Originally Published MPMN January 2004

PRODUCT UPDATE

Recent Advances in Molding Technology

To stay competitive, suppliers of molding services and equipment have learned to keep their eyes glued to the bottom line. Several companies that have found novel ways to optimize processes and compress costs are profiled in this section. For example, one firm has developed a two-component mold for syringe plungers, thus eliminating assembly operations. Metal-injection molding is touted by another company as a time-saving technique for the high-volume production of intricate metal components. On the equipment and tooling front, a continuous vacuum forming system is described as a desirable alternative to blow molding machines, while cavity pressure sensors, argues another supplier, should be part of every molder's toolbox. And speaking of tools, if you're in the market for molding services, you will find yet one more indispensable resource on page 66: MPMN's Molding Services Buyers Guide.

Two-Component Mold Eliminates Syringe-Plunger Assembly Operations

A two-component mold that fabricates syringe plungers does away with the need to assemble the bodies and the tips. The tips are molded first, after which they are transferred to plunger-body mold cavities. Each cycle produces complete plungers, thus reducing contamination concerns. Mold and die maker Boucherie USA Inc. has a patent pending for the process.

"The part is never cleaner than when it falls from the mold," says John C. Williams, manager of the company's plastic technology business unit. "By eliminating a step in the assembly process, we have reduced the products' exposure to contaminants."

The absence of visible injection points and parting lines is cited as another benefit of the process. It also creates a permanent bond between the plunger tip and syringe body. In addition, says Williams, "we can achieve very fast cycle times . . . in some cases under 7.5 seconds."

The plunger tips are made from Santoprene TPE 8281-55 from Advanced Elastomer Systems. The material complies with ISO 10993 and USP Class VI guidelines, is latex free, and is compatible with most forms of sterilization. Its compression set ensures reliable sealability, and it withstands exposure to a range of temperatures.

Boucherie also recently announced that it has developed a Shuttle Mold that, it says, may have medical product applications. An external station cools the first-shot molded parts, shuttles them to the overmolding cavities, and removes the finished part.

The molds are typically designed in a stack configuration. This enables the use of high-cavitation molds with a standard clamp and small press. Because it allows for short cycle times, the Shuttle Mold is suited for high-volume production processes, according to the firm.

Metal-Injection Molding Touted as Alternative to Small Parts Machining

A company that provides metal-injection molding (MIM) services describes the technology as a cost-effective alternative to machining. Parts can be manufactured in 15 to 20 seconds by means of MIM compared with the 15 to 20 minutes that machining might require, according to Morgan Advanced Ceramics. The technique is suited for the high-volume production of intricate metal components. Laparoscopic instruments are among the products that would benefit from this method.

MIM is defined as a net-shaping process in which a fine metal powder, typically smaller than 20 µm, is mixed with a binder system to create feedstock. Common binders are a combination of waxes and organic materials, which may include thermoplastics or thermosets along with surfactants and other additives. The feedstock is injected into a mold cavity using molding machines that are very similar to traditional plastic-injection molders. Most of the binder is removed by means of a thermochemical process. The parts are then placed in a sintering furnace, where any remaining binder is removed and the parts are sintered to their final dimensions. The end result is a near-net-shape part with a typical density of 98%. Depending on the part, this can be the final step, or secondary operations can be performed.

MIM parts can be comparable in strength to parts machined from wrought metal. They can be created with complex features such as cross-drilled holes, undercuts, and fins, and generally do not require secondary machining. In most cases, several parts of an assembly can be molded simultaneously.

The technique also provides a cost advantage for the production of custom components, according to Morgan Advanced Ceramics. MIM allows for the development of specific blends to suit specific customer applications.

The MIM process is described in a Metal Injection Molding Design Guide that can be downloaded in a pdf format atwww.morganadvancedceramics.com. 

Vacuum Forming System Introduced

An alternative to blow molding technology, a continuous vacuum forming (CVF) system can be used in vertical and horizontal format for both low- and high-volume production. The system, which was recently introduced by HPM Div., Taylor's Industrial Services LLC, minimizes the number of components and holds down production costs.

"In CVF systems, the resin is pulled to the outer mold wall instead of being pushed there by internal pressure," explains product manager Chris Turner. Several complete molds are arranged in a contiguous loop. The molds move continuously, capturing the resin. This technique reduces process variability, adds Turner, and allows the use of low-viscosity resins. Because of the continuous movement and end-to-end tooling design, flash and pinch scrap is reduced, thereby reducing processing costs.

The CVF system can incorporate interchangeable molds for fast product changeovers. It requires neither hydraulic fluid nor waterfor mold cooling.

The equipment is a "perfect fit for niche markets," according to Turner, including the medical device sector. "It significantly improves the return on investment because of the process cost savings. The CVF system has a higher efficiency conversion rate of pellets to the finished part, enabling molders to expand applications and to be more competitive."

Lifters Boost Undercut Capabilities

A lifter system that is actuated from a slide rather than a static base in the ejector plate offers OEMs and mold makers increased flexibility. The VectorForm Lifter System, developed by Takao Injection Mold Engineering and distributed by D-M-E Co., allows application designers to incorporate undercuts that are twice as deep as were previously possible. Alternatively, mold designers can cut ejector strokes in half if they choose to maintain existing undercut geometries.

Whereas most lifter systems recommend a maximum angle of 15°, VectorForm can accommodate angles greater than 30° because of the sliding base. Multiple lifter cores can be integrated into a single system, thus eliminating the need for separate lifters when processing parts with multiple undercuts in the same line of draw. Actuating multiple lifter cores with a single system results in significant savings in cost and space within the mold. Small housings and enclosures are among the products that would benefit.

A design guide that provides application examples and detailed design and installation guidelines is available from the company.

Temperature Sensor Optimizes Molding Process

Pressure and temperature both have an influence on the injection molding process. While cavity pressure measurement is a widespread practice, cavity temperature measurements often are not part of a molder's standard operating procedures, according to Priamus Systems Technologies LLC. Yet they canyield substantial benefits, according to the firm.

Priamus has developed a cavity temperature sensor that is attached to a flexible connecting cable. The sensor housing measures 12.5 mm long and only 1 mm diam. The compact construction makes it compatible with small moldings and accelerates readings.

Placed at the end of the fill, the sensor's signal can actuate automatic switchovers to holding pressure. Unlike conventional switchover methods, this process can respond to variations in viscosity.

Sequential molding applications can be controlled by placing a temperature sensor at each gate. As soon as the melt reaches the sensor, it sends a digital signal to the controller, which opens or closes the valve gate depending on the position of the melt.

Copyright ©2004 Medical Product Manufacturing News