EPS Pattern making by CNC Router

The similarity between lost wax casting and lost foam casting (LFC) is almost the same. The main difference is the use of EPS (expanded polystyrene) instead of wax. EPS is the disposable element. The only difference is the pattern remains in the sand mold. The hot metal will decompose the mold. The origin of this process dates back to 1958. H. F. Shroyer the originator called it the full mold process. In the early days, the patterns were machined on expanded polystyrene blocks and molded in sand that had furan resin as a bonding agent. Luckily, the patent expired in 1980 and it became available in the public domain.

The process of casting using EPS patterns explained in the following steps

• Patterns machined with pre-expanded EPS 
• Pattern is coated with refractory
• Pattern is placed in a flask
• Sand is filled into the flask
• Liquid metal is poured into the flask
• EPS melts or vaporizes
• Pattern is shaken loose for the casting to emerge

The alternative for EPS is expanded polymethyl methacrylate (EPMMA). Sometimes the two are mixed together to obtain a blend. Polycarbonate is another material that used in the LFC process.

Forming the Pattern

These are the various steps in the pattern making

• Design the part
• Tooling design for the EPS foam
• Tooling design decides initial dimensions
• Different sections of foam design
• Ultimate foam pattern quality and fusion of foam to refractory coating

Tool design of foam patterns take into account holes in the foam and pullbacks for undercuts. The design also incorporates collapsible cores for making large internal hollow sections in the foam. The complexity of the design involves making several sections of foam that are joined together in a final assembly to arrive at the final pattern To carve each foam section a tool and suitable fixture is designed so that correct alignment of sections are glued.

Tool designs generally are a long process. With the advent of the CNC router tool design and foam section carving is automated. Prototyping involved gluing hand carved foam sections and the resulting cast was inferior in quality that needed careful machining. Today 3d printers have made complex designing of parts user friendly. The same design is transferred via CAD / Cam software to an EPS shaping CNC router machine. The router creates the foam patterns. When all the foam sections are assembled together the pattern is filled with unbonded sand. Hot metal is poured and allowed to cool. The foam vaporizes. The sand mold is shaken loose and reused for the next casting process. The resulting cast is almost perfect that requires very little machining.

Cylinder blocks for automobiles use this process widely. Formula one engine constructors like McLaren and Ferrari have their own pattern making workshops that are state-of-the-art.

OMNI CNC EPS shaping router machine is widely used in die and mold industries. The machine‘s versatility can be gauged because it is used on expanded polystyrene, wood, and other non-metallic molds.

They have found special use in

• automotive foam mold
• wooden ship modeling
• wooden aviation modeling
• model trains 

Multifaceted Use of Wooden Crown Moldings

Wooden crown moldings have been used as decorative motifs from time immemorial. The early wood workers used various profiles that gave different shadow effects. Wood moldings were made from solid wood until gypsum or plaster of paris made its entrance and provided an alternative. With engineered woods and plastics, profiling of trims has reached another level for interior decorative trim.

Moldings have beveled edgings on two faces that are at right angles to each other. This allows fixing them to the wall and the ceilings. There are plain moldings, sprung moldings, cyma moldings, and ogee moldings among others. Moldings were introduced to add the dimension of shadow play on a wall. Adding a small overhang to the surface of the wall created different patterns of light and shadow to give an architectural effect. By changing the shape of the overhang, graded shadow effects became possible.

Decorative moldings from stone, plaster and wood are normal. Cyclopedia printed in 1728 has a chapter devoted for various types of moldings under the heading Table of Architecture. Woodworking tools were commissioned that were termed as specialized planes. At one time, a woodworking shop had to have as many molding planes as were the designs. You can imagine the shop with hundreds of planes. In the 19th century, the English multi-plane became the wood workers choice for molding work. This tool allowed interchangeable blades. When the crown moldings became large (in the order of 6inches or more) then pushing the plane required great force Sometimes two people needed to push and pull a plane for oversized moldings.

Today this is not a problem. Any woodworking CNC router will do the job in a matter of minutes. Profiles of moldings are stored as readymade drawings. The design can also be tweaked and in no time, a new molding design can be carved. Interchangeable router bits can cut variety of profiles.

Other than using between ceiling and wall, crown moldings are used in imaginative ways to enhance modern architecture with an ornate look. Using below the countertop of a kitchen island is one of the best ways of enhancing kitchen architecture. Adding molding to a plain door will instantly transform the door into an architectural delight and make it the focal point.Moldings are increasingly used to frame mirrors that will make it look more like an art piece.