方法的拼音7.1 INTRODUCTION
After lathes, milling machines are the most widely ud for manufacturing applications. In milling, the workpiece is fed into a rotating milling cutter, which is a multi-point tool as shown in Fig. 7.1, unlike a lathe, which us a single point cutting tool. The tool ud in milling is called the milling cutter.
Fig. 7.1Schematic diagram of a milling operation史上最牛小孩打架
革命先烈The milling process is characterid by:
(i)Interrupted cutting Each of the cutting edges removes material
for only a part of the rotation of the milling cutter. As a result, the cutting edge has time to cool before it again removes material.
Thus the milling operation is much more cooler compared to the turning operation. This allows for a much larger material rates.
(ii)Small size of chips Though the size of the chips is small, in view of the multiple cutting edges in contact a large amount of material is removed and as a result the component is generally completed in
a single pass unlike the turning process which requires a large
number of cuts for finishing.
(iii)Variation in chip thickness This contributes to the non-steady state cyclic conditions of varying cutting forces during the contact of the cutting edge with the chip thickness varying from zero to maximum size or vice versa. This cyclic variation of the force can excite any of the natural frequencies of the machine tool system and is harmful to the tool life and surface finish generated
A milling machine is one of the most versatile machine tools. It is adaptable for quantity production as well as in job shops and tool rooms. The versatility of milling is becau of the large variety of accessories and tools available with milling machines. The typical tolerance expected from the process is about ±0.050 mm.
7.2 TYPES OF MILLING MACHINES
To satisfy various requirements milling machines come in a number of sizes and varieties. In view of the large material removal rates
milling machines come with a very rigid spindle and large power. The varieties of milling machines available are:
(i) Knee and Column type
(a) horizontal
(b) vertical211工程
(c) universal
(d) turret type
The are the general purpo milling machines, which have a high degree of flexibility and are employed for all types of works including batch manufacturing. A large variety of attachments to improve the flexibility are available for this class of milling machines.
(ii) Production (Bed) type捧心西子
(a) simplex
(b) duplex
(c) triplex
The machines are generally meant for regular production involving large batch sizes. The flexibility
is relatively less in the machines which is suitable for productivity enhancement.
(iii) Plano millers
The machines are ud only for very large workpieces involving table travels in meters.
(iv) Special type
(a) Rotary table
(b) Drum type
(c) Copy milling (Die sinking machines)
牛郎织女的故事缩写(d) Key way milling machines
(e) Spline shaft milling machines
The machines provide special facilities to suit specific applications that are not catered to by the other class of milling machines.
7.2.1 Knee and Column Milling Machines
The knee(升降台) and column type is the most commonly ud machine in view of its flexibility and easier tup. A typical machine construction is shown in Fig. 7.2 for the horizontal axis. The knee hous the feed mechanism and mounts the saddle and table. The table basically has the T-slots running along the X-axis for the purpo of work holding. The table moves along the X-axis on the saddle while the saddle moves along the Y-axis on the guide ways provided on the knee.
The feed is provided either manually with a hand wheel or connected for automatic by the lead screw, which in turn is coupled to the main spindle drive. The knee can move up and down (Z-axis) on a dovetail provided on the column.
Fig. 7.2 Horizontal knee and column type milling machine
The massive column at the back of the machine hous all the power train including the motor and the spindle gearbox. The power for feeding the table lead screw is taken from the main motor through a parate feed gearbox. Sometimes a parate feed motor is provided for the feed gearbox as well.
While the longitudinal and traver motions are provided with automatic motion, the raising of the knee is generally made manually.
The spindle is located at the top end of the column. The arbour ud to mount the milling cutters is mounted in the spindle and is provided with a support on the other end to take care of the heavy cutting forces by means of an overarm with bearing. As shown in Fig.
7.2 the overarm extends from the column with a rigid design. The spindle no has the standard Mor taper of the suitable size香飘飘奶茶
o站长工具depending upon the machine size.
