January 2007 Mechanical Engineering Departments: Tech Focus, Pt. 2

This section was edited by Associate Editor Alan S. Brown.

Technology Focus part 2:
Materials and Assembly

Radar Controls
Pneumatics

Looking for a faster, more accurate way to position pneumatic linear drives? Germany's Festo AG & Co. KG says its new microwave sensors not only deliver 0.02 millimeter resolution, but also improve equipment flexibility, run in hostile environments, and reduce the need for customization.

Microwaves are the technology behind radar, and Festo uses its microwaves the same way. It mounts a small sensor on the pneumatic tube's endcap. The sensor bounces a microwave pulse off the moving piston. By measuring the travel time of the signal, the sensor can determine position down to 0.02 mm, according to Armin Seitz, who manages Festo's sensors business.

Moreover, the system maintains its high resolution down to zero distance from the sensor. This lets Festo speed up the work stroke and slow down the piston as it returns to the end position without mechanical shock absorbers, which are susceptible to wear.

Microwave sensors can also provide built-in diagnostics. Their high resolution quickly detects vibrations created by wearing parts, off-axis motion, and friction. This reduces the need for periodic inspection and gives workers the advance warning that they need to schedule down time for repairs.

Microwaves differ from competing technologies in many ways, including flexibility, Seitz said. Most proximity, potentiometer, and ultrasonic sensors require customization. Engineers and their vendors must customize the placement and optimization of sensors for each application. "Our customers can use the exact same mechanical design for every application," Seitz said. "We will be able to deliver it in any length they want, and do it within 24 hours."

Magnetic proximity sensors are installed outside the cylinder barrel at each position that requires feedback. If users need to measure cylinder position between proximity sensors, they must add additional displacement encoders. Installation is complicated, requires optimization of the magnetic fields, and must be redone if users want to optimize or reset the system. Optical sensors work well, but are vulnerable to contaminants. Ultrasound sensors have lower resolution and often have trouble coping with rapid heat and pressure variations within the cylinder.

Because Festo's sensors stay inside the tube, they are ideal for food, beverage, and pharmaceutical applications where equipment requires periodic washdown. They are also insensitive to the electromagnetic fields generated by transformers, motors, and welding guns.

Seitz concedes that microwaves are currently more expensive than ultrasonics or potentiometers, but says mass production of microwave semiconductors could slash costs by a factor of 10.

Cold Casings
by Jeffrey Winters

A little more than a year ago, a string of companies approached Steven Moore, co-owner of Chesapeake Plastic Manufacturing in Lusby, Md., all with a similar proposition—produce molds with a lead time of just two to three weeks. Unfortunately, his company couldn't do the job, nor could anyone else.

"It would take a couple weeks just to get something shipped from overseas," Moore said, "and due to consolidation, the local manufacturers' lead times start at eight weeks. The companies wound up shelving the projects."

Sensing a business opportunity, Moore and Mark McGrath spun off a new subsidiary called CPM Fastools to take on jobs that have to be done more quickly than traditional tools can handle them. But to turn their products around fast, Moore and McGrath would have to adopt an innovative technology.

CPM Fastools turned to rapid prototyping, which produces parts layer by layer from CAD designs. It first investigated a process that produced molds from metal mixed with a plastic binder and then burned off the plastic and sintered the powders into a metal part in a furnace. Then, Moore and McGrath also looked at a laser sintering machine produced by EOS, a manufacturer based in Krailling, Germany. EOS uses lasers to consolidate each metal layer directly, creating parts that are usable right out of the machine. This would enable CPM Fastools to reduce the time and costs needed to produce molds. But there were some concerns about the durability of the results.

"We were told that the process creates so much stress that after 50 or 100 cycles, we'd see internal cracking," Moore said.

To reduce the amount of stress, CPM Fastools added a step: After laser sintering, the mold components are cryogenically treated. Using liquid nitrogen, the materials are chilled to some Ð240¡F and kept at that temperature for 24 hours. This cryogenic processing helps homogenize the crystal size in the metal parts, leading to fewer weak spots.

Thanks to this one-two punch, Moore said, his company can turn around orders in less than half the time, and for a fraction of the cost. One of its first projects, for instance, involved an electronics packager that made some last-minute changes to a design. After receiving estimates of up to four months for the project, the company turned to CPM Fastools, which was able to turn around the production tooling in just four weeks.

Economy CNC
by Harry Hutchinson

A Wisconsin company has decided that if there is a personal computer, there should be a personal computer numerically controlled milling machine, too. The company, Tormach LLC in Waunakee, Wis., has come out with one that it calls the PCNC 1100 and offers for less than $7,000.

Tormach's personal computer numerically controlled milling machine sacrifices speed to bring in a parts-making mill for less than $7,000.

According to the company's chief executive, Greg Jackson, the main difference between the Model 1100 and a CNC machine going for $40,000 or more is speed. The high-speed servos have been removed, but there is no loss of accuracy, Jackson said, and the machine has been built to industrial standards so it can be used full-time.

But then, its purpose isn't high-speed production. Instead, it is something that Jackson calls "subtractive prototyping."

Rapid prototyping machines generate sample parts, usually from resin powders quick-cured under light. A 3-D CAD rendering can be turned into something the designer can hold in a matter of hours. Tormach says its machine will allow the prototype to be of any metal compatible with milling, including iron, steel, titanium, and chromium alloys.

The machine, which is operated from a PC, has a 1.5-hp spindle and can run at spindle speeds between 300 and 4,500 rpm. It can handle workpieces up to 500 pounds, according to the company's literature. Travel is 18 by 9.5 inches along horizontal axes and 16.25 inches vertical. The company also offers enhancements, including a fourth axis, 20,000-rpm spindle, and quick-change tooling system.

Tormach is quoting a price of $6,800 for the machine, without a table. Depending on the installation, final cost could be between $10,000 and $12,000, Jackson said.