Pemeliharaan

budi.harsanto@gmail.com

Manajemen Operasi

Definisi

MAINTENANCE: semua aktivitas yang berkaitan dengan

menjaga sistem dan peralatan agar selalu dalam keadaan

siap pakai.

RELIABILITY: Probabilitas suatu bagian/suku cadang dari

mesin/produk dapat berjalan dengan baik untuk jangka

waktu tertentu dalam kondisi yang ditentukan.

Tujuan

Menjaga kemampuan

sistem dalam

keadaan siap pakai

dan mengendalikan

pembiayaannya.

Mengapa Pemeliharaan Penting..

Karena berpengaruh langsung pada:

1. Kapasitas produksi

2. Biaya produksi

3. Kualitas produk dan jasa

4. Keselamatan pelanggan dan tenaga kerja

5. Kepuasan pelanggan

Posisi Maintenance dlm Perusahaan..

Di bawah Dept. Operasi atau,

Langsung di bawah Direksi.

Level manajer maintenance ditentukan oleh The

importance of maintenance for the organization.

Departemen maintenance biasanya dibagi 2:

Bangunan (& Pekarangan)

Peralatan

4 Taktik

Reliability Tactics

1. Improving individual components

2. Providing redundancy

Maintenance Tactics

1. PREVENTIVE MAINTENANCE Implementing or improving preventive maintenance

2. BREAKDOWN MAINTENANCE Increasing repair capabilities or speed

Umur Mesin

Umur Ekonomis

Eksternal

Internal

Umur Teknis

*Maintenance membuat umur ekonomis mendekati umur teknis.

Preventive Maintenance

Keeping machinery and equipment

running.

Designing technical and human system

that will keep the productive process

working within tolerance.

A. Langkah Pencegahan

Feel - Rasakan

Inspection - Periksa

Tighten - Kencangkan

Clean - Bersihkan

Adjust - Setel

Lubrication - Lumasi

B. Overhaul (Bongkar)

C. Repair (Perbaiki)

D. Maintenance Scheduling.

Breakdown Maintenance

Perbaikan.

Dilakukan setelah mesin rusak.

Jenis Maintenance

Menurut Biaya Most necessary maintenance

Trouble Free Maintenance

Faktor Penentu Kualitatif

Jenis Maintenance Vital atau tidaknya alat tsb

Daya tahan alat tsb

Struktur kelengkapan pabrik (layout)

Line layout Trouble free

Process layout Tdk harus trouble free

Repair, Replacement & Overhaul

Keputusan2 untuk membongkar dan mengganti. Dapat dikaitkan dengan

biaya modal dan operasional (termasuk biaya mantenance) dari peralatan.

Biaya operasional naik untuk sementara.

Adanya kenaikan biaya sedikit demi sedikit, hingga akhirnya sampai pada penggantian yg dapat dibenarkan.

Adanya beda biaya modal dan biaya reparasi mesin baru dengan mesin lama dapat mempengaruhi keputusan dilakukannya penggantian, karena rancangan mesin baru punya

kemajuan yg disebabkan adanya mekansime/otomatisasi yang bisa meringankan biaya tenga

kerja dan biaya2 maintenance.

Biaya

Operasional

Repair Overhaul Replacement

Best Practice

Walt Disney Company intolerant of failure or

breakdown

United Parcel Service

Dedicated drivers who operate

the same truck every day

Dedicated mechanics who

maintain the same group of

vehicle.

Improving Individual Components

System reliability (Rs) is a product of

individual reliability.

Rs = R1 * R2 * R3 * ...

0.90 0.80 0.99

Ex:

Rs = 0.90 x 0.80 x 0.99 = 0.713 or 71.3%

Evaluating Maintenance

Reliability

Probability that an item will function for a given time

Mean time between failures (MTBF)

Average time between failures of a repairable item

Failure rate

Reciprocal of MTBF

Formula

Number of failures

Failure Rate(%) = FR(%) = * 100%

Number of units tested

Number of failures

Failure Per Operating Hour(n) = FR(N) =

Operating time

1 Mean Time Between Failure = MTBF = FR(N)

Example

Twenty air-conditioning systems designed for use by astronauts in NASA space shuttles were operated for 1,000 hours at NASAs Huntsville, Alabama test facility. Two of the systems failed during the test one after 200 hours and the other after 600 hours. Compute

a. The percentage of failures,

b. Number of failures per operating hour and

c. MTBF

Answer

a) FR (%) = 10%

b) FR (N) = 0.000106 failure/unit-hr

c) MTBF = 9,434 hour

Providing Redundancy

Back Up

Redudancy is provided

to ensure that if one

component fails, the

system has recourse to

another.

Perfect Computer System

No bug, no crash

Extraordinarily reliable

Fighter jets

Space shuttle

Nuclear power plants

Providing Redundancy

Ex: reliability of a component is 0.80 and we back it up with another component with reliability 0.80.

Reliabilty result = 0.80 + [0.80 x (1-0.80)] = 0.96

Probability of

first

component

working

Probability of

second

component

working

+

Probability of

needing

second

component

* = P(R)

F-14

Only 10% of the F-14s software is used to fly the plane

40% used to automatic testing and verification

50% is redundancy

Tomcat F-14

Other Example

R1

0.90

R2 R3

0.90

0.80

0.80 0.99

After redundancy P (R) = 0.94

Preventive Breakdown

Routine inspection & servicing

Prevents failures

Basis for doing

Time: Every day

Usage: Every 300 pieces

Inspection: Control chart

deviations

Types of Maintenance

Non-routine inspection

& servicing

Remedial

Basis for doing

Equipment failure

Preventive & Breakdown

PREVENTIVE MAINTENANCE

Meliputi inspeksi rutin untuk menjaga fasilitas peralatan

dalam kondisi baik dan mencegah kerusakan

BREAKDOWN MAINTENANCE

Memperbaiki peralatan yang telah rusak

Formula

Expected number of breakdowns

= [(number of breakdowns)x(corresponding frequency)]

Expected breakdown cost

= (Expected number of breakdowns)x(cost per breakdown)

Preventive Maintenance cost

= Expected breakdowns cost if service contract signed

+ cost of service contract

Contoh Aplikasi

Suatu perusahaan beroperasi dengan

mengunakan sistem komputer. Dalam

waktu 20 bulan terjadi kerusakan

pada perangkat komputer yang ada.

Biaya perbaikan setiap kali terjadi

kerusakan adalah Rp 300 ribu

Jumlah Kerusakan

Jumlah Bulan Terjadinya Kerusakan

0 2

1 8

2 6

3 4

Total 20

Saat ini perusahaan menerima tawaran kontrak

preventive maintenance dari pihak ketiga. Meskipun

misalnya nanti perusahaan memutuskan untuk

menerima penawaran preventive maintenance tersebut,

kerusakan akan tetap terjadi dengan perkiraan rata-rata

kerusakan satu mesin per bulan. Nilai kontrak yang

ditawarkan adalah Rp 150 ribu per bulan.

4-Langkah Pengerjaan

1. Hitung expected number of breakdowns (tanpa preventive maintenance)

2. Hitung expected breakdown cost per month (tanpa preventive maintenance)

3. Hitung expected breakdown cost per month (dengan preventive maintenance)

4. Bandingkan kedua pilihan yang ada.

Jawaban

1. Expected number of breakdowns = 1,6

kerusakan per bulan.

2. Expected breakdown cost = Rp

480.000 per bulan

3. Preventive Maintenance cost = Rp

450.000 per bulan

4. Tanpa Preventive Rp 480.000 sedangkan dengan

preventive Rp 450.000

Terima tawaran kontrak.

Breakdown Maintenance

Reliability and preventive maintenance are

seldom perfect.

Good Maintenance facility:

Well-trained personnel

Adequate resources

Ability to establish a repair plan and priorities

Ability and authority to do material planning

Ability to identify the cause of breakdowns

Ability to design ways to extend MTBF.

Isu Mengenai Pemeliharaan

TPM (Total Productive Maintenance)

Combines total quality management with strategic view of

maintenance from process and equipment design to preventive

maintenance.

Reducing variability & Improving Reliability designing machines that are reliable, easy to operate and easy to maintain.

Emphasizing total cost of ownership when purchasing machines, so that service and maintenance are included in the cost.

Developing preventive maintenance plans that utilize the best practices of operators, maintenance departments and depot services.

Training workers to operate and maintain their own machines.

Challenger

28 Januari 1986

73 detik

Bocor tangki bahan bakar

bagian kanan.

Columbia

1 Februari 2003

Meledak saat akan

mendarat