This project was to replace a manual process that used a handheld router with a fully automated milling machine. This reduced the cut time from 8 hours to 3 minutes, greatly improved ergonomics, and the overall quality of the cut. The left and right wings of the aircraft are attached to a center wing that runs through the fuselage of this large cargo aircraft via a butt joint. This requires a very precise mating surface across the 28 locations where the bolts tie the wing sections together, called wing nodes.
Each of the three wing sections are about 50 feet long. Cutting a precision plane on the wing mating surfaces with a milling machine seems like an obvious choice, but the wing sections are so large, the cost of a CNC milling machine and the time it would take to move and clamp the wing sections in place were cost prohibitive. So, this process had been done with a hand router for 50 years.
As is very common with Delta Sigma designed machines – we looked at the constraints from a different perspective from the way a task like this is traditionally done. Creating the mate-plane with a milling machine was an obvious choice and for this application, a very specific CNC Mill could be designed and built by taking these factors into consideration:
- A standard CNC mill can make almost anything – this mill only needs to make ONE thing
- Therefore, we could make a CNC Mill that can be brought to the wing instead of taking the wing to the milling machine
- The wing is very strong and can be used as part of the strength of the Wing Mill
- The four corners of the wing face are cut to the correct surface plane in the prior step of the assembly process and can thus be used as a dependable reference for the Wing Mill
Designing The Wing Milling Machine
The Wing Mill was designed with two major parts – the inner and outer frame. The inner frame hangs inside the outer frame. The outer frame moves about on air casters which makes it very simple to move and position. The outer frame is positioned about 6 inches from the end of the wing’s mating surface – this is not a critical distance nor is being strait to the wing important. The inner frame hangs from a sliding gimbal that allows it to extend outside the outer frame by about 10 inches and slide in the wing fore/aft dimension about the same.
The inner frame is the actual milling machine, yet it can be easily moved with the fingertips of one hand to align to the four corner nodes. Once aligned, four Delta Sigma designed “pins” clamp the Wing Mill to the wing’s mating surface. There are four faces the Wing Mill can cut: Center Wing Left, Center Wing Right, Outer Left Wing, and Outer Right Wing. When the Wing Mill pins are inserted, the system automatically determines which face it is attached to and runs the appropriate program when started.
After the cut is complete, the system has a built-in laser measurement system which is used to inspect each of the nodes and create a report. The entire process to move the Wing Mill into position, align and attach it to the wing, cut and inspect, generate the report with pass/fail of each node, remove the pins, and return the Wing Mill to storage is 20-30 minutes.
Thoughts On Process Automation
When considering automation for a process that is currently done manually, a common mistake is that people are looking at ways for a machine to do the thing a human did in the same or similar way. This is easy to understand when you consider the people that have been responsible for that process for years see that process as “how it is done”. An outsider with expertise in automating manual processes – not expertise in your special process – can look at things with a different perspective more easily. When an outsider’s perspective is applied, it is common that things that seemed unlike candidates for automation become very good candidates.
Companies automate processes for all kinds of reasons. The following list is the most common reasons Delta Sigma has been given as the primary objectives to a system design:
- Improve first-time quality
- Improve ergonomics
- Improve safety
- Reduce floor space footprint
- Reduce span time/increase rate
- Reduce material consumption
- Reduce overall costs