From: Aerospace Manufacturing Magazine
by : Mike Richardson, September 2018
How JJ Churchill is using Blue Photon Workholding Technology to meet their manufacturing needs.
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.”
Time to meet your maker
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.”
Machines talk to machines
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.”
Adept at adaptation
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.”
This article about Blue Photon Technology and Workholding Systems LLC originally appeared in Modern Machine Shop magazine.
Written by Derek Korn
Precision Grinding and Manufacturing uses an atypical means to fixture thin parts that are prone to flexing when conventional workholding clamps are used: adhesive cured by UV light.
Operators must take care not to distort such parts while tightening clamps, otherwise the parts will spring back to their natural state once the clamps are removed after machining.
Vibration can also be an issue for parts like these if they aren’t rigidly fixtured, meaning a quality surface finish might be tough to achieve and cutting parameters might have to be dialed back, extending cycle times. Finding a way to effectively fixture complex, contoured parts can be just as difficult.
Ray Bray says Precision Grinding and Manufacturing (PGM) fought these problems in the past. Mr. Bray is a project engineer for the Rochester, New York, contract shop that specializes in complex, short-run, often repeating work for industries including aerospace, automotive, medical, military, optics, photonics and telecommunications.
Bray says PGM has employed a variety of unconventional methods to more effectively secure relatively thin workpieces for machining over the years, going so far as to use clay, lead and sandbags to supplement conventional mechanical clamps in an effort to minimize vibration.
You won’t find those types of workholding workarounds being applied there today. Instead, the shop uses an advanced, albeit atypical technology that is particularly effective for fixturing flexible parts.
In short, this technology uses adhesive to temporarily bond a workpiece to numerous cylindrical grippers installed in a fixture plate. Once the adhesive is cured via ultraviolet (UV) light, the workpiece is securely held at a known datum location in an undistorted, freestate condition.
After machining, the adhesive bonds between the grippers and workpiece are easily broken and any excess adhesive is removed from the completed part via a quick, steamcleaning wash.
"A workholding solution that uses adhesive cured by ultraviolet light enables PGM to accurately fixture thin parts such as this magnesium casting without causing them to flex, which can happen when conventional mechanical clamps are used."
Mr. Bray says that while this workholding technique isn’t appropriate for every job that runs through the shop, it has opened opportunities to win work that, in the past, PGM might not have considered bidding on due to the inherent fixturing challenges. It has also enabled PGM to improve existing fixtures the shop uses for jobs that regularly repeat.
William Hockenberger established PGM in 1967. The shop is now led by his son Mike, who is president and CEO. Business has been good over the years, and PGM has recently completed a 20,000-square-foot facility addition, bringing total floor space to 68,000 square feet.
PGM has a wealth of CNC equipment, including machining centers, turning centers and grinding machines. Milling represents the bulk of the work performed there today, for which the shop uses VMCs with four- and five-axis capability as well as HMCs with pallet pools.
William Hockenberger’s son Todd, PGM’s coporate vice president, explains that because a good portion of that milling work involves thin and complex workpieces, the shop has continuously looked for more effective ways to secure those types of parts for machining.
A few years ago, PGM learned about photo-activated adhesive workholding (PAAW) technology that was developed at Penn State University, which looked to be well-suited for such troublesome parts. PAAW technology was invented by Professor Edward De Meter, who was awarded two patents covering it. In 2012, Professor De Meter and others formed Blue Photon Technology and Workholding Systems LLC to market the technology to industry end users.
Mr. Bray says the fixture design process using the PAAW system is similar to other more conventional fixtures. In many cases, the shop will create a fixture plate with three hard datum points for a part to rest upon so its location is known in space. (Temporary pins can be used to ensure that the part is installed correctly on the fixture plate.)
PAAW grippers are positioned at various locations, and oftentimes a gripper is used at each hard datum point. The number of grippers used largely depends on the size of the part and its geometry. The threaded grippers install in the top of the fixture plate and require a through-hole to enable the UV light to pass up and through the gripper to cure the adhesive.
The photos below show the process for fixturing and removing a workpiece using the PAAW system:
The photos above demonstrate the process for fixturing and removing a magnesium casting that PGM machines on a four-axis VMC using the PAAW system. With the fixture plate installed on the machine’s rotary table, operator Alan Jedik dabs the top of each pin with a bit of adhesive. He then installs the casting onto the fixture, which rests on the three hard datum points, and inserts the UV light source’s light guide into each of the three grippers located at those datum points. It typically takes 30 seconds for the UV light to cure the adhesive on each gripper. Mr. Jedik rotates the fixture for easier access to the remaining six grippers and cures the adhesive at each of those points. The part program can begin once the table is rotated back to its proper position.
After machining is completed, a T-handle wrench is used to back off each gripper, twisting the element and shearing the adhesive bond with the workpiece. The workpiece can then be taken off the fixture and a subsequent cleaning operation using a portable steam cleaning device is used to remove any cured adhesive that remains on the workpiece. Adhesive must also be scraped off of the tip of each gripper using a metal scale or straightedge before a subsequent workpiece can be fixtured for machining.
The gaps between the workpiece and grippers (thus, the thickness of the adhesive) can range from 0.010 to 0.125 inch depending on the flatness of the part. The uncured adhesive, which is non-toxic, is sufficiently viscous that it won’t run off grippers regardless of orientation. Axial holding force depends on gripper size and can range from 250 to 800 pounds when using Blue Photon’s BlueGrip S1 adhesive.
Grippers are made from hardened, corrosion-resistant stainless steel and have a black oxide finish. For repeat jobs, PGM will commonly leave the fixtures intact with the grippers still installed and store them for later use. Otherwise, the grippers can be removed and installed in other fixtures created for new jobs. The latter is most often the case for PGM, because new work continuously flows through the shop.
PGM has found that the PAAW system can be used in conjunction with conventional clamps, too, as evidenced with the part shown above for the printing industry. The shop had fixtured this long, relatively skinny part using only mechanical clamps on a tombstone for op. 10 and op. 20 work on one of its pallet-pool HMCs.
However, it was challenging and time-consuming for operators to mechanically secure either end of the part without causing it to twist about its longitudinal axis.
This long, thin part, which is machined on one of the shop’s pallet-pool HMCs, is secured via conventional mechanical clamps and PAAW grippers. Mechanical clamps were previously used on either end of the fixture, but they tended to cause the part to twist as the clamps were tightened. These were replaced with the grippers, which eliminated the twist issue. For this part, an op. 20 milling operation removes any adhesive that might remain after the op. 10 fixturing, as shown in the photo on the right.
Rather than completely revamping the original fixture, Mr. Bray retained the mechanical clamping elements for the middle section of the part, but added two PAAW grippers to either end of the fixture.
Operators clamp the middle section of the part as they always have, but use the PAAW system to secure the ends of the part so these ends remain in a free state and there’s no chance of causing the part to twist.
After op. 10 work, the part is flipped and refixtured, and an op. 20 milling operation removes whatever cured adhesive remains from the op. 10 fixturing. Therefore, it’s only necessary to steam clean adhesive left behind from the op. 20 fixturing in this case.
Thus far, PGM has used the PAAW system for a couple dozen jobs in materials including aluminum, magnesium and stainless steel. Blue Photon says the PAAW system can also be used with composites and ceramics. The shop currently has three portable UV light source units that can easily be transported to machines throughout the shop.
The system will be used to a greater extent for production as well as toolroom work and CMM part inspection as PGM gains more experience with it and experiments with BlueGrip adhesives. Todd Hockenberger says it sometimes serves as a selling point for customers that are either having problems with other part vendors or readily recognize how tough their new design will be to fixture.
The shop has a good chance at winning those types of jobs once the customers understand how the system can be applied to their applications. In addition, it can help shorten product design cycles because fixture design is no longer the challenge it once was when mechanical clamps seemingly were the only option.
"This is big," Mr. Hockenberger says, "because PGM tries to get involved as early as possible in each customer’s new product design cycle to offer design for manufacturability (DFM) advice to minimize production time and cost, and get the product to the market faster."
Precision Grinding and Manufacturing: call 585-458-4300 or visit pgmcorp.com.
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