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Shop Solutions: Retooling Speeds Prop Machining

It takes a lot of prop to push a racing boat across the water at speeds up to and over 200 mph. And it takes a lot of world-class machining to convert a stainless or titanium casting or forging into a high-performance prop.

Hering Propellers (Marysville, WA) does it every day, and judging from their reputation, they’ve got the process down pat. Their props dominate the world of offshore racing, and their entire product line was recognized, winning Powerboat magazine’s 2010 Readers Choice Award.

Thanks to a process re-engineering and retooling initiative by Ben Robertson, director of engineering, the company completes machining props in a quarter of the time it took previously. Props with either with five or six blades once took over 80 hr of milling with 100% operator attention. Now they’re done in about 22 hr untended and often "lights-out."

Key to the gain was the switch from solid HSS end mills to an indexable-carbide Form Master Pro button cutter from Ingersoll Cutting Tools (Rockford, IL) for rough milling. Greater strength of the cutter enabled larger stepovers and deeper cuts, and less chatter despite the long reaches involved in five-axis propeller machining. Such stability also makes it possible to machine closer to final net shape during the roughing phase, reducing finishing time from a two-pass to a single-pass finishing operation. Aggressive chipbreakers on the inserts broke stainless steel’s notoriously long, stringy chips into uniform little C shapes that are easily disposed of.Putting their heads together at Hering Propeller to plan toolpaths for the next racing prop are (L to R) Greg Eaton, operator, Ingersoll's Chris Murray, and engineering director Ben Robertson.

Hering, which has been in business for more than 40 years, is a 15-employee shop that runs one shift a day five or six days a week. Machines are solely Okumas from Gosiger, and tooling is exclusively sourced from Ingersoll. "Standardizing on one machine vendor and one tooling vendor benefits us in a lot of ways," says Robertson. "They both deliver the best product and service in the industry and we get true partners in problem solving and better answers sooner."

Most of their props start as stainless castings, but the titanium prop business has grown steadily along with their premier line of forgings for extreme-horsepower boats. Though Hering makes hundreds of different propellers, as a machining problem they all share more similarities than differences. It’s multiaxis work, with all curves; and never any straight cuts. Machining involves long reaches to mill in near the hub and milling over large unsupported areas of the workpiece—more so as the blades come nearer to finished shape. "Machining the blades is very prone to the ‘tuning fork’ effect," Robertson explains. "The slightest instability in the cutter can resonate into an undamped vibration in the blade, and there goes your finish."

Hering’s historic use of high-speed steel cutters comes naturally. The company used to be in the HSS end mill business, so they have a lot of capability to grind and sharpen solid HSS end mills. About three years ago, after Robertson joined Hering, the company decided to take a completely fresh look at their prop manufacturing processes. At about the same time, Hering’s titanium prop business was really taking off, with its own manufacturing procedures due for standardization.

A quick analysis showed that milling was the biggest production step from a time and cost standpoint. So naturally Robertson started there. During a regular plant walk-through with Ingersoll field rep Chris Murray, discussion topics of better ways to do the milling included toolpaths and stepovers along with the tooling itself. "We both saw it more as a process re-engineering effort than just a drop-in tooling replacement," Robertson explains.

The initial recommendation was the Form Master Pro with serrated chipbreaking inserts, which Murray figured could cut milling cycle time by at least half—largely by roughing closer to finish size and leaving less metal to remove during the slower finish milling stage. Trial runs confirmed that projection and then some. Hering brought in other vendors as well, running trials on a short list of tools that seemed most promising. Several contenders did almost as well as the Form Master Pro in rigid setups but not on the unsupported blades. "Cutting action and chip control with the Ingersoll cutter were far more stable over the entire blade area than with any of the others tested—so much so that I saw the potential for untended operation with that particular tool," says Robertson. "I hadn’t even thought of such a possibility until we saw that first trial."

Milling a 16.5" (419-mm) diam five-blade cast stainless propeller illustrates the difference in cutting performance. Previously, Hering rough-milled that part in a single pass with a house-made 1" (25.4-mm) HSS end mill with positive rake in the flutes, and finished it in two passes with an Ingersoll Speedball ball mill. Parameters for roughing were 2 ipm (50.8 mm/min) at 250 rpm with a 0.150" (3.8-mm) stepover. The depth of cut varied depending on the part being made and the casting used. If they ran any faster, vibration crept in when cutting near the unsupported blade tips. "It was like trying to machine a tuning fork," says Robertson. Eighteen hours and two or three tool changes later, roughing was complete, leaving 0.050" (1.3 mm) of stock for finishing. The operation required constant operator attention between different machining sections primarily due to the unreliable processes. Finishing was done in two passes at 50 ipm (1.3 m/min) at 1500 rpm/0.01" (0.25-mm) stepover. It required around 30 hr and four tool changes per part. Each tool change was done manually so when process finished at night time, the machine sat idle until the next morning.

Initial test runs with the 1.5" (38-mm) Form Master Pro were done at about Ingersoll’s recommended 16 ipm (406 mm/min) at 1050 rpm and 0.030–0.040" (0.76–1-mm) stepover for the roughing. "It’s an entirely different technique than the cutter is designed for. It’s more like side milling or swarf cutting than straight end milling," says Murray. This combination reduced roughing cycle time to about 8 hr and brought the part to within 0.015" (0.38 mm) of final net shape, promising a dramatic saving in finishing time. Moreover, the chips came off in uniform, easy to control C-shapes with absolute reliability and no operator intervention. Finishing, with the same tool as before, then took just 10 hr and a single pass. Roughing on unsupported surfaces of the prop is more side milling than end milling.  Switching to Ingersoll's Form Master Pro cutter and serrated inserts for the rough milling operation reduced total roughing and finishing time from 80 to 22 hr.

"In recent months, we’ve dialed up the parameters well beyond Ingersoll’s initial recommendations, so we’re actually completing all milling—roughing and finishing—in just 22 hours on an operational basis," Robertson says. Roughing time went from as much as 40 hours to eight. Finishing time dropped from 30 hours to ten. Standard parameters for roughing today are around 22 ipm (559 mm/min) at 1175 RPM and a 0.070–0.100" (1.78–2.54-mm) stepover. To minimize the "tuning fork" chatter effect, Hering’s strategy is to feed a little slower and take a larger cut to engage the insert more which stabilizes it better. "With the positive-rake geometry of the Form Master Pro and the swarf cutting approach, we can utilize 20–50% of the available cutting depth without risking tool damage, chatter or loss of accuracy. And the process is stable under even the longest-reach conditions."

At slower speeds and feeds, Hering uses the same basic process and tooling with equal success on their new titanium props. "There’s no vibration despite the long reaches and largely unsupported machined surfaces, and the inserts last through six hours of cutting time," Robertson concludes. ME

For more information on Ingersoll Cutting Tools, go to www.ingersoll-imc.com, or phone 815-387-6600.

 

Online Panel Machine Shop

An online machine shop combines high-speed machining technology from Datron Dynamics Inc. (Milford, NH) and with the shop’s design software to provide a custom design and manufacturing service for front panels. Online customers can download software, design a front panel, order, and wait for delivery of the finished product in quantities from single units to production runs.

Front Panel Express LLC was established with one Datron machining center in Seattle, WA in 2002, by German sister company Schaeffer AG owners Kai and Jörg Schaeffer, and partner Christian Blöss. Until 1988, custom front panels were made by hand, using drills and files. Today, they are designed online by customers using the free Front Panel Designer software and then machined on Datron high-speed machining centers.

The idea for Front Panel Designer came from the realization that many engineers designing other electronic products faced a similar challenge sourcing small runs of custom front panels. Schaeffer developed a CAD/CAM system adapted to the production of front panels, which allows customer designs to be quickly and efficiently transferred to a CNC machine. The emergence of the internet made this technology readily available to customers, many of whom were coming from the US. Demand from R&D engineers, small companies, and hobbyists was so great that soon business called for another Datron machine and a larger production facility.

In 2007, Front Panel Express moved to their current location, an 8300 ft² (771-m²) manufacturing facility, where they will soon be adding an additional 6000 ft² (557 m²) of manufacturing space and have recently added their sixth Datron high-speed machining center. The company now serves customers in North America and Australia. With a four-year head start, Berlin-based Schaeffer AG has 10 Datron machines and serves all of Europe.

 Front panels are customer-designed using the free Front Panel Designer software to create machining programs for the Datron high-speed machining centers.

As the company grew, so did their customization offering. A wide range of colored aluminum and plastics were made available, as well as engraving styles and a variety of colored infilling and powder-coating options. From the customer’s perspective, the four-step customization process is as easy as download, design, order, and receive. The Front Panel Designer Software is a front-end interface that allows non-machinists to easily make a custom product by selecting from a variety of materials ranging in thickness and color, placing holes, slots, and engraving and even picking from a wide range of infill colors and powder-coating options. What the users see on the screen is what they will get in the finished product. Once they’re done designing, they automatically get a price calculation so they can adjust the design to meet budget requirements.

Behind the scenes there’s a little more to it than that. It’s a "silent customer service" that’s invisible to the customer but guarantees the quality of the product they receive. With very few orders requiring a customer phone call, Front Panel Express reviews every file generated by online customers. Before machining begins, the company corrects errors to prevent design flaws or suggests improvements or ways to increase machining efficiency when they are noted. While this simplicity attracts a lot of hobbyists, the software is also robust enough to allow larger customers—companies like Lockheed and Boeing—to take drawings prepared for other panel manufacturers and convert them.

Much of this process is enabled by the Datron Machine’s DLL software interface, which allows importing of external data sources. On the back end, some elements are Datron code and some are Front Panel Express code. For example, the font library and cut outs are Datron and the DXF imports are Front Panel Express. The Datron DLL allows them to work in concert and for the conversion of all of the data to a final milling code. In the case of DXF imports, if there are any broken lines or open spaces after the conversion, the software alerts the user with a red flashing arrow pointing to the problem area. The software limits tool sizes (up to 3 mm) and the number of material thicknesses (up to 10 mm) to keep things within the parameters of the Datron machining center. In this way the amount of stock that needs to be maintained is minimized, lowering overhead and containing costs. Savings are passed on to the customer.Clayton Olander, Front Panel Express machine operator, downloads the program and selects the appropriate stock and sets the blank for machining front panels.

The end result is a process that converts overviews, prints a milling tag, sets quantity, color, and position for batch machining in the case of a multiple panel order, and even prioritizes jobs by delivery date. All the operator has to do is place the correct blank in the chuck and enter an order number. The Datron machine loads the milling file or macro file, automatically finds a zero point, probes the blank, and begins machining. The Z Probe on the Datron machine scans the surface of the blank and lets the operator know that it’s the right one for the job, which minimizes waste. It also ensures accuracy and the quality of the finished part, which is critical to its functionality and customer satisfaction.

According to Scott Hoveland, Front Panel Express production manager, "The plug-and-play flexibility of the Datron machine is one benefit, and the industrial reliability is another. With six Datron machines on our floor, 2010 was the first time we had a service technician come to visit since 2002, and that’s just amazing." Hoveland cites the Datron track record of dependability since it contrasts so much from his previous experience with large VMCs. "When those larger machines went down, we’d have to wait until the service technician came out before we could even find out what was wrong, and then have to wait for parts to be ordered and for the technician to come back out and fix it."

The Datron machines allow for remote diagnostics, and 90% of the time problems can be solved over the phone within an hour—in many cases without any exchange of parts. With the push of a button the Windows-based control performs auto diagnostics and produces e-mailable Anomaly Reports that show machine status and recall any errors that may have led to the issue. This helps them to swiftly diagnose the problem and, if necessary, get a spare part out the door and delivered to the customer on the next business day. Then, by use of phone or e-mail, their skilled technicians walk the operator through part replacement. Once the part is replaced, the operator simply reboots, the machine performs an automatic re-calibration, and the customer’s production resumes. 

The VacuMate vacuum table contributes to the efficiency of the manufacturing process by quickly and efficiently securing flat workpieces to the bed of the machining system. Thin stock, which could be secured only with great difficulties before, is now secured in seconds. This includes plastic foils as thin as 0.001" (0.03 mm) as well as 0.250" (6.35-mm)-thick large aluminum sheets. The coolant used for machining aluminum is a fine mist of ethanol which provides a better cut and quickly evaporates. Parts come off the machine clean, with no need for secondary operations like degreasing or deburring.

Front Panel Express CEO Diane Haensel explains that while the relationship between her company and the end customer can be seamless since the transfer of information often occurs online, the relationship between Front Panel Express and their vendor, Datron, can be more hands on. She says, "If I have a question, I know that with a single call I can speak to their president." Haensel continues, "Plus, Datron offers ongoing instruction like Datron University that I’ve personally attended, and that kind of training allows us to offer a superior service to our customers." ME

For more information on Datron Dynamics Inc. go to www.datron.com, or phone 603-672-8890.

 

Machinist Ricky Dunning of Quality Screw Machine uses Hilm-Bock Twin Vises with machinable jaws to make camshaft spacers for Caterpillar.Workholding for New VMC Jobs

Screw-machine shops are typically limited to specific types of jobs using bar stock. Quality Screw Machine Products Inc. (St. Louis) manufactures products from carbon steel, stainless, alloy steel, brass, aluminum, and copper for a wide range of products including valves, fittings, couplings, threaded inserts and bodies, and hydraulic and pneumatic components, among others. Bar capacity ranges from 1/8 to 3½" (3.175–88,9-mm) diam in a 16,000 ft² (1486-m²) facility.

With the recent slowdown in the economy, Quality Screw Machine decided to expand its capabilities beyond that of the traditional multispindle screw machine job shop to include cutting edge CNC technology. So when the company purchased two VMCs in 2009, it opened itself up to a whole new range of jobs, allowing the company to run multiple parts more efficiently.

The problem, though, was that the shop now had to purchase workholding equipment specific to each new job. This could be expensive. Most companies would have a toolroom filled with workholding devices from past jobs. Quality hadn’t had a need for the devices before, so it had to start from scratch.

The solution came in the form of Hilma-Bock vises with machinable jaws from Carr Lane Roemheld Mfg. Co. (Ellisville, MO). Quality Screw Machine purchased several of the twin vises in 4 and 6" (101.6–152.4-mm) sizes. These mechanical twin vises feature quick-change aluminum jaws that snap on and off, allowing jaw changes in a few seconds without the need for additional tools, bolts, or pins. The System Bock TV 100 and 150 twin vises are designed for workpieces with complex clamping and contact contours.

The twin vises have a high-strength aluminum body with hardened-and-ground steel guideways, along with two large outlets on each side for chips and coolant. The best feature of the vise is the aluminum soft jaws that can be completely milled out to suit the required workpiece contour (both sides can be used). So rather than purchase a lot of expensive dedicated workholders for each job, the same vises can be used over and over with the only repeating expense being a new set of machinable jaws.

Quality Screw Machine recently needed to machine camshaft spacers for Caterpillar, for example, and managed to satisfy all of its workholding needs with Hilma-Bock Vises. Terry Bolen, general manager of Quality Screw Machine, explains: "We are able to machine the jaws to the particular part and continue to use them until the job is done. We use 4" [101.6-mm] jaws to make the Caterpillar slug, which is a camshaft spacer. We are running 6000 pieces with 10 holes per piece. The vises allow us to make a quick change and are great for pallet changes. We have loaded them on a Midaco pallet shuttle, with six vises. We have three on each, allowing us the capability to load and unload while the other shuttle is being machined. This gives us tremendous flexibility and accuracy."

These twin vises clamp two workpieces simultaneously against a fixed center jaw, and are slotted in both directions for 20-mm fixture keys to provide accurate mounting on T-slotted machine tables. Locating pins provide exact positioning of the center jaw. The leadscrew assembly provides a down-thrust effect and is fully sealed to keep out dirt and chips.

Another option is mounting on a modular tooling plate, such as Carr Lane’s plates with holes in a 2" (50.8-mm) grid pattern for repeatable locating in both X and Y axes. The vises have two 5/8" (15.875-mm) diam locating holes for repeatable mounting and can be fastened with socket-head cap screws to the mounting slots.

Tower clamping systems are available from Carr Lane Roemheld with three to six sides, containing double vises on each side that each clamp two workpieces simultaneously against a fixed center jaw. The vises come in manual and hydraulic versions. The high-strength and light-weight vises offer a highly flexible and fast workholding system for VMCs.

"We also have 6" [152.4-mm] jaws which we are using on other jobs," says Bolen, "so it’s economical. We can continue to use the vises and just buy the jaws, which we can machine for each job. We save money, but we still get a lot of flexibility and high accuracy." ME

For more information on Carr Lane Roemheld, e-mail engr@clrh.com,
or phone 636-386-8022.

  

 

This article was first published in the July 2011 edition of Manufacturing Engineering magazine.  Click here for PDF


Published Date : 7/1/2011

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