ICT

What is RAM?

Random Access Memory (RAM) provides space for your computer to read and write data to be accessed by the CPU (central processing unit). When people refer to a computer's memory, they usually mean its RAM.

If you add more RAM to your computer, you reduce the number of times your CPU must read data from your hard disk. This usually allows your computer to work considerably faster, as RAM is many times faster than a hard disk.

RAM is volatile, so data stored in RAM stays there only as long as your computer is running. As soon as you turn the computer off, the data stored in RAM disappears.

Note: On a PC, different parts of RAM may be more or less easily accessible to programs. For example, cache RAM is made up of very high-speed RAM chips which sit between the CPU and main RAM, storing (i.e., caching) memory accesses by the CPU. Cache RAM helps to alleviate the gap between the speed of a CPU's megahertz rating and the ability of RAM to respond and deliver data. It reduces how often the CPU must wait for data from main memory.

milling

WHAT IS MILLING?

Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. The cutting action of the many teeth around the milling cutter provides a fast method of machining. The machined surface may be flat,angular, or curved. The surface may also be milled to any combination of shapes. The machine for holding the workpiece, rotating the cutter, and feeding it is known as the Milling machine.

View a typical milling operation. This movie is from the MIT-NMIS Machine Shop Tutori

al

CLASSIFICATION OF MIL

LING

· Peripheral Milling

In peripheral (or slab) milling, the milled surface is generated by teeth locate

d on the periphery of the cutter body. The axis of cutter rotation is generally in a plane parallel to the workpiece surface to be

machined.

(Kalpakjian S., Introduction to Manufacturing Processes)

· Face Milling

In face milling, the cutter is mounted on a spindle having an axis of rotation perpendicular to the workpiece surface. The milled surface results from the action of cutting edges located on the periphery and face of the cutter.

· End Milling

The cutter in end milling generally rotates on an axis vertical to the workpiece. It can be tilted to machine tapered surfaces. Cutting teeth are located on both the end face of the cutter and the periphery of the cutter body.

METHODS OF MILLING

· Up Milling

Up milling is also referred to as conventional milling

. The direction of the cutter rotation

opposes the feed motion. For example,

if the cutter rotates clockwise , the workpiece is fed to the right in up milling.

(Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)

· Down Milling

Down milling is also referred to as climb milling. The direction of cutter rotation is same as the feed motion. For example, if the cutter rotates counterclockwise , the workpiece is fed to the right in down milling.

(Boothroyd G. & Knight W., Fundamentals of Machining and Machine Tools)

The chip formation in down milling is opposite to the chip formation in up milling. The figure for down milling shows that the cutter tooth is almost parallel to the top surface of the workpiece. The cutter tooth begins to mill the full chip thickness. Then the chip thickness gradually decreases.

Other milling operations are shown in the figure.

Milling: Introduction Milling is as fundamental as drilling among powered metal cutting processes.

Milling is versatile for a basic machining process, but because the milling set up has so many degrees of freedom, milling is usually less accurate than turning or grinding unless especially rigid fixturing is implemented.

For manual machining, milling is essential to fabricate any object that is not axially symmetric. There is a wide range of different milling machines, ranging from manual light-duty Bridgeports™ to huge CNC machines for milling parts hundreds of feet long. Below is illustrated the process at the cutting area.

Milling: Column-and-Knee Manual Mill Below is illustrated a typical column-and-knee type manual mill. Such manual mills are common in job shops that specialize in parts that are low volume and quickly fabricated. Such job shops are often termed "model shops" because of the prototyping nature of the work.

The parts of the manual mill are separated below. The knee moves up and down the column on guideways in the column. The table can move in x and y on the knee, and the milling head can move up and down.