MIGHTY GIVES BLOW MOLD MAKER THE LEADING EDGE

By: Tom Walsh

Blow molding is a standard process for the production of hollow objects. The products may be simple, such as aoda bottles, or have a complex three-dimensional shape, such as gas tanks, car bumpers, or children's toys. Blow molding dates back to at least 1890, when it was used to produce celluloid baby rattles. From that time forward, many companies have tried numberous means to produce blow molded parts in a variety of materials. The first polyethylene bottle was blown in 1942 and now the US produces over 30 million plastic bottles each year.

Making blow molds is an exacting process. Blow molding machines work by forming hollow objects by extruding plastic into an accumulator head, which creates parisons (molten tubes of thermoplastics) that is blown outward to take the ahape of the mold cavity. The mold design greatly affects the final product in the blow molding process. The position of cooling channels and / or high conductivity metals in the mold is especially important for controlling th epolymer / mold heat exchange. In addition, the parison experirnces large deformation during the extrusion, pinch-off and blow molding process. In order to obtain the desired wall thickness, the flow rate and thickness of the extruded fluid must be controlled. A leader in the manufacture of these molds is Fremont Plastic Molds, Inc., located in Fremont, Ohio.

FRREMONT PLASTIC MOLDS

Founded in 1962, Fremont Plastic Molds, Inc. is the largest producer of blow molded fuel tank tooling in North America. In addition, the company specializes in developing molds for hollow plastic components which includes toys, a wide variety of household products, coolers, bumper end caps, drum molds, car spoilers, washer bottles, and automotive interior ductwork. Customers include Ford Motor Company, Rubbermaid, and Igloo, Inc.

During the last four years Fremont tripled sales and doubled the size of their organization. In 1992, FPM initiated an aggressive program of purchasing CNC machines and CAD / CAM hardware and software. In 1995, FPM moved to its present facilities and this large modern building houses personnel dedicated to making it the most technically advanced blow mold manufacturing company in the world. Success is attributed to the adoption of better equipment (which includes seven Mighty vertical machining centers), a revitalized organizational structure, and the most experienced blow mold tooling people in the country, and this effort for improvement continues today.

According to Martin Cass, President of Fremont Plastic Molds, 'The size and rugged nature of CNC machining cneters from Mighty make them ideal for the industry. We tried other CNC mills an dfound that they were not conductive to this type of tooling.

FPM used to spend approximately 200-300 man-hours to manufacture a die model and a duplicating pattern that would assist us in cutting the cavities. Now we cut cavities in 4-5 days using unique CAM software and durable machine tools from Mighty. The new tools have brought production tooling leadtime down from 14 weeks to 7 weeks and rapid prototype tooling lead-time is only two to four weeks.'

THE HEART OF THE OPERATION

Machine tools are the heart of FPM's operation. The major players in their CNC operation are VMCs from Mighty USA. they have three Mighty VMC Bridge B-2000G models and three Mighty VMCs, a model V-500P, a model V-1250G, and a model V-1500G. Recently they acquired a Mighty V-2100.

The bridge models have a travel of 83" x 59.5" x 28". Column and base of the three machines are made of Meehanite high grade cast iron that is specially heat treated to relieve stress and to ensure the structure is free of distortion for its lifetime. An innovative 60° slant beam evenly distributes 50% of the thrust force from the Y-axis to the massive, allowing the spindle centerline to be only 8" from the beam surface. The oversized slideways ensure maximum cutting stability and th eoverall design is excellent for cutting operations such as die steel. The spindle is supported with Class 7 precision bearings and an automatic lubricating / coolant system in the gearbox facilites continuous cycling of the lubricant oil. Oil, which is cooled by the spindle chiller, circulates through the spindle jacket to prevent heat generation inside the spindle bearing. In turn, these features ensure heavy cutting capacity.

The Mighty Bridge B-2000G has a high-speed chain-type 30 tool (#50 taper) automatic tool changer that is the pacesetter for the industry. The ATC unit uses a quality hydraulic indexing motor to store and retrieve tools and completely avoids any spindle or bearing damage while changing tools. A program controlled door on the tool magazine ensures complete protection from chips and dust during the cutting and tool changing operation.

All the Mighty bridges feature the Meldas 335M ultra high-performance controls, high-precision digital AC-Servo motor / drive and digital spindle motor / drive with continuous status display capability. The all-digital intelligent and modular structure is achieved via a parallel data bus link, thus ensuring future expandability, ease of fine tuning and maintenance as well as an instant detailed display of servo I/O status, graphic tool path, and ladder diagram.

Because precision machining requires both skill and technical expertise, VMCs that rated high in geometry and construction were required. The three Mighty VMCs are heavy-duty, high-quality CNC vertical machining centers that allow great precision machining of die mold contouring. The column, bed and saddle are oversized, fully ribbed and can easily support heavy loads without table deflection. To achieve precision machining, an accurate, stiff, and stable spindle was equally important. The Mighty uses a cartridge-type spindle that is made of chromium-molybdenum alloy steel that is supported by very precise angular contact bearings. The spindle more than meets the stability required for precision machining of the die molds.

Trevel for the three Mighty VMCs is as follows: model V-500P 21" x 16" x 20"; model V-1250G 40" x 24 " x 24"; and model V-1500 61" x 32" x 24.5". All VMCs have a drum type automatic tool changer.

The VIPER V-2100 is one of the toughest C frame VMCs available on the market. Built on a heavy duty Meehanite casting to ensure maximum rigidity, the V-2100 is ideal die mold contouring. Featuring large box ways that have been induction hardened with Turcite B and precision grounded, all axes are reinforced to provide the highest degree of rigidity and stability.

Employing large ballscrew assemblies, the ballscrews are located in the exact center of each axis, which effectively eliminates heat and lost motion. High torque AC servo units are directly coupled to the ballscrews, moving the axis faster and overall, the complete assembly allows more precision.

The VIPER V-2100 is equipped with AC digital motors and features the Mitsubish Meldas 530 or Fanuc 18MC CNC 3D graphic control system with a 32-bit CPU. Featuring multi-window capability, the controller utilizes user-freidndly interfacing.

All of FPM's Mighty CNC machines are equipped with high-speed tapping. Tapping time is reduced by as much as 50% over conventional tapping eliminating the need for costly, floating-type tap holders. A direct synchronous sensor is built into the spindle motor. The digital control achieves a perfectly synchronous rotation of the spindle and Z axis servo motor.

PC-BASED CAD / CAM TECHNOLOGY

In addition to its CNC machine tools, Martin states that software and hardware is equally important. Six mold designers and six CNC programmers are kept quite busy in this segment of a complete design through manufacturing operation. FPM uses a Pentium Pro PC-based CAD / CAM system built around Autodesk's Mechanical Desktop (a suite of mechanical design software comprised of AutoCAD Release 13 with AutoSurf, AutoCAD Designer, and the AutoCAD IGES Translator) and hyperMill from OPEN MIND Software Technologies, Inc. Fremont engineers use Mechanical Desktop's flexibility for 2D and 3D design and free-form surface modeling. For CAM applications they integrate hyperMILL with Mechanical Desktop to provide high-end performance for 3D, gouge-free machining of multiple surfaces and solids.

According to Martin, 'When F ord delivers solid models created in Pro / ENGINEER, we use IGES Translator and Mechanical Desktop to create surfaces that are very clean. Previously, customers encourage the use of the computer solutions they use. With our CAD / CAM setup, compatibility is no longer an issue.'

QUALITY ASSURANCE

Martin states, 'We are firm believers when Ford states, Quality is job number one. FPM has a DEA Coordinate Measuring Machine with a Renishaw Probe (27" x 35" x 70") and our technician is ISO 9000 experienced. This market is very competitive and experiencing large growth in fuel tanks and automotive parts. There is development of better engineering resins and improvement in blow molding techniques. By staying abrest of recent developments and incorporating software with leading edge machine tools we literally knock the socks off our competitors by providing shorter lead times for large industrial tooling.'