Week14 Nota

1

3605The term computer-aided design and drafting (CADD) refers to the entire spectrum of drawing with the aid of computer, from straight lines to color animation.

An immense range of artistic capabilities resides under the heading of CADD, and drafting is just one of them.

Productivity gains realized by the use of CADD tools are directly related to the proper use of those tools.

In any discipline of drawing and design are directly related to the function of the part, model, or layout.

For example, a part such as a wing-nut would not be designed and drawn using tight tolerances whereas machine screws used in precision equipment would.

In addition, a simple part that is to be mass manufactured without additional testing and analysis can be drawn quickly as 2-D multiview drawing.

But a prototype design of a new component that must be analyzed and tested would best be developed as a 3-D solid model.

STE

3443The abbreviation 2-D refers to two-dimensional having only length and width (or width and height) dimensions.

The views of the object appear in the flat form and are normally rotated 90º from each other.

This form of drafting is best used for objects that will not require analysis, testing, and visualization and will not be used for presentation purposes.

Two-dimensional drawings are most often dimensioned and contain notes and text that describe features and details on the part, map, or plan.

Object initially drawn using 3-D techniques are often composed of lines connecting corners of the object.

These individual points on the object are referred to as vectors. Technically a vector is a quantity having magnitude (length) and direction, but this can be simplified to say that a vector is a line defined by two end points.

EDU

2

3443Therefore, a 3-D model must be composed of numerical values for each corner of the object.

Lines connecting these corners appear as wires, hence the name wireframe.

Three-dimensional wireframes are themselves not very useful because they are difficult to visualize.

Wireframes are usually the basis for creating other types of 3-D models.

Three-dimensional surface and solid models are often displayed as wireframes for purpose of redisplaying (regenerating) the model quickly.

Three-dimensional modeling is an part of the design, manufacturing, and construction industry, and contributes to increased productivity in all aspects of a project.

A 3-D surface model is a “hollow” object on which flat planes connect all corners of the object, and geometry is described by its surfaces.

EDU

3443For example, automobile body panels require the construction of accurate surface shapes.

High-end surface modeling software allows the user to create surface models that can be edited, analyzed, and tested. These files can then be used in the manufacture of the part.

Basic surface modeling software is used to create realistic presentation models. Basic surface models appear to the solid but contain no mass property data.

Surface characteristics such as color, texture, light, and shadows can be applied to the model in order to create a more realistic presentation.

Surface models are also used for situations in which the presentation of the object is important, such as the shaded and rendered objects used in architectural presentation, television commercials, movies, and computer animations.

In addition, this type of model is used in 3-D worlds, which are composite models designed for geographical information systems (GIS), video games, and virtual reality applications.

EDU

3

3443A 3-D solid modeling is a 3-D modeling method that accurately describes both the exterior and interior of a part or assembly.

A solid model is constructed using solid primitives such as boxes, cones, spheres, and cylinders.

These objects are combined, subtracted, edited to create the final model. Materials can be specified for the model, which can then be submitted to testing and analysis.

In addition, the solid model can be assigned surface properties and lighting for use in accurate presentations.

An additional aspect of solid models that enhances productivity and usefulness is the ability to cut through any part of the model to create sections.

This allows designers and engineers to view and edit the model while looking at interior features.

EDU

3443The solid model can also be used to quickly create a prototype composed plastic. This discipline is called rapid prototyping.

CADD is used in all aspects of drafting, design, and engineering, and in the disciplines of architecture, HVAC, structural, civil, process piping, landscape design, pattern making, machine design, and solid modeling.

Computers are integral to the manufacturing process. Computerized welding machine, machining centers, punch-press machines, and laser-cutting machine are commonplace.

Computer-aided manufacturing (CAM) is a discipline requires the use of computers to assist in the creation or modification of manufacturing control data, plans, or operations.

Today, many firms/industries engaged in computer-aided design/computer-aided manufacturing (CAD/CAM).

In CAD/CAM system, a part is designed on the computer and transmitted directly to the computer-driven machine tools that manufacture the part.

EDU

4

3443Within that process there are other computerized steps along the way:

a. The CAD program is used to create the product geometry. This can be in the form of 2-D dimensioned multiview drawings, or as 3-D models.

b. The drawing geometry is then used in the CAM program to generate instructions for the computer numerical control (CNC) machine tools. This is commonly referred to as CAD/CAM integration.

c. The CAM program then uses a series of commands to instruct CNC machine tools by setting up tool paths. The tool paths includes the selection of specific tools to accomplish the desired operation.

d. The CAM programmer then just establishes the desired tool and tool path. The final CNC program is generated when the postprocessor is run. A postprocessor is an integral piece of software that converts a generic, CAM system tool path into usable CNC machine code (G-code). The CNC program is a sequential list of machining operations in the form of a code that is used to machine the part as needed.

e. The CNC program is then verified using software’s simulator. f. The CNC code is created. g. Then it is time to prove out the program on the CNC machine tool. The program

is run to manufacture the desired number of parts.

EDU

3443Computer numerical control (CNC) also known as numerical control (NC) is just one critical aspect of CAM in which a computerized controller uses motors to drive each axis of a machine such as a mill to manufacture parts in a production environment.

The motor of the machine rotate based on the direction, speed, and length of time that is specified in the CNC program file.

CNC was a major innovation in product development as well as manufacturing. It has lead to increased productivity because the consistency of the process has lowered manufacturing costs, increased product quality, and led to the development of new techniques.

Rapid prototyping (RP) is a manufacturing process by which a solid physical model of a part is made directly from 3-D CAD model data, without any special tooling.

An RP model is a physical 3-D model that can be created far more quickly than by using standard manufacturing process.

EDU

5

Control is needed in the implementation of an activity to monitor, standardize, ensure safety and ensure success. A system may face excessive wastage, activity disorder, jeopardize the users and lead to unachievable goals.

Type of control systems including hydraulic, pneumatic, electrical and electronics. In addition, energy and work are controlled to ensure work is done accordingly and pose no hazard to users.

The control can be done by manual, semi-automatic or fully automatic means.

The manual control requires continuous human observation and if there is negligence, it may result in loses such as overflow of water in uncontrolled tap.

Before hydraulic system was developed, a mechanical machine was typically had levers, ropes, chains and gears typically used to carry out daily routines such as moving wood, carrying water and rocks.

The usage of this mechanical machine was limited to light jobs and for a short period of time only. Today, hydraulic system is widely applied in heavy works such as brake in heavy vehicle, crane, backhoe, lorry, satellite and aircraft wing control.

REKA BENTUK & PEMBANGUNAN PRODUK

EDU3443

WEEK14

Hydraulic technology was developed in 1795. The word hydraulic was taken from the Greek word ‘hydro’ which means water.

Hydraulic is used for incompressible liquid that is used to transfer energy, control force and movement.

In hydraulic circuit, force, pressure, work and power are crucial in determining the efficiency of its operation.

Calculation and estimation are required to determine those parameters. Otherwise, the task required cannot be completed and there is possibility that these components may damage due to excessive force.

Force and pressure are interrelated in determining the hydraulic ability.

Force can be used to move an object, for example a cylinder. The magnitude of force is determined by the inertia of the object. Force can be calculated by multiplying pressure (p) and area (A).


EDU3443

WEEK14

6


EDU3443

WEEK14

Mechanical force is applied to piston is transferred to another place through fluid. The pipe or cylinder size (area) changes the magnitude of the transferred force.

The magnitude of the force is proportional to the area as expressed by: (Force = Pressure x Area). Figure 1 shows the outcome of different forces produced by pistons of different areas.


EDU3443

WEEK14

7

Pressure (p) is the act of pressing an object. Pressure is defined as the ratio of the force (F) acting on a surface area (A).

Pressure is measured in pascal (Pa) or newton per meter square (N/m ) in SI unit.

The bar is a unit used to obtain smaller values of pascal (Pa has larger unit digits). In SI unit, pressure in bar is referred to as absolute pressure.

According to Pascal’s law, the pressure exerted on an enclosed fluid is transmitted undiminishly throughout the fluid and acts equally in all directions.


EDU3443

WEEK14

Pressure applied to a fluid, will be affected by factors such as area, friction and fluid density which can occur in the following conditions:

a) Pipe to smallb) Pipe too longc) Too many jointsd) Too many bendse) Liquid too dense

Figure 2 shows the pressure reduction causes by distance. As the distance increases, the pressure decreases due to increase in area.


EDU3443

WEEK14

8

Work (W) is done when force is exerted on an object and causes the object to move parallel to the direction of the force from a specific distance.

Force and distance determine the work to be done.

The unit of work (W) is Joule or newton.meter (N.m).

The relationship between force, work and distance as follows:


EDU3443

WEEK14

Power is the rate at which a work is done. The unit for power is newton meter per second or watt. The following formula is used to calculate power:

Power is an exerted force can be calculated by using the following formula:

P = F x v= force x velocity

Example 1A car hydraulic brake system has two cylinders. The first cylinder has cross-sectional area of 0.15m . During braking, a pressure of 20N/m is applied to the first cylinder piston. What is the force that could be exerted by the second cylinder (at tyre) if its cross sectional area is 0.15m ?


EDU3443

WEEK14

9

Solution: The force to the first cylinder when the brake pas is pushed equivalent to

The force to the second cylinder on the brake disc during braking equivalent to


EDU3443

WEEK14

Example 2On the way home, your father’s car tyre is punctured. You used a car jack to elevate the car and then removed the flat tyre. The jack piston moves 3 cm if 300 N force is exerted on the jack cylinder. Calculate the power and work done if the jacking work took 1 minute.

Solution

Work (W) = F (N) x d (m)= 300 N x 0.3 m= 90 Nm

Power (P) = work done (W) / time taken (t)= 90 Nm / 60 s= 1.5 Nms or 1.5 watt


EDU3443

WEEK14

10

Exercise 1Your friend’s weight is 50 kg. The area of both of this feet is 100 cm . What is the pressure P acting on one of his leg? (Answer = 98100 N/m )

Exercise 2The fluid from the pump has a pressure of 2 bar. What is the force exerted if the area of the cylinder piston is 2 m , 3 m , 4 m . What is the formula used? (Answer = 400 000 N, 600 000 N, 80 000 N – force is directly proportional to the cross sectional area)


EDU3443

WEEK14

In order to operate the hydraulic system, the following four main sections are required:

a) supply service section

b) fluid control section

c) actuator or transducer section

d) energy transfer/transmitter section

Figure 4 shows block diagram of the hydraulic system.


EDU3443

WEEK14

11


EDU3443

WEEK14

Electronic control uses semiconductor components as components in control.

There are several components used in electronic control namely diode, transistor and tyristor (SCR, Diac, Triac).

Diode is semiconductor component that allows electric current to flow in one direction. Diodes have two terminals. The arrow of the circuit symbol shows the direction in which the current can flow.

Diode functions as rectifier which convert converts alternating current to direct current. Diodes are the electrical version of a valve and early diodes were actually called valves.


EDU3443

WEEK14

12

Diode are made from a combination of two extrinsic semiconductors, the P-type material and the N-type material.

The joint between the P-type material and N-type material is called the PN junction.

In N type semiconductor, electrons become a majority charges. Similarly, a P-type semiconductor has majority hole charges.


EDU3443

WEEK14

Electricity uses up a little energy pushing its way through the diode, rather like a person pushing through a door with a spring.

This means that there is a small voltage across a conducting diode, it is called the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon.

The forward voltage drop of a diode is almost constant whatever the current passing through the diode so they have a very steep characteristic (current-voltage graph).


EDU3443

WEEK14

13

When a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny current of a few µA or less.

This can be ignored in most circuits because it will be very much smaller than the current flowing in the forward direction.

However, all diodes have a maximum reverse voltage(usually 50V or more) and if this is exceeded the diode will fail and pass a large current in the reverse direction, this is called breakdown.


EDU3443

WEEK14

Transistors amplify current, for example they can be used to amplify the small output current from a logic chip so that it can operate a lamp, relay or other high current device.

In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage.

A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on).

The amount of current amplification is called the current gain, symbol hFE.


EDU3443

WEEK14

14

There are two types of standard transistors, NPN and PNP, with different circuit symbols.

The letters refer to the layers of semiconductor material used to make the transistor.

Most transistors used today are NPN because this is the easiest type to make from silicon.

The leads are labelled base (B), collector (C) and emitter (E).


EDU3443

WEEK14

Transistors have three leads which must be connected the correct way round.

Transistors can be damaged by heat when soldering or by misuse in a circuit.

Use a multileter to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range.

Test each pair of leads both ways (six tests in total): • The base-emitter (BE) junction should behave like a diode and

conduct one way only. • The base-collector (BC) junction should behave like a diode and

conduct one way only. • The collector-emitter (CE) should not conduct either way.


EDU3443

WEEK14

15

Electric control is define as a component which control electric devices based on determined workflow. For instance, electric motor is one of the devices that need a special control.

All the components used in electric control circuit can be categorized into two:

1.Main control device: components which connect the circuit the main load.

2.Driving device: components used to control or regulate the main control device.

Main components used in electric control are fuse, relay control, relay overload, lights, timer, circuit breaker, switch and push button.


EDU3443

WEEK14

Figure 1 shows the usage of control components in electric control circuit.


EDU3443

WEEK14

16

Contactor is an electromagnetic switch. The functions of a contactor is to safely connect and disconnect the circuit.

Generally, contactor is used with other control components to control the circuit load as light and electric motor.

Contactor consists of coils, soft iron cores, contactor and lever.

Every contactor consists of two parts: static lever and movable parts.

The movable part is integrated with lever to the soft iron core.

Two types of contactor available are main contactor and auxiliary contactor.


EDU3443

WEEK14

Main contactor used in main circuit. Usually have high rating ampere and only consists of normally open contactor.

Auxiliary contactor used in control circuit with low rating ampere. It consists of normally open contactor and normally closed contactor.

Auxiliary contactor are used to: 1.Construct the hold circuit.2.Construct the electrical cross lock circuit.3.Control the other control circuit like sequential control circuit.4.Construct the circuit for driven lights, bell and etc.


EDU3443

WEEK14

17


EDU3443

WEEK14

Week14 Nota

Documents