A Machine Tool BuilderGives His Perspective

Scott Walker is President of Mitsui Seiki USA Inc. He graduated from Wentworth Institute / Massachusetts Institute of Technology with a BS Degree in both Mechanical Engineering and Aeronautical Engineering. He also received a MBA from Rensselaer Polytechnical Institute.

AMD: Have you witnessed any change in the Aerospace Industry over the past 5 to 7 years?

SCOTT: Yes, I have. One would be in structural components. Structural components have traditionally been made out of an aluminum frame and/or a composite frame material. On the new aircraft, in order to take a lot of weight out of the aircraft, the thinking was to go strictly to a composite structure. However, the composite direction has not been as successful as originally hoped. So, OEMs have moved to a new type of titanium material. This particular grade of titanium has a lot of nickel in it. With this titanium, wing structure ribbings can be made thinner than those made with aluminum, and the strength is far superior. The downside of it is that it's extremely difficult to machine. Tests have shown that the most economical way to machine this material is to use cobalt cutters at very low RPMs with deep cut depths, similar to the way aluminum used to be cut in the old days. We're developing a machine now that can machine at very low RPMs, take deep depth-of-cuts, and be able to handle low-frequency machining.

The other change that I've seen is on the jet engine side of the business. Take, for example, the new versions of air-taxi concept aircraft. One particular commuter aircraft holds six people. I understand that there are approximately 3,000 orders for this aircraft currently. The engines on these aircraft will be used to the end of their useful life, and then discarded. There will not be any replacement parts. There are two engines on this aircraft, with each one costing around $150,000. Since the cost of production on these engines is significantly less, the thinking is to spend less capital, and produce engines significantly faster than in the past. In fact, there's a whole revolution of new manufacturing processes that are being developed in this area to take significant costs out of engine components. It's the "reduce cost" mandate.

Another trend is that jet-engine components had traditionally been machined, and now grinding is gaining in popularity. I believe this is an area of development that needs to be considered by machine tool builders going after aerospace, since there's a lot of nickel in hot stage components, and nickel is difficult to machine economically. These new grinders are more like machining centers, complete with wheel changers, large coolant delivery systems, and rough and finish grinding capabilities. I believe machine tool builders will have to take their machining centers and/or grinders and make them more automated and versatile. I see this taking place in the next six to eight years on the machine tool side, in order to accommodate high nickel-content alloy material.

AMD: You've mentioned the use of titanium. Have you heard of a titanium 55-53 being produced in Russia?

SCOTT: Yes and we have a proprietary machine being tested to cut this material now. The new material requires a "heavy metal" machine designed specifically for this type of application. Machine tools are typically designed for general purposes, but with the economical environment in the aircraft industry, specific accommodations are required to provide the maximum ROI.

AMD: At IMTS you mentioned that the jigboring machine is making a comeback in the aerospace industry. Can you tell me a little bit about the reasoning behind that comment?

SCOTT: When an aircraft comes in for repair, which many of them are doing now from the war, it is completely disassembled and all of the components are inspected. At that point, there is a decision to replace, repair, or rework. Jigborers are designed exactly for that kind of work. For example, the engine-starter gearbox usually has a milled face that is used for the assembly of the gearbox. These contact surfaces mount into the gearbox case itself, and that plane is the critical location for all of the perpendicular bore locations to attach the high-speed drive shafts. A jigbore is designed so that the table surface is really the master gage of the machine. When something is set down on that table, all of the other axes of the machine are directly aligned with that table surface. You would think all machine tools are built like that, but they aren't. That is the reason in the aircraft industry, and specifically in the repair area, the jigbore business has picked up.

AMD: Both Boeing and Airbus are attracting attention for their use of advanced materials from metal structures to advanced composites in combination with high-performance metal alloys, such as titanium. Do you view this as a problem for machine tool builders, cutting tool manufacturers, or a combination of both?

A jigbore is designed so that the table surface is really the master gage of the machine," says Scott Walker,President of Mitsui Seiki USA Inc.

SCOTT: The tendency has been to build high-speed machines because they are in demand. These high-speed machines produce high torque at 4,000 rpm and up, but are not capable of cutting these hard alloys that we've discussed because the machining speeds are typically under 500 rpm. Some builders have stayed with the boxway, heavy-duty style design machine tools and focused on the hard-to-machine alloys. What has happened is, the heavy metal area is becoming a huge market and machine tool builders have to get in it. Machine tool builders need to take a serious look at this particular market segment and invest the money into the development of lower cost gear spindles to provide adequate torque. Also, to remove lots of stock, the tool taper interfaces need to be analyzed because with substantial depths-of-cut required to remove stock economically, the bending movement loads can exceed the current tool taper interface. Also the machines need vibrational characteristics that can handle low-frequency cutting in the 13Hz - 220Hz range.

AMD: The more titanium that's going to be needed in the aerospace industry creates a critical need to improve machining efficiency, because there just isn't enough capacity right now. What is Mitsui Seiki doing to address this situation?

SCOTT: I have an R & D effort with a customer right now to develop the spindle and the machine structure to accommodate low-frequency cutting. Mitsui Seiki has already delivered about eight machines that are being applied in this application. We are also developing machines to accommodate core competency areas, while lowering production costs. We recently launched a new 5-axis product called Vertex, and the majority of those are going into the aircraft engine area for point and flank milling

AMD: Do you have any parting thoughts or suggestions that you'd like to add?

SCOTT: I would like to know where all this titanium is going to come from! At the moment it appears that Russia is the prime supplier, and they don't want to make forged parts. But when you're bringing over a piece of plate that's worth $300,000, and you've machined away 97% of it, you've got all this scrap left in your bin and you've got to ship it all back to Russia and have it melted down and reprocessed. Russia may become the roughing titanium capital of the world. I think it would be a lot cheaper to do the roughing over there and keep the material over there and ship the rough part so the builders of the components can do the finishing. Now, the thing that's interesting, based on the current research, is that roughing the parts is easy, finishing it is difficult, and that's what we're perfecting right now at Mitsui Seiki.