Erdem Ozdemir 030070307 - 2nd Week Definitions

Functional Layout

Production System

New –Better Definition

In a Junctional layout, equipment of the same type is eolocaled This may also be described as being process oriented (examples of processes in this context arc turning, milling etc). Functional layout is the prevailing layout in mixed produc­tion, where a large number of products are manufactured in small volumes. Ma­chines are organised after types with similar functions and are usually referred to as grouping of different machines for part manufacturing and machining such as drilling machines, milling machines, grinding machines, turning machines, pres­ses, see Fig. 8.9.

The order flows between the different machine groups depending on which op­erations are involved for making a certain product. A machine or a group of simi­lar machines thus constitute a planning point. Machines can be manned by an operator per machine or one operator can handle several machines depending on the actual level of automation of the equipment Capacity utilisation may theoreti­cally be high in a functional layout, in addition to the possibility for flexibility due to large routing possibilities. Flexibility is also achieved since it is possible to choose the machine in a group that is available at a particular moment. Theoreti­cally, Junctional layout has many advantages for manufacturing in smaller series of many different products.

In reality, one disadvantage is linked to control and coordination, since a large part of the throughput time for a product is waiting between operations. Thus, queues are built up at different machines and waiting times occur lor transport between machine groups causing the need for extensive planning. As disturbances occur for some reason in a machine, there is a risk that the subsequent machineswill be affected by interrupts causing urgent rescheduling. Consequences are su­perfluous stock, long throughput times that lead to high tie-up of assets, and low delivery precision. There is also a risk of quality problems and rejections.

(Monica Bellgran,Kristina Säfsten, Production Development: Design and Operation of Production Systems,  Pg: 206-207)

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In a functional layout, machines performing similar functions are organised in one center. For example, drilling is done in the drilling cell, face milling in the face milling cell, so on. Such a layout is adopted when different products must be produced intermittently at the same set of work stations. A functional layout is usually adopted when the volume of parts produced is too low to allow human and capital recources to be set aside exclusively for a particular set of parts. An advantage of the functional layout is that employee suopervision can be more specialized. However a functional layout tends to increase setup costs, and throughput time because of the frequent change overfro part type to the next. 

(George Winston Zobrist, Chung You Ho, Progress in robotics and intelligent systems, Volume 1, p.263-264)

Materials Handling

Production System

New-Better Definition

Malcrials handling is defined as movement of material of any form (raw, finished, packaged, solid, liquid, gas, light and heavy) from one location to another location either in a restricted path by manual or mechanical aids. The movement may be horizontal, vertical or may be combination of both.

Advantages Of Materials Handling

There are so many advantages of materials handling systems, some of important advantages are listed below :

(a) Reduction in material handling and indirect labour cost.

(b) Improvement in the productivity,

(c) Better use of floor space and facilities,

(d) Reduced cost of transportation

(e) Less fatigue to the workers

(f) Improved work environment,

(g) Reduction in bottlenecks,

(h) Greater flexibility.

 (I) improvement in the safety and reduction in the accidents.

(J) Improved material flow i.e., less backtracking and reduction in inventory.

Disadvantages Of Material Handling

Although material handling systems o tll-rs so many advantages but there are few disadvantages also which are listed below :

(a)    Initial cost of the equipment in the most of cases is high.

(b)  Skilled labour or operator is required to operate almost all types of material handling systems.

(c)  If not operated well there are concerns of horrible accidents and hazards.
(d) Regular maintenance is required.

(e) Inventory carrying cost is high in some cases.

(f) Installation and operating cost is high.

(Keshava Chanda Arora,Vikas V. Shinde, Aspects of Materials Handling, Pg:1-3)

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Material Handling: Material Handling is defined as the functions and systems associated with the transportation, storage and control of materials and parts in the total manufacturing cycle of the product. Several factors have to be considered in selecting a suitable material - handling method for a particular manufacturing operation:

1- Shape, weight and characteristics of the parts

2- Types and distances of movements, and the position and orientation of the parts during movement and at their final destination.

3- Conditions of the path along which the parts are to be transported.

4- Degree of automation, the level of control desired, and integration with other systems and equipment.

5- Operator skill required

6- Economic considerations

(Manufacturing Engineering and Technology, S. Kalpakjian, S.R. Schmid, 5th Edition Pages: 1163 - 1164)

Open-Loop Control

Control System

New – Better Definition

Those systems in which the output has no effect on the control action, i.e. on the input are called open-loop control systems. In other words, in an open-loop control system, the output is neither measured nor fed back for comparison with the input Open-loop control systems arc not feedback systems. Any control system that operates on a time basis is open-loop.

In any open-loop control system, the output is not compared with the reference input. Thus, to each reference input there corresponds a fixed operating condition; as a result the accuracy of the system depends on the calibration. In the presence of disturbances, an open-loop control system will not perform the desired task because when the output changes due to disturbances, it is not followed bv changes in input to correct the output In open-loop control systems, the changes in output are corrected by changing the input manually. Open-loop control systems can be used in practice only if the relationship between the input and the output is known and if there are neither internal nor external disturbances. One practical example of an open-loop control system is a washing machine—soaking, washing and rinsing in the washer operate on a time basis. The machine does not measure the output signal, i.e. the cleanliness of the clothes. A traffic control system that operates by means of signals on a time basis is another example of an open-loop control system. A room heater without any temperature sensing device is also an example of an open-loop control system. The general block diagram of an open-loop system is shown in Figure I.I.

(Anand Kumar, Control Systems, Pg:3-4)

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Every control system, including CNC systems, may be designed as either an open or a closed loop control system. Open-loop systems provide no check or measurement to modify orthat a specific position has actually been reached. No feed back information is passed from the machine tool back to the controller. Stepping motor-driven systems are examples of open-loop NC control. Open loop control provides relatively cheap solution to NC control systems, while closed-loop control is especially suited for varying load conditions and contouring control systems.

(Niebel B., Draper A., Wysk R., Modern Manufacturing Process Engineering,1989 ,p. 860)

The Multiclass System

Manufacturing

New – Better Definition

It is a classification and coding system developed by the organization for industrial research. The system is relatively flexible, allowing the user company to customize the classification and coding scheme 10 a large extent to fit its own products and applications. Multiclass can be used for a variety of different types of manufactured items, including machined and sheet metal parts, tooling, electronics, purchased parts, assemblies and subassemblies, machine tools and other elements. Up to nine different types of components can be included within a single multiclass software structure. Multiclass uses a hierarchical or decision tree coding structure in which the succeeding digits depend on values of the previous digits. In the application of the system, a series of menus, pick lists, tables and other interactive prompting routines arc used to code the part. This helps to organize and provide the coding procedure. The coding structure consists of upto 30 digits. These arc divided into two regions: one provided by OIR and the second designed by the user to meet specific needs and requirements. A prefix precedes the code number and is used to identify the type of part (e.g.. a prefix value of 1 indicates machined and sheet metal parts). For a machined part, the coding for the first 18-digit positions (after the prefix) is summarized in Table 15.4.

(Lalit Narayan Et Al., Computer Aided Design And Manufacturing, Pg: 363)

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The multiclass system was developed to help automate and standardize several design, production,and management functions and involves up to 30 digits. It is used interactively with a computer that asks the user a number of questions.On the basis of the answers given, the computer automatically assigns a code number to the part.

         

(Kalpakjian S. & Schmid S., Manufacturing Engineering and Technology, p.1215)

Finite Loading

Product Management

New-Better Definition:

Finite loading creates a detailed schedule of all orders and all work centers with stop and start dales assigned for each operation. The start and stop dates are computed using the output from MRP combined with lead times gencralcd for each open or planned order. In addition, as the sequencing for each operation is generated, the amount of load on each resource is also determined. With infinite loading the placement of the load is unlimited by the amount of capacity available {sec Fig. 27). With finite loading the placement of the load is limited by the amount of capacity available (sec Fig. 28).

Notice that in the first period finite loading did not fill all the available capacity. However, beginning in the second period demand is pushed into succeeding periods (the future) so that it does not exceed capacity. Notice also that an additional period is used to absorb the demand as it is pushed out of period 6 into period 7. This method is known as finite set forward.

(Robert E. Stein,Marcel Dekker (Firma comercial), RE-Engineering the Manufacturing System: Applying the Theory of Constraints, Pg:31-33)

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Finite loading is a technique for not allowing work to be loaded beyond the stated capacity

of a work center. It assumes that there is a defined limit to available capacity at any

workstation. If enough capacity is not available at a workstation because of other shop

orders, the orders has to be rescheduled in a different time period. The prioritizing of

work is based on predetermined rules such as work center completion date and operation

availability.

CRP uses infinite loading in conjunction with backward scheduling, to generate the capacity

requirements plan, or work center load reports. Operation sequencing, which is a part

of production activity control, uses finite loading and various forms of scheduling.

Before finite loading can begin, however, priorities must be established for individual orders.

The highest priority orders get first claim on the available capacity in each work.

(Mukhopadhyay, S.K., Production Planning and Control: Text and Cases, 2004, Prentice

Hall India Pvt., Limited, pg.147)