Precision Cleaning and Machining with Minimal Waste and Increased Profitability

Manufacturing waste is generally thought of as any material resource used in a production
process that does not go out as part of the product and costs money to dispose of. However, manufacturing waste also exists in many other forms such as excessive factory space use for equipment (production and waste treatment equipment), inefficient material and process flows, inefficient use of facility labor and lost productivity of both labor and equipment. These types of waste significantly impact a company’s bottom line too, but are often obscured in overhead accounts or generally overlooked in the cost analysis of a manufacturing operation.

In an era of intense global competition with unbalanced labor costs, managers must have the skills necessary to identify and eliminate various manufacturing waste in their operations to improve business profitability. Numerous educational resources are available to manufacturers that teach the methods for the identification and financial accounting of manufacturing waste1- 5.

In addition to waste reduction knowledge, manufacturers of advanced products need state-of-the-art technologies and implementation strategies for successful design and execution of waste reduction programs. Waste reduction programs may include one or a combination of the following technology components:
• Cleaner and greener manufacturing technology to eliminate or reduce environmental waste
• Flexible automation, modular and clustered assembly operations (cells) to reduce operational waste
• More adaptable and flexible production tools and methodologies to improve efficiency and productivity in low volume-high mix-high value production
• Advanced dry cleaning and machining technology for improved quality and reliability imposed by advanced materials, manufacturing methods and processes and applications

This article introduces manufacturing managers to Carbon Dioxide (CO2) technology as a tool for improving the performance of production cleaning, assembly processes and machining operations while eliminating operational and resource waste. CO2 technology prevents or eliminates waste at the source by modifying cleaning, assembly and machining processes using clean and green chemistry, unique tool and process implementations. CO2 technology is a clean and lean manufacturing tool that increases both productibility and profitability.

Clean and Lean Manufacturing Practices

Clean and lean manufacturing practices are continuous preventive measures that concentrate on optimizing manufacturing resources and manufacturing processes to minimize or eliminate wastes of various forms. Clean manufacturing practices help companies achieve maximum productivity with minimal waste. One of its principal benefits to companies is that clean manufacturing reduces operating cost—especially in the areas of chemical management—wasted raw materials, waste collection and treatment and pollution control. Clean manufacturing provides opportunities to reduce regulatory obligations, risks and associated costs, and increases manufacturing process efficiency and productivity. Thus, clean manufacturing has a natural synergy with lean manufacturing, a related waste reduction focus that emphasizes manufacturing actions and operations to maximize efficiency. A lean focus can require clean manufacturing techniques in order to achieve lean goals.

Clean manufacturing practices should therefore incorporate both clean and lean elements where practical, and aim to reduce or eliminate both operational and resource wastes as they relate to manufacturing and assembly processes. This broader perspective of the clean manufacturing strategy is enabled with advanced CO2 technology.

Environmental Benefits of CO2 Technology

Substantial and unmatched environmental benefits are derived from CO2 technology. The U.S. Environmental Protection Agency (EPA) has determined that CO2 chemistry is an environmentally benign alternative for the manufacturing industry because there is no net increase in global warming gases or environmental damage as a result of using CO2 6.
Removing or minimizing the use of organic compounds such as petroleum derived cutting and cleaning fluids in manufacturing processes—and in particular not having to produce as much of these compounds and replacing them with CO2,—will lower energy usage, lower emissions of global warming gases and improve water, air quality and natural resource conservation. CO2 is a cost- and performance-effective replacement in a variety of cleaning and machining applications.

CO2 Technology as a Clean and Lean Manufacturing Strategy

CO2 technology eliminates or significantly reduces waste generation at the production operation level (source) by modifying manufacturing processes. CO2 uniquely modifies cleaning, assembly processes requiring critical cleaning and machining operations in two ways:
• Physically—shape, size, space, application and configuration
• Chemically—solvency, toxicity, wetness and chemical process

For example, due to CO2’s inherent dry chemistry, CO2 cleaning technology may be uniquely implemented in a variety of cleaning equipment and process configurations to meet the needs of most lean production layouts and product flow requirements. Possible configurations and manufacturing waste reduction benefits are summarized in Table 1.

Replacing conventional surface cleaning agents with CO2’s green chemistry eliminates process inputs such as liquid cleaning solvents, detergents, deionized rinse water and heated air dryers, among other waste-producing inputs. In another example, CO2-based advanced minimum quantity cooling lubrication (AMQCL), uses small amounts of bio-based lubricants entrained in an adjustable cooling spray. AMQCL may be used to replace flooded application of cutting fluids, deionized water and associated waste-producing operations such as cutting fluids management, sludge waste collection and machining mist air pollution control.

Conventional Cleaning and Machining Processes

Machining and cleaning are two common manufacturing processes, which are typically performed sequentially in a production cycle (see Figure 1). Conventional batch and queue manufacturing flow for a machining operation followed by a cleaning operation often involves redundant operations and wasteproducing inputs. Manufacturing wastes produced in these operations may comprise one or more of the following elements:
• Inefficient materials and process flow
• Higher energy usage
• Excessive Floor Space usage
• Unnecessary product and personnel movement
• Potential for larger batch rejects
• Larger capital outlays
• Higher production labor costs
• Environmental wastes
• Lost productivity

Examples of specific cleaning and machining activities that produce a manufacturing waste include:
• Moving products off-line or out of cells to clean them and then returning them back to the line or cell
• Filtering and treating spent alkaline cleaning chemistries
• Monitoring cleaning and machining fluid chemistries
• Rinsing parts
• Drying parts
• Treatment and disposal of spent cleaning and machining agents
• Completing waste hauling manifests
• Environmental reports
• Deionized water treatment
• Rinse water treatment and disposal

CO2 as a Clean Manufacturing Solution

CO2-enabled machining and cleaning operations eliminate many of the waste elements found in conventional cleaning and machining processes. Examples include:
• Materials selection and productivity—CO2 does not require associated environmental, health and safety management, and greatly minimizes equipment cleaning and maintenance requirements
• Energy conservation—CO2 eliminates the need for additional energy to heat cleaning baths, dry parts or evaporate and concentrate waste by-products
• Waste reduction and elimination—CO2 does not itself become a waste by-product; CO2 eliminates the wasteful consumption, treatment and disposal of water, wastewater and associated solid wastes
• Air pollution reduction—CO2 is not considered an air pollutant, is non-toxic and odorless within the factory atmosphere
• Space and process step reduction—CO2-enabled processes can reduce multiple processing steps to a single step and perform in less space; sometimes no extra space is needed if the CO2 process is integrated directly into or onto an existing manufacturing platform such as a bonder, dispenser, machining tool or production line

CO2 technology also reduces wastes within machining and cleaning operations in other unique ways, and is illustrated in the following sections.

CO2 Cleaning in the Factory

Advanced CO2 cleaning technology is available in the form of spray and immersion processes including composite sprays, hybrid snow-plasma sprays, centrifugal liquid carbon dioxide cleaning systems, supercritical fluid extraction systems and fluids purification and management systems. CO2 cleaning and surface treatment applications are diverse and include precision degreasing, departiculation, outgassing, drying, disinfection and surface modification/ functionalization. A number of articles describe the benefits to end-users of this emerging cleaning technology7-12.

CO2 cleaning technology delivers many clean and lean waste reduction benefits to manufacturers including the elimination of toxics, reduction of cleaning steps, lower energy costs and improved cleaning quality and consistency, among many other benefits. In one company, summarized in Figure 2, an automated centrifugal CO2 degreasing system replaced an ultrasonic solvent cleaning system with an 82 percent reduction in utilities, a 68 percent reduction in materials, an 83 percent reduction in cleaning equipment maintenance and a 100 percent reduction in environmental, health and safety costs. Another benefit realized by the centrifugal CO2 precision degreasing process is that the machining oils (contaminants) are not contaminated with residual cleaning agent, which allows the reclaimed oils to be recycled directly back into the screw machining operations.

In another company, a major disk drive manufacturer reduced drive rework cost-per-clean up to 88 percent by eliminating the manufacturing wastes associated with parts disassembly, component scrap, aqueous cleaning and drying operations. A pair of SCARA robots precision clean both sides of various disk drive components during assembly (build-clean) in a cleaning configuration, which is uniquely enabled with CO2 technology (see Figure 3).

Another company eliminated multiple bond pad cleaning and preparation steps with a single step hybrid spray cleaning process using a carbon dioxide plasma and solid spray treatment (see Figure 4). The process reduced labor requirements, space and improved the reliability of the wire bonding operation, reducing product defects by 50 percent.

Unique Cleaning and Assembly Tool Configurations

In many high tech manufacturing operations, a product may be cleaned several times throughout the production cycle (i.e., build-clean). Part assembly operations requiring cleaning include cutting, drilling, trimming, micromachining, ultrasonic bonding, wire bonding, adhesive bonding, microwelding, dicing, abrasive finishing, polishing, stamping and inspection, among many other manufacturing and assembly operations. Traditionally, precision cleaning is performed as an “island” operation using, for example, a stand-alone spray cleaner, vapor degreaser, ultrasonic cleaning system, rinsing and drying stations. Moreover, isolation of the cleaning process from the assembly tool and process is a necessity due to the inherent chemical and physical (space) incompatibilities between conventional wet cleaning operations and most assembly processes and tools. CO2 technology changes all of this.

CO2 cleaning operations are easily integrated with assembly tools and processes to form lean and clean assembly cells (see Figure 5). Clean-assembly tools such as clean-machining, clean-stamping, clean-dispensing and clean-welding systems, among others, save both space and time. Clean-assembly tools may be clustered with virtually any type and number of manufacturing operations to reduce floor space, increase productivity, decrease part and people movement and cost of ownership.

CO2 Lean Machining Technology

Machining and metalworking operations predominantly employ a flooding coolant spray that is as old as the industry itself. In the past, flooding may have been necessary to compensate for excessive heat generated due to the inferior performance of cutting methods, tools, materials, machines and fluids. Today, “more is better” is not universally applicable to cutting fluids. In fact, for many operations flooding is wasteful, costly and may even be a detriment to the performance of advanced machining processes, materials and equipment.

The literature suggests that operational costs related to the use of flooded cooling lubricants can range between 7 percent and 17 percent of the total costs of the manufactured workpiece. Intangible costs to a business must also be considered. For example, cutting fluids, especially those containing petroleum oils, have become a huge liability. No matter how safe and environmentally friendly a cutting fluid may be, governmental regulations demand special handling the moment it is poured into a sump.

The initial purchase of a cutting fluid is merely the beginning of a much more expensive endeavor. According to a TechSolve, Inc., a non-profit consulting firm and testing laboratory based in Cincinnati, OH, for every $1 of coolant purchased, operational costs associated with using, maintaining and disposing of it can be more than $10 (see Figure 6). The real costs associated with cutting fluid purchases include the labor involved in mixing and transporting the fluids as well as machine draining and cleaning. In addition, deionized water make-up and coolant concentrate replenishment costs with coolant maintenance and disposal costs all contribute to a very high coolant life-cycle cost.

A new patented and patents pending CO2-enabled cooling lubrication technology has been recently introduced called Advanced Minimum Quantity Cooling Lubrication (AMQCL). AMQCL technology employs simple but powerful physics and engineering principles to provide an advanced ability to penetrate, cool, clean and lubricate a cutting zone. AMQCL resolves many of the negative characteristics of conventional machining fluid processes and can be implemented along side many older and newer metalworking machinery, tools and fluids, augmenting a successful conversion to cleaner and leaner machining operations (see Figure 7). AMQCL eliminates coolant-generated wastes and provides the opportunity to increase machining productivity in the form of longer tool life, increased speeds and depths of cut, and increased machine use, all of which can substantially improve the profitability of a machining operation.

The AMQCL spray system combines a source of propellant gas (i.e., compressed air), minute amounts of bio-based lubricants (i.e., vegetable oils) and CO2 in various concentrations to form an infinitely adjustable cooling lubricating machining spray (see Figure 8). The combinational use of renewable bio-based feedstocks such as CO2 and vegetable lubricants provides an environmentally sound and worker friendly alternative to petroleum-based cooling lubricants. Vegetable-based lubricants offer significant advantages such as superior tool lubricity, better surface finish, higher feed rates and a safer chemistry. Using a biobased lubricant in minimum quantity application eliminates the costs associated with treatment, environmental compliance and disposal, among other operational cost factors. Bio-based cooling and lubricating fluids are biodegradable, non-toxic, have low volatile organic compounds (VOCs) emissions, a high flash point and no offensive odor.

AMQCL uniquely controls machining heat using both a physical and chemical effect. Frictional heat generated at the cutting edge is eliminated through the delivery of reactive lubricants (chemical effect), including carbon dioxide itself, which produce beneficial tribochemical reactions. The majority of the machining heat produced by the deformation of the material itself is removed using adjustable spray compositions containing microscopic particles of solid carbon dioxide, which impact hot surfaces at high velocity and remove heat through a phase change (physical effect) phenomenon. Using a physicochemical approach, heat generation is controlled and heat is not allowed to accumulate in the tool or workpiece which would cause temperatures to rise. An example of the cutting performance achievable with AMQCL as compared to conventional flooded coolant application is shown in Figure 9. The AMQCL spray is directed into the cutting zone between the machining tool and cutting surfaces comprising a composite surface of metal, epoxy and ceramic. Most notable from the photomicrographs is the improved surface quality, lack of grooving and smearing of the soft metal and lack of staining of the outer ceramic surface.

The Bottom Line

The bottom line is that CO2 technology reduces manufacturing waste and improves profitability. It accomplishes this task in unique ways and for very practical manufacturing applications and requirements. It’s worth the effort for every manufacturer to seriously consider CO2 technology for its cleaning and machining operations as well as OEMs to enable new clean-assembly tool possibilities for their customers.


David Jackson began his career in the CO2 development field in 1984. As group head of precision cleaning and contamination control at Hughes Aircraft Company, he developed several CO2-based cleaning technologies which were patented and subsequently commercialized. David founded the Deflex Corporation in 1992, a CO2 cleaning technology development company, where he continued to develop and advance the field. In his present position as senior vice president of Marketing and Technology Development, he is responsible for the CO2 technology, market and business development for Cool Clean Technologies, Inc. (Eagan, MN). David has a bachelor’s degree in chemistry and has patented and commercialized numerous CO2 products over the past 15 years. The CO2 technology described in this article is protected under numerous issued and pending patents and is available from Cool Clean Technologies, Inc. For more information visit the Web site at www.coolclean.com.

References
1. An Introduction to Environmental Accounting as a Business Management Tool, United States Environmental Protection Agency, EPA 742-R-95-001, June 1995
2. Lean Manufacturing and the Environment: Research on Advanced Manufacturing Systems and the Environment and Recommendations for Leveraging better Environmental Performance, United States Environmental Protection Agency, EPA 100-R-03-005, October 2003
3. The EPA Manual for Waste Minimization Opportunity Assessments, United States Environmental Protection Agency, EPA/600/2-88-025, April 1988
4. How to Be Green and Stay in the Black, Department of Navy, NAVSO P-3680, October 1997
5. Schwendeman, T., “Pollution Prevention Can Pay”, Industrial Heating, December 2003
6. United States Environmental Protection Agency, 40 CFR Part 82, Protection of Stratospheric Ozone; Listing of Substitutes for Ozone-Depleting Substances.
7. Jackson, D. et al, “Today’s Forecast – It Looks like Snow”, Precision Cleaning, Volume VII, Number 5, May 1999
8. Darvin, C. et al, “ Demonstration of Liquid CO2 as an Alternative for Metal Parts Cleaning, Precision Cleaning, Volume IV, Number 9, September 1996
9. Chittick, R.C., “Using CO2 Snow to Correct Drive Level Dependence in Quartz Crystal Resonators”, Precision Cleaning, Volume V, Number 6, June 1997
10. Jackson, D., “Liquid CO2 Immersion Cleaning- The Users Point of View”, Parts
Cleaning, pp 32-37, April 1999
11. Jackson, D., “Making the Case for CO2”, CLEANTECH February 2004
12. Jackson, D., “CO2 in the Miniature Manufacturing Process”, MicroTEC, October 2004.