T&P Chapter 13
Total Page：16
File Type：pdf, Size：1020Kb
CHAPTER 13 Milling Methods Metal Removal Cutting-Tool Materials and Machines Metal Removal Methods Machinability of Metals Single Point Machining Turning Tools and Operations Turning Methods and Machines 13.1 Introduction grouped into three general classes. Grooving and Threading Modern milling machines look much • Column and Knee Machines Shaping and Planing the same as they did 25 years ago. • Bed Type Milling Machines However, they now must cut super • Special Purpose Machines Hole Making Processes alloys, titanium, and high tensile steels The common subtypes are also iden- Drills and Drilling Operations to closer tolerances and at faster rates tified and discussed. Drilling Methods and Machines then previously. To handle these re- Boring Operations and Machines quirements, the new milling machines 13.2.1 Column and Knee Reaming and Tapping provide higher horsepower, greater Machines stiffness, and wider speed and feed Column and knee milling machines Multi Point Machining ranges than before. In addition, more are made in both vertical and horizon- Milling Cutters and Operations accurate lead screws, closer alignment, tal types. The schematic diagrams Milling Methods and Machines numerical control (NC) and computer (Fig. 13.2a and Fig.13.2b) show both Broaches and Broaching numerical control (CNC) all result in types of machines. Versatility is a ma- Saws and Sawing faster work with better finishes and jor feature of knee and column milling greater accuracy than ever before at- machines. On a basic machine of this Abrasive Processes tained. A modern CNC vertical mill- type, the table, saddle, and knee can be Grinding Wheels and Operations ing machine is shown in Figure 13.1 moved. Many accessories such as uni- Grinding Methods and Machines versal vises, rotary tables, and dividing Lapping and Honing 13.2 Types of Milling Machines heads, further increase the versatility The many types of milling machines of this type of machine. used in manufacturing have been Regardless of whether the machine is of the vertical or horizontal type, several components on all column and knee milling machines are similar, ex- cept for size and minor variations be- cause of manufacturer’s preference. These similarities are described in terms of general shape, geometric rela- tionship to the rest of the machine, function, and the material from which the components are made. Figure George Schneider, Jr. CMfgE 13.3a shows a standard vertical milling Professor Emeritus machine and Figure 13.3b shows a 3 Engineering Technology axis CNC vertical milling machine Lawrence Technological University A universal Horizontal Column and Former Chairman Knee milling machine is shown in Detroit Chapter ONE Figure 13.4. Society of Manufacturing Engineers Column: The column, which is Former President usually combined with the base as a International Excutive Board Society of Carbide & Tool Engineers single casting, is cast gray iron or ductile iron. The column houses the Lawrence Tech.- www.ltu.edu spindle, bearings, and the necessary Prentice Hall- www.prenhall.com FIGURE 13.1: Modern CNC vertical gears, clutches, shafts, pumps, and milling machine (Courtesy Ingersoll shifting mechanisms for transmitting Milling Machine Co.) www.toolingandproduction.com Chapter 13/Tooling & Production 1 Chap. 13: Milling Methods & Machines Motor Arbor Overarm Overarm Z′ Spindle Outboard bearing Y′ nose and arbor support Column Table Quill X X ( axis) Spindle Saddle Z (Z axis) Table Z Knee Column Y (Y axis) Saddle X Y Elevating screw Knee Z′ Base Elevating screw Base (a) (b) FIGURE 13.4: A universal horizontal- spindle column and knee type milling FIGURE 13.2: Schematic illustration of the motions and components (a) of a machine. (Courtesy Summit Machine vertical-spindle column and knee type milling machine and (b) of a horizontal- Tool Manufacturing Corp.) spindle column and knee type of machine. Spindles are hollow so that a drawbar can be used to hold arbors securely in place. The front of the spindle is machined to accept standard arbors. The two keys that fit into corresponding slots in the arbor do the actual driving of the arbor. The internal taper, which is accurately ground so that it is concen- tric with the spindle, locates the arbor. Knee: The knee is a casting that is moved up or down the slide on the front of the column by the elevating screw. Two dovetail or square slides are machined at 90 degrees to each other. The vertical slide mates with the slide on the front of the column, and (a) (b) the horizontal slide carries the saddle. It contains the necessary gears, screws, FIGURE 13.3: (a) Stand vertical-spindle column and knee type milling machine. and other mechanisms to provide (Courtesy Bridgeport Machinery, Inc.) (b) Three-axis CNC vertical-spindle column power feeds in all directions. The and knee type milling machine. (Courtesy Chevalier Machinery, Inc.) operator can select various feed rates power from the electric motor to the angle to the face of the column in both with the controls mounted on the knee. spindle at the selected speed. The the lateral and vertical planes. The Saddle: The saddle for a plain gears usually run in oil and are made of tolerances are very close and are usu- milling machine is a casting with two carburized alloy steel for long life. ally expressed in minutes or seconds of slides machined at an exact 90 degree Some of the necessary controls are arc. The large hole in the face of the angle to each other. The lower slide usually mounted on the side of the column casting is for the spindle. The fits the slide on the top of the knee, and column. hole is very accurately bored perpen- the upper slide accepts the slide on the The base is usually hollow, and in dicular to the front slide in two planes bottom of the table. The surfaces of the many cases serves as a sump for the and parallel to the upper slide. slides that make contact with the knee cutting fluid. A pump and filtration Spindle: On a horizontal milling and the table are parallel to each other. system can be installed in the base. machine, the spindle is one of the most Locks for both the cross slide and table The hole in the center of the base critical parts. It is usually machined is fitted to the saddle, along with the houses the support for the screw that from an alloy steel forging and is heat nuts that engage with the cross feed raises and lowers the knee. treated to resist wear, vibration, thrust, and table feed screws. The machined vertical slide on the and bending loads. The spindle is On a universal milling machine the front of the column may be of the usually supported by a combination of saddle is made in two pieces and is square or dovetail type. The knee ball and straight roller bearings, or by more complex because it must allow moves up and down on this slide. The tapered roller bearings that absorb both the table to swivel through a limited slide must be machined at a 90 degree radial loads and end thrust loads. arc. The lower part has a dovetail slide 2 Tooling & Production/Chapter 13 www.toolingandproduction.com Chap. 13: Milling Methods & Machines milling machine is often ideal for this kind of work. In this machine the table is supported directly on a heavy bed, while the column is placed behind the bed. A CNC bed-type milling machine is shown in Figure 13.5. and an opera- tional set-up with three spindles is shown in Figure 13.6. There are several advantages of the bed-type machine, particularly for pro- duction runs. Hydraulic table feeds are possible; the hydraulic components be- ing housed in the bed casting. This allows very high feed forces; variable feed rates during any given cut, and FIGURE 13.5: CNC bed type milling machine. (Courtesy WMW Machinery Co., automatic table cycling. The spindle Inc.) may be raised or lowered by a cam and template arrangement to produce spe- Acme thread. cial contours. The basically heavier Milling machines with construction allows more power to be vertical spindles (see Fig. supplied to the spindle, which gives 13.3a), are available in a higher productivity through faster large variety of types and metal removal. Duplex bed-type mill- sizes. The head, which ing machines have two columns and houses the spindle, motor, spindles for milling two surfaces on a and feed controls, is fully part simultaneously. A large 5-axis universal and can be placed CNC bed-type milling machine is at a compound angle to the shown in Figure 13.7. surface of the table. The The chief disadvantage of a bed-type ram, to which the head is milling machine compared to one of attached, can be moved for- the knee and column type is that it is ward and back and locked in less versatile for machining small FIGURE 13.6: Machining operation showing a bed- any position. A turret on top parts. Its advantages lie in its higher type milling machine with three heads (Courtesy: of the column allows the productivity, its adaptability to large Cincinnati Machine) head and ram assembly to sized machines, and its ease of modifi- swing laterally, increasing cation to special applications. that fits the top of the knee and a the reach of the head of the machine. circular slide above it is graduated in Some ram-type milling machines 13.2.3 Special Purpose degrees for a small portion of its pe- can be used for both vertical and hori- Milling Machines riphery. The upper portion of the zontal milling. On ram-type vertical As industrial products have become saddle consists of a circular face that mills that have the motor fits against the lower circular slide, a in the column, power is central pivot point, and a dovetail slide transmitted to the spindle that accepts the table.