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Penentuan Layout Fasilitas

Pendahuluan

Layout is one of the key decisions that determine the long-run efficiency of operations. Layout

has numerous strategic implications because it establishes an organization's competitive priorities

in regard to capacity, processes, flexibility, and cost, as well as quality of work life, customercontact, and image. An effective layout can help an organization achieve a strategic advantage

that supports differentiation, low cost, or response.

Layout decisions entails determining the placement of departments, workstations, machines, and

stock-holding points within a productive facility. Its general objective is to arrange theseelements in a way that ensure a smooth work flows (in a factory) or a particular traffic pattern (in

a service organization). The inputs to the layout decisions are

1. Specification of objectives of the system in terms of output and flexibility

2. Estimation of products or service demand in the system

3. Processing requirements in terms of number of operations and amount of flow between

departments and work centers, and

4. Space availability within the facility itself.

In all cases, layout design must consider how to achieve the following

1. Higher utilization of space, equipment, and people2. Improved flow of information, materials, or people

3. Improved employee morale and safer working conditions

4. Improved customer--client interaction

5. Flexibility (whatever the layout is now, it will need to change)

Because only a few of several types of layout can be modeled mathematically, layout and design

of physical facilities still something of an art. However, we do know that a good layout requires

determining:

Material handling equipment

Managerial must decide about equipment to be used, including conveyors, cranes,

automated storage and retrieval systems, and automatic carts to deliver and store material.

Capacity and space requirements

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Only when personnel, machines, and equipment requirements are known, can we proceed

with layout and provide space for each component. In the case of office work, operations

managers must make judgements about the space requirements for each employee.Management must also consider allowances for safety requirements that address noise,

dust, fumes, temperature, and space around equipment and machines.

Environment and aesthetics

Layout concerns often require decisions about windows, planters, and height of partitionto facilitate airflow, to reduce noise, to provide privacy, and so forth.

Flows of information

Communication is important to any company and must be facilitate by the layout. This

issue may require decisions about proximity as well as decisions about open spaces

versus half-height dividers versus private offices.

Cost of moving between various work areas

There may be unique considerations related to moving materials or the importance of

certain areas being next to each other.

Tipe dan Struktur Aliran Proses

Sebelum membahas tentang tipe-tipe layout, terlebih dahulu akan diketengahkan berbagai jenistipe aliran proses (process flow type)produksi/operasi. Pada dasarnya aliran proses

produksi/operasi dapat dibedakan menjadi 3 (tiga) jenis, yaitu 1) aliran proses konversi

(conversion processes) seperti proses untuk merubah biji-biji besi menjadi lempengan baja; 2)proses pabrikasi (fabrication processes) seperti proses pembuatan emas batangan menjadiperhiasan; dan 3) proses asembling (assembly processes) seperti di dalam pembuatan mobil

meskipun ada juga yang menyatakan bahwa proses pembuatan mobil ini disebut dengan istilah

production line.

Sementara itu, struktur aliran proses dapat dikelompokkan menjadi 4 (empat) kategori, yaitu:

Job Shop

Struktur aliran proses yang memproduksi batch yang kecil dari sejumlah besar variasi

produk. Sebagian besar di antaranya memerlukan langkah-langkah atau urutan(sequence) proses yang berbeda. Sebagai contoh adalah perusahaan pencetakan komersial

dan perusahaan pembuat pesawat udara.

Batch

Merupakan aliran proses job shop yang distandardisasikan, seperti aliran proses yang

dimiliki oleh manufaktur yang beroperasi dengan permintaan produk yang relatif stabil,

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dengan masing-masing produk dibuat di dalam batch secara periodik, sebagian untuk

memenuhi pesanan konsumen dan sebagian lagi disimpan sebagai persediaan. Sebagian

besar dari produk-produk ini mengikuti pola proses yang hampir sama, misalnyaperalatan berat, komponen-komponen elektronik, dan bahan-bahan kimian yang khusus.

Assembly Line

Merupakan struktur aliran proses yang membuat produk melalui pergerakan dari stasiun

kerja ke stasiun kerja di dalam tingkat yang terkendali, dan mengikuti urutan produksiyang ditetapkan.

Continuous flow

Aliran proses continuous mengarah kepada suatu tipe aliran proses yang memproduksi

sejumlah besar produk, sementara tipe produk yang dihasilkan sudah distandardisasi,artinya tidak ada variasi produk sama sekali.

Basic Production Layout Formats

The formats by which departments are arranged in a facility are defined by the general pattern of

workflow, and are of three basic types and one hybrid type. Many manufacturing facilities

present combination of two layout types. For example, a given floor may be laid out by process,while another floor may be laid out by product.

A process layout (also called a job shop or functional layout) is one where similar equipment of

functions are grouped together, such as all lathes in one are and all stamping machines inanother. A part being worked on then travels, according to the established sequence ofoperations, from area to area, where the proper machines are located for each operation. This

type of layout typical of hospitals, for example, where we find areas dedicated to particular type

of medical care, such as maternity wards and intensive care units.

A product layout (also called a flow-shop layout) is one in which equipment or work processesare arranged according to progressive steps by which the product is made. The path for each part

is, in effect, a straight line. Production lines for shoes, chemical plant, and car washes are all

product layouts.

A group technology (cellular) layout groups dissimilar machines into work centers (or cells) towork on products that have similar shapes and processing requirements. A GT layout is similar

to process layout in that cells are designed to perform s specific set of processes, an it is similar

to product layout in that cells are dedicated to a limited range of products.

In a fixed-position layout, the product (by virtue of its bulk or weight) remains at one location.

Manufacturing equipment is moved to the product rather than vice versa. Shipyards, construction

sites, and movie lots, are examples of this format.

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Assembly-Line Balancing

Basic Assumptions

1. Volume is adequate for high equipment utilization

2. Product demand is stable enough to justify high investment in specialized equipment

3. Product is standardized or approaching a phase of its life cycle that justifies investment in

specialized equipment

4. Supplies of raw materials and components are adequate and of uniform quality

(adequately standardized) to ensure that they will work with the specialized equipment.

Steps in Assembly-Line Balancing

1. Specify the sequential relationship among tasks using a precedence diagram--that consistsof circles and arrows

2. Determining the required cycle time (CT)

3. Determining the theoretical minimum number of workstations required to satisfy the

cycle time constraint

4. Select a primary rules by which tasks are to be assigned to workstations, and a secondary

rule to break ties (i.e. longest operations time, largest number of following tasks, shortest

operations time, or least number of following tasks)

5. Assign tasks, one at a time, to the first workstation until the sum of the tasks times is

equal to the cycle time, or no other tasks are feasible because of time or sequence

restriction. Repeat the process for workstation 2, workstation 3, and so on, until all tasks

are assigned.

6. Evaluate the efficiency of the balance derived

7. If efficiency is unsatisfactory, rebalance using different decision rule.