Background and History
In this section you will learn
- What is batch manufacturing
- The reasons for creating the standard
Manufacturing operations can be generally classified as discrete, continuous, or batch
Discrete processes involve the production of things. A part or a specific quantity of parts in a group moves from one workstation to another, gaining value at each location as work is performed. In a discrete process, each thing or part maintains its unique identity. A great example of a discrete manufacturing process is the production of automobiles.
Continuous processes involve the continuous flow of material through various processing equipment. Once a continuous process is operating in a steady state, the goal is to produce a consistent product no matter how long the operation may run. The production of gasoline is often thought of as key example of a continuous process.
According to the S88 standard, a batch process is defined as
a process that leads to the production of finite quantities of material by subjecting quantities of input materials to an ordered set of processing activities over a finite period of time using one or more pieces of equipment.
Instead of a continuous flow that can go on for days or weeks, batch processing involves limited quantities of material called (are you ready for this?) batches. By the nature of the process, batch manufacturing is discontinuous. That is, you start with some raw material, do something with it, send it on its way, and start all over again with some new raw material.
Batch manufacturing is also not discrete. There are no things that you can easily separate or identify. Sure, you can place a portion of a batch into some specific container, like a bottle of soy sauce, but that doesn’t make the process discrete. If you combine a whole bunch of uniquely stamped gas caps in a box and mix them up, you can still identify each one individually. You can individually mark bottles of soy sauce, but the sauce inside the bottle is still part of the same batch and cannot be distinguished from one bottle to the next. The distinguishing factor of a product like soy sauce is the batch or lot from which it was bottled. That’s why you’ll see some type of batch or lot identifier printed on the cap or label.
Why a batch control standard?
Producing a product consistently is always a top priority. Once a process is repeatable, you can then work on issues like reducing cost, waste, or both. Consistently producing products with batch manufacturing is especially tricky. Unlike continuous processes, which may run for a long time, brand-new batches are created often. And unlike both discrete and continuous processes, it may not be possible to determine if the batch is being made correctly while it is being made. You may have to wait until the batch is complete before checking. If it’s a bad batch, you can try to correct it or you may have to trash it. The point is to make a batch right the first time.
So, the control of the batch process (or as we automation engineers like to call it, batch control) is a very important aspect of batch manufacturing. For years, companies faced four challenges with batch control:
- No universal model existed for batch control
- Users had a difficult time communicating their batch processing requirements
- Engineers found it hard to integrate solutions from different vendors
- Engineers and users had a difficult time configuring batch control solutions
All of these problems led to expensive batch control systems that often did not meet all of the needs of the users and were difficult to maintain. And so, in 1988, ISA formed the S88 committee (no relation between the year and committee number) to address batch control.
So, now you know how it all started. Let’s move forward by figuring out what S88 really is from the big-picture perspective.