by, Bernard Martin

As carbide end mills gain higher and higher speeds and metal removal rates there has also been a trend by round tool manufacturers to tighten up the tolerances on both the cutting diameter and the shank diameter to improve concentricity. At the same time, shrink fit holders have become more and more popular because they hold a tighter concentricity as well.  To achieve this both the shank and the bore now have similar surface finishes and this has led to a problem  The tools pull out in the cut.

Shrink fit holders are the most accurate for TIR as the toolholder engages completely around round shank tools with a bore tolerance of -0.0001" to  -0.0003".  As high performance end mills have tightened shank tolerances to the same range of -0.0001" to  -0.0003" they have used finer and finer grain grinding wheels which give the shanks a 'shiny' appearance. 

Shiny means that the superfinished shank has a lower coefficient of friction. So, although the TIR is tighter, the shank is more "slippery".   End mills traditionally had surface finish of about 8 μin on the tool shank. But that's changed.  It's been recommended that tool shanks used in shrink fit holders should not have a finish finer than 16 μin. for optimum holding power, but tell that to the guy who just superfinished the end mill to a super cocncentric tolerance that you don't want it looking that good.

Everyone know that the last thing you want is for the end mill to slip in the middle of a heavy cut or on the finishing pass of a high tolerance part.  These 'hi performance' end mills, often times have higher helix angles which are great for ejecting chips but also create a higher pull out force on that slippery shank. And reducing the helix angle is not the answer.

We  already know that the gripping pressure is a function of the interference between the tool shank  and the shrink fit toolholder bore. Most shrink fit holders have a already bore surface finish of between 12 μin. and 16 μin.  So they are ground to a very high tolerance and have about the same surface finish as the toolholder shank.

End mill manufacturers and machinist have tried a variety of methods over the years to stop the tools from pulling out. This has ranged from grit blasting the shank to rubbing chalk on the shank, but most everyone in the industry has felt that the problem really needs to be addressed by the longer life toolholder rather than the replaceable cutting tool.

MCLEAN, Va. (December 9, 2019)
U.S. manufacturing technology orders totaled $376 million in October 2019 according to the latest U.S. Manufacturing Technology Orders (USMTO) Report published by AMT – The Association For Manufacturing Technology.

October orders increased 2 percent over September 2019. New orders placed in October 2019 fell 21 percent from October 2018, which was one of the best Octobers in USMTO history.

Despite month over month gains, the gap between the year-to-date totals grew larger with the addition of October data. Orders placed to date in 2019 totaled $3.75 billion, a decrease of 18.4 percent from the annual total through October 2018.

The industrial machinery manufacturing sector experienced robust growth in October 2019. Orders from machine shops grew at a modest pace but have not returned to their later-summer levels. The automotive sector increased orders by about 40 percent in October, while the aerospace sector decreased orders by slightly over ten percent.

“Since March, job shops have accounted for an unusually large share of orders, reflecting the fact that large players deflected capital spending decisions to their sub-tier supply chain,” said Douglas K. Woods, president of The Association For Manufacturing Technology. That trend began a reversal in October, however, as companies of all sizes placed orders.

Our research and the data point to a shifting of capital investment activity from small companies downstream to tier two and one suppliers. Based on quotations activity, orders in November and December are likely to be from larger companies expiring their capital spending budgets rather than small manufacturers continuing to invest at their second and third quarter rates.”  

“It’s clear that a lack of stability in the market coupled with the shifting winds on trade issues are dampening U.S. manufacturers’ enthusiasm for investing in new capital equipment. At the same time, we are nearly half way through the Tax Reform’s five-year window of providing lower tax rates and investment incentives.

The former creates instability, and while the latter should be creating an urgency to invest, our analysts and leading industry economists believe that the confluence of drivers will yield a positive impact on the market in late 2020 and throughout 2021.”  

From: Aerospace Manufacturing Magazine
by : Mike Richardson, September 2018

Mike Richardson meets JJ Churchill’s executive chairman, Andrew Churchill to hear about the latest developments of its aerofoil blade machining techniques with the help of a new workholding concept called Blue Photon.

A first-tier expert in the production of gas turbine blades from forgings, castings and solid billet, JJ Churchill says it has halved machining operations on specific critical parts using Blue Photon technology – which is marketed in the UK and Europe by NCMT.

Blue Photon technology enables engineers to realise benefits not possible previously with mechanical fixtures alone. JJ Churchill has utilised the Blue Photon technology in an innovative way to deliver huge productivity benefits for its customers.

Here, the technology is applied to a titanium aluminide aerofoil blade component which is an extremely difficult material to fixture and machine. Blue Photon fixes the component to the workholding fixture with an adhesive, which when cured under UV light, is strong enough for the most rigorous machining techniques including 5‐axis CNC. The process is a replacement for encapsulation, providing reduced fixture complexity.

“You can often see real value by looking outside your sector at the typical technologies used on the products you make instead of just within your supply chain – it’s what I call horizontal innovation,” begins JJ Churchill’s executive chairman, Andrew Churchill. “Workholding is a classic example, i.e. how well a company can drive its process and quality performance is directly connected to how well it can repeatedly, robustly and rigidly hold the workpiece it is machining, otherwise it will never achieve a process-capable machining solution.

“We’re very interested in how we can best hold aerofoil blades. They possess a beautiful, sinuous shape, but are very difficult to clamp efficiently. Conventionally, a blade is secured using hard-point fixturing and a clamping solution which is expensive to make and has numerous drawbacks. Alternatively, the blade can be encapsulated by being placed in a mould and adding a low melting point metal or resin alloy, which takes it from a sinuous aerofoil shape to a solid block. This is expensive, and the design of the encapsulation fixturing is complex because it requires cooling water channels and electrical contacts, as well as moving parts and a decontamination at the end of the process.”

"A technique derived from prismatic machining, when exposed to UV light, the plastic polymer cross-links and sets. We pick up the datum points on the blade forging which allows us to use Blue Photon plastic glue to adhere a new set of datum points through a metal fixture with sapphire waveguides onto the blade. And because it’s a square shape, it can be clamped much more efficiently. After blade machining, the glued-on metal datum block is simply removed and the finished blade product is washed off with warm water. It’s a radical approach – we’ve taken Blue Photon’s licensee, NCMT’s intellectual property and developed the know-how for aerofoil manufacturing applications.

“In terms of benefits, we no longer need to design a complex and expensive encapsulation fixture, we can machine more faces of the blade, we’ve removed the slow-melting alloy encapsulation and part decontamination processes. Combined with other novel manufacturing processes such as additive manufacturing removes substantial amounts of lead-time from the new product introduction (NPI) process. Typically, we remove a quarter of the lead-time and about a quarter of the cost of NPI on a blade using the combination of Blue Photon and additive manufacture of coordinate measuring machine (CMM) fixtures. It’s incredibly powerful because if you can respond rapidly to NPI, you stand a better chance of getting the volume work of an aero engine programme.”

Once the blade root and tip have been machined, the workpiece is transferred to one of JJ Churchill’s Starrag LX051 5‐axis machining centres. The workpiece is held in specifically‐developed fixturing for the fast and effective complete machining of the aerofoil from forged blanks that are, at most, 5mm oversize.

“We’ve had Starrag machines for well over ten years, but we work with a relatively small number of top-notch, global machine tool suppliers. It’s really important to develop a deep relationship with those suppliers. We will visit them at least once a year to get involved with their R&D activities, so that we understand what is coming through as potential opportunities. We could wait and see what the large OEMs are pushing in terms of technologies – or we can get aggressively involved, help them solve some of their problems and get the opportunity to be partner with them on some of the technical developments going forward. We’ve done this very successfully in a number of areas.

“We usually get two years of advance notice of winning volume production contracts on any given programme. Volume production means building a bespoke cell, which requires investment and poses the question: in terms of single-piece flow, what is the best technology to drive global cost-competitiveness and process capability for this specific customer? We have a shortlist of potential machine tool suppliers where we can form a partnership, sign a non-disclosure agreement and put the supplier alongside our engineers to develop a proposal. This can form the basis of a long-term contract. We will then build the production cell and deploy it.”

ll this talk of the potential volume production hints at product process capability and robust process stability. How much importance does Churchill place on Industry 4.0, automation and the advent of ‘smart tools’ in general?

"We produce gas turbine blades for engines that will be in service for decades. If we’re still making them the same way whilst competitor economies like Germany continue to drive the application of Big Data and Industry 4.0 as a productivity advantage, then the UK will eventually lose out.

“More in the ‘here and now’ is automation. The use of robotics in a high labour cost economy will have its place – and the UK is a high labour cost economy. We’re looking at how we can link together our VIPER grinding centres and CMMs and automate them. The first step is a ‘pick and place’ robot: a robot arm and end-effector selects a turbine casting, places it on the grinding machine, removes it on completion and places it on the CMM. This offers some advantages but it’s not really earth-shattering.
“The real value is gained with closed-loop adaptive machining. The robot does what I’ve just described, but when it gets to the CMM, the CMM talks to both it and the grinding machine and says for example, ‘this is a nonconforming blade, there is a material-on condition, so we need to re-program and postprocess back to the grinder and remove more material from these features’. Completely without human intervention, this closed-loop output from the CMM is fed back to the CNC grinder, regrinds that blade and re-measures it to establish that it now conforms.

“This is adaptive machining. Even more exciting is where there are upper and lower feature control limits. If that feature is beginning to drift inside the upper and lower control limits, the operator will either take action or simply wait and see. However, in a closed-loop adaptive environment, if the feature begins to drift, the output from the CMM data linked into the VIPER grinding machine can adjust accordingly to make minute incremental offset changes and nurse it to hit closer to nominal all the time. This is what we will be doing and we’ve already designed a cell which is ready for the robots and designed with closed-loop adaptive machining in mind.”

Churchill then poses a relevant question: what does this mean to employment? After all that has already been discussed, it doesn’t surprise me to hear him say that as a rapidly growing business, JJ Churchill will be re-deploying its employees internally and re-skilling them accordingly.

“Companies will need to accurately plan a growth curve so that they can redeploy their labour. We want to take the experience our workforce has gained over the years and keep it, but retrain and augment it with the kinds of skillsets that will be needed to get the most out of digital manufacturing.

“We will also be looking to ensure our apprentices join us with ‘digital-ready’ skills. We’ll need people with grinding skills and those of being able to interact with robotics and programming, whilst operators with lower skillsets can be employed to ensure the cell is fed with raw material. It will require huge changes in our industry’s skillsets and it’s one that we’re eyes wide open to, but it will be a challenge for our sector as a whole in moving forward.”
www.jjchurchill.com
www.ncmt.co.uk