MARKING SCHEME
EMMQ2016 Y4S1 B.ENG EEMQ 4145
QUESTION ONE (30 Marks)
a) i) Part Programming is the procedure of creating a series of coded numerical instructions
required to control machine tool. The coded instructions consist of letters, numbers and
symbols functionally arranged in form of blocks called G-and-M codes, 2 marks ✓.
ii) Geometric modeling is the mathematical representation of an object’s topological
(connectivity and associativity) and geometrical data (shape and dimensions) using CAD
software. CAD software allows the mathematical description of an object to be displayed
as an image on the screen of computer. 2 marks ✓.
b) The various difference between NC and CNC machine in tabular form are as follows: 6
marks ✓.
S.no NC Machine CNC Machine
1. Here NC stands for Numerical Control ½ ✓ CNC stands for Computer Numerical Control. ½ ✓
It is defined as the machine which is controlled by It is defined as the machine which is used to control
the set of instructions in the form of numbers, the motions of the workpiece and tool with the help
letters and symbols. The set of instructions is called of prepared program in computer. The program is
2. as program. ½ ✓ written in alphanumeric data. ½ ✓
In CNC machine the programs are fed directly into
In NC machine the programs are fed into the punch the computer by a small key board similar to our
3. cards. ½ ✓ traditional keyboard. ½ ✓
4. Modification in the program is difficult. ½ ✓ Modification in the program is very easy. ½ ✓
5. High skilled operator is required. ½ ✓ Less skilled operator is required. ½ ✓
6. Cost of the machine is less. ½ ✓ Cost of the CNC machine is high. ½ ✓
7. Maintenance cost is less½ ✓ Maintenance cost is high. ½ ✓
The programs in the NC machine cannot be stored. In CNC machines, the programs can be stored in the
8. ½✓ computer and can be used again and again. ✓
It offers less flexibility and computational capability. It offers additional flexibility and computational
9. ½✓ capability. ½ ✓
10. The accuracy is less as compared with the CNC. ½ ✓ It has high accuracy. ½ ✓
It requires more time for the execution of the job. ½ It takes very less time in the execution of the job. ½
11. ✓ ✓
12. It is not possible to run it continuously. ½ ✓ It can be run continuously for 24 hours of a day. ½ ✓
1
, c) Advantages of Using CNC Over Conventional Method of Manufacture:5 marks ✓.
➢ Reduced Labor Costs; One Experienced Machinist for Multiple Machines✓.
In the case of conventional machining, every machine needs a dedicated technician with
experience, skill, and extensive knowledge of the machine in hand. In contrast, CNC
machining is hugely controlled by a software program and requires very little human
interaction apart from the initial set up and data feeding. CNC machining also demands
less advanced training, further reducing the labor costs. With computers playing a major
role, the chances of human error and compromised workplace safety are also reduced by
a high percentage.
➢ Large Quantity; Highest Quality✓.
Because it requires manual effort, conventional machining is mostly set for low volume,
small-quantity projects. CNC machines, however, are built to provide maximum accuracy
whether they are tasked to produce a few dozen metal machined parts or thousands of
them.
Their high-quality material gives them resistance to wear and tear, which is common with
conventional machining. As a result, they can run 24 hours a day with timely but quick
maintenance. Additionally, CNC machining utilizes advanced software, which can be
updated regularly per specifications, to allow for the easy manufacture of super-complex
parts.
CNC machines also come with automated cooling systems, reducing the chances of heat
damage. Many advanced machine models come with built-in chip storage and a conveyor
belt for chip management.
➢ Part Replication is 100x better✓.
Built to control exact velocity and positioning, CNC machines can produce several
thousands of 100% identical parts in a record time, a feat that is impossible to achieve
with handheld or conventional machining. Machines can be programmed to apply the
same cut or do the same finishing repeatedly without compromising on the quality of the
machined part. Conventional machining, on the other hand, requires a skilled operator to
manually place the tool at every step of the machining process, which obviously would
take a lot of time and patience. And even with such dedication, variations are to be
expected.
➢ No Prototypes Necessary✓.
Prototypes are needed to simulate designs and map their feasibility. Before CNC, every
manufacturer would chalk out actionable prototypes, test-run them, and then work on the
machining process. When done manually, this whole routine usually took several days or
sometimes even months. The introduction of CNC machines ushered in software
programming wherein you could input your design and visually see if you could work
with it under realistic scenarios. This means no extra expenses for prototype
development, shorter production times, and a bare minimum labor cost.
➢ Ability to Develop Complex Parts✓.
CNC machines can be reprogrammed and updated at any time, giving them the liberty to
produce 3D, 4D or even 5D parts with ease. This allows for a smoother shift between
2
EMMQ2016 Y4S1 B.ENG EEMQ 4145
QUESTION ONE (30 Marks)
a) i) Part Programming is the procedure of creating a series of coded numerical instructions
required to control machine tool. The coded instructions consist of letters, numbers and
symbols functionally arranged in form of blocks called G-and-M codes, 2 marks ✓.
ii) Geometric modeling is the mathematical representation of an object’s topological
(connectivity and associativity) and geometrical data (shape and dimensions) using CAD
software. CAD software allows the mathematical description of an object to be displayed
as an image on the screen of computer. 2 marks ✓.
b) The various difference between NC and CNC machine in tabular form are as follows: 6
marks ✓.
S.no NC Machine CNC Machine
1. Here NC stands for Numerical Control ½ ✓ CNC stands for Computer Numerical Control. ½ ✓
It is defined as the machine which is controlled by It is defined as the machine which is used to control
the set of instructions in the form of numbers, the motions of the workpiece and tool with the help
letters and symbols. The set of instructions is called of prepared program in computer. The program is
2. as program. ½ ✓ written in alphanumeric data. ½ ✓
In CNC machine the programs are fed directly into
In NC machine the programs are fed into the punch the computer by a small key board similar to our
3. cards. ½ ✓ traditional keyboard. ½ ✓
4. Modification in the program is difficult. ½ ✓ Modification in the program is very easy. ½ ✓
5. High skilled operator is required. ½ ✓ Less skilled operator is required. ½ ✓
6. Cost of the machine is less. ½ ✓ Cost of the CNC machine is high. ½ ✓
7. Maintenance cost is less½ ✓ Maintenance cost is high. ½ ✓
The programs in the NC machine cannot be stored. In CNC machines, the programs can be stored in the
8. ½✓ computer and can be used again and again. ✓
It offers less flexibility and computational capability. It offers additional flexibility and computational
9. ½✓ capability. ½ ✓
10. The accuracy is less as compared with the CNC. ½ ✓ It has high accuracy. ½ ✓
It requires more time for the execution of the job. ½ It takes very less time in the execution of the job. ½
11. ✓ ✓
12. It is not possible to run it continuously. ½ ✓ It can be run continuously for 24 hours of a day. ½ ✓
1
, c) Advantages of Using CNC Over Conventional Method of Manufacture:5 marks ✓.
➢ Reduced Labor Costs; One Experienced Machinist for Multiple Machines✓.
In the case of conventional machining, every machine needs a dedicated technician with
experience, skill, and extensive knowledge of the machine in hand. In contrast, CNC
machining is hugely controlled by a software program and requires very little human
interaction apart from the initial set up and data feeding. CNC machining also demands
less advanced training, further reducing the labor costs. With computers playing a major
role, the chances of human error and compromised workplace safety are also reduced by
a high percentage.
➢ Large Quantity; Highest Quality✓.
Because it requires manual effort, conventional machining is mostly set for low volume,
small-quantity projects. CNC machines, however, are built to provide maximum accuracy
whether they are tasked to produce a few dozen metal machined parts or thousands of
them.
Their high-quality material gives them resistance to wear and tear, which is common with
conventional machining. As a result, they can run 24 hours a day with timely but quick
maintenance. Additionally, CNC machining utilizes advanced software, which can be
updated regularly per specifications, to allow for the easy manufacture of super-complex
parts.
CNC machines also come with automated cooling systems, reducing the chances of heat
damage. Many advanced machine models come with built-in chip storage and a conveyor
belt for chip management.
➢ Part Replication is 100x better✓.
Built to control exact velocity and positioning, CNC machines can produce several
thousands of 100% identical parts in a record time, a feat that is impossible to achieve
with handheld or conventional machining. Machines can be programmed to apply the
same cut or do the same finishing repeatedly without compromising on the quality of the
machined part. Conventional machining, on the other hand, requires a skilled operator to
manually place the tool at every step of the machining process, which obviously would
take a lot of time and patience. And even with such dedication, variations are to be
expected.
➢ No Prototypes Necessary✓.
Prototypes are needed to simulate designs and map their feasibility. Before CNC, every
manufacturer would chalk out actionable prototypes, test-run them, and then work on the
machining process. When done manually, this whole routine usually took several days or
sometimes even months. The introduction of CNC machines ushered in software
programming wherein you could input your design and visually see if you could work
with it under realistic scenarios. This means no extra expenses for prototype
development, shorter production times, and a bare minimum labor cost.
➢ Ability to Develop Complex Parts✓.
CNC machines can be reprogrammed and updated at any time, giving them the liberty to
produce 3D, 4D or even 5D parts with ease. This allows for a smoother shift between
2
