, multi-spindle automatic lathes can turn out finished products at the rate of

1 every 5 sec.

Shapers, Planers, Drilling and Milling Machines

A shaper utilizes a single-point tool in a tool holder mounted on the end of the ram.

Cutting is generally done on the forward stroke. The tool is lifted slightly by the clapper

box to prevent excessive drag across the work, which is fed under the tool during the

return stroke in preparation for the next cut. The column houses the operating

mechanisms of the shaper and also serves as a mounting unit for the work-supporting

table. The table can be moved in two directions mutually perpendicular to the ram. The

tool slide is used to control the depth of cut and is manually fed. It can be rotated

through 90 deg. on either side of its normal vertical position, which allows feeding the

tool at an angle to the surface of the table.

Two types of driving mechanisms for shapers are a modified whitworth quick-return

mechanism and a hydraulic drive. For the whitworth mechanism, the motor drives the

bull gear, which drives a crank arm with an adjustable crank pin to control the length of

stroke. As the bull gear rotates, the rocker arm is forced to reciprocate, imparting this

motion to the shaper ram.

The motor on a hydraulic shaper is used only to drive the hydraulic pump. The

remainder of the shaper motions are controlled by the direction of the flow of the

hydraulic oil. The cutting stroke of the mechanically driven shaper uses 220 deg. Of

rotation of the bull gear, while the return stroke uses 140 deg. This gives a cutting stroke

to return stroke ratio of 1.6 to 1. The hydraulic shaper has an advantage of infinitely

variable cutting speeds. The principal disadvantage of this type of machine is the lack of

a definite limit at the end of the ram stroke, While may allow a few thousandths of an

inch variation in stroke length.

Planers are similar to shapers because both machines are primarily used to produce

flat and angular surfaces. However ,planers are capable of accommodating much larger

workpieces than horizontal plane providing a straight-line cutting and feed action.

Single-point cutting tools are mounted on an overhead cross rail and along the vertically

supported columns. The cutting tools are fed into or away from the workplace on either

the horizontal or vertical plane, thus being capable of four straight-line feed motions.

Cutting speeds are slow on the planer because of the workplace size and type of

cutting tool being used. In order to increase the production of the planer, multiple

tooling stations are employed. Another method of increasing production is to mount a

number of workpieces on the table at the same time. The planer size is designated by the

maximum workplace capacity of the machine. The height, width, and length of the

workplace that can be accommodated on the planer’s worktable varies with the type of

planer.

Upright drilling machines or drill presses are available in a variety of sizes and types,

and are equipped with a sufficient range of spindle speeds and automatic feeds to fit the

needs of most industries. Radial drilling machines are used to drill workpieces that are

too large or cumbersome to conveniently move. The spindle with the speed and feed

changing mechanism is mounted on the radial arm; by combining the movement of the

radial arm around column and the movement of the spindle assembly along the arm, it is

possible to align the spindle and the drill to any position within reach of the machine.

Plain radial drilling machines provide only for vertical movement of the spindle;

universal machines allow the spindle to swivel about an axis normal to the radial arm to

rotate about a horizontal axis, thus permitting drilling at any angle.

A multispindle drilling machine has one or more heads that drive the spindles through

universal joints and telescoping splined shafts. All spindles are usually driven by the

same motor and fed simultaneously to drill the desired number of holes.

The milling operation involves metal removal with a rotating cutter. It includes

removal of metal from the surface of a workpiece, enlarging holes, and form cutting,

such as threads and gear teeth.

Within a knee and column type of milling machine the column is the main supporting

member for the other components, and includes the base containing the drive motor, the

spindle, extremity by a bearing in the overarm. The knee is held on the column in

dovetail slots, the saddle is fastened to the knee in dovetail slots, and the table is

attached to the saddle. Thus, the build-up of the knee and column machine provides

three motions relative to the cutter. The fourth motion may be provided by swiveling the

table around a vertical axis provided on the saddle.

Fixed-bed milling machines are designed to provide more rigidity than the knee and

column type. The table is mounted directly on the machine base, which provides the

rigidity necessary for absorbing heavy cutting load, and allows only longitudinal motion

to the table. Vertical motion is obtained by moving the entire cutting head.

Tracer milling is characterized by coordinated or synchronized movements of either

the paths of the cutter and tracing elements, or the paths of the workpiece and model.

The tracing finger follow the shape of the master pattern, and the cutter heads duplicate

the tracer motion.

The following are general design considerations for milling:

(1) Wherever possible, the part should be designed so that a maximum number of

surfaces can be milled from one setting.

(2) Design for the use of multiple cutters to mill several surfaces simultaneously.

(3) The largest flat surface will be milled first, so that all dimensions are best

referred to such surface.

(4) Square inside corners are not possible, since the cutter rotates.

Grinding Machines

Grinding machines utilize abrasive grains, bonded into various shapes and sizes of

wheels and belts to be used as the cutting agent. Grinding operations are used to impart

a high-quality surface finish on the workpiece is improved since tolerances of 0.00025

mm are possible in grinding operations. Grinding machines are classified according to

the type of surface produced. Common surfaces and classifications of grinding

machines are surface, cylindrical, and special machines.

The grinding process is of extreme importance in production work for several

reasons.

(1) It is the most common method for cutting hardened tool steel of other

heat-treated steel. Parts are first machined in the un-heat-treated condition,

and then ground to the desired dimensions and surface finish.

(2) It can provide surface finish to 0.5 um without extreme cost.

(3) The grinding operation can assure dimensions in a relatively short time,

since machines are built to provide motions in incremente of

ten-thousandths of an inch, instead of thousandths as is common in s can be

other machines.

(4) Extremely small and thin parts can be finished by this method, since light

pressure is used and the tendency for the part to deflect away from the

cutter is miniminzed.

On a cylindrical grinding machine the depth of cut is controlled by moving the wheel

head, which includes both the wheel and its drive motor. Coolants are provided to

reduce heat distortion and to remove chips and abrasive dust.

机床基础

许多情况下，初步成型加工出来的工件必须在尺寸和表面光洁度进一步精整，以满足设计的技术要求。为了满足公差的精度要求，需要从工件上去掉少量材料。通常机床就是用于这种加工的设备。

在美国，材料切削是一个很大的产业，其费用每年超过36×109美元，包括材料、劳动力、管理费、机床装运费等费用。通过销售、设计、在车间中操作机器以及在相关企业中工作，60%的机械和工业工程技术的大学毕业生都跟机械加工工业有某些关系。因此，工科学学生在他的学习课程中花时间投身材料切削和机床的学习研究是很明智的。

机床为切削刀具提供把工件工件加工成所需尺寸的方法，通过其基本部件的功能，控制刀具和工件的支承关系。这些基本部件是：

（1） 床身和机架。这是机床的主要部件，它支撑主轴和拖板箱并把它们连接在一起。在负载时，床身和机架的变形和振动必须保持最小。

（2） 拖板箱和导轨。机床部件（如拖板箱）的移动，通常是在精确的导轨面上的直线运动。

（3） 主轴和轴承。轴旋转时产生角位移，轴的位置在机床中必须极其精确、稳定，一般通过主轴和轴承的精度来提供保征。

（4） 动力装置。机床普遍采用的动力装置是电动机。合理布置各个电机可以使皮带和齿轮传动装置减至最少。

（5） 传动连接机构。连接机构是一般术语，用来代表机械、液压、气动和电动的机构，这些机构和确定的角位移和线性位移相关联。

机加工可以分成两大类：

（1） 粗加工，其金属切除率高，因为切削力大，但尺寸精度较低。

（2） 精加工，其金属切除率低，因为切削力小，但尺寸精度和表面光洁度较高。

因此，与粗加工相比，精加工更应该重视静载荷和动载荷（例如由不平衡的砂轮引起的动载荷）的影响。此外，加工精度通常不会受到由于作用力而引起的

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变形程度的影响。

有是也用铸钢或碳钢制造机床床身，但一般都用铸铁制造机床床身。因为铸铁便宜，刚性好，耐压强度高，并且能减弱机床操作中的振动。为了避免床身铸件截面过大，可以精心设计筋条来提高床身的抗弯曲应力和抗扭转应力。筋条的两种基本类型是箱型和片状斜支承型。箱型结构便于生产，箱壁上的孔口便于型芯的定位和取出。片状斜支撑筋条有较大的抗扭刚度并能使截面间的碎屑掉落，它常常用于车床床身。

机床的拖板箱和导轨可以定位和引导彼此相对运动的零部件，通常是改变刀具相对于工件的位置。运动一般是直线平移，但也有时是旋转，例如沿着工件的螺旋角方向把万能螺纹磨床上的砂轮头转动一个角度。拖板箱的基本几何结构形状是平的、V形的、燕尾槽形的和圆柱形的。根据用途，这些构件可以分别使用或以各种方法组合使用。导轨的特性如下：

（1） 运动精度。当拖板沿直线运动时，这条直线必须位于两个相互垂直的平面内，必须没有滑动旋转。机床导轨的直线度公差一般是0-0.02毫米每米，在水平面上这个公差可以使滑轨凸起，以补偿滑轨的下陷。

（2） 调节方式。为了便于装配、维持精度和限制由于磨损而引起的滑动构件之间的“窜动”，有时在拖板内装入扁条，这个扁条被叫做“镶条”。通常该镶条用穿过长孔的沉头螺钉支柱，用平头螺钉调整好后再用锁紧螺母上紧。

（3） 润滑。导轨的润滑方式有以下两种：（i）间歇润滑，通过润滑油脂或油壶进行，适用于运动速度低而不频繁使用的场合。（ii）连续润滑，例如通过计量阀和管道将润滑油送到润滑点，用这种方法形成的油膜应该很薄，以避免使拖板“浮起”。如果滑移表面是镜平面，油就会被挤出而导致表面粘滞。因而在实际使用中，拖板滑移表面要经过凹面砂轮的磨削和刮研。这两种方法产生微小的表面下陷，可以存油，这样在所有点都不会发生零件的完全分离，保持拖

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板的正确位置。

（4） 防护。为了维持导轨的良好状态，必须满足以下条件：（i）防止外面的物质（如碎屑）的进入。如果难以做到，就应该选用形状符合要求的导轨以避免碎屑在导轨上存留，例如倒V形导轨。（ii）润滑油的保持。在垂直或倾斜的导轨面上使用的油应该能粘在导轨面上。市场上到处都有这种专用润滑油。油的粘度应该足够高，以避免被切削液冲走。（iii）用防护罩来防止意外的损坏。

车床

一台车床实现三个主要功能：（i）牢固地支持工件或刀架和刀具；（ii）提供工件和刀具之间的相对运动；（iii）提供一定范围的走刀和切削速度。

以去除切屑形式来加工金属的机床分类如下：

主要使用单点切削刀具的机床包括：普通车床，塔式车床，仿型车床，单轴自动车床，多轴自动车床，牛头刨床和龙门刨床，镗床。

使用多点切削刀具的机床包括：钻床，铣床，拉床，锯床，齿轮切割机床。

使用随机点切削刀具的机床包括：化学蚀刻铣削，电火花加工，超声波加工。

车床借助于转动的工件对着刀具来切去金属材料，以产生外圆柱面、内圆柱面或锥形表面。车床普遍靠端面切削来加工工件表面。在端面切削加工中，工件旋转，而刀具作垂直于回转轴线方向的移动。

普通车床（见图1，略）是最基本的车床，是研制其他车床的基础。驱动电机装在床身的基础上并通过齿轮、皮带来驱动主轴。主轴是一根坚固的空心轴，装在重型轴承之间，其前端用来安装驱动盘（花盘），以便把确定的运动传到工件上。该驱动盘可以借助螺纹、凸轮锁紧机构或借助一个螺纹垫圈和键固定在主轴上。

车床的床身是铸铁件，它提供精确磨削过的滑动表面（导轨），上面放有拖板。车床拖板是H型的铸件，刀具安装在拖板的刀架上。溜板箱装在托板前面，内装有驱动齿轮，可以顺着导轨或横过导轨移动刀具和拖板以提供所希望的刀具运动。

拖板上面的小刀架能使刀的夹具旋转任意角度。小刀架上的手轮和丝杆可以使刀具做线性运动，另一个手轮和进给螺纹提供横向进给使小刀架垂直于导轨移

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动。溜板箱中的齿轮可以在拖板沿着导轨和横跨导轨移动时提供动力进给。进给箱齿轮将运动传给拖板并控制刀具相对与工件的运动速度。由于进给箱的移动运动是由主轴齿轮驱动的，因此进给直接与主轴速度有关。进给箱齿轮传动机构也用于加工螺纹并能加工4扣到224扣每英寸的螺纹。

进给箱和车床溜板箱之间的连接轴是光杆和丝杆。许多车床制造商把这两种杆合并成一种杆，这样虽然降低了成本但同时也降低了精度。进给杆（光杆）提供道具的运动，以便提高工件的精度和表面光洁度。螺纹导杆（丝杆）提供精确的（螺纹）导程，是螺纹切削所必须的。光杆通过摩擦离合器驱动，在刀具切削超载时可以进行打滑保护。但丝杆里没有这种安全装置，因为螺纹加工不允许打滑。由于螺纹全深很难一次走刀加工完成，因此装设一个螺纹指示盘以便于下次走刀时用以重新对刀。

车床的尾座装有一根很精确的轴，轴上的锥孔用来安装钻头、钻夹、铰刀和车床顶尖。尾座可以沿着车床导轨移动以适应工件的不同长度，也可以把刀具推向工件。尾座可以相对导轨偏移以加工锥体或锥形表面。

转塔车床基本上具有某种附加特性的普通车床，用于半自动加工和减少人工操作误差。转塔车床的拖板设有T形槽以便在车床导轨两侧安装夹刀装置。这样，当转塔转入到合适的位置，可以正确地安装刀具以便进行切削。拖板装有自动挡鉄以便控制刀具行程，提供良好的重复切削。转塔车床的尾座是六角形结构，可以安装六把刀具。虽然操作前刀具和挡鉄的安装要花大量时间，但一旦装刀完成，稍微熟练的工人就可以连续地重复操作，直到刀具变钝需要更换为止。这样，为加工所做的准备时间相对于所制造的零件数量是合理的时候，使用转塔车床在经济上才算可行的。

多轴自动车床装有四、五、六或八根主轴，在每根主轴中装一个工件。各主轴可以围绕着一根中心主轴来转换位置，而主刀具溜板可以接近所有的主轴。每根轴位上都装有一侧向可以独立操作的刀具滑板。由于各刀具滑板都是靠凸轮操作的，因此加工准备可能要花几天时间，因而至少需要5000件的批量生产，它的使用才是合理的。这种机床的主要优点是所有的刀具能同时工作，因而一个工人

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可以看管几部机床。对于相对简单的零件，多轴自动车床可以在五秒钟内生产加工出一件产品。

牛头刨、龙门刨、钻床和铣床

牛头刨床使用的是装在滑枕一端的夹具上的单点刀具。切削加工通常在向前的行程中进行。刀具被抬刀架稍稍抬举，以避免工件表面被严重拖刮。在返回行程中，刀具下面的工作进给，为下一次切削做准备。立式床身内装有牛头刨的操作机构，床身上装有支持工件的工作台。工作台可在滑枕互相垂直的两个方向上移动。刀具滑块用来控制切割深度并依靠手动进给。它可以在其法向垂直位置的两侧回转900角，这样可以相对于工作台表面成一个角度进给刀具。

牛头刨床有两种类型的驱动机构：改进的惠氏快回机构和液压驱动机构。对于惠氏机构，电动机驱动大齿轮，大齿轮驱动曲柄，行程长度通过可调节的曲柄销来控制。当大齿轮旋转时，摇臂受力而往复运动，并把运动传递给牛头刨滑枕。

液压牛头刨的电动机仅仅用来驱动液压泵。牛头刨的运动靠液压油的流向控制。机械驱动的牛头刨的切削行程只利用了大齿轮旋转的2200，而返回行程则用了1400.这样切削行程与返回行程之速度比为1.6比1。液压牛头刨有一个优点，即切削速度可无级变速。这类机床的主要缺点是在滑枕冲程的终端缺乏确定的限制，可能有千分之几英寸的行程程度误差。

龙门刨非常类似于牛头刨，因为这两种刨床都主要加工平面和斜面，然而龙门刨更适合于加工大型工件。龙门刨的加工场所在工作台上，能够在水平面上往复运动，提供直线的切削和进给运动。刨刀装在横向悬梁上，并受到垂直方向的立柱的支承。刨刀可以在水平和垂直方向进刀和退刀，提供四个方向的直线进给运动。

由于使用的刀具的类型和加工场所的尺寸，龙门刨的切削速度较低。为了提高龙门刨床的生产能力，可以使用多刀切削加工中心。另一个增加产量的方法是同时在工作台上安放多个工件。龙门刨的大小取决于加工场所的最大尺寸，也就是说加工场所的长度、宽度和高度要适应各种龙门刨的工作台的类型。

立式钻床或手摇钻床有各种规格和类型，主轴的调速范围大并能根据多数行

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业的要求自动进给。摇臂钻床用来钻削那种很笨重、不便搬动的工作。摇臂上安装的主轴能够进行速度调节并装有进给调节机构。通过转臂绕立柱的转动和主轴组件沿摇臂的移动，可以把主轴和钻头移到机器所能达到的任何位置。

普通摇臂钻床只能使主轴垂直运动，而万能摇臂钻床允许主轴围绕垂直于摇臂的轴线旋转，摇臂绕着水平轴线旋转，这样可以在任何角度下钻削。

多轴钻床具有一个或多个通过万向接头和可伸缩的花键轴来驱动主轴的装置。所有的主轴通常都由同一部电动机驱动并同时进给以便钻削出所要求的孔数。

铣削工艺用旋转的刀具来切去金属。它包括从工件表面切去金属、扩孔和成型切削。例如螺纹加工和齿轮加工。

升降台式的的铣床内，立柱是其它零件的主要支承构件，其基座包括驱动电机、主轴和刀具。刀具装于主轴的刀杆上，并且通过悬臂内的轴承支承在其外端上。升降台装在立柱的燕尾槽里，鞍座在燕尾槽里与升降台固定在一起，工作台被连接在鞍座上。这样，升降台和立柱可以提供相对于刀具的三个运动。借助工作台绕着鞍座上的垂直轴线旋转，可以提供第四个运动。

床身固定的铣床比升降式和立柱式的刚性更好。工作台被直接安装在机床基座上，提供了吸收重大切削载荷所需要的刚性，而且仅允许相对于工作台的纵向运动。垂直运动靠移动整个刀头获得。

仿型铣床的特点或者是刀具与仿型元件的运动轨迹同步，垂直运动靠移动整个刀头获得。仿型模型的形状轮廓运动，而刀头重复仿型运动。

铣削工艺设计所考虑的一般原则是：

（1） 只要有可能，将零件设计成安装一次能铣削表面的数量最多：

（2） 为了能够使多刀铣削，将零件设计成能同时铣削几个表面；

（3） 应当首先铣最大的平面，这样，所有尺寸都能同时铣削几个平面为基准；

（4） 由于铣刀是回转的，所以不可能铣削方形内角。

磨床

磨床把磨料粘接成各种形状和大小的轮子和带子作为切削介质。磨削工艺可

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以加工出表面光洁度质量很高的零件，并提高零件的尺寸精度，因为磨削的公差可以达到0.00025mm。磨床根据加工出的表面的形状分类。根据加工一般表面分类，磨床有表面磨床、外圆磨床和专用磨床。

磨削加工在工件生产中显得极为重要，有如下几个原因：

（1） 磨削加工是切削淬硬过的工具钢或其它热处理过的钢的最通用的方法。零件可以先加工再热处理，最后磨削到所要求的尺寸和表面光洁度。

（2）

（3）

磨削加工能磨出的表面光洁度为0.5微米，而费用并不昂贵。

磨削加工可在相对短的时间内保证尺寸精度，因为磨床能提供增量为万分之一英寸的进刀运动，而不是像其它机床那样仅有千分之几英寸。

（4） 可加工极小而薄的零件。由于施加的磨削压力很小，减小了工件偏离刀具的趋势。

在外圆磨床上，吃刀深度靠移动砂轮头来控制，包括控制砂轮及其驱动电机。冷却剂用来减少热变形，带走切屑和磨削粉尘。

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