Workpiece materials, spindle speeds, shapes, and sizes all play a role
When sizing up an application for a milling toolholder, it is necessary to consider the materials being machined, how aggressively metal is going to be removed, and any machining conditions that are likely to present a challenge to tooling security. By now, the pros and cons of hydraulic, mechanical, and heat-assisted shrink-fit systems are well known and results well documented. Tools must perform under widely different machining conditions, but the most common requirement is that tools are held with strong gripping force to provide the best runout, the highest precision, and least opportunity for quality-robbing vibration. Toolholding solutions are available to guard against catastrophic failure due to cutter pullout in machining the toughest materials or in high- speed or high-production applications, often using standard cutters wherever possible.
Toolholder Change for Truck Steering Component Is Big Winner
Changes from one toolholding system to another can have significant impact on the cycle times and productivity even in the highest volume applications. In a high-volume machining environment like the automotive and trucking industries, changing toolholders isn’t something that is done without sufficient confidence that the change will positively affect cycle time, production, and quality.
Such was the case at an automotive manufacturer based in the Midwest. Two specific end-milling applications for a nodular iron sand-cast component for a truck steering column were evaluated to find a solution for too-frequent tool changes due to excessive wear. The castings which were somewhat difficult to hold were being machined on Feeler vertical machining centers. Using hydraulic toolholders, the inserts had to be indexed after 400 cycles for a total of 800 parts. Annual requirement is 1.4-million assemblies, each consisting of one of these machined parts.
The customer’s manufacturing engineer was looking for a solution to extend uptime on the application by testing other grades of inserts. “I was brought in to look at a milling application where tool life was very poor,” said Brett Kischnick, application engineer, Horn USA Inc. (Franklin, TN). “I felt that the Fahrion Centro P toolholding system could offer considerable improvement over the hydraulic toolholder that was being used for the 1″ [25.4-mm] indexable end mill with ¾” [19.05-mm] shank,” said Kischnick. The switch to the Fahrion Centro P toolholder using the same indexable inserts improved tool life to 600 cycles for a total of 1200 parts. “At first I did not believe Mr. Kischnick when he said the Fahrion toolholders would make a substantial increase in tool life but am certainly glad I gave it a try,” said the manufacturing engineer.
The Fahrion toolholder system consists of a new toolholder, a new collet, and a new nut. An adjustable torque wrench is used to properly torque the collet nut down, tightening it exactly the same way each time. “The holder and the nut have a thicker cross section that allows the extra torque without deforming the collet. In addition, the extra reinforcement of the chuck body to the diameter of the clamping nut produces superior stability with maximum compactness,” said Kischnick.
The Fahrion Centro P features clamping torque of the clamping nut of 140 N•m with tool shank hardened, ground Rz 2.5, and free of grease. The holder offers 100% higher clamping force than standard collet chucks, the toolholder is ground to 1-µm taper in the front to taper in the back. The collet is a maximum of 2 µm therefore the combined system runout accuracy is less than 3 µm.
A high degree of concentricity and repeatability of the Centro P toolholding system is ensured by the 30° trapezoidal thread with ground, extra-long, double-length guide. “The ground thread and guide ensure perfect centering of the clamping nut on the chuck, achieving even distribution of load and minimal imbalance,” said Kischnick. “Clamping forces are distributed evenly over the gripped area of the cutting tool shank, making the Centro P suitable for dry processes and hard milling, and ideal for drilling, counter-sinking, reaming, milling, tapping, and high-performance, high-speed cutting applications.”
Perfection Is Aero, Defense Company’s Requirement
APN Inc. (Quebec, Canada) has invested in the latest advanced digital machining technology to enable it to meet requirements for manufacturing high-precision, difficult-to-machine components for the aerospace, automotive, defense, and optical industries, The family-owned company has a commitment to perfection which it “considers to be non-negotiable” and has ISO-9001 and AS 9100-C certifications and a DQCR certification from Pratt & Whitney.
In its digital machining arsenal, APN numbers five Huron five-axis machining centers with a maximum speed of 24,000 rpm and two three-axis machining centers with 18,000-rpm spindles. Turning is done with Nakamura multiaxis CNC lathes, and grinding by CNC Combi-Tec CNC grinders. For its milling performance, APN management recognized the need for better performance from its toolholding which was inconsistent, particularly with regard to toolholder balance.
Milling performance has been dramatically improved by switching to the powRgrip toolholding system from Rego-Fix Tool Corp. (Indianapolis, IN). The switch from heat shrink fit toolholding and standard ER collet holders was made to provide repeatability and balance consistency required for high-speed machining. APN is typically machining materials ranging from stainless steels, tool steels, Inconel, and titanium to copper, and plastic. Required machining tolerances for most of the shop’s parts are typically 0.0005″ (0.013 mm), with some as tight as 0.0002″ (0.005 mm).
Once installed the powRgrip system has delivered high concentricity (TIR) with deviations of less than 3 μm for tool lengths up to 3×D and length pre-adjustment with a repeat accuracy within 10 μm. Holders are now 100% balanced to G 2.5 at 22,000 rpm for steep taper-style holders and G 2.5 at 25,000 rpm for HSK-style powRgrip holders. APN’s high-speed, high-performance milling machines now run either Rego-Fix powRgrip holders or ER collets. The company has one powRgrip tool-changing unit and more than 150 powRgrip holders that make up about 60% of the shop’s entire tooling. Some shrink-fit holders are still in use to get the promised tooling return on investment.
Workpieces are typically small with three-quarters of them measuring less than 3″ (76 mm) square, and half of those smaller than 1″ (25.4-mm) square. Tool sizes are typically under 1/4″ (6.4 mm) in diameter with some drills measuring as small as 0.015″ (0.4-mm) diameter. Job lot sizes vary from five to a thousand with an average of about 20. Half of these are regularly scheduled jobs/orders, while the other half are first-run jobs. At any given time, APN can be processing as many as 500 completely different jobs on its shop floor at one time.
Locking Tools Securely in Place by Holder Design
Companies like APN are benefiting from the ability of the powRgrip toolholding system to dampen vibration. This capability is critical as machine tool spindle speeds and feed rates continue to increase. It’s axiomatic: the better a toolholder controls or even eliminates vibration, the tighter its TIR. The tighter a holder’s TIR, the more it helps increase tool life as well as improve part accuracies and surface finishes.
Rego-Fix’s powRgrip mechanical tool holding system and its follow on secuRgrip system ensure concentricity (TIR) and achieve high vibration dampening due to the functional contact surfaces between its toolholders and collets, and the collets and tool shanks. The powRgrip system absorbs vibrations by creating “material breaks.” The process starts with a cutting tool, typically made from anything from high-speed steel to carbide to cobalt, with each material having its own specific vibration frequency or harmonics. The cutting tool is held in a collet that is also made from a particular type of steel then inserted into a powRgrip toolholder made from a different type of steel.
Unlike systems that require modified tool shanks, the secuRgrip system uses a special threaded insert or key that eliminates the need to alter cutters. The simple and effective design is part of the company’s well-established powRgrip mechanical toolholding system and one that allows the use of any off-the-shelf tool as long as it has a common standard Weldon flat on its shank.
Rego-Fix’s powRgrip and secuRgrip are also faster than other systems when it comes to exchanging tools. Removing a tool from a holder and installing another takes about 10 seconds. Heat-shrink holders, on the other hand, must be heated, the cutter installed, then put in a chiller for 2 or 3 minutes before the tool can be used.
Mechanical-base tooling innovations such as Rego-Fix’s powRgrip and secuRgrip provide shops with solutions for their machining challenges, especially those involving tough materials such as titanium and Inconel. With these toolholding systems, shops can increase cutting tool life, experience significant cost advantages and run their cutting tools at the highest speeds and feeds to increase productivity while also improving part surface finish quality.
Existing powRgrip holders are easily transformed into a secuRgrip holder by simply threading the outside of any powRgrip PG 25 or PG 32 holder for accepting the cap nut. Rego-Fix can either supply the necessary thread specifications or factory-threaded holders. The secuRgrip holders accommodate cutter diameters from 0.472″ up to 1.000″ (12–25.4 mm). And with holder body tensile strengths higher than those of the cutting tools being held, the secuRgrip holders will withstand cutting forces that could break the cutters before ever damaging the toolholder itself.
Standard Tooling Works Well with Milling Chuck Design
BIG Kaiser Precision Tooling Inc. (Hoffman Estates, IL) has made two recent major product introductions: one aimed at machining the toughest heat-resistant superalloys with standard tools and the other aimed at handling the smallest tools down to 3-mm diameter with a hydraulic toolholding system.
“Up until recently, hydraulic chucks for very small tools, specifically for tools 3 mm/1/8″, diameter weren’t available,” said Alan Miller, engineering manager. “The reason came down to how hydraulic chucks work. There is an interference fit between the bore of the hydraulic chuck and the cutting tool itself. We have been able to redesign the hydraulic system with a very tight tolerancing of the bore, allowing us to clamp down to 3-mm diameter. The new small hydraulic chuck is geared toward extremely high-speed finishing work for the medical and mold-and-die industries,” said Miller. “We can make them as small as HSK 32 for very high speed micro-style machining at spindle speeds up to 45,000 rpm and get the surface footage necessary for very fine surface finishing.”
To address the issue of tool pull out that can be encountered when machining heat-resistant superalloys (HRSA) like titanium and Inconel, BIG Kaiser has introduced its Mega Perfect Grip milling chuck. “One of the things that we’ve done is take the existing standard holder for end mills and used the Weldon flat to keep the tool from pulling out of the holder. We came up with a modification of our existing milling chuck product line called the Mega Perfect Grip milling chuck. We insert a key basically inside of the Weldon flat that drops into a special location on the end-mill holders so that when you drop it in and rotate it so that the flat locks into an internal groove. Once you close the milling chuck, it isn’t possible for the product to pull out,” said Miller.
The Mega Perfect Grip milling chucks combine the cutting performance of heavy-duty milling chucks with security against pullout of solid side lock toolholders. High-pressure and high-volume jet-through coolant is a standard feature.
“We talk about Inconels and stainless steels, but aluminum generates a lot of axial force at high speed and tries to pull the tool out of the holder. All of the tools for these applications, for high-speed aluminum and heavy roughing all require tool security. When people see the Mega Perfect Grip milling chucks, the simplicity of the system is obvious to them and it’s easy to implement,” said Miller. “Before these developments in secure toolholding, the only way to hold the tool was through side lock setscrew. But for today’s CAT 50 machines and the HSK A100 and A125 machines where you need a lot of horsepower and high torque for bigger heavy-duty aerospace applications, the Mega Perfect Grip milling chucks offer the toolholding security and confidence that manufacturers require,” said Miller.
Intelligent Spindle Nose for an Ultra-Precise Tool Change
After several years of collaboration with two industrial associates from the Allgäu region of Germany, GROB engineers have found a solution for dealing with chips during a tool change: the GROB motor spindle with an intelligent spindle nose. With this GROB innovation, after an automatic tool change, the tool interface checks with ultra-precision for the presence of chips. Because this chip-in-spindle check is also cycle-time neutral and no alterations are required in the machine‘s working area, for many machining centers this development is an excellent way for improving reliability during an automatic tool change.
What happens is that sensors in the spindle nose detect any asymmetric deformation caused by chips at the tool fixing point and assess it. The information is transmitted via high-frequency radio signals to the machine control, which then flags up the faulty tool change. The energy for the sensors in the spindle nose is supplied through one stationary and one rotating induction coil. The combined electronics and gaging technology affect only the design of the spindle face. The reading is taken when the spindle is at a standstill immediately after tool clamping. When the reading is taking place, the feed axes move to the new machining position. The accuracy of the system is impressive. Chips are reliably detected, which at a distance of 150 mm from the face contact on the HSK A63 toolholder can cause a change in concentricity at the tool of only 0.01 mm. It is immaterial whether the chips are in the tool taper or in the face contact area.
For more information from GROB Systems Inc., go to www.grobgroup.com, or phone 419-358-9015.
This article was first published in the August 2015 edition of Manufacturing Engineering magazine.