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Innovations in Workholding

By Frank Burke Contributing Editor, SME Media

Providers respond to new manufacturing demands and technologies

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The RoboTrex automatic handling system from Lang operates the machining center from an automation cart, which serves as a storage medium for the vises. Depending on part size, the cart can store up to 42 vises.

Not long ago, the mention of workholding might call to mind the traditional vise or three-jaw chuck. The integral nature of proper fixturing to successful machining has forever changed that paradigm and made workholding as critical to the manufacturing process as any of the machines or systems of which it is a part.

Always key to accuracy and repeatability, workholding techniques, materials, and strategies continually evolve in response to more complex parts, improved machining capabilities, and emerging connectivity requirements to meet the needs of Industry 4.0.

Challenged by non-traditional materials, generative design, and smaller production runs, manufacturers have a new appreciation of the importance of workholding. Good workholding makes machining easier and more profitable.

The increasing demand for components machined from conventional hard materials—including titanium, stainless steel, and customized alloys, as well as ceramics and glass—means more aggressive machining with higher speeds and feeds. This in turn has prompted the development of new workholding designs.

Challenges occur on many levels, extending from basic size and strength considerations to problems of resonance and harmonics. Reese Johnson, customer support supervisor, applications specialist, at Vektek, Emporia, Kan., a manufacturer of hydraulic clamping devices, commented, “As you create more cutting forces, you need higher holding capacities—but without adding size to the workholding device. In response, we’ve developed high-capacity work supports that have the same footprint as our current products.”

Eric Nekich, operations, technology & inside sales at Lang Technovation Co., Hartland, Wis., noted that “many new machining concepts can be much easier on your workholding and can even use less workholding to achieve the desired results—for example, smaller, more compact chucks and vises.” He thinks this is especially helpful in new alloys that are prone to workpiece deformation at high clamping forces. “At the same time, you need to ensure that your workholding is rigid and can support the increased speeds and feeds” while providing proper clearance for access and optimum toolpaths, he said.

Rigidity Vital in Workholding

Brian Rich, project engineer at Kurt Manufacturing-Industrial Products Division, Minneapolis, a supplier of workholding, hydraulics, and other components, observed, “The biggest factors when it comes to aggressive machining are rigidity, repeatability, and resonance. Harmonics can be a significant problem and frequently remain undetected in automated set-ups. As a result, we’re creating pre-developed systems that not only address part-holding capability but allow for quick change.”

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A demand style, two-stage electric/hydraulic workholding pump from Vektek. In operation, the pump turns on, builds to the preset pressure, then turns off. In the event of pressure decay, a pressure switch auto­mati­cally restarts the pump to replenish system clamping pressure.

Colin Frost, COO of St. Louis-based Carr Lane Manufacturing Co., commented on the need for evolutionary capability. “High-speed milling and drilling have changed the type and size of solutions desired by customers. To allow for a larger machining surface, they tend to use more edge-clamping devices. The advent of automation and the need for quick-change capability prompted us to develop an edge clamp that is mechanical but that can be easily upgraded to hydraulic applications as automation is incorporated.”

Hainbuch America of Germantown, Wis., supplies customers with workholding devices for rotational parts. According to the company, the Hainbuch product line allows fast changeover for both ID and OD applications without sacrificing repeatability and precision. “Rigidity and repeatability have always been the most critical aspects of workholding,” said Jim McCraw, applications engineer. “With the advancements in machine and cutting tool design, as well as the technological upgrades in programming and applications, poor workholding makes itself evident.”

High-feed milling changes traditional cutting forces in both amount and direction, while high-speed drilling can fail due to vibration. Given shorter runs of more complex parts, fast changeover is now crucial to making money in manufacturing. “We design and build our products to ensure that rigidity carries over in applications where weaknesses can stack up. This is critical if the entire system is to succeed,” he said.

Multiaxis Machining Challenges

The advantages of multiaxis machining are revolutionizing part production in virtually every segment of manufacturing and every part size. Five-axis machining centers are rapidly becoming the “standard,” both in terms of new machine sales and retrofits to existing units. Mill-turn units and Swiss-style machining applications are critical to producing parts in industries ranging from aerospace to medical implants.

The challenges in a multiaxis environment include accessibility of the cutting tool to the part, as well as actuation of the workholding device. Nekich from Lang Technovation explained, “Workholding that allows you to access all the sides of the part without jeopardizing holding power is a must. It is also important that achieving this level of access doesn’t ‘break the bank’ by adding extra operations involving excessive workpiece preparation—such as dovetails. Our Makro-Grip form-closure technology was designed to help manufacturers move away from the time and expense of cutting dovetails.”

He also noted that locating the workpiece in the fixture without the use of stops is also very important. An end-stop will cut off access to a side of the part that would otherwise be machined in the first operation. “Because of the C axis, you must also use workholding that allows you to repeat quickly and with precision on the center of rotation. Zero-point systems are especially helpful for this,” said Nekich.

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A Kurt Cluster Tower multi-part fixture. The eight-station tower offers fast loading of parts, and its internalized hydraulic piston/nut saves space. The unit includes Kurt’s AngLock precision clamping and rigid construction for vibration dampening. It is available in English and metric versions.

Problems with dovetail clamping were also noted by Frost. “Several techniques popular for smaller workpieces include the use of vises and dovetail clamping, but both have specific limitations. Dovetail clamping requires that additional work be performed on the workpiece for additional operations. This can negate the advantage of multiaxis machining. Vises, on the other hand, can limit the size and type of the workpiece. Larger workpieces benefit from using edge clamping or even no clamping, using a zero-point system. We have responded to customers with both modular manual systems and fully automated hydraulic solutions.”

When it comes to multiaxis machining, it is essential that the workholding device provide secure holding capability without impinging the access of the tool to the part, according to Rich of Kurt Manufacturing-Industrial Products Division. “Because multiaxis machining is desirable from the standpoint of time savings, the use of quick-change fixturing is a preferred means of augmenting efficiencies.”

The question of actuation as it relates to both the workholding device and the machine is the key consideration. Vektek’s Johnson noted, “it’s more difficult to incorporate hydraulic pressure in many five-axis machining applications.”

Hainbuch’s McCraw agreed: “For rotational parts, we’ve developed several designs with a minimal overall profile in mind that resolve the question of clearances for both ID and OD clamping.” Again, rigidity is especially important as the profile is reduced. Another challenge can be the actuation of workholding devices. “We address this by offering pneumatic, hydraulic, and manual actuation for our workholding in order to prepare for any option the machine is equipped with. These actuation sources are all modular in design,” he said.

Workholding Adapts to Automation

The increased use of automation and robotics has been a key driver in the development of improved workholding methods. When it comes to robotic parts placement, multiple factors must be considered. Frost from Carr Lane noted, “Robots, like CNC machines, are exact. They struggle to analyze and adjust to thousands of minutiae related to the position of the workpiece, the machine, and the workholding. Therefore, workholding for use with robotic loading is complex—especially when it comes to delicate or high precision applications.”

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MCP-series five-axis vises from Carr Lane/Roemheld allow unrestricted tool access for multiple-side machining. They offer mechanical or hydraulic clamping and have base widths of 40, 60, 100, and 125 mm.

In these situations, workholding must allow for small misalignments between the systems and still ensure that accurate locating and clamping of the workpiece occurs. These applications also use power workholding (i.e., workholding that is machine activated) to allow for unattended operation. The workpiece has to be loaded properly before placing the machine in cycle. “We’ve developed a Rest Button to ensure proper loading in applications such as these,” said Frost.

Rich emphasized the need for fine tuning of robotic clamping systems. “Depending on the parts in the automated process, the robot arm has to address the part in such a way that it can be correctly placed in the workholding device for machining. This might mean designing a special vise, clamp, or other way of grasping the workpiece,” he said.

Nekich from Lang Technovation thinks a good workholding system offers great process reliability, and that modularity should allow the manufacturer to extend the automation process organically over time. “When done correctly, proper workholding will enhance the capability of the automated system,” he said. “A modular workholding solution combined with an automation system increases flexibility and capacity.”

An example he cited would be workpiece exchange vs. fixture exchange in the machine tool tending system. With workpiece exchange, expensive hydraulic automatic utilities can be required inside the machine tool, and the end effector will more than likely be dedicated to a specific part. While this can make sense for high-volume parts, it can be counterproductive for smaller to mid-size production runs.

“High-mix facilities and smaller shops should be looking at systems that exchange the fixture, and this is where the workholding is key,” Nekich said. For instance, using a vise creates a clamping scenario that can support a number of different sized parts, so one automation system that uses vises can cover a number of different run sizes and part types. “Our Makro-Grip vises are sold with a gripper and storage interface for automated loading and unloading of the fixture as a standard. The vises can be used manually at first and later incorporated into an automated system, saving the cost of new workholding devices,” he explained.

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The Hainbuch TOPlus IQ chuck offers permanent, ongoing, electronic, real-time clamping force measurement and change analysis under rotation, according to the manufacturer.

With the automation of rotational parts systems, McCraw visualizes the economic advantages of incorporating existing equipment. “We recognize the importance of being able to automate cells and operations within today’s manufacturing environment. At Hainbuch, we’ve been offering and refining clamping heads, integral end-stops, and even chucks designed for changing with automation. This allows consistent changeover in not just part-to-part but job-to-job situations—and making the change quickly and with precise repeatability. Customers are looking for advances in this area to stay competitive in both cost and, in some cases, with a limited workforce. Selecting the right products early on can allow that to happen, and the ability to retrofit our systems to existing machines can result in cost savings.”

Johnson of Vektek sees the need for workholding in automated systems to move beyond the mechanical aspects. “When it comes to automation, there is a very real need for more sensing and feedback on the part of the workholding system,” he said. “The feedback has to be wireless. As we look at the connectivity required by Industry 4.0 and the Industrial Internet of Things (IIoT), we need sensors and systems that operate in real time to record data that ensures that the clamping force is constant.”

“Workholding equipment hasn’t evolved to the point where it should be regarding the IIoT,” said Kurt’s Rich. “The ideal system could measure clamping force, harmonics, and output work offsets, and alert operators about maintenance or fixture location.” For instance, a workholding device could be capable of sensing whether or not the correct part was placed within it.

“As important as the ability to gather data is, we have to know how to use it most effectively,” said Frost. Within our own operations, we and our partner, Roemheld, are developing innovative solutions that can monitor clamping force and collect other pertinent operational information.”

Nekich emphasized the need for simplicity. “Providing easily accessible and accurate fixture models is very important. As critical as performance data and monitoring are, we need to appreciate the virtue of simplicity and not drown ourselves in irrelevant data streams simply because we can.”

New Developments Mean New Challenges

As the future unfolds, many of the dramatic advances in manufacturing—including new materials, coatings, techniques and technologies—bring their own challenges as well as advantages. The recognition of the importance of workholding has resulted in research and development that is bringing about changes, both large and small, that will impact manufacturing at every level. “There is a benefit in productivity jumping from vertical to horizontal machining in four-axis applications. The difficulty for some shops can be the capital costs and supporting that investment in CAM software and training,” observed Rich. “Consider using a VMC with an indexer and Kurt Cluster Tower or five-axis vise. In a short time, you will see productivity gains from your existing equipment.”

Johnson sees the need for greater versatility in fixture design, as well as a surging emphasis on energy savings. “We’ve developed an improved hydraulic pump that consumes less energy and produces more volume. The reception of our Advanced Workholding Pump has been positive. The more parts a fixture can accommodate, the less energy is required and the more efficient it becomes.”

Nekich from Lang Technovation addressed the advantages of intuitive probing. “You can probe a feature on the fixture that, in combination with machine tool macros, can automatically call the correct program.” Solutions that allow for quickly exchanging profiles for net-shape clamping are important for post-op milling in additive manufacturing, he added.

“At Carr Lane, we are really excited about the possibilities of different materials and material coatings,” said Frost. “On-Size is our new line of components made from Invar 36, a high-nickel alloy that virtually does not change shape even when heated.” He noted that this allows components to be more easily used in applications such as carbon fiber molding and plastic molding.

Carr Lane has also started using coatings to provide wear resistance on critical dimension items like locating pins. “By giving our locating pins these super-hard coatings, the maintenance interval for the replacement of these pins critical to the dimensional accuracy is typically doubled,” he said. Anything that results in longer service represents a significant cost savings.

He also noted that the company is working on electric power clamps from its partner company, Roemheld. “Electric has several advantages over hydraulic, including the fact that customers typically do not need a special power source, such as a pump,” said Frost. The clamps will not leak and contaminate workpieces, machines, or products, and because of exact control, it is possible to monitor the absolute position of the clamp through the entire stroke.

McCraw from Hainbuch stressed the importance of working with customers to provide specialized workholding devices for individual application needs. There are times when standard catalog applications will not fit the application no matter how many catalogs or websites are searched. That is the time to pursue specials.

“Our company has designed thousands of special applications, and we consistently draw on that experience to satisfy a customer’s exact parameters,” he said. “As some of these applications are requested frequently, we’ve introduced new standard product lines based on a need recognized by multiple special requests. This allows affordability for smaller budgets. One especially exciting development is what we call the ‘IQ’ chuck. The challenge was to ‘take smart choices out of the hands of smart people.’” The chuck measures clamping force and temperature and contains measuring sensors to detect differences between the sub-spindle and major spindles.

“Many of the new generation of parts are thin-walled or possess otherwise ‘delicate’ features. We’ve developed specialized clamping force reduction mechanisms that provide precise and accurate clamping, absorb shocks and vibrations, and can do it all without damaging the part,” McGraw concluded.

New Materials, Production Methods Redefine Workholding

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Precision Metal Product’s CAD drawing of a multi-part fixture and the finished unit.

While much of the interest in 3D printing has been centered on prototype and part production, Precision Metal Products Inc. (PMP), Milford, Conn., a job shop serving a variety of industries, is pioneering its use in the development of specialized fixtures.

According to PMP Vice President Sean O’Brien, “Many of the parts that we build require specialized workholding methods and tooling. In 2017, we discussed our applications with the people at Methods Machine Tools, and they suggested the Markforged X7. After some very convincing demonstrations, we purchased the machine. Our first success involved a stainless steel medical device less than 0.100" (2.54 mm) in diameter. Using 3D printing, we created a 5 × 5 × 3" (127 × 127 × 76.2-mm) printed box with a 0.5" (12.7 mm) hole in the center. This enabled us to access the workpiece on all sides and, using magnets affixed to the corners, to catch the parts as they were completed.”

Moving forward, PMP designers developed soft-jaw chucks that successfully fixtured parts made from 17-4 stainless. The material used for the chucks was Markforged’s Onyx, composed of thermoplastic with chopped carbon fiber. O’Brien commented, “Methods Machine was exceptionally helpful in working with us and we are now considering the purchase of a Markforged Metal X printer, which will be used for both parts and fixtures. Our customer base is moving toward production runs of lower quantities and a higher mix. As a result, 3D printing will not only speed the process but result in greater cost efficiencies.”

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Precision Metal Product’s CAD drawing of a multi-part fixture and the finished unit.

Engineered Propulsion Systems (EPS), New Richmond, Wis. is in the final stages of certifying a diesel-powered engine for private aircraft. According to Ryan Kuebker, EPS special projects coordinator, “Because our design is original and many of the parts were complex, it was necessary to create a large number of fixtures for both milling and turning operations. In the course of development, a number of the parts required change and rework so the fixtures that we used had to be designed with flexibility in mind.”

The development and prototype phase required an extensive number of fixtures, all of which were cataloged and saved. Ryan noted, “The engine is now being certified, which means that in a short time we will be moving into production. We are currently working with our existing workholding stock to modify existing units and to use what we learned in the creation of newer fixtures in the production of small- to medium-lot components capable of meeting our initial marketing needs. We are also evaluating ways to more effectively and efficiently meet the future challenges of increased production.”

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