By Bill Loomis
President
Poly Design, Inc.
Garland, Texas

Switching from conventional power tools to a computerized numerical control (CNC) router helped reduce the time to produce automated wet process machines from 1900 to 1000 hours. Poly Design was able to reduce its price for a three-position automatic transfer machine that cleans cassette boats filled with CD-ROMs or semiconductor wafers by 25% to $275,000 while increasing its profit margin. For example, in the past it took five days to cut the parts for the eight cassette boats used this machine and two days for assembly. The CNC router automatically cuts the parts in only four hours and its accuracy is so much higher than power tools that assembly time is reduced from two days to one day. The time savings for producing one machine (1900-1000=900 hrs.) more than pays for the router at any reasonable hourly labor rate.

Poly Design produces a wide range of clean room equipment including wet process stations, equipment for process stations, stainless steel fixtures, quartz cleaning stations, desiccators and storage cabinets, chemical transporting carts and benches and work tables. Each unit produced by the firm is designed to solve a specific application problem and no two units are exactly alike. While some applications require the design of an entirely new assembly, most need only a minor modification to one of the company’s broad line of existing products.

Automated transfer machines

One of the firm’s more popular products is automated transfer stations designed for cleaning cassette boats. These machines replace a slow and difficult manual process in which components are loaded into boats and then dipped into a series of several tanks filled with cleaning fluids. The boats, which weigh about 16-pounds when fully loaded, must be held submerged in three different tanks and shaken for about 10 minutes in each order to thoroughly clean one load. One operator is able to process about 200 parts every hour using this approach and the job has a potential risk of repetitive stress injury.

Poly Design has automated this cleaning process with a transfer machine that provides superior cleaning and a cycle time of only 4 minutes. This machine processes 1500 units per hour and the danger of injury is eliminated by the fact that rather than continuously dipping and shaking the boats, the operator only needs to load a boat onto the machine every 4 minutes. The machine also includes a wet loading area that holds four runs at a time, a filtered and recirculating heated acid bath, two quick dump rinsers, a stainless steel ultrasonic cleaning tank and a wet unload area that also holds four runs.

Plastic machining

Each station is 4.5 feet wide, 12 feet long and 7 feet high. The majority of the machine, including the cabinets for each station, the shell tanks and the baskets, is machined from polypropylene, although the boats are made of polyvinylidene fluoride (PVDF). These types of plastics are used because they are corrosion-resistant and do not emit particles that might contaminate electronic components. In the past, the panels and other components used to build the cabinets and tanks were machined using table saws, routers and hand saws. This was a time-consuming manual process. It took one person about 40 hours to cut out and prepare the parts for the eight baskets used for one machine, for example. Cutting out all of the components needed for one machine took about 900 hours.

The polypropylene components are assembled using a Laramie welding gun that directs heated air onto the joint. First, the joints are tacked together with the welding gun, then triangular polypropylene welding rod is melted into the joint to create the final weld. The relatively poor accuracy of the power tools used in the past meant that a considerable amount of touchup work and hand fitting was required during the assembly process. As a result, it took three to five people about 900 hours or a total of about 3600 hours to assemble and test the machine.

Innovative router

In an effort to reduce the amount of labor required to produce these machines, Poly Design managers evaluated a number of different CNC machine tools. First, they considered conventional machining centers but they discovered that the cost of a machine large enough to handle the 4 foot by 8 foot sheets used to produce the components would have been around $200,000. Next, the company looked at a new breed of gantry routers that interface with CAD systems, have a large cutting area, and a relative low price. These machines are not capable of handling heavy cuts in ferrous metals, however, they can handle heavy cuts in plastic and wood and light cuts in metal which made them ideally suited for Poly Design’s workload.

Poly Design managers looked at several machines of this type and ended up purchasing the Techno Series III from Techno-Isel, New Hyde Park, New York. The selected this machine because it offers an unusually good mix of accuracy, size and price. The machine's 0.0002 inch resolution and repeatability and 0.003 inch/foot absolute accuracy ensure that plastic components are faithful representations of the designs created on the computer. The machine’s working area of 59 inches by 102 inches with a Z-axis height of 8 inches is large enough to handle everything that Poly Design makes. The price is less than $42,000 and includes CNC software used to program the machine.

Computerized machining

Now, the firm’s engineers begin the design process by using the FastCAD or AutoCAD Lite software to sketch out their design on the computer. By manipulating their model on the screen, panning, zooming and rotating, they are able to validate all critical dimensional relationships before they even begin to cut plastic. To provide a final validation step, they put a marker in the machine spindle and used it to trace the outline of the program on posterboard. Once the components for a machine are designed, they are nested together onto a 4 foot by 8 foot pattern to minimize waste. This optimization of the nesting process has saved a considerable amount of material relative to hand nesting.

The Techno router cuts out the parts considerably faster than the previous manual process. It takes only 4 hours, for example, to cut out the parts for all 8 baskets for one transfer machine. All of the components needed for a machine can be produced in only 100 hours of cutting, a reduction of about 89% compared to power tools. Further savings have been achieved because the machine does not even require the continuous presence of an operator. The operator typically performs some other operation nearby. When the machine completes all the components nested on one sheet, the operator loads a new program and a new sheet and restarts the router.

Greater accuracy

The Techno machine's accuracy is the result of several features inherent to the table, such as the use of ball screws and servo motors. For example, anti-backlash ball screws permit play-free motion that makes it possible to produce accurate circles and inlays. The ballscrews have excellent power transmission due to the rolling ball contact between the nut and screw. This rolling contact also ensures longer life and greater rigidity during the life of the system because of the reduced wear as compared to ACME screws and nuts, which have a sliding friction contact.

Faster assembly

The much higher level of accuracy achieved by the router saves a considerable period of time during the assembly process. Everything fits together perfectly, so the need for manual finishing and fitting has been eliminated. As a result, two people can assembly and test a machine in only 700 hours. The total assembly time is only 1400 hours, a 61% reduction. Besides these time savings, the quality of the finished machine has been improved. Customers notice that everything fits together better and opens and closes more smoothly. Servicing the machines built with the router has also become much simpler since the components are now all interchangeable.

1) Stainless steel storage cabinet produced by Poly Design.
2) Poly Pro storage cabinet produced by Poly Design.
3) Acid bottle cart produced by Poly Design.
4-5) The Techno-Isel router used by Poly Design.