Originally Published MDDI May 2005

Cover Story >> Molding

The Many Facets of Modern Molding

New developments make their mark on molded devices and components.

William Leventon

Many forms of change are combining to reshape medical device molding. New equipment is giving a boost to molding precision and consistency, while an array of novel processes are cutting costs and reducing cycle times. What's more, many new molded parts are lighter and better made than their predecessors.

Other important changes are transforming operations within the walls of contract molding firms. These companies are developing leaner operations that meet stringent new quality standards and regulatory requirements. Contract firms are also taking on new responsibilities to satisfy their ever-more-demanding medical device customers.

Molding is one of many jobs done for OEMs at the facilities of Avail Medical Products, a contract manufacturer based in Fort Worth, TX. At Avail, all-electric machines continue to replace hydraulic machines in the company's molding operations. Avail prefers electric machines because they provide good precision during the injection process, which results in improved part quality and shot-to-shot consistency, according to Scott White, a senior vice president at the company.
Electric machines offer other advantages as well, White notes. These include the following:

• Energy efficiency. Moving parts only draw power when engaged.
• Clean operation. No hydraulic oil is needed to run the machine. “It's always a benefit when you're not adding contaminant to a cleanroom environment,” he says.
• Advanced logic systems. These systems allow shot-to-shot corrections for viscosity changes in molding materials.

However, electric machines cost roughly twice as much as their hydraulic counterparts, notes Jeff Somple, president of northern operations at Mack Molding Co. (Arlington, VT). “So unless you know you can fully utilize the machine, it's probably not going to be worth the investment.”

In addition to electric machines, some molding operations are being equipped with transducers that take pressure readings inside the mold cavity. These pressure readings help molders determine how well a process is being managed, says Joe Pack, vice president of sales and marketing for Moll Industries Inc., a plastics-injection molder based in Dallas. Transducer readings also help molders satisfy customer and regulatory requirements for part quality, Pack adds.

Process Developments
In-mold transducers provide constant real-time process data during scientific injection molding (SIM). SIM is used in the molding operations of Seattle-based Vaupell Inc. At Vaupell, SIM equipment monitors material-viscosity variations and controls the press so the process produces parts with consistent dimensional and physical properties, notes Phil Cashen, the company's business development manager.

According to Cashen, SIM also improves processing efficiencies, which results in reduced scrap losses. This has become particularly important at Vaupell, which molds expensive resins that have replaced metals in the manufacture of implants. “When you're working with materials that cost $1500 per pound, a 5% improvement in scrap rate is significant,” Cashen days.

Not all parts require SIM, which adds training and equipment costs to a molding operation. But in the majority of cases, the added costs amount to less than 10% of the cost of a mold, says Cashen, who notes that most of Vaupell's customers think this is a reasonable price to pay for SIM's processing benefits.

Benefits also accrue to companies that use overmolding, a technique that adds a “soft touch” to many consumer products. In the medical industry, the process is gaining popularity among manufacturers of surgical instruments who are overmolding thermoplastic elastomers onto the handles of their products. This is done to give doctors a better grip on devices covered with blood or other body fluids during surgery, Somple says.

At Mack, overmolding is done in two ways. One is to mold the substrate, then remove the resulting part from the mold and place it into a second mold, where the soft-touch material is added to it. The second way is to use a two-shot machine that can produce both the underlying and soft-touch layers. The two-shot process has become fairly common at Mack, though high tooling costs make it impractical for some low-volume projects, says Stefan Rasch, a business unit director at the firm.

Two-shot and multishot molding consolidate several molding operations in a single machine, eliminating secondary handling and assembly steps. This simplifies the process of making multimaterial products. For example, some fluid-handling devices require an elastomer sealing surface, notes Tom Podesta, vice president of healthcare sales and marketing for The Tech Group Inc. (Scottsdale, AZ), a contract injection molding firm.

Gas Assist for the Medical Industry

For a number of years, molders in other industries have been reaping the advantages of a process known as gas-assist injection molding. Now, Somple sees gas assist making inroads in the medical industry. The process features a unit that introduces a certain volume of gas (usually nitrogen) into a mold cavity filled with plastic. The gas evacuates resin from thick areas of a plastic part. By hollowing out sections that would otherwise be made of solid plastic, the gas-assist process produces lighter and less-expensive parts, Rasch says.

In addition, gas assist can affect cycle time, much of which consists of the time a part spends cooling in the mold. The more plastic there is to cool, the more time a part must sit in the mold. By hollowing out thick plastic sections, gas assist reduces cooling time and thereby speeds up the production cycle, Somple notes.

Above all, medical customers value speed in manufacturing operations. “Their single biggest cost is time,” says Jay Riddle, president of Advanced Technology (Corona, CA).

Fast production is the main goal and purpose of Riddle's company. In 10 days, he says, Advanced Technology can produce production-quality parts suitable for testing in an FDA approval process. Key to this rapid production is the company's Time Compression Technology (TCT), which includes several key components:

• A cell structure for mold making. Each tool is assigned to a cell, where a single person is responsible for designing and building it. When changes are made to the design, the tool is usually sent back to the same cell for modification.
• Unique tool material. Tools are made of a proprietary CNC-machined material developed by the company.
• Special software. Software developed by the company enables fast and easy part machining, Riddle says.

Normally, it takes four to six months to develop and produce a plastic part, according to Riddle. But TCT can help reduce that time to less than a month, he claims. “That's almost priceless to our customers,” he says. On the downside, the TCT system can't make parts with dimensions greater than 7.5 in. In addition, parts produced by TCT tooling are usually 20–30% more expensive than those that come from conventional molds.

Change Comes to Contractors

Reducing production time is also a top priority of The Tech Group, which uses lean manufacturing principles in mold building. The company applies lean principles to the whole process, from the time a purchase order is received to the time the finished product goes out the door. The lean principles eliminate unnecessary steps and reduce lead time. The company even works with suppliers to identify and eliminate bottlenecks in their processes. As a result of this comprehensive lean program, the firm can shave weeks off a mold-building operation, Podesta claims.

Besides production speed, device companies are becoming more insistent about ISO compliance, Cashen reports. So last year, his firm officially came into compliance with ISO 13485:2003, which is aimed at medical device manufacturers. The standard specifies requirements for a quality management system that will satisfy customers and regulators.

To comply with the standard, Vaupell made a number of important changes such as upgrading equipment to provide more-precise measurements. According to Cashen, these changes have boosted the company's molding quality, efficiency, and consistency. In addition, they have significantly reduced bioburden level. In sum, “the standard has really improved our operation,” he says.

Today, though, it sometimes takes more than a first-rate molding operation to win business from medical device OEMs. For example, Pack notes, a growing number of medical companies want Moll to handle validation-related tasks. “In the past, many customers would at least help with validation,” Pack says. “But now, more of them are telling us, ‘You will validate the product'—even to the point where we're the ones submitting data to FDA.”

Some device companies are even insisting that Moll accept legal responsibility for the components, subassemblies, and finished devices it produces. “There's been a liability shift” from the OEM to the molder, Pack says. Although this shift exposes the molder to potential legal troubles, Moll accepts the responsibility, which Pack calls “a cost of doing business in some cases.”

To avoid the consequences of making flawed parts, medical molders are focusing more on risk analysis of manufacturing equipment. When Avail develops mold tools, for example, the company uses failure mode and effects analysis (FMEA). As the name suggests, FMEA is used to identify potential failure modes, determine their effect on a product, and identify actions that will head off failures. At Avail, White says, FMEA helps molding personnel find and address possible problems before manufacturing begins.

During the manufacturing process, Avail tries to minimize the production of defective parts through the use of statistical process control (SPC). Requested by a growing number of Avail's customers, SPC helps the company spot trends that are moving a manufacturing process toward a tolerance limit. “We're being driven by the trend rather than the defect,” White explains. “Before the process gets out of a particular tolerance band, we're already making course corrections. So we're keeping the process in a range that always produces good parts.”

SPC depends on inspectors who periodically take measurements of molded parts. Data from the measurement equipment are used to create control charts that are analyzed to spot worrisome drifts in the manufacturing process. Besides preventing the production of flawed parts, SPC reduces downtime and the cost of molding operations, according to White.

Cost Concerns

Until recently, Pack says, cost was not an item of great concern to many people working for medical device companies. “Most engineers designed medical parts solely for fit and function. They wouldn't care how much it cost to make the part,” he says. “Now, they're still designing for fit and function. But when the design is done, they might say, ‘Whoa, that costs too much. We have to find ways to get the cost down.' So they go back and do a cost analysis on the part.”

In part, Pack contends, this change in attitude can be traced to companies that sell consumer products. “The Dells, the Wal-Marts, the big automotive firms of the world are negotiating prices a lot better now,” he says. “And the models of those companies are starting to affect the medical industry. So are people from those companies, who are starting to move into positions in the medical industry.”

Under normal circumstances, Mack has found that medical device designers aren't overly concerned about the cost of molding materials. According to Somple, material content accounts for a relatively small portion of the total cost of a medical device. “A medical instrument that costs several hundred dollars might have 50 cents worth of plastic resin on the handle,” he says. “So when medical device companies look at plastic, they're normally more concerned about performance than cost.”

But circumstances have been far from normal during the last year, which has seen raw-material prices jump anywhere from 20 to 100%. “This has really come as a shock to some of our customers,” Somple says. “They're telling us, ‘You have to do something to help me offset these cost increases.'”

Fortunately, Mack personnel can do several things to help customers smarting from soaring material costs. For instance, they can recommend alternative materials that are less expensive but still meet the customer's design requirements. They can also redesign the product to reduce material content, consolidate parts, and/or quicken the molding process.

For their part, Somple says, customers can do something that will help themselves and Mack: “They can give us more work. There's a lot we can do [to lower costs] when we have economies of scale in areas like material purchasing and overhead allocation.”

Besides asking for cost-cutting suggestions, more of Mack's medical customers are requesting design help. Twice in the last year, in fact, the company has dispatched one of its own people to work with a customer's product development team.

Why would medical device companies ask for Mack's designers rather than hiring their own? Somple thinks it's an easier way for customers to deal with a short-term spike in demand for personnel during the design phase of a project. “If they use our people, they don't have to hire people and then let them go after the project is over,” he explains.

In addition, Somple notes, companies find it helpful to include someone in the design process who's also part of the manufacturing operation. “The person we send understands our equipment, processes, and limitations,” he says. “And during the development process, that person will be focused on designing for manufacturability, which should result in a more cost-effective product and a quicker launch.”

Advanced Technology also provides help with design for manufacturability to medical customers, who are coming in with increasingly complex parts. “We go through a design review to find out what the customer has to have, versus what the customer wants,” Riddle says.

During these reviews, Riddle and his colleagues are often able to change nonessential design features in order to make parts more manufacturable. For instance, they'll turn a design with thick and thin wall sections into one with more-consistent wall thicknesses.

They'll also replace sharp corners with fillet radii. Normally, this switch has no effect on a part. But it might reduce tooling costs by a third, Riddle notes. “When melted plastic is flowing into the tool, it would much rather flow around a round corner than a sharp edge,” he says. “A lot of engineers don't pay attention to that. But we'll make an issue of it and ask if sharp corners really need to be in the design.”

A Look Ahead

People involved in medical molding see more changes coming to an already much-changed industry. For one thing, Cashen expects an increase in strategic alliances between molders and equipment suppliers. These alliances will help molders meet the needs of firms that make minimally invasive devices and other products that are becoming ever more diminutive and presenting ever-greater molding challenges.

To satisfy these customers, Cashen says, Vaupell will be calling on its equipment partners. They will have to provide special presses that produce highly precise and consistent results beyond the capabilities of commercially available machines. Already, he notes, Vaupell is in the early stages of a collaborative project that will provide the company with customized equipment to meet the precision requirements of a demanding new medical device design.

As for processes, Somple anticipates increasing use of water-assist molding technology. Like the gas-assist process, water assist enables molders to hollow out thick plastic sections. But, as the name suggests, the new process relies on water, which is less expensive than nitrogen. In addition, the water serves as an internal coolant that reduces the necessary cooling time for molded parts. Thus, Rasch notes, water assist provides even greater cycle-time reductions than the gas-assist process.

Water assist has yet to take hold in the medical industry, Rasch says. But there are many possible medical applications, including the molding of railing systems for hospital beds. Normally metal today, such railings could be made of plastic sections hollowed out by the water-assist process.

Besides developing the company's first water-assist part, Mack has been investigating another innovative process: molding radio-frequency identification (RFID) chips into medical devices. With embedded RF emitters, devices can be tracked all along the supply chain to improve inventory management.

RFID tracking can also be done once a device is in use in a hospital. “It allows you build up a history of an instrument—how many times it's been used in surgery, how many autoclave cycles it's been through,” Somple says. Thus, he notes, an embedded RFID chip “almost makes the plastic an intelligent part of the device.”

William Leventon is a freelance writer who frequently contributes to MD&DI. He is based in Somers Point, NJ.

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