Machine PartsMachine PartsUnit 2

Application

EDM can produce ______ and ___________.

Injection molds ,finished parts.

Nowadays it is the most widely-used non-traditional machining process, mainly to produce injection molds and dies, for mass production of very common objects.今天电火花加工是用途最广的非传统加工工艺，主要用来制造注塑模具。这些注塑模具在常用产品的批量生产中有着重要的用途。

Application

What’s the main idea of the first paragraph?

EDM, a widely -used non-traditional machining process, is used in a large number of industrial areas.

Application

What are the advantages of EDM over traditional methods?

Firstly, any material that conducts electricity can be machined. Secondly, complex cutting geometry, sharp angles and internal corners can be produced. Final surface state with low rugosity ( 粗糙度） and precise machining are other important advantages. Moreover, there is no mechanical stress on the machined piece, no rotation of workpiece or tool is necessary, and the machines have a high autonomy.

Surface Roughness

Surface roughness, often shortened to roughness, is a measure of the texture of a surface.

Application The disadvantages are as follows:______________

The disadvantages are the relatively low material removal rate, surface modification of the machined workpiece, and limited size of workpiece and tool.

Principles

The workpiece and an electrode can be considered as the cutting tool.(T/F)

A dielectric liquid is between the workpiece and the electrode. (T/F)

EDMThere is mechanical contact between the electrodes during EDM process.(T/F)

Both electrode and workpiece have to be electrically conductive because erosion is produced by electrical discharges.(T/F)

The breakdown of the dielectric is initiated by____________________________________.moving the electrode towards the

workpiece.

The location of breakdown is generally between ____________________________________.the closest points of the electrode

and of the workpiece.

EDM

The liquid dielectric plays a crucial role.

The liquid dielectric cools down the electrodes. It guarantees a high plasma pressure and therefore a high removing force on the molten metal when the plasma collapses. It solidifies the molten metal into small spherical particles, and it also flushes away these particles.

Chain Drives 链传动

Chain Drives 链传动

外链板

内链板

套筒滚子

销轴

Chain Drives 链传动

Side plates （内外）链板

pins 销轴

Bushings(sleeves) 套筒

rollers 滚子

Sprocket wheels 链轮

Chain Drives 链传动

Chain Drives 链传动

A pin link consists of two side plates connected by two pins inserted into holes in the side plates.销轴连接是将销轴插入外链板的孔中来连接两个外链板。

A roller link consists of two side plates connected by two press-fitted bushings, on which two hardened steel rollers are free to rotate.

滚子连接是将两套筒与内链板进行过盈连接 , 然后将硬化钢滚子套上，滚子可以在套筒上自由转动。

http://jpkc.nwpu.edu.cn/jp2003/jxsj/ZST/ZS01.htm

Chain Drives 链传动

把一根以上的单列链并列、用长销轴联接起来的链称为多排链。链的排数愈多，承载能力愈高，但链的制造与安装精度要求也愈高，且愈难使各排链受力均匀，将大大降低多排链的使用寿命，故排数不宜超过 4 排。当传动功率较大时，可采用两根或两根以上的双排链或三排链。

Standard roller chains are available in single strands or in multiple strands. In the latter type, two or more chains are joined by common pins that keep the rollers in the separate strands in proper alignment.

标准滚子链有单排和多排之分。多排滚子链是将两根以上的链条用一根长销轴联结起来，滚子整齐排列。

Chain Drives 链传动The speed ratio for a single drive should be limited to about 10:1, the preferred shaft center distance is from 30 to 35 times the distance between the rollers and chain speeds greater than about 2500 feet (800 meters) per minute are not recommended.单个驱动的速度比一般控制在 10∶ 1 范围内，比较合适的轴中心距离一般为 30 到 35 倍滚柱与滚柱之间的距离，链条速度一般不要超过每分钟 2500 英尺 ( 每分钟 800 米 ) 。当几个平行轴一起驱动时，滚柱链条传动尤为合适。

Chain Drives 链传动The speed ratio for a single drive should be limited to about 10:1, the preferred shaft center distance is from 30 to 35 times the distance between the rollers and chain speeds greater than about 2500 feet (800 meters) per minute are not recommended. Where several parallel shafts are to be driven without a single slip , roller chains are particularly well suited. 单个链传动的传动比应小于 10 ，而轴中心距离最好应控制在滚子节距的 30-35 倍，链速须小于 800 米 / 分钟。当需要在多个平行轴间进行传动，而且不能有打滑时，滚子链传动非常适合。

Chain Drives 链传动An inverted tooth, or silent chain is essentially an assemblage of gear racks, each with two teeth, pivotally connected to form a close chain with the teeth on the inside, and meshing with conjugate teeth on the sprocket wheels.

Chain Drives 链传动An inverted tooth, or silent chain is essentially an assemblage of gear racks, each with two teeth, pivotally connected to form a close chain with the teeth on the inside, and meshing with conjugate teeth on the sprocket wheels.

译文 1 ：齿型链条或低噪音链条基本上就是齿轮齿条的组合件，每个齿条有两个齿，轴向连接形成一个封闭的、内面有齿的链条，链轮上有共轭齿。

译文 2 ：齿型链条或无声噪音链条基本上就是齿条组合件，每个齿条有两个齿，齿与齿铰接形成一个内面有齿的封闭链条；链条与链轮上的共轭齿啮合。

Chain Drives 链传动The links are pin-connected flat steel plates usually having straight-sided teeth with an included angle （夹角） of 60 degrees.

译文：齿形链由若干组平面钢板铰接而成。链板两侧工作面为直边，夹角为 60° 。

Chain Drives 链传动Compared with roller-chain drives, silent-chain drives can transmit more load for the same width.

Bead Chains 滚珠链The sprockets may be steel, die-cast zinc or aluminum or molded nylon.

译文 2 ：链轮材料可以是钢、锌铝压铸件或是铸造尼龙。

译文 1 ：链轮可以是钢、锻压或铸造的锌、或尼龙等。

FastenersFasteners 紧固件紧固件

According to the text, there are three types of fasteners described as follows:________________

Removable, semi permanent, and permanent type.

Ordinary nut-and-bolt fastener 普通的螺栓螺帽连接

FastenersFasteners 紧固件紧固件

riveted joints 铆接

Cotter pin 开口销

welded joints 焊接

FastenersFasteners 紧固件紧固件What’s the main idea of the paragraph “the importance of fasteners can be realized…”

The importance of fasteners should be realized for producing any complex product.

In this paragraph the author uses some intensifier to convey his/her idea, and what are they?

any, literally, single, serious, must be

FastenersFasteners 紧固件紧固件Since they are so widely used, it is essential that these fasteners attain maximum effectiveness at the lowest possible cost.原译：由于它们广泛使用，这些连接件基本上可以以最低的成本获得最大的效率。

改译：由于其用途广泛，因此如何使其以最低的成本取得最大的成效是很重要的。

What does “engineer” mean ?

“design”

FastenersFasteners 紧固件紧固件The lock washer is useful only when the bolt might loosen because of a relative change between the length of the bolt and the parts assembled by it.

只有当由于螺栓和被连接件之间的相对运动使螺栓可能松动时防松垫圈才会起作用。

FastenersFasteners 紧固件紧固件The lock washer is useful only when the bolt might loosen because of a relative change between the length of the bolt and the parts assembled by it.只有当由于螺栓和被连接件之间的相对运动使螺栓可能松动时防松垫圈才会起作用。

FastenersFasteners 紧固件紧固件This change in the length of the bolt can be caused by a number of factors__ creep (蠕变） , loss of resilience(弹性 ), difference in thermal expansion between the bolt and the bolted members, or wear.

螺栓长度的变化可能是由于螺栓内部蠕变、松弛、螺栓和被连接件的热膨胀差异以及磨损等原因造成的。

The difference between lock The difference between lock washer and spring washerwasher and spring washer

1.锁紧垫圈 : 外或内圆周有多个翘齿 ,刺压在支承面上 , 能有效防止紧固件松动 ,弹力均匀 ,防松效果好 , 但不宜用于经常拆卸和材料较软处 .

2.弹簧垫圈 : 以弹性及斜切口的摩擦和嵌入防止紧固件松动 , 在被连接件与螺栓或螺母间形成一个硬的支承面 , 使负荷分布更加均匀 , 广泛用于经常拆卸的螺纹连接及对放松性能要求不高的场合。

Shaft Shaft 轴轴The most common shape for shafts is circular and the cross section can be either solid or hollow( hollow shafts can result in weight savings).What does the sentence “hollow shafts can result in weight savings” mean?

Why shafts must be rigid enough?

To prevent overloading of the supporting bearings

Shaft Shaft 轴轴These devices introduce forces which attempts to bend the shaft.

通过这些零件传来的力可能会使轴产生弯曲变形。

vt. 1. 介绍 , 引见 2. 提出 , 提出供讨论 3. 引进 , 采用 4.  将…放 [ 插 ] 入 5.  作为…的开头 6. 带领；引导 7.  使开始；引出 8. [美国英语 ]推销 (新产品

Shaft Shaft 轴轴For diameters less than 3 in., the usual shaft material is__________________________________; for sizes from 3 in. to 5 in., shafts are _____________________; for sizes above 5 in., shafts are ____________________ to size.

cold-rolled steel containing about 0.4 percent carbon

Cold-rolled or forged

forged and machined

Why is it safe to use plastic shaft in electrical application?

Because plastic is a poor conductor of electricity.

CouplingsCouplings 联轴器联轴器

BearingBearing 轴承轴承

Why the reduction of friction is a prime consideration for bearings?

Friction results in loss of power, the generation of heat, and increased wear of mating surfaces.

BearingBearing 轴承轴承

How to achieve satisfactory performance of bearings when there are moderate loads and speeds?

To make a right selection of a standard bearing on the basis of load rating.

The deflection of the bearing elements will become important where loads are high, although this is usually of less magnitude than that of the shafts or other components associated with the bearing.(Translation)

当载荷较高时轴承部件的变形就显得非常重要，尽管这种变形与轴或是与轴承一起工作的零部件相比通常要小一些。

BearingBearing 轴承轴承

Can you explain the sentence “sealing arrangements must be chosen with regard to the hostility of the environment”?

Sealing methods must be considered to protect the bearings from contaminants.

Why bearings must be sealed ?

Because wear is primarily associated with the coming of contaminants.

BearingBearing 轴承轴承

What’s the main idea of this paragraph?

Machine designer should be concerned about with bearing selection and the condition for correct installation.

BearingBearing 轴承轴承