Carbon fiber lightweighting for low-cost vehicle prototyping

Electric vehicle and race car designers are big fans of carbon fiber reinforced plastics – strong-as-steel composites that slash vehicle weights. Lightweighting isn’t only good for boosting acceleration and range, it can also speed computer numeric control (CNC) machining of some materials while cutting system costs.

Building on experience gained through custom surfboard production, Santa Clara, California-based Autoscale Inc.’s CNC technology for cutting light-grade wood, foam, concrete, or aluminum can slash router system costs by about 90%. Capable of producing objects up to 16ft long, the machines integrate carbon fiber materials with high-precision motion control technology from linear motion specialists Thomson Industries.

The CNC system uses a router, hotwire, or other cutting technology appropriate for softer materials such as light woods or expanded polystyrene (EPS) foams. Gantries guide the cutting tools along the X- and Y-axis, while an arm on the Z-axis moves the tools vertically.

Lightweighting

Most CNC cutting systems use steel for the frame and all moving parts.

“When we started building larger routers, we were kind of like a dog chasing his tail,” Autoscale Founder and Owner Dan Bolfing says. “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 lb, including the gantry, carriage, and all the gear boxes, profile rails, ball screws, and other mechanisms.”

After experimenting with lighter material alternatives, Bolfing and his engineering team opted to replace steel with carbon fiber because it provides faster, easier gantry assembly.

Steel expands and contracts – twisting, turning, and flexing as temperatures change – and ensuring straight gantries took two weeks. After being welded, gantry components had to be straightened and assembled. Following testing to demonstrate straightness, gantries were pulled apart, powder coated, and reassembled.

With carbon fiber, designers can create patterns and molds in advance, and the design will always be faithful to the pattern. Production time decreased to one week instead of two.

Improved productivity, however, was a happy byproduct. The big driver in the shift was weight. Replacing steel slashed weight 10x – the gantry and moving parts fell to 350 lb from 3,500 lb, eliminating the rigidity-vs.-speed tradeoff.

Compared to a steel gantry based system that may cut at 300ipm to 400ipm, the carbon fiber-based system cuts at 800ipm without vibration. Lowering top-end speed and ramp times accelerates the time it takes a system to reach its top speed, further reducing processing time.

“You never want to accelerate at full throttle,” Bolfing says. “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 300ipm on a detailed part because you are going to be constantly accelerating and decelerating,” Bolfing adds. With carbon, however, you can shorten the acceleration distance by 90%, 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.”

Precision control

Key to precision are linear guides controlling the X- and Y-axis and ball screws. Autoscale chose Thomson linear guides to ensure high precision, reliability, and adaptability.

“Thomson is the only company that provides a 16ft profile rail,” Bolfing says. “With any other vendor we would have to splice two shorter pieces together, which challenges accuracy and durability.”

For router-based operations, which tend to have a higher load, Thomson provides profile rail linear guides for smooth, precise guidance of the milling head. Thomson also supplied Super Ball Bushing bearings, which have 27x the travel life of conventional linear bearings. The bearings offer increased load capacity, self-aligning capabilities, lightweight materials, adjustability, and a low coefficient of friction.

www.autoscalecnc.com

www.thomsonlinear.com