Assembly and batch production differ in terms of scale. In assembly-line production, products are produced in continuous streams. In contrast, in batch production, products are produced in groups. As a result, batch production may result in delays due to a pause in production between batch runs, as opposed to the steady supply characterized by assembly-line production. Also due to the pause in production characterized by batch production, assembly lines tend to be less flexible since it is more difficult to make quick changes when producing at high-output levels. At these levels, products are produced in large amounts, quickly and efficiently, but if consumer demand suddenly drops, it may result in a large amount of waste since assembly-line production can't be paused as quickly as batch production. Also, manufacturers run the risk of producing large amounts of products that are impaired due to assembly error. In contrast to batch producers, assembly-line producers can't easily shut down the machines and start over. Assembly-line production is more stagnant but also takes less time to produce.
Assembly lines, in which items are made by a production line, are generally more efficient than batch processes, in which products are made in groups rather than in a continuous way. Assembly lines are generally more efficient than batch processes, in part because assembly lines involve economies of scale. That is, they involve the production of a large number of items, so the cost of making each item is lowered. Manufacturers are often able to buy products at a discount when they buy in bulk. In addition, assembly lines are efficient because each person or machine performs a function that they repeat and perfect, making them and the entire process more efficient. Finally, assembly lines do not require manufacturers to take time to shut down and reconfigure machines and processes as batch processes do. However, assembly lines can be inflexible, as they cannot create customized or special products.
It will not be entirely correct to say that assembly-line processes are more efficient than batch processes. Both these types of processes can be the most efficient or not so efficient for specific applications depending upon the nature of operations performed and the volume of work.
To begin with, as the name itself indicates, assembly-line method is appropriate only for operations involving assembling of two or more components into a composite product. It it cannot be used when the operation involving processing of single inputs. Further, assembly line technique is suitable only for very high production rates. Thus assembly-line methods are used primarily for high volume consumer durable goods such as automobile, and home appliances.
Batch processing on the other hand can be used for any type of production. However, when the non-assembly operations with very high rate of production is required it is better to use some method of automated or continuous production. Yarn spinning is a good example of such high speed automated production process.
Some production processes are such that batch processes continues to be the best alternative for even very high level of production. For example, Pig iron is produced in blast furnace in batch mode.
Even coming to consideration of flexibility, the assembly line process is less flexible because it is designed that way. When the product is standard there is no need for the process to be flexible. However, it is worthwhile to note that now Assembly lines are being designed to provide a considerable higher level or flexibility than was the case in the past.
In case of batch production also the flexibility of the process will depend on the way the process is designed. Let us once again take the example of the blast furnace operations. It is a batch process but has very little flexibility. This process is not designed to be flexible, simply because flexibility is not required.