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.
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
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
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.
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.
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.
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.
The mechanical characteristics of many materials can make them difficult to thread using traditional cutting technologies. Chip control and work hardening can be an obstacle to efficient machining. Cold thread forming (thread rolling) often can be used to efficiently improve machinability.
Thread rolling is especially efficient in many Nickel, Monel, Inconel, Titanium, Silicon Bronze, Copper, Brass, Copper alloys and Aluminum alloys. Typically, these materials can be threaded faster and at lower cost through rolling. The chip-less cold formed method adds strength and improves thread performance and is amendable to today’s modern production equipment. Identifying a material grade can quickly determine if rolling is a benefit both in thread cost and thread quality.
Most common thread forms UNC, UNF, UNEF, M, MF, MEF, Acme, Stub Acme and Whitworth are several thread types that are good candidates for rolling. Other forms are also capable. We can quickly identify your specific need and determine capability.
The long-term performance of a thread rolling tool is
directly related to wear of the spindles, bearings, backing plate and face
plate of the rolling head. Wear of any or all these components will manifest
initially in pronounced taper of the finished thread. Older style heads were
equipped with needle bearings while newer style heads utilized carbide
bushings. The carbide helped to maintain parallel form for longer life cycle
than the needles. Correcting taper generally requires replacing one or more of
the contributing components. In a pinch, the straightness is achieved through
preparation of a counter tapered part prep. This can squeeze additional life
out of the tool without the time and cost of immediate repair or part
We inspect, evaluate and quote repair cost and time when
tool performance becomes suspect and the inspection is scheduled regarding
Roll threading with a threading head on a Hydromat transfer machine required modification of the operating station of the machine to include an operating trigger mechanism to trip the threading attachment once it was in the correct position to thread.
The latest offering from LMT Fette is a unique EW style tool that uses the part as the trip mechanism. A rotating mandril inside the head is engaged by the part and collapses the tool on itself through a 4 millimeter air gap. This compression trips the tool activates the thread rolls and resets itself once the toll retracts. The mandril accurately positions the thread location and prevents any unwanted forward movement of the part from its gripping jaws. No special mechanism is required of the machine operating station. This eliminates the need for station modifications that typically add $20,000 to the machine cost. If no part is in position to thread no compression takes place and the head is not tripped removing potential for false tripping.
What you want/need to know
Sintered carbide was discovered in the early 1920’s in Essen Germany as a resultant of a furnace explosion at the Krupp Iron and Steel Works. It was developed and played an important role in German military production during WW2. The Allied nations acquired carbide knowledge following the fall of the Hitler regime. While all carbide products offered today are sourced from the limited suppliers of the carbide powders. The recipe, tool design and coatings vary from manufacturer to manufacturer and have improved dramatically since 1950. Modern carbide products have been designed to run at speeds and feeds that will shorten cycle times and improve tool life. The biggest mistake made with carbide application is ignoring the information provided by the manufacturer. Adhering to the suggested feeds and speeds provided by each manufacturer guarantees maximum tool performance. Surface speed is the most important followed by feed rate. Depth of cut has the least impact on tool life. Ignoring the manufacturers recommendations will seriously degrade tool life and product output.