Cutting costs and production time in large-scale CNC
Jul. 13, 2017 - Automated production of large objects, such as auto body prototypes, boat hulls and surfboards, traditionally requires computerized numerical control (CNC) systems that can cost close to a million dollars.
But now, through an integration of advanced composite materials and high-precision motion control technology from Thomson Industries, a Silicon Valley company, the cost for CNC systems for cutting light-grade materials, such as wood, foam, concrete or aluminum, has been reduced by about 90 per cent.
Redefining CNC price/performance
Building on experience gained through custom surfboard production, Santa Clara, Calif.-based Autoscale has developed CNC technology that can produce objects with lengths up to 16 feet. See the image below.
On the business end of a CNC system for softer materials is a router, hotwire or other cutting technology appropriate for materials, such as light woods or Expanded Polystyrene (EPS) foams. Following advanced algorithms, which product designers create for mainstream CAD/CAM software, frame components — known as gantries — guide the cutting tools along the X-Y axes, while an arm on the Z axis moves the tools vertically to add the third dimension to the product. For most mainstream systems today, the frame and all of the moving parts are composed of steel.
“When we started building larger routers, we were kind of like a dog chasing his tail,” said Autoscale founder and owner Dan Bolfing. “We wanted rigidity and speed. But adding rigidity to the moving parts also added weight, which slows the system down and adds cost. Our first models were weighing in at around 3,500 pounds, including the gantry, carriage and all the gear boxes, profile rails ball screws and other mechanisms. This is not far from what the rest of the industry was doing with steel, but we wanted to do better.”
Replacing steel with carbon fibre
After much experimentation with lighter material alternatives, Bolfing and his engineering team concluded that replacing steel with carbon fibre would offer many advantages. For one, it would be easier and faster to produce the gantries. Steel expands and contracts, and it was taking up to two weeks to get the steel gantries straight. After being welded together, they would have to be straightened and assembled. When it was determined that they were straight enough, they were pulled apart, powder coated and reassembled. Carbon fibre, on the other hand, allowed the creation of patterns and molds in advance, and when the design was laid out in the carbon fibre, it would always be faithful to the pattern, unlike steel, which twisted, turned and flexed as the temperature changed.
Most dramatic, however, was that in addition to nearly halving production time — from two weeks to about one — carbon fibre was much lighter than steel, reducing the weight of all moving parts from 3,500 pounds to 350 pounds, virtually eliminating the industry-wide rigidity/speed tradeoff, says the company. Where a steel gantry-based system might cut at 300 to 400 inches per minute, the carbon fibre-based system could cut at 800 inches per minute without vibration.
Moreover, the speed advantage comes not only in top-end speed but in ramp time as well, shortening the time it takes a system to reach its top speed, thus further reducing processing time.
“You never want to accelerate at full throttle,” said Bolfing. “With a heavy gantry, you have to ramp slowly — accelerating and decelerating at the beginning and end of every cut. The lighter the gantry, the faster you can accomplish that. With a steel gantry, you are never going to get up to 300 inches a minute on a detailed part because you are going to be constantly accelerating and decelerating. With carbon, however, you can shorten the acceleration distance by 90 per cent, which is especially valuable in finishing parts in foam, clay or soft plastics. You run faster without having drastic acceleration requirements cutting into your production time.”
The key to this system’s meticulous operation, it says, is the effective use of linear guides which control the X-Y axes, and ball screws. Autoscale says it chose Thomson linear guides based on their “high precision, reliability and adaptability.”
“Thomson is the only company that provides a 16-foot profile rail,” said Bolfing. “With any other vendor, we would have to splice two shorter pieces together, which challenges accuracy and durability.”