Thermwood Corporation, a major U.S. based manufacturer of CNC routers, has embarked on a program to develop Large Scale Additive Manufacturing (LSAM) which can perform both the “additive” and “subtractive” functions on the same machine. This approach, called “near net shape”, uses a high volume thermoplastic printer to quickly create a part that is nearly, but not exactly, the final net shape. A “subtractive” function then machines the part to the exact final net shape. In its final form, Thermwood’s system will perform both the “Additive” and “Subtractive” functions on the same machine.

MeltShape Technology 

Both vertical walls and horizontal slabs were successfully built during initial testing

A more complex pattern was also created and trimmed as part of the testing process

Thermwood’s development system has performed well during initial additive testing. It has been tested through its entire operating range. This startup effort included initial validation of an all new “MeltShape Technology”. Melt shaping promises enhanced control of layer shape and improved bonding between layers. This new patent pending approach uses one or more shaping wheels to shape, form and compress the hot plastic melt as it is being extruded, insuring that each new layer is the proper shape and thickness and that it bonds firmly to previously applied material.  Melt shaping offers a new and promising technique in the advancement of large scale additive manufacturing. 

Featuring an extruder from American Kuhne

Kevin Slusarz, American Kuhne vice president of process technology, assisted with the start-up effort.  American Kuhne, a Graham Group Company, supplied the custom extrusion system for Thermwood’s development machine. The extrusion system performed flawlessly during initial testing. Extruder controls are designed to smoothly network and integrate with the machine control. “We are quite pleased to have a partner like American Kuhne as part of this development program” says Ken Susnjara, Thermwood’s CEO. 

20% Carbon Graphite Filled ABS

The material processed during startup testing was a 20% carbon graphite filled ABS from Techmer ES. Thermwood is in discussions with other material supplier to test their material in this new application. 

MeltShaping Approach 

Thermwood’s melt shaping approach to adding material offers several significant advantages. Because layers are rolled together, rather than tamped together, air between layers is squeezed out during the additive process, so it is much less likely that air becomes trapped between layers. This was borne out during initial testing which produced virtually void free walls. This addresses the problem of trapped air delaminating layers when a part is processed through a heated autoclave, which is a common requirement for aerospace parts and patterns.  

Full Six Axis Articulated Additive Deposition Head 

This approach uses a melt shaping wheel that interact with the extruded thermoplastic bead while it is still hot and pliable. The shaping wheel is servo controlled so it can track the direction of machine motion. The Thermwood machine is a full six axis system, five axes to position the head in any orientation and the sixth axis to align the shaping wheels to the machine motion direction. Thermwood has added a software feature to its Q Core CNC control called “Tangential Following” which automatically keeps the shaping wheel aligned with the direction of machine motion without the need for six axis programming. This eliminates the need for a specialized CAD/CAM system to handle the sixth axis and allows the use of virtually any five-axis CAD/CAM system to program machine motion. 

Multiple Shaping Modules

Thermwood envisions different shaping wheels, each imparting specific characteristics to the hot plastic bead. 

Further Details

Because of its five axis head configuration, material can be applied at an angle or onto a curved surfaces in addition to traditional horizontal layers. This capability opens new processing possibilities and supports free form additive manufacturing techniques not currently possible. 

Thermwood’s initial test machine, which can print parts up to ten foot by ten foot by five foot thick, is expected to be fitted with a five axis “subtractive” gantry trim system in the next few months at which time all functions can be performed on the same machine. 

Ongoing Development

Thermwood Corporation, a leading U.S. based manufacturer of CNC routers, has announced a program to develop a 3D Additive Manufacturing System, capable of making large carbon graphite reinforced composite thermoplastic components.

Near Net Shape Approach

Thermwood’s systems utilizes a “near net shape” approach where a relatively large extruder, mounted to the machine, is used to heat, melt and deposit, or “print”, carbon graphite filled thermoplastic material to quickly create a structure which is almost, but not quite the exact final shape. That structure, when it cools and hardens is then five axis machined to the final net shape. 

Up to Sixty Feet Long

These new systems will be based on Thermwood’s Model 77, semi-enclosed, high wall gantry machine structures, which are currently offered in sizes up to sixty feet long. For the plastic extruder, Thermwood turned to American Kuhne, the preferred provider of engineered solutions for plastic, rubber & silicone extrusion, who developed a custom system, which integrates tightly, both mechanically and electronically, with Thermwood’s CNC machine. This allows not only the machine but also the plastic extruder to be controlled and managed by a central CNC control, insuring smooth integration and increasing both capability and flexibility. 

Optional Additive and Subtractive on the Same Machine

With the addition of a second gantry, both the “Additive” and “Subtractive” processes can be performed on the same machine. The second “Subtractive” gantry will be offered as an option. Companies that already have five axis machining capacity and want to work with Additive Manufacturing may only require “Additive” machine capability as they can use existing equipment for the “Subtractive” part of the process. 

Full Six Axis Articulated Additive Deposition Head

Thermwood’s systems will feature full six axis articulated additive deposition head, allowing it to build layered structures on both a horizontal plane as well as planes canted in any direction up to ninety degrees from horizontal. Management believes this capability will be important as technology advances and more complex structures are required. 

Further Details

Thermwood’s initial development machine, which is nearing completion, can make parts up to ten foot by ten foot by five foot high, is equipped with a 20HP, 1 ¾ inch diameter, 24-1 L/D extruder and support equipment capable of processing over 100 pounds of material per hour. Despite the relatively heavy weight of the extrusion system and head, which are both mounted on and move with the machine, the machine generates impressive performance with high acceleration rates and high feed rate capability. 

Ongoing Development

This is an ongoing research and development program and Thermwood Management cannot say when commercial systems might be available to the market, but they believe this technology represents a major opportunity and that “Additive Manufacturing” will become a significant factor in the future of manufacturing. Thermwood believes it is in a unique position to pursue this emerging technology since, at one time, it was a plastic processing company that operated large plastic extruders in a production environment. Thermwood is already a major manufacturer of the “Subtractive” machinery part of the equation and this same technology is the basis of the “Additive” equipment.

Thermwood also designs, builds and programs its own sophisticated CNC controls which it can tailor to any new requirements and also has experience developing sophisticated design and CAD/CAM software packages which are also an important part of this new technology.