HOW JIT WORKS &

PUSH PULL SYSTEMS

Present by :- Janmejay Munjani

How JIT(Just in Time) Works

▪ JIT begins with a master schedule drawn for one to three months. This is communicated to the production personnel on the shop floor and to the suppliers, who in turn, are expected to schedule their work accordingly. Within a production month, the master schedule is ‘leveled’ on a daily basis. This is done by identifying the product into “runner", “repeaters”, and “strangers”. These terms reflecting the volume and frequency of demand runners denote high volume product, and strangers denote occasionally produced products.

JIT supply chains

JIT = Automotive manufacturers1. Fixed bill of materials(BOM)2. Small product line 3. Ramp up production to

volume4. Linear & constant demand

for product5. Vendors box - close - #1

priority6. Payables = receivables 5-6-2015 8-6-2015

5-7-2015 8-7-2015

5• Delays = stock out - lost sales cost

inventory - lost gross

profit - lost

costumers• Management – pre-limit

freight cost

The goal is to:

▪ reduce delivery lead times,

▪ cut inventory,

▪ reduce the amount of defects,

▪ improve staff productivity and

▪ make sure products are delivered on time

Effects of JIT Production

The block diagram to illustrate the effects of JIT. The major effects of JIT are in the following areas:▪Productivity improvement.▪Set-up time improvement.▪Inventory reduction.▪Quality improvement.▪Space savings.▪Lead times reduction.

JIT improves productivity in the following ways:

1.Smaller lot size inventories.2.Smaller buffer inventories.3.Less scrap.4.Less direct labour wasted on rework.5.Less indirect cost of inventories.6.Less space for inventories.7.Less equipment to handle inventories.8.Less inventory accounting.9.Less physical inventory control effort.

Pull and Push Systems

In a pull system, product is made to order. In the pull system, when a worker runs low on parts, a request is passed back to previous operations for replacement parts. This procedure is repeated throughout the manufacturing operation. As a result, lot sizes must be small and set up times must be short. Also materials handling must be minimized and quality must be very good. JIT utilizes pull system for production.

In a push system, the product is made to stock. This requires lot of storage space, buffer inventories, etc. it is not preferred by JIT manufacturing.

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The Key Difference Between Push and Pull

▪Push Systems: schedule work releases based on demand.

– inherently due-date driven– control release rate,

observe WIP level

▪Pull Systems: authorize work releases based on system status.

– inherently rate driven– control WIP level, observe

throughput

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What Pull is Not!

▪ Make-to-Order: – Material requirements planning (MRP) with firm orders on master

production schedule(MPS) is make-to-order.– But it does not limit WIP and is therefore a push system.

▪ Make-to-Stock:– Pull systems do replenish inventory voids.– But jobs can be associated with customer orders.

▪ Forecast Free: – Toyota’s classic system made cars to forecasts.– Use of takt times or production smoothing often involves production

without firm orders (and hence forecasts).

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Push and Pull Examples

▪ Are the following systems essentially push or essentially pull?

–Soda vending machine:–“Pure” MRP system:–Doctor’s office:–Supermarket (goods on shelves):–Order entry server at Amazon.com:

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Advantages of Pull Systems

▪Low Unit Cost:– low inventory– reduced space– little rework

▪High External Quality:– high internal quality– pressure for good quality– promotion of good quality

(e.g., defect detection)

▪Good Customer Service:– short cycle times– steady, predictable

output stream

▪Flexibility:– avoids committing jobs

too early– encourages floating

capacity

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The Magic of Pull

▪ Pulling Everywhere?

You don’t never make nothin’ and send it no place. Somebody has to come get it.

▪ – Hall 1983

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Pull Benefits Achieved by WIP

▪Reduces Costs:– prevents WIP explosions– reduces average WIP – reduces engineering

changes

▪Improves Quality:– pressure for higher

quality– improved defect

detection– improved

communication

▪Improves Customer Service:– reduces cycle time

variability– pressure to reduce sources

of process variability – promotes shorter lead times

and better on-time performance

▪Maintains Flexibility:– avoids early release (like air

traffic control)– less direct congestion– less reliance on forecasts– promotes floating capacity