Clean machining: Clean room use growing to optimize specialized processes
With increasing frequency, access to controlled environments for attenuating temperature, humidity, dust, dirt, particulates and microorganisms is essential for shops competing for high-end micromanufacturing jobs. Historically, clean rooms were used primarily for cleaning, assembly and packaging operations. Today, they are also being used to control potential contamination and improve accuracy within molding, machining and inspection operations.
Various types of clean rooms are available, including soft-sided, hard-walled and modular styles. Shown is the Series 591 portable clean room from Clean Air Products. The free-standing, modular, prefabricated clean rooms are available from Class 100,000 to Class 10 and feature open spans from 6’ to 34’. Photo courtesy Clean Air Products.
The following “crash course” on clean rooms is based on interviews with two clean room suppliers and three micromanufacturers that have installed them.
When and why are clean rooms used for micromachining? The naïveté of this question made some of our respondents laugh. Clean rooms are typically used to keep the controlled environments cleaner than surrounding areas, and temperature and humidity within acceptable ranges. The room or enclosure may protect parts from the incursion of dust being blown from other parts with an air hose at nearby machining operations. As a result, most clean rooms are under positive pressure.
However, the question is actually not as naïve as it sounds, because sometimes clean rooms and equipment enclosures are designed to keep things in—such as dust from exotic work materials, chemical fumes and the like. These rooms rely on negative pressure.
Ambient temperature may be controlled because it affects dimensional control of molded and machined parts. For example, a 7° C shift in temperature can cause a tool to grow or shrink by 0.01mm. That’s not much by conventional standards but poses real problems for parts manufactured to micron tolerances.
Humidity can promote bacterial growth, cause parts to corrode or impede subsequent bonding operations. One manufacturer interviewed strives to control humidity around his milling equipment to within 10 to 15 percent and may even put off some sensitive manufacturing operations during hot and humid summer days.
Some clean rooms control electrostatic discharge, which can zap electronics by overloading tiny circuits with heavy transient charges, burning them out.
The driver behind all of these considerations is the need to meet increasingly stringent cleanliness and precision requirements for a growing list of industries. All of the respondents agreed that most OEMs producing pristine or sterile products demand exceptionally clean parts, even though these OEMs may be cleaning, assembling, filling and packaging the end product in their own clean room. They appreciate, if not insist on, their suppliers having clean rooms so they don’t have to be as concerned about extraneous contamination entering their own processes.
What types of manufacturers require clean rooms? Our respondents were happy to inform us that clean rooms are a growth business. Medical device, electronics, defense and aerospace component manufacturers are all big users. The trend toward marrying a wide range of electromechanical devices (for instance, tiny windshield wiper motors) with computer chips is currently driving a lively interest in clean rooms for both parts manufacturing and assembly operations to ensure that the electronics are not compromised by the incursion of particles created during conventional manufacturing.
Can clean rooms make a contribution to micromachining operations? Definitely. For example, the need to control thermal growth of the part or tooling is a critical factor when microparts have dimensions that must be held within microns. MicroEDMs and conventional machine tools may have special enclosures that do a good job of controlling temperature. However, this equipment—enclosure and all—may also be housed in a clean room that maintains temperature within ±1° C so that inspection equipment will measure the parts under thermal conditions comparable to those under which they were manufactured.
Even builders of conventional products like motorcycles are insisting that critical components for their fuel-injection systems be machined and packaged in clean rooms so that there is no danger that a particle of dust will plug a critical orifice.
How are clean rooms classified? Clean rooms are typically classified according to the number and size of particles within a given volume of air. The two most common standards are the now-defunct U.S. Federal Standard 209E and ISO14644-1, which replaced it. The 209E standard was cancelled by the General Services Administration of the U.S. Department of Cmmerce on Nov. 29, 2001, but is still widely used.
The old Federal standard had six classes for clean rooms: 100,000, 10,000, 1,000, 100, 10 and 1, with one being the cleanest. The ISO Classes 8 through 3 correspond to these, with classes 2 and 1 being even cleaner.
The lower-number classes are typically found in industries like silicon chip and pharmaceutical manufacturing. Clean rooms used by micromanufacturers are most frequently Class 8 or Class 7. The classification only tells part of the story, however, because there are many other features of a clean room’s design that have little if anything to do with its class.
What are the key components of clean room and temperature control systems? The key component of a clean room is the filtration system (otherwise called a fan/filter, OPA filter or HEPA filter). This primary system may be used in conjunction with a wide range of additional systems, such as dehumidifiers, air conditioning and bag-in/bag-out filters that make it easy to remove dangerous contaminants and incinerate them.
Soft-sided clean rooms are like tents with open bottoms. Positive pressure prevents particles from entering the room. They can be purchased for about $40 per square foot. Hard-walled clean rooms range from $120 to $200-plus per square foot, depending on the room’s class and the complexity of its particle filtration system and other environmental controls. Modular clean rooms cost less and can be disassembled and moved. They are treated as equipment, not construction, so they depreciate faster. Conventionally constructed clean rooms typically cost more, but they allow for the greatest degree of design flexibility.
Operating costs include such things as power for various electromechanical systems, materials (filtration, cleaning, gowns, mats, etc.), maintenance and staff training.
Clean rooms frequently require certification. Some clean room manufacturers offer this service; however, independent consultants, such as those who perform ISO certification audits, are a better choice for those who wish to avoid the appearance of a conflict of interest. Monitoring devices may be installed in clean rooms to provide ongoing verification that the desired standards are being met.
Advanced Research Corp. machines aerospace and scientific instrument microparts in a class 10,000 clean room. The company operates an enclosed small hole popper (microEDM) with its own environmental controls. Still, external temperature control is important to ensure that parts measured away from the machine are under comparable thermal conditions. Photo courtesy ARC.
Albright Technologies' shop supervisor, Jim Smith, "gowns up" before entering the company's Class 10,000 clean room. Photo courtesy Albright Technologies.
Does having a clean room help solicit micromachining jobs? Maybe. It stands to reason that having a clean room could open the door to new jobs. However, the manufacturers consulted said that their decision to install a clean room had little to do with impressing prospective customers and more to do with optimizing specialized processes the companies had developed for making high-value-added products. To them it was an essential ingredient, so they did not hesitate to build what they needed.
In other cases, OEMs that want to minimize sources of contamination often drive the micromanufacturer’s decision to build a clean room. Manufacturers that adopt a “build it and they will come” attitude may have a hard time justifying the expense if they don’t come.
How to avoid grief
All of our respondents agreed that the three most important factors in developing a successful clean room operation for micromanufacturing are:
- Know the requirements. Understand completely the requirements of your customers and your processes and design and operate your clean room accordingly. Find out exactly which environmental factors need to be controlled and to what degree. Some manufacturers interview their customer’s customer to get a more accurate idea of the requirements. One manufacturer estimated the cost of change orders at $1,500 each. So, getting the specs right the first time can be a real money saver.
- Develop a mindset. The people who work in clean rooms are themselves a major source of contamination. Workers must develop a mindset embracing the strict disciplines governing dress, behavior and part handling. This requires thorough training at the outset and continual reinforcement of correct practices.
- Fill it. Have a realistic plan for acquiring a sufficient amount of work to keep your clean room operating profitably. An unused room—regardless of how clean it is—is a money waster. µ
About the author: Joel Cassola is a freelance journalist and Web content consultant with more than 25 years of experience reporting on manufacturing systems and software. E-mail: email@example.com.
The part manufacturers interviewed for this article offered the following perspectives on keeping their operations clean and under control.
Made in a Class 10,000 clean room. Albright Technologies, Leominster, Mass., built a Class 10,000 clean room primarily to control particulates and temperature during proprietary silicone molding and inspection processes for implantable microscale drug-delivery devices. A half-million devices can be manufactured from just one pound of material.
Albright Technologies built a Class 10,000 clean room to control particulates and temperature during silicone molding and inspection processes. Photo courtesy Albright Technologies.
David Comeau, Albright’s president, said designing and building his fixed-wall clean room cost about $150,000. The company decided to build the Class 10,000 clean room instead of a Class 100,000 room, which would have been adequate, because the cost difference was not substantial. While the company was designing and installing its clean room, it also obtained ISO 13485 certification for medical device manufacturing.
Micromachining in clean rooms. ARC Technologies, White Bear Lake, Minn., machines microparts for the aerospace and scientific instruments industries in a class 10,000 clean room.
Advanced Research Corp. Vice President Marlow Roberts said the biggest issue is temperature consistency. “If you are holding 2µm tolerances or ultrahigh-precision pitching accuracies, you need temperature consistency throughout. If you use long cutting processes at varying temperatures, [the workpiece] grows or shrinks, so how do you know where you’re at?”
The company operates a small hole popper (Sodick AE05 microEDM). Even though the system has its own enclosure with environmental controls, external temperature control is important to ensure that parts can be measured away from the machine under comparable thermal conditions.
Near-clean room controls. Micro Precision Parts Manufacturing of Vancouver, British Columbia, does not have a certified clean room, but many systems are in place to control dust and dirt (air filtration and sticky mats), humidity and temperature.
Company president Steve Cotton said that since a single speck of dust can ruin the finish on medical microparts, the parts are vacuum cleaned using a 30µm filter and wrapped in a lint-free material prior to shipping.
Albright Technologies Inc.
Micro Precision Parts Manufacturing Ltd.
Clean Room Suppliers
Clean Air Products
(800) 325-4259, x305