DESIGN ASPECT OF ABRASIVE CUTTING MACHINE
DESIGN
Design is undoubtedly a creative
process, engineer with a ‘flair’ for design is as a rule a man with a logical
decision making ability by which he explores all possible solutions to a given
problem and arrives at an optimum after carefully analyzing all the
alternatives.
Until a decade, any design which was
technically feasible is capable of being manufactured, would generally go
through to production irrespective of the time or cost involved. However, the
need to find practically new design solutions to keep ensuring higher
productivity has in recent times greatly increased the expenditure on design.
Design is progressively becoming a team activity as optimum solutions can be
found only by considering a large number of factors of diverse nature with
which the designer may not always be well conversant.
The block diagram shows how design
is related to different engineering, economic, natural, and social sciences.
In view of the heavy
responsibilities on the designer and the large expenditure involved in
designing a new machine. It is necessary to streamline the design process so
that a sound design solutions is achieved with minimum expenditure.
The design process for designing a
new machine tool as follows:
- Requirement (Goal)
- Precise definition of requirement after modification, expansion
- Technical specification
- Development of proper kinematic solution and selection of proper layout
- Design calculations for various units of machine tool.
- Design of components and parts
- Part and assembly drawings
- Technical specifications
- Prototype fabrication and testing
- Production and marketing
The design process is carried out in three important stages
- Design proposal
- Preliminary design
- Detailed design
At
the end of each stage, the design must be subjected to a critical feasibility
analysis and a technical report prepared and submitted to the customer. The
steps involved in the design process will be elaborated as follows.
a)
Requirement
The
customer outlines the requirement by furnishing information about the parts for
machining of which he wants the machine tool to be designed. The information
should include the nomenclature of parts and their annual output, the
dimensions and shapes of surfaces to be machined, materials of the parts,
machining tolerances, and the quality of surface finish required. This
information serves as the basis of for selecting appropriate machining methods
and cutting tools.
The
customer, owing to his lack of specialist knowledge, may often not be in a
position to define his need exactly. The designer must first of all check that
the requirement of a new design is genuine and a suitable product does not
already exist. A consideration in undertaking a new design, in the presence of
available solutions, may be the need to make the product economically viable by
reducing its cost. The designer must, therefore, make a preliminary assessment
of the requirement to see whether it is economically feasible. If necessary, he
may, in consolation with the customer, modify or expand the requirement to
increase the market potential of the designed machine tool.
b)
Technical specification
The
technical specification is a listing of parameters that are essential for the
design. The information furnished by the customer about the parts forms the
basis of determining important machine tool specifications. In general, the
designer should frame the specifications in a manner that does not
unnecessarily narrow the range of possible solutions. It should be remembered
that incorrect specifications are one of the major sources of over design and
redundant features in the finished product.
c)
Selection of proper kinematic solution and layout
After
technical specifications have been laid down, the designer explores the
combinations of relative motions that can ensure machining of surfaces of
required shapes and dimensions. The different possibilities are evaluated and
those found technically feasible are selected. Kinematic solution on the basis
motion combination are now developed. All these solutions are analyzed for
their technical feasibility and infeasible solutions are screened. A kinematic
solution correlates the motion of the workpiece and cutting tool and can be
realized in a number of layouts of major machine tool units. A technical
feasibility analysis, keeping in mind the constrains of the requirement and
technical specifications, is again carried out to select the best possible
layout.
d)
Design calculations
Design
calculations cover the design of the major units of the machine tools. These
calculations are done in accordance with design procedures only for those
versions that are found most suitable on the basis of the preceeding analysis.
The final version is selected comparing the economic feasibility of implementation
of alternatives.
e)
Drawings of components and assemblies
These
drawings are made for the version that finally selected. The drawings must be
complete with dimensions, tolerances and manufacturing specifications
(including the manufacturing method to be employed). Special care should be
taken during the stages of design, calculations and detailed drawings to make
use of standard components and assemblies as far as possible.
It
should be appreciated that design is essentially an iterative process. The
feedback that is received after prototype fabrication and testing, and
particularly after marketing the product must be carefully analyzed to make
appropriate changes in technical specifications and subsequent design. In the
design process itself, the designer should adopt a flexible attitude and be
prepared to make modifications in the technical specifications and even the
requirement.
GENERAL CONSIDERATIONS IN DESIGN OF ABRASIVE CUT OFF MACHINE
Following are the general
considerations in designing “Abrasive cut off machine” and its components.
1.
Type of load and stresses caused by the load:
The
load, on a machine component, may act in several ways due to which the internal
stresses are set up. In our project, radial load acts on the bearings.
2.
Motion of the parts of kinematics of the machine:
The
successful operation of any machine depends largely upon the simplest
arrangement of the parts which will give the motion required.
In our project, motion required is
rotary motion to abrasive cut off wheel. 1 H. P. single phase motor is used as
elector drive for providing rotary motion to a cut off wheel shaft by means of
v belt and pulley.
3.
Selection of materials:
It
is essential that a designer should have a through knowledge of the properties
of the materials and their behaviour under working conditions. Some of the
important characteristics of materials are strength, durability, flexibility,
weight, resistance to heat and corrosion, ability to cast, welded or hardened,
machinability, electrical conductivity etc.
C-20
and C-45 is selected as material for machine components.
4.
Form and size of the parts:
The
form size are based on judgement. The smallest practicable cross – section may
be used, but it may be checked that the stresses induced in the designed cross
– section are reasonably safe. In order to design any machine part for form and
size, it is necessary to know the forces which the part must sustain.
5.
Frictional resistance and lubrication
There
is always a loss of power due to frictional resistance and it should be noted
that the friction of starting is higher than that of running friction. A
careful attention must be given to the matter of lubrication of all surfaces
which move in contact with others, whether in rotating or ball bearings.
6.
Convenient and economical features:
In
designing, the operating features of the machine should be carefully studied.
If parts are to be changed on account of wear or breakage, easy access should
be provided and the necessity of removing other parts to accomplish, this
should be avoided if possible.
7.
Use of standard parts:
The
use of standard parts of closely related to cost. These part should be used
whenever possible.
8.
Safety of operation:
Machine
is dangerous to operate. Any moving part of machine which is within the zone of
a worker is considered an accident hazard and may be cause of an injury. Hence
we have provided safety guard for belt and safety guard for cut off wheel, in
such way that they should in no way interface with operations of the machine.
9.
Workshop facilities:
A
design engineer should be familiar with the limitations of his employer’s
workshop in order to avoid the necessity of having workdone in some other
workshop.
10. No.
of machines to be manufactured:
The
number of machines to be manufactured affects the design in a number of ways.
The engineering and shop costs which are called fixed changes or overhead
expenses are distributed over the number of machines to be manufactured.
11. Cost
of construction:
The
cost of construction of machine is the most important consideration involved in
design. The aim of design engineer under all conditions, should be to reduce
the manufacturing costs to the minimum.
12. Assembling:
Every
machine or structure must be assembled as a unit before it can function.
GENERAL PROCEDURE IN MACHINE DESIGN
In designing a machine component,
there is no rigid rule. The problem may be attempted in several ways. The
general procedure to solve a design problem is as follows:
1.
First of all
make a complete statement of the problem, indicating the purpose for which the
machine is to designed.
2.
Select the
possible groups of mechanisms which will give the desired motion.
3.
Find the forces
acting on each member of the machine and the energy transmitted by each other.
4.
Select the
material best suited for each member of the machine.
5.
Find the size
of each member for each member of the machine by considering the forces acting
and the permissible stresses of the material used. Each member does not deflect
or deform that the permissible limit.
6.
Modify the size
of the member to agree with the past experience and judgement to facilitate
manufacture.
7.
Draw the
detailed drawing of each component and the assembly of the machine with
complete specification for the manufacturing process suggested.
SELECTION OF MATERIALS
Selection of a proper material for the machine component
is one of the most important steps in the process of machine design. The best
material is one which will serve the desired objective at minimum cost. It is
not always easy to select such material
and the process may involve the trial and error method. The following factors
should be considered while selecting the materials.
i)
Availability:
The material should be readily available in the market, in large enough
quantities to meet the requirement.
ii)
Cost: For every
application there is a limiting cost beyond which the designer has to consider
other alternative materials. In cost analysis, there are two facotors:
a)
Cost of material
b)
Cost of processing the material into finished goods. It
is likely that the cost of material might be low, but the processing may
involve costly machining operations.
iii)
Mechanical
properties: The important mechanical
properties of materials from the considerations of the design are strength,
rigidity, toughness, resilience, shock resistance, wear resistance, creep
characteristics, corrosion resistance, frictional properties and hardness.
These properties are measured in terms of following quantities.
Strength
(static load) Ultimate
tensile strength
Strength
(fluctuating load) Endurance
strength
Rigidity Modulus
of elasticity
Ductility Percentage
elongation
Hardness Brinell
or Rockwell hardness no.
Toughness Charpy
or load impact value
Frictional
properties Coefficient
of friction
iv)
Manufacturing considerations: Machinability of material is important
consideration in selection. Sometimes, expensive material is more economical
than a low priced one, which is difficult to machine. Where the product is of a
complex shape, casting properties are important. The manufacturing process such
as casting, rolling, extrension, welding and machining govern the selection of
material.
ENGINEERING REQUIREMENTS OF MATERIALS
Engg. Requirement of materials means
as to what is expected from materials so that the same can be successfully used
for making engineering components.
1)
Fabrication requirement: It means that material should be able to get
shaped and joined easily, fabrication requirements relate themselves with
materials Machinability, ductility, castability, heat treatment, weldability
etc.
2)
Service requirement:
It implies that material selected for the purpose must stand upto
service demands like proper strength, wear resistance, corrosion resistance.
3)
Economic requirement:
It demands that engineering part should be made with minimum overall
cost which may be achieved by proper selection of both technical and marketing
variables.
MOUNTING OF ABRASIVE WHEEL
Great care must be taken in mounting
the abrasive wheels on the abrasive wheel spindle or shat. The abrasive wheel
must be mounted correctly on the spindle for the purpose of satisfactory
operation and safety. The following points should be considered while mounting
abrasive wheel on the spindle.
- First, the wheel should be visually and closely inspected just before mounting to make sure that the wheel have not been damaged in transportation of wheel, storage of wheel or other wise. The ringing test conducted on abrasive wheel. A clean ringing, vibrating sound must be heard. When wheel is subjected to ringing test. For this test, cut off wheel is put on order and it is subjected to slight hammer blows.
- The abrasive wheel should be easily fitted on the spindle. The wheel should not be forced on the spindle.
- There must be a flange on each side of the wheel to avoid local concentration of pressure.
- The washer should be used the nut. By using washer any unevenness of the wheel surface is balanced and a tight joint is obtained.
- The sides of the wheel and the flanges which clamp them should be flat and bear evently all round.
- The wheel guard should be placed and tightened before the machine started or work. After mounting the abrasive wheel, the machine is started. The abrasive wheel should be allowed to idle for a period of about 10 to 15 min.
- The nut should be tightened to hold the wheel firmly. Undue tightness is necessary and undesirable as excessive clamping strain liable to damage the wheel.
ADVANTAGES OF ABRASIVE CUT OFF MACHINE
- Hard materials can be cut.
- Surface finish is better.
- It is very fast and ideal for high volume production especially on small bar stock.
- Machine is less time consuming than the other cutting process. As in hacksaw machine there is reciprocating motion and one cutting stroke and one idle stroke. But in abrasive cut off machine there rotary motion of cutting which continous motion of cutting.
- We can get desired accuracy and desired angle of cutting which we will not get from the other cutting process.
- Very less efforts are required to the operator.
- Where mass production of identical workpieces are required, this machine plays vital role.
- Machine is flexible and shifted to anywhere, we are required to carry cut off process.
- For holding job, vice is used, so sufficient grip is there.
- Upto 8 mm thickness pipe or rod can be cut off.
- Whole assembly is mounted on table, so operation can done by sitting on the chair.
- It is very much economical because using the abrasive wheel, we can cut different types of metals.
- There is no danger of explosion, so operator can easily cut the metals withour feeling danger.
- Semiskilled or unskilled labour is sufficient.
- Machine is very simple in construction.
- Maintenance of machine is less.
- Machine id portable and also weight is less.
- Thin slender part like “I” beam, channel, small bar can be cut with less vibration.
LIMITATIONS OF MACHINE
1.
The power consumption is high.
2.
Heavy weight than other cutting equipments.
3.
The machine makes noise while cutting.
4.
Not suitable for thick large size solid bars.
5.
Possibility of accidents when wheel breaks.
6.
As wheel thickness is 3.2 mm, for cutting of any
material more than 3.2 mm material is wasted.
APPLICATION OF MACHINE
- For making tables, benches, windows, we use these machines for cutting rods and pipes.
- This machines is also used to cut castings free of runners. Particularly for very small investment castings.
- For cut off long bars, small bars of castings in straight way as well as for angular cuts.
- Contour cutting can be done by this machine.
- For cutting metal plates, sheets, strips, coils, tube, forging.
- For cutting long cut extended bars into work piece lengths for milling, turning, drilling processes.
No comments:
Post a Comment