Chapter I
1.1 Introduction
The ability of any nation to manufacture is essential but to deploy that ability in a certain nation is the trick as every nation defers from one another, so in order to enhance Arab nation ability to manufacture we will provide a better cheaper design for a CNC milling machine.
The Primary Objective of This Project is to present and develop a prototype for a substitution of the expensive hard to acquire machining facility for the Middle East industrial society; these machining facilities include the regular Turning, Drilling, Shaping, Milling, and Grinding Machines.
Our primary survey concluded that there always must be a turning machine beside a milling machine, but a milling machine (CNC milling machine) can include the rest of processes required within its operation to a good degree and the turning operation to an acceptable degree. So we chose the milling machine as our initial model to undergo our optimization plan. Therefore our Primary objective of choice is to Design a Basic Three Axis CNC milling machine. Also to manufacture a working Prototype for this machine fabricated all with nationally available components in order to minimize its cost but maintains an acceptable level of accuracy to suite a Computer Numerical Control Machine. Another Thing that we must point out is that in order to accomplish this project we need more than one trial to find the suitable combination of components and specs to pursue in order that this machine comes to light.
1.2 Proposed Approach
A new approach is needed that approach is based upon the 2010-2015 World Outlook for Computer Numerical Controls [1]. The results of that survey were mainly based upon word wide research includes Middle East and North Africa. These results showed that any machine tool required for the Egyptian industrial society could be one of the following: Turning, Drilling, Shaping, Milling, and Grinding. So the first step was to pick up the operation over which this thesis will focus on. Milling can include in its operation: Drilling, Shaping, and Grinding. And might contain Turning under certain conditions. So milling was chosen. And this result might be verified by the fact that 90% of the working machine tools in the field of traditional CNC machines are either Milling or Turning Centers.
Now we will compare different configuration of milling machines
Case 1: A Universal Milling Machine.
Case 2: A regular CNC Milling Machine.
Case 3: Gantry style CNC Milling Machine.
Case 1: A Universal Milling Machine
From Cost point of view: Cost is high because of the usage of large material to build the bulky parts of the machine tool might be as high as a CNC Milling Machine
From Design point of view: Design level might be considered low compared with the design required in both the regular CNC machine and our machine.
From Accuracy Point of view: Accuracy is very low compared to the other two cases but could be difficulty approached with the use of very skilled labor and with high cost.
Case 2: A regular CNC machine
From Cost Point of view: Cost is much higher because of the usage of both large material amounts with high machining grade as will as the cost of the motion control equipments.
From Design Point of view: Design is better than the first case for every part is designed to enhance the entire machining operation.
From Accuracy Point of view: Attained accuracy is very high due to perfect guide ways assisted by ball screws along with feed back control.
Case 3: A gantry CNC milling machine
From Cost Point of view: Cost is mush less than the later case and might be less that the first case as the entire machine is only build from a metal sheet and some Bars.
From Design Point of view: Design is much sophisticated than the first and the second case as the design is optimized to hold the predetermined forces as a light weight structure.
From Accuracy Point of view: Accuracy is for sure less than the second case but higher than the first case as there is no feedback control technique employed.
Discussion of results:
For case 1: Universal Milling Machine
- Our results don’t imply that the use of that machine is not appropriate but we only mean that each application requires a certain machine and also each goal.
- The cost is very high in EGYPT as almost all of them is imported but not made in EGYPT but there maintenance and overhauling is available domestically.
For Case 2: three axis CNC milling machine Vertical Column type.
- The usage of this type of machines in any workshop requires a great deal of money so most of the manufacturers comprises between money and accuracy.
- The cost is definitely much higher as there is almost no one building or even providing maintenance for these machines in EGYPT.
For Case 3: Gantry style CNC milling machine.
- The usage of this machine is aimed to workshops who would like to get both cheap machining with good accuracy.
- The cost is very low as of the innovative design of putting the entire axis moving over each other rather than independent from each other as in the regular design of any CNC machine
Chapter II
Literature Review
2.1 Milling Machine
Milling is the process of machining flat, curved, or irregular surfaces by feeding the work piece against a rotating cutter containing a number of cutting edges. The milling machine consists basically of a motor driven spindle, which mounts and revolves the milling cutter, and a reciprocating adjustable worktable, which mounts and feeds the work piece.
2.1.2 Milling Machine History
Unlike lathes, which have been known for thousands of years, milling machines are less than two hundred years old. Because they require much more power than hand-driven lathes, their introduction had to wait for the invention of industrial water and steam power. Also, all their mechanical components had to first be made available, such as accurately fitted slides, large castings to resist cutting forces, calibrated lead screws, and hardened steel cutting tools.
Eli Whitney is credited with inventing the first milling machine about 1818, but the knee-and-column support arrangement of the universal milling machine of Joseph A. Brown (later of Brown and Sharpe) dates from 1862 and marks an important step in the machine’s development. During the last half of the nineteenth Century, milling machines gradually replaced shapers and planers which have lathe-type, single-point tool bits that move over the work in a straight line and scrape off metal one stroke at a time. Milling machines, with their continuous cutting action, not only remove metal faster than shapers and planers, they perform additional operations like cutting helices for gears and twist drills. Today, milling machines greatly outnumber shaping and planning machines. Americans in New England and later the Midwest continuously added features leading to the modern milling machine.
Another important development came in the 1930s when Rudolph Bannow and Magnus Wahlstrom brought out the Bridgeport-style vertical milling machine. This design offers versatility and economy in place of the higher metal removal rates of traditional horizontal milling machines. Because of this versatility, there are more Bridgeport-style mills in existence today than any other milling machine design. Horizontal mills are now usually reserved for production applications where high metal removal rates on identical parts are needed, not prototyping and short runs. Bridgeport-style machines are also called knee-and-column machines and turret mills.
For production applications, there are large, expensive milling machines with three or more axes under computer control. Some machines perform all operations including automatic tool changing. However, today there is an intermediate step between a manual mill and a fully automated one. Adding a computer, digital readouts, and actuators to the X- and Y-axes of a Bridgeport-style mill does this. Not only can this enhanced machine tirelessly perform all its existing repetitive functions, it also has added new capabilities.
Now the mill can engrave (drive the tool to cut numbers and letters in various sizes and fonts), cut radii and angles without a rotary table, make islands, pockets, and cut ellipses, and frames. Entering the position, diameter and number of holes, automates cutting a bolt-hole pattern; the system does the math. The computer can automatically compensate for the reduced diameter of re sharp end milling cutters, saving time and money. The system can be manually programmed through its control panel, use stored programs, “learn” new tasks by memorizing a series of manual operations as the operator makes the first part, or accept files from CAD programs.
2.1.1 Type of MILLING MACHINES
Milling machine are classified on the base of the position of their spindle. The spindle operates in either a vertical or horizontal position or on base of construction. In a following section we represent the different type of milling machine.
Column Knee-type Milling Machine Fig 2 machines are characterized by a vertically adjustable worktable resting on a saddle which is supported by a knee. The knee is a massive casting that rides vertically on the milling machine column and can be clamped rigidly to have column in a position where the milling head and milling machine spindle are properly adjusted for operation. The plain vertical column knee type machines are characterized by a spindle located vertically, parallel to the column face, and mounted in a sliding head that can be fed up and down by hand or power. Modern vertical milling machines are designed so the entire head can also swivel to permit working on angular surfaces. The plain horizontal milling machine’s column contains the drive motor and gearing and a fixed position horizontal milling machine spindle. An adjustable overhead arm containing one or more arbor supports projects forward from the top of the column. The arm and arbor supports are used to stabilize long arbors. Supports can be moved along the overhead arm to support the arbor where support is desired depending on the position of the milling cutter or cutters.
UNIVERSAL MILLING MACHINE The basic difference between a universal milling machine and a plain column knee type milling machine is the addition of table swivel housing between the table and the saddle of the universal machine. This permits the table to swing up to 45° in either direction for angular and helical milling operations. The universal machine can be fitted with various attachments such as the indexing fixture, rotary table, slotting and rack cutting attachments, and various special fixtures.