Originally Published EMDM September 2005
Engineering Insight
Metal Fabricator Gains Competitive Advantage through Automation
An automated microabrasive blasting and grinding system helps to meet demand for large batches of custom products.
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| Integrating microabrasive blasting as a secondary step in the machining process requires precise positioning of the nozzles and the fixtures that hold the workpiece. |
Family-owned and -operated since 1922, Popper Precision Instruments Inc. (New Hyde Park, NY, USA) supplies OEM instruments, specialty probes for liquid-handling devices, and custom procedural needles, among other products.
It has more than 1000 items in stock. Demand for custom products has surged over the years, to the point where individual products are now produced in batches of thousands at a time. This evolution has led the company to adapt its production processes.
"In an increasingly competitive market, efficiency is the key to survival," says engineering manager John Perry. "Our goal has been to achieve this efficiency through automation." One of the company’s recent projects along these lines combines single-step microabrasive blasting and grinding into an automated process.
"Many of our products require custom cutting, grinding, end forming,
and surface treatment," says Perry. "Microabrasive blasting has become an integral step in our manufacturing process."
Abrasive Methods
A refined form of sandblasting for precision manufacturing applications, manual microabrasive blasting has been used in needle manufacturing for decades. The process uses high-pressure compressed air to force micron-sized abrasive media through a nozzle to affect a product’s surface. Various effects can be achieved by altering the pressure or the media. Surfaces can be deburred or textured without causing dimensional changes to the part, making microabrasive blasting an ideal tool for use on cannulae and other specialty needles, according to Perry.
Popper uses the technique to deburr the inner and outer diameters of cannulae, texture the blunt ends of needles to improve bond strength, improve the surface appearance of instruments, and impart echogenic properties to devices. Regarding the last application, Perry explains that customers increasingly request products that are compatible with ultrasound visualization. "Because modern ultrasounds are unable to easily pick up shiny surfaces, matting the surface of the needle or probe allows the doctor to follow it on screen while it travels through the body," he notes.
Microblasting typically has been conducted at manual workstations. "With the increased quantity and variety of products moving through the facility, it was in our best interest to automate," says Perry. "When we are running small lots of approximately 250 pieces, a manual station is still the most cost-effective approach. But with production requirements growing to 500, 1,000 or 10,000 pieces per run," he adds, "manual blasting is just too slow and operator intensive."
Trial and Error
Popper initially identified the main factors of automation as uniform coverage, controlled blast time, and proper nozzle angle. Theories were tested by integrating the microabrasive blasting equipment into a cabinet equipped with tooling to hold the parts at the correct angle and location for complete coverage. The operator only needed to load and unload the needles.
"Based on initial test runs, we found that our blasting system was not robust enough for the demands that we were placing on it," says Perry. "We worked with the equipment manufacturer to select an appropriate system for our needs. Selecting a system that has been engineered to operate in an automated environment is critical."
Once the blasting unit was installed, company engineers began to customize the system to suit the application. "Initially, we had selected polyurethane abrasive hose for this system. It was the same material that we were using on our manual stations. Several bends were needed in the hose, and it quickly became apparent that the bends posed a weak link in our system," explains Perry. The firm experimented with several materials before settling on stainless steel. While this meant that the lines would be limited to fixed positions, the stainless-steel lines last 10 times longer than their polyurethane counterparts, Perry adds.
Finding an Angle
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| Automation systems developed by Popper Precision Instruments can process 9- to 11-in. needle strips. |
To remove the burr from the heel area of a needle, the abrasive stream must strike at an exact location and angle. An experienced operator has an intuitive feel for this process. On an automated system, however, the nozzle must be held at the proper angle and distance from the grind to remove the burr. The nozzle angle controls how the stream of abrasive will strike the burr. If the nozzle is angled correctly, it will carefully lift the burr away from the needle and round the edge of the heel at the same time.
Proper nozzle distance also must be determined. As the nozzle is moved away from the part, the spray diameter increases. The nozzle must be placed so that the beads are focused on the burr, not the point.
In addition, nozzle shape must be considered. Microabrasive blasting nozzles are available in many different sizes and shapes, from small round units to large rectangular ones. Rectangular nozzles increase the spray diameter in one direction without increasing the overall blast diameter.
"These variables were combined with pressure, abrasive flow rate, and blast duration to create the proper profile for our needles," says Perry. "The complexity of integrating all of the variables was challenging." In particular, automating operations that previously relied on the manipulations of a skilled operator was not as easy as it might seem. "We had to go back to the drawing board several times, studying masking and tooling to maximize production throughput," says Perry.
The finished system uses two nozzles to deburr the needles. One nozzle projects glass beads to kick out the burr, while the other one forces the burr through the tube. Pressure and bead flow are carefully controlled to avoid destroying the heel area by creating a serrated edge.
"Our efforts in automation have led to a new level of production capabilities," says Perry. "In needle applications, an operator now simply loads the tubes, shuts the door, and hits the button. The fixture flips up and grinds out the primary angle on about 125 needles at a time. Then the grinding gear moves out of the way, and the fixture rotates the needles into position for blasting," he explains. The blaster nozzles are programmed to slide down into position. One nozzle blasts at an angle, causing the burr to lift up, and the other nozzle blasts straight down, separating the burr from the grind. The grind mechanism then moves back in to cut the secondary angles for a sharp tip. The entire cycle takes only 21 1/2 minutes.
Popper documents every job setup, from the size of the blast media to nozzle positions and distances. These data allow the firm to accelerate setup for new jobs. "We are able to review our notes and quickly determine the best parameters for a new product," says Perry. "This formula is now part of our competitive advantage, and a valuable resource to our customers."
To learn more about Popper Precision Instruments Inc., visit RequestLink.
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