Composite Metal Tooling…
                                 Technology of the Future

Global Competitiveness Has Never Been More Critical for Plastics Processing


Process Developed and Article Contributed by:
Randy Lewis
P. R. Lewis Consulting Company
Lake Wiley, South Carolina

We lament the fact that more and more of our molds and Injection molding business is going off-shore.  We have to ask ourselves, "What the hey are we doing about it?"  Detroit experienced this years ago and got leaner, meaner, and built a better product.  Is it about time we got off our sympathy horse and began to create new technologies to restore the good old U. S. of A. to her rightful place on the world stage of plastics processing.

Randy Lewis, inventor of this new technology has put his money where his mouth is.  He too saw his business going elsewhere but refused to acquiesce and rollover and play dead.

Randy has accomplished this by building a better mold.  That is to say, a mold that will perform more efficiently because of rapid heat transfer, thus creating faster cycles.

Composite Metal Tooling Mold                        

This mold has no cooling on the A side because the three-action movement makes it virtually impossible to incorporate pipe cooling into all of the moving steel. It was quoted at $15,240 to install cooling and improve the surface with CMT. Projected savings were calculated to be $10,900/month based on expected cycle reduction.

Faster cycles produce more parts for the same time and overhead.  "Piece-part price is what it is all about".  Randy does this with composite metal tooling.  This he accomplishes with high heat transfer metals and surface hardening.

Composite Metal Tooling (CMT) is designed to do for a mold what no single material of construction can do. It features a core of a proprietary metal called Heat Transfer Metal (HTM), which reportedly is easily machined or formed to a desired shape, and combines it with salt bath heat treating of a through-hardened steel. The result is a tough, hard, and slick mold with a high degree of thermal conductivity, which speeds cycles and improves the consistency of either thermoset or thermoplastic molded parts.

The CMT approach also can be used to make screw and barrel assemblies. An agreement has been reached with a major screw and barrel manufacturer to begin the development of this application. In addition, HTM can be used in channels where a mold's heat transfer medium flows--it is not subject to calcium plate-out or oxidation--or anywhere optimum heat control is a must.

"When we consider that molds are nothing but high-pressure heat exchangers, we understand that materials other than tool steel would be able to provide better heat transfer, but for the problems of strength and wear," says Randy Lewis, president of P.R. Lewis Enterprises (Lake Wylie, S.C.) and the inventor of the CMT process. "The molding industry has come to accept very poor heat transfer as the price for tool life."

"Basically," he continues, "this new composite method can through-harden an H-13 or S-7 cavity to 50 to 52 Rockwell C and passes the cavity through a heat treatment process that takes the surface hardness to 72 Rockwell C up to .020 inch deep. All the steel in the cavity not needed for strength is removed and is replaced with HTM, which improves heat transfer characteristics by two to five times."

Balanced Heat Flow
Lewis says his HTM mystery metal functions very much like a heat pipe. Both are not in direct contact with the melt and both are encased in steel. However, unlike heat pipes, he says HTM never needs replacing if the mold is accidentally overheated. Also, HTM can easily be machined or bent to fit intricate shapes. Heat pipes cannot.

He stresses that HTM is not meant to replace heat pipes. Heat pipes move more heat over a longer distance, but he says HTM can reduce the amount of steel through which the heat has to be moved.

"The ultimate goal in using HTM is not just to move heat faster, but to balance the heat flow in the mold so that cooling or heating is not limited by the properties of solid steel. Removing portions of the tool steel and replacing it with HTM can accomplish this."

Though easily shaped, HTM is strong enough to support 44 percent of what H-13 tool steel will bear. If, for example, 44 percent of the steel mass of a mold is replaced with HTM, Lewis says that the CMT mold will be just as thermally conductive as one made completely from beryllium copper. HTM has a coefficient of thermal conductivity that is reportedly more than nine times that of steel and twice that of aluminum.

Bathing in Salt
Various hardening methods were considered to increase the wear resistance and service life of the tooling, while reducing the coefficient of friction where the plastic contacts steel. Lewis chose through hardening with surface hardening. He says surface hardening steel that is not through hardened only increases the hardness of the steel by a few thousandths of an inch. Below this, the metal is at its original state.

"Conventional surface hardening leaves an extremely hard but brittle area in contact with the plastic," he says. If the mold is struck hard enough to dent the soft base steel, the hardened layer cracks and chips off. However, through hardening imparts hardening properties all the way through the mass of certain types of steel. Though Lewis admits that it can't achieve as great a hardening of the steel surface as surface hardening, it is not subject to surface chipping.

Through-hardened steel is often plated to achieve a desired surface hardness. But plating--hard chrome plating, for instance--is subject to chipping and other maintenance troubles as well. That's why Lewis says he opted for salt bath surface heat treatment. In this process, through-hardened steel is placed in a heated vat of salt under vacuum and the temperature is raised. The steel's surface is molecularly altered to a depth of .020 inch. There is nothing to chip off, as it is a part of the steel.

Worth Its Wait
Salt bathing raises surface hardness by 10 Rockwell C and increases the toughness of the base metal. Surfaces also become more slippery--more so than hard chrome--for easier mold release. And Lewis says they are more chemically resistant than stainless steel surfaces. HTM can be placed below the .020-inch hardened surface.

The cost of using CMT during initial construction or retrofitting depends on its application. But Lewis contends that the price is small when compared to the increased profitability generated by more thermally efficient manufacturing.

"In many cases, just the reduction in heat-up time can pay for the additional cost," he said.

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