mid-term examination september, 2016 - …...operation or cause premature wearing, either of which...

RAMAKANT RANA http://www.ramakantrana.com/CIM/

(Asst. Prof.) 1st Sessional Paper (Sep. 2016)

http://www.RamaKantRana.com/CIM/

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(Write your Roll No. immediately) Roll No.: __________________

Mid-Term Examination September, 2016

7th Semester [B.Tech (MAE)] Subject: Computer Integrated Manufacturing Paper Code: ETME-403

Time: 1 hour 30 min. Max Marks: 30

NOTE: 1. Attempt three questions in total 2. Q. No. 1 is compulsory. Attempt any two more questions from remaining three questions.

Q 1. Answer the following questions:

i. Explain ANY TWO of the following: (4) i. ATC along with its advantages ii. Ball screw mechanism. iii. Work Holding Devices iv. Machining Centre

ii. What are Constructional features of CNC machines? (2) iii. Explain ISO Specification Of Cutting Tools. (2) iv. Explain the following codes: (2)

i. G01 ii. G03 iii. G90 iv. G91

Q 2. Write the program using G-Codes and M-Codes for CNC Turning (you are not allowed to use canned cycle commands for this program, and step size should not be more than 1.5mm): (10)

Q 3.

i. Classify the Cutting Tools on the basis of following: (6) i. Setting up of Tool, ii. Tool Construction and iii. Cutting Tool Material

ii. Discuss the following: (4) i. Personal / Distributed Network and ii. Local Area Network

Q 4. i. What is program Zero Point and also explain Axes Designation for CNC Turning and

Milling part programming. (5) ii. Explain Canned Cycles of CNC Part-Programming with example(s). (5)

http://www.ramakantrana.com/CIM/





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Q1. i.i

Figure 1: ATC

An Automatic Tool Changer (ATC) is used in Computerized Numerical Control (CNC) machine

tools to improve the production and tool carrying capacity of the machine. ATC changes the tool very quickly, reducing the non-productive time. Generally, it is used to improve the capacity of the machine to work with a numbers of tools. It is also used to change worn out or broken tools. It is one more step towards complete automation (Figure 1: ATC).

The tool change activity requires the following motions: a. The spindle stops at the correct orientation for the tool change arm to pick the tool

from the spindle. b. Tool change arm moves to the spindle. c. Tool change arm picks the tool from the spindle. d. Tool change arm indexes to reach the tool magazine. e. Tool magazine indexes so that the tool from the spindle can be placed. f. The tool is placed in the tool magazine. g. The tool magazine indexes to bring the required tool to the tool change position. h. Tool change arm picks the tool from the tool magazine. i. Tool change arm indexes to reach the spindle. j. New tool is placed in the spindle. k. Tool change arm moves back to its parking position.

----(1 marks)

Advantages of automatic tool changer

Increase in operator safety by changing tools automatically Changes the tools in seconds for maintenance and repair Increases flexibility Heavy and large multi-tools can easily be handled Decreases total production time

----(+1 marks) VIDEO Help:

https://www.youtube.com/watch?v=rrxHBsPyUj4



https://en.wikipedia.org/wiki/CNC

https://en.wikipedia.org/wiki/Machine_tools

https://en.wikipedia.org/wiki/Machine_tools

https://www.youtube.com/watch?v=rrxHBsPyUj4




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Q1 i.ii Ball Screw

Ball screw is also called as Ball Bearing Screw or Recirculating Ball Screw. It consists of a screw spindle, a nut, balls and integrated ball return mechanism a shown in Figure 2. The flanged nut is attached to the moving part of CNC machine tool. As the screw rotates, the nut translates the moving part along the guide ways. However, since the groove in the ball screw is helical, its steel balls roll along the helical groove, and, then, they may go out of the ball nut unless they are arrested at a certain spot. Thus, it is necessary to change their path after they have reached a certain spot by guiding them, one after another, back to their “starting point” (formation of a recirculation path). The recirculation parts play that role. When the screw shaft is rotating, as shown in Figure 2, a steel ball at point (A) travels 3 turns of screw groove, rolling along the grooves of the screw shaft and the ball nut, and eventually reaches point (B). Then, the ball is forced to change its pathway at the tip of the tube, passing back through the tube, until it finally returns to point (A). Whenever the nut strokes on the screw shaft, the balls repeat the same recirculation inside the return tube.

---(2 Marks)

Figure 2: Ball Screw

When debris or foreign matter enter the inside of the nut, it could affect smoothness in operation or cause premature wearing, either of which could adversely affect the ball screw's functions. To prevent such things from occurring, seals are provided to keep contaminants out. There are various types of seals viz. plastic seal or brush type of seal used in ball-screw drives.

Advantages of ball screws

1) Highly efficient and reliable. 2) Less starting torque. 3) Lower co efficient of friction compared to sliding type screws and run at cooler

temperatures






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4) Power transmission efficiency is very high and is of the order of 95 %. 5) Could be easily preloaded to eliminate backlash. 6) The friction force is virtually independent of the travel velocity and the friction at rest

is very small; consequently, the stick-slip phenomenon is practically absent, ensuring uniformity of motion.

7) Has longer thread life hence need to be replaced less frequently. 8) Ball screws are well -suited to high through output, high speed applications or those

with continuous or long cycle times. 9) Smooth movement over full range of travel.

Disadvantages of ball screws

1) Tend to vibrate. 2) Require periodic overhauling to maintain their efficiency. 3) Inclusion of dirt or foreign particles reduces the life of the screws. 4) Not as stiff as other power screws, thus deflection and critical speed can cause

difficulties. 5) They are not self-locking screws hence cannot be used in holding devices such as vices. 6) Require high levels of lubrication.

VIDEO Help: https://www.youtube.com/watch?v=kl6qNn9-nkk

Q1 i.iii Work Holding Devices for CNC Machines

In the CNC machines, fixtures are still required to locate and hold the work pieces while machining. The work holding devices should have the following uniqueness:

a. Work holding devices must have required accuracy and must have matching

reference surfaces with the reference system. b. Work holding devices are allowed to perform a number of operations on different

faces in a single setting. c. Work holding devices must enable quick loading and unloading. d. Work holding devices must be fool-proofing to avoid incorrect loading of the job. e. Work holding devices must be sufficient rigidity to fully withstand the cutting forces. f. Work holding devices must be safe in use and loading and unloading. g. Work holding devices must have a sufficient of clamping force for use of full roughing

cuts. h. Work holding devices must be simple in construction maximum as possible.

Automatic pallet change over systems are used in modern CNC machines. These pallets

simply move for interchanging their positions on the machine table. While machining is being done on a job kept on one pallet, the other pallets are accessible to the operator for clamping and unclamping raw material or finished product. This saves a lot of material handling and set up time, resulting in higher productivity.



https://www.youtube.com/watch?v=kl6qNn9-nkk




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Figure 3: Work holding devices

VIDEO Help: https://www.youtube.com/watch?v=qots_2j_8gk

Q1 i.iv CNC MACHINING CENTERS

The machining centre, developed in the late 50’s is a machine tool capable of multiple

machining operations on a work part in one setup under NC program control.

Classification

Machining centres are classified as vertical, horizontal, or universal. The designation refers

to the orientation of the machine spindle.

1. A Vertical Machining Centre has its spindle on a vertical axis relative to the work table. A vertical machining centre (VMC) is typically used for flat work that requires tool access from top. E.g. mould and die cavities, Large components of aircraft

2. A Horizontal Machining Centre (HMC) is used for cube shaped parts where tool access can be best achieved on the sides of the cube.

3. A universal machining centre (UMC) has a work head that swivels its spindle axis to any angle between horizontal and vertical making this a very flexible machine tool. E.g.: Aerofoil shapes, curvilinear geometries.



https://www.youtube.com/watch?v=qots_2j_8gk




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Figure 4 (a):Vertical Machining

Centre Figure 4 (b): Horizontal Machining Centre

Figure 4 (c): 5-Axis CNC Vertical machining Centre

VIDEO Help: https://www.youtube.com/watch?v=yf7ucg-w5MQ



https://www.youtube.com/watch?v=yf7ucg-w5MQ




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Q1 ii

Constructional details of CNC machines

In general, a CNC machine tool consists of the following units: 1. Computers 2. Control System 3. Drive Motors 4. Tool Changers

According to the construction of CNC machine tools, it works in the following (simplified) manner:- 1. The CNC machine controlled by the computer reads the program and translates it into

machine language, which is a programming language of binary notation used on computers, not on CNC machines.

2. When the operator starts the execution cycle, the computer translates the binary codes into electronic pulses which are automatically sent to the machine’s power units. The control unit compares the number of pulses sent and received.

3. When the motor receives each pulse, they automatically transform the pulses into rotations that drive the spindle and lead screw, causing the spindle to rotate and slide or move the table. The part on the milling machine table or the tool in the lathe turret is driven to a position specified by the program.

Briefly explain Computers, Control System, Drive Motors & Tool Changers.

VIDEO Help: https://www.youtube.com/watch?v=ejQ84POvJaM

---(2 Marks)



https://www.youtube.com/watch?v=ejQ84POvJaM




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Q1 iii

---(2 Marks)

Q1 iv

G01 Rapid positioning G03 Circular interpolation, counter clockwise G90 Absolute programming G91 Incremental programming

---(2 Marks)

VIDEO Help: https://www.youtube.com/watch?v=AKhKPc-_ywE&list=PLgxljY6GqukhpyC9iBMQ4A1GmlzThFvcz

G00 & G01 In Hindi https://www.youtube.com/watch?v=8lDx9WcPz24



https://www.youtube.com/watch?v=AKhKPc-_ywE&list=PLgxljY6GqukhpyC9iBMQ4A1GmlzThFvcz

https://www.youtube.com/watch?v=AKhKPc-_ywE&list=PLgxljY6GqukhpyC9iBMQ4A1GmlzThFvcz

https://www.youtube.com/watch?v=8lDx9WcPz24




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Q2

Starting of the program --- (2 Marks)

Facing and Turning --- (+2 Marks)

Tapering --- (+2 Marks)

Step Turning --- (+2 Marks)

Ending of programme using M-Codes --- (+2 Marks)

Q3 i (i.i, i.ii, i.iii) Cutting tools are available in three basic material types: high-speed steel, tungsten

carbide, and ceramic. High-speed steel is generally used on aluminum and other nonferrous alloys, while tungsten carbide is used on high-silicon aluminum, steels, stainless steels, and exotic metals. Ceramic inserts are used on hard steels and exotic metals. Inserted carbide tooling is becoming the preferred tooling for many CNC applications. For the full utilization of CNC machines it is essential to pay due attention to the selection and usage of tooling, namely tool holders, cutting tools and work holding devices. The tools for CNC machines must be quickly changeable to reduce non-cutting time, preset and reset outside the machine, high degree of interchangeability, increased reliability and high rigidity.

The cutting tools can be classified on the basis of setting up of tool, tool construction and cutting tool material:

On the Basis of Setting up of Cutting Tool a. Preset tools. b. Qualified tools. c. Semi qualified tools.

--- (2 Marks)

On the Basis of Cutting Tool Construction

a. Solid tools. b. Brazed tools. c. Inserted bit tools.

--- (+2 Marks)

On the Basis of Cutting Tool Material a. High speed steel (HSS). b. High carbon tool steel (HCS). c. Cast alloy. d. Cemented carbide. e. Ceramics. f. Boraon Nitride. g. Diamond. h. Sialon.

--- (+2 Marks)






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Q3 ii.i

Distributed Networking is a distributed computing network system, said to be

"distributed" when the computer programming and the data to be worked on are spread out over more than one computer. Usually, this is implemented over a network. Prior to the emergence of low-cost desktop computer power, computing was generally centralized to one computer. Although such centers still exist, distribution networking applications and data operate more efficiently over a mix of desktop workstations, local area network servers, regional servers, Web servers, and other servers. One popular trend is client/server computing. This is the principle that a client computer can provide certain capabilities for a user and request others from other computers that provide services for the clients. (The Web's Hypertext Transfer Protocol is an example of this idea.) Enterprises that have grown in scale over the years and those that are continuing to grow are finding it extremely challenging to manage their distributed network in the traditional client/server computing model. The recent developments in the field of cloud computing has opened up new possibilities. Cloud-based networking vendors have started to sprout offering solutions for enterprise distributed networking needs. Whether it turns out to revolutionize the distributed networking space or turns out to be another craze remains to be seen.

--- (2 Marks)

Q3 ii.ii A Local Area Network (LAN) is a computer network that interconnects computers within

a limited area such as a residence, school, laboratory, university campus or office building and has its network equipment and interconnects locally managed. By contrast, a wide area network (WAN), not only covers a larger geographic distance, but also generally involves leased telecommunication circuits or Internet links.

Figure 5: Local Area Network (LAN)

--- (+2 Marks)

Q4 i Selection of Zero Point

In order to define certain points on a workpiece in this manner, you will first have to decide where to put the coordinate system on the workpiece, especially where to place the zero point.






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For milling, the zero point (or reference point) of all dimensions may be placed anywhere on the workpiece. Let's call this zero point 'workpiece zero' (WZ) or workpiece datum. To save trouble of unnecessary calculations it is advisable to place workpiece zero at that point on a part drawing on which most of the dimensions are based. See Figure 6 & 7. A workpiece datum maybe defined as a point, line or surface from which dimensions are referenced. It major may not be within the workpiece area. The symbol used to denote workpiece zero is:

Figure 6: Example of Zero Point Options on Workpiece

Figure 7: Examples of Component with Zero Point in Workpiece Centre

For turning operations the X axis zero is normally positioned on the centreline of the spindle

axis. The Z axis zero can be positioned on the front face of the workpiece or on the face of the workpiece or on the face of the chuck. See Figure 8.

Figure 8: X0 Z0 Positions for Turning Operations

---(2 Marks)

Machine Axes

The primary axes of a machine are designated as X, Y, Z and can have positive or negative values.






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The Z-axis is always parallel to the main spindle of the machine (see Figure 9). It does

not matter whether the spindle carries the workpiece or the tooling, therefore the Z-axis can be either vertical or horizontal. On milling, boring and drilling machines the spindle is the tool rotating means while on cylindrical grinders and lathes the spindle is the work rotating means. Positive Z-movement always increases the distance between the work and the tool. The X-axis of motion is horizontal and parallel to the work-holding surface. If Z is horizontal, positive X is to the right looking from the spindle towards the workpiece. If Z is vertical, when looking from the spindle towards its supporting column, positive X is to the right.

The Y-axis of motion is perpendicular to both the X and Z axes. Positive Y is in the direction which would make a right-handed set of coordinates.

CNC lathes only have two major axes X and Z. There is no Y-axis.

Figure 9 (a): X, Y, Z Axes for VMC Figure 9 (b): X, Y, Z Axes for HMC

Figure 9 (c): X, Y, Z Axes for Turning Centre

---(+3 Marks)






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Q4 ii

A Canned Cycle is a way of conveniently performing repetitive CNC machine operations. Canned cycles automate certain machining functions such as drilling, boring, tapping, pocketing, etc... Canned cycles are so called because they allow a concise way to program a machine to produce a feature of a part. A canned cycle is also known as a fixed cycle. A canned cycle is usually permanently stored as a pre-program in the machine's controller and cannot be altered by the user.

Advantages

a. The conciseness of canned cycles allows for quicker and easier development of programs at the machine.

b. As canned cycles reduce the number of blocks in a program, the storage space occupied by the program is less and the programmer escapes the tedium of writing the same instructions again and again. This reduces the potential for errors, and locating any errors that do exist is easier in a shorter program.

c. Job setup is also facilitated by canned cycles. Some canned cycles exist which are designed for use by machine tool operators for simple job set-up and measuring tasks.

---(2 Marks)

Examples of Canned Cycles

G73 High speed peck drilling cycle

G74 Left-hand tapping cycle

G76 Precision boring cycle

G80 Cancel any fixed cycle

G81 Drilling cycle

G82 Drilling cycle with dwell

G83 Peck drilling cycle

G84 Right-hand tapping cycle

G85 Boring cycle

G86 Boring cycle

G87 Back boring cycle

G88 Boring cycle

G89 Boring cycle

---(+1 Marks) Explanation of any one of the above code

---(+2 Marks)



mid-term examination september, 2016 - …...operation or cause premature wearing, either of which...

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