Menyelaraskan dan Menyeimbangkan Proses (Synchronizing and Balancing Processes)

Sinkronisasi (Keselarasan) Pull production diarahkan oleh a repetitive, level production schedule untuk memenuhi demand production rate = demand rate Semua upstream operations harus diselaraskan agar berproduksi pada laju yang dibutuhkan Parts harus mengalir dengan lancar, tanpa menimbulkan persediaan Ini dicapai dengan menetapkan Cycle Time (CT) pada semua operasi yang berdasarkan pada CT perakitan akhir (final assembly) KEY MESSAGE Required cycle time of all operations is based on the final level schedule. TALKING POINTS Cycle time implies repetitive production, with a unit rolling off the line every so many seconds. By using a mixed, level schedule for the final output stage, the finished products do roll off the line at repetitive intervals based on the demand for them. The required cycle times of all upstream operations must match the required CT of the final operation. If the final stage is smooth and repetitive, then upstream operations will also be smooth and repetitive.

Synchronized Flow Mixed Model, make-to-order computer assembly KEY MESSAGE This shows how components are used at a repetitive rate in final assembly. TALKING POINTS The CT for each component is synchronized with the final assembly CT. This is fairly uniform and predictable. Disk drive assembly station

Synchronized Flow KEY MESSAGE Here we see many components flowing to main assembly. TALKING POINTS Ideally, the “rate of flow” of parts and components is uniform and repetitive everywhere. This is analogous to several streams flowing smoothly into a river.

Menentukan Cycle Time untuk Mensinkronkan Proses Products Daily requirments (units) A 200 B 100 C 50 All Products 350 Asumsikan 420 menit per hari untuk produksi Cycle Time produk yang dibutuhkan adalah: Products Cycle Time (detik) A 420 x 60 / 200 = 126 B 420 x 60 /100 = 252 C 420 x 60 / 50 = 504 All Products 420 x 60 / 350 = 72 Mixed Model Production (MMP) sequence: A-A-B-A-B-A-C dengan repetisi 50 kali

Bottleneck Scheduling Seringkali satu atau lebih upstream operations tidak mempunyai kapasitas yang mencukupi sesuai jadwal produksi akhir yang telah direncanakan (planned final production schedule) Produksi aktual dibatasi oleh “bottlenecks” Produksi harus dijadwalkan berdasarkan bottlenecks KEY MESSAGE Bottlenecks are operations that can’t keep up with demand. TALKING POINTS Plant capacity is limited by the operations with the lowest capacity, known as bottlenecks. The bottlenecks limit production only if the demand is greater than the available capacity. In those cases, production is scheduled based on bottleneck capacity instead of demand.

Prinsip Drum-Buffer-Rope System Tetapkan CT produksi berdasarkan bottleneck capacity (drum) Pastikan tersedia penyangga WIP di depan stasiun bottleneck sehingga tidak pernah kehabisan pekerjaan (buffer) Produksi tarik (pull production) sampai stasiun bottleneck (rope) KEY MESSAGE Bottlenecks are scheduled using the Drum-Buffer-Rope system. TALKING POINTS The drum-buffer-rope system was first described by Eli Goldratt in his book “The Goal”. The system is sometimes known as “synchronous manufacturing”. While his ideas seem independent of the larger theme of lean production, they complement it nicely.

Drum-Buffer-Rope Pekerjaan-pekerjaan (jobs) diberikan pada lini A dan B berdasarkan pemberian order pada bottleneck Jangan khawatir tentang operasi-operasi setelah bottleneck karena operasi-operasi tersebut bekerja lebih cepat dari bottleneck Jadwal pengiriman didasarkan pada lead time sepanjang proses

Drum-Buffer-Rope (lanjutan) Tujuan: meningkatkan kapasitas bottleneck Ketika bottleneck ditingkatkan, operasi lain akan menjadi bottleneck Dimana semestinya bottleneck ditempatkan? Kapan perlu khawatir tentang operasi-operasi setelah bottleneck?

Menarik dari Bottleneck Kartu Kanban digunakan untuk merilis material ke sistem ketika bottleneck merilis material Pesanan-pesanan pekerjaan (job orders) dijaga dalam backlog pada bottleneck Kanban mencakup: – Routing sequence – Quantity

Balancing Setelah Cycle Time (CT) semua operasi ditetapkan, kapasitas harus disesuaikan sehinga CT aktual mendekati CT yang diinginkan KEY MESSAGE Balancing adjusts capacity to match required CT. TALKING POINTS Line balancing is a well known subject in manufacturing, and most of the principles apply to lean manufacturing as well. Lean production facilities are not as well controlled and predictable as traditional fixed flow lines, though. In traditional line balancing, the line makes just one thing, and the cycle time is known precisely. In lean production, several things are made and the cycle time for each one varies, and is an average only.

Traditional Line Balancing Digunakan untuk product layouts atau assembly lines Buat precedence diagram tugas-tugas Jaringan menunjukkan urutan tugas-tugas yang dibutuhkan Bagi pekerjaan-pekerjaan ke dalam elemen-elemen kerja Alokasikan elemen-elemen kerja ke workstations Seimbangkan jumlah pekerjaan pada tiap workstation KEY MESSAGE This slide summarizes the traditional line balancing problem.

Balancing for Mixed Model Production MMP melibatkan produksi model-model berbeda dengan task times yang berbeda pada lini yang sama Gunakan weighted average times untuk menghitung workstation task times KEY MESSAGE Balancing for mixed model production is more difficult. TALKING POINTS In MMP, each model requires a slightly different amount of time at each operation. Balancing is done using weighted average task times. There needs to be provision to allow variation in task times as well.

The Weighted Average Time Rule Tentukan persentase produk-produk Gunakan persentase-persentase tersebut untuk membuat weighted task time untuk task i Tambahkan task time tersebut hingga melewati CT yang dibutuhkan

The Weighted Average Time Rule: Contoh

Cara Lain untuk Mencapai Keseimbangan Dynamic balance Secara dinamis mengalokasikan tugas-tugas ke workstation-workstation berbeda untuk menyamakan beban kerja (para bekerja saling membantu) Parallel lines Membagi lini atas dua operasi paralel untuk mereduksi CT KEY MESSAGE Other methods can also be used to achieve balance. TALKING POINTS Lean producers are constantly reallocating tasks to different stations to improve balance. This might be done every time the level schedule is updated. Workers might also help each other to improve balance. A worker who has finished a task helps someone who isn’t finished.

Balancing for Synchronous Flow Penyeimbangan dengan menggunakan continuous improvement dan realokasi pekerja Eliminate wasteful steps Reallocate tasks Reduce number of workers and repeat KEY MESSAGE Continuous improvement and waste reduction lead to performing the same tasks with fewer workers. TALKING POINTS By eliminating and streamlining wasteful steps, it is often possible to reduce the number of workers needed. Again, overzealous application of this can result in a highly stressed and overworked workforce!

Balancing through Worker Reassignment Seimbangkan kembali sehingga semua idle time dipindahkan ke seorang pekerja Temukan cara untuk mereduksi task time sehingga seorang pekerja dapat dipindahkan (ditugaskan ulang pada suatu tempat) KEY MESSAGE Rebalancing seeks to reduce the number of workers required. TALKING POINTS It is important that the workers eliminated from the process are reassigned elsewhere and do not loose their jobs. However, over time lean producers require a smaller workforce than traditional manufacturers.

Balancing Required CT Unbalanced, required CT can’t be achieved KEY MESSAGE Here is an unbalanced process. TALKING POINTS Worker 2 has too much work, and can’t meet the required CT. Unbalanced, required CT can’t be achieved

Balancing Required CT Balanced with equal idle time KEY MESSAGE Spreading idle time equally is not desired. TALKING POINTS It seems logical to spread the idle time equally among workers, but that doesn’t lead to improvement even though their jobs will be easier. Balanced with equal idle time

Balancing Required CT KEY MESSAGE To force improvement, all idle time is shifted to one worker. TALKING POINTS Here, three workers are working very hard, and the third has little to do. If the process can be improved further, the remaining work of the fourth worker can be reassigned to the other three. The result is that the process now requires only 3 workers instead of 4. The downside is increased stress on the remaining workers. There have been several studies indicating how serious this problem can be in lean manufacturing plants. Balanced, all idle time allocated to worker 4. Improve the process so that worker 4 is not needed.

Mengadaptasi Perubahan Jadwal Mengubah hari kerja produksi Overtime Extra shifts Mengubah laju produksi Mudah jika CT aktual < CT yang dibutuhkan Meningkatkan kapasitas dengan menambah pekerja Kombinasikan dua cara di atas KEY MESSAGE Lean manufacturers have several ways to accommodate changing demand.