Task 2　Machinery Manufacturing

Part A

Text

1.2.1　Metal Cutting Technology

The six basic techniques of machining metal include turning，milling，planning，grinding，drilling and boring.

Turning is type of metal processing operation where a cutting tool is used to remove the unwanted material to produce a desired product，and is generally performed on lathe.In turning process，the rotation of spindle is the main movement，and the turning tool’s move is the feed movement.Horizontal lathe is shown as Fig.1-2-1.

After lathes，milling machines are the most widely used for manufacturing applications.Vertical and horizontal milling machine is shown as Fig.1-2-2.Milling consists of machining a piece of metal by bringing it into contact with a rotating cutting tool which has multiple cutting-edges.There are many types of milling machines designed for various kinds of work.Some of the shapes produced by milling machines are extremely simple，like the slots and flat surfaces produced by circular saws.Other shapes are more complex and may consist of a variety of combinations of flat and curved surfaces depending on the shape given to the cutting-edges of the tool and on the travel path of the tool.

Planning metal with a machine tool is a process similar to planning wood with a hand plane.The essential difference lies in the fact that the cutting tool remains in a fixed position while the workpiece is moved back and forth beneath.Planners are usually used for processing large workpiece.A shaper（Fig.1-2-3）differs from a planer in that the workpiece is held stationary and the cutting tool travels back and forth.

Grinding machining is important processing technology in mechanical manufacturing.Grinding tool is a rotating abrasive wheel.The abrasive wheel simulates a milling cutter with a large number of miniature cutting edges.The process is often used for the final finishing process to obtain high accuracy dimensions and better surface finish of a part that has been heat-treated to make it very hard.That is because grinding can correct distortion that may have resulted from heat treatment.Grinding can be performed on plat，cylindrical and internal surface by employing specialized machining tools on grinding machine.In recent years，grinding has also found increased application in heavy-duty metal removal operations.Universal grinder is shown as Fig.1-2-4.

Drilling involves producing through or blind holes in a solid metal by a cutting tool，which rotates around its axis，against the workpiece.Radial drilling machine is shown as Fig.1-2-5.Drilling operation can be carried out either by hand drill or by drilling machine.Usually，the tool rotates around its spindle while the workpiece is fixed firmly in the latter.Drilling consists of cutting a round hole by means of a rotating drill.The drill can have either one or more cutting edges and corresponding flutes which can be straight or helical.The function of flutes is to provide outlet passages for the chips generated during the drilling operation and also to allow lubricant and coolant to reach cutting edges and the surface being machined.The most common used drills in production are twist drill，center drill，gun drill and spade drill.

Boring，on the other hand，involves the finishing of a hole already drilled or cored by means of rotating，offset，single-point tool.On some boring machines，the tool is stationary and the workpiece revolves，on others，the reverse is true.Boring machine is shown as Fig.1-2-6.

1.2.2　Cutting Tool

1.Cutting tool materials and property

Cutting tools properties include high hardness and the ability to retain it even at the elevated-temperatures generated during cutting.They also include toughness，abrasion resistance，and the ability to withstand high bearing pressures.A cutting material is selected to suit the cutting conditions，such as the workpiece material，cutting speed，production tare，coolants used and so on.The commonly used cutting tool materials are plain carbon steel，alloy steel，high-speed steel，cemented carbides，diamond，etc.

2.Common tools of turning

Turning operations use one cutting edge at a time.The commonly used turning tools are as follows：external turning tool [Fig.1-2-7（a）]，groove tool [Fig.1-2-7（b）]，thread tool[Fig.1-2-7（c）]，internal turning tools [Fig.1-2-7（d）]，twist drill [Fig.1-2-7（e）] and center drill[Fig.1-2-7（f）]，etc.

External turning tool is used for turning cylinder，taper and facing surface.Groove tool is used in parting the workpiece or cut off the workpiece.Thread tools is used to cut a standard 60degree thread.Internal turning tool is used in a boring operation.Center drill is used to provide positioning for drilling operation.

3.Common cutters of milling

The face milling cutter is used to milling of the upper surface [Fig.1-2-8（a）]；keyway cutters are used to machine contour [Fig.1-2-8（b）]，holes drilled with the center drill[Fig.1-2-8（c）]，twist drill [Fig.1-2-8（d）] and reamer [Fig.1-2-8（e）].

4.Geometry of cutting tool

The cutting part of cutting tool includes a face for passing chips and a flank directed to the workpiece.The intersecting face and flank form a cutting edge.The tool performance depends on its material and angles which mainly include：nose angle，rake angle，relief angle and cutting edge angle.

Rake angle decides the tartness degree of tool，the larger of the rake angle，the more tartness.Rake angles can be positive，negative，or zero.Its value usually varies between 0°and 15°，whereas the back rake angle is usually taken as 0°.

Relief angles serve to eliminate rubbing between the workpiece and the end flank.The degree of relief angle has important effect on surface quality of the workpiece.At the same time，relief angle affects the intensity of tool edge.It can also affect the tartness degree of tool.Usually，the values of each of these angles range between 4° and 6°（rough machining）or 8°and 12°（finish machining）.

1.2.3　Cutting Dosages

1.Cutting speed

Cutting speed for milling is the speed at the outside edge of the milling cutter as it is rotating.A milling cutter must spin.The rate at which the cutting tool rotates is called the spindle speed，measured in r/min（revolutions per minute）.

Each cutter has its own spindle speed，depending on the type of material being cut and the size（diameter）of the cutter.When cutting the same type of material，the smaller the cutter，the faster it must rotate.

For lathe operation，the cutting speed is defined as the rate at which a point on the circumference of the workpiece passes the cutting tool.It is the number of feet traveled in the circumferential direction by a given point on the surface of the workpiece per minute.The relationship between the cutting speed and spindle speed can be given by the following equation：

Cutting speed=πDn/1000

Where：D—diameter of the workpiece，mm；

n—spindle speed，r/min.

Every material has an ideal cutting speed.This is the optimum speed at which the material can be cut safely，in order to obtain a good quality of finish.The cutting speed is dependant primarily upon the material being machined as well as the material of the cutting tool and can be obtained from handbooks，provided by cutting tool manufacturers.There are also other variables that affect the optimal value of the cutting speed.These include the tool geometry，the type of lubricant or coolant，the feed rate，and the depth of cut.

2.Feed rate

The feed rate is that the distance the tool advances into the workpiece per revolution of the workpiece.The selection of a suitable feed rate depends upon many factors，such as the required surface finish，the depth of cut and the geometry of the tool used.Finer feed rate produces better surface finish，whereas higher feed rate reduces the machining time.Therefore，it is generally recommended to use higher feed rate for roughing operations and finer feed rate for finishing operations.Recommended values for feed rate，which can be taken as guidelines，are found in handbooks provided by cutting tool manufacturers.

Feed rate is usually measured in inches per minute.For milling operation it is the revolution per minute times the number of teeth in the cutter.Due to variations in cutter sizes，number of teeth and revolutions per minute，all feed rate should be calculated from feed per tooth.

The feed rate per tooth must be converted into feed rate per minute before you can make the feed rate setting on the machine.The formula for converting feed rate is as follows：

feed rate（in/min）=spindle speed×chip load×teeth

It must also be mentioned that using a chip load that is too small will cause excessive tool wear，so don’t just set the feed rate low and think this is correct.

3.Cut depth

Depth of cut is defined as the distance that the cutting tools is plunged into the workpiece.It is typically measured in millimeters.For turning operation，the depth of cut can be calculated by the following equation：

ap=（dw-dm）/2

Where：ap—depth of cut（Fig.1-2-9）；

dw—the diameter of the new surface（Fig.1-2-9）；

dm—the diameter of the finished surface（Fig.1-2-9）.

To determine the depth of cut we must first select the proper cutting tool，the proper machine and a suitable setup.The depth of cut directly influences the tool life.If the depth of cut is too large，the insert may be overloaded，causing immediate breakage.The handbooks provide the recommended ranges for depths of cut（ap）for each insert.If the depth of cut is too small，the resulting side forces will not be sufficient to properly deflect the tool.Vibration and instability may occur.In the finishing operation，it is important to select a small depth of cut and a small corner radius.

If your CNC machine is used with incorrect spindle speed，feed rate and depth of cut，your work may be machined with a poor surface finish or the workpiece or cutter could be damaged.There are many factors that would affect these values，including：

●The condition of the machine.

●The type of material being machined.

●The clamping method used to the stock on the CNC machine.

●The type of cutting tool used.

●The diameter of the cutting tool.

●Material type of the cutting tool.

New Words and Phrases

grinding [ˈgraɪndɪŋ]　　v.磨碎，嚼碎（grind的现在分词）

boring [ˈbɔːriŋ]　　n.钻孔，钻屑

abrasive [əˈbreɪsɪv]　　adj.有磨蚀作用的，摩擦的，粗糙的

abrasion [əˈbreɪʒn]　　n.磨损，擦伤处

resistance？[rɪˈzɪstəns]　　n.阻力，抵抗，抗力

cemented carbides　　烧结碳化物，硬质合金

diamond [ˈdaɪəmənd]　　n.钻石，金刚石

groove [gruːv]　　n.沟，槽

keyway [ˈkiːweɪ]　　n.键沟

flank [flæŋk]　　n.侧面，侧腹，侧边

thermal [ˈθɜːml]　　adj.热的，保热的，温热的

consumption [kənˈsʌmpʃn]　　n.消费，耗尽

chip [tʃɪp]　　n.碎片vt.刻，削成，从……上削下一小片

synthetic [sɪnˈθetɪk]　　adj.合成的，人造的n.合成物，合成纤维，合成剂

emulsion [ɪˈmʌlʃnz]　　n.乳剂，乳胶

rake angle　　倾角，前角，翘角

relief angle　　后角

cutting edge　　切削刃

plain carbon steel　　碳素钢

groove tool　　切槽刀

cutting dosage　　切削用量

feed rate　　进给量

recommended value　　推荐值

cutting fluid　　切削液

synthetic oil　　合成油

Exercises

Ⅰ.Match column A with column B.

Ⅱ.Mark the following statements with T（true）or F（false）.

（　）1.In turning process，the rotation of spindle is the feed movement，and the turning tool’s move is the main movement.

（　）2.Groove tool is used in parting the workpiece or cut off the workpiece.

（　）3.The twist drill is the most common type of drill and used for rough drilling operation.

（　）4.Relief angle decides the tartness degree of tool，the larger of the relief angle，the more tartness.

（　）5.The feed rate per tooth is too small will cause excessive tool wear so don’t just set the feed rate low and think this is correct.

Ⅲ.Answer the following questions briefly according to the text.

1.How many kinds are there in techniques of machining metal？

2.What function is relief angle？

3.What are the factors that affect the cutting speed？

4.How to select the feed rate for roughing operation？

5.What is the definition of cut depth？

Part B

Reading Material Cutting Fluids

1.Functions of cutting fluids

①Reduce friction and wear，thus improving tool life and the surface finish of the workpiece.

②Cool the cutting zone，thus improving tool life and reducing the temperature and thermal distortion of the workpiece.

③Reduce forces and energy consumption.

④Flush away the chips from the cutting zone，and thus prevent the chips from interfering with the cutting process.

⑤Protect the machined surface.

2.Types of cutting fluids

（1）Synthetic oils

Synthetic oils typically are used for low-speed operations where temperature rise is not significant.

（2）Emulsions

Emulsions are a mixture of oil and water and additives，generally are used for high-speed operations because temperature rise is significant.The presence of water makes emulsions very effective coolants.