Lead time
The cycle time (English throughput time, lead time ) is the time it takes for an object or an entity to pass through a system. The calculation of the cycle time is dependent on the particular system and entity types.
Run time in the manufacturing
The throughput time is a central concept of production control. In production, the cycle time defined as the time required from the start of machining up to the completion of a product. Specifically, the processing time is it composed of setup time, processing time and wait time; for some authors can be seen separately, the transport time.
Within the sequence of the problem, which is solved by scheduling, the time can be distinguished as follows:
- The wait time is the waiting time of the unwanted product within the production system.
- The processing time is the time required for the technical preparation of the product. Accordingly, this also includes desired wait time such as drying after coating.
- The setup time is derived from the property of some resources to perform various operations. For this purpose, the resource must, however, be placed in the right state ( ready ). A simple example is a kitchen machine which has to be equipped only with the correct blade for a scheduled processing.
- The transport time is the time required to transport the product before and after processing
A fundamental distinction REFA after species for
Since the distinction is irrelevant to the lead time, and the times for the people and the resources are symmetrically defined, it is called for the passage time as a term of implementation. This major and minor implementation form the execution time. Together with the company resulting from the expiration of conditional interrupt meantime, they form the scheduled run time ( by a working system ). The actual transit time may be extended over the planned yet by an additional time, formed of times for fault conditional interrupting and additional penetrations.
For the processing time by several systems of work adding their individual throughput times with the addition of each intermediate time, the sun represents, warehousing and transportation times between the working systems. This REFA causes, given the factual blur of the above, the usual definition ( When exactly is the beginning of processing: the grant of the construction contract provision of the material first step and when exactly is the completion of product:? ? Final treatment provision in the mail ... ) a clear indication of what belongs to the passage of time and what is not.
To use as a key figure can be divided by Duration in mean flow time and job-related processing time. In this connection, the cycle time is the time for the entire production order complexes.
Reduce cycle time
The aim in the production should always be to keep the costs of a construction contract as low as possible. This can be achieved inter alia by reducing throughput time, where in reducing the quality of the production may not be affected.
- There are first, the ability to increase the capacity of a work station. Due to the higher capacity can be made in the same time (throughput). The concept is only useful at bottlenecks (see: Theory of constraints, bottleneck (logistics), production program )
- Secondly, the throughput can be increased by increasing the intensity (for example, increasing the electric power ), since the relationship between processing time and throughput is reversed. The possibilities are usually low but, as usually the optimal performance of equipment and the best pace for humans is already scheduled.
- To save setup time, can carry out similar contracts that are to be made in a timely manner will be consolidated into a single job ( lot). This is not created for each job set-up time, but only for the first. By increasing the batch size, the average lead time can be reduced at each individual work system; the lead times for orders and average processing times can be characterized but significantly increase because of the additional waiting and idle times. Lot formation also limits the flexibility and ability to deliver.
- The main potential lies therefore in the organization of order processing and organization of work. For example, the aim of the concepts one- piece flow and Chaku - Chaku on cycle time reduction in more varied series production.
- The transport times can be reduced ( slightly ) by the production are sensibly arranged and high-frequency transport systems are used.
- If a product sub-lots for transport ( transport lot <> production lot ) formed, a first sub-lot of work system B can be processed further by overlapping operations while working system A produces the second sublot. Ideally, you're back at One -piece flow and Chaku - Chaku.
Throughput times for heterogeneous production
For complex technical products, which are composed of many individual parts and assemblies, and are produced in heterogeneous production areas, the respective lead times are often very different. One way to reduce the throughput time is to outsource individual production sections of sequential production lines and to parallelize the production partially. This procedure is often found in the automotive industry. There, for example, the vehicle doors are removed at the start of final assembly and then completed in separate door assemblies. At the end of the assembly line these doors are then delivered and installed to the final assembly line. Or it will be the transfer of certain production volumes from a service provider or a supplier in a pre-assembly. The pre-assembled module is then often just- in-sequence, installed in the vehicle. If the cycle times differ greatly between the areas of production, another possibility is to set up several parallel production lines or flexible manufacturing cells for specific parts or assemblies.
Act of Little
According to the law of Little following relationship between lead time, inventory and throughput applies:
Where:
DLZ: cycle time (unit: time)
WIP: stocks that are within the process ( unit: piece )
Throughput: Process emissions within a certain time (unit: piece per time )