Machining Processes

Machining processes are the techniques used for removing material from a workpiece (an item that is being manufactured). This article summarizes the three main categories of machining processes; discusses the desirable characteristics of machining processes; and examines aspects of nontraditional machining processes. Finally, the article defines terms and concepts that are relevant to the topic of machining processes.

Keywords Abrasive Processes; Cutting Processes; Disruptive Technology; Laser; Machining; Machining Processes; Manufacture; Milling; Nontraditional Processes; Outsourcing; Prototype; Turning; Waterjet Cutting Processes; Workpiece

Manufacturing > Machining Processes

Overview

Definitions

Our study of machining processes begins with definitions for two important terms:

• Workpiece
• Machining Processes

Workpiece

In the manufacturing industry, a workpiece refers to an item that is in the process of being manufactured.

Machining Processes

Machining processes are the techniques used for removing material from a workpiece. Generally, machining processes can be grouped into three categories of processes:

• Cutting processes: These processes utilize single-point or multipoint cutting tools, each with a clearly defined geometry. Machining processes that are considered to be in the cutting processes category include milling (cutting material with a rotary cutter) and turning (rotating the workpiece in order to cut cylindrical parts). Basically, cutting processes involve the machining of an external surface with the workpiece rotating. Most often, it utilizes a single-point cutting tool.
• Abrasive processes: These processes include methods such as grinding.
• Nontraditional processes: These processes utilize electrical, chemical, or optimal sources of energy. See "Laser micromachining" and "Waterjet cutting" in the Applications section (Michigan Technological University, 2007).

Choosing the Appropriate Machining Processes

How do manufacturers go about choosing the appropriate machining processes?

Manufacturers choose their machining processes based on a combination of factors dictated by their own unique circumstances, the workpiece itself, ease and safety of use, and cost. Haftl (2007) presents a table containing five machining processes for metals.

The table provides a ball park price for the equipment for each process and indicates how each process performs in six categories: Thickness of material machined; type of material machined; ability to make perpendicular cuts; speed of cutting; best features; and worst features.

Desirable Characteristics of Machining Processes

Regardless of the type of machining process, manufacturers strive to ensure that the processes will exhibit the following four desirable characteristics:

• Suitability

• Safety

• Accuracy
• Cost-effectiveness

Suitability

The first desirable characteristic of machining processes is suitability. Suitability indicates that the machining processes are appropriate for the composition of the workpieces being machined. Certain machining processes are only suitable for thin or rigid materials. Other machining processes are only effective for cutting very small pieces.

Safety

The second desirable characteristic of machining processes is safety.

Machining processes safety covers three areas:

• The item
• The workers or operators
• The environment

Item Safety

Item safety ensures that the machined part or item meets safety standards for usage. When discussing machining processes, we might typically think of user safety in relation to end products such as tools, furniture, or other household items. However, machining processes are also used on food products, which would require scrupulous adherence to sanitary requirements. See "Example of Waterjet Cutting: Frozen Fruit" in the Applications/Further Insights section.

Worker or Operator Safety

Worker or operator safety ensures that the machining processes and tools are safe for the workers or operators who are performing the machining process tasks.

The U.S Department of Labor oversees compliance of fair labor practices, including safe working conditions. The U.S. Occupational Safety & Health Administration (OSHA), an agency within the Department of Labor, enforces the federal laws and regulations concerning safe working conditions. In addition, OSHA encourages individual states to set up their own occupational safety and health programs that OSHA monitors after approving them. To date, 26 states have set up OSHA-approved safety and health programs (United States Occupational Safety & Health Administration, n.d.).

The issues surrounding safety guards for machines are reviewed in "Materials address safety guarding issues" (Metalworking Production, 2005, p. 15). According to the article, the frequent opening and closing of machine guards can cause serious occupational injuries. In addition, the removal of machine safety guards very often leads to industrial accidents. So, why would anyone remove the safety guards on machines? It seems that guard systems that are often heavy steel or wire mesh are difficult to use; therefore, the guards are more likely to be removed or bypassed. The solution proposed in the article is to replace heavy machine guards with guards made of lighter, more flexible materials, such as Perspex with gas spring supports or glass with rotating wiper portholes. These two types of machine guards provide a weightless, balanced lift when the doors are opened and also allow for clearer observation of the work process.

Environmental Safety

Environmental safety ensures that the machining processes and their byproducts do not pose hazards to the environment. In addition to any state and local environmental regulations, manufacturers must comply with the laws and regulations of the U.S. Environmental Protection Agency.

Accuracy

The third desirable characteristic of machining processes is accuracy. Accuracy refers to the ability of the machining processes to consistently yield an item that accurately meets specifications on the first cut.

Cost-effectiveness

The last desirable characteristic of machining processes is cost-effectiveness. To be cost-effective, the machining processes need to be performed at a cost that yields a profit for the manufacturer but is still affordable for customers.

The cost-effectiveness of machining processes is mainly affected by the following factors:

• The price of materials
• The price and reliability of equipment
• The availability of skilled labor
• The cost of compensation for employees
• The cost of overhead (rent, insurance, utilities)
• The speed of the machining processes
• The manufacturer's competitive position in the marketplace

The Price of Materials

Although the price of materials is largely dictated by supply and demand, manufacturers still negotiate for the best prices from suppliers.

The Price & Reliability of Equipment

Manufacturers will of course attempt to negotiate the best prices for the purchase or rental of their equipment. However, the reliability of the equipment — how long it can operate perfectly without the need for repair or replacement — affects both the true cost of the equipment and the speed of machining processes.

The Availability of Skilled Labor

Access to a skilled labor pool is crucial for manufacturers. Skilled labor includes the employees who operate the machines and the employees who supervise them and the plants. If a manufacturer outsources part or all of his machining processes to another company, he must be certain that the other company has access to an adequate, skilled labor pool.

The Cost of Compensation for Employees

The cost of employee compensation, which includes wages and benefits, such as health insurance and vacation allotment, is a major factor in how cost-effectively a manufacturer can operate.

The Cost of Overhead (Rent, Insurance, Utilities)

While rent, purchase prices for buildings, and insurance can certainly be negotiated, overhead costs such as utilities usually cannot be negotiated. Savings can accrue however, by reducing space requirements. Or, the cost of overhead can be maximized by performing machining processes 24 hours a day.

The Speed of the Machining Processes

Naturally, the faster workpieces can be machined, the lower the cost of machining them because more pieces are being produced per worker hour and the remaining facets of the manufacturing process can be continued faster.

The Manufacturer's Competitive Position in the Marketplace

A manufacturing company that has established itself as consistently reliable and competitively-priced will be better able to attract customers with profitable, repeat orders.

Case Study: Making a Profit with a Seemingly Profitless Strategy

The making of a prototype — an original model or pattern for an item to be produced — is a slow, trial and error process which is therefore not a profitable one. Richard Alfoni, the owner of Eastern Science, a manufacturer of mechanical parts based in Rowley, MA agrees. In fact, Alfoni admits that his company makes absolutely no profit by machining prototypes. Yet, his company engages in machining prototypes as an integral part of its business strategy.

Alfoni cites two main reasons that his company machines prototypes (Korn, 2004):

• He uses prototyping as a marketing strategy: His company is likely to win any subsequent production work for the item prototyped.
• He uses the machining of prototypes as a continuing education tool for his employees: The machining of prototypes allows him to train employees to be flexible by working with a variety of techniques on innovative equipment. The novelty of producing prototypes also keeps employees excited about their work.

Applications

Aspects of Machining Processes

In this section, we will investigate machining processes further by examining two aspects:

• Features of two nontraditional categories of machining processes:
• Laser micromachining
• Waterjet cutting
• New developments in machining processes

Nontraditional Categories

The first aspect of machining processes that we will examine discusses the features of two nontraditional categories:

• Laser micromachining
• Waterjet cutting

Laser Micromachining

Laser micromachining works by aiming a laser beam directly at a workpiece to perform the cut.

Advantages of Laser Micromachining

Rizvi (2006) explains that the advantages of laser micromachining include the following benefits:

• Wide material coverage: Almost any material can be cut accurately by laser micromachining.
• High precision: Laser micromachining allows for reproducible, accurate cutting down to very minute dimensions.
• Non-contact machining: Tool wear is not an issue. Also, this feature allows the cutting of materials that are difficult to handle, such as very thin foils.
• Flexibility: Laser micromachining tools can be easily and quickly reconfigured for several tasks.
• Single-stage processing: Laser micromachining is a single-state, dry processing method that offers high reproducibility and minimal debris. The dry processing feature reduces the need for complex stages and therefore offers an effective process for rapid prototyping.

Waterjet Cutting

Waterjet cutting is a type of machining process that is a form of micro erosion. It works by forcing a large volume of water through a small orifice in a nozzle. The water causes pressurized steam to form cracks in the workpiece, enabling the waterjet to erode the surface until the material is cut through.

Advantages of Waterjet Cutting

The advantages of waterjet cutting include the following:

• It is effective for cutting small pieces because the concentrated steam allows for very close cutting with less damage to components.
• The micro-machining features of waterjet cutting conserve material.
• Waterjet cutting does not produce potentially harmful dust or particles that are produced by other types of machining processes such as grinding.
• When an abrasive is added to the water, it can be used to cut tool steel without generating the heat that is caused by conventional machining processes. This is a significant advantage because heat can alter the structure of the tool and thus comprise its strength.
• When used to cut wood, abrasive waterjet cutting leaves a smooth finish that eliminates the need to sand the wood.
• Waterjet cutting can be easily programmed to produce prototype parts quickly and cheaply.

Disadvantages of Waterjet Cutting

Waterjet cutting is generally limited to machining lower strength materials that are soft and crack easily. Although it can be used to cut harder material like tool steel (as noted above under "advantages"), the cutting time increases greatly, which decreases output and thereby increases the cost per piece.

Waterjet cutting cannot cut very thick parts accurately (Michigan Technological University, 2007).

Example of Waterjet Cutting: Frozen Fruit

Jet Edge, a Minnesota-based waterjet manufacturer, was asked to test cut a frozen block of cherries for a company that supplied cherries for the making of preserves. Based on the results, the company ordered a machine (Haftl, 2007).

New Developments in Machining Processes

Albert (2007) refers to disruptive technology — radically new and different, untried methods — as he reviews some of the new machining processes developments from the Machining Technology Laboratory (MTL). Founded in 2006, MTL is a research & development initiative that fosters partnerships between machine tool builders, too manufacturers, and other interested parties, for the purpose of discovering innovative metal-working processes.

Here are four new developments generated by MTL:

• Spinning Tool
• Nitro-milling
• Water Gage
• Grinding Wheels

Spinning Tool

The spinning tool rotates as it engages the workpiece. It allows for more rigidity in the cutting process, which makes the cut more stable and allows the heat generated to spread around the surface and dissipate, rather than build up on the cutting edge. These features increase cutting speed — metal removal rates are five times greater — and also spread out the wear and tear on tools; increase in tool life is 20 fold.

Nitro-milling

Nitro-milling allows the workpiece to rotate faster, allowing for a doubling of metal removal rates. Like the spinning tool process described above, nitro-milling more evenly distributes the wear and tear on tools, increasing their lifespan by four fold.

Water Gage

The water gage offers a new way to measure critical workpiece features while it is in the machine. The water gage accomplishes this measuring by aiming high-pressure streams of coolant at the workpiece surfaces and calculating backflow pressure to produce a readout of part dimensions. This ability to provide in-process measurements shortens cycle time and enhances machine utilization by preventing down-time due to inspection delays.

Grinding Wheels

MTL is exploring the use of grinding wheels to power live tooling stations that allow the sharpening or renewing of tools automatically without removing them from the machine. This innovation would allow machines to run without operator intervention, perhaps for as long as several weeks.

High tech processes

New computer assisted processes allow for extreme precision. These processes include electrical discharge machining (EDM) and ultrasonic-assisted EDM, which use algorithms to achieve a very high accuracy rate (Shabgard, Badamchizadeh, Ranjbary & Amini, 2013). Sensor-based fixtures placed in machine stations used in a multi-station machining processes (MMP) ensure energy and cost efficiences (Abellan-Nebot, Liu & Romero Subirón, 2012).

Conclusion

Machining processes are generally grouped into three categories: Cutting processes, abrasive processes, and nontraditional, or energy-based processes. Manufacturers choose their machining processes based upon how well they meet four factors: Suitability, safety, accuracy, and cost-effectiveness. Due to the significance of these four factors, manufacturers will continue to search for methods that enhance their value by seeking out newer materials, safer techniques, more reliable and versatile equipment, and more efficient strategies for machining processes.

Terms & Concepts

Abrasive Processes: Machining processes that involve methods such as grinding.

Cutting Processes: Machining processes that utilize single-point or multipoint cutting tools, each with a clearly defined geometry.

Disruptive Technology: Abandoning the old method and replacing it with a new and radically different method that hasn't yet been considered (Albert, 2007).

Laser: A device that utilizes the natural oscillations of atoms or molecules between energy levels for generating coherent electromagnetic radiation usually in the ultraviolet, visible, or infrared regions of the spectrum (Merriam-Webster's collegiate dictionary, 2000).

Machining: Removal of material from a workpiece (Michigan Technological University, 2007)

Machining Processes: Techniques for removing material from a workpiece that usually can be grouped into one of three categories: Cutting processes, abrasive processes, and nontraditional processes.

Manufacture: To make a product from raw materials by hand or by machine (Merriam-Webster's collegiate dictionary, 2000).

Milling: Milling is the process of cutting away material by feeding a workpiece past a rotating multiple tooth cutter. Milling is a fast method of machining that may be used on flat, angular, or curved surfaces (Michigan Technological University, 2007).

Nontraditional Processes: Machining processes that utilize electrical, chemical, or optimal sources of energy.

Outsourcing: The procuring of services or products from an outside supplier or manufacturer in order to cut costs (Brooks, 2004).

Prototype: An original model on which something is patterned; a first full-scale and usually functional form of a new type or design of a construction (Merriam-Webster's collegiate dictionary, 2000).

Turning: A machining operation that produces cylindrical parts. Basically, it is the machining of an external surface with the workpiece rotating. Most often, it uses a single-point cutting tool (Michigan Technological University, 2007).

Waterjet Cutting Processes: Machining processes that work by forcing a large volume of water through a small orifice in a nozzle. The water causes pressurized steam to form cracks in the workpiece, enabling the waterjet to erode the surface until the material is cut through.

Workpiece: A piece of work in process of manufacture (Merriam-Webster's collegiate dictionary, 2000).

Bibliography

Abellán, J. V., & Liu, J. J. (2013). Variation propagation modelling for multi-station machining processes with fixtures based on locating surfaces. International Journal of Production Research, 51, 4667-4681. Retrieved November 15, 2013, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=89552355&site=ehost-live

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Albert, M. (2007). From out of the lab. Modern Machine Shop, 80, 100-106. Retrieved July 19, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25401808&site=ehost-live

Brooks, G. (2004). What is outsourcing? New Media Age, 2004(Supplement), 4-4. Retrieved June 11, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=15578248&site=ehost-live

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Felix, C. (2007). Boost throughput with multitasking. Production Machining, 7, 36-40. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25392113&site=ehost-live

Gupta, D. P., Gopalakrishnan, B. B., Chaudhari, S. A., & Jalali, S. S. (2011). Development of an integrated model for process planning and parameter selection for machining processes. International Journal of Production Research, 49, 6301-6319. Retrieved November 15, 2013, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=65500978&site=ehost-live

Haftl, L. (2007). No profit, no business. American Machinist, 151, 28-29. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=24309472&site=ehost-live

Haftl, L. (2007). Make sure the process suits the job. American Machinist, 151, 33-37. Retrieved July 28, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25829876&site=ehost-live

Korn, D. (2007). The laser's role in micromachining metals. Modern Machine Shop, 79, 94-97. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=24771978&site=ehost-live

Korn, D. (2004). Prototyping has its place. Modern Machine Shop, 77, 84-88. Retrieved July 31, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=14705223&site=ehost-live

Korn, D. (2007). A quick look at PEEK machining. Modern Machine Shop, 80, 84-86. Retrieved July 19, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25401806&site=ehost-live

Materials address safety guarding issues. (2005). Metalworking Production, 149, 15-15. Retrieved July 31, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=16987776&site=ehost-live

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Shabgard, M. R., Badamchizadeh, M. A., Ranjbary, G. G., & Amini, K. K. (2013). Fuzzy approach to select machining parameters in electrical discharge machining (EDM) and ultrasonic-assisted EDM processes. Journal of Manufacturing Systems, 32, 32-39. Retrieved November 15, 2013, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=85154802&site=ehost-live

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Suggested Reading

Bramlet, C. (2007). Finding the right words and the right process. Modern Machine Shop, 80, 90-96. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25401807&site=ehost-live

Bramlet, C. (2007). A fresh face in machining. Modern Machine Shop, 79, 116-123. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=24510262&site=ehost-live

The right mix of tooling and machines streamlines process. (2007). Modern Machine Shop, 80, 132-139. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25790760&site=ehost-live

Young, F. (2007). Why we use honing. Modern Machine Shop, 79, 92-97. Retrieved July 23, 2007, from EBSCO Online Database Business Source Complete. http://search.ebscohost.com/login.aspx?direct=true&db=bth&AN=25082617&site=ehost-live