How To Classify Flexible Level Of System

Published Date: 02 Nov 2017

Group Technology:

Group technology means to sort out your work parts into different families which are similar in design or processes.

Where GT is used?

1- You are using Batch Production and the layout of your plant is Process oriented.

2-You can make groups of your products which are similar.

Pre-Requisites of GT:-

Sort out the groups or families of Parts.

Making Cells of Production Machines.

Advantages of GT:-

You can standardize your tools, JIGS etc.

Material Handling cost is reduced because you are limited to Cells.

Within a small cell Process Planning is easier.

Tool changeover time is reduced resulting in less lead time.

Less WIP Inventory.

Efficient Communication within small Cells.

Quality improves as you work in a cell on few products or processes.

Part Families:-

Part families mean the parts are similar in design or in sequence of operation. So you make a group of the parts which is called part family.

Advantages of making part families:-

-less material handling

-less changeover time

-low WIP Inventory

How to make part Families:-

There are three methods:

-Visual Inspection

-Parts Classification and Coding

-Production Flow Analysis

1-Visual Inspection

In this method you make photographs of parts or look at parts and make their families or groups. This is the least complex and simplest method of part classification.

2-Part Classification and coding technique

In this classification system you look at the design or operation of parts and make its family accordingly. This is not a standardized method because each company has very different products from other.

Advantages of Part Classification and coding technique:-

-Easy Design Retrieval: you can easily sort out a part depending on design or operation and you can modify it.

-Computer Aided Process Planning: you can make a route sheet for a new part having similar operation or design to your existing parts.

-Design of Machine Cell: the codes given to parts assist in making the cells of similar operations or design.

Properties of Part Classification and coding technique:-

Arrangement of parts having similar Design

Arrangement of parts having similar operations

Arrangement of parts having both design and manufacturing similarities

Opitz Coding and classification for parts:-

This system was devised by a German named H. Opitz. This was the well-known system for classification. It consists of nine digits 12345 6789 ABCD

12345 these digits are known as form code which shows circular part and also show features holes, threads, Grooves etc. 6789 is called supplementary code this identifies starting material, shape of raw material, specification limits.

The ABCD part is called secondary code which specifies different operations and sequence of operations ABCD codes will be identified by the industry depending upon its products.

For example this code of 26006 depicts the following details:

Digit 1=2 Length/Diameter=121/26=4.65

Digit 2=6 Part is having external Groove

Digit 3=0 there is no hole in the part

Digit 4=0 There is no plane surface machining on the part

Digit 5=6 There part is having teeth of spur gear

Production Flow Analysis:-

This is a method of making parts families and the formation of work cells. It does not use the design of the product but it uses the route sheet of the product. The parts having similar path in routes are identified and classified. Then these families of work parts will be used for the formation of the work cells which is our ultimate objective.

The PFA method has the following steps:-

Collection of data

Reading the operations performed on a part from the route sheet. We can easily find the operations performed on the work piece and hence the machines involved.

Finding the process Route

All the machines are given codes depending upon sequence of operation. From the route sheet then we make route for that part.

Formation of PFA chart

After process route for a product a chart also called Incident Matrix is made which shows every operation on each part in a random order.

Analyze the Cluster

Then the operations are arranged in proper sequence which was not in a sequence and thus different work cells are formed. Rank order clustering technique is exclusively used for this purpose.

Cellular manufacturing:-

Cellular manufacturing is the implementation of GT in which dissimilar parts or operations are accumulated in a cell instead of conventional process oriented layout.

The advantages are following:-

Less lead time

Less WIP inventory

Specialization in a specific job results in high quality

Easy production planning and control

Less changeover time

Idea of Composite part:-

Composite part is the representative of cell. All the operations performed in the cell are performed on a single part which shows. For example we have a cell and we can perform the following four operations on different parts in the cell drilling, broaching, turning, face milling. The representative composite part will have all three operations performed on it. So we can take the advantage that if a new part is ordered to manufacture we can easily tell the operations performed in which cell.

Types of part movement:-

Repeat operation

In repeat operation the part is processed on the same machine again and again.

In-sequence move

In this movement the part move forward each time after operation on a machine.

By pass moves

In this type of movement the part move two or more machines forward for further operations.

Backtracking

In this type of movement the work part is moved backwards for processes.

Types of layouts used in work cells:-

U-shaped

This is the most common used layout in GT. At one end work enters and leaves at another end. With the advantages of all moves either bypassing, in sequence or backtracking.

Loop layout

The arrangement of machines in such layout is elliptical. Loading and unloading stations are at same point. When backtracking is required this layout is suitable.

Flow or in-line layout

This type of layout consists of straight alignment of machines at one end the work enters and at opposite it exits. When the product have a linear sequence such a layout is preferable.

Rectangle shaped layout

Such a layout is almost similar to loop layout except the sharp corners rounded in loop. Both have same use.

Concept of key machine:-

There is always one or more machine/s in your set which is critical for you. Either it is expensive or having unique operations. It is suggested that you have to keep the utilization of your key machine maximum. In other words you simply try to make that critical machine a bottleneck.

Chap#19 Flexible Manufacturing Systems

What is a flexible manufacturing system?

FMS is the most complex and technologically machine cell type used to make a cellular manufacturing. Where FMS technology is applied:-

The plant is making parts in batches or using manned cells, and you want automate your plant.

The parts can be classified in groups depending upon design or processes.

The products are medium volume neither job shop nor mass production that is 5,000 to 75,000 parts per annum.

To install an FMS you should have more capital as compared to manned cells. For implementing FMS you should have sophisticated technology and sufficient skills to implement that technology. With high initial cost the FMS have advantages like high machine utilization, less space covered, easy interchangeability of tools, highest labor productivity and less manufacturing lead times. The loading unloading, processes, material transportation, changing of tools etc. all are highly automated. CNC machining centers are used commonly in an FMS.

What do we mean by Flexibility?

Flexibility in terms of manufacturing is defined as:

The capability of a system to identify a specific part or part styles.

Sudden change of operation instructions.

Quick change of tools JIGS and fixtures.

Criteria for a system to be called an FMS:-

Part variety test: can your system operate different parts in one setup?

Schedule change test: If the part families differ slightly or production quantities increase or decrease can your system accommodate these changes?

Error recovery test: If there is failure in machine due to some reasons can your system continues production in such situation?

New part test: If you get order of a new part can your system accommodate that part without major changes in the existing setup?

If the answer to above four questions is "YES" it means your system is an FMS.

In the above discussion point 1 & 2 are necessary and critical while the 3 & 4 are somehow softer and can be implemented at other stages as well.

Different Types of flexible manufacturing system:

As every Manufacturing firm make unique products so there will be criteria to categorize the FMS depending upon the annual production, no. of machines and whether they assemble or manufacture parts or both. Let us briefly explain these criteria one by one:-

Number of machines: (1) Single machine cells, (2) Flexible manufacturing cell (FMC), (3) Flexible manufacturing system (FMS).

A single machine cell consists of only one CNC machine and automatic load unload, transport and storage system. If less production is desired this type of machine cell is used. This cell meets the three criteria of FMS except recovery of the system in case of any malfunction because there I only one machine so after repairs you can continue production.

A flexible manufacturing cell (FMC) contains of two or three CNC machining centers (milling or turning centers) and material transport system. These types of system have less storage capacity. This system satisfies all four criteria for flexibility.

An FMS (flexible manufacturing system) have four or more processing stations interconnected to material transport system and to a computer system. The difference between an FMS & FMC is that FMS consists of four or more machines while FMC three or two machines. Another difference is that FMS include some supporting operations as well like part washing areas etc. another difference is that FMS have more and complex machinery rather than FMC.

How to classify Flexible level of system?

A dedicated Flexible Manufacturing System is mostly use to make parts in high quantities. It uses more specialized machines. It increases the production rate. This type of system increases productivity.

A random order FMS is best when there are large families. The machines used in this system are more general purpose. This system increases flexibility.

Different workstations in FMS

Load/Unload Stations: The loading and unloading station is link between the FMS and remaining factory. This is the place from where raw material moves to different cells for different operations. This station is link with material handling system through computer in an FMS.

Machining Stations: In machining stations in an FMS are CNC machining centers (CNC turning and milling centers) most probably CNC milling and drilling are used.

Assembly Operations: including manufacturing processes assembly operations are also done in an FMS. Though mostly in assembly operations human workers involved but, it can also be automated. Industrial robots are used for this purpose.

Major Functions of material handling system in an FMS:-

Random motion of parts: In an FMS the material handling system allows the parts to adopt a different path in case of traffic congestion.

Enable to tackle different part geometries:- The holding devices in an FMS enable to handle different parts geometries or sizes. The JIGS and fixture used for this purpose can automatically quickly change the parts as well.

Stores the material temporarily:- while moving the material in different states like raw material, semi-finished or finished the material handling system is storing the inventory as well.

Make Loading/Unloading easy:- The work stations at which material is loaded or unloaded it is provided by the material handling system.

Human Resources in an FMS:-

Humans are very important in an FMS though they work a little but, they have vital role in an FMS. The common roles performed by a human are as follows:-

They load the raw material to be processed

They remove the finished products

Changeover and setup tools

Overhaul and maintain the equipment used in the firm

Make the part programs for different parts

Operate and control the computerized system

Overall manage the firm

Benefits of an FMS:-

High machine usage:- As the machines are all automated and the transporting system used there is efficient so the utilization of machines is very high because in case of any failure redundant machines can be operated so the production schedule did not disturb.

Less Machines are needed:- As the machines are used maximum so less machines are requires because the machines can operate in three shifts as well.

Reduced space of factory:- As less machines are used in an FMS so less space will be required to accommodate the machines.

Shorter lead times:- The machines in an FMS are used to maximum extent so lead times are shorter.

Less labor:- Everything is almost automated so the labor content decreases.

More production than conventional systems:- As higher machine utilization is in FMS so you win more orders than ordinary you can pay attention to unattended customers as well.

Different Problems faced in how to plan and implement an FMS:-

Selecting part families:-The boundaries of an FMS should be carefully selected. Only few parts can be included in a family.

Selecting Equipment:- The part families selected will decide that how much and which machines are required.

Size, shape etc.:- The physical shape, state, size and weight will decide the machines and the material handling system.

Production quantities:- The production size will determine that how many and what type of machines are required and the suitable material handling system.

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