We need to look at the assembly because it is a key activity in manufacturing, as most products consist of several parts which must be collected together and secured for product to function.
Also it give us degree of movement freedom and mobility for various elements and enable material differentiation .therefore the various assembly methods can be classified into three elementary methods, manual assembly, mechanical assembly and robotic assembly
Assembly is very common, and perhaps regarded as necessary, but we should try to avoid it where ever we can, that way effects have been in over the years to find other methods to avoid assembly.
Due to high cost of labour, another method was considered, which is the automation and its main goals is to integrate various aspects of manufacturing operations to improve quality and minimize time cycle and labour cost.
Also it improves productivity, reduce human involvement, raise level of safety to personnel and reduce cost in raw material.
1.1 Flexibility is where the various individual manufacturing systems are incorporated into a single large scale system, in which the production of parts is controlled with the aid of a computer, and the advantages of this production system is a high flexibility for small effort and short time required to manufacture a new product.
1.2 Manual assembly: in manual assembly, the most significant factors are the sensors available in the form of vision, touch and sometimes hearing, also the ability of the assembler to make sensible judgment very quickly.
For parts with tolerances defects, the judgment becomes important when assembly, and the possibility that exist are: the part inserted can not reach its final location or the pert reaches the final location but does not give the require assembly.
Manual assembly is used in production situation where the work to be performed can be divided into small tasks, and the advantages in using manual assembly is using specialisation of labour by giving each one set of tasks to do repeat ably , this require high labour content therefore results in high cost.
It is a system where mechanical, electrical and computer-based system is used to operate and control production, this technology includes automatic machine tools, automatic assembly machines, industrial robot, storage automatic inspection system, feed back control and computer process control.
Types of automations : Fixed automation ,Flexible automation and programmable automation.
Reasons for Automating : some of these important reasons for automating are as follows :
Increase productivity, this mean grater out pit per hour of labour input , higher production rate achieved with automation than with manual operation.
High cost of labour: is enforcing business leaders to substitute machines for human labour.
Labour shortage.
Safety: by using automation the operation and transferring the operator from an active participation to a super visionary roll, work is made safer.
High cost of raw material: in manufacturing results in the need for greater efficiency is using this material, the reduction of scrap is one of these benefits.
Therefore when large production required quantity and high production rates, automation is used and examples of these products are:
Electric components.
Electronic components.
Bolting plants.
Tablet manufacturing plants etc.
1.4 The advantages of automated systems are:
Reduce labour cost and manufacturing lead time.
Increase labour productivity.
Improve product quality.
Increase production rate.
Reduce material handling cost and time.
Increase manufacturing control.
Improve workers safety.
Overcome limitation of manual labour,
Too expensive.
Some tasks are too difficult to automate.
Problems with physical access to work location.
Short product life cycle.
Usually one of a kind product is produced.
Reduce the risk of product failure.
1.5 The objective of the assignment is try to implement all the knowledge gained in the automation module on the chosen artefact “the electric switch”, and the intention is to disassemble the exercise, study it carefully and design a system to be assembled in large quantities and cost effectiveness by means of automation and manual processes.
Marketing history
The single electric switch is the most common type of switches, as it is found in
every house, office or factory, it is essential to the power source as its simple and
easy to use and economic due to low price.
There are more than one type on this off/on switch, single, double and they are
made of different type materials, plastic ,steel coated , chrome plated etc ,this
makes its prices varies
The main components of the lighting switch are:
Base: it is usually made of plastic material (pvc), and some manufacturer makes
them from chrome plated steel or any other safe long life material.
The switch button: it is the mechanical part of the switch ( acts as actuator), as its main function is to initiate the switch circuit operation (open and close), and is made of the same material as the base. For safety reasons the material should be a very good insulator.
2b- Spring: it is a small spring made of good steel, and is part of the mechanical
action, and assists in switching the power from on to off and vice versa
also due to its elasticity it last along time and prevents contact between solid parts.
Housing: this is the main part of the switch, as it contains all the electrical parts (terminals and their accessories), and is moulded plastic products ,which makes it good insulator to all the power terminals.
3a- Terminal (1) : consists of a block ,element, and a screw for tightening the
electrical wire, brass or copper is usually the martial that terminals are made of ,
and as known are good electricity conductors. (This is the common terminal)
3b- Terminals (2) & (3), made from the same material as terminal (1), the contacts
in all terminal are made of low resistance metal that makes or break the circuit
Each terminal consist of block (3b), element (3b1) and wire fasten screw (3b2).
Screw: fastens the housing assembly to the main base
1
2
2a
3
3a
3a1
3a2
3b
3b1
3b2
4
Base
Button
spring
Housing
Terminal 1(block)
Element
Screw
Terminal 2”block”(2 ea )
Element (2ea)
Screw (2ea)
Fastening screws
1
2
3
4
5
6
7
8
9
Load Assembly base into work carrier
Assembly subassembly Button
Assembly subassembly Terminal 1
Assembly subassembly Terminal 2
Assembly subassembly Terminal 3
Assembly subassembly housing to base
Check
Assembly screw
Remove compete switch
switch
Base
1
Button sub assy 2
Sub assembly housing
3
Screw
4
2
2a
3
Terminal 3a
3b (2 each)
3a
3a 1
3a 2
3b(2)
3b1(2)
3b2 (2)
b) Product structure
2
2b
4
1
3
3a
3a1
3a2
3b
3b1
3b2
c) Assembly structure based components
2
1
6
7
8
9
5
3
4
d) Assembly structure based on subassemblies
Product and Assembly Structure Charts
Component
description
Component number
Functional analysis
Manufacturing analysis
Feeding/loading analysis
Gripping Process
Work holding process
Inspection Process
Non Assembly Process
Sub assembly Total
Assembly Total
1.2
Base
1
A
1.3
2.2
1.5
Button
2
A
1.2
1
1
1
Spring
2a
A
2.1
1
1
Housing
3
A
1.3
2.2
1
Terminal 1
3a
A
1.5
1.5
1
Element
3a1
A
2.4
4
1
Screw
3a2
B
2.1
2.2
1
Terminal 2
3b
A
1.5
1.5
1
Element
3b1
A
2.4
4
1
Screw
3b2
B
2.1
2.2
1
1.5
Screw
4
B
2.1
2.2
1
Total
11
20
23
13.7
Design Efficiency = A component 8 x 100% = 72
Total Compts 11
Feeding Handling Ratio = Index Total ___20_____ = 1.8
A copmts 11
Fitting Ratio = Gripp-fit fix = __________________
A Compts
The design for assembly addresses product structure simplification; sense the total number of parts in a product is a key indicator of product assembly quality
A number on different DFA methods have bee development, and to be any interest to designers they need to be:
Complete i.e. have objectivity and creativity.
Systematic- which helps to ensure that all relevant issues are considered i.e. the organization of objective and creative parts of DFA methods.
Measurable and user-friendly
3.1 Lucas Method the method is based around an” assembly sequence flowchart”. The Lucas/Hull group has developed a knowledge based evaluation technique, it follows a procedure in which the important aspects of assemble and component manufacture are considered and rated. The system is to be integrated into a CAD system, where it should be possible to obtain the information required for the analysis work with the minimum of effort and time.
- Functional analysis
- Handling analysis, and this can be manual or feeding assembly
-Fitting analysis
Depending on this method the Artefact was disassembled and a view drawn shown all components (pieces), also a build up structure and an assembly structure were made (page 6).
3.2 Functional Analysis: is carried out according to the rule of value analysis and activities, degree of functional importance is then categorized.
Each activity is put to the system in turn, a description and name is given for parts.
The assembly parts for the artefact were carefully investigated and categorised into either “A” parts (demand by function) and “B” parts, and these by design only, from that the design for efficiency was:
NO of “A” components x100
Total NO of components
8 x 100 = 72%
11
As all components and subassemblies manufactured in different places and will be presented to same point for assembly so our analysis considered three areas:
Handling difficulties
The size of the component
The weight of the component
The transfer mechanism of a flow line must not only move partially completed work parts or assemblies between stations, it must also orient and locate the parts in the correct position for processing at each station, the general method for transporting can be classified to:
Continuous transfer
Synchronous transfer
Power and free transfer
The most suitable type of transport system for a given application depends on the following factors:
-The type of operation to be performed.
The number of stations on the line.
The work piece size and weight.
There are a various types of parts feeding devises and the most common are:
- Hopper, where components are loaded at the work station, they usually loaded into the hopper in bulk; this means they are randomly orientated in the hopper.
- Parts feeder: This mechanism removes the components from the hopper one at a time for delivery.
- Orientator: where proper orientation is established
- Feed back: used to transfer the components from the hopper and parts feeder to the location of the assembly work head.
The quality of gripping is the ability to hold a part in a way that allows the part to be inserted with the proviso that insertion is possible.
In manual assembly, the parts handling does not have gripping problems because of ability of people to perform insertion operation despite poor relationship between the mating parts.
The best grip must be a three point grip whose lines of action equally
spaced and act through a common point
Another common possibility is a three point grip, where positional errors perpendicular to the direction of grip are possible.
For flexible assembly it is advised to do the following for different tasks:
Use a universal gripper.
Use a turret of gripper.
Use gripper changing.
Use special multi-purpose gripper
The gripping is usually used for the parts witch are difficult to assemble in position due to its size or shape, and this case it is needed when assembly of the power wiring screws and the terminals in the housing.
In manual insertion, the basic insertion action is different to the automatic one. The part being inserted is deliberately misaligned so that contact is established between the mating parts, a combination of touch and sight then interact with the movement to do the operation.
There are three examples show this:
Even in blind situation, one a contact has been made the insertion operation is easy. Attempts by operator to achieve a relatively open tolerance insertion with out mating parts touching are usually unsuccessful.
People are not good at close tolerances.
In automated assembly no touch is needed if there is good alignment.
There are common design roles for assembly processes:
Insert from vertically.
Use chambers, tapers to assist in alignment.
Choose open tolerances as possible.
Do not have more than one insertion site.
Design so the can be released as soon as insertion has started
From the previous analysis tables there are two steps can be taken to redesign the “switch” or artefact:
- The terminal should come as a complete unit, this means the element is welded to the block and the screw in position, this will minimise the steps of the assembly and safe time and cost.
- The housing can be assembled to base by means of” snap fitting instead of the fastening screws.
The outcome of this redesign will result in:
A Reducing parts count
B Ensuring a visible assembly process at a minimum cost
C Reliable automatic assembly achieved
d- Standardisation of components
The FMS provides the efficiency of mass production for batch production, and its main advantages are:
- Increased productivity
- Shorten preparation time for new products
- Reduction of inventory parts
- Saving of labour cost
- Improved product quality
- Attracting skilled people
- Improved operators safety
4.1 Activity Flow Chart
Vibrator Bowel
5
Refuse tray
Poka Yoka
Stack magazine
Linear vibrator
1
4
2
3
Full Ballet
Pallet Magazine
6
ROBOT
Rotary Bowel Feeder
Feed the housing by means of a stack magazine, this magazine must be set up for each “switch” variant. (The housing should be held into the work carrier and secured).
Feed subassembly terminal 1 with the aid of a ballet magazine.
Feed subassembly terminals 2&3 with the aid of a ballet magazine.
Feed the base by the aid of a linear vibrator.
Feed button in base by the aid of vibrator bowel.
Feed the spring by the means of vibratory bowel feeder
Place the subassembly housing on base by means of snap.
Remove of acceptable completed assemblies with the aid of an index transfer system provided with ballets.
The sequences are handled with a Scara Robot with a gripper change system which are used to handle the terminals.
There are 3 work stations in this assembly, the assembly of the housing station, the assembly of the base station, and the third is the completed assembly station
The feed devises used are
Ballet magazine.
Stack magazine.
Linear vibrator.
Vibrator bowel
Poka Yoka : is used to test if the terminals are fitted in position or not.
The advantages of the proposal of re-designing the artefact could be summarized in the following:
Lower manpower cost.
Less automation or feeders) used.
Less time.
More productivity.
More safety
The cost after the re-design proposal should in general be cut down, and regarding the implementation stages there is no transfer from manual to semi-automation noted, but the main changes occurred are in the terminals, as they feed pre-assembled, so this will reduce time ,automated equipment and tooling.
Also the fasten screw is replaced by means of snap fitting, which will result in increase of the “A” numbers and therefore increase in the overhaul efficiency.
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