Notes about a certain topic, Study notes of Principles of Machine Tool Design

Download Notes about a certain topic and more Study notes Principles of Machine Tool Design in PDF only on Docsity! Introduction The drilling machine or drill press is essential in any metal-working shop. Fundamentally, a drilling machine consists of a spindle (which turns the drill and which can be advanced into the work, either automatically or by hand) and the work table which holds the workpiece rigidly in position as the hole is drilled. A drilling machine is used primarily to produce holes in metal; however, operations such as tapping, reaming, counterboring, countersinking, and spot facing can also be performed. err Ny, ih? 2. Column The column is an accurate cylindrical post which fits into the base. The table, which is fitted to the column, may be adjusted to any point between the base and head. The drill press head is mounted near the top of the column. ' TABLE CLAMP 3. Table The table, either round or rectangular in NN shape, is used to support the workpiece to be machined. The table, whose surface is at 90° to the column, may be raised, lowered, and swiveled around the column. Slots are provided in most tables to allow jigs, fixtures, or large workpieces to be clamped directly to the table. COLUMN “mage M 4. Drilling Head The head, mounted close to the top of the column. Contains the mechanism which is used to revolve, contains the mechanism which is used to revolve the cutting tool and advance into the workpiece. The spindle, which is a round shaft that holds and drives the cutting tool, is house in the spindle veptn stop sleeve or quill. The end of the spindle may have a SPINDLE tapered hole to hold taper shank tools, or may be SLEEVE threaded or tapered for attaching a drill chuck. nee ~ DRILLING HEAD HAND FEED LEVER The hand feed lever is used to control the vertical movement of the spindle sleeve and the cutting tool. A depth stop, attached to the spindle sleeve, can be set to control the depth that a cutting tool enters the workpiece. 2. Upright Drilling Machine The standard upright drilling machine is similar to the sensitive type drill except that it is larger and heavier. The basic differences are: It is equipped with gear box to provide a greater variety of speeds. The spindle may be advanced manually by a hand lever or hand wheel and automatically by the feed mechanism. The table may be raised or lowered by means of a table raising mechanism. Some models are equipped with reservoir in the base for the storage of the coolant. BAG 3 5. Multi-spindle Drilling Machine In the Multi-spindle drilling machine, there are many spindles mounted on one head to allow many holes to be drilled simultaneously. 6. Numerical control drilling machine can automatically change tooling with a turret or_automatic tool changer. Speeds, feeds, and table position is controlled using a computer program. Standard Drilling Operations Drilling machines may be used for performing a variety of operations besides drilling a round hole. A few of the more standard operations, and work setups will be briefly discussed. 1. Reaming Is the operation of sizing and producing a smooth round hole from a previously drilled or bored hole with the use of a cutting tool having several cutting edges. 2. Tapping Is the operation of cutting internal threads in a hole with a cutting tool called a tap. Special machines or gun taps are used with a tapping attachments when 1. Reaming 2. Tapping this operation is performed by power in a machine. 3. Counterboring Is the operation of enlarging the top of a previously drilled hole to a given depth to provide a square shoulder for the head of a bold or a cap screw. 3. Counterboring 2 4. Countersinking Is the operation of producing a tapered or cone-shaped enlargement to the end of a hole. 4. Countersinking Common Types of Drill Chucks. * Key Type Drill Chucks. Are the most common. They have three jaws that move in or out simultaneously when the outer sleeve is turned. The drill is placed in the chuck and the outer sleeve turned by hand until the jaws are snug on the drill shank. The sleeve is then tightened with the key causing the drill to be held securely and accurately. * Keyless Drill Chucks. Are used more in production work since the chuck may be loosened or tightened without a key. It is designed to hold small drills accurately. The drill is gripped or released quickly and easily by means of a hand. 2. Drill Sleeves Are used to adapt the cutting tool shank to the machine spindle if the taper on the cutting tool is smaller than the tapered hole in the spindle. 3. Drill Socket A drill socket is used when the hole in the spindle of the drill press is too small for the taper shank of the drill. The drill is first mounted in the socket and then the socket is inserted into the drill press spindle. Drill socket may also be used as extension socket to provide extra length Twist Drills Twist drills are end cutting tools used to produce holes in most types of material. On standard drill two helical grooves, or flutes, are cut lengthwise around the body of the drill. They provide cutting edges and space for the cutting to escape in the drilling process. Since drills are one of the most efficient cutting tools it is necessary to know the main parts, the correct speeds for drilling various materials in order to use them most efficiently. err: We WA, SV 7 1 Z IRL SO A A LEE. LELLELELL EF 13PC TITANIUM HEX SHANK DRILL BITS SET 2 “mage EN 2. Body The body is the portion of the drill between the shank and the point. It consist of a number of parts important to the efficiency of the cutting action. e Flutes Fliargin wiath) The flutes are two or helical grooves cut around the body of the drill. They form the cutting edges, admit cutting fluid, and allow chips to escape from the hole. Depth of body clearance Margin Body clearance Flute Profile ="S, Flute width \ ze, Chisel edge ange /\ 7 WY ° Margin LY The margin is the narrow, raised section Land width on the body of a drill. It is immediately next to the flutes and extends along the entire length of the flutes. Its purpose is to provide a full size to the drill body and cutting edges. e Body Clearance The body clearance is the undercut portion of the body between the margin and the flutes. It is made smaller to reduce friction between the drill and the hole during the drilling operation. e Web The web is the thin partition in the center of the drill which extends the full length of the flutes. This part forms the chisel edge at the cutting end of the drill. The web gradually increases in thickness to ward the shank to give the drill strength. “mage in? 3. Point The point of a twist drill consist of the chisel edge, lips, lip clearance, and heel. e Chisel Edge The chisel edge is the chisel shaped portion of the drill point. lip clearance cutting edge or lip e Cutting Lips The cutting lip of the drill is the part of the point that actually cuts away the material when a hole is drilled. It is ordinary as sharp as the edge of a knife. There is a cutting lip for each flute of the drill. cutting edge or lip chisel edge heel * Lip Clearance The lip clearance is the relief which is ground on the point of the drill extending from the cutting lips back to the heel. The average cutting lip clearance is from 8 to 12°, depending upon the hardness or softness of the material to be drilled. Cutting Speeds and Feeds The most important factors which the operator must consider when selecting the proper speeds and feeds are the diameter and material of the cutting tool, and the type of material being cut. The factors will determine what speeds and feeds should be used and therefore will affect the amount of time it takes to perform the operation. Production time will be wasted if the speed and/or feed are set too low, while the cutting tool will show premature wear if the speed and/or feed are set too high. The ideal speed and feed for any job is where the combination of the best production rate and the best tool life is attained. oo! Rotation err: (RPM) Twist crilt Workpiece Velocity Approaches "Zero" at Center Point a? Coty Mage Cutting Speeds The speed of a twist is generally referred to as cutting speed, surface speed, or peripheral speed. It is the distance that a point on the circumference of a drill will travel in 1 minute. A wide range of drills and drill sizes is used to cut various metals; an equally wide range of speeds is required for the drill to cut efficiently. For every job, there is the problem of choosing the drill speed which will result in the best production rates and the least amount of downtime for drilling various types of materials. The Most economical drilling speed depends upon many variables such as: The type and hardness of the material The diameter and the material of the drill The depth of the hole The type and condition of the drill press The efficiency of the cutting fluid employed the accuracy and quality of the hole required The rigidity of the work setup NAY RYNP “mage ME Revolutions per minute (rpm) The number of revolutions of the drill necessary to attain the proper cutting speed for the metal being machined is called the revolutions per minute (rpm). A small drill operating at the same rpm as a larger drill will travel fewer feet per minute; it naturally would cut more efficiently at a higher number of rpm. To determine the correct number of rpm of a drill press spindle for a given size drill, the following should be known. 1. The type of material to be drilled 2. The recommended cutting speed of the material 3. The type of material from which the drill is made. Formula: Cutting speed cs rpm = —_ Drillcircumference 1D Table: Drill Feeds Drill Size Inches millimeter 1/8 and smaller 3 and smaller 1/8 to% 3to6 ” tor 6 to 13 % tol 13 to 25 1to1% 25 to 38 Feed per Revolution inches millimeter 0.001 to 0.002 0.02 to 0.05 0.002 to 0.004 0.05 to 0.10 0.004 to 0.007 0.10 to 0.18 0.007 to 0.015 0.18 to 0.38 0.015 to 0.025 0.38 to 0.63 “mage “mage The total time needed to drill and finish a hole. Every production needs a time frame to finish a certain job in order to meet deadlines. Thus, processing time will eventually help planners to manage their operations with efficiency and maximum operations output. Processing Time for Drilling Formula: travel speed . L . T= Feed speed rpm “Y= Fsqyrpmy Y Where: T =processing time L_ =total drilling distance f = feed rpm = revolutions per minute Fs =feed speed i = no. of holes “mage Problems Set 1: ale 1. Ifa machinist wanted to drill a % inch hole in a piece of machine steel using a high speed steel drill. At what speed in revolutions per minute should he operate the drill press? 2. Find the revolutions per minute of an 8 mm drill if it is used to cut and aluminum workpiece using a high carbon steel drill. 3. The rpm setting of the drill press is set to 600 rpm. What is the maximum diameter in inches of a high speed drill if it is used to drill a tool steel material? 4. A drill press has the following rpm settings; 350, 600, 1100, & 1600. What rpm setting must be used if a 15 mm high speed steel drill is used to cut brass workpiece? 5. A machine operator drills a hole of a 3/8 inch diameter to a stainless steel using a carbon steel drill. He sets the drill press rpm setting to 900 rpm. Is the he operating at correct setting? If not, then what must be the correct rpm setting considering that the machine has the following rpm settings of 300, 600, 900, 1200, and 1800?