Different types of production can be used within a manufacturing organization. Production methods fall into three main categories; however, all production methods can be assisted with CAM and CAD equipment (Computer Aided Manufacture and Computer Aided Design – respectively).
Job Production and Prototype Production
Job Production is used when a product is produced with the labor of one or few workers and is scarcely used for bulk and large scale production. It is mainly used for one-off products or prototypes, as it is inefficient; however, quality is greatly enhanced with job production compared to other methods. Individual wedding cakes and made-to-measure suits are examples of job production. New small firms often use job production before they get a chance or have the means to expand. Job Production is highly motivating for workers because it gives the workers an opportunity to produce the whole product and take pride in it.
Boutique Manufacturing
Contrary to jobbing production, the method Boutique Manufacturing is suitable for the production of very small to small batches, i.e. orders of a few units up to several dozens of similar or equal goods. The workflow organization of a Boutique Manufacturing entity can be a mixture of both jobbing and batch production but involves higher standardization than job production. Boutique Manufacturing is often organized with single workplaces or production cells carrying out a number of subsequent production steps until completion of certain components or even the whole product; large assembly lines are generally not used. The flexibility and variety of products able to be produced in the entity therefore are much higher than with the more standardized method of batch production.
Batch Production
Batch production is a technique used in manufacturing, in which the object in question is created stage by stage over a series of workstations, and different batches of products are made. Together with job production (one-off production) and mass production (flow production or continuous production) it is one of the three main production methods.
Batch production is the method used to produce or process any product in groups or batches where the products in the batch go through the whole production process together. An example would be when a bakery produces each different type of bread separately and each object (in this case, bread) is not produced continuously. Batch production is used in many different ways and is most suited to when there is a need for a quality/quantity balance. This technique is probably the most commonly used method for organizing manufacture and promotes specialist labor, as very often batch production involves a small number of persons. Batch production occurs when many similar items are produced together. Each batch goes through one stage of the production process before moving onto next stage.
Batch production is most common in bakeries and in the manufacture of sports shoes, pharmaceutical ingredients (APIs), purifying water, inks, paints and adhesives. In the manufacture of inks and paints, a technique called a color-run is used. A color-run is where one manufactures the lightest color first, such as light yellow followed by the next increasingly darker color such as orange, then red and so on until reaching black and then starts over again.
Advantages and disadvantages
There are several advantages of batch production; it can reduce initial capital outlay (the cost of setting up the machines) because a single production line can be used to produce several products. As shown in the example, batch production can be useful for small businesses that cannot afford to run continuous production lines. If a retailer buys a batch of a product that does not sell, then the producer can cease production without having to sustain huge losses. Batch production is also useful for a factory that makes seasonal items, products for which it is difficult to forecast demand, a trial run for production, or products that have a high profit margin.
Batch production also has some drawbacks. There are inefficiencies associated with batch production as equipment must be stopped, re-configured, and its output tested before the next batch can be produced. Idle time between batches is known as downtime. The time between consecutive batches is known as cycle time. Cycle time variation is a Lean Manufacturing metric.
Continuous production is used for products that are made in a similar manner. For example, a certain car model has the same body shape and therefore, many of the same model cars can be made at the same time without stopping, decreasing manufacturing cost.
Flow Production
Flow production (Process Production) is also a very common method of production. Flow production is when the product is built up through many segregated stages; the product is built upon at each stage and then passed directly to the next stage where it is built upon again. The production method is financially the most efficient and effective because there is less of a need for skilled workers.
Continuous Production
Continuous usually means operating 24 hours per day, seven days per week with infrequent maintenance shutdowns, such as semi-annual or annual. Some chemical plants can operate for more than one or two years without a shutdown. Blast furnaces can run four to ten years without stopping. Continuous production is a flow production method used to manufacture, produce, or process materials without interruption. Continuous production is called a continuous process or a continuous flow process because the materials, either dry bulk or fluids that are being processed are continuously in motion, undergoing chemical reactions or subject to mechanical or heat treatment. Continuous processing is contrasted with batch production.
Common Processess
Some common continuous processes are the following:
- Oil refining
- Chemicals
- Synthetic fibers
- Fertilizers
- Pulp and paper
- Blast furnace (iron)
- Metal smelting
- Power stations
- Natural gas processing
- Sanitary waste water treatment
- Continuous casting of steel
- Rotary kilns for calcining lime or cement
- Float glass
Production workers in continuous production commonly work in rotating shifts.
Processes are operated continuously for practical as well as economic reasons. Most of these industries are very capital intensive and the management is therefore very concerned about lost operating time.
Shutting down and starting up many continuous processes typically results in off quality product that must be reprocessed or disposed of. Many tanks, vessels and pipes cannot be left full of materials because of unwanted chemical reactions, settling of suspended materials or crystallization or hardening of materials. Also, cycling temperatures and pressures from starting up and shutting down certain processes (line kilns, boilers, blast furnaces, pressure vessels, etc.) may cause metal fatigue or other wear from pressure or thermal cycling.
In the more complex operations there are sequential shut down and start up procedures that must be carefully followed in order to protect personnel and equipment. Typically a start up or shut down will take several hours.
Continuous processes use process control to automate and control operational variables such as flow rates, tank levels, pressures, temperatures and machine speeds.
Semi-continuous Processes
Many processes such as assembly lines and light manufacturing that can be easily shut down and restarted are today considered semi-continuous. These can be operated for one or two shifts if necessary.
History
The oldest continuous flow processes is the blast furnace for producing pig iron. The blast furnace is intermittently charged with ore, fuel and flux and intermittently tapped for molten pig iron and slag; however, the chemical reaction of reducing the iron and silicon and later oxidizing the silicon is continuous.
Semi-continuous processes, such as machine manufacturing of cigarettes, were called “continuous” when they appeared.
Many truly continuous processes of today were originally batch operations.
The Fourdrinier paper machine, patented in 1799, was one of the earliest of the industrial revolution era continuous manufacturing processes. It produced a continuous web of paper that was formed, pressed, dried and reeled up in a roll. Previously paper had been made in individual sheets.
Another early continuous processes was Oliver Evans’es flour mill (ca. 1785), which was fully automated.
Early chemical production and oil refining was done in batches until process control was sufficiently developed to allow remote control and automation for continuous processing. Processes began to operate continuously during the 19th century. By the early 20th century continuous processes were common.
Shut-downs
In addition to performing maintenance, shut downs are also when process modifications are performed. These include installing new equipment in the main process flow or tying-in or making provisions to tie-in sub-processes or equipment that can be installed while the process is operating.
Shut-downs of complicated processes may take weeks or months of planning. Typically a series of meetings takes place for co-ordination and planning. These typically involve the various departments such as maintenance, power, engineering, safety and operating units.
All work is done according to a carefully sequenced schedule that incorporates the various trades involved, such as pipe-fitters, millwrights, mechanics, laborers, etc., and the necessary equipment (cranes, mobile equipment, air compressors, welding machines, scaffolding, etc.) and all supplies (spare parts, steel, pipe, wiring, nuts and bolts) and provisions for power in case power will also be off as part of the outage. Often one or more outside contractors perform some of the work, especially if new equipment is installed.
Safety
Safety meetings are typically held before and during shutdowns. Other safety measures include providing adequate ventilation to hot areas or areas where oxygen may become depleted or toxic gases may be present and checking vessels and other enclosed areas for adequate levels of oxygen and insure absence of toxic or explosive gases. Any machines that are going to be worked on must be electrically disconnected, usually through the motor starter, so that it cannot operate. It is common practice to put a padlock on the motor starter, which can only be unlocked by the person or persons who is or are endangered by performing the work. Other disconnect means include removing couplings between the motor and the equipment or by using mechanical means to keep the equipment from moving. Valves on pipes connected to vessels that workers will enter are chained and locked closed, unless some other means is taken to insure that nothing will come through the pipes.
Continuous Processor (Equipment)
Continuous Production can be supplemented using a Continuous Processor. Continuous Processors are designed to mix viscous products on a continuous basis by utilizing a combination of mixing and conveying action. The Paddles within the mixing chamber (barrel) are mounted on two co-rotating shafts that are responsible for mixing the material. The barrels and paddles are contoured in such a way that the paddles create a self-wiping action between themselves minimizing buildup of product except for the normal operating clearances of the moving parts. Barrels may also be heated or cooled to optimize the mixing cycle. Unlike an extruder, the Continuous Processor void volume mixing area is consistent the entire length of the barrel ensuring better mixing and little to no pressure build up. The Continuous Processor works by metering powders, granules, liquids, etc. into the mixing chamber of the machine. Several variables allow the Continuous Processor to be versatile for a wide variety of mixing operations:
- Barrel Temperature
- Agitator speed
- Fed rate, accuracy of feed
- Retention time (function of feed rate and volume of product within mixing chamber)
Continuous Processors are used in the following processes:
- Compounding
- Mixing
- Kneading
- Shearing
- Crystallizing
- Encapsulating
The Continuous Processor has an unlimited material mixing capabilities but, it has proven its ability to mix:
- Plastics
- Adhesives
- Pigments
- Composites
- Candy
- Gum
- Paste
- Toners
- Peanut Butter
- Waste Products
Computer Aided Manufacture and Computer Aided Design
Computer Aided Design (CAD) is the use of a wide range of computer-based software tools that assist engineers and architects alike.
Text adapted from “Methods of Production” and “Continuous Production” by Saylor Academy under a CC BY: Attribution license.