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Learn about the purpose and operational parts of milling machines, as well as milling machine accessories and attachments. Explore the history and types of milling machines, and understand the selection and use of milling machine cutters.
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Milling Machines Lecture Prepared by: Gp Capt Dr HamidUllah Khan Niazi
Objectives • After completing this unit you should be able to: • Recognize and explain the purpose of four milling machines • Know the purposes of the main operational parts of a horizontal and a vertical milling machine • Recognize and state the purposes of four milling machine accessories and attachments.
Milling Machine-Introduction • Milling Machines are machine tools used to produce one or more machines surface accurately on a work piece. This is done by one or more rotary milling cutters having single or multiple cutting edges. The work piece is held securely on the work table with the help of a work holding device and is then brought in contact with a revolving cutter
History • First Milling machine came into existence in 1770 and was of French origin • Milling cutter was first developed in 1782 by Jacque de Vauconson • The first successful milling machine was designed by Eli Whitney in the year 1818 • Joseph R. Brown invented the first milling machine in year 1861
Types of Milling Machines Horizontal Milling Machine i) Manufacturing Type ii) Special Type iii) Knee- and- Column Type Manufacturing Type • The Plain Manufacturing Type • The Small Plain Automatic Knee-Column Type • The Tracer Controlled Milling Machine Special Type Milling Machine Machining Centers
Types-Continued Manufacturing Type: In which the cutter height is controlled by vertical movement of the head stock Special Type: It is designed for specific milling operations Knee-Column Type: In which the relationship between the cutter height and the work is controlled by vertical movement of the table
Milling Machine Cutters • Milling machine cutters should be properly selected in order to achieve best results. • Proper selection of spindle speed for any cutter is important to see how milling machine performs with different cutters, as cutters are manufactured in many types and sizes. • Most Milling cutters are made of High Speed Steel or Tungsten Carbide. • High Speed Steel, consisting of Iron with various amounts of carbon, tungsten, chromium etc are used for solid milling cutters since it possesses all the qualities required for a milling cutter. • When a higher rate of production is required and harder metal are being machined then cemented carbides replace HSS cutters. • Cemented Carbide Cutters are 3 to 10 times faster than high-speed steel cutter, although they are costly and expensive but they are more efficient than HSS while cutting harder metals.
Reading Assignment • Read the first five cutters in detail and you will get a quiz in this reading assignment.
Cutting Speed, Feed and Depth of Cut • The most important factors affecting the efficiency of a milling operation are cutting speed, feed and depth of cut. If the cutter moves slow time will be wasted, while excessive speed results in loss of time in replacing and grinding of cutter. Somewhere between these two extremes is the efficient cutting speed for the material being machined. The rate at which the work is fed into the revolving cutter is important. • Too high and too slow feed will only shorten the life of cutter. • Therefore, speed, feed and depth of cut are three important factors in any milling machine.
Cutting Speed • Cutting speed of a metal may be defined as the speed, in surface feet per minute (s f/min) or meters per minute (m/min) at which the metal may be machined efficiently. • When work is machined in a milling machine, the cutter must be revolved at a specific number of r/min depending on its diameter to achieve the proper cutting speed. • Since different type of metals vary in structure, hardness and machinability, different cutting speed must be used for each type of metal and for various cutter materials
Feed of Milling Machine • Milling Feed may be defined as the distance in inches ( or millimeters) per minute that the work moves into the cutter. • The milling feed is determined by multiplying the chip size desired, the number of teeth in the cutter, and the r/min of the cutter. • Chip or feed per tooth is the amount of material that should be removed by each tooth of the cutter as it revolves and advances into the work. • The feed rate used on a milling machine depends on a variety of factor such as the depth and width of the cut, design or type of cutter, the sharpness of the cutter and the strength and uniformity of the work piece. • The ideal rate of feed may be determined as follows: Feed= no. of cutter teeth x feed/tooth x cutter r/min
Methods of Indexing • There are different types of Indexing that can be performed on Milling machine. Important of these are Direct Indexing, Simple Indexing and Angular Indexing. Apart from these Differential Indexing is also an important type of indexing.
Milling Machine Operations Different Milling operations that are performed on a Milling machine are: • Face Milling • Plain Milling • Side Milling • Straddle Milling • Gang Milling • Sawing and Slitting
Face Milling: is the process of producing a flat surface at right angles to the cutter axis. The cutter used for face milling are generally inserted are tooth cutters or shell end mills. Face Milling cutters are made in size of 6” . Side Milling: is often used to machine a vertical surface on the sides or ends of the work piece. Straddle Milling: involves the use of two side milling cutters to machine the opposite sides of a work piece. Application of Straddle milling involve milling of square and hexagonal heads on bolts Gang Milling: Gang milling is the fastest method of milling used a great deal in production work. It is performed by using two or more cutters on the arbor to produce the desired shape. The cutters may be a combination of plain and side milling cutters. Sawing and Slitting: Metal slitting saws may be used for milling narrow slots and for cutting off work. Plain slitting saws, because of their own thin cross-section are rather fragile cutting tools, if they are not used carefully they will break easily. Horizontal Milling Operations
Milling machine is one of the versatile machine tools found in the industry
Assignment # 2 • Do problems on Indexing i.e. direct indexing, simple indexing, angular indexing and indexing in minutes etc.
Summary • A wide variety of milling machines are required by industry to meet the job requirements of the many parts which must be machined. To make milling machines more versatile, a large variety of accessories and attachments are available so that each machine can perform more operations on each workpiece.
Next Time • We will study about Gear and Gear cutting
