Process vs. Discrete Manufacturing
What are the similarities and differences between process and discrete manufacturing, and how can control engineers best equip themselves for these processes?
To characterize is human. With the myriad of industries and manufacturing facilities in the world, and new ones being developed each year, it is useful to characterize them. This way, common problems can be addressed across a large swath of industries, and perhaps contrasted with industries in another category to develop alternative solutions.
In general, manufacturing can be broken down into two types: process and discrete. Some muddiness occurs between categories. Sometimes, a facility can fall into either of these, depending on current production methods.
What is Process Manufacturing?
Process manufacturing is the creation of a continuous product that is difficult to separate once created. The products created are often metered out into containers for sale to the public or perhaps fed directly into another industrial facility for use. Often, the products have undergone a major, irreversible physical or chemical reaction, such that the original components are no longer easy to separate.
Figure 1. You can see the chemicals separated at first and then mixed into red paint. Video used courtesy of Pronto Industrial Paints
Consider the manufacture of latex paint. The starting materials include the components that form the latex: coloring agents, anti-foaming agents, thickeners, and other such ingredients. They are blended together, a few reactions occur, and the liquid flows into paint cans or is supplied directly to another downstream process.
The paint, once manufactured, is hard to separate; the chemical reactions have occurred, and it is unlikely the average person could separate the thickeners from the bulk of the liquid once it has been blended. This is why it is considered process manufacturing.
What is Discrete Manufacturing?
In discrete manufacturing, individual parts or devices are created. Discrete manufacturing is sometimes referred to as “assembly” because the manufacturing process is typically adding or subtracting material from a device as it is routed through the plant. The end product can potentially be disassembled and divided into the parts that make up its assembly.
Vehicles are an example of discrete manufacturing. From the early days with Henry Ford to the modern automated plant, the process still involves assembly. A frame is pulled along an assembly line, where the engine, transmission, wheels, and suspension components are mounted. Seats and instrument clusters, body panels, and other large components are installed next, followed by windows and various fitting installations.
Figure 2. This automotive assembly line is an example of discrete manufacturing.
When the car rolls off the assembly line, it could drive straight to a junkyard, and the crew could disassemble it the same way, removing each of these components. No chemical reactions occurred, no major physical changes; all of the same components are present and recognizable.
Commonalities Between Process and Discrete Manufacturing
Both styles of manufacturing require the same types of production parameters. Whether producing canned soup or electric motors, manufacturers are trying to reduce costs and increase profits. Therefore, they will both measure some form of throughput, meaning how much of something leaves the factor, operational costs, or how much it costs to produce each item or a standard unit of volume, and a few other parameters.
In both cases, engineers must improve uptime on equipment and optimize routing and tool utilization to reduce operational costs. They must find ways to improve the utility, raw material, and labor efficiency while maintaining or increasing throughput for the plant as a whole. All of this requires extensive collaboration between internal departments.
Just because throughput is increased in one division doesn’t mean that it is the best solution. For example, adding ferrosilicon to the melt increases flowability in steel production, and more steel is produced. However, it tends to react with the furnace lining, causing more frequent maintenance stops. Regardless of whether performing process or discrete manufacturing, all changes to production should go through a change acceptance process to ensure that the total profit will increase.
Figure 3. Steel leaving a continuous caster is an example of process engineering. Image used courtesy of pxfuel
Finally, but most importantly, both types of facilities require the same level of safety planning and training. Many hazards are found in both types of manufacturing facilities, and injuries and fatalities happen in both. While the Occupational Safety and Health Administration (OSHA) has some industry-specific protocols, there is much overlap between the two manufacturing categories.
Unique Challenges to Process and Discrete Manufacturing
While both manufacturing fields are similar, they also have some key differences that lead to unique challenges for each category.
In process manufacturing, part of the challenge in optimization is predicting the raw material input and having supplies arrive at the right time (e.g., just-in-time or lean manufacturing). While it is a concern in discrete manufacturing, it is slightly easier to predict the quantities of parts needed.
For example, if an electronics (discrete) manufacturer needs four small amplifier chips per product, they will likely purchase some multiple of four chips. Instead, imagine a steel foundry that produces structural shapes, such as I-beams. They pour and roll steel continuously, much of which comes from scrap steel.
To make the process repeatable for quality control purposes, small “master alloys” are added to alter the chemistry slightly, based on test samples throughout the process. Depending on the scrap source, which may come from shredded I-beams, appliances, automobile bodies, and other sources, the chemistry may vary significantly day-to-day.
This means the supply of master alloy that must be on hand will be used at varying rates and is incredibly difficult to model and predict. Furthermore, many process manufacturing operations deal with items with short shelf-life, such as food products, chemicals, and others, which means overstocking these raw materials often leads to waste.
Discrete manufacturing has its own difficulties. Often, continuous process manufacturing has obvious routing with very little decision and transport time. Chemicals are piped directly from a reactor to a distillation column, or steel blooms are cut and travel directly to the rolling mill. In discrete manufacturing, machined parts may have multiple paths, and optimization involves picking the most logical path for each item. This may mean changing run orders of process equipment based on supply or maintenance schedules or sending products back for reworking or repair operations after inspection.
Consider a mounting bracket for an alternator. It requires a hole drilled, one weld, and two bolted pieces, but the order does not matter. The plant engineer or technician can look ahead and decide to perform the drilling operations first to build up some inventory. Then, they can take the drill down for routine maintenance and send the inventory to the weld station.
Process and discrete manufacturing operations are impacted by similar issues, but also have some unique challenges. Because no manufacturing operation is truly “process” or “discrete,” engineers should learn to solve problems in both fields to make the most from their facility. In the coming weeks, we will dive into the equipment needed for process engineering and how remote monitoring is advancing the process industries.