CFRP milling:
A fine line between nightmare and lightweight vision

The factors opposing CFRP are the high amount of energy used in production, unresolved issues of disposal and the fact that recycling has been slow to get up and running. Why is CFRP still a green material?

Grimme: When CFRP is processed, this produces electrically conductive and combustible dusts that can harm people’s health. We have managed to develop methods which make it possible to filter almost all the dusts that are produced during machining in a CNC machining centre. We were very keen here to reliably protect not just the machine itself, but also the humans operating it from the dusts created during the milling process.

Grimme: It’s absolutely true that the issue of disposal has not been definitively resolved. What matters is that the material is recycled. There are very good possible solutions: Some waste management companies do in fact offer a complete disposal option that is documented. At present, roughly half of the initial material can be reprocessed. That’s not enough though. Research is currently being done to develop technologies that can separate the material into different substances. But given the clear benefits, I am certain that even better solutions will be available soon. For the more that CFRP is used, the more experience and know-how the CFRP manufacturers will gain too. It’s also well worthwhile for many industries to conduct research in this field.

Which also brings me back to your question: CFRP is a material that does not have a natural origin. However, it does combine many perfect characteristics and helps to preserve natural resources. For example, the composite material is five times lighter compared to steel, does not rust and is much more robust. This helps the aviation and automotive industries in particular to develop eco-friendly designs for transport and logistics. In addition, CFRP can be shaped as you want without too much effort. So all in all, I would say that: CFRP is a material that really helps us to progress towards a green future and is rightly described as the black high-tech gold.

How do you help companies that are breaking new ground with CFRP machining?

Grimme: Most companies are aware of the risks that milling CFRP entails. Any consultation and development work primarily involves the details of implementation. The huge amount of dust that is produced requires special technical solutions which need to be integrated into the respective business. It is not just the CNC milling centre itself that needs an appropriate space, but also the extraction unit. On the other hand, the control cabinet does not just require a technical solution to prevent the ingress of dust. The control cabinet also cannot simply be placed right next to a CNC machine. This is because the dusts will cause short-circuits if they get inside. This does not take very much: A single fibre, thinner than a hair, is sufficient: Then it will go bang! We consider all of this in our planning.

The increase in electric mobility means that the demand for lightweight construction with CFRP is also increasing: For example, you recently won multiple BMW tenders to construct a five-axis gantry rotary table milling machine to machine side section components at the Landshut factory. With orders like these, how do you handle the requirements for the milling quality, which are actually very high for visible components that are on display?

Grimme: We are a leading manufacturer for machining composite materials and plastics. The milling quality is not the issue, because our machines are designed for this. We have been developing CNC machines that deliver top-class milling quality for more than 30 years. There are now three of our machines operating at BMW’s factory in Landshut.

CFRP chips and dusts present a particular challenge: If they are not extracted reliably, the machine operators may suffer damage to their mucous membrane, fibrosis of the lungs, cancer or asthma. At BMW you are therefore relying on a newly developed, powerful machine for extracting the fine dust from several sides, an additional medium-pressure machine for filtering the suspended particulate matter, and a blow-off and extraction machine for the insertion area.

Is this typical, is there not a standard solution?

Settele: We do have standard solutions which we adapt to the customer’s component size and individual manufacturing. One example of our standard solutions is our CNC inclined bed machine with a rotary table and ingenious extraction system. The CFRP component is milled in a sealed-off machine cabin: The operator places it on outside of the milling cabin and never enters the milling chamber during production. The milling chamber is designed so that almost all of the dust can be extracted.

The extraction takes place during the actual milling before the dust can spread. The fixture is also designed to remove the dust immediately. The extraction is done through the milling cutter holder directly next to and along the cut contour. The milling head has an additional extraction unit which removes the dust so that there is the least possible spread of CFRP dusts within the cabin.

In addition, the air containing the rest of the suspended particulate matter is extracted from the milling cabin during CFRP machining. This efficient extraction system for suspended particulate matter works with a high-pressure and a medium-pressure installation which produces different flows. The air is purified following extraction with special filters. It can be fed back into the building or released into the open air. The installation is designed to provide constant checks of the filtering process and protection of the operator. The extraction system features filter breakage monitoring. If it fails, this is registered by a police filter. So we never leave anything to chance with CFRP machining.