Making a Case for PVD Recoating Systems

The following is a case study conducted and prepared by Muncie Power Products, Inc., and Ionbond LLC explaining how recoating can benefit your production process.

Muncie Power Products, Inc., of Tulsa, Oklahoma, has been in the auxiliary power business since 1935 and started manufacturing Power Take Off (PTO) units in 1986. In addition to PTOs, Muncie also provides wet line systems, dump pumps, gear pumps, snow and ice control systems, and hydraulic control valves. William D. Whiteis, tooling services supervisor, Jim George, production supervisor, and Steve Terry, senior manufacturing engineer, comprise the team responsible for recent process innovations. Muncie Power Products is dedicated to the design, manufacture, marketing, and distribution of products that meet or exceed the industry’s quality standards. Anything less is unacceptable. Figure 1

Ionbond LLC (formally Multi-Arc Inc.) has been a vendor for Muncie Power Products since 1989. The relationship, according to Whiteis, started with PVD coatings over 15 years ago. “A formal testing program was established with Ionbond in November, 1989, involving hob cutters,” he says. “The results of these tests were significant. For example, recoated hob cutters produced 25-30 percent more parts with only .015-.020 to grind off at the time of resharping versus .035-0.75 per regrind on an uncoated cutter. Therefore, not only did the recoated cutter produce more parts, but it also realized an increase in the number of times it could be resharpened during its life. Quality improvements such as surface finish and involute gear profile were also realized, along with increased productivity.”

The Recoating System
When a coated hob or form cutter is reconditioned, the coating on the face of the form is lost. After resharpening, buildup and cratering on the resharpened and exposed surfaces become the primary failure modes. This standard wear pattern can be eliminated and the original tool performance restored by replacing the coating on the face of the form. Chart 1 Recoating lowers tool costs and, more importantly, it improves productivity by allowing users to optimize the number of parts between reconditioning, the number of reconditions possible, and the machine rates. Part quality has also shown substantial improvement.

Recoating offers distinct benefits to the users of shaper cutters, broaches, end mills, and hobs. For best results it is necessary to completely remove the coating from all surfaces involved in the cutting operations so that the recoating system results in a new single- or multi-layer coating on the tool. Figure 2

Surface finish is a critical component: The better the surface finish, the better the coating adhesion will be, and the better the success of the recoating system. For example, Muncie produces between a 3-5 micron finish on all regrinds for recoating.
Chart 2

Recoating Success Story
Muncie’s hobs are coated in Ionbond’s QS9000-certified West Chicago Coating Center. Upon arrival, hobs are stripped of the old coating, cleaned, and recoated. Stripping is offered on all HSS hobs and shapers with every recoat. The turnaround is one week from door-to-door, which enables tool float to be minimized.
Figure 3

Initially, Muncie did not want to move from a M4 substrate to a bridge material (Rex 76 or P121). After speaking with a few hob manufactures, the company decided to use its remaining inventory of M4 substrate hobs and make a switch to a M45/30 substrate. The consensus is that the M4 substrate could be used on the dry hobbing machine, even though this may not be a general practice in the industry. Ionbond’s 7-13T – AlTiN coating and 7-22 HP-TiN were applied to both M4 and M45/30 hobs with great success.

There are currently a total of 85 programs running on the dry hobbing machine, which produces 52 different parts. The accompanying charts represent four of those programs and their critical data.

The AlTiN 7-13T coating that is run on jobs 1 and 3 is a single layer coating (M45/30 substrate). This coating and substrate allows for high speeds and feeds when compared to M4 substrate and the HP-TiN. The higher aluminum content in this coating allows for a higher oxidation temperature 800c/1450f for the AlTiN compared to HP-TiN at 500c/950f. This increased oxidation level insures that the heat generated in this faster cut will be dispersed evenly in the cutting action. Figure 4

The hardness of both films is different, which plays a key role when higher speeds and feeds are present as well as the added strength of the M45 substrate. Coating hardness is measured in Vickers. The AlTiN coating is 4500 (+/- 500) Vickers, the HP-TiN is measured at 2900 (+/- 200) Vickers.

Both jobs 2 and 4 run HP-TiN 7-22 (M4 substrate in a range of 255 to 300 RPM). Whiteis was told that running an M4 substrate dry was not an accepted process. “Muncie likes a challenge,” he says, and in this case he clearly had a point. The idea that Muncie had to move to a M45/30 substrate before depleting the M4 inventory was the catalyst in making the M4 work.

Keys for Success
Overall hob care at the customer site: Solid manufacturing practices with regards to set-up; fixturing and regrinding will pay big benefits. Surface finish is very important at the regrinding stage. The better the surface finish, the better the coating adhesion. The practice of stripping the old coating off the hob with each recoating is a major factor in the success of this system. When a coated hob is “new” the coating thickness ranges from 3-5 microns by some manufactures and 4-6 microns by others. By stripping off the old coating and reapplying the original thickness the hob could be equated to a “new” hob. In cases where hobs are not stripped with each recoating, coating buildup on the flank of the hob tooth could produce unwanted results. Figure 5

The objective of the Ionbond recoating system is to reduce tooling costs, improve shop productivity, improve machine utilization, and minimize purchasing paperwork. The benefits include a reduction in tool grinding time, a reduction in tool inventory, improved productivity, and a reduction in direct labor costs per part.

Ionbond LLC developed the first commercial arc PVD coating using the Ionbond process. Ionbond continues to engineer coatings to meet the specific needs of industrial customers. With key coating properties deposited via cathodic arc, enhanced arc, and unbalanced magnetron sputtering, Ionbond coatings offer high hardness, low coefficient of friction, chemical stability, and high oxidation thresholds, as well as corrosion resistance coatings. Today Ionbond offers both single and multi-layer PVD coatings. Product offering includes, TiN, AlTiN, TiAlN, TiCN, CrN, ZrN, MoST, and TetraBond coatings. These coatings have a wide verity of uses in metal cutting, fabrication, plastic molding, medical devices, decorative, and wear component markets. Figure 6

Ionbond also offers a large variety of Chemical Vapor Disposition (CVD) coatings. This family of multi-layered coatings engineered for carbide cutting tools and hot forming dies. Proprietary process techniques, such as the Moderate Temperature (MT-CVD) process, are used to optimize the coatings for milling, turning, grooving, threading, cut-off, and extrusion applications.

Figure 7 In the CVD process, the coating is deposited from a reactive gas atmosphere usually containing metal halide vapors. The high temperature nature of CVD effectively restricts its use to parts which are not affected by the high temperatures used, e.g. sintered carbide, ceramic, and loose tolerance steel components. When coating carbide, the MT-CVD process with its lower deposition temperature eliminates or minimizes the loss of transverse rupture strength associated with higher temperature CVD processes.