If Thread Rolling Doesn’t Excite Manufacturers, What Will?

For many CNC applications thread rolling is the best choice for creating higher quality external threads in one pass without chips. The technology has spanned years on multi spindle machines, engine lathes and dedicated thread rolling machines. CNC machines can particularly benefit from rolling technology in dramatically reduced cycle times with equally dramatic thread quality improvement. Single point threading on a CNC machine has an advantage when parts production volume is small. This advantage disappears when volume increases. Frequently even in low volume production, rolled threads are specified by the end user due to the quality issue of the threaded part.

Aviation and military parts are frequently specified as a rolled thread regardless of lot size. The technical advantages of a rolled thread are dramatic. Since rolling is a cold forging process it yields no chips and typically requires 90% less cycle time to produce a thread. The rolling process creates much higher yield strength in the material as well as far improved surface finish. These characteristics have made the process important in today’s automotive plants. Rolled threads exhibit higher strength, greater wear resistance, greater corrosion resistance and greater galling resistance. Qualities desired by automakers to minimize warranty failure. Valve stems are an excellent example of a threaded part that benefits from corrosion resistance. A rolled thread maintains better accuracy from part to part than a cut thread simply by removing the wear aspect of a cutting tool that allows cut dimensions to drift. Consider an automotive application that uses a single point machine cut thread in a blazing 4.8 seconds of cycle time. We can all agree this machine time is impressive but let’s roll the thread with a radial head in 0.2 seconds.

Can 4.6 seconds per piece in cycle improvement impact cost over 5 million parts?

Can better part quality with lower recall potential excite a manufacturer?

Most external threads regardless of description can be rolled. Most materials, even the difficult to machine, can be rolled with ease and efficiency. Unlike cutting, tool changes decrease dramatically with rolling. This adds yet another dimension to cost savings by reducing time for insert indexing. While you currently are not building space stations, supersonic aircraft or nuclear submarines if your rolling threads your sharing their technology.

It Started with the Wheel and Later Led to the Telephone and Electricity

It started with the wheel and later led to the telephone and electricity. Invention and discovery continue to change the face of our world as we know it. Thread rolling developed in the early twentieth century and has mostly remained constant since its invention. While difficult materials can be rolled the life of the rolls themselves are limited when compared to mild steels. Nitriding was one means of improving roll life and reducing part cost but also had marginal benefit. Recently a new method has emerged that has shown the ability to improve tool life dramatically. It requires secondary processing of the basic thread roll that adds time to delivery as well as an increase in roll cost by 50% to 70% above the cost of the manufactured roll but the results can be staggering.

We presently have a customer running 17-4PH Stainless Steel that is achieving a 1,000% increase in basic thread roll life. The cost benefit is dramatic, the downside for us is a 10-fold reduction in roll sales to this customer. We pride ourselves on our attention to technology and the goal of being the most valued supplier our customers do business with.

The new technology to improve wear resistance on thread rolls can probably be used on any part that sees friction wear as a failure mode. We can offset our thread roll sales loss by employing the technology into other tools not presently strong in our sales forecasts. Parts that fail due to friction, gears, wear plates, hobs, mold and die plates as well as a multitude of other components could well be strong candidates for improvement. Is friction a contributor to your tooling cost?  Contact us, we would like to offer a solution and allow you to speak with our end users that are on the cusp of dramatic change in threading cost.

Which Materials Thread Roll Well?

While we often extol the various attributes of cold formed (rolled) threads, the materials that can be rolled are seldom outlined in broad terms.

Steels are virtually all roll-able. Included in the steel family are Structural, Case Hardening, Nitriding, Free Cutting, Heat Treatable, Tempered, Tool Steel, High Speed, Stainless, Cast Steel, Malleable Iron and Cast Iron with an elongation factor greater than 8%.

Rollability is also practical in Copper, Copper Alloys, Zinc Alloys, Aluminum Alloys and Titanium Alloys. In addition, Nickel, Monel, Hastelloy, Inconel, Waspaloy and Titanium are also good candidates for rolling.  

The principle deciding factor in the ability of any material to cold form (roll) is an elongation factor greater than 8 percent. As can be seen by the listing many of these same materials are difficult to machine and tough on tooling. Roll life varies throughout the variety of material applications but cost per thread is always an advantage rolling has over cutting.

The tensile strength of a rolled thread will increase from about 40% to as much as 300% in some materials. The tensile strength improvement makes rolling highly desirable in military, aviation and automotive applications. Marine applications using Nitronix 50 and 60 are especially suited to rolling. This is a material with notorious work hardening ability.

We can predict with relative accuracy if your material is a good candidate for thread rolling. Does it conform to the materials we’ve outlined and is the hardness less than 40 on the Rockwell C scale? If you’re processing one or more of these materials daily and not rolling but cutting your threads you’re adding cost and lowering the quality of your finished product.

Which Threading Method is Most Cost Effective?

In the real time world of contract manufacturing, picture your company landing a contract to produce 80,000 threaded stainless-steel connectors. The specified thread detail calls out a class 3 aviation thread. You could choose to single point, chase, or roll the threads. Would either option impact your bottom line? ABSOLUTLY !

Single pointing will likely produce 100 threads per cutting edge of the insert used. From the first part to the final part per edge, insert wear will allow drift in the minor, pitch and major diameter. It may introduce the need to deburr as well as require 10 or more passes to complete each thread.  Cycle times for threading will likely exceed 10 seconds per thread. Indexing the tooling every 100 pieces adds cumulative down time. While the insert cost is relatively low, cycle time and down time add significant cost to the final product.

Chasing reduces the cycle time but also has the potential for burr creation as well as the need to regrind chasers.

Rolling will yield as much as 100 times the volume of threads without a tooling change. Rolled threads will never require deburring. The minor diameter and pitch diameter of a rolled thread are a function of the roll design and will never waiver. The major diameter is a function of the blank size but since the major diameter of any class of thread is typically an allowance of .010 normal turning tools will see extended life.

Cycle time will be on an order of 1 inch of completed thread per second of cycle. This is typically 10 times faster than cutting the thread. The tensile strength of the rolled thread will typically double from the stated tensile of the raw material. Servicing the tool with roll replacement can be done in minutes on the machine. Since labor cost is the largest factor in determining the overall cost of each part, cycle time to produce the part and service time to renew and replace tooling are the biggest factors in calculating profitability. Understanding these circumstances makes thread rolling the obvious choice for maximizing profitability. Rolling yields the highest quality product in the shortest possible cycle time. Cycle time and profitability are codependent.

Leaded Fuels, Spark Plugs and Thread Rolling

Rolling threads on various materials became a necessity in high volume manufacturing in the US following its discovery in Germany after the second world war.

The most dramatic effect was in the production of spark plugs. In the US alone, more than 10 million spark plugs were being produced daily by several manufacturers. Leaded fuels were necessary to lubricate engine valves but subsequently fowled spark plugs limiting their useful life to about 10,000 miles. When lead was outlawed in motor fuels in the 1970’s hardened valve seats became the standard and without lead fowling spark plugs, spark plug life increased more than 10-fold. This reduced product demand 10-fold. Thread rolling migrated from multi spindle screw machines to modern CNC machines for the very same reasons.

Cold forming of threads became equally important in lower volume production from a time and cost consideration. Threads can be formed typically at 1 inch of thread per second of cycle time. A cold formed thread has greater yield strength and surface quality than a cut thread. Many materials that are difficult to cut are easy to roll. Time cycles and part volume create significant value in throughput cost. This value impacts on the final cost of the finished product.

In a job shop atmosphere, it can be the strategic difference between winning the quote or losing the work to a lower bidder. Rolled threads can reduce the effects of corrosion improving life cycles in many applications. The relative ease of applying this technology to today’s metal working machines makes it even more important as a value-added component of the modern machine shop.

We can evaluate your part, your process and your machine when applying the application of thread rolling to your operation. Thread rolling was once conceived as a “black art” but is truly a straight forward application driven technology easily applied in any modern machine shop. Many military and aviation components demand rolled threads for strength and surface quality. Let us help with your application.  The cost implications can be the leverage your company needs to improve profitability.

From Bump Rolling to Modern Rolling Techniques – Thread Rolling

The earliest form of producing a rolled thread came from a technique called bump rolling. This utilized a single roll that pressed the form into the material with side pressure. While it was the original approach to rolling threads it certainly earned the craft the nick name of “black art”.  It took painstaking effort to achieve set up success and was helped by the wide use of soft leaded steels. Set ups were best done “When the moon was in the seventh house and Jupiter aligned with Mars”. Despite its perils it could be productive and most certainly became the catalyst for developing more robust attachments and machines.

Further development brought about robust mechanical devices that could be pneumatic or purely cam driven. Few of the early devices could be used easily on modern CNC equipment but remain in use today on multi spindle automatic machines. Pneumatic devices require dry filtered air for best performance. Pneumatic delivery systems during high humidity days are notorious for compressing water out of the air and fouling the operation of the tool resulting in sketchy tool performance.  The pure mechanical devices are unencumbered by humidity.

Today’s materials with the removal of lead from most manufacturing have created a new set of demands on the tools and machines that frequently demand rolled threads for quality and economy. Virtually all machine applications have one or more tool selections available to achieve an economical end result. Review your application with us. We can recommend one or more solutions to your specific needs.

Thread Rolling Styles

Cold Forming (rolling) threads in metal has been used in the United States for about 65 years. Originally developed in Germany the technology migrated to the US in the 1950’s. Initially used on multi spindle screw machines the tooling styles have been altered to accommodate use on virtually all of today’s existing machine styles. Multi Spindle, Manual, Rotary Transfer and CNC Turning and Milling Centers.

Three styles of tooling have been developed for very specific applications. Axial rolling uses either a two-roll concept or 3 and 5 roll concepts. This style can create unlimited thread lengths by producing one thread pitch at a time. Process time is about 1 inch of thread length per second of cycle time. The process this style supports leaves 2 or more partially finished threads at the end of the thread journal. An undercut in the part design that can mask the unfinished thread will allow gauging to a shoulder with a full thread form.

Parts designed with less than a 2-pitch clearance to a shoulder can be rolled with a Tangential Style attachment. The Tangential tool is a 2-roll side entry tool. It can be used on multi spindle and CNC applications where the machine has mechanical control of tool movement. The Tangential process can roll within 1/2 pitch length to a shoulder with a full thread. Thread length is limited to the width of the roll and the complete thread form is rolled at once. Cycle time for this concept is typically 2-3 seconds for a complete thread.

A third and unusual method is available in the form of a Radial attachment. A Radial tool is a three-roll approach that has the same length limitations as Tangential tooling. The rolls are ground eccentrically and when at rest clear the part to be rolled. There is no regard for feed rates. When in position the head is tripped, and the rolls make 1 revolution to achieve a finished thread. Typical cycle time is 2 tenths of a second. The tool can mount on any machine that can rotate the tool or the work piece. It has become the tool of choice in high volume machining. It runs on any machine and frequently used in automotive production on CNC machines due to its short cycle time.

In any application where time and cost are relevant we have a thread rolling approach that will efficiently reduce both. Reviewing a drawing of your part will determine the style most suited to your specific needs.

Thread Rolling Works with Both High and Low Volume Jobs

Rolling threads on various materials became a necessity in high volume manufacturing in the US following its discovery in Germany after the second world war.

The most dramatic effect was in the production of spark plugs. In the US alone more than 10 million spark plugs were being produced daily by several manufacturers. Leaded fuels were necessary to lubricate engine valves but subsequently fowled spark plugs limiting their useful life to about 10,000 miles. When lead was outlawed in motor fuels in the 1970’s hardened valve seats became the standard and without lead deteriorating spark plug life increased more than 10-fold. This reduced product demand equally.

Thread rolling migrated from multi spindle screw machines to modern CNC machines for the very same reasons. Cold forming of threads became equally important in lower volume production from a time and cost consideration. Threads can be formed typically at 1 inch of thread per second of cycle time. A cold formed thread has greater yield strength and surface quality than a cut thread. Many materials that are difficult to cut are easy to roll. Time cycles and part volume create significant value in throughput cost. This value impacts on the final cost of the finished product. In a job shop atmosphere, it can be the strategic difference between winning the quote or losing the work to a lower bidder. Rolled threads can reduce the effects of corrosion improving life cycles in many applications. The relative ease of applying this technology to today’s metal working machines makes it even more important as a value-added component of the modern machine shop.

We can evaluate your part, your process and your machine when applying the application of thread rolling to your operation. Thread rolling was once conceived as a “black art” but is truly a straight forward application driven technology easily applied in any modern machine shop. Many military and aviation components demand rolled threads for strength and surface quality. Let us help with your application.  The cost implications can be the leverage your company needs to improve profitability.

Tap Strength

Roll Form Tapping can increase the tensile strength of an internal thread up to twice the tensile strength of a cut thread. Carbide taps will decrease the cycle time required to thread by at least a factor of two.

Fette offers a carbide nib form tap assembled on a steel shank to take advantage of the speed potential while preserving overall tap strength to tangential forces. The improved cycle times are sweetened by tap life that can be more than 10 times the life of a steel tap.

Machining Aluminum Can Be Most Cost Effective With PCD Inserts

Machining Aluminum can be most cost effective with PCD inserts, however, insert cost is very high. Most Aluminum is milled and turned with carbide inserts honed for sharpness and polished to aid in chip flow. The best of both worlds is a development by LMT Fette in Germany using a coating process defined as Plasma CVD. The coating is applied to a honed insert and increases insert life while maintaining the edge integrity. As an added benefit Milling speeds can be as high as 6000sfm and turning speeds to 10,000 sfm. Speeds significantly improve throughput and insert life can be 10 times longer than uncoated inserts. Insert cost is comparable to uncoated polished inserts.