Just in Time (JIT)
In a JIT system, the company will produce only what is needed, when it is needed, and only in the quantity needed. JIT means "exactly at the appointed time."
For a system to be considered Lean, it must be able to make any product currently in production in any combination, so shifting demand can be accommodated immediately. In fact, the ability to design, schedule and make exactly what the customer wants just when he wants it is what allows you to limit your reliance on forecasts and simply make what the customer actually tells you they need.
By far the greatest benefit of JIT is product quality. By producing only the quantity needed, defects can be detected and corrected quickly before large inventories of bad parts are produced. Through lowered levels of inventory, JIT also provides reduced exposure to scrap and rework costs, as well as accelerating the incorporation of engineering changes – all contributing to increased responsiveness and flexibility. In the office area, this means timely information when the user needs it.
Leaning the supply chain is purposefully designed to quickly and obviously uncover problems and issues by putting stress on the weakest link. The sense of urgency that a flow-based, just-in-time system creates stimulates people most closely associated with the process to think about constraints and improve constantly and forever.
JIT will surface the constraints; celebrate their discovery, then fix them – fast.
Pull
In simplest terms, pull means that no one upstream should produce a good or service until the customer downstream asks for it.
Pull refers to a system of cascading production and delivery instructions from downstream to upstream activities in which nothing is produced by the upstream supplier until the downstream customer signals a need. The execution of this downstream demand becomes the authorization for the upstream workstation to make more. The quantity produced is the quantity ordered; if no demand is coming from a downstream consumer, then nothing is produced.
As a consumer-initiated material movement technique, a pull system fights complexity (constantly changing customer orders for products with multiple variations) with simplicity (versus computers regenerating schedules for every process). With proper execution, a pull system permits products or services to be built or created more rapidly and only as needed based on the actual conditions existing on the factory floor or office, effectively minimizing at-risk inventory resulting from engineering changes, newer information or producibility issues.
Kanban
Communicating a need.
American supermarkets are famous for being a place where consumers get what is needed, when it is needed and in the amount needed. Why should other industries be any different? In a pull system, a kanban is the triggering mechanism that regulates the flow of product, services or information between each supplier-customer connection.
Acting as a signaling device, the primary purpose of a kanban is to restrain production, effectively capping the amount of work-in-process. Taking the form of a card, a cart or an empty square between workstations, kanbans provide information relative to what to produce, when to produce it, in what quantity and where it is to be delivered. With kanban, communication is clear and unambiguous; there is no fuzziness in determining who provides what to whom and when.
Load Leveling
Neutralizing variable demand by distributing both the volume and mix of total orders evenly over sequential time periods.
All other things being equal, the more the flow of work varies, the greater the incidence of creating waste. The concept of leveling or smoothing is to diminish the quantity oscillations in production. This is accomplished by equalizing the amount of work and ensuring that the work itself is performed at an even pace. Without removing such fluctuations, a pull system – indeed JIT itself – will fail.
Load leveling enables a company to produce several different parts products or services in varying lot sizes, closely mirroring the same mix of products or services that are being sold or demanded. The equalization of both the quantities and different types entails the sequencing of orders in a uniform, repetitive pattern and smoothing the day-to-day variations in total orders. In short, the goal of load leveling is to produce the same amount of product every period.
Line Balancing
Balancing workloads of sequential operations achieves a steady and consistent workflow.
Line balance is extremely important to be able to reduce queues and work-in-process to achieve a continuous process flow. Balancing involves assigning and redesigning the work performed in an attempt to make cycle times at all workstations approximately equal. Achieving balance is an imperative. Failure to balance operations results in labor inefficiency and scheduling complications inherent in batch operations.
Takt Time
Acting as a drum beat or rhythm across the entire operation, takt time sets the pace at which all work cells must produce in order to meet customer demand.
Takt time is a calculated figure that tells how often you have to produce a unit, whether product or service, to satisfy demand. In essence, you are setting yourself to your customer’s watch. Cycle time on the other hand is the actual time taken to accomplish each task within a process. The goal of JIT is to bring the cycle time as close as possible to takt time without exceeding it.
Takt time is determined by dividing the time available by the quantity of product or service the customer is demanding. For example, if a customer requests 200 widgets per day and a company operates 400 minutes a day, the takt time is two minutes per widget. In this case, a widget must be produced every two minutes in order to satisfy demand. The heartbeat of a Lean system, takt time sets the pace of production to match the rate of customer demand.
The important thing about takt time is that when existing orders do not require the full utilization of equipment and workers, takt time is increased. The machinery or equipment is slowed down and cross-trained workers perform several jobs in the work cell while excess workers are assigned to other tasks (e.g., kaizens). This reverses the age-old tendency to work ahead and build inventories if no orders are immediately on hand. When all activities are synchronized to takt time, the waste of over-production is eliminated.
Single-Piece Flow
Single or one-piece flow is simply the fastest, most affordable way to build products or create services.
Single-piece flow is the quickest way for material to get from point A to point B, with the shortest cycle time and the least amount of work-in-process. Operating so products flow one piece at a time (or as close to the ideal batch size of one) allows the producer to deliver products or services sooner and more affordably by reducing storage and transportation requirements, and lowering the risk of damage and obsolescence.
Single-piece flow exists when products move through a process one unit at a time, at a rate determined by the needs of the customer. By reconfiguring assembly lines or work areas into cells based on single-piece flow, you can substantially reduce leadtime and the number of defects passed on to downstream operations.
Setup Reduction
Reducing setup times gives equipment and processes the flexibility to produce a small quantity and thus a wide variety of product. As setup times approach zero, order quantities can approach one.
The heart of JIT and the principal enabler of single-piece flow, setups involve changing dies, cutting tools or operation methods according to the specifications of a particular product. A setup is the elapsed time between the finished piece of one type and the first good piece of another part and consists of both internal and external time.
Internal setup: those setup activities that are conducted when the machine or equipment is shut down, such as mounting and removing dies. Such activities interrupt run time.
External setup: those activities that take place while the machine is running, such as transporting dies between storage and machine or preparing the next job to be run. Such activities are external to the run time and don’t interrupt it.
There are eight Single Minute Exchange of Die (SMED) techniques that will lead to setup reduction:
- Technique 1 – Separate Internal from External Setup Operations – Clearly identify internal setup activity and external setup activity. Standardize and document both.
- Technique 2 – Convert internal to external setup operations - Because setups have such a dramatic effect on both flexibility and throughput, it is important to convert internal setup activity into external setup activity. By externalizing the majority of setup activity, you can minimize downtime and optimize the mix and velocity of items produced in the factory
- Technique 3 - Standardize functions, not shape – functionally standardize all setups
- Technique 4 – Use functional clamping or eliminate fasteners altogether
- Technique 5 – Use Intermediate Jigs and Fixtures - Reduce delays due to adjustment during internal setup operations using standardized jigs and fixtures. While the work piece attached to one fixture is being processed, the next piece can be adjusted on a second fixture. Standardization is the key.
- Technique 6 – Adopt Parallel Operations – Use two people to perform setup, reducing setup time due to economies of motion.
- Technique 7 – Eliminate Adjustments – Examine initial settings and precisely determine the correct position/setting. Adjustments become less of a factor as settings become more accurate. Also, adjustments can be eliminated when the number of settings are limited and unvarying.
- Technique 8 - Mechanization
|
